ANATOMY OF THE HUMAN BODY BY HENRY GRAY, F.R.S. FELLOW OF THE ROYAL COLLEGE OF SURGEONS; LECTURER ON ANATOMY AT ST. GEORGE’S HOSPITAL MEDICAL SCHOOL, LONDON TWENTIETH EDITION THOROUGHLY REVISED AND RE-EDITED BY WARREN H. LEWIS, B.S., M.D. PROFESSOR OF PHYSIOLOGICAL ANATOMY, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD TUlustratefc witb 1247 Engravings LEA & FEBIGER PHILADELPHIA AND NEW YORK 1918 Copyright LEA & FEBIGER 1918 THE FIRST EDITION OF THIS WORK WAS DEDICATED TO SIR BENJAMIN COLLINS BRODIE, Bart., F.R.S., D.C.L IN ADMIRATION OF HIS GREAT TALENTS AND IN REMEMBRANCE OF MANY ACTS OF KINDNESS SHOWN TO THE ORIGINAL AUTHOR OF THE BOOK FROM AN EARLY PERIOD OF HIS PROFESSIONAL CAREER PREFACE TO THE TWENTIETH EDITION. Since the publication of the first English edition of this work in 1858 and the first American edition in 1859 great advances in the subject of Anatomy have been made, especially in microscopic anatomy and the anatomy of the embryo. This knowledge was embodied from time to time in the successive editions until finally considerable portions of the text, sometimes sections, were devoted to these sub- jects. However, the main text has always remained primarily a descriptive anatomy of the human body. In the present edition the special sections on embryology and histology have been distributed among the subjects under which they naturally belong. New matter on physiological anatomy, laws of bone architecture, the mechanics and variations of muscles have been added, occupying much of the space formerly devoted to the sections on applied anatomy. The sections on the ductless glands and the nervous system have been largely rewritten. In the latter a more rational presentation of the sympathetic nervous system has been achieved through the use of diagrams and descriptions based on physiological and pharmacological work. The central connections of the spinal and cranial nerves are also emphasized. Illustrations have been added wherever important points could be made more clear, and throughout the work colored pictures have been even more extensively us§d than heretofore. In this respect special mention might be made of the central nervous system and the section on the muscles. In the section on Svndesmology six illustrations are used from Quain’s Anatomy through the courtesy of the publishers, Messrs. Longmans, Green & Company, of London. The use of the B. N. A. nomenclature in English has been retained practically unchanged in this edition and important references to the literature have been added at the end of each section. As a practical work on the subject for the student, Gray’s Anatomy has always been recognized and appreciated. The plan originally formulated, which has proved so successful, has been adhered to as much as possible. It is interesting to note that although Henry Gray saw only the first edition, much of the original text persists and many of his illustrations are still in use. Bearing this in mind it has been the endeavor of the Editor to supply only such changes as advances in the science made necessary in order that this work may reflect the latest accessions to anatomical knowledge. Baltimore, 1918. W. H. L. CONTENTS. EMBRYOLOGY The Animal Cell. Cytoplasm 35 Nucleus 36 Reproduction of Cells 36 Prophase 36 Metaphase 36 Anaphase 36 Telophase ... ... 38 The Ovum. Yolk 39 Germinal Vesicle 40 Coverings of the Ovum 40 Maturation of the Ovum 40 The Spermatozoon ... 42 Fertilization of the Ovum . . 44 Segmentation of the Fertilized Ovum. The Primitive Streak; Formation of the Mesoderm 47 Ectoderm 47 Entoderm 49 Mesoderm 49 The Neural Groove and Tube . . 50 The Notochord .... 52 The Primitive Segments . . 52 Separation of the Embryo . . 53 The Yolk-sac .... 54 Development of the Fetal Membranes and Placenta. The Allantois 54 The Amnion 56 The Umbilical Cord and Body-stalk ... 57 Implantation or Imbedding of the Ovum . 58 The Decidua 59 The Chorion 60 The Placenta 62 Fetal Portion 62 Maternal Portion 63 Separation of the Placenta .... 64 The Branchial Region. The Branchial or Visceral Arches and Pharyn- geal Pouches 65 The Nose and Face 67 The Limbs 71 Development of the Body Cavities . . 72 The Form of the Embryo at Different Stages of its Growth . ... 74 OSTEOLOGY. Long Bones 79 Short Bones 79 Flat Bones 79 Irregular Bones . . . 80 Surfaces of Bones . 80 Development of the Skeleton. The Skeleton 80 The Vertebral Column 80 The Ribs 82 The Sternum 83 The Skull 83 Bone. Structure and Physical Properties ... 86 Periosteum 87 Marrow 87 Vessels and Nerves of Bone 88 Minute Anatomy 89 Chemical Composition 91 Ossification 91 Intramembranous Ossification ... 91 Intercartilaginous Ossification ... 93 The Vertebral Column. General Characteristics of a Vertebra. The Cervical Vertebra 97 The First Cervical Vertebra .... 99 The Second Cervical Vertebra . . . 100 The Seventh Cervical Vertebra . . . 101 The Thoracic Vertebra 102 The First Thoracic Vertebra . . . 104 The Ninth Thoracic Vertebra . . . 104 The Tenth Thoracic Vertebra . . . 104 The Eleventh Thoracic Vertebra . . 104 The Twelfth Thoracic Vertebra . . . 104 The Lumbar Vertebrae 104 The Fifth Lumbar Vertebra . . . . 106 The Sacral and Coccygeal Vertebrae . . . 106 The Sacrum 106 The Coccyx Ill Ossification of the Vertebral Column . . Ill The Vertebral Column as a Whole. Curves 114 Surfaces 114 Vertebral Canal . . 116 The Thorax. Boundaries 117 The Sternum 119 Manubrium 120 Body 120 Xiphoid Process 121 The Ribs 123 Common Characteristics of the Ribs . 123 Peculiar Ribs 125 First Rib 125 Second Rib 125 Tenth Rib 126 Eleventh and Twelfth Ribs . . 126 The Costal Cartilages 127 10 CONTENTS Skull. The Cranial Bones. The Occipital Bone 129 The Squama 129 Lateral Parts 131 Basilar Parts 132 Angles 132 The Parietal Bone . 133 The Frontal Bone 135 Squama 135 Orbital or Horizontal Part . . . . 137 The Temporal Bone 138 The Squama 139 Mastoid Portion 141 Petrous Portion 142 Tympanic Part 145 Styloid Process 145 The Sphenoid Bone 147 Body 147 The Great Wings 149 The Small Wings 151 Pterygoid Processes 151 The Sphenoidal Conchse 152 Ethmoid bone 153 Cribriform plate 153 Perpendicular Plate 154 Labyrinth or Lateral Mass .... 154 Sutural or Wormian Bones 156 The Facial Bones. The Nasal Bones 156 The Maxillae (Upper Jaw) 157 The Maxillary Sinus or Antrum of High- more 160 The Zygomatic Process 161 The Frontal Process 161 The Alveolar Process 161 The Palatine Process 162 Changes Produced in the Maxilla by Age 163 The Lacrimal Bone 163 The Zygomatic Bone 164 The Palatine Bone 166 The Horizontal Part 167 The Vertical Part 167 The Pyramidal Process or Tuberosity . 168 The Orbital Process 168 The Sphenoidal Process 169 The Inferior Nasal Concha 169 The Vomer 170 The Mandible (Lower Jaw) 172 Changes Produced in the Mandible by Age 175 The Hyoid Bone 177 The Exterior of the Skull. Norma Verticalis 178 Norma Basalis .179 Norma Lateralis 182 The Temporal Fossa 183 The Infratemporal Fossa . . . .184 The Pterygopalatine Fossa . . . . 185 Norma Occipitalis 185 Norma Frontalis 185 The Orbits 188 The Interior of the Skull. Inner Surface of the Skull-cap .... 189 Under Surface of the Base of the Skull . . 190 The Anterior Fossa 190 The Middle Fossa 190 The Posterior Fossa 192 The Nasal Cavity 194 Anterior Nasal Aperture 196 Differences in the Skull Due to Age . . . 196 Sexual Differences in the Skull .... 197 Craniology 197 The Extremities. The Bones of the Upper Extremity. The Clavicle 200 Lateral Third 200 Medial Two-thirds 201 The Sternal Extremity 202 The Acromial Extremity 202 The Scapula 202 The Spine 203 The Acromion 203 The Coracoid Process 207 The Humerus 209 Upper Extremity 209 The Head 209 The Anatomical Neck .... 209 The Greater Tubercle .... 209 The Lesser Tubercle .... 209 The Body or Shaft 209 The Lower Extremity 212 The Ulna 214 The Upper Extremity 214 The Olecranon 214 The Coronoid Process .... 214 The Semilunar Notch .... 215 The Radial Notch 215 The Body or Shaft 215 The Lower Extremity 218 The Radius 219 The Upper Extremity 219 The Body or Shaft 219 The Lower Extremity 220 The Hand. The Carpus 221 Common Characteristics of the Carpal Bones 221 Bones of the Proximal Row .... 221 The Navicular Bone . . . .221 The Lunate Bone 224 The Triangular Bone .... 224 The Pisiform Bone 225 Bones of the Distal Row .... 225 The Greater Multangular Bone . 225 The Lesser Multangular Bone . . 225 The Capitate Bone 226 The Hamate Bone 227 The Metacarpus 227 Common Characteristics of the Meta- carpal Bones 227 Characteristics of the Individual Meta- carpal Bones 228 The First Metacarpal Bone . . 228 The Second Metacarpal Bone . . 228 The Third Metacarpal Bone . . 228 The Fourth Metacarpal Bone . . 228 The Fifth Metacarpal Bone . . 228 The Phalanges of the Hand 230 Ossification of the Bones of the Hand . . 230 The Bones of the Lower Extremity. The Hip Bone 231 The Ilium 231 The Body 231 The Ala 232 The Ischium 234 The Body 234 The Superior Ramus .... 235 The Inferior Ramus 235 The Pubis 236 The Body 236 The Superior Ramus .... 236 The Inferior Ramus 237 The Acetabulum 237 The Obturator Foramen . . . 237 The Pelvis 238 The Greater or False Pelvis .... 238 The Lesser or True Pelvis .... 239 Axes ... 240 Position of the Pelvis 241 Differences between Male and Female Pelves 241 Abnormalities 242 CONTENTS 11 The Femur 242 The Upper Extremity 243 The Head 243 The Neck 243 The Trochanters 244 The Body or Shaft, 246 The Lower Extremity 247 The Architecture of the Femur . 248 The Patella 255 The Tibia 256 The Upper Extremity 256 The Body or Shaft 257 The Lower Extremity 259 The Fibula 260 The Upper Extremity or Head . . . 260 The Body or Shaft 260 The Lower Extremity or Lateral Malleolus 262 The Foot. The Tarsus 263 The Calcaneus 263 The Tarsus— The Talus 266 The Cuboid Bone 269 The Navicular Bone 270 The First Cuneiform Bone .... 270 The Second Cuneiform Bone . . .271 The Third Cuneiform Bone .... 271 The Metatarsus 272 Common Characteristics of the Meta- tarsal Bones 272 Characteristics of the Individual Meta- tarsal Bones 272 The First Metatarsal Bone . . . 272 The Second Metatarsal Bone . . 273 The Third Metatarsal Bone . . 274 The Fourth Metatarsal Bone . . 274 The Fifth Metatarsal Bone . . 274 The Phalanges of the Foot 275 Ossification of the Bones of the Foot . . 275 Comparison of the Bones of the Hand and Foot 276 The Sesamoid Bones 277 SYNDESMOLOGY Bone 279 Hyaline Cartilage 279 Articular Cartilage 280 Costal Cartilage 281 White Fibrocartilage 281 Interarticular Fibrocartilages . . . 281 Connecting Fibrocartilages .... 282 Circumferential Fibrocartilages . . . 282 Stratiform Fibrocartilages .... 282 Ligaments 282 The Articular Capsules 282 Mucous Sheaths 283 Bursae Mucosae 283 Development of the Joints . . 283 Classification of Joints Synarthrosis 284 Sutura 284 Schindylesis 284 Gomphosis * 284 Synchondrosis 284 Amphiarthrosis 285 Diathrosis 285 Ginglimus 285 Trochoid 285 Condyloid 286 Articulation by Reciprocal Reception . 286 Enarthrosis 286 Arthrodia 286 The Kind of Movement Admitted in Joints. Gliding Movement 286 Angular Movement 286 Circumduction 286 Rotation . ’ 287 Ligamentous Action of Muscles .... 287 Articulations of the Trunk. Articulations of the Vertebral Column . . 287 Articulations of Vertebral Bodies . . 287 The Anterior Longitudinal Liga- ment 287 The Posterior Longitudinal Liga- ment 288 The Intervertebral Fibrocartilages 289 Structure 289 Articulations of Vertebral Arches . . 289 The Articular Capsules .... 290 The Ligamenta Flava .... 290 The Supraspinal Ligament . . . 290 Articulations of the Vertebral Column— Articulations of Vertebral Arches— The Ligamentum Nuchae . . . 290 The Interspinal Ligaments . . . 291 The Inter transverse Ligaments . 291 Articulation of the Atlas with the Epistro- • pheus or Axis 292 The Articular Capsules 292 The Anterior Atlantoaxial Ligament . 293 . The Posterior Atlantoaxial Ligament . 293 The Transverse Ligament of the Atlas . 293 Articulations of the Vertebral Column with the Cranium 295 Articulation of the Atlas with the Occipital Bone 295 The Articular Capsules .... 295 The Anterior Atlantooccipital Mem- brane 295 The Posterior Atlantooccipital Mem- brane 296 %The Lateral Ligaments .... 296 Ligaments Connecting the Axis with the Occipital Bone 296 The Membrana Tectoria . . . 296 The Alar Ligaments 296 Articulation of the Mandible 297 The Articular Capsule 297 The Temporomandibular Ligament . 297 The Sphenomandibular Ligament . . 297 The Articular Disk 298 The Stylomandibular Ligament . . . 298 Costovertebral Articulations 299 Articulations of the Heads of the Ribs . 299 The Articular Capsule .... 299 The Radiate Ligament .... 299 The Interarticular Ligament . . 300 Costotransverse Articulations . . . 300 The Articular Capsule .... 301 The Anterior Costotransverse Liga- ment 301 The Posterior Costotransverse Liga- ment 301 The Ligament of the Neck of the Rib 302 The Ligament of the Tubercle of the Rib 302 Sternocostal Articulations 302 The Articular Capsules 302 The Radiate Sternocostal Ligaments . 302 The Interarticular Sternocostal Liga- ment ... 303 The Costoxiphoid Ligaments . . . 304 Interchondral Articulations .... 304 Costochondral Articulations .... 304 Articulation of the Manubrium and Body of the Sternum 304 Mechanism of the Thorax .... 304 12 CONTENTS Articulation of the Vertebral Column with the Pelvis 306 The Iliolumbar Ligament .... 306 Articulations of the Pelvis 306 Sacroiliac Articulation 306 The Anterior Sacroiliac Ligament . 307 The Posterior Sacroiliac Ligament. 307 The Interosseous Sacroiliac Liga- ment 308 Ligaments Connecting the Sacrum and Ischium 309 The Sacrotuberous Ligament . 309 The Sacrospinous Ligament . . 309 Sacrococcygeal Symphysis . . . . 309 The Anterior Sacrococcygeal Liga- ment 309 The Posterior Sacrococcygeal Liga- ment 309 The Lateral Sacrococcygeal Liga- ment 310 The Interarticular Ligaments . . 310 The Pubic Symphysis 310 The Anterior Pubic Ligament . . 310 The Posterior Pubic Ligament . . 310 The Superior Pubic Ligament . . 310 The Arcuate Pubic Ligament . . 310 The Interpubic Fribrocartilaginous Lamina 311 Mechanism of the Pelvis 311 Articulations of the Upper Extremity. Sternoclavicular Articulation 313 The Articular Capsule 313 The Anterior Sternoclavicular Ligament 313 The Posterior Sternoclavicular Liga- ment 313 The Interclavicular Ligament . . . 314 The Costoclavicular Ligament . . . 314 The Articular Disk 314 Acromioclavicular Articulation . . . .315 The Articular Capsule 315 The Superior Acromioclavicular Liga- ment 315 The Inferior Acromioclavicular Liga- ment 315 The Articular Disk 315 The Coracoclavicular Ligament . . .315 The Trapezoid Ligament . . . .315 The Conoid Ligament 315 The Ligaments of the Scapula . . . . 316 The Coracoacromial Ligament . . . 316 The Superior Transverse Ligament . . 317 The Inferior Transverse Ligament . . 317 Humeral Articulation or Shoulder-joint . . 317 The Articular Capsule 317 The Coracohumeral Ligament . . . 318 Glenohumeral Ligaments . . . . 318 The Transverse Humeral Ligament . 319 The Glenoidal Labrum 319 Bursae 319 Elbow-joint 321 The Anterior Ligament 321 The Posterior Ligament 322 The Ulnar Collateral Ligament . . . 322 The Radial Collateral Ligament . . 322 Radioulnar Articulation 324 Proximal Radioulnar Articulation . . 324 The Annular Ligament .... 324 Middle Radioulnar Union .... 325 The Oblique Cord 325 The Interosseous Membrane . . 325 Distal Radioulnar Articulation . . . 325 The Volar Radioulnar Ligament . 325 The Dorsal Radioulnar Ligament . 325 The Articular Disk 325 Radiocarpal Articulation or Wrist-joint . . 327 The Volar Radiocarpal Ligament . . 327 The Dorsal Radiocarpal Ligament . . 328 The Ulnar Collateral Ligament . . . 328 The Radial Collateral Ligament . . 328 Intercarpal Articulations 328 Articulations of the Proximal Row of Carpal Bones 328 Intercarpal Articulations— Articulations of the Proximal Row of Carpa Bones— The Dorsal Ligaments .... 328 The Volar Ligaments .... 328 The Interosseous Ligaments . 328 Articulations of the Distal Row of Carpal Bones 329 The Dorsal Ligaments .... 329 The Volar Ligaments .... 329 The Interosseous Ligaments . . 329 Articulations of the Two Rows of Carpal Bones with Each Other . 329 The Volar Ligaments .... 329 The Dorsal Ligaments .... 329 The Collateral Ligaments . 329 Carpometacarpal Articulations .... 330 Carpometacarpal Articulation of the Thumb 330 Articulations of the Other Four Meta- carpal Bones with the Carpus . 331 The Dorsal Ligaments . . . .331 The Volar Ligaments . . . .331 The Interosseous Ligaments . . 331- Intermetacarpal Articulations . . . .331 The Transverse Metacarpal Ligament . 331 Metacarpophalangeal Articulations . . . 332 The Volar Ligaments 332 The Collateral Ligaments .... 332 Articulations of the Digits 333 Articulations of the Lower Extremity. Coxal Articulation or Hip-joint .... 333 The Articular Capsule 334 The Iliofemoral Ligament .... 335 The Pubocapsular Ligament . . . 335 The Ischiocapsular Ligament . . . 335 The Ligamentum Tetes Femoris . . 336 The Glenoidal Labrum 336 The Transverse Acetabular Ligament . 336 The Knee-joint 339 The Articular Capsule 340 The Ligamentum Patellae .... 340 The Oblique Popliteal Ligament . . 340 The Tibial Collateral Ligament . . .341 The Fibular Collateral Ligament . . 341 The Cruciate Ligaments ..... 342 The Anterior Cruciate Ligament . 342 The Posterior Cruciate Ligament . 342 The Menisci 342 The Medial Meniscus .... 343 The Lateral Meniscus .... 343 The Transverse Ligament .... 343 The Coronary Ligaments .... 343 Bursae 345 Articulations between the Tibia and Fibula. 347 Tibiofibular Articulation .... 348 The Articular Capsule .... 348 The Anterior Ligament .... 348 The Posterior Ligament . . . 348 Interosseous Membrane 348 Tibiofibular Syndesmosis .... 348 The Anterior Ligament .... 348 The Posterior Ligament . . . 348 The Inferior Transverse Ligament 349 The Interosseous Ligament . . 349 Talocrural Articulation or Ankle-joint . . 349 The Articular Capsule 350 The Deltoid Ligament 350 The Anterior Talofibular Ligament . 351 The Posterior Talofibular Ligament . 351 The Calcaneofibular Ligament . . .351 Intertarsal Articulations . _ 352 Talocalcaneal Articulation .... 352 The Articular Capsule .... 352 The Anterior Talocalcaneal Liga- ment 352 The Posterior Talocalcaneal Liga- ment # 352 The Lateral Talocalcaneal Liga- ment 352 The Medial Talocalcaneal Liga- ment 353 CONTENTS 13 Intertarsal Articulations—■ Talocalcaneal Articulation— The Interosseous Talocalcaneal Ligament 353 Talocalcaneonavicular Articulation . . 353 The Articular Capsule .... 354 The Dorsal Talonavicular Ligament 354 Calcaneocuboid Articulation . . . 354 The Articular Capsule .... 354 TheDorsalCalcaneocuboidLigament 354 The Bifurcated Ligament . . . 354 The Long Plantar Ligament . 354 The Plantar Calcaneocuboid Liga- ment 354 The Ligaments Connecting the Calca- neus and Navicular .... 355 The Plantar Calcaneonavicular Ligament 355 Cuneonavicular Articulation . . . 356 The Dorsal Ligaments .... 356 The Plantar Ligaments .... 356 Cubbideonavicular Articulation . . . 356 The Dorsal Ligament .... 357 Intertarsal Articulations— Cuboideonavicular Articulation— The Plantar Ligament .... 357 The Interosseous Ligament . . 357 Intercuneiform and Cuneocuboid Articu- lation 357 The Dorsal Ligaments .... 357 The Plantar Ligaments .... 357 The Interosseous Ligaments . . 357 Tarsometatarsal Articulations .... 358 The Dorsal Ligaments 358 The Plantar Ligaments 358 The Interosseous Ligaments .... 358 Intermetatarsal Articulations 358 The Dorsal Ligaments 358 The Plantar Ligaments . . . . . 358 The Interosseous Ligaments .... 358 The Transverse Metatarsal Ligament . 359 Metatarsophalangeal Articulations . . . 359 The Plantar Ligaments 359 The Collateral Ligaments .... 359 Articulations of the Digits 359 Arches of the Foot 360 MYOLOGY. Mechanics of Muscle. The Direction of Muscle Pull .... 363 The Action of Muscle Pull on Tendon . . 364 The Strength of Muscles 364 The Work Accomplished by Muscles . . 365 The Action of Muscles on Joints . . . 368 Development of the Muscles. The Ventro-lateral Muscles of the Neck . . 371 Muscles of the Shoulder Girdle and Arm . 371 The Muscles of the Leg 372 The Muscles of the Head 372 Striped or Voluntary Muscle 373 Vessels and Nerves of Striped Muscle . . 376 Tendons, Aponeuroses, and Fasciae. Tendons 376 Aponeuroses 376 Fasciae 376 The Fascle and Muscles of the Head. The Muscles of the Scalp. The Skin of the Scalp 378 The Superficial Fascia 378 Epicranius 378 Occipitalis 379 Frontalis 379 Galea Aponeurotica 380 The Muscles of the Eyelid. Orbicularis Oculi 380 Corrugator 381 The Muscles of the Nose. Procerus ... 382 Nasalis 382 Depressor Septi [ 382 Dilator Naris Posterior 382 Dilator Naris Anterior 382 The Muscles of the Mouth. Quadratus Labii Superioris 383 Caninus 383 Zygomaticus [ [ 383 Mentalis 383 Quadratus Labii Inferioris • 383 Triangularis 383 Buccinator 384 Pterygomandibular Raph6 .... 384 Orbicularis Oris . 384 Risorius 385 The Muscles of Mastication. Parotideomasseteric Fascia 385 Masseter 385 Temporal Fascia 386 Temporalis 386 Pterygoideus Externus 386 Pterygoideus Internus 387 The Fasci.e and Mtjscles of the Antero- lateral Region of the Neck. The Superficial Cervical Muscle. Superficial Fascia 387 Platysma 388 Variations 388 The Lateral Cervical Muscles. The Fascia Colli * 388 Sternocleidomastoideus 390 Variations 390 Triangles of the Neck 390 The Supra- and Infrahyoid Muscles. Digastricus 391 Variations 391 Stylohyoideus 392 Variations 392 The Stylohyoid Ligament .... 392 Mylohyoideus 393 Variations 393 Geniohyoideus 393 Sternohyoideus 393 Variations 393 Sternothyreoideus 393 Variations 394 Thyreohyoideus 394 Omohyoideus 394 Variations 394 The Anterior Vertebral Muscles. Longus Colli 394 Longus Capitis 395 Rectus Capitis Anterior 395 Rectus Capitis Lateralis 395 14 CONTENTS The Lateral Vertebral Muscles. Scalenus Anterior 396 Scalenus Medius 396 Scalenus Posterior 396 Variations 396 The Fasciae and Muscles of the Thunk. The Deep Muscles of the Back. The Lumbodorsal Fascia 397 Splenius Capitis 397 Splenius Cervicis 397 Variations 397 Sacrospinalis 397 Iliocostalis Lumborum 399 Iliocostalis Dorsi 399 Iliocostalis Cervicis ...... 399 Longissimus Dorsi 399 Longissimus Cervicis 399 Longissimus Capitis 399 Spinalis Dorsi 399 Spinalis Cervicis 400 Spinalis Capitis 400 Semispinalis Dorsi 400 Semispinalis Cervicis 400 Semispinalis Capitis 400 Mul'tifidus 400 Rotatores 400 Interspinales 400 Extensor Coccygis 401 Intertransversarii 401 The Suboccipital Muscles. RectuS Capitis Posterior Major .... 401 Rectus Capitis Posterior Minor . . . .401 Obliquus Capitis Inferior 402 Obliquus Capitis Superior 402 The Suboccipital Triangle .... 402 The Muscles of the Thorax. Intercostal Fascia 402 Intercostales 403 Intercostales Externi 403 Variations 403 Intercostales Interni 403 Subcostales 403 Transversus Thoracis 403 Levatores Costarum 403 Serratus Posterior Superior 404 Variations 404 Serratus Posterior Inferior 404 Variations 404 Diaphragm 404 Medial Lumbocostal Arch .... 404 Lateral Lumbocostal Arch .... 405 The Crura 405 The Central Tendon 406 Openings in the Diaphragm . . . 406 Variations 406 Mechanism of Respiration 407 The Muscles and Fascice of the Abdomen. The Antero-lateral Muscles of the Abdomen 408 'The Superficial Fascia 408 Obliquus Externus Abdominis . . . 409 Aponeurosis of the Obliquus Externus Abdominis . 410 Subcutaneous Inguinal Ring . 410 The Intercrural Fibers . . 410 The Inguinal Ligament . . 411 The Lacunar Ligament . . 412 The Reflected Inguinal Liga- ment 412 Ligament of Cooper . . . 412 Variations 412 ; Obliquus Internus Abdominis . . . 412 Variations 414 ! Cremaster .414 Transversus Abdominis 414 The Antero-lateral Muscles of the Abdomen— Transversus Abdominis— Variations 414 Inguinal Aponeurotic Falx . . , 414 Rectus Abdominis 415 Pyramidalis 416 Variations 417 The Linea Alba 417 The Lineae Semilunares 417 The Transversalis Fascia . . . .418 The Abdominal Inguinal Ring . . 418 The Inguinal Canal 418 Extraperitoneal Connective Tissue . 418 The Deep Crural Arch 419 The Posterior Muscles of the Abdomen . . 419 The Fascia Covering the Quadratus Lumborum 419 Quadratus Lumborum 420 Variations 420 The Muscles and Fasciae of the Pelvis. Pelvic Fascia 420 Levator Ani ' ’ 422 Coccygeus ] 424 The Muscles and Fascia: of the Perineum. Muscles of the Anal Region 424 The Superficial Fascia .*.... 424 The Deep Fascia 425 Ischiorectal Fossa 425 The Corrugator Cutis Ani .... ”425 Sphincter Ani Externus 425 Sphincter Ani Internus 426 The Muscles of the Urogenital Region in the Male 426 Superficial Fascia 426 The Central Tendinous Point of the ■ Perineum 427 Transversus Perinaei Superficialis . . 427 Variations 427 Bulbocavernosus 428 Ischiocavernosus 428 The Deep Fascia 428 Transversus Perinaei Profundus . . 429 Sphincter Urethrae Membranaceae . . 429 The Muscles of the Urogenital Region in the Female 430 Transversus Perinaei Superficialis . . 43o Bulbocavernosus 430 Ischiocavernosus 430 Transversus Perinaei Profundus . ! 431 The Fascia and Muscles of the Upper Extremity. The Muscles Connecting the Upper Extremity to the Vertebral Column. Superficial Fascia 432 Deep Fascia ' 432 Trapezius 432 ’ Variations 432 Latissimus Dorsi 432 Variations 434 Rhomboideus Major 434 Rhomboideus Minor 434 Variations 435 Levator scapulae 435 Variations 435 The Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. Superficial Fascia 435 Pectoralis Major 436 Variations 437 Coracoclavicular Fascia 437 Pectoralis Minor 438 Variations 438 Subclavius 438 Variations .' 438 Serratus Anterior 438 Variations 430 CONTENTS 15 The Muscles and Fascice of the Shoulder. Deep Fascia 439 Deltoideus 439 Variations 440 Subscapular Fascia 440 Subscapularis 440 Supraspinatous Fascia 440 Supraspinatus 440 Infraspinatous Fascia 441 Infraspinatus 441 Teres Minor 441 Variations 442 Teres Major 442 The Muscles and Fascice of the Arm. Brachial Fascia 442 Coracobrachialis 443 Variations . 443 Biceps Brachii 443 Variations 444 Brachialis 444 Variations 444 Triceps Brachii 444 Variations 445 The Muscles and Fascice of the Forearm. Antibrachial Fascia 445 The Volar Antibrachial Muscles .... 445 The Superficial Group 446 Pronator Teres 446 Variations 446 Flexor Carpi Radialis .... 446 Variations 446 Palmaris Longus 446 Variations 446 Flexor Carpi Ulnaris .... 447 Variations 447 Flexor Digitorum Sublimis . . 448 Variations 448 The Deep Group 448 Flexor Digitorum Profundus 448 Fibrous Sheaths of the Flexor Tendons 448 Variations 449 Flexor Pollicis Longus .... 449 Variations 449 Pronator Quadratus . . . . .449 Variations 450 The Dorsal Antibrachial Muscles. . . . 451 The Superficial Group 451 Brachioradialis 451 Variations . . . . .451 Extensor Carpi Radialis Longus . 452 Extensor Carpi Radialis Brevis 452 Variations 452 Extensor Digitorum Communis 452 Variations 454 Extensor Digiti Quinti Proprius 454 Variations 454 Extensor Carpi Ulnaris .... 454 Variations 454 Anconseus 454 The Deep Group 454 Supinator 454 Abductor Pollicis Longus . . 455 Variations 455 Extensor Pollicis Brevis . . . 455 Variations 455 Extensor Pollicis Longus . . 455 Extensor Indicis Proprius . . 456 . Variations 456 The Muscles and Fascice of the Hand. Volar Carpal Ligament 456 Transverse Carpal Ligament 456 The Mucous Sheaths of the Tendons on the Front of the Wrist 457 Dorsal Carpal Ligament . . . 458 The Mucous Sheaths of the Tendons on the Back of the Wrist 459 Palmar Aponeurosis 460 Superficial Transverse Ligament of the Fingers 46! The Lateral Volar Muscles 461 Abductor Pollicis Brevis . . . ] ! 461 Opponens Pollicis ....... 461 Flexor Pollicis Brevis 461 Adductor Pollicis (Obliquus) . ! ’ 462 Adductor Pollicis (Transversus) . . 462 Variations 462 The Medial.Volar Muscles 462 Palmaris Brevis . . . . . ’ ’ 463 Abductor Digiti Quinti ! ! ' [ 463 Flexor Digiti Quinti Brevis .... 464 Opponens Digiti Quinti 464 Variations 464 The Intermediate Muscles 464 Lumbricales ’ 464 Variations ’ 464 Interossei ] 464 Interossei Dorsales 464 Interossei Volares 465 The Muscles and Fascle of the Lower Extremity. The Muscles and Fascia; of the Iliac Region. ! The Fasda Covering the Psoas and Iliacus 4H6 Psoas Major 467 Psoas Minor . . . 467 I Iliacus ’ ’ ' 467 Vanations 467 The Muscles and Fascice of the Thigh. The Aiterior Femoral Muscles .... 467 Superficial Fascia 468 Daep Fascia ' 468 The Fossa Ovalis 469 Sartorius 476 Variations 470 Quadriceps Femoris 470 Rectus Femoris 470 Vastus Lateralis 470 Vastus Medialis 471 Vastus Intermedius 471 Articularis Genu 471 Tie Medial Femoral Muscles . . . .471 Gracilis 471 Pectineus 472 Adductor Longus 472 Adductor Brevis 473 Adductor Magnus 473 Variations 474 The Muscles of the Gluteal Region . . . 474 Glutams Maximus 474 Burs® 474 Glutams Medius ....... 474 Variations 475 Glutreus Minimus 475 Variations 475 Piriformis 476 Variations ’ 476 Tensor Fascise Latss 476 Obturctor Membrane 477 Obtuntor Internus 477 Gema li 477 gemellus Superior ....'. 477 lemellus Inferior . 477 Qua*ratus Femoris 477 Obftrator Externus 477 The Po-erior Femoral Muscles ' 478 Biaps Femoris 473 Variations 479 Smitendinosus * 479 Bmimembranosus 479 Variations 479 The Muscles and Fasciae of the Leg. Tb Anterior Crural Muscles 480 Deep Fascia 480 Tibialis Anterior 480 Variations ..... ' 480 CONTENTS 16 The Mucous Sheaths of the Tendons Around the Ankle 489 The Muscles and Fasciae of the Foot. The Dorsal Muscle of the Foot .... 490 Extensor Digitorum Brevis .... 490 Variations 490 The Plantar Muscles of the Foot . . . 490 Plantar Aponeurosis 490 The First Layer 491 Abductor Hallucis 491 Variations . . . . 491 Flexor Digitorum Brevis . . . 491 Variations 492 Fibrous Sheaths of the Flexor Tendons 492 Abductor Digiti Quinti .... 492 Variations 492 The Second Layer 493 Quadratus Plantse 493 Variations 493 Lumbricales .* 493 Variations 493 The Third Layer 493 Flexor Hallucis Brevis .... 493 Variations 493 Adductor Hallucis 493 Variations . . . . . 494 Flexor Digiti Quinti Brevis . . 494 The Fourth Layer 495 Interossei 495 Interossei Dorsales .... 495 Interossei Plantares . . . 495 The Anterior Crural Muscles— Extensor Hallucis Longus .... 481 Variations . . . ■ • • • • 481 Extensor Digitorum Longus .... 481 Variations 482 Peronseus Tertius 482 The Posterior Crural Muscles .... 482 The Superficial Group ..... 482 Gastrocnemius ...... 482 Variations 483 Soleus 483 Variations 483 Tendo Calcaneus 483 Plantaris 483 The Deep Group . . . _ . • • • 483 Deep Transverse Fascia . . . 483 Popliteus 484 Variations i 485 Flexor Hallucis Longus .... 485 Variations 485 Flexor Digitorum Longus . . . 485 Variations 485 Tibialis Posterior 485 The Lateral Crural Muscles 486 Peronseus Longus 486 Peronaeus Brevis 486 Variations 487 The Fascice Around the Ankle. Transverse Crural Ligament 488 Cruciate Crural Ligament 488 Laciniate Ligament 489 Peroneal Retinacula 489 angiology. Structure of Arteries 498 j Capillaries 499 Sinusoids 501 Structure of Veins 591 The Blood. General Composition of the Blood . . . 503 Blood Corpuscles 513 Colored or Red Corpuscles . . . 503 Colorless Corpuscles or Leukocytes 504 Development of the Vascular System. Further Development oi the Heart . . . 508 The Valves of the Heart 514 Further Development of the Arteries . . 515 The Anterior Ventral Aorta; . . . 516 The Aortic Arches 516 The Dorsal Aortie 517 Further Development of the Veins . . . 518 The Visceral Veins 518 The Parietal Veins 520 Inferior Vena Cava ...... 520 Venous Sinuses of the Dura Mater . 522 The Thoracic Cavity. The Cavity of the Thorax 524 The Upper Opening of the Thorax . . . 524 The Lower Opening of the Thorax . . . 524 The Pericardium. Structure of the Pericardium 525 The Heart. Size 526 Component Parts 526 Right Atrium 528 Sinus Venarum 528 Auricula 528 Right Ventricle 531 Left Atrium 533 Auricula 533 Left Ventricle 535 Ventricular Septum 535 Structure of the Heart ...... 535 The Cardiac Cycle and the Actions of the Valves 538 Peculiarities in the Vascular System in the Fetus. Fetal Circulation 540 Changes in the Vascular System at Birth . 542 TXE ARTERIES. The Pulmonary Artery . . . ' . . 543 Relations 545 The Aorta. The Ascending Aorta. Relations Branches 5$ Branches of the Ascending Aorta— The Coronary Arteries 546 Right Coronary Artery .... 546 Left Coronary Artery .... 547 Peculiarities 547 The Arch of the Aorta. Relations 547 Peculiarities 548 CONTENTS 17 Branches 548 Peculiarities 548 The Innominate Artery 548 Relations 548 Branches 549 Thyreoidea Ima 549 Collateral Circulation 549 The Arteries of the Head and Neck. The Common Carotid Artery. Relations 549 Peculiarities 551 Collateral Circulation 551 The External Carotid Artery 551 Relations 552 Branches 552 Superior Thyroid Artery . . . 552 Relations 552 Branches 552 Lingual Artery 553 Relations 553 Branches 553 External Maxillary Artery . . . 553 Relations 554 Branches 554 Peculiarities 556 Occipital Artery . . . , . . 556 Course and Relations . . . 556 Branches 556 Posterior Auricular Artery . . . 557 Branches 557 Ascending Pharyngeal Artery . . 557 Branches 558 Superficial Temporal Artery . . 558 Relations ...... 558 Branches 558 Internal Maxillary Artery . . . 559 Branches 560 The Triangles of the Neck 562 Anterior Triangle 563 Inferior Carotid or Muscular Tri- angle . 563 Superior Carotid or Carotid Tri- angle ... 564 Submaxillary or Digastric Tri- angle 564 Suprahyoid Triangle .... 565 Posterior Triangle 565 Occipital Triangle 565 Subclavian Triangle 565 The Internal Carotid Artery 566 Course and Relations 567 Cervical Portion 567 Petrous Portion 567 Cavernous Portion 567 Cerebral Portion 567 Peculiarities 567 Branches 568 Caroticotympanic . . . . . 568 Artery of the Pterygoid Canal . . 568 Cavernous 568 Hypophyseal 568 Semilunar 568 Anterior Meningeal 568 Ophthalmic artery 568 Branches 568 Anterior Cerebral Artery . . . 571 Branches 571 Middle Cerebral Artery . . . 572 Branches . . . . . . 573 Posterior Communicating Artery . 573 Anterior Choroidal Artery . . . 574 The Arteries' of the Brain. The Ganglionic System 575 The Cortical Arterial System 575 The Arteries of the Upper Extremity. The Subclavian Artery. First Part of the Right Subclavian Artery . 576 Relations ......... 576 First Part of the Left Subclavian Artery . 577 Relations 577 Second and Third Parts of the Subclavian Artery 577 Relations 577 Relations 677 Peculiarities 577 Collateral Circulation 578 Branches 678 Vertebral Artery 578 Relations 578 Branches 579 Thyrocervical Trunk 581 Branches 581 Peculiarities 583 Internal Mammary Artery .... 584 Relations 584 Branches 584 The Costocervical Trunk .... 585 The Axilla. Boundaries 585 Contents 586 The Axillary Artery 586 Relations 586 Collateral Circulation 587 Branches 587 The Highest Thoracic Artery . . 587 The Thoracoacromial Artery . . 588 The Lateral Thoracic Artery . . 588 The Subscapular Artery . . . 588 The Posterior Humeral Circumflex Artery . . 589 The Anterior Humeral Circumflex Artery 589 Peculiarities 589 The Brachial Artery 589 Relations 589 The Anticubital Fossa 589 Peculiarities 590 Collateral Circulation 590 Branches . 590 The Arteria Profunda Brachii . . 591 The Nutrient Artery . . . .591 The Superior Ulnar Collateral Artery 591 The Inferior Ulnar Collateral Artery 592 Muscular Branches 592 The Anastomosis Around the Elbow-j oint 592 The Radial Artery 592 Relations 592 Peculiarities 594 Branches 594 Radial Recurrent Artery . . . 594 Muscular 594 Volar Carpal 594 Superficial Volar 594 Dorsal Carpal 594 Arteria Princeps Pollicis . . . 595 Arteria Volaris Indicis Radialis . 595 Deep Volar Arch 595 Volar Metacarpal Arteries . . . 595 Perforating 595 Recurrent 595 The Ulnar Artery 595 Relations 595 Peculiarities 596 Branches 596 Anterior Ulnar Recurrent Artery . 596 Posterior Ulnar Recurrent Artery . 596 Common Interosseous Artery . . 596 Muscular 598 Volar Carpal 598 Dorsal Carpal 598 Deep Volar 598 Superficial Volar 598 Relations 598 18 CONTENTS The Arteries of the Trunk. The Descending Aorta. The Thoracic Aorta 598 Relations . 599 Peculiarities 599 Branches 600 Pericardial 600 Bronchial 600 Esophageal 600 Mediastinal 600 Interoostal Arteries 600 Branches ... .601 Subcostal Arteries 601 Superior Phrenic 601 The Abdominal Aorta 602 Relations 603 Collateral Circulation 603 Branches 603 The Celiac Artery 603 Relations . . . . . . 603 The Superior Mesenteric Artery . 606 Branches . . . . • . • 607 The Inferior Mesenteric Artery . 609 Branches . . . . . . 610 The Middle Suprarenal Arteries . 610 The Renal Arteries . . . . . 610 The Internal Spermatic Arteries . 611 The Ovarian Arteries . . . . 611 The Inferior Phrenic Arteries . . 612 The Lumbar Arteries .... 612 The Middle Sacral Artery . . . 613 The Common Iliac Arteries. Peculiarities . 614 Collateral Circulation 614 The Hypogastric Artery 614 Relations 614 Peculiarities 615 Collateral Circulation 615 Branches . 615 Superior Vesical Artery .... 615 Middle Vesical Artery . . . . 615 Inferior Vesical Artery . . . . 615 Middle Hemorrhoidal Artery . . 615 Uterine Artery 615 Vaginal Artery ...... 616 Obturator Artery 616 Branches ...... 616 Peculiarities . . . . . . 617 Internal Pudendal Artery . . . 617 Relations 618 Peculiarities 618 Branches 618 Inferior Gluteal Artery .... 620 Branches . . v . . 620 Lateral Sacral Arteries . . . . 621 Superior Gluteal Artery . . . 622 The External Iliac Artery 622 Relations 622 Collateral Circulation 622 Branches 622 Inferior Epigastric Artery . . . 623 Branches 623 Peculiarities 623 Deep Iliac Circumflex Artery . . 623 The Arteries of the Lower Extremity. The Femoral Artery. The Femoral Sheath 625 The Femoral Triangle 626 The Adductor Canal 627 Relations of the Femoral Artery .... 627 Peculiarities of the Femoral Artery . . . 629 Collateral Circulation 629 Branches . . • _ 629 Superficial Epigastric Artery . . . 629 Superficial Iliac Circumflex Artery . . 629 Superficial External Pudendal Artery . 629 Deep External Pudendal Artery . . 629 Muscular 629 Profunda Femoris Artery .... 629 Relations 630 Peculiarities 630 Branches 630 Highest Genicular Artery . . . .631 The Popliteal Fossa 631 Boundaries 631 Contents 632 The Popliteal Artery 632 Relations 632 Peculiarities 633 Branches 633 Superior Muscular 633 Sural Arteries 633 Cutaneous Branches .... 633 Superior Genicular Arteries . . 633 Middle Genicular Artery . . . 633 Inferior Genicular Arteries . . . 633 The Anastomosis Around the Knee- joint 634 The Anterior Tibial Artery 634 Relations 635 Peculiarities 635 Branches 635 Posterior Tibial Recurrent Artery . 635 Fibular Artery 635 Anterior Tibial Recurrent Artery . 635 Muscular Branches 635 Anterior Medial Malleolar Artery . 635 Anterior Lateral Malleolar Artery . 635 The Dorsalis Pedis 636 Relations 636 Peculiarities 636 Branches 637 Lateral Tarsal Artery . . . . 637 Medial Tarsal Artery . . . .637 Arcuate Artery 637 Deep Plantar Artery .... 637 The Posterior Tibial Artery 637 Relations 637 Peculiarities 63 S Branches 638 Peroneal Artery 638 Peculiarities 638 Branches 638 Nutrient Artery 638 Muscular Branches 639 Posterior Medial Malleolar Artery 639 Communicating Branch .... 639 Medial Calcaneal 639 Medial Plantar Artery .... 639 Lateral Plantar Artery .... 639 Branches 640 THE VEINS The Pulmonary Veins . . 642 The Systemic Veins. The Veins of the Heart. Coronary Sinus 642 Tributaries 642 The Veins of the Head and Neck. The Veins of the Exterior of the Head and Face 644 The Frontal Vein 644 The Veins of the Exterior of the Head and Face— The Supraorbital Vein 645 The Angular Vein 645 The Anterior Facial Vein .... 645 Tributaries ....... 645 . The Superficial Temporal Vein . . . 645 Tributaries 645 The Pterygoid Plexus 645 The Internal Maxillary Vein. . . 646 The Posterior Facial Vein .... 646 The Posterior Auricular Vein . 646 The Occipital Vein 646 CONTENTS 19 The Veins of the Neck 646 The External Jugular Vein .... 646 Tributaries 647 The Posterior External Jugular Vein ! 647 The Anterior Jugular Vein .... 647 The Internal Jugular Vein .... 648 Tributaries 648 The Vertebral Vein 649 Tributaries 650 The Diploic Veins 651 The Veins of the Brain 652 The Cerebral Veins 652 The External Veins 652 The Superior Cerebral Vein . . 652 The Middle Cerebral Vein . . . 652 The Inferior Cerebral Vein . . . 652 The Internal Cerebral Veins . . • 653 The Great Cerebral Vein . . . 653 The Cerebellar Veins 653 The Sinuses of the Dura Mater. Ophthalmic Veins and Emissary Veins . . . 654 The Superior Sagittal Sinus .... 654 The Inferior Sagittal Sinus .... 655 The Straight Sinus 655 The Transverse Sinuses 657 The Occipital Sinus 658 The Confluence of the Sinuses . . . 658 The Cavernous Sinuses 658 The Ophthalmic Veins 658 The Superior Ophthalmic Vein 659 The Inferior Ophthalmic Vein . . 659 The Intercavernous Sinuses . . . .659 The Superior Petrosal Sinus .... 659 The Inferior Petrosal Sinus .... 659 The Basilar Plexus 660 The Emissary Veins 660 The Veins of the Upper Extremity and Thorax. The Superficial Veins of the Upper Extremity 660 Digital Veins 660 The Cephalic Vein 661 The Accessory Cephalic Vein . 662 The Basilic Vein 662 The Median Antibrachial Vein . . . 662 The Deep Veins of the Upper Extremity . 663 Deep Veins of the Hand 663 Deep Veins of the Forearm .... 663 The Brachial Veins 663 The Axillary Vein ...... 663 The Subclavian Vein 664 Tributaries 664 The Veins of the Thorax 664 The Innominate Veins 664 The Right Innominate Vein . 664 The Left Innominate Vein . . . 666 Tributaries 666 Peculiarities . .... 666 The Internal Mammary Veins . . . 666 The Inferior Thyroid Veins .... 666 The Highest Intercostal Vein . . . 666 The Superior Vena Cava .... 666 Relations 667 The Azygos Vein 667 Tributaries 667 The Hemiazygos Veins . . 667 The Veins of the Thorax— The Azygos Vein— The Accessory Hemiazygos Veins 667 The Bronchial Veins 667 The Veins of the Vertebral Column . . ! 667 The External Vertebral Venous Plexuses 668 The Internal Vertebral Venous Plexuses 668 The Basivertebral Veins 668 The Intervertebral Veins .... 669 The Veins of the Medulla Spinalis . . 669 The Veins of the Lower Extremity, Abdomen, and Pelvis. The Superficial Veins of the Lower Extremity 669 The Dorsal Digital Veins 669 The Great Saphenous Vein .... 669 Tributaries 670 The Small Saphenous Vein .... 670 The Deep Veins of the Lower Extremity . 671 The Plantar Digital Veins . . . .671 The Posterior Tibial Veins .... 672 The Anterior Tibial Veins .... 672 The Popliteal Vein 672 The Femoral Vein 672 The Deep Femoral Vein . . . 672 The Veins of the Abdomen and Pelvis . . 672 The External Iliac Vein 672 Tributaries 672 The Hypogastric Veins 673 Tributaries 673 The Hemorrhoidal Plexus .... 676 The Pudendal Plexus 676 The Vesical Plexus 676 The Dorsal Veins of the Penis . . 1 676 The Uterine Plexuses 676 The Vaginal Plexuses 677 The Common Iliac Veins .... 677 The Middle Sacral Veins . . . 677 Peculiarities 677 The Inferior Vena Cava ...."! 677 Relations 678 Peculiarities 678 Applied Anatomy 678 Tributaries 678 Lumbar Veins • 678 Spermatic Veins .... 678 Ovarian Veins 679 Renal Veins 679 Suprarenal Veins .... 679 Inferior Phrenic Veins . . . 679 Hepatic Veins 680 The Portal System of Veins. The Portal Vein 681 Tributaries 681 The Lienal Vein .681 Tributaries 681 The Superior Mesenteric Vein . ! 682 Tributaries 682 The Coronary Vein 682 The Pyloric Vein 682 The Cystic Vein 682 The Parumbilical Veins .... 682 THE LYMPHATIC SYSTEM. The Development of the Lymphatic Vessels 683 Lymphatic Capillaries 684 Distribution \ 084 Lymphatic Vessels 687 Structure of Lymphatic Vessels . . ’ 687 lhe Lymph Glands 688 Structure of Lymph Glands .... 688 Hemolymph Nodes 690 Lymph 690 The Thoracic Duct. The Cistema Chyli 691 Tributaries 691 The Right Lymphatic Duct . . . ! ! 691 Tributaries 692 The Lymphatics of the Head, Face, and Neck. The Lymph Glands of the Head .... 692 The Occipital Glands 692 The Posterior Auricular Glands . . . 693 The Anterior Auricular Glands . . . 693 The Parotid Glands 693 The Facial Glands 694 The Deep Facial Glands 694 The Lingual Glands ’ 694 The Retropharyngeal Glands . . . 694 The Lymphatic Vessels of the Scalp . 694 The Lymphatic Vessels of the Auricula and External Acoustic Meatus . . 694 The Lymphatic Vessels of the Face . 695 20 CONTENTS The Lymph Glands of the Head— The Lymphatic Vessels of the Nasal Cavities #•••••• 695 The Lymphatic Vessels of the Mouth . 695 The Lymphatic Vessels of the Palatine Tonsil 695 The Lymphatic Vessels of the Tongue . 69b The Lymph Glands of the Neck .... 697 The Submaxillary Glands . . . 697 The Submental or Suprahyoid Glands . 6J7 The Superficial Cervical Glands . . • 697 The Anterior Cervical Glands . . - 697 The Deep Cervical Glands . . _ . • 697 The Lymphatic Vessels of the Skin and Muscles of the Neck 698 The Lymphatics of the Upper Extremity. The Lymph Glands of the Upper Extremity 699 The Superficial Lymph Glands . . . 699 The Deep Lymph Glands .... 699 The Axillary Glands .... 699 The Lymphatic Vessels of the Upper Extremity . . . • • 700 The Superficial Lymphatic Vessels . . 700 The Deep Lymphatic Vessels . . . 701 The Lymphatics of the Lower Extremity. The Lymph Glands of the Lower Extremity 701 The Anterior Tibial Gland .... 701 The Popliteal Glands 701 The Inguinal Glands ,702 The Lymphatic Vessels of the Lower Extremity 703 The Superficial Lymphatic Vessels . . 703 The Deep Lymphatic Vessels . . . 703 The Lymphatics of the Abdomen and Pelvis. The Lymph Glands of the Abdomen and Pelvis 703 The Parietal Glands 703 , The External Iliac Glands . . . 703 The Common Iliac Glands . . . 704 The Epigastric Glands .... 704 The Iliac Circumflex Glands . . 704 The Hypogastric Glands . . .704 The Sacral Glands 704 The Lumbar Glands . . . 705 The Lymphatic Vessels of the Abdomen and Pelvis 706 The Superficial Vessels 706 The Deep Vessels 706 The Lymphatic Vessels of the Perineum and External Genitals 706 The Visceral Glands . . . ' . . • 706 The Gastric Glands 706 The Hepatic Glands .... 706 The Pancreaticolienial Glands . . 706 The Superior Mesenteric Glands . . 709 The Mesenteric Glands .... 709 The Ileocolic Glands .... 709 The Mesocolic Glands .... 70J The Inferior Mesenteric Glands . • <10 The Lymphatic Vessels of the Abdominal and Pelvic Viscera 710 The Lymphatic Vessels of the Abdomina and Pelvic Viscera— The Lymphatic Vessels of the Subdia- phragmatic Portions of the Digestive Tube 710 The Lymphatic Vessels of the Stomach 710 The Lymphatic Vessels of the Duodenum 710 The Lymphatic Vessels of the Jejunum and Ileum 710 The Lymphatic Vessels of the Vermiform Process and Cecum 710 The Lymphatic Vessels of the Colon . 711 The Lymphatic Vessels of the Anus, Anal Canal, and Rectum .... 711 The Lymphatic Vessels of the Liver . 711 The Lymphatic Vessels of the Gall- bladder 711 The Lymphatic Vessels of the Pancreas 711 The Lymphatic Vessels of the Spleen and Suprarenal Glands . . . . _. . 711 The Lymphatic Vessels of the Urinary Organs . . _ 712 The Lymphatic Vessels of the Kidney 712 The Lymphatic Vessels of the Ureter 712 The Lymphatic Vessels of the Bladder 712 The Lymphatic Vessels of the Prostate 713 The Lymphatic Vessels of the Urethra ... ... 713 The Lymphatic Vessels of the Repro- ductive Organs 713 The Lvmphatic Vessels of the Testes • 713 The Lymphatic Vessels of the Ductus Deferens 713 The Lymphatic Vessels of the Ovary 714 The Lymphatic Vessels of the Uterine Tube 714 The Lymphatic Vessels of the Uterus . . t 714 The Lymphatic Vessels of the Vagina 714 The Lymphatics of the Thorax. The Parietal Lymph Glands 715 The Sternal Glands 715 The Intercostal Glands 715 The Diaphragmatic Glands . . . • 715 The Superficial Lymphatic Vessels of the Thoracic Wall 715 The Lymphatic Vessels of the Mamma. 715 The Deep Lymphatic Vessels of the Thoracic Wall . • • • ■ ■ • ■ • • The Visceral Lymph Glands . . . 717 The Anterior Mediastinal Glands . . 717 The Posterior Mediastinal Glands . . 717 The Tracheobronchial Glands . . 717 The Lymphatic Vessels of the Thoracic Viscera • • 718 The Lymphatic Vessels of the Heart . 718 The Lymphatic Vessels of the Lungs . 718 The Lymphatic Vessels of the Pleura . 09 The Lymphatic Vessels of the Thymus 719 The Lymphatic Vessels of the Eso- phagus 719 NEUROLOGY Ganglia Neuron Theory • • Fasciculi, Tracts or Fiber Systems . . • Development of the Nervous System. The Medulla Spinalis 733 The Spinal Nerves '“J? The Brain ‘ao Structure of the Nervous System. Neuroglia Z99 Nerve Cells „9. Nerve Fibers ** Wallerian Degeneration Non-medullated Fibers • • • • ; ‘" Structure of the Peripheral Nerves and Origin:? and Terminations of Nerves . . • '29 CONTENTS 21 The Brain— The Hind-brain or Rhombencephalon . 738 The Mid-brain or Mesencephalon . . 741 The Fore-brain or Prosencephalon . 741 The Diencephalon 742 The Telencephalon 743 The Commissures 746 Fissures and Sulci 747 The Cranial Nerves 748 The Spinal Cord or Medulla Spinalis. Enlargements 751 Fissures and Sulci 752 The Anterior Median Fissure 752 The Posterior Median Sulcus . 752 The Internal Structure of the Medulla Spinalis 753 The Gray Substance 753 Structure of the Gray Substance . 755 The White Substance 758 Nerve Fasciculi 759 Roots of the Spinal Nerves 764 The Anterior Nerve Root .... 764 The Posterior Root 764 The Brain or Encephalon. General Considerations and Divisions . . 766 The Hind-brain or Rhombencephalon. The Medulla Oblongata 767 The Anterior Median Fissure . . . 767 The Posterior Median Fissure . . . 767 Internal Structure of the Medulla Oblongata 775 The Cerebrospinal Fasciculi 775 Gray Substance of the Medulla Oblongata 779 Inferior Peduncle 782 Formatio Reticularis .... 784 The Pons 785 Structure 785 The Cerebellum 788 Lobes of the Cerebellum 788 Internal Structure of the Cerebellum . 791 The White Substance . . . .791 Projection Fibres .... 791 The Gray Substance .... 794 Microscopic Appearance of the Cortex 794 The Fourth Ventricle 797 Angles 797 Lateral Boundaries 797 Choroid Plexuses 798 Openings in the Roof 798 Rhomboid Fossa 798 The Mid-brain or Mesencephalon. The Cerebral Peduncles 800 Structure of the Cerebral Peduncles . 801 The Gray Substance .... 802 The White Substance .... 803 The Corpora Quadrigemina 805 Structure of the Corpora Quadrigemina 806 The Cerebral Aqueduct 806 The Fore-brain or Prosencephalon. The Diencephalon 807 The Thalamencephalon 808 Structure 810 Connections 810 The Metathalamus 811 The Epithalamus 812 The Hypothalamus 812 The Optic Chiasma 814 The Optic Tracts 814 The Third Ventricle - 815 The Interpeduncular Fossa . . . .816 The Telencephalon 817 The Cerebral Hemispheres 817 The Longitudinal Cerebral Fissure . 818 The Surfaces of the Cerebral Hemi- spheres 818 The Lateral Cerebral Fissure . . . 819 The Central Sulcus 819 The Parietooccipital Fissure .... 820 The Calcarine Fissure 820 The Cingulate Sulcus 820 The Collateral Fissure 820 The Sulcus Circularis 821 The Lobes of the Hemispheres . . . 821 The Frontal Lobe 821 The Parietal Lobe 822 The Occipital Lobe 823 The Temporal Lobe 823 The Insula 825 The Limbic Lobe 825 The Rhinencephalon 826 The Olfactory Lobe 826 The Interior of the Cerebral Hemi- spheres 827 The Corpus Callosum .... 828 The Lateral Ventricles .... 829 The Fornix 838 The Interventricular Foramen . . 840 The Anterior Commissure . . . 840 The Septum Pellucidum.... 840 The Choroid Plexus of the Lateral Ventricle 840 Structure of the Cerebral Hemi- spheres 842 Structure of the Cerebral Cortex . . 845 Special Types of Cerebral Cortex . . 847 Weight of Encephalon 848 Cerebral Localization 849 Composition and Central Connections of the Spinal Nerves. The Intrinsic Spinal Reflex Paths . . . 850 Sensory Pathways from the Spinal Cord to the Brain 851 Composition and Central Connections of the Cranial Nerves. The Hypoglossal Nerve 855 The Accessory Nerve 855 The Vagus Nerve 855 The Glossopharyngeal Nerve 856 The Acoustic Nerve 857 The Vestibular Nerve 860 The Facial Nerve 861 The Abducens Nerve 861 The Trigeminal Nerve 862 The Trochlear Nerve 863 The Oculomotor Nerve 863 The Optic Nerve 864 The Olfactory Nerves 866 Pathways from the Brain to the Spinal Cord. The Motor Tract 870 The Meninges of the Brain and Medulla Spinalis. The Dura Mater 872 The Cranial Dura Mater .... 872 Processes 873 Structure : 875 The Spinal Dura Mater 875 Structure 876 The Arachnoid 876 The Cranial Part 876 The Spinal Part 876 Structure 876 The Subarachnoid Cavity .... 876 The Subarachnoid Cisternae .... 876 The Arachnoid Villi 878 Structure 878 The Pia Mater 878 The Cranial Pia Mater 879 The Spinal Pia Mater 879 The Ligamentum Denticulatum . 880 22 CONTENTS The Cerebrospinal Fluid . . 880 The Cranial Nerves. The Olfactory Nerves . . 881 The Optic Nerve. The Optic Chiasma 883 The Optic Tract 884 The Oculomotor Nerve . . . 884 The Trochlear Nerve .... 885 The Trigeminal Nerve. The Semilunar Ganglion 886 The Ophthalmic Nerve 887 The Lacrimal Nerve .... . 887 The Frontal Nerve 887 The Nasociliary Nerve 888 The Ciliary Ganglion 888 The Maxillary Nerve 889 Branches 889 The Middle Meningeal Nerve . . 889 The Zygomatic Nerve .... 889 The Sphenopalatine . . . . . 890 The Posterior Superior Alveolar . 890 The Middle Superior Alveolar . . 891 The Anterior Superior Alveolar . 891 The Inferior Palpebral . .891 The External Nasal 891 The Superior Labial . . . . 891 The Sphenopalatine Ganglion . . 891 The Mandibular Nerve 893 Branches 894 The Nervus Spinosus .... 894 The Internal Pterygoid Nerve . . 894 The Masseteric Nerve .... 894 The Deep Temporal Nerves . . 895 The Buccinator Nerve .... 895 The External Pterygoid Nerve . 895 The Auriculotemporal Nerve . . 895 The Lingual Nerve 895 The Inferior Alveolar Nerve . . 896 The Otic Ganglion 897 The Submaxillary Ganglion . . 898 Trigeminal Nerve Reflexes 899 ■ The Abducent Nerve .... 899 The Facial Nerve. The Greater Superficial Petrosal Nerve . . 903 The Nerve to the Stapedius ...... 904 The Chorda Tympani Nerve 904 The Posterior Auricular Nerve . . . . 905 The Digastric Branch 905 The Stylohyoid Branch 905 The Temporal Branches 905 The Zygomatic Branches 905 The Buccal Branches 905 The Mandibular Branch 905 The Cervical Branch 905 The Acoustic Nerve. The Cochlear Nerve 906 The Vestibular Nerve 906 The Glossopharyngeal Nerve. The Superior Ganglion 908 The Petrous Ganglion 908 The Tympanic Nerve 909 The Carotid Branches 909 The Pharyngeal Branches .... 909 The Muscular Branches 909 The Tonsillar Branches 909 The Lingual Branches 909 The Vagus Nerve. The Jugular Ganglion 911 The Ganglion Nodosum 911 The Ganglion Nodosum— The Meningeal Branch 911 The Auricular Branch 911 The Pharyngeal Branch 911 The Superior Laryngeal Nerve . . . 912 The Recurrent Nerve 912 The Superior Cardiac Branches . . . 912 The Inferior Cardiac Branches . . . 912 The Anterior Bronchial Branches . . 913 The Posterior Bronchial Branches . . 913 The Esophageal Branches .... 913 The Gastric Branches 913 The Celiac Branches 913 The Hepatic Branches 913 The Accessory Nerve. The Cranial Part 913 The Spinal Part 913 The Hypoglossal Nerve. Branches of Communication 915 Branches of Distribution 916 The Meningeal Branches .... 916 The Descending Ramus 916 The Thyrohyoid Branch 916 The Muscular Branches 916 The Spinal Nerves. Nerve Roots 916 The Anterior Root 916 The Posterior Root 916 The Spinal Ganglia 917 Structure ........ 917 Connections with Sympathetic . . . 920 Structure 920 Divisions of the Spinal Nerves . . . .921 The Posterior Divisions 921 The Cervical Nerves . . . .921 The Thoracic Nerves .... 923 The Lumbar Nerves .... 924 The Sacral Nerves 924 The Coccygeal Nerve .... 925 The Anterior Divisions 925 The Cervical Nerves .... 925 The Cervical Plexus . . . 925 Great Auricular Nerve . 926 Cutaneous Cervical Nerve 927 Supraclavicular Nerves 928 Communicantes Cervicales 928 Phrenic Nerve .... 928 The Brachial Plexus . . . 930 Relations 931 Dorsal Scapular Nerve . 932 Suprascapular Nerve . . 932 Nerve to Subclavius . 933 Long Thoracic Nerve . 933 Anterior Thoracic Nerves 933 Subscapular Nerves . . 933 Thoracodorsal Nerve . 934 Axillary Nerve . . 934 • . Musculocutaneous Nerve 935 Medial Antibrachial Cuta- neous Nerve . . 937 Medial Brachial Cuta- neous Nerve . . .937 Median Nerve . . . .938 Ulnar Nerve .... 939 Radial Nerve .... 943 The Thoracic Nerves . . . . 944 First Thoracic Nerve . . . 945 Upper Thoracic Nerves . . 945 Lower Thoracic Nerves . . 948 The Lumbosacral Plexus . . . 948 The Lumbar Nerves . . . 948 The Lumbar Plexus 949 Iliohypogastric Nerve 950 • Ilioinguinal Nerve . 952 Genitofemoral Nerve 953 Lateral Femoral Cuta- neous Nerve . 953 Obturator Nerve . 953 CONTENTS 23 Divisions of the Spinal Nerves— The Anterior Divisions— The Lumbosacral Plexus— The Lumbar Nerves— The Lumbar Plexus— Accessory Obturator Nerve .... 955 Femoral Nerve . . 955 Saphenous Nerve. . 956 The Sacral and Coccygeal Nerves 957 The Sacral Plexus . . 957 Relations . . . 957 Nerve to Quadratus Femoris and Gemellus Inferior 957 Nerve to Obturator Internus and Ge- mellus Superior . 958 Nerve to Piriformis 959 Superior Gluteal Nerve .... 959 Inferior Gluteal Nerve .... 959 Posterior Femoral Cutaneous Nerve 959 Sciatic Nerve . . 960 Tibial Nerve . . 960 Lateral Plantar Nerve 963 Common Peroneal Nerve .... 964 Deep Peroneal Nerve 965 Superficial Peroneal Nerve .... 966 The Pudendal Plexus . 966 Perforating Cuta- neous Nerve . . 967 Pudendal Nerve . 967 Anococcygeal Nerve 968 The Sympathetic Nerves. The Cranial Sympathetica 970 The Sacral Sympathetica 973 The Thoracolumbar Sympathetica . . . 974 The Sympathetic Trunks 976 Connections with the Spinal Nerves . . 976 Development 977 The Cephalic Portion of the Sympathetic System. The Internal Carotid Plexus .... 977 The Cavernous Plexus 978 The Cervical Portion of the Sympathetic System. The Superior Cervical Ganglion . . . 978 Branches 978 The Middle Cervical Ganglion .... 979 Branches 979 The Inferior Cervical Ganglion .... 980 Branches 981 The Thoracic Portion of the Sympathetic System. The Greater Splanchnic Nerve .... 981 The Lesser Splanchnic Nerve .... 981 The Lowest Splanchnic Nerve .... 981 The Abdominal Portion of the Sympathetic System . . . .982 The Pelvic Portion of the Sympathetic System .... 984 The Great Plexuses of the Sympathetic System. The Cardiac Plexus 984 The Celiac Plexus 985 Phrenic Plexus 985 Hepatic Plexus 986 Lienal Plexus 986 Superior Gastric Plexus 987 Suprarenal Plexus 987 Renal Plexus 987 Spermatic Plexus 987 Superior Mesenteric Plexus . . . 987 Abdominal Aortic Plexus .... 987 Inferior Mesenteric Plexus .... 987 The Hypogastric Plexus 987 The Pelvic Plexuses 987 The Middle Hemorrhoidal Plexus . . 988 The Vesical Plexus 988 The Prostatic Plexus 988 The Vaginal Plexus 989 The Uterine Plexus 989 THE ORGANS OF TIIE SENSES AND THE COMMON INTEGUMENT. The Peripheral Organs of the Special Senses. The Organs of Taste. Structure 991 The Organ of Smell. The External Nose 992 Structure 992 The Nasal Cavity 994 The Lateral Wall 994 The Medial Wall 995 The Mucous Membrane .... 996 Structure 996 The Accessory Sinuses of the Nose . . . 998 The Frontal Sinuses 998 The Ethmoidal Air Cells .... 998 The Sphenoidal Sinuses 998 The Maxillary Sinus 999 The Organ of Sight. Development 1001 The Tunics of the Eye ....!! 1005 The Fibrous Tunic 1005 The Sclera 1005 Structure 1006 The Cornea 1006 Structure 1007 The Tunics of the Eye— The Vascular Tunic 1009 The Choroid 1009 Structure 1010 The Ciliary Body 1010 Structure 1011 The Iris 1012 Structure 1013 Membrana Pupillaris .... 1014 The Retina 1014 Structure 1015 The Refracting Media 1018 The Aqueous Humor 1018 The Vitreous Body 1018 The Crystalline Lens 1019 Structure 1020 The Accessory Organs of the Eye . . . 1021 The Ocular Muscles 1021 Levator Palpebrge Superioris . . 1021 The Recti 1022 Obliquus Oculi Superior . 1022 Obliquus Oculi Inferior . 1023 The Fascia Bulb 1024 The Orbital Fascia 1025 The Eyebrows 1025 The Eyelids 1025 The Lateral Palpebral Commis- sure 1025 The Eyelashes 1025 Structure of the Eyelids . 1025 The Tarsal Glands 1026 24 CONTENTS The Accessory Organs of the Eye— Structure of the Tarsal Glands . 1026 The Conjunctiva 1026 The Palpebral Portion .... 1027 The Bulbar Portion .... 1027 The Lacrimal Apparatus .... 1028 The Lacrimal Gland .... 1028 Structure 1028 The Lacrimal Ducts .... 1028 The Lacrimal Sac 1028 Structure 1029 The Nasolacrimal Duct . . . 1029 The Organ of Hearing. Development 1029 The External Ear 1033 The Auricula or Pinna 1033 Structure 1034 The External Acoustic Meatus . . 1036 Relations . . . . . . . 1037 The Middle Ear or Tympanic Cavity . . 1037 The Tegumental Wall or Roof . . . 1038 The Jugular Wall or Floor .... 1038 The Membranous or Lateral Wall . 1038 The Tympanic Membrane .... 1039 Structure 1039 The Labyrinthic or Medial Wall . . 1040 The Mastoid or Posterior Wall . . 1042 The Carotid or Anterior Wall . . . 1042 The Auditory Tube 1042 The Auditory Ossicles 1044 The Malleus 1044 The Incus 1044 The Stapes ........ 1045 Articulations of the Auditory Ossicles 1045 Ligaments of the Ossicles .... 1045 The Muscles of the Tympanic Cavity 1046 The Tensor Tympani .... 1046 The Stapedius 1046 The Internal Ear or Labyrinth .... 1047 The Osseous Labyrinth 1047 The Internal Ear or Labyrinth— The Osseous Labyrinth— The Vestibule 1047 The Bony Semicircular Canals . 1049 The Cochlea 1050 The Membranous Labyrinth . . . 1051 The Utricle 1051 The Saccule 1052 The Semicircular Ducts . . . 1052 Structure 1052 The Ductus Cochlearis . . . 1054 The Basilar Membrane . . . 1056 The Spiral Organ of Corti . . 1056 Hair Cells 1057 Peripheral Terminations of Nerves of General Sensations. Free Nerve-endings 1059 Special End-organs 1059 End-bulbs of Krause 1060 Tactile Corpuscles of Grandry .... 1060 Pacinian Corpuscles 1060 Corpuscles of Golgi and Mazzoni . . . 1061 Tactile Corpuscles of Wagner and Meissner 1061 Corpuscles of Ruffini 1061 Neurotendinous Spindles 1061 Neuromuscular Spindles 1061 The Comon Integument. The Epidermis, Cuticle, or Scarf Skin . 1062 The Corium, Cutis Vera, Dermis, or True Skin 1065 Development 1066 The Appendages of the Skin. The Nails 1066 The Hairs 1067 The Sebaceous Glands 1069 The Sudoriferous or Sweat Glands . . . 1070 SPLANCHNOLOGY. The Respiratory Apparatus. Development 1071 The Larynx. The Cartilages of the Larynx .... 1073 The Thyroid Cartilage 1073 The Cricoid Cartilage 1074 The Arytenoid Cartilage . . . . 1075 The Corniculate Cartilages . . . . 1075 The Cuneiform Cartilages .... 1075 The Epiglottis 1075 Structure 1076 The Ligaments of the Larynx . . . . 1076 The Extrinsic Ligaments . . . . 1076 The Intrinsic Ligaments .... 1077 The Interior of the Larynx 1078 The Ventricular Folds 1079 The Vocal Folds 1079 The Ventricle of the Larynx . . . 1080 The Rima Glottidis 1080 The Muscles of the Larynx 1081 Cricothyreoideus 1081 Cricoarytsenoideus Posterior . . . 1082 Cricoarytamoideus Lateralis . . . 1082 Arytsenoideus 1082 Thyreoarytaenoideus 1083 The Trachea and Bronchi. Relations • . . 1084 The Right Bronchus 1085 The Left Bronchus 1085 Structure 1086 The Pleurae. Reflections of the Pleura 1088 Pulmonary Ligament 1090 Structure of Pleura 1090 The Mediastinum. Superior Mediastinum 1090 Anterior Mediastinum 1092 Middle Mediastinum 1092 Posterior Mediastinum 1093 The Lungs. The Apex of the Lungs 1094 The Base of the Lungs 1094 Surfaces of the Lungs 1094 Borders of the Lungs 1096 Fissures and Lobes of the Lungs . . . 1096 The Root of the Lung 1097 Divisions of the Bronchi 1097 Structure of the Lungs 1098 The Digestive Apparatus. The Digestive Tube 1100 The Development of the Digestive Tube 1101 The Mouth 1101 The Salivary Glands . . . . 1102 The Tongue 1102 The Palatine Tonsils .... 1103 The Further Development of the Digestive Tube 1103 The Rectum and Anal Canal . . 1108 CONTENTS 25 The Mouth. The Vestibule of the Mouth 1110 The Mouth Cavity Proper 1110 ' Structure 1110 The Lips 1111 1 The Labial Glands 1111 The Cheeks 1112 Structure 1112 The Gums 1112 The Palate 1112 The Hard Palate 1112 The Soft Palate 1112 The Teeth 1112 General Characteristics 1114 The Permanent Teeth 1115 The Canine Teeth 1117 The Premolar or Bicuspid Teeth . 1118 The Molar Teeth 1118 The Deciduous Teeth 1118 Structure of the Teeth 1118 Development of the Teeth .... 1121 Development of the Deciduous Teeth 1122 Development of the Permanent Teeth 1124 Eruption of the Teeth 1124 The Tongue 1125 The Root of the Tongue .... 1125 The Apex of the Tongue .... 1125 The Dorsum of the Tongue . . . 1125 The Papilla) of the Tongue . . . . 1126 The Muscles of the Tongue . . . 1128 Genioglossus 1129 Hyoglossus 1129 Chondroglossus 1130 Styloglossus 1130 Longitudinalis Lingum Superior 1130 Longitudinalis Lingua) Inferior 1130 Transversus Lingua) . . . 1130 Verticalis Lingua) 1131 Structure of the Tongue . . . . 1131 Glands of the Tongue 1131 The Salivary Glands 1132 The Parotid Gland 1132 Structures within the Gland . . 1134 The Parotid Duct 1134 Structure 1134 The Submaxillary Gland . . . 1135 The Submaxillary Duct . . . 1135 The Sublingual Gland 1136 Structure of the Salivary Gland . . 1136 Accessory Glands 1137 The Fauces. The Glossopalatine Arch 1137 The Pharyngopalatine Arch 1137 The Palatine Tonsils 1137 Structure 1139 The Palatine Aponeurosis 1139 The Muscles of the Palate .... 1139 Levator Veli Palatini . . . . 1139 Tensor Veli Palatini . . . . 1139 Musculus Uvulse 1139 Glossopalatinus 1139 Paryngopalatinus 1139 The Pharynx. The Nasal Part of the Pharynx .... 1141 The Oral Part of the Pharynx .... 1142 The Laryngeal Part of the Pharynx . . 1142 The Muscles of the Pharynx .... 1142 Constrictor Pharyngis Inferior . . . 1142 Constrictor Pharyngis Medius . . . 1142 Constrictor Pharyngis Superior . . 1142 Stylopharyngeus 1142 Salpingopharyngeus 1142 Structure of the Pharynx 1143 The Esophagus. Relations 1145 Structure 1146 The Abdomen. Boundaries of the Abdomen 1147 The Apertures in the Walls of the Abdomen 1147 Regions of the Abdomen 1147 The Peritoneum 1149 Vertical Dispositions of the Main Peri- toneal Cavity 1150 Vertical Disposition of the Omental Bursa 1152 Horizontal Disposition of the Peri- toneum 1153 In the Pelvis 1153 In the Lower Abdomen . . . 1154 In the Upper Abdomen . . . 1155 The Omenta 1156 The Mesenteries 1157 The Peritoneal Recesses or Fossae . . 1158 The Duodenal Fossae .... 1159 The Cecal Fossae 1160 The Intersigmoid Fossa . . . 1161 The Stomach. Openings of the Stomach 1161 Curvatures of the Stomach 1162 Surfaces of the Stomach 1162 Component Parts of the Stomach . . . 1163 Position of the Stomach 1163 Interior of the Stomach 1164 Pyloric Valve 1164 Structure of the Stomach 1164 The Gastric Glands 1166 The Small Intestine. The Duodenum 1169 Relations . 1169 The Jejunum and Ileum 1170 Meckel’s Diverticulum 1172 Structure 1172 The Large Intestine. The Cecum 1177 The Vermiform Process or Appendix . 1178 Structure . 1179 The Colic Valve 1179 The Colon 1180 The Ascending Colon 1180 The Transverse Colon 1180 The Descending Colon 1181 The Iliac Colon 1182 The Sigmoid Colon 1182 The Rectum 1183 Relations of the Rectum .... 1184 The Anal Canal 1184 Structure of the Colon 1184 The Liver. Surfaces of the Liver 1188 Fossae of the Liver 1191 Lobes of the Liver 1191 Ligaments of the Liver 1192 Fixation of the Liver 1193 Development of the Liver 1193 Structure of the Liver . . _ . . . . 1195 Excretory Apparatus of the Liver . . . 1197 The Hepatic Duct 1197 The Gall-bladder 1197 Relations 1197 Structure 1198 The Common Bile Duct .... 1198 Structure 1199 The Pancreas. Relations 1200 The Pancreatic Duct 1202 Development of the Pancreas .... 1202 Structure . 1203 26 CONTENTS The Urogenital Apparatus. Development of the Urinary and Generative Organs The Pronephros and Wolffian Duct . . 1205 The Mesonephros, Mullerian Duct, and Genital Gland 1205 The Mullerian Ducts 1206 Genital Glands 1207 The Ovary 1207 The Testis 1210 Descent of the Ovaries 1211 The Metanephros and the Permanent Kidney 1211 The Urinary Bladder 1212 The Prostate 1213 External Organs of Generation .... 1213 The Urethra . 1215 The Urinary Organs. The Kidneys 1215 Relations 1215 Surfaces 1215 Borders 1218 Extremities 1219 Fixation of the Kidney .... 1220 General Structure of the Kidney . . 1220 The Ureters 1225 The Ureter Proper 1226 Structure 1227 Variations 1227 The Urinary Bladder 1227 The Empty Bladder ..... 1227 The Distended Bladder 1228 The Bladder in the Child .... 1229 The Female Bladder 1230 The Ligaments of the Bladder . . . 1231 The Interior of the Bladder . . . 1231 Structure 1232 Abnormalities 1233 The Male Urethra 1234 The Prostatic Portion 1234 The Membranous Portion .... 1235 The Cavernous Portion 1235 Structure 1235 Congenital Defects 1235 The Female Urethra 1236 Structure 1236 Th Male Genital Organs. The Testes and their Coverings .... 1236 The Scrotum 1237 The Intercrural Fascia .... 1238 The Cremaster Muscle 1238 The Infundibuliform Fascia . . . 1239 The Tunica Vaginalis 1239 The Inguinal Canal ....... 1239 The Spermatic Cord 1239 Structure of the Spermatic Cord . 1239 The Testes 1240 The Epididymis 1242 Appendages of the Testis and Epi- didymis 1242 The Tunica Vaginalis . . 1242 The Tunica Albuginea . . 1242 The Tunica Vasculosa . . 1243 Structure 1243 Peculiarities 1245 Fhe Ductus Deferens 1245 The Ductuli Aberrantes .... 1246 Paradidymis 1246 Structure 1246 The Vesiculse Seminales 1246 Structure 1247 The Ejaculatory Ducts 1247 Structure 1247 The Penis 1247 The Corpora Cavernosa Penis . . . 1248 The Corpus Cavernosum Urethrae . 1248 Structure of the Penis . . . . . • 1250 The Prostate 1251 Structure 1253 The Bulbourethral Glands 1253 Structure 1253 The Female Genital Organs. The Ovaries 1254 The Epoophoron 1255 The Paroophoron 1255 Structure 1255 Vesicular Ovarian Follicles .... 1256 Discharge of the Ovum 1256 Corpus Luteum 1256 The Uterine Tube 1257 Structure 1257 The Uterus 1258 The Body 1259 The Cervix 1259 The Interior of the Uterus .... 1260 The Cavity of the Body . . 1260 The Canal of the Cervix . . 1260 The Ligaments of the Uterus . . . 1260 Structure 1262 The Vagina 1264 Relations 1264 Structure 1264 The External Organs . . . . . . . 1264 The Mons Pubis . . . . . . . 1265 The Labia Majora 1265 The Labia Minora 1265 The Clitoris 1266 The Vestibule 1266 The Bulb of the Vestibule .... 1266 The Greater Vestibular Glands 1266 The Mammae 1267 The Mammary Papilla or Nipple . 1267 Development 1267 Structure 1267 The Ductless Glands. The Thyroid Gland. Development 1270 Structure 1271 The Parathyroid Glands. Development 1272 Structure 1273 The Thymus. Development 1273 Structure 1274 The Hypophysis Cerebri. Development 1276 The Pineal Body. Structure 1277 The Chromaphil and Cortical Systems. Development 1277 The Suprarenal Glands / . 1278 Development 1278 Relations 1278 Accessory Suprarenals 1279 Structure 1279 Glomus Caroticum 1281 Glomus Coccygeum 1281 The Spleen. Development 1282 Relation 1282 Structure 1283 CONTENTS 27 SURFACE ANATOMY AND SURFACE MARKINGS. Surface Anatomy of the Head and Neck. The Bones 1287 The Joints and Muscles 1288 The Arteries 12!H) Surface Markings of Special Regions of the Head and Neck. The Cranium 1291 The Scalp 1291 Bony Landmarks 1291 The Brain 1292 Vessels 1294 The Face 1294 External Maxillary Artery .... 1294 Trigeminal Nervo 1295 Parotid Gland 1295 The Nose 1296 The Mouth 1296 The Eye 1299 The Ear 1300 The Tympanic Antrum 1301 The Neck 1301 Muscles 1302 Arteries 1302 Veins 1303 Nerves 1303 Submaxillary Gland 1303 Surface Anatomy of the Back. Bones 1303 i Muscles 1304 Surface Markings of the Back. Bony Landmarks 1305 Medulla Spinalis 1306 Spinal Nerves 1307 Surface Anatomy of the Thorax. Bones 1307 Muscles 1307 Mamma 1308 Surface Markings of the Thorax. Bony Landmarks 1308 Diaphragm 1309 Surface Lines 1309 Pleurae 1309 Lungs 1310 Trachea 1311 Esophagus 1311 Heart 1311 Arteries 1312 Veins 1312 Surface Anatomy of the Abdomen. Skin 1313 Bones 1313 Muscles 1313 Vessels 1313 Viscera 1313 Surface Markings of the Abdomen. Bony Landmarks 1315 Muscles 1315 Surface Lines 1315 Stomach 1317 Duodenum 1319 Small Intestine 1319 Cecum and Vermiform Process . . . . 1319 Ascending Colon 1319 Transverse Colon 1319 Descending Colon 1320 Iliac Colon 1320 Liver 1320 Pancreas 1320 Spleen 1320 Kidneys 1320 • Ureters 1321 Vessels 1321 Nerves 1322 Surface Anatomy of the Perineum. Skin 1322 Bones 1322 Muscles and Ligaments 1322 Surface Markings of the Perineum. Rectum and Anal Canal 1322 Male Urogenital Organs 1323 | Female Urogenital Organs 1323 Surface Anatomy of the Upper Extremity. Skin 1325 Bones 1326 Articulations 1327 Muscles 1327 Arteries 1331 Veins 1331 Nerves 1331 Surface Markings of the Upper Extremity. Bony Landmarks 1331 Articulations 1331 Muscles 1332 Mucous Sheaths 1334 Arteries 1334 Nerves 1335 Surface Anatomy of the Lower Extremity. Skin v1336 Bones . 133G Articulations 1338 Muscles 1338 Arteries 1341 Veins 1342 ; Nerves 1342 ; Surface Markings of the Lower Extremity. Bony Landmarks 1342 Articulations 1343 > Muscles 1343 ! Mucous Sheaths 1343 5 Arteries 1343 5 Veins 1346 1 Nerves 1346 ANATOM ICA L BIBLIOGRAPHY. INDEXES. Anatomical Bibliography of the Concilium Bibliographicum. Bibliographic Service; Wistar Institute of Anatomy, 1917— Bibliographic Anatomique, 1893- Index Medicus, 1879- Index Catalogue of the Library of the Surgeon-General’s Office, U. S. Army, 1880- Jahresberichte iiber die Fortschritte der Anatomie und Physrologie, 1856-1894. Jahresberichte iiber die Fortschritte der Anatomie und Entwicklungsgeschichte, 1895- JOURNALS. The Anatomical Record, 1906- The American Journal of Anatomy, 1901— Anatomische Hefte, 1892- Anatomischer Anzeiger, 1886- Archives d’Anatomie Microscopique, 1897- Archiv fiir Anatomie und Physiologie, 1795- Arehiv fiir Entwicklungsmechanik der Organismen, 1894- Archiv fiir Microskopische Anatomie, 1865- Archivo Italiano di Anatomia e di Embriologia, 1902- Biological Bulletin, 1900- Brain, 1878- Bibliographie Anatomique, 1893- Contributions to Embryology, Carnegie Institution of Washington, 1914- Comptes Rendus de I Association des Anatomistes, 1899- Gegenbaur’s Morphologisches Jahrbuch, 1876- International Monatsschrift fiir Anatomie und Histologie, 1884- The Journal of Anatomy and Physiology, 1867- Journal of Comparative Neurology, 1891- Journal de 1’Anatomie et de Physiologie, etc., 1864- Journal of Experimental Zoology, 1904- Journal of Morphology, 1887- Le Nevraxe, 1900- Morphologische Arbeiten, 1892-1898. Petrus Camper Nederlandsche Bijdragen tot de Anatomie, 1902- Proceedings of the Royal Society, Series B. Quarterly Journal of Microscopical Science, 1853- Zeitschrift fiir Morphologie und Anthropologie, 1899- Zeitschrift fiir Wissenschaftliche Mikroskopie, 1884- ( xxv iii) Pages 29-32 missing ANATOMY OF THE HUMAN BODY. INTRODUCTION. term human anatomy comprises a consideration of the various structures -L which make up the human organism. In a restricted sense it deals merely with the parts which form the fully developed individual and which can be ren- dered e\ ident to the naked eye by various methods of dissection. Kegarded from such a standpoint it may be studied by two methods: (1) the various structures may be separately considered—systematic anatomy; or (2) the organs and tissues may be studied in relation to one another—topographical or regional anatomy. It is, however, of much advantage to add to the facts ascertained by naked- eye dissection those obtained by the use of the microscope. This introduces two fields of investigation, viz., the study of the minute structure of the various component parts of the body histology—and the study of the human organism in its immature condition, i. e., the various stages of its intrauterine develop- ment from the fertilized ovum up to the period when it assumes an independent existence—embryology. Owing to the difficulty of obtaining material illustrating all the stages of this early development, gaps must be filled up by observations on the development of lower forms—comparative embryology, or by a consideration of adult forms in the line of human ancestry—comparative anatomy. The direct application of the facts of human anatomy to the various pathological conditions which may occur constitutes the subject of applied anatomy. Finally, the appre- ciation of structures on or immediately underlying the surface of the body is frequently made the subject of special study—surface anatomy. Systematic Anatomy.—The various systems of which the human body is composed are grouped under the following headings: 1. Osteology—the bony system or skeleton. 2. Syndesmology—the articulations or joints. 3. Myology—the muscles. With the description of the muscles it is convenient to include that of the fascke which are so intimately connected with them. 4. Angiology the vascular system, comprising the heart, bloodvessels, lymphatic vessels, and lymph glands. 5. Neurology—the nervous system. The organs of sense may be included in this system. 6. Splanchnology —the visceral system. Topographically the viscera form two groups, viz., the thoracic viscera and the abdomino-pelvic viscera. The heart, a thoracic viscus, is best considered with the vascular system. The rest 33 34 INTRODUCTION of the viscera may be grouped according to their functions: (a) the respiratory apparatus; (6) the digestive apparatus; and (c) the urogenital apparatus. Strictly speaking, the third subgroup should include only such components of the urogenital apparatus as are included within the abdomino-pelvic cavity, but it is convenient to study under this heading certain parts which lie in relation to the surface of the body, e. g., the testes and the external organs of generation. For descriptive purposes the body is supposed to be in the erect posture, with the arms hanging by the sides and the palms of the hands directed forward. The median plane is a vertical antero-posterior plane, passing through the center of the trunk. This plane will pass approximately through the sagittal suture of the skull, and hence any plane parallel to it is termed a sagittal plane. A vertical plane at right angles to the median plane passes, roughly speaking, through the central part of the coronal suture or through a line parallel to it; such a plane is known as a frontal plane or sometimes as a coronal plane. A plane at right angles to both the median and frontal planes is termed a transverse plane. The terms anterior or ventral, and posterior or dorsal, are employed to indicate the relation of parts to the front or back of the body or limbs, and the terms superior or cephalic, and inferior or caudal, to indicate the relative levels of different structures; structures nearer to or farther from the median plane are referred to as medial or lateral respectively. The terms superficial and deep are strictly confined to descriptions of the relative depth from the surface of the various structures; external and internal are reserved almost entirely for describing the walls of cavities or of hollow viscera. In the case of the limbs the words proximal and distal refer to the relative distance from the attached end of the limb. EMBRYOLOGY. THE term Embryology, in its widest sense, is applied to the various changes which take place during the growth of an animal from the egg to the adult condition: it is, however, usually restricted to the phenomena which occur before birth. Embryology may be studied from two aspects: (1) that of ontogeny, which deals only with the development of the individual; and (2) that of phylogeny, which concerns itself with the evolutionary history of the animal kingdom. In vertebrate animals the development of a new being can only take place when a female germ cell or ovum has been fertilized by a male germ cell or spermatozoon. The ovum is a nucleated cell, and all the complicated changes by which the various tissues and organs of the body are formed from it, after it has been fertilized, are the result of two general processes, viz., segmentation and differentiation of cells. Thus, the fertilized ovum undergoes repeated segmentation into a number of cells which at first closely resemble one another, but are, sooner or later, differentiated into two groups: (1) somatic cells, the function of which is to build up the various tissues of the body; and (2) germinal cells, which become imbedded in the sexual glands—the ovaries in the female and the testes in the male—and are destined for the perpetuation of the species. Having regard to the main purpose of this work, it is impossible, in the space available in this section, to describe fully, or illustrate adequately, all the phenom- ena which occur in the different stages of the development of the human body. Only the principal facts are given, and the student is referred for further details to one or other of the text-books1 on human embryology. All the tissues and organs of the body originate from a microscopic structure (the fertilized ovum), which consists of a soft jelly-like material enclosed in a membrane and containing a vesicle or small spherical body inside which are one or more denser spots. This may be regarded as a complete cell. All the solid tissues consist largely of cells essentially similar to it in nature but differing in external form. In the higher organisms a cell may be defined as “a nucleated mass of proto- plasm of microscopic size.” Its two essentials, therefore, are: a soft jelly-like material, similar to that found in the ovum, and usually styled cytoplasm, and a small spherical body imbedded in it, and termed a nucleus. Some of the unicellular protozoa contain no nuclei but granular particles which, like true nuclei, stain with basic dyes. The other constituents of the ovum, viz., its limiting membrane and the denser spot contained in the nucleus, called the nucleolus, are not essential to the type cell, and in fact many cells exist without them. Cytoplasm (protoplasm) is a material probably of variable constitution during life, but yielding on its disintegration bodies chiefly of proteid nature. Lecithin and cholesterin are constantly found in it, as well as inorganic salts, chief among THE ANIMAL CELL. 1 Manual of Human Embryology, Keibel and Mall; Handbuch der vergleichenden und experimentellen Entwickel- ungslehre der Wirbeltiere, Oskar Hertwig; Lehrbuch der Entwickelungsgeschichte, Bonnet; The Physiology of Reproduction, Marshall. 36 EMBRYOLOGY which are the phosphates and chlorides of potassium, sodium, and calcium. It is of a semifluid, viscid consistence, and probably colloidal in nature. The living cytoplasm appears to consist of a homogeneous and structureless ground-substance in which are embedded granules of various types. The mitochondria are the most constant type of granule and vary in form from granules to rods and threads. Their function is unknown. Some of the granules are proteid in nature and prob- ably essential constituents; others are fat, glycogen, or pigment granules, and are regarded as adventitious material taken in from without, and hence are styled cell-inclusions or paraplasm. When, however, cells have been “fixed” by reagents a fibrillar or granular appearance can often be made out under a high power of the microscope. The fibrils are usually arranged in a network or reticulum, to which the term spongioplasm is applied, the clear substance in the meshes being termed hyaloplasm. The size and shape of the meshes of the spongioplasm vary in different cells and in different parts of the same cell. The relative amounts of spongioplasm and hyaloplasm also vary in different cells, the latter preponderating in the young cell and the former increasing at the expense of the hyaloplasm as the cell grows. Such appearances in fixed cells are no indication whatsoever of the existence of Centrosome consisting of cen- irosphere enclosing two ct n- trioles Cell wall Nucleolus Nuclear 'membrane Net-knot of chromatin form- ing a pseudo-nucleolus 'Chromatin network Vacuole Cell-inclusions (paraplasm) Fig. 1.—Diagram of a cell. (Modified from Wilson.) similar structures in the living, although there must have been something in the living cell to give rise to the fixed structures. The peripheral layer of a cell is in all cases modified, either by the formation of a definite cell membrane as in the ovum, or more frequently in the case of animal cells, by a transformation, probably chemical in nature, which is only recognizable by the fact that the surface of the cell behaves as a semipermeable membrane. Nucleus.—The nucleus is a minute body, imbedded in the protoplasm, and usually of a spherical or oval form, its size having little relation to that of the cell. It is surrounded by a well-defined wall, the nuclear membrane; this encloses the nuclear substance (nuclear matrix), which is composed of a homogeneous material in which is usually embedded one or two nucleoli. In fixed cells the nucleus seems to consist of a clear substance or karyoplasm and a network or karyomitome. The former is probably of the same nature as the hyaloplasm of the cell, but the latter, which forms also the wall of the nucleus, differs from the spongioplasm of the cell substance. It consists of fibers or filaments arranged in a reticular manner. These filaments are composed of a homogeneous material known as linin, which stains with acid dyes and contains embedded in its substance particles which have a strong affinity for basic dyes. These basophil granules have been named chromatin THE ANIMAL CELL 37 or basichromatin and owe their staining properties to the presence of nucleic acid. Within the nuclear matrix are one or more highly refracting bodies, termed nucleoli, connected with the nuclear membrane by the nuclear filaments. They are regarded as being of two kinds. Some are mere local condensations (“net-knots”) of the chromatin; these are irregular in shape and are termed pseudo-nucleoli; others are distinct bodies differing from the pseudo-nucleoli both in nature and chemical composition; they may be termed true nucleoli, and are usually found in resting cells. The true nucleoli are oxyphil, i. e., they stain with acid dyes. Most living cells contain, in addition to their protoplasm and nucleus, a small particle which usually lies near the nucleus and is termed the centrosome. In the middle of the centrosome is a minute body called the centriole, and surrounding this is a clear spherical mass known as the centrosphere. The protoplasm surround- ing the centrosphere is frequently arranged in radiating fibrillar rows of granules, forming what is termed the attraction sphere. Reproduction of Cells.—Reproduction of cells is effected either by direct or by indirect division. In reproduction by direct division the nucleus becomes constricted in its center, assuming an hour-glass shape, and then divides into two. This is fol- lowed by a cleavage or division of the whole protoplasmic mass of the cell; and thus two daughter cells are formed, each containing a nucleus. These daughter cells are at first smaller than the original mother cell; but they grow, and the process may be repeated in them, so that multiplication may take plage rapidly. Indirect divsion or karyokinesis (karyomitosis) has been observed in all the tissues—genera- tive cells, epithelial tissue, connective tissue, muscular tissue, and nerve tissue. It is possible that cell division may always take place by the indirect method. The process of indirect cell division is characterized by a series of complex changes in the nucleus, leading to its subdivision; this is followed by cleavage of the cell protoplasm. Starting with the nucleus in the quiescent or resting stage, these changes may be briefly grouped under the four following phases (Fig. 2). 1. Prophase.—The nuclear network of chromatin filaments assumes the form of a twisted skein or spirem, while the nuclear membrane and nucleolus disappear. The convoluted skein of chromatin divides into a definite number of V-shaped segments or chromosomes. The number of chromosomes varies in different animals, but is constant for all the cells in an animal of any given species; in man the number is given by Flemming and Duesberg as twenty-four.1 Coincidently with or pre- ceding these changes the centriole, which usually lies by the side of the nucleus, undergoes subdivision, and the two resulting centrioles, each surrounded by a centrosphere, are seen to be connected by a spindle of delicate achromatic fibers the achromatic spindle. The centrioles move away from each other—one toward either extremity of the nucleus—and the fibrils of the achromatic spindle are cor- respondingly lengthened. A line encircling the spindle midway between its ex- tremities or poles is named the equator, and around this the V-shaped chromosomes arrange themselves in the form of a star, thus constituting the mother star or monaster. 2. Metaphase. — Each V-shaped chromosome now undergoes longitudinal cleavage into two equal parts or daughter chromosomes, the cleavage commencing at the apex of the V and extending along its divergent limbs. 3. Anaphase.—The daughter chromosomes, thus separated, travel in opposite directions along the fibrils of the achromatic spindle toward the centrioles, around which they group themselves, and thus two star-like figures are formed, one at either pole of the achromatic spindle. This constitutes the diaster. The daughter chromosomes now arrange themselves into a skein or spirem, and eventually form the network of chromatin which is characteristic of the resting nucleus. Dr. J. Duesberg, Anat. Anz., Band xxviii, S. 47. 38 EMBRYOLOGY 4. Telophase.—The cell protoplasm begins to appear constricted around the equator of the achromatic spindle, where double rows of granules are also sometimes seen. The constriction deepens and the original cell gradually becomes divided into two new cells, each with its own nucleus and centrosome, which assume the ordinary positions occupied by such structures in the resting stage. The nuclear membrane and nucleolus are also differentiated during this phase. Fia. 2.—Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic division. (Schafer.) I to III, prophase; IV, metaphase; V and VI, anaphase; VII and \ III, telophase. THE OVUM. The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries. Each primitive germ cell gives rise, by repeated divisions, to a number of smaller cells termed oogonia, from which the ova or primary oocytes are developed. Human ova are extremely minute, measuring about 0.2 mm. in diameter, and are enclosed within the egg follicles of the ovaries; as a rule each follicle contains THE OVUM 39 a single ovum, but sometimes two or more are present.1 By the enlargement and subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and conveyed by the uterine tube to the cavity of the uterus. Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being. In appearance and structure the ovum (Fig. 3) differs little from an ordinary cell, but distinctive names have been applied to its several parts; thus, the cell substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and the nucleolus as the germinal spot. The ovum is enclosed within a thick, trans- Fid. 3.—Human ovum examined fresh in the liquor folliculi. (Waldeyer.) The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. parent envelope, the zona striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata. Yolk.—The yolk comprises (1) the cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm; this is frequently termed the formative yolk; (2) the nutritive yolk or deutoplasm, which consists of numerous rounded granules of fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian ovum the nutritive volk is extremelv small in amount, and is of service in nourish- See description of the ovary on a future page. 40 EMBRYOLOGY ing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout the whole period of incubation. The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole are present and lie in the immediate neighborhood of the nucleus. Germinal Vesicle.—The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position, but becomes eccentric as the grow th of the ovum proceeds. Its structure is that of an ordinary cell-nucleus, viz., it consists of a reticulum or karyomitome, the meshes of which are filled with karyoplasm, while connected with, or imbedded in, the reticulum are a number of chromatin masses or chromosomes, which may present the appearance of a skein or may assume the form of rods or loops.. The nucleus is enclosed by a delicate nuclear membrane, and contains in its interior a well-defined nucleolus or germinal spot. . . Coverings of the Ovum.—The zona striata or zona pellucida (Fig. 3) is a thick membrane, which, under the higher powers of the microscope, is seen to be radially striated. It persists for some time after fertilization has occurred, and may serve for protection during the earlier stages of segmentation. It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both. The corona radiata (Fig. 3) consists or two or three strata of cells; they are derived from the cells of the follicle, and adhere to the outer surface of the zona striata when the ovum is set free from the follicle; the cells are radially arranged around the zona, those of the innermost layer being columnar in shape. The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum. The phenomena attending the discharge of the ova from the follicles belong more to the ordinary functions of the ovary than to the general subject of embry- ology, and are therefore described with the anatomy of the ovaries.1 Maturation of the Ovum.—Before an ovum can be fertilized it must undergo a process of maturation or ripening. This takes place previous to or immediately after its escape from the follicle, and consists essentially of an unequal subdivision of the ovum (Fig. 4) first into two and then into four cells. Three of the four cells are small, incapable of further development, and are termed polar bodies or polocytes, while the fourth is large, and constitutes the mature ovum, lhe process of maturation has not been observed in the human ovum, but has been carefully studied in the ova of some of the lower animals, to which the following description applies* It was pointed out on page 37 that the number of chromosomes found in the nucleus is constant for all the cells in an animal of any given species, and that in man the number is probably twenty-four. This applies not only to the somatic cells but to the primitive ova and their descendants. For the purpose of illustrating the process of maturation a species may be taken in which the number of nuclear chromosomes is four (Fig. 5). If an ovum from such be observed at the beginning of the maturation process it will be seen that the number of its chromosomes is apparently reduced to two. In reality, however, the number is doubled, since each chromosome consists of four granules grouped to form a tetrad. During the metaphase (see page 37) each tetrad divides into two dyads, which are equally 1 See description of the ovary on a future page. THE OVUM 41 distributed between the nuclei of the two cells formed by the first division of the ovum. One of the cells is almost as large as the original ovum, and is named’ the secondary oocyte; the other is small, and is termed the first polar body. The Fig. 4.—Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In I the polar spindle (sp) has advanced to the surface of the egg. In II a small elevation (pbl) is formed which receives half of the spindle. In III the elevation is constricted off, forming the first polar body (pbl), and a second spindle is formed. In IV is seen a second elevation which in V has been constricted off as the second polar body (p65). Out of the remainder of the spindle (f.vn in VI) the female pronucleus is developed. secondary oocyte now undergoes subdivision, during which each dyad divides and contributes a single chromosome to the nucleus of each of the two resulting cells. Primary oocyte Primary oiicyie (commencing maturation) Secondary oocyte First polar body Mature ovum Polar bodies Fig. 5.—Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. This second division is also unequal, producing a large cell which constitutes the mature ovum, and a small cell, the second polar body. The first polar body fre- quently divides while the second is being formed, and as a final result four cells 42 EMBRYOLOGY are produced, viz., the mature ovum and three polar bodies, each of which con- tains two chromosomes, i. e., one-half the number present in the nuclei of the somatic cells of members of the same species. The nucleus of the mature ovum is termed the female pronucleus. THE SPERMATOZOON. The spermatozoa or male germ cells are developed in the testes and are present in enormous numbers in the seminal fluid. Each consists of a small but greatly modified cell. The human spermatozoon possesses a head, a neck, a connecting piece or body, and a tail (Fig. 6). Head s •Perforator Neele Connecting piece V Head-cap Tail i Anterior centriole Posterior centriole Spiral thread Mitochondria sheath Terminal disc End-piece Axial filament Fig. 6.—Human spermatozoon. Diagrammatic. A. Surface view. B. Profile view. In C the head, neck, and connecting piece are more highly magnified. The head is oval or elliptical, but flattened, so that when viewed in profile it is pear-shaped. Its anterior two-thirds are covered by a layer of modified proto- plasm, which is named the head-cap. This, in some animals, c. g., the salamander, is prolonged into a barbed spear-like process or perforator, which probably facilitates the entrance of the spermatozoon into the ovum. The posterior part of the head exhibits an affinity for certain reagents, and presents a transversely striated appear- ance, being crossed by three or four dark bands. In some animals a central rod- like filament extends forward for about two-thirds of the length of the head, wdiile in others a rounded body is seen near its center. The head contains a mass of THE SPERMATOZOON 43 chromatin, and is generally regarded as the nucleus of the cell surrounded by a thin envelope. The neck is less constricted in the human spermatozoon than in those of some of the lower animals. The anterior centriole, represented by two or three rounded particles, is situated at the junction of the head and neck, and behind it is a band of homogeneous substance. The connecting piece or body is rod-like, and is limited behind by a terminal disk. The posterior centriole is placed at the junction of the body and neck and, like the anterior, consists of two or three rounded particles. From this centriole an axial filament, surrounded by a sheath, runs backward through the body and tail. In the body the sheath of the axial filament is encircled by a spiral thread, around which is an envelope containing mitochondria granules, and termed the mitochondria sheath. The tail is of great length, and consists of the axial thread or filament, sur- rounded by its sheath, which may contain a spiral thread or may present a striated appearance. The terminal portion or end-piece of the tail consists of the axial filament only. Primary oocyte Primary spermatocyte Secondary oocyte Secondary spermatocytes Mature ovum Polar bodies Spermatids Fia. 7.—Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids ’ (young spermatozoa). Krause gives the length of the human spermatozoon as between 52 p and 62/z, the head measuring 4 to 5p, the connecting piece 6/x, and the tail from 41/x to 52^. By virtue of their tails, which act as propellers, the spermatozoa are capable of free movement, and if placed in favorable surroundings, e. g., in the female pas- sages, will retain their vitality and power of fertilizing for several days. In certain animals, e. g., bats, it has been proved that spermatozoa retained in the female passages for several months are capable of fertilizing. The spermatozoa are developed from the primitive germ cells which have become imbedded in the testes, and the stages of their development are very similar to those of the maturation of the ovum. The primary germ cells undergo division and produce a number of cells termed spermatogonia, and from these the primary spermatocytes are derived. Each primary spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into twro spermatids or young spermatozoa; from this it will be seen that a primary spermatocyte gives rise to four spermatozoa. On comparing this process with that of the maturation of the ovum (Fig. 7) it will be observed that the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the primary oocyte to two cells, the secondary oocyte and the first polar body. Again, the two secondary sperma- 44 EMBRYOLOGY tocytes by their subdivision give origin to four spermatozoa, and the secondary oocyte and first polar body to four cells, the mature ovum and three polar bodies. In the development of the spermatozoa, as in the maturation of the ovum, there is a reduction of the nuclear chromosomes to one-half of those present in the primary spermatocyte. But here the similarity ends, for it must be noted that the four spermatozoa are of equal size, and each is capable of fertilizing a mature ovum, whereas the three polar bodies are not only very much smaller than the mature ovum but are incapable of further development, and may be regarded as abortive ova. FERTILIZATION OF THE OVUM. Fertilization consists in the union of the spermatozoon with the mature ovum (Fig. 8). Nothing is known regarding the fertilization of the human ovum, but Polar bodies- Female 'pronucleus Female 'pronucleus Male pronucleus Male jjronucleus Female pronucleus- Male pronucleus ' Fused pronuclei Segmentation nucleus Segmentation nucleus (■commencing division) Fig. 8.—The process of fertilization in the ovum of a mouse. (After Sobotta.) the various stages of the process have been studied in other mammals, and from the knowledge so obtained it is believed that fertilization of the human ovum takes place in the lateral or ampullary part of the uterine tube, and the ovum is then conveyed along the tube to the cavity of the uterus-1—a journey probably occupy- ing seven or eight days and during which the ovum loses its corona radiata and zona striata and undergoes segmentation. Sometimes the fertilized ovum is arrested in the uterine tube, and there undergoes development, giving rise to a tubal preg- nancy; or it may fall into the abdominal cavity and produce an abdominal preg- nancy. Occasionally the ovum is not expelled from the follicle when the latter ruptures, but is fertilized within the follicle and produces what is known as an ovarian pregnancy. Under normal conditions only one spermatozoon enters the yolk and takes part in the process of fertilization. At the point where the sperma SEGMENTATION OF THE FERTILIZED OVUM 45 tozoon is about to pierce, the yolk is drawn out into a conical elevation, termed the cone of attraction. As soon as the spermatozoon has entered the yolk, the per- ipheral portion of the latter is transformed into a membrane, the vitelline membrane which prevents the passage of additional spermatozoa. Occasionally a second spermatozoon may enter the yolk, thus giving rise to a condition of polyspermy: when this occurs the ovum usually develops in an abnormal manner and gives rise to a monstrosity. Having pierced the yolk, the spermatozoon loses its tail, while its head and connecting piece assume the form of a nucleus containing a cluster of chromosomes. This constitutes the male pronucleus, and associated with it there are a centriole and centrosome. The male pronucleus passes more deeply into the yolk, and coincidently with this the granules of the cytoplasm surrounding it become radially arranged. The male and female pronuclei migrate toward each other, and. meeting near the center of the yolk, fuse to form a new nucleus, the segmentation nucleus, which therefore contains both male and female nuclear substance; the former transmits the individualities of the male ancestors, the latter those of the female ancestors, to the future embryo. By the union of the male and female pronuclei the number of chromosomes is restored to that which is present in the nuclei of the somatic cells. Fig. 9.—First stages of segmentation of a mammalian ovum. Semidiagrammatic. (From a drawing by Allen Thomson.) z.p. Zona striata, p.gl. Polar bodies, a. Two-cell stage, b. Four-cell stage, c. Eight-cell stage. d, e. Morula stage. SEGMENTATION OF THE FERTILIZED OVUM The early segmentation of the human ovum has not yet been observed, but judging from what is known to occur in other mammals it may be regarded as certain that the process starts immediately after the ovum has been fertilized, i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits the usual mitotic changes, and these are succeeded by a division of the ovum into two cells of nearly equal size.1 The process is repeated again and again, so that 1 In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed through- out the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed holoblastic. In the ova of birds, reptiles, and fishes where the nutritive yolk forms by far the larger portion of the egg, the cleavage is limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic.. Again, it has been observed, in some of the lower animals, that the pronuclei do not fuse but merely lie in apposition. At the commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the equator of the nuclear spindle and then divide; an equal number of male and female chromosomes travel to the opposite poles of the spindle, and thus the male and female pronuclei contribute equal shares of chromatin to the nuclei of the two cells which result from the subdivision of the fertilized ovum 46 EMBRYOLOGY the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the result that a mass of cells is found within the zona striata, and to this mass the term morula is applied (Fig. 9). The segmentation of the mammalian ovum may not take place in the regular sequence of two, four, eight, etc., since one of the two first formed cells may subdivide more rapidly than the other, giving rise to a three- or a five-cell stage. The cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which Inner cell-mass Blastodermic vesicle Entoderm Trophoblast Fia. 10.—Blastodermic vesicle of Vespertilio murinus. (After van Beneden. Inner cell-mass Trophoblast Embryonic ectoderm Entoderm Fig. 11.—Section through embryonic disk of Vespertilio murinus. (After van Beneden.) Amniotic cavity Syncytio trophoblast Maternal bloodvessels, Cytotrophoblast Embryonic ectoderm Entoderm Fig. 12.—Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. (After van Beneden,) does not contribute to the formation of the embryo proper, and an inner cell-mass, from which the embryo is developed. Fluid collects between tjie trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into a vesicle, the blastodermic vesicle (Fig. 10). The inner cell-mass remains in con- tact, however, with the trophoblast at one pole of the ovum; this is named the embryonic pole, since it indicates the situation where the future embryo will be developed. The cells of the trophoblast become differentiated into two strata: an SEGMENTATION OF THE FERTILIZED OVUM 47 outer, termed the syncytium or syncytiotrophoblast, so named because it consists of a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells; and an inner layer, the cytotrophoblast or layer of Langhans, in which the cell outlines are defined. As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta. On the deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differ- entiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear between the remaining cells of the mass (Fig. 11), and by the enlargement and coalescence of these spaces a cavity, termed the amniotic cavity (Fig. 12), is gradually developed. The floor of this cavity is formed by the embryonic disk composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell- mass and lying in apposition with the entoderm. The Primitive Streak; Formation of the Mesoderm.—The embryonic disk becomes oval and then pear-shaped, the wider end being directed forward. Near the narrow, posterior end an opaque streak, the primitive streak (Figs. 13 and 14), makes its appearance and extends along the middle of the disk for about one-half of its length; at the anterior end of the streak there is a knob- like thickening termed Hensen’s knot. A shallow groove, the primitive groove, appears on the surface of the streak, and the anterior end of this groove communicates by means of an aperture, the blastophore, with the yolk-sac. The primitive streak is produced by a thickening of the axial part of the ectoderm, the cells of which multiply, grow downward, and blend with those of the subjacent entoderm (Fig. 15). From the sides of the primitive streak a third layer of cells, the mesoderm, extends lateralward between the ectoderm and entoderm; the caudal end of the primitive streak forms the cloacal membrane. The extension of the mesoderm takes place throughout the whole of the embry- onic and extra-embryonic areas of the ovum, except in certain regions. One of these is seen immediately in front of the neural tube. Here the mesoderm extends forward in the form of two crescentic masses, which meet in the middle line so as to enclose behind them an area which is devoid of mesoderm. Over this area the ectoderm and entoderm come into direct contact with each other and constitute a thin membrane, the buccopharyngeal membrane, which forms a septum between the primitive mouth and pharynx. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is afterward developed, and this region is therefore designated the pericardial area. A second region where the mesoderm is absent, at least for a time, is that imme- diately in front of the pericardial area. This is termed the proamniotic area, and is the region where the proamnion is developed; in man, however, a proamnion is apparently never formed. A third region is at the hind end of the embryo where the ectoderm and entoderm come into apposition and form the cloacal membrane. The blastoderm now consists of three layers, named from without inward: ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives rise to certain tissues of the body.1 Ectoderm.—The ectoderm consists of columnar cells, which are, however, somewhat flattened or cubical toward the margin of the embryonic disk. It forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, Fig. 13.—Surface view of embryo of a rabbit. (After Kolliker.) arg. Embryonic disk. vr. Primitive streak. 1 The mode of formation of the germ layers in the human ovum has not yet been observed; in the youngest known human ovum (viz., that described by Bryce and Teacher), all three layers are already present and the mesoderm is split into its two layers. The extra-embryonic celom is of considerable size, and scattered mesodermal strands are seen stretching between the mesoderm of the yolk-sac and that of the chorion. EMBRYOLOGY 48 Yolk-sac Notochord Amnion Amnion Neurenteric canal Primitive streak Allantois in body-stalk Flo 14— Surface view of embryo of Hylobates concolor. (After Selenka.) The amnion has been opened to expose the embryonic disk. Fig. 15.—Series of transverse sections through the disk of IV pass through the disk, in front of Hensen’s knot and shows only the ec ... . . jn jjj jy, and V the mesoderm through Hensen’s knot, which is seen in 1 tapering awa> in o le P rtt n(j jy ;a observed to be continuous into is seen springing from the keel-like thickening of the ectoderm, which in the entoderm. SEGMENTATION OF THE FERTILIZED OVUM 49 sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it also are derived the enamel of the teeth, and the anterior lobe of the hypophysis cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the neuro-epithelium of the sense organs. Entoderm.—The entoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm), the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas, Fig. 16.—A series of transverse sections through an embryo of the dog. (After Bonnet.) Section I is the most anterior. In V the neural plate is spread out nearly flat. The series shows the uprising of the neural folds to form the neural canal, a. Aortse. c. Intermediate cell mass. ect. Ectoderm, ent. Entoderm, h, h. Rudiments of endothelial heart tubes. In III, IV, and V the scattered cells represented between the entoderm and splanchnic layer of meso- derm are the vasoformative cells which give origin in front, according to Bonnet, to the heart tubes, h; l.p. Lateral plate still undivided in I, II, and III; in IV and V split into somatic (aw) and splanchnic (sp) layers of mesoderm. mes. Mesoderm, p. Pericardium, so. Primitive segment. the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, and air cells of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus. Mesoderm.—The mesoderm consists of loosely arranged branched cells sur- rounded by a considerable amount of intercellular fluid. From it the remaining tissues of the body are developed. The endothelial lining of the heart and blood- vessels and the blood corpuscles are, however, regarded by some as being of ento- dermal origin. As the mesoderm develops between the ectoderm and entoderm it is separated into lateral halves by the neural tube and notochord, presently to be described. A 50 EMBRYOLOGY longitudinal groove appears on the dorsal surface of either half and divides it into a medial column, the paraxial mesoderm, lying on the side of the neural tube, and a lateral portion, the lateral mesoderm. The mesoderm in the floor of the groove connects the paraxial with the lateral mesoderm and is known as the intermediate cell-mass; in it the genito-urinary organs are developed. The lateral mesoderm splits into two layers, an outer or somatic, which becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure; and an inner or splanchnic, which adheres to the entoderm, and with it forms the splanchnopleure (Fig. 16). The space between the two layers of the lateral mesoderm is termed the celom. THE NEURAL GROOVE AND TUBE. In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line (Fig. 16). These are named the neural folds; they commence some little distance Yolk-sac Amnion Neural groove Neurenteric canal Primitive streak Body-stalk Fig. 17.—Human embryo—length, 2 mm. Dorsal view, with the amnion laid open. X 30. (After Graf Spee.) behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove (Figs. 16, 17). The groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or canal (Fig. 18), the ectodermal wall of which forms the rudiment of the nervous system. After the coalescence of the neural folds over the anterior end of the primitive streak, the blastopore no longer opens on the surface but into the closed canal of the neural tube, and thus a transitory communication, the neurenteric canal, is established between the neural tube and the primitive digestive tube. The coalescence of the neural folds occurs first in the region of the hind-brain, and from there extends forward and backward; toward the end of the third week the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess which is in contact, for a time, with the overlying ectoderm; the hinder part of the neural groove presents for a time a rhomboidal shape, and to this THE NEURAL GROOVE AND TUBE 51 expanded portion the term sinus rhomboidalis has been applied (Fig. 18). Before the neural groove is closed a ridge of ectodermal cells appears along the prominent margin of each neural fold; this is termed the neural crest or ganglion ridge, and from it the spinal and cranial nerve ganglia and the ganglia of the sympathetic nervous system are developed. By the upward growth of the mesoderm the neural tube is ultimately separated from the overlying ectoderm. Head fold of amnion partly covering the fare-bruin Mid-brain Hind-brain Nerve ganglion Auditory vesicle Heart Vitelline vein Fourteenth primitive segment Paraxial mesoderm Neural fold Sinus rhomboulalis Remains of 'primitive streak Fig. 18.—Chick embryo of thirty-three hours’ incubation, viewed from the dorsal aspect. X 30. (From Duval's “Atlas d’Embryologie.”) The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future fore-brain (pros- encephalon), mid-brain (mesencephalon), and hind-brain (rhombencephalon) (Fig. 18). The walls of the vesicles are developed into the nervous tissue and neuroglia of the brain, and their cavities are modified to form its ventricles. The remainder 52 EMBRYOLOGY of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall the nervous and neuroglial elements of the medulla spinalis are developed while the cavity persists as the central canal. THE NOTOCHORD The notochord (Fig. 19) consists of a rod of cells situated on the ventral aspect of the neural tube; it constitutes the foundation of the axial skeleton, since around it the segments of the vertebral column are formed. Its appearance synchronizes with that of the neural tube. On the ventral aspect of the neural groove an axial thickening of the entoderm takes place; this thickening assumes the appearance of a furrow—the chordal furrow—the margins of which come into contact, and so convert it into a solid rod of cells—the notochord—which is then separated from the entoderm. It extends throughout the entire length of the future vertebral Neural canal Primitive segment Wolffian duct Ectoderm Celom Somatic mesoderm Entoderm, Notochord Aorta Splanchnic mesoderm Fig. 19.—Transverse section of a chick embryo of forty-five hours’ incubation. (Balfour.) column, and reaches as far as the anterior end of the mid-brain, where it ends in a hook-like extremity in the region of the future dorsum sellse of the sphenoid bone. It lies at first between the neural tube and the entoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medial- ward and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull and vertebral column, and the membranes of the brain and medulla spinalis are developed. THE PRIMITIVE SEGMENTS Toward the end of the second week transverse segmentation of the paraxial mesoderm begins, and it is converted into a series of well-defined, more or less cubical masses, the primitive segments (Figs. 18, 19, 20), which occupy the entire length of the trunk on either side of the middle line from the occipital region of the head. Each segment contains a central cavity—myoccel —which, however, is soon filled with angular and spindle-shaped cells. The primitive segments lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are con- nected to the lateral mesoderm by the inter- mediate cell-mass. Those of the trunk mav Yolk-sac Cut edge of amnion Primitive segments Neural folds Neurenteric canal Fig. 20.—Dorsum of human embryo, 2.11 mm. in length. (After Eternod.) SEPARATION OF THE EMBRYO 53 be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head are usually described as being four in number. In mammals primitive segments of the head can be recognized only in the occipital region, but a study of the lower vertebrates leads to the belief that they are present also in the anterior part of the head, and that altogether nine segments are represented in the cephalic region. SEPARATION OF THE EMBRYO. The embryo increases rapidly in size, but the circumference of the embryonic disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of relatively slow growth and gradually comes to form a constriction between the embryo and the greater part of the yolk-sac. By means of this constriction, which corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within the embryo and constitutes the primitive digestive tube. V illi of chorion Chorion Amnion Mesoderm. Embryonic disk Body-stalk Rudiment of heart Primitive streak Allantois Yolk-sac Entoderm Mesoderm Bloodvessel Fig. 21.—Section through the embryo which is represented in Fig. 17. (After Graf Spec.) The embryo increases more rapidly in length than in width, and its cephalic and caudal ends soon extend beyond the corresponding parts of the circumference of the embryonic disk and are bent in a ventral direction to form the cephalic and caudal folds respectively (Figs. 26 and 27). The cephalic fold is first formed, and as the proamniotic area (page 47) lying immediately in front of the pericardial area (page 47) forms the anterior limit of the circumference of the embryonic disk, the forward growth of the head necessarily carries with it the posterior end of the pericardial area, so that this area and the buccopharyngeal membrane are folded back under the head of the embryo which now encloses a diverticulum of the yolk-sac named the fore-gut. The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk, but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the yolk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut 54 EMBRYOLOGY and the hind-gut there exists for a time a wide opening into the yolk-sac, but the latter is gradually reduced to a small pear-shaped sac (sometimes termed the umbilical vesicle), and the channel of communication is at the same time narrowed and elongated to form a tube called the vitelline duct. THE YOLK-SAC. The yolk-sac (Figs. 22 and 23) is situated on the ventral aspect of the embryo; it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence. Blood is conveyed to the wall of the sac by the primitive aortae, and after circulating through a wide-meshed capil- lary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, and by means of it nutritive material is absorbed from the yolk-sac and conveyed to the embryo. At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. The vesicle can be seen in the after-birth as a small, somewhat oval-shaped body Heart -Amnion Mandibular arch Hyoid arch\ Fare-limb Heart Yolk-sac Maxillary process Eye Bodv-stalh Hind-limb Fig. 22.—Human embryo of 2.6 mm. (His.) Fig. 23.—Human embryo from thirty-one to thirty-four days. (His.) whose diameter varies from 1 mm. to 5 mm.; it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta. As a rule the duct undergoes complete obliteration during the seventh week, but in about three per cent, of cases its proximal part persists as a diverticulum from the small intestine, Meckel’s diverticulum, which is situated about three or four feet above the ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA. The Allantois (Figs. 25 to 28).—The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backward with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels. DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 55 In reptiles, birds, and many mammals the allantois becomes expanded into a vesicle which projects into the extra-embryonic celom. If its further development be traced in the bird, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by Amniotic cavity Amniotic cavity Yolk-sac • Body-stalk Allantois Chorion Yolk-sac - Chor ion Fig. 24.—Diagram showing earliest observed stagi of human ovum. Fig. 23.—Diagram illustrating early formation of allantois and differentiation of bodv-stalk. the two allantoic or umbilical arteries, which are continuous with the primitive aortse, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic circulation, which is of the utmost importance in connection with the respiration and nutrition of the chick, is established. Oxygen is taken from, and carbonic acid is given up to the atmosphere through the egg-shell, while nutritive materials are at the same time absorbed by the blood from the yolk. Amniotic cavity Embryo Placental villi Body-stalk Placental villi - Body-stalk Allantois Y olk-sac Allantois Heart Yolk-sac - Chorion Fore-giit Heart Amniotic cavity Embryo Fig. 26.—Diagram showing later stage of allan- toic development with commencing constriction of the yolk-sac. Fig. 27.—Diagram showing the expansion of amnion and delimitation of the umbilicus. In man and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface. The human embryo, on the other hand, as was pointed out by His, is never wholly separated from the chorion, its 56 EMBRYOLOGY tail end being from the first connected with the chorion by means of a thick band of mesoderm, named the body-stalk (Bauchstiel); into this stalk the tube of the allantois extends (Fig. 21). The Amnion.—The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota;” but not in amphibia and fishes, which are consequently termed “ Anamnia.” In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac (Figs. 24 and 32), and, as indicated on page 46, appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk—the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the meso- dermal lining of the chorion. When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) be- gins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of preg- nancy, after which it diminishes somewhat; at the end of preg- nancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent, of solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal. In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. This, the amniotic fold (Fig. 29), first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and grad- ually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom. Placental villi Yolk-sac , TYWti/XCAXh COT(t Allantois Heart Digestive tube Embryo Fig. 28.—Diagram illustrating a later stage in the development of the umbilical cord. Amniotic cavity 57 DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA The Umbilical Cord and Body-stalk.—The umbilical cord (Fig. 28) attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the false amnion or serose villi of chorion, ' post.root ga.7iyl. Ji ''amnion neural iceanae notochord 4 -muscle plate primitive aortic card.Vein Wolffian body and- duct coelom digestive tube ijolk-sac. Fro. 29.—Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle line. (From Quain’s Anatomy.) Ectoderm, blue; mesoderm, red; entoderm and notochord, black. \mnion Umbilical cord Umbilical cord Yolk-sac Chorion Vitelline duct Placenta Fig. 30.—Fetus of about eight weeks, enclosed in the amnion. Magnified a little over two diameters. (Drawn from stereoscopic photographs lent by Prof. A. Thomson, Oxford.) 58 EMBRYOLOGY length of the fetus, i. e., about 50 cm., but it may be greatly diminished or increased. The rudiment of the umbilical cord is represented by the tissue which connects the rapidly growing embryo with the extra-embryonic area of the ovum. Included in this tissue are the body-stalk and the vitelline duct—the former containing the allantoic diverticulum and the umbilical vessels, the latter forming the communica- tion between the digestive tube and the yolk-sac. The body-stalk is the posterior segment of the embryonic area, and is attached to the chorion. It consists of a plate of mesoderm covered by thickened ectoderm on which a trace of the neural groove can be seen, indicating its continuity with the embryo. Kunning through its mesoderm are the two umbilical arteries and the two umbilical veins, together with the canal of the allantois—the last being lined by entoderm (Fig. 31). Its dorsal surface is covered by the amnion, while its ventral surface is bounded by the extra- embryonic celom, and is in contact with the vitelline duct and yolk-sac. With the rapid elongation of the embryo and the formation of the tail fold, the body stalk comes to lie on the ventral surface of the embryo (Figs. 27 and 28), where " Somatic mesoderm Amniotic cavity A mnion Splanchnic mesoderm - Neural groove Entoderm - Neurenteric canal Vitelline veins1. Body-stalk Fig. 31.—Model of human embryo 1.3 mm. long. (After Eternod.) its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral leaves of somatopleure then grow round on each side, and, meeting on the ventral aspect of the allantois, enclose the vitelline duct and vessels, together with a part of the extra-embryonic celom; the latter is ultimately obliterated. The cord is covered by a layer of ectoderm which is continuous with that of the amnion, and its various constitutents are enveloped by embryonic gelatinous tissue, jelly of Wharton. The vitelline vessels and duct, together with the right umbilical vein, undergo atrophy and disappear; and thus the cord, at birth, contains a pair of umbilical arteries and one (the left) umbilical vein. Implantation or Imbedding of the Ovum.—As described (page 44), fertilization of the ovum occurs in the lateral or ampullary end of the uterine tube and is immediately followed by segmentation. On reaching the cavity of the uterus the segmented ovum adheres like a parasite to the uterine mucous membrane, destroys the epithelium over the area of contact, and excavates for itself a cavity in the mucous membrane in which it becomes imbedded. In the ovum described by DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 59 Bryce and Teacher1 the point of entrance was visible as a small gap closed by a mass of fibrin and leucocytes; in the ovum described by Peters2 the opening was covered by a mushroom-shaped mass of fibrin and blood-clot (Fig. 32), the narrow stalk of which plugged the aperture in the mucous membrane. Soon, however, all trace of the opening is lost and the ovum is then completely surrounded by the uterine mucous membrane. The structure actively concerned in the process of excavation is the trophoblast of the ovum, which possesses the power of dissolving and absorbing the uterine tissues. The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal tissues and open into the maternal bloodvessels, with the result that the spaces in the trophoblastic network are filled with maternal blood; these spaces com- municate freely with one another and become greatly distended and form the intervillous space. Fig. 32.—Section through ovum imbedded in the uterine decidua. Semididgrammatic. (After Peters.) am. Amniotic cavity, b.c. Blood-clot. b.s. Body-stalk, eel. Embryonic ectoderm, ent. Entoderm, mes. Mesoderm. m.v. Maternal vessels, tr. Trophoblast. u.e. Uterine epithelium, u.g. Uterine glands, y.s. Yolk-sac. The Decidua.—Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous membrane are greatly increased; its glands are elongated and open on its free surface by funnel-shaped orifices, while their deeper portions are tortuous and dilated into irregular spaces. The interglandular tissue is also increased in quantity, and is crowded with large round, oval, or polygonal cells, termed decidual cells. These changes are well advanced by the second month of pregnancy, when the mucous membrane consists of the following strata (Fig. 33): (1) stratum compactum, next 1 Contribution to the study of the early development and imbedding of the human ovum, 1908. * Die Einbettung des menschlichen Eies, 1899. 60 EMBRYOLOGY the free surface; in this the uterine glands are only slightly expanded, and are lined by columnar cells; (2) stratum spongiosum, in which the gland tubes are greatly dilated and very tortuous, and are ultimately separated from one another by only a small amount of interglandular tissue, while their lining cells are flattened or cubical; (3) a thin unaltered or boundary layer, next the uterine muscular fibers, containing the deepest parts of the uterine glands, which are not dilated, and are lined with columnar epithelium; it is from this epithelium that the epithelial lining of the uterus is re- generated after pregnancy. Distinc- tive names are applied to different portions of the decidua. The part which covers in the ovum is named the decidua capsularis; the portion which intervenes between the ovum and the uterine wall is named the decidua basalis or decidua placentalis; it is here that the placenta is subsequently developed. The part of the decidua which lines the remainder of the body of the uterus is known as the decidua vera or decidua parietalis. Coincidently with the growth of the embryo, the decidua capsularis is thinned and extended (Fig. 34) and the space between it and the decidua vera is gradually obliterated, so that by the third month of pregnancy the two are in contact. By the fifth month of pregnancy the decidua cap- sularis has practically disappeared, while during the succeeding months the decidua vera also undergoes atrophy, owing to the increased press- ure. The glands of the stratum com- pactum are obliterated, and their epithelium is lost. In the stratum spongiosum the glands are compressed and appear as slit-like fissures, while their epithelium undergoes degener- ation. In the unaltered or boundary layer, however, the glandular epithe- lium retains a columnar or cubical form. The Chorion (Figs. 23 to 28).—The chorion consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the soma- tic mesoderm; with this latter the amnion is in contact. The trophoblast is made up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth Mucous membran Muscular fibers - Stratum compactum Stratum spongiosum Unaltered or boundary layer Muscular fibers Fig. 33.—Diagrammatic sections of the uterine mucous membrane: A. The non-pregnant uterus. B. The preg- nant uterus, showing the thickened mucous membrane and the altered condition of the uterine glands. (Kundrat and Engelmann.) DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 61 of the embryo. The chorionic villi are at first small and non-vascular, and consist of trophoblast only, but they increase in size and ramify, while the mesoderm, carrying branches of the umbilical vessels, grows into them, and in this way they are vascularized. Blood is carried to the villi by the branches of the umbilical Placental villi imbedded in the Decidua placentalis Uterine tube Allantois Cavity of uterus Yolk-sac Umbilical cord with its con- tained vessels Cavity of amnion Decidua vera or parietal is Non-'placental villi im- bedded in the decidua capsularis Plug of mucus in the cervix uteri Fig. 34.—Sectional plan of the gravid uterus in the third and fourth month. (Modified from Wagner.) arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the umbilical veins. Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size (Fig. 25), but after this they develop unequally. The greater part of the chorion Trophoblast Mesoderm Branches of umbilical vessels Fig. 35.—Transverse section of a chorionic villus. is in contact with the decidua capsularis (Fig. 34), and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion lseve; as it takes no share in the formation of the placenta, it 62 EMBRYOLOGY is also named the non-placental part of the chorion. On the other hand, the villi on that part of the chorion which is in contact with the decidua placentalis increase greatly in size and complexity, and hence this part is named the chorion frondosum (Kg. 28). Uterine vessels Uterine glands Syncytiotrophoblast Cytotrophoblast Mesoderm Fig. 36.—Primary chorionic villi. Diagrammatic. (Modified from Bryce. Intervillous space The Placenta.—The placenta connects the fetus to the uterine wall, and is the organ by means of which the nutritive, respiratory, and excretory functions of the fetus are carried on. It is composed of fetal and maternal portions. Fetal Portion.—The fetal portion of the placenta consists of the villi of the chorion frondosum; these branch repeatedly, and increase enormously in size. These greatly ramified villi are suspended in the intervillous space, and are bathed Uterine vessels Uterine glands Syncytiotrophoblast Core of mesoderm with fetal vessels Cytotrophoblast Mesoderm Intervillous space Fig. 37.—Secondary chorionic villi. Diagrammatic. (Modified from Bryce.) in maternal blood, which is conveyed to the space by the uterine arteries and carried away by the uterine veins. A branch of an umbilical artery enters each villus and ends in a capillary plexus from which the blood is drained by a tributary of the umbilical vein. The vessels of the villus are surrounded by a thin layer of mesoderm consisting of gelatinous connective tissue, which is covered by two DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 63 strata of ectodermal cells derived from the trophoblast: the deeper stratum, next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; the superficial, in contact with the maternal blood, the syncytiotrophoblast (Figs. 36 and 37). After the fifth month the two strata of cells are replaced by a single layer of somewhat flattened cells. Maternal Portion.—The maternal portion of the placenta is formed by the decidua placentalis containing the intervillous space. As already explained, this space is produced by the enlargement and intercommunication of the spaces in the trophoblastic network. The changes involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate. Between this plate and the uterine muscular fibres are the stratum spongiosum and the boundary layer; Wall of uterus Umbilical cord Cervix uteri Fig. 38.—Fetus in utero, between fifth and sixth months. through these and the basal plate the uterine arteries and veins pass to and from the intervillous space. The endothelial lining of the uterine vessels ceases at the point where they terminate in the intervillous space which is lined by the syncytio- trophoblast. Portions of the stratum compactum persist and are condensed to form a series of septa, which extend from the basal plate through the thickness of the placenta and subdivide it into the lobules or cotyledons seen on the uterine surface of the detached placenta. The fetal and maternal blood currents traverse the placenta, the former passing through the bloodvessels of the placental villi and the latter through the inter- villous space (Fig. 39). The two currents do not intermingle, being separated from each other by the delicate walls of the villi. Nevertheless, the fetal blood is able to absorb, through the walls of the villi, oxygen and nutritive materials from the 64 EMBRYOLOGY maternal blood, and give up to the latter its waste products. The blood, so purified, is carried back to the fetus by the umbilical vein. It will thus be seen that the placenta not only establishes a mechanical connection between the mother and the fetus, but subserves for the latter the purposes of nutrition, respiration, and ex- cretion. In favor of the view that the placenta possesses certain selective powers may be mentioned the fact that glucose is more plentiful in the maternal than in the fetal blood. It is interesting to note also that the proportion of iron, and of lime and potash, in the fetus is increased during the last months of pregnancy. Further, there is evidence that the maternal leucocytes may migrate into the fetal blood, since leucocytes are much more numerous in the blood of the umbilical vein than in that of the umbilical arteries. The placenta is usually attached near the fundus uteri, and more frequently on the posterior than on the anterior wall of the uterus. It may, however, occupy a lower position and, in rare cases, its site is close to the orificium internum uteri, which it may occlude, thus giving rise to the condition known as placenta previa. Limiting or boundary layer Stratum spongiosum Placental septum Maternal vessels Villus Trophoblast Chorion Amnion Umbilical arteries ~ Umbilical vein _ Marginal sinus Umbilical cord_ Fig. 39.—Scheme of placental circulation. Separation of the Placenta.—After the child is born, the placenta and membranes are expelled from the uterus as the after-birth. The separation of the placenta from the uterine wall takes place through the stratum spongiosum, and necessarily causes rupture of the uterine vessels. The orifices of the torn vessels are, however, closed by the firm contraction of the uterine muscular fibers, and thus postpartuvi hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the proliferation and extension of the epithelium which lines the persistent portions of the uterine glands in the unaltered layer of the decidua. The expelled placenta appears as a discoid mass which weighs about 450 gm. and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., but this diminishes rapidly toward the circumference of the disk, which is continu- ous with the membranes. Its uterine surface is divided by a series of fissures into lobules or cotyledons, the fissures containing the remains of the septa which extended between the maternal and fetal portions. Most of these septa end in irregular or pointed processes; others, especially those near the edge of the placenta, pass THE BRANCHIAL REGION 65 through its thickness and are attached to the chorion. In the early months these septa convey branches of the uterine arteries which open into the intervillous space on the surfaces of the septa. The fetal surface of the placenta is smooth, being closely invested by the amnion. Seen through the latter, the chorion presents a mottled appearance, consisting of gray, purple, or yellowish areas. The umbilical cord is usually attached near the center of the placenta, but may be inserted anywhere between the center and the margin; in some cases it is inserted into the membranes, i. e., the velamentous insertion. From the attach- ment of the cord the larger branches of the umbilical vessels radiate under the amnion, the veins being deeper and larger than the arteries. The remains of the vitelline duct and yolk-sac may be sometimes observed beneath the amnion, close to the cord, the former as an attenuated thread, the latter as a minute sac. On section, the placenta presents a soft, spongy appearance, caused by the greatly branched villi; surrounding them is a varying amount of maternal blood giving the dark red color to the placenta. Many of the larger villi extend from the chorionic to the decidual surface, while others are attached to the septa which separate the cotyledons; but the great majority of the villi hang free in the inter- villous space. Mid-brain Hind-brain Eye Fore-brain Auditory vesicle Stomodeum Visceral arches Mandibular arch Heart— Olfactory pit Maxillary 'process imnion (cut) Mandibular arch Hyoid arch Third arch Body-stalk Fig. 40.—Embryo between eighteen and twenty-one days. (His.) Fig. 41.—Head end of human embryo, about the end of the fourth week. (From model by Peter.) THE BRANCHIAL REGION. The Branchial or Visceral Arches and Pharyngeal Pouches.—In the lateral walls of the anterior part of the fore-gut five.pharyngeal pouches appear (Fig. 42); each of the upper four pouches is prolonged into a dorsal and a ventral diverticulum. Over these pouches corresponding indentations of the ectoderm occur, forming what are known as the branchial or outer pharyngeal grooves. The intervening mesoderm is pressed aside and the ectoderm comes for a time into contact with the ento- dermal lining of the fore-gut, and the two layers unite along the floors of the grooves to form thin closing membranes between the fore-gut and the exterior. Later the mesoderm again penetrates between the entoderm and the ectoderm. In gill-bearing animals the closing membranes disappear, and the grooves become 66 EMBRYOLOGY complete clefts, the gill-clefts, opening from the pharynx on to the exterior; perfo- ration, however, does not occur in birds or mammals. The grooves separate a series of rounded bars or arches, the branchial or visceral arches, in which thickening of the mesoderm takes place (Figs. 40 and 41). The dorsal ends of these arches are attached to the sides of the head, while the ventral extremities ultimately meet in the middle line of the neck. In all, six arches make their appearance, but of these only the first four are visible externally. The first arch is named the mandibular, and the second the hyoid; the others have no distinctive names. In each arch a cartilaginous bar, consisting of right and left halves, is developed, and with each of these there is one of the primitive aortic arches. The mandibular arch lies between the first branchial groove and the stomodeum; from it are developed the lower lip, the mandible, the muscles of mastication, and the anterior part of the tongue. Its cartilaginous bar is formed by what are known as Meckel’s carti- lages (right and left) (Fig. 43); above this the incus is developed. The dorsal end of each cartilage is connected with the ear-capsule and is ossified to form the malleus; the ventral ends meet each other in the region of the symphysis menti, and are usually regarded as undergoing ossification to form that portion of the mandible which contains the incisor teeth. The intervening part of the cartilage disappears; the portion immediately adjacent to the malleus is replaced by fibrous membrane, which constitutes the spheno-mandibular ligament, Lateral tongue Thyroid elevations diverticulum Entrance to larynx Fro. 42. Floor of pharynx of embryo shown in Malleus Tympanic ring Mandible Meckel's cartilage Incus Hyoid bone Fig. 43.—Head and neck of a human embryo eighteen weeks old, with Meckel’s cartilage and hyoid bar exposed. (After KbUiker.) while from the connective tissue covering the remainder of the cartilage the greater part of the mandible is ossified. From the dorsal ends of the mandibular arch a triangular process, the maxillary process, grows forward on either side and forms the cheek and lateral part of the upper lip. The second or hyoid arch assists in forming the side and front of the neck. From its cartilage are developed the styloid process, stylohyoid ligament, and lesser cornu of the hyoid bone. The stages prob- THE BRANCHIAL REGION 67 ably arises in the upper part of this arch. The cartilage of the third arch gives origin to the greater cornu of the hyoid bone. The ventral ends of the second and third arches unite with those of the opposite side, and form a transverse band, from which the body of the hyoid bone and the posterior part of the tongue are devel- oped. The ventral portions of the cartilages of the fourth and fifth arches unite to form the thyroid cartilage; from the cartilages of the sixth arch the cricoid and arytenoid cartilages and the cartilages of the trachea are developed. The mandibular and hyoid arches grow more rapidly than those behind them, with the result that the latter become, to a certain extent, telescoped within the former, and a deep depression, the sinus cervicalis, is formed on either side of the neck. This sinus is bounded in front by the hyoid arch, and behind by the thoracic wall; it is ultimately obliterated by the fusion of its walls. From the first branchial groove the concha auriculae and external acoustic meatus are developed, while around the groove there appear, on the mandibular and hyoid arches, a number of swellings from which the auricula or pinna is formed. The first pharyngeal pouch is prolonged dorsally to form the auditory tube and the tympanic cavity; the closing membrane between the mandibular and hyoid arches Membranous capsule over cerebral hemisphere Fronto-nasal process Lateral nasal process Eye Globular 'process Maxillary process Stomodeum Mandibular arch Ilyomandibular cleft Fig. 44.—Under surface of the head of a human embryo about twenty-nine days old. (After His.) is invaded by mesoderm, and forms the tympanic membrane. No traces of the second, third, and fourth branchial grooves persist. The inner part of the second pharyngeal pouch is named the sinus tonsillaris; in it the tonsil is developed, above which a trace of the sinus persists as the supratonsillar fossa. The fossa of Rosen- miiller or lateral recess of the pharynx is by some regarded as a persistent part of the second pharyngeal pouch, but it is probably developed as a secondary forma- tion. From the third pharyngeal pouch the thymus arises as an entodermal diver- ticulum on either side, and from the fourth pouches small diverticula project and become incorporated with, the thymus, but in man these diverticula probably never form true thymus tissue. The parathyroids also arise as diverticula from the third and fourth pouches. From the fifth pouches the ultimobranchial bodies originate and are enveloped by the lateral prolongations of the median thyroid rudiment; they do not, however, form true thyroid tissue, nor are any traces of them found in the human adult. The Nose and Face.—During the third week two areas of thickened ectoderm, the olfactory areas, appear immediately under the fore-brain in the anterior wall of the stomodeum, one on either side of a region termed the fronto-nasal process (Fig. 44). By the upgrowth of the surrounding parts these areas are converted into pits, 68 EMBRYOLOGY the olfactory pits, which indent the fronto-nasal process and divide it into a medial and two lateral nasal processes (Fig. 45). The rounded lateral angles of the medial process constitute the globular processes of His. The olfactory pits form Future apex of nose Future apex of nose Medial nasal process Olfactory pit Medial nasal process Olfactory pit .Lateral nasal process Lateral nasal process ■Globular 'process Maxillary process Globular process Maxillary process Stomodeum Roof of pharynx Mandibular arch Hypophyseal diverticulum Dorsal wall of pharynx Fig. 45.—Head end of human embryo of about thirty to thirty-one days. (From model by Peters.) Fig. 46.—Same embryo as shown in Fig. 45, with front wall of pharynx removed. the rudiments of the nasal cavities, and from their ectodermal lining the epithe- lium of the nasal cavities, with the exception of that of the inferior meatuses, is derived. The globular processes are prolonged backward as plates, termed the nasal laminae: these laminae are at first some distance apart, but, gradually approach- Lateral nasal 'pro- cess - Globular processes Fig. 47.—Head of a human embryo of about eight weeks, in which the nose and mouth are formed. (His.) Fig. 48.—Diagram showing the regions of the adult face and neck related to the fronto-nasal process and the branchial arches. ing, they ultimately fuse and form the nasal septum; the processes themselves meet in the middle line, and form the premaxillse and the philtrum or central part of the upper lip (Fig. 48). The depressed part of the medial nasal process THE BRANCHIAL REGION 69 between the globular processes forms the lower part of the nasal septum or columella; while above this is seen a prominent angle, which becomes the future apex (Figs. 45, 46), and still higher a flat area, the future bridge, of the nose. The lateral nasal processes form the alse of the nose. Continuous with the dorsal end of the mandibular arch, and growing forward from its cephalic border, is a triangular process, the maxillary process, the ventral extremity of which is separated from the mandibular arch by a > shaped notch Nares Primitive palate Nasal cavity Buceonasal membranes Fig. 49.—Primitive palate of a human embryo of thirty-seven to thirty-eight days. (From model by Peters.) On the left side the lateral wall of the nasal cavity has been removed. (Fig. 44). The maxillary process forms the lateral wall and floor of the orbit, and in it are ossified the zygomatic bone and the greater part of the maxilla; it meets with the lateral na§al process, from which, however, it is separated for a time by a groove, the naso-optic furrow, that extends from the furrow encircling the eyeball to the olfactory pit. The maxillary processes ultimately fuse with the lateral nasal and globular processes, and form the lateral parts of the upper lip Globular process Mouth of olfactory pit, or naris Palatine 'process of globular process , Lens Palatine part of maxillary process Eye Maxillary process Pharynx Fia. 50.—The roof of the mouth of a human embryo, aged about two and a half months, showing the mode of formation of the palate. (His.) and the posterior boundaries of the nares (Figs. 47, 48). From the third to the fifth month the nares are filled by masses of epithelium, on the breaking down and disappearance of which the permanent openings are produced. The maxillary process also gives rise to the lower portion of the lateral wall of the nasal cavity. The roof of the nose and the remaining parts of the lateral wall, viz., the ethmoidal labyrinth, the inferior nasal concha, the lateral cartilage, and the lateral crus of the alar cartilage, are developed in the lateral nasal process. By the fusion of the 70 EMBRYOLOGY maxillary and nasal processes in the roof of the stomodeum the primitive palate (Fig. 49) is formed, and the olfactory pits extend backward above it. The pos- terior end of each pit is closed by an epithelial membrane, the bucco-nasal membrane, formed by the apposition of the nasal and stomodeal epithelium. By the rupture of these membranes the primitive choanae or openings between the olfactory pits and the stomodeum are established. The floor of the nasal cavity is completed by the development of a pair of shelf-like palatine processes which extend medial- ward from the maxillary processes (Figs. 50 and 51); these coalesce with each other in the middle line, and constitute the entire palate, except a small part in front which is formed by the premaxillary bones. Two apertures persist for a time between the palatine processes and the premaxillae and represent the permanent channels which in the lower animals connect the nose and mouth. The union of the parts which form the palate commences in front, the premaxillary and palatine processes joining in the eighth week, while the region of the future hard palate Lateral part of_ nasal capsule Cartilage of nasal septum Inferior concha Vomeronasal organ of Jacobson Inferior meatus Vomeronasal cartilage Inferior meatus Palatine •process- Cavity of mouth Fia. 51.—Frontal section of nasal cavities of a human embryo 28 mm. long. (Kollmann.) is completed by the ninth, and that of the soft palate by the eleventh week. By the completion of the palate the permanent choanse are formed and are situated a considerable distance behind the primitive choanse. The deformity known as cleft palate results from a non-union of the palatine processes, and that of hare- lip through a non-union of the maxillary and globular processes (see page 199). The nasal cavity becomes divided by a vertical septum, which extends downward and backward from the medial nasal process and nasal laminae, and unites below with the palatine processes. Into this septum a plate of cartilage extends from the tinder aspect of the ethmoid plate of the chodrocranium. The anterior part of this cartilaginous plate persists as the septal cartilage of the nose and the medial crus of the alar cartilage, but the posterior and upper parts are replaced by the vomer and perpendicular plate of the ethmoid. On either side of the nasal septum, at its lower and anterior part, the ectoderm is invaginated to form a blind pouch or diverticulum, which extends backward and upward into the nasal septum and is supported by a curved plate of cartilage. These pouches form the rudiments of THE BRANCHIAL REGION 71 the vomero-nasal organs of Jacobson, which open below, close to the junction of the premaxillary and maxillary bones. The Limbs.—The limbs begin to make their appearance in the third week as small elevations or buds at the side of the trunk (Fig. 52). Prolongations from the muscle- and cutis-plates of several primitive segments extend into each bud, and carry with them the anterior divisions of the corresponding spinal nerves. The nerves supplying the limbs indicate the number of primitive segments which contribute to their formation—the upper limb being derived from seven, viz., fourth cervical to second thoracic inclusive, and the lower limb from ten, viz., twelfth thoracic to fourth sacral inclusive. The axial part of the mesoderm of the limb-bud becomes condensed and converted into its cartilaginous skeleton, and by the ossification of this the bones of the limbs are formed. By the sixth week the three chief divisions of the limbs are marked off by furrows—the upper into arm, forearm, and hand; the lower into thigh, leg, and foot (Fig. 53). The limbs are at first directed backward nearly parallel to the long axis of the trunk, Auricula Heart Mandibular arch Hyoid arch\ Fore-limb Maxillary 'process Eye None ' * Fore-limb Digits ' Hind-limb Hind-limb Umbilical cord Fig. 52.—Human embryo from thirty-one to thirty four days. (His.) Fig. 53.—Embryo of about six weeks. (His. and each presents two surfaces and two borders. Of the surfaces, one—the future flexor surface of the limb—is directed ventrally; the other, the extensor surface, dorsally; one border, the preaxial, looks forward toward the cephalic end of the embryo, and the other, the postaxial, backward toward the caudal end. The lateral epicondyle of the humerus, the radius, and the thumb lie along the preaxial border of the upper limb; and the medial epicondyle of the femur, the tibia, and the great toe along the corresponding border of the lower limb. The preaxial part is derived from the anterior segments, the postaxial from the posterior segments of the limb- bud; and this explains, to a large extent, the innervation of the adult limb, the nerves of the more anterior segments being distributed along the preaxial (radial or tibial), and those of the more posterior along the postaxial (ulnar or fibular) border of the limb. The limbs next undergo a rotation or torsion through an angle of 90° around their long axes the rotation being effected almost entirely at the limb girdles. In the upper limb the rotation is outward and forward; in the lower limb, inward and backward. As a consequence of this rotation the preaxial (radial) 72 EMBRYOLOGY border of the fore-limb is directed lateralward, and the preaxial (tibial) border of the hind-limb is directed medialward; thus the flexor surface of the fore-limb is turned forward, and that of the hind-limb backward. DEVELOPMENT OF THE BODY CAVITIES. In the human embryo described by Peters the mesoderm outside the embryonic disk is split into two layers enclosing an extra-embryonic coelom; there is no trace of an intra-embryonic coelom. At a later stage four cavities are formed within the embryo, viz., one on either side within the mesoderm of the pericardial area, and one in either lateral mass of the general mesoderm. All these are at first independent of each other and of the extra-embryonic celom, but later they become continuous. The two cavities in the general mesoderm unite on the ventral aspect of the gut and form the pleuro-peritoneal cavity, which becomes continuous with the remains of the extra-embryonic celom around the umbilicus; the two cavities in the peri- cardial area rapidly join to form a single pericardial cavity, and this from two lateral diverticula extend caudalward to open into the pleuro-peritoneal cavity (Fig. 54). Mesentery Pleural cavity\ Iswng Mesoderm surrounding duct of Cuvier Pleuro-pericardial opening 'Dorsal mesocardium 'Heart Pericardium Fig. 54.—Figure obtained by combining several successive sections of a human embryo of about the fourth week (From Kollmann.) The upper arrow is in the pleuroperitoneal opening, the lower in the pleuropericardial. Between the two latter diverticula is a mass of mesoderm containing the ducts of Cuvier, and this is continuous ventrally with the mesoderm in which the umbili- cal veins are passing to the sinus venosus. A septum of mesoderm thus extends across the body of the embryo. It is attached in front to the body-wall between the pericardium and umbilicus; behind to the body-wall at the level of the second cervical segment; laterally it is deficient where the pericardial and pleuro-peri- toneal cavities communicate, while it is perforated in the middle line by the fore- gut. This partition is termed the septum transversum, and is at first a bulky plate of tissue. As development proceeds the dorsal end of the septum is carried grad- ually caudal ward, and when it reaches the fifth cervical segment muscular tissue with the phrenic nerve grows into it. It continues to recede, however, until it reaches the position of the adult diaphragm on the bodies of the upper lumbar vertebrae. The liver buds grow into the septum transversum and undergo development there. The lung buds meantime have grown out from the fore-gut, and project laterally into the forepart of the pleuro-peritoneal cavity; the developing stomach and liver are imbedded in the septum transversum; caudal to this the intestines project into the back part of the pleuro-peritoneal cavity (Fig. 55). Owing to the descent of DEVELOPMENT OF THE BODY CAVITIES 73 the dorsal end of the septum transversum the lung buds come to lie above tlie septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity (still, however, in free communication with one another) may be recognized; the pericardial cavity opens into the pleural part. Left due of Cuvier Esophagus RiglU duct of Cuvier Mesoderm surrounding duct Pleuro-pericardial opening Ridge growing across opening ■Dorsal mesentery Omental bursa Peritoneal recess Stomach Fio. 55.—Upper part of celom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) The ultimate separation of the permanent cavities from one another is effected by the growth of a ridge of tissue on either side from the mesoderm surrounding Aorta Pleural cavity Esophag Lung — Inferior vena cava Body wall Pericardium Fio. 56.—Diagram of transverse section through rabbit embryo. (After Keith.) the duct of Cuvier (Figs. 54, 55). The front part of this ridge grows across and obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- peritoneal opening. With the continued growth of the lungs the pleural cavities are pushed forward 74 EMBRYOLOGY in the body-wall toward the ventral median line, thus separating the pericardium from the lateral thoracic walls (Fig. 53). The further development of the peritoneal cavity has been described with the de.velopment of the digestive tube (page 168 et seq.). Stemn-costal part of Diaphragma Central tendon of Diaphragma Inferior vena cava (Esophagus Vertebral part of Diaphragma, Spleen Colon Posterior mediastinal cavity i-Aorta Suprarenal gland Eleventh rib Twelfth rib Spino-costal hiatus Left pleura Right pleura Fig. 57.—The thoracic aspect of the diaphragm of a newly born child in which the communication between the peritoneum and pleura has not been closed on the left side; the position of the opening is marked on the right side by the spinocostal hiatus. (After Keith.) THE FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH. First Week.—During this period the ovum is in the uterine tube. Having been fertilized in the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the uterus. Peters1 described a specimen, the age of which he reckoned as from three to four days. It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside this Heart Amnion ' Body-stalk Chorion Fig. 58.—Human embryo about fifteen days old. (His.) was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous villous processes—some consisting of trophoblast only, others possessing a core of mesoderm— projected from the surface of the ovum into the surrounding decidua. Inside this sac the rudi- ment of the embryo was found in the form of a patch of ectoderm, covered by a small but com- 1 Die Einbettung des menschlichen Eies, 1899. FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 75 pletely closed amnion. It possessed a minute yolk-sac and was surrounded by mesoderm, which was connected by a band to that lining the trophoblast (Fig. 32).1 Second Week.—By the end of this week the ovum has increased considerably in size, and the majority of its villi are vascularized. The embryo has assumed a definite form, and its cephalic and caudal extremities are easily distinguished. The neural folds are partly united. The embryo Mid-brain Hind-brain Fore-brain ~ Auditory vesicle Stomodeum Mandibular arch Visceral arches Heart Amnion (cut) Body-stalk Fig. 59.—Human embryo between eighteen and twenty-one days old. (His. is more completely separated from the yolk-sac, and the paraxial mesoderm is being divided into the primitive segments (Fig. 58). Third Week.—By the end of the third week the embryo is strongly curved, and the primitive segments number about thirty. The primary divisions of the brain are visible, and the optic Heart Fore-limb Hyoid arch „ Mandibular arch Maxillary process Eye Olfactory pit Chorion' Hind-limb Fig. 60.—Human embryo, twenty-seven to thirty days old. (His.) and auditory vesicles are formed. Four branchial grooves are present: the stomodeum is well- marked, and the bucco-pharyngeal membrane has disappeared. The rudiments of the limbs are seen as short buds, and the Wolffian bodies are visible (Fig. 59). 1 Bryce and Teacher (Early Development and Imbedding of the Human Ovum, 1908) have described an ovum which they regard as thirteen to fourteen days old. In it the two vesicles, the amnion and yolk-sac, were present, but there was no trace of a layer of embryonic ectoderm. They are of opinion that the age of Peters’ ovum has been understated, and estimate it as between thirteen and one-half and fourteen and one-half days. 76 EM BRYOLOGY Fourth Week.—The embryo is markedly curved on itself, and when viewed in profile is almost circular in outline. The cerebral hemispheres appear as hollow buds, and the elevations which form the rudiments of the auricula are visible. The limbs now appear as oval flattened projec- tions (Fig. 60). Heart Mandibular arch' Hyoid arch v .Fore-limb Maxillary process Eye Hind-limb Fig. 61.—Human embryo, thirty-one to thirty-four days old. (His.) Fifth Week.—The embryo is less curved and the head is relatively of large size. Differentiation of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloacal tubercle is evident (Fig. 61). >Auricula Eye- Nose / Fore-limb Digits r _ Hind-limb Umbilical cord Fig. 62.—Human embryo of about six weeks. (His,) Fia. 63.—Human embryo about eight and a half weeks old. (His.) Sixth Week.—The curvature of the embryo is further diminished. The branchial grooves— except the first—have disappeared, and the rudiments of the fingers and toes can be recognized (Fig. 62). Seventh and Eighth Weeks.—The flexure of the head is gradually reduced and the neck is somewhat lengthened. The upper lip is completed and the nose is more prominent. The nostrils FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 77 are directed forward and the palate is not completely developed. The eyelids are present in the shape of folds above and below the eye, and the different parts of the auricula are distinguish- able. By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 63). Third Month.—The head is extended and the neck is lengthened. The eyelids meet and fuse, remaining closed until the end of the sixth month. The limbs are well-developed and nails appear on the digits. The external generative organs are so far differentiated that it is possible to dis- tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs be included it is from 9 to 10 cm. Fourth Month.—The loop of gut which projected into the umbilical cord is withdrawn within the fetus. The hairs begin to make their appearance. There is a general increase in size so that by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included it is from 16 to 20 cm. Fifth Month.—It is during this month that the first movements of the fetus are usually ob- served The eruption of hair on the head commences, and the vernix caseosa begins to be deposited. By the end of this month the total length of the fetus, including the legs, is from 25 to 27 cm Sixth Month.—The body is covered by fine hairs (lanugo) and the deposit of vernix caseosa is considerable. The papillae of the skin are developed and the free border of the nail projects from the corium of the dermis. Measured from vertex to heels, the total length of the fetus at the end of this month is from 30 to 32 cm. Seventh Month.—The pupillary membrane atrophies and the eyelids are open. The testis descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the end of the seventh month is from 35 to 36 cm. The weight is a little over three pounds. Eighth Month.—The skin assumes a pink color and is now entirely coated with vernix caseosa, and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, at the end of the eighth month is about 40 cm., and the weight varies between four and one-half and five and one-half pounds. Ninth Month.—The lanugo has largely disappeared from the trunk. The umbilicus is almost in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from six and one-half to eight pounds, and measures from head to heels about 50 cm. BIBLIOGRAPHY. Broman: Normale und abnorme Entwicklung des Menschen, 1911. Bryce, Teacher and Kerr: Contributions to the Study of the Early Development and Imbedding of the Human Ovum, 1908. Hertwig, O.: Handbuch der Vergleichenden und Experimenteden Entwicklungslehre der Wirbeltiere, 1906. His, W.: Anatomie menschlicher Embryonen, 1880-1885. Hochstetter, F.: Bilder der ausseren Koperform einiger menschlicher Embryonen aus den beiden ersten Monaten der Entwicklung, 1907. Keibel and Elze: Normentafel zur Entwicklungsgeschichte des Menschen, 1908. Keibel and Mall: Manual of Human Embryology, 1910-1912. Kollmann, J.: Handatlas der Entwicklungsgeschichte des Menschen, 1907. Kollmann, J.: Lehrbuch der Entwicklungsgeschichte des Menschen, 1898. Mall: Contribution to the Study of the Pathology of the Human Embryo, Jour, of Morph., 1908. See also contributions to Embryology of the Carnegie Institution of Washington. Mall: Development of the Human Coelom, Jour, of Morph., 1897. Peters, H.: Ueber die Einbettung des menschlichen Eies und das friiheste bisher bekannte menschliche Placentationsstadium, 1899. OSTEOLOGY. rPHE general framework of the body is built up mainly of a series of bones, -L supplemented, however, in certain regions by pieces of cartilage; the bony part of the framework constitutes the skeleton. In the skeleton of the adult there are 206 distinct bones, as follows:— Vertebral column . 26 Axial Skull . 22 Skeleton Hyoid bone ... . 1 Ribs and sternum . . 25 — 74 Appendicular J Upper extremities . . 64 Skeleton i Lower extremities . . 62 — 126 Auditory ossicles 6 Total 206 The patellae are included in this enumeration, but the smaller sesamoid bones are not reckoned. Bones are divisible into four classes: Long, Short, Flat, and Irregular. Long Bones.—The long bones are found in the limbs, and each consists of a body or shaft and two extremities. The body, or diaphysis is cylindrical, with a central cavity termed the medullary canal; the wall consists of dense, compact tissue of considerable thickness in the middle part of the body, but becoming thinner toward the extremities; within the medullary canal is some cancellous tissue, scanty in the middle of the body but greater in amount toward the ends. The extremities are generally expanded, for the purposes of articulation and to afford broad surfaces for muscular attachment. They are usually developed from sep- arate centers of ossification termed epiphyses, and consist of cancellous tissue surrounded by thin compact bone. The medullary canal and the spaces in the cancellous tissue are filled with marrow. The long bones are not straight, but curved, the curve generally taking place in two planes, thus affording greater strength to the bone. The bones belonging to this class are: the clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges. Short Bones.—Where a part of the skeleton is intended for strength and com- pactness combined with limited movement, it is constructed of a number of short bones, as in the carpus and tarsus. These consist of cancellous tissue covered by a thin crust of compact substance. The patellae, together with the other sesamoid bones, are by some regarded as short bones. Flat Bones.—Where the principal requirement is either extensive protection or the provision of broad surfaces for muscular attachment, the bones are expanded into broad, flat plates, as in the skull and the scapula. These bones are composed of two thin layers of compact tissue enclosing between them a variable quantity of cancellous tissue. In the cranial bones, the layers of compact tissue are famili- arly known as the tables of the skull; the outer one is thick and tough; the inner is thin, dense, and brittle, and hence is termed the vitreous table. The intervening 79 80 OSTEOLOGY cancellous tissue is called the diploe, and this, in certain regions of the skull, becomes absorbed so as to leave spaces filled with air (air-sinuses) between the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, scapula, os coxae (hip bone), sternum, ribs, and, according to some, the patella. Irregular Bones.—The irregular bones are such as, from their peculiar form, cannot be grouped under the preceding heads. They consist of cancellous tissue enclosed within a thin layer of compact bone. The irregular bones are: the vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid. Surfaces of Bones.—If the surface of a bone be examined, certain eminences and depressions are seen. These eminences and depressions are of two kinds: articular and non-articular. Well-marked examples of articular eminences are found in the heads of the humerus and femur; and of articular depressions in the glenoid cavity of the scapula, and the acetabulum of the hip bone. Non-articular eminences are designated according to their form. Thus, a broad, rough, uneven elevation is called a tuberosity, protuberance, or process, a small, rough prominence, a tubercle; a sharp, slender pointed eminence, a spine; a narrow, rough elevation, running some way along the surface, a ridge, crest, or line. Non-articular depres- sions are also of variable form, and are described as fossae, pits, depressions, grooves, furrows, fissures, notches, etc. These non-articular eminences and depressions serve to increase the extent of surface for the attachment of ligaments and muscles, and are usually well-marked in proportion to the muscularity of the subject. A short perforation is called a foramen, a longer passage a canal. DEVELOPMENT OF THE SKELETON. The Skeleton.—The skeleton is of mesodermal origin, and may be divided into (a) that of the trunk (axial skeleton), comprising the vertebral column, skull, ribs, and sternum, and (6) that of the limbs (appendicular skeleton). The Vertebral Column.—The notochord (Fig. 19) is a temporary structure and forms a central axis, around which the segments of the vertebral column are devel- oped.1 It is derived from the entoderm, and consists of a rod of cells, which lies on the ventral aspect of the neural tube and reaches from the anterior end of the mid-brain to the extremity of the tail. On either side of it is a column of paraxial mesoderm which becomes subdivided into a number of more or less cubical seg- ments, the primitive segments (Figs. 19 and 20). These are separated from one another by intersegmental septa and are arranged symmetrically on either side of the neural tube and notochord: to every segment a spinal nerve is distributed. At first each segment contains a central cavity, the myocoel, but this is soon filled with a core of angular and spindle-shaped cells. The cells of the segment become differentiated into three groups, which form respectively the cutis-plate or derma- tome, the muscle-plate or myotome, and the sclerotome (Fig. 64). The cutis-plate is placed on the lateral and dorsal aspect of the myocoel, and from it the true skin of the corresponding segment is derived; the muscle-plate is situated on the medial side of the cutis-plate and furnishes the muscles of the segment. The cells of the sclerotome are largely derived from those forming the core of the myocoel, and lie next the notochord. Fusion of the individual sclerotomes in an antero-posterior direction soon takes place, and thus a continuous strand of cells, the sclerotogenous layer, is formed along the ventro-lateral aspects of the neural tube. The cells of this layer proliferate rapidly, and extending medialward surround the notochord; at the same time they grow backward on the lateral aspects of the neural tube and eventually surround it, and thus the notochord and neural tube are enveloped I 1 In the amphioxus the notochord persists and forms the only representative of a skeleton in that animal. DEVELOPMENT OF THE SKELETON 81 by a continuous sheath of mesoderm, which is termed the membranous vertebral column. In this mesoderm the original segments are still distinguishable, but each is now differentiated into two portions, an anterior, consisting of loosely arranged cells, and a posterior, of more condensed tissue (Fig. 65, A and B). Between the two portions the rudiment of the intervertebral fibro- cartilage is laid down (Fig. 65, C). Cells from the pos- terior mass grow into the intervals between the myo- tonies (Fig. 65, B and C) of the corresponding and suc- ceeding segments, and extend both dorsally and ventrally; the dorsal extensions sur- round the neural tube and represent the future verte- bral arch, while the ventral extend into the body-wall as the costal processes. The hinder part of the posterior mass joins the anterior mass of the succeeding segment to form the vertebral body. Each vertebral body is there- fore a composite of two segments, being formed from the posterior portion of one segment and the anterior part of that immediately behind it. The vertebral Fig. 64.—Transverse section of a human embryo of the third week to show the differentiation of the primitive segment. (Kollmann.) ao. Aorta, m.p. Muscle-plate, n.c. Neural canal, sc. Sclerotome, s p. cutis-plate. Myotome Anterior portion of sclerotome Notochord Intervertebral fibrocartilage Posterior 'portion of sclerotome Inter my olomic septum Centrum Notochord Costal 'process Fiq. 65.—Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent segments. and costal arches are derivatives of the posterior part of the segment in front of the intersegmental septum with which they are associated. 82 OSTEOLOGY This stage is succeeded by that of the cartilaginous vertebral column. In the fourth week two cartilaginous centers make their appearance, one on either side of the notochord; these extend around the notochord and form the body of the cartil- aginous vertebra. A second pair of cartilaginous foci appear in the lateral parts of the vertebral bow, and grow backward on either side of the neural tube to form the cartilaginous vertebral arch, and a separate cartilaginous center appears for each costal process. By the eighth week the cartilaginous arch has fused with the body, and in the fourth month the two halves of the arch are joined on the dorsal aspect of the neural tube. The spinous process is developed from the junction of the two halves of the vertebral arch. The transverse process grows out from the vertebral arch behind the costal process. In the upper cervical vertebrae a band of mesodermal tissue connects the ends of the vertebral arches across the ventral surfaces of the intervertebral fibrocartilages. This is termed the hypochordal bar or brace; in all except the first it is transitory and disappears by fusing with the fibrocartilages. In the atlas, however, the entire bow persists and undergoes chondrification; it develops into the anterior arch of the bone, while the cartilage representing the body of the atlas forms the dens or odontoid process which fuses with the body of the second cervical vertebra. Anterior longitudinal ligament Posteriorlongiludinal ligament Cartilaginous end of vertebral body Nucleus pulposus Intervertebral fibro- cartilage Slight enlargement of notochord in the cartilaginous vertebral body Fig. 66.—Sagittal section through an intervertebral fibrocartilage and adjacent parts of two vertebrae of an advanced sheep’s embryo. (Kolliker.) The portions of the notochord which are surrounded by the bodies of the verte- brae atrophy, and ultimately disappear, while those which lie in the centers of the intervertebral fibrocartilages undergo enlargement, and persist throughout life as the central nucleus pulposus of the fibrocartilages (Fig. 66). The Ribs.—The ribs are formed from the ventral or costal processes of the primitive vertebral bows, the processes extending between the muscle-plates. In the thoracic region of the vertebral column the costal processes grow lateralward to form a series of arches, the primitive costal arches. As already described, the transverse process grows out behind the vertebral end of each arch. It is at first connected to the costal process by continuous mesoderm, but this becomes differ- entiated later to form the costotransverse ligament; between the costal process and the tip of the transverse process the costotransverse joint is formed by absorption. The costal process becomes separated from the vertebral bow by the development of the costocentral joint. In the cervical vertebrae (Fig. 67) the trans- verse process forms the posterior boundary of the foramen transversarium, while the costal process corresponding to the head and neck of the rib fuses with the DEVELOPMENT OF THE SKELETON 83 body of the vertebra, and forms the antero-lateral boundary of the foramen. The distal portions of the primitive costal arches remain undeveloped; occasionally the arch of the seventh cervical vertebra undergoes greater development, and by the formation of costovertebral joints is separated off as a rib. In the lumbar region the distal portions of the primitive costal arches fail; the proximal portions fuse wdth the transverse processes to form the transverse processes of descriptive anatomy. Occasionally a movable rib is developed in connection wdth the first lumbar vertebra. In the sacral region costal processes are developed only in connection with the upper three, or it may be four, vertebrae; the processes of adjacent segments fuse with one another to form the lateral parts of the sacrum. The coccygeal vertebrae are devoid of costal processes. CERVICAL LUMBAR SACRAL Fig. 67.—Diagrams showing the portions of the adult vertebra derived respectively from the bodies, vertebral arches, and costal processes of the embryonic vertebra. The bodies are represented in yellow, the vertebral arches in red, and the costal processes in blue. THORACIC The Sternum.—The ventral ends of the ribs become united to one another by a longitudinal bar termed the sternal plate, and opposite the first seven pairs of ribs these sternal plates fuse in the middle line to form the manubrium and body of the sternum. The xiphoid process is formed by a backward extension of the sternal plates. The Skull.—Up to a certain stage the development of the skull corresponds with that of the vertebral column; but it is modified later in association with the expan- sion of the brain-vesicles, the formation of the organs of smell, sight, and hearing, and the development of the mouth and pharynx. 84 OSTEOLOGY The notochord extends as far forward as the anterior end of the mid-brain, and becomes partly surrounded by mesoderm (Fig. 68). The posterior part of this meso- dermal investment corresponds with the basilar part of the occipital bone, and shows a subdivision into four segments, which are separated by the roots of the hypo- glossal nerve. The mesoderm then extends over the brain-vesicles, and thus the entire brain is enclosed by a mesodermal investment, which is termed the membran- ous cranium. From the inner layer of this the bones of the skull and the membranes of the brain are developed; from the outer layer the muscles, bloodvessels, true skin, and subcutaneous tissues of the scalp. In the shark and dog-fish this membranous cranium undergoes complete chondrifi- cation, and forms the cartilaginous skull or chondrocranium of these animals. In mammals, on the other hand, the process of chondrification is limited to the base of the skull—the roof and sides being covered in by membrane. Thus the bones of the base of the skull are preceded by cartilage, those of the roof and sides by membrane. The posterior part of the base of the skull is developed around the notochord, and exhibits a segmented condition analogous to that of the vertebral column, while the anterior part arises in front of the notochord and shows no regular segmentation. The base of the skull may therefore be divided into (a) a chordal or vertebral, and (6) a prechordal or prevertebral portion. Fossa liypo'physeos Mesoderm of base of skull Parachordal cartilage Notochord Anterior arch of atlas Notochord Body of a xis Third cervical vertebra Fig. 68.—Sagittal section of cephalic end of noto- chord. (Keibel.) Situation of olfactory pit Ethmoid plate and nasal septums Situation of eyeball Olfactory organ \ Fossa Extension around olfactory organ hypophyseos Foramina for olfactory nerves Trabecula Eyeball Fossa crann hypophyseos Situation of auditory vesicle Basilar plate Auditory vesicle Parachordal cartilage •Notochord Notochord' Fig. 69.—Diagrams of the cartilaginous cranium. (Wiedersheim. In the lower vertebrates two pairs of cartilages are developed, viz., a pair of parachordal cartilages, one on either side of the notochord; and a pair of pre- chordal cartilages, the trabeculae cranii, in front of the notochord (Fig. 66). The parachordal cartilages (Fig. 69) unite to form a basilar plate, from which the car- tilaginous part of the occipital bone and the basi-sphenoid are developed. On the lateral aspects of the parachordal cartilages the auditory vesicles are situated, DEVELOPMENT OF THE SKELETON 85 and the mesoderm, enclosing them is soon converted into cartilage, forming the cartilaginous ear-capsules. These cartilaginous ear-capsules, which are of an oval shape, fuse with the sides of the basilar plate, and from them arise the petrous and mastoid portions of the temporal bones. The trabeculae cranii (Fig. 69) are two curved bars of cartilage which embrace the hypophysis cerebri; their posterior ends soon unite with the basilar plate, while their anterior ends join to form the ethmoidal plate, which extends forward between the fore-brain and the olfactory pits. Later the trabeculae meet and fuse below the hypophysis, forming the floor Crista galli . Cribriform plate Small wing of sphenoid Optic foramen Great wing of sphenoid Meckel's cartilage Malleus> Sella turcica Incus - Dorsum sellae Canal for facial nerve. Int. acoustic meat J ugular foramen Fossa subarcuata Ear capsule Ductus ended. Canal for hypoglossal nerve Foramen magnum Flo. 70.—Model of the chondrocranium of a human embryo, 8 cm. long. (Hertwig. The membrane bones are « not represented. of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis from the stomodeum. The median part of the ethmoidal plate forms the bony and cartilaginous parts of the nasal septum. From the lateral margins of the trabeculae cranii three processes grow out on either side. The anterior forms the ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle gives rise to the small wing of the sphenoid, while from the posterior the great wing and lateral pterygoid plate of the sphenoid are developed (Figs. 70, 71). The bones of the vault are of membranous formation, and are termed dermal or covering bones. They are partly developed from the mesoderm of the membranous 86 OSTEOLOGY cranium, and partly from that which lies outside the entoderm of the fore- gut. They comprise the upper part of the occipital squama (interparietal), the squamae and tympanic parts of the temporals, the parietals, the frontal, the vomer, the medial pterygoid plates, and the bones of the face. Some of them remain distinct throughout life, e. g., parietal and frontal, while others join with the bones of the chondrocranium, e. g., interparietal, squamae of temporals, and medial pterygoid plates. Recent observations have shown that, in mammals, the basi-cranial cartilage, both in the chordal and prechordal regions of the base of the skull, is developed as a single plate which extends from behind forward. In man, however, its posterior part shows an indication of being developed from two chondrifying centers which fuse rapidly in front and below. The anterior and posterior thirds of the cartilage surround the notochord, but its middle third lies on the dorsal aspect of the noto- chord, which in this region is placed between the cartilage and the wall of the pharynx. Optic foramen Small icing of sphenoid Great wing of sphenoid Nasal capsule Canal for facial nerve Sept. nasi legmen tyrnp. Incus Maxilla• Vomer Palatine bone Mandible' Meckel's cart. Handle °f malleus Fen. cochleae Styloid process Cricoid cart. Thyroid cart. Canal for hypoglossal nerve Fiq. 71.—The same model as shown in Fig. 70 from the left side. Certain of the membrane bones of the right side are represented in yellow. BONE Structure and Physical Properties.—Bone is one of the hardest structures of the animal body; it possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is pinkish-white externally, and deep red within. On examining a section of any bone, it is seen to be composed of two kinds of tissue, one of which is dense in texture, like ivory, and is termed compact tissue; the other consists of slender fibers and lamellae, which join to form a reticular structure; this, from its resemblance to lattice-work, is called cancellous tissue. The compact tissue is always placed on the exterior of the bone, the cancellous in the interior. The relative quantity of these two kinds of tissue varies in different bones, and in different parts of the same bone, according as strength or lightness is requisite. Close examination of the compact tissue shows it to be extremely porous, so that the difference in structure between it and the cancellous tissue depends merely upon the different amount of solid matter, and the size and number of spaces in each; the cavities are small in the compact tissue and the solid matter between BONE 87 them abundant, while in the cancellous tissue the spaces are large and the solid matter is in smaller quantity. Bone during life is permeated by vessels, and is enclosed, except where it is coated with articular cartilage, in a fibrous membrane, the periosteum, by means of which many of these vessels reach the hard tissue. If the periosteum be stripped from the surface of the living bone, small bleeding points are seen which mark the entrance of the periosteal vessels; and on section during life every part of the bone exudes blood from the minute vessels which ramify in it. The interior of each of the long bones of the limbs presents a cylindrical cavity filled with marrow and lined by a highly vascular areolar structure, called the medullary membrane. The Strength of Bone Compared with other Materials Ultimate strength. Substance. Weight in pounds per Pounds per square inch. Tesion. Compression. Shear. Medium steel 490 65,000 60,000 40,000 Granite 170 1,500 15,000 2,000 Oak, white 46 12,500! 7,000! 4,0002 Compact bone (low) 119 13,200l 18,000! 11,800* Compact bone (high) 17,700! 24,000i 7,15Qi Periosteum.—The periosteum adheres to the surface of each of the bones in nearly every part, but not to cartilaginous extremities. When strong tendons or ligaments are attached to a bone, the periosteum is incorporated with them. It consists of two layers closely united together, the outer one formed chiefly of connective tissue, containing occasionally a few fat cells; the inner one, of elastic fibers of the finer kind, forming dense membranous networks, which again can be separated into several layers. In young bones the periosteum is thick and very vascular, and is intimately connected at either end of the bone with the epiphysial cartilage, but less closely with the body of the bone, from which it is separated by a layer of soft tissue, containing a number of granular corpuscles or osteoblasts, by which ossification proceeds on the exterior of the young bone. Later in life the periosteum is thinner and less vascular, and the osteoblasts are converted into an epithelioid layer on the deep surface of the periosteum. The periosteum serves as a nidus for the ramification of the vessels previous to their distribution in the bone; hence the liability of bone to exfoliation or necrosis when denuded of this membrane by injury or disease. Fine nerves and lymphatics, which generally accompany the arteries, may also be demonstrated in the periosteum. Marrow.—The marrow not only fills up the cylindrical cavities in the bodies of the long bones, but also occupies the spaces of the cancellous tissue and extends into the larger bony canals (Haversian canals) which contain the bloodvessels. It differs in composition in different bones. In the bodies of the long bones the marrow is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue and vessels, and 3 of fluid with extractive matter; it consists of a basis of connective tissue supporting numerous bloodvessels and cells, most of which are fat cells but some are “marrow cells,” such as occur in the red marrow to be immediately described. In the flat and short bones, in the articular ends of the long bones, in the bodies of the vertebrae, in the cranial diploe, and in the sternum and ribs the marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of solid matter consisting of cell-globulin, nucleoprotein, extractives, salts, and only a small proportion of fat. The red marrow consists of a small quantity of connective tissue, bloodvessels, and numerous cells (Fig. 72), some few of which are fat cells, 1 Indicates stresses with the grain, i. e., when the load is parallel to the long axis of the material, or parallel to the direction of the fibers of the material. Indicates unit-stresses across the grain, i. e., at right angles to the direction of the fibers of the material. 88 OSTEOLOGY but the great majority are roundish nucleated cells, the true “marrow cells” of Kolliker. These marrow cells proper, or myelocytes, resemble in appearance lymphoid corpuscles, and like them are ameboid; they generally have a hyaline protoplasm, though some show granules either oxyphil or basophil in reaction. A number of eosinophil cells are also present. Among the marrow cells may be seen smaller cells, which possess a slightly pinkish hue; these are the erythroblasts or normoblasts, from which the red corpuscles of the adult are derived, and which may be regarded as descendants of the nucleated colored corpuscles of the embryo. Giant cells (myeloplaxes, osteoclasts), large, multinucleated, protoplasmic masses, are also to be found in both sorts of adult marrow, but more particularly in red marrow. They were believed by Kolliker to be concerned in the absorption of bone matrix, and hence the name which he gave to them—osteoclasts. They excavate in the bone small shallow pits or cavities, which are named Howship’s foveolae, and in these they are found lying. Normoblast with dividing nucleus Myelocyte Eosinophil cell Erythrocyte Normoblasts Myelocyte dividing Myeloplaxe Myelocyte Myelocyte ■' Fat Fat~ Fig. 72.—Human bone marrow. Highly magnified. Vessels and Nerves of Bone.—The bloodvessels of bone are very numerous. Those of the compact tissue are derived from a close and dense network of vessels ramify- ing in the periosteum. From this membrane vessels pass into the minute orifices in the compact tissue, and run through the canals which traverse its substance. The cancellous tissue is supplied in a similar way, but by less numerous and larger vessels, which, perforating the outer compact tissue, are distributed to the cavities of the spongy portion of the bone. In the long bones, numerous apertures may be seen at the ends near the articular surfaces; some of these give passage to the arteries of the larger set of vessels referred to; but the most numerous and largest apertures are for some of the veins of the cancellous tissue, which emerge apart from the arteries. The marrow in the body of a long bone is supplied by one large artery (or sometimes more), which enters the bone at the nutrient foramen (situated in most cases near the center of the body), and perforates obliquely the compact structure. The medullary or nutrient artery, usually accompanied by one or two veins, sends branches upward and downward, which ramify in the medul- lary membrane, and give twigs to the adjoining canals. The ramifications of this BONE 89 vessel anastomose with the arteries of the cancellous and compact tissues. In most of the flat, and in many of the short spongy bones, one or more large apertures are observed, which transmit to the central parts of the bone vessels corresponding to the nutrient arteries and veins. The veins emerge from the long bones in three places (Kolliker): (1) one or two large veins accompany the artery; (2) numerous large and small veins emerge at the articular extremities; (3) many small veins pass out of the compact substance. In the flat cranial bones the veins are large, very numerous, and run in tortuous canals in the diploic tissue, the sides of the canals being formed by thin lamellae of bone, perforated here and there for the passage of branches from the adjacent cancelli. The same condition is also found in all cancellous tissue, the veins being enclosed and supported by osseous material, and having exceedingly thin coats. When a bone is divided, the vessels remain patulous, and do not contract in the canals in which they are contained. Lymphatic vessels, in addition to those found in the periosteum, have been traced by Cruikshank into the substance of bone, and Klein describes them as running in the Haversian canals. Nerves are distributed freely to the periosteum, and accom- pany the nutrient arteries into the interior of the bone. They are said by Kolliker to be most numerous in the articular extremities of the long bones, in the vertebrae, and in the larger flat bones. Fig. 73.—Transverse section of compact tissue bone. Magnified. (Sharpey.) Minute Anatomy.—A transverse section of dense bone may be cut with a saw and ground down until it is sufficiently thin. If this be examined with a rather low power the bone will be seen to be mapped out into a number of circular districts each consisting of a central hole surrounded by a number of concentric rings. These districts are termed Haversian systems; the central hole is an Haversian canal, and the rings are layers of bony tissue arranged concentrically around the central canal, and termed lamellae. More- over, on closer examination it will be found that between these lamellae, and therefore also arranged concentrically around the central canal, are a number of little dark spots, the lacunae, and that these lacunae are connected with each other and with the central Haversian canal by a number of fine dark lines, which radiate like the spokes of a wheel and are called canaliculi. Filling in the irregular intervals which are left between these circular systems are other lamellae, with their lacunae and canaliculi running in various directions, but more or less curved (Fig. 73); they are termed interstitial lamellae. Again, other lamellae, found on the surface of the bone, are arranged parallel to its circumference; they are termed circum- 90 OSTEOLOGY ferential, or by some authors primary or fundamental lamellae, to distinguish them from those laid down around the axes of the Haversian canals, which are then termed secondary or special lamellae. The Haversian canals, seen in a transverse section of bone as round holes at or about the center of each Haversian system, may be demonstrated to be true canals if a longitudinal section be made (Fig. 74). It will then be seen that the canals run parallel with the longitudinal axis of the bone for a short distance and then branch and communicate. They vary considerably in size, some being as much as 0.12 mm. in diameter; the average size is, however, about 0.05 mm. Near the medullary cavity the canals are larger than those near the surface of the bone. Each canal contains one or two bloodvessels, with a small quantity of delicate connective tissue and some nerve filaments. In the larger ones there are also lymphatic vessels, and cells with branching processes which communicate, through the canalculi, with the branched processes of certain bone cells in the substance of the bone. Those canals near the surface of the bone open upon it by minute orifices, and those near the medullary cavity open in the same way into this space, so that the whole of the bone is permeated by a system of bloodvessels running through the bony canals in the centers of the Haversian systems. The lamellae are thin plates of bony tissue encircling the central canal, and may be com- pared, for the sake of illustration, to a number of sheets of paper pasted one over another around a central hollow cylinder. After macerating a piece of bone in dilute mineral acid, these lamellae may be stripped off in a Fig. 75.—Perforating fibers, human parietal bone, decalcified. (H. Muller.) a, perforating fibers in situ; b, fibres drawn out of their sockets; c, sockets. Fig. 74.—Section parallel to the surface from the body of the femur. X 100. a, Haver- sian canals; b, lacun® seen from the side; c, others seen from the surface in lamellae, which are cut horizontally. longitudinal direction as thin films. If one of these be examined with a high power of the microscope; it will be found to be composed of a finely reticular structure, made up of very slender transparent fibers, decussating obliquely; and coalescing at the points of intersection; these fibers are composed of fine fibrils identical with those of white connective tissue. The intercellular matrix between the fibers is impregnated by calcareous deposit which the acid dissolves. In many places the various lamellae may be seen to be held together by tapering fibers, which run obliquely through them, pinning or bolting them together; they were first de- scribed by Sharpey, and were named by him perforating fibers (Fig. 75). The Lacunae are situated between the lamellae, and consist of a number of oblong BONE 91 spaces. In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots. Each lacuna is occupied during life by a branched cell, termed a bone-cell or bone-corpuscle, the processes from which extend into the canaliculi (Fig. 76). The Canaliculi are exceedingly minute channels, crossing the lamellae and con- necting the lacunae with neighboring lacunae and also with the Haversian canal. From the Haversian canal a number of canaliculi are given off, which radiate from it, and open into the first set of lacunae between the first and second lamellae. From these lacunae a second set of canaliculi is given off; these run outward to the next series of lacunae, and so on until the periphery of the Haversian system is reached; here the canaliculi given off from the last series of lacunae do not communi- cate with the lacunae of neighboring Haversian systems, but after passing outward for a short distance form loops and return to their own lacunae. Thus every part of an Haversian system is supplied with nutrient fluids derived from the vessels in the Haversian canal and distributed through the canaliculi and lacunae. The bone cells are contained in the lacunae, which, however, they do not completely fill. They are flattened nucleated branched cells, homologous with those of connective tissue; the branches, especially in young bones, pass into the canaliculi from the lacunae. In thin plates of bone (as in the walls of the spaces of cancellous tissue) the Haversian canals are absent, and the canaliculi open into the spaces of the cancellous tissue (medullary spaces), which thus have the same function as the Haversian canals. Chemical Composition.—Bone consists of an animal and an earthy part intimately com- bined together. The animal part may be obtained by immersing a bone for a considerable time in dilute mineral acid, after which process the bone comes out exactly the same shape as before, but perfectly flexible, so that a long bone (one of the ribs, for example) can easily be tied in a knot. If now a transverse section is made (Fig. 77) the same general arrangement of the Haversian canals, lamellae, lacunae, and canaliculi is seen. The earthy part may be separately obtained by calcination, by which the animal matter is completely burnt out. The bone will still retain its original form, but it will be white and brittle, will have lost about one-third of its original weight, and will crumble down with the slightest force. The earthy matter is composed chiefly of calcium phosphate, about 58 per cent, of the weight of the bone, calcium carbonate about 7 per cent., calcium fluoride and magnesium phos- phate from 1 to 2 per cent, each and sodium chloride less than 1 per cent.; they confer on bone its hardness and rigidity, while the animal matter (ossein) determines its tenacity. Ossification.—Some bones are preceded by membrane, such as those forming the roof and sides of the skull; others, such as the bones of the limbs, are preceded by rods of cartilage. Hence two kinds of ossification are described: the intra- membranous and the intracartilaginous. Intramembranous Ossification.—In the case of bones which are developed in membrane, no cartilaginous mould precedes the appearance of the bony tissue. The membrane which occupies the place of the future bone is of the nature of con- nective tissue, and ultimately forms the periosteum; it is composed of fibers and granular cells in a matrix. The peripheral portion is more fibrous, while, in the Fig. 76.—Nucleated bone cells and their processes, contained in the bone lacunae and their canaliculi respectively. From a section through the vertebra of an adult mouse. (Klein and Noble Smith.) 92 OSTEOLOGY interior the cells or osteoblasts predominate; the whole tissue is richly supplied with bloodvessels. At the outset of the process of bone formation a little network of spicules is noticed radiating from the point or center of ossification. These rays consist at their growing points of a network of fine clear fibers and granular Haversian canal Done corpuscle Bone corpuscle between inter- stitial lamellae Fig. 77.—Transverse section of body of human fibula, decalcified. X 250. corpuscles with an intervening ground substance (Fig. 78). The fibers are termed osteogenetic fibers, and are made up of fine fibrils differing little from those of white fibrous tissue. The membrane soon assumes a dark and granular appearance from the deposition of calcareous granules in the fibers and in the intervening matrix, Osteogeneiic fibers Union of adjacent spicules Calcified deposit between the fibers OsteoblastsZ. Bony spicules Fig. 78.—Part of the growing edge of the developing parietal bone of a fetal cat. (After J. Lawrence.) and in the calcified material some of the granular corpuscles or osteoblasts are enclosed. By the fusion of the calcareous granules the tissue again assumes a more transparent appearance, but the fibers are no longer so distinctly seen. The involved osteoblasts form the corpuscles of the future bone, the spaces in BONE 93 which they are enclosed constituting the lacunae. As the osteogenetic fibers grow out to the periphery they continue to calcify, and give rise to fresh bone spicules. Thus a network of bone is formed, the meshes of which contain the bloodvessels and a delicate connective tissue crowded with osteoblasts. The bony trabeculae thicken by the addition of fresh layers of bone formed by the osteoblasts on their surface, and the meshes are correspondingly encroached upon. Subsequently successive layers of bony tissue are deposited under the periosteum and around the larger vascular channels which become the Haversian canals, so that the bone increases much in thickness. Intercartilaginous Ossification.—Just before ossification begins the mass is entirely cartilaginous, and in a long bone, which may be taken as an example, the process commences in the center and proceeds toward the extremities, which for some time remain cartilaginous. Subsequently a similar process commences in one or more places in those extremities and gradually extends through them. The extremities do not, however, become joined to the body of the bone by bony tissue until growth has ceased; between the body and either -extremity a layer of cartilaginous tissue termed the epiphysial cartilage persists for a definite period. The first step in the ossification of the cartilage is that the cartilage cells, at the point where ossification is com- mencing and which is termed a center of ossification, enlarge and arrange themselves in rows (Fig. 79). The matrix in which they are imbedded increases in quantity, so that the cells become further separated from each other. A deposit of calcareous material now takes place in this matrix, between the rows of cells, so that they become separated from each other by longi- tudinal columns of calcified matrix, presenting a granular and opaque ap- pearance. Here and there the matrix between two cells of the same row also becomes calcified, and transverse bars of calcified substance stretch across from one calcareous column to another. Thus there are longitudinal groups of the cartilage cells enclosed in oblong cavities, the walls of which are formed of calcified matrix which cuts off all nutrition from the cells; the cells, in consequence, atrophy, leaving spaces called the primary areolae. At the same time that this process is going on in the center of the solid bar of cartilage, certain changes are taking place on its surface. This is covered by a very vascular membrane, the perichondrium, entirely similar to the embryonic connective tissue already described as constituting the basis of membrane bone; on the inner surface of this—that is to say, on the surface in contact with the cartilage—are gathered the formative cells, the osteoblasts. By the agency of these cells a thin layer of bony tissue is formed between the peri- Fia. 79.—Section of fetal bone of cat. ir. Irruption of the subperiosteal tissue, p. Fibrous layer of the perios- teum. o. Layer of osteoblasts, im. Subperiosteal bony deposit. (From Quain’s “Anatomy,” E. A. Schafer.) 94 OSTEOLOGY chondrium and the cartilage, by the intramembranous mode of ossification just described. There are then, in this first stage of ossification, two processes going on simultaneously: in the center of the cartilage the formation of a number of oblong spaces, formed of calcified matrix and containing the withered cartilage cells, and on the surface of the cartilage the formation of a layer of true mem- brane bone. The second stage consists in the prolongation into the cartilage of processes of the deeper or osteogenetic layer of the perichondrium, which has now become periosteum (Fig. 79, ir). The processes consist of bloodvessels and cells—osteoblasts, or bone-formers, and osteoclasts, or bone-destroyers. The latter are similar to the giant cells (myeloplaxes) found in marrow, and they excavate passages through the new-formed bony layer by absorption, and pass through it into the calcified matrix (Fig. 80). Wherever these processes come in con- tact with the calcified walls of the primary areolae they absorb them, and thus cause a fusion of the original cavities and the formation of larger spaces, which are termed the secondary areolae or medullary spaces. These secondary spaces become filled with embryonic marrow, consisting of osteoblasts and vessels, derived, in the manner described above, from the osteogenetic layer of the periosteum (Fig. 80). . Thus far there has been traced the forma- tion of enlarged spaces (secondary areolae), the perforated walls of which are still formed by calcified cartilage matrix, containing an embryonic marrow derived from the processes sent in from the osteogenetic layer of the periosteum, and consisting of bloodvessels and osteoblasts. The walls of these secondary areolae are at this time of only inconsiderable thickness, but they become thickened by the deposition of layers of true bone on their sur- face. This process takes place in the follow- ing manner: Some of the osteoblasts of the embryonic marrow, after undergoing rapid division, arrange themselves as an epithelioid layer on the surface of the wall of the space (Fig. 81). This layer of osteoblasts forms a bony stratum, and thus the wall of the space becomes gradually covered with a layer of Osteoclasts- Fig. 80.—Part of a longitudinal section of the developing femur of a rabbit, a. Flattened cartilage cells, b. Enlarged cartilage cells, c, d._ Newly formed bone. e. Osteoblasts. /. Giant cells or osteoclasts. g, h. Shrunken cartilage cells. (From “Atlas of Histology,’* Klein and Noble Smith.) Osteoblasts Fig. 81.—Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo. (Kolliker.) true osseous substance in which some of the bone-forming cells are included as bone corpuscles. The next stage in the process consists in the removal of these primary bone spicules by the osteoclasts. One of these giant cells may be found lying in a Howship’s foveola at the free end of each spicule. The removal of the BONE 95 primary spicules goes on pari passu with the formation of permanent bone by the periosteum, and in this way the medullary cavity of the body of the bone is formed. This series of changes has been gradually proceeding toward the end of the body of the bone, so that in the ossifying bone all the changes described above may be seen in different parts, from the true bone at the center of the body to the hyaline cartilage at the extremities. While the ossification of the cartilaginous body is extending toward the articular ends, the cartilage immediately in advance of the osseous tissue continues to grow until the length of the adult bone is reached. During the period of growth the articular end, or epiphysis, remains for some time entirely cartilaginous, then a bony center appears, and initiates in it the process of intracartilaginous ossification; but this process never extends to any great distance. The epiphysis remains separated from the body by a narrow cartilaginous layer for a definite time. This layer ultimately ossifies, the distinc- tion between body and epiphysis is obliterated, and the bone assumes its completed form and shape. The same remarks also apply to such processes of bone as are separately ossified, e. g., the trochanters of the femur. The bones therefore con- tinue to grow until the body has acquired its full stature. They increase in length by ossification continuing to extend behind the epiphysial cartilage, which goes on growing in advance of the ossifying process. They increase in circumference by deposition of new bone, from the deeper layer of the periosteum, on their exter- nal surface, and at the same time an absorption takes place from within, by which the medullary cavities are increased. The permanent bone formed by the periosteum when first laid down is cancellous in structure. Later the osteoblasts contained in its spaces become arranged in the concentric layers characteristic of the Haversian systems, and are included as bone corpuscles. The number of ossific centers varies in different bones. In most of the short bones ossification commences at a single point near the center, and proceeds toward the surface. In the long bones there is a central point of ossification for the body or diaphysis: and one or more for each extremity, the epiphysis. That for the body is the first to appear. The times of union of the epiphyses with the body vary inversely with the dates at which their ossifications began (with the exception of the fibula) and regulate the direction of the nutrient arteries of the bones. Thus, the nutrient arteries of the bones of the arm and forearm are directed toward the elbow, since the epiphyses at this joint become united to the bodies before those at the opposite extremities. In the lower limb, on the other hand, the nutrient arteries are directed away from the knee: that is, upward in the femur, downward in the tibia and fibula; and in them it is observed that the upper epiphysis of the femur, and the lower epiphyses of the tibia and fibula, unite first with the bodies. Where there is only one epiphysis, the nutrient artery is directed toward the other end of the bone; as toward the acromial end of the clavicle, toward the distal ends of the metacarpal bone of the thumb and the metatarsal bone of the great toe, and toward the proximal ends of the other metacarpal and metatarsal bones. Parsons1 groups epiphyses under three headings, viz.: (1) pressure epiphyses, appearing at the articular ends of the bones and transmitting “the weight of the body from bone to bone;” (2) traction epiphyses, associated with the insertion of muscles and “originally sesamoid structures though not necessarily sesamoid bones;” and (3) atavistic epiphyses, representing parts of the skeleton, which at one time formed separate bones, but which have lost their function, “and only appear as separate ossifications in early life.” 1 Jour, of Anat. and Phys., vols. xxxviii, xxxix, and xlii. 96 OSTEOLOGY THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS; SPINAL COLUMN). The vertebral column is a flexuous and flexible column, formed of a series of bones called vertebrae. The vertebrae are thirty-three in number, and are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they occupy; there are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal. This number is sometimes increased by .an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished. The vertebrae in the upper three regions of the column remain distinct through- out life, and are known as true or movable vertebrae; those of the sacral and coccygeal regions, on the other hand, are termed false or fixed vertebrae, because they are united with one another in the adult to form two bones—five forming the upper bone or sacrum, and four the terminal bone or coccyx. With the exception of the first and second cervical, the true or movable vertebrae present certain common characteristics which are best studied by examining one from the middle of the thoracic region. GENERAL CHARACTERISTICS OF A VERTEBRA. A typical vertebra consists of two essential parts—viz., an anterior segment, the body, and a posterior part, the vertebral or neural arch; these enclose a foramen, the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair of laminae, and supports seven processes—viz., foyr articular, two transverse, and one spinous. Costal fovea~ Pedicle or roof of vertebral arch Lamina / Superior articular process Fig. 82.—A typical thoracic vertebra, viewed from above. When the vertebrae are articulated with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels. Body (corpus vertebrae).—The body is the largest part of a vertebra, and is more or less cylindrical in shape. Its upper and lower surfaces are flattened and THE CERVICAL VERTEBRA 97 rough, and give attachment to the intervertebral fibrocartilages, and each presents a rim around its circumference. In front, the body is convex from side to side and concave from above downward. Behind, it is flat from above downward and slightly concave from side to side. Its anterior surface presents a few small apertures, for the passage of nutrient vessels; on the posterior surface is a single large, irregular aperture, or occasionally more than one, for the exit of the basi- vertebral veins from the body of the vertebra. Pedicles (radices arci vertebrae).—The pedicles are two short, thick processes, which project backward, one on either side, from the upper part of the body, at the junction of its posterior and lateral surfaces. The concavities above and below the pedicles are named the vertebral notches; and when the vertebrae are articulated, the notches of each contiguous pair of bones form the intervertebral foramina, already referred to. Laminae.—The laminae are two broad plates directed backward and medialward from the pedicles. They fuse in the middle line posteriorly, and so complete the posterior boundary of the vertebral foramen. Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava. Processes.—Spinous Process (processus spinosus).—The spinous process is directed backward and downward from the junction of the laminae, and serves for the attachment of muscles and ligaments. Articular Processes.—The articular processes, two superior and two inferior, spring from the junctions of the pedicles and laminae. The superior project upward, and their articular surfaces are directed more or less backward; the inferior project downward, and their surfaces look more or less forward. The articular surfaces are coated with hyaline cartilage. Transverse Processes (;processus transversi).—The transverse processes, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They serve for the attachment of muscles and ligaments. Structure of a Vertebra (Fig. 83).—The body is composed of cancellous tissue, covered by a thin coating of compact bone; the latter is perforated by numerous orifices, some of large size for the passage of vessels; the interior of the bone is traversed by one or two large canals, for the reception of veins, which converge toward a single large, irregular aperture, or several small apertures, at the posterior part of the body. The thin bony lamellae of the cancellous tissue are more pronounced in lines perpendicular to the upper and lower surfaces and are developed in response to greater pressure in this direction (Fig. 83). The arch and processes projecting from it have thick coverings of compact tissue. The Cervical Vertebrae (Verte- brae Cervicales). The cervical vertebrae (Fig. 84) are the smallest of the true vertebrae, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present excep- tional features and must be separately described; the following characteristics are common to the remaining four. The body is small, and broader from side to side than from before backward The anterior and posterior surfaces are flattened and of equal depth; the former Fio. 83.—Sagittal section of a lumbar vertebra. 98 OSTEOLOGY is placed on a lower level than the latter, and its inferior border is prolonged downward, so as to overlap the upper and forepart of the vertebra below. The upper surface is concave transversely, and presents a projecting lip on either side; the lower surface is concave from before backward, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the subjacent vertebra. The pedicles are directed lateralward and backward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, Anterior tubercle of transverse process Transverse process transversarium Foramen Posterior tubercle of • transverse 'process Superior articular process Inferior articular process Spinoiis process Fig. 84.—A cervical vertebra. narrower. The laminae are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form. The spinous process is short and bifid, the two divisions being often of unequal size. The superior and inferior articular processes on either side are fused to form an articular pillar, which projects lateral- ward from the junction of the pedicle and lamina. The articular facets are flat and of an oval form: the superior look backward, upward, and slightly medial- ward: the inferior forward, downward, and slightly lateralward. The transverse processes are each pierced by the foramen transversarium, which, in the upper six Superior articular surface Articular pillar Anterior tubercle of. transverse process Body Sulcus for nerve Posterior tubercle of transverse process Spinous process Fig. 85.—Side view of a typical cervical vertebra. vertebrae, gives passage to the vertebral artery and vein and a plexus of sympa- thetic nerves. Each process consists of an anterior and a posterior part. The anterior portion is the homologue of the rib in the thoracic region, and is there- fore named the costal process or costal element: it arises from the side of the body, is directed lateralward in front of the foramen, and ends in a tubercle, the anterior tubercle. The posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and lateralward; it ends in a flattened vertical tubercle, the posterior tubercle. These two parts THE CERVICAL VERTEBRAE 99 are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve.1 First Cervical Vertebra.—The first cervical vertebra (Fig. 86) is named the atlas because it supports the globe of the head. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra. Its other peculiarities are that it has no spinous process, is ring-like, and consists of an anterior and a posterior arch and two lateral masses. The anterior arch forms about one-fifth of the ring: its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process (dens) of the axis. The upper and lower borders respectively give attachment to the anterior atlanto- occipital membrane and the anterior atlantoaxial ligament; the former connects it with the occipital bone above, and the latter with the axis below. The posterior arch forms about two-fifths of the circumference of the ring: it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores. The diminutive size of this process pre- vents any interference with the movements between the atlas and the skull. The posterior part of the arch presents above and behind a rounded edge for Anterior tubercle Outline of section of odontoid 'process Outline of section of trans verse atlantal ligament Transverse 'process Foramen transver- sanum Groove for vertebral artery and first cervical nerve Posterior tubercle Fig. 86.—First cervical vertebra, or atlas. the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is a groove (sulcus arterice vertebralis), sometimes converted into a foramen by a delicate bony spiculum which arches backward from the posterior end of the superior articular process. This groove represents the superior vertebral notch, and serves for the transmission of the vertebral artery, which, after ascending through the foramen in the transverse process, winds around the lateral mass in a direction backward and medialward; it also transmits the suboccipital (first spinal) nerve. On the under surface of the posterior arch, behind the articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlanto- axial ligament, which connects it with the axis. The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head. Each carries two articular facets, a superior and an inferior. The superior facets are of large size, oval, concave, and approach each other in front, but diverge behind: they are directed upward, medialward, and a little backward, each forming a cup for the corresponding condyle of the occipital bone, and are admirably adapted to the nodding movements of the head. Not infrequently they are 1 The costal element of a cervical vertebra not only includes the portion which springs from the side of the body, but the anterior and posterior tubercles and the bar of bone which connects them (Fig. 67). 100 OSTEOLOGY partially subdivided by indentations which encroach upon their margins. The inferior articular facets are circular in form, flattened or slightly convex and directed downward and medialward, articulating with the axis, and permitting the rotatory movements of the head. Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts—the anterior or smaller receiving the odontoid process of the axis, the posterior transmitting the medulla spinalis and its membranes. This part of the vertebral canal is of considerable size, much greater than is required for the accommodation of the medulla spinalis, and hence lateral displacement of the atlas may occur without compression of this structure. The transverse processes are large; they project lateralward and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversarium is directed from below, upward and backward. Dens .For alar ligaments For trans. ligament of atlas Superior articular surface Foramen transversarium Spinous jyrocess Fig. 87.—Second cervical vertebra, or epistropheus, from above. Second Cervical Vertebra.—The second cervical vertebra (Fig. 87 and 88) is named the epistropheus or axis because it forms the pivot upon which the first vertebra, carrying the head, rotates. The most distinctive characteristic of this bone is the strong odontoid process which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- sents in front a median longitudinal ridge, separating two lateral depressions for the attachment of the Longus colli muscles. Its under surface is concave from before backward and covex from side to side. The dens or odontoid process exhibits a slight constriction or neck, where it joins the body. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process hi position. The apex is pointed, and gives attachment to the apical odontoid ligament; below the apex the process is somewhat enlarged, and pre- sents on either side a rough impression for the attachment of the alar ligament; these ligaments connect the process to the occipital bone. The internal structure THE CERVICAL VERTEBR/E 101 of the odontoid process is more compact than that of the body. The pedicles are broad and strong, especially in front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces. The laminae are thick and strong, and the vertebral Odontoid process Rough surface for alar ligament Articular facet for anterior arch of atlas Groove for transverse atlantal ligament Body Spinous process Transverse process I nferior articular process Fig. 88.—Second cervical vertebra, epistropheus, or axis, from the side. foramen large, but smaller than that of the atlas. The transverse processes are very small, and each ends in a single tubercle; each is perforated by the foramen transversarium, which is directed obliquely upward and lateralward. The superior articular surfaces are round, slightly convex, directed upward and lateralward, and are supported on the body, pedicles, and transverse processes. The inferior articular surfaces have the same direction as those of the other cervical vertebrae. The supe- rior vertebral notches are very shal- low, and lie behind the articular processes; the inferior lie in front of the articular processes, as in the other cervical vertebrae. The spinous process is large, very strong, deeply channelled on its under surface, and presents a bifid, tuberculated extremity. The Seventh Cervical Vertebra (Fig. 89).—The most distinctive characteristic of this vertebra is the existence of a long and promi- nent spinous process, hence the name vertebra prominens. This pro- cess is thick, nearly horizontal in direction, not bifurcated, but ter- minating in a tubercle to which the lower end of the ligamentum nuchae is attached. The transverse processes are of considerable size, their posterior roots are large and prominent, while the anterior are small and faintly marked; the upper surface of each has usually a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. The foramen Body Transverse process Superior articular surface Post, root Superior articular surface Fia. 89.—Seventh cervical vertebra. Spinous process 102 OSTEOLOGY transversarium may be as large as that in the other cervical vertebrae, but is generally smaller on one or both sides; occasionally it is double, sometimes it is absent. On the left side it occasionally gives passage to the vertebral artery; more frequently the vertebral vein traverses it on both sides; but the usual arrangement is for both artery and vein to pass in front of the transverse pro- cess, and not through the foramen. Sometimes the anterior root of the trans- verse process attains a large size and exists as a separate bone, which is known as a cervical rib. The Thoracic Vertebrae (Vertebrae Thoracales) The thoracic vertebrae (Fig. 90) are intermediate in size between those of the cervical and lumbar regions; they increase in size from above downward, the upper vertebrae being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. Superior articular process Demi-facet for head of rib Facet for articular part of tubercle of rib Demi-facet for head of rib Inferior articular 'process Fig. 90.—A thoracic vertebra. The bodies in the middle of the thoracic region are heart-shaped, and as broad in the antero-posterior as in the transverse direction. At the ends of the thoracic region they resemble respectively those of the cervical and lumbar vertebrae. They are slightly thicker behind than in front, flat above and below, convex from side to side in front, deeply concave behind, and slightly constricted laterally and in front. They present, on either side, two costal demi-facets, one above, near the root of the pedicle, the other below, in front of the inferior vertebral notch; these are covered with cartilage in the fresh state, and, when the vertebrae are articulated with one another, form, with the intervening intervertebral fibro- cartilages, oval surfaces for the reception of the heads of the ribs. The pedicles are directed backward and slightly upward, and the inferior vertebral notches are of large size, and deeper than in any other region of the vertebral column. The laminae are broad, thick, and imbricated—that is to say, they overlap those of subjacent vertebrae like tiles on a roof. The vertebral foramen is small, and of a circular form. The spinous process is long, triangular on coronal section, directed obliquely downward, and ends in a tuberculated extremity. These processes THE THORACIC VERTEBRAE 103 overlap from the fifth to the eighth, but are less oblique in direction above and below. The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminae; their articular facets are practi- cally flat, and are directed backward and a little lateralward and upward. The inferior articular processes are fused to a considerable extent with the laminae, An entire facet above; a demi-facet below A demi-facet above One entire facet ( One entire facet. < No facet on trans. proc. ( which is rudimentary One entire facet, {No facet on trans- verse process. Infer.artic. process convex and turned lateralwards Fig. 91.—Peculiar thoracic vertebrae. and project but slightly beyond their lower borders; their facets are directed forward and a little medialward and downward. The transverse processes arise from the arch behind the superior articular processes and pedicles; they are thick, strong, and of considerable length, directed obliquely backward and lateralward, and each ends in a clubbed extremity, on the front of which is a small, concave surface, for articulation with the tubercle of a rib. 104 OSTEOLOGY The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certain peculiarities, and must be specially considered (Fig. 91). The First Thoracic Vertebra has, on either side of the body, an entire, articular facet for the head of the first rib, and a demi-facet for the upper half of the head of the second rib. The body is like that of a cervical vertebra, being broad trans- versely; its upper surface is concave, and lipped on either side. The superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal. The transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae. The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- jects however, it has two demi-facets on either side; when this occurs the tenth has only demi-facets at the upper part. The Tenth Thoracic Vertebra has (except in the cases just mentioned) an entire articular facet on either side, which is placed partly on the lateral surface of the pedicle. In the Eleventh Thoracic Vertebra the body approaches in its form and size to that of the lumbar vertebrae. The articular facets for the heads of the ribs are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the thoracic region. The spinous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, and have on articular facets. The Twelfth Thoracic Vertebra has the same general characteristics as the eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateralward, like those of the lumbar vertebrae; by the general form of the body, laminae, and spinous process, in which it resembles the lumbar vertebrae; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mammillary and accessory processes of the lumbar vertebrae. Traces of similar elevations are found on the transverse processes of the tenth and eleventh thoracic vertebrae. Superior articular process Fig. 92.—A lumbar vertebra seen from the side. The Lumbar Vertebrae (Vertebrae Lumbales) The lumbar vertebrae (Figs. 92 and 93) are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body. The body is large, wider from side to side than from before backward, and a little thicker in front than behind. It is flattened or slightly concave above and THE LUMBAR VERTEBRAE 105 below, concave behind, and deeply constricted in front and at the sides. The pedicles are very strong, directed backward from the upper part of the body; Inferior articular process Transverse process Mamillary process Accessory process Superior articular process Fig. 93.—A lumbar vertebra from above and behind. consequently, the inferior vertebral notches are of considerable depth. The laminae are broad, short, and strong; the vertebral foramen is triangular, larger Fig. 94.—Fifth lumbar vertebra, from above. than in the thoracic, but smaller than in the cervical region. The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in 106 OSTEOLOGY a rough, uneven border, thickest below where it is occasionally notched. The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets on the superior processes are concave, and look backward and medial ward; those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than the latter, since in the articulated column the inferior articular processes are embraced by the superior processes of the subjacent vertebra. The transverse processes are long, slender, and horizontal in the upper three lumbar vertebrae; they incline a little upward in the lower two. In the upper three verte- brae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the pedicles and posterior parts of the bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs. Of the three tubercles noticed in connection with the transverse processes of the lower thoracic vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process; the inferior is situated at the back part of the base of the transverse process, and is called the accessory process (Fig. 93). The Fifth Lumbar Vertebra (Fig. 94) is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacro- vertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes; and by the thickness of its transverse processes, which spring from the body as well as from the pedicles. The Sacral and Coccygeal Vertebrae. The sacral and coccygeal vertebrae consist at an early period of life of nine separate segments which are united in the adult, so as to form two bones, five entering into the formation of the sacrum, four into that of the coccyx. Some- times the coccyx consists of five bones; occasionally the number is reduced to three. The Sacrum (os sacrum).—The sacrum is a large, triangular bone, situated in the lower part of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones; its upper part or base articulates with the last lumbar vertebra, its apex with the coccyx. It is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebral angle when articulated with the last lumbar vertebra; its central part is projected backward, so as to give increased capacity to the pelvic cavity. Pelvic Surface (facies yelvina).—The pelvic surface (Fig. 95) is concave from above downward, and slightly so from side to side. Its middle part is crossed by four transverse ridges, the positions of which correspond with the original planes of separation between the five segments of the bone. The portions of bone intervening between the ridges are the bodies of the sacral vertebrae. The body of the first segment is of large size, and in form resembles that of a lumbar vertebra; the succeeding ones diminish from above downward, are flattened from before backward, and curved so as to accommodate themselves to the form of the sacrum, being concave in front, convex behind. At the ends of the ridges are seen the anterior sacral foramina, four in number on either side, somewhat rounded in form, diminishing in size from above downward, and directed lateralward and forward; they give exit to the anterior divisions of the sacral nerves and entrance to the lateral sacral arteries. Lateral to these foramina are the lateral parts of the sacrum, each consisting of five separate segments at an early period of life; in the adult, these are blended with the bodies and with each other. Each lateral part is tra- THE SACRAL AND COCCYGEAL VERTEBRA? 107 versed by four broad, shallow grooves, which lodge the anterior divisions of the sacral nerves, and are separated by prominent ridges of bone which give origin to the Piriformis muscle. If a sagittal section be made through the center of the sacrum (Fig. 99), the bodies are seen to be united at their circumferences by bone, wide intervals being left centrally, which, in the fresh state, are filled by the intervertebral fibro- cartilages. In some bones this union is more complete between the lower than the upper segments. Dorsal Surface (facies dorsalis).—The dorsal surface (Fig. 96) is convex and narrower than the pelvic. In the middle line it displays a crest, the middle sacral crest, surmounted by three or four tubercles, the rudimentary spinous processes Fig. 95.—Sacrum, pelvic surface. of the upper three or four sacral vertebrse. On either side of the middle sacral crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, the floor of the groove being formed by the united laminae of the corresponding vertebrae. The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior wall of the sacral canal. On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct sacral articular crests. The articular processes of the first sacral vertebra are large and oval in shape; their facets are concave from side to side, look backward and medialward, and articulate with the facets on the inferior processes of the fifth lumbar vertebra. The tubercles which represent the inferior articular processes of the fifth sacral vertebra are prolonged downward as rounded 108 OSTEOLOGY processes, which are named the sacral cornua, and are connected to the cornua of the coccyx. Lateral to the articular processes are the four posterior sacral foramina; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves. On the lateral side of the posterior sacral foramina is a series of tubercles, which represent the transverse processes of the sacral vertebrce, and form the lateral crests of the sacrum. The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac liga- ments; and those of the fourth and fifth to the sacrotuberous ligaments. Latissimus dorsi Sacrospinalis - Sacrospinalis Upper half of fifth posterior sacral foramen Fig. 96.—Sacrum, dorsal surface. Lateral Surface.—The lateral surface is broad above, but narrowed into a thin edge below. The upper half presents in front an ear-shaped surface, the auricular surface, covered with cartilage in the fresh state, for articulation with the ilium. Behind it is a rough surface, the sacral tuberosity, on which are three deep and uneven impressions, for the attachment of the posterior sacroiliac ligament. The lower half is thin, and ends in a projection called the inferior lateral angle; medial to this angle is a notch, which is converted into a foramen by the trans- verse process of the first piece of the coccyx, and transmits the anterior division of the fifth sacral nerve. The thin lower half of the lateral surface gives attachment to the sacrotuberous and sacrospinous ligaments, to some fibers of the Glutaeus maximus behind, and to the Coccygeus in front. Base (basis oss. sacri).—The base of the sacrum, which is broad and expanded, is directed upward and forward. In the middle is a large oval articular surface, THE SACRAL AND COCCYGEAL VERTEBRAE 109 the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral Articular process - Medial sacral crest Body Cornu of sacrum/ Cornu of coccyx Fig 97.—Lateral surfaces of sacrum and coccyx. Sacral canal A rticular process Fig 98.—Base of sacrum. 110 OSTEOLOGY fibrocartilage. Behind this is the large triangular orifice of the sacral canal, which is completed by the laminae and spinous process of the first sacral vertebra. The superior articular processes project from it on either side; they are oval, concave, directed backward and medialward, like the superior articular processes of a lumbar vertebra. They are attached to the body of the first sacral vertebra and to the alae by short thick pedicles; on the upper surface of each pedicle is a vertebral notch, which forms the lower part of the foramen between the last lumbar and first sacral vertebrae. On either side of the body is a large triangular surface, which supports the Psoas major and the lumbosacral trunk, and in the articulated pelvis is continuous with the iliac fossa. This is called the ala; it is slightly concave Cornua / L_ Budim. l Trans, prac. Anterior Surface externus Posterior surface Fig. 99.—Median sagittal section of the sacrum. Fig. 100.—Coccyx. from side to side, convex from before backward, and gives attachment to a few of the fibers of the Iliacus. The posterior fourth of the ala represents the trans- verse process, and its anterior three-fourths the costal process of the first sacral segment. Apex (apex oss. sacri).—The apex is directed downward, and presents an oval facet for articulation with the coccyx. Vertebral Canal (canalis sacralis; sacral canal).—The vertebral canal (Fig. 99) runs throughout the greater part of the bone; above, it is triangular in form; below, its posterior wall is incomplete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and its walls are perforated by the anterior and posterior sacral foramina through which these nerves pass out. THE SACRAL AND COCCYGEAL VERTEBRAE 111 Structure.—The sacrum consists of cancellous tissue enveloped by a thin layer of compact bone. Articulations.—The sacrum articulates with four bones; the last lumbar vertebra above, the coccyx below, and the hip bone on either side. Differences in the Sacrum of the Male and Female.—In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obliquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent. In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female. Variations.—The sacrum, in some cases, consists of six pieces; occasionally the number is reduced to four. The bodies of the first and second vertebrae may fail to unite. Sometimes the uppermost transverse tubercles are not joined to the rest of the ala on one or both sides, or the sacral canal may be open throughout a considerable part of its length, in consequence of the imperfect development of the laminae and spinous processes. The sacrum, also, varies con- siderably with respect to its degree of curvature. The Coccyx (os coccygis).—The coccyx (Fig. 100) is usually formed of four rudimentary vertebrae; the number may however be increased to five or diminished to three. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. All the segments are destitute of pedicles, laminae, and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the last three diminish in size from above downward, and are usually fused with one another. Surfaces.—The anterior surface is slightly concave, and marked with three trans- verse grooves which indicate the junctions of the different segments. It gives attachment to the anterior sacrococcygeal ligament and the Levatores ani, and supports part of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. Of these, the superior pair are large, and are called the coccygeal cornua; they project upward, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve. Borders.—The lateral borders are thin, and exhibit a series of small eminences, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened from before backward, and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the anterior division of the fifth sacral nerve; the others diminish in size from above downward, and are often wanting. The borders of the coccyx are narrow, and give attachment on either side to the sacro- tuberous and sacrospinous ligaments, to the Coccygeus in front of the ligaments, and to the Glutseus maximus behind them. Base.—The base presents an oval surface for articulation with the sacrum. Apex.—The apex is rounded, and has attached to it the tendon of the Sphincter ani externus. It may be bifid, and is sometimes deflected to one or other side. Ossification of the Vertebral Column.—Each cartilaginous vertebra isossified from three primary centers (Fig. 101), two for the vertebral arch and one for the body.1 Ossification of the vertebral arches begins in the upper cervical vertebra; about the seventh or eighth week of fetal life, and grad- ually extends down the column. The ossific granules first appear in the situations where the trans- verse processes afterward project, and spread backward to the spinous process forward into the pedicles, and lateralward into the transverse and articular processes. Ossification of thebodies begins about the eighth week in the lower thoracic region, and subsequently extends upward and down- ward along the column. The center for the body does not give rise to the whole of the body of the adult vertebra, the postero-lateral portions of which are ossified by extensions from the verte- bral arch centers. The body of the vertebra during the first few years of life shows, therefore, 1 A vertebra is occasionally found in which the body consists of two lateral portions—a condition which proves that the body is sometimes ossified from two primary centers, one on either side of the middle line. 112 OSTEOLOGY two synchondroses, neurocentral synchondroses, traversing it along the planes of junction of the three centers (Fig. 102). In the thoracic region, the facets for the heads of the ribs lie behind the neurocentral synchondroses and are ossified from the centers for the vertebral arch. At birth the vertebra consists of three pieces, the body and the halves of the vertebral arch. Dur- ing the first year the halves of the arch unite behind, union taking place first in the lumbar region and then extending upward through the thoracic and cervical regions. About the third year the bodies of the upper cervical vertebrae are joined to the arches on either side; in the lower lumbar verte- brae the union is not completed until the sixth year. Before puberty, no other Fig. 101.—Ossification of a vertebra By 3 primary centers 1 for body (Slh week) 1 for each vertebral arch (lih or Slh week) Fig. 102. By 3 secondary centers . Neurocentral synchondrosis 1 for each trans. process 16th year Additional centers for costal elements * At birth 1 for spinous process (Kith year) By 2 additional plates Fig. 103. Fig. 107 1 for upper surface' of body 1 for under surface of body 16tli year By 3 centers Fig. 104.—Atlas. 1 for anter. arch (end of l.sf year) .1 for each lateral mass At -h yrs 7lh week Fig. 105.—Axis. By 7 centers 2nd year Fig. 108 - 6th month Exceptional cases Two epiphysial plates for each lateral surface * 1 for each vertebral arch (7lh or 8th v eek) 1 for body (4th month) Fig. 106.—Lumbar vertebra. 1 for under surface of body At 2i>th year 2 additional centers for mammillary processes Fig. 107-109.—Ossification of the sacrum. changes occur, excepting a gradual increase of these primary centers, the upper and under sur- faces of the bodies and the ends of the transverse and spinous processes being cartilaginous. THE SACRAL AND COCCYGEAL VERTEBRAE 113 About the sixteenth year (Fig. 102), five secondary centers appear, one for the tip of each transverse process, one for the extremity of the spinous process, one for the upper and one for the lower surface of the body (Fig. 103). These fuse with the rest of the bone about the age of twenty-five. Exceptions to this mode of development occur in the first, second, and seventh cervical verte- brae, and in the lumbar vertebrae. Atlas.—-The atlas is usually ossified from three centers (Fig. 104). Of these, one appears in each lateral mass about the seventh week of fetal life, and extends backward; at birth, these portions of bone are separated from one another behind by a narrow interval filled with cartilage. Between the third and fourth years they unite either directly or through the medium of a separate center developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a separate center appears about the end of the first year after birth, and joins the lateral masses from the sixth to the eighth year—the lines of union extending across the anterior portions of the superior articular facets. Occasionally there is no separate center, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses; sometimes this arch is ossified from two centers, one on either side of the middle line. Epistropheus or Axis.—The axis is ossified from five primary and two secondary centers (Fig. 105). The body and vertebral arch are ossified in the same manner as the corresponding parts in the other vertebrae, viz., one center for the body, and two for the vertebral arch. The centers for the arch appear about the seventh or eighth week of fetal fife, that for the body about the foirth or fifth month. The dens or odontoid process consists originally of a continuation upward of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month of fetal life, two centers make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece of cartilage. The base of the process is separated from the body by a cartilaginous disk, which gradually becomes ossified at its circumference, but remains cartilaginous in its center until advanced age. In this cartilage, rudiments of the lower epiphysial lamella of the atlas and the upper epiphysial lamella of the axis-may sometimes be found. The apex of the odontoid process has a separate center which appears in the second and joins about the twelfth year; this is the upper epiphysial lamella of the atlas. In addition to these there is a secondary center for a thin epiphysial plate on the under surface of the body of the bone. The Seventh Cervical Vertebra.—The anterior or costal part of the transverse process of this vertebra is sometimes ossified from a separate center which appears about the sixth month of fetal life, and joins the body and posterior part of the transverse process between the fifth and sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened lateralward and forward, constitutes what is known as a cervical rib. Separate ossific centers have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. Lumbar Vertebrae.—The lumbar vertebrae (Fig. 106) have each two additional centers, for the mammillary processes. The transverse process of the first lumbar is sometimes developed as a separate piece, which may remain permanently ununited with the rest of the bone, thus form- ing a lumbar peculiarity, however, rarely met with. Sacrum (Figs. 107 to 110).—The body of each sacral vertebra is ossified from a primary center and two epiphysial plates, one for its upper and another for its under surface, while each vertebral arch is ossi- fied from two centers. The anterior portions of the lateral parts have six additional centers, two for each of the first three vertebrse; these represent the costal elements, and make their ap- pearance above and lateral to the anterior sacral foramina (Figs. 107, 108). On each lateral surface two epiphysial plates are developed (Figs. 109, 110): one for the auric- ular surface, and another for the remaining part of the thin lateral edge of the bone.1 Periods of Ossification.—About the eighth or ninth week of fetal life, ossification of the central part of the body of the first sacral vertebra commences, and is rapidly followed by deposit of ossific matter in the second and third; ossification does not commence in the bodies of the lower two segments until between the fifth and eighth months of fetal life. Between the sixth Center for neural arch Center for neural arch. Costal Costal element~ element. Center for body. Lateral epiphysis. Lateral epiphysis. Fio. 110.—Base of young sacrum. 1 The ehds of the spinous processes of the upper three sacral vertebra are sometimes developed from separate epiphyses, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mammillary pro- cesses of the first sacral vertebra; twelve—six on either side—in connection with the costal elements (two each for the first and second and one each fcrr the third and fourth) and eight for the transverse processes—four on either side—one each for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of the sacrum is formed by the extension and union of the third and fourth “costal” and fourth and fifth "transverse” epiphyses. 114 OSTEOLOGY and eighth months ossification of the vertebral arches takes place; and about the same time the costal centers for the lateral parts make their appearance. The junctions of the vertebral arches with the bodies take place in the lower vertebrae as early as the second year, but are not effected in the uppermost until the fifth or sixth year. About the sixteenth year the epiphysial plates for the upper and under surfaces of the bodies are formed; and between the eighteenth and twentieth years, those for the lateral surfaces make their appearance. The bodies of the sacral vertebrae are, during early life, separated from each other by intervertebral fibrocartilages, but about the eighteenth year the two lowest segments become united by bone, and the process of bony union gradually extends upward, with the result that between the twenty-fifth and thirtieth years of life all the segments are united. On examining a sagittal section of the sacrum, the situa- tions of the intervertebral fibrocartilages are indicated by a series of oval cavities (Fig. 99). Coccyx.—The coccyx is ossified from four centers, one for each segment. The ossific nuclei make their appearance in the following order: in the first segment between the first and fourth years; in the second between the fifth and tenth years; in the third between the tenth and fifteenth years; in the fourth between the fourteenth and twentieth years. As age advances, the segments unite with one another, the union between the first and second segments being frequently delayed until after the age of twenty-five or thirty. At a late period of life, especially in females, the coccyx often fuses with the sacrum. THE VERTEBRAL COLUMN AS A WHOLE. The vertebral column is situated in the median line, as the posterior part of the trunk; its average length in the male is about 71 cm. Of this length the cervical part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length. Curves.—Viewed laterally (Fig. Ill), the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins at the apex of the odontoid process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. The thoracic curve, concave for- ward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward. The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk. The vertebral column has also a slight lateral curvature, the convexity of which is directed toward the right side. This may be produced by muscular action, most persons using the right arm in preference to the left, especially in making long-continued efforts, when the body is curved to the right side. In support of this explanation it has been found that in one or two individuals who were left- handed, the convexity was to the left side. By others this curvature is regarded as being produced by the aortic arch and upper part of the descending thoracic aorta—a view which is supported by the fact that in cases where the viscera are transposed and the aorta is on the right side, the convexity of the curve is directed to the left side. Surfaces.—Anterior Surface.—When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx. THE VERTEBRAL COLUMN AS A WHOLE 115 Posterior Surface.—The posterior surface of the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short and horizontal, with bifid extremities. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly hori- zontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line—a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the vertebral grooves are the articular processes, and still more later- ally the transverse processes. In the tho- racic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the inter- vertebral foramina. Lateral Surfaces.—The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lum- bar regions, and by the transverse processes in the thoracic region. They present, in front, the sides of the bodies of the verte- brae, marked in the thoracic region by the facets for articulation with the heads of the ribs. More posteriorly are the inter- vertebral foramina, formed by the juxta- position of the vertebral notches, oval in 1st cervical or Atlas 2nd cervical or Axis 1st thoracic -s' 1st lumbar - Fig. 1H.—Lateral view of the vertebral column. 116 OSTEOLOGY shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions. Vertebral Canal.—The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, viz., the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited. Abnormalities.—Occasionally the coalescence of the laminae is not completed, and conse- quently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (dura mater and arachnoid), and generally of the medulla spinalis itself, takes place, constituting the malformation known as spina bifida. This condition is most common in the lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout the whole length of the canal may remain incomplete. First thoracic First lumbar Fig. 112.—The thorax from in front. THE THORAX. The skeleton of the thorax or chest (Figs. 112, 113, 114) is an osseo-cartilaginous cage, containing and protecting the principal organs of respiration and circulation. THE THORAX 117 It is conical in shape, being narrow above and broad below, flattened from before backward, and longer behind than in front. It is somewhat reniform on trans- verse section on account of the projection of the vertebral bodies into the cavity. —First thoracic First lumbar Fia. 113.—The thorax from behind. Boundaries—The posterior surface is formed by the twelve thoracic vertebra? and the posterior parts of the ribs. It is convex from above downward, and pre- sents on either side of the middle line a deep groove, in consequence of the lateral and backward direction which the ribs take from their vertebral extremities to their angles. The anterior surface, formed by the sternum and costal cartilages, is flattened or slightly convex, and inclined from above downward and forward! The lateral surfaces are convex; they are formed by the ribs, separated from each other by the intercostal spaces, eleven in number, which are occupied by the Intercostal muscles and membranes. The upper opening of the thorax is reniform in shape, being broader from side to side than from before backward. It is formed by the first thoracic vertebra behind, the upper margin of the sternum in front, and the first rib on either side. 118 OSTEOLOGY It slopes downward and forward, so that the anterior part of the opening is on a lower level than the posterior. Its antero-posterior diameter is about 5 cm., and its transverse diameter about 10 cm. The lower opening is formed by the twelfth thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on either side and form an angle, the subcostal angle, into the apex of which the First thoracic— •,Sternum Twelfth thoracic- First lumbar- Fig. 114.—The thorax from the right. Xiphoid process projects. The lower opening is wider transversely than from before backward, and slopes obliquely downward and backward, it is closed by the diaphragm which forms the floor of the thorax. The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 2. The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower part of the body of the second. 4. The upper ribs are more movable, and so allow a greater enlargement of the upper part of the thorax. 119 THE STERNUM The Sternum (Breast Bone). The sternum (Figs. 115 to 117) is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs STERNOCLEIDOMASTOIDEUS SUBCLAVIUS \ Fia. 115.—Anterior surface of sternum and costa cartilages. of ribs. It consists of three parts, named from above downward, the manubrium, the body or gladiolus, and the xiphoid process; in early life the body consists of four segments or sternebrae. In its natural position the inclination of the bone is oblique from above, downward and forward. It is slightly convex in front and concave 120 OSTEOLOGY behind; broad above, becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. Its average length in the adult is about 17 cm., and is rather greater in the male than in the female. Manubrium (manubrium sterni).—The manubrium is of a somewhat quad- rangular form, broad and thick above, narrow below at its junction with the body. Surfaces.—Its anterior surface, convex from side to side, concave from above downward, is smooth, and affords attachment on either side to the sternal origins of the Pectoralis major and Sternocleidomastoideus. Sometimes the ridges limiting the attachments of these muscles are very distinct. Its posterior surface, concave and smooth, affords attachment on either side to the Sterno- hyoideus and Sternothyreoideus. STERNO- HYOID For ls£ - costal canilage Articular surface for clavicle Depression for 1st costal cartilage Manubrium Sternal angle , Demifacets for 2nd costal cartilage - Facet fop 3rd costal cartilage Body Facet for Ath costal cartilage Facet for 5th costal cartilage ■Facet for 6th costal cartilage Facet for 7th costal cartilage Xiphoid process Xiphoid process— Fig. 116.—Posterior surface of sternum. Fio. 117.—Lateral border of sternum. Borders.—The superior border is the thickest and presents at its center the jugular or presternal notch; on either side of the notch is an oval articular surface, directed upward, backward, and lateralward, for articulation with the sternal end of the clavicle. The inferior border, oval and rough, is covered in a fresh state with a thin layer of cartilage, for articulation with the body. The lateral borders are each marked above by a depression for the first costal cartilage, and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for the reception of the costal cartilage of the second rib. Between the depression for the first costal cartilage and the demi-facet for the second is a narrow, curved edge, which slopes from above downward and medialward. Body (corpus sterni; gladiolus).—The body, considerably longer, narrower, and thinner than the manubrium, attains its greatest breadth close to the lower end. Surfaces.—Its anterior surface is nearly flat, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, THE STERNUM 121 fourth, and fifth articular depressions.1 It affords attachment on either side to the sternal origin of the Pectoralis major. At the junction of the third and fourth pieces of the body is occasionally seen an orifice, the sternal foramen, of varying size and form. The posterior surface, slightly concave, is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the Transversus thoracis takes origin. Borders.—The superior border is oval and articulates with the manubrium, the junction of the two forming the sternal angle (angulus Ludovici2). The inferior border is narrow, and articulates with the xiphoid process. Each lateral border (Fig. 117), at its superior angle, has a small facet, which with a similar facet on the manubrium, forms a cavity for the cartilage of the second rib; below,this are four angular depressions which receive the cartilages of the third, fourth, fifth, and sixth ribs, while the inferior angle has a small facet, which, with a cor- responding one on the xiphoid process, forms a notch for the cartilage of the seventh rib. These articular depressions are separated by a series of curved interarticular intervals, which diminish in length from above downward, and correspond to the intercostal spaces. Most of the cartilages belonging to the true ribs, as will be seen from the foregoing description, articulate with the sternum at the lines of junction of its primitive component segments. This is well seen in many of the lower animals, where the parts of the bone remain ununited longer than in man. Xiphoid Process (;processus xiphoideus; ensiform or xiphoid appendix).—The xiphoid process is the smallest of the three pieces: it is thin and elongated, cartilaginous in structure in youth, but more or less ossified at its upper part in the adult. Surfaces.—Its anterior surface affords attachment on either side to the anterior costoxiphoid ligament and a small part of the llectus abdominis; its posterior sur- face, to the posterior costoxiphoid ligament and to some of the fibers of the dia- phragm and Transversus thoracis, its lateral borders, to the aponeuroses of the abdominal muscles. Above, it articulates with the lower end of the body, and on the front of each superior angle presents a facet for part of the cartilage of the seventh rib; below, by its pointed extremity, it gives attachment to the linea alba. The xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one or other side. Structure.—The sternum is composed of highly vascular cancellous tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles. Ossification.—The sternum originally consists of two cartilaginous bars, situated one on either side of the median plane and connected with the cartilages of the upper nine ribs of its own side. These two bars fuse with each other along the middle line to form the cartilaginous sternum which is ossified from six centers: one for the manubrium, four for the body, and one for the xiphoid process (Fig. 118). The ossific centers appear in the intervals between the articular depressions for the costal cartilages, in the following order: in the manubrium and first piece of the body, during the sixth month; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between the fifth and eighteenth years. The centers make their appearance at the upper parts of the seg- ments, and proceed gradually downward.3 To these may be added the occasional existence of two small episternal centers, which make their appearance one on either side of the jugular notch; they are probably vestiges of the episternal bone of the monotremata and lizards. Occasionally some of the segments are formed from more than one center, the number and position of which vary (Fig. 120). Thus, the first piece may have two, three, or even six centers. When two are 1 Pateraon (The Human Sternum, 1904), who examined 524 specimens, points out that these ridges are altogether absent in 26.7 per cent.; that in 69 per cent, a ridge exists opposite the third costal attachment; in 39 per cent, opposite the fourth; and in 4 per cent, only, opposite the fifth. 2 Named after the French surgeon Antoine Louis, 1723-1792. The Latin name angulus Ludovici is not infrequently mistranslated into English as “ the angle of Ludwig. ” 3 Out of 141 sterna between the time of birth and the age of sixteen years, Paterson (op. cit.) found the fourth or lowest center for the body present only in thirty-eight cases—i. e., 26.9 per cent. 122 OSTEOLOGY 1 for manubrium 6th month Time of appearance ' e 3 4 5 4 for body 7th month 1st year after birth 1 for xiphoid process 5th to 18th year Fig. 118.—Ossification of the sternum. Rarely unite, except in old age Time of union Between puberty and the 25th year Soon after puberty Partly cartilaginous to advanced life. Fig. 119 for first piece, two or more centers In number of centers for third for fourth for fifth for second piece, usually one placed laterally Fig. 120.—Peculiarities. In mode of union Arrest of ossification of lateral pieces, producing : -Sternal fissure, and - Sternal foramen Fig. 121 THE RIBS 123 present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen (Fig. 121), or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as ftssura sterni; these conditions are further explained by the manner in which the cartilaginous sternum is formed. More rarely still the upper end of the sternum may be divided by a fissure. Union of the various centers of the body begins about puberty, and proceeds from below upward (Fig. 119); by the age of twenty-five they are all united. The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however, the bony tissue is generally only superficial, the central portion of the intervening cartilage remaining unossified. Articulations.—The sternum articulates on either side with the clavicle and upper seven costal cartilages. The Ribs (Costae). The ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number on either side; but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with the vertebral column, and in front, through the intervention of the costal cartilages, with the sternum (Fig. 115); they are called true or vertebro-sternal ribs.1 The remaining five are false ribs; of these, the first three have their cartilages attached to the cartilage of the rib above (vertebro-chondral): the last two are free at their anterior extremities and are termed floating or vertebral ribs. The ribs vary in their direction, the upper ones being less oblique than the lower; the obliquity reaches its maximum at the ninth rib, and gradually decreases from that rib to the twelfth. The ribs are situated one below the other in such a manner that spaces called intercostal spaces are left between them. The length of each space corresponds to that of the adjacent ribs and their cartilages; the breadth is greater in front than behind, and between the upper than the lower ribs. The ribs increase in length from the first to the seventh, below which they diminish to the twelfth. In breadth they decrease from above downward; in the upper ten the greatest breadth is at the sternal extremity. Common Characteristics of the Ribs (Figs. 122, 123).—A rib from the middle of the series should be taken in order to study the common characteristics of these bones. Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, and an intervening portion—the body or shaft. Posterior Extremity.—The posterior or vertebral extremity presents for examination a head, neck, and tubercle. The head is marked by a kidney-shaped articular surface, divided by a hori- zontal crest into two facets for articulation with the depression formed on the bodies of two adjacent thoracic vertebrae; the upper facet is the smaller; to the crest is attached the interarticular ligament. The neck is the flattened portion which extends lateralward from the head; it is about 2.5 cm. long, and is placed in front of the transverse process of the lower of the two vertebrae with which the head articulates. Its anterior surface is flat and smooth, its posterior rough for the attachment of the ligament of the neck, and perforated by numerous foramina. Of its two borders the superior presents a rough crest (crista colli costce) for the attachment of the anterior costotransverse ligament; its inferior border is rounded. On the posterior surface at the junction of the neck and body, and nearer the lower than the upper border, is an eminence 1 Sometimes the eighth rib cartilage articulates with the sternum; this condition occurs more frequently on the right than on the left side. 124 OSTEOLOGY the tubercle; it consists of an articular and a non-articular portion. The articular portion, the lower and more medial of the two, presents a small, oval surface for Non-articular part of tubercle Angle Articular part of tubercle articulation with the end of the transverse pro- cess of the lower of the two vertebrae to which the head is connected. The non-articular por- tion is a rough elevation, and affords attach- ment to the ligament of the tubercle. The tubercle is much more prominent in the upper than in the lower ribs. Body.—The body or shaft is thin and flat, with two surfaces, an external and an internal; and two borders, a superior and an inferior. The external surface is convex, smooth, and marked, a little in front of the tubercle, by a prominent line, directed downward and lateral- ward; this gives attachment to a tendon of the Uiocostalis, and is called the angle. At this point the rib is bent in two directions, and at the same time twisted on its long axis. If the rib be laid upon its lower border, the portion of the body in front of the angle rests upon this border, while the portion behind the angle is bent medialward and at the same time tilted upward; as the result of the twist- ing, the external surface, behind the angle, looks downward, and in front of the angle, slightly upward. The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The por- tion between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the Longissimus dorsi. The internal surface is concave, smooth, directed a little upward behind the angle, a little down- ward in front of it, and is marked by a ridge •which commences at the lower extremity of the head; this ridge is strongly marked as far as the angle, and gradually becomes lost at the junction of the anterior and middle thirds of the bone. Between it and the inferior border is a groove, the costal groove, for the intercostal vessels and nerve. At the back part of the bone, this groove belongs to the ■Costal groove Body Fig. 122.—A central rib of the left side. Inferior aspect. THE RIBS 125 inferior border, but just in front of the angle, where it is deepest and broadest, it is on the internal surface. The superior edge of the groove is rounded and serves for the attachment of an Intercostalis internus; the inferior edge corresponds to the lower margin of the rib, and gives attachment to an Intercostalis externus. Within the groove are seen the orifices of numerous small foramina for nutrient vessels which traverse the shaft obliquely from before backward. The superior border, thick and rounded, is marked by an external and an internal lip, more distinct behind than in front, which serve for the attachment of Intercostales externus and internus. The inferior border is thin, and has attached to it an Inter- costalis externus. Anterior Extremity.—The anterior or sternal extremity is flattened, and presents a porous, oval, concave depression, into which the costal cartilage is received. Peculiar Ribs.—The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require special consideration. Demifacet for vertebra - Jnterarlicular crest Demifacet for vertebra Articular part of tubercle Non-articular part of tubercle Costal groove Fig. 123.—A central rib of the left side, viewed from behind. First Rib.—The first rib (Fig. 124) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward. The head is small, rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, is placed on the outer border. There is no angle, but at the tubercle the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the Scalenus anterior; the anterior groove transmits the subclavian vein, the posterior the subclavian artery and the lowest trunk of the brachial plexus.1 Behind the posterior groove is a rough area for the attachment of the Scalenus medius. The under surface is smooth, and destitute of a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the Serratus anterior; the inner border is concave, thin, and sharp, and marked about its center by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs. Second Rib.—The second rib (Fig. 125) is much longer than the first, but has a very similar curvature. The non-articular portion of the tubercle is occasionally 1 Anat. Anzeiger, 1910, Band xxxvi. 126 OSTEOLOGY only feebly marked. The angle is slight, and situated close to the tubercle. The body is not twisted, so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of the lower part of the Fig. 124 Fig. 125 Angle- First digitation of Serratus anterior Fig. 126 Single articular fcxet Fig. 127 Single articular facet - Fig. 128 Single articular facet Fios. 124 to 128.—Peculiar ribs. first and the whole of the second digitation of the Serratus anterior; behind and above this is attached the Scalenus posterior. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove. Tenth Rib.—The tenth rib (Fig. 126) has only a single articular facet on its head. Eleventh and Twelfth Ribs.—The eleventh and twelfth ribs (Figs. 127 and 128) have each a single articular facet on the head, which is of rather large size; they THE COSTAL CARTILAGES 127 have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove. The twelfth has neither; it is much shorter than the eleventh, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first. Structure.—The ribs consist of highly vascular cancellous tissue, enclosed in a thin layer of compact bone. Ossification.—Each rib, with the exception of the last two, is ossified from four centers; a primary center for the body, and three epiphysial centers, one for the head and one each for the articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only two centers, those for the tubercles being wanting. Ossification begins near the angle toward the end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses for the head and tubercle make their appearance between the sixteenth and twentieth years, and are united to the body about the twenty-fifth year. Fawcett1 states that “in all probability there is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib. The Costal Cartilages (Cartilagines Costales). The costal cartilages (Fig. 115) are bars of hyaline cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax. The first seven pairs are connected with the sternum; the next three are each articulated with the lower border of the cartilage of the pre- ceding rib; the last two have pointed extremities, which end in the wall of the abdomen. Like the ribs, the costal cartilages vary in their length, breadth, and direction. They increase in length from the first to the seventh, then gradually decrease to the twelfth. Their breadth, as well as that of the intervals between them, diminishes from the first to the last. They are broad at their attachments to the ribs, and taper toward their sternal extremities, excepting the first two, which are of the same breadth throughout, and the sixth, seventh, and eighth, which are enlarged where their margins are in contact. They also vary in direc- tion: the first descends a little, the second is horizontal, the third ascends slightly, while the others are angular, following the course of the ribs for a short distance, and then ascending to the sternum or preceding cartilage. Each costal cartilage presents two surfaces, two borders, and two extremities. Surfaces.—The anterior surface is convex, and looks forward and upward: that of the first gives attachment to the costoclavicular ligament and the Subclavius muscle; those of the first six or seven at their sternal ends, to the Pectoralis major. The others are covered by, and give partial attachment to, some of the flat muscles of the abdomen. The posterior surface is concave, and directed backward and downward; that of the first gives attachment to the Sternothyroideus, those of the third to the sixth inclusive to the Transversus thoracis, and the six or seven inferior ones to the Transversus abdominis and the diaphragm. Borders.—Of the two borders the superior is concave, the inferior convex; they afford attachment to the Intercostales interni: the upper border of the sixth gives attachment also to the Pectoralis major. The inferior borders of the sixth, seventh, eighth, and ninth cartilages present heel-like projections at the points of greatest convexity. These projections carry smooth oblong facets which articulate respec- tively with facets on slight projections from the upper borders of the seventh, eighth, ninth, and tenth cartilages. Extremities.—The lateral end of each cartilage is continuous with the osseous tissue of the rib to which it belongs. The medial end of the first is continuous with the sternum; the medial ends of the six succeeding ones are rounded and are received into shallow concavities on the lateral margins of the sternum. The medial ends of the eighth, ninth, and tenth costal cartilages are pointed, and are connected each with the cartilage immediately above. Those of the eleventh and twelfth are pointed and free. In old age the costal cartilages are prone to undergo superficial ossification. 1 Journal of Anatomy and Physiology, vol. xlv. 128 OSTEOLOGY Cervical ribs derived from the seventh cervical vertebra (page 83) are of not infrequent occur- rence, and are important clinically because they may give rise to obscure nervous or vascular symptoms. The cervical rib may be a mere epiphysis articulating only with the transverse process of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or without a body. It extends lateralward, or forward and lateralward, into the posterior triangle of the neck, where it may terminate in a free end or may join the first thoracic rib, the first costal cartilage, or the sternum.1 It varies much in shape, size, direction, and mobility. If it reach far enough forward, part of the brachial plexus and the subclavian artery and vein cross over it, and are apt to suffer compression in so doing. Pressure on the artery may obstruct the circula- tion so much that arterial thrombosis results, causing gangrene of the finger tips. Pressure on the nerves is commoner, and affects the eighth cervical and first thoracic nerves, causing paralysis of the muscles they supply, and neuralgic pains and paresthesia in the area of skin to which they are distributed: no oculopupillary changes are to be found. The thorax is frequently found to be altered in shape in certain diseases. In rickets, the ends of the ribs, where they join the costal cartilages, become enlarged, giving rise to the so-called “rickety rosary,” which in mild cases is only found on the internal surface of the thorax. Lateral to these enlargements the softened ribs sink in, so as to present a groove passing downward and lateralward on either side of the sternum. This bone is forced forward by the bending of the ribs, and the antero-posterior diameter of the chest is increased. The ribs affected are the second to the eighth, the lower ones being prevented from falling in by the pres- ence of the liver, stomach, and spleen; and when the abdomen is distended, as it often is in rickets, the lower ribs may be pushed outward, causing a transverse groove (Harrison’s sulcus) just above the costal arch. This deformity or forward projection of the sternum, often asymmetrical, is known as 'pigeon breast, and may be taken as evidence of active or old rickets except in cases of primary spinal curvature. In many instances it is associated in children with obstruction in the upper air passages, due to enlarged tonsils or adenoid growths. In some rickety children or adults, and also in others who give no history or further evidence of having had rickets, an opposite condition obtains. The lower part of the sternum and often the xiphoid process as well are deeply depressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. This is known as funnel breast (German, Trichterbrust); it never appears to produce the least disturbance of any of the vital functions. The phthisical chest is often long and narrow, and with great obliquity of the ribs and projection of the scapulae. In pulmonary emphysema the chest is enlarged in all its diameters, and presents on section an almost circular outline. It has received the name of the barrel-shaped chest. In severe cases of lateral curvature of the vertebral column the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebrae which takes place in this disease, the ribs opposite the convexity of the dorsal curve become extremely convex behind, being thrown out and bulging, and at the same time flattened in front, so that the two ends of the same rib are almost parallel. Coincidently with this the ribs on the opposite side, on the concavity of the curve, are sunk and depressed behind, and bulging and convex in front. THE SKULL. The skull is supported on the summit of the vertebral column, and is of an oval shape, wider behind than in front. It is composed of a series of flattened or irregular bones which, with one exception (the mandible), are immovably jointed together. It is divisible into two parts: (1) the cranium, which lodges and protects the brain, consists of eight bones, and (2) the skeleton of the face, of fourteen, as follows: Occipital. Two Parietals. Frontal. Two Temporals. Sphenoidal. Ethmoidal. Cranium, 8 bones - Skull, 22 bones Two Nasals. Two Maxillae. Two Lacrimals. Two Zygomatics. Two Palatines. Two Inferior Nasal Conchae. Vomer. Mandible. Face, 14 bones 1 W. Thorburn, The Medical Chronicle, Manchester, 1907, 4th series, xiv, No. 3 THE OCCIPITAL BONE 129 In the Basle nomenclature, certain bones developed in association with the nasal capsule, viz., the inferior nasal conchse, the lacrimals, the nasals, and the vomer, are grouped as cranial and not as facial bones. The hyoid bone, situated at the root of the tongue and attached to the base of the skull by ligaments, is described in this section. THE CRANIAL BONES (OSSA CRANH). The Occipital Bone (Os Occipitale). The occipital bone (Figs. 129, 130), situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal. Highest nuchal line Hypoglossal canal Constrictor pharyngis superior Fig. 129.—Occipital bone. Outer surface. The curved, expanded plate behind the foramen magnum is named the squama; the thick, somewhat quadrilateral piece in front of the foramen is called the basilar part, whilst on either side of the foramen is the lateral portion. The Squama {squama occipitalis).—The squama, situated above and behind the foramen magnum, is curved from above downward and from side to side. Surfaces.—The external surface is convex and presents midway between the summit of the bone and the foramen magnum a prominence, the external occipital protuberance. Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest nuchal line, and to it the galea aponeurotica is attached. The lower 130 OSTEOLOGY is termed the superior nuchal line. That part of the squama which lies above the highest nuchal lines is named the planum occipitale, and is covered by the Occipitalis muscle; that below, termed the planum nuchale, is rough and irregular for the attachment of several muscles. From the external occipital protuberance a ridge or crest, the median nuchal line, often faintly marked, descends to the fora- men magnum, and affords attachment to the ligamentum nuchse; running from the middle of this line across either half of the nuchal plane is the inferior nuchal line? Several muscles are attached to the outer surface of the squama, thus: the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion to the Sternocleidomastoideus and Splenius capitis: into the surface between Sujierio r A ngle Fig. 130.—Oceipita Ibone. Inner surface. the superior and inferior nuchal lines the Semispinalis capitis and the Obliquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the Recti capitis posteriores major and minor. The posterior atlantooccipital membrane is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen. The internal surface is deeply concave and divided into four fossae by a cruciate eminence. The upper two fossae are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum. At the point of intersection of the four divisions of the cruciate eminence is the internal occipital protuberance. From this protuberance the upper division of the cruciate eminence runs to the superior angle of the bone, and on THE OCCIPITAL BONE 131 one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus; to the margins of this sulcus the falx cerebri is attached. The lower division of the cruciate eminence is prominent, and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli; in the attached margin of this falx is the occipital sinus, which is sometimes duplicated. In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuber- ance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli. The groove on the right side is usually larger than that on the left, and is continuous with that for the superior sagittal sinus. Exceptions to this condition are, however, not infrequent; the left may be larger than the right or the two may be almost equal in size. The angle of union of the superior sagittal and trans- verse sinuses is named the confluence of the sinuses (torcular Herophili1), and its position is indicated by a depression situated on one or other side of the protuberance. Lateral Parts (pars lateralis).—The lateral parts are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas. The condyles are oval or reniform in shape, and their anterior extremities, directed forward and medialward, are closer together than their posterior, and encroach on the basilar portion of the bone; the posterior extremities extend back to the level of the middle of the foramen magnum. The articular surfaces of the condyles are convex from before backward and from side to side, and look downward and lateralward. To their margins are attached the capsules of the atlantooccipital articulations, and on the medial side of each is a rough impression or tubercle for the alar ligament. At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal (anterior condyloid foramen). This begins on the cranial surface of the bone immediately above the foramen magnum, and is directed lateralward and forward above the condyle. It may be partially or completely divided into two by a spicule of bone; it gives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal branch of the ascending pharyngeal artery. Behind either condyle is a depression, the condyloid fossa, which receives the posterior margin of the superior facet of the atlas when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal, through which an emissary vein passes from the transverse sinus. Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular fora- men. The jugular notch may be divided into two by a bony spicule, the intra- jugular process, which projects lateralward above the hypoglossal canal. The under surface of the jugular process is rough, and gives attachment to the Rectus capitis lateralis muscle and the lateral atlantooccipital ligament; from this surface an eminence, the paramastoid process, sometimes projects downward, and may be of sufficient length to reach, and articulate with, the transverse process of the atlas. Laterally the jugular process presents a rough quadrilateral or tri- angular area which is joined to the jugular surface of the temporal bone by a plate of cartilage; after the age of twenty-five this plate tends to ossify. The upper surface of the lateral part presents an oval eminence, the jugular tubercle, which overlies the hypoglossal canal and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus, and accessory nerves. On the 1 The columns of blood coming in different directions were supposed to be pressed together at this point (torcular. a wine press). 132 OSTEOLOGY upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with the jugular notch. This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of the condyloid canal. Basilar Part (pars basilaris).—The basilar part extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined to the body of the sphenoid by a plate of cartilage. By the twenty-fifth year this cartil- aginous plate is ossified, and the occipital and sphenoid form a continuous bone. Surfaces.—On its lower surface, about 1 cm. in front of the foramen magnum, is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. On either side of the middle line the Longus capitis and Rectus capitis anterior are inserted, and immediately in front of the foramen magnum the anterior atlantooccipital membrane is attached. The upper surface presents a broad, shallow groove which inclines upward and forward from the foramen magnum; it supports the medulla oblongata, and near the margin of the foramen magnum gives attachment to the membrana tectoria. On the lateral margins of this surface are faint grooves for the inferior petrosal sinuses. Foramen Magnum.—The foramen magnum is a large oval aperture with its long diameter antero-posterior; it is wider behind than in front where it is encroached upon by the condyles. It transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the membrana tectoria and alar ligaments. Angles.—The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The inferior angle is fused with the body of the sphenoid. The lateral angles are situated at the extremities of the grooves for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal and the mastoid part of the temporal. Borders. -— The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form by this union the lambdoidal suture. The inferior borders extend from the lateral angles to the inferior angle; the upper half of each articulates with the mastoid portion of the corresponding temporal, the lower half with the petrous part of the same bone. These two por- tions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen. Structure.—The occipital, like the other cranial bones, consists of two compact lamella?, called the outer and inner tables, between which is the cancellous tissue or diploe; the bone is especially thick at the ridges, protuberances, condyles, and anterior part of the basilar part; in the inferior fossae it is thin, semitransparent, and destitute of diploe. Ossification (Fig. 131).—The planum occipitale of the squama is developed in membrane, and may remain separate throughout life when it constitutes the interparietal bone; the rest of Planum (.capita e Planum nuthae Kerckring's center Lateral Part Basilar part Fig. 131.—Occipital bone at birth. THE PARIETAL BONE 133 the bone is developed in cartilage. The number of nuclei for the planum occipitale is usually given as four, two appearing near the middle line about the second month, and two some little distance from the middle line about the third month of fetal life. The planum nuchale of the squama is ossified from two centers, which appear about the seventh week of fetal life and soon unite to form a single piece. Union of the upper and lower portions of the squama takes place in the third month of fetal life. An occasional center (Kerckring) appears in the posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squama before birth. Each of the lateral parts begins to ossify from a single center during the eighth week of fetal life. The basilar portion is ossified from two centers, one in front of the other; these appear about the sixth week of fetal life and rapidly coalesce. Mall1 states that the planum occipitale is ossified from two centers and the basilar portion from one. About the fourth year the squama and the two lateral portions unite, and about the sixth year the bone consists of a single piece. Between the eighteenth and twenty- fifth years the occipital and sphenoid become united, forming a single bone. Articulations.—The occipital articulates with six bones: the two parietals, the two temporals, the sphenoid, and the atlas. The Parietal Bone (Os Parietale). The parietal bones form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles. Articulates with opposite parietal bone Articulates with frontal hone Articulates with occipital hone temporal squama With sphenoid With mastoid portion of temporal bone Fig. 132.—Left parietal bone. Outer surface. Surfaces.—The external surface (Fig. 132) is convex, smooth, and marked near the center by an eminence, the parietal eminence {tuber parietale), which indicates the point where ossification commenced. Crossing the middle of the bone in an 1 American Journal of Anatomy, 1906, vol. v. 134 OSTEOLOGY arched direction are two curved lines, the superior and inferior temporal lines; the former gives attachment to the temporal fascia, and the latter indicates the upper limit of the muscular origin of the Temporalis. Above these lines the bone is covered by the galea aponeurotica; below them it forms part of the temporal fossa, and affords attachment to the Temporalis muscle. At the back part and close to the upper or'sagittal border is the parietal foramen, which transmits a vein to the superior sagittal sinus, and sometimes a small branch of the occipital artery; it is not constantly present, and its size varies considerably. The internal surface (Fig. 133) is concave; it presents depressions corresponding to the cerebral convolutions, and numerous furrows for the ramifications of the middle meningeal vessel 51 the latter run upward and backward from the sphenoidal angle, and from the central and posterior part of the squamous border. Along the upper margin is a shallow groove, which, together with that on the opposite Occipital angle Fronial angle Mastoid angle Sphenoidal angle Fig. 133.—Left parietal bone. Inner surface. parietal, forms a channel, the sagittal sulcus, for the superior sagittal sinus; the edges of the sulcus afford attachment to the falx cerebri. Near the groove are several depressions, best marked in the skulls of old persons, for the arachnoid granulations (Pacchionian bodies). In the groove is the internal opening of the parietal foramen when that aperture exists. Borders.—The sagittal border, the longest and thickest, is dentated and articu- lates with its fellow of the opposite side, forming the sagittal suture. The squamous border is divided into three parts: of these, the anterior is thin and pointed, bevelled at the expense of the outer surface, and overlapped by the tip of the great wing of the sphenoid; the middle portion is arched, bevelled at the expense of the outer surface, and overlapped by the squama of the temporal; the posterior part is thick and serrated for articulation with the mastoid portion of the temporal. The 1 Journal of Anatomy and Physiology, 1912, vol. xlvi. THE FRONTAL BONE 135 frontal border is deeply serrated, and bevelled at the expense of the outer surface above and of the inner below; it articulates with the frontal bone, forming one- half of the coronal suture. The occipital border, deeply denticulated, articulates with the occipital, forming one-half of the lambdoidal suture. Angles.—The frontal angle is practically a right angle, and corresponds with the point of meeting of the sagittal and coronal sutures; this point is named the bregma; in the fetal skull and for about a year and a half after birth this region is membranous, and is called the anterior fontanelle. The sphenoidal angle, thin and acute, is received into the interval between the frontal bone and the great wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes a canal, for the anterior divisions of the middle meningeal artery. The occipital angle is rounded and corresponds with the point of meeting of the sagittal and lambdoidal sutures—a point which is termed the lambda; in the fetus this part of the skull is membranous, and is called the posterior fontanelle. The mastoid angle is truncated; it articulates with the occipital bone and with the mastoid portion of the temporal, and presents on its inner surface a broad, shallow groove which lodges part of the transverse sinus. The point of meeting of this angle with the occipital and the mastoid part of the temporal is named the asterion. Ossification.—The parietal bone is ossified in membrane from a single center, which appears at the parietal eminence about the eighth week of fetal life. Ossification gradually extends in a radial manner from the center toward the margins of the bone; the angles are consequently the parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone is divided into two parts, upper and lower, by an antero-posterior suture. Articulations.—The parietal articulates with five bones: the opposite parietal, the occipital, frontal, temporal, and sphenoid. The Frontal Bone (Os Frontale). The frontal bone resembles a cockle-shell in form, and consists of two portions —a vertical portion, the squama, corresponding with the region of the forehead; and an orbital or horizontal portion, .which enters into the formation of the roofs of the orbital and nasal cavities. Squama (squama frontalis).—Surfaces.—The external surface (Fig. 134) of this portion is convex and usually exhibits, in the lower part of the middle line, the remains of the frontal or metopic suture; in infancy this suture divides the bone into two, a condition which may persist throughout life. On either side of this suture, about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal emi- nence (tuber frontale). These eminences vary in size in different individuals, are occasionally unsymmetrical, and are especially prominent in young skulls; the sur- face of the bone above them is smooth, and covered by the galea aponeurotica. Below the frontal eminences, and separated from them by a shallow groove, are two arched elevations, the superciliary arches; these are prominent medially, and are joined to one another by a smooth elevation named the glabella. They are larger in the male than in the female, and their degree of prominence depends to some extent on the size of the frontal air sinuses;1 prominent ridges are, how- ever, occasionally associated with small air sinuses. Beneath each superciliary arch is a curved and prominent margin, the supraorbital margin, which forms the upper boundary of the base of the orbit, and separates the squama from the orbital portion of the bone. The lateral part of this margin is sharp and prominent, affording to the eye, in that situation, considerable protection from injury; the medial part is rounded. At the junction of its medial and intermediate thirds is 1 Some confusion is occasioned to students commencing the Study of anatomy by the name “sinus” having been given to two different kinds of space connected with the skull. It may be as well, therefore, to state here that the “sinuses” in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous channels which convey the blood from the brain, while the “sinuses” external to the cranial cavity (the frontal, sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves; they communicate with the nasal cavities and contain air. 136 OSTEOLOGY a notch, sometimes converted into a foramen, the supraorbital notch or foramen, which transmits the supraorbital vessels and nerve. A small aperture in the upper part of the notch transmits a vein from the diploe to join the supraorbital vein. The supraorbital margin ends laterally in the zygomatic process, which is strong and prominent, and articulates with the zygomatic bone. Running upward and backward from this process is a well-marked line, the temporal line, which divides into the upper and lower temporal lines, continuous, in the articulated skull, with the corresponding lines on the parietal bone. The area below and behind the tem- poral line forms the anterior part of the temporal fossa, and gives origin to the Temporalis muscle. Between the supraorbital margins the squama projects down- ward to a level below that of the zygomatic processes; this portion is known as the nasal part and presents a rough, uneven interval, the nasal notch, which articulates Orbicularis oculi' Nasal part Zygomatic process Frontal || spine Fig. 134.—Frontal bone. Outer surface. on either side of the middle line with the nasal bone, and laterally with the frontal process of the maxilla and with the lacrimal. The term nasion is applied to the middle of the frontonasal suture. From the center of the notch the nasal process projects downward and forward beneath the nasal bones and frontal processes of the maxillae, and supports the bridge of the nose. The nasal process ends below in a sharp spine, and on either side of this is a small grooved surface which enters into the formation of the roof of the corresponding nasal cavity. The spine forms part of the septum of the nose, articulating in front with the crest of the nasal bones and behind with the perpendicular plate of the ethmoid. The internal surface (Fig. 135) of the squama is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. THE FRONTAL BONE 137 The crest ends below in a small notch which is converted into a foramen, the fora- men cecum, by articulation with the ethmoid. This foramen varies in size in different subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. On either side of the middle line the bone presents depressions for the convolutions of the brain, and numerous small furrows for the anterior branches of the middle meningeal vessels. Several small, irregular fossae may also be seen on either side of the sagittal sulcus, for the reception of the arachnoid granulations. Orbital or Horizontal Part (pars orbitalis).—This portion consists of two thin triangular plates, the orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch. _ Supraorbital foramen With maxilla ' Frontal sinus With perpendicular plate of ethmoid With nasal Under surface of nasal process forming part of roof of nose Fig. 135.—Frontal bone. Inner surface. Surfaces.—The inferior surface (Fig. 135) of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depres- sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- ment of the cartilaginous pulley of the Obliquus oculi superior. The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels. The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. Two grooves cross these edges transversely; they are converted into the anterior 138 OSTEOLOGY and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses. These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical. Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty. They vary in size in different persons, and are larger in men than in women.1 They are lined by mucous mem- brane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct. Borders.—The border of the squama is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. Structure.—The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact laminae; the diploic tissue is absent in the regions occupied by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facility with which instruments can penetrate the cranium through this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of only two tables. Ossification (Fig. 136). — The frontal bone is ossified in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin. From each of these centers ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centers, on either side of the middle line; similar centers appear in the nasal part and zygo- matic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi’s researches indicate that de- velopment begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty. Articulations. — The frontal articulates with twelve bones: the sphenoid, the eth- moid, the two parietals, the two nasals, the two maxillae, the two lacrimals, and the two zygomatics. Squama Nasal part Zygomatic process Fig. 130.—Frontal bone at birth. Spine The Temporal Bone (Os Temporale). The temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the styloid process. 1 Aldren Turner (The Accessory Sinuses of the Nose, 1901) gives the following measurements for a sinus of average size: height, 134 inches; breadth, 1 inch; depth from before backward, 1 inch. THE TEMPORAL BONE 139 The Squama (squama temporalis).—The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent. Surfaces.—Its outer surface (Fig. 137) is smooth and convex; it affords attach- ment to the Temporalis muscle, and forms part of the temporal fossa; on its hinder part is a vertical groove for the middle temporal artery. A curved line, the tem- poral line, or supramastoid crest, runs backward and upward across its posterior part; it serves for the attachment of the temporal fascia, and limits the origin of the Temporalis muscle. The boundary between the squama and the mastoid portion of the bone, as indicated by traces of the original suture, lies about 1 cm. below this line. Projecting from the lower part of the squama is a long, arched process, the zygomatic process. This process is at first directed'lateralward, its two surfaces looking upward and downward; it then appears as if twisted inward , Groove for middle temporal artery Parietal notch Suprameatal triangle Occipitalis Articular tubercle Post-glenoid process Mandibular fossa Petrotympanic fissure Vaginal process Styloglossus Tympanic part Occipital groove Stylohyoideus Fia. 137.—Left temporal bone. Outer surface. Styloid process upon itself, and runs forward, its surfaces now looking medial ward and lateral ward. The superior border is long, thin, and sharp, and serves for the attachment of the temporal fascia; the inferior, short, thick, and arched, has attached to it some fibers of the Masseter. The lateral surface is convex and subcutaneous; the medial is concave, and affords attachment to the Masseter. The anterior end is deeply serrated and articulates with the zygomatic bone. The posterior end is connected to the squama by two roots, the anterior and posterior roots. The posterior root, a prolongation of the upper border, is strongly marked; it runs backward above the external acoustic meatus, and is continuous with the temporal line. The anterior root, continuous with the lower border, is short but broad and strong; it is directed medialward and ends in a rounded eminence, the articular tubercle (eminentia articularis). This tubercle forms the front boundary of the mandibular fossa, 140 OSTEOLOGY and in the fresh state is covered with cartilage. In front of the articular tubercle is a small triangular area which assists in forming the infratemporal fossa; this area is separated from the outer surface of the squama by a ridge which is continu- ous behind with the anterior root of the zygomatic process, and in front, in the articulated skull, with the infratemporal crest on the great wing of the sphenoid. Between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process is the area called the suprameatal triangle (Macewren), or mastoid fossa, through which an instrument may be pushed into the tympanic antrum. At the junction of the anterior root with the zygomatic process is a pro- jection for the attachment of the temporomandibular ligament; and behind the anterior root is an oval depression, forming part of the mandibular fossa, for the reception of the condyle of the mandible. The mandibular fossa (glenoid fossa) Parietal notch Eminentia arcuala Mastoid foramen Aquceductus vestibuli Aquceductus cochleae Internal acoustic meatus Fio. 138.—Left temporal bone. Inner surface. is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is divided into two parts by a narrow slit, the petrotympanic fissure (Glaseriart fissure). The anterior part, formed by the squama, is smooth, covered in the fresh state with cartilage, and articulates with the condyle of the mandible. Behind this part of the fossa is a small conical eminence; this is the representative of a prominent tubercle which, in some mammals, descends behind the condyle of the mandible, and prevents its backward displacement. The posterior part of the mandibular fossa, formed by the tympanic part of the bone, is non-articular, and sometimes lodges a portion of the parotid gland. The petrotympanic fissure leads into the middle ear or tympanic cavity; it lodges the anterior process of the malleus, and transmits the tympanic branch of the internal maxillary artery. The chorda THE TEMPORAL BONE 141 tympani nerve passes through a canal (canal of Iluguier), separated from the an- terior edge of the petrotympanic fissure by a thin scale of bone and situated on the lateral side of the auditory tube, in the retiring angle between the squama and the petrous portion of the temporal. The internal surface of the squama (Fig. 138) is concave; it presents depressions corresponding to the convolutions of the temporal lobe, of the brain, and grooves for the branches of the middle meningeal vessels. Borders.—The superior border is thin, and bevelled at the expense of the internal table, so as to overlap the squamous border of the parietal bone, forming with it the squamosal suture. Posteriorly, the superior border forms an angle, the parietal notch, with the mastoid portion of the bone. The antero-inferior border is thick, serrated, and bevelled at the expense of the inner table above and of the outer below, for articulation with the great wing of the sphenoid. Mastoid Portion (pars mastoidea).—The mastoid portion forms the posterior part of the bone. Tympanic antrum Tegmen tympani Prominence of lateral semicircular canal Prominence of facial canal Fenestra vestibuli Bristle in semicanal for Tensor tympani Septum canalis musculctvbarii Bristle in hiatus of facial canal Carotid canal Promontory Bony part of auditory tube Bristle in pyramid Fenestra cochleae Bristle in stylomastoid foramen Sulcus tympanicus Mastoid cells Fig. 139.—Coronal section of right temporal bone. Surfaces.—Its outer surface (Fig. 137) is rough, and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one of these, of large size, situated near the posterior border, is termed the mastoid foramen; it transmits a vein to the transverse sinus and a small branch of the occipi- tal artery to the dura mater. The position and size of this foramen are very variable; it is not always present; sometimes it is situated in the occipital bone, or in the suture between the temporal and the occipital. The mastoid portion is continued below into a conical projection, the mastoid process, the size and form of which vary somewhat; it is larger in the male than in the female. This process serves for the attachment of the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis. On the medial side of the process is a deep groove, the mastoid notch (digastric fossa), for the attachment of the Digastricus; medial to this is a shallow furrow, the occipital groove, which lodges the occipital artery. 142 OSTEOLOGY The inner surface of the mastoid portion presents a deep, curved groove, the sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen. The groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone, and even this may be partly deficient. Borders.—The superior border of the mastoid portion is broad and serrated, for articulation with the mastoid angle of the parietal. The posterior border, also serrated, articulates with the inferior border of the occipital between the lateral angle and jugular process. Anteriorly the mastoid portion is fused with the descending process of the squama above; below it enters into the formation of the external acoustic meatus and the tympanic cavity. A section of the mastoid process (Fig. 139) shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit the greatest possible variety as to their size and number. At the upper and front part of the process they are large and irregular and contain air, but toward the lower part they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally they are entirely absent, and the mastoid is then solid throughout. In addition to these a large irregular cavity is situated at the upper and front part of the bone. It is called the tympanic antrum, and must be distin- guished from the mastoid cells, though it communicates with them. Like the mas- toid cells it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity, with which it communicates. The tympanic antrum is bounded above by a thin plate of bone, the tegmen tympani, which separates it from the middle fossa of the base of the skull; below by the mastoid process; later- ally by the squama just below the temporal line, and medially by the lateral semi- circular canal of the internal ear which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic or epitympanic recess. The tympanic antrum is a cavity of some considerable size at the time of birth; the mastoid air cells may be regarded as diverticula from the antrum, and begin to appear at or before birth; by the fifth year they are well-marked, but their development is not completed until toward puberty. Petrous Portion (pars petrosa [pyramis]).—The petrous portion or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital. Directed medialward, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. Base.—The base is fused with the internal surfaces of the squama and mastoid portion. Apex.—The apex, rough and uneven, is received into the angular interval between the posterior border of the great wing of the sphenoid and the basilar part of the occipital; it presents the anterior or internal orifice of the carotid canal, and forms the postero-lateral boundary of the foramen lacerum. Surfaces.—The anterior surface forms the posterior part of the middle fossa of the base of the skull, and is continuous with the inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are distinct even at a late period of life. It is marked by depressions for the convolu- tions of the brain, and presents six points for examination: (1) near the center, an eminence (eminentia arcuata) which indicates the situation of the superior semi- circular canal; (2) in front of and a little lateral to this eminence, a depression indi- cating the position of the tympanic cavity: here the layer of bone which separates the tympanic from the cranial cavity is extremely thin, and is known as the tegmen tympani; (3) a shallow groove, sometimes double, leading lateralward and backward to an oblique opening, the hiatus of the facial canal, for the passage of the greater superficial petrosal nerve and the petrosal branch of the middle men- THE TEMPORAL BONE 143 ingeal artery; (4) lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, the termination of the carotid canal, the wall of which in this situation is deficient in front; (6) above this canal the shallow trigeminal impression for the reception of the semilunar ganglion. The posterior surface (Fig. 138) forms the front part of the posterior fossa of the base of the skull, and is continuous with the inner surface of the mastoid portion. Near the center is a large orifice, the internal acoustic meatus, the size of which varies considerably; its margins are smooth and rounded, and it leads into a short canal, about 1 cm. in length, which runs lateralward. It transmits the facial and acoustic nerves and the internal auditory branch of the basilar artery. The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the crista falciformis, into two unequal portions (Fig. 140). Each portion is further subdivided by a vertical ridge into an anterior and a posterior part. In the portion beneath the crista falciformis are three sets of foramina; one group, just below the posterior part of the crest, situated in the area cribrosa media, consists of several small openings for the nerves to the saccule; below and behind this area is the foramen singulare, or opening for the nerve to the posterior semicircular duct; in front of and below the first is the tractus spiralis foraminosus, consisting of a number of small spirally arranged openings, which encircle the canalis centralis cochlese; these openings together with this central canal transmit the nerves to the cochlea. The portion above the crista falciformis presents behind, the area cribrosa superior, pierced by a series of small openings, for the passage of the nerves to the utricle and the superior and lateral semicircular ducts, and, in front, the area facials, with one large opening, the com- mencement of the canal for the facial nerve (aquseductus Fallopii). Behind the internal acoustic meatus is a small slit almost hidden by a thin plate of bone, leading to a canal, the aquseductus vestibuli, which transmits the ductus endolymphaticus together with a small artery and vein. Above and between these two openings is -an irregular depression which lodges a process of the dura mater and transmits a small vein; in the infant this depression is repre- sented by a large fossa, the subarcuate fossa, which extends backward as a blind tunnel under the superior semicircular canal. The inferior surface (Fig. 141) is rough and irregular, and forms part of the exterior of the base of the skull. It presents eleven points for examination: (1) near the apex is a rough surface, quadrilateral in form, which serves partly for the attachment of the Levator veli palatini and the cartilaginous portion of the audi- tory tube, and partly for connection with the basilar part of the occipital bone through the intervention of some dense fibrous tissue; (2) behind this is the large circular aperture of the carotid canal, which ascends at first vertically, and then, making a bend, runs horizontally forward and medial ward; it transmits into the cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial to the opening for the carotid canal and close to its posterior border, in front of the jugular fossa, is a triangular depression; at the apex of this is a small opening, the Fig. 140.—Diagrammatic view of the fundus of the right internal acoustic meatus. (Testut.) 1. Crista falciformis. 2. Area facialis, with (2') internal opening of the facial canal. 3. Ridge separating the area facialis from the area crib- rosa superior. 4. Area cribrosa superior, with (4') openings for nerve filaments. 5. Anterior inferior cribriform area, with (5') the tractus spiralis foraminosus, and (5") the canalis cen- tralis of the cochlea. 6. Ridge separating the tractus spiralis foraminosus from the area crib- rosa media. 7. Area cribrosa media, with (7') orifices for nerves to saccule. 8. Foramen singulare. 144 OSTEOLOGY aquaeductus cochleae, which lodges a tubular prolongation of the dura mater establish- ing a communication between the perilymphatic space and the subarachnoid space, and transmits a vein from the cochlea to join the internal jugular; (4) behind these openings is a deep depression, the jugular fossa, of variable depth and size in different skulls; it lodges the bulb of the internal jugular vein; (5) in the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus for the passage of the tympanic branch of the glossopharyngeal nerve; (6) in the lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the auricular branch of the vagus nerve; (7) behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the fresh state, and articulating with the jugular process of the occipital bone; (8) extending backward from the carotid canal is the vaginal process, a sheath-like plate of bone, which divides Semicanals for auditory tube arid Tensor tympani Lev. veli palatini - Rough quadrilateral surface Inferior tympanic canaliculus Opening of carotid canal Aquceduetus cochleae' Siyloplui ry ngeus Mastoid canaliculus ' Jugular fossa - Vaginal process' Styloid process' Stylomastoid foramen' Tympanomastoid fissure Jugular surface' Fig. 141.—Left temporal bone. Inferior surface. behind into two laminae; the lateral lamina is continuous with the tympanic part of the bone, the medial with the lateral margin of the jugular surface; (9) between these laminae is the styloid process, a sharp spine, about 2.5 cm. in length; (10) between the styloid and mastoid processes is the stylomastoid foramen; it is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery; (11) situated between the tympanic portion and the mastoid process is the tympanomastoid fissure, for the exit of the auricular branch of the vagus nerve. Angles.—The superior angle, the longest, is grooved for the superior petrosal sinus, and gives attachment to the tentorium cerebelli; at its medial extremity is a notch, in which the trigeminal nerve lies. The posterior angle is intermediate in length between the superior and the anterior. Its medial half is marked by a sulcus, which forms, with a corresponding sulcus on the occipital bone, the channel for the inferior petrosal sinus. Its lateral half presents an excavation —the jugular fossa—which, with the jugular notch on the occipital, forms the THE TEMPORAL BONE 145 jugular foramen; an eminence occasionally projects from the center of the fossa, and divides the foramen into two. The anterior angle is divided into two parts —a lateral joined to the squama by a suture {petrosquamous), the remains of which are more or less distinct; a medial, free, which articulates with the spinous process of the sphenoid. At the angle of junction of the petrous part and the squama are two canals, one above the other, and separated by a thin plate of bone, the septum canalis musculotubarii (processus cochlear if or mis)', both canals lead into the tympanic cavity. The upper one (semicanalis in. tensoris tympani) transmits the Tensor tympani, the lower one {semicanalis tubce auditivce) forms the bony part of the auditory tube. The tympanic cavity, auditory ossicles, and internal ear, are described with the organ of hearing. Tympanic Part (pars tympanica).—The tympanic part is a curved plate of bone lying below the squama and in front of the mastoid process. Surfaces.—Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony external acoustic meatus. Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland. Borders.—Its lateral border is free and rough, and gives attachment to the car- tilaginous part of the external acoustic meatus. Internally, the tympanic part is fused with the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube. Posteriorly, it blends with the squama and mastoid part, and forms the anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally with the back of the postglenoid process, while medially it bounds the petro- tympanic fissure. The medial part of the lower border is thin and sharp; its lateral part splits to enclose the root of the styloid process, and is therefore named the vaginal process. The central portion of the tympanic part is thin, and in a consid- erable percentage of skulls is perforated by a hole, the foramen of Huschke. The external acoustic meatus is nearly 2 cm. long and is directed inward and slightly forward: at the same time it forms a slight curve, so that the floor of the canal is convex upward. In sagittal section it presents an oval or elliptical shape with the long axis directed downward and slightly backward. Its anterior wall and floor and the lower part of its posterior wall are formed by the tympanic part; the roof and upper part of the posterior wall by the squama. Its inner end is closed, in the recent state, by the tympanic membrane; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, imme- diately below which there is sometimes seen a small spine, the suprameatal spine, situated at the upper and posterior part of the orifice. Styloid Process (processus styloideus).—The styloid process is slender, pointed, and of varying length; it projects downward and forward, from the under surface of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the vaginal process of the tympanic portion, while its distal part (stylohyal) gives attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament extends from the apex of the process to the lesser cornu of the hyoid bone, and in some instances is partially, in others completely, ossified. Structure.—The structure of the squama is like that of the other cranial bones: the mastoid portion is spongy, and the petrous portion dense and hard. Ossification.—The temporal bone is ossified from eight centers, exclusive of those for the internal ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for 146 OSTEOLOGY the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just before the close of fetal life (Fig. 142) the temporal bone consists of three principal parts: 1. The squama is ossified in membrane from a single nucleus, which appears near the root of the zygomatic process about the second month. 2. The petromastoid part is developed from four centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month. One (prodtic) appears in the neighborhood of the eminentia arcuata, spreads in front and above the internal acoustic meatus and extends to the apex of the bone; it forms part of the Septum canalis musculot ubarii Fenestra vestibuli Tympanic antrum Sulcus tympanicus Bristle in facial canal Lateral wall of tympanic antrum Fig. 142.—The three principal parts of the tempora bone at birth. 1. Outer surface of petromastoid part. 2. Outer surface of tympanic ring. 3. Inner surface of squama. cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second (opisthotic) appears at the promontory on the medial wall of the tympanic cavity and surrounds the fenestra cochleae; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid canal, invests the lateral and lower part of the cochlea, and spreads medially below the internal acoustic meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth Squama Squama Petrosquamous suture Petrosquamous suture Eminentia arcuata ■Tympanic ring Fossa subarcuata Petromastoid portion Fig. 143.—Temporal bone at birth. Outer aspect. Fig. 144.—Temporal bone at birth. Inner aspect. Internal acoustic meatus (epiotic) appears near the posterior semicircular canal and extends to form the mastoid process (Vrolik). 3. The tympanic ring is an incomplete circle, in the concavity of which is a groove, the tympanic sulcus, for the attachment of the circumference of the tympanic membrane. This ring expands to form the tympanic part, and is ossified in membrane from a single center which appears about the third month. The styloid process is developed from the proximal part of the cartilage of the second branchial or hyoid arch by two centers: one for the proximal part, the tympanohyal, appears before birth; the other, comprising the rest of the process, is named the THE SPHENOID BONE 147 stylohyal, and does not appear until after birth. The tympanic ring unites with the squama shortly before birth; the petromastoid part and squama join during the first year, and the tym- panohyal portion of the styloid process about the same time (Figs. 143, 144). The stylohyal does not unite with the rest of the bone until after puberty, and in some skulls never at all. The chief subsequent changes in the temporal bone apart from increase in size are: (1) The tympanic ring extends outward and backward to form the tympanic part. This extension does not, however, take place at an equal rate all around the circumference of the ring, but occurs most rapidly on its anterior and posterior portions, and these outgrowths meet and blend, and thus, for a time, there exists in the floor of the meatus a foramen, the foramen of Huschke; this foramen is usually closed about the fifth year, but may persist throughout life. (2) The mandibular fossa is at first extremely shallow, and looks lateralward as well as downward; it becomes deeper and is ultimately directed downward. Its change in direction is accounted for as follows. The part of the squama which forms the fossa lies at first below the level of the zygomatic process. As, however, the base of the skull increases in width, this lower part of the squama is directed hori- zontally inward to contribute to the middle fossa of the skull, and its surfaces therefore come to look upward and downward; the attached portion of the zygomatic process also becomes everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at first quite flat, and the stylomastoid foramen and rudimentary styloid process lie immediately behind the tympanic ring. With the development of the air cells the outer part of the mastoid portion grows downward and forward to form the mastoid process, and the styloid process and stylomastoid foramen now come to he on the under surface. The descent of the foramen is necessarily accompanied by a corresponding lengthening of the facial canal. (4) The downward and forward growth of the mastoid process also pushes forward the tympanic part, so that the portion of it which formed the original floor of the meatus and contained the foramen of Huschke is ultimately found in the anterior wall. (5) The fossa subarcuata becomes filled up and almost obliterated. Articulations.—The temporal articulates with five bones: occipital, parietal, sphenoid, mandible and zygomatic. The Sphenoid Bone (Os Sphenoidale). The sphenoid bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. It somewhat resembles a bat with its wings extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below. Body (corpus sphenoidale).—The body, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal air sinuses, which are separated from each other by a septum. Surfaces.—The superior surface of the body (Fig. 145) presents in front a promi- nent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain. This surface is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove {optic groove), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery into the orbital cavity. Behind the chiasmatic groove is an elevation, the tuberculum sell®; and still more posteriorly, a deep depression, the sella turcica, the deepest part of which lodges the hypophysis cerebri and is known as the fossa hypophyseos. The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes, while the posterior boundary is formed by a square- shaped plate of bone, the dorsum sellae, ending at its superior angles in two tubercles, the posterior clinoid processes, the size and form of which vary considerably in different individuals. The posterior clinoid processes deepen the sella turcica, and give attachment to the tentorium cerebelli. On either side of the dorsum sell® is a notch for the passage of the abducent nerve, and below the notch a sharp process, the petrosal process, which articulates with the apex of the petrous portion of the temporal bone, and forms the medial boundary of the foramen lacerum. 148 OSTEOLOGY Behind the dorsum sellre is a shallow depression, the clivus, which slopes obliquely backward, and is continuous with the groove on the basilar portion of the occipital bone; it supports the upper part of the pons. Posterior Clinoid process Middle Clinoid process Groove for olfactory \ lobe Ethmoidal spine With ethmoid With parietal Optic foramen Superior orbital fissure Foramen rotund um - Foramen Vesalii' Foramen ovale- Foramen spinosum- l For abducent nerve Spina angularis Petrosal \ process With palatine Fig. 145.—Sphenoid bone. Upper surface. The lateral surfaces of the body are united with the great wings and the medial pterygoid plates. Above the attachment of each great wing is a broad groove, curved something like the italic letter f; it lodges the internal carotid artery and the cavernous sinus, and is named the carotid groove. Along the posterior part Sphenoidal crest Artie, with perpendicular• plate of ethm oid Infratemporal crest Pharyngeal canal Groove for ala of vomer- nostrum- A rtic. with vomer ■ Tensor vel palatini Medial pterygoid plate. Hamulus. Fig. 146.—Sphenoid bone. Anterior and inferior surfaces. of the lateral margin of this groove, in the angle between the body and great wing, is a ridge of bone, called the lingula. The posterior surface, quadrilateral in form (Fig. 147), is joined, during infancy and adolescence, to the basilar part of the occipital bone by a plate of cartilage. THE SPHENOID BONE 149 Between the eighteenth and twenty-fifth years this becomes ossified, ossification commencing above and extending downward. The anterior surface of the body (Fig. 146) presents, in the middle line, a vertical crest, the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid, and forms part of the septum of the nose. On either side of the crest is an irregular opening leading into the corresponding sphenoidal air sinus. These sinuses are two large, irregular cavities hollowed out of the interior of the body of the bone, and separated from one another by a bony septum, which is commonly bent to one or the other side. They vary considerably in form and size,1 are seldom symmetrical, and are often partially subdivided by irregular bony laminae. Occasionally, they extend into the basilar part of the occipital nearly as far as the foramen magnum. They begin to be developed before birth, and are of a consid- erable size by the age of six. They are partially closed, in front and belowr, by two thin, curved plates of bone, the sphenoidal conchae (see page 152), leaving in the articulated skull a round opening at the upper part of each sinus by which it com- Anterior clinoid process Posterior clinoid process Notch Jor abducent nerve Superior orbital fissure 'oramen rotundum Scaphoid fossa'' SPterygoid canal Spina angulans Pterygoid /ossa— Lateral pterygoid lamina Medial pterygoid lamina Vaginal process Hamulus I. Rostrum Fig. 147.—Sphenoid bone. Upper and posterior surfaces municates with the upper and back part of the nasal cavity and occasionally with the posterior ethmoidal air cells. The lateral margin of the anterior surface is serrated, and articulates with the lamina papyracea of the ethmoid, completing the posterior ethmoidal cells; the lower margin articulates with the orbital process of the palatine bone, and the upper with the orbital plate of the frontal bone. The inferior surface presents, in the middle line, a triangular spine, the sphenoidal rostrum, which is continuous with the sphenoidal crest on the anterior surface, and is received in a deep fissure between the alae of the vomer. On either side of the rostrum is a projecting lamina, the vaginal process, directed medialward from the base of the medial pterygoid plate, with wdiich it will be described. The Great Wings (aloe magnoe).—The great wings, or ali-sphenoids, are two strong processes of bone, which arise from the sides of the body, and are curved upward, lateralward, and backward; the posterior part of each projects as a tri- angular process which fits into the angle between the squama and the petrous 1 Aldren Turner (op. cit.) gives the following as their average measurements: vertical height, ’/s inch: antero-posterior depth. 7/sinch; transverse breadth, % inch. 150 OSTEOLOGY portion of the temporal and presents at its apex a downwardly directed process, the spina angularis (sphenoidal spine). Surfaces.—The superior or cerebral surface of each great wing (Fig. 145) forms part of the middle fossa of the skull; it is deeply concave, and presents depressions for the convolutions of the temporal lobe of the brain. At its anterior and medial part is a circular aperture, the foramen rotundum, for the transmission of the maxil- lary nerve. Behind and lateral to this is the foramen ovale, for the transmission of the mandibular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve.1 Medial to the foramen ovale, a small aperture, the foramen Vesalii, may occasionally be seen opposite the root of the pterygoid process; it opens below near the scaphoid fossa, and transmits a small vein from the cavernous sinus. Lastly, in the posterior angle, near to and in front of the spine, is a short canal, sometimes double, the foramen spinosum, which transmits the middle meningeal vessels and a recurrent branch from the mandibular nerve. The lateral surface (Fig. 146) is convex, and divided by a transverse ridge, the infratemporal crest, into two portions. The superior or temporal portion, convex from above downward, concave from before backward, forms a part of the tem- poral fossa, and gives attachment to the Temporalis; the inferior or infratemporal, smaller in size and concave, enters into the formation of the infratemporal fossa, and, together with the infratemporal crest, affords attachment to the Pterygoideus externus. It is pierced by the foramen ovale and foramen spinosum, and at its posterior part is the spina angularis, which is frequently grooved on its medial surface for the chorda tympani nerve. To the spina angularis are attached the sphenomandibular ligament and the Tensor veli palatini. Medial to the anterior extremity of the infratemporal crest is a triangular process which serves to increase the attachment of the Pterygoideus externus; extending downward and medialward from this process on to the front part of the lateral pterygoid plate is a ridge which forms the anterior limit of the infratemporal surface, and, in the articulated skull, the posterior boundary of the pterygomaxillary fissure. The orbital surface of the great wing (Fig. 146), smooth, and quadrilateral in shape, is directed forward and medialward and forms the posterior part of the lateral wall of the orbit. Its upper serrated edge articulates with the orbital plate of the frontal. Its inferior rounded border forms the postero-lateral boundary of the inferior orbital fissure. Its medial sharp margin forms the lower boundary of the superior orbital fissure and has projecting from about its center a little tubercle which gives attachment to the inferior head of the Rectus lateralis oculi; at the upper part of this margin is a notch for the transmission of a recurrent branch of the lacrimal artery. Its lateral margin is serrated and articulates with the zygomatic bone. Below the medial end of the superior orbital fissure is a grooved surface, which forms the posterior wall of the pterygopalatine fossa, and is pierced by the foramen rotundum. Margin (Fig. 145).—Commencing from behind, that portion of the circum- ference of the great wing which extends from the body to the spine is irregular. Its medial half forms the anterior boundary of the foramen lacerum, and presents the posterior aperture of the pterygoid canal for the passage of the correspond- ing nerve and artery. Its lateral half articulates, by means of a synchondrosis, with the petrous portion of the temporal, and between the two bones on the under surface of the skull, is a furrow, the sulcus tubae, for the lodgement of the cartilaginous part of the auditory tube. In front of the spine the circumference presents a concave, serrated edge, bevelled at the expense of the inner table below, and of the outer table above, for articulation with the temporal squama. At the tip of the great wing is a triangular portion, bevelled at the expense of the 1 The lesser superficial petrosal nerve sometimes passes through a special canal (canaliculus innominatus of Arnold) situated medial to the foramen spinosum. THE SPHENOID BONE 151 internal surface, for articulation with the sphenoidal angle of the parietal bone; this region is named the pterion. Medial to this is a triangular, serrated surface, for articulation with the frontal bone; this surface is continuous medially with the sharp edge, which forms the lower boundary of the superior orbital fissure, and laterally with the serrated margin for articulation with the zygomatic bone. The Small Wings {aloe parvce).—The small wings or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points (Fig. 145). Surfaces.—The superior surface of each is flat, and supports part of the frontal lobe of the brain. The inferior surface forms the back part of the roof of the orbit, and the upper boundary of the superior orbital fissure. This fissure is of a triangular form, and leads from the cavity of the cranium into that of the orbit: it is bounded medially by the body; above, by the small wing; below, by the medial margin of the orbital surface of the great wing; and is completed laterally by the frontal bone. It transmits the oculomotor, trochlear, and abducent nerves, the three branches of the ophthalmic division of the trigeminal nerve, some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle menin- geal artery, a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic vein. Borders.—The anterior border is serrated for articulation with the frontal bone. The posterior border, smooth and rounded, is received into the lateral fissure of the brain; the medial end of this border forms the anterior clinoid process, which gives attachment to the tentorium cerebelli; it is sometimes joined to the middle clinoid process by a spicule of bone, and when this occurs the termination of the groove for the internal carotid artery is converted into a foramen (carotico-clinoid). The small wing is connected to the body by two roots, the upper thin and flat, the lower thick and triangular; between the two roots is the optic foramen, for the transmission of the optic nerve and ophthalmic artery. Pterygoid Processes {processus pterygoidei).—The pterygoid processes, -one on either side, descend perpendicularly from the regions where the body and great wings unite. Each process consists of a medial and a lateral plate, the upper parts of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove, descends on the front of the line of fusion. The plates are separated below by an angular cleft, the pterygoid fissure, the margins of which are rough for articulation with the pyramidal process of the palatine bone. The two plates diverge behind and enclose between them a V-shaped fossa, the pterygoid fossa, which contains the Pterygoideus interims and Tensor veli palatini. Above this fossa is a small, oval, shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini. The anterior surface of the pterygoid process is broad and triangular near its root, where it forms the posterior wall of the pterygopalatine fossa and presents the anterior orifice of the pterygoid canal. Lateral Pterygoid Plate.—The lateral pterygoid plate is broad, thin, and everted; its lateral surface forms part of the medial wall of the infratemporal fossa, and gives attachment to the Pterygoideus externus; its medial surface forms part of the pterygoid fossa, and gives attachment to the Pterygoideus interims. Medial Pterygoid Plate.—The medial pterygoid plate is narrower and longer than the lateral; it curves lateralward at its lower extremity into a hook-like pro- cess, the pterygoid hamulus, around which the tendon of the Tensor veli palatini glides. The lateral surface of this plate forms part of the pterygoid fossa, the medial surface constitutes the lateral boundary of the choana or posterior aperture of the corresponding nasal cavity. Superiorly the medial plate is prolonged on to the under surface of the body as a thin lamina, named the vaginal process, which articulates in front with the sphenoidal process of the palatine and behind this with the ala of the vomer. The angular prominence between the posterior margin 152 OSTEOLOGY of the vaginal process and the medial border of the scaphoid fossa is named the pterygoid tubercle, and immediately above this is the posterior opening of the pterygoid canal. On the under surface of the vaginal process is a furrow, which is converted into a canal by the sphenoidal process of the palatine bone, for the transmission of the pharyngeal branch of the internal maxillary artery and the pharyngeal nerve from the sphenopalatine ganglion. The pharyngeal aponeurosis is attached to the entire length of the posterior edge of the medial plate, and the Constrictor pharyngis superior takes origin from its lower third. Projecting backward from near the middle of the posterior edge of this plate is an angular process, the processus tubarius, which supports the pharyngeal end of the auditory tube. The anterior margin of the plate articulates with the posterior border of the vertical part of the palatine bone. The Sphenoidal Conchse (concha sphenoidales; sphenoidal tnrbinated processes). —The sphenoidal conchse are two thin, curved plates, situated at the anterior and lower part of the body of the sphenoid. An aperture of variable size exists in the anterior wall of each, and through this the sphenoidal sinus opens into the nasal cavity. Each is irregular in form, and tapers to a point behind, being broader and thinner in front. Its upper surface is concave, and looks toward the cavity of the sinus; its under surface is convex, and forms part of the roof of the corre- sponding nasal cavity. Each bone articulates in front with the ethmoid, laterally with the palatine; its pointed posterior extremity is placed above the vomer, and is received between the root of the pterygoid process laterally and the rostrum of the sphenoid medially. A small portion of the sphenoidal concha sometimes enters into the formation of the medial wall of the orbit, between the lamina papyracea of the ethmoid in front, the orbital plate of the palatine below, and the frontal bone above. Ossification.—Until the seventh or eighth month of fetal life the body of the sphenoid consists of two parts, viz., one in front of the tuberculum sella;, the presphenoid, with which the small wings are continuous; the other, comprising the sella turcica and dorsum sellae, the postsphenoid, I with which are associated the great wings, and pterygoid processes. The greater part of the bone is ossified in cartilage. There are fourteen centers in all, six for the presphenoid and eight for the postsphenoid. Presphenoid.—About the ninth week of fetal life an ossific center appears for each of the small wings (orbitosphenoids) just lateral to the optic foramen; shortly afterward two nuclei appear in the pre- sphenoid part of the body. The sphe- noidal concha; are each developed from a center which makes its appearance about the fifth month;1 at birth they consist of small triangular lamina;, and it is not until the third year that they become hollowed out and cone- shaped; about the fourth year they fuse with the labyrinths of the ethmoid, and between the ninth and twelfth years they unite with the sphenoid. Postsphenoid.—The first ossific nuclei are those for the great wings (ali-sphenoids)2. One makes its appearance in each wing between the foramen rotundum and foramen ovale about the eighth week. The orbital plate and that part of the sphenoid which is found in the temporal fossa, as well as the lateral pterygoid plate, are ossified in membrane (Fawcett)3. Soon after, the centers for the postsphenoid part of the body appear, one on either side of the sella turcica, and become blended together about the middle of fetal life. Each medial pterygoid plate (with the exception of its hamulus) is ossified in membrane, and its center probably appears about the ninth or tenth week; the hamulus becomes chondrified during the third month, and almost at once undergoes Fig. 148.—Sphenoid bone at birth. Posterior aspect. 1 According to Cleland, each sphenoidal concha is ossified from four centers. 2 Mall, Am. Jour. Anat., 1906, states that the pterygoid center appears first in an embryo fifty-seven days old. 3 Journal of Anatomy and Physiology, 1910, vol. xliv. THE ETHMOID BONE 153 ossification (Fawcett).1 The medial joins the lateral pterygoid plate about the sixth month. About the fourth month a center appears for each lingula and speedily joins the rest of the bone. The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone is in three pieces (Fig. 148): a central, consisting of the body and small wings, and two lateral, each comprising a great wing and pterygoid process. In the first year after birth the great wings and body unite, and the small wings extend inward above the anterior part of the body, and, meeting with each other in the middle line, form an elevated smooth surface, termed the jugum sphenoidale. By the twenty-fifth year the sphenoid and occipital are completely fused. Between the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis cranio- pharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal ecto- derm is transmitted. The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not attain their full size until after puberty. Intrinsic Ligaments of the Sphenoid.—The more important of these are: the pterygospinous, stretching between the spina angularis and the lateral pterygoid plate (see cervical fascia); the interclinoid, a fibrous process joining the anterior to the posterior clinoid process; and the caroticoclinoid, connecting the anterior to the middle clinoid process. These ligaments occa- sionally ossify. Articulations.—The sphenoid articulates with twelve bones: four single, the vomer, ethmoid, frontal, and occipital; and four paired, the parietal, temporal, zygomatic, and palatine.2 The Ethmoid Bone (Os Ethmoidale). The ethmoid bone is exceedingly light and spongy, and cubical in shape; it is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the cranium; a perpendicular plate, constituting part of the nasal septum; and two lateral masses or labyrinths. Cribiform Plate (lamina cribrosa; horizontal lamina).—The cribriform plate (Fig. 149) is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a cock’s comb. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. Its anterior border, short and thick, articulates with the frontal bone, and presents two small pro- jecting alae, which are received into corresponding depressions in the frontal bone and complete the foramen cecum. Its sides are smooth, and sometimes bulging from the presence of a small air sinus in the interior. On either side of the crista galli, the cribri- form plate is narrow and deeply grooved; it supports the olfactory bulb and is perforated by fora- mina for the passage of the olfac- tory nerves. The foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity; those at the medial and lateral parts of the groove are larger—the former transmit the nerves to the upper part of the nasal septum, the latter those to the superior nasal concha. At the front part of the cribriform Perpendicular plate Ala Crista galli Cribriform plate Anterior ethmoidal groove Posterior ethmoidal groove Fig. 149.—Ethmoid bone from above. 1 Anatomischer Anzeiger, March, 1905. It also sometimes articulates with the tuberosity of the maxilla (see page 159). 154 OSTEOLOGY plate, on either side of the crista galli, is a small fissure which is occupied by a process of dura mater. Lateral to this fissure is a notch or foramen which trans- mits the nasociliary nerve; from this notch a groove extends backward to the anterior ethmoidal foramen. Fig. 150.—Perpendicular plate of ethmoid. Shown by removing the right labyrinth. Perpendicular Plate (lamina perpendicularis; vertical plate).—The perpendicular plate (Figs. 150, 151) is a thin, flattened lamina, polygonal in form, which descends from the under surface of the cribriform plate, and assists in forming the septum of the nose; it is generally deflected a little to one or other side. The anterior border articulates with the spine of the frontal bone and the crest of the nasal bones. The posterior border articulates by its upper half with the sphenoidal crest, by its lower with the vomer. The inferior border is thicker than the posterior, and serves for the attachment of the septal cartilage of the nose. The surfaces of the plate are smooth, except above, where numerous grooves and canals are seen; these lead from the medial foramina on the cribriform plate and lodge filaments of the olfactory nerves. The Labyrinth or Lateral Mass (labyrinthus ethnoidalis) consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, and posterior, and inter- posed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part of the corresponding nasal cavity. In the disarticulated bone many of these cells are opened into, but when the bones are articulated, they are closed in at every part, except where they open into the nasal cavity. Surfaces.—The upper surface of the laby- rinth (Fig. 149) presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone. Crossing this surface are two grooves, converted into canals by articulation with the frontal; they are the anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. The posterior surface presents large irregular cellular cavities, which are closed in Crista galli Labyrinth Superior nasal concha Superior meatus Uncinate process Middle nasal concha Fig. 151.—Ethmoid bone from behind. Perpendicular plate THE ETHMOID BONE 155 by articulation with the sphenoidal concha and orbital process of the palatine. The lateral surface (Fig. 152) is formed of a thin, smooth, oblong plate, the lamina papyracea (os planum), which covers in the middle and posterior ethmoidal cells Ala Ethmoidal cells Perpendicular plate Uncinate process Fig. 152.—Ethmoid bone from the right side. and forms a large part of the medial wall of the orbit; it articulates above with the orbital plate of the frontal bone, below with the maxilla and orbital process of the palatine, in front with the lacrimal, and behind with the sphenoid. In front of the lamina papyracea are some broken air cells which are overlapped and completed by the lacrimal bone and the frontal process of the maxilla. A Frontal sinus Crista galli Sella turcica Uncinate process of ethmoid Openings into maxillary sinus maxiuary sinus Medial pterygoid plate Hamulus Fig. 153.—Lateral wall of nasal cavity, showing ethmoid bone in position. curved lamina, the uncinate process, projects downward and backward from this part of the labyrinth; it forms a small part of the medial wall of the maxillary sinus, and articulates with the ethmoidal process of the inferior nasal concha. 156 OSTEOLOGY The medial surface of the labyrinth (Fig. 153) forms part of the lateral wall of the corresponding nasal cavity. It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha. It is rough, and marked above by numerous grooves, directed nearly vertically downward from the cribriform plate; they lodge branches of the olfactory nerves, which are distributed to the mucous mem- brane covering the superior nasal concha. The back part of the surface is sub- divided by a narrow oblique fissure, the superior meatus of the nose, bounded above by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells open into this meatus. Below, and in front of the superior meatus, is the convex surface of the middle nasal concha; it extends along the whole length of the medial surface of the labyrinth, and its lower margin is free and thick. The lateral surface of the middle concha is concave, and assists in forming the middle meatus of the nose. The middle ethmoidal cells open into the central part of this meatus, and a sinuous passage, termed the infundibulum, extends upward and forward through the labyrinth and communicates with the anterior ethmoidal cells, and in about 50 per cent, of skulls is continued upward as the frontonasal duct into the frontal sinus. Ossification.—The ethmoid is ossified in the cartilage of the nasal capsule by three centers: one for the perpendicular plate, and one for each labyrinth. The labyrinths are first developed, ossific granules making their appearance in the region of the lamina papyracea between the fourth and fifth months of fetal life, and extending into the conchse. At birth, the bone consists of the two labyrinths, which are small and ill-developed. During the first year after birth, the perpendicular plate and crista galli begin to ossify from a single center, and are joined to the labyrinths about the beginning of the second year. The cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. The development of the ethmoidal cells begins during fetal life. Articulations.—The ethmoid articulates with fifteen bones: four of the cranium—the frontal, the sphenoid, and the two sphenoidal concha?; and eleven of the face—the two nasals, two maxillae, two lacrimals, two palatines, two inferior nasal conchse, and the vomer. Sutural or Wormian1 Bones.—In addition to the usual centers of ossification of the cranium, others may occur in the course of the sutures, giving rise to irregular, isolated bones, termed sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, but are occasionally seen at the fontanelles, especially the posterior. One, the 'pterion ossicle, sometimes exists between the sphenoidal angle of the parietal and the great wing of the sphenoid. They have a tendency to'be more or less symmetrical on the two sides of the skull, and vary much in size. Their number is generally limited to two or three; but more than a hundred have been found in the skull of an adult hydrocephalic subject. THE FACIAL BONES (OSSA FACIEI). The Nasal Bones (Ossa Nasalia). The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, “the bridge” of the nose (Fig. 190). Each has two surfaces and four borders. Surfaces.—The outer surface (Fig. 155) is concavoconvex from above downward, convex from side to side; it is covered by the Procerus and Compressor naris, and perforated about its center by a foramen, for the transmission of a small vein. The inner surface (Fig. 150) is concave from side to'side, and is traversed from above downward, by a groove for the passage of a branch of the nasociliary nerve. Borders.—The superior border is narrow, thick, and serrated for articulation with the nasal notch of the frontal bone. The inferior border is thin, and gives attaeh- 1 Ole Worm, Professor of Anatomy at Copenhagen, 1624-1639, was erroneously supposed to have given the first detailed description of these bones. THE MAX ILL HZ 157 ment to the lateral cartilage of the nose; near its middle is a notch which marks the end of the groove just referred to. The lateral border is serrated, bevelled at the expense of the inner surface above, and of the outer below, to articulate with the frontal process of the maxilla. The medial border, thicker above than Fossa for lacrimal sac Infraorbital foramen - Fig. 154.—Articulation of nasal and lacrimal bones with maxilla. below, articulates with its fellow of the opposite side, and is prolonged behind into a vertical crest, which forms part of the nasal septum: this crest articulates, from above downward, with the spine of the frontal, the perpendicular plate of the ethmoid, and the septal cartilage of the nose. Foramen for vein Crest Groove for nerve Fig. 155.—Right nasal bone. Outer surface. Fig. 156.—Right nasal bone. Inner surface. Ossification.—Each bone is ossified from one center, which appears at the beginning of the third month of fetal life in the membrane overlying the front part of the cartilaginous nasal .capsule. Articulations.—The nasal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the opposite nasal and the maxilla. The Maxillae (Upper Jaw). The maxillae are the largest bones of the face, excepting the mandible, and form, by their union, the whole of the upper jaw. Each assists in forming the 158 OSTEOLOGY boundaries of three cavities, viz., the roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation of two fossae, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and palatine. The Body (corpus maxilla;).—The body is somewhat pyramidal in shape, and contains a large cavity, the maxillary sinus (antrum of Highmore). It has four surfaces—an anterior, a posterior or infratemporal, a superior or orbital, and a medial or nasal. Surfaces.—The anterior surface (Fig. 157) is directed forward and lateralward. It presents at its lower part a series of eminences corresponding to the positions of the roots of the teeth. Just above those of the incisor teeth is a depression, the incisive fossa, which gives origin to the Depressor alee nasi; to the alveolar border below the fossa is attached a slip of the Orbicularis oris; above and a little ■Lacrimal tubercle Med. palp. lig. Dilatator naris posterior •Alveolar canals Incisive Jossa Maxillary tuberosity Premolars Fig. 157.—Left maxilla. Outer surface. lateral to it, the Nasalis arises. Lateral to the incisive fossa is another depression, the canine fossa; it is larger and deeper than the incisive fossa, and is separated from it by a vertical ridge, the canine eminence, corresponding to the socket of the canine tooth; the canine fossa gives origin to the Caninus. Above the fossa is the infraorbital foramen, the end of the infraorbital canal; it transmits the infra- orbital vessels and nerve. Above the foramen is the margin of the orbit, which affords attachment to part of the Quadratus labii superioris. Medially, the anterior surface is limited by a deep concavity, the nasal notch, the margin of which gives attachment to the Dilatator naris posterior and ends below in a pointed process, which with its fellow of the opposite side forms the anterior nasal spine. The infratemporal surface (Fig. 157) is convex, directed backward and lateral- ward, and forms part of the infratemporal fossa. It is separated from the anterior surface by the zygomatic process and by a strong ridge, extending upward from the socket of the first molar tooth. It is pierced about its center by the apertures of the alveolar canals, which transmit the posterior superior alveolar vessels and nerves. At the lower part of this surface is a rounded eminence, the maxillary THE MAXJLLdE 159 tuberosity, especially prominent after the growth of the wisdom tooth; it is rough on its lateral side for articulation with the pyramidal process of the palatine bone and in some cases articulates with the lateral pterygoid plate of the sphenoid. It gives origin to a few fibers of the Pterygoideus internus. Immediately above this is a smooth surface, wdiich forms the anterior boundary of the pterygopalatine fossa, and presents a groove, for the maxillary nerve; this groove is directed lateral- ward and slightly upward, and is continuous with the infraorbital groove on the orbital surface. The orbital surface (Fig. 157) is smooth and triangular, and forms the greater part of the floor of the orbit. It is bounded medially by an irregular margin which in front presents a notch, the lacrimal notch; behind this notch the margin articu- lates with the lacrimal, the lamina papyracea of the ethmoid and the orbital process of the palatine. It is bounded behind by a smooth rounded edge which forms the anterior margin of the inferior orbital fissure, and sometimes articulates at its lateral extremity writh the orbital surface of the great wing of the sphenoid. With frontal Bones partially closing orifice of sinus marked in red With nasal hone Inferior nasal concha Ethmoid Palatine •Ant. nasal spine Bristle passed through incisive canal Fig. 158.—Left maxilla. Nasal surface. It is limited in front by part of the circumference of the orbit, which is continuous medially with the frontal process, and laterally wTith the zyogmatic process. Near the middle of the posterior part of the orbital surface is the infraorbital groove, for the passage of the infraorbital vessels and nerve. The groove begins at the middle of the posterior border, wThere it is continuous with that near the upper edge of the infratemporal surface, and, passing forward, ends in a canal, which subdivides into two branches. One of the canals, the infraorbital canal, opens just below the margin of the orbit; the other, which is smaller, runs downward in the substance of the anterior wTall of the maxillary sinus, and transmits the anterior superior alveolar vessels and nerve to the front teeth of the maxilla. From the back part of the infraorbital canal, a second small canal is sometimes given off; it runs downward in the lateral wall of the sinus, and conveys the middle alveolar nerve to the premolar teeth. At the medial and forepart of the orbital surface, just lateral to the lacrimal groove, is a depression, which gives origin to the Obliquus oculi inferior. 160 OSTEOLOGY The nasal surface (Fig. 158) presents a large, irregular opening leading into the maxillary sinus. At the upper border of this aperture are some broken air cells, which, in the articulated skull, are closed in by the ethmoid and lacrimal bones. Below the aperture is a smooth concavity which forms part of the inferior meatus of the nasal cavity, and behind it is a rough surface for articulation with the per- pendicular part of the palatine bone; this surface is traversed by a groove, com- mencing near the middle of the posterior border and running obliquely downward and forward; the groove is converted into a canal, the pterygopalatine canal, by the palatine bone. In front of the opening of the sinus is a deep groove, the lacrimal groove, which is converted into the nasolacrimal canal, by the lacrimal bone and inferior nasal concha; this canal opens into the inferior meatus of the nose and transmits the nasolacrimal duct. More anteriorly is an oblique ridge, the conchal crest, for articulation with the inferior nasal concha. The shallow concavity above this ridge forms part of the atrium of the middle meatus of the nose, and that below it, part of the inferior meatus. Frontal sinus Anterior ethmoidal foramen ,Posterior ethmoidal foramen Orbital process of palatine Optic foramen Sphenopalatine foramen Sella turcica Probe in foramen rot undum / Fossa for lacrimal sac Uncinate process of ethmoid Openings of maxillary sinus Inferior nasal concha Probe in pterygopalatine canal Probe in pterygoid canal Palatine bone Lateral pterygoid plate Pyramidal process of palatine Fig. 159.—Left maxillary sinus opened from the exterior. The Maxillary Sinus or Antrum of Highmore (sinus maxillaris).—The maxillary sinus is a large pyramidal cavity, within the body of the maxilla: its apex, directed lateralward, is formed by the zygomatic process; its base, directed medialward, by the lateral wall of the nose. Its walls are everywhere exceedingly thin, and correspond to the nasal orbital, anterior, and infratemporal surfaces of the body of the bone. Its nasal wall, or base, presents, in the disarticulated bone, a large, irregular aperture, communicating with the nasal cavity. In the articulated skull this aperture is much reduced in size by the following bones: the uncinate process of the ethmoid above, the ethmoidal process of the inferior nasal concha below, the vertical part of the palatine behind, and a small part of the lacrimal above and in front (Figs. 158, 159); the sinus communicates with the middle meatus THE MAXILLA 161 of the nose, generally by two small apertures left between the above-mentioned bones. In the fresh state, usually only one small opening exists, near the upper part of the cavity; the other is closed by mucous membrane. On the posterior wall are the alveolar canals, transmitting the posterior superior alveolar vessels and nerves to the molar teeth. The floor is formed by the alveolar process of the maxilla, and, if the sinus be of an average size, is on a level with the floor of the nose; if the sinus be large it reaches below this level. Projecting into the floor of the antrum are several conical processes, correspond- ing to the roots of the first and second molar teeth;1 in some cases the floor is perforated by the fangs of the teeth. The infraorbital canal usually projects into the cavity as a well-marked ridge extending from the roof to the anterior wall; additional ridges are sometimes seen in the posterior wall of the cavity, and are caused by the alveolar canals. The size of the cavity varies in different skulls, and even on the two sides of the same skull.2 The Zygomatic Process (processus zygomaticus; malar process).—The zygomatic process is a rough triangular eminence, situated at the angle of separation of the anterior, zygomatic, and orbital surfaces. In front it forms part of the anterior surface; behind, it is concave, and forms part of the infratemporal fossa; above, it is rough and serrated for articulation with the zygomatic bone; while below, it presents the prominent arched border which marks the division between the anterior and infratemporal surfaces. ' The Frontal Process (processus frontalis; nasal process).—The frontal process is a strong plate, which projects upward, medialward, and backward, by the side of the nose, forming part of its lateral boundary. Its lateral surface is smooth, continuous with the anterior surface of the body, and gives attachment to the Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament. Its medial surface forms part of the lateral wall of the nasal cavity; at its upper part is a rough, uneven area, which articulates with the ethmoid, closing in the anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the posterior end of which articulates with the middle nasal concha, while the anterior part is termed the agger nasi; the crest forms the upper limit of the atrium of the middle meatus. The upper border articulates with the frontal bone and the anterior with the nasal; the posterior border is thick, and hollowed into a groove, which is continuous below with the lacrimal groove on the nasal surface of the body: by the articulation of the medial margin of the groove with the anterior border of the lacrimal a corresponding groove on the lacrimal is brought into continuity, and together they form the lacrimal fossa for the lodgement of the lacrimal sac. The lateral margin of the groove is named the anterior lacrimal crest, and is con- tinuous below with the orbital margin; at its junction with the orbital surface is a small tubercle, the lacrimal tubercle, which serves as a guide to the position of the lacrimal sac. The Alveolar Process (processus alveolaris).—The alveolar process is the thickest and most spongy part of the bone. It is broader behind than in front, and exca- vated into deep cavities for the reception of the teeth. These cavities are eight in number, and vary in size and depth according to the teeth they contain. That for the canine tooth is the deepest; those for the molars are the widest, and are subdivided into minor cavities by septa; those for the incisors are single, but deep and narrow. The Buccinator arises from the outer surface of this process, as far forward as the first molar tooth. When the maxillae are articulated with each other, their alveolar processes together form the alveolar arch; the center of the anterior margin of this arch is named the alveolar point. 1 The number of teeth whose roots are in relation with the floor of the antrum is variable. The sinus “may extend so as to be in relation to all the teeth of the true maxilla, from the canine to the dens sapientice. ” _ (Salter.) 2 Aldren Turner (op. cit.) gives the following measurements as those of an average sized sinus: vertical height opposite first molar tooth, 1 Yi inch; transverse breadth, 1 inch; and antero-posterior depth, 134 inch. 162 OSTEOLOGY The Palatine Process (processus palatinus; palatal process).—The palatine process, thick and strong, is horizontal and projects medialward from the nasal surface of the bone. It forms a considerable part of the floor of the nose and the roof of the mouth and is much thicker in front than behind. Its inferior surface (Fig. 1G0) is concave, rough and uneven, and forms, with the palatine process of the opposite bone, the anterior three-fourths of the hard plate. It is perforated by numerous foramina for the passage of the nutrient vessels; is channelled at the back part of its lateral border by a groove, sometimes a canal, for the transmission of the descending palatine vessels and the anterior palatine nerve from the spheno- palatine ganglion; and presents little depressions for the lodgement of the palatine glands. When the two maxillae are articulated, a funnel-shaped opening, the incisive foramen, is seen in the middle line, immediately behind the incisor teeth. In this opening the orifices of two lateral canals are visible; they are named the Incisive canals Incisive foramen Foramina of Scarpa Palatine process of maxilla Greater palatine foramen Horizontal plate of palatine bone Fig. 160.—The bony palate and alveolar arch. Lesser palatine foramina incisive canals or foramina of Stenson; through each of them passes the terminal branch of the descending palatine artery and the nasopalatine nerve. Occasionally two additional canals are present in the middle line; they are termed the foramina of Scarpa, and when present transmit the nasopalatine nerves, the left passing through the anterior, and the right through the posterior canal. On the under surface of the palatine process, a delicate linear suture, well seen in young skulls, may sometimes be noticed extending lateralward and forward on either side from the incisive foramen to the interval between the lateral incisor and the canine tooth. The small part in front of this suture constitutes the premaxilla (os incisimim), which in most vertebrates forms an independent bone; it includes the whole thick- ness of the alveolus, the corresponding part of the floor of the nose and the anterior nasal spine, and contains the sockets of the incisor teeth. The upper surface of the palatine process is concave from side to side, smooth, and forms the greater part of the floor of the nasal cavity. It presents, close to its medial margin, the THE LACRIMAL BONE 163 upper orifice of the incisive canal. The lateral border of the process is iftcorporated with the rest of the bone. The medial border is thicker in front than behind, and is raised above into a ridge, the nasal crest, which, with the corresponding ridge of the opposite bone, forms a groove for the reception of the vomer. The front part of this ridge rises to a considerable height, and is named the incisor crest; it is prolonged forward into a sharp process, which forms, together with a similar process of the opposite bone, the anterior nasal spine. The 'posterior border is ser- rated for articulation with the horizontal part of the palatine bone. Ossification.—The maxilla is ossified in membrane. Mall1 and Fawcett2 maintain that it is ossified from two centers only, one for the maxilla proper and one for the premaxilla. These centers appear during the sixth week of fetal life and unite in the beginning of the third month, but the suture between the two portions persists on the palate until nearly middle life. Mall states that the frontal process is developed from both centers. The maxillary sinus appears as a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does not reach its full size until after the second dentition. The maxilla was formerly described as ossifying from six centers, viz., one, the orbitonasal, forms that portion of the body of the bone which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and the lateral wall of the nasal cavity; a second, the zygomatic, gives origin to the portion which lies lateral to the infraorbital canal, including the zygomatic process; from a third, the palatine, is developed the palatine process posterior to the incisive canal together with the adjoining part of the nasal wall; a fourth, the premaxillary, forms the incisive bone which carries the incisor Fig. 161.-—Anterior surface of maxilla at birth, Fig. 162.—Inferior surface of maxilla at birth teeth and corresponds to the premaxilla of the lower vertebrates;3 a fifth, the nasal, gives rise to the frontal process and the portion above the canine tooth; and a sixth, the infravomerine, lies between the palatine and premaxillary centers and beneath the vomer; this center, together with the corresponding center of the opposite bone, separates the incisive canals from each other. Articulations.—The maxilla articulates with nine bones: two of the cranium, the frontal and ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate of the sphenoid. At birth the transverse and antero-posterior diameters of the bone are each greater than the vertical. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest, owing to the development of the alveblar process and the increase in size of the sinus. In old age the bone reverts in some measure to the infantile condition; its height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the lower part of the bone contracted and reduced in thickness. CHANGES PRODUCED IN THE MAXILLA BY AGE. The Lacrimal Bone (Os Lacrimale) The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit (Fig. 164). It has two surfaces and four borders. 1 American Journal of Anatomy, 1906, vol. v. 2 Journal of Anatomy and Physiology, 1911, vol. xlv. 3 Some anatomists believe that the premaxillary bone is ossified by two centers (see page 299). 164 OSTEOLOGY Surfaces?—The lateral or orbital surface (Fig. 163) is divided by a vertical ridge, the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is thus completed. The upper part of this fossa lodges the lacrimal sac, the lower part, the naso- lacrimal duct. The portion behind the crest is smooth, and forms part of the medial wall of the orbit. The crest, with a part of the orbital surface imme- diately behind it, gives origin to the lacrimal part of the Orbicularis oculi and ends below in a small, hook-like projection, the lacrimal hamulus, which articu- lates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the lacrimal canal; it sometimes exists as a separate piece, and is then called the lesser lacrimal bone. The medial or nasal surface presents a longitudinal furrow, corresponding to the crest on the lateral surface. The area in front of this furrow forms part of the middle meatus of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells. Borders.—Of the jour borders the anterior articulates with the frontal process of the maxilla; the posterior with the lamina papyracea of the ethmoid; the superior with the frontal bone. The inferior is divided by the lower edge of the posterior lacri- mal crest into two parts: the posterior part articulates with the orbital plate of the maxilla; the anterior is prolonged downward as the descending process, which articulates with the lacrimal process of the inferior nasal concha, and assists in forming the canal for the nasolacrimal duct. Ossification.—The lacrimal is ossified from a single center, which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule. Articulations.—The lacrimal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the maxilla and the inferior nasal concha. vrith Frontal I I 1 i / w'‘ With Infer, nasal concha Fig. 163.—Left lacri- mal bone. Orbital sur- face. Enlarged. The zygomatic bone is small and quadrangular, and is situated at the upper and lateral part of the face: it forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossae (Fig. 164). It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders. Surfaces.—The malar surface (Fig. 165) is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomatico- facial nerve and vessels; below this foramen is a slight elevation, which gives origin to the Zygomaticus. The temporal surface (Fig. 166), directed backward and medialward, is concave, presenting medially a rough, triangular area, for articulation with the maxilla, and laterally a smooth, concave surface, the upper part of which forms the anterior boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near the center of this surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve. Processes.—The frontosphenoidal process is thick and serrated, and articulates with the zygomatic process of the frontal bone. On its orbital surface, just within the orbital margin and about 11 mm. below the zygomaticofrontal suture is a tubercle of varying size and form, but present in 95 per cent, of skulls (Whitnall1). The Zygomatic Bone (Os Zygomaticum; Malar Bone) 1 Journal of Anatomy and Physiology, vol. xlv. The structures attached to this tubercle are: (1) the check ligament of the Rectus lateralis; (2) the lateral end of the aponeurosis of the Levator palpebr* superioris; (3) the suspensory ligament of the eye (Lockwood); and (4) the lateral extremities of the superior and inferior tarsi. THE ZYGOMATIC BONE 165 The orbital process is a thick, strong plate, projecting backward and medialward from the orbital margin. Its antero-medial surface forms, by its junction with the orbital surface of the maxilla and with the great wing of the sphenoid, part of the floor and lateral wall of the orbit. On it are seen the orifices of two canals, Fig. 164.—Left zygomatic bone in situ. the zygomaticoorbital foramina; one of these canals opens into the temporal fossa, the other on the malar surface of the bone; the former transmits the zygomatico- temporal, the latter the zygomaticofacial nerve. Its postero-lateral surface, smooth and convex, forms parts of the temporal and infratemporal fossae. Its anterior margin, smooth and rounded, is part of the circumference of the orbit. Its superior With Frontal Bristles passed through zygomatico- orbital foramina Fig. 165.—Left zygomatic bone. Malar surface. Fig. 166.—Left zygomatic bone. Temporal surface. margin, rough, and directed horizontally, articulates with the frontal bone behind the zygomatic process. Its posterior margin is serrated for articulation, with the great wing of the sphenoid and the orbital surface of the maxilla. At the angle of junction of the sphenoidal and maxillary portions, a short, concave, non-articular 166 OSTEOLOGY part is generally seen; this forms the anterior boundary of the inferior orbital fissure: occasionally, this non-articular part is absent, the fissure then being completed by the junction of the maxilla and sphenoid, or by the interposition of a small sutural bone in the angular interval between them. The maxillary process presents a rough, triangular surface which articulates with the maxilla. The temporal process, long, narrow, and serrated, articulates with the zygomatic process of the temporal. Borders.—The antero-superior or orbital border is smooth, concave, and forms a considerable part of the circumference of the orbit. The antero-inferior or maxil- lary border is rough, and bevelled at the expense of its inner table, to articulate with the maxilla; near the orbital margin it gives origin to the Quadratus labii superioris. The postero-superior or temporal border, curved like an italic letter /, is continuous above with the commencement of the temporal line, and below with the upper border of the zygomatic arch; the temporal fascia is attached to it. The postero-inferior or zygomatic border affords attachment by its rough edge to the Masseter. Ossification.—The zygomatic bone is generally described as ossifying from three centers— one for the malar and two for the orbital portion; these appear about the eighth week and fuse about the fifth month of fetal life. Mall describes it as being ossified from one center which appears just beneath and to the lateral side of the orbit. After birth, the bone is sometimes divided by a horizontal suture into an upper larger, and a lower smaller division. In some quad- rumana the zygomatic bone consists of two parts, an orbital and a malar. Articulations.—The zygomatic articulates with four bones: the frontal, sphenoidal, temporal, and maxilla. Groove for nasolacrimal duct Frontal process Maxillary sinus Orbital process Sphenopalatine notch \ Sphenoidal process s. -Conchal crest Conchal crest- Fig. 167.—Articulation of left palatine bone with maxilla. The Palatine Bone (Os Palatinum; Palate Bone). The palatine bone is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid (Fig. 167). It contributes to the walls of three cavities: the floor and lateral wall of the nasal cavity, the roof of the mouth, and the floor of the orbit; it enters into the formation of two fossae, the pterygopalatine and pterygoid fossae; and one fissure, the inferior orbital fissure. The palatine bone somewhat resembles the letter L, and consists of a horizontal and a vertical part and three outstanding processes—viz., the pyramidal THE PALATINE BONE 167 process, which is directed backward and lateralward from the junction of the two parts, and the orbital and sphenoidal processes, which surmount the vertical part, and are separated by a deep notch, the sphenopalatine notch. The Horizontal Part (pars horizontalis; horizontal plate) (Figs. 168, 169).—The horizontal part is quadrilateral, and has two surfaces and four borders. Surfaces.—The superior surface, concave from side to side, forms the back part of the floor of the nasal cavity. The inferior surface, slightly concave and rough, forms, with the corresponding surface of the opposite bone, the posterior fourth of the hard palate. Near its posterior margin may be seen a more or less marked transverse ridge for the attachment of part of the aponeurosis of the Tensor veli palatini. Maxillary surface Superior meatus. Sphenopalat ine foramen Sphenopalatine foramen- VERTICAL PAItT VERTICAL PART Pterygo- palatine . canal ' Sphenoidal process Articular portion Maxillary ■process Non-articular portion Posterior nasal spine Pyramidal process Musculuh uvulce HORIZONTAL PART HORIZONTAL PART Fig. 168.—Left palatine bone. Nasal aspect Enlarged. Fio. 169.—Left palatine bone. Posterior aspect. Enlarged. Borders.—The anterior border is serrated, and articulates with the palatine process of the maxilla. The posterior border is concave, free, and serves for the attachment of the soft palate. Its medial end is sharp and pointed, and, when united with that of the opposite bone, forms a projecting process, the posterior nasal spine for the attachment of the Musculus uvula?. The lateral border is united with the lower margin of the perpendicular part, and is grooved by the lower end of the pterygopalatine canal. The medial border, the thickest, is serrated for articu- lation with its fellow of the opposite side; its superior edge is raised into a ridge, which, united with the ridge of the opposite bone, forms the nasal crest for articu- lation with the posterior part of the lower edge of the vomer. The Vertical Part (pars perpendicularis; perpendicular plate) (Figs. 1G8, 169).— The vertical part is thin, of an oblong form, and presents two surfaces and four borders. Surfaces.—The nasal surface exhibits at its lower part a broad, shallow depres- sion, which forms part of the inferior meatus of the nose. Immediately above this is a well-marked horizontal ridge, the conchal crest, for articulation with the inferior nasal concha; still higher is a second broad, shallow depression, which forms part of the middle meatus, and is limited above by a horizontal crest less prominent than the inferior, the ethmoidal crest, for articulation with the middle nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which forms part of the superior meatus. 168 OSTEOLOGY The maxillary surface is rough and irregular throughout the greater part of its extent, for articulation with the nasal surface of the maxilla; its upper and back part is smooth where it enters into the formation of the pterygopalatine fossa; it is also smooth in front, where it forms the posterior part of the medial wall of the maxillary sinus. On the posterior part of this surface is a deep vertical groove, converted into the pterygopalatine canal, by articulation with the maxilla; this canal transmits the descending palatine vessels, and the anterior palatine nerve. Borders.—The anterior border is thin and irregular; opposite the conchal crest is a pointed, projecting lamina, the maxillary process, which is directed forward, and closes in the low’er and back part of the opening of the maxillary sinus. The posterior border (Fig. 169) presents a deep groove, the edges of which are serrated for articulation with the medial pterygoid plate of the sphenoid. This border is continuous above with the sphenoidal process; below it expands into the pyramidal process. The superior border supports the orbital process in front and the sphenoidal process behind. These processes are separated by the sphenopalatine notch, which is converted into the sphenopalatine foramen by the under surface of the body of the sphenoid. In the articulated skull this foramen leads from the pterygopalatine fossa into the posterior part of the superior meatus of the nose, and transmits the sphenopalatine vessels and the superior nasal and nasopalatine nerves. The inferior border is fused with the lateral edge of the horizontal part, and immediately in front of the pyramidal process is grooved by the lower end of the pterygopalatine,canal. The Pyramidal Process or Tuberosity (processus pyramidalis).—The pyramidal process projects backward and lateralward from the junction of the horizontal and vertical parts, and is received into the angular interval between the lower extremities of the pterygoid plates. On its posterior surface is a smooth, grooved, triangular area, limited on either side by a rough articular furrow. The furrows articulate with the pterygoid plates, while the grooved intermediate area completes the lower part of the pterygoid fossa and gives origin to a few fibers of the Ptery- goideus internus. The anterior part of the lateral surface is rough, for articulation with the tuberosity of the maxilla; its posterior part consists of a smooth triangular area which appears, in the articulated skull, between the tuberosity of the maxilla and the lower part of the lateral pterygoid plate, and completes the lower part of the infratemporal fossa. On the base of the pyramidal process, close to its union with the horizontal part, are the lesser palatine foramina for the transmis- sion of the posterior and middle palatine nerves. The Orbital Process (processus orbitalis).—The orbital process is placed on a higher level than the sphenoidal, and is directed upward and lateralward from the front of the vertical part, to which it is connected by a constricted neck. It presents five surfaces, which enclose an air cell. Of these surfaces, three are articu- lar and two non-articular. The articular surfaces are: (1) the anterior or maxillary, directed forward, lateralward, and downward, of an oblong form, and rough for articulation with the maxilla; (2) the posterior or sphenoidal, directed backward, upward, and medialward; it presents the opening of the air cell, which usually communicates with the sphenoidal sinus; tli'e margins of the opening are serrated for articulation with the sphenoidal concha; (3) the medial or ethmoidal, directed forward, articulates with the labyrinth of the ethmoid. In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells. More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal sinus. The non-articular surfaces are: (1) the superior or orbital, directed upward and lateralward; it is triangular in shape, and forms the back part of the floor of the orbit; and (2) the lateral, of an oblong form, directed toward the pterygopalatine fossa; it is separated THE INFERIOR NASAL CONCHA 169 from the orbital surface by a rounded border, which enters into the formation of the inferior orbital fissure. The Sphenoidal Process {'processus sphenoidalis).—The sphenoidal process is a thin, compressed plate, much smaller than the orbital, and directed upward and medialward. It presents three surfaces and two borders. The superior surface articulates with the root of the pterygoid process and the under surface of the sphenoidal concha, its medial border reaching as far as the ala of the vomer; it presents a groove which contributes to the formation of the pharyngeal canal. The medial surface is concave, and forms part of the lateral wall of the nasal cavity. The lateral surface is divided into an articular and a non-arti'cular portion: the former is rough, for articulation with the medial pterygoid plate; the latter is smooth, and forms part of the pterygopalatine fossa. The anterior border forms the posterior boundary of the sphenopalatine notch. The posterior border, ser- rated at the expense of the outer table, articulates with the medial pterygoid plate. The orbital and sphenoidal processes are separated from one another by the sphenopalatine notch. Sometimes the two processes are united above, and form between them a complete foramen (Fig. 168), or the notch may be crossed by one or more spicules of bone, giving rise to two or more foramina. Ossification.—The palatine bone is ossified in membrane from a single center, which makes its appearance about the sixth or eighth week of fetal life at the angle of junction of the two parts of the bone. From this point ossification spreads medialward to the horizontal part, downward into the pyramidal process, and upward into the vertical part. Some authorities describe the bone as ossifying from four centers: one for the pyramidal process and portion of the vertical part behind the pterygopalatine groove; a second for the rest of the vertical and the horizontal parts; a third for the orbital, and a fourth for the sphenoidal process. At the time of birth the height of the vertical part is about equal to the transverse width of the horizontal part, whereas in the adult the former measures about twice as much as the latter. Articulations.—The palatine articulates with six bones: the sphenoid, ethmoid, maxilla, inferior nasal concha, vomer, and opposite palatine. The Inferior Nasal Concha (Concha Nasalis Inferior; Inferior Turbinated Bone). The inferior nasal concha extends horizontally along the lateral wall of the nasal cavity (Fig. 170) and consists of a lamina of spongy bone, curled upon itself like a scroll. It has two surfaces, two borders, and two extremities. The medial surface (Fig. 171) is convex, perforated by numerous apertures, and traversed by longitudinal grooves for the lodgement of vessels. The lateral surface is concave (Fig. 172), and forms part of the inferior meatus. Its upper border is thin, irregular, and connected to various bones along the lateral wall of the nasal cavity. It may be divided into three portions: of these, the anterior articulates with the conchal crest of the maxilla; the posterior with the conchal crest of the palatine; the middle portion presents three well-marked processes, which vary much in their size and form. Of these, the anterior or lacrimal process is small and pointed and is situated at the junction of the anterior fourth with the posterior three-fourths of the bone: it articulates, by its apex, with the descend- ing process of the lacrimal bone, and, by its margins, with the groove on the back of the frontal process of the maxilla, and thus assists in forming the canal for the nasolacrimal duct. Behind this process a broad, thin plate, the ethmoidal process, ascends to join the uncinate process of the ethmoid; from its lower border a thin lamina, the maxillary process, curves downward and lateralward; it articulates with the maxilla and forms a part of the medial wall of the maxillary sinus. The inferior border is free, thick, and cellular in structure, more especially in the middle of the bone. Both extremities are more or less pointed, the posterior being the more tapering. 170 OSTEOLOGY Ossification.—The inferior nasal concha is ossified from a single center, which appears about the fifth month of fetal life in the lateral wall of the cartilaginous nasal capsule. Articulations.—The inferior nasal concha articulates with four bones: the ethmoid, maxilla, lacrimal, and palatine. Frontal sinus Crista galli Sella turcica Uncinate process ~ oj ethmoid Openings into maxillary sinus Medial 'pterygoid plate Pterygoid hamulus Fig. 170.—Lateral wall of right nasal cavity showing inferior concha in situ. Fig. 171.—Right inferior nasal concha. Medial surface. Fio. 172.—Right inferior nasal concha. Lateral surface. The Vomer The vomer is situated in the median plane, but its anterior portion is frequently bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum (Fig. 173); it has two surfaces and four borders. The surfaces (Fig. 174) are marked by small furrows for blood- vessels, and on each is the nasopalatine groove, which runs obliquely downward and forward, and lodges the nasopalatine nerve and vessels. The superior border, the thickest, presents a deep furrow, bounded on either side by a horizontal pro- jecting ala of bone; the furrow receives the rostrum of the sphenoid, while the margins of the alee articulate with the vaginal processes of the medial pterygoid plates of the sphenoid behind, and with the sphenoidal processes of the palatine bones in front. The inferior border articulates with the crest formed by the maxillae THE VOMER 171 and palatine bones. The anterior border is the longest and slopes downward and forward. Its upper half is fused with the perpendicular plate of the ethmoid; its lower half is grooved for the inferior margin of the septal cartilage of the nose. The posterior border is free, concave, and separates the choanse. It is thick and bifid above, thin below. Rostrum of sphenoid Crest of nasal bones- Frontal spine • Space for triangular cartilage of septum .Crest of palatines 'Crest of maxillae Fig. 173.—Median wall of left nasal cavity showing vomer in situ. Ossification.—At an early period the septum of the nose consists of a plate of cartilage, the ethmovomerine cartilage. The postero-superior part of this cartilage is ossified to form the per- pendicular plate of the ethmoid; its antero-inferior portion persists as the septal cartilage, while the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centers, one on either side of the middle line, appear about the eighth week of fetal life in this part of the membrane, and hence the vomer consists primarily of two lamella:. About the third month Fig. 174.—The vomer. Fia. 175.—Vomer of infant. these unite below, and thus a deep groove is formed in which the cartilage is lodged. As growth proceeds, the union of the lamellae extends upward and forward, and at the same time the intervening plate of cartilage undergoes absorption. By the age of puberty the lamellae are almost completely united to form a median plate, but evidence of the bilaminar origin of the bone is seen in the everted alae of its upper border and the groove on its anterior margin. 172 OSTEOLOGY Articulations.—The vomer articulates with six bones: two of the cranium, the sphenoid and ethmoid; and four of the face, the two maxill® and the two palatine bones; it also articulates with the septal cartilage of the nose. The Mandible (Mandibula; Inferior Maxillary Bone; Lower Jaw). The mandible, the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles. The Body (corpus mandibulce).—The body is curved somewhat like a horseshoe, and has two surfaces and two borders. Surfaces.—The external surface (Fig. 17G) is marked in the median line by a faint ridge, indicating the symphysis or line of junction of the two pieces of which the bone is composed at an early period of life. This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is de- Coronoid process Condyle TEMPORALIS ~ Mental protuberance Groove for external maxillary artery -Angle Fig. 176.—Mandible. Outer surface. Side view. pressed in the center but raised on either side to form the mental tubercle. On either side of the symphysis, just below the incisor teeth, is a depression, the incisive fossa, which gives origin to the Mentalis and a small portion of the Orbicularis oris. Below the second premolar tooth, on either side, midway between the upper and lower borders of the body, is the mental foramen, for the passage of the mental vessels and nerve. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus; it affords attachment to the Quadratus labii inferioris and Triangularis; the Platysma is attached below it. The internal surface (Fig. 177) is concave from side to side. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the Genioglossi. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the Geniohyoidei. In some cases the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Above the mental spines a median foramen and furrow are some- times seen; they mark the line of union of the halves of the bone. Below the mental THE MANDIBLE 173 spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the Digastricus. Extending upward and backward on either side from the lower part of the symphysis is the mylohyoid line, which gives origin to the Mylohyoideus; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the Constrictor pharyngis superior, and to the pterygomandibular raphe. Above the anterior part of this line is a smooth triangular area against which the sublingual gland rests, and below the hinder part, an oval fossa for the submaxillary gland. Borders.—The superior or alveolar border, wider behind than in front, is hollowed into cavities, for the reception of the teeth; these cavities are sixteen in number, and vary in depth and size according to the teeth which they contain. To the outer lip of the superior border, on either side, the Buccinator is attached as far forward as the first molar tooth. The inferior border is rounded, longer than the superior, and thicker in front than behind; at the point where it joins the lower border of the ramus a shallow groove; for the external maxillary artery, may be present. Genio- glossua Genio- hyoideus Mylohyoid line BODY Fig. 177.—Mandible. Inner surface. Side view. The Ramus (ramus mandibulce; perpendicular portion).—The ramus is quadri- lateral in shape, and has two surfaces, four borders, and two processes. Surfaces.—The lateral surface (Fig. 176) is flat and marked by oblique ridges at its lower part; it gives attachment throughout nearly the whole of its extent to the Masseter. The medial surface (Fig. 177) presents about its center the oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. The margin of this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula mandibulse, which gives attachment to the sphenomandibular ligament; at its lower and back part is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylo- hyoid vessels and nerve. Behind this groove is a rough surface, for the insertion of the Pterygoideus internus. The mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. 174 OSTEOLOGY In the posterior two-thirds of the bone the canal is situated nearer the internal surface of the mandible; and in the anterior third, nearer its external surface. It contains the inferior alveolar vessels and nerve, from which branches are dis- tributed to the teeth. The lower border of the ramus is thick, straight, and con- tinuous with the inferior border of the body of the bone. At its junction with the posterior bonier is the angle of the mandible, which may be either inverted or everted and is marked by rough, oblique ridges on each side, for the attachment of the Masseter laterally, and the Pterygoideus internus medially; the stylomandibular ligament is attached to the angle between these muscles. The anterior border is thin above, thicker below, and continuous with the oblique line. The posterior border is thick, smooth, rounded, and covered by the parotid gland. The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the mandibular notch. The Coronoid Process (processus coronoideus) is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuous below with the anterior border of the ramus; its posterior border is concave and forms the anterior boundary of the mandibular notch. Its lateral surface is smooth, and affords insertion to the Temporalis and Masseter. Its medial surface gives insertion to the Temporalis, and presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth. Between this ridge and the anterior border is a grooved triangular area, the upper part of which gives attachment to the Temporalis, the lower part to some fibers of the Buccinator. The Condyloid Process (processus condyloideus) is thicker than the coronoid, and consists of two portions: the condyle, and the constricted portion which sup- ports it, the neck. The condyle presents an articular surface for articulation with the articular disk of the temporomandibular joint; it is convex from before back- ward and from side to side, and extends farther on the posterior than on the ante- rior surface. Its long axis is directed medialward and slightly backward, and if prolonged to the middle line will meet that of the opposite condyle near the ante- rior margin of the foramen magnum. At the lateral extremity of the condyle is a small tubercle for the attachment of the temporomandibular ligament. The neck is flattened from before backward, and strengthened by ridges which descend from the forepart and sides of the condyle. Its posterior surface is convex; its anterior presents a depression for the attachment of the Pterygoideus externus. The mandibular notch, separating the two processes, is a deep semilunar depres- sion, and is crossed by the masseteric vessels and nerve. Ossification.—The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckel’s cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see p. 66), and are two in number, a right and a left. Their proximal or cranial ends are connected with the ear capsules, and their distal extremities are joined to one another at the symphysis by mesodermal tissue. They run forward immediately below the condyles and then, bending downward, lie in a groove near the lower border of the bone; in front of the canine tooth they incline upward to the symphysis. From the proximal end of each cartilage the malleus and incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular ligament. Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. Ossification takes place in the membrane covering the outer surface of the ventral end of Meckel’s cartilage (Figs. 178 to 181), and each half of the bone is formed from a single center which appears, near the mental foramen, about the sixth week of fetal life. By the tenth week the portion of Meckel’s cartilage which lies below and behind the incisor teeth is surrounded and invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- ance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei in the front part of both alveolar walls and along the front of the lower border of the bone. These accessory nuclei possess no separate ossific centers, but are invaded by the surrounding membrane THE MANDIBLE 175 bone and undergo absorption. The inner alveolar border, usually described as arising from a separate ossific center (splenial center), is formed in the human mandible by an ingrowth from the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first year. The foregoing description of the ossification of the mandible is based on the researches of Low1 and Fawcett,2 and differs somewhat from that usually given. Articulations.—The mandible articulates with the two temporal bones. ,Lingual nerve Inf. alveolar n. Mental nerve Inf. alveolar n. Lingual nerve Auriculo- temporal n. Stapes "Chorda tympani -Facial nerve. Facial nerve Mylohyoid nerve Mylohyoid nerve Chorda tympani Reichert's cartilage Fig. 178.—Mandible of human embryo 24 mm. long. Outer aspect. (From model by Low.) Fig. 179.—Mandible of human embryo 24 mm. long. Inner aspect. (From model by Low.) Mandibular nerve Meckel's cartilage Mental nerve Fig. 180.—Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled (From model by Low.) Anterior process of malleus Auriculotemporal nerve Lingual nerve Meckel’s cartilage Inf. alveolar nerve Ant. process of malleus Chorda tympani Fig. 181.—Mandible of human embryo 95 mm. long. Inner aspect. Nuclei of cartilage stippled, (From model by Low.) Symphysis Mylohyoid nerve CHANGES PRODUCED IN THE MANDIBLE BY AGE At birth (Fig, 182) the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal is of large size, and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process is of comparatively large size, and projects above the level of the condyle. 1 Proceedings of the Anatomical and Anthropological Society of the University of Aberdeen, 1905, and Journal of Anatomy and Physiology, vol. xliv. 2 Journal of the American Medical Association, September 2, 1905. OSTEOLOGY 176 Fig. 182.—At birth. Fig. 183.—In childhood. Fig. 184.—In the adult. Fig. 185.—In old age. Side view of the mandible at different periods of life. THE HYOID BONE 177 After birth (Fig. 183) the two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but more especially behind the mental foramen, to provide space for the three additional teeth devel- oped in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles; but the alveolar portion is the deeper of the two, and, consequently, the chief part of the body lies above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the mylohyoid line; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°. In the adult (Fig. 184) the alveolar and subdental portions of the body are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°. In old age (Fig. 185) the bone becomes greatly reduced -in size, for with the loss of the teeth the alveolar process is absorbed, and, consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is close to the alveolar border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the condyle is more or less bent backward. The Hyoid Bone (Os Hyoideum; Lingual Bone). The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It consists of five segments, viz., a body, two greater cornua, and two lesser cornua. The Body or Basihyal (corpus oss. hyoidei).—The body or central part is of a quadrilateral form. Its anterior surface (Fig. 186) is convex and directed forward and upward. It is crossed in its upper half by a well-marked transverse ridge with a slight downward convexity, and in many cases a vertical median ridge divides it into two lateral halves. The portion of the vertical ridge above the transverse line is present in a majority of specimens, but the lower por- tion is evident only in rare cases. The anterior surface gives insertion to the Genio- hyoideus in the greater part of its extent both above and below the transverse ridge; a portion of the origin of the Hyoglossus notches the lateral margin of the Geniohyoideus attachment. Below the transverse ridge the Mylo- hyoideus, Sternohyoideus, and Omohyoideus are inserted. The posterior surface is smooth, concave, directed backward and downward, and separated from the epi- glottis by the hyothyroid membrane and a quantity of loose areolar tissue; a bursa intervenes between it and the hyothyroid membrane. The superior border is rounded, and gives attachment to the hyothyroid membrane and some aponeurotic fibers of the Genioglossus. The inferior border affords insertion medially to the Sternohyoideus and laterally to the Omohyoideus and occasionally a portion of the Thyreohyoideus. It also gives attachment to the Levator glandulse thyreoidese, when this muscle is present. In early life the lateral borders are connected to the greater cornua by synchondroses; after middle life usually by bony union. cornu Constrictor Pharyngis Mebius. Hyoglossgs Lessor cornu Chonbroglossus Genioglossus DlGASTRICtTS & STYLOHYOIBEUS Body THYREOHYOIDEC0 OMOHYOIBEUS Geniohyoideus Fio. 186.—Hyoid bone. Anterior surface. Enlarged. Mylohyoibeus Sternohyoibeus 178 OSTEOLOGY The Greater Cornua or Thyrohyals (cornua majora).—The greater cornua project backward from the lateral borders of the body; they are flattened from above downward and diminish in size from before backward; each ends in a tubercle to which is fixed the lateral hyothyroid ligament. The upper surface is rough close to its lateral border, for muscular attachments: the largest of these are the origins of the Ilyoglossus and Constrictor pharyngis medius which extend along the whole Jength of the cornu; the Pigastricus and Stylohyoideus have small insertions in front of these near the junction of the body with the cornu. To the medial border the hyothyroid membrane is attached, while the anterior half of the lateral border gives insertion to the Thyreohyoideus. The Lesser Cornua or Ceratohyals (cornua minora).—The lesser cprnu are two small, conical eminences, attached by their bases to the angles of junction between the body and greater cornua. They are connected to the body of the bone by fibrous tissue, and occasionally to the greater cornua by distinct diarthrodial joints, which usually persist throughout life, but occasionally become ankylosed. The lesser cornua are situated in the line of the transverse ridge on the body and appear to be morphological continuations of it (Parsons1). The apex of each cornu gives attachment to the stylohyoid ligament;2 the Chondroglossus rises from the medial side of the base. Ossification.—The hyoid is ossified from six centers: two for the body, and one for each cornu. Ossification commences in the greater cornua toward the end of fetal life, in the body shortly afterward, and in the lesser cornua during the first or second year after birth. THE EXTERIOR OF THE SKULL. The skull as a whole may be viewed from different points, and the views so obtained are termed the normse of the skull; thus, it may be examined from above (norma verticalis), from below (norma basalis), from the side (norma lateralis), from behind (norma occipitalis), or from the front (norma frontalis). Norma Verticalis.—When viewed from above the outline presented varies greatly in different skulls; in some it is more or less oval, in others more nearly circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, nearly transverse in direction, between the frontal and parietals; (2) the sagittal sutures, medially placed, between the parietal bones, and deeply serrated in its anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the parietals and the occipital. The point of junction of the sagittal and coronal suture is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they indicate respectively the positions of the anterior and posterior fontanelles in the fetal skull. On either side of the sagittal suture are the parietal eminence and parietal foramen—the latter, however, is frequently absent on one or both sides. The skull is often somewhat flattened in the neighborhood of the parietal foramina, and the term obelion is applied to that point of the sagittal suture which is on a level with the foramina. In front is the glabella, and on its lateral aspects are the superciliary arches, and above these the frontal eminences. Immediately above the glabella may be seen the remains of the frontal suture; in a small percentage of skulls this suture persists and extends along the middle line to the bregma. Passing backward and upward from the zygomatic processes of the frontal bone are the temporal lines, which mark the upper limits of the temporal fossae. The zygomatic arches may or may not be seen projecting beyond the anterior portions of these lines. 1 See article on “The Topography and Morphology of the Human Hyoid Bone,” by F. G. Parsons, Journal of Anatomy and Physiology, vol. xliii. 2 These ligaments in many animals are distinct bones, and in man may undergo partial ossification. THE EXTERIOR OF THE SKULL 179 Norma Basalis (Fig. 187).—The inferior surface of the base of the skull, exclu- sive of the mandible, is bounded in front by the incisor teeth in the maxillae; behind, Incisors Canine Incisive canal Prcemolars Transmits left tiasopalatine nerve Transmits descending palatine vessels Transmits right nasopalatine nerve Lesser palatine foramina Posterior nasal spine Musculus uvulae Pterygoid hamulus Sphenoidal process of palatine Pharyngeal canal Tensor tympani Pharyngeal tubercle Situation of auditory tube and semicanal for Tensor tympani Tensor veil palatini Inferior tympanic canaliculus Aquaeductus cochleae ' Jugular foramen Mastoid canaliculus Tympanomastoid fissure Fora/men Fig. 187.—Base of skull. Inferior surface. 180 OSTEOLOGY by the superior nuchal lines of the occipital; and laterally by the alveolar arch, the lower border of the zygomatic bone, the zygomatic arch and an imaginary line extending from it to the mastoid process and extremity of the superior nuchal line of the occipital. It is formed by the palatine processes of the maxillae and palatine bones, the vomer, the pterygoid processes, the under surfaces of the great wings, spinous processes, and part of the body of the sphenoid, the under surfaces of the squamae and mastoid and petrous portions of the temporals, and the under surface of the occipital bone. The anterior part or hard palate projects below the level of the rest of the surface, and is bounded in front and laterally by the alveolar arch containing the sixteen teeth of the maxillae. Immediately behind the incisor teeth is the incisive foramen. In this foramen are two lateral apertures, the openings of the incisive canals (foramina of Stenson) which transmit the anterior branches of the descending palatine vessels, and the nasopalatine nerves. Occasionally two additional canals are present in the incisive foramen; they are termed the foramina of Scarpa and are situated in the middle line; when present they transmit the nasopalatine nerves. The vault of the hard palate is concave, uneven, perforated by numerous foramina, marked by depressions for the palatine glands, and traversed by a crucial suture formed by the junction of the four bones of which it is composed. In the young skull a suture may be seen ex- tending on either side from the incisive foramen to the interval between the lateral incisor and canine teeth, and marking off the os incisivum or premaxillary bone. At either posterior angle of the hard palate is the greater palatine foramen, for the transmission of the descending palatine vessels and anterior palatine nerve; and running forward and medialward from it a groove, for the same vessels and nerve. Behind the posterior palatine foramen is the pyramidal process of the palatine bone, perforated by one or more lesser palatine foramina, and marked by the commence- ment of a transverse ridge, for the attachment of the tendinous expansion of the Tensor veli palatini. Projecting backward from the center of the posterior border of the hard palate is the posterior nasal spine, for the attachment of the Musculus uvulse. Behind and above the hard palate are the choanae, measuring about 2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are separated from one another by the vomer, and each is bounded above by the body of the sphenoid, below by the horizontal part of the palatine bone, and laterally by the medial pterygoid plate of the sphenoid. At the superior border of the vomer may be seen the expanded alse of this bone, receiving between them the ros- trum of the sphenoid. Near the lateral margins of the alse of the vomer, at the roots of the pterygoid processes, are the pharyngeal canals. The pterygoid process presents near its base the pterygoid canal, for the transmission of a nerve and artery. The medial pterygoid plate is long and narrow; on the lateral side of its base is the scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity the hamulus, around which the tendon of this muscle turns. The lateral pterygoid plate is broad; its lateral surface forms the medial boundary of the infratemporal fossa, and affords attachment to the Pterygoideus externus. Behind the nasal cavities is the basilar portion of the occipital bone, presenting near its center the pharyngeal tubercle for the attachment of the fibrous raphe of the pharynx, with depressions on either side for the insertions of the Rectus capitis anterior and Longus capitis. At the base of the lateral pterygoid plate is the foramen ovale, for the transmission of the mandibular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve; behind this are the foramen spinosum which transmits the middle meningeal vessels, and the promi- nent spina angularis (sphenoidal spine), which gives attachment to the spheno- mandibular.ligament and the Tensor veli palatini. Lateral to the spina angularis is the mandibular fossa, divided into two parts by the petrotympanic fissure; the anterior portion, concave, bounded in front by the articular tubercle, THE EXTERIOR OF THE SKULL 181 serves for the articulation of the condyle of the mandible; the posterior portion, rough and bounded behind by the tympanic part of the temporal, is sometimes occupied by a part of the parotid gland. Emerging from between the laminae of the vaginal process of the tympanic part is the styloid process; and at the base of this process is the stylomastoid foramen, for the exit of the facial nerve, and entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between the tympanic part and the mastoid process, is the tympanomastoid fissure, for the auricular branch of the vagus. Upon the medial side of the mastoid process is the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, the occipital groove for the occipital artery. At the base of the medial pterygoid plate is a large and somewhat triangular aperture, the foramen laceram, bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and medially by the body of the sphenoid and basilar portion of the occipital bone; it presents in front the posterior orifice of the ptery- goid canal; behind, the aperture of the carotid canal. The lower part of this opening is filled up in the fresh state by a fibrocartilaginous plate, across the upper or cerebral surface of wrhich the internal carotid artery passes. Lateral to this aperture is a groove, the sulcus tubae auditivse, between the petrous part of the temporal and the great wing of the sphenoid. This sulcus is directed lateralward and backward from the root of the medial pterygoid plate and lodges the cartilaginous part of the auditory tube; it is continuous behind with the canal in the temporal bone which forms the bony part of the same tube. At the bottom of this sulcus is a narrow cleft, the petrosphenoidal fissure, which is occupied, in the fresh condition, by a plate of cartilage. Behind this fissure is the under surface of the petrous portion of the temporal bone, presenting, near its apex, the quadrilateral rough surface, part of which affords attachment to the Levator veli palatini; lateral to this surface is the orifice of the carotid canal, and medial to it, the depression leading to the aquseductus cochleae, the former transmitting the internal carotid artery and the carotid plexus of the sympathetic, the latter serving for the passage of a vein from the cochlea. Behind the carotid canal is the jugular foramen, a large aperture, formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side, and may be subdivided into three compartments. The anterior compartment transmits the inferior petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory nerves; the posterior, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries. On the ridge of bone dividing the carotid canal from the jugular foramen is the inferior tympanic canaliculus for the transmission of the tympanic branch of the glossopharyngeal nerve; and on the wall of the jugular foramen, near the root of the styloid process, is the mastoid canaliculus for the passage of the auricular branch of the vagus nerve. Extending forward from the jugular foramen to the foramen lacerum is the petrooccipital fissure occupied, in the fresh state, by a plate of cartilage. Behind the basilar portion of the occipital bone is the foramen magnum, bounded laterally by the occipital condyles, the medial sides of which are rough for the attachment of the alar ligaments. Lateral to each condyle is the jugular process which gives attachment to the Rectus capitis lateralis muscle and the lateral atlantooccipital ligament. The foramen magnum transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the ligaments connecting the occipital bone with the axis. The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion. In front of each condyle is the canal for the passage of the hypoglossal nerve and a meningeal artery. Behind each condyle is the condyloid fossa, perforated on one or both sides by the condyloid canal, for the transmission of a vein from the transverse sinus. Behind the foramen magnum 182 OSTEOLOGY is the median nuchal line ending above at the external occipital protuberance, while on either side are the superior and inferior nuchal lines; these, as well as the surfaces of bone between them, are rough for the attachment of the muscles which are enumerated on pages 129 and 130. Norma Lateralis (Fig. 188).’—When viewed from the side the skull is seen to consist of the cranium above and behind, and of the face below and in front. The cranium is somewhat ovoid in shape, but its contour varies in different cases and depends largely on the length and height of the skull and on the degree of promi- nence of the superciliary arches and frontal eminences. Entering into its formation are the frontal, the parietal, the occipital, the temporal, and the great wing of the Fig. 188.—Side view of the skull. sphenoid. These bones are joined to one another and to the zygomatic by the follow- ing sutures: the zygomaticotemporal between the zygomatic process of the temporal and the temporal process of the zygomatic; the zygomaticofrontal uniting the zygo- matic bone with the zygomatic process of the frontal; the sutures surrounding the great wing of the sphenoid, viz., the sphenozygomatic in front, the sphenofrontal and sphenoparietal above, and the sphenosquamosal behind. The sphenoparietal suture varies in length in different skulls, and is absent in those cases where the frontal articulates with the temporal squama. The point corresponding with the posterior end of the sphenoparietal suture is named the pterion; it is situated about 3 cm. behind, and a little above the level of the zygomatic process of the frontal bone. THE EXTERIOR OF THE SKULL 183 The squamosal suture arches backward from the pterion and connects the tem- poral squama with the lower border of the parietal: this suture is continuous behind with the short, nearly horizontal parietomastoid suture, which unites the mastoid process of the temporal with the region of the mastoid angle of the parietal. Extending from above downward and forward across the cranium are the coronal and lambdoidal sutures; the former connects the parietals with the frontal, the latter, the parietals with the occipital. The lambdoidal suture is continuous below with the occipitomastoid suture between the occipital and the mastoid portion of the temporal. In or near the last suture is the mastoid foramen, for the transmission of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, and lambdoidal sutures is known as the asterion. Immediately above the orbital margin is the superciliary arch, and, at a higher level, the frontal eminence. Near the center of the parietal bone is the parietal eminence. Posteriorly is the ex- ternal occipital protuberance, from which the superior nuchal line may be followed forward to the mastoid process. Arching across the side of the cranium are the temporal lines, which mark the upper limit of the temporal fossa. The Temporal Fossa (fossa temporalis).—The temporal fossa is'bounded above and behind by the temporal lines, which extend from the zygomatic process of the frontal bone upward and backward across the frontal and parietal bones, and then curve downward and forward to become continuous with the supramastoid crest and the posterior root of the zygomatic arch. The point where the upper temporal line cuts the coronal suture is named the stephanion. The temporal fossa is bounded in front by the frontal and zygomatic bones, and opening on the back of the latter is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic arch, formed by the zygomatic and temporal bones; below, it is separated from the infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, and by a ridge, continuous with this crest, which is carried backward across the temporal squama to the anterior root of the zygomatic process. In front and below, the fossa communicates with the orbital cavity through the inferior orbital or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and temporal bones. It is traversed by vascular furrows; one, usually well-marked, runs upward above and in front of the external acoustic meatus, and lodges the middle temporal artery. Two others, frequently indistinct, may be observed on the anterior part of the floor, and are for the anterior and posterior deep temporal arteries. The temporal fossa contains the Temporalis muscle and its vessels and nerves, together with the zygomaticotemporal nerve. The zygomatic arch is formed by the zygomatic process of the temporal and the temporal process of the zygomatic, the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible. The zygomatic process of the temporal arises by two roots, an anterior, directed inward in front of the mandibular fossa, where it expands to form the articular tubercle, and a posterior, which runs backward above the external acoustic meatus and is continuous with the supramastoid crest. The upper border of the arch gives attachment to the temporal fascia; the lower border and medial surface give origin to the Masseter. Below the posterior root of the zygomatic arch is the elliptical orifice of the external acoustic meatus, bounded in front, below, and behind by the tympanic part of the temporal bone; to its outer margin the cartilaginous segment of the external acoustic meatus is attached. The small triangular area between the posterior root of the zygomatic arch and the postero-superior part of the orifice is termed the suprameatal triangle, on the anterior border of which a small spinous process, the suprameatal spine, is sometimes seen. Between the tympanic part and the articular tubercle is the mandibular fossa, divided into twm parts by the 184 OSTEOLOGY petrotympanic fissure. The anterior and larger part of the fossa articulates with the condyle of the mandible and is limited behind by the external acoustic meatus: the posterior part sometimes lodges a portion of the parotid gland. The styloid process extends downward and forward for a variable distance from the lower part of the tympanic part, and gives attachment to the Styloglossus, Stylohy- oideus, and Stylopharyngeus, and to the stylohyoid and stylomandibular ligaments. Projecting downward behind the external acoustic meatus is the mastoid process, to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis are attached. The Infratemporal Fossa (fossa infratemporalis; zygomatic fossa) (Fig. 189).—The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla External acoustic meatus Tympanic part of temporal Inferior orbital fissure Mandibular cavity Styloid process Pterygomaxillary fissure Infratemporal crest Zygomatic process {cut) Lateral pterygoid plate Pterygoid hamulus Fig. 189.—Left infratemporal fossa. and the ridge which descends from its zygomatic process; behind, by the articular tubercle of the temporal and the spina angularis of the sphenoid; above, by the great wing of the sphenoid below the infratemporal crest, and by the under surface of the temporal squama; below, by the alveolar border of the maxilla; medially, by the lateral pterygoid plate. It contains the lower part of the Temporalis, the Pterygoidei internus and externus, the internal maxillary vessels, and the man- dibular and maxillary nerves. The foramen ovale and foramen spinosum open on its roof, and the alveolar canals on its anterior wall. At its upper and medial part are two fissures, which together form a T-shaped fissure, the horizontal limb being named the inferior orbital, and the vertical one the pterygomaxillary. The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), horizontal in direction, opens into the lateral and back part of the orbit. It is bounded above by the lower border of the orbital surface of the great wing of the THE EXTERIOR OF THE SKULL 185 sphenoid; below, by the lateral border of the orbital surface of the maxilla and the orbital process of the palatine bone; laterally, by a small part of the zygomatic bone :x medially, it joins at right angles with the pterygomaxillary fissure. Through the inferior orbital fissure the orbit communicates with the temporal, infratem- poral, and pterygopalatine fossae; the fissure transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, the ascending branches from the sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein with the pterygoid venous plexus. The pterygomaxillary fissure is vertical, and descends at right angles from the medial end of the preceding; it is a triangular interval, formed by the diver- gence of the maxilla from the pterygoid process of the sphenoid. It connects the infratemporal with the pterygopalatine fossa, and transmits the terminal part of the internal maxillary artery. The Pterygopalatine Fossa (fossa pterygopalatina; sphenomaxillary fossa).—The pterygopalatine fossa is a small, triangular space at the angle of junction of the inferior orbital and pterygomaxillary fissures, and placed beneath the apex of the orbit. It is bounded above by the under surface of the body of the sphenoid and by the orbital process of the palatine bone; in front, by the infratemporal surface of the maxilla; behind, by the base of the pterygoid process and lower part of the anterior surface of the great wing of the sphenoid; medially, by the vertical part of the palatine bone with its orbital and sphenoidal processes. This fossa communicates with the orbit by the inferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by the pterygo- maxillary fissure. Five foramina open into it. Of these, three are on the posterior wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, in this order downward and medialward. On the medial wall is the sphenopalatine foramen, and below is the superior orifice of the pterygopalatine canal. The fossa contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part of the internal maxillary artery. Norma Occipitalis.—When viewed from behind the cranium presents a more or less circular outline. In the middle line is the posterior part of the sagittal suture connecting the parietal bones; extending downward and lateralward from the hinder end of the sagittal suture is the deeply serrated lambdoidal suture join- ing the parietals to the occipital and continuous below with the parietomastoid and occipitomastoid sutures; it frequently contains one or more sutural bones. Near the middle of the occipital squama is the external occipital protuberance or inion, and extending lateralward from it on either side is the superior nuchal line, and above this the faintly marked highest nuchal line. The part of the squama above the inion and highest lines is named the planum occipitale, and is covered by the Occipitalis muscle; the part below is termed the planum nuchale, and is divided by the median nuchal line which runs downward and forward from the inion to the foramen magnum; this ridge gives attachment to the ligamentum nuchae. The muscles attached to the planum nuchale are enumerated on p. 130. Below and in front are the mastoid processes, convex laterally and grooved medially by the mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for the passage of the mastoid emissary vein. Norma Frontalis (Fig. 190).—When viewed from the front the skull exhibits a somewhat oval outline, limited above by the frontal bone, below by the body of the mandible, and laterally by the zygomatic bones and the mandibular rami. The upper part, formed by the frontal squama, is smooth and convex. The lower part, made up of the bones of the face, is irregular; it is excavated laterally by the orbital cavities, and presents in the middle line the anterior nasal aperture leading to the 1 Occasionally the maxilla and the sphenoid articulate with each other at the anterior extremity of this fissure; the zygomatic is then excluded from it. 186 OSTEOLOGY nasal cavities, and below this the transverse slit between the upper and lower dental arcades. Above, the frontal eminences stand out more or less prominently, and beneath these are the superciliary arches, joined to one another in the middle by the glabella. On and above the glabella a trace of the frontal suture sometimes persists; beneath it is the frontonasal suture,* the mid-point of which is termed the nasion. Behind and below the frontonasal suture the frontal articulates with the frontal process of the maxilla and with the lacrimal. Arching transversely below the superciliary arches is the upper part of the margin of the orbit, thin and promi- Supraorbital foramen Superior orbital fissure Lamina papyracea of ethmoid — f - Lacrimal Inferior orbital fissure Zygomaticofacial foramen Infraorbital foramen , Nasal cavity Inferior nasal concha Mental foramen Fig. 190.—The skull from the front. nent in its lateral two-thirds, rounded in its medial third, and presenting, at the junction of these two portions, the supraorbital notch or foramen for the supra- orbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic process which articulates with the zygomatic bone, and from it the temporal line extends upward and backward. Below the frontonasal suture is the bridge of the nose, convex from side to side, concavo-convex from above downward, and formed by the two nasal bones supported in the middle line by the perpendicular plate of the ethmoid, and laterally by the frontal processes of the maxillae which are prolonged upward between the nasal and lacrimal bones and form the lower and THE EXTERIOR OF THE SKULL 187 medial part of the circumference of each orbit. Below the nasal bones and between the maxillae is the anterior aperture of the nose, pyriform in shape, with the narrow end directed upward. Laterally this opening is bounded by sharp margins, to which the lateral and alar cartilages of the nose are attached; below, the margins are thicker and curve medialward and forward to end in the anterior nasal spine. On looking into the nasal cavity, the bony septum which separates the nasal cavities presents, in front, a large triangular deficiency; this, in the fresh state, is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal cavity the anterior part of the inferior nasal concha is visible. Below and lateral to the anterior nasal aperture are the anterior surfaces of the maxillae, each perforated, near the lower margin of the orbit, by the infraorbital foramen for the Nasal bone Lacrtmal sulcus Zygomatic hone Maxilla Infraorbital groove Ant. ethmoidal cells Nasal septum Probe in Middle ethmoidal cells infundibulum -Inferior orbital fissure Superior nasal concha Post, ethmoidal cells Superior meatus _Palatine hone Sphenoidal hone Foramen rotundum Sphenoidal sinuses Foramen ovale Foramen spinosum Fig. 191.—Horizontal section of nasal and orbita cavities. Carotid canal passage of the infraorbital nerve and vessels. Below and medial to this foramen is the canine eminence separating the incisive from the canine fossa. Beneath these fossae are the alveolar processes of the maxillae containing the upper teeth, which overlap the teeth of the mandible in front. The zygomatic bone on either side forms the prominence of the cheek, the lower and lateral portion of the orbital cavity, and the anterior part of the zygomatic arch. It articulates medially with the maxilla, behind with the zygomatic process of the temporal, and above with the great wing of the sphenoid and the zygomatic process of the frontal; it is per- forated by the zygomaticofacial foramen for the passage of the zygomaticofacial nerve. On the body of the mandible is a median ridge, indicating the position of the symphysis; this ridge divides below to enclose the mental protuberance, the lateral angles of which constitute the mental tubercles. Below the incisor teeth 188 OSTEOLOGY is the incisive fossa, and beneath the second premolar tooth the mental foramen which transmits the mental nerve and vessels. The oblique line runs upward from the mental tubercle and is continuous behind with the anterior border of the ramus. The posterior border of the ramus runs downward and forward from the condyle to the angle, which is frequently more or less everted. The Orbits (orbitoe) (Fig. 190).—The orbits are two quadrilateral pyramidal cavi- ties, situated at the upper and anterior part of the face, their bases being directed forward and lateralward, and their apices backward and medial ward, so that their long axes, if continued backward, would meet over the body of the sphenoid. Each presents for examination a roof, a floor, a medial and a lateral wall, a base, and an apex. Frontal sinus Posterior ethmoidal foramen Anterior ethmoidal foramen" Orbital process of palatine. / Optic foramen Sphenopalatine foramen Sella turcica Probe in foramen rotundum Fossa for lacrimal sac Uncinate process _ of ethmoid Openings of maxillary sinus Probe in pterygoid canal Inferior nasal concha "Probe in pterygopalatine canal 'Palatine hone Lateral pterygoid plate Pyramidal process of palatine Fig. 192.—Medial wall of left orbit. The roof is concave, directed downward, and slightly forward, and formed in front by the orbital plate of the frontal; behind by the small wing of the sphenoid. It presents medially the trochlear fovea for the attachment of the cartilaginous pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal gland; and posteriorly, the suture between the frontal bone and the small wing of the sphenoid. The floor is directed upward and lateralward, and is of less extent than the roof; it is formed chiefly by the orbital surface of the maxilla; in front and laterally, by the orbital process of the zygomatic bone, and behind and medially, to a small extent, by the orbital process of the palatine. At its medial angle is the upper opening of the nasolacrimal canal, immediately to the lateral side of which is a depression for the origin of the Obliquus oculi inferior. On its lateral part is the suture between the maxilla and zygomatic bone, and at its posterior part that between the maxilla and the orbital process of the palatine. Running forward near the middle of the floor is the infraorbital groove, ending in front in the infra- orbital canal and transmitting the infraorbital nerve and vessels. THE INTERIOR OF THE SKULL 189 The medial wall (Fig. 192) is nearly vertical, and is formed from before back- ward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid in front of the optic foramen. Sometimes the sphenoidal concha forms a small part of this wall (see page 152). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimo- ethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which the lacrimal part of the Orbicularis oculi arises. At the junction of the medial wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and sphenofrontal sutures. The point of junction of the anterior border of the lacrimal with the frontal is named the dacryon. In the frontoethmoidal suture are the anterior and posterior ethmoidal foramina, the former transmitting the nasociliary nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and vessels. The lateral wall, directed medialward and forward, is formed by the orbital process of the zygomatic and the orbital surface of the great wing of the sphenoid; these are united by the sphenozygomatic suture which terminates below at the front end of the inferior orbital fissure. On the orbital process of the zygomatic bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which transmit the branches of the zygomatic nerve. Between the roof and the lateral wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves enter the orbital cavity, also some filaments from the cavernous plexus of the sympathetic and the orbital branches of the middle meningeal artery. Passing backward through the fissure are the ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the floor are separated posteriorly by the inferior orbital fissure which transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches from the sphenopalatine ganglion. The base of the orbit, quadrilateral in shape, is formed above by the supra- orbital arch of the frontal bone, in which is the supraorbital notch or foramen for the passage of the supraorbital vessels and nerve; below by the zygomatic bone and maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic bone and the zygomatic process of the frontal joined by the zygomaticofrontal suture; medially by the frontal bone and the frontal process of the maxilla united by the frontomaxillary suture. The apex, situated at the back of the orbit, corresponds to the optic foramen1 a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. It will thus be seen that there are nine openings communicating with each orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic foramen, and the canal for the nasolacrimal duct. THE INTERIOR OF THE SKULL. Inner Surface of the Skull-cap.—The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrow's for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several 1 Some anatomists describe the apex of the orbit as corresponding with the medial end of the superior orbital fissure. It seems better, however, to adopt the statement in the text, since the ocular muscles take origin around the optic foramen, and diverge from it to the bulb of the eye. 190 OSTEOLOGY depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present. It is crossed, in front, by the coronal suture, and behind by the lambdoidal, while the sagittal lies in the medial plane between the parietal bones. Upper Surface of the Base of the Skull (Fig. 193).—The upper surface of the base of the skull or floor of the cranial cavity presents three fossae, called the anterior, middle, and posterior cranial fossae. Anterior Fossa (fossa cranii anterior).-—The floor of the anterior fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and sup- port the frontal lobes of the cerebrum; they are convex and marked by depressions for the brain convolutions, and grooves for branches of the meningeal vessels. The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attach- ment of the falx cerebri; the foramen cecum, between the frontal bone and the crista galli of the ethmoid, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus; behind the foramen cecum, the crista galli, the free margin of which affords attachment to the falx cerebri; on either side of the crista galli, the olfactory groove formed by the cribriform plate, which supports the olfactory Tulb and presents foramina for the transmission of the olfactory nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfac- tory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned; the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve. Farther back in the middle line is the ethmoidal spine, bounded behind by a slight elevation separating two shallow lon- gitudinal grooves which support the olfactory lobes. Behind this is the anterior margin of the chiasmatic groove, running lateralward on either side to the upper margin of the optic foramen. The Middle Fossa (fossa cranii media).—The middle fossa, deeper than the pre- ceding, is narrow in the middle, and wide at the sides of the skull. It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; behind, by the superior angles of the petrous portions of the temporals and the dorsum sellse; laterally by the temporal squamae, sphenoidal angles of the parietals, and great wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. The middle part of the fossa presents, in front, the chiasmatic groove and tuber- culum sellse; the chiasmatic groove ends on either side at the optic foramen, which transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli. Behind the tuberculum selloe is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellse, the upper angles of which are surmounted by the posterior clinoid processes: these afford attachment to the tentorium cerebelli, and below each is a notch for THE INTERIOR OF THE SKULL 191 the abducent nerve. On either side of the sella turcica is the carotid groove, which is broad, shallow, and curved somewhat like the italic letter /. It begins behind Grooves for anter. meningeal vessels Groove for super, sagittal sinus For amen caecum Crista galli- Groove for nasociliary nerve Anterior ethmoidal foramen Slit for nasociliary nerve Posterior ethmoidal foramen Orifices for olfactory nerves Ethmoidal spine - Olfactory grooves - Chiasmatic groove Optic foramen- Anterior clinoid process Tuberculum sellae Middle clinoid process Posterior clinoid process Groove for abducent nerve Orifice of carotid canal Foramen lacerum Depression for semilunar ganglion Internal acoustic meatus Groove for superior petrosal sinus Slit for dura mater J ugular foramen Aquceductu8 vestibuli- Hypoglossal canal - Condyloid fora men F o v am e n AT a g n u ni Mastoid foramen Posterior meningeal grooves Fio. 193.—Base of the skull. Upper surface. at the foramen lacerum, and ends on the medial side of the anterior clinoid process, where it is sometimes converted into a foramen (carotico-clinoid) by the union of the anterior with the middle clinoid process; posteriorly, it is bounded laterally 192 OSTEOLOGY by the lingula. This groove lodges the cavernous sinus and the internal carotid artery, the latter being surrounded by a plexus of sympathetic nerves. The lateral parts of the middle fossa are of considerable depth, and support the temporal lobes of the brain. They are marked by depressions for the brain convolutions and traversed by furrows for the anterior and posterior branches of the middle meningeal vessels. These furrows begin near the foramen spinosum, and the anterior runs forward and upward to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs lateralward and backward across the temporal squama and passes on to the parietal near the middle of its lower border. The following apertures are also to be seen. In front is the superior orbital fissure, bounded above by the small wing, below, by the great wing, and medially, by the body of the sphenoid; it is usually completed laterally by the orbital plate of the frontal bone. It transmits to the orbital cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves, some filaments from the cavernous plexus of the sympathetic, and the orbital branch of the middle meningeal artery; and from the orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins. Behind the medial end of the superior orbital fissure is the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral to the foramen rotundum is the foramen ovale, which transmits the mandibular nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve.1 Medial to the foramen ovale is the foramen Vesalii, which varies in size in different individuals, and is often absent; when present, it opens below at the lateral side of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale is the foramen spinosum, for the passage of the middle meningeal vessels, and a recurrent branch from the mandibular nerve. Medial to the foramen ovale is the foramen lacerum; in the fresh state the lower part of this aperture is filled up by a layer of fibrocartilage, while its upper and inner parts transmit the internal carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the pterygoid canal and a meningeal branch from the ascending pharyngeal artery pierce the layer of fibrocartilage. On the anterior surface of the petrous portion of the temporal bone are seen the eminence caused by the projection of the superior semicircular canal; in front of and a little lateral to this a depression corresponding to the roof of the tympanic cavity; the groove leading to the hiatus of the facial canal, for the transmission of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery; beneath it, the smaller groove, for the pas- sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the depression for the semilunar ganglion and the orifice of the carotid canal. The Posterior Fossa (fossa cranii 'posterior).—The posterior fossa is the largest and deepest of the three. It is formed by the dorsum sella? and clivus of the sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. It is separated from the middle fossa in and near the median line by the dorsum sellae of the sphenoid and on either side by the superior angle of the petrous por- tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, is grooved for the superior petrosal sinus, and presents at its medial end a notch upon which the trigeminal nerve rests. The fossa is limited behind by the grooves for the transverse sinuses. In its center is the foramen magnum, on either side of which is a rough tubercle for the attachment of the alar ligaments; a little above this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal branch from the ascending pharyngeal artery. In front of the foramen magnum 1 See footnote, page 150. THE INTERIOR OF THE SKULL 193 the basilar portion of the occipital and the posterior part of the body of the sphenoid form a grooved surface which supports the medulla oblongata and pons; in the young skull these bones are joined by a synchondrosis. This grooved surface is separated on either side from the petrous portion of the temporal by the petro- occipital fissure, which is occupied in the fresh state by a plate of cartilage; the fissure is continuous behind with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal. The anterior portion of this foramen transmits the inferior petrosal sinus; the posterior portion, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Above the jugular foramen is the internal acoustic meatus, for the facial and acoustic nerves and internal auditory artery; behind and lateral Nasal bone r- Frontal process of maxilla Inf. nasal concha Pterygoid hamulus 1 Palatine bone Fig. 194.—Sagittal section of skull. to this is the slit-like opening leading into the aquseductus vestibuli, which lodges the ductus endolymphaticus; while between these, and near the superior angle of the petrous portion, is a small triangular depression, the remains of the fossa sub- arcuata, which lodges a process of the dura mater and occasionally transmits a small vein. Behind the foramen magnum are the inferior occipital fossae, which support the hemispheres of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinus. The posterior fossae are surmounted by the deep grooves for the transverse sinuses. Each of these channels, in its passage to the jugular foramen, grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, and ends at the back part of the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen; and, just previous to its termina- tion, the condyloid canal opens into it; neither opening is constant. 194 OSTEOLOGY The Nasal Cavity (cavum nasi; nasal fossa).—The nasal cavities are two irregular spaces, situated one on either side of the middle line of the face, extending from the base of the cranium to the roof of the mouth, and separated from each other by a thin vertical septum. They open on the face through the pear-shaped anterior nasal aperture, and their posterior openings or choanse communicate, in the fresh state, with the nasal part of the pharynx. They are much narrower above than below, and in the middle than at their anterior or posterior openings: their depth, which is considerable, is greatest in the middle. They communicate with the frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded by a roof, a floor, a medial and a lateral wall. The roof (Figs. 195, 196) is horizontal in its central part, but slopes down- ward in front and behind; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, Rostrum of sphenoid Crest of nasal bones- Frontal spine Space for triangular cartilage of septum Crest of palatines Crest of maxilla5 Fig. 195.—Medial wall of left nasal fossa. by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate -of the ethmoid are the foramina for the olfactory nerves, and on the posterior part of the roof is the opening into the sphenoidal sinus. The floor is flattened from before backward and concave from side to side. It is formed by the palatine process of the maxilla and the horizontal part of the palatine bone; near its anterior end is the opening of the incisive canal. The medial wall (septum nasi) (Fig. 195), is frequently deflected to one or other side, more often to the left than to the right. It is formed, in front, by the crest of the nasal bones and frontal spine; in the middle, by the perpendicular plate of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, by the crest of the maxillfe and palatine bones. It presents, in front, a large, triangular notch, which receives the cartilage of the septum; and behind, the free edge of the vomer. Its surface is marked by numerous furrows for vessels THE INTERIOR OF THE SKULL 195 and nerves and by the grooves for the nasopalatine nerve, and is traversed by sutures connecting the bones of which it is formed. The lateral wall (Fig. 196) is formed, in front, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal concha; behind, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three irregular antero- posterior passages, termed’the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, occupies the middle third of the lateral wall. It lies between the superior and middle nasal conchse; the spheno- palatine foramen opens into it behind, and the posterior ethmoidal cells in front. The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed above and behind the superior concha. The middle meatus is situated between the middle and inferior conchte, and extends from the anterior to the posterior end of Nasal bone Frontal spine Probe passed through nasolacrimal canal Cribriform plate of ethmoid, Sphenoid Bristle passed through infundibulum Frontal proc. of maxilla Lacrimal Ethmoid TJncinate proc. of ethmoid Inferior nasal concha Palatine Superior meatus Middle meatus Inferior meatus Anterior nasal spine Palatine proc. of naxilla Horizontal part of palatine Posterior nasal spine Incisive canal— Fig. 196.—Roof, floor, and lateral wall of left nasal cavity. the latter. The lateral wall of this meatus can be satisfactorily studied only after the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, which communicates in front with the anterior ethmoidal cells and in rather more than fifty per cent, of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus. Below the bulla ethmoidalis and hidden by the unci- nate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare); an accessory opening is frequently present above the posterior part of the inferior nasal concha. The inferior meatus, the largest of the three, is the space between the inferior concha and the floor of the nasal cavity. It extends almost the entire 196 OSTEOLOGY length of the lateral wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the nasolacrimal canal. The Anterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose. It is bounded above by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillae; and below by the same borders, where they curve medialward to join each other at the anterior nasal spine. The choanae are each bounded above by the under surface of the body of the sphenoid and ala of the vomer; below, by the posterior border of the horizontal part of the palatine bone; laterally, by the medial pterygoid plate; they are separated from each other by the posterior border of the vomer. DIFFERENCES IN THE SKULL DUE TO AGE. At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult. The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossi- fication of the skull bones is not completed, and many of them, e. g., the occipital, temp- orals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified mem- branous intervals, termed fontanelles, are seen at the angles of the parietal bones; these fontanelles are six in number: two, an ante- rior and a posterior, are situated in the middle line, and two, an antero-lateral and a postero- lateral, on either side. The anterior or bregmatic fontanelle (Fig. 197) is the largest, and is placed at the junc- tion of the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measures about 4 cm. in its antero-posterior and 2.5 cm. in its transverse diameter. The 'posterior fontanelle is triangular in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fontanelles (Fig. 198) are small, irregular in shape, and correspond re- spectively with the sphenoidal and mastoid angles of the parietal bones. An additional fontanelle is sometimes seen in the sagittal suture at the region of the obelion. The fontanelles are usually closed by the growth and extension of the bones which surround them, but sometimes they are the sites of separate ossific centers which develop into itfirmii f , • _ . sutural bones. The posterior and lateral fon- tanelles are obliterated within a month or two after birth, but the anterior is not completely closed until about the middle of the second year. The smallness of the face at birth is mainly accounted for by the rudimentary condition of the maxilla) and mandible, the non-eruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and the lower border of the anterior nasal aperture is only a little below the level of the orbital floor. With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these changes are still more marked after the second dentition. The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporals have reached their fidl size and the orbital cavities are only a little smaller than those of the adult. Growth is slow from the seventh year until the approach Frontal fonticulus Fig. 197.—Skull at birth, showing frontal and occipital fonticuli. Occipital fonticulus CRANIOLOGY 197 of puberty, when a second period of activity occurs: this results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the develop- ment of the air sinuses. v Obliteration of the sutures of the vault of the skull takes place as age advances. This process may commence between the ages of thirty and forty, and is first seen on the inner surface, and some ten years later on the outer surface of the skull. The dates given are, however, only approxi- mate, as it is impossible to state with anything like accuracy the time at which the sutures are closed. Obliteration usually occurs first in the posterior part of the sagittal suture, next in the coronal, and then in the lambdoidal. In old age the skull generally becomes thinner and lighter, but in a small proportion of cases it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- ing feature of the old skull is the diminution in the size of the maxillae and mandible consequent on the loss of the teeth and the absorption of the alveolar processes. This is associated with a marked reduction in the vertical measurement of the face and with an alteration in the angles of the mandible. Frontal fonticulus Mastoid fonticulus Sphenoidal fonticulus Fig. 198.—Skull at birth, showing sphenoidal and mastoid fonticuli. SEXUAL DIFFERENCES IN THE SKULL. Until the age of puberty there is little difference between the skull of the female and that of the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- what flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillae and mandible and their contained teeth smaller. From what has been said it will be seen that more of the infantile characteristics are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respective characteristics are so indistinct that the determination of the sex may be difficult or impossible. CRANIOLOGY. Skulls vary in size and shape, and the term craniology is applied to the study of these varia- tions. The capacity of the cranial cavity constitutes a good index of the size of the brain which it contained, and is most conveniently arrived at by filling the cavity with shot and measuring the contents in a graduated vessel. Skulls may be classified according to their capacities as follows: 1. Microcephalic, with a capacity of less than 1350 c.cm.—e. g., those of native Australians and Andaman Islanders. 2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm.—e. g., those of African negroes and Chinese. 3 Megacephalic, with a capacity of over 1450 c.cm.—e. g., those of Europeans, Japanese, and Eskimos. 198 OSTEOLOGY In comparing the shape of one skull with that of another it is necessary to adopt some definite position in which the skulls should be placed during the process of examination. They should be so placed that a line carried through the lower margin of the orbit and upper margin of the external acoustic meatus is in the horizontal plane. The normae of one skull can then be com- pared with those of another, and the differences in contour and surface form noted. Further, it is necessary that the various linear measurements used to determine the shape of the skull should be made between definite and easily localized points on its surface. The principal points may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. The Points in the Median Plane are the: Mental Point. The most prominent point of the chin. Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar arch. Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base of the anterior nasal spine. Nasion. The central point of the frontonasal suture. Glabella. The point in the middle line at the level of the superciliary arches. Ophryon. The point in the middle line of the forehead at the level where the temporal lines most nearly approach each other. Bregma. The meeting point of the coronal and sagittal sutures. Obelion. A point in the sagittal suture on a level with the parietal foramina. Lambda. The point of junction of the sagittal and lambdoidal sutures. Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. Inion. The external occipital protuberance. Opisthion. The mid-point of the posterior margin of the foramen magnum. Basion. The mid-point of the anterior margin of the foramen magnum. The Points on Either Side of the Median Plane are the: Gonion. The outer margin of the angle of the mandible. Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal bone and the frontal process of the maxilla. Stephanion. The point where the temporal line intersects the coronal suture. Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the parietal. Auricular Point. The center of the orifice of the external acoustic meatus. Asterion. The point of meeting of the lambdoidal, mastooccipital, and mastoparietal sutures. The horizontal circumference of the cranium is measured in a plane passing through the glabella (Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 50 cm. in the female and 52.5 cm. in the male. The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the vertex to the opisthion: while the basinasal length is the distance between the basion and the nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, represent the vertical circumference of the cranium. The length is measured from the glabella to the occipital point, while the breadth or greatest transverse diameter is usually found near the external acoustic meatus. The proportion of breadth to length *s termed the cephalic index or index of breadth. The height is usually measured from the basion to the bregma, and the proportion of height , , (height X 100) . , to length length constitutes the vertical or height index. In studying the face the principal points to be noticed are the proportion of its length and breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection of the jaws. The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible be wanting, to the alveolar point; while its width is represented by the distance between the zygomatic arches. By comparing the length with the width of the face, skulls may be divided into two groups; dolichofacial or leptoprosope (long faced) and brachyfacial or chemoprosope (short faced). The orbital index signifies the proportion which the orbital height bears to the orbital width, thus: orbital height X 100 orbital width The nasal index expresses the proportion which the width of the anterior nasal aperture bears to the height of the nose, the latter being measured from the nasion to the lower margin of the nasal aperture, thus: nasal width X 100 nasal height CRANIO LOGY 199 The degree of projection of the jaws is determined by the gnathic or alveolar index, which repre- sents the proportion between the basialveolar and basinasal lengths, thus: # basialveolar length X 100 basinasal length The following table, modified from that given by Duckworth,1 illustrates how these different indices may be utilized in the classification of skulls: Index. Classification. Nomenclature. Examples. 1. Cephalic Below 75 Between 75 and 80 Above 80 Dolichocephalic MesaticephaUc Brachycephalic Kaffirs and Native Australians. Europeans and Chinese. Mongolians and Andamans. 2. Orbital Below 84 Between 84 and 89 Above 89 Microseme Mesoseme Megaseme Tasmanians and Native Austra- lians. Europeans. Chinese and Polynesians. 3. Nasal Below 48 Between 48 and 53 Above 53 Leptorhine Mesorhine Platyrhine Europeans. Japanese and Chinese. Negroes and Native Australians. 4. Gnathic Below 98 Between 98 and 103 Above 103 Orthognathous Mesognathous Prognathous Europeans. Chinese and Japanese. Native Australians. The chief function of the skull is to protect the brain, and therefore those portions of the skull which are most exposed to external violence are thicker than those which are shielded from injury by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamae, being protected by the temporales muscles, and the inferior occipital fossae, being shielded by the muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented by its elasticity, its rounded shape, and its construction of a number of secondary elastic arches, each made up of a single bone. The manner in which vibrations are transmitted through the bones of the skull is also of importance as regards its protective mechanism, at all events as far as the base is concerned. In the vault, the bones being of a fairly equal thickness and density, vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the varying thickness and density of the bones, this is not so; and therefore in this situation there are special buttresses which serve to carry the vibrations in certain definite directions. At the front of the skull, on either side, is the ridge which separates the anterior from the middle fossa of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; and if any violence is applied to the vault, the vibrations would be carried along these buttresses to the sella turcica, where they meet. This part has been termed the “center of resistance,” and here there is a special protective mechanism to guard the brain. The subarachnoid cavity at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion to shield the brain from injury. In like manner, when violence is applied to the base of the skull, as in falls upon the feet, the vibrations are carried backward through the occipital crest, and forward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. In connection with the bones of the face a common malformation is cleft palate. The cleft usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend through the soft palate; or the posterior part of the whole of the hard palate may be involved, the cleft extending as far forward as the incisive foramen. In the severest forms, the cleft extends through the alveolus and passes between the incisive or premaxillary bone and the rest of the max- illa; that is to say, between the lateral incisor and canine teeth. In some instances, the cleft runs between the central and lateral incisor teeth; and this has induced some anatomists to believe that the premaxillary bone is devel- oped from two centers (Fig. 199) and not from one, as was stated on p. 163. The medial segment, bearing a central incisor, is called an endognathion; the lateral segment, bear- ing the lateral incisor, is called a mesognathion. The cleft may affect one or both sides; if the latter, the central part is frequently displaced forward and re- mains united to the septum of the nose, the deficiency in the alveolus being complicated with a cleft Endognalhion Mesognalhion Exognathion Fig. 199.—The premaxilla and its sutures. (After Albrecht.) 1 Morphology and Anthropology, by W. L. H. Duckworth, M.A., Cambridge University Press. 200 OSTEOLOGY in the lip (hare-lip). On examining a cleft palate in which the alveolus is not implicated, the cleft will generally appear to be in the median line, but occasionally is unilateral and in some cases bilat- eral. To understand this it must be bornein mind that three processes are concerned in the formation of the palate—the palatine processes of the two maxillae, which grow in horizontally and unite in the middle line, and the ethmovomerine process, which grows downward from the base of the skull and frontonasal process to unite with the palatine processes in the middle line. In those cases where the palatine processes fail to unite with each other and with the medial process, the cleft of the palate is median; where one palatine process unites with the medial septum, the other failing to do so, the cleft in the palate is unilateral. In some cases where the palatine pro- cesses fail to meet in the middle, the ethmovomerine process grows downward between them and thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as a rule, the union of the various processes progresses from before backward, and therefore the posterior part of the palate is more frequently defective than the anterior. THE EXTREMITIES. The bones by which the upper and lower limbs are attached to the trunk con- stitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle of the superior extremity is formed by the scapulae and clavicles, and is imperfect in front and behind. In front, however, it is completed by the upper end of the sternum, with which the medial ends of the clavicles articulate. Behind, it is widely imperfect, the scapulae being connected to the trunk by muscles only. The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, which articulate with each other in front, at the symphysis pubis. It is imperfect behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, with the sacrum, is a complete ring, massive and comparatively rigid, in marked contrast to the lightness and mobility of the shoulder girdle. THE BONES OF THE UPPER EXTREMITY (OSSA EXTREMITATIS SUPERIORIS). The Clavicle (Clavicula; Collar Bone). The clavicle (Figs. 200, 201) forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter/, and placed nearly horizon- tally at the upper and anterior part of the thorax, immediately above the first rib. It articulates medially with the manubrium sterni, and laterally with the acromion of the scapula.1 It presents a double curvature, the convexity being directed forward at the sternal end, and the concavity at the scapular end. Its lateral third is flattened from above downward, while its medial two-thirds is of a rounded or prismatic form. Lateral Third.—The lateral third has two surfaces, an upper and a lower; and two borders, an anterior and a posterior. Surface.—The upper surface is flat, rough, and marked by impressions for the attachments of the Deltoideus in front, and the Trapezius behind; between these impressions a small portion of the bone is subcutaneous. The under surface is flat. At its posterior border, near the point where the prismatic joins with the flattened portion, is a rough eminence, the coracoid tuberosity (conoid tubercle); this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament. From this tuberosity an oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and afford attachment to the trapezoid ligament. 1 The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly absent in those animals whose fore-limbs are used only for progression, but is present for the most part in animals whose anterior extremities are clawed and used for prehension, though in some of them—as, for instance, in a large number of the carnivora—it is merely a rudimentary bone suspended among the muscles, and not articulating with either the scapula or sternum. THE CLAVICLE 201 Borders.—The anterior border is concave, thin, and rough, and gives attachment to the Deltoideus. The posterior border is convex, rough, thicker than the anterior, and gives attachment to the Trapezius. Medial Two-thirds.—The medial two-thirds constitute the prismatic portion of the bone, which is curved so as to be convex in front, concave behind, and is marked by three borders, separating three surfaces. Borders.—The anterior border is continuous with the anterior margin of the flat portion. Its lateral part is smooth, and corresponds to the interval between the attachments of the Fectoralis major and Deltoideus; its medial part forms the lower boundary of an elliptical surface for the attachment of the clavicular portion Sternal extremity Acromial extremity Fig. 200.—Left clavicle. Superior surface. of the Pectoralis major, and approaches the posterior border of the bone. The superior border is continuous with the posterior margin of the flat portion, and separates the anterior from the posterior surface. Smooth and rounded laterally, it becomes rough toward the medial third for the attachment of the Sternocleido- mastoideus, and ends at the upper angle of the sternal extremity. The posterior or subclavian border separates the posterior from the inferior surface, and extends from the coracoid tuberosity to the costal tuberosity; it forms the posterior boun- dary of the groove for the Subclavius, and gives attachment to a layer of cervical fascia which envelops the Omohyoideus. Articular capsule Articular capsule Fig. 201.—Left clavicle. Inferior surface. Surfaces.—The anterior surface is included between the superior and anterior borders. Its lateral part looks upward, and is continuous with the superior sur- face of the flattened portion; it is smooth, convex, and nearly subcutaneous, being covered only by the Platysma. Medially it is divided by a narrow subcutaneous area into two parts: a lower, elliptical in form, and directed forward, for the attachment of the Pectoralis major; and an upper for the attachment of the Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks backward toward the root of the neck. It is limited, above, by the superior border; below, by the subclavian border; medially, by the margin of the sternal extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, 202 OSTEOLOGY and is in relation, by its lower part, with the transverse scapular vessels. This surface, at the junction of the curves of the bone, is also in relation with the brachial plexus of nerves and the subclavian vessels. It gives attachment, near the sternal extremity, to part of the Sternohyoideus; and presents, near the middle, an oblique foramen directed lateralward, which transmits the chief nutrient artery of the bone. Sometimes there are two foramina on the posterior surface, or one on the posterior and another on the inferior surface. The inferior or subclavian surface is bounded, in front, by the anterior border; behind, by the subclavian border. It is narrowed medially, but gradually increases in width laterally, and is contin- uous with the under surface of the flat portion. On its medial part is a broad rough surface, the costal tuberosity (rhomboid, impression), rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line which gives attachment to the intermuscular septum of the Subclavius. The Sternal Extremity (extremitas sternalis; internal extremity).—The sternal extremity of the clavicle is triangular in form, directed medialward, and a little downward and forward; it presents an articular facet, concave from before back- ward, convex from above downward, which articulates with the manubrium sterni through the intervention of an articular disk. The lower part of the facet is con- tinued on to the inferior surface of the bone as a small semi-oval area for articula- tion with the cartilage of the first rib. The circumference of the articular surface is rough, for the attachment of numerous ligaments; the upper angle gives attach- ment to the articular disk. The Acromial Extremity (extremitas acromialis; outer extremity).—The acromial extremity presents a small, flattened, oval surface directed obliquely downward, for articulation with the acromion of the scapula. The circumference of the articular facet is rough, especially above, for the attachment of the acromio- clavicular ligaments. In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the male. In those persons who perform considerable manual labor it becomes thicker and more curved, and its ridges for muscular attachment are prominently marked. Structure.—The clavicle consists of cancellous tissue, enveloped by a compact layer, which is much thibker in the intermediate part than at the extremities of the bone. Ossification.—The clavicle begins to ossify before any other bone in the body; it is ossified from three centers—viz., two primary centers, a medial and a lateral, for the body,1 which appear during the fifth or sixth week of fetal life; and a secondary center for the sternal end, which appears about the eighteenth or twentieth year, and unites with the rest of the bone about the twenty-fifth year. The Scapula (Shoulder Blade). The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- gular bone, with two surfaces, three borders, and three angles. Surfaces.—The costal or ventral surface (Fig. 202) presents a broad concavity, the subscapular fossa. The medial two-thirds of the fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle. The fossa is separated from the vertebral border by smooth triangular areas at the medial and inferior angles, and in the interval between these by a narrow ridge which is often deficient. These triangular areas and the intervening ridge afford attachment to the Serratus anterior. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself 1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. THE SCAPULA 203 along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. The dorsal surface (Fig. 203) is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa. The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus. The infraspinatous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a promi- nent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. The dorsal surface is marked near the axillary border by an elevated ridge, which runs from the lowrer part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor. The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its center by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor. Its lower third presents a broader, somewhat triangular surface, which gives origin to the Teres major, and over which the Latis- simus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other. The Spine (spina scapulce).—The spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. It begins at the vertical border by a smooth, triangular area over which the tendon of inser- tion of the lower part of the Trapezius glides, and, gradually becoming more ele- vated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border. It presents two surfaces and three borders. Its superior surface is concave; it assits in forming the supraspinatous fossa, and gives origin to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous fossa, gives origin to a portion of the Infraspinatus, and presents near its center the orifice of a nutrient canal. Of the three borders, the anterior is attached to the dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents two lips and an intervening rough interval. The Trapezius is attached to the supe- rior lip, and a rough tubercle is generally seen on that portion of the spine which receives the tendon of insertion of the lower part of this muscle. The Deltoideus is attached to the whole length of the inferior lip. The interval between the lips is subcutaneous and partly covered by the tendinous fibers of these muscles. The lateral border, or base, the shortest of the three, is slightly concave; its edge, thick and round, is continuous above with the under surface of the acromion, below with the neck of the scapula. It forms the medial boundary of the great scapular notch, which serves to connect the supra- and infraspinatous fossae. The Acromion.—The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the 204 OSTEOLOGY glenoid cavity. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the Trapezius, and presents about its center a small, oval surface for articulation with the acromial end of the clavicle. Coracoacromial ligament Articular capsule Articular capsule Fig. 202.—Left scapula. Costal surface. Its apex, which corresponds to the point of meeting of these two borders in front, is thin, and has attached to it the coracoacromial ligament. Borders.—Of the three borders of the scapula, the superior is the shortest and thinnest; it is concave, and extends from the medial angle to the base of the cora- coid process. At its lateral part is a deep, semicircular notch, the scapular notch, THE SCAPULA 205 formed partly by the base of the coracoid process. This notch is converted into a foramen by the superior transverse ligament, and serves for the passage of the suprascapular nerve; sometimes the ligament is ossified. The adjacent part of the superior border affords attachment to the Omohyoideus. The axillary border Coracohumeral ligament Coraco-acromial ligament Trapezoid ligament Conoid ligament Articular capsule Fxo. 203.—Left scapula. Dorsal surface. is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Tri- ceps brachii; in front of this is a longitudinal groove, which extends as far as the 206 OSTEOLOGY lower third of this border, and affords origin to part of the Subscapularis. The inferior third is thin and sharp, and serves for the attachment of a few fibers of the Teres major behind, and of the Subscapularis in front. The vertebral border is the longest of the three, and extends from the medial to the inferior angle. It is arched, intermediate in thickness between the superior and the axillary borders, and the portion of it above the spine forms an obtuse angle with the part below. This border presents an anterior and a posterior lip, and an intermediate narrow area. The anterior lip affords attachment to the Serratus anterior; the posterior lip, to the Supraspinatus above the spine, the Infraspinatus below; the area Fig. 204.—Posterior view of the thorax and shoulder girdle. (After Morris.) between the two lips, to the Levator scapulre above the triangular surface at the commencement of the spine, to the Rhomboideus minor on the edge of that surface, and to the Rhomboideus major below it; this last is attached by means of a fibrous arch, connected above to the lower part of the triangular surface at the base of the spine, and below to the lower part of the border. Angles.—Of the three angles, the medial, formed by the junction of the superior and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, and gives attachment to a few fibers of the Levator scapulae. The inferior angle, thick and rough, is formed by the union of the vertebral and axillary borders; its dorsal surface affords attachment to the Teres major and frequently to a few THE SCAPULA 207 fibers of the Latissimus dorsi. The lateral angle is the thickest part of the bone, and is sometimes called the head of the scapula. On it is a shallow pyriform, articular surface, the glenoid cavity, which is directed lateralward and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest. The surface is covered wdth cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibro- cartilaginous structure, the glenoidal labrum, which deepens the cavity. At its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the Biceps brachii is attached. The neck of the scapula is the slightly constricted portion which sur- rounds the head; it is more dis- tinct below and behind than above and in front. The Coracoid Process (processus coracoideus).—The coracoid pro- cess is a thick curved process at- tached by a broad base to the upper part of the neck of the scapula; it runs at first upwrard and medialward; then, becoming smaller, it changes its direction, and projects forward and lateral- ward. The ascending portion, flattened from before backward, presents in front a smooth con- cave surface, across which the Subscapularis passes. The hori- zontal portion is flattened from above downward; its upper sur- face is convex and irregular, and gives attachment to the Pector- alis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the cora- coacromial ligament; the apex is embraced by the conjoined tendon of origin of the Coracobrachialis and short head of the Biceps brachii and gives attachment to the coracoclavicular fascia. On the medial part of the root of the coracoid process is a rough im- pression for the attachment of the conoid ligament; and running from it obliquely forward and lateralward, on to the upper surface of the horizontal portion, is an elevated ridge for the attachment of the trapezoid ligament. Structure.—The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous Supraglenoid tubercle Acromion Coracoid process Spine ''Glenoid cavity Infraglenoid tubercle For Subscapularis -Axillary border Fig. 205.—Left scapula. Lateral view. — Inferior angle 208 OSTEOLOGY fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue. Ossification (Fig. 206).—The scapula is ossified from seven or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle. Ossification of the body begins about the second month of fetal life, by the formation of an irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends so as to form the chief part of the bone, the spine growing up from its dorsal surface about the third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succes- sion, and usually in the following order; first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two separate nuclei of the acromion unite, and then join with the extension from the spine. The upper third Fig. 206.—Plan of ossification of the scapula. From seven centers. of the glenoid cavity is ossified from a separate center (subcoracoid), which makes its appear- ance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. Further, an epiphysial plate appears for the lower part of the glenoid cavity, while the tip of the coracoid process frequently presents a separate nucleus. These various epiphyses are joined to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone. THE HUMERUS 209 The Humerus (Arm Bone). The humerus (Figs. 207, 208) is the longest and largest bone of the upper extremity; it is divisible into a body and two extremities. Upper Extremity.—The upper extremity consists of a large rounded head joined to the body by a constricted portion called the neck, and two eminences, the greater and lesser tubercles. The Head (caput humeri).—The head, nearly hemispherical in form,1 is directed upward, medialward, and a little backward, and articulates with the glenoid cavity of the scapula. The circumference of its articular surface is slightly constricted and is termed the anatomical neck, in contradistinction to a constriction below the tubercles called the surgical neck which is frequently the seat of fracture. Fracture of the anatomical neck rarely occurs. The Anatomical Neck (collum anatomicum) is obliquely directed, forming an obtuse angle with the body. It is best marked in the lower half of its circum- ference ; in the upper half it is represented by a narrow groove separating the head from the tubercles. It affords attachment to the articular capsule of the shoulder- joint, and is perforated by numerous vascular foramina. The Greater Tubercle (ituberculum majus; greater tuberosity).—The greater tubercle is situated lateral to the head and lesser tubercle. Its upper surface is rounded and marked by three flat impressions: the highest of these gives insertion to the Supraspinatus; the middle to the Infraspinatus; the lowest one, and the body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body. The Lesser Tubercle (tuberculum minus; lesser tuberosity).—The lesser tubercle, although smaller, is more prominent than the greater: it is situated in front, and is directed medialward and forward. Above and in front it presents an impression for the insertion of the tendon of the Subscapularis. The tubercles are separated from each other by a deep groove, the intertubercular groove (bicipital groove), which lodges the long tendon of the Biceps brachii and transmits a branch of the anterior humeral circumflex artery to the shoulder-joint. It runs obliquely downward, and ends* near the junction of the upper with the middle third of the bone. In the fresh state its upper part is covered with a thin layer of cartilage, lined by a prolongation of the synovial membrane of the shoulder-joint; its lower portion gives insertion to the tendon of the Latissimus dorsi. It is deep and narrow above, and becomes shallow and a little broader as it descends. Its lips are called, respectively, the crests of the greater and lesser tubercles (bicipital ridges), and form the upper parts of the anterior and medial borders of the body of the bone. The Body or Shaft (corpus humeri).—The body is almost cylindrical in the upper half of its extent, prismatic and flattened below, and has three borders and three surfaces. Borders.—The anterior border runs from the front of the greater tubercle above to the coronoid fossa below, separating the antero-medial from the antero-lateral surface. Its upper part is a prominent ridge, the crest of the greater tubercle; it serves for the insertion of the tendon of the Pectoralis major. About its center it forms the anterior boundary of the deltoid tuberosity; below, it is smooth and rounded, affording attachment to the Brachialis. The lateral border runs from the back part of the greater tubercle to the 1 Though the head is nearly hemispherical in form, its margin, as Humphry has shown, is by no means a true circle. Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and back- ward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface in this direction—that is to say, obliquely upward, lateralward, and forward. 210 OSTEOLOGY Articular capsule Surqfnai Neck Brachioradialis Extensor carpi radialis ■ longus Articular capsule Common origin of Extensor carpi rad. brev. ,, digilorum communis ,, digiti quinti prop. ,, carpi ulnaris Supinator Common origin o_ Flexor carpi radialis Palmaris longus Flexor digitorum sublimis Flexor carpi ulnaris Fig. 207.—Left humerus. Anterior view THE HUMERUS 211 lateral epicondyle, and separates the antero- lateral from the posterior surface. Its upper half is rounded and indistinctly marked, serv- ing for the attachment of the lower part of the insertion of the Teres minor, and below this giving origin to the lateral head of the Triceps brachii; its center is traversed by a broad but shallow oblique depression, the radial sulcus (■musculospiral groove). Its lower part forms a prominent, rough margin, a little curved from behind forward, the lateral supracondylar ridge, which presents an anterior lip for the origin of the Brachioradialis above, and Extensor carpi radialis longus below, a posterior lip for the Triceps brachii, and an intermediate ridge for the attachment of the lateral intermuscu- lar septum. The medial border extends from the lesser tubercle to the medial epicondyle. Its upper third consists of a prominent ridge, the crest of the lesser tubercle, which gives insertion to the tendon of the Teres major. About its center is a slight impression for the insertion of the Coracobrachialis, and just below this is the entrance of the nutrient canal, directed down- ward; sometimes there is a second nutrient canal at the commencement of the radial sulcus. The inferior third of this border is raised into a slight ridge, the medial supracondylar ridge, which becomes very prominent below; it pre- sents an anterior lip for the origins of the Brachialis and Pronator teres, a posterior lip for the medial head of the Triceps brachii, and an intermediate ridge for the attachment of the medial intermuscular septum. Surfaces.—The antero-lateral surface is di- rected lateralward above, where it is smooth, rounded, and covered by the Deltoideus; for- ward and lateralward below, where it is slightly concave from above downward, and gives origin to part of the Brachialis. About the middle of this surface is a rough, triangular elevation, the deltoid tuberosity for the insertion of the Deltoideus; below this is the radial sulcus, directed obliquely from behind, forward, and downward, and transmitting the radial nerve and profunda artery. The antero-medial surface, less extensive than the antero-lateral, is directed medialward above, forward and medialward below; its upper part is narrow, and forms the floor of the intertuber- cular groove which gives insertion to the tendon of the Latissimus dorsi; its middle part is slightly rough for the attachment of some of Articular capsule Articular capsule Fig. 208.—Left humerus Posterior view. 212 OSTEOLOGY the fibers of the tendon of insertion of the Coracobrachialis; its lower part is smooth, concave from above downward, and gives origin to the Brachialis.1 The posterior surface appears somewhat twisted, so that its upper part is directed a little medial ward, its lower part backward and a little lateral ward. Nearly the whole of this surface is covered by the lateral and medial heads of the Triceps brachii, the former arising above, the latter below the radial sulcus. The Lower Extremity.—The lower extremity is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge. Projecting on either side are the lateral and medial epicondyles. The articular surface extends a little lower than the epicondyles, and is curved slightly forward; its medial extremity occupies a lower level than the lateral. The lateral portion of this surface consists of a smooth, rounded eminence, named the capitulum of the humerus; it articulates with the cup- shaped depression on the head of the radius, and is limited to the front and lower part of the bone. On the medial side of this eminence is a shallow groove, in which is received the medial margin of the head of the radius. Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed. The medial portion of the articular surface is named the trochlea, and presents a deep depression be- tween two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity. The lateral border separates it from the groove which articulates with the margin of the head of the radius. The medial border is thicker, of greater length, and consequently more prominent, than the lateral. The grooved portion of the artic- ular surface fits accurately within the semilunar notch of the ulna; it is broader and deeper on the posterior than on the anterior aspect of the bone, and is inclined obliquely downward and forward toward the medial side. Above the front part of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. Above the back part of the troch- lea is a deep triangular depression, the olecranon fossa, in which the summit of the olecranon is received in extension of the forearm. These fossae are separated from one another by a thin, transparent lamina of bone, which is sometimes perforated by a supratrochlear foramen; they are lined in the fresh state by the synovial membrane of the elbow-joint, and their margins afford attachment to the anterior and posterior ligaments of this articulation. The lateral epicondyle is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. The medial epicondyle, larger and more prominent than the lateral, is directed a little backward; it gives attach- ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, and to a common tendon of origin of some of the Flexor muscles of the forearm; the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles are continuous above with the supracondylar ridges. Structure.—The extremities consist of cancellous tissue, covered with a thin, compact layer (Fig. 209); the body is composed of a cylinder of compact tissue, thicker at the center than toward the extremities, and contains a large medullary canal which extends along its whole length. 1 A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infre- quently found projecting from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondyle. It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by this fibrous band the median nerve and brachial artery pass, when these structures deviate from their usual course. Sometimes the nerve alone is transmitted through it, or the nerve may be accompanied by the ulnar artery, in cases of high division of the brachial. A well-marked groove is usually found behind the process, in which the nerve and artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably serves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. THE HUMERUS 213 Ossification (Figs. 210, 211).—The humerus is ossi- fied from eight centers, one for each of the following parts: the body, the head, the greater tubercle, the lesser tubercle, the capitulum, the trochlea, and one for each epicondyle. The center for the body appears near the middle of the bone in the eighth week of fetal life, and soon extends toward the extremities. At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous. During the first year, sometimes before birth, ossification commences in the head of the bone, and during the third year the center for the greater tubercle, and during the fifth that for the lesser tubercle, make their appearance. By the sixth year the centers for the head and tubercles have joined, so as to form a single large epiphysis, which fuses with the body about the twentieth year. The lower end of the humerus is ossified as follows. At the end of the second year ossification begins in the capitulum, and extends medialward, to form the chief part of the articular end of the bone; the center for the medial part of the trochlea appears about the age of twelve. Ossifi- cation begins in the medial epicondyle about the fifth year, and in the lateral about the thirteenth or four- teenth year. About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articu- lating surface, having already joined, unite with the body, and at the eighteenth year the medial epicon- dyle becomes joined to it. Epiphysial line Fig. 209.—Longitudinal section of head of left humerus. Epiphyses of head and' tubercles blend at fifth year, and unite with body at twentieth year Unites with body} at eighteenth year J Fig. 210.—Plan of ossification of the humerus. Fig. 211.—Epiphysial lines of humerus in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. 214 OSTEOLOGY The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the medial side of the forearm, parallel with the radius. It is divisible into a body and two extremities. Its upper extremity, of great thickness and strength, forms a large part of the elbow-joint; the bone diminishes in size from above downward, its lower extremity being very small, and excluded from the wrist-joint by the interposition of an articular disk. The Upper Extremity (;proximal extremity) (Fig. 212).—The upper extremity presents two curved processes, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches. The Olecranon (olecranon process).—The olecra- non is a large, thick, curved eminence, situated at the upper and back part of the ulna. It is bent forward at the summit so as to present a promi- nent lip which is received into the olecranon fossa of the humerus in extension of the forearm. Its base is contracted where it joins the body and the narrowest part of the upper end of the ulna. Its posterior surface, directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. Its superior surface is of quadrilateral form, marked behind by a rough impression for the insertion of the Triceps brachii; and in front, near the margin, by a slight transverse groove for the attachment of part of the posterior ligament of the elbowr-joint. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. Its borders present continuations of the groove on the margin of the superior surface; they serve for the attach- ment of ligaments, viz., the back part of the ulnar collateral ligament medially, and the posterior ligament laterally. From the medial border a part of the Flexor carpi ulnaris arises; while to the lateral border the Anconaeus is attached. The Coronoid Process (processus coronoideus).— The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna. Its base is continuous with the body of the bone, and of considerable strength. Its apex is pointed, slightly curved upward, and in flexion of the forearm is received into the coronoid fossa of the humerus. Its upper surface is smooth, concave, and forms the lower part of the semilunar notch. Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the Brachialis. At the junction of this surface with the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the Brachialis; to the lateral border of this tuberosity the oblique cord is attached. Its lateral surface presents a narrow, oblong, articular depression, the radial notch. Its medial surface, by its prominent, The Ulna (Elbow Bone).1 Olecranon a Coronoid process Fig. 212.—Upper extremity of left ulna. Lateral aspect. 1 In the anatomical position, the forearm is placed in extension and supination with the palm looking forward and the thumb on the outer side. THE ULNA 215 free margin, serves for the attachment of part of the ulnar collateral ligament. At the front part of this surface is a small rounded eminence for the origin of one head of the Flexor digitorum sublimis; behind the eminence is a depression for part of the origin of the Flexor digitorum profundus; descending from the eminence is a ridge which gives origin to one head of the Pronator teres. Fre- quently, the Flexor pollicis longus arises from the lower part of the coronoid process by a rounded bundle of muscular fibers. The Semilunar Notch (incisura semilunaris; greater sigmoid cavity).—The semi- lunar notch is a large depression, formed by the olecranon and the coronoid process, and serving for articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process. The notch is concave from above downward, and divided into a medial and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transversely; the lateral is convex above, slightly concave below. The Radial Notch (-incisura radialis; lesser sigmoid cavity).—The radial notch is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before backward, and its prominent extremities serve for the attach- ment of the annular ligament. The Body or Shaft (corpus ulnoe).—The body at its upper part is prismatic in form, and curved so as to be convex behind and lateralward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward, and has three borders and three surfaces. Borders.—The volar border (margo volaris; anterior border) begins above at the prominent medial angle of the coronoid process, and ends below in front of the styloid process. Its upper part, well-defined, and its middle portion, smooth and rounded, give origin to the Flexor digitorum profundus; its lower fourth serves for the origin of the Pronator quadratus. This border separates the volar from the medial surface. The dorsal border (margo dorsalis; posterior border) begins above at the apex of the triangular subcutaneous surface at the back part of the olecranon, and ends below at the back of the styloid process; it is well-marked in the upper three- fourths, and gives attachment to an aponeurosis which affords a common origin to the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- fundus; its lower fourth is smooth and rounded. This border separates the medial from the dorsal surface. The interosseous crest (crista interossea; external or interosseous border) begins above by the union of two lines, which converge from the extremities of the radial notch and enclose between .them a triangular space for the origin of part of the Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the interosseous mem- brane, and separates the volar from the dorsal surface. Surfaces.—The volar surface (facies volaris; anterior surface), much broader above than below, is concave in its upper three-fourths, and gives origin to the Flexor digitorum profundus; its lower fourth, also concave, is covered by the Pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely dowmward and medialward, which marks the extent of origin of the Pronator quadratus. At the junction of the upper with the middle third of the bone is the nutrient canal, directed obliquely upward. The dorsal surface (facies dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the middle; narrow, smooth, and rounded below. On its upper part is an oblique 216 OSTEOLOGY ULNA Articular capsule RADIUS Flexor digitorum. sublimis Pronator teres Occasional origin of Flexor pollicis longue Radial origin of Flexor digitorum sublimis Articular capsule Brachioradialis Groove for Abductor pollicis longus and Extensor pollicis brevis Styloid process Styloid 'process Fig. 213.—Bones of left forearm. Anterior aspect. THE ULNA 217 ULNA Articular capsule RADIUS Flexor digitorum sublimis {Extensor carpi vlnaris Flexor carpi vlnaris Flexor digitorum pro- fundus Articular capsule {Abductor pollicis longus Extensor pollicis brevis i Far Extensor carpi ulnaris For Ext. carpi radially longus For Extensor digiti quinti proprius For Extensor carvi radialis brevis For Extensor pollicis longus p f Extensor indicia proprius 0T \ Extensor digitorum communis Fig. 214.—Bones of left forearm. Posterior aspect. 218 OSTEOLOGY ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the Anconseus, while the upper part of the ridge affords attachment to the Supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis longus, and the Extensor indicis proprius. The medial surface (facies medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the Elexor digitorum profundus; its lower fourth is subcutaneous. Appears at tenth year Olecranon Joins body at sixteenth year Appears at fourth year Joins body at twentieth year Inferior extremity Fig. 215.—Plan of ossification of the ulna. From three centers. Fig. 216.—Epiphysial lines of ulna in a young adult. Lateral aspect. The lines of attachment of the articular capsules are in blue. The Lower Extremity (distal extremity).—The lower extremity of the ulna is small, and presents two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process. The head presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius. The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the Extensor carpi ulnaris. THE RADIUS 219 Structure.—The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellae parallel. From the inner surface of this plate and the compact layer below it trabeculae arch forward toward the olecranon and coronoid and cross other trabeculae, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabeculae curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabeculae at the lower end have a more longitudinal direction. Ossification (Figs. 215,216).—The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. Articulations.—The ulna articulates with the humerus and radius. The Radius. The radius (Figs. 213, 214) is situated on the lateral side of the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist- joint. It is a long bone, prismatic in form and slightly curved longitudinally. It has a body and two extremities. The Upper Extremity (proximal extremity).—The upper extremity presents a head, neck, and tuberosity. The head is of a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament. The head is supported on a round, smooth, and con- stricted portion called the neck, on the back of which is a slight ridge for the inser- tion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on which a bursa is interposed between the tendon and the bone. The Body or Shaft (corpus radii).—The body is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces. Borders.—The volar border (margo volaris; anterior border) extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is promi- nent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the Flexor digitorum sublimis and Flexor pollicis longus; the surface above the line gives insertion to part of the Supinator. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted. The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. It is indistinct above and below, but well-marked in the middle third of the bone. The interosseous crest (crista interossea; internal or interosseous border) begins above, at the back part of the tuberosity, and its upper part is rounded and indis- tinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch. To the posterior of the two ridges the lower part of the interosseous 220 OSTEOLOGY membrane is attached, while the triangular surface between the ridges gives inser- tion to part of the Pronator quadratus. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. Surface.—The volar surface (facies volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and flat in its lower fourth, and affords insertion to the Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward. The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the Extensor pollicis brevis below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone. The lateral surface (facies lateralis; external surface) is convex throughout its entire extent. Its upper third gives insertion to the Supinator. About its center is a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow, and covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis. The Lower Extremity.—The lower extremity is large, of quadrilateral form, and provided with two articular surfaces—one below, for the carpus, and another at the medial side, for the ulna. The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the navicular bone; the medial, quadri- lateral, with the lunate bone. The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna. These two articular surfaces are separated by a promi- nent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation. This end of the bone has three non-articular surfaces—volar, dorsal, and lateral. The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament. The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side, the first groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral of these two transmits the tendon of the Extensor carpi radialis longus, the medial the tendon of the Extensor carpi radialis brevis. The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the Extensor pollicis longus. The third is broad, for the passage of the tendons of the Extensor indicis proprius and Extensor digitorum communis. The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the Brachioradialis, and by its apex to the radial collateral ligament of the wrist-joint. The lateral surface of this process is marked by a flat groove, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis. Structure.—The long narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and thinnest at the extremities except over the cup-shaped articular surface (fovea) of the head where it is thickened. The trabecula? of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli; they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. Ossification (Figs. 217, 218).—The radius is ossified from three centers: one for the body, and one for either extremity. That for the body makes its appearance near the center of the bone, during the eighth week of fetal life. About the end of the second year, ossification commences THE CARPUS 221 in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. Appears at_ fifth year Head Unites with body about puberty Appears at second year Unites with body about twentieth year Lower extremity Fio. 217.—Plan of ossification of the radius. From three centers. Fig. 218.—Epiphysial lines of radius in a young adult. Anterior aspect. The line of attachment of the articular capsule of the wrist-joint is in blue. THE HAND. The skeleton of the hand (Figs. 219, 220) is subdivided into three segments: the carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or bones of the digits. The Carpus (Ossa Carpi). The carpal bones, eight in number, are arranged in two rows. Those of the proximal row, from the radial to the ulnar side, are named the navicular, lunate, triangular, and pisiform; those of the distal row, in the same order, are named the greater multangular, lesser multangular, capitate, and hamate. Common Characteristics of the Carpal Bones.—Each bone (excepting the pisi- form) presents six surfaces. Of these the volar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the navicular and lunate. The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar, viz., cancellous tissue enclosed in a layer of compact bone. Bones of the Proximal Row (upper row).—The Navicular Bone (os naviculare manus; scaphoid bone) (Fig. 221).—-The navicular bone is the largest bone of the proximal row, and has received its name from its fancied resemblance to a boat. It is situated at the radial side of the carpus, its long axis being from above downward, lateralward, and forward. The superior surface is convex, smooth, of triangular shape, and artic- 222 OSTEOLOGY ulates with the lower end of the radius. The inferior surface, directed downward, lateralward, and backward, is also smooth, convex, and triangular, and is divided by a slight ridge into two parts, the lateral articulating with the greater multangu- lar, the medial with the lesser multangular. On the dorsal surface is a narrow, rough groove, which runs the entire length of the bone, and serves for the attach- ment of ligaments. The volar surface is concave above, and elevated at its lower and lateral part into a rounded projection, the tubercle, which is directed forward Carpus Groove for tendon of Flexor carpi radialiS .Opponens pollicis Flexor carpi ulnaris •Flexor pollicis brevis /Abductor pollicis LONGUS Flexor digiti quinti brevis Opponens digiti quinti Metacarpus Sesamoid bones \ Abductor \ pollicis ‘ Abductor pollicis Flexor brevis'i AND I Abductor f DIGITI QUINTI. / Flexor ' 1 l POLLICIS BREVIS ' BREVIS Phalang es Flexor POLLICIS" LONGUS Flexor DIGITORUM SUBLIMIS /ff Flexor DIGITORUM ■ PROFUNDUS Flexor DIGIT. SUBLIMIS Flexor digitorum SUBLIMIS Flexor digitorum sublimis Flexor digitorum PROFUNDUS Flexor DIGITORUM PROFUNDUS Flexor digitorum profundus Fig. 219.—Bones of the left hand. Volar surface. THE CARPUS 223 and gives attachment to the transverse carpal ligament and sometimes origin to a few fibers of the Abductor pollicis brevis. The lateral surface is rough and narrow, and gives attachment to the radial collateral ligament of the wrist. The medial surface presents two articular facets; of these, the superior or smaller is flattened of semilunar form, and articulates with the lunate bone; the inferior or larger is concave, forming with the lunate a concavity for the head of the capitate bone. Carpus Ext. carpi radialis L0NGU3 " Ext. carpi ulnaris Ext. carpi radialis BREVIS i Metacarpus Ext. POLLICIS„ BREVIS Ext. POLLICTv 10NGUS 1 Phalanges / U Row 2— Row Ext. digit./ I COMMUN. & IExt. digiti S L yUINTI Ext. digitorum COMMUNIS AND Ext. indicis PROPRIUS. 'ext. oicit. / common. \ y*Rovp e*T- 0,0,r. 00 MMUft,. < Fia. 220.—Bones of the left hand. Dorsal surface. 224 OSTEOLOGY Articulations.—The navicular articulates with five bones: the radius proximally, greater and lesser multangulars distally, and capitate and lunate medially. The Lunate Bone (os lunatum; semilunar bone) (Fig. 222).—The lunate bone may be distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row of the carpus, between the navicular and triangular. The superior surface, convex and smooth, articulates with the radius. The inferior surface is deeply concave, and of greater extent from before backward than trans- For radius For lunate Tubercle For greater multangular For lesser multangular For capitate Fig. 221.—The left navicular bone versely: it articulates with the head of the capitate, and, by a long, narrow facet (separated by a ridge from the general surface), with the hamate. The dorsal and volar surfaces are rough, for the attachment of ligaments, the former being the broader, and of a somewhat rounded form. The lateral surface presents a For triangular For radius For navicular For hamate For capitate Fig. 222.—The left lunate bone. narrow, flattened, semilunar facet for articulation with the navicular. The medial surface is marked by a smooth, quadrilateral facet, for articulation with the triangular. Articulations.—The lunate articulates with five bones: the radius proximally, capitate and hamate distally, navicular laterally, and triangular medially. For pisiform For lunate For triangular For hamate Fig. 223.—The left triangular bone. Fio. 224.—The left pisiform bone. The Triangular Bone (os triquetum; cuneiform bone) (Fig. 223).—The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments. The volar surface presents, on its medial part, THE CARPUS 225 an oval faqet, for articulation with the pisiform; its lateral part is rough for liga- mentous attachment. The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate. The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist. Articulations.—The triangular articulates with three bones: the lunate laterally, the pisiform in front, the hamate distally; and with the triangular articular disk which separates it from the lower end of the ulna. The Pisiform Bone (os pisiforme) (Fig. 224).—The pisiform bone may be known by its small size, and by its presenting a single articular facet. It is situated on a plane anterior to the other carpal bones and is spheroidal in form. Its dorsal surface presents a smooth, oval facet, for articulation with the triangular: this facet approaches the superior, but not the inferior border of the bone. The volar surface is rounded and rough, and gives attachment to the transverse carpal ligament, and to the Flexor carpi ulnaris and Abductor digiti quinti. The lateral and medial surfaces are also rough, the former being concave, the latter usually convex. Articulation.—The pisiform articulates with one bone, the triangular. Bones of the Distal Row (lower row).—The Greater Multangular Bone (os mul- tangulum majus; trapezium) (Fig. 225).—The greater multangular bone may be distinguished by a deep groove on its volar surface. It is situated at the radial side of the carpus, between the navicular and the first metacarpal bone. The superior surface is directed upward and mediahvard; medially it is smooth, and articulates with the navicular; laterally it is rough and continuous with the lateral surface. The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base For lesser multangular Groove For navicular For lesser multangular For 2nd metacarpal Ridge For lsi metacarpal For 2nd metacarpal Fig. 225.—The left greater multangular bone of the first metacarpal bone. The dorsal surface is rough. The volar surface is narrow and rough. At its upper part is a deep groove, running from above obliquely downward and mediahvard; it transmits the tendon of the Flexor carpi radialis, and is bounded laterally by an oblique ridge. This surface gives origin to the Opponens pollicis and to the Abductor and Flexor pollicis brevis; it also affords attachment to the transverse carpal ligament. The lateral surface is broad and rough, for the attachment of ligaments. The medial surface presents two facets; the upper, large and concave, articulates with the lesser multangular; the lower, small and oval, with the base of the second metacarpal. Articulations.—The greater multangular articulates with four bones: the navicular proximally, the first metacarpal distally, and the lesser multangular and second metacarpal medially. The Lesser Multangular Bone (os multangulum minus; trapezoid bone) (Fig. 226). —The lesser multangular is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the volar surface; and by its having four articular facets touching each other, and separated by sharp edges. The superior surface, quadrilateral, 226 OSTEOLOGY smooth, and slightly concave, articulates with the navicular. The inferior surface articulates with the proximal end of the second metacarpal bone; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The dorsal and volar surfaces are rough for the attachment of ligaments, the former being the larger of the two. The lateral surface, convex and smooth, articulates with the greater multangular. The medial surface is con- cave and smooth in front, for artic- ulation with the capitate; rough behind, for the attachment of an interosseous ligament. Articulations.—The lesser multangular articulates with four bones: the navicular proximally, second metacarpal distally, greater multangular laterally, and capitate medially. The Capitate Bone (os capitatum; os magnum) (Fig. 227).—The capitate bone is the largest of the carpal bones, and occupies the center of the wrist. It presents, above, a rounded portion or head, which is received into the concavity formed by Volar surface For greater multangular For navicular Dorsal surface For capitate For metacarpal Fig. 226.—The left lesser multangular bone. For lunate Far navicular For hamate- For lesser multangular For 3rd metacarpal For 2nd metacarpal For 4th metacarpal Volar surface Fig. 227.—The left capitate bone. the navicular and lunate; a constricted portion or neck; and below this, the body. The superior surface is round, smooth, and articulates with the lunate. The inferior surface is divided by twro ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest. The dorsal surface is broad and rough. The volar surface is narrow7, rounded, and rough, for the attachment of ligaments and a part of the Adductor pollicis obliquus. For lunate For capitate For tr iangular For 4th metacarpal For 5th metacarpal Hamvlus For 5th metacarpal The lateral surface articulates with the lesser multangular by a small facet at its anterior inferior angle, behind which is a rough depression for the attach- ment of an interosseous ligament. Above this is a deep, rough groove, forming part of the neck, and serving for the attachment of ligaments; it is bounded supe- riorly by a smooth, convex surface, for articulation with the navicular. The medial Fio. 228.—The left hamate bone. THE METACARPUS 227 surface articulates with the hamate by a smooth, concave, oblong facet, which occupies its posterior and superior parts; it is rough in front, for the attachment of an interosseous ligament. Articulations.—The capitate articulates with seven bones: the navicular and lunate proximally, the second, third, and fourth metacarpals distally, the lesser multangular on the radial side, and the hamate on the ulnar side. The Hamate Bone {os hamatum; unciform bone) (Fig. 228).—The hamate bone may be readily distinguished by its wedge-shaped form, and the hook-like process which projects from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward. The superior surface, the apex of the wedge, is narrow, convex, smooth, and articulates with the lunate. The inferior surface articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge. The dorsal surface is triangular and rough for ligamentous attachment. The volar surface presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and lateralward. This process gives attachment, by its apex, to the transverse carpal ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor tendons into the palm of the hand. It is one of the four eminences on the front of the carpus to which the transverse carpal ligament of the wrist is attached; the others being the pisiform medially, the oblique ridge of the greater multangular and the tubercle of the navicular laterally. The medial surface articulates with the triangular bone by an oblong facet, cut obliquely from above, downward and medialward. The lateral surface articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments. Articulations.—The hamate articulates with five bones: the lunate proximally, the fourth and fifth metacarpals distally, the triangular medially, the capitate laterally. The Metacarpus. The metacarpus consists of five cylindrical bones which are numbered from the lateral side (ossa metacarpalia I-V); each consists of a body and two extremities. Common Characteristics of the Metacarpal Bones.—The Body (corpus; shaft).— The body is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal. The medial and lateral surfaces are concave, for the attachment of the Interossei, and separated from one another by a prominent anterior ridge. The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in the fresh state, by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the Interossei dorsales. To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpo- phalangeal joints. The Base or Carpal Extremity (basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments. The Head or Digital Extremity (capitulum) presents an oblong surface markedly convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. It is broader, and extends farther up- 228 OSTEOLOGY ward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint. The dorsal surface, broad and flat, supports the Extensor tendons; the volar surface is grooved in the middle line for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface. Characteristics of the Individual Metacarpal Bones.—The First Metacarpal Bone (os metacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm. The body is flattened and broad on its dorsal surface, and does not present the ridge which is found on the other metacarpal bones; its volar surface is concave from above downward. On its radial border is inserted the Opponens pollicis; its ulnar border gives origin to the lateral head of the first Interosseus dorsalis. The base presents a concavo-convex surface, for articulation with the greater multangular; it has no facets on its sides, but on its radial side is a tubercle for the insertion of the Abductor pollicis longus. The head is less convex than those of the other metacarpal bones, and is broader from side to side than from before backward. On its volar surface are two articular eminences, of which the lateral is the larger, for the two sesamoid bones in the tendons of the Flexor pollicis brevis. The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index finger) (Fig. 230) is the longest, and its base the largest, of the four remaining bones. Its base is prolonged upward and medialward, forming a prominent ridge. It presents four articular facets: three on the upper surface and one on the ulnar side. Of the facets on the upper surface the intermediate is the largest and is concave from side to side, convex from before backward for articulation with the lesser multangular; the lateral is small, flat and oval for articulation with the greater multangular; the medial, on the summit of the ridge, is long and narrow for articu- lation with the capitate. The facet on the ulnar side articulates with the third metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface and the Flexor carpi radialis on the rolar surface of the base. The Third Metacarpal Bone (os metacarpale III; metacarpal bone of the middle finger) (Fig. 231) is a little smaller than the second. The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the Extensor carpi radialis brevis. The carpal articular facet is concave behind, flat in front, and articulates with the capitate. On the radial side is a smooth, concave facet for articulation with the second metacarpal, and on the ulnar side two small oval facets for the fourth metacarpal. The Fourth Metacarpal Bone (os metacarpale IV; metacarpal bone of the ring finger) (Fig. 232) is shorter and smaller than the third. The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate, and a small one laterally for the capitate. On the radial side are two oval facets, for articulation with the third metacarpal; and on the ulnar side a single concave facet, for the fifth metacarpal. The Fifth Metacarpal Bone (os metacarpale V; metacarpal bone of the little finger) (Fig. 233) presents on its base one facet on its superior surface, which is concavo- For greater multangular j)or greater multangular Fig. 229.—The first metacarpal (Left.) THE METACARPUS 229 convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal. On its ulnar side is a prominent tubercle for the inser- tion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body I For leaser multangular \ For greater multangular For 3rd metacarpal \ For capitate \ For lesser ! mult- angular Styloid process For 2nd meta- carpal For capitate For 4:lh metacarpal Fig. 230.—The sectond metacarpal. (Left.) Fig. 231.—The third metacarpal. (Left.) is divided by an oblique ridge, which extends from near the ulnar side of the base to the radial side of the head. The lateral part of this surface serves for the attach- ment of the fourth Interosseus dorsalis; the medial part is smooth, triangular, and covered by the Extensor tendons of the little finger. For capitate For 3rd metacarpal For hamate For 5th meta- carpal For 4th metacarpal For hamate Fig. 232.—The fourth metacarpal. (Left.) Fiq. 233.—The fifth metacarpal. (Left.) Articulations.—Besides their phalangeal articulations, the metacarpal bones articulate as follows: the first with the greater multangular; the second with the greater multangular, lesser multangular, capitate and third metacarpal; the third with the capitate and second and fourth metacarpals; the fourth with the capitate, hamate, and third and fifth metacarpals; and the fifth with the hamate and fourth metacarpal. 230 OSTEOLOGY The Phalanges of the Hand (Phalanges Digitorum Manus). The phalanges are fourteen in number, three for each finger, and two for the thumb. Each consists of a body and two extremities. The body tapers from above downward, is convex posteriorly, concave in front from above downward, flat from side to side; its sides are marked by rough ridges which give attachment to the fibrous sheaths of the Flexor tendons. The proximal extremities of the bones of the first row present oval, concave articular surfaces, broader from side to side than from before backward. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge. The distal extremities are smaller than the proximal, and each ends in two condyles separated by a shallow groove; the articular surface extends farther on the volar than on the dorsal surface, a condition best marked in the bones of the first row. The ungual phalanges are convex on their dorsal and flat on their volar surfaces; they are recognized by their small size, and by a roughened, elevated surface of a horseshoe form on the volar surface of the distal extremity of each which serves to support the sensitive pulp of the finger. CARPUS One center for each hone : All cartilaginous at birth METACARPALS OF FINGERS Two centers for each hone : One for body One for head PHALANGES Two centers for each hone : One for body One for 'proximal extremity Fig. 234.—Plan of ossification of the hand, Articulations.—In the four fingers the phalanges of the first row articulate with those of the second row and with the metacarpals; the phalanges of the second row with those of the first and third rows, and the ungual phalanges with those of the second row. In the thumb, which has only two phalanges, the first phalanx articulates by its proximal extremity with the meta- carpal bone and by its distal with the ungual phalanx. Ossification of the Bones of the Hand.—The carpal bones are each ossified from a single center, and ossification proceeds in the following order (Fig. 234): in the capitate and hamate, during THE HIP BONE 231 the first year, the former preceding the latter; in the triangular, during the third year; in the lunate and greater multangular, during the fifth year, the former preceding the latter; in the navicular, during the sixth year; in the lesser multangular, during the eighth year; and in the pisiform, about the twelfth year Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying between the navicular, lesser multangular, and capitate. During the second month of fetal life it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navic- ular. Sometimes the styloid process of the third metacarpal is detached and forms an additional ossicle. The metacarpal bones are each ossified from two centers: one for the body and one for the distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one for the base of the first metacarpal bone.1 The first metacarpal bone is therefore ossified in the same manner as the phalanges, and this has led some anatomists to regard the thumb as being made up of three phalanges, and not of a metacarpal bone and two phalanges. Ossification com- mences in the middle of the body about the eighth or ninth week of fetal life, the centers for the second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; about the third year the distal extremities of the metacarpals of the fingers, and the base of the metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year. The phalanges are each ossified from two centers: one for the body, and one for the proximal extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of the proximal extremity commences in the bones of the first row between the third and fourth years, and a year later in those of the second and third rows. The two centers become united in each row between the eighteenth and twentieth years. In the ungual phalanges the centers for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the ungual phalanges are the first to ossify. THE BONES OF THE LOWER EXTREMITY (OSSA EXTREMITATIS INFERIORIS). The Hip Bone (Os Coxae; Innominate Bone). The hip bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. It meets its fellow on the opposite side in the middle line in front, and together they form the sides and anterior wall of the pelvic cavity. It consists of three parts, the ilium, ischium, and pubis, which are distinct from each other in the young subject, but are fused in the adult; the union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum, which is situated near the middle of the outer surface of the bone. The ilium, so-called because it supports the flank, is the superior broad and expanded portion which extends upward from the acetabulum. The ischium is the lowest and strongest portion of the bone; it proceeds downward from the acetab- ulum, expands into a large tuberosity, and then, curving forward, forms, with the pubis, a large aperture, the obturator foramen. The pubis extends medialward and downward from the acetabulum and articulates in the middle line with the bone of the opposite side: it front of the pelvis and supports the external organs of generation. The Ilium (os ilii).—The ilium is divisible into two parts, the body and the ala; the separation is indicated on the internal surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum. The Body (corpus oss. ilii).—The body enters into the formation of the acetab- ulum, of which it forms rather less than tw'o-fifths. Its external surface is partly articular, partly non-articular; the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the Obturator internus. Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union. 1 Allen Thomson demonstrated the fact that the first metacarpal bone is often developed from three centers: that is to say, there is a separate nucleus for the distal end, forming a distinct epiphysis visible at the age of seven or eight years. He also stated that there are traces of a proximal epiphysis in the second metacarpal bone, Journal of Anatomy and Physiology, 1889. 232 OSTEOLOGY The Ala (ala oss. ilii).—The ala is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two borders—an anterior and a posterior. The external surface (Fig. 235), known as the dorsum ilii, is directed backward and lateral- ward behind, and downward and lateralward in front. It is smooth, convex in front, Ant. superior spine Posterior i superior•“ spine Posterior - inferior spine ■Anterior inferior spine Articular capsule Ligamentum teres Gemellus superior _ Pectineus Spine of ischium- Rectus abdominis Pyramidalis Gemellus inferior - Adductor longus Fig. 235.—Right hip bone. External surface. deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders. This surface is crossed in an arched direction by three lines—the posterior, anterior, and inferior gluteal lines. The posterior gluteal line (superior curved line), the short- est of the three, begins at the crest, about 5 cm. in front of its posterior extremity; it is at first distinctly marked, but as it passes downward to the upper part of the THE HIP BONE 233 greater sciatic notch, where it ends, it becomes less distinct, and is often altogether lost. Behind this line is a narrow semilunar surface, the upper part of which is rough and gives origin to a portion of the Gluteus maximus; the lower part is smooth and has no muscular fibers attached to it. The anterior gluteal line (middle curved line), the longest of the three, begins at the crest, about 4 cm. behind its anterior extremity, and, taking a curved direction downward and backward, ends % Levator ani Constrictor urethrae Transversus perincei superfic. Crus penis Ischiocavernosus Pig. 236.—Right hip bone. Internal surface. at the upper part of the greater sciatic notch. The space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Gluteus medius. Near the middle of this line a nutrient foramen is often seen. The inferior gluteal line (inferior curved line), the least distinct of the three, begins in front at the notch on the anterior border, and, curving backward and downward, ends near the middle of the greater sciatic notch. The surface of bone included 234 OSTEOLOGY between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutseus minimus. Between the inferior gluteal line and the upper part of the acetabulum is a rough, shallow groove, from which the reflected tendon of the Rectus femoris arises. The internal surface (Fig. 236) of the ala is bounded above by the crest, below, by the arcuate line; in front and behind, by the anterior and posterior borders. It presents a large, smooth, concave surface, called the iliac fossa, which gives origin to the Iliacus and is perforated at its inner part by a nutrient canal; and below this a smooth, rounded border, the arcuate line, which runs downward, for- ward, and medialward. Behind the iliac fossa is a rough surface, divided into two portions, an anterior and a posterior. The anterior surface (auricular surface), so called from its resemblance in shape to the ear, is coated with cartilage in the fresh state, and articulates with a similar surface on the side of the sacrum. The posterior portion, known as the iliac tuberosity, is elevated and rough, for the attachment of the posterior sacroiliac ligaments and for the origins of the Sacrospinalis and Multifidus. Below and in front of the auricular surface is the preauricular sulcus, more commonly present and better marked in the female than in the male; to it is attached the pelvic portion of the anterior sacroiliac ligament. The crest of the ilium is convex in its general outline but is sinuously curved, being concave inward in front, concave outward behind. It is thinner at the center than at the extremities, and ends in the anterior and posterior superior iliac spines. The surface of the crest is broad, and divided into external and internal lips, and an intermediate line. About 5 cm. behind the anterior superior iliac spine there is a prominent tubercle on the outer lip. To the external lip are attached the Tensor fascise latfe, Obliquus externus abdominis, and Latissimus dorsi, and along its whole length the fascia lata; to the intermediate line the Obliquus internus abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, Quadratus lumborum, Sacrospinalis, and Iliacus. The anterior border of the ala is concave. It presents two projections, separated by a notch. Of these, the uppermost, situated at the junction of the crest and anterior border, is called the anterior superior iliac spine; its outer border gives attachment to the fascia lata, and the Tensor fascife latte, its inner border, to the Iliacus; while its extremity affords attachment to the inguinal ligament and gives origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius takes origin and across which the lateral femoral cutaneous nerve passes. Below the notch is the anterior inferior iliac spine, which ends in the upper lip of the acetabulum; it gives attachment to the straight tendon of the Rectus femoris and to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine is a broad, shallow groove, over which the Iliacus and Psoas major pass. This groove is bounded medially by an eminence, the iliopectineal eminence, which marks the point of union of the ilium and pubis. The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The former serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds with the posterior extremity of the auricular surface. Below the posterior inferior spine is a deep notch, the greater sciatic notch. The Ischium (os ischii).—The ischium forms the lower and back part of the hip bone. It is divisible into three portions—a body and two rami. The Body (corpus oss. ischii).—The body enters into and constitutes a little more than two-fifths of the acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the THE HIP BONE 235 Obturator internus. Its anterior border projects as the posterior obturator tubercle; from its posterior border there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects. The external surface of the spine gives attachment to the Gemellus superior, its internal surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed extremity the sacrospinous ligament is attached. Above the spine is a large notch, the greater sciatic notch, converted into a foramen by the sacrospinous ligament; it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of these, the superior gluteal vessels and nerve pass out above the Piriformis, the other structures below it. Below the spine is a smaller notch, the lesser sciatic notch; it is smooth, coated in the recent state with cartilage, the surface of which presents two or three ridges corresponding to the subdivisions of the tendon of the Obturator internus, which winds over it. It is converted into a foramen by the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and nerve. The Superior Ramus (ramus superior oss. ischii; descending ramus).—The superior ramus projects downward and backward from the body and presents for examination three surfaces: external, internal, and posterior. The external surface is quadrilateral in shape. It is bounded above by a groove which lodges the tendon of the Obturator externus; below, it is continuous with the inferior ramus; in front it is limited by the posterior margin of the obturator foramen; behind, a prominent margin separates it from the posterior surface. In front of this margin the surface gives origin to the Quadratus femoris, and anterior to this to some of the fibers of origin of the Obturator externus; the lower part of the sur- face gives origin to part of the Adductor magnus. The internal surface forms part of the bony wall of the lesser pelvis. In front it is limited by the posterior margin of the obturator foramen. Below, it is bounded by a sharp ridge which gives attachment to a falciform prolongation of the sacrotuberous ligament, and, more anteriorly, gives origin to the Transversus perinsei and Ischiocavernosus. Poste- riorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion. The lower portion is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts; the outer gives attachment to the Adductor magnus, the inner to the sacrotuberous ligament. The upper portion is subdivided into two areas by an oblique ridge, which runs downward and out- ward; from the upper and outer area the Semimembranosus arises; from the lower and inner, the long head of the Biceps femoris and the Semitendinosus. The Inferior Ramus (ramus inferior oss. ischii; ascending ramus).—The inferior ramus is the thin, flattened part of the ischium, which ascends from the superior ramus, and joins the inferior ramus of the pubis—the junction being indicated in the adult by a raised line. The outer surface is uneven for the origin of the Obturator externus and some of the fibers of the Adductor magnus; its inner surface forms part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly everted, forms part of the outlet of the pelvis, and presents two ridges and an intervening space. The ridges are continuous with similar ones on the inferior ramus of the pubis: to the outer is attached the deep layer of the superficial peri- neal fascia (fascia of Colies), and to the inner the inferior fascia of the urogenital diaphragm. If these two ridges be traced downward, they will be found to join with each other just behind the point of origin of the Transversus perinsei; here the two layers of fascia are continuous behind the posterior border of the muscle. To the intervening space, just in front of the point of junction of the ridges, the OSTEOLOGY Transversus periruei is attached, and in front of this a portion of the crus penis vel clitoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and forms part of the medial margin of the obturator foramen. The Pubis (os pubis).—The pubis, the anterior part of the hip bone, is divisible into a body, a superior and an inferior ramus. The Body (corpus oss. pubis).—The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser pelvis and gives origin to a portion of the Obturator internus. The Superior Ramus (ramus superior oss. pubis; ascending ramus).—The superior ramus extends from the body to the median plane where it articulates with its fellow of the opposite side. It is conveniently described in two portions, viz., a medial flattened part and a narrow lateral prismoid portion. The Medial Portion of the superior ramus, formerly described as the body of the pubis, is somewhat quadrilateral in shape, and presents for examination two surfaces and three borders. The anterior surface is rough, directed downward and outward, and serves for the origin of various muscles. The Adductor longus arises from the upper and medial angle, immediately below the crest; lower down, the Obturator externus, the Adductor brevis, and the upper part of the Gracilis take origin. The posterior surface, convex from above downward, concave from side to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin to the Levator ani and Obturator internus, and attachment to the puboprostatic ligaments and to a few muscular fibers prolonged from the bladder. The upper border presents a prominent tubercle, the pubic tubercle (pubic spine), which pro- jects forward; the inferior crus of the subcutaneous inguinal ring (external abdominal ring), and the inguinal ligament (Poupart’s ligament) are attached to it. Passing upward and lateralward from the pubic tubercle is a well-defined ridge, forming a part of the pectineal line which marks the brim of the lesser pelvis: to it are attached a portion of the inguinal falx (conjoined tendon of Obliquus internus and Transversus), the lacunar ligament (Gimbernat’s ligament), and the reflected inguinal ligament (triangular fascia). Medial to the pubic tubercle is the crest, which extends from this process to the medial end of the bone. It affords attach- ment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The point of junction of the crest with the medial border of the bone is called the angle; to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal ring is attached. The medial border is articular; it is oval, and is marked by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of a thin layer of cartilage, which intervenes between it and the interpubic fibrocartilaginous lamina. The lateral border presents a sharp margin, the obturator crest, which forms part of the circumference of the obturator foramen and affords attachment to the obturator membrane. The Lateral Portion of the ascending ramus has three surfaces: superior, inferior, and posterior. The superior surface presents a continuation of the pectineal line, already mentioned as commencing at the pubic tubercle. In front of this line, the surface of bone is triangular in form, wider laterally than medially, and is covered by the Pectineus. The surface is bounded, laterally, by a rough eminence, the iliopectineal eminence, which serves to indicate the point of junction of the ilium and pubis, and below by a prominent ridge which extends from the acetabular notch to the pubic tubercle. The inferior surface forms the upper boundary of the obturator foramen, and presents, laterally, a broad and deep, oblique groove, for the passage of the obturator vessels and nerve; and medially, a sharp margin, the obturator crest, forming part of the circumference of the obturator foramen, and giving attachment to the obturator membrane. The posterior surface consti- THE HIP BONE 237 tutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from above downward, and affords origin to some fibers of the Obturator internus. The Inferior Ramus (ramus inferior oss. pubis; descending ramus).—The inferior ramus is thin and flattened. It passes lateral ward and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen. Its anterior surface is rough, for the origin of muscles—the Gracilis along its medial border, a portion of the Obturator externus where it enters into the formation of the obturator foramen, and between these two, the Adductores brevis and magnus, the former being the more medial. The posterior surface is smooth, and gives origin to the Obturator internus, and, close to the medial margin, to the Constrictor urethrae. The medial border is thick, rough, and everted, especially in females. It presents two ridges, separated by an intervening space. The ridges extend downward, and are continuous with similar ridges on the inferior ramus of the ischium; to the external is attached the fascia of Colies, and to the internal the inferior fascia of the urogenital diaphragm. The lateral border is thin and sharp, forms part of the circumference of the obturator foramen, and gives attachment to the obturator membrane. The Acetabulum (cotyloid cavity).—The acetabulum is a deep, cup-shaped, hemi- spherical depression, directed downward, lateralward, and forward. It is formed medially by the pubis, above by the ilium, laterally and below by the ischium; a little less than two-fifths is contributed by the ilium, a little more than two- fifths by the ischium, and the remaining fifth by the pubis. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attach- ment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and deepens the surface for articulation. It presents below a deep notch, the acetabular notch, which is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity: this depression is perforated by numerous apertures, and lodges a mass of fat. The notch is converted into a foramen by the transverse ligament; through the foramen nutrient vessels and nerves enter the joint; the margins of the notch serve for the attachment of the ligamentum teres. The rest of the acetabulum is formed by a curved articular surface, the lunate surface, for articulation with the head of the femur. The Obturator Foramen (foramen obturatum; thyroid foramen).—The obturator foramen is a large aperture, situated between the ischium and pubis. In the male it is large and of an oval form, its longest diameter slanting obliquely from before backward; in the female it is smaller, and more triangular. It is bounded by a thin, uneven margin, to which a strong membrane is attached, and presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward. This groove is converted into a canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch; the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis. Through the canal the obturator vessels and nerve pass out of the pelvis. Structure.—The thicker parts of the bone consist of cancellous tissue, enclosed between two layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and center of the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. Ossification (Fig. 237).—The hip bone is ossified from eight centers: three primary—one each for the ilium, ischium, and pubis; and five secondary—one each for the crest of the ilium, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or more for the Y-shaped piece at the bottom of the acetabulum. The centers appear in the follow- ing order: in the lower part of the ilium, immediately above the greater sciatic notch, about the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; 238 OSTEOLOGY in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone. About the thirteenth or fourteenth year, the three primary centers have extended their growth into the bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification, often by two or more centers. One of these, the os acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum. The ilium and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped portion. At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis. Articulations.—The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur. By eight centers | TJiree Vrim/jrV {Mum. Ischium, and Pubis) 33 ( Ji ive secondary Fig. 237.—Plan of ossification of the hip bone. The three primary centers unite through a Y-shaped piece about puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. The Pelvis. The pelvis, so called from its resemblance to a basin, is a bony ring, interposed between the movable vertebne of the vertebral column which it supports, and the lower limbs upon which it rests; it is stronger and more massively constructed than the wall of the cranial or thoracic cavities, and is composed of four bones: the two hip bones laterally and in front and the sacrum and coccyx behind. The pelvis is divided by an oblique plane passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis pubis, into the greater and the lesser pelvis. The circumference of this plane is termed the linea terminalis or pelvic brim. The Greater or False Pelvis (pelvis major).—The greater pelvis is the expanded portion of the cavity situated above and in front of the pelvic brim. It is bounded on either side by the ilium; in front it is incomplete, presenting a wide interval between the anterior borders of the ilia, which is filled up in the fresh state by THE PELVIS 239 the parietes of the abdomen; behind is a deep notch on either side between the ilium and the base of the sacrum. It supports the intestines, and transmits part of their weight to the anterior wall of the abdomen. The Lesser or True Pelvis (pelvis minor).—The lesser pelvis is that part of the pelvic cavity which is situated below and behind the pelvic brim. Its bony walls are more complete than those of the greater pelvis. For convenience of descrip- tion, it is divided into an inlet bounded by the superior circumference, and outlet bounded by the inferior circumference, and a cavity. The Superior Circumference.—The superior circumference forms the brim of the pelvis, the included space being called the superior aperture or inlet (apertura pelvis [minoris] superior) (Fig. 238). It is formed laterally by the pectineal and arcuate lines, in front by the crests of the pubes, and behind by the anterior margin of the base of the sacrum and sacrovertebral angle. The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum. It has three principal diameters: antero-posterior, transverse, and oblique. The antero- posterior or conjugate diameter extends from the sacrovertebral angle to the sym- Fig. 238.—Diameters of superior aperture of lesser pelvis (female). physis pubis; its average measurement is about 110 mm. in the female. The transverse diameter extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; its aver- age measurement is about 135 mm. in the female. The oblique diameter extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side; its average measurement is about 125 mm. in the female. The cavity of the lesser pelvis is bounded in front and below by the pubic sym- physis and the superior rami of the pubes; above and behind, by the pelvic surfaces of the sacrum and coccyx, which, curving forward above and below, contract the superior and inferior apertures of the cavity; laterally, by a broad, smooth, quadrangular area of bone, corresponding to the inner surfaces of the body and superior ramus of the ischium and that part of the ilium which is below the arcuate line. From this description it will be seen that the cavity of the lesser pelvis is a short, curved canal, considerably deeper on its posterior than on its anterior wall. It contains, in the fresh subject, the pelvic colon, rectum, bladder, and some of the organs of generation. The rectum is placed at the back of the pelvis, in the curve of the sacrum and coccyx; the bladder is in front, behind the pubic sym- physis. In the female the uterus and vagina occupy the interval between these viscera. 240 OSTEOLOGY The Lower Circumference.—The lower circumference of the pelvis is very irregular; the space enclosed by it is named the inferior aperture or outlet (apertura pelvis [minoris] inferior) (Fig. 239), and is bounded behind by the point of the coccyx, and laterally by the ischial tuberosities. These eminences are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior Fig. 239.—Diameters of inferior aperture of lesser pelvis (female). rami of the ischium and pubis on either side. The other notches, one on either side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments. When the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded, in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia; later- ally, by the ischial tuberosities; and behind, by the sacrotuberous ligaments and the tip of the coccyx. The diameters of the outlet of the pelvis are two, antero-posterior and transverse. The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female. It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone. The transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female.1 Axes (Fig. 240).—A line at right angles to the plane of the superior aperture at its center would, if prolonged, pass through the umbilicus above and the middle of the coccyx below; the axis of the superior aperture is therefore directed downward and backward. The axis of the inferior aperture, produced upward, would touch the base of the sacrum, and is also directed downward, and slightly backward. The axis of the cavity—i. e., an axis at right angles to a series of planes between those of the superior and inferior apertures Fio. 240.—Median sagittal section of pelvis. 1 The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors no doubt due mainly to differences in the physique and stature of the population from whom the measurements have been taken. THE PELVIS 241 —is curved like the cavity itself: this curve corresponds to the concavity of the sacrum and coccyx, the extremities being indicated by the central points of the superior and inferior apertures. A knowledge of the direction of these axes serves to explain the course of the fetus in its passage through the pelvis during parturition. Position of the Pelvis (Fig. 240).—In the erect posture, the pelvis is placed obliquely with regard to the trunk: the plane of the superior aperture forms an angle of from 50° to 60°, and that of the inferior aperture one of about 15° with the horizontal plane. The pelvic surface of the symphysis pubis looks upward and backward, the concavity of the sacrum and coccyx downward and forward. The position of the pelvis in the erect posture may be indicated by holding it so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same vertical plane. Fig. 241.—Male pelvis. Differences between the Male and Female Pelves.—The female pelvis (Fig. 242) is distinguished from that of the male (Fig. 241) by its bones being more delicate and its depth less. The whole pelvis is less massive, and its muscular impressions are slightly marked. The ilia are less sloped, and the anterior iliac spines more widely separated; hence the greater lateral prominence of the hips. The preauricular sulcus is more commonly present and better marked. The supe- rior aperture of the lesser pelvis is larger in the female than in the male; it is more nearly circular, and its obliquity is greater. The cavity is shallower and wider; the sacrum is shorter wider, and its upper part is less curved; the obturator foramina are triangular in shape and smaller in size than in the male. The inferior aperture is larger and the coccyx more movable. The sciatic notches are wider and shallower, and the spines of the ischia project less inward. The acetabula are smaller and look more distinctly forward (Derry1). The ischial tuberosities and the acetabula are wider apart, and the former are more everted. The pubic symphysis is less deep, and the pubic arch is wider and more rounded than in the male, where it is an angle rather than an arch. 1 Journal of Anatomy and Physiology, vol. xliii. 242 OSTEOLOGY The size of the pelvis varies not only in the two sexes, but also in different members of the same sex, and does not appear to be influenced in any way by the height of the individual. Women of short stature, as a rule, have broad pelves. Occasionally the pelvis is equally contracted in all its dimensions, so much so that all its diameters measure 12.5 mm. less than the average, and this even in well-formed women of average height. The principal divergences, however, are found at the superior aperture, and affect the relation of the antero-posterior to the transverse diameter. Thus the superior aperture may be elliptical either in a transverse or an antero-posterior direction, the transverse diameter in the former, and the antero-posterior in the latter, greatly exceeding the other diameters; in other instances it is almost circular. Fig. 242.—Female pelvis. In the fetus, and for several years after birth, the pelvis is smaller in proportion than in the adult, and the projection of the sacrovertebral angle less marked. The characteristic differences between the male and female pelvis are distinctly indicated as early as the fourth month of fetal life. Abnormalities.—There is arrest of development in the bones of the pelvis in cases of extro- version of the bladder; the anterior part of the pelvic girdle is deficient, the superior rami of the pubes are imperfectly developed, and the symphysis is absent. “The pubic bones are sepa- rated to the extent of from two to four inches, the superior rami shortened and directed forward, and the obturator foramen diminished in size, narrowed, and turned outward. The iliac bones are straightened out more than normal. The sacrum is very peculiar. The lateral curve, instead of being concave, is flattened out or even convex, with the iliosacral facets turned more outward than normal, while the vertical curve is straightened.”1 The Femur (Thigh Bone). The femur (Figs. 244, 245), the longest and strongest bone in the skeleton, is almost perfectly cylindrical in the greater part of its extent. In the erect posture it is not vertical, being separated above from its fellow by a considerable interval, which corresponds to the breadth of the pelvis, but inclining gradually downward and medialward, so as to approach its fellow toward its lower part, for the purpose of bringing the knee-joint near the line of gravity of the body. The degree of this inclination varies in different persons, and is greater in the female than in the male, 1 Wood, Heath’s Dictionary of Practical Surgery, i, 426. THE FEMUR 243 on account of the greater breadth of the pelvis. The femur, like other long bones, is divisible into a body and two extremities. The Upper Extremity (proximal extremity, Fig. 243).—The upper extremity presents for examination a head, a neck, a greater and a lesser trochanter. The Head (caput femoris).—The head which is globular and forms rather more than a hemisphere, is directed upward, medialward, and a little forward, the greater part of its convexity being above and in front. Its surface is smooth, coated with cartilage in the fresh state, except over an ovoid depression, the fovea capitis femoris, which is situated a little below and behind the center of the head, and gives attachment to the ligamentum teres. The Neck (collum femoris).—The neck is a flattened pyramidal process of bone, connecting the head with the body, and forming with the latter a wide angle open- ing medialward. The angle is widest in infancy, and becomes lessened during growth, so that at puberty it forms a gentle curve from the axis of the body of the bone. In the adult, the neck forms an angle of about 125° with the body, but this varies in inverse proportion to the development of the pelvis and the stature. In Obturator internus and Gemelli Piriformis Insertion of Obturator externus Fovea capitis, for lig. teres Greater trochanter Lesser trochanter Fig. 243.—Upper extremity of right femur viewed from behind and above. the female, in consequence of the increased width of the pelvis, the neck of the femur forms more nearly a right angle with the body than it does in the male. The angle decreases during the period of growth, but after full growth has been attained it does not usually undergo any change, even in old age; it varies con- siderably in different persons of the same age. It is smaller in short than in long bones, and when the pelvis is wide. In addition to projecting upward and medial- ward from the body of the femur, the neck also projects somewhat forward; the amount of this forward projection is extremely variable, but on an average is from 12° to 14°. The neck is flattened from before backward, contracted in the middle, and broader laterally than medially. The vertical diameter of the lateral half is in- creased by the obliquity of the lower edge, which slopes downward to join the body at the level of the lesser trochanter, so that it measures one-third more than the antero-posterior diameter. The medial half is smaller and of a more circular shape. The anterior surface of the neck is perforated by numerous vascular foramina. Along the upper part of the line of junction of the anterior surface with the head is a shallow groove, best marked in elderly subjects; this 244 OSTEOLOGY Obturator internus and Oemelli Fovea capitis groove lodges the orbicular fibers of the capsule of the hip-joint. The posterior surface is smooth, and is broader and more concave than the anterior: the posterior part of the capsule of the hip-joint is attached to it about 1 cm. above the intertrochanteric crest. The superior border is short and thick, and ends laterally at the greater trochanter; its surface is perforated by large foramina. The inferior border, long and narrow, curves a little backward, to end at the lesser trochanter. The Trochanters.—The trochan- ters are prominent processes which afford leverage to the muscles that rotate the thigh on its axis. They are two in number, the greater and the lesser. The Greater Trochanter (;trochanter major; great trochanter) is a large, irregular, quadrilateral eminence, situated at the junction of the neck with the upper part of the body. It is directed a little lateralward and backward, and, in the adult, is about 1 cm. lower than the head. It has two surfaces and four borders. The lateral surface, quadrilateral in form, is broad, rough, convex, and marked by a diagonal impression, which extends from the postero-superior to the antero-inferior angle, and serves for the insertion of the ten- don of the Gluteus medius. Above the impression is a triangular sur- face, sometimes rough for part of the tendon of the same muscle, sometimes smooth for the inter- position of a bursa between the tendon and the bone. Below and behind the diagonal impression is a smooth, triangular surface, over which the tendon of the Gluteus maximus plays, a bursa being inter- posed. The medial surface, of much less extent than the lateral, pre- sents at its base a deep depression, the trochanteric fossa (digital fossa), for the insertion of the tendon of the Obturator externus, and above and in front of this an impression for the insertion of the Obtura- tuon u Piriformis Tubercle Articular capsule Lateral epicondyle l Articular capsule Adductor ~tubercle - Medial epicondyle Fia. 244.—Right femur. Anterior surface. THE FEMUR 245 tor internus and Gemelli. The superior border is free; it is thick and irregular, and marked near the center by an impression for the insertion of the Piriformis. The inferior border corresponds to the line of junction of the base of the trochanter with the lateral surface of the body; it is marked by a rough, prominent, slightly curved ridge, which gives origin to the upper part of the Vastus lateralis. The anterior border is prominent and some- what irregular; it affords inser- tion at its lateral part to the Glutseus minimus. The posterior border is very prominent and appears as a free, rounded edge, which bounds the back part of the trochanteric fossa. The Lesser Trochanter (tro- chanter minor; small trochanter) is a conical eminence, which varies in size in different sub- jects; it projects from the lower and back part of the base of the neck. From its apex three well- marked borders extend; two of these are above—a medial con- tinuous with the lower border of the neck, a lateral with the intertrochanteric crest; the in- ferior border is continuous with the middle division of the linea aspera. The summit of the tro- chanter is rough, and gives in- sertion to the tendon of the Psoas major. A prominence, of variable size, occurs at the junction of the upper part of the neck with the greater trochanter, and is called the tubercle of the femur; it is the point of meeting of five muscles: the Gluteus minimus laterally, the Vastus lateralis below, and the tendon of the Obturator internus and two Gemelli above. Running ob- liquely downward and medial- ward from the tubercle is the intertrochanteric line (spiral line of the femur); it winds around the medial side of the body of the bone, below the lesser tro- Articular capsule Medial Adductor epicondyle tubercle 1 1 hater al epicondyle Groove for tendon of Popliteus Articular capsule Fig. 245.—Right femur. Posterior surface, 246 OSTEOLOGY chanter, and ends about 5 cm. below this eminence in the linea aspera. Its upper half is rough, and affords attachment to the iliofemoral ligament of the hip-joint; its lower half is less prominent, and gives origin to the upper part of the Vastus medialis. Running obliquely downward and medialward from the summit of the greater trochanter on the posterior surface of the neck is a prominent ridge, the intertrochanteric crest. Its upper half forms the posterior border of the greater tro- chanter, and its lower half runs downward and medialward to the lesser trochanter. A slight ridge is sometimes seen commencing about the middle of the intertrochan- teric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata, and gives attachment to the Quad- ratus femoris and a few fibers of the Adductor magnus. Generally there is merely a slight thickening about the middle of the intertrochanteric crest, marking the attachment of the upper part of the Quadratus femoris. The Body or Shaft (corpus femoris).—The body, almost cylindrical in form, is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front, and con- cave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera. It presents for examination three borders, separating three surfaces. Of the borders, one, the linea aspera, is posterior, one is medial, and the other, lateral. The linea aspera (Fig. 245) is a prominent longitudinal ridge or crest, on the middle third of the bone, presenting a medial and a lateral lip, and a narrow rough, intermediate line. Above, the linea aspera is prolonged by three ridges. The lateral ridge is very rough, and runs almost vertically upward to the base of the greater trochanter. It is termed the gluteal tuberosity, and gives attachment to part of the Gluta?us maximus: its upper part is often elongated into a roughened crest, on which a more or less well-marked, rounded tubercle, the third trochanter, is occasionally developed. The intermediate ridge or pectineal line is continued to the base of the lesser trochanter and gives attachment to the Pectineus; the medial ridge is lost in the intertrochanteric line; between these two a portion of the Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing between them a triangular area, the popliteal surface, upon which the popliteal artery rests. Of these two ridges, the lateral is the more prominent, and descends to the summit of the lateral condyle. The medial is less marked, especially at its upper part, where it is crossed by the femoral artery. It ends below at the summit of the medial condyle, in a small tubercle, the adductor tubercle, which affords insertion to the tendon of the Adductor magnus. From the medial lip of the linea aspera and its prolongations above and below, the Vastus medialis arises; and from the lateral lip and its upward prolongation, the Vastus lateralis takes origin. The Adductor magnus is inserted into the linea aspera, and to its lateral prolongation above, and its medial prolongation below. Between the Vastus lateralis and the Adductor magnus two muscles are attached —viz., the Glutseus maximus inserted above, and the short head of the Biceps femoris arising below. Betweeen the Adductor magnus and the Vastus medialis four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis and Adductor longus below. The linea aspera is perforated a little below its center by the nutrient canal, which is directed obliquely upward. The other two borders of the femur are only slightly marked: the lateral border extends from the antero-inferior angle of the greater trochanter to the anterior extremity of the lateral condyle; the medial border from the intertrochanteric line, at a point opposite the lesser trochanter, to the anterior extremity of the medial condyle. The anterior surface includes that portion of the shaft which is situated between the lateral and medial borders. It is smooth, convex, broader above and below than in the center. From the upper three-fourths of this surface the Vastus inter- medius arises; the lower fourth is separated from the muscle by the intervention THE FEMUR 247 of the synovial membrane of the knee-joint and a bursa; from the upper part of it the Articularis genu takes origin. The lateral surface includes the portion between the lateral border and the linea aspera; it is continuous above with the correspond- ing surface of the greater trochanter, below with that of the lateral condyle: from its upper three-fourths the Vastus intermedius takes origin. The medial surface includes the portion between the medial border and the linea aspera; it is continu- ous above with the lower border of the neck, below' with the medial side of the medial condyle: it is covered by the Vastus medialis. The Lower Extremity (distal extremity), (Fig. 246).—The lower extremity, larger than the upper, is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior; it consists of tw'o oblong eminences know'n as the condyles. In front, the condyles are but slightly prominent, and are separated from one another by a smooth shallow articular depression called the patellar surface; behind, they project considerably, and the interval between them forms a deep notch, the intercondyloid fossa. The lateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters, the medial condyle is the longer and, wrhen the femur is held with its body perpendicular, projects to a lower -Medial groove Lateral groove Medial epicondyle ■Semilunar area Lateral epicondyle Fia. 246.—Lower extremity of right femur viewed from below. level. When, however, the femur is in its natural oblique position the lower sur- faces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost directly antero-posterior, but that of the medial runs backward and mediahvard. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid line, and below by the central part of the posterior margin of the patellar surface. The posterior cruciate ligament of the knee-joint is attached to the lower and front part of the medial wall of the fossa and the anterior cruciate ligament to an impres- sion on the upper and back part of its lateral wall. Each condyle is surmounted by an elevation, the epicondyle. The medial epicondyle is a large convex eminence to which the tibial collateral ligament of the knee-joint is attached. At its upper part is the adductor tubercle, already referred to, and behind it is a rough impres- sion which gives origin to the medial head of the Gastrocnemius. The lateral epicondyle, smaller and less prominent than the medial, gives attachment to the fibular collateral ligament of the knee-joint. Directly below it is a small depression from which a smooth well-marked groove curves obliquely upward and backward to the posterior extremity of the condyle. This groove is separated from the articular surface of the condyle by a prominent lip across which a second, shallower groove runs vertically downward from the depression. In the fresh state these grooves are covered with cartilage. The Popliteus arises from the depression; its tendon lies in the oblique groove when the knee is flexed and in the vertical 248 OSTEOLOGY groove when the knee is extended. Above and behind the lateral epicondyle is an area for the origin of the lateral head of the Gastrocnemius, above and to the medial side of which the Plantaris arises. The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella; it presents a median groove which extends down- ward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. The lower and posterior parts of the articular surface constitute the tibial surfaces for articulation with the corresponding condyles of the tibia and menisci. These surfaces are separated from one another by the intercondyloid fossa and from the patellar surface by faint grooves which extend obliquely across the condyles. The lateral groove is the better marked; it runs lateralward and forward from the front part of the intercondyloid fossa, and expands to form a triangular depression. When the knee-joint is fully extended, the triangular depression rests upon the anterior portion of the lateral meniscus, and the medial part of the groove comes into con- tact with the medial margin of the lateral articular surface of the tibia in front of the lateral tubercle of the tibial intercondyloid eminence. The medial groove is less distinct than the lateral. It does not reach as far as the intercondyloid fossa and therefore exists only on the medial part of the condyle; it receives the anterior edge of the medial meniscus when the knee-joint is extended. Where the groove ceases laterally the patellar surface is seen to be continued backward as a semilunar area close to the anterior part of the intercondyloid fossa; this semi- lunar area articulates with the medial vertical facet of the patella in forced flexion of the knee-joint. The tibial surfaces of the condyles are convex from side to side and from before backward. Each presents a double curve, its posterior segment being an arc of a circle, its anterior, part of a cycloid.1 The Architecture of the Femur.—Koch2 by mathematical analysis has “shown that in every part of the femur there is a remarkable adaptation of the inner structure of the bone to the machan- ical requirements due to the load on the femur-head. The various parts of the femur taken together form a single mechanical structure wonderfully well-adapted for the efficient, economical transmission of the loads from the acetabulum to the tibia; a structure in which every element contributes its modicum of strength in the manner required by theoretical mechanics for maximum efficiency.” “The internal structure is everywhere so formed as to provide in an efficient manner for all the internal stresses which occur due to the load on the femur-head. Throughout the femur, with the load on the femur-head, the bony material is arranged in the paths of the maximum internal stresses, which are thereby resisted with the greatest efficiency, and hence with maximum economy of material.” “The conclusion is inevitable that the inner structure and outer form of the femur are governed by the conditions of maximum stress to which the bone is subjected normally by the preponderant load on the femur-head; that is, by the body weight transmitted to the femur-head through the acetabulum.” “The femur obeys the mechanical laws that govern other elastic bodies under stress; the relation between the computed internal stresses due to the load on the femur-head, and the internal structure of the different portions of the femur is in very close agreement with the theoretical relations that should exist between stress and structure for maximum economy and efficiency; and, therefore, it is believed that the following laws of bone structure have been demonstrated for the femur: “1. The inner structure and external form of human bone are closely adapted to the mechanical conditions existing at every point in the bone. “2. The inner architecture of normal bone is determined by definite and exact requirements of mathematical and mechanical laws to produce a maximum of strength with a minimum of material.” The Inner Architecture of the Upper Femur.—“The spongy bone of the upper femur (to the lower limit of the lesser trochanter) is composed of two distinct systems of trabeculae arranged in curved paths: one, which has its origin in the medial (inner) side of the shaft and curving upward 1 A cycloid is a curve traced by a point in the circumference of a wheel when the wheel is rolled along in a straight line. 2 The Laws of Bone Architecture. Am. Jour, of Anat., 21, 1917. The following paragraphs are taken almost ver- batum from Koch’s article in which we have the first correct mathematical analysis of the femur in support of the theory of the functional form of bone proposed by Wolff and also by Roux. THE FEMUR 249 in a fan-like radiation to the opposite side of the bone; the other, having origin in the lateral (outer) portion of the shaft and arching upward and medially to end in the upper surface of the greater trochanter, neck and head. These two systems intersect each other at right angles. “A. Medial (Compressive) System of Trabeculae.—As the compact bone of the medial (inner) part of the shaft nears the head of the femur it gradually becomes thinner and finally reaches the articular surface of the head as a very thin layer. From a point at about the lower level of the Fig. 247.—Frontal longitudinal midsection of upper femur. lesser trochanter, 2\ to 3 inches from the lower limit of the articular surface of the head, the trabecula? branch off from the shaft in smooth curves, spreading radially to cross to the opposite side in two well-defined groups: a lower, or secondary group, and an upper, or principal group. “a. The Secondary Compressive Group.—This group of trabecula? leaves the inner border of the shaft beginning at about the level of the lesser trochanter, and for a distance of almost 2 inches along the curving shaft, with which the separate trabecula? make an angle of about 45 degrees. 250 OSTEOLOGY They curve outwardly and upwardly to cross in radiating smooth curves to the opposite side. The lower filaments end in the region of the greater trochanter: the adjacent filaments above these pursue a more nearly vertical course and end in the upper portion of the neck of the femur. The trabeculae of this group are thin and with wide spaces between them. As they traverse the space between the medial and lateral surfaces of the bone they cross at right angles the system of curved trabecula; which arise from the lateral (outer) portion of the shaft. (Figs. 247 and 249.) “b. The Principal Compressive Group.—This group of trabeculae (Figs. 247 and 249) springs from the medial portion of the shaft just above the group above-described, and spreads upward and in slightly radial smooth curved lines to reach the upper portion of the articular surface of the head of the femur. These trabeculae are placed very closely together and are the thickest ones seen in the upper femur. They are a prolongation of the shaft from which they spring in straight Fig. 248.—Diagram of the lines of stress in the upper femur, based upon the mathematical analysis of the right femur. These result from the combination of the different kinds of stresses at each point in the femur. (After Koch.) lines which gradually curve to meet at right-angles the articular surface. There is no change as they cross the epiphyseal line. They also intersect at right-angles the system of lines which rise from the lateral side of the femur. “This system of principal and secondary compressive trabecula; corresponds in position and in curvature with the lines of maximum compressive stress, which were traced out in the mathematical analysis of this portion of the femur. (Figs. 247 and 250.) “B. Lateral (Tensile) System of Trabeculae.—As the compact bone of the outer portion of the shaft approaches the greater trochanter it gradually decreases in thickness. Beginning at a point about 1 inch below the level of the lower border of the greater trochanter, numerous thin trabecula' are given off from the outer portion of the shaft. These trabeculae lie in three distinct groups. “c. The Greater Trochanter Group.—These trabeculae rise from the outer part of the shaft just below the greater trochanter and rise in thin, curving lines to cross the region of the greater trochanter and end in its upper surface. Some of these filaments are poorly defined. This group THE FEMUR 251 + INDICATES COMPRESSIVE STRESS — •• TENSILE STRESS ONLY MAXIMUM STRESSES ARE SHOWN (IN POUNDS PER SQ. IN.) NOTE:-STRESSES DUE TO OTHER LOADS MAY BE FOUND BY MULTI- PLYING THE STRESSES IN THE FIGURE BY THE RATIO BETWEEN THE LOAD AND 100 LBS. Fig. 249.—Frontal longitudinal midsection of left femur. Taken from the same subject as the one that was analyzed and shown in Figs. 248 and 250. j of natural size. (After Koch.) Fig. 250. — Diagram of the computed lines of maximum stress in the normal femur. The section numbers 2, 4, 6, 8, etc., show the positions of the transverse sections analyzed. The amounts of the maximum tensile and compressive stress at the various sections are given for a load of 100 pounds on the femur-head. For the standing position (“at at- tention”) these stresses are multiplied by 0.6, for walking by 1.6 and for running by 3.2. (After Koch.) 252 OSTEOLOGY intersects the traibeculae of group (a) which rise from the opposite side. The trabeculae of this group evidently carry small stresses, as is shown by their slenderness. “d. The Principal Tensile Group.—This group springs from the outer part of the shaft imme- diately below group c, and curves convexly upward and inward in nearly parallel lines across the neck of the femur and ends in the inferior portion of the head. These trabeculae are somewhat thinner and more widely spaced than those of the principal compressive group (b). All the trabec- ulae of this group cross those of groups (a) and (b) at right angles. This group is the most impor- tant of the lateral system (tensile) and, as will be shown later, the greatest tensile stresses of the upper femur are carried by the trabeculae of this group. “e. The Secondary Tensile Group.—This group consists of the trabeculae which spring from the outer side of the shaft and lie below those of the preceding group. They curve upward and medially across the axis of the femur and end more or less irregularly after crossing the midline, but a number of these filaments end in the medial portion of the shaft and neck. They cross at right angles the trabeculae of group (a). 0 = COMPRESSION • = TENSION © = COMP. & TENSION NEUTRAL AXIS Fig. 251.—Intensity of the maximum tensile and compressive stresses in the upper femur. Computed for the load of 100 pounds on the right femur. Corresponds to the upper part of Fig. 250. (After Koch.) “In general, the trabeculae of the tensile system are lighter in structure than those of the com- pressive system in corresponding positions. The significance of the difference in thickness of these two systems is that the thickness of the trabecula? varies with the intensity of the stresses at any given point. Comparison of Fig. 247 with Fig. 251 will show that the trabecula? of the com- pressive system carry heavier stresses than those of the tensile system in corresponding positions. For example, the maximum tensile stress at section 8 (Fig. 251) in the outermost fiber is 771 pounds per square inch, and at the corresponding point on the compressive side the compressive stress is 954 pounds per square inch. Similar comparisons may be made at other points, which confirm the conclusion that the thickness and closeness of spacing of the trabeculae varies in proportion to the intensity of the stresses carried by them. “It will be seen that the trabecula? lie exactly in the paths of the maximum tensile and com- pressive stresses (compare Figs. 247, 248 and 251), and hence these trabeculae carry these stresses in the most economical manner. This is in accordance with the well-recognized principle of mechanics that the most direct manner of transmitting stress is in the direction in which the stress acts. THE FEMUR 253 “Fig. 249 shows a longitudinal frontal section through the left femur, which is the mate of the right femur on which the mathematical analysis was made. In this midsection the system of tensile trabeculae, which rises from the lateral (outer) part of the shaft and crosses over the central area to end in the medial portion of the shaft, neck and head, is clearly shown. This figure also shows the compressive system of trabeculae which rises on the medial portion of the shaft and crosses the central area to end in the head, neck and greater trochanter. By comparing the posi- tion of these two systems of trabeculae shown in Fig. 249 with the lines of maximum and minimum stresses shown in Figs. 248 and 250 it is seen that the tensile system of trabeculae corresponds exactly with the position of the lines of maximum and minimum tensile stresses which were determined by mathematical analysis. In a similar manner, the compressive system of trabeculae in Fig. 249 corresponds exactly with the lines of maximum and minimum compressive stresses computed by mathematical analysis. “ The amount of vertical shear varies almost uniformly from a maximum of 90 pounds (90 per cent, of the load on the femur-head) midway between sections 4 and 6, to a minimum of —5.7 pounds at section 18” (Fig. 251). There is a gradual diminution of the spongy bone from section 6 to section 18 parallel with the diminished intensities of the vertical shear. 1. The trabeculae of the' upper femur, as shown in frontal sections, are arranged in two general syste'ms, compressive and tensile, which correspond in position with the lines of maximum and minimum stresses in the femur determined by the mathematical analysis of the femur as a mechan- ical structure. 2. The thickness and spacing of the trabeculae vary with the intensity of the maximum stresses at various points in the upper femur, being thickest and most closely spaced in the regions where the greatest stresses occur. 3. The amount of bony material in the spongy bone of the upper femur varies in proportion to the intensity of the shearing force at the various sections. 4. The arrangement of the trabeculae in the positions of maximum stresses is such that the greatest strength is secured with a minimum of material. Significance of the Inner Architecture of the Shaft.—1. Economy for resisting shear. The shearing stresses are at a minimum in the shaft. “It is clear that a minimum amount of material will be required to resist the shearing stresses.” As horizontal and vertical shearing stresses are most efficiently resisted by material placed near the neutral plane, in this region a minimum amount of material will be needed near the neutral axis. In the shaft there is very little if any material in the central space, practically the only material near the neutral plane beiijg in the compact bone, but lying at a distance from the neutral axis. This conforms to the requirement of mechanics for economy, as a minimum of material is provided for resisting shearing stresses where these stresses are a minimum. 2. Economy for resisting bending moment. “The pending moment increases from a minimum at section 4 to a maximum between sections 16 and 18, then gradually decreases almost uniformly to 0 near section 75.” “To resist bending moment stresses most effectively the material should be as far from the neutral axis as possible.” It is evident that the hollow shaft of the femur is an efficient structure for resisting bending moment stresses, all of the material in the shaft being relatively at a considerable distance from the neutral axis. It is evident that the hollow shaft provides efficiently for resisting bending moment not only due to the load on the femur-head, but from any other loads tending to produce bending in other planes. 3. Economy for resisting axial stress. The inner architecture of the shaft is adapted to resist in the most efficient manner the com- bined action of the minimal shearing forces and the axial and maximum bending stresses. The structure of the shaft is such as to secure great strength with a relatively small amount of material. The Distal Portion of the Femur.—In frontal section (Fig. 249) in the distal 6 inches of the femur “there are to be seen two main systems of trabecula?, a longitudinal and a transverse system. The trabeculae of the former rise from the inner wall of the shaft and continue in per- fectly straight lines parallel to the axis of the shaft and proceed to the epiphyseal line, whence they continue in more or less curved lines to meet the articular surface of the knee-joint at right angles at every point. Near the center there are a few thin, delicate, longitudinal trabeculae which spring from the longitudinal trabeculae just described, to which they are joined by fine transverse filaments that lie in planes parallel to the sagittal plane. “The trabeculae of the transverse system are somewhat lighter in structure than those of the longitudinal system, and consist of numerous trabeculae at right angles to the latter. “As the distal end of the femur is approached the shaft gradually becomes thinner until the articular surface is reached, where there remains only a thin shell of compact bone. With the gradual thinning of the compact bone of the shaft, there is a simultaneous increase in the amount of the spongy bone, and a gradual flaring of the femur which gives this portion of the bone a gradually increasing gross area of cross-section. “There is a marked thickening of the shell of bone in the region of the intercondyloid fossa where the anterior and posterior crucial ligaments are attached. This thickened area is about 254 OSTEOLOGY 0.4 inch in diameter and consists of compact bone from which a number of thick trabeculae pass at right angles to the main longitudinal system. The inner structure of the bone is here evidently adapted to the efficient distribution of the stresses arising from this ligamentary at- tachment. “Near the distal end of the femur the longi- tudinal trabeculae gradually assume curved paths and end perpendicularly to the articular surface at every point. Such a structure is in accordance with the principles of mechanics, as stresses can be communicated through a frictionless joint only in a direction perpendic- ular to the joint surface at every point. “With practically no increase in the amount of bony material used, there is a greatly increased stability produced by the expansion of the lower femur from a hollow shaft of compact bone to a structure of much larger cross-section almost entirely composed of spongy bone. “ Significance of the Inner Architecture of the Distal Part of the Femur.—The function of the lower end of the femur is to transmit through a hinged joint the loads carried by the femur. For stability the width of the bearing on which the hinge action occurs should be relatively large. For economy of material the expansion of the end bearing should be as lightly constructed as is consistent with proper strength. In accordance with the principles of mechanics Appears at 4th year ; joins body about 18th yr.J Appears at end of 1st yr. ; joins body about 18th yr. Appears 13fA-14fA year ; joins body about 18th year Appears at 9th month of fetal life Joins body at 20th year Fig. 252.—Plan of ossification of the femur. From five centers. Lower extremity Fig. 253.—Epiphysial lines of femur in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. Fig. 254.—Epiphysial lines of femur in a young adult. Posterior aspect. The lines of attachment of the articular capsules are in blue. THE PATELLA 255 the most efficient manner in which stresses are transmitted is by the arrangement of the resist- ing material in lines parallel to the direction in which the stresses occur and in the paths taken by the stresses. Theoretically the most efficient manner to attain these objects would be to pro- long the innermost filaments of the bone as straight lines parallel to the longitudinal axis of the bone, and gradually to flare the outer shell of compact bone outward, and continuing to give off filaments of bone parallel to the longitudinal axis as the distal end of the femur is approached. These filaments should be well-braced transversely and each should carry its proportionate part of the total load, parallel to the longitudinal axis, transmitting it eventually to the articular surface, and in a direction perpendicular to that surface.” Referring to Fig. 249, it is seen that the large expansion of the bone is produced by the gradual transition of the hollow shaft of compact bone to cancellated bone, resulting in the production of a much larger volume. The trabeculae are given off from the shaft in lines parallel to the longitudinal axis, and are braced transversely by two series of trabeculae at right angles to each other, in the same manner as required theoretically for economy. Although the action of the muscles exerts an appreciable effect on the stresses in the femur, it is relatively small and very complex to analyze and has not been considered in the above analysis. Ossification (Figs. 252, 253, 254).—The femur is ossified from five centers: one for the body, one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, except the clavicle, it is the first to show traces of ossification; this commences in the middle of the body, at about the seventh week of fetal life, and rapidly extends upward and downward. The centers in the epiphyses appear in the following order: in the lower end of the bone, at the ninth month of fetal fife (from this center the condyles and epicondyles are formed); in the head, at the end of the first year after birth; in the greater trochanter, during the fourth year; and in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the epiphyses are joined to the body is the reverse of that of their appearance; they are not united until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, lastly, the inferior extremity, which is not united until the twentieth year. The Patella (Knee Cap). The patella (Figs. 255, 256) is a flat, triangular bone, situated on the front of the knee-joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris, and resembles these bones (1) in being developed in a tendon; (2) in its center of ossification presenting a knotty or tuberculated outline; (3) in being composed mainly of dense cancellous tissue. It serves to protect the front of the joint, and increases the leverage of the Quadriceps femoris by making it act at a greater angle. It has an anterior and a posterior surface three borders, and an apex. * Surfaces.—The anterior surface is convex, perforated by small apertures for the passage of nutrient vessels, and marked by numerous rough, longitudinal striae. This surface is covered, in the recent state, by an expansion from the tendon of the Quadriceps femoris, which is continuous below with the superficial fibers of the ligamentum patellae. It is separated from the integument by a bursa. The posterior surface presents above a smooth, oval, articular area, divided into two facets by a vertical ridge; the ridge corresponds to the groove on the patellar surface of the femur, and the facets to the medial and lateral parts of the same surface; the lateral facet is the broader and deeper. Below the articular surface is a rough, convex, non-articular area, the lower half of which gives attachment to the ligamentum patella; the upper half is separated from the head of the tibia by adipose tissue. Borders.—The base or superior border is thick, and sloped from behind, down- ward, and forward: it gives attachment to that portion of the Quadriceps femoris Fig. 255.—Right patella. Anterior surface. Fig. 256.—Right patella. Posterior surface. 256 OSTEOLOGY which is derived from the Itectus femoris and Vastus intermedius. The medial and lateral borders are thinner and converge below: they give attachment to those portions of the Quadriceps femoris which are derived from the Vasti lateralis and medialis. Apex.—The apex is pointed, and gives attachment to the ligamentum patellae. Structure.—The patella consists of a nearly uniform dense cancellous tissue, covered by a thin compact lamina. The cancelli immediately beneath the anterior surface are arranged parallel with it. In the rest of the bone they radiate from the articular surface toward the other parts of the bone. Ossification.—The patella is ossified from a single center, which usually makes its appearance in the second or third year, but may be delayed until the sixth year. More rarely, the bone is developed by two centers, placed side by side. Ossification is completed about the age of puberty. Articulation.—The patella articulates with the femur. The Tibia (Shin Bone). Thte tibia (Figs. 258, 259) is situated at the medial side of the leg, and, excepting the femur, is the longest bone of the skeleton. It is prismoid in form, expanded above, where it enters into the knee-joint, contracted in the lower third, and again enlarged but to a lesser extent below. In the male, its direction is vertical, and parallel with the bone of the opposite side; but in the female it has a slightly oblique direction downward and lateralward, to compensate for the greater obliquity of the femur. It has a body and two extremities. The Upper Extremity (proximal extremity). —The upper extremity is large, and expanded into two eminences, the medial and lateral condyles. The superior articular surface pre- sents two smooth articular facets (Fig. 257). The medial facet, oval in shape, is slightly concave from side to side, and from before backward. The lateral, nearly circular, is concave from side to side, but slightly convex from before backward, especially at its posterior part, where it is prolonged on to the posterior surface for a short distance. The central portions of these facets articulate with the con- dyles of the femur, while their peripheral portions support the menisci of the knee-joint, which here intervene between the two bones. Between the artic- ular facets, but nearer the posterior than the anterior aspect of the bone, is the intercondyloid eminence (spine of tibia), surmounted on either side by a prominent tubercle, on to the sides of which the articular facets are prolonged; in front of and behind the intercondyloid eminence are rough depressions for the attachment of the anterior and posterior cruciate ligaments and the menisci. The anterior surfaces of the condyles are continuous with one another, forming a large somewhat flattened area; this area is triangular, broad above, and perforated by large vascular foramina; narrow below where it ends in a large oblong elevation, the tuberosity of the tibia, which gives attachment to the ligamentum patellaj; a bursa intervenes between the deep surface of the ligament and the part'of the bone immediately above the tuberosity. Posteriorly, the condyles are separated from each other by a shallow depression, the posterior intercondyloid fossa, which gives attachment to part of the posterior cruciate ligament of the knee-joint. The medial condyle presents posteriorly a deep transverse groove, for the insertion of the tendon of Tuberosity Intercondyloid eminence, Fig. 257.—Upper surface of right tibia. THE TIBIA 257 the Semimembranosus. Its medial surf aceis convex, rough, and promi- nent; it gives attachment to the tibial collateral ligament. The lat- eral condyle presents posteriorly a flat articular facet, nearly circular in form, directed downward, back- ward, and lateralward, for articu- lation with the head of the fibula. Its lateral surface is convex, rough, and prominent in front: on it is an eminence, situated on a level with the upper border of the tuber- osity and at the junction of its anterior and lateral surfaces, for the attachment of the iliotibial band. Just below this a part of the Extensor digitorum longus takes origin and a slip from the tendon of the Biceps femoris is inserted. The Body or Shaft (corpus tibiae). —The body has three borders and three surfaces. Borders.—The anterior crest or border, the most prominent of the three, commences above at the tuberosity, and ends below at the anterior margin of the medial malleolus. It is sinuous and prominent in the upper two-thirds of its extent, but smooth and rounded below; it gives attach- ment to the deep fascia of the leg. The medial border is smooth and rounded above and below, but more prominent in the center; it begins at the back part of the medial condyle, and ends at the posterior border of the medial malleolus; its upper part gives attachment to the tibial collat- eral ligament of the knee-joint to the extent of about 5 cm., and insertion to some fibers of the Popliteus; from its middle third some fibers of the Soleus and Flexor digitorum longus take origin. The interosseous crest or lateral border is thin and prominent, espe- cially its central part, and gives at- tachment to the interosseous mem- brane; it commences above in front of the fibular articular facet, and Articular capsule Styloid process Fibular collateral ligament fibula! TIBIA Articular capsule Lateral malleolus Medial malleolus Fig. 258.—Bones of the right leg. Anterior surface. 258 OSTEOLOGY bifurcates below, to form the boundaries of a triangular rough surface, for the attachment of the interosseous ligament connecting the tibia and fibula. Surfaces.—The medial surface is smooth, convex, and broader above than below; its upper third, directed forward and medial ward, is covered by the aponeurosis derived from the tendon of the Sartorius, and by the tendons of the Gracilis and Semitendinosus, all of which are inserted nearly as far for- ward as the anterior crest; in the rest of its extent it is sub- cutaneous. The lateral surface is narrower than the medial; its upper two- thirds present a shallow groove for the origin of the Tibialis anterior; its lower third is smooth, convex, curves grad- ually forward to the anterior aspect of the bone, and is covered by the tendons of the Tibialis anterior, Extensor hal- lucis longus, and Extensor digi- torum longus, arranged in this order from the medial side. The posterior surface (Fig. 259) presents, at its upper part, a prominent ridge, the popliteal line, which extends obliquely downward from the back part of the articular facet for the fibula to the medial border, at the junction of its upper and middle thirds; it marks the lower limit of the insertion of the Popliteus, serves for the attachment of the fascia covering this muscle, and gives origin to part of the Soleus, Flexor digitorum longus, and Tibialis posterior. The triangular area, above this line, gives insertion to the Popliteus. The middle third of the poste- rior surface is divided by a ver- tical ridge into two parts; the ridge begins at the popliteal line and is well-marked above, but indistinct below; the medial and broader portion gives origin to the Flexor digitorum longus, the lateral and narrower to part of the Tibialis posterior. The Articular j capsule Articular capsule Styloid process TIBIA FIBULA Articulates with talus Articular capsule Fiq. 259.—Bones of the right leg. Posterior surface. THE TIBIA 259 remaining part of the posterior surface is smooth and covered by the Tibialis posterior, Flexor digitorum longus, and Flexor hallucis longus. Immediately below the popliteal line is the nutrient foramen, which is large and directed obliquely downward. The Lower Extremity (distal extremity).—The lower extremity, much smaller than the upper, presents five surfaces; it is prolonged downward on its medial side as a strong process, the medial malleolus. Surfaces.—The inferior articular surface is quadrilateral, and smooth for articu- lation with the talus. It is concave from before backward, broader in front than behind, and traversed from before backward by a slight elevation, separating two depressions. It is continuous with that on the medial malleolus. Upper extremity Appears before orj shortly after birth Joins body about 20th year Appears at 2nd_ year Joins body about 18 = angle of insertion of muscle fibers into tendon. cos — — cos z 60° = 0.50000 m 0.5 = — t = \ m m If z 4> = 72° 30' cos = | z = 41° 20' cos = f z = 90° cos = 0 z 4> = 0° cos = 1 The more acute the angle 4>, that is the smaller the angle, the greater the component acting in the direction of the tendon pull. At 41° 20' three-fourths of the pull would be exerted in the direction of the tendon and at 0° the entire strength. On the other hand, the greater the angle the smaller the tendon component; at 72° 30' one-third the muscle strength would act in the direction of the tendon and at 90° the tendon component would be nil. The Strength of Muscles.—The strength of a muscle depends upon the number of fibers in what is known as the physiological cross-section, that is, a section which passes through practically all of the fibers. In a muscle with parallel or nearly parallel fibers which have the same direction as the tendon this corresponds to the anatomical cross-section, but in unipinnate and bipinnate muscles the physiological cross-section may be nearly at right angles to the anatomical cross-section as shown in Fig. 365. Since Huber has shown that muscle fibers in a single fasciculus of a given muscle vary greatly in length, in some fasciculi from 9 mm. to 30.4 mm., it is unlikely that the physiological cross-section will pass through all the fibers. Estimates have been made of the strength of muscles and it is probable that coarse- fibered muscles are somewhat stronger per square centimeter of physiological Fig. 364 MECHANICS OF MUSCLE 365 cross-section than are the fine-fibered muscles. Fick estimates the average strength as about 10 kg. per square cm. This is known as the absolute muscle strength. The total strength of a muscle would be equal to the number of square centimeters in its physiological cross-section X 10 kg. Fig. 365.—A, fusiform; B, unipinnate; C, bipinnate; P.C.S., physiological cross-section. The Work Accomplished by Muscles.—For practical uses this should be expressed in kilogrammeters. In order to reckon the amount of work which a muscle can perform under the most favorable conditions it is necessary to know (1) its physio- logical cross-section (2) the maximum shortening, and (3) the position of the joint when the latter is obtained. Work = lifted weight X height through which the weight is lifted; or Work = tension X distance; tension = physiological cross-section X absolute muscle strength. If a muscle has a physiological cross-section of 5 sq. cm. its tension strength = 5 X 10 or 50 kg. If it shortens 5 cm. the work = 50 X .05 = 2.5 kilogrammeters. If one determines then the physiological cross-section and multiplies the absolute muscle strength, 10 kg. by this, the amount of tension is easily obtained. Then one must determine only the amount of shortening of the muscle for any particular position of the joint in order to determine the amount of work the muscle can do, since work = tension X distance. The tension of a muscle is, howevsr, not constant during the course of contraction but is continually decreasing during contraction. It is at a maximum at the begin- ning and gradually decreases. This can be illustrated by the work diagram Fig. 366. A M D (ordinate) = tension. A V X (abscissa) = shortening. A D = tension of muscle in extended or antagonistic position. A V = amount of actual shortening. > A M = tension in midposition = absolute muscle strength. D V = shows how the tension sinks from maximum (in the extended position of the muscle) where it is about double that in the midposition (M) to nothing on complete contraction. 366 MYOLOGY A A D V = work diagram, in reality the hypothenose is not straight but has a concave curve. The A has the same area as the rectangle A M M' V. A M = the average tension. Work = A M X A V kilogrammeters if the size of the ordinate as expressed in kilograms and the abscissa in meters. TENSION SHORTENING Fig. 366 Although the muscle works with a changing tension, yet the accomplishment is the same as if it were contracting with the tension of the midposition. In reality the amount of work is somewhat greater since even in extreme con- traction the muscle still retains a certain amount of tension so that the maximum amount of work is more nearly like A D X. We know that a muscle may have an extreme actual shortening of about 80 per cent, of its length when the tendon of insertion is cut. The trapezoid A D S V represents more nearly the amount of work, but since there are only approximate values and AD S V is not much larger than A M M' V, we may use the latter. Only the tension and amount of shortening are needed to determine the amount of work of the muscle. Neither the lever arm nor the fiber angle in pinnate muscles need be considered. The diagram Fig. 367 shows that the lever arm is of no importance for deter- mining the amount of work the muscle performs. J B and J B1 = two bones jointed at J. CD and E F — the direction of the pull of two muscles of equal cross-section, each having a muscle tension of 1000 gms. The centers of the attachments are such that perpendiculars J c and J e to C D and E F are equal to 40 and 23 mm. respectively, J c = 40 mm. and J e — 23 mm. The static moments are equal to 1000 X 40 and 1000 X 23,.therefore the first muscle can hold a much larger load (L) on the bone J Bl at IF (100 mm. from J) than the second muscle whose load can be designated as L1. Equilibrium exists for the first muscle if L X 100 = 1000 X 40 or L = = 400 gms. For the second muscle L1 X100 = 1000 X 23. T, 1000 X 23 Ll = jqq = 230 gms. If we suppose J B to be fixed and J B1 to move in the plane of the paper about J and the muscle C D to shorten 5 mm. C d = C D — 5 mm. and with the tension of 1000 gms., J B1 will take the position J B2 and the load (L) will be lifted from IF to H\ MECHANICS OF MUSCLE 367 If the second muscle likewise shortens 5 mm. then E f = E F — 5 mm., and with the tension of 1000 gms. the bone J Bl will take the position J Bs and the weight or load (Ll) will be lifted from Hl to H3. The question now is to prove that the work done is the same in both cases, namely, 5 X 1000 grammillimeters. If so, 400 X H1 H2 = 230 X Hl IP = 5000 grammillimeters. Since the two radii C d and C d' are very long as compared with the arc d d! we may consider this short arc as a line J_ to C D at d', likewise the arc f f may be considered as a straight line _[_ to E F. In the same manner we can consider the short arcs F f, D d, Hl H2 and IP H3 J_ to the line J Bl. The sides I) d' and F fr of the A D d d' and F ff' are each 5 mm. The lever arm D J = 60 mm. and J F = 30 mm. Fig. 367 The A 1) d d' is similar to the A I) c J r, r 300 hence D d : 5 :: 60 : 40 D d = also IP IP : Dd :: 100 : 60 IP H2 : 100 : 60 Hl H2 = ~ The A F f f is similar to F e J 150 hence F f :5 :: 30 : 23 Ff = -p also IP IP : Ff :: 100 : 30 W W : :: 100 : 30 //' //! = 400 X = 230 X = 5000 24 69 Thus we see that the work of the two muscles depends on the size of the contrac- tion and on the tension and not on the lever arm in very small contractions or in 368 MYOLOGY the summation of such contractions and therefore for large contractions. In the first muscle a large load is moved through a short distance and in the second muscle a lighter load is moved through a greater distance. The amount of work accomplished by pinnate muscles is not dependent upon the angle of insertion of the muscle fibers into the tendon, as will be seen by the following diagram Fig. 368. T' T = direction of the tendon pull. w a = direction of muscle fiber before con- traction. mf = direction of muscle fiber after contrac- tion. v = amount of contraction. m = tension of the muscle. $ = angle of insertion of muscle fiber. t = tendon component = m X cos = the weight carried by the tendon to balance the muscle tension. d = distance tendon is drawn up. (1) m X v = work done by the muscle fiber. (2) t X d = work done by the movement of the tendon. If we consider the distance v as being very short then the line b c can be dealt with as though it were perpendicular to a c. then v = d X cos <6 or d = —-— cos 4> t since t = m X cos 4> or m = —— cos t m X v = X d X cos = t X d cos (j) If this is true for very minute contractions it is likewise true for a series of such contraction and hence for larger contractions. If we assume that $ = 60°, m = 10 kg. and v = 5 mm., the work done by the contracting muscle fiber — m v or 10 X 5 kilogrammilli- meters. v cos Z 60° = hence t = \ m\ and d = y = 2r;|m = 5 kg.; and 2 v = 10mm. 2 hence t d = 50 kilogrammillimeters or the work done by the movement of the tendon in lifting the load of 5 kg. a distance of 10 mm., and is exactly the same as that done by the muscle fiber. The load on the tendon is but one-half the tension of the muscle, but the distance through which the load is lifted is twice that of the amount of shortening of the muscle. If = 41° 20' then cos = f hence t = f m and d = f v and t d = mv In pinnate muscles, then, we have the rather unexpected condition in which the same amount of movement of the tendon can be accomplished with less contrac- tion of the muscle than in muscles where the fibers have the same direction as the tendon. The Action of Muscles on Joints.—If we consider now the action of a single muscle extending over a single joint in which one bone is fixed and the other movable, we Fig. 368 MECHANICS OF MUSCLE 369 will find that muscle pull can be resolved into two components, a turning com- ponent and a friction or pressure component as shown in Fig. 369. Fig. 369 D F = the fixed bone from which the muscle takes its origin. D K = the movable bone. 01 = a line from the middle of origin to the middle of insertion. I M = size and direction of the muscle pull. If the parallelogram is constructed with 11 and M b X to D K, then 11 = the turning component and I b = the component which acts against the joint. The size of the two components depends upon the insertion angle 0. The smaller this angle the smaller the turning component, and the nearer this angle 0 is to 90° the larger the turning component. II = I M X sin $ I b = I M X cos (j> If 4> = 90° cos 0 = 0, sine 0 = 1 hence I b = 0 and 11 = I m If 0 = 0° cos 0 = 1, sine 0 = 0 hence 7 6 = 1 and / £ = 0 With movements of the bone D K the angle of insertion is continually changing, and hence the two components are changing in value. Fig. 370 If, for example, the distance from origin 0 to the joint J) is greater than from D to 7, as in the Brachialis or Biceps muscles, the turning component increases until the insertion angle 0 = 90°, which is the optimum angle for muscle action, while the pressure component gradually decreases. If the movement continues beyond 370 MYOLOGY this point the turning component gradually decreases and the pressure component changes into a component which tends to draw the two bones apart and which gradually increases as shown in Fig. 370. When the bone D K is in such a position that the insertion angle = 41° 20' the pressure component = f I m and the turning component \ I m, at 60° the two components are equal, at 90° the pressure component = 0 and the turning com- ponent — I M and at 131° 21' the pressure component has been converted into a pulling component = \ I M and the turning component = f / M. Fig. 371 If, for example, the distance from the origin 0 to the joint 1) is less than the dis- tance from the insertion I to the joint D, as in the Brachioradialis muscle, the insertion angle increases with the flexion but never reaches 90°. The turning component gradually increases to a certain point and then slowly decreases as shown in Fig. 371, while the pressure component gradually decreases and then slowly increases. It always remains large and its action is always in the direction of the joint. Levers.—The majority of the muscles of the body act on bones as the power on levers. Levers of the III class are the most common, as the action of the Biceps, and the Brachialis muscles on the forearm bones. Levers of the I Class are found in movements of the head where the occipito-atlantal joint acts as the fulcrum and the muscles on the back of the neck as the power. Another common example is Fig. 372 the foot when one raises the body by contracting the Gastrocnemius and Soleus. Here the ankle-joint acts as the fulcrum and the pressure of the toes on the ground as the weight. This is frequently, though wrongly, considered a lever of the II Class. If one were to stand on one’s head with the legs up and with a weight on the plantar surface of the toes, it is easy to see that we would have a lever of the I Class if the weight were raised by contraction of the Gastrocnemius muscle. The confusion has arisen by not considering the fact that the fulcrum and the powder in all three classes of levers must have a common basis of action, as shown in Fig. 372. DEVELOPMENT OF THE MUSCLES 371 If the fulcrum rests on the earth the power must either directly or indirectly push from the earth or be attached to the earth either by gravity or otherwise if it pulls toward the earth. If the power were attached to the weight no lever action could be obtained. There are no levers of the II Class represented in the body. DEVELOPMENT OF THE MUSCLES. Both the cross-striated and smooth muscles, with the exception of a few that are of ectodermal origin, arise from the mesoderm. The intrinsic muscles of the trunk are derived from the myotomes while the muscles of the head and limbs differentiate directly from the mesoderm. The Myotomic Muscles.—The intrinsic muscles of the trunk which are derived directly from the myotomes are conveniently treated in two groups, the deep muscles of the back and the thoraco-abdominal muscles. The deep muscles of the back extend from the sacral to the occipital region and vary much in length and size. They act chiefly on the vertebral column. The shorter muscles, such as the Interspinales, Intertransversarii, the deeper layers of the Multifidus, the Rotatores, Levatores costarum, Obliquus capitis inferior, Obliquus capitis superior and Rectus capitis posterior minor which extend between adjoining vertebrae, retain the primitive segmentation of the myotomes. Other muscles, such as the Splenius capitis, Splenius cervicis, Sacrospinalis, Semispinalis, Multifidus, lliocostalis, Longissimus, Spinales, Semispinales, and Rectus capitis posterior major, which extend over several vertebrae, are formed by the fusion of successive myotomes and the splitting into longitudinal columns. The fascia lumbo-dorsalis develops between the true myotomic muscles and the more superficial ones which migrate over the back such as the Trapezius, Rhom- boideus, and Latissimus. The anterior vertebral muscles, the Longus colli, Longus capitis, Rectus capitis anterior and Rectus capitis lateralis are derived from the ventral part of the cervical myotomes as are probably also the Scaleni. The thoraco-abdominal muscles arise through the ventral extension of the thoracic myotomes into the body wall. This process takes place coincident with the ventral extension of the ribs. In the thoracic region the primitive myotomic segments still persist as the intercostal muscles, but over the abdomen these ventral myotomic processes fuse into a sheet which splits in various ways to form the Rectus, the Obliquus externus and internus, and the Transversalis. Such muscles as the Pectoralis major and minor and the Serratus anterior do not belong to the above group. The Ventrolateral Muscles of the Neck.—The intrinsic muscles of the tongue, the Infrahyoid muscles and the diaphragm are derived from a more or less continuous premuscle mass which extends on each side from the tongue into the lateral region of the upper half of the neck and into it early extend the hypoglossal and branches of the upper cervical nerves. The two halves which form the Infrahyoid muscles and the diaphragm are at first widely separated from each other by the heart. As the latter descends into the thorax the diaphragmatic portion of each lateral mass is carried with its nerve down into the thorax and the laterally placed Infra- hyoid muscles move toward the midventral line of the neck. Muscles of the Shoulder Girdle and Arm.—The Trapezius and Sternocleidomas- toideus arise from a common premuscle mass in the occipital region just caudal to the last branchial arch; as the mass increases in size it spreads downward to the shoulder girdle to which it later becomes attached. It also spreads backward and downward to the spinous processes, gaining attachment at a still later period. 372 MYOLOGY The Levator scapulae, Serratus anterior and the Rhomboids arise from premuscle tissue in the lower cervical region and undergo extensive migration. The Latissimus dorsi and Teres major are associated in their origin from the premuscle sheath of the arm as are also the two Pectoral muscles when the arm bud lies in the lower cervical region. The intrinsic muscles of the arm develop in situ from the mesoderm of the arm bud and probably do not receive cells or buds from the myotomes. The nerves enter the arm bud when it still lies in the cervical region and as the arm shifts caudally over the thorax the lower cervical nerves which unite to form the brachial plexus, acquire a caudal direction. The Muscles of the Leg.—The muscles of the leg like those of the arm develop in situ from the mesoderma of the leg bud, the myotomes apparently taking no part in their formation. The Muscles of the Head.—The muscles of the orbit arise from the mesoderm over the dorsal and caudal sides of the optic stalk. The muscles of mastication arise from the mesoderm of the mandibular arch. The mandibular division of the trigeminal nerve enters this premuscle mass before it splits into the Temporal, Masseter and Ptervgoideus. The facial muscles (muscles of expression) arise from the mesoderm of the hyoid arch. The facial nerve enters this mass before it begins to split, and as the muscle mass spreads out over the face and head and neck it splits more orless incompletely into the various muscles. The early differentiation of the muscular system apparently goes on independ- ently of the nervous system and only later does it appear that muscles are dependent on the functional stimuli of the nerves for their continued existence and growth. Although the nervous system does not influence muscle differentiation, the nerves, owing to their early attachments to the muscle rudiments, are in a general way indicators of the position of origin of many of the muscles and likewise in many instances the nerves indicate the paths along which the developing muscles have migrated during development. The muscle of the diaphragm, for example, has its origin in the region of the fourth and fifth cervical segments. The phrenic nerve enters the muscle mass while the latter is in this region and is drawn out as the diaphragm migrates through the thorax. The Trapezius and Sternocleidomastoideus arise in the lateral occipital region as a common muscle mass, into which at a very early period the nervus accessorius extends and as the muscle mass migrates and extends caudally the nerve is carried with it. The Pectoralis major and minor arise in the cervical region, receive their nerves while in this position and as the muscle mass migrates and extends caudally over the thorax the nerves are carried along. The Latissimus dorsi and Serratus anterior are excellent examples of migrating muscles whose nerve supply indicates their origin in the cervical region. The Rectus abdominis and the other abdominal muscles migrate or shift from a lateral to a ventrolateral or abdominal position, carrying with them the nerves. The facial nerve, which early enters the common facial muscle mass of the second branchial or hyoid arch, is dragged about with the muscle as it spreads over the head and face and neck, and as the muscle splits into the various muscles of expression, the nerve is correspondingly split. The mandibular division of the trigeminal nerve enters at an early time the muscle mass in the mandibular arch and as this mass splits and migrates apart to form the muscles of mastication the nerve splits into its various branches. The nerve supply then serves as a key to the common origin of certain groups of muscles. The muscles supplied by the oculomotor nerve arise from a single mass in the eye region; the lingual muscles arise from a common mass supplied by the hypoglossal nerve. DEVELOPMENT OF THE MUSCLES 373 Striped or Voluntary Muscle.—Striped or voluntary muscle is composed of bundles of fibers each enclosed in a delicate web called the perimysium in contradistinction to the sheath of areolar tissue which invests the entire muscle, the epimysium. The bundles are termed fasciculi; they are prismatic in shape, of different sizes in different muscles, and are for the most part placed parallel to one another, though they have a tendency to converge toward their tendinous attachments. Each fasciculus is made up of a strand of fibers, which also run parallel with each other, and are separated from one another by a delicate connective tissue derived from the perimysium and termed endomysium. This does not form the sheath of the fibers, but serves to support the bloodvessels and nerves ramifying between them. A muscular fiber may be said to consist of a soft contractile substance, enclosed in a tubular sheath named by Bowman the sarcolemma. The fibers are cylindrical or prismatic in shape (Fig. 373), and are of no great length, not exceeding, as a rule, 40 mm. Huber1 has recently found that the muscle fibers in the adductor muscle of the thigh of the rabbit vary greatly in length even in the same .fasciculus. In a fasciculus 40 mm. in length the fibers varied from 30.4 mm. to 9 mm. in length. Their breadth varies in man from 0.01 to 0.1 mm. As a rule, the fibers do not Pig. 373.—Transverse section of human striped muscle fibers. X 255. Fig. 374.—Striped muscle fibers from tongue of cat. X 250. divide or anastomose; but occasionally, especially in the tongue and facial mus- cles, they may be seen to divide into several branches. In the substance of the muscle, the fibers end by tapering extremities which are joined to the ends of other fibers by the sarcolemma. At the tendinous end of the muscle the sareo- lemma appears to blend with a small bundle of fibers, into which the tendon becomes subdivided, while the muscular substance ends abruptly and can be readily made to retract from the point of junction. The areolar tissue between the fibers appears to be prolonged more or less into the tendon, so as to form a kind of sheath around the tendon bundles for a longer or shorter distance. When muscular fibers are attached to skin or mucous membranes, their fibers become continuous with those of the areolar tissue. The sarcolemma, or tubular sheath of the fiber, is a transparent, elastic, and apparently homogeneous membrane of considerable toughness, so that it some- times remains entire when the included substance is ruptured. On the internal surface of the sarcolemma in mammalia, and also in the substance of the fiber in frogs, elongated nuclei are seen, and in connection with these is a little granular protoplasm. Upon examination of a voluntary muscular fiber by transmitted light, it is ’Anat. Rec., 1916, 11. 374 MYOLOGY found to be marked by alternate light and dark bands or striae, which pass trans- versely across the fiber (Fig. 374). When examined by polarized light the dark bands are found to be doubly refracting (anisotropic), while the clear stripes are singly refracting (isotropic). The dark and light bands are of nearly equal breadth, and alternate with great regularity; they vary in breadth from about 1 to 2/x. If the surface be carefully focussed, rows of granules will be de- tected at the points of junction of the dark and light bands, and very fine longitudinal lines may be seen run- ning through the dark bands and joining these granules together. By treating the specimen with certain reagents (e. g., chloride of gold) fine lines may be seen running transversely between the granules and uniting them together. This appearance is believed to be due to a reticulum or network of interstitial substance lying between the contractile portions of the muscle. The longitudinal striation gives the fiber the appearance of being made up of a bundle of fibrils which have been termed sarcostyles or muscle columns, and if the fiber be hardened in alcohol, it can be broken up longitu- dinally and the sarcostyles separated from each other (Fig. 375.) The retic- ulum, with its longitudinal and trans- verse meshes, is called sarcoplasm. In a transverse section, the muscular fiber is seen to be divided into a number of areas, called the areas of Cohnheim, more or less polyhedral in shape and con- sisting of the transversely divided sarcostyles, surrounded by transparent sarco- plasm (Fig. 373). Fig. 375.—A. Portion of a medium-sized human muscular fiber. Magnified nearly 800 diameters. B. Separa ed bundles of fibrils, equally magnified, a, a. Larger, and b, b, smaller collections, c. Still smaller, d, d. The smallest which could be detached. Fig. 376.—Diagram of a sarcomere. (After Schafer.) A. In moderately extended condition. B. In a contracted condition, k, k. Membranes of Krause. H. Line or plane of Hensen. S.E. Poriferous sarcous element. Upon closer examination, and by somewhat altering the focus, the appearances become more complicated, and are susceptible of various interpretations. The transverse striation, which in Fig. 374 appears as a mere alternation of dark and light bands, is resolved into the appearance seen in Fig. 375, which shows a series of broad dark bands, separated by light bands, each of which is divided into two DEVELOPMENT OF THE MUSCLES 375 by a dark dotted line. This line is termed Dobie’s line or Krause’s membrane (Fig. 376, k), because it was believed by Krause to be an actual membrane, con- tinuous with the sarcolemma, and dividing the light band into two compartments. In addition to the membrane of Krause, fine clear lines may be made out, with a sufficiently high power, crossing the center of the dark band; these are known as the lines of Hensen (Fig. 376, H). Schafer has worked out the minute anatomy of muscular fiber, particularly in the wing muscles of insects, which are peculiarly adapted for this purpose on account of the large amount of interstitial sarcoplasm which separates the sarco- styles. In the following description that given by Schafer will be closely followed. A sarcostyle may be said to be made up of successive portions, each of which is termed a sarcomere. The sarcomere is situated between two membranes of Krause and consists of (1) a central dark part, which forms a portion of the dark band of the whole fiber, and is named a sarcous element. This sarcous element really consists of two parts, superimposed one on the top of the other, and when the fiber is stretched these two parts become separated from each other at the line of Flensen (Fig. 376, A). (2) On either side of this central dark portion is a clear layer, most visible when the fiber is extended; this is situated between the dark center and the membrane of Krause, and when the sarcomeres are joined together to form the sarcostyle, constitutes the light band of the striated muscular fiber. When the sarcostyle is extended, the clear intervals are well-marked and plainly to be seen; when, on the other hand, the sarcostyle is contracted, that is to say, when the muscle is in a state of contraction, these clear portions are very small or they may have disappeared altogether (Fig. 376, B). When the sarcostyle is stretched to its full extent, not only is the clear portion well-marked, but the dark portion—the sarcous element—is separated into its two constituents along the line of Hensen. The sarcous element does not lie free in the sarcomere, for when the sarcostyle is stretched, so as to render the clear portion visible, very fine lines, which are probably septa, may be seen running through it from the sarcous element to the membrane of Krause. Schafer explains these phenomena in the following way: He considers that each sarcous element is made up of a number of longitudinal channels, which open into the clear part toward the membrane of Krause but are closed at the line of Hensen. When the muscular fiber is contracted the clear part of the muscular substance is driven into these channels or tubes, and is therefore hidden from sight, but at the same time it swells up the sarcous element and widens and shortens the sarcomere. When, on the other hand, the fiber is extended, this clear sub- stance is driven out of the tubes and collects between the sarcous element and the membrane of Krause, and gives the appearance of the light part between these two structures; by this means it elongates and narrows the sarcomere. If this view be true, it is a matter of great interest, and, as Schafer has shown, harmonizes the contraction of muscle with the ameboid action of protoplasm. In an ameboid cell, there is a framework of spongioplasm, which stains with hematoxylin and similar reagents, enclosing in its meshes a clear substance, hyalo- plasm, which will not stain with these reagents. Under stimulation the hyaloplasm passes into the pores of the spongioplasm; without stimulation it tends to pass out as in the formation of pseudopodia. In muscle there is the same thing, viz., a framework of spongioplasm staining with hematoxylin—the substance of the sarcous element—and this encloses a clear hyaloplasm, the clear substance of the sarcomere, which resists staining with this reagent. During contraction of the muscle—i. e., stimulation—this clear substance passes into the pores of the spongio- plasm; while during extension of the muscle—i. e., when there is no stimulation— it tends to pass out of the spongioplasm. In this way the contraction is brought about: under stimulation the proto- 376 MYOLOGY plasmic material (the clear substance of the sarcomere) recedes into the sarcous element, causing the sarcomere to widen out and shorten. The contraction of the muscle is merely the sum total of this widening out and shortening of these bodies. Vessels and Nerves of Striped Muscle.—The capillaries or striped muscle are very abundant, and form a sort of rectangular network, the branches of which run longitudinally in the endomysium between the muscular fibers, and are joined at short intervals by transverse anastomosing branches. In the red muscles of the rabbit dilatations occur on the transverse branches of the capillary network. The larger vascular channels, arteries and veins, are found only in the perimysium, between the muscular fasciculi. Nerves are profusely distributed to striped muscle. Their mode of termination is described on page 730. The existence of lymphatic vessels in striped muscle has not been ascertained, though they have been found in tendons and in the sheaths of the muscles. Ossification of muscular tissue as a result of repeated strain or injury is not infrequent. It is oftenest found about the tendon of the Adductor longus and Vastus medialis in horsemen, or in the Pectoralis major and Deltoideus of soldiers. It may take the form of exostoses firmly fixed to the bone—e. g., “rider’s bone” on the femur—or of layers or spicules of bone lying in the muscles or their fasciae and tendons. Busse states that these bony deposits are preceded by a hemorrhagic myositis due to injury, the effused blood organizing and being finally converted into bone. In the rarer disease, progressive myositis ossificans, there is an unexplained tendency for practically any of the voluntary muscles to become converted into solid and brittle bony masses which are completely rigid. Tendons are white, glistening, fibrous cords, varying in length and thickness, sometimes round, sometimes flattened, and devoid of elasticity. They consist almost entirely of white fibrous tissue, the fibrils of which have an undulating course parallel with each other and are firmly united together. When boiled in water tendon is almost completely converted into gelatin, the white fibers being composed of the albuminoid collagen, which is often regarded as the anhydride of gelatin. They are very sparingly supplied with bloodvessels, the smaller tendons presenting in their interior no trace of them. Nerves supplying tendons have special modifications of their terminal fibers, named organs of Golgi. Aponeuroses are flattened or ribbon-shaped tendons, of a pearly white color, iridescent, glistening, and similar in structure to the tendons. They are only sparingly supplied with bloodvessels. The tendons and aponeuroses are connected, on the one hand, with the muscles, and, on the other hand, with the movable structures, as the bones, cartilages liga- ments, and fibrous membranes (for instance, the sclera). Where the muscular fibers are in a direct line with those of the tendon or aponeurosis, the two are directly continuous. But where the muscular fibers join the tendon or aponeurosis at an oblique angle, they end, according to Kolliker, in rounded extremities which are received into corresponding depressions on the surface of the latter, the connective tissue between the muscular fibers being continuous with that of the tendon. The latter mode of attachment occurs in all the penniform and bipenniform muscles, and in those muscles the tendons of which commence in a membranous form, as the Gastrocnemius and Soleus. The fasciae are fibroareolar or aponeurotic laminae, of variable thickness and strength, found in all regions of the body, investing the softer and more delicate organs. During the process of development many of the cells of the mesoderm are differentiated into bones, muscles, vessels, etc.; the cells of the mesoderm which are not so utilized form an investment for these structures and are differentiated into the true skin and the fasciae of the body. They have been subdivided, from the situations in which they occur, into superficial and deep. TENDONS, APONEUROSES, AND FASCIAE. TENDONS, APONEUROSES, AND FASC1/E 377 The superficial fascia is found immediately beneath the integument over almost the entire surface of the body. It connects the skin with the deep fascia, and consists of fibroareolar tissue, containing in its meshes pellicles of fat in varying quantity. Fibro-areolar tissue is composed of white fibers and yellow elastic fibers intercrossing in all directions, and united together by a homogeneous cement or ground substance, the matrix. The cells of areolar tissue are of four principal kinds: (1) Flattened lamellar cells, which may be either branched or unbranched. The branched lamellar cells are composed of clear cytoplasm, and contain oval nuclei; the processes of these cells may unite so as to form an open network, as in the cornea. The unbranched cells are joined edge to edge like the cells of an epithelium; the “ tendon cells,” pres- ently to be described, are examples of this variety. (2) Clasmatocytes, large irregular cells characterized by the presence of granules or vacuoles in their protoplasm, Plasma cell White fibres Elastic fibres Fibrillaled cell Fig. 377.—Subcutaneous tissue from a young rabbit. Highly magnified. (Schafer.) Lamellar cell and containing oval nuclei. (3) Granule cells (Mastzellen), which are ovoid or spheroidal in shape. They are formed of a soft protoplasm, containing granules which are basophil in character. (4) Plasma cells of Waldeyer, usually spheroidal and distinguished by containing a vacuolated protoplasm. The vacuoles are filled with fluid, and the protoplasm between the spaces is clear, with occasionally a few scattered basophil granules. In addition to these four typical forms of connective-tissue corpuscles, areolar tissue may be seen to possess wandering cells, i. e., leucocytes which have emigrated from the neighboring vessels; in some instances, as in the choroid coat of the eye cells filled with granules of pigment (pigment cells) are found. The cells lie in spaces in the ground substance between the bundles of fibers, and these spaces may be brought into view by treating the tissue with nitrate of silver and exposing it to the light. This will color the ground substance and leave the cell-spaces unstained. 378 MYOLOGY Fat is entirely absent in the subcutaneous tissue of the eyelids, of the penis and scrotum, and of the labia minora. It varies in thickness in different parts of the body; in the groin it is so thick that it may be subdivided into several lamina?. Beneath the fatty layer there is generally another layer of superficial fascia, com- paratively devoid of adipose tissue, in which the trunks of the subcutaneous vessels and nerves are found, as the superficial epigastric vessels in the abdominal region, the superficial veins in the forearm, the saphenous veins in the leg and thigh, and the superficial lymph glands. Certain cutaneous muscles also are situated in the super- ficial fascia, as the Platysma in the neck, and the Orbicularis oculi around the eyelids. This fascia is most distinct at the lower part of the abdomen, perineum, and extremi- ties; it is very thin in those regions where muscular fibers are inserted into the integument, as on the side of the neck, the face, and around the margin of the anus. It is very dense in the scalp, in the palms of the hands, and soles of the feet, forming a fibro-fatty layer, which binds the integument firmly to the underlying structures. The superficial fascia connects the skin to the subjacent parts, facilitates the movement of the skin, serves as a soft nidus for the passage of vessels and nerves to the integument, and retains the warmth of the body, since the fat contained in its areolae is a bad conductor of heat. The deep fascia is a dense, inelastic, fibrous membrane, forming sheaths for the muscles, and in some cases affording them broad surfaces for attachment. It consists of shining tendinous fibers, placed parallel with one another, and connected together by other fibers disposed in a rectilinear manner. It forms a strong invest- ment which not only binds down collectively the muscles in each region, but gives a separate sheath to each, as well as to the vessels and nerves. The fasciae are thick in unprotected situations, as on the lateral side of a limb, and thinner on the medial side. The deep fasciae assist the muscles in their actions, by the degree of tension and pressure they make upon their surfaces; the degree of tension and pressure is regulated by the associated muscles, as, for instance, by the Tensor fasciae latae and Glutaeus maximus in the thigh, by the Biceps in the upper and lower extremi- ties, and Palmaris longus in the hand. In the limbs, the fasciae not only invest the entire limb, but give off septa which separate the various muscles, and are attached to the periosteum: these prolongations of fasciae are usually spoken of as intermuscular septa. The Fasciae and Muscles may be arranged, according to the general division of the body, into those of the head and neck; of the trunk; of the upper extremity; and of the lower extremity. THE FASCL® AND MUSCLES OF THE HEAD. I. THE MUSCLE OF THE SCALP. Epicranius. The Skin of the Scalp.—This is thicker than in any other part of the body. It is intimately adherent to the superficial fascia, which attaches it firmly to the underlying aponeurosis and muscle. Movements of the muscle move the skin. The hair follicles are very closely set together, and extend throughout the whole thickness of the skin. It also contains a number of sebaceous glands. The superficial fascia in the cranial region is a firm, dense, fibro-fatty layer, intimately adherent to the integument, and to the Epicranius and its tendinous aponeurosis; it is continuous, behind, with the superficial fascia at the back of the neck; and, laterally, is continued over the temporal fascia. It contains between its layers the superficial vessels and nerves and much granular fat. The Epicranius (Occipitofrontalis) (Fig. 378) is a broad, musculofibrous layer, THE MUSCLE OF THE SCALP 379 which covers the whole of one side of the vertex of the skull, from the occipital bone to the eyebrow. It consists of two parts, the Occipitalis and the Frontalis, connected by an intervening tendinous aponeurosis, the galea aponeurotica. The Occipitalis, thin and quadrilateral in form, arises by tendinous fibers from the lateral two-thirds of the superior nuchal line of the occipital bone, and from the mastoid part of the temporal. It ends in the galea aponeurotica. Corrugator- Dilatator naris ant. Dilatator naris post Depressor septi Nasalis Mentalis- Fig. 378.—Muscles of the head, face, and neck. The Frontalis is thin, of a quadrilateral form, and intimately adherent to the superficial fascia. It is broader than the Occipitalis and its fibers are longer and paler in color. It has no bony attachments. Its medial fibers are continuous with those of the Procerus; its immediate fibers blend with the Corrugator and Orbicu- laris oculi; and its lateral fibers are also blended with the latter muscle over the zygomatic process of the frontal bone. From these attachments the fibers are directed upward, and join the galea aponeurotica below the coronal suture. 380 MYOLOGY The medial margins of the Frontales are joined together for some distance above the root of the nose; but between the Occipitales there is a considerable, though variable, interval, occupied by the galea aponeurotica. The galea aponeurotica (epicranial aponeurosis) covers the upper part of the cranium; behind, it is attached, in the interval between its union with the Occipi- tales, to the external occipital protuberance and highest nuchal lines of the occipital bone; in front, it forms a short and narrow prolongation between its union with the Frontales. On either side it gives origin to the Auriculares anterior and supe- rior; in this situation it loses its aponeurotic character, and is continued over the temporal fascia to the zygomatic arch as a layer of laminated areolar tissue. It is closely connected to the integument by the firm, dense, fibro-fatty layer which forms the superficial fascia of the scalp: it is attached to the pericranium by loose cellular tissue, which allows the aponeurosis, carrying with it the integument to move through a considerable distance. Variations.—Both Frontalis and Occipitalis vary considerably in size and in extent of attach- ment; either may be absent; fusion of Frontalis to skin has been noted. Nerves.—The Frontalis is supplied by the temporal branches of the facial nerve, and the Occipitalis by the posterior auricular branch of the same nerve. Actions.—The Frontales raise the eyebrows and the skin over the root of the nose, and at the same time draw the scalp forward, throwing the integument of the forehead into transverse wrinkles. The Occipitales draw the scalp backward. By bringing alternately into action the Frontales and Occipitales the entire scalp may be moved forward and backward. In the ordinary action of the muscles, the eyebrows are elevated, and at the same time the aponeurosis is fixed by the Occipitales, thus giving to the face the expression of surprise; if the action be exaggerated, the eyebrows are still further raised, and the skin of the forehead thrown into transverse wrinkles, as in the expression of fright or horror. A thin muscular slip, the Transversus nuchse, is present in a considerable pro- portion (25 per cent.) of cases; it arises from the external occipital protuberance or from the superior nuchal line, either superficial or deep to the Trapezius; it is frequently inserted with the Auricularis posterior, but may join the posterior edge of the Sternocleidomastoideus. II. THE MUSCLES OF THE EYELIDS. The muscles of the eyelids are: Levator palpebrse superioris. Orbicularis oculi. Corrugator. The Levator palpebrse superioris is described with the Anatomy of the Eye. The Orbicularis oculi (Orbicularis palpebrarum) (Fig. 379) arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short fibrous band, the medial palpebral ligament. From this origin, the fibers are directed lateral- ward, forming a broad and thin layer, which occupies the eyelids or palpebrae, surrounds the circumference of the orbit, and spreads over the temple, and down- ward on the cheek. The palpebral portion of the muscle is thin and pale; it arises from the bifurcation of the medial palpebral ligament, forms a series of concentric curves, and is inserted into the lateral palpebral raphe. The orbital portion is thicker and of a reddish color; its fibers form a complete ellipse without interruption at the lateral palpebral commissure; the upper fibers of this portion blend with the Frontalis and Corrugator. The lacrimal part (Tensor tarsi) is a small, thin muscle, about 6 mm. in breadth and 12 mm. in length, situated behind the medial palpebral ligament and lacrimal sac (Fig. 379). It arises from the posterior crest and adjacent part of the orbital surface of the lacrimal bone, and passing behind the lacrimal sac, divides into two slips, upper and lowTer, which are inserted into the superior and inferior tarsi medial to the puncta lacrimalia; occasionally it is very indistinct. THE MUSCLES OF THE EYELIDS 381 The medial palpebral ligament (tendo oculi), about 4 mm. in length and 2 mm. in breadth, is attached to the frontal process of the maxilla in front of the lacrimal groove. Crossing the lacrimal sac, it divides into two parts, upper and lower, each attached to the medial end of the corresponding tarsus. As the ligament crosses the lacrimal sac, a strong aponeurotic lamina is given off from its posterior surface; this expands over the sac, and is attached to the posterior lacrimal crest. The lateral palpebral raphe is a much weaker structure than the medial palpebral ligament. It is attached to the margin of the frontosphenoidal process of the zygomatic bone, and passes medialward to the lateral commissure of the eyelids, where it divides into two slips, which are attached to the margins of the respective tarsi. Probc in frontal sinus Probe in ant. eth- moidal cells Crista galli Lacrimal part of Orbicularis oculi Probe in lacrimal sac {Probes from frontal sinus and ant. eth- moidal cells Middle meatus Septum of nose Probe in nasolacrimal duct Infraorbital nerve and artery Fig. 379.—Left orbicularis oculi, seen from behind. The Corrugator1 (Corrugator supercilii) is a small, narrow, pyramidal muscle, placed at the medial end of the eyebrow, beneath the Frontalis and Orbicularis oculi. It arises from the medial end of the superciliary arch; and its fibers pass upward and lateralward, between the palpebral and orbital portions of the Orbicu- laris oculi, and are inserted into the deep surface of the skin, above the middle of the orbital arch. Nerves.—The Orbicularis oculi and Corrugator are supplied by the facial nerve. Actions.—The Orbicularis oculi is the sphincter muscle of the eyelids. The palpebral portion acts involuntarily, closing the lids gently, as in sleep or in blinking; the orbital portion is subject to the will. When the entire muscle is brought into action, the skin of the forehead, temple, and cheek is drawn toward the medial angle of the orbit, and the eyelids are firmly closed, as in photophobia. The skin thus drawn upon is thrown into folds, especially radiating from the lateral angle of the eyelids; these folds become permanent in old age, and form the so-called “crows’ feet.” The Levator palpebrse superioris is the direct antagonist of this muscle; it raises the upper eyelid and exposes the front of the bulb of the eye. Each time the eyelids are closed through the action of the Orbicularis, the medial palpebral ligament is tightened, the wall of the lacrimal sac is thus drawn lateralward and forward, so that a vacuum is made in it and the 1 The corrugator is not recognized as a separate muscle in the Basle Nomenclature. 382 MYOLOGY tears are sucked along the lacrimal canals into it. The lacrimal part of the Orbicularis oculi draws the eyelids and the ends of the lacrimal canals medialward and compresses them against the surface of the globe of the eye, thus placing them in the most favorable situation for receiving the tears; it also compresses the lacrimal sac. The Corrugator draws the eyebrow downward and medialward, producing the vertical wrinkles of the forehead. It is the “frowning” muscle, and may be regarded as the principal muscle in the expression of suffering. III. THE MUSCLES OF THE NOSE (Fig. 378) The muscles of the nose comprise: Procerus. Nasalis. Depressor septi. Dilatator naris posterior. Dilatator naris anterior. The Procerus (Pyramidalis nasi) is a small pyramidal slip arising by tendinous fibers from the fascia covering the lower part of the nasal bone and upper part of the lateral nasal cartilage; it is inserted into the skin over the part of the forehead between the two eyebrows, its fibers decussating with those of the Frontalis. The Nasalis (Compressor naris) consists of two parts, transverse and alar. The transverse part arises from the maxilla, above and lateral to the incisive fossa; its fibers proceed upward and medialward, expanding into a thin aponeurosis which is continuous on the bridge of the nose with that of the muscle of the oppo- site side, and with the aponeurosis of the Procerus. The alar part is attached by one end to the greater alar cartilage, and by the other to the integument at the point of the nose. The Depressor septi (Depressor aloe nasi) arises from the incisive fossa of the maxilla; its fibers ascend to be inserted into the septum and back part of the ala of the nose. It lies between the mucous membrane and muscular structure of the lip. The Dilatator naris posterior is placed partly beneath the Quadratus labii superioris. It arises from the margin of the nasal notch of the maxilla, and from the lesser alar cartilages, and is inserted into the skin near the margin of the nostril. The Dilatator naris anterior is a delicate fasciculus, passing from the greater alar cartilage to the integument near the margin of the nostril; it is situated in front of the preceding. Variations.—These muscles vary in size and strength or may be absent. Nerves.—All the muscles of this group are supplied by the facial nerve. Actions.—The Procerus draws down the medial angle of the eyebrows and produces transverse wrinkles over the bridge of the nose. The two Dilatatores enlarge the aperture of the nares. Their action in ordinary breathing is to resist the tendency of the nostrils to close from atmos- pheric pressure, but in difficult breathing, as well as in some emotions, such as anger, they con- tract strongly. The Depressor septi is a direct antagonist of the other muscles of the nose, drawing the ala of the nose downward, and thereby constricting the aperture of the nares. The Nasalis depresses the cartilaginous part of the nose and draws the ala toward the septum. IV. THE MUSCLES OF THE MOUTH The muscles of the mouth are: Quadratus labii superioris. Caninus. Zygomaticus. Mentalis. Quadratus labii inferioris. Triangularis. Buccinator. Orbicularis oris. Risorius. THE MUSCLES OF THE MOUTH 383 The Quadratus labii superioris is a broad sheet, the origin of which extends from the side of the nose to the zygomatic bone. Its medial fibers form the angular head, which arises by a pointed extremity from the upper part of the frontal process of the maxilla and passing obliquely downward and lateralward divides into two slips. One of these is inserted into the greater alar cartilage and skin of the nose; the other is prolonged into the lateral part of the upper lip, blending with the infraorbital head and with the Orbicularis oris. The intermediate portion or infraorbital head arises from the lower margin of the orbit immediately above the infraorbital foramen, some of its fibers being attached to the maxilla, others to the zygomatic bone. Its fibers converge, to be inserted into the muscular substance of the upper lip between the angular head and the Caninus. The lateral fibers, forming the zygomatic head, arise from the malar surface of the zygomatic bone immediately behind the zygomaticomaxillary suture and pass downward and medialward to the upper lip. The Caninus (Levator anguli oris) arises from the canine fossa, immediately below the infraorbital foramen; its fibers are inserted into the angle of the mouth, intermingling with those of the Zygomaticus, Triangularis, and Orbicularis oris. The Zygomaticus (Zygomaticus major) arises from the zygomatic bone, in front of the zygomaticotemporal suture, and descending obliquely with a medial inclina- tion, is inserted into the angle of the mouth, where it blends with the fibers of the Caninus, Orbicularis oris, and Triangularis. Nerves.—This group of muscles is supplied by the facial nerve. Actions.—The Quadratus labii superioris is the proper elevator of the upper lip, carrying it at the same time a little forward. Its angular head acts as a dilator of the naris; the infraorbital and zygomatic heads assist in forming the nasolabial furrow, which passes from the side of the nose to the upper lip and gives to the face an expression of sadness. When the whole muscle is in action it gives to the countenance an expression of contempt and disdain. The Quad- ratus labii superioris raises the angle of the mouth and assists the Caninus in producing the nasolabial furrow. The Zygomaticus draws the angle of the mouth backward and upward, as in laughing. The Mentalis (Levator menti) is a small conical fasciculus, situated at the side of the frenulum of the lowTer lip. It arises from the incisive fossa of the mandible, and descends to be inserted into the integument of the chin. The Quadratus labii inferioris (Depressor labii inferioris; Quadratus menti) is a small quadrilateral muscle. It arises from the oblique line of the mandible, between the symphysis and the mental foramen, and passes upward and medial- ward, to be inserted into the integument of the lower lip, its fibers blending with the Orbicularis oris, and with those of its fellow of the opposite side. At its origin it is continuous with the fibers of the Platysma. Much yellow fat is intermingled with the fibers of this muscle. The Triangularis (Depressor anguli oris) arises from the oblique line of the mandible, whence its fibers converge, to be inserted, by a narrow fasciculus, into the angle of the mouth. At its origin it is continuous wdth the Platysma, and at its insertion with the Orbicularis oris and Ilisorius; some of its fibers are directly continuous with those of the Caninus, and others are occasionally found crossing from the muscle of one side to that of the other; these latter fibers constitute the Trans versus menti. Nerves.—This group of muscles is supplied by the facial nerve. Actions.—The Mentalis raises and protrudes the lower lip, and at the same time wrinkles the skin of the chin, expressing doubt or disdain. The Quadratus labii inferioris draws the lower lip directly downward and a little lateralward, as in the expression of irony. The Triangularis depresses the angle of the mouth, being the antagonist of the Caninus and Zygomaticus; acting with the Caninus, it will draw the angle of the mouth medialward. The Platysma which retracts and depresses the angle of the mouth belongs with this group. 384 MYOLOGY The Buccinator (Fig. 380) is a thin quadrilateral muscle, occupying the interval between the maxilla and the mandible at the side of the face. It arises from the outer surfaces of the alveolar processes of the maxilla and mandible, corresponding to the three molar teeth; and behind, from the anterior border of the pterygomandib- ular raphe which separates it from the Constrictor pharyngis superior. The fibers converge toward the angle of the mouth, where the central fibers intersect each other, those from below being continuous with the upper segment of the Orbicu- laris oris, and those from above with the lowTer segment; the upper and lower fibers are continued forward into the corre- sponding lip without decussation. Fig. 380.—Muscles of the pharynx and cheek. Fig. 381.—Scheme showing arrangement of fibers of Orbicularis oris. Relations.—-The Buccinator is covered by the buccopharyngeal fascia, and is in relation by its superficial surface, behind, with a large mass of fat, which separates it from the ramus of the mandible, the Masseter, and a small portion of the Temporalis; this fat has been named the suctorial pad, because it is supposed to assist in the act of sucking. The parotid duct pierces the Buccinator opposite the second molar tooth of the maxilla. The deep surface is in relation with the buccal glands and mucous membrane of the mouth. The pterygomandibular raphe (pterygomandibular ligament) is a tendinous band of the buccopharyngeal fascia, attached by one extremity to the hamulus of the medial pterygoid plate, and by the other to the posterior end of the mylohyoid line of the mandible. Its medial surface is covered by the mucous membrane of the mouth. Its lateral surface is separated from the ramus of the mandible by a quantity of adipose tissue. Its posterior border gives attachment to the Constrictor pharyngis superior; its anterior border, to part of the Buccinator (Fig. 380). The Orbicularis oris (Fig. 381) is not a simple sphincter muscle like the Orbic- ularis oculi; it consists of numerous strata of muscular fibers surrounding the orifice of the mouth but having different direction. It consists partly of fibers derived from the other facial muscles which are inserted into the lips, and partly of fibers proper to the lips. Of the former, a considerable number are derived from the Buccinator and form the deeper stratum of the Orbicularis. Some of the Buccinator fibers—namely, those near the middle of the muscle—decussate at the angle of the mouth, those arising from the maxilla passing to the lower lip, and those from the mandible to the upper lip. The uppermost and lowermost fibers of the Buccinator pass across the lips from side to side without decussation. Superficial to this stratum is a second, formed on either side by the Caninus and THE MUSCLES OF MASTICATION 385 Triangularis, which cross each other at the angle of the mouth; those from the Caninus passing to the lower lip, and those from the Triangularis to the upper lip, along which they run, to be inserted into the skin near the median line. In addi- tion to these there are fibers from the Quadratus labii superioris, the Zygomaticus, and the Quadratus labii inferioris; these intermingle with the transverse fibers above described, and have principally an oblique direction. The proper fibers of the lips are oblique, and pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. Finally there are fibers by which the muscle is connected with the maxillae and the septum of the nose above and with the mandible below. In the upper lip these consist of two bands, lateral and medial, on either side of the middle line; the lateral band (to. incisivus labii superioris) arises from the alveolar border of the maxilla, opposite the lateral incisor tooth, and arching lateralward is continuous with the other muscles at the angle of the mouth; the medial band (to. nasolabialis) connects the upper lip to the back of the septum of the nose. The interval between the two medial bands corresponds with the depression, called the philtrum, seen on the lip beneath the septum of the nose. The additional fibers for the lower lip constitute a slip (to. incisivus labii inferioris) on either side of the middle line; this arises from the mandible, lateral to the Mentalis, and intermingles with the other muscles at the angle of the mouth. The Risorius arises in the fascia over the Masseter and, passing horizontally forward, superficial to the Platysma, is inserted into the skin at the angle of the mouth (Fig. 378). It is a narrow bundle of fibers, broadest at its origin, but varies much in its size and form. Variations.—The zygomatic head of the Quadratus labii superioris and Risorius are frequently absent and more rarely the Zygomaticus. The Zygomaticus and Risorius may be doubled or the latter greatly enlarged or blended with the Platysma. Nerves.—The muscles in this group are all supplied by the facial nerve. Actions.—The Orbicularis oris in its ordinary action effects the direct closure of the lips; by its deep fibers, assisted by the oblique ones, it closely applies the lips to the alveolar arch. The superficial part, consisting principally of the decussating fibers, brings the lips together and also protrudes them forward. The Buccinators compress the cheeks, so that, during the process of mastication, the food is kept under the immediate pressure of the teeth. When the cheeks have been previously distended with air, the Buccinator muscles expel it from between the lips, as in blowing a trumpet; hence the name (buccina, a trumpet). The Risorius retracts the angle of the mouth, and produces an unpleasant grinning expression. For more extensive consideration of the facial muscles, see Charles Darwin, Expression of the Emotions in Man and Animals. IV. THE MUSCLES OF MASTICATION, The chief muscles of mastication are Masseter. Temporalis. Pterygoideus externus. Pterygoideus internus. Parotideomasseteric Fascia {masseteric fascia).—Covering the Masseter, and firmly connected with it, is a strong layer of fascia derived from the deep cervical fascia. Above, this fascia is attached to the lower border of the zygomatic arch, and behind, it invests the parotid gland. The Masseter (Fig. 378) is a thick, somewhat quadrilateral muscle, consisting of two portions, superficial and deep. The superficial portion, the larger, arises by a thick, tendinous aponeurosis from the zygomatic process of the maxilla, and from the anterior two-thirds of the lower border of the zygomatic arch: its fibers pass downward and backward, to be inserted into the angle and lower half of the lateral surface of the ramus of the mandible. The deep portion is much smaller, 386 MYOLOGY and more muscular in texture; it arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch; its fibers pass downward and forward, to be inserted into the upper half of the ramus and the lateral surface of the coronoid process of the mandible. The deep portion of the muscle is partly concealed, in front, by the superficial portion; behind, it is covered by the parotid gland. The fibers of the two portions are continuous at their insertion. Temporal Fascia.—The temporal fascia covers the Temporalis muscle. It is a strong, fibrous investment, covered, laterally, by the Auricularis anterior and supe- rior, by the galea aponeurotica, and by part of the Orbicularis oculi. The super- ficial temporal vessels and the auriculotemporal nerve cross it from below upward. Above, it is a single layer, attached to the entire extent of the superior temporal line; but below, where it is fixed to the zygomatic arch, it consists of two layers, one of which is inserted into the lateral, and the other into the medial border of the arch. A small quantity of fat, the orbital branch of the superficial temporal artery, and a filament from the zygomatic branch of the maxillary nerve, are contained between these two layers. It affords attachment by its deep surface to the super- ficial fibers of the Temporalis. Fig. 382.—The Temporalis; the zygomatic arch and Masseter have been removed. The Temporalis (Temporal muscle) (Fig. 382) is a broad, radiating muscle, situated at the side of the head. It arises from the whole of the temporal fossa (except that portion of it which is formed by the zygomatic bone) and from the deep surface of the temporal fascia. Its fibers converge as they descend, and end in a tendon, which passes deep to the zygomatic arch and is inserted into the medial surface, apex, and anterior border of the cOronoid process, and the anterior border of the ramus of the mandible nearly as far forward as the last molar tooth. The Pterygoideus externus (.External pterygoid muscle) (Fig. 383) is a short, thick muscle, somewhat conical in form, which extends almost horizontally between the infratemporal fossa and the condyle of the mandible. It arises by two heads; an upper from the lower part of the lateral surface of the great wing of the sphenoid and from the infratemporal crest; a lower from the lateral surface of the lateral pterygoid plate. Its fibers pass horizontally backward and lateralward, to be THE SUPERFICIAL CERVICAL MUSCLE 387 inserted into a depression in front of the neck of the condyle of the mandible, and into the front margin of the articular disk of the temporomandibular articulation. The Pterygoideus internus (Internal pterygoid muscle) (Fig. 383) is a thick, quad- rilateral muscle. It arises from the medial surface of the lateral pterygoid plate and the grooved surface of the pyramidal process of the palatine bone; it has a second slip of origin from the lateral surfaces of the pyramidal process of the pala- tine and tuberosity of the maxilla. Its fibers pass downward, lateralward, and backward, and are inserted, by a strong tendinous lamina, into the lower and back part of the medial surface of the ramus and angle of the mandible, as high as the mandibular foramen. Fia. 383.—The Pterygoidei; the zygomatic arch and a portion of the ramua of the mandible have been removed. Nerves.—The muscles of mastication are supplied by the mandibular nerve. Actions.—The Temporalis, Masseter, and Pterygoideus internus raise the mandible against the maxillae with great force. The Pterygoideus externus assists in opening the mouth, but its main action is to draw forward the condyle and articular disk so that the mandible is protruded and the inferior incisors projected in front of the upper; in this action it is assisted by the Ptery- goideus internus. The mandible is retracted by the posterior fibers of the Temporalis. If the Pterygoidei internus and externus of one side act, the corresponding side of the mandible is drawn forward while the opposite condyle remains comparatively fixed, and side-to-side move- ments. such as occur during the trituration of food, take place. THE FASCIA AND MUSCLES OF THE ANTERO-LATERAL REGION OF THE NECK. The antero-lateral muscles of the neck may be arranged into the following groups: I. Superficial Cervical. II. Lateral Cervical. III. Supra- and Infrahyoid. IV. Anterior Vertebral. V. Lateral Vertebral. I. THE SUPERFICIAL CERVICAL MUSCLE. The Superficial Fascia of the neck is a thin lamina investing the Platysma, and is hardly demonstrable as a separate membrane. Platysma. 388 MYOLOGY The Platysma (Fig. 378) is a broad sheet arising from the fascia covering the upper parts of the Pectoralis major and Deltoideus; its fibers cross the clavicle, and proceed obliquely upward and medialward along the side of the neck. The anterior fibers interlace, below and behind the symphysis menti, with the fibers of the muscle of the opposite side; the posterior fibers cross the mandible, some being inserted into the bone below the oblique line, others into the skin and sub- cutaneous tissue of the lower part of the face, many of these fibers blending with the muscles about the angle and lower part of the mouth. Sometimes fibers can be traced to the Zygomaticus, or to the margin of the Orbicularis oculi. Beneath the Platysma, the external jugular vein descends from the angle of the mandible to the clavicle. Variations occur in the extension over the face and over the clavicle and shoulder; it may be absent or interdigitate with the muscle of the opposite side in front of the neck; attachment to clavicle, mastoid process or occipital bone occurs. A more or less independent fasciculus, the Occipitalis minor. may extend from the fascia over the Trapezius to fascia over the insertion of the Sternocleidomastoideus. Nerve.—The Platysma is supplied by the cervical branch of the facial nerve. Actions.—When the entire Platysma is in action it produces a slight wrinkling of the surface of the skin of the neck in an oblique direction. Its anterior portion, the thickest part of the muscle, depresses the lower jaw; it also serves to draw down the lower lip and angle of the mouth in the expression of melancholy. II. THE LATERAL CERVICAL MUSCLES The lateral muscles are: Trapezius and Sternocleidomastoideus. The Trapezius is described on page 432. The Fascia Colli (deep cervical fascia) (Fig. 384).—The fascia colli lies under cover of the Platysma, and invests the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column. The investing portion of the fascia is attached behind to the ligamentum nuchae and to the spinous process of the seventh cervical vertebra. It forms a thin in- vestment to the Trapezius, and at the anterior border of this muscle is continued forward as a rather loose areolar layer, covering the posterior triangle of the neck, to the posterior border of the Sternocleidomastoideus, where it begins to assume the appearance of a fascial membrane. Along the hinder edge of the Sterno- cleidomastoideus it divides to enclose the muscle, and at the anterior margin again forms a single lamella, which covers the anterior triangle of the neck, and reaches forward to the middle line, wrhere it is continuous with the corresponding part from the opposite side of the neck. In the middle line of the neck it is attached to the symphysis menti and the body of the hyoid bone. Above, the fascia is attached to the superior nuchal line of the occipital, to the mastoid process of the temporal, and to the whole length of the inferior border of the body of the mandible. Opposite the angle of the mandible the fascia is very strong, and binds the anterior edge of the Sternocleidomastoideus firmly to that bone. Between the mandible and the mastoid process it ensheathes the parotid gland—the layer which covers the gland extends upward under the name of the parotideomasseterie fascia and is fixed to the zygomatic arch. From the part which passes under the parotid gland a strong band extends upward to the styloid process, forming the stylomandibular ligament. Two other bands may be defined: the sphenomandibular (page 297) and the pterygospinous ligaments. The pterygospinous ligament stretches from the upper part of the posterior border of the lateral ptery- goid plate to the spinous process of the sphenoid. It occasionally ossifies, and in such cases, between its upper border and the base of the skull, a foramen is formed which transmits the branches of the mandibular nerve to the muscles of mastication. THE LATERAL CERVICAL MUSCLES 389 Below, the fascia is attached to the acromion, the clavicle, and the manubrium sterni. Some little distance above the last it splits into two layers, superficial and deep. The former is attached to the anterior border of the manubrium, the latter to its posterior border and to the interclavicular ligament. Between these two layers is a slit-like interval, the suprasternal space (space of Burns); it contains a small quantity of areolar tissue, the lower portions of the anterior jugular veins and their transverse connecting branch, the sternal heads of the Sternocleido- mastoidei, and sometimes a lymph gland. Omohyoideus Ant. jugular vein Thyroid gland S ternohyoideus Common carotid anery Sternothyreoideus Int. jugular vein Sternocle idomastoideus Trachea Vagus nerve" Esophagus Ext. jugular vein 8th cervical vertebra Scalenus anterior Vertebral vessels Scalenus medius' Splenius colli Levator scapula Semispinalis colli Trapezius Semi spinal is capitis Splenius capitis Fio. 384.—Section of the neck at about the level of the sixth cervical vertebra. Showing the arrangement of the fascia coli. The fascia which lines the deep surface of the Sternocleidomastoideus gives off the following processes: (1) A process envelops the tendon at the Omohyoideus, and binds it down to the sternum and first costal cartilage. (2) A strong sheath, the carotid sheath, encloses the carotid artery, internal jugular vein, and vagus nerve. (3) The prevertebral fascia extends medialward behind the carotid vessels, where it assists in forming their sheath, and passes in front of the prevertebral muscles. It forms the posterior limit of a fibrous compartment, which contains the larynx and trachea, the thyroid gland, and the pharynx and esophagus. The 390 MYOLOGY prevertebral fascia is fixed above to the base of the skull, and below is continued into the thorax in front of the Longus colli muscles. Parallel to the carotid sheath and along its medial aspect the prevertebral fascia gives off a thin lamina, the buccopharyngeal fascia, which closely invests the Constrictor muscles of the pharynx, and is continued forward from the Constrictor pharyngis superior on to the Buc- cinator. It is attached to the prevertebral layer by loose connective tissue only, and thus an easily distended space, the retropharyngeal space, is found between them. This space is limited above by the base of the skull, while below it extends behind the esophagus into the posterior mediastinal cavity of the thorax. The pre- vertebral fascia is prolonged downward and Iateralward behind the carotid vessels and in front of the Scaleni, and forms a sheath for the brachial nerves and sub- clavian vessels in the posterior triangle of the neck; it is continued under the clavicle as the axillary sheath and is attached to the deep surface of the coracoclavicular fascia. Immediately above and behind the clavicle an areolar space exists between the investing layer and the sheath of the subclavian vessels, and in this space are found the lower part of the external jugular vein, the descending clavicular nerves, the transverse scapular and transverse cervical vessels, and the inferior belly of the Omohyoideus muscle. This space is limited below by the fusion of the coraco- clavicular fascia with the anterior wall of the axillary sheath. (4) The pretrachial fascia extends medially in front of the carotid vessels, and assists in forming the carotid sheath. It is continued behind the depressor muscles of the hyoid bone, and, after enveloping the thyroid gland, is prolonged in front of the trachea to meet the corresponding layer of the opposite side. Above, it is fixed to the hyoid bone, while below it is carried downward in front of the trachea and large vessels at the root of the neck, and ultimately blends with the fibrous pericardium. This layer is fused on either side with the prevertebral fascia, and with it completes the compartment containing the larynx and trachea, the thyroid gland, and the pharynx and esophagus.1 The Sternocleidomastoideus (Sternoniastoid muscle) (Fig. 385) passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end. It arises from the sternum and clavicle by two heads. The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed upward, Iateralward, and backward. The lateral or clavicular head, composed of fleshy and aponeurotic fibers, arises from the superior border and anterior surface of the medial third of the clavicle; it is directed almost vertically upward. The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone. Variations.—The Sternocleidomastoideus varies much in the extent of its origin from the clavicle: in some cases the clavicular head may be as narrow as the sternal; in others it may be as much as 7.5 cm. in breadth. When the clavicular origin is broad, it is occasionally subdivided into several slips, separated by narrow intervals. More rarely, the adjoining margins of the Sterno- cleidomastoideus and Trapezius have been found in contact. The Supraclavicularis muscle arises from the manubrium behind the Sternocleidomastoideus and passes behind the Sternocleido- mastoideus to the upper surface of the clavicle. Triangles of the Neck.—This muscle divides the quadrilateral area of the side of the neck into two triangles, an anterior and a posterior. The boundaries of the anterior triangle are, in front, the median line of the neck; above, the lower border of the body of the mandible, and an imaginary line drawn from the angle of the mandible to the Sternocleidomastoideus; behind, the anterior border of the Sternocleidomastoideus. The apex of the triangle is at the upper 1 F. G. Parsons (Journal of Anatomy and Physiology, vol. xliv) regards the carotid sheath and the fascial planes in the neck as structures which are artificially produced by dissection. THE SUPRA- AND INFRAHYOID MUSCLES 391 border of the sternum. The boundaries of the posterior triangle are, in front, the posterior border of the Sternocleidomastoideus; below, the middle third of the clavicle; behind, the anterior margin of the Trapezius. The apex corresponds with the meeting of the Sternocleidomastoideus and Trapezius on the occipital bone. The anatomy of these triangles will be more fully described with that of the vessels of the neck (p. 562). Nerves.—The Sternocleidomastoideus is supplied by the accessory nerve and branches from the anterior divisions of the second and third cervical nerves. Actions.—When only one Sternocleidomastoideus acts, it draws the head toward the shoulder of the same side, assisted by the Splenius and the Obliquus capitis inferior of the opposite side. At the same time it rotates the head so as to carry the face toward the opposite side. Acting together from their sternoclavicular attachments the muscles will flex the cervical part of the vertebral column. If the head be fixed, the two muscles assist in elevating the thorax in forced inspiration. Fig. 385.—Muscles of the neck. Lateral view. m. THE SUPRA- AND INFRAHYOID MUSCLES (Figs. 385, 386) The suprahyoid muscles are Digastricus. Stylohyoideus. Mylohyoideus. Geniohyoideus. The Digastricus (Digastric muscle) consists of two fleshy bellies united by an intermediate rounded tendon. It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. The posterior belly, longer than the anterior, arises from the mastoid notch of the temporal bone and passes downward and forward. The anterior belly arises from a depression on the inner side of the lower border of the mandible, close to the symphysis, and passes downward and backward. The twTo bellies end in an intermediate tendon which perforates the Stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone by a fibrous loop, which is 392 MYOLOGY sometimes lined by a mucous sheath.. A broad aponeurotic layer is given off from the tendon of the Digastricus on either side, to be attached to the body and greater cornu of the hyoid bone; this is termed the suprahyoid aponeurosis. Variations are numerous. The posterior belly may arise partly or entirely from the styloid process, or be connected by a slip to the middle or inferior constrictor; the anterior belly may be double or extra slips from this belly may pass to the jaw or Mylohyoideus or decussate with a similar slip on opposite side; anterior belly may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. The tendon may pass in front, more rarely behind the Stylo- hoideus. The Mentohyoideus muscle passes from the body of hyoid bone to chin. The Digastricus divides the anterior triangle of the neck into three smaller triangle (1) the submaxillary triangle, bounded above by the lower border of the body of the mandible, and a line drawn from its angle to the Sternocleidorpastoideus, below by the posterior belly of the Digastricus and the Stylohyoideus, in front by the anterior belly of the Digastricus; (2) the carotid triangle, bounded above by the posterior belly of the Digastricus and Stylohyoideus, behind by the Sternocleidomastoideus, below by the Omohyoideus; (3) the suprahyoid or sub- mental triangle, bounded laterally by the anterior belly of the Digastricus, medially by the middle line of the neck from the hyoid bone to the symphysis menti, and interiorly by the body of the hyoid bone. Fig. 386.—Muscles of the neck. Anterior view. The Stylohyoideus (Stylohyoid muscle) is a slender muscle, lying in front of, and above, the posterior belly of the Digastricus. It arises from the back and lateral surface of the styloid process, near the base; and, passing downward and forward, is inserted into the body of the hyoid bone, at its junction with the greater cornu, and just above the Omohyoideus. It is perforated, near its insertion, by the tendon of the Digastricus. Variations.—It may be absent or doubled, lie beneath the carotid artery, or be inserted into the Omohyoideus, Thyreohyoideus, or Mylohyoideus. The Stylohyoid Ligament (ligamentum stylohyoideus).—In connection with the Stylohyoideus muscle a ligamentous band, the stylohyoid ligament, may be THE SUPRA- AND INFRAHYOID MUSCLES 393 described. It is a fibrous cord, which is attached to the tip of the styloid process of the temporal and the lesser cornu of the hyoid bone. It frequently contains a little cartilage in its center, is often partially ossified, and in many animals forms a distinct bone, the epihyal. The Mylohyoideus (Mylohyoid muscle), flat and triangular, is situated imme- diately above the anterior belly of the Digastricus, and forms, with its fellow of the opposite side, a muscular floor for the cavity of the mouth. It arises from the whole length of the mylohyoid line of the mandible, extending from the symphysis in front to the last molar tooth behind. The posterior fibers pass medialward and slightly downward, to be inserted into the body of the hyoid bone. The middle and anterior fibers are inserted into a median fibrous raphe extending from the sym- physis menti to the hyoid bone, where they join at an angle with the fibers of the opposite muscle. This median raphe is sometimes wanting; the fibers of the two muscles are then continuous. Variations.—It may be united to or replaced by the anterior belly of the Digastricus; accessory slips to other hyoid muscles are frequent. The Geniohyoideus (Geniohyoid muscle) is a narrow muscle, situated above the medial border of the Mylohyoideus. It arises from the inferior mental spine on the back of the symphysis menti, and runs backward and slightly downward, to be inserted into the anterior surface of the body of the hyoid bone; it lies in con- tact with its fellow of the opposite side. Variations.—It may be blended with the one on opposite side or double; slips to greater cornu of hyoid bone and Genioglossus occur. Nerves.—The Mylohyoideus and anterior belly of the Digastricus are supplied by the mylo- hyoid branch of the inferior alveolar; the Stylohyoideus and posterior belly of the Digastricus, by the facial; the Geniohyoideus, by the hypoglossal. Actions.—These muscles perform two very important actions. During the act of deglutition they raise the hyoid bone, and with it the base of the tongue; when the hyoid bone is fixed by its depressors and those of the larynx, they depress the mandible. During the first act of degluti- tion, when the mass of food is being driven from the mouth into the pharynx, the hyoid bone and with it the tongue, is carried upward and forward by the anterior bellies of the Digastrici, the Mylohyoidei, and Geniohyoidei. In the second act, when the mass is passing through the pharynx, the direct elevation of the hyoid bone takes place by the combined action of all the muscles; and after the food has passed, the hyoid bone is carried upward and backward by the posterior bellies of the Digastrici and the Stylohyoidei, which assist in preventing the return of the food into the mouth. The infrahyoid muscles are: Sternohyoideus. Sternothyreoideus. Thyreohyoideus. Omohyoideus. The Sternohyoideus (Sternohyoid muscle) is a thin, narrow muscle, which arises from the posterior surface of the medial end of the clavicle, the posterior sterno- clavicular ligament, and the upper and posterior part of the manubrium sterni. Passing upward and medialward, it is inserted, by short, tendinous fibers, into the lower border of the body of the hyoid bone. Below, this muscle is separated from its fellow by a considerable interval; but the two muscles come into contact with one another in the middle of their course, and from this upward, lie side by side. It sometimes presents, immediately above its origin, a transverse tendinous inscription. Variations.—Doubling; accessory slips (Cleidohyoideus); absence. The Sternothyreoideus (Sternothyroid muscle) is shorter and wider than the preceding muscle, beneath which it is situated. It arises from the posterior surface of the manubrium sterni, below the origin of the Sternohyoideus, and from the edge of the cartilage of the first rib, and sometimes that of the second rib, it is inserted 394 MYOLOGY into the oblique line on the lamina of the thyroid cartilage. This muscle is in close contact with its fellow at the lower part of the neck, but diverges somewhat as it ascends; it is occasionally traversed by a transverse or oblique tendinous inscription. Variations.—Doubling; absence; accessory slips to Thyreohyoideus, Inferior constrictor, or carotid sheath. The Thyreohyoideus (Thyrohyoid muscle) is a small, quadrilateral muscle appearing like an upward continuation of the Sternothyreoideus. It arises from the oblique line on the lamina of the thyroid cartilage, and is inserted into the lower border of the greater cornu of the hyoid bone. The Omohyoideus (Omohyoid muscle) consists of two fleshy bellies united by a central tendon. It arises from the upper border of the scapula, and occasionally from the superior transverse ligament which crosses the scapular notch, its extent of attachment to the scapula varying from a few millimetres to 2.5 cm. From this origin, the inferior belly forms a flat, narrow fasciculus, which inclines forward and slightly upward across the lower part of the neck, being bound down to the clavicle by a fibrous expansion; it then passes behind the Sternocleidomastoideus, becomes tendinous and changes its direction, forming an obtuse angle. It ends in the superior belly, which passes almost vertically upward, close to the lateral border of the Sternohyoideus, to be inserted into the lower border of the body of the hyoid bone, lateral to the insertion of the Sternohyoideus. The central tendon of this muscle varies much in length and form, and is held in position by a process of the deep cervical fascia, which sheaths it, and is prolonged down to be attached to the clavicle and first rib; it is by this means that the angular form of the muscle is maintained. Variations.—Doubling; absence; origin from clavicle; absence or doubling of either belly. The inferior belly of the Omohyoideus divides the posterior triangle of the neck into an upper or occipital triangle and a lower or subclavian triangle, while its superior belly divides the anterior triangle into an upper or carotid triangle and a lower or muscular triangle. Nerves.—The Infrahyoid muscles are supplied by branches from the first three cervical nerves. From the first two nerves the branch joins the hypoglossal trunk, runs with it some distance, and sends off a branch to the Thyreohyoideus; it then leaves the hypoglossal to form the descendens hypoglossi and unites with the communicantes cervicalis from the second and third cervical nerves to form the ansa hypoglossi from which nerves pass to the other Infrahyoid muscles. Actions.—These muscles depress the larynx and hyoid bone, after they have been drawn up with the pharynx in the act of deglutition. The Omohyoidei not only depress the hyoid bone, but carry it backward and to one or the other side. They are concerned especially in prolonged inspiratory efforts; for by rendering the lower part of the cervical fascia tense they lessen the inward suction of the soft parts, which would otherwise compress the great vessels and the apices of the lungs. The Thyreohyoideus may act as an elevator of the thyroid cartilage, when the hyoid bone ascends, drawing the thyroid cartilage up behind the hyoid bone. The Sterno- thyreoideus acts as a depressor of the thyroid cartilage. IV. THE ANTERIOR VERTEBRAL MUSCLES (Fig. 387) The anterior vertebral muscles are: Longus colli. Longus capitis. Rectus capitis anterior Rectus capitis lateralis The Longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra. It is broad in the middle, narrow and pointed at either end, and consists of three portions, a superior oblique, an inferior oblique, and a vertical. The superior oblique portion arises from the anterior tubercles of the transverse processes of the third, fourth, and fifth cervical vertebrae; and, ascending obliquely with a medial inclination, is inserted by a narrow THE ANTERIOR VERTEBRAL MUSCLES 395 tendon into the tubercle on the anterior arch of the atlas. The inferior oblique portion, the smallest part of the muscle, arises from the front of the bodies of the first two or three thoracic vertebrae; and, ascending obliquely in a lateral direction, is inserted into the anterior tubercles of the transverse processes of the fifth and sixth cervical vertebrae. The vertical portion arises, below, from the front of the bodies of the upper three thoracic and lower three cervical vertebrae, and is in- serted into the front of the bodies of the second, third, and fourth cervical vertebrae. The Longus capitis (Rectus capitis anticus major), broad and thick above, narrow below, arises by four tendinous slips, from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and ascends, converging toward its fellow of the opposite side, to be inserted into the inferior surface of the basilar part of the occipital bone. Fig. 387.—The anterior vertebral muscles. The Rectus capitis anterior (Rectus capitis anticus minor) is a short, flat muscle, situated immediately behind the upper part of the Longus capitis. It arises from the anterior surface of the lateral mass of the atlas, and from the root of its transverse process, and passing obliquely upward and medialward, is inserted into the inferior surface of the basilar part of the occipital bone immediately in front of the foramen magnum. The Rectus capitis lateralis, a short, flat’ muscle, arises from the upper surface of the transverse process of the atlas, and is inserted into the under surface of the jugular process of the occipital bone. Nerves.—The Rectus capitis anterior and the Rectus capitis lateralis are supplied from the loop between the first and second cervical nerves; the Longus capitis, by branches from the 396 MYOLOGY first, second, and third cervical; the Longus colli, by branches from the second to the seventh cervical nerves. Actions.—The Longus capitis and Rectus capitis anterior are the direct antagonists of the muscles at the back of the neck, serving to restore the head to its natural position after it has been drawn backward. These muscles also flex the head, and from their obliquity, rotate it, so as to turn the face to one or the other side. The Rectus lateralis, acting on one side, bends the head laterally. The Longus colli flexes and slightly rotates the cervical portion of the vertebral column. V. THE LATERAL VERTEBRAL MUSCLES (Fig. 387). The lateral vertebral muscles are: Scalenus anterior. Scalenus posterior. Scalenus medius. The Scalenus anterior (Scalenus anticus) lies deeply at the side of the neck, behind the Sternocleidomastoideus. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the rib in front of the subclavian groove. The Scalenus medius, the largest and longest of the three Scaleni, arises from the posterior tubercles of the transverse processes of the lower six cervical vertebrae, and descending along the side of the vertebral column, is inserted by a broad attachment into the upper surface of the first rib, between the tubercle and the subclavian groove. The Scalenus posterior (Scalenus posticus), the smallest and most deeply seated of the three Scaleni, arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the lower two or three cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the Serratus anterior. It is occasionally blended with the Scalenus medius. Variations.—The Scaleni muscles vary considerably in their attachments and in the arrange- ment of their fibers. A slip from the Scalenus anticus may pass behind the subclavian artery. The Scalenus posticus may be absent or extend to the third rib. The Scalenus pleuralis muscle extends from the transverse process of the seventh cervical vertebra to the fascia supporting the dome of the pleura and inner border of first rib. Nerves.—The Scaleni are supplied by branches from the second to the seventh cervical nerves. Actions.—When the Scaleni act from above, they elevate the first and second ribs, and are, therefore, inspiratory muscles. Acting from below, they bend the vertebral column to one or other side; if the muscles of both sides act, the vertebral column is slightly flexed. THE FASCLffi AND MUSCLES OF THE TRUNK. The muscles of the trunk may be arranged in six groups: I. Deep Muscles of the Back. II. Suboccipital Muscles. III. Muscles of the Thorax. IV. Muscles of the Abdomen. V. Muscles of the Pelvis. VI. Muscles of the Perineum. I. THE DEEP MUSCLES OF THE BACK (Fig. 388). The deep or intrinsic muscles of the back consist of a complex group of muscles extending from the pelvis to the skull. They are: Splenius capitis. Splenius cervicis. Sacrospinalis. Semispinalis. Multifidus. Rotatores. Interspinales. Intertransversarli. THE DEEP MUSCLES OF THE BACK 397 The Lumbodorsal Fascia (fascia lumbodorsalis; lumbar aponeurosis and vertebral fascia).—The lumbodorsal fascia is a deep investing membrane which covers the deep muscles of the back of the trunk. Above, it passes in front of the Serratus posterior superior and is continuous with a similar investing layer on the back of the neck—the nuchal fascia. In the thoracic region the lumbodorsal fascia is a thin fibrous lamina which serves to bind down the Extensor muscles of the vertebral column and to separate them from the muscles connecting the vertebral column to the upper extremity. It contains both longitudinal and transverse fibers, and is attached, medially, to the spinous processes of the thoracic vertebrae; laterally to the angles of the ribs. In the lumbar region the fascia (lumbar aponeurosis) is in two layers, anterior and posterior (Figs. 388, 409). The posterior layer is attached to the spinous processes of the lumbar and sacral vertebrae and to the supraspinal ligament; the anterior layer is attached, medially, to the tips of the transverse processes of the lumbar vertebrae and to the intertransverse ligaments, below, to the iliolumbar ligament, and above, to the lumbocostal ligament. The two layers unite at the lateral margin of the Sacrospinalis, to form the tendon of origin of the Transversus abdominis. The aponeurosis of origin of the Serratus posterior inferior and the Latissimus dorsi are intimately blended with the lumbodorsal fascia. „Obliquus externua Obliquus interims Transversus Fascia on I Quad. Lumb. Lumbodorsal fascia 'Anterior layer n Fig. 388.—Diagram of a transverse section of the posterior abdominal wall, to show the disposition of the lumboaorsal fascia. Posterior layer The Splenius capitis (Fig. 409) arises from the lower half of the ligamentum nuchse, from the spinous process of the seventh cervical vertebra, and from the spinous processes of the upper three or four thoracic vertebrae. The fibers of the muscle are directed upward and lateralward and are inserted, under cover of the Sternocleidomastoideus, into the mastoid process of the temporal bone, and into the rough surface on the occipital bone just below the lateral third of the superior nuchal line. The Splenius cervicis (Splenius colli) (Fig. 409) arises by a narrow tendinous band from the spinous processes of the third to the sixth thoracic vertebrae; it is inserted, by tendinous fasciculi, into the posterior tubercles of the transverse processes of the upper two or three cervical vertebrae. Variations.—The origin is frequently moved up or down one or two vertebra;. Accessory slips are occasionally found. Nerves.—The Splenii are supplied by the lateral branches of the posterior divisions of the middle and lower cervical nerves. Actions.—The Splenii of the two sides, acting together, draw the head directly backward, assisting the Trapezius and Semispinalis capitis; acting separately, they draw the head to one side, and slightly rotate it, turning the face to the same side. They also assist in supporting the head in the erect position. The Sacrospinalis (Erector spince) (Fig. 389), and its prolongations in the thoracic and cervical regions, lie in the groove on the side of the vertebral column. 398 MYOLOGY They are covered in the lumbar and thoracic regions by the lumbodorsal fascia, and in the cervical region by the nuchal fascia. This large muscular and tendinous Occipital bone M ultifidus First thoracic vertebra- ~First rib - Second rib J.Third rib First lumbar vertebra- First sacral vertebra^ Fig. 389.—Deep muscles of the back. THE DEEP MUSCLES OF THE BACK 399 mass varies in size and structure at different parts of the vertebral column. In the sacral region it is narrow and pointed, and at its origin chiefly tendinous in structure. In the lumbar region it is larger, and forms a thick fleshy mass which, on being followed upward, is subdivided into three columns; these gradually diminish in size as they ascend to be inserted into the vertebrse and ribs. The Sacrospinalis arises from the anterior surface of a broad and thick tendon, which is attached to the medial crest of the sacrum, to the spinous processes of the lumbar and the eleventh and twelfth thoracic vertebrse, and the supraspinal ligament, to the back part of the inner lip of the iliac crests and to the lateral crests of the sacrum, where it blends with the sacrotuberous and posterior sacro- iliac ligaments. Some of its fibers are continuous with the fibers of origin of the Glutseus maximus. The muscular fibers form a large fleshy mass which splits, in the upper lumbar region into three columns, viz., a lateral, the Iliocostalis, an intermediate, the Longissimus, and a medial, the Spinalis. Each of these consists from below upward, of three parts, as follows: Lateral Column. Iliocostalis. (a) I. lumborum. (b) I. dorsi. (c) I. cervicis. Intermediate Column. Longissimus. (a) L. dorsi. (b) L. cervicis. (c) L. capitis. Medial Column. Spinalis. (a) S. dorsi. (b) S. cervicis. (c) S. capitis. The Iliocostalis lumborum (Iliocostalis muscle; Sacrolumbalis muscle) is inserted, by six or seven flattened tendons, into the inferior borders of the angles of the lower six or seven ribs. The Iliocostalis dorsi (Musculus accessorius) arises by flattened tendons from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the Iliocostalis lumborum; these become muscular, and are inserted into the upper borders of the angles of the upper six ribs and into the back of the transverse process of the seventh cervical vertebra. The Iliocostalis cervicis (Cervicalis ascendens) arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the trans- verse processes of the fourth, fifth, and sixth cervical vertebrse. The Longissimus dorsi is the intermediate and largest of the continuations of the Sacrospinalis. In the lumbar region, where it is as yet blended with the Ilio- costalis lumborum, some of its fibers are attached to the whole length of the pos- terior surfaces of the transverse processes and the accessory processes of the lumbar vertebrse, and to the anterior layer of the lumbodorsal fascia. In the thoracic region it is inserted, by rounded tendons, into the tips of the transverse processes of all the thoracic vertebrse, and by fleshy processes into the lower nine or ten ribs between their tubercles and angles. The Longissimus cervicis (Transversalis cervicis), situated medial to the Longis- simus dorsi, arises by long thin tendons from the summits of the transverse pro- cesses of the upper four or five thoracic vertebrse, and is inserted by similar tendons into the posterior tubercles of the transverse processes of the cervical vertebrse from the second to the sixth inclusive. The Longissimus capitis (Trachelomastoid muscle) lies medial to the Longissimus cervicis, between it and the Semispinalis capitis. It arises by tendons from the transverse processes of the upper four or five thoracic vertebrse, and the artic- ular processes of the lower three or four cervical vertebrse, and is inserted into the posterior margin of the mastoid process, beneath the Splenius capitis and Sterno- cleidomastoideus. It is almost always crossed by a tendinous intersection near its insertion. The Spinalis dorsi, the medial continuation of the Sacrospinalis, is scarcely separable as a distinct muscle. It is situated at the medial side of the Longissimus 400 MYOLOGY dorsi, and is intimately blended with it; it arises by three or four tendons from the spinous processes of the first two lumbar and the last two thoracic vertebrae: these, uniting, form a small muscle which is inserted by separate tendons into the spinous processes of the upper thoracic vertebrae, the number varying from four to eight. It is intimately united with the Semispinalis dorsi, situated beneath it. The Spinalis cervicis (Spinalis colli) is an inconstant muscle, which arises from the lower part of the ligamentum nuchae, the spinous process of the seventh cer- vical, and sometimes from the spinous processes of the first and second thoracic vertebrae, and is inserted into the spinous process of the axis, and occasionally into the spinous processes of the two vertebrae below it. The Spinalis capitis (Biventer cervicis) is usually inseparably connected with the Semispinalis capitis (see below). The Semispinalis dorsi consists of thin, narrow, fleshy fasciculi, interposed between tendons of considerable length. It arises by a series of small tendons from the transverse processes of the sixth to the tenth thoracic vertebrae, and is inserted, by tendons, into the spinous processes of the upper four thoracic and lower two cervical vertebrae. The Semispinalis cervicis (Semispinalis colli), thicker than the preceding, arises by a series of tendinous and fleshy fibers from the transverse processes of the upper five or six thoracic vertebrae, and is inserted into the cervical spinous processes, from the axis to the fifth inclusive. The fasciculus connected with the axis is the largest, and is chiefly muscular in structure. The Semispinalis capitis (Complexus) is situated at the upper and back part of the neck, beneath the Splenius, and medial to the Longissimus cervicis and capitis. It arises by a series of tendons from the tips of the transverse processes of the upper six or seven thoracic and the seventh cervical vertebrae, and from the articular processes of the three cervical above this. The tendons, uniting, form a broad muscle, which passes upward, and is inserted between the superior and inferior nuchal lines of the occipital bone. The medial part, usually more or less distinct from the remainder of the muscle, is frequently termed the Spinalis capitis; it is also named the Biventer cervicis since it is traversed by an imperfect tendinous inscription. The Multifidus (Multifidus spince) consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the ver- tebrae, from the sacrum to the axis. In the sacral region, these fasciculi arise from the back of the sacrum, as low as the fourth sacral foramen, from the aponeu- rosis of origin of the Sacrospinalis, from the medial surface of the posterior superior iliac spine, and from the posterior sacroiliac ligaments; in the lumbar region, from all the mamillary processes; in the thoracic region, from all the transverse processes; and in the cervical region, from the articular processes of the lower four vertebrae. Each fasciculus, passing obliquely upward and medialward, is inserted into the whole length of the spinous process of one of the vertebrae above. These fasciculi vary in length: the most superficial, the longest, pass from one vertebra to the third or fourth above; those next in order run from one vertebra to the second or third above; while the deepest connect two contiguous vertebrae. The Rotatores (Rotatores spince) lie beneath the Multifidus and are found only in the thoracic region; they are eleven in number on either side. Each muscle is small and somewhat quadrilateral in form; it arises from the upper and back part of the transverse process, and is inserted into the lower border and lateral surface of the lamina of the vertebra above, the fibers extending as far as the root of the spinous process. The first is found between the first and second thoracic vertebrae; the last, between the eleventh and twelfth. Sometimes the number of these muscles is diminished by the absence of one or more from the upper or lower end. The Interspinales are short muscular fasciculi, placed in pairs between the THE SUBOCCIPITAL MUSCLES 401 spinous processes of the contiguous vertebrae, one on either side of the interspinal ligament. In the cervical region they are most distinct, and consist of six pairs, the first being situated between the axis and third vertebra, and the last between the seventh cervical and the first thoracic. They are small narrow bundles, attached, above and below, to the apices of the spinous processes. In the thoracic region, they are found between the first and second vertebrae, and sometimes be- tween the second and third, and between the eleventh and twelfth. In the lumbar region there are four pairs in the intervals between the five lumbar vertebrae. There is also occasionally one between the last thoracic and first lumbar, and one between the fifth lumbar and the sacrum. The Extensor coccygis is a slender muscular fasciculus, which is not always present; it extends over the lower part of the posterior surface of the sacrum and coccyx. It arises by tendinous fibers from the last segment of the sacrum, or first piece of the coccyx, and passes downward to be inserted into the lower part of the coccyx. It is a rudiment of the Extensor muscle of the caudal vertebrse of the lower animals. The Intertransversarii (Intertransversales) are small muscles placed between the transverse processes of the vertebrse. In the cervical region they are best developed, consisting of rounded muscular and tendinous fasciculi, and are placed in pairs, passing between the anterior and the posterior tubercles respectively of the transverse processes of two contiguous vertebrse, and separated from one another by an anterior primary division of the cervical nerve, which lies in the groove between them. The muscles connecting the anterior tubercles are termed the Intertransversarii anteriores; those between the posterior tubercles, the Inter- transversarii posteriores; both sets are supplied by the anterior divisions of the spinal nerves (Lickley1). There are seven pairs of these muscles, the first pair being between the atlas and axis, and the last pair between the seventh cervical and first thoracic vertebrse. In the thoracic region they are present between the transverse processes of the lower three thoracic vertebrse, and between the trans- verse processes of the last thoracic and the first lumbar. In the lumbar region they are arranged in pairs, on either side of the vertebral column, one set occupy- ing the entire interspace between the transverse processes of the lumbar vertebrse, the Intertransversarii laterales; the other set, Intertransversarii mediates, passing from the accessory process of one vertebra to the mammillary of the vertebra below. The Intertransversarii laterales are supplied by the anterior divisions, and the Intertransversarii mediates by the posterior divisions of the spinal nerves (Lichley, op. cit.). H. THE SUBOCCIPITAL MUSCLES (Fig. 389). The suboccipital group comprises: Rectus capitis posterior major. Rectus capitis posterior minor. Obliquus capitis inferior. Obliquus capitis superior The Rectus capitis posterior major (Rectus capitis posticus major) arises by a pointed tendon from the spinous process of the axis, and, becoming broader as it ascends, is inserted into the lateral part of the inferior nuchal line of the occipital bone and the surface of the bone immediately below the line. As the muscles of the two sides pass upward and lateralward, they leave between them a triangular space, in which the Recti capitis posteriores minores are seen. The Rectus capitis posterior minor (Rectus capitis posticus minor) arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, and, widening as it ascends, is inserted into the medial part of the inferior nuchal line of the occipital bone and the surface between it and the foramen magnum. 1 Journal of Anatomy and Physiology, 1904, vol. xxxix. 402 MYOLOGY The Obliquus capitis inferior (Obliquus inferior), the larger of the two Oblique muscles, arises from the apex of the spinous process of the axis, and passes lateral- ward and slightly upward, to be inserted into the lower and back part of the transverse process of the atlas. The Obliquus capitis superior (Obliquus superior), narrow below, wide and expanded above, arises by tendinous fibers from the upper surface of the transverse process of the atlas, joining with the insertion of the preceding. It passes upward and medialward, and is inserted into the occipital bone, between the superior and inferior nuchal lines, lateral to the Semispinalis capitis. The Suboccipital Triangle.—Between the Obliqui and the Rectus capitis posterior major is the suboccipital triangle. It is bounded, above and medially, by the Rectus capitis posterior major; above and laterally, by the Obliquus capitis superior; below and laterally, by the Obliquus capitis inferior. It is covered by a layer of dense fibro-fatty tissue, situated beneath the Semi- spinalis capitis. The floor is formed by the posterior occipito-atlantal membrane, and the posterior arch of the atlas. In the deep groove on the upper surface of the posterior arch of the atlas are the vertebral artery and the first cervical or suboccipital nerve. Nerves.—The deep muscles of the back and the suboccipital muscles are supplied by the posterior primary divisions of the spinal nerves. Actions.—The Sacrospinalis and its upward continuations and the Spinales serve to main- tain the vertebral column in the erect posture; they also serve to bend the trunk backward when it is required to counterbalance the influence of any weight at the front of the body—as, for instance, when a heavy weight is suspended from the neck, or when there is any great abdominal distension, as in pregnancy or dropsy; the peculiar gait under such circumstances depends upon the vertebral column being drawn backward, by the counterbalancing action of the Sacrospinales. The muscles which form the continuation of the Sacrospinales on to the head and neck steady those parts and fix them in the upright position. If the Iliocostalis lumborum and Longissimus dorsi of one side act, they serve to draw down the chest and vertebral column to the correspond- ing side. The Iliocostales cervicis, taking their fixed points from the cervical vertebrae, elevate those ribs to which they are attached; taking their fixed points from the ribs, both muscles help to extend the neck; while one muscle bends the neck to its own side. When both Longissimi cervicis act from below, they bend the neck backward. When both Longissimi capitis act from below, they bend the head backward; while, if only one muscle acts, the face is turned to the side on which the muscle is acting, and then the head is bent to the shoulder. The two Recti draw the head backward. The Rectus capitis posterior major, owing to its obliquity, rotates the skull, with the atlas, around the odontoid process, turning the face to the same side. The Multifidus acts successively upon the different parts of the column; thus, the sacrum furnishes a fixed point from which the fasciculi of this muscle acts upon the lumbar region; which in turn becomes the fixed point for the fasciculi moving the thoracic region, and so on throughout the entire length of the column. The Multifidus also serves to rotate the column, so that the front of the trunk is turned to the side opposite to that from which the muscle acts, this muscle being assisted in its action by the Obliquus externus abdominis. The Obliquus capitis superior draws the head backward and to its own side. The Obliquus inferior rotates the atlas, and with it the skull, around the odontoid process, turning the face to the same side. When the Semispinales of the two sides act together, they help to extend the vertebral column; when the muscles of only one side act, they rotate the thoracic and cervical parts of the column, turning the body to the opposite side. The Semispinales capitis draw the head directly backward; if one muscle acts, it draws the head to one side, and rotates it so that the face is turned to the opposite side. The Interspinales by approximating the spinous processes help to extend the column. The Inter- transversarii approximate the transverse processes, and help to bend the column to one side. The Rotatores assist the Multifidus to rotate the vertebral column, so that the front of the trunk is turned to the side opposite to that from which the muscles act. III. THE MUSCLES OF THE THORAX. The muscles belonging to this group are the Intercostales externi. Intercostales interni. Subcostales. Trans versus thoracis. Levatores costarum. Serratus posterior superior Serratus posterior inferior. Diaphragm. Intercostal Fasciae.—In each intercostal space thin but firm layers of fascia cover the outer surface of the Intercostalis externus and the inner surface of the THE MUSCLES OF THE THORAX 403 Intercostalis interims; and a third, more delicate layer, is interposed between the two planes of muscular fibers. They are best marked in those situations where the muscular fibers are deficient, as between the Intercostales externi and sternum in front, and between the Intercostales interni and vertebral column behind. The Intercostales (Intercostal muscles) (Fig. 411) are two thin planes of muscular and tendinous fibers occupying each of the intercostal spaces. They are named external and internal from their surface relations—the external being superficial to the internal. The Intercostales externi (External intercostals) are eleven in number on either side. They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes, which are continued forward to the sternum. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the Intercostales interni, and their fibers are directed obliquely downward and lateral- ward on the back of the thorax, and downward, forward, and medialward on the front. Variations.—Continuation with the Obliquus externus or Serratus anterior: A Supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs. The Intercostales interni (Internal intercostals) are also eleven in number on either side. They commence anteriorly at the sternum, in the interspaces between the cartilages of the true ribs, and at the anterior extremities of the cartilages of the false ribs, and extend backward as far as the angles of the ribs, whence they are continued to the vertebral column by thin aponeuroses, the posterior intercostal membranes. Each arises from the ridge on the inner surface of a rib, as well as from the corresponding costal cartilage, and is inserted into the upper border of the rib below. Their fibers are also directed obliquely, but pass in a direction opposite to those of the Intercostales externi. The Subcostales (Infracostales) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax; each arises from the inner surface of one rib near its angle, and is inserted into the inner surface of the second or third rib below. Their fibers run in the same direction as those of the Intercostales interni. The Transversus thoracis (Triangularis sterni) is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest (Fig. 390). It arises on either side from the lower third of the posterior surface of the body of the sternum, from the posterior surface of the xiphoid process, and from the sternal ends of the costal cartilages of the lower three or four true ribs. Its fibers diverge upward and lateralward, to be inserted by slips into the lower borders and inner surfaces of the costal cartilages of the second, third, fourth, fifth, and sixth ribs. The lowrest fibers of this muscle are horizontal in their direc- tion, and are continuous with those of the Transversus abdominis; the intermediate fibers are oblique, while the highest are almost vertical. This muscle varies in its attachments, not only in different subjects, but on opposite sides of the same subject. The Levatores costarum (Fig. 389), twelve in number on either side, are small tendinous and fleshy bundles, which arise from the ends of the transverse pro- cesses of the seventh cervical and upper eleven thoracic vertebrae; they pass obliquely downward and lateralward, like the fibers of the Intercostales externi, and each is inserted into the outer surface of the rib immediately below the vertebra from which it takes origin, between the tubercle and the angle (Levatores costarum breves). Each of the four lower muscles divides into two fasciculi, one 404 MYOLOGY of which is inserted as above described; the other passes down to the second rib below its origin (Levatores costarum longi). The Serratus posterior superior {Serratus posticus superior) is a thin, quadri- lateral muscle, situated at the upper and back part of the thorax. It arises by a thin and broad aponeurosis from the lower part of the ligamentum nuchae, from the spinous processes of the seventh cervical and upper two or three thoracic vertebrae and from the supraspinal liga- ment. Inclining downward and lateral- ward it becomes muscular, and is in- serted, by four fleshy digitations, into the upper borders of the second, third, fourth, and fifth ribs, a little beyond their angles. Variations.—Increase or decrease in size and number of slips or entire absence. The Serratus posterior inferior (Ser- ratus posticus inferior) (Fig. 409) is sit- uated at the junction of the thoracic and lumbar regions: it is of an irreg- ularly quadrilateral form, broader than the preceding, and separated from it by a wide interval. It arises by a thin aponeurosis from the spinous processes of the lower two thoracic and upper twTo or three lumbar vertebrae, and from the supraspinal ligament. Passing obliquely upward and lateralward, it becomes fleshy, and divides into four flat digitations, which are inserted into the inferior borders of the lower four ribs, a little beyond their angles. The , thin aponeurosis of origin is intimately blended with the lumbodorsal fascia, and aponeurosis of the Latissimus dorsi. Variations.—Increase or decrease in size and number of slips or entire absence. Nerves.—The muscles of this group are supplied by the intercostal nerves. The Diaphragm (Fig. 391) is a dome-shaped musculofibrous septum which separates the thoracic from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter. Its peripheral part consists of muscular fibers which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon. The muscular fibers may be grouped according to their origins into three parts —sternal, costal, and lumbar. The sternal part arises by two fleshy slips from the back of the xiphoid process; the costal part from the inner surfaces of the car- tilages and adjacent portions of the lower six ribs on either side, interdigitating with the Transversus abdominis; and the lumbar part from aponeurotic arches, named the lumbocostal arches, and from the lumbar vertebrae by two pillars or crura. There are two lumbocostal arches, a medial and a lateral, on either side. The Medial Lumbocostal Arch (arcus lumbocostalis medialis [Halleri]; internal arcuate ligament) is a tendinous arch in the fascia covering the upper part of the Psoas major; medially, it is continuous with the lateral tendinous margin of the corresponding crus, and is attached to the side of the body of the first or second Sternal origin of Diaphragm **• THE MUSCLES OF THE THORAX 405 lumbar vertebra; laterally, it is fixed to the front of the transverse process of the first and, sometimes also, to that of the second lumbar vertebra. The Lateral Lumbocostal Arch (arcus lumbocostalis lateralis [Halleri]; external arcuate ligament) arches across the upper part of the Quadratus lumborum, and is attached, medially, to the front of the transverse process of the first lumbar vertebra, and, laterally, to the tip and lower margin of the twelfth rib. The Crura.—At their origins the crura are tendinous in structure, and blend with the anterior longitudinal ligament of the vertebral column. The right crus, larger and longer than the left, arises from the anterior surfaces of the bodies and intervertebral fibrocartilages of the upper three lumbar vertebrae, while the left crus arises from the corresponding parts of the upper two only. The medial ten- dinous margins of the crura pass forward and medialward, and meet in the middle line to form an arch across the front of the aorta; this arch is often poorly defined. Xiphoid process Opening for Lesser Splanchnic Nerve Last Rib From this series of origins the fibers of the diaphragm converge to be inserted into the central tendon. The fibers arising from the xiphoid process are very short, and occasionally aponeurotic; those from the medial and lateral lumbocostal arches, and more especially those from the ribs and their cartilages, are longer, and describe marked curves as they ascend and converge to their insertion. The fibers of the crura diverge as they ascend, the most lateral being directed upward and lateralward to the central tendon. The medial fibers of the right crus ascend on the left side of the esophageal hiatus, and occasionally a fasciculus of the left crus crosses the aorta and runs obliquely through the fibers of the right crus toward the vena caval foramen (Low1). Fig. 391.—The diaphragm. Under surface. 1 Journal of Anatomy and Physiology, vol. xlii. 406 MYOLOGY The Central Tendon.—The central tendon of the diaphragm is a thin but strong aponeurosis situated near the center of the vault formed by the muscle, but some- what closer to the front than to the back of the thorax, so that the posterior muscu- lar fibers are the longer. It is situated immediately below the pericardium, with which it is partially blended. It is shaped somewhat like a trefoil leaf, consisting of three divisions or leaflets separated from one another by slight indentations. The right leaflet is the largest, the middle, directed toward the xiphoid process, the next in size, and the left the smallest. In structure the tendon is composed of several planes of fibers, which intersect one another at various angles and unite into straight or curved bundles—an arrangement which gives it additional strength. Openings in the Diaphragm.—The diaphragm is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen. Three large openings—the aortic, the esophageal, and the vena caval—and a series of smaller ones are described. The aortic hiatus is the lowest and most posterior of the large apertures; it lies at the level of the twelfth thoracic vertebra. Strictly speaking, it is not an aperture in the diaphragm but an osseoaponeurotic opening between it and the vertebral column, and therefore behind the diaphragm; occasionally some tendinous fibers prolonged across the bodies of the vertebrae from the medial parts of the lowTer ends of the crura pass behind the aorta, and thus convert the hiatus into a fibrous ring. The hiatus is situated slightly to the left of the middle line, and is bounded in front by the crura, and behind by the body of the first lumbar vertebra. Through it pass the aorta, the azygos vein, and the thoracic duct; occasionally the azygos vein is transmitted through the right crus. The esophageal hiatus is situated in the muscular part of the diaphragm at the level of the tenth thoracic vertebra, and is elliptical in shape. It is placed above, in front, and a little to the left of the aortic hiatus, and transmits the esophagus, the vagus nerves, and some small esophageal arteries. The vena caval foramen is the highest of the three, and is situated about the level of the fibrocartilage between the eighth and ninth thoracic vertebrae. It is quad- rilateral in form, and is placed at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. It transmits the inferior vena cava, the wall of which is adherent to the margins of the opening, and some branches of the right phrenic nerve. Of the lesser apertures, two in the right crus transmit the greater and lesser right splanchnic nerves; three in the left crus give passage to the greater and lesser left splanchnic nerves and the hemiazygos vein. The gangliated trunks of the sympathetic usually enter the abdominal cavity behind the diaphragm, under the medial lumbocostal arches. On either side two small intervals exist at which the muscular fibers of the diaphragm are deficient and are replaced by areolar tissue. One between the sternal and costal parts transmits the superior epigastric branch of the internal mammary artery and some lymphatics from the abdominal wall and convex surface of the liver. The other, between the fibers springing from the medial and lateral lumbocostal arches, is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only. Variations.—The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers. $ Nerves.—The diaphragm is supplied by the phrenic and lower intercostal nerves. Actions.—The diaphragm is the principal muscle of inspiration, and presents the form of a dome concave toward the abdomen. The central part of the dome is tendinous, and the peri- cardium is attached to its upper surface; the circumference is muscular. During inspiration the lowest ribs are fixed, and from these and the crura the muscular fibers contract and draw down- ward and forward the central tendon with the attached pericardium. In this movement the curvature of the diaphragm is scarcely altered, the dome moving downward nearly parallel THE MUSCLES OF THE THORAX 407 to its original position and pushing before it the abdominal viscera. The descent of the abdominal viscera is permitted by the elasticity of the abdominal wall, but the limit of this is soon reached. The central tendon applied to the abdominal viscera then becomes a fixed point for the action of the diaphragm, the effect of which is to elevate the lower ribs and through them to push forward the body of the sternum and the upper ribs. The right cupola of the diaphragm, lying on the liver, has a greater resistance to overcome than the left, which lies over the stomach, but to compensate for this the right crus and the fibers of the right side generally are stronger than those of the left. In all expulsive acts the diaphragm is called into action to give additional power to each expulsive effort. Thus, before sneezing, coughing, laughing, crying, or vomiting, and previous to the expulsion of urine or feces, or of the fetus from the uterus, a deep inspiration takes place. The height of the diaphragm is constantly varying during respiration; it also varies with the degree of distension of the stomach and intestines and with the size of the liver. After a forced expiration the right cupola is on a level in front with the fourth costal cartilage, at the side with the fifth, sixth, and seventh ribs, and behind with the eighth rib; the left cupola is a little lower than the right. Halls Dally1 states that the absolute range of movement between deep inspira- tion and deep expiration averages in the male and female 30 mm. on the right side and 28 mm. on the left; in quiet respiration the average movement is 12.5 mm. on the right side and 12 mm. on the left. Skiagraphy shows that the height of the diaphragm in the thorax varies considerably with the position of the body. It stands highest when the body is horizontal and the patient on his back, and in this position it performs the largest respiratory excursions with normal breathing. When the body is erect the dome of the diaphragm falls, and its respiratory movements become smaller. The dome falls still lower when the sitting posture is assumed, and in this position its respiratory excursions are smallest. These facts may, perhaps, explain why it is that patients suffering from severe dyspnoea are most comfortable and least short of breath when they sit up. When the body is horizontal and the patient on his side, the two halves of the diaphragm do not behave alike. The uppermost half sinks to a level lower even than when the patient sits, and moves little with respiration; the lower half rises higher in the thorax than it does when the patient is supine, and its respiratory excursions are much increased. In unilateral disease of the pleura or lungs analogous interference with the position or movement of the diaphragm can generally be observed skiagraphically. It appears that the position of the diaphragm in the thorax depends upon three main factors, viz.: (1) the elastic retraction of the lung tissue, tending to pull it upward; (2) the pressure exerted on its under surface by the viscera; this naturally tends to be a negative pressure, or down- ward suction, when the patient sits or stands, and positive, or an upward pressure, when he lies; (3) the intra-abdominal tension due to the abdominal muscles. These are in a state of contrac- tion in the standing position and not in the sitting; hence the diaphragm, when the patient stands, is pushed up higher than when he sits. The Intercostales interni and externi have probably no action in moving the ribs. They con- tract simultaneously and form strong elastic supports which prevent the intercostal spaces being pushed out or drawn in during respiration. The anterior portions of the Intercostales interni probably have an additional function in keeping the sternocostal and interchondral joint sur- faces in apposition, the posterior parts of the Intercostales externi performing a similar function for the costovertebral articulations. The Levatores costarum being inserted near the fulcra of the ribs can have little action on the ribs; they act as rotators and lateral flexors of the vertebral column. The Transversus thoracis draws down the costal cartilages, and is therefore a muscle of expiration. The Serrati are respiratory muscles. The Serratus posterior superior elevates the ribs and is therefore an inspiratory muscle. The Serratus posterior inferior draws the lower ribs down- ward and backward, and thus elongates the thorax; it also fixes the lower ribs, thus assisting the inspiratory action of the diaphragm and resisting the tendency it has to draw the lower ribs upward and forward. It must therefore be regarded as a muscle of inspiration. Mechanism of Respiration.—The respiratory movements must be examined during (a) quiet respiration, and (b) deep respiration. Quiet Respiration.—The first and second pairs of ribs are fixed by the resistance of the cervical structures; the last pair, and through it the eleventh, by the Quadratus lumborum. The other ribs are elevated, so that the first two intercostal spaces are diminished while the others are increased in width. It has already been shown (p. 304) tha,t elevation of the third, fourth, fifth, and sixth ribs leads to an increase in the antero-posterior and transverse diameters of the thorax; the vertical diameter is increased by the descent of the diaphragmatic dome so that the lungs are expanded in all directions except backward and upward. Elevation of the eighth, ninth, and tenth ribs is accompanied by a lateral and backward movement, leading to an increase in the transverse diameter of the upper part of the abdomen; the elasticity of the anterior abdominal 1 Journal of Anatomy and Physiology, 1908, vol. xliii. 408 MYOLOGY wall allows a slight increase in the antero-posterior diameter of this part, and in this way the decrease in the vertical diameter of the abdomen is compensated and space provided for its displaced viscera. Expiration is effected by the elastic recoil of its walls and by the action of the abdominal muscles, which push back the viscera displaced downward by the diaphragm. Deep Respiration.—All the movements of quiet respiration are here carried out, but to a greater extent. In deep inspiration the shoulders and the vertebral borders of the scapulae are fixed and the limb muscles, Trapezius, Serratus anterior, Pectorales, and Latissimus dorsi, are called into play. The Scaleni are in strong action, and the Sternocleidomastoidei also assist when the head is fixed by drawing up the sternum and by fixing the clavicles. The first rib is therefore no longer stationary, but, with the sternum, is raised; with it all the other ribs except the last are raised to a higher level. In conjunction with the increased descent of the diaphragm this provides for a considerable augmentation of all the thoracic diameters. The anterior abdomi- nal muscles come into action so that the umbilicus is drawn upward and backward, but this allows the diaphragm to exert a more powerful influence on the lower ribs; the transverse diam- eter of the upper part of the abdomen is greatly increased and the subcostal angle opened out. The deeper muscles of the back, e. g., the Serrati posteriores superiores and the Sacrospinales and their continuations, are also brought into action; the thoracic curve of the vertebral column is partially straightened, and the whole column, above the lower lumbar vertebrae, drawn back- ward. This increases the antero-posterior diameters of the thorax and upper part of the abdomen and widens the intercostal spaces. Deep expiration is effected by the recoil of the walls and by the contraction of the antero-lateral muscles of the abdominal wall, and the Serrati posteriores inferiores and Transversus thoracis. Halls Dally (op. cit.) gives the following figures as representing the average changes which occur during deepest possible respiration. The manubrium sterni moves 30 mm. in an upward and 14 mm. in a forward direction; the width of the subcostal angle, at a level of 30 mm. below the articulation between the body of the sternum and the xiphoid process, is increased by 26 mm.; the umbilicus is retracted and drawn upward for a distance of 13 mm. IV. THE MUSCLES AND FASCLffi OF THE ABDOMEN. The muscles of the abdomen may be divided into two groups: (1) the antero- lateral muscles; (2) the posterior muscles. 1. The Antero-lateral Muscles of the Abdomen. The muscles of this group are: Obliquus externus. Obliquus interims. Transversus. Rectus. Pvramidalis. The Superficial Fascia.—The superficial fascia of the abdomen consists, over the greater part of the abdominal wall, of a single layer containing a variable amount of fat; but near the groin it is easily divisible into two layers, between which are found the superficial vessels and nerves and the superficial inguinal lymph glands. The superficial layer (fascia of Camper) is thick, areolar in texture, and contains in its meshes a varying quantity of adipose tissue. Below, it passes over the inguinal ligament, and is continuous with the superficial fascia of the thigh. In the male, Camper’s fascia is continued over the penis and outer surface of the spermatic cord to the scrotum, where it helps to form the dartos. As it passes to the scrotum it changes its characteristics, becoming thin, destitute of adipose tissue, and of a pale reddish color, and in the scrotum it acquires some involuntary muscular fibers. From the scrotum it may be traced backward into continuity with the superficial fascia of the perineum. In the female, Camper’s fascia is continued from the abdomen into the labia majora. The deep layer (fascia of Scarpa) is thinner and more membranous in character than the superficial, and contains a considerable quantity of yellow elastic fibers. It is loosely connected by areolar tissue to the aponeurosis of the Obliquus externus abdominis, but in the middle line it is more intimately adherent to the linea alba and to the symphysis pubis, and is prolonged on to the dorsum of the penis, form- THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 409 ing the fundiform ligament; above, it is continuous with the superficial fascia over the rest of the trunk; below and laterally, it blends with the fascia lata of the thigh a little below the inguinal ligament; medially and below, it is continued over the penis and spermatic cord to the scrotum, where it helps to form the dartos. From the scrotum it may be traced backward into continuity with the deep layer of the superficial fascia of the perineum (fascia of Colies). In the female, it is con- tinued into the labia majora and thence to the fascia of Colies. Subcutaneous inguinal ring Lacunar ligament Pig. 392.—The Obliquus extemus abdominis. The Obliquus externus abdominis (External or descending oblique muscle) (Fig. 392), situated on the lateral and anterior parts of the abdomen, is the largest and the most superficial of the three flat muscles in this region. It is broad, thin, and irregularly quadrilateral, its muscular portion occupying the side, its aponeurosis the anterior wall of the abdomen. It arises, by eight fleshy digitations, from the external surfaces and inferior borders of the lower eight ribs; these digitations are arranged in an oblique line which runs downward and backward, the upper 410 MYOLOGY ones being attached close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages. The five superior serrations increase in size from above downward, and are received between corresponding processes of the Serratus anterior; the three lower ones diminish in size from above downward and receive between them corresponding processes from the Latissimus dorsi. From these attachments the fleshy fibers proceed in various directions. Those from the lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest; the middle and upper fibers, directed downward and forward, end in an aponeurosis, opposite a line drawn from the prominence of the ninth costal cartilage to the anterior superior iliac spine. The aponeurosis of the Obliquus extemus abdominis is a thin but strong mem- branous structure, the fibers of which are directed downward and medial ward. It is joined with that of the opposite muscle along the middle line, and covers the whole of the front of the abdomen; above, it is covered by and gives origin to the lower fibers of the Pectoralis major; below, its fibers are closely aggregated together, and extend obliquely across from the anterior superior iliac spine to the pubic tubercle and the pectineal line. In the middle line, it interlaces with the aponeurosis of the opposite muscle, forming the linea alba, which extends from the xiphoid process to the symphysis pubis. That portion of the aponeurosis which extends between the anterior superior iliac spine and the pubic tubercle is a thick band, folded inward, and continuous below with the fascia lata; it is called the inguinal ligament. The portion which is reflected from the inguinal ligament at the pubic tubercle is attached to the pectineal line and is called the lacunar ligament. From the point of attachment of the latter to the pectineal line, a few fibers pass upward and medialward, behind the medial crus of the subcutaneous inguinal ring, to the linea alba; they diverge as they ascend, and form a thin triangular fibrous band which is called the reflected inguinal ligament. In the aponeurosis of the Obliquus externus, immediately above the crest of the pubis, is a triangular opening, the subcutaneous inguinal ring, formed by a separation of the fibers of the aponeurosis in this situation. The following structures require further description, viz., the subcutaneous inguinal ring, the intercrural fibers and fascia, and the inguinal, lacunar, and reflected inguinal ligaments. The Subcutaneous Inguinal Ring (annulus inguinalis subcutaneus; external abdominal ring) (Fig. 393).—The subcutaneous inguinal ring is an interval in the aponeurosis of the Obliquus externus, just above and lateral to the crest of the pubis. The aperture is oblique in direction, somewhat triangular in form, and corresponds with the course of the fibers of the aponeurosis. It usually measures from base to apex about 2.5 cm., and transversely about 1.25 cm. It is bounded below by the crest of the pubis; on either side by the margins of the opening in the aponeurosis, which are called the crura of the ring; and above, by a series of curved intercrural fibers. The inferior crus (external pillar) is the stronger and is formed by that portion of the inguinal ligament which is inserted into the pubic tubercle; it is curved so as to form a kind of groove, upon which, in the male, the spermatic cord rests. The superior crus (internal pillar) is a broad, thin, flat band, attached to the front of the symphysis pubis and interlacing with its fellow of the opposite side. The subcutaneous inguinal ring gives passage to the spermatic cord and ilio- inguinal nerve in the male, and to the round ligament of the uterus and the ilioinguinal nerve in the female; it is much larger in men than in women, on account of the large size of the spermatic cord. The Intercrural Fibers (fibres intercrurales; intercolumnar fibers).—The intercrural fibers are a series of curved tendinous fibers, which arch across the lower part of THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 411 the aponeurosis of the Obliquus externus, describing curves with the convexities downward. They have received their name from stretching across between the two crura of the subcutaneous inguinal ring, and they are much thicker and stronger at the inferior crus, where they are connected to the inguinal ligament, than supe- riorly, where they are inserted into the linea alba. The intercrural fibers increase the strength of the lower part of the aponeurosis, and prevent the divergence of the crura from one another; they are more strongly developed in the male than in the female. As they pass across the subcutaneous inguinal ring, they are connected together by delicate fibrous tissue, forming a fascia, called the intercrural fascia. This inter- Superficial iliac circumflex vein inguinal ring Superficial epigastric vein Fig. 393.—The subcutaneous inguinal ring. crural fascia is continued down as a tubular prolongation around the spermatic cord and testis, and encloses them in a sheath; hence it is also called the external spermatic fascia. The subcutaneous inguinal ring is seen as a distinct aperture only after the intercrural fascia has been removed. The Inguinal Ligament (ligamentum inguinale [Pouparti] ; Poupart’s ligament) (Fig. 394).—The inguinal ligament is the lower border of the aponeurosis of the Obliquus externus, and extends from the anterior superior iliac spine to the pubic tubercle. From this latter point it is reflected backward and lateralward to be attached to the pectineal line for about 1.25 cm., forming the lacunar ligament. Its general direction is convex downward toward the thigh, where it is continuous with the fascia lata. Its lateral half is rounded, and oblique in direction; its 412 MYOLOGY medial half gradually widens at its attachment to the pubis, is more horizontal in direction, and lies beneath the spermatic cord. The Lacunar Ligament (ligamentum lacunare [Gimbernati] ; Gimbernat's ligament) (Fig. 394).—The lacunar ligament is that part of the aponeurosis of the Obliquus externus which is reflected backward and lateralward, and is attached to the pecti- neal line. It is about 1.25 cm. long, larger in the male than in the female, almost horizontal in direction in the erect posture, and of a triangular form with the base directed lateralward. Its base is concave, thin, and sharp, and forms the medial boundary of the femoral ring. Its apex corresponds to the pubic tubercle. Its posterior margin is attached to the pectineal line, and is continuous with the pectineal fascia. Its anterior margin is attached to the inguinal ligament. Its surfaces are directed upward and downward. Ant. sup. iliac spine- Obturator canal Lacunar ligament Pubic tubercle Symphysis pubis Transverse acetabular ligament Fig. 394.—The inguinal and lacunar ligaments. The Reflected Inguinal Ligament (ligamentum inguinale reflexum [ Collesi]; trian- gular fascia).—The reflected inguinal ligament is a layer of tendinous fibers of a triangular shape, formed by an expansion from the lacunar ligament and the inferior crus of the subcutaneous inguinal ring. It passes medialward behind the spermatic cord, and expands into a somewhat fan-shaped band, lying behind the superior crus of the subcutaneous inguinal ring, and in front of the inguinal aponeurotic falx, and interlaces with the ligament of the other side of the linea alba (Fig. 396). Ligament of Cooper.—This is a strong fibrous band, which was first described by Sir Astley Cooper. It extends lateralward from the base of the lacunar ligament (Fig. 394) along the pectineal line, to which it is attached. It is strengthened by the pectineal fascia, and by a lateral expansion from the lower attachment of the linea alba (adminiculum lineae albce). Variations.—The Obliquus externus may show decrease or doubling of its attachments to the ribs; addition slips from lumbar aponeurosis; doubling between lower ribs and ilium or inguinal ligament. Rarely tendinous inscriptions occur. The Obliquus internus abdominis (Internal or ascending oblique muscle) (Fig. 395), thinner and smaller than the Obliquus externus, beneath which it lies, is of THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 413 an irregularly quadrilateral form, and situated at the lateral and anterior parts of the abdomen. It arises, by fleshy fibers, from the lateral half of the grooved upper surface of the inguinal ligament, from the anterior two-thirds of the middle lip of the iliac crest, and from the posterior lamella of the lumbodorsal fascia. From this origin the fibers diverge; those from the inguinal ligament, few in number and paler in color than the rest, arch downward and medialward across the sper- matic cord in the male and the round ligament of the uterus in the female, and, becoming tendinous, are inserted, conjointly with those of the Transversus, into the crest of the pubis and medial part of the pectineal line behind the lacunar ligament, forming what is known as the inguinal aponeurotic falx. Those from the Inguinal apo neurotic falx Cremaster Fig. 395.—The Obliquus interims abdominis. anterior third of the iliac origin are horizontal in their direction, and, becoming tendinous along the lower fourth of the linea semilunaris, pass in front of the Rectus abdominis to be inserted into the linea alba. Those arising from the middle third of the iliac origin run obliquely upward and medialward, and end in an aponeurosis; this divides at the lateral border of the Rectus into two lamellae, which are con- tinued forward, one in front of and the other behind this muscle, to the linea alba: the posterior lamella has an attachment to the cartilages of the seventh, eighth, and ninth ribs. The most posterior fibers pass almost vertically upward, to be inserted into the inferior borders of the cartilages of the three lower ribs, being continuous with the Intercostales interni. 414 MYOLOGY Variations. Occasionally, tendinous inscriptions occur from the tips of the tenth or eleventh cartilages or even from the ninth; an additional slip to the ninth cartilage is sometimes found; separation between iliac and inguinal parts may occur. The Cremaster (Fig. 396) is a thin muscular layer, composed of a number of fasciculi which arise from the middle of the inguinal ligament where its fibers are continuous with those of the Obliquus internus and also occasion- ally with the Transversus. It passes along the lateral side of the spermatic cord, descends with it through the sub- cutaneous inguinal ring upon the front and sides of the cord, and forms a series of loops which differ in thickness and length in different subjects. At the upper part of the cord the loops are short, but they become in succession longer and longer, the longest reaching down as low as the testis, where a few are inserted into the tunica vaginalis. These loops are united together by areolar tissue, and form a thin cover- ing over the cord and testis, the cremas- teric fascia. The fibers ascend along the medial side of the cord, and are inserted by a small pointed tendon into the tubercle and crest of the pubis and into the front of the sheath of the Rectus abdominis. The Transversus abdominis (Trans- versalis muscle) (Fig. 397), so called from the direction of its fibers, is the most internal of the flat muscles of the abdomen, being placed imme- diately beneath the Obliquus internus. It arises, by fleshy fibers, from the lateral third of the inguinal ligament, from the anterior three-fourths of the inner lip of the iliac crest, from the inner surfaces of the cartilages of the lower six ribs, interdigitating with the diaphragm, and from the lumbodorsal fascia. The muscle ends in front in a broad aponeurosis, the lower fibers of which curve downward and medialward, and are inserted, together with those of the Obliquus internus, into the crest of the pubis and pectineal line, forming the ingui- nal aponeurotic falx. Throughout the rest of its extent the aponeurosis passes horizontally to the middle line, and is inserted into the linea alba; its upper three-fourths lie behind the Rectus and blend with the posterior lamella of the aponeurosis of the Obliquus internus; its lower fourth is in front of the Rectus. Variations.—It may be more or less fused with the Obliquus internus or absent. The spermatic cord may pierce its lower border. Slender muscle slips from the ileopectineal line to transversalis fascia, the aponeurosis of the Transversus abdominis, or the outer end of the linea semicircularis and other slender slips are occasionally found. The inguinal aponeurotic falx (falx aponeurotica inguinalis; conjoined tendon of Internal oblique and Transversalis muscle) of the Obliquus internus and Trans- versus is mainly formed by the lower part of the tendon of the Transversus, and is inserted into the crest of the pubis and pectineal line immediately behind the subcutaneous inguinal ring, serving to protect what would otherwise be a Fig. 396.—The Cremaster. THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 415 weak point in the abdominal wall. Lateral to the falx is a ligamentous band con- nected with the lower margin of the Transversus and extending down in front of the inferior epigastric artery to the superior ramus of the pubis; it is termed the inter- foveolar ligament of Hesselbach (Fig. 398) and sometimes contains a few muscular fibers. Tendinous inscriptions / / x Ltnea alba Fig. 397.—The Transversus abdominis, Rectus abdominis, and Pyramidalis. The Rectus abdominis (Fig. 397) is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba. It is much broader, but thinner, above than below, and arises by two tendons; the lateral or larger is attached to the crest of the pubis, the medial interlaces with its fellow of the opposite side, and is con- nected with the ligaments covering the front of the symphysis pubis. The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs. The upper portion, attached principally to the cartilage of the 416 MYOLOGY fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself. Some fibers are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process. The Rectus is crossed by fibrous bands, three in number, which are named the tendinous inscriptions; one is usually situated opposite the umbilicus, one at the extremity of the xiphoid process, and the third about midway between the xiphoid process and the umbilicus. These inscriptions pass transversely or obliquely across the muscle in a zigzag course; they rarely extend completely through its substance and may pass only halfway across it; they are intimately adherent in front to the sheath of the muscle. Sometimes one or two additional inscriptions, generally incomplete, are present below the umbilicus. Linea semicircularis Transversus Rectus abdominis Obliquus internus Inferior epigastric artery and vein Fig. 398.—The interfoveolar ligament, seen from in front. (Modified from Braune.) Inguinal aponeurotic falx interfoveolar ligament The Rectus is enclosed in a sheath (Fig. 399) formed by the aponeuroses of the Obliqui and Transversus, which are arranged in the following manner. At the lateral margin of the Rectus, the aponeurosis of the Obliquus internus divides into two lamellse, one of which passes in front of the Rectus, blending with the aponeurosis of the Obliquus externus, the other, behind it, blending with the aponeurosis of the Transversus, and these, joining again at the medial border of the Rectus, are inserted into the linea alba. This arrangement of the aponeurosis exists from the costal margin to midway between the umbilicus and symphysis pubis, where the posterior wall of the sheath ends in a thin curved margin, the linea semicircu- laris, the concavity of which is directed downward: below this level the aponeuroses of all three muscles pass in front of the Rectus. The Rectus, in the situation where its sheath is deficient below, is separated from the peritoneum by the transversalis fascia (Fig. 400). Since the tendons of the Obliquus internus and Transversus only reach as high as the costal margin, it follows that above this level the sheath of the Rectus is deficient behind, the muscle resting directly on the cartilages of the ribs, and being covered merely by the tendon of the Obliquus externus. The Pyramidalis (Fig. 397) is a small triangular muscle, placed at the lower part of the abdomen, in front of the Rectus, and contained in the sheath of that THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 417 muscle. It arises by tendinous fibers from the front of the pubis and the anterior pubic ligament; the fleshy portion of the muscle passes upward, diminishing in size as it ascends, and ends by a pointed extremity which is inserted into the linea alba, midway between the umbilicus and pubis. This muscle may be wanting on one or both sides; the lower end of the Rectus then becomes proportionately increased in size. Occasionally it is double on one side, and the muscles of the two sides are sometimes of unequal size. It may extend higher than the level stated. Peritoneum j Transversalis fascia Linea alba Obliquus externus. Obliquus intemus* Fig. 399.—Diagram of sheath of Rectus. Transversus ' Besides the Rectus and Pyramidalis, the sheath of the Rectus contains the superior and inferior epigastric arteries, and the lower intercostal nerves. Variations.—The Rectus may insert as high as the fourth or third rib or mav fail to reach the fifth. Fibers may spring from the lower part of the linea alba. Nerves. The abdominal muscles are supplied by the lower intercostal nerves. The Obliquus internus and Transversus also receive filaments from the anterior branch of the iliohypogastric and sometimes from the ilioinguinal. The Cremaster is supplied by the external spermatic branch of the genitofemoral and the Pyramidalis usually by the twelfth thoracic. The Linea Alba.—The linea alba is a tendinous raphe in the middle line of the abdomen, stretching between the xiphoid process and the symphysis pubis. It is placed between the medial borders of the Recti, and is formed by the blending of the aponeuroses of the Obliqui and Trans- versi. It is narrow below, corresponding to the linear interval existing between the Recti; but broader above, where these muscles diverge from one another. At its lower end the linea alba has a double attachment—its superficial fibers passing in front of the medial heads of the Recti to the symphysis pubis, while its deeper fibers form a triangular lamella, attached behind the Recti to the posterior lip of the crest of the pubis, and named the adminiculum lineae albae. It presents apertures for the passage of vessels and nerves; the umbilicus, which in the fetus exists as an aperture and transmits the umbilical vessels, is closed in the adult. Peritoneum Obliquus externus _ Transversalis fascia Lined alba Obliquus intemus Fig. 400.—Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis Trans versus ' The Lineae Semilunares.—The line* semilunares are two curved tendinous lines placed one on either side of the linea alba. Each corresponds with the lateral border of the Rectus, extends from the cartilage of the ninth rib to the pubic tubercle, and is formed by the aponeurosis of the Obliquus internus at its line of division to enclose the Rectus, reinforced in front by that of the Obliquus externus, and behind by that of the Transversus. Actions.—When the pelvis and thorax are fixed, the abdominal muscles compress the abdominal viscera by constricting the cavity of the abdomen, in which action they are materially assisted by the descent of the diaphragm. By these means assistance is given in expelling the feces from the rectum, the urine from the bladder, the fetus from the uterus, and the contents of the stomach in vomiting. If the pelvis and vertebral column be fixed, these muscles compress the lower part of the thorax, materially assisting expiration. If the pelvis alone be fixed, the thorax is bent directly forward, when the muscles of both sides act; when the muscles of only one side contract, the trunk is bent toward that side and rotated toward the opposite side. 418 MYOLOGY If the thorax be fixed, the muscles, acting together, draw the pelvis upward, as in climbing; or, acting singly, they draw the pelvis upward, and bend the vertebral column to one side or the other. The Recti, acting from below, depress the thorax, and consequently flex the vertebral column; when acting from above, they flex the pelvis upon, the vertebral column. The Pyramidales are tensors of the linea alba. The Transversalis Fascia.—The transversalis fascia is a thin aponeurotic membrane which lies between the inner surface of the Transversus and the extraperitoneal fat. It forms part of the general layer of fascia lining the abdominal parietes, and is directly continuous with the iliac and pelvic fascise. In the inguinal region, the transversalis fascia is thick and dense in structure and is joined by fibers from the aponeurosis of the Transversus, but it becomes thin as it ascends to the dia- phragm, and blends with the fascia covering the under surface of this muscle. Behind, it is lost in the fat which covers the posterior surfaces of the kidneys. Below, it has the following attachments: 'posteriorly, to the whole length of the iliac crest, between the attachments of the Transversus and Iliacus; between the ante- rior superior iliac spine and the femoral vessels it is connected to the posterior margin of the inguinal ligament, and is there continuous with the iliac fascia. Medial to the femoral vessels it is thin and attached to the pubis and pectineal line, behind the inguinal aponeurotic falx, with which it is united; it descends in front of the femoral vessels to form the anterior wall of the femoral sheath. Beneath the inguinal ligament it is strengthened by a band of fibrous tissue, which is only loosely connected to the ligament, and is specialized as the deep crural arch. The spermatic cord in the male and the round ligament of the uterus in the female pass through the transversalis fascia at a spot called the abdominal inguinal ring. This opening is not visible externally, since the transversalis fascia is prolonged on these structures as the infundibuliform fascia. The Abdominal Inguinal Ring (annulus inguinalis abdominis; internal or deep abdominal ring).—The abdominal inguinal ring is situated in the transversalis fascia, midway between the anterior superior iliac spine and the symphysis pubis, and about 1.25 cm. above the inguinal ligament (Fig. 401). It is of an oval form, the long axis of the oval being vertical; it varies in size in different subjects, and is much larger in the male than in the female. It is bounded, above and laterally, by the arched lower margin of the Transversus; below and medially, by the inferior epigastric vessels. It transmits the spermatic cord in the male and the round ligament of the uterus in the female. From its circumference a thin funnel-shaped membrane, the infundibuliform fascia, is continued around the cord and testis, enclosing them in a distinct covering. The Inguinal Canal (canalis inguinalis; spermatic canal).—The inguinal canal contains the spermatic cord and the ilioinguinal nerve in the male, and the round ligament of the uterus and the ilioinguinal nerve in the female. It is an oblique canal about 4 cm. long, slanting downward and medialward, and placed parallel with and a little above the inguinal ligament; it extends from the abdominal inguinal ring to the subcutaneous inguinal ring. It is bounded, in front, by the integument and superficial fascia, by the aponeurosis of the Obliquus externus throughout its whole length, and by the Obliquus interims in its lateral third; behind, by the reflected inguinal ligament, the inguinal aponeurotic falx, the trans- versalis fascia, the extraperitoneal connective tissue and the peritoneum; above, by the arched fibers of Obliquus internus and Transversus abdominis; below, by the union of the transversalis fascia with the inguinal ligament, and at its medial end by the lacunar ligament. Extraperitoneal Connective Tissue.—Between the inner surface of the general layer of the fascia which lines the interior of the abdominal and pelvic cavities, and the peritoneum, there is a considerable amount of connective tissue, termed the extraperitoneal or subperitoneal connective tissue. THE POSTERIOR MUSCLES OF THE ABDOMEN 419 The parietal portion lines the cavity in varying quantities in different situations. It is especially abundant on the posterior wall of the abdomen, and particularly around the kidneys, where it contains much fat. On the anterior wall of the abdo- men, except in the pubic region, and on the lateral wall above the iliac crest, it is scanty, and here the transversalis fascia is more closely connected with the peritoneum. There is a considerable amount of extraperitoneal connective tissue in the pelvis. The visceral portion follows the course of the branches of the abdominal aorta between the layers of the mesenteries and other folds of peritoneum which connect the various viscera to the abdominal wall. The two portions are directly con- tinuous with each other. Abdominal inguinal ring Inf. epigastric artery Fig. 401.—The abdominal inguinal ring. The Deep Crural Arch.—Curving over the external iliac vessels, at the spot where they become femoral, on the abdominal side of the inguinal ligaments and loosely connected with it, is a thickened band of fibers called the deep crural arch. It is apparently a thickening of the transversalis fascia joined laterally to the center of the lower margin of the inguinal ligament, and arching across the front of the femoral sheath to be inserted by a broad attachment into the pubic tubercle and pectineal line, behind the inguinal aponeurotic falx. In some subjects this structure is not very prominently marked, and not infrequently it is altogether wanting. 2. The Posterior Muscles of the Abdomen. Psoas major. Psoas minor. Iliacus. Quadratus lumborum. The Psoas major, the Psoas minor, and the Iliacus, with the fasche covering them, will be described with the muscles of the lower extremity (see page 406). The Fascia Covering the Quadratus Lumborum.—This is a thin layer attached, medially, to the bases of the transverse processes of the lumbar vertebrae; below, 420 MYOLOGY to the iliolumbar ligament; above, to the apex and lower border of the last rib. The upper margin of this fascia, which extends from the transverse process of the first lumbar vertebra to the apex and lower border of the last rib, constitutes the lateral lumbocostal arch (page 405). Laterally, it blends with the lumbodorsal fascia, the anterior layer of which intervenes between the Quadratus lumborum and the Sacrospinalis. The Quadratus lumborum (Fig. 389, page 398) is irregularly quadrilateral in shape, and broader below than above. It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for about half its length, and by four small tendons into the apices of the transverse processes of the upper four lumbar vertebrae. Occasionally a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebrae, and is inserted into the lower margin of the last rib. In front of the Quadratus lumborum are the colon, the kidney, the Psoas major and minor, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves. Variations.—The number of attachments to the vertebra? and the extent of its attachment to the last rib vary. Nerve Supply.—The twelfth thoracic and first and second lumbar nerves supply this muscle. Actions.—The Quadratus lumborum draws down the last rib, and acts as a muscle of inspira- tion by helping to fix the origin of the diaphragm. If the thorax and vertebral column are fixed, it may act upon the pelvis, raising it toward its own side when only one muscle is put in action; and when both muscles act together, either from below or above, they flex the trunk. V. THE MUSCLES AND FASCLE OF THE PELVIS Obturator internus. Piriformis. Levator ani. Coccygeus. The muscles within the pelvis may be divided into two groups: (1) the Obturator internus and the Piriformis, which are muscles of the lower extremity, and will be described with these (pages 476 and 477); (2) the Levator ani and the Coccygeus, which together form the pelvic diaphragm and are associated wTith the pelvic viscera. The classification of the two groups under a common heading is convenient in connection with the fasciae investing the muscles. These fasciae are closely related to one another and to the deep fascia of the perineum, and in addition have special connections with the fibrous coverings of the pelvic viscera; it is customary there- fore to describe them together under the term pelvic fascia. Pelvic Fascia.—The fascia of the pelvis may be resolved into: (a) the facial sheaths of the Obturator internus, Piriformis, and pelvic diaphragm; (b) the fascia associated with the pelvic viscera. The fascia of the Obturator internus covers the pelvic surface of, and is attached around the margin of the origin of, the muscle. Above, it is loosely connected to the back part of the arcuate line, and here it is continuous with the iliac fascia. In front of this, as it follows the line of origin of the Obturator internus, it gradually separates from the iliac fascia and the continuity between the two is retained only through the periosteum. It arches beneath the obturator vessels and nerve, com- pleting the obturator canal, and at the front of the pelvis is attached to the back of the superior ramus of the pubis. Below, the obturator fascia is attached to the falciform process of the sacrotuberous ligament and to the pubic arch, wrhere it becomes continuous with the superior fascia of the urogenital diaphragm. Behind, it is prolonged into the gluteal region. The internal pudendal vessels and pudendal nerve cross the pelvic surface of THE MUSCLES AND FASCIAE OF THE PELVIS 421 the Obturator internus and are enclosed in a special canal—Alcock’s canal— formed by the obturator fascia. The fascia of the Piriformis is very thin and is attached to the front of the sacrum and the sides of the greater sciatic foramen; it is prolonged on the muscle into the gluteal region.. At its sacral attachment around the margins of the anterior sacral foramina it comes into intimate association with and ensheathes the nerves emerging from these foramina. Hence the sacral nerves are frequently described as lying behind the fascia. The internal iliac vessels and their branches, on the other hand, lie in the subperitoneal tissue in front of the fascia, and the branches to the gluteal region emerge in special sheaths of this tissue, above and below the Piriformis muscle. Interior of bladder i Diaphragmatic part of pelvic ■ fascia [ Superior ' I layer j Inferior ( layer Tendinous arch Fascia endopelvina / Vesicula seminalis Ductus deferens / - Alcocls’s canal Rectovesical layer Fig. 402.—Coronal section of pelvis, showing arrangement of fasciae. Viewed from behind. (Diagrammatic.) The diaphragmatic part of the pelvic fascia (Fig. 402) covers both surfaces of the Levatores ani. The inferior layer is known as the anal fascia; it is attached above to the obturator fascia along the line of origin of the Levator ani, while below it is continuous with the superior fascia of the urogenital diaphragm, and with the fascia on the Sphincter ani internus. The layer covering the upper surface of the pelvic diaphragm follows, above, the line of origin of the Levator ani and is there- fore somewhat variable. In front it is attached to the back of the symphysis pubis about 2 cm. above its lower border. It can then be traced laterally across the back of the superior ramus of the pubis for a distance of about 1.25 cm., when it reaches the obturator fascia. It is attached to this fascia along a line which pursues a somewhat irregular course to the spine of the ischium. The irregularity of this line is due to the fact that the origin of the Levator ani, which in lower forms is from the pelvic brim, is in man lower down, on the obturator fascia. Tendinous fibers of origin of the muscle are therefore often found extending up toward, and in some cases reaching, the pelvic brim, and on these the fascia is carried. It will be evident that the fascia covering that part of the Obturator internus which lies above the origin of the Levator ani is a composite fascia and includes the following: (a) the obturator fascia; (b) the fascia of the Levator ani; (c) degenerated fibers of origin of the Levator ani. 422 MYOLOGY The lower margin of the fascia covering the upper surface of the pelvic diaphragm is attached along the line of insertion of the Levator ani. At the level of a line extending from the lower part of the symphysis pubis to the spine of the ischium is a thickened whitish band in this upper layer of the diaphragmatic part of the pelvic fascia. It is termed the tendinous arch or white line of the pelvic fascia, and marks the line of attachment of the special fascia (pars endopelvina fascioe pelvis) which is associated with the pelvic viscera. Peritoneum Vesical layer Fascia of ( urogenital f diaphragm f r Superior layer Inferior , layer Yesicula seminalis Rectovesical layer Capsule of prostate Transversus perincei superficialis Rectal layer t Colles' fascia Pig. 403.—Median sagittal section of pelvis, showing arrangement of fasciis. Urogenital diaphragm The endopelvic part of the pelvic fascia is continued over the various pelvic viscera (Fig. 403) to form for them fibrous coverings which will be described later (see section on Splanchnology). It is attached to the diaphragmatic part of the pelvic fascia along the tendinous arch, and has been subdivided in accordance with the viscera to which it is related. Thus its anterior part, known as the vesical layer, forms the anterior and lateral ligaments of the bladder. Its middle part crosses the floor of the pelvis between the rectum and vesiculae seminales as the rectovesical layer; in the female this is perforated by the vagina. Its posterior portion passes to the side of the rectum; it forms a loose sheath for the rectum, but is firmly attached around the anal canal; this portion is known as the rectal layer. The Levator ani (Fig. 404) is a broad, thin muscle, situated on the side of the pelvis. It is attached to the inner surface of the side of the lesser pelvis, and unites THE MUSCLES AND FASCIAE OF THE PELVIS 423 with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It supports the viscera in this cavity, and surrounds the various structures which pass through it. It arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia. Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a vary- ing distance above the arch, in some cases reaching nearly as high as the canal Superior glutceal vessels Obturator nerve and vessels Left lobe of prostate (cut) Anococcygeal raphe Fig. 404.—Left Levator ani from within. for the obturator vessels and nerve. The fibers pass downward and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous raphe (anococcygeal raphe), which extends between the coccyx and the margin of the anus. The middle fibers are inserted into the side of the rectum, blending with the fibers of the Sphincter muscles; lastly, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the Sphincter ani externus and Transversus perinsei, at the central tendinous point of the perineum. 424 MYOLOGY The anterior portion is occasionally separated from the rest of the muscle by connective tissue. From this circumstance, as well as from its peculiar relation with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of Levator prostatse. In the female the anterior fibers of the Levator ani descend upon the side of the vagina. The Levator ani may be divided into iliococcygeal and pubococcygeal parts. The Iliococcygeus arises from the ischial spine and from the posterior part of the tendinous arch of the pelvic fascia, and is attached to the coccyx and anococcygeal raph4; it is usually thin, and may fail entirely, or be largely replaced by fibrous tissue. An accessory slip at its posterior part is sometimes named the Iliosacralis. The Pubococcygeus arises from the back of the pubis and from the anterior part of the obturator fascia, and “is directed backward almost horizontally along the side of the anal canal toward the coccyx and sacrum, to which it finds attachment. Between the termination of the vertebral column and the anus, the two Pubococcygei muscles come together and form a thick, fibromuscular layer lying on the raphe formed by the Iliococcygei” (Peter Thompson). The greater part of this muscle is inserted into the coccyx and into the last one or two pieces of the sacrum. This insertion into the vertebral column is, however, not admitted by all observers. The fibers which form a sling for the rectum are named the Pubo- rectalis or Sphincter recti. They arise from the lower part of the symphysis pubis, and from the superior fascia of the urogenital diaphragm. They meet with the corresponding fibers of the opposite side around the lower part of the rectum, and form for it a strong sling. Nerve Supply.—The Levator ani is supplied by a branch from the fourth sacral nerve and by a branch which is sometimes derived from the perineal, sometimes from the inferior hemor- rhoidal division of the pudendal nerve. The Coccygeus (Fig. 404) is situated behind the preceding. It is a triangular plane of muscular and tendinous fibers, arising by its apex from the spine of the ischium and sacrospinous ligament, and inserted by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. It assists the Levator ani and Piriformis in closing in the back part of the outlet of the pelvis. Nerve Supply.—The Coccygeus is supplied by a branch from the fourth and fifth sacral nerves. Actions.—The Levatores ani constrict the lower end of the rectum and vagina. They elevate and invert the lower end of the rectum after it has been protruded and everted during the expul- sion of the feces. They are also muscles of forced expiration. The Coccygei pull forward and support the coccyx, after it has been pressed backward during defecation or parturition. The Levatores ani and Coccygei together form a muscular diaphragm which supports the pelvic viscera. The perineum corresponds to the outlet of the pelvis. Its deep boundaries are—in front, the pubic arch and the arcuate ligament of the pubis; behind, the tip of the coccyx; and on either side the inferior rami of the pubis and ischium, and the sacrotuberous ligament. The space is somewhat lozenge-shaped and is limited on the surface of the body by the scrotum in front, by the buttocks behind, and laterally by the medial side of the thigh. A line drawn transversely across in front of the ischial tuberosities divides the space into two portions. The pos- terior contains the termination of the anal canal and is known as the anal region; the anterior, which contains the external urogenital organs, is termed the urogenital region. The muscles of the perineum may therefore be divided into two groups: 1. Those of the anal region. 2. Those of the urogenital region: A, In the male; b, In the female. VI. THE MUSCLES AND FASCIA3 OF THE PERINEUM. 1. The Muscles of the Anal Region. Corrugator cutis ani. Sphincter ani externus. Sphincter ani internus. The Superficial Fascia.—The superficial fascia is very thick, areolar in texture, and contains much fat in its meshes. On either side a pad of fatty tissue extends THE MUSCLES OF THE ANAL REGION 425 deeply between the Levator ani and Obturator internus into a space known as the ischiorectal fossa. The Deep Fascia.—The deep fascia forms the lining of the ischiorectal fossa; it comprises the anal fascia, and the portion of obturator fascia below the origin of Levator ani. Ischiorectal Fossa (fossa ischiorectalis) (Fig. 405).—The fossa is somewhat pris- matic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fascke. It is bounded medially by the Sphincter ani externus and the anal fascia; laterally, by the tuberosity of the ischium and the obturator fascia; anteriorly, by the fascia of Colies covering the Transversus perinaei superficialis, and by the inferior fascia of the urogenital diaphragm; posteriorly, by the Glutseus maximus and the sacrotuberous ligament. Crossing the space transversely are the inferior hemorrhoidal vessels and nerves; Fig. 405.—The perineum. The integument and superficial layer of superficial fascia reflected at the back part are the perineal and perforating cutaneous branches of the pudendal plexus; while from the forepart the posterior scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie in Alcock’s canal on the lateral wall. The fossa is filled with fatty tissue across which numerous fibrous bands extend from side to side. The Corrugator Cutis Ani.—Around the anus is a thin stratum of involuntary muscular fiber, which radiates from the orifice. Medially the fibers fade off into the submucous tissue, while laterally they blend with the true skin. By its contrac- tion it raises the skin into ridges around the margin of the anus. The Sphincter ani externus (External sphincter ani) (Fig 405) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. It measures about 8 to 10 cm. in length, from its anterior to its posterior extremity, and is about 2.5 cm. broad opposite the anus. It consists of two strata, superficial and deep. The superficial, constituting 426 MYOLOGY the main portion of the muscle, arises from a narrow tendinous band, the anococcy- geal raphe, which stretches from the tip of the coccyx to the posterior margin of the anus; it forms two flattened planes of muscular tissue, which encircle the anus and meet in front to be inserted into the central tendinous point of the perineum, joining with the Transversus perinsei superficialis, the Levator ani, and the Bul- bocavernosus. The deeper portion forms a complete sphincter to the anal canal. Its fibers surround the canal, closely applied to the Sphincter ani internus, and in front blend with the other muscles at the central point of the perineum. In a considerable proportion of cases the fibers decussate in front of the anus, and are continuous with the Transversi perinsei superficiales. Posteriorly, they are not attached to the coccyx, but are continuous with those of the opposite side behind the anal canal. The upper edge of the muscle is ill-defined, since fibers are given off from it to join the Levator ani. Nerve Supply.—A branch from the fourth sacral and twigs from the inferior hemorrhoidal branch of the pudendal supply the muscle. Actions.—The action of this muscle is peculiar. (1) It is, like other muscles, always in a state of tonic contraction, and having no antagonistic muscle it keeps the anal canal and orifice closed. (2) It can be put into a condition of greater contraction under the influence of the will, so as more firmly to occlude the anal aperture, in expiratory efforts unconnected with defecation. (3) Taking its fixed point at the coccyx, it helps to fix the central point of the perineum, so that the Bulbocavernosus may act from this fixed point. The Sphincter ani internus (Internal sphincter ani) is a muscular ring which surrounds about 2.5 cm. of the anal canal; its inferior border is in contact with, but quite separate from, the Sphincter ani externus. It is about 5 mm. thick, and is formed by an aggregation of the involuntary circular fibers of the intestine. Its lower border is about 6 mm. from the orifice of the anus. Actions.—Its action is entirely involuntary. It helps the Sphincter ani externus to occlude the anal aperture and aids in the expulsion of the feces. 2. a. The Muscles of the Urogenital Region in the Male (Fig. 406). Transversus perinsei superficialis. Bulbocavernosus. Ischiocavernosus. Transversus perinsei profundus. Sphincter urethrae membranacese. Superficial Fascia.—The superficial fascia of this region consists of two layers, superficial and deep. The superficial layer is thick, loose, areolar in texture, and contains in its meshes much adipose tissue, the amount of which varies in different subjects. In front, it is continuous with the dartos tunic of the scrotum; behind, with the subcuta- neous areolar tissue surrounding the anus; and, on either side, with the same fascia on the inner sides of the thighs. In the middle line, it is adherent to the skin on the raphe and to the deep layer of the superficial fascia. The deep layer of superficial fascia (fascia of Colies) (Fig. 405) is thin, aponeurotic in structure, and of considerable strength, serving to bind down the muscles of the root of the penis. It is continuous, in front, with the dartos tunic, the deep fascia of the penis, the fascia of the spermatic cord, and Scarpa’s fascia upon the anterior wall of the abdomen; on either side it is firmly attached to the margins of the rami of the pubis and ischium, lateral to the crus penis and as far back as the tuberosity of the ischium; posteriorly, it curves around the Transversi perinsei superficiales to join the lower margin of the inferior fascia of the urogenital dia- phragm. In the middle line, it is connected with the superficial fascia and with the median septum of the Bulbocavernosus. This fascia not only covers the muscles in this region, but at its back part sends upward a vertical septum from its deep surface, which separates the posterior portion of the subjacent space into two. THE MUSCLES OF THE UROGENITAL REGION IN THE MALE 427 The Central Tendinous Point of the Perineum.—This is a fibrous point in the middle line of the perineum, between the urethra and anus, and about 1.25 cm. in front of the latter. At this point six muscles converge and are attached: viz., the Sphincter ani externus, the Bulbocavernosus, the two Transversi perinaei super- ficiales, and the anterior fibers of the Levatores ani. Fig. 406.—Muscles of male perineum. The Transversus perinsei superficialis (Transversus penned; Superficial transverse perineal muscle) is a narrow muscular slip, which passes more or less transversely across the perineal space in front of the anus. It arises by tendinous fibers from the inner and forepart of the tuberosity of the ischium, and, running medialward, is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, with the Sphincter ani externus behind, and with the Bulbocavernosus in front. In some cases, the fibers of the deeper layer of the Sphincter ani externus decussate in front of the anus and are con- tinued into this muscle. Occasionally it gives off fibers, which join with the Bulbocavernosus of the same side. Variations are numerous. It may be absent or double, or insert into Bulbocavernosus or External sphincter. 428 MYOLOGY Actions.—The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavernosus (Ejaculator urines; Accelerator urines) is placed in the middle line of the perineum, in front of the anus. It consists of two symmetrical parts, united along the median line by a tendinous raphe. It arises from the cen- tral tendinous point of the perineum and from the median raphe in front. Its fibers diverge like the barbs of a quill-pen; the most posterior form a thin layer, which is lost on the inferior fascia of the urogenital diaphragm; the middle fibers encircle the bulb and adjacent parts, of the corpus cavernosum urethrae, and join with the fibers of the opposite side, on the upper part of the corpus cavernosum urethrae, in a strong aponeurosis; the anterior fibers, spread out over the side of the corpus cavernosum penis, to be inserted partly into that body, anterior to the Ischiocavernosus, occasionally extending to the pubis, and partly ending in a tendinous expansion which covers the dorsal vessels of the penis. The latter fibers are best seen by dividing the muscle longitudinally, and reflecting it from the surface of the corpus cavernosum urethrae. Actions.—This muscle serves to empty the canal of the urethra, after the bladder has expelled its contents; during the greater part of the act of micturition its fibers are relaxed, and it only comes into action at the end of the process. The middle fibers are supposed by Krause to assist in the erection of the corpus cavernosum urethra?, by compressing the erectile tissue of the bulb. The anterior fibers, according to Tyrrel, also contribute to the erection of the penis by compressing the deep dorsal vein of the penis as they are inserted into, and continuous with, the fascia of the penis. The Ischiocavernosus (Erector penis) covers the crus penis. It is an elongated muscle, broader in the middle than at either end, and situated on the lateral bound- ary of the perineum. It arises by tendinous and fleshy fibers from the inner sur- face of the tuberosity of the ischium, behind the crus penis; and from the rami of the pubis and ischium on either side of the crus. From these points fleshy fibers succeed, and end in an aponeurosis which is inserted into the sides and under surface of the crus penis. Action.—The Ischiocavernosus compresses the crus penis, and retards the return of the blood through the veins, and thus serves to maintain the organ erect. Between the muscles just examined a triangular space exists, bounded medially by the Bulbo- cavernosus, laterally by the Ischiocavernosus, and behind by the Transversus perinsei super- ficialis; the floor is formed by the inferior fascia of the urogenital diaphragm. Running from behind forward in the space are the posterior scrotal vessels and nerves, and the perineal branch of the posterior femoral cutaneous nerve; the transverse perineal artery courses along its posterior boundary on the Transversus perina?i superficialis. The Deep Fascia.—The deep fascia of the urogenital region forms an investment for the Transversus perinsei profundus and the Sphincter urethrae membranacese, but within it lie also the deep vessels and nerves of this part, the whole forming a transverse septum which is known as the urogenital diaphragm. From its shape it is usually termed the triangular ligament, and is stretched almost horizontally across the pubic arch, so as to close in the front part of the outlet of the pelvis. It consists of two dense membranous laminae (Fig. 407), which are united along their posterior borders, but are separated in front by intervening structures. The superficial of these two layers, the inferior fascia of the urogenital diaphragm, is tri- angular in shape, and about 4 cm. in depth. Its apex is directed forward, and is separated from the arcuate pubic ligament by an oval opening for the transmission of the deep dorsal vein of the penis. Its lateral margins are attached on either side to the inferior rami of the pubis and ischium, above the crus penis. Its base is directed toward the rectum, and connected to the central tendinous point of the perineum. It is continuous with the deep layer of the superficial fascia behind the Transversus perinsei superficialis, and with the inferior layer of the diaphragmatic THE MUSCLES OF THE UROGENITAL REGION IN THE MALE 429 part of the pelvic fascia. It is perforated, about 2.5 cm. below the symphysis pubis, by the urethra, the aperture for which is circular and about G mm. in diameter by the arteries to the bulb and the ducts of the bulbourethral glands close to the urethral orifice; by the deep arteries of the penis, one on either side close to the pubic arch and about halfway along the attached margin of the fascia; by the dorsal arteries and nerves of the penis near the apex of the fascia. Its base is also perfor- ated by the perineal vessels and nerves, while between its apex and the arcuate pubic ligament the deep dorsal vein of the penis passes upward into the pelvis. If the inferior fascia of the urogenital diaphragm be detached on either side, the following structures will be seen between it and the superior fascia: the deep dorsal vein of the penis; the membranous portion of the urethra; the Transversus perinsei profundus and Sphincter urethrae membranaceae muscles; the bulbo- urethral glands and their ducts; the pudendal vessels and dorsal nerves of the penis; the arteries and nerves of the urethral bulb, and a plexus of veins. Interior of . bladder Fascia of urogenital T ap( ■ j. \ I Inferior diaphragm [ Bulbocavernosus I schiocavernosus Fig. 407.—Coronal section of anterior part of pelvis, through the pubic arch. Seen from in front. (Diagrammatic.) The superior fascia of the urogenital diaphragm is continuous with the obturator fascia and stretches across the pubic arch. If the obturator fascia be traced medially after leaving the Obturator internus muscle, it will be found attached by some of its deeper or anterior fibers to the inner margin of the pubic arch, while its super- ficial or posterior fibers pass over this attachment to become continuous with the superior fascia of the urogenital diaphragm. Behind, this layer of the fascia is continuous with the inferior fascia and with the fascia of Colies; in front it is con- tinuous with the fascial sheath of the prostate, and is fused with the inferior fascia to form the transverse ligament of the pelvis. The Transversus perinaei profundus arises from the inferior rami of the ischium and runs to the median line, where it interlaces in a tendinous raphe with its fellow of the opposite side. It lies in the same plane as the Sphincter urethrae membran- aceae; formerly the two muscles were described together as the Constrictor urethrae. The Sphincter urethrae membranaceae surrounds the whole length of the mem- branous portion of the urethra, and is enclosed in the fasciae of the urogenital dia- phragm. Its external fibers arise from the junction of the inferior rami of the pubis 430 MYOLOGY and ischium to the extent of 1.25 to 2 cm., and from the neighboring fasciae. They arch across the front of the urethra and bulbourethral glands, pass around the urethra, and behind it unite with the muscle of the opposite side, by means of a tendinous raphe. Its innermost fibers form a continuous circular investment for the membranous urethra. Nerve Supply.—The perineal branch of the pudendal nerve supplies this group of muscles. Actions.—The muscles of both sides act together as a sphincter, compressing the membranous portion of the urethra. During the transmission of fluids they, like the Bulbocavernosus, are relaxed, and only come into action at the end of the process to eject the last drops of the fluid. 2. b. The Muscles of the Urogenital Region in the Female (Fig. 408). Transversus perinsei superficialis. Bulbocavernosus. Ischiocavernosus. Transversus perinsei profundus. Sphincter urethrae membranaceae. The Transversus perinsei superficialis (Transversus penned; Superficial trans- verse perineal muscle) in the female is a narrow muscular slip, which arises by a small tendon from the inner and forepart of the tuberosity of the ischium, and is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, the Sphincter ani externus behind, and the Bulbocavernosus in front. Action.—The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavernosus (Sphincter vagina) surrounds the orifice of the vagina. It covers the lateral parts of the vestibular bulbs, and is attached posteriorly to the central tendinous point of the perineum, where it blends with the Sphincter ani externus. Its fibers pass forward on either side of the vagina to be inserted into the corpora cavernosa clitoridis, a fasciculus crossing over the body of the organ so as to compress the deep dorsal vein. Actions.—The Bulbocavernosus diminishes the orifice of the vagina. The anterior fibers contribute to the erection of the clitoris, as they are inserted into and are continuous with the fascia of the clitoris, compressing the deep dorsal vein during the contraction of the muscle. The Ischiocavernosus (Erector clitoridis) is smaller than the corresponding muscle in the male. It covers the unattached surface of the crus clitoridis. It is an elongated muscle, broader at the middle than at either end, and situated on the side of the lateral boundary of the perineum. It arises by tendinous and fleshy fibers from the inner surface of the tuberosity of the ischium, behind the crus clitoridis; from the surface of the crus; and from the adjacent portion of the ramus of the ischium. From these points fleshy fibers succeed, and end in an aponeurosis, which is inserted into the sides and under surface of the crus clitoridis. Actions.—The Ischiocavernosus compresses the crus clitoridis and retards the return of blood through the veins, and thus serves to maintain the organ erect. The fascia of the urogenital diaphragm in the female is not so strong as in the male. It is attached to the pubic arch, its apex being connected with the arcuate pubic ligament. It is divided in the middle line by the aperture of the vagina, with the external coat of which it becomes blended, and in front of this is perfor- ated by the urethra. Its posterior border is continuous, as in the male, with the deep layer of the superficial fascia around the Transversus perinsei superficialis. Like the corresponding fascia in the male, it consists of two layers, between which are to be found the following structures: the deep dorsal vein of the clitoris, a portion of the urethra and the Constrictor urethra muscle, the larger vestibular THE MUSCLES AND FASCIAE OF THE UPPER EXTREMITY 431 glands and their ducts; the internal pudendal vessels and the dorsal nerves of the clitoris; the arteries and nerves of the bulbi vestibuli, and a plexus of veins. The Transversus perinsei profundus arises from the inferior rami of the ischium and runs across to the side of the vagina. The Sphincter urethrae membranaceae (Constrictor urethrae), like the corresponding muscle on the male, consists of external Clitoris Urethra Vagina Sphincter ani externus Fig. 408.—Muscles of the female perineum. (Modified from a drawing by Peter Thompson.) and internal fibers. The external fibers arise on either side from the margin of the inferior ramus of the pubis. They are directed across the pubic arch in front of the urethra, and pass around it to blend with the muscular fibers of the opposite side, between the urethra and vagina. The innermost fibers encircle the lower end of the urethra. Nerve Supply.—The muscles of this group are supplied by the perineal branch of the pudendal. THE MUSCLES AND FASCLffi OF THE UPPER EXTREMITY. The muscles of the upper extremity are divisible into groups, corresponding with the different regions of the limb. I. Muscles Connecting the Upper Extremity to the Vertebral Column. II. Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. III. Muscles of the Shoulder. IV. Muscles of the Arm. V. Muscles of the Forearm. VI. Muscles of the Hand. 432 MYOLOGY I. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE VERTEBRAL COLUMN The muscles of this group are: Trapezius. Latissimus dorsi. Rhomboideus major. Rhomboideus minor. Levator scapula. Superficial Fascia.—The superficial fascia of the back forms a layer of con- siderable thickness and strength, and contains a quantity of granular fat. It is continuous with the general superficial fascia. Deep Fascia.—The deep fascia is a dense fibrous layer, attached above to the superior nuchal line of the occipital bone; in the middle line it is attached to the ligamentum nuchae and supraspinal ligament, and to the spinous processes of all the vertebrae below the seventh cervical; laterally, in the neck it is continuous with the deep cervical fascia; over the shoulder it is attached to the spine of the scapula and to the acromion, and is continued downward over the Deltoideus to the arm; on the thorax it is continuous with the deep fascia of the axilla and chest, and on the abdomen with that covering the abdominal muscles; below, it is attached to the crest of the ilium. The Trapezius (Fig. 409) is a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protu- berance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nucha?, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibers proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibers are inserted into the posterior border of the lateral third of the clavicle; the middle fibers into the medial margin of the acromion, and into the supe- rior lip of the posterior border of the spine of the scapula; the inferior fibers con- verge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebrae, and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corre- sponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra. Variations.—The attachments to the dorsal vertebrae are often reduced and the lower ones are often wanting; the occipital attachment is often wanting; separation between cervical and dorsal portions is frequent. Extensive deficiencies and complete absence occur. The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it. The Latissimus dorsi (Fig. 409) is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region, and is gradually con- tracted into a narrow fasciculus at its insertion into the humerus. It arises by tendinous fibers from the spinous processes of the lower six thoracic vertebrae and from the posterior layer of the lumbodorsal fascia (see page 397), by which it is attached to the spines of the lumbar and sacral vertebrae, to the supraspinal ligament, and to the posterior part of the crest of the ilium. It also arises by MUSCLES OF THE UPPER EXTREMITY 433 I/wmbar triangle Fig 409.—Muscles connecting the upper extremity to the vertebral column. 434 MYOLOGY muscular fibers from the external lip of the crest of the ilium lateral to the margin of the Sacrospinalis, and from the three or four lower ribs by fleshy digitations, which are interposed between similar processes of the Obliquus abdominis externus (Fig. 392, page 409). From this extensive origin the fibers pass in different direc- tions, the upper ones horizontally, the middle obliquely upward, and the lower vertically upward, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and usually receives a few fibers from it. The muscle curves around the lower border of the Teres major, and is twisted upon itself, so that the superior fibers become at first posterior and then inferior, and the vertical fibers at first anterior and then superior. It ends in a quadrilateral tendon, about 7 cm. long, which passes in front of the tendon of the Teres major, and is inserted into the bottom of the intertubercular groove of the humerus; its insertion extends higher on the humerus than that of the tendon of the Pectoralis major. The lower border of its tendon is united with that of the Teres major, the surfaces of the two being separated near their insertions by a bursa; another bursa is sometimes inter- posed between the muscle and the inferior angle of the scapula. The tendon of the muscle gives off an expansion to the deep fascia of the arm. Variations.—The number of dorsal vertebrae to which it is attached vary from four to seven or eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium. A muscular slip, the axillary arch, varying from 7 to 10 cm. in length, and from 5 to 15 mm. in breadth, occasionally springs from the upper edge of the Latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the Pectoralis major, the Coracobrachialis, or the fascia over the Biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually selected for the application of a ligature, and may mislead the surgeon during the operation. It is present in about 7 per cent, of subjects and may be easily recognized by the transverse direction of its fibers. A fibrous slip usually passes from the lower border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the Triceps brachii. This is occasionally muscular, and is the representative of the Dorsoepitrochlearis brachii of apes. The lateral margin of the Latissimus dorsi is separated below from the Obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the Obliquus internus abdominis. Another triangle is situated behind the scapula. It is bounded above by the Trapezius, below by the Latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the Rhomboideus major. If the scapula be drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation. The space is there- fore known as the triangle of auscultation. Nerves.—The Trapezius is supplied by the accessory nerve, and by branches from the third and fourth cervical nerves; the Latissimus dorsi by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve. The Rhomboideus major (Fig. 409) arises by tendinous fibers from the spinous processes of the second, third, fourth, and fifth thoracic vertebrae and the supra- spinal ligament, and is inserted into a narrow tendinous arch, attached above to the lower part of the triangular surface at the root of the spine of the scapula; below to the inferior angle, the arch being connected to the vertebral border by a thin membrane. When the arch extends, as it occasionally does, only a short distance, the muscular fibers are inserted directly into the scapula. The Rhomboideus minor (Fig. 409) arises from the lower part of the ligamentum nuchse and from the spinous processes of the seventh cervical and first thoracic vertebrae. It is inserted into the base of the triangular smooth surface at the root of the spine of the scapula, and is usually separated from the Rhomboideus major MUSCLES OF THE UPPER EXTREMITY 435 by a slight interval, but the adjacent margins of the two muscles are occasionally united. Variations.—The vertebral and scapular attachments of the two muscles vary in extent. A small slip from the scapula to the occipital bone close to the minor occasionally occurs, the Rhom- boideus occipitalis muscle. The Levator scapulae- (Levator anguli scapulae') (Fig. 4G9) is situated at the back and side of the neck. It arises by tendinous slips from the transverse pro- cesses of the atlas and axis and from the posterior tubercles of the transverse processes of the third and fourth cervical vertebrae. It is inserted into the verte- bral border of the scapula, between the medial angle and the triangular smooth surface at the root of the spine. Variations.—The number of vertebral attachments varies; a slip may extend to the occipital or mastoid, to the Trapezius, Scalene or Serratus anterior, or to the first or second rib. The muscle may be subdivided into several distinct parts from origin to insertion. Levator claviculce from the transverse processes of one or two upper cervical vertebrae to the outer end of the clavicle corre- sponds to a muscle of lower animals. More or less union with the Serratus anterior. Nerves.—The Rhomboidei are supplied by the dorsal scapular nerve from the fifth cervical; the Levator scapulae by the third and fourth cervical nerves, and frequently by a branch from the dorsal scapular. Actions.—The movements effected by the preceding muscles are numerous, as may be con- ceived from their extensive attachments. When the whole Trapezius is in action it retracts the scapula and braces back the shoulder; if the head be fixed, the upper part of the muscle will elevate the point of the shoulder, as in supporting weights; when the lower fibers contract they assist in depressing the scapula. The middle and lower fibers of the muscle rotate the scapula, causing elevation of the acromion. If the shoulders be fixed, the Trapezii, acting together, will draw the head directly backward; or if only one act, the head is drawn to the corresponding side. When the Latissimus dorsi acts upon the humerus, it depresses and draws it backward, and at the same time rotates it inward. It is the muscle which is principally employed in giving a downward blow, as in felling a tree or in sabre practice. If the arm be fixed, the muscle may act in various ways upon the trunk; thus, it may raise the lower ribs and assist in forcible inspira- tion; or, if both arms be fixed, the two muscles may assist the abdominal muscles and Pectorales in suspending and drawing the trunk forward, as in climbing. If the head be fixed, the Levator scapula; raises the medial angle of the scapula; if the shoulder be fixed, the muscle inclines the neck to the corresponding side and rotates it in the same direc- tion. The Rhomboidei carry the inferior angle backward and upward, thus producing a slight rotation of the scapula upon the side of the chest, the Rhomboideus major acting especially on the inferior angle of the scapula, through the tendinous arch by which it is inserted. The Rhom- boidei, acting together with the middle and inferior fibers of the Trapezius, will retract the scapula. H. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE ANTERIOR AND LATERAL THORACIC WALLS. The muscles of the anterior and lateral thoracic regions are: Pectoralis major. Pectoralis' minor. Subclavius. Serratus anterior. Superficial Fascia.—The superficial fascia of the anterior thoracic region is con- tinuous with that of the neck and upper extremity above, and of the abdomen below. It encloses the mamma and gives off numerous septa which pass into the gland, supporting its various lobes. From the fascia over the front of the mamma, fibrous processes pass forward to the integument and papilla; these were called by Sir A. Cooper the ligamenta suspensoria. Pectoral Fascia.—The pectoral fascia is a thin lamina, covering the surface of the Pectoralis major, and sending numerous prolongations between its fasciculi: it is attached, in the middle line, to the front of the sternum; above, to the clavicle; laterally and below it is continuous with the fascia of the shoulder, axilla,, and thorax. It is very thin over the upper part of the Pectoralis major, but thicker 436 MYOLOGY in the interval between it and the Latissimus dorsi, where it closes in the axillary space and forms the axillary fascia; it divides at the lateral margin of the Latis- simus dorsi into two layers, one of which passes in front of, and the other behind it; these proceed as far as the spinous processes of the thoracic vertebrae, to which they are attached. As the fascia leaves the lower edge of the Pectoralis major to cross the floor of the axilla it sends a layer upward under cover of the muscle; this lamina splits to envelop the Pectoralis minor, at the upper edge of which it is continuous with the coracoclavicular fascia. The hollow of the armpit, seen when the arm is abducted, is produced mainly by the traction of this fascia on the axillary floor, and hence the lamina is sometimes named the suspensory ligament of the axilla. At the lower part of the thoracic region the deep fascia is well-developed, and is continuous with the fibrous sheaths of the Recti abdominis. Pig. 410.—-Superficial muscles of the chest and front of the arm. The Pectoralis major (Fig. 410) is a thick, fan-shaped muscle, situated at the upper and forepart of the chest. It arises from the anterior surface of the sternal half of the clavicle; from half the breadth of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib; from the MUSCLES OF THE UPPER EXTREMITY 437 cartilages of all the true ribs, with the exception, frequently, of the first or seventh, or both, and from the aponeurosis of the Obliquus externus abdominis. From this extensive origin the fibers converge toward their insertion; those arising from the clavicle pass obliquely downward and lateralward, and are usually separated from the rest by a slight interval; those from the lower part of the sternum, and the cartilages of the lower true ribs, run upward and lateralward; while the middle fibers pass horizontally. They all end in a flat tendon, about 5 cm. broad, which is inserted into the crest of the greater tubercle of the humerus. This tendon con- sists of two laminae, placed one in front of the other, and usually blended together below. The anterior lamina, the thicker, receives the clavicular and the uppermost sternal fibers; they are inserted in the same order as that in which they arise: that is to say, the most lateral of the clavicular fibers are inserted at the upper part of the anterior lamina; the uppermost sternal fibers pass down to the lower part of the lamina which extends as low as the tendon of the Deltoideus and joins with it. The posterior lamina of the tendon receives the attachment of the greater part of the sternal portion and the deep fibers, i. e., those from the costal cartilages. These deep fibers, and particularly those from the lower costal cartilages, ascend the higher, turning backward successively behind the superficial and upper ones, so that the tendon appears to be twisted. The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given off which covers the intertubercular groove and blends with the capsule of the shoulder- joint. From the deepest fibers of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia of the arm. Variations.—The more frequent variations are greater or less extent of attachment to the ribs and sternum, varying size of the abdominal part or its absence, greater or less extent of separation of sternocostal and clavicular parts, fusion of clavicular part with deltoid, decussation in front of the sternum. Deficiency or absence of the sternocostal part is not uncommon. Absence of the clavicular part is less frequent. Rarely the whole muscle is wanting. Costocoracoideus is a muscular band occasionally found arising from the ribs or aponeurosis of the External oblique between the Pectoralis major and Latissimus dorsi and inserted into the coracoid process. Chondro-epitrochlearis is a muscular slip occasionally found arising from the costal cartilages or from the aponeurosis of the External oblique below the Pectoralis major or from the Pectoralis. major itself. The insertion is variable on the inner side of the arm to fascia, intermuscular septum or internal condyle. Sternalis, in front of the sternal end of the Pectoralis major parallel to the margin of the sternum. It is supplied by the anterior thoracic nerves and is probably a misplaced part of the pectoralis. Coracoclavicular Fascia (fascia coracoclavicularis; costocoracoid membrane; clavi- pectoral fascia).—The coracoclavicular fascia is a strong fascia situated under cover of the clavicular portion of the Pectoralis major. It occupies the interval between the Pectoralis minor and Subclavius, and protects the axillary vessels and nerves. Traced upward, it splits to enclose the Subclavius, and its two layers are attached to the clavicle, one in front of and the other behind the muscle; the latter layer fuses with the deep cervical fascia and with the sheath of the axillary vessels. Medially, it blends with the fascia covering the first two intercostal spaces, and is attached also to the first rib medial to the origin of the Subclavius. Laterally, it is very thick and dense, and is attached to the coracoid process. The portion extending from the first rib to the coracoid process is often whiter and denser than the rest, and is sometimes called the costocoracoid ligament. Below this it is thin, and at the upper border of the Pectoralis minor it splits into two layers to invest the muscle; from the lower border of the Pectoralis minor it is continued downward to join the axillary fascia, and lateralward to join the fascia over the short head of the Biceps brachii. The coracoclavicular fascia is pierced by the cephalic vein, thoracoacromial artery and vein, and external anterior thoracic nerve. 438 MYOLOGY The Pectoralis minor (Fig. 411) is a thin, triangular muscle, situated at the upper part of the thorax, beneath the Pectoralis major. It arises from the upper margins and outer surfaces of the third, fourth, and fifth ribs, near their cartilage and from the aponeuroses covering the Intercostalis; the fibers pass upward and lateralward and converge to form a flat tendon, which is inserted into the medial border and upper surface of the coracoid process of the scapula. Variations.—Origin from second, third and fourth or fifth ribs. The tendon of insertion may extend over the coracoid process to the greater tubercle. May be split into several parts. Absence rare. Pectoralis minimus, first rib-cartilage to coracoid process. Rare. Fig. 411.—Deep muscles of the chest and front of the arm, with the boundaries of the axilla. The Subclavius (Fig. 411) is a small triangular muscle, placed between the clavicle and the first rib. It arises by a short, thick tendon from the first rib and its cartilage at their junction, in front of the costoclavicular ligament; the fleshy fibers proceed obliquely upward and lateralward, to be inserted into the groove on the under surface of the clavicle between the costoclavicular and conoid ligaments. Variations.—Insertion into coracoid process instead of clavicle or into both clavicle and coracoid process. Sternoscapular fasciculus to the upper border of scapula. Sternoclavicularis from manu- brium to clavicle between Pectoralis major and coracoclavicular fascia. The Serratus anterior (Serratus magnus) (Fig. 411) is a thin muscular sheet, situated between the ribs and the scapida at the upper and lateral part of THE MUSCLES AND FASCIM OF THE SHOULDER 439 the chest. It arises by fleshy digitations from the outer surfaces and superior borders of the upper eight or nine ribs, and from the aponeuroses covering the intervening Intercostales. Each digitation (except the first) arises from the corresponding rib; the first springs from the first and second ribs; and from the fascia covering the first intercostal space. From this extensive attachment the fibers pass backward, closely applied to the chest-wall, and reach the vertebral border of the scapula, and are inserted into its ventral surface in the following manner. The first digitation is inserted into a triangular area on the ventral surface of the medial angle. The next two digitations spread out to form a thin, triangular sheet, the base of which is directed backward and is inserted into nearly the whole length of the ventral surface of the vertebral border. The lower five or six digita- tions converge to form a fan-shaped mass, the apex of which is inserted, by muscular and tendinous fibers, into a triangular impression on the ventral surface of the inferior angle. The lower four slips interdigitate at their origins with the upper five slips of the Obliquus externus abdominis. Variations.—Attachment to tenth rib. Absence of attachments to first rib, to one or more of the lower ribs. Division into three parts; absence or defect of middle part. Union with Levator scapulae, External intercostals or External oblique. Nerves.—The Pectoralis major is supplied by the medial and lateral anterior thoracic nerves; through these nerves the muscle receives filaments from all the spinal nerves entering into the formation of the brachial plexus; the Pectoralis minor receives its fibers from the eighth cervical and first thoracic nerves through the medial anterior thoracic nerve. The Subclavius is suplied by a filament from the fifth and sixth cervical nerves; the Serratus anterior is supplied by the long thoracic, which is derived from the fifth, sixth, and seventh cervical nerves. Actions.—If the arm has been raised by the Deltoideus, the Pectoralis major will, conjointly with the Latissimus dorsi and Teres major, depress it to the side of the chest. If acting alone, it adducts and draws forward the arm, bringing it across the front of the chest, and at the same time rotates it inward. The Pectoralis minor depresses the point of the shoulder, drawing the scapula downward and medialward toward the thorax, and throwing the inferior angle back- ward. The Subclavius depresses the shoulder, carrying it downward and forward. When the arms are fixed, all three of these muscles act upon the ribs; drawing them upward and expand- ing the chest, and thus becoming very important agents in forced inspiration. The Serratus anterior, as a whole, carries the scapula forward, and at the same time raises the vertebral border of the bone. It is therefore concerned in the action of pushing. Its lower and stronger fibers move forward the lower angle and assist the Trapezius in rotating the bone at the sternoclavicular joint, and thus assist this muscle in raising the acromion and supporting weights upon the shoulder. It is also an assistant to the Deltoideus in raising the arm, inasmuch as during the action of this latter muscle it fixes the scapula and so steadies the glenoid cavity on which the head of the humerus rotates. After the Deltoideus has raised the arm to a right angle with the trunk, the Serratus anterior and the Trapezius, by rotating the scapula, raise the arm into an almost vertical position. It is possible that when the shoulders are fixed the lower fibers of the Serratus anterior may assist in raising and everting the ribs; but it is not the important inspiratory muscle it was formerly believed to be. III. THE MUSCLES AND FASCLffi OF THE SHOULDER. In this group are included: Deltoideus. Subscapularis. Supraspinatus. Infraspinatus. Teres minor. Teres major. Deep Fascia.—The deep fascia covering the Deltoideus invests the muscle, and sends numerous septa between its fasciculi. In front it is continuous with the fascia covering the Pectoralis major; behind, where it is thick and strong, with that covering the Infraspinatus; above, it is attached to the clavicle, the acromion, and the spine of the scapula; below, it is continuous with the deep fascia of the arm. The Deltoideus {Deltoid muscle) (Fig. 410) is a large, thick, triangular muscle, which covers the shoulder-joint in front, behind, and laterally. It arises from the anterior 440 MYOLOGY border and upper surface of the lateral third of the clavicle; from the lateral margin and upper surface of the acromion, and from the lower lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end. From this extensive origin the fibers converge toward their insertion, the middle passing vertically, the anterior obliquely backward and lateralward, the posterior obliquely forward and lateralward; they unite in a thick tendon, which is inserted into the deltoid prominence on the middle of the lateral side of the body of the humerus. At its insertion the muscle gives off an expansion to the deep fascia of the arm. This muscle is remarkably coarse in texture, and the arrangement of its fibers is somewhat peculiar; the central portion of the muscle—that is to say, the part arising from the acromion—consists of oblique fibers; these arise in a bipenniform manner from the sides of the tendinous intersections, generally four in number, which are attached above to the acromion and pass downward parallel to one another in the substance of the muscle. The oblique fibers thus formed are inserted into similar tendinous intersections, generally three in number, which pass upward from the insertion of the muscle and alternate with the descending septa. The portions of the muscle arising from the clavicle and spine of the scapula are not arranged in this manner, but are inserted into the margins of the inferior tendon. Variations.—Large variations uncommon. More or less splitting common. Continuation into the Trapezius; fusion with the Pectoralis major; additional slips from the vertebral border of the scapula, infraspinous fascia and axillary border of scapula not uncommon. Insertion varies in extent or rarely is prolonged to origin of Brachioradialis. Nerves.—The Deltoideus is supplied by the fifth and sixth cervical through the axillary nerve. Actions.—The Deltoideus raises the arm from the side, so as to bring it at right angles with the trunk. Its anterior fibers, assisted by the Pectoralis major, draw the arm forward; and its posterior fibers, aided by the Teres major and Latissimus dorsi, draw it backward. Subscapular Fascia (fascia subscapularis).—The subscapular fascia is a thin membrane attached to the entire circumference of the subscapular fossa, and affording attachment by its deep surface to some of the fibers of the Sub- scapularis. The Subscapularis (Fig. 411) is a large triangular muscle which fills the sub- scapular fossa, and arises from its medial two-thirds and from the lower two- thirds of the groove on the axillary border of the bone. Some fibers arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis, which separates the muscle from the Teres major and the long head of the Triceps brachii. The fibers pass lateralward, and, gradually converging, end in a tendon which is inserted into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. The tendon of the muscle is separated from the neck of the scapula by a large bursa, which communicates with the cavity of the shoulder-joint through an aperture in the capsule. Nerves.—The Subscapularis is supplied by the fifth and sixth cervical nerves through the upper and lower subscapular nerves. Actions.—The Subscapularis rotates the head of the humerus inward; when the arm is raised, it draws the humerus forward and downward. It is a powerful defence to the front of the shoulder- joint, preventing displacement of the head of the humerus. Supraspinatous Fascia {fascia supraspinata).—The supraspinatous fascia com- pletes the osseofibrous case in which the Supraspinatus muscle is contained; it affords attachment, by its deep surface, to some of the fibers of the muscle. It is thick medially, but thinner laterally under the coracoacromial ligament. The Supraspinatus (Fig. 412) occupies the whole of the supraspinatous fossa, arising from its medial two-thirds, and from the strong supraspinatous fascia. The muscular fibers converge to a tendon, which crosses the upper part of the THE MUSCLES AND FASCIJE OF THE SHOULDER 441 shoulder-joint, and is inserted into the highest of the three impressions on the greater tubercle of the humerus; the tendon is intimately adherent to the capsule of the shoulder-joint. Infraspinatous Fascia (fascia infraspinata).—The infraspinatous fascia is a dense fibrous membrane, covering the Infraspinatous muscle and fixed to the circumfer- ence of the infraspinatous fossa; it affords attachment, by its deep surface, to some fibers of that muscle. It is intimately attached to the deltoid fascia along the over- lapping border of the Deltoideus. Fig. 412.—Muscles on the dorsum of the scapula, and the Triceps brachii. The Infraspinatus (Fig. 412) is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa; it arises by fleshy fibers from its medial two- thirds, and by tendinous fibers from the ridges on its surface; it also arises from the infraspinatous fascia wThich covers it, and separates it from the Teretes major and minor. The fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity. The Teres minor (Fig. 412) is a narrow, elongated muscle, which arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminae, one of which separates it from the Infraspinatus, the other from the Teres major. Its fibers run obliquely upward and lateralward; the upper ones end in a tendon which is inserted into the lowest of the three impressions on the greater tubercle of the humerus; the lowest fibers are inserted directly into the humerus immediately below this impression. The 442 MYOLOGY tendon of this muscle passes across, and is united with, the posterior part of the capsule of the shoulder-joint. Variations.—It is sometimes inseparable from the Infraspinatus. The Teres major (Fig. 412) is a thick but somewhat flattened muscle, which arises from the oval area on the dorsal surface of the inferior angle of the scapula, and from the fibrous septa interposed between the muscle and the Teres minor and Infraspinatus; the fibers are directed upward and lateralward, and end in a flat tendon, about 5 cm. long, which is inserted into the crest of the lesser tubercle of the humerus. The tendon, at its insertion, lies behind that of the Latissimus dorsi, from which it is separated by a bursa, the two tendons being, however, united along their lower borders for a short distance. Nerves.—The Supraspinatus and Infraspinatus are supplied by the fifth and sixth cervical nerves through the suprascapular nerve; the Teres minor, by the fifth cervical, through the axillary; and the Teres major, by the fifth and sixth cervical, through the lowest subscapular. Actions.—The Supraspinatus assists the Deltoideus in raising the arm from the side of the trunk and fixes the head of the humerus in the glenoid cavity. The Infraspinatus and Teres minor rotate the head of the humerus outward; they also assist in carrying the arm backward. One of the most important uses of these three muscles is to protect the shoulder-joint, the Supra- spinatus supporting it above, and the Infraspinatus and Teres minor behind. The Teres major assists the Latissimus dorsi in drawing the previously raised humerus downward and backward, and in rotating it inward; when the arm is fixed it may assist the Pectorales and the Latissimus dorsi in drawing the trunk forward. IV. THE MUSCLES AND FASCIA OF THE ARM The muscles of the arm are: Coracobrachialis. Biceps brachii. Brachialis. Triceps brachii. Brachial Fascia (fascia brachii; deep fascia of the arm).—The brachial fascia is continuous with that covering the Deltoideus and the Pectoralis major, by means of which it is attached, above, to the clavicle, acromion, and spine of the scapula; it forms a thin, loose, membranous sheath for the muscles of the arm, and sends septa between them; it is composed of fibers disposed in a circular or spiral direc- tion, and connected together by vertical and oblique fibers. It differs in thickness at different parts, being thin over the Biceps brachii, but thicker where it covers the Triceps brachii, and over the epicondyles of the humerus: it is strengthened by fibrous aponeuroses, derived from the Pectoralis major and Latissimus dorsi medially, and from the Deltoideus laterally. On either side it gives off a strong intermuscular septum, which is attached to the corresponding supracondylar ridge and epicondyle of the humerus. The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle, along the lateral supra- condylar ridge, to the lateral epicondyle; it is blended with the tendon of the Del- toideus, gives attachment to the Triceps brachii behind, to the Brachialis, Brachio- radialis, and Extensor carpi radialis longus in front, and is perforated by the radial nerve and profunda branch of the brachial artery. The medial intermuscular septum, thicker than the preceding, extends from the lower part of the crest of the lesser tubercle of the humerus below the Teres major, along the medial supra- condylar ridge to the medial epicondyle; it is blended with the tendon of the Coracobrachialis, and affords attachment to the Triceps brachii behind and the Brachialis in front. It is perforated by the ulnar nerve, the superior ulnar collateral artery, and the posterior branch of the inferior ulnar collateral artery. At the elbow, the deep fascia is attached to the epicondyles of the humerus and the olecranon of the ulna, and is continuous with the deep fascia of the forearm. THE MUSCLES AND FASCIAE OF THE ARM 443 Just below the middle of the arm, on its medial side, is an oval opening in the deep fascia, which transmits the basilic vein and some lymphatic vessels. The Coracobrachialis (Fig. 411), the smallest of the three muscles in this region, is situated at the upper and medial part of the arm. It arises from the apex of the coracoid process, in common with the short head of the Biceps brachii, and from the intermuscular septum between the two muscles; it is inserted by means of a flat tendon into an impression at the middle of the medial surface and border of the body of the humerus between the origins of the Triceps brachii and Brachialis. It is perforated by the musculocutaneous nerve. Lateral antibrachial cutaneous nerve Biceps brachii M. Brachial artery and veins Median nerve Cephalic vein-. Medial antibrachial cuianeous nerve -Basilic vein - Ulnar nerve Superior ulnar collateral artery Brachialis M Brachialis M- Medial intermuscular septum of humerus Radial nerve--* "Humerus Dorsal antibrachial cutaneous nerve Radial collateral artery’ Lateral intermuscular septum of humerus Triceps brachii M. Fig. 413.—Cross-section through the middle of upper arm. (Eycleshymer and Sehoemaker.1) Variations.—A bony head may reach the medial epicondyle; a short head more rarely found may insert into the lesser tubercle. The Biceps brachii (Biceps; Biceps flexor cubiti) (Fig. 411) is a long fusiform muscle, placed on the front of the arm, and arising by two heads, from which circumstance it has received its name. The short head arises by a thick flattened tendon from the apex of the coracoid process, in common with the Coracobrachialis. The long head arises from the supraglenoid tuberosity at the upper margin of the glenoid cavity, and is continuous with the glenoidal labrum. This tendon, enclosed in a special sheath of the synovial membrane of the shoulder-joint, arches over the head of the humerus; it emerges from the capsule through an opening close to the humeral attachment of the ligament, and descends in the intertubercular groove; it is retained in the groove by the transverse humeral ligament and by a fibrous prolongation from the tendon of the Pectoralis major. Each tendon is succeeded by an elongated muscular belly, and the two bellies, although closely applied to each other, can readily be separated until within about 7.5 cm. of the elbow-joint. Here they end in a flattened tendon, which is inserted into the rough posterior portion of the tuberosity of the radius, a bursa being interposed between the tendon and the front part of the tuberosity. As the tendon of the muscle approaches the radius it is twisted upon itself, so that its anterior surface becomes 1 A Cross-section Anatomy, New York, 1911. 444 MYOLOGY lateral and is applied to the tuberosity of the radius at its insertion. Opposite the bend of the elbow the tendon gives off, from its medial side, a broad aponeu- rosis, the lacertus fibrosus (bicipital fascia) which passes obliquely downward and medialward across the brachial artery, and is continuous with the deep fascia covering the origins of the Flexor muscles of the forearm (Fig. 410). Variations.—A third head (10 per cent.) to the Biceps brachii is occasionally found, arising at the upper and medial part of the Brachialis, with the fibers of which it is continuous, and inserted into the lacertus fibrosus and medial side of the tendon of the muscle. In most cases this additional slip lies behind the brachial artery in its coarse down the arm. In some instances the third head consists of two slips, which pass down, one in front of and the other behind the artery, concealing the vessel in the lower half of the arm. More rarely a fourth head occurs arising from the outer side of the humerus, from the intertubercular groove, or from the greater tubercle. Other heads are occasionally found. Slips sometimes pass from the inner border of the muscle over the brachial artery to the medial intermuscular septum, or the medial epicondyle; more rarely to the Pronator teres or Brachialis. The long head may be absent or arise from the intertubercular groove. The Brachialis (Brachialis anticus) (Fig. 411) covers the front of the elbow-joint and the lower half of the humerus. It arises from the lower half of the front of the humerus, commencing above at the insertion of the Deltoideus, which it embraces by two angular processes. Its origin extends below to within 2.5 cm. of the margin of the articular surface. It also arises from the intermuscular septa, but more extensively from the medial than the lateral; it is separated from the lateral below by the Brachioradialis and Extensor carpi radialis longus. Its fibers converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process. Variations.—Occasionally doubled; additional slips to the Supinator, Pronator teres, Biceps, lacertus fibrosus, or radius are more rarely found. Nerves.—The Coracobrachialis, Biceps brachii and Brachialis are supplied by the musculo- cutaneous nerve; the Brachialis usually receives an additional filament from the radial. The Coracobrachialis receives its supply primarily from the seventh cervical, the Biceps brachii and Brachialis from the fifth and sixth cervical nerves. Actions.—The Coracobrachialis draws the humerus forward and medialward, and at the same time assists in retaining the head of the bone in contact with the glenoid cavity. The Biceps brachii is a flexor of the elbow and, to a less extent, of the shoulder; it is also a powerful supinator, and serves to render tense the deep fascia of the forearm by means of the lacertus fibrosus given off from its tendon. The Brachialis is a flexor of'the forearm, and forms an impor- tant defence to the elbow-joint. When the forearm is fixed, the Biceps brachii and Brachialis flex the arm upon the forearm, as in efforts of climbing. The Triceps brachii (Triceps; Triceps extensor cuhiti) (Fig. 412) is situated on the back of the arm, extending the entire length of the dorsal surface of the humerus. It is of large size, and arises by three heads (long, lateral, and medial), hence its name. The long head arises by a flattened tendon from the infraglenoid tuberosity of the scapula, being blended at its upper part with the capsule of the shoulder- joint; the muscular fibers pass downward between the two other heads of the muscle, and join with them in the tendon of insertion. The lateral head arises from the posterior surface of the body of the humerus, between the insertion of the Teres minor and the upper part of the groove for the radial nerve, and from the lateral border of the humerus and the lateral intermus- cular septum; the fibers from this origin converge toward the tendon of insertion. The medial head arises from the posterior surface of the body of the humerus, below the groove for the radial nerve; it is narrow and pointed above, and extends from the insertion of the Teres major to within 2.5 cm. of the trochlea: it also arises from the medial border of the humerus and from the back of the whole length of the medial intermuscular septum. Some of the fibers are directed downward to the olecranon, while others converge to the tendon of insertion. The tendon of the Triceps brachii begins about the middle of the muscle: it con- THE VOLAR ANTIBRACHIAL MUSCLES 445 sists of two aponeurotic laminae, one of which is subcutaneous and covers the back of the lower half of the muscle; the other is more deeply seated in the substance of the muscle. After receiving the attachment of the muscular fibers, the two lamellae join together above the elbow, and are inserted, for the most part, into the posterior portion of the upper surface of' the olecranon; a band of fibers is, however, continued downward, on the lateral side, over the Anconaeus, to blend with the deep fascia of the forearm. The long head of the Triceps brachii descends between the Teres minor and Teres major, dividing the triangular space between these two muscles and the humerus into two smaller spaces, one triangular, the other quadrangular (Fig. 412). The triangular space contains the scapular circumflex vessels; it is bounded by the Teres minor above, the Teres major below, and the scapular head of the Triceps laterally. The quadrangular space transmits the posterior humeral circumflex vessels and the axillary nerve; it is bounded by the Teres minor and capsule of the shoulder-joint above, the Teres major below, the long head of the Triceps brachii medially, and the humerus laterally. Variations.—A fourth head from the inner part of the humerus; a slip between Triceps and Latissimus dorsi corresponding to the Dorso-epitrochlearis. The Subanconaeus is the name given to a few fibers which spring from the deep surface of the lower part of the Triceps brachii, and are inserted into the posterior ligament and synovial membrane of the elbow-joint. Nerves.—The Triceps brachii is supplied by the seventh and eighth cervical nerves through the radial nerve. Actions.—The Triceps brachii is the great extensor muscle of the forearm, and is the direct antagonist of the Biceps brachii and Brachialis. When the arm is extended, the long head of the muscle may assist the Teres major and Latissimus dorsi in drawing the humerus backward and in adducting it to the thorax. The long head supports the under part of the shoulder-joint. The Subanconseus draws up the synovial membrane of the elbow-joint during extension of the forearm. V. THE MUSCLES AND FASCLffi OF THE FOREARM. Antibrachial Fascia (fascia antibrachii; deep fascia of the forearm).—The anti- brachial fascia continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is at- tached, behind, to the olecranon and dorsal border of the ulna, and gives off from its deep surface numerous intermuscular septa, which enclose each muscle separately. Over the Flexor tendons as they approach the wrist it is especially thickened, and forms the volar carpal ligament. This is continuous with the transverse carpal liga- ment, and forms a sheath for the tendon of the Palmaris longus which passes over the transverse carpal ligament to be inserted into the palmar aponeurosis. Behind, near the wrist-joint, it is thickened by the addition of many transverse fibers, and forms the dorsal carpal ligament. It is much thicker on the dorsal than on the volar surface, and at the lower than at the upper part of the forearm, and is strengthened above by tendinous fibers derived from the Biceps brachii in front, and from the Triceps brachii behind. It gives origin to muscular fibers, especially at the upper part of the medial and lateral sides of the forearm, and forms the boundaries of a series of cone-shaped cavities, in which the muscles are contained. Besides the vertical septa separating the individual muscles, transverse septa are given off both on the volar and dorsal surfaces of the forearm, separating the deep from the superficial layers of muscles. Apertures exist in the fascia for the passage of vessels and nerves; one of these apertures of large size, situated at the front of the elbow, serves for the passage of a communicating branch between the superficial and deep veins. The antibrachial or forearm muscles may be divided into a volar and a dorsal group. 1. The Volar Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. 446 MYOLOGY The Superficial Group (Fig. 414). Pronator teres. Flexor carpi radialis. Palmaris longus. Flexor carpi ulnaris. Flexor digitorum sublimis. The muscles of this group take origin from the medial epicondyle of the humerus by a common tendon; they receive additional fibers from the deep fascia of the fore- arm near the elbow, and from the septa which pass from this fascia between the individual muscles. The Pronator teres has two heads of origin—humeral and ulnar. The humeral head, the larger and more superficial, arises immediately above the medial epi- condyle, and from the tendon common to the origin of the other muscles; also from the intermuscular septum between it and the Flexor carpi radialis and from the antibrachial fascia. The ulnar head is a thin fasciculus, which arises from the medial side of the coronoid process of the ulna, and joins the preceding at an acute angle. The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes ob- liquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius. The lateral border of the muscle forms the medial boundary of a triangular hollow situated in front of the elbow-joint and containing the brachial artery, median nerve, and tendon of the Biceps brachii. Variations.—Absence of ulnar head; additional slips from the medial intermuscular septum, from the Biceps and from the Brachialis anticus occasionally occur. The Flexor carpi radialis lies on the medial side of the preceding muscle. It arises from the medial epicondyle by the common tendon; from the fascia of the forearm; and from the intermuscular septa between it and the Pronator teres laterally, the Palmaris longus medially, and the Flexor digitorum sublimis beneath. Slender and aponeurotic in structure at its commencement, it increases in size, and ends in a tendon which forms rather more than the lower half of its length. This tendon passes through a canal in the lateral part of the transverse carpal ligament and runs through a groove on the greater multangular bone; the groove is converted into a canal by fibrous tissue, and lined by a mucous sheath. The ten- don is inserted into the base of the second metacarpal bone, and sends a slip to the base of the third metacarpal bone. The radial artery, in the lower part of the forearm, lies between the tendon of this muscle and the Brachioradialis. Variations.—Slips frorii the tendon of the Biceps, the lacertus fibrosus, the coronoid, and the radius have been found. Its insertion often varies and may be mostly into the annular ligament, the trapezium, or the fourth metacarpal as well as the second or third. The muscle may be absent. The Palmaris longus is a slender, fusiform muscle, lying on the medial side of the preceding. It arises from the medial epicondyle of the humerus by the common tendon, from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia. It ends in a slender, flattened tendon, which passes over the upper part of the transverse carpal ligament, and is inserted into the central part of the transverse carpal ligament and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thumb. Variations.—One of the most variable muscles in the body. This muscle is often absent about (10 per cent.), and is subject to many variations; it may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may be double. Slips of origin from the coronoid process or from the radius have been seen. THE VOLAR ANTIBRACHIAL MUSCLES 447 Partial or complete insertion into the fascia of the forearm, into the tendon of the Flexor carpi ulnaris and pisiform bone, into the navicular, and into the muscles of the little finger have been observed. The Flexor carpi ulnaris lies along the ulnar side of the forearm. It arises by two heads, humeral and ulnar, connected by a tendinous arch, beneath which the ulnar nerve ■ and posterior ulnar recurrent artery pass. The humeral head arises from the Fig. 414.—Front of the left forearm. Superficial muscles. Fig. 415.—Front of the left forearm. Deep muscles. 448 MYOLOGY medial epicondyle of the humerus by the common tendon; the lunar head arises from the medial margin of the olecranon and from the upper two-thirds of the dorsal border of the ulna by an aponeurosis, common to it and the Extensor carpi ulnaris and Flexor digitorum profundus; and from the intermuscular septum between it and the Flexor digitorum sublimis. The fibers end in a tendon, which occupies the anterior part of the lower half of the muscle and is inserted into the pisiform bone, and is prolonged from this to the hamate and fifth metacarpal bones by the pisohamate and pisometacarpal ligaments; it is also attached by a few fibers to the transverse carpal ligament. The ulnar vessels and nerve lie on the lateral side of the tendon of this muscle, in the lower two-thirds of the forearm. Variations.—Slips of origin from the coronoid. The Epitrochleo-anconceus, a small muscle often present runs from the back of the inner condyle to the olecranon, over the ulnar nerve. The Flexor digitorum sublimis is placed beneath the previous muscle; it is the largest of the muscles of the superficial group, and arises by three heads— humeral, ulnar, and radial. The humeral head arises from the medial epicondyle of the humerus by the common tendon, from the ulnar collateral ligament of the elbow-joint, and from the intermuscular septa between it and the preceding muscles. The ulnar head arises from the medial side of the coronoid process, above the ulnar origin of the Pronator teres (see Fig. 213, page 216). The radial head arises from the oblique line of the radius, extending from the radial tuberosity to the insertion of the Pronator teres. The muscle speedily separates into two planes of muscular fibers, superficial and deep: the superficial plane divides into two parts which end in tendons for the middle and ring fingers; the deep plane gives off a muscular slip to join the portion of the superficial plane which is asso- ciated wdth the tendon of the ring finger, and then divides into two parts, which end in tendons for the index and little fingers. As the four tendons thus formed pass beneath the transverse carpal ligament into the palm of the hand, they are arranged in pairs, the superficial pair going to the middle and ring fingers, the deep pair to the index and little fingers. The tendons diverge from one another in the palm and form dorsal relations to the superficial volar arch and digital branches of the median and ulnar nerves. Opposite the bases of the first phalanges each tendon divides into two slips to allow of the passage of the corresponding tendon of the Flexor digitorum profundus; the two slips then reunite and form a grooved channel for the reception of the accompanying tendon of the Flexor digitorum profundus. Finally the tendon divides and is inserted into the sides of the second phalanx about its middle. Variations.—Absence of radial head, of little finger portion; accessory slips from ulnar tuberosity to the index and middle finger portions; from the inner head to the Flexor profundus; from the ulnar or annular ligament to the little finger. The Deep Group (Fig. 415). Flexor digitorum profundus. Flexor pollicis longus. Pronator quadratus. The Flexor digitorum profundus is situated on the ulnar side of the forearm, immediately beneath the superficial Flexors. It arises from the upper three- fourths of the volar and medial surfaces of the body of the ulna, embracing the insertion of the Brachialis above, and extending below to within a short distance of the Pronator quadratus. It also arises from a depression on the medial side of the coronoid process; by an aponeurosis from the upper three-fourths of the dorsal border of the ulna, in common with the Flexor and Extensor carpi ulnaris; and from the ulnar half of the interosseous membrane. The muscle ends in four tendons which run under the transverse carpal ligament dorsal to the tendons of the Flexor THE VOLAR ANTIBRACHIAL MUSCLES 449 digitorum sublimis. Opposite the first phalanges the tendons pass through the openings in the tendons of the Flexor digitorum sublimis, and are finally inserted into the bases of the last phalanges. The portion of the muscle for the index finger is usually distinct throughout, but the tendons for the middle, ring, and little fingers are connected together by areolar tissue and tendinous slips, as far as the palm of the hand. Fibrous Sheaths of the Flexor Tendons.—After leaving the palm, the tendons of the Flexores digitorum sublimis and profundus lie in osseo-aponeurotic canals (Fig. 427), formed behind by the phalanges and in front by strong*fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the middle of the proximal and second phalanges the bands (digital vaginal ligaments) are very strong, and the fibers are transverse; but opposite the joints they are much thinner, and consist of annular and cruciate ligamentous fibers. Each canal contains a mucous sheath, which is reflected on the contained tendons. Within each canal the tendons of the Flexores digitorum sublimis and profundus are connected to each other, and to the phalanges, by slender, tendinous bands, called vincula tendina (Fig. 416). There are two sets of these; (a) the vincula brevia, which are two in number in each finger, and consist of triangular bands of fibers, one connecting the tendon of the Flexor digitorum sublimis to the front of the first interphalangeal joint and head of the first phalanx, and the other the tendon of the Flexor digitorum profundus to the front of the second interphalan- geal joint and head of the second phalanx; (6) the vincula longa, which connect the under surfaces of the tendons of the Flexor digitorum profundus to those of the subjacent Flexor sublimis after the tendons of the former have passed through the latter. Variations.—The index finger portion may arise partly from the upper part of the radius. Slips from the inner head of the Flexor sublimis, medial epicondyle, or the coronoid are found. Connec- tion with the Flexor pollicis longus. Four small muscles, the Lumbricales, are connected with the tendons of the Flexor profundus in the palm. They will be described with the muscles of the hand (page 464). The Flexor pollicis longus is situated on the radial side of the forearm, lying in the same plane as the preceding. It arises from the grooved volar surface of the body of the radius, extending from immediately below the tuberosity and oblique line to within a short distance of the Pronator quadratus. It arises also from the adjacent part of the interosseous membrane, and generally by a fleshy slip from the medial border of the coronoid process, or from the medial epicondyle of the humerus. The fibers end in a flattened tendon, which passes beneath the transverse carpal ligament, is then lodged between the lateral head of the Flexor pollicis brevis and the oblique part of the Adductor pollicis, and, entering an osseo- aponeurotic canal similar to those for the Flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb. The volar interosseous nerve and vessels pass downward on the front of the interosseous membrane between the Flexor pollicis longus and Flexor digitorum profundus. Variations.—Slips may connect with Flexor sublimis, or Profundus, or Pronator teres. An addi- tional tendon to the index finger is sometimes found. The Pronator quadratus is a small, flat, quadrilateral muscle, extending across the front of the lower parts of the radius and ulna. It arises from the pronator ridge on the lower part of the volar surface of the body of the ulna; from the medial part of the volar surface of the lower fourth of the ulna; and from a strong apon- eurosis wdiich covers the medial third of the muscle. The fibers pass lateralward 450 MYOLOGY and slightly downward, to be inserted into the lower fourth of the lateral border and the volar surface of the body of the radius. The deeper fibers of the muscle are inserted into the triangular area above the ulnar notch of the radius—an attachment comparable with the origin of the Supinator from the triangular area below the radial notch of the ulna. Tendon of Ext. carpi rad. longus Tendon of Abductor pollicis longus 'Greater multangular bone -Radial artery Tendon of Ext. digitorum communis ■Tendon of Ext. pollicis brevis Tendon of Extensor indicis proprius First Lumbricalis. 1endon of Ext. pollicis longus -Tendon of Ext. pollicis longus Flexor digitorum profundus Flexor digitorum sublimis Vincula brevia Vincula longa Fig. 416.—Tendons of forefinger and vincula tendina Variations.—Rarely absent; split into two or three layers; increased attachment upward or downward. Nerves.—All the muscles of the superficial layer are supplied by the median nerve, excepting the Flexor carpi ulnaris, which is supplied by the ulnar. The Pronator teres, the Flexor carpi radialis, and the Palmaris longus derive their supply primarily from the sixth cervical nerve; the Flexor digitorum sublimis from the seventh and eighth cervical and first thoracic nerves, and the Flexor carpi ulnaris from the eighth cervical and first thoracic. Of the deep layer, the Flexor digitorum profundus is supplied by the eighth cervical and first thoracic through the ulnar, and the volar interosseous branch of the median. The Flexor pollicis longus and Pronator quadratus are supplied by the eighth cervical and first thoracic through the volar interosseous branch of the median. Actions.—These muscles act upon the forearm, the wrist, and hand. The Pronator teres rotates the radius upon the ulna, rendering the hand prone; when the radius is fixed, it assists in flexing the forearm. The Flexor carpi radialis is a flexor and abductor of the wrist; it also assists in pronating the hand, and in bending the elbow. The Flexor carpi ulnaris is a flexor and adductor of the wrist; it also assists in bending the elbow. The Palmaris longus is a flexor of the wrist-joint; it also assists in flexing the elbow. The Flexor digitorum sublimis flexes first the middle and then the proximal phalanges; it also assists in flexing the wrist and elbow. The Flexor digitorum profundus is one of the flexors of the phalanges. After the Flexor sublimis has bent the second phalanx, the Flexor profundus flexes the terminal one; but it cannot do so until after the contraction of the superficial muscle. It also assists in flexing the wrist. The THE DORSAL ANTIBRACHIAL MUSCLES 451 Flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists in flexing the wrist. The Pronator quadratus rotates the radius upon the ulna, rendering the hand prone. Flexor carpi radialis M. Median nerve Antibrachial interos- seous membrane Palmaris longus M. Medial antibrachial cutaneous nerve [vo/ar branch] Lateral antibrachial cutaneous nerve\ Radial artery and nerve'' Flexor digitorum sublimis M. Cephalic vein'. Ulnar artery and nerve Brachioradialis M. Flexor pollicis longus M.~ Flexor digitorum profundus M. Radius - -Flexor carpi ulnaris Tendo m. pronatoris teretis Basilic vein Extensores carpi radiales, longus and brevis Mm. Ulna Extensor digitorum/ communis M. Extensor carpi ulnar is M. Abductor pollicis longus M. Extensor pollicis longus M. Volar interosseous artery and volar antibrachial interosseous nerve Extensor , digiti quinti proprius M. and dor- sal interosseous artery Fig. 417.—Cross-section through the middle of the forearm. (Eycleshymer and Schoemaker.) 2. The Dorsal Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The Superficial Group (Fig. 418). Brachioradialis. Extensor carpi radialis longus. Extensor carpi radialis brevis. Extensor digitorum communis. Extensor digiti quinti proprius Extensor carpi ulnaris. Anconseus. The Brachioradialis (Supinator longus) is the most superficial muscle on the radial side of the forearm. It arises from the upper two-thirds of the lateral supracondylar ridge of the humerus, and from the lateral intermuscular septum, being limited above by the groove for the radial nerve. Interposed between it and the Brachialis are the radial nerve and the anastomosis between the anterior branch of the profunda artery and the radial recurrent. The fibers end above the middle of the forearm in a flat tendon, which is inserted into the lateral side of the base of the styloid process of the radius. The tendon is crossed near its insertion by the tendons of the Abductor pollicis longus and Extensor pollicis brevis; on its ulnar side is the radial artery. Variations.—Fusion with the Brachialis; tendon of insertion may be divided into two or three slips; insertion partial or complete into the middle of the radius, fasciculi to the tendon of the Biceps, the tuberosity or oblique line of the radius; slips to the Extensor carpi radialis longus or Abductor pollicis longus; absence; rarely doubled. 452 MYOLOGY The Extensor carpi radialis longus (Extensor carpi radialis longior) is placed partly beneath the Brachioradialis. It arises from the lower third of the lateral supracon- dylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the common tendon of origin of the Extensor muscles of the forearm. The fibers end. at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius, beneath the Abductor pollicis longus and Extensor pollicis brevis; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the Extensor carpi radialis brevis, immediately behind the styloid process. It is inserted into the dorsal surface of the base of the second metacarpal bone, on its radial side. The Extensor carpi radialis brevis (Extensor carpi radialis brevior) is shorter and thicker than the preceding muscle, beneath which it is placed. It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles. The fibers end about the middle of the forearm in a flat tendon, which is closely connected with that of the preceding muscle, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, then beneath the dorsal carpal ligament, and is inserted into the dorsal surface of the base of the third metacarpal bone on its radial side. Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis, longus, and separated from it by a faint ridge. The tendons of the two preceding muscles pass through the same compartment of the dorsal carpal ligament in a single mucous sheath. Variations.—Either muscle may split into two or three tendons of insertion to the second and third or even the fourth metacarpal. The two muscles may unite into a single belly with two tendons. Cross slips between the two muscles may occur. The Extensor carpi radialis inter- medins rarely arises as a distinct muscle from the humerus, but is not uncommon as an accessory slip from one or both muscles to the second or third or both metacarpals. The Extensor carpi radialis accessorius is occasionally found arising from the humerus with or below the Extensor carpi radialis longus and inserted into the first metacarpal, the Abductor pollicis brevis, the First dorsal interosseous, or elsewhere. The Extensor digitorum communis arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia. It divides below into four tendons, which pass, together with that of the Extensor indicis proprius, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the second and third phalanges of the fingers in the following manner. Opposite the meta- carpophalangeal articulation each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx and is reinforced, in this situation, by the tendons of the Inter- ossei and Lumbricalis. Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second^phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the Extensor indicis proprius, which lies on its ulnar side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateralward to the second tendon, and the other THE DORSAL ANTIBRACH1AL MUSCLES 453 Medial epicondyle Lateral epicondyle — Extensor carpi radialis brevis Extensor carpi radialis longus Abductor pollicis ~~ longus Ext. pollicis brevis Ext. pollicis _ longus I EXTENSOR “ CARPI ULNARIS Tendon of Ext. indicts Fig. 418.—Posterior surface of the forearm. Superficial muscles. Fig. 419.—Posterior surface of the forearm. Deep muscles. 454 MYOLOGY passing from the same tendon downward and medialward to the fourth. Occa- sionally the first tendon is connected to the second by a thin transverse band. Variations.—An increase or decrease in the number of tendons is common; an additional slip to the thumb is sometimes present. The Extensor digiti quinti proprius (Extensor minimi digiti) is a slender muscle placed on the medial side of the Extensor digitorum communis, with which it is generally connected. It arises from the common Extensor tendon by a thin tendinous slip, from the intermuscular septa between it and the adjacent muscles. Its tendon runs through a compartment of the dorsal carpal ligament behind the distal radio-ulnar joint, then divides into two as it crosses the hand, and finally joins the expansion of the Extensor digitorum communis tendon on the dorsum of the first phalanx of the little finger. Variations.—An additional fibrous slip from the lateral epicondyle; the tendon of insertion may not divide or may send a slip to the ring finger. Absence of muscle rare; fusion of the belly with the Extensor digitorum communis not uncommon. The Extensor carpi ulnaris lies on the ulnar side of the forearm. It arises from the lateral epicondyle of the humerus, by the common tendon; by an aponeu- rosis from the dorsal border of the ulna in common with the Flexor carpi ulnaris and the Flexor digitorum profundus; and from the deep fascia of the forearm. If ends in a tendon, which runs in a groove between the head and the styloid process of the ulna, passing through a separate compartment of the dorsal carpal ligament, and is inserted into the prominent tubercle on the ulnar side of the base of the fifth metacarpal bone. Variations.—Doubling; reduction to tendinous band; insertion partially into fourth metacarpal. In many cases (52 per cent.) a slip is continued from the insertion of the tendon anteriorly over the Opponens digiti quinti, to the fascia covering that muscle, the metacarpal bone, the capsule of the metacarpophalangeal articulation, or the first phalanx of the little finger. This slip may be replaced by a muscular fasciculus arising from or near the pisiform. The Anconseus is a small triangular muscle which is placed on the back of the elbow-joint, and appears to be a continuation of the Triceps brachii. It arises by a separate tendon from the back part of the lateral epicondyle of the humerus; its fibers diverge and are inserted into the side of the olecranon, and upper fourth of the dorsal surface of the body of the ulna. The Deep Group (Fig. 419). Supinator. Abductor pollicis longus. Extensor pollicis brevis'. Extensor pollicis longus. Extensor indicis proprius. The Supinator (Supinator brevis) (Fig. 420) is a broad muscle, curved around the upper third of the radius. It consists of two planes of fibers, between which the deep branch of the radial nerve lies. The two planes arise in common—the superficial one by tendinous and the deeper by muscular fibers—from the lateral epicondyle of the humerus; from the radial collateral ligament of the elbow-joint, and the annular ligament; from the ridge on the ulna, which runs obliquely down- ward from the dorsal end of the radial notch; from the triangular depression below the notch; and from a tendinous expansion which covers the surface of the muscle. The superficial fibers surround the upper part of the radius, and are inserted into the lateral edge of the radial tuberosity and the oblique line of the radius, as low down as the insertion of the Pronator teres. The upper fibers of the deeper plane THE DORSAL ANTIBRACH1AL MUSCLES 455 form a sling-like fasciculus, which encircles the neck of the radius above the tuber- osity and is attached to the back part of its medial surface; the greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces of the body of the radius, midway between the oblique line and the head of the bone. The Abductor pollicis longus (Ex- tensor oss. metacarpi pollicis) lies im- mediately below the Supinator and is sometimes united with it. It arises from the lateral part of the dorsal surface of the body of the ulna below the insertion of the Anco- nseus, from the interosseous mem- brane, and from the middle third of the dorsal surface of the body of the radius. Passing obliquely downward and lateralward, it ends in a tendon, which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the Extensor pollicis brevis, and is inserted into the radial side of the base of the first metacarpal bone. It occasionally gives off two slips near its insertion: one to the greater multangular bone and the other to blend with the origin of the Abduc- tor pollicis brevis. Variations. — More or less doubling of muscle and tendon with insertion of the extra tendon into the first metacarpal, the greater multangular, or into the Abductor pollicis brevis or Opponens pollicis. The Extensor pollicis brevis (.Ex- tensor primi internodii pollicis) lies on the medial side of, and is closely connected with, the Abductor pollicis longus. It arises from the dorsal surface of the body of the radius below that muscle, and from the interosseous membrane. Its direction is similar to that of the Abductor pollicis longus, its tendon passing through the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb. Variations.—Absence; fusion of tendon with that of the Extensor pollicis longus. The Extensor pollicis longus (.Extensor secundi internodii pollicis) is much larger than the preceding muscle, the origin of which it partly covers. It arises from the lateral part of the middle third of the dorsal stirface of the body of the ulna below the origin of the Abductor pollicis longus, and from the interosseous mem- brane. It ends in a tendon, which passes through a separate compartment in the dorsal carpal ligament, lying in a narrow, oblique groove on the back of the lower end of the radius. It then crosses obliquely the tendons of the Extensores carpi radialis longus and brevis, and is separated from the Extensor brevis pollicis by a triangular interval, in which the radial artery is found; and is finally inserted into the base of the last phalanx of the thumb. The radial artery is crossed by the Lateral epicondyle Radial collaterallig. Annular ligament Deep branch of radial nerve Interosseous recurrent art. Deep branch of radial nerve Dorsal interosseous art. Fig. 420.—The Supinator. 456 MYOLOGY tendons of the Abductor pollicis longus and of the Extensores pollicis longus and brevis. The Extensor indicis proprius (Extensor indicis) is a narrow, elongated muscle, placed medial to, and parallel with, the preceding. It arises, from the dorsal sur- face of the body of the ulna below the origin of the Extensor pollicis longus, and from the interosseous membrane. Its tendon passes under the dorsal carpal ligament in the same compartment as that which transmits the tendons of the Extensor digitorum communis, and opposite the head of the second metacarpal bone, joins the ulnar side of the tendon of the Extensor digitorum communis which belongs to the index finger. Variations.—Doubling; the ulnar part may pass beneath the dorsal carpal ligament with the Extensor digitorum communis; a slip from the tendon may pass to the index finger. Nerves.—The Brachioradialis is supplied by the fifth and sixth, the Extensores carpi radialis longus and brevis by the sixth and seventh, and the Anconams by the seventh and eighth cervical nerves, through the radial nerve; 'the remaining muscles are innervated through the deep radial nerve, the Supinator being supplied by the sixth, and all the other muscles by the seventh cervical. Actions.—The muscles of the lateral and dorsal aspects of the forearm, which comprise all the Extensor muscles and the Supinator, act upon the forearm, wrist, and hand; they are the direct antagonists of the Pronator and Flexor muscles. The Anconseus assists the Triceps in extending the forearm. The Brachioradialis is a flexor of the elbow-joint, but only acts as such when the movement of flexion has been initiated by the Biceps brachii and Brachialis. The action of the Supinator is suggested by its name; it assists the Biceps in bringing the hand into the supine position. The Extensor carpi radialis longus extends the wrist and abducts the hand. It may also assist in bending the elbow-joint; at all events it serves to fix or steady this articula- tion. The Extensor carpi radialis brevis extends the wrist, and may also act slightly as an abductor of the hand. The Extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint. The Extensor digitorum communis extends the phalanges, then the wrist, and finally the elbow. It acts prin- cipally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the Interossei and Lumbricales. It tends to separate the fingers as it extends them. The Extensor digiti quinti proprius extends the little finger, and by its continued action assists in extending the wrist. It is owing to this muscle that the little finger can be extended or pointed while the others are flexed. The chief action of the Abductor pollicis longus is to carry the thumb laterally from the palm of the hand. By its continued action it helps to extend and abduct the wrist. The Extensor pollicis brevis extends the proximal phalanx, and the Extensor pollicis longus the terminal phalanx of the thumb; by their continued action they help to extend and abduct the wrist. The Extensor indicis proprius extends the index finger, and by its continued action assists in extending the wrist. VI. THE MUSCLES AND FASCLffi OF THE HAND. The muscles of the hand are subdivided into three groups: (1) those of the thumb, which occupy the radial side and produce the thenar eminence; (2) those of the little finger, which occupy the ulnar side and give rise to the hypothenar eminence; (3) those in the middle of the palm and between the metacarpal bones. Volar Carpal Ligament (ligamentum carpi volare).—The volar carpal ligament is the thickened band of antibrachial fascia which extends from the radius to the ulna over the Flexor tendons as they enter the wrist. Transverse Carpal Ligament (ligamentum carpi transversum; anterior annular ligament) (Figs. 421, 422).—The transverse carpal ligament is a strong, fibrous band, which arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, through which the Flexor tendons of the digits and the median nerve pass. It is attached, medially, to the pisiform and the hamulus of the hamate bone; laterally, to the tuberosity of the navicular, and to the medial part of the volar surface and the ridge of the greater multangular. It is continuous, above, with the volar carpal ligament; and below, with the palmar aponeurosis. It is crossed by the ulnar vessels and nerve, and the cutaneous branches of the median and ulnar nerves. At its lateral end is the tendon of the THE MUSCLES AND FASCIAE OF THE HAND 457 Flexor carpi radialis, which lies in the groove on the greater multangular between the attachments of the ligament to the bone. On its volar surface the tendons of the Palmaris longus and Flexor carpi ulnaris are partly inserted; below, it gives origin to the short muscles of the thumb and little finger Median nerve Flexor dig. sublimis Palmaris longus Flex. poll. long. \ Ulnar artery Flex. carp. rad. Ulnar nerve Flex. carp. uln. Radial artery Abd. poll. long. Ext. poll brev. Flex. dig. profundus. Ext. carp. rad. long. Ext. carp. rad. brev. Ext. poll. long. Distal radio-ulnar artic. Ext. carp. uln. Ext. indicts, prop. Ext. dig. commun. Ext. dig. quinti 'prop. Fig. 421.—Transverse section across distal ends of radius and ulna. The Mucous Sheaths of the Tendons on the Front of the Wrist.—Two sheaths envelop the tendons as they pass beneath the transverse carpal ligament, one for the Flexores digitorum sublimis and profundus, the other for the Flexor pollicis longus (Fig. 423). They extend into the forearm for about 2.5 cm. above the transverse carpal ligament, and occasionally communicate with each other under Flex. 'poll. long. Median nerve Transverse carpal ligament Palmar is longus Flex, carpi rad. Muscles of thumb Flex. dig. sublimis Ulnar art. and nerve Abd. poll. long. Muscles of little finger Ext. poll. brev. „ Ext. carp, rad. long. Flex. dig. profundus / Radial artery Ext. carp. uln. Ext. carp. rad. brev. Ext. dig. quinti prop. Ext. poll, long. Ext. indicis prop. Ext. dig. communis Pig, 422.—Transverse section across the wrist and digits. the ligament. The sheath which surrounds the Flexores digitorum extends down- ward about half-way along the metacarpal bones, where it ends in blind diverticula around the tendons to the index, middle, and ring fingers. It is prolonged on the tendons to the little finger and usually communicates with the mucous 458 MYOLOGY sheath of these tendons. The sheath of the tendon of the Flexor pollicis longus is continued along the thumb as far as the insertion of the tendon. The mucous sheaths enveloping the terminal parts of the tendons of the Flexores digitorum have been described on page 449. Sheaths of terminal parts of Flexores digitorum Muscles of hypo- thenar eminence Muscles of thenar eminence Common sheath of Flexores digitorum sublimis and 'profundus Sheath of Flexor pollicis longus Sheath oj Flexor carpi radialis Flexor carpi ulnaris Fig. 423.—The mucous sheaths of the tendons on the front of the wrist and digits. Dorsal Carpal Ligament (ligamentum carpi dorsale; posterior annular ligament) (Figs. 421, 422).—The dorsal carpal ligament is a strong, fibrous band, extending obliquely downward and medialward across the back of the wrist, and consisting of part of the deep fascia of the back of the forearm, strengthened by the addition of some transverse fibers. It is attached, medially, to the styloid process of the ulna THE MUSCLES AND FASCIAE OF THE HAND 459 and to the triangular and pisiform bones; laterally, to the lateral margin of the radius; and, in its passage across the wrist, to the ridges on the dorsal surface of the radius. Abd. poll. long. Ext. carp. rad. long. Ext. carp. rad. brev. Fig. 424.—The mucous sheaths of the tendons on the back of the wrist. The Mucous Sheaths of the Tendons on the Back of the Wrist.—Between the dorsal carpal ligament and the bones six compartments are formed for the passage of tendons, each compartment having a separate mucous sheath. One is found in each of the following positions (Fig. 424): (1) on the lateral side of the styloid pro- cess, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis; (2) behind the styloid process, for the tendons of the Extensores carpi radialis 460 MYOLOGY longus and brevis; (3) about the middle of the dorsal surface of the radius, for the tendon of the Extensor pollicis longus; (4) to the medial side of the latter, for the tendons of the Extensor digitorum communis and Extensor indicis proprius; (5) opposite the interval between the radius and ulna, for the Extensor digiti quinti proprius; (6) between the head and styloid process of the ulna, for the tendon of the Extensor carpi ulnaris. The sheaths lining these compartments extend from above the dorsal carpal ligament; those for the tendons of Abductor pollicis longus, Extensor brevis pollicis, Extensores carpi radialis, and Extensor carpi ulnaris stop immediately proximal to the bases of the metacarpal bones, while the sheaths for Extensor communis digitorum, Extensor indicis proprius, and Extensor digiti quinti proprius are prolonged to the junction of the proximal and intermediate thirds of the metacarpus. Proper digital artery and nerve Ulnar artery and nerve Fig. 425.—The palmar aponeurosis. Palmar Aponeurosis (aponeurosis palmaris; palmar fascia) (Fig. 425). — The palmar aponeurosis invests the muscles of the palm, and consists of central, lateral, and medial portions. The central portion occupies the middle of the palm, is triangular in shape, and of great strength and thickness. Its apex is continuous with the lower margin of the transverse carpal ligament, and receives the expanded tendon of the Pal- THE LATERAL VOLAR MUSCLES 461 maris longus. Its base divides beiow into four slips, one for each finger. Each slip gives off superficial fibers to the skin of the palm and finger, those to the palm joining the skin at the furrow corresponding to the metacarpophalangeal articula- tions, and those to the fingers passing into the skin at the transverse fold at the bases of the fingers. The deeper part of each slip subdivides into two processes, which are inserted into the fibrous sheaths of the Flexor tendons. From the sides of these processes offsets are attached to the transverse metacarpal ligament. By this arrangement short channels are formed on the front of the heads of the metacarpal bones; through these the Flexor tendons pass. The intervals between the four slips transmit the digital vessels and nerves, and the tendons of the Lum- bricales. At the points of division into the slips mentioned, numerous strong, transverse fasciculi bind the separate processes together. The central part of the palmar aponeurosis is intimately bound to the integument by dense fibroareolar tissue forming the superficial palmar fascia, and gives origin by its medial margin to the Palmaris brevis. It covers the superficial volar arch, the tendons of the Flexor muscles, and the branches of the median and ulnar nerves; and on either side it gives off a septum, which is continuous with the interosseous aponeurosis, and separates the intermediate from the collateral groups of muscles. The lateral and medial portions of the palmar aponeurosis are thin, fibrous layers, which cover, on the radial side, the muscles of the ball of the thumb, and, on the ulnar side, the muscles of the little finger; they are continuous with the central portion and with the fascia on the dorsum of the hand. The Superficial Transverse Ligament of the Fingers is a thin band of transverse fasciculi (Fig. 425); it stretches across the roots of the four fingers, and is closely attached to the skin of the clefts, and medially to the fifth metacarpal bone, forming a sort of rudimentary web. Beneath it the digital vessels and nerves pass to their destinations. 1. The Lateral Volar Muscles (Figs. 426, 427) Abductor pollicis brevis. Opponens pollicis. Flexor pollicis brevis. Adductor pollicis (obliquus). Adductor pollicis (transversus). The Abductor pollicis brevis (.Abductor pollicis) is a thin, flat muscle, placed immediately beneath the integument. It arises from the transverse carpal liga- ment, the tuberosity of the navicular, and the ridge of the greater multangular, frequently by two distinct slips. Running lateralward and downward, it is inserted by a thin, flat tendon into the radial side of the base of the first phalanx of the thumb and the capsule of the metacarpophalangeal articulation. The Opponens pollicis is a small, triangular muscle, placed beneath the pre- ceding. It arises from the ridge on the greater multangular and from the trans- verse carpal ligament, passes downward and lateralward, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side. The Flexor pollicis brevis consists of two portions, lateral and medial. The lateral and more superficial portion arises from the lower border of the transverse carpal ligament and the lower part of the ridge on the greater multangular bone; it passes along the radial side of the tendon of the Flexor pollicis longus, and, becoming tendinous, is inserted into the radial side of the base of the first phalanx of the thumb; in its tendon of insertion there is a sesamoid bone. Ihe medial and deeper portion of the muscle is very small, and arises from the ulnar side of the first metacarpal bone between the Adductor pollicis (obliquus) and the lateral head of the first Interosseous dorsalis, and is inserted into the ulnar side of the base of the first phalanx with the Adductor pollicis (obliquus). The medial part of the Flexor brevis pollicis is sometimes described as the first Interosseous volaris. 462 MYOLOGY The Adductor pollicis (obliquus) (Adductor obliquus pollicis) arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the Flexor carpi radialis. From this origin the greater number of fibers pass obliquely downward and con- verge to a tendon, which, uniting with the tendons of the medial portion of the Flexor pollicis brevis and the transverse part of the Adductor, is inserted into the ulnar side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon. A considerable fasciculus, however, passes more obliquely beneath the tendon of the Flexor pollicis longus to join the lateral portion of the Flexor brevis and the Abductor pollicis brevis. - Pisometacarpal lig. Fig. 426.—The muscles of the thumb. The Adductor pollicis (transversus) (Adductor transversus pollicis) (Fig. 426) is the most deeply seated of this group of muscles. It is of a triangular form arising by a broad base from the lower two-thirds of the volar surface of the third metacarpal bone; the fibers converge, to be inserted with the medial part of the Flexor pollicis brevis and the Adductor pollicis (obliquus) into the ulnar side of the base of the first phalanx of the thumb. Variations.—The Abductor pollicis brevis is often divided into an outer and an inner part; accessory slips from the tendon of the Abductor pollicis longus or Palmaris longus, more rarely from the Extensor carpi radialis longus, from the styloid process or Opponens pollicis or from the skin over the thenar eminence. The deep head of the Flexor pollicis brevis may be absent or enlarged. The two adductors vary in their relative extent and in the closeness of their connection. The Adductor obliquus may receive a slip from the transverse metacarpal ligament. Nerves.—The Abductor brevis, Opponens, and lateral head of the Flexor pollicis brevis are supplied by the sixth and seventh cervical nerves through the median nerve; the medial head of the Flexor brevis, and the Adductor, by the eighth cervical through the ulnar nerve. Actions.—The Abductor pollicis brevis draws the thumb forward in a plane at right angles to that of the palm of the hand. The Abductor pollicis is the opponent of this muscle, and approxi- mates the thumb to the palm. The Opponens pollicis flexes the metacarpal bone, i. e., draws it medialward over the palm; the Flexor pollicis brevis flexes and adducts the proximal phalanx. 2. The Medial Volar Muscles (Figs. 426, 427). Palmaris brevis. Abductor digiti quinti. Flexor digiti quinti brevis. Opponens digiti quinti. THE MEDIAL VOLAR MUSCLES 463 The Palmaris brevis is a thin, quadrilateral muscle, placed beneath the integu- ment of the ulnar side of the hand. It arises by tendinous fasciculi from the transverse carpal ligament and palmar aponeurosis; the fleshy fibers are inserted into the skin on the ulnar border of the palm of the hand. Fig. 427.—The muscles of the left hand. Palmar surface. The Abductor digiti quinti (Abductor minimi digiti) is situated on the ulnar border of the palm of the hand. It arises from the pisiform bone and from the tendon of the Flexor carpi ulnaris, and ends in a flat tendon, which divides into two slips; one is inserted into the ulnar side of the base of the first phalanx of the little finger; the other into the ulnar border of the aponeurosis of the Extensor digiti quinti proprius. 464 MYOLOGY The Flexor digiti quinti brevis (Flexor brevis minimi digiti) lies on the same plane as the preceding muscle, on its radial side. It arises from the convex surface of the hamulus of the hamate bone, and the volar surface of the transverse carpal ligament, and is inserted into the ulnar side of the base of the first phalanx of the little finger. It is separated from the Abductor, at its origin, by the deep branches of the ulnar artery and nerve. This muscle is sometimes wanting; the Abductor is then, usually, of large size. The Opponens digiti quinti (Opponens minimi digiti) (Fig. 426) is of a tri- angular form, and placed immediately beneath the preceding muscles. It arises from the convexity of the hamulus of the hamate bone, and contiguous portion of the transverse carpal ligament; it is inserted into the whole length of the meta- carpal bone of the little finger, along its ulnar margin. Variations.—The Palmaris brevis varies greatly in size. The Abductor digiti quinti may be divided into two or three slips or united with the Flexor digiti quinti brevis. Accessory head from the tendon of the Flexor carpi ulnaris, the transverse carpal ligament, the fascia of the forearm or the tendon of the Palmaris longus. A portion of the muscle may insert into the metacarpal, or separate slips the Pisimetacarpus, Pisiuncinatus or the Pisiannularis muscle may exist. Nerves.—All the muscles of this group are supplied by the eighth cervical nerve through the ulnar nerve. Actions.—The Abductor and Flexor digiti quinti brevis abduct the little finger from the ring finger and assist in flexing the proximal phalanx. The Opponens digiti quinti draws forward the fifth metacarpal bone, so as to deepen the hollow of the palm. The Palmaris brevis corrugates the skin on the ulnar side of the palm. 3. The Intermediate Muscles. Lumbricales Interossei. The Lumbricales (Fig. 427) are four small fleshy fasciculi, associated with the tendons of the Flexor digitorum profundus. The first and second arise from the radial sides and volar surfaces of the tendons of the index and middle fingers respectively; the third, from the contiguous sides of the tendons of the middle and ring fingers; and the fourth, from the contiguous sides of the tendons of the ring and little fingers. Each passes to the radial side of the corresponding finger, and opposite the metacarpophalangeal articulation is inserted into the tendinous expansion of the Extensor digitorum communis covering the dorsal aspect of the finger. Variations.—The Lumbricales vary in number from two to five or six and there is considerable variation in insertions. The Interossei (Figs. 428, 429) are so named from occupying the intervals between the metacarpal bones, and are divided into two sets, a dorsal and a volar. The Interossei dorsales (Dorsal interossei) are four in number, and occupy the intervals between the metacarpal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metacarpal bones, but more exten- sively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the first phalanges and into the aponeuroses of the tendons of the Extensor digitorum communis. Between the double origin of each of these muscles is a narrow triangular interval; through the first of these the radial artery passes; through each of the other three a perforating branch from the deep volar arch is transmitted. The first or Abductor indicis is larger than the others. It is flat, triangular in form, and arises by two heads, separated by a fibrous arch for the passage of the radial artery from the dorsum to the palm of the hand. The lateral head arises from the proximal half of the ulnar border of the first metacarpal bone; the medial head, from almost the entire length of the radial border of the second metacarpal bone; the tendon is inserted into the radial side of the index finger. The second THE MUSCLES AND F ASCI HI OF THE LOWER EXTREMITY 465 and third are inserted into the middle finger, the former into its radial, the latter into its ulnar side. The fourth is inserted into the ulnar side of the ring finger. The Interossei volares (Palmar interossei), three in number, are smaller than' the Interossei dorsales, and placed upon the volar surfaces of the metacarpal bones, rather than between them. Each arises from the entire length of the metacarpal bone of one finger, and is inserted into the side of the base of the first phalanx and aponeurotic expansion of the Extensor communis tendon to the same finger. The first arises from the ulnar side of the second metacarpal bone, and is inserted into the same side of the first phalanx of the index finger. The second arises from the radial side of the fourth metacarpal bone, and is inserted into the same side of the ring finger. The third arises from the radial side of the fifth metacarpal bone, and is inserted into the same side of the little finger. From this account it may be seen that each finger is provided with two Interossei, with the exception of the little finger, in which the Abductor takes the place of one of the pair. As already mentioned (p. 461), the medial head of the Flexor pollicis brevis is sometimes described as the Interosseus volaris primus. Fig. 428.—The Interossei dorsales of left hand. Fig. 429.—The Interossei volares of left hand. Nerves.—The two lateral Lumbricales are supplied by the sixth and seventh cervical nerves, through the third and fourth digital branches of the median nerve; the two medial Lumbricales and all the Interossei are supplied by the eighth cervical nerve, through the deep palmar branch of the ulnar nerve. The third Lumbricalis frequently receives a twig from the median. Actions.—The Interossei volares adduct the fingers to an imaginary line drawn longitudinally through the center of the middle finger; and the Interossei dorsales abduct the fingers from that line. In addition to this the Interossei, in conjunction with the Lumbricales, flex the first phalanges at the metacarpophalangeal joints, and extend the second and third phalanges in consequence of their insertions into the expansions of the Extensor tendons, the Extensor digitorum communis is believed to act almost entirely on the first phalanges. THE MUSCLES AND FASCLE OF THE LOWER EXTREMITY. The muscles of the lower extremity are subdivided into groups corresponding with the different regions of the limb. I. Muscles of the Iliac Region. II. Muscles of the Thigh. III. Muscles of the Leg. IV. Muscles of the Foot. 466 MYOLOGY I. THE MUSCLES AND FASCLffi OF THE ILIAC REGION (Fig. 430). Psoas major. Psoas minor. Iliacus. The Fascia Covering the Psoas and Iliacus is thin above, and becomes gradually thicker below as it approaches the inguinal ligament. The portion covering the Psoas is thickened above to form the medial lumbocostal arch, which stretches from the transverse process of the first lumbar vertebra to the body of the second. Medially, it is attached by a series of arched processes to the intervertebral fibro- cartilages, and prominent margins of the bodies of the vertebrae, and to the upper part of the sacrum; the intervals left, opposite the con- stricted portions of the bodies, transmit the lumbar arteries and veins and filaments of the sympathetic trunk. Laterally, above the crest of the ilium, it is continuous with the fascia covering the front of the Quadratus lumborum (see page 419), while below the crest of the ilium it is continuous with the fascia covering the Iliacus. The portions investing the Iliacus (fascia iliaca; iliac fascia) is connected, laterally to the whole length of the inner lip of the iliac crest; and medially, to the linea terminalis of the lesser pelvis, where it is continuous with the peri- osteum. At the iliopectineal eminence it re- ceives the tendon of insertion of the Psoas minor, when that muscle exists. Lateral to the femoral vessels it is intimately connected to the posterior margin of the inguinal ligament, and is continuous with the transversalis fascia. Immediately lateral to the femoral vessels the iliac fascia is prolonged backward and medial- ward from the inguinal ligament as a band, the iliopectineal fascia, which is attached to the iliopectineal eminence. This fascia divides the space between the inguinal ligament and the hip bone into two lacunae or compart- ments, the medial of which transmits the femoral vessels, the lateral the Psoas major and Iliacus and the femoral nerve. Medial to the vessels the iliac fascia is attached to the pectineal line behind the inguinal apo- neurotic falx, where it is again continuous with the transversalis fascia. On the thigh the fasciae of the Iliacus and Psoas form a single sheet termed the iliopectineal fascia. Where the external iliac vessels pass into the thigh, the fascia descends behind them, forming the pos- terior wall of the femoral sheath. The portion of the iliopectineal fascia which passes behind Fig. 430—Muscles of the iliac and anterior femoral regions. THE ANTERIOR FEMORAL MUSCLES 467 the femoral vessels is also attached to the pectineal line beyond the limits of the attachment of the inguinal aponeurotic falx; at this part it is continuous with the pectineal fascia. The external iliac vessels lie in front of the iliac fascia, but all the branches of the lumbar plexus are behind it; it is separated from the peri- toneum by a quantity of loose areolar tissue. The Psoas major (Psoas magnus) (Fig. 430) is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It arises (1) from the anterior surfaces of the bases and lower borders of the transverse processes of all the lumbar vertebrae; (2) from the sides of the bodies and the corre- sponding intervertebral fibrocartilages of the last thoracic and all the lumbar verte- brae by five slips, each of which is attached to the adjacent upper and lower margins of two vertebrae, and to the intervertebral fibrocartilage; (3) from a series of tendinous arches which extend across the constricted parts of the bodies of the lumbar vertebrae between the previous slips; the lumbar arteries and veins, and filaments from the sympathetic trunk pass beneath these tendinous arches. The muscle proceeds downward across the brim of the lesser pelvis, and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip-joint and ends in a tendon; the tendon receives nearly the whole of the fibers of the Iliacus and is inserted into the lesser trochanter of the femur. A large bursa which may communicate with the cavity of the hip-joint, separates the tendon from the pubis and the capsule of the joint. The Psoas minor (Psoas parvus) is a long slender muscle, placed in front of the Psoas major. It arises from the sides of the bodies of the twelfth thoracic and first lumbar vertebrae and from the fibrocartilage between them. It ends in a long flat tendon which is inserted into the pectineal line and iliopectineal eminence, and, by its lateral border, into the iliac fascia. This muscle is often absent. The Iliacus is a flat, triangular muscle, which fills the iliac fossa. It arises from the upper twTo-thirds of this fossa, and from the inner lip of the iliac crest; behind, from the anterior sacroiliac and the iliolumbar ligaments, and base of the sacrum; in front, it reaches as far as the anterior superior and anterior inferior iliac spines, and the notch between them. The fibers converge to be inserted into the lateral side of the tendon of the Psoas major, some of them being prolonged on to the body of the femur for about 2.5 cm. below and in front of the lesser trochanter.1 Variations.—The Iliacus minor or Iliocapsularis, a small detached part of the Iliacus is frequently present. It arises from the anterior inferior spine of the ilium and is inserted into the lower part of the intertrochanteric line of the femur or into the iliofemoral ligament. Nerves.—The Psoas major is supplied by branches of the second and third lumbar nerve; the Psoas minor by a branch of the first lumbar nerve; and the Iliacus by branches of the second and third lumbar nerves through the femoral nerve. Actions.—The Psoas major, acting from above, flexes the thigh upon the pelvis, being assisted by the Iliacus; acting from below, with the femur fixed, it bends the lumbar portion of the verte- bral column forward and to its own side, and then, in conjunction with the Iliacus, tilts the pelvis forward. When the muscles of both sides are acting from below, they serve to maintain the erect posture by supporting the vertebral column and pelvis upon the femora, or in continued action bend the trunk and pelvis forward, as in raising the trunk from the recumbent posture. The Psoas minor is a tensor of the iliac fascia. II. THE MUSCLES AND FASCIAE OF THE THIGH. 1. The Anterior Femoral Muscles (Fig. 430). Rectus femoris. Vastus lateralis. Vastus medialis. Vastus intermedius. 0 , . bartorius. Quadriceps femoris. Articularis genu. 1 The Psoas major and iliacus are sometimes regarded as a single muscle named the Iliopsoas. 468 MYOLOGY Superficial Fascia.—The superficial fascia forms a continuous layer over the whole of the thigh; it consists of areolar tissue containing in its meshes much fat, and may be separated into two or more layers, between which are found the superficial vessels and nerves. It varies in thickness in different parts of the limb; in the groin it is thick, and the two layers are separated from one another by the superficial inguinal lymph glands, the great saphenous vein, and several smaller vessels. The superficial layer is continuous above with the superficial fascia of the abdomen. The deep layer of the superficial fascia is a very thin, fibrous stratum, best marked on the medial side of the great saphenous vein and below the inguinal ligament. It is placed beneath the subcutaneous vessels and nerves and upon the surface of the fascia lata. It is intimately adherent to the fascia lata a little below the inguinal ligament. It covers the fossa ovalis (saphenous opening), being closely united to its circumference, and is connected to the sheath of the femoral vessels. The portion of fascia covering this fossa is perforated by the great saphenous vein and by numerous blood and lymphatic vessels, hence it has been termed the fascia cribrosa, the openings for these vessels having been likened to the holes in a sieve. A large subcutaneous bursa is found in the superficial fascia over the patella. Deep Fascia.—The deep fascia of the thigh is named, from its great extent, the fascia lata; it constitutes an investment for the whole of this region of the limb, but varies in thickness in different parts. Thus, it is thicker in the upper and lateral part of the thigh, where it receives a fibrous expansion from the Glutseus maximus, and where the Tensor fascise lata1 is inserted between its layers; it is very thin behind and at the upper and medial part, where it covers the Adductor muscles, and again becomes stronger around the knee, receiving fibrous expansions from the tendon of the Biceps femoris laterally, from* the Sartorius medially, and from the Quadriceps femoris in front. The fascia lata is attached, above and behind, to the back of the sacrum and coccyx; laterally, to the iliac crest; in front, to the inguinal ligament, and to the superior ramus of the pubis; and medially, to the inferior ramus of the pubis, to the inferior ramus and tuberosity of the ischium, and to the lower border of the sacrotuberous ligament. From its attachment to the iliac crest it passes down over the Glutseus medius to the upper border of the Glutseus maximus, where it splits into two layers, one passing superficial to and the other beneath this muscle; at the lower border of the muscle the two layers reunite. Laterally, the fascia lata receives the greater part of the tendon of insertion of the Glutseus maximus, and becomes proportionately thickened. The portion of the fascia lata attached to the front part of the iliac crest, and corresponding to the origin of the Tensor fasciae latse, extends down the lateral side of the thigh as two layers, one superficial to and the other beneath this muscle; at the lower end of the muscle these two layers unite and form a strong band, having first received the insertion of the muscle. This band is continued downward, under the name of the iliotibial band (tractus iliotibialis) and is attached to the lateral condyle of the tibia. The part of the iliotibial band which lies beneath the Tensor fasciae latse is prolonged upward to join the lateral part of the capsule of the hip-joint. Below, the fasciae lata is attached to all the prominent points around the knee- joint, viz., the condyles of the femur and tibia, and the head of the fibula. On either side of the patella it is strengthened by transverse fibers from the lower parts of the Vasti, which are attached to and support this bone. Of these the lateral are the stronger, and are continuous with the iliotibial band. The deep surface of the fascia lata gives off two strong intermuscular septa, which are attached to the whole length of the linea aspera and its prolongations above and below; the lateral and stronger one, which extends from the insertion of the Glutseus maximus to the lateral condyle, separates the Vastus lateralis in front from the short head of the Biceps femoris behind, and gives partial origin to these mus- cles; the medial and thinner one separates the Vastus medialis from the Adduc- THE ANTERIOR FEMORAL MUSCLES 469 tores and Pectineus. Besides these there are numerous smaller septa, separating the individual muscles, and enclosing each in a distinct sheath. The Fossa Ovalis (saphenous opening) (Fig. 431).—At the upper and medial part of the thigh, a little below the medial end of the inguinal ligament, is a large oval-shaped aperture in the fascia lata; it transmits the great saphenous vein, and other, smaller vessels, and is termed the fossa ovalis. The fascia cribrosa, which is pierced by the structures passing through the opening, closes the aperture and must be removed to expose it. The fascia lata in this part of the thigh is described as consisting of a superficial and a deep portion. Fig. 431.—The fossa ovalis. The superficial portion of the fascia lata is the part on the lateral side of the fossa ovalis. It is attached, laterally, to the crest and anterior superior spine of the ilium, to the whole length of the inguinal ligament, and to the pectineal line in con- junction with the lacunar ligament. From the tubercle of the pubis it is reflected downward and lateralwrard, as an arched margin, the falciform margin, forming the lateral boundary of the fossa ovalis; this margin overlies and is adherent to the anterior layer of the sheath of the femoral vessels: to its edge is attached the fascia cribrosa. The upward and medial prolongation of the falciform margin is named the superior cornu; its downward and medial prolongation, the inferior cornu. The latter is well-defined, and is continuous behind the great saphenous vein with the pectineal fascia* The deep portion is situated on the medial side of the fossa ovalis, and at the lower margin of the fossa is continuous with the superficial portion; traced upward, 470 MYOLOGY it covers the Pectineus, Adductor longus, and Gracilis, and, passing behind the sheath of the femoral vessels, to which it is closely united, is continuous with the iliopectineal fascia, and is attached to the pectineal line. From this description it may be observed that the superficial portion of the fascia lata lies in front of the femoral vessels, and the deep portion behind them, so that an apparent aperture exists between the two, through which the great saphenous passes to join the femoral vein. The Sartorius, the longest muscle in the body, is narrow and ribbon-like; it arises by tendinous fibers from the anterior superior iliac spine and the upper half of the notch below it. It passes obliquely across the upper and anterior part of the thigh, from the lateral to the medial side of the limb, then descends vertically, as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon. This curves obliquely forward and expands into a broad apon- eurosis, which is inserted, in front of the Gracilis and Semitendinous, into the upper part of the medial surface of the body of the tibia, nearly as far forward as the anterior crest. The upper part of the aponeurosis is curved backward over the upper edge of the tendon of the Gracilis so as to be inserted behind it. An offset, from its upper margin, blends with the capsule of the knee-joint, and another from its lower border, with the fascia on the medial side of the leg. Variations.—Slips of origin from the outer end of the inguinal ligament, the notch of the ilium, the ilio-pectineal line or the pubis occur. The muscle may be split into two parts, and one part may be inserted into the fascia lata, the femur, the ligament of the patella or the tendon of the Semitendinosus. The tendon of insertion may end in the fascia lata, the capsule of the knee- joint, or the fascia of the leg. The muscle may be absent. The Quadriceps femoris (Quadriceps extensor) includes the four remaining muscles on the front of the thigh. It is the great extensor muscle of the leg, forming a large fleshy mass which covers the front and sides of the femur. It is subdivided into separate portions, which have received distinctive names. One occupying the middle of the thigh, and connected above with the ilium, is called from its straight course the Rectus femoris. The other three lie in immediate connection with the body of the femur, which they cover from the trochanters to the condyles. The portion on the lateral side of the femur is termed the Vastus lateralis; that covering the medial side, the Vastus medialis; and that in front, the Vastus intermedius. The Rectus femoris is situated in the middle of the front of the thigh; it is fusi- form in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis. It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, fro.m a groove above the brim of the acetabulum. The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular fibers arise. The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flat- tened tendon, is inserted into the base of the patella. The Vastus lateralis (Vastus externus) is the largest part of the Quadriceps femoris. It arises by a broad aponeurosis, which is attached to the upper part of the intertrochanteric line, to the anterior and inferior borders of the greater tro- chanter, to the lateral lip of the gluteal tuberosity, and to the upper half of the lateral lip of the linea aspera; this aponeurosis covers the upper three-fourths of the muscle, and from its deep surface many fibers take origin. A few additional fibers arise from the tendon of the Glutaeus maximus, and from the lateral inter- muscular septum between the Vastus lateralis and short head of the Biceps femoris. The fibers form a large fleshy mass, which is attached to a strong aponeurosis, placed on the deep surface of the lower part of the muscle: this aponeurosis becomes THE MEDIAL FEMORAL MUSCLES 471 contracted and thickened into a flat tendon inserted into the lateral border of the patella, blending with the Quadriceps femoris tendon, and giving an expansion to the capsule of the knee-joint. The Vastus medialis and Vastus intermedius appear to be inseparably united, but when the Rectus femoris has been reflected a narrow interval will be observed extending upward from the medial border of the patella between the two muscles, and the separation may be continued as far as the lower part of the intertrochan- teric line, where, however, the two muscles are frequently continuous. The Vastus medialis ('Vastus interims) arises from the lower half of the inter- trochanteric line, the medial lip of the linea aspera, the upper part of the medial supracondylar line, the tendons of the Adductor longus and the Adductor magnus and the medial intermuscular septum. Its fibers are directed downward and for- ward, and are chiefly attached to an aponeurosis which lies on the deep surface of the muscle and is inserted into the medial border of the patella and the Quad- riceps femoris tendon, an expansion being sent to the capsule of the knee-joint. The Vastus intermedius (Crureus) arises from the front and lateral surfaces of the body of the femur in its upper two-thirds and from the lower part of the lateral intermuscular septum. Its fibers end in a superficial aponeurosis, which forms the deep part of the Quadriceps femoris tendon. The tendons of the different portions of the Quadriceps unite at the lower part of the thigh, so as to form a single strong tendon, which is inserted into the base of the patella, some few fibers passing over it to blend with the ligamentum patellae. More properly, the patella may be regarded as a sesamoid bone, developed in the tendon of the Quadriceps; and the ligamentum patellae, which is continued from the apex of the patella to the tuberosity of the tibia, as the proper tendon of insertion of the muscle, the medial and lateral patellar retinacula (see p. 338) being expan- sions from its borders. A bursa, which usually communicates with the cavity of the knee-joint, is situated between the femur and the portion of the Quadriceps tendon above the patella; another is interposed between the tendon and the upper part of the front of the tibia; and a third, the prepatellar bursa, is placed over the patella itself. The Articularis genu (Subcrureus) is a small muscle, usually distinct from the Vastus intermedius, but occasionally blended with it; it arises from the anterior surface of the lower part of the body of the femur, and is inserted into the upper part of the synovial membrane of the knee-joint. It sometimes consists of several separate muscular bundles. Nerves.—The muscles of this region are supplied by the second, third, and fourth lumbar nerves, through the femoral nerve. Actions.—The Sartorius flexes the leg upon the thigh, and, continuing to act, flexes the thigh upon the pelvis; it next abducts and rotates the thigh outward. When the knee is bent, the Sartorius assists the Semitendinosus, Semimembranosus, and Popliteus in rotating the tibia inward. Taking its fixed point from the leg, it flexes the pelvis upon the thigh, and, if one muscle acts, assists in rotating the pelvis. The Quadriceps femoris extends the leg upon the thigh. The Rectus femoris assists the Psoas major and Iliacus in supporting the pelvis and trunk upon the femur. It also assists in flexing the thigh on the pelvis, or if the thigh be fixed it will flex the pelvis. The Vastus medialis draws the patella medialward as well as upward. 2. The Medial Femoral Muscles. Gracilis. Pectineus. Adductor longus. Adductor brevis. Adductor magnus. The Gracilis (Fig. 430) is the most superficial muscle on the medial side of the thigh. It is thin and flattened, broad above, narrow and tapering below\ It arises by a thin aponeurosis from the anterior margins of the lower half of the symphysis pubis and the upper half of the pubic arch. The fibers run vertically downward, and end in a rounded tendon, which passes behind the medial condyle of the femur, curves around the medial condyle of the tibia, where it becomes flat- 472 MYOLOGY tened, and is inserted into the upper part of the medial surface of the body of the tibia, below the condyle. A few of the fibers of the lower part of the tendon are prolonged into the deep fascia of the leg. At its insertion the tendon is situated immediately above that of the Semitendinosus, and its upper edge is overlapped by the tendon of the Sartorius, with which it is in part blended. It is separated from the tibial collateral ligament of the knee-joint, by a bursa common to it and the tendon of the Semitendinosus. Rectus femoris M. Femur Deep femoral artery and vein Vastus intermedins M.’u Linea aspera Sartorius M. .Saphenous nerve Femoral vein and artery Intermediate ■ cutaneous nerve Great saphenous vein Adductor longus M. ’Gracilis M. Intermuscular septum of median femoral Vastus lateralis M. .Perforating artery and vein Intermuscular septum of lateral femoral • Semimembranosus M ■ Biceps femoris M. [caput breve] i Ischiadic N. Posterior femoral cutaneous nerve '• Semitendinosus M. Biceps femoris M. [caput longum] Adductor magnus M. Fig. 432.—Cross-section through the middle of the thigh. (Eycleshymer and Schoemaker.) The Pectineus (Fig. 430) is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh. It arises from the pectineal line, and to a slight extent from the surface of bone in front of it, between the iliopectineal eminence and tubercle of the pubis, and from the fascia covering the anterior surface of the muscle; the fibers pass downward, backward, and lateral- ward, to be inserted into a rough line leading from the lesser trochanter to the linea aspera. The Adductor longus (Fig. 433), the most superficial of the three Adductores, is a triangular muscle, lying in the same plane as the Pectineus. It arises by a flat, narrow tendon, from the front of the pubis, at the angle of junction of the crest THE MEDIAL FEMORAL MUSCLES 473 with the symphysis; and soon expands into a broad fleshy belly. This passes downward, backward, and lateralward, and is inserted, by an aponeurosis, into the linea aspera, between the Vastus medialis and the Adductor magnus, with both of which it is usually blended. The Adductor brevis (Fig. 433) is situ- ated immediately behind the two preceding muscles. It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the Gracilis and Obturator externus. Its fibers, passing backward, lateralward, and downward, are inserted, by an aponeurosis, into the line leading from the lesser trochanter to the linea aspera and into the upper part of the linea aspera, immediately behind the Pectin- eus and upper part of the Adductor longus. The Adductor magnus (Fig. 433) is a large triangular muscle, situated on the medial side of the thigh. It arises from a small part of the inferior ramus of the pubis, from the inferior ramus of the ischium, and from the outer margin of the inferior part of the tuberosity of the ischium. Those fibers which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line leading from the greater trochanter to the linea aspera, medial to the Gluteus maximus; those from the ramus of the ischium are directed downward and lat- eralward w ith different degrees of obliquity, to be inserted, by means of a broad aponeu- rosis, into the linea aspera and the upper part of its medial prolongation below. The medial portion of the muscle, composed principally of the fibers arising from the tuberosity of the ischium, forms a thick fleshy mass consisting of coarse bundles which descend almost vertically, and end about the lower third of the thigh in a rounded tendon which is inserted into the adductor tubercle on the medial condyle of the femur, and is connected by a fibrous expansion to the line leading upward from the tubercle to the linea aspera. At the insertion of the muscle, there is a series of osseoaponeurotic openings, formed by tendi- nous arches attached to the bone. The upper four openings are small, and give passage to the perforating branches of the profunda femoris artery. The lowest is of large size, and transmits the femoral vessels to the popliteal fossa. Adductor tubercle Fig. 433.—Deep muscles of the medial femoral region. 474 MYOLOGY Variations.—The Pectineus is sometimes divided into an outer part supplied by the femoral nerve and an inner part supplied by the obturator nerve. The muscle may be attached to or inserted into the capsule of the hip-joint. The Adductor longus may be double, may extend to the knee, or be more or less united with the Pectineus. The Adductor brevis may be divided into two or three parts, or it may be united to the Adductor magnus. The Adductor magnus may be more or less segmented, the anterior and superior portion is often described as a separate muscle, the Adductor minimus. The muscle may be fused with the Quadratus femoris. Nerves.—The three Adductores and the Gracilis are supplied by the third and fourth lumbar nerves through the obturator nerve; the Adductor magnus receiving an additional branch from the sacral plexus through the sciatic. The Pectineus is supplied by the second, third, and fourth lumbar nerves through the femoral nerve, and by the third lumbar through the accessory obturator when this latter exists. Occasionally it receives a branch from the obturator nerve.1 Actions.—The Pectineus and three Adductores adduct the thigh powerfully; they are especially used in horse exercise, the sides of the saddle being grasped between the knees by the contraction of these muscles. In consequence of the obliquity of their insertions into the linea aspera, they rotate the thigh outward, assisting the external Rotators, and when the limb has been abducted, they draw it medialward, carrying the thigh across that of the opposite side. The Pectineus and Adductores brevis and longus assist the Psoas major and Iliacus in flexing the thigh upon the pelvis. In progression, all these muscles assist in drawing forward the lower limb. The Gracilis assists the Sartorius in flexing the leg and rotating it inward; it is also an adductor of the thigh. If the lower extremities be fixed, these muscles, taking their fixed points below, may act upon the pelvis, serving to maintain the body in an erect posture; or, if their action be continued, flex the pelvis forward upon the femur. 3. The Muscles of the Gluteal Region (Fig. 434). Glutseus maximus. Glutseus medius. Glutseus minimus. Tensor fa seise latse. Piriformis. Obturator internus. Gemellus superior. Gemellus inferior. Quadratus femoris. Obturator externus. The Glutseus maximus, the most superficial muscle in the gluteal region, is a broad and thick fleshy mass of a quadrilateral shape, and forms the prominence of the nates. Its large size is one of the most characteristic features of the muscular system in man, connected as it is with the power he has of maintaining the trunk in the erect posture. The muscle is remarkably coarse in structure, being made up of fasciculi lying parallel with one another and collected together into large bundles separated by fibrous septa. It arises from the posterior gluteal line of the ilium, and the rough portion of bone including the crest, immediately above and behind it; from the posterior surface of the lower part of the sacrum and the side of the coccyx; from the aponeurosis of the Sacrospinalis, the sacrotuberous ligament, and the fascia (gluteal aponeurosis) covering the Glutseus medius. The fibers are directed obliquely downward and lateralward; those forming the upper and larger portion of the muscle, together with the superficial fibers of the lower portion, end in a thick tendinous lamina, which passes across the greater trochanter, and is inserted into the iliotibial band of the fascia lata; the deeper fibers of the lower portion of the muscle are inserted into the gluteal tuberosity between the Vastus lateralis and Adductor magnus. Bursae.—Three bursae are usually found in relation with the deep surface of this muscle. One of these, of large size, and generally multilocular, separates it from the greater trochanter; a second, often wanting, is situated on the tuberosity of the ischium; a third is found between the tendon of the muscle and that of the Vastus lateralis. The Glutseus medius is a broad, thick, radiating muscle, situated on the outer surface of the pelvis. Its posterior third is covered by the Glutseus maximus, its 1 The Pectineus may consist of two incompletely separated strata; the lateral or dorsal stratum, which is constant, is supplied by a branch from the femoral nerve, or in the absence of this branch by the accessory obturator nerve, the medial or ventral stratum, when present, is supplied by the obturator nerve.—A. M. Paterson. Journal of Anatomy and Physiology, xxvi, 43. THE MUSCLES OF THE GLUTEAL REGION 475 anterior two-thirds by the gluteal aponeurosis, which separates it from the superficial fascia and integument. It arises from the outer surface of the ilium between the iliac crest and posterior glu- teal line above, and the anterior gluteal line below; it also arises from the gluteal aponeurosis covering its outer surface. The fibers converge to a strong flat- tened tendon, which is inserted into the oblique ridge which runs downward and forward on the lateral surface of the greater tro- chanter. A bursa separates the tendon of the muscle from’ the surface of the trochanter over which it glides. Variations. — The posterior border may be more or less closely united to the Piriformis, or some of the fibers end on its tendon. The Glutaeus minimus, the small- est of the three Glutsei, is placed immediately beneath the preced- ing. It is fan-shaped, arising from the outer surface of the ilium, between the anterior and inferior gluteal lines, and behind, from the margin of the greater sciatic notch. The fibers converge to the deep surface of a radiated aponeurosis, and this ends in a tendon which is inserted into an impression on the anterior border of the greater trochanter, and gives an expansion to the capsule of the hip-joint. A bursa is interposed between the tendon and the greater trochanter. Be- tween the Glutseus medius and Glutseus minimus are the deep branches of the superior gluteal vessels and the superior gluteal nerve. The deep surface of the Glutseus minimus is in relation with the reflected tendon of the Rectus femoris and the capsule of the hip-joint. Variations.—The muscle may be di- vided into an anterior and a posterior part, or it may send slips to the Piri- formis, the Gemellus superior or the outer part of the origin of the Vastus lateralis. Medial hamstring tendons Lateral hamstring tendon Sartorius Gracilis Biceps femoris Semitendinosus Semi- membranosus Fig. 434.—Muscles of the gluteal and posterior femoral regions. 476 MYOLOGY The Tensor fasciae latse (Tensor fascioe femoris) arises from the anterior part of the outer lip of the iliac crest; from the outer surface of the anterior superior iliac spine, and part of the outer border of the notch below it, between the Glutseus medius and Sartorius; and from the deep surface of the fascia lata. It is inserted between the two layers of the iliotibial band of the fascia lata about the junction of the middle and upper thirds of the thigh. The Piriformis is a flat muscle, pyramidal in shape, lying almost parallel with the posterior margin of the Glutseus medius. It is situated partly within the pelvis against its posterior wall, and partly at the back of the hip-joint. It arises from the front of the sacrum by three fleshy digitations, attached to the portions of bone between the first, second, third, and fourth anterior sacral foramina, and to the grooves leading from the foramina: a few fibers also arise from the margin of the greater sciatic foramen, and from the anterior surface of the sacrotuberous ligament. The muscle passes out of the pelvis through the greater sciatic fora- men, the upper part of which it fills, and is inserted by a rounded tendon into the upper border of the greater trochanter behind, but often partly blended with, the common tendon of the Obturator internus and Gemelli. Variations.—It is frequently pierced by the common peroneal nerve and thus divided more or less into two parts. It may be united with the Glut ecus medius, or send fibers to the Glutseus minimus or receive fibers from the Gemellus superior. It may have only one or two sacral attach- ments or be inserted in to the capsule of the hip-joint. It may be absent. Ant. sup. iliac spine~~~ Obturator canal Lacunar ligament Pubic tubercle Symphysis pubis Transverse acetabular ligament Fig. 435.—The obturator membrane. Obturator Membrane (Fig. 435).—The obturator membrane is a thin fibrous sheet, which almost completely closes the obturator foramen. Its fibers are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and completes the obturator canal for the pas- sage of the obturator vessels and nerve. The membrane is attached to the sharp margin of the obturator foramen except at its lower lateral angle, where it is fixed THE MUSCLES OF THE GLUTEAL REGION 477 to the pelvic surface of the inferior ramus of the ischium, i. e., within the margin. Both obturator muscles are connected with this membrane. The Obturator internus is situated partly within the lesser pelvis, and partly at the back of the hip-joint. It arises from the inner surface of the antero-lateral wall of the pelvis, where it surrounds the greater part of the obturator foramen, being attached to the inferior rami of the pubis and ischium, and at the side to the inner surface of the hip bone below and behind the pelvic brim, reaching from the upper part of the greater sciatic foramen above and behind to the obturator fora- men below and in front. It also arises from the pelvic surface of the obturator membrane except in the posterior part, from the tendinous arch which completes the canal for the passage of the obturator vessels and nerve, and to a slight extent from the obturator fascia, which covers the muscle. The fibers converge rapidly toward the lesser sciatic foramen, and end in four or five tendinous bands, which are found on the deep surface of the muscle; these bands are reflected at a right angle over the grooved surface of the ischium between its spine and tuberosity. This bony surface is covered by smooth cartilage, which is separated from the tendon by a bursa, and presents one or more ridges corresponding with the furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic fora- men and unite into a single flattened tendon, which passes horizontally across the capsule of the hip-joint, and, after receiving the attachments of the Gemelli, is inserted into the forepart of the medial surface of the greater trochanter above the trochanteric fossa. A bursa, narrow and elongated in form, is usually found between the tendon and the capsule of the hip-joint; it occasionally communicates with the bursa between the tendon and the ischium. The Gemelli are two small muscular fasciculi, accessories to the tendon of the Obturator internus which is received into a groove between them. The Gemellus superior, the smaller of the two, arises from the outer surface of the spine of the ischium, blends with the upper part of the tendon of the Obturator internus, and is inserted with it into the medial surface of the greater trochanter. It is sometimes wanting. The Gemellus inferior arises from the upper part of the tuberosity of the ischium, immediately below the groove for the Obturator internus tendon. It blends with the lower part of the tendon of the Obturator internus, and is inserted with it it into the medial surface of the greater trochanter. Rarely absent. The Quadratus femoris is a flat, quadrilateral muscle, between the Gemellus inferior and the upper margin of the Adductor magnus; it is separated from the latter by the terminal branches of the medial femoral circumflex vessels. It arises from the upper part of the external border of the tuberosity of the ischium, and is inserted into the upper part of the linea quadrata—that is, the line which extends vertically downward from the intertrochanteric crest. A bursa is often found between the front of this muscle and the lesser trochanter. Sometimes absent. The Obturator externus (Fig. 436) is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis. It arises from the margin of bone immediately around the medial side of the obturator foramen, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves. The fibers springing from the pubic arch extend on to the inner sur- face of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane. The fibers converge and pass backward, lateralward, and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip- joint and is inserted into the trochanteric fossa of the femur. The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the 478 MYOLOGY obturator nerve reaches the thigh by passing in front of the muscle, and the posterior branch by piercing it. Nerves.—The Glutseus maximus is supplied by the fifth lumbar and first and second sacral nerves through the inferior gluteal nerve; the Glutsei medius and minimus and the Tensor fasciae latae by the fourth and fifth lumbar and first sacral nerves through the superior gluteal; the Piri- formis is supplied by the first and second sacral nerves; the Gemellus inferior and Quadrat us femoris by the last lumbar and first sacral nerves; the Gemellus superior and Obturator internus by the first, second, and third sacral nerves, and the Obturator externus by the third and fourth lumbar nerves through the obturator. Head of femur Obturator nerve 'Ant. inf. iliac spine Fig. 436.—The Obturator externus. Actions.—When the Glutams maximus takes its fixed point from the pelvis, it extends the femur and brings the bent thigh into a line with the body. Taking its fixed point from below, it acts upon the pelvis, supporting it and the trunk upon the head of the femur; this is especially obvious in standing on one leg. Its most powerful action is to cause the body to regain the erect position after stooping, by drawing the pelvis backward, being assisted in this action by the Biceps femoris, Semitendinosus, and Semimembranosus. The Glutaeus maximus is a tensor of the fascia lata, and by its connection with the iliotibial band steadies the femur on the articular surfaces of the tibia during standing, when the Extensor muscles are relaxed. The lower part of the muscle also acts as an adductor and external rotator of the limb. The Glutsei medius and minimus abduct the thigh, when the limb is extended, and are principally called into action in supporting the body on one limb, in conjunction with the Tensor fasciae latae. Their anterior fibers, by drawing the greater trochanter forward, rotate the thigh inward, in which action they are also assisted by the Tensor fasciae latae. The Tensor fasciae latae is a tensor, of the fascia lata; continuing its action, the oblique direction of its fibers enables it to abduct the thigh and to rotate it inward. In the erect posture, acting from below, it will serve to steady the pelvis upon the head of the femur; and by means of the iliotibial band it steadies the condyles of the femur on the articular surfaces of the tibia, and assists the Glutaeus maximus in supporting the knee in the extended position. The remaining muscles are powerful external rotators of the thigh. In the sitting posture, when the thigh is fiexed upon the pelvis, their action as rotators ceases, and they become abductors, with the exception of the Obturator externus, which still rotates the femur outward. 4. The Posterior Femoral Muscles (Hamstring Muscles) (Fig. 434). Biceps femoris. Semitendinosus. Semimembranosus. The Biceps femoris (Biceps) is situated on the posterior and lateral aspect of the thigh. It has two heads of origin; one, the long head, arises from the lower and inner THE POSTERIOR FEMORAL MUSCLES 479 impression on the back part of the tuberosity of the ischium, by a tendon common to it and the Semitendinosus, and from the lower part of the sacrotuberous liga- ment; the other, the short head, arises from the lateral lip of the linea aspera, between the Adductor magnus and Vastus lateralis, extending up almost as high as the insertion of the Gluteus maximus; from the lateral prolongation of the linea aspera to within 5 cm. of the lateral condyle; and from the lateral inter- muscular septum. The fibers of the long head form a fusiform belly, which passes obliquely downward and lateral ward across the sciatic nerve to end in an aponeu- rosis which covers the posterior surface of the muscle, and receives the fibers of the short head; this aponeurosis becomes gradually contracted into a tendon, which is inserted into the lateral side of the head of the fibula, and by a small slip into the lateral condyle of the tibia. At its insertion the tendon divides into two portions, which embrace the fibular collateral ligament of the knee-joint. From the posterior border of the tendon a thin expansion is given off to the fascia of the leg. The tendon of insertion of this muscle forms the lateral hamstring; the common peroneal nerve descends along its medial border. Variations.—The short head may be absent; additional heads may arise from the ischial tuberosity, the linea aspera, the medial supracondylar ridge of the femur or from various other parts. A slip may pass to the Gastrocnemius. The Semitendinosus, remarkable for the great length of its tendon of insertion, is situated at the posterior and medial aspect of the thigh. It arises from the lower and medial impression on the tuberosity of the ischium, by a tendon common to it and the long head of the Biceps femoris; it also arises from an aponeurosis which connects the adjacent surfaces of the two muscles to the extent of about 7.5 cm. from their origin. The muscle is fusiform and ends a little below the middle of the thigh in a long round tendon which lies along the medial side of the popliteal fossa; it then curves around the medial condyle of the tibia and passes over the tibial collateral ligament of the knee-joint, from which it is separated by a bursa, and is inserted into the upper part of the medial surface of the body of the tibia, nearly as far forward as its anterior crest. At its insertion it gives off from its lower border a prolongation to the deep fascia of the leg and lies behind the tendon of the Sartorius, and below that of the Gracilis, to which it is united. A tendinous intersection is usually observed about the middle of the muscle. The Semimembranosus, so called from its membranous tendon of origin, is situ- ated at the back and medial side of the thigh. It arises by a thick tendon from the upper and outer impression on the tuberosity of the ischium, above and lateral to the Biceps femoris and Semitendinosus. The tendon of origin expands into an aponeurosis, which covers the upper part of the anterior surface of the muscle; from this aponeurosis muscular fibers arise, and converge to another aponeurosis which covers the lower part of the posterior surface of the muscle and contracts into the tendon of insertion. It is inserted mainly into the horizontal groove on the posterior medial aspect of the medial condyle of the tibia. The tendon of insertion gives off certain fibrous expansions: one, of considerable size, passes upward and lateralward to be inserted into the back part of the lateral condyle of the femur, forming part of the oblique popliteal ligament of the knee-joint; a second is continued downward to the fascia which covers the Popliteus muscle; while a few fibers join the tibial collateral ligament of the joint and the fascia of the leg. The muscle overlaps the upper part of the popliteal vessels. Variations.—It may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or Adductor magnus. The tendons of insertion of the two preceding muscles form the medial ham- strings. 480 MYOLOGY Nerves.—The muscles of this region are supplied by the fourth and fifth lumbar and the first, second, and third sacral nerves; the nerve to the short head of the Biceps femoris is derived from the common peroneal, the other muscles are supplied through the tibial nerve. Actions.—The hamstring muscles flex the leg upon the thigh. When the knee is semiflexed, the Biceps femoris in consequence of its oblique direction rotates the leg slightly outward; and the Semitendinosus, and to a slight extent the Semimembranosus, rotate the leg inward, assist- ing the Popliteus. Taking their fixed point from below, these muscles serve to support the pelvis upon the head of the femur, and to draw the trunk directly backward, as in raising it from the stooping position or in feats of strength, when the body is thrown backward in the form of an arch. As already indicated on page 285, complete flexion of the hip cannot be effected unless the knee-joint is also flexed, on account of the shortness of the hamstring muscles. III. THE MUSCLES AND FASCIAE OF THE LEG. The muscles of the leg may be divided into three groups: anterior, posterior, and lateral. 1. The Anterior Crural Muscles (Fig. 437) Tibialis anterior. Extensor hallucis longus. Extensor digitorum longus. Peronseus tertius. Deep Fascia (fascia cruris).—The deep fascia of the leg forms a complete invest- ment to the muscles, and is fused with the periosteum over the subcutaneous surfaces of the bones. It is continuous above with the fascia lata, and is attached around the knee to the patella, the ligamentum patellse, the tuberosity and con- dyles of the tibia, and the head of the fibula. Behind, it forms the popliteal fascia, covering in the popliteal fossa; here it is strengthened by transverse fibers, and perforated by the small saphenous vein. It receives an expansion from the tendon of the Biceps femoris laterally, and from the tendons of the Sartorius, Gracilis, Semitendinosus, and Semimembranosus medially; in front, it blends with the peri- osteum covering the subcutaneous surface of the tibia, and with that covering the head and malleolus of the fibula; below, it is continuous with the transverse crural and laciniate ligaments. It is thick and dense in the upper and anterior part of the leg, and gives attachment, by its deep surface, to the Tibialis anterior and Extensor digitorum longus; but thinner behind, where it covers the Gastroc- nemius and Soleus. It gives off from its deep surface, on the lateral side of the leg, two strong intermuscular septa, the anterior and posterior peroneal septa, which enclose the Peronsei longus and brevis, and separate them from the muscles of the anterior and posterior crural regions, and several more slender processes which enclose the individual muscles in each region. A broad transverse intermuscular septum, called the deep transverse fascia of the leg, intervenes between the super- ficial and deep posterior crural muscles. The Tibialis anterior (Tibialis anticus) is situated on the lateral side of the tibia; it is thick and fleshy above, tendinous below. It arises from the lateral condyle and upper half or two-thirds of the lateral surface of the body of the tibia; from the adjoining part of the interosseous membrane; from the deep surface of the fascia; and from the intermuscular septum between it and the Extensor digitorum longus. The fibers run vertically downward, and end in a tendon, which is apparent on the anterior surface of the muscle at the lower third of the leg. After passing through the most medial compartments of the transverse and cruciate crural ligaments, it is inserted into the medial and under surface of the first cuneiform bone, and the base of the first metatarsal bone. This muscle overlaps the anterior tibial vessels and deep peroneal nerve in the upper part of the leg. Variations.—A deep portion of the muscle is rarely inserted into the talus, or a tendinous slip may pass to the head of the first metatarsal bone or the base of the first phalanx of the great toe. The Tibiofasczalis anterior, a small muscle from the lower part of the tibia to the transverse or cruciate crural ligaments or deep fascia. THE ANTERIOR CRURAL MUSCLES 481 The Extensor hallucis longus (Extensor proprius hallucis) is a thin muscle, situated between the Tibialis anterior and the Extensor digitorum longus. It arises from the anterior surface of the fibula for about the middle two-fourths of its extent, medial to the origin of the Extensor digi- torum longus; it also arises from the interosseous membrane to a similar extent. The anterior tibial vessels and deep peroneal nerve lie between it and the Tibialis anterior. The fibers pass downward, and end in a tendon, which occupies the anterior border of the muscle, passes through a distinct compartment in the cruciate crural ligament, crosses from the lateral to the medial side of the anterior tibial vessels near the bend of the ankle, and is inserted into the base of the distal phalanx of the great toe. Opposite the metatarso- phalangeal articulation, the tendon gives off a thin prolongation on either side, to cover the surface of the joint. An expansion from the medial side of the tendon is usually inserted into the base of the proximal phalanx. Variations.—Occasionally united at its origin with the Extensor digitorum longus. Extensor ossis metatarsi hal- lucis, a small muscle, sometimes found as a slip from the Extensor hallucis longus, or from the Tibialis anterior, or from the Extensor digitorum longus, or as a distinct mus- cle; it traverses the same compartment of the transverse ligament with the Extensor hallucis longus. The Extensor digitorum longus is a penniform muscle, situated at the lateral part of the front of the leg. It arises from the lateral condyle of the tibia; from the upper three-fourths of the anterior surface of the body of the fibula; from the upper part of the interosseous membrane; from the deep surface of the fascia; and from the intermuscular septa between it and the Tibialis anterior on the medial, and the Peronsei on the lateral side. Between it and the Tibialis anterior are the upper portions of the anterior tibial vessels and deep peroneal nerve. The tendon passes under the transverse and cruciate crural ligaments in company with the Peronseus tertius, and divides into four slips, which run forward on the dorsum of the foot, and are inserted into the second and third phalanges of the four lesser toes. The ten- dons to the second, third, and fourth toes are each joined, opposite the metatarsophalangeal articulation, on the lateral side by a tendon of the Extensor digitorum brevis. The tendons are inserted in the following manner: each receives a fibrous expansion from the Interossei and Lum- bricalis, and then spreads out into a broad apon- eurosis, which covers the dorsal surface of the Cruciate crural ligament Fig. 437.—Muscles of the front of the leg. 482 MYOLOGY first phalanx: this aponeurosis, at the articulation of the first with the second phalanx, divides into three slips—an intermediate, which is inserted into the base of the second phalanx; and two collateral slips, which, after uniting on the dorsal surface of the second phalanx, are continued onward, to be inserted into the base of the third phalanx. Variations.—This muscle varies considerably in the modes of origin and the arrangement of its various tendons. The tendons to the second and fifth toes may be found doubled, or extra slips are given off from one or more tendons to their corresponding metatarsal bones, or to the short extensor, or to one of the interosseous muscles. A slip to the great toe from the innermost tendon has been found. The Peronseus tertius is a part of the Extensor digitorum longus, and might be described as its fifth tendon. The fibers belonging to this tendon arise from the lower third or more of the anterior surfaca of the fibula; from the lower part of the interosseous membrane; and from an intermuscular septum between it and the Peronseus brevis. The tendon, after passing under the transverse and cruciate crural ligaments in the same canal as the Extensor digitorum longus, is inserted into the dorsal surface of the base of the metatarsal bone of the little toe. This muscle is sometimes wanting. Nerves.—These muscles are supplied by the fourth and* fifth lumbar and first sacral nerves through the deep peroneal nerve. Actions.—The Tibialis anterior and Peronseus tertius are the direct flexors of the foot at the ankle-joint; the former muscle, when acting in conjunction with the Tibialis posterior, raises the medial border of the foot, i. e., inverts the foot; and the latter, acting with the Peronaei brevis and longus, raises the lateral border of the foot, i. e., everts the foot. The Extensor digitorum longus and Extensor hallucis longus extend the phalanges of the toes, and, continuing their action, flex the foot upon the leg. Taking their fixed points from below, in the erect posture, all these muscles serve to fix the bones of the leg in the perpendicular position, and give increased strength to the ankle-joint. 2. The Posterior Crural Muscles. The muscles of the back of the leg are subdivided into twTo groups—superficial and deep. Those of the superficial group constitute a powerful muscular mass, forming the calf of the leg. Their large size is one of the most characteristic features of the muscular apparatus in man, and bears a direct relation to his erect attitude and his mode of progression. The Superficial Group (Fig. 438). Gastrocnemius. Soleus. Plantaris. The Gastrocnemius is the most superficial muscle, and forms the greater part of the calf. It arises by two heads, which are connected to the condyles of the femur by strong, flat tendons. The medial and larger head takes its origin from a depression at the upper and back part of the medial condyle and from the adjacent part of the femur. The lateral head arises from an impression on the side of the lateral condyle and from the posterior surface of the femur immediately above the lateral part of the condyle. Both heads, also, arise from the subjacent part of the capsule of the knee. Each tendon spreads out into an aponeurosis, which covers the posterior surface of that portion of the muscle to which it belongs. From the anterior surfaces of these tendinous expansions, muscular fibers are given off; those of the medial head being thicker and extending lower than those of the lateral. The fibers unite at an angle in the middle line of the muscle in a tendinous raphe, which expands into a broad aponeurosis on the anterior surface of the muscle, and into this the remaining fibers are inserted. The aponeurosis, gradually contracting, unites with the tendon of the Soleus, and forms with it the tendo calcaneus. THE POSTERIOR CRURAL MUSCLES 483 Variations.—Absence of the outer head or of the entire muscle. Extra slips from the popliteal surface of the femur. The Soleus is a broad flat muscle situated immediately in front of the Gastroc- nemius. It arises by tendinous fibers from the back of the head of the fibula, and from the upper third of the posterior surface of the body of the bone; from the popliteal line, and the middle third of the medial border of the tibia; some fibers also arise from a tendinous arch placed between the tibial and fibular origins of the muscle, in front of which the popliteal vessels and tibial nerve run. The fibers end in an aponeurosis which covers the posterior surface of the muscle, and, gradually becoming thicker and narrower, joins with the tendon of the Gastroc- nemius, and forms with it the tendo calcaneus. Variations.—Accessory head to its lower and inner part usually ending in the tendocalcaneus, or the calcaneus, or the laciniate ligament. The Gastrocnemius and Soleus together form a muscular mass which is occa- sionally described as the Triceps surse; its tendon of insertion is the tendo calcaneus. Tendo Calcaneus (tendo Achillis).—The tendo calcaneus, the common tendon of the Gastrocnemius and Soleus, is the thickest and strongest in the body. It is about 15 cm. long, and begins near the middle of the leg, but receives fleshy fibers on its anterior surface, almost to its lower end. Gradually becoming contracted below, it is inserted into the middle part of the posterior surface of the calcaneus, a bursa being interposed between the tendon and the upper part of this surface. The ten- don spreads out somewhat at its lower end, so that its narrowest part is about 4 cm. above its insertion. It is covered by the fascia and the integument, and is separated from the deep muscles and vessels by a considerable interval filled up with areolar and adipose tissue. Along its lateral side, but superficial to it, is the small saphenous vein. The Plantaris is placed between the Gastrocnemius and Soleus. It arises from the lower part of the lateral prolongation of the linea aspera, and from the oblique popliteal ligament of the knee-joint. It forms a small fusiform belly, from 7 to 10 cm. long, ending in a long slender tendon which crosses obliquely between the two muscles of the calf, and runs along the medial border of the tendo calcaneus, to be inserted with it into the posterior part of the calcaneus. This muscle is some- times double, and at other times wanting. Occasionally, its tendon is lost in the laciniate ligament, or in the fascia of the leg. Nerves.—The Gastrocnemius and Soleus are supplied by the first and second sacral nerves, and the Plantaris by the fourth and fifth lumbar and first sacral nerves, through the tibial nerve. Actions.—The muscles of the calf are the chief extensors of the foot at the ankle-joint. They possess considerable power, and - are constantly called into use in standing, walking, dancing, and leaping; hence the large size they usually present. In walking, these muscles raise the heel, from the ground; the body being thus supported on the raised foot, the opposite limb can be carried forward. In standing, the Soleus, taking its fixed point from below, steadies the leg upon the foot and prevents the body from falling forward. The Gastrocnemius, acting from below, serves to flex the femur upon the tibia, assisted by the Popliteus. The Plantaris is the rudiment of a large muscle which in some of the lower animals is continued over the calcaneus to be inserted into the plantar aponeurosis. In man it is an accessory to the Gastrocnemius, extending the ankle if the foot be free, or bending the knee if the foot be fixed. The Deep Group (Fig. 439). Popliteus. Flexor hallucis longus. Flexor digitorum longus. Tibialis posterior. Deep Transverse Fascia.—The deep transverse fascia of the leg is a transversely placed, intermuscular septum, between the superficial and deep muscles of the back of the leg. At the sides it is connected to the margins of the tibia and 484 MYOLOGY fibula. Above, where it covers the Popliteus, it is thick and dense, and receives an expansion from the tendon of the Semimembranosus; it is thinner in the middle ; Flex. hall. long. Tendons of < Flex. dig. long. ( | Tibialis posterior Tendons of Peronae longus et brevis Fig. 438.—Muscles of the back of the leg. Superficial layer. Fig. 439.—Muscles of the back of the leg. Deep layer. of the leg; but below, where it covers the tendons passing behind the malleoli, it is thickened and continuous with the laciniate ligament. The Popliteus is a thin, flat, triangular muscle, which forms the lower part of THE POSTERIOR CRURAL MUSCLES 485 the floor of the popliteal fossa. It arises by a strong tendon about 2.5 cm. long, from a depression at the anterior part of the groove on the lateral condyle of the femur, and to a small extent from the oblique popliteal ligament of the knee-joint; and is inserted into the medial two-thirds of the triangular surface above the pop- liteal line on the posterior surface of the body of the tibia, and into the tendinous expansion covering the surface of the muscle. Variations.—Additional head from the sesamoid bone in the outer head of the Gastrocnemius. Popliteus minor, rare, origin from femur on the inner side of the Plantaris, insertion into the pos- terior ligament of the knee-joint. Peroneotibialis, 14 per cent., origin inner side of the head of the fibula, insertion into the upper end of the oblique line of the tibia, it lies beneath the Popliteus. The Flexor hallucis longus is situated on the fibular side of the leg. It arises from the inferior two-thirds of the posterior surface of the body of the fibula, with the exception of 2.5 cm. at its lowest part; from the lower part of the interosseous membrane; from an intermuscular septum between it and the Peronaei, laterally, and from the fascia covering the Tibialis posterior, medially. The fibers pass obliquely downward and backward, and end in a tendon which occupies nearly the whole length of the posterior surface of the muscle. This tendon lies in a groove which crosses the posterior surface of the lower end of the tibia, the posterior surface of the talus, and the under surface of the sustentaculum tali of the calca- neus; in the sole of the foot it runs forward between the two heads of the Flexor hallucis brevis, and is inserted into the base of the last phalanx of the great toe. The grooves on the talus and calcaneus, which contain the tendon of the muscle, are converted by tendinous fibers into distinct canals, lined by a mucous sheath. As the tendon passes forward in the sole of the foot, it is situated above, and crosses from the lateral to the medial side of the tendon of the Flexor digitorum longus, to which it is connected by a fibrous slip. Variations.—"Usually a slip runs to the Flexor digitorum and frequently an additional slip runs from the Flexor digitorum to the Flexor hallucis. P eroneocalcaneus internus, rare, origin below or outside the Flexor hallucis from the back of the fibula, passes over the sustentaculum tali with the Flexor hallucis and is inserted into the calcaneum. The Flexor digitorum longus is situated on the tibial side of the leg. At its origin it is thin and pointed, but it gradually increases in size as it descends. It arises from the posterior surface of the body of the tibia, from immediately below the popliteal line to within 7 or 8 cm. of its lower extremity, medial to the tibial origin of the Tibialis posterior; it also arises from the fascia covering the Tibialis posterior. The fibers end in a tendon, which runs nearly the whole length of the posterior surface of the muscle. This tendon passes behind the medial malleolus, in a groove, common to it and the Tibialis posterior, but separated from the latter by a fibrous septum, each tendon being contained in a special compartment lined by a separate mucous sheath. It passes obliquely forward and lateralward, super- ficial to the deltoid ligament of the ankle-joint, into the sole of the foot (Fig. 444), where it crosses below the tendon of the Flexor hallucis longus, and receives from it a strong tendinous slip. It then expands and is joined by the Quadratus plantse, and finally divides into four tendons, which are inserted into the bases of the last phalanges of the second, third, fourth, and fifth toes, each tendon passing through an opening in the corresponding tendon of the Flexor digitorum brevis opposite the base of the first phalanx. Variations.—Flexor accessorius longus digitorum, not infrequent, origin from fibula, or tibia, or the deep fascia and ending in a tendon which, after passing beneath the laciniate ligament, joins the tendon of the long flexor or the Quadratus plant®. The Tibialis posterior (Tibialis posticus) lies between the two preceding muscles, and is the most deeply seated of the muscles on the back of the leg. It begins above by two pointed processes, separated by an angular interval through which 486 MYOLOGY the anterior tibial vessels pass forward to the front of the leg. It arises from the whole of the posterior surface of the interosseous membrane, excepting its lowest part; from the lateral portion of the posterior surface of the body of the tibia, between the commencement of the popliteal line above and the junction of the middle and lower thirds of the body below; and from the upper two-thirds of the medial surface of the fibula; some fibers also arise from the deep transverse fascia, and from the intermuscular septa separating it from the adjacent muscles. In the lower fourth of the leg its tendon passes in front of that of the Flexor digitorum longus and lies with it in a groove behind the medial malleolus, but enclosed in a separate sheath; it next passes under the laciniate and over the deltoid ligament into the foot, and then beneath the plantar calcaneonavicular ligament. The tendon contains a sesamoid fibrocartilage, as it runs under the plantar calcaneo- navicular ligament. It is inserted into the tuberosity of the navicular bone, and gives off fibrous expansions, one of which passes backward to the sustentaculum tali of the calcaneus, others forward and lateralward to the three cuneiforms, the cuboid, and the bases of the second, third, and fourth metatarsal bones. Nerves.—The Popliteus is supplied by the fourth and fifth lumbar and first sacral nerves, the Flexor digitorum longus and Tibialis posterior by the fifth lumbar and first sacral, and the Flexor hallucis longus by the fifth lumbar and the first and second sacral nerves, through the tibial nerve. Actions.—The Popliteus assists in flexing the leg upon the thigh; when the leg is flexed, it will rotate the tibia inward. It is especially called into action at the beginning of the act of bending the knee, inasmuch as it produces the slight inward rotation of the tibia which is essential in the early stage of this movement. The Tibialis posterior is a direct extensor of the foot at the ankle- joint; acting in conjunction with the Tibialis anterior, it turns the sole of the foot upward and medialward, i. e., inverts the foot, antagonizing the Peronsei, which turn it upward and lateral- ward (evert it). In the sole of the foot the tendon of the Tibialis posterior lies directly below the plantar calcaneonavicular ligament, and is therefore an important factor in maintaining the arch of the foot. The Flexor digitorum longus and Flexor hallucis longus are the direct flexors of the phalanges, and, continuing their action, extend the foot upon the leg; they assist the Gastroc- nemius and Soleus in extending the foot, as in the act of walking, or in standing on tiptoe. In consequence of the oblique direction of its tendons the Flexor digitorum longus would draw the toes medialward, were it not for the Quadratus plantse, which is inserted into the lateral side of the tendon, and draws it to the middle line of the foot. Taking their fixed point from the foot, these muscles serve to maintain the upright posture by steadying the tibia and fibula perpendicularly upon the talus. Peronseus longus. 3. The Lateral Crural Muscles (Fig. 439) / Peronseus brevis. The Peronseus longus is situated at the upper part of the lateral side of the leg, and is the more superficial of the two muscles. It arises from the head and upper two-thirds of the lateral surface of the body of the fibula, from the deep surface of the fascia, and from the intermuscular septa between it and the muscles on the front and back of the leg; occasionally also by a few fibers from the lateral condyle of the tibia. Between its attachments to the head and to the body of the fibula there is a gap through which the common peroneal nerve passes to the front of the leg. It ends in a long tendon, which runs behind the lateral malleolus, in a groove common to it and the tendon of the Peronseus brevis, behind which it lies; the groove is converted into a canal by the superior peroneal retinaculum, and the tendons in it are contained in a common mucous sheath. The tendon then extends obliquely forward across the lateral side of the calcaneus, below the troch- lear process, and the tendon of the Peronseus brevis, and under cover of the inferior peroneal retinaculum. It crosses the lateral side of the cuboid, and then runs on the under surface of that bone in a groove which is converted into a canal by the long plantar ligament; the tendon then crosses the sole of the foot obliquely, and is inserted into the lateral side of the base of the first metatarsal bone and the lateral THE LATERAL CRURAL MUSCLES 487 side of the first cuneiform. Occasionally it sends a slip to the base of the second metatarsal bone. The tendon changes its direction at two points: first, behind the lateral malleolus; secondly, on the cuboid bone; in both of these situations the ten- don is thickened, and, in the latter, a sesamoid fibrocartilage (sometimes a bone), is usually developed in its substance. Tibialis anterior M. Interosseous membrane'' .Tibia Extensores longi digi- torum et hallucis Mm. Flexor digitorum / longus M. Great saphenous vein and saphenous nerve Deep peroneal nerve and anterior tibial artery and vein ■Posterior tibial vein and artery Peroncei longus and brevis Mm.' ■Tibial nerve Superficial peroneal. nerve Soleus M, Fibula' '•Tendo m. plantaris Peroneal artery, and vein ''Gastrocnemius M. Gastrocnemius M: Small saphenous vein 'nMedian cutaneous Lateral cutaneous nerve The Peronseus brevis lies under cover of the Peronseus longus, and is a shorter and smaller muscle. It arises from the lower two-thirds of the lateral surface of the body of the fibula; medial to the Peromeus longus; and from the intermuscular septa separating it from the adjacent muscles on the front and back of the leg. The fibers pass vertically downward, and end in a tendon which runs behind the lateral malleolus along with but in front of that of the preceding muscle, the two tendons being enclosed in the same compartment, and lubricated by a common mucous sheath. It then runs forward on the lateral side of the calcaneus, above the trochlear process and the tendon of the Peromeus longus, and is inserted into the tuberosity at the base of the fifth metatarsal bone, on its lateral side. On the lateral surface of the calcaneus the tendons of the Peronsei longus and brevis occupy separate osseoaponeurotic canals formed by the calcaneus and the perineal retinacula; each tendon is enveloped by a forward prolongation of the common mucous sheath. Variations.—-Fusion of the two peronsei is rare. -A slip from the Peronseus longus to the base of the third, fourth or fifth metatarsal bone, or to the Adductor hallucis is occasionally seen. Peronceus accessorius, origin from the fibula between the longus and brevis, joins the tendon of the longus in the sole of the foot. Peronceus quinti digiti, rare, origin lower fourth of the fibula under the brevis, insertion into the Extensor aponeurosis of the little toe. More common as a slip of the tendon of the Peronseus brevis. Peronceus quartus, 13 per cent. (Gruber), origin back of fibula between the brevis and the Plexor hallucis, insertion into the peroneal spine of the calcaneum, (peroneocalcaneus externum), or less frequently into the tuberosity of the cuboid (peroneocuboideus). Nerves.—The Peronsei longus and brevis are supplied by the fourth and fifth lumbar and first sacral nerves through the superficial peroneal nerve. Fig. 440.—Cross-section through middle of leg. (Eycleshymer and Schoemaker.) 488 MYOLOGY Actions.—The Peronsei longus and brevis extend the foot upon the leg, in conjunction with the Tibialis posterior, antagonizing the Tibialis anterior and Peronseus tertius, which are flexors of the foot. The Peromeus longus also everts the sole of the foot, and from the oblique direction of the tendon across the sole of the foot is an important agent in the maintenance of the trans- verse arch. Taking their fixed points below, the Peronsei serve to steady the leg upon the foot. This is especially the case in standing upon one leg, when the tendency of the superincumbent weight is to throw the leg medialward; the Peronseus longus overcomes this tendency by drawing on the lateral side of the leg. THE FASCIA AROUND THE ANKLE. Fibrous bands, or thickened portions of the fascia, bind down the tendons in front of and behind the ankle in their passage to the foot. They comprise three ligaments, viz., the transverse crural, the cruciate crural and the laciniate; and the superior and inferior peroneal retinacula. Tibialis anterior Extensor dig. longus 'Ext. hall. long. Ext. dig. brevis Terulo calcaneus Peronceus longus Peronceus brevis Peronceus tertius Fig. 441.—The mucous sheaths of the tendons around the ankle. ateral aspect. Transverse Crural Ligament (ligamentum transversum cruris; upper part of anterior annular ligament) (Fig. 441).—The transverse crural ligament binds down the tendons of Extensor digitorum longus, Extensor hallucis longus, Peromeus tertius, and Tibialis anterior as they descend on the front of the tibia and fibula; under it are found also the anterior tibial vessels and deep peroneal nerve. It is attached laterally to the lower end of the fibula, and medially to the tibia; above it is con- tinuous with the fascia of the leg. Cruciate Crural Ligament (ligamentum cruciatum cruris; lower part of anterior annular ligament) (Figs. 441, 442).—The cruciate crural ligament is a Y-shaped band placed in front of the ankle-joint, the stem of the Y being attached laterally to the upper surface of the calcaneus, in front of the depression for the interosseous talocalcanean ligament; it is directed medialward as a double layer, one lamina passing in front of, and the other behind, the tendons of the Peronaeus tertius and Extensor digitorum longus. At the medial border of the latter tendon these two layers join together, forming a compartment in which the tendons are enclosed. From the medial extremity of this sheath the two limbs of the Y diverge: one is directed upward and medialward, to be attached to the tibial malleolus, passing over the Extensor hallucis longus and the vessels and nerves, but enclosing THE FASCIA AROUND THE ANKLE 489 the Tibialis anterior by a splitting of its fibers. The other limb extends downward and medialward, to be attached to the border of the plantar aponeurosis, and passes over the tendons of the Extensor hallucis longus and Tibialis anterior and also the vessels and nerves. Laciniate Ligament (ligamentum laciniatum; internal annular ligament).—The laciniate ligament is a strong fibrous band, extending from the tibial malleolus above to the margin of the calcaneus below, converting a series of bony grooves in this situation into canals for the passage of the tendons of the Flexor muscles and the posterior tibial vessels and tibial nerve into the sole of the foot. It is continuous by its upper border with the deep fascia of the leg, and by its lower border with the plantar aponeurosis and the fibers of origin of the Abductor hallucis muscle. Enumerated from the medial side, the four canals which it forms transmit the tendon of the Tibialis posterior; the tendon of the Flexor digitorum longus; the posterior tibial vessels and tibial nerve, which run through a broad space beneath the ligament; and lastly, in a canal formed partly by the talus, the tendon of the Flexor hallucis longus. Tibialis anterior Tibialis 'posterior Ext. hall. long. Flexor dig. longus Flexor hallucis longus Bursa Fig. 442.—The mucous sheaths of the tendons around the ankle. Medial aspect. Tendocalcaneus Peroneal Retinacula.— The peroneal retinacula are fibrous bands which bind down the tendons of the Peronsei longus and brevis as they run across the lateral side of the ankle. The fibers of the superior retinaculum (external annular ligament) are attached above to the lateral malleolus and below to the lateral surface of the calcaneus. The fibers of the inferior retinaculum are continuous in front with those of the cruciate crural ligament; behind they are attached to the lateral surface of the calcaneus; some of the fibers are fixed to the peroneal trochlea, forming a septum between the tendons of the Peronafi longus and brevis. The Mucous Sheaths of the Tendons Around the Ankle.—All the tendons crossing the ankle-joint are enclosed for part of their length in mucous sheaths which have an almost uniform length of about 8 cm. each. On the front of the ankle (Tig. 441) the sheath for the Tibialis anterior extends from the upper margin of the trans- verse crural ligament to the interval between the diverging limbs of the cruciate ligament; those for the Extensor digitorum longus and Extensor hallucis longus reach upward to just above the level of the tips of the malleoli, the former being the higher. The sheath of the Extensor hallucis longus is prolonged on to the base of the first metatarsal bone, while that of the Extensor digitorum longus reaches 490 MYOLOGY only to the level of the base of the fifth metatarsal. On the medial side of the ankle (Fig. 442) the sheath for the Tibialis posterior extends highest up—to about 4 cm. above the tip of the malleolus—while below it stops just short of the tuber- osity of the navicular. The sheath for Flexor hallucis longus reaches up to the level of the tip of the malleolus, while that for the Flexor digitorum longus is slightly higher; the former is continued to the base of the first metatarsal, but the latter stops opposite the first cuneiform bone. On the lateral side of the ankle (Fig. 441) a sheath which is single for the greater part of its extent encloses the Peronsei longus and brevis. It extends upward for about 4 cm. above the tip of the malleolus and downward and forward for about the same distance. IV. THE MUSCLES AND FASCL® OF THE FOOT. 1. The Dorsal Muscle of the Foot. Extensor digitorum brevis. The fascia on the dorsum of the foot is a thin membranous layer, continuous above with the transverse and cruciate crural ligaments; on either side it blends with the plantar aponeurosis; anteriorly it forms a sheath for the tendons on the dorsum of the foot. The Extensor digitorum brevis (Fig. 441) is a broad, thin muscle, which arises from the forepart of the upper and lateral surfaces of the calcaneus, in front of the groove for the Peronseus brevis; from the lateral talocalcanean ligament; and from the common limb of the cruciate crural ligament. It passes obliquely across the dorsum of the foot, and ends in four tendons. The most medial, which is the largest, is inserted into the dorsal surface of the base of the first phalanx of the great toe, crossing the dorsalis pedis artery; it is frequently described as a separate muscle—the Extensor hallucis brevis. The other three are inserted into the lateral sides of the tendons of the Extensor digitorum longus of the second, third, and fourth toes. Variations.—Accessory slips of origin from the talus and navicular, or from the external cunei- form and third metatarsal bones to the second slip of the muscle, and one from the cuboid to the third slip have been observed. The tendons vary in number and position; they may be reduced to two, or one of them may be doubled, or an additional slip may pass to the little toe. A super- numerary slip ending on one of the metatarsophalangeal articulations, or joining a dorsal inter- osseous muscle is not uncommon. Deep slips between this muscle and the Dorsal interossei occur. Nerves.—It is supplied by the deep peroneal nerve. Actions.—The Extensor digitorum brevis extends the phalanges of the four toes into which it is inserted, but in the great toe acts only on the first phalanx. The obliquity of its direction counteracts the oblique movement given to the toes by the long Extensor, so that when both muscles act, the toes are evenly extended. 2. The Plantar Muscles of the Foot. Plantar Aponeurosis (aponeurosis plantaris; plantar fascia).—The plantar apo- neurosis is of great strength, and consists of pearly white glistening fibers, disposed, for the most part, longitudinally: it is divided into central, lateral, and medial portions. The central portion, the thickest, is narrow behind and attached to the medial process of the tuberosity of the calcaneus, posterior to the origin of the Flexor digitorum brevis; and becoming broader and thinner in front, divides near the heads of the metatarsal bones into five processes, one for each of the toes. Each of these processes divides opposite the metatarsophalangeal articulation into two strata, superficial and deep. The superficial stratum is inserted into the skin of THE PLANTAR MUSCLES OF THE FOOT 491 the transverse sulcus which separates the toes'from the sole. The deeper stratum divides into two slips which embrace the side of the Flexor tendons of the toes, and blend with the sheaths of the tendons, and with the transverse metatarsal ligament, thus forming a series of arches through which the tendons of the short and long Flexors pass to the toes. The intervals left between the five processes allow the digital vessels and nerves and the tendons of the Lumbricales to become superficial. At the point of division of the aponeurosis, numerous transverse fasciculi are superadded; these serve to increase the strength of the aponeurosis at this part by binding the processes together, and connecting them with the integu- ment. The central portion of the plantar aponeurosis is continuous with the lateral and medial portions and sends upward into the foot, at the lines of junction, two strong vertical intermuscular septa, broader in front than behind, which separate the intermediate from the lateral and medial plantar groups of muscles; from these again are derived thinner transverse septa which separate the various layers of muscles in this region. The upper surface of this aponeurosis gives origin behind to the Flexor digitorum brevis. The lateral and medial portions of the plantar aponeurosis are thinner than the central piece, and cover the sides of the sole of the foot. The lateral portion covers the under surface of the Abductor digiti quinti; it is thin in front and thick behind, where it forms a strong band between the lateral process of the tuberosity of the calcaneus and the base of the fifth metatarsal bone; it is continuous medially with the central portion of the plantar aponeurosis, and laterally with the dorsal fascia. The medial portion is thin, and covers the under surface of the Abductor hallucis; it is attached behind to the laciniate ligament, and is continuous around the side of the foot with the dorsal fascia, and laterally with the central portion of the plantar aponeurosis. The muscles in the plantar region of the foot may be divided into three groups, in a similar manner to those in the hand. Those of the medial plantar region are connected with the great toe, and correspond with those of the thumb; those of the lateral plantar region are connected with the little toe, and correspond with those of the little finger; and those of the intermediate plantar region are connected with the tendons intervening between the two former groups. But in order to facilitate the description of these muscles, it is more convenient to divide them into four layers, in the order in which they are successively exposed. The First Layer (Fig. 443). Abductor hallucis. Flexor digitorum brevis. Abductor digiti quinti. The Abductor hallucis lies along the medial border of the foot and covers the origins of the plantar vessels and nerves. It arises from the medial process of the tuberosity of the calcaneus, from the laciniate ligament, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor digitorum brevis. The fibers end in a tendon, which is inserted, together with the medial tendon of the Flexor hallucis brevis, into the tibial side of the base of the first phalanx of the great toe. Variations.—Slip to the base of the first phalanx of the second toe. The Flexor digitorum brevis lies in the middle of the sole of the foot, imme- diately above the central part of the plantar aponeurosis, with which it is firmly united. Its deep surface is separated from the lateral plantar vessels and nerves 492 MYOLOGY by a thin layer of fascia. It arises by a narrow tendon, from the medial process of the tuberosity of the calcaneus, from the central part of the plantar aponeurosis, and from the intermuscular septa between it and the adjacent muscles. It passes forward, and divides into four tendons, one for each of the four lesser toes. Oppo- site the bases of the first phalanges, each tendon divides into two slips, to allow of the passage of the corresponding tendon of the Flexor digitorum longus; the two portions of the tendon then unite and form a grooved channel for the reception of the accompanying long Flexor tendon. Finally, it divides a second time, and is inserted into the sides of the second phalanx about its middle. The mode of division of the tendons of the Flexor digitorum brevis, and of their insertion into the phalanges, is analogous to that of the tendons of the Flexor digitorum sublimis in the hand. Variations.—Slip to the little toe frequently wanting, 23 per cent.; or it may be replaced by a small fusiform muscle arising from the long flexor tendon or from the Quadratus plantse. Fibrous Sheaths of the Flexor Tendons.—The terminal portions of the tendons of the long and short Flexor muscles are contained in osseoaponeurotic canals similar in their ar- rangement to those in the fingers. These canals are formed above by the phalanges and below by fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the bodies of the proximal and second pha- langes the fibrous bands are strong, and the fibers are transverse; but opposite the joints they are much thinner, and the fibers are directed obliquely. Each canal contains a mucous sheath, which is reflected on the con- tained tendons. The Abductor digiti quinti (Abductor minimi digiti) lies along the lateral border of the foot, and is in relation by its medial margin with the lateral plantar vessels and nerves. It arises, by a broad origin, from the lateral process of the tuberosity of the calcaneus, from the under surface of the calcaneus between the two pro- cesses of the tuberosity, from the forepart of the medial process, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor d igitorum brevis. Its tendon, after gliding over a smooth facet on the under surface of the base of the fifth metatarsal bone, is inserted, with the Flexor digiti quinti brevis, into the fibular side of the base of the first phalanx of the fifth toe. Variations.—Slips of origin from the tuberosity at the base of the fifth metatarsal. Abductor ossis metatarsi quinti, origin external tubercle of the calcaneus, insertion into tuberosity of the fifth metatarsal bone in common with or beneath the outer margin of the plantar fascia. Fig. 443.—Muscles of the sole of the foot. First layer. THE PLANTAR MUSCLES OF THE FOOT 493 The Second Layer (Fig. 444). Quadratus plant*. Lumbricales. The Quadratus plantse (Flexor accessorius) is separated from the muscles of the first layer by the lateral plantar vessels and nerve. It arises by two heads, which are separated from each other by the long plantar ligament: the medial or larger head is muscular, and is attached to the medial concave surface of the calcaneus, below the groove which lodges the tendon of the Flexor hallucis longus; the lateral head, flat and tendinous, arises from the lateral border of the inferior surface of the calcaneus, in front of the lateral process of its tuberosity, and from the long plantar ligament. The two portions join at an acute angle, and end in a flattened band which is inserted into the lateral margin and upper and under sur- faces of the tendon of the Flexor digitorum longus, forming a kind of groove, in which the tendon is lodged. It usually sends slips to those tendons of the Flexor digitorum longus which pass to the second, third, and fourth toes. Variations.—Lateral head often wanting; entire muscle absent. Variation in the number of digital tendons to which fibers can be traced. Most frequent offsets are sent to the second, third and fourth toes; in many cases to the fifth as well; occasionally to two toes only. The Lumbricales are four small muscles, accessory to the tendons of the Flexor digitorum longus and numbered from the medial side of the foot; they arise from these tendons, as far back as their angles of division, each springing from two tendons, except the first. The muscles end in tendons, which pass forward on the medial sides of the four lesser toes, and are inserted into the expansions of the tendons of the Extensor digitorum longus on the dorsal surfaces of the first phalanges. Variations.—Absence of one or more; doubling of the third or fourth. Insertion partly or wholly into the first phalanges. , The Third Layer (Fig. 445). Flexor hallucis brevis. Adductor hallucis. Flexor digiti quinti brevis. The Flexor hallucis brevis arises, by a pointed tendinous process, from the medial part of the under surface of the cuboid bone, from the contiguous portion of the third cuneiform, and froip the prolongation of the tendon of the Tibialis posterior which is attached to that bone. It divides in front into two portions, which are inserted into the medial and lateral sides of the base of the first phalanx of the great toe, a sesamoid bone being present in each tendon at its insertion. The medial portion is blended with the Abductor hallucis previous to its insertion; the lateral portion with the Adductor hallucis; the tendon of the Flexor hallucis longus lies in a groove between them; the lateral portion is sometimes described as the first Interosseous plantaris. Variations.—Origin subject to considerable variafton; it often receives fibers from the calcaneus or long plantar ligament. Attachment to the cuboid sometimes wanting. Slip to first phalanx of the second toe. The Adductor hallucis (Adductor obliquus hallucis) arises by two heads—oblique and transverse. The oblique head is a large, thick, fleshy mass, crossing the foot obliquely and occupying the hollow space under the first, second, third, and fourth metatarsal bones. It arises from the bases of the second, third, and fourth meta- tarsal bones, and from the sheath of the tendon of the Peronseus longus, and is inserted, together with the lateral portion of the Flexor hallucis brevis, into the lateral side of the base of the first phalanx of the great toe. rI he transverse head (Transversus pedis) is a narrow, flat fasciculus wdiich arises from the plantar meta- 494 MYOLOGY tarsophalangeal ligaments of the third, fourth, and fifth toes (sometimes only from the third and fourth), and from the transverse ligament of the metatarsus. It is inserted into the lateral side of the base of the first phalanx of the great toe, its fibers blending with the tendon of insertion of the oblique head. Fig. 444.—Muscles of the sole of the foot. Second layer. Fig. 445.—Muscles of the sole of the foot. Third layer. Variations.—Slips to the base of the first phalanx of the second toe. Opponens hallucis, occasional slips from the adductor to the metatarsal bone of the great toe. The Abductor, Flexor brevis, and Adductor of the great toe, like the similar muscles of the thumb, give off, at their insertions, fibrous expansions to blend with the tendons of the Extensor digitorum longus. The Flexor digiti quinti brevis (Flexor brevis minimi digiti) lies under the metatarsal bone of the little toe, and resembles one of the Interossei. It arises from the base of the fifth metatarsal bone, and from the sheath of the Peronseus longus; its tendon is inserted into the lateral side of the base of the first phalanx of the fifth toe. Occasionally a few of the deeper fibers are inserted into the lateral part of the distal half of the fifth metatarsal bone; these are described by some as a distinct muscle, the Opponens digiti quinti. THE PLANTAR MUSCLES OF THE FOOT 495 The Fourth Layer. Interossei. The Interossei in the foot are similar to those in the hand, with this exception, that they are grouped around the middle line of the second digit, instead of that of the third. They are seven in number, and consist of two groups, dorsal and plantar. The Interossei dorsales (Dorsal interossei) (Fig. 446), four in number, are situated between the metatarsal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metatarsal bones between which it is placed; their tendons are inserted into the bases of the first phalanges, and into the aponeurosis of the tendons of the Extensor digitorum longus. In the angular interval left between the heads of each of the three lateral muscles, one of the perforating arteries passes to the dorsum of the foot; through the space between the heads of the first muscle the deep plantar branch of the dorsalis pedis artery enters the sole of the foot. The first is inserted into the medial side of the second toe; the other three are inserted into the lateral sides of the second, third, and fourth toes. Fig. 446.—The Interossei dorsales. Left foot, Fio. 447.—The Interossei plantares. Left foot. The Interossei plantares (Plantar interossei) (Fig. 447), three in number, lie beneath rather than between the metatarsal bones, and each is connected with but one metatarsal bone. They arise from the bases and medial sides of the bodies of the third, fourth, and fifth "metatarsal bones, and are inserted into the medial sides of the bases of the first phalanges of the same toes, and into the aponeuroses of the tendons of the Extensor digitorum longus. Nerves.—The Flexor digitorum brevis, the Flexor hallucis brevis, the Abductor hallucis, and the first Lumbricalis are supplied by the medial plantar nerve; all the other muscles in the sole of the foot by the lateral plantar. The first Interosseous dorsalis frequently receives an extra filament from the medial branch of the deep peroneal nerve on the dorsum of the foot, and the second Interosseous dorsalis a twig from the lateral branch of the same nerve. Actions.—AH the muscles of the foot act upon the toes, and may be grouped as abductors, adductors, flexors, or extensors. The abductors are the Interossei dorsales, the Abductor hallucis, 496 MYOLOGY and the Abductor digiti quinti. The Interossei dorsales are abductors from an imaginary line passing through the axis of the second toe, so that the first muscle draws the second toe medial- ward, toward the great toe, the second muscle draws the same toe lateralward, and the third and fourth draw the third and fourth toes in the same direction. Like the Interossei in the hand, each assists in flexing the first phalanx and extending the second and third phalanges. The Abductor hallucis abducts the great toe from the second, and also flexes its proximal phalanx. In the same way the action of the Abductor digiti quinti is twofold, as an abductor of this toe from the fourth, and also as a flexor of its proximal phalanx. The adductors are the Interossei plantares and the Adductor hallucis. The Interossei plantares adduct the third, fourth, and fifth toes toward the imaginary line passing through the second toe, and by means of their inser- tions into the aponeuroses of the Extensor tendons they assist in flexing the proximal phalanges and extending the middle and terminal phalanges. The oblique head of the Adductor hallucis is chiefly concerned in adducting the great toe toward the second one, but also assists in flexing this toe; the transverse head approximates all the toes and thus increases the curve of the trans- verse arch of the metatarsus. The flexors are the Flexor digitorum brevis, the Quadratus plant®, the Flexor hallucis brevis, the Flexor digiti quinti brevis, and the Lumbricales. The Flexor digitorum brevis flexes the second phalanges upon the first, and, continuing its action, flexes the first phalanges also, and brings the toes together. The Quadratus plant® assists the Flexor digi- torum longus and converts the oblique pull of the tendons of that muscle into a direct backward pull upon the toes. The Flexor digiti quinti brevis flexes the little toe and draws its metatarsal bone downward and medialward. The Lumbricales, like the corresponding muscles in the hand, assist in flexing the proximal phalanges, and by their insertions into the tendons of the Extensor digitorum longus aid that muscle in straightening the middle and terminal phalanges. The Extensor digitorum brevis extends the first phalanx of the great toe and assists the long Extensor in extending the next three toes, and at the same time gives to the toes a lateral direction when they are extended. BIBLIOGRAPHY. Bardeen, C. R.: Development and Variation, etc., of the Inferior Extremity, etc., Am. Jour. Anat., 1907, vi. Bardeen and Lewis: Development of the Back, Body Wall and Limbs in Man, Am. Jour. Anat., 1901, i. Eisler, P.: Die Muskeln des Stammes, v. Bardeleben’s Handbuch der Anatomie des Menschen, Bd. ii, Abt. ii, Teil 1. Fick, R.: Anatomie und Mechanik der Gelenke unter Beriicksichtigung der bewegenden Muskeln, v. Bardeleben’s Handbuch der Anatomie des Menschen, Bd. ii, Abt. i, Teil 2 and 3. Frohse and Frankel: Die Muskeln des Menschlichen Beines; Die Muskeln des Menschlichen Armes, Handbuch der Anatomie des Menschen, von Bardeleben, Bd. ii, Abt. ii, Teil 2, A and B. Henle, J.: Handbuch der Systematischen Anatomie des Menschen, 1871-79. Koch, J. C.: The Laws of Bone Architecture, Am. Jour. Anat., 1917, xxi. Le Double: Traite des Variations du Systeme Musculaire de L’Homme, 1897. Lewis, W. H.: Development of the Arm in Man, Am. Jour. Anat., 1901, i. Lewis, W. H.: Development of the Muscular System, Iveibel and Mall, Manual of Human Embryology. Poirier, P., et Charpy, A.: Traite d’Anatomie, 1899-1901. * Testut, L.: Traite d’Anatomie Humaine, 1893-94. Wolfe, J.: Das Gesetz der Transformation der Knochen, Berlin, 1892. ANGIOLOGY. rPHE vascular system is divided for descriptive purposes into (a) the blood vascular system, which comprises the heart and bloodvessels for the circula- tion of the blood; and (b) the lymph vascular system, consisting of lymph glands and lymphatic vessels, through which a colorless fluid, the lymph, circulates. It must be noted, however, that the two systems communicate with each other and are intimately associated developmentallv. The heart is the central organ of the blood vascular system, and consists of a hollow muscle; by its contraction the blood is pumped to all parts of the body through a complicated series of tubes, termed arteries. The arteries undergo enormous ramification in their course throughout the body, and end in minute vessels, called arterioles, which in their turn open into a close-meshed network of microscopic vessels, termed capillaries. After the blood has passed through the capillaries it is collected into a series of larger vessels, called veins, by which it is returned to the heart. The passage of the blood through the heart and blood- vessels constitutes what is termed the circulation of the blood, of which the following is an outline. The human heart is divided by septa into right and left halves, and each half is further divided into two cavities, an upper termed the atrium and a lower the ventricle. The heart therefore consists of four chambers, two, the right atrium and right ventricle, forming the right half, and two, the left atrium and left ventricle the left half. The right half of the heart contains venous or impure blood; the left, arterial or pure blood. The atria are receiving chambers, and the ventricles dis- tributing ones. From the cavity of the left ventricle the pure blood is carried into a large artery, the aorta, through the numerous branches of which it is distributed to all parts of the body, with the exception of the lungs. In its passage through the capillaries of the body the blood gives up to the tissues the materials necessary for their growth and nourishment, and at the same time receives from the tissues the waste products resulting from their metabolism. In doing so it is changed from arterial into venous blood, which is collected by the veins and through them returned to the right atrium of the heart. From this cavity the impure blood passes into the right ventricle, and is thence conveyed through the pulmonary arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, and is then carried to the left atrium by the pulmonary veins. From the left atrium it passes into the left ventricle, from which the cycle once more begins. The course of the blood from the left ventricle through the body generally to the right side of the heart constitutes the greater or systemic circulation, while its passage from the right ventricle through the lungs to the left side of the heart is termed the lesser or pulmonary circulation. It is necessary, however, to state that the blood which circulates through the spleen, pancreas, stomach, small intestine, and the greater part of the large intes- tine is not returned directly from these organs to the heart, but is conveyed by the portal vein to the liver. In the liver this vein divides, like an artery, and ultimately ends in capillary-like vessels (sinusoids), from which the rootlets of a series of veins, called the hepatic veins, arise; these carry the blood into the inferior vena cava, 498 ANGIOLOGY whence it is conveyed to the right atrium. From this it will be seen that the blood contained in the portal vein passes through two sets of vessels: (1) the capillaries in the spleen, pancreas, stomach, etc., and (2) the sinusoids in the liver. The blood in the portal vein carries certain of the products of digestion: the carbo- hydrates, which are mostly taken up by the liver cells and stored as glycogen, and the protein products which remain in solution and are carried into the general circulation to the various tissues and organs of the body. Speaking generally, the arteries may be said to contain pure and the veins impure blood. This is true of the systemic, but not of the pulmonary vessels, since it has been seen that the impure blood is conveyed from the heart to the lungs by the pulmonary arteries, and the pure blood returned from the lungs to the heart by the pulmonary veins. Arteries, therefore, must be defined as vessels which convey blood from the heart, and veins as vessels which return blood to the heart. f Structure of Arteries (Fig. 448).—The arteries are composed of three coats: an internal or endothelial coat (tunica intima of Kolliker); a middle or muscular coat (tunica media); and an external or connective-tissue coat (tunica adventitia). The two inner coats together are very easily separated from the external, as by the ordinary operation of tying a ligature around an artery. If a fine string be tied forcibly upon an artery and then taken off, the external coat will be found undivided, but the two inner coats are divided in the track of the ligature and can easily be further dissected from the outer coat. The inner coat (tunica intima) can be separated from the middle by a little maceration, or it may be stripped off in small pieces; but, on account of its friability, it cannot be separated as a complete mem- brane. It is a fine, transparent, colorless structure which is highly elastic, and, after death, is commonly corrugated into longitudinal wrinkles. The inner coat consists of: (1) A layer of pavement endothelium, the cells of which are polygonal, oval, or fusiform, and have very distinct round or oval nuclei. This endothelium is brought into view most distinctly by staining with nitrate of silver. (2) A subendothelial layer, consisting of delicate connective tissue with branched cells lying in the interspaces of the tissue; in arteries of less than 2 mm. in diameter the sub- endothelial layer consists of a single stratum of stel- late cells, and the connective tissue is only largely developed in vessels of a considerable size. (3) An elastic or fenestrated layer, which consists of a mem- brane containing a net-work of elastic fibers, having principally a longitudinal direction, and in which, under the microscope, small elongated apertures or perforations may be seen, giving it a fenestrated ap- pearance. It was therefore called by Henle the fenes- trated membrane. This membrane forms the chief thickness of the inner coat, and can be separated into several layers, some of which present the appearance of a net-work of longitudinal elastic fibers, and others a more membranous character, marked by pale lines having a longitudinal direction. In minute arteries the fenestrated membrane is a very thin layer; but in the larger arteries, and especially in the aorta, it has a very considerable thickness. The middle coat (tunica media) is distinguished from the inner by its color and by the trans- verse arrangement of its fibers. In the smaller arteries it consists principally of plain muscle fibers in fine bundles, arranged in lamellae and disposed circularly around the vessel. These lamellae vary in number according to the size of the vessel; the smallest arteries having only a single layer (Fig. 449), and those slightly larger three or four layers. It is to this coat that the thickness of the wall of the artery is mainly due (Fig. 448A, m). In the larger arteries, as the Fig. 448.—Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. X 350. (Klein and Noble Smith.) A. Artery, showing the nucleated endo- thelium, e, which lines it; the vessel being con- tracted, the endothelial cells appear very thick. Underneath the endothelium is the wavy elastic lamina. The chief part of the wall of the vessel is occupied by the circular muscle coat m; the rod-shaped nuclei of the muscle cells are well seen. Outside this is a, part of the adventitia. This is composed of bundles of connective tissue fibers, shown in section, with the nuclei of the connec- tive tissue corpuscles. The adventitia gradually merges into the surrounding connective tissue. V. Vein showing a thin endothelial membrane, e, raised accidentally from the intima, which on account of its delicacy is seen as a mere line on the media m. This latter is composed of a few circular unstriped muscle cells a. The adventitia, similar in structure to that of an artery. STRUCTURE OF ARTERIES 499 iliac, femoral, and carotid, elastic fibers unite to form lamellae which alternate with the layers of muscular fibers; these lamellae are united to one another by elastic fibers which pass between the muscular bundles, and are connected with the fenestrated membrane of the inner coat (Fig. 450). In the largest arteries, as the aorta and innominate, the amount of elastic tissue is very considerable; in these vessels a few bundles of white connective tissue also have been found in the middle coat. The muscle fiber cells are about 50,a in length and contain well-marked, rod- shaped nuclei, which are often slightly curved. Che external coat (tunica adventitia) consists mainly of fine and closely felted bundles of white connective tissue, but also contains elastic fibers in all but the smallest arteries. The elastic tissue is much more abundant next the tunica media, and it is sometimes described as forming here, between the adventitia and media, a special layer, the tunica elastica externa of Henle. This layer is most marked in arteries of medium size. In the largest vessels the external coat is relatively thin; but in small arteries it is of greater proportionate thickness. In the smaller arteries it consists of a single layer of white connec- tive tissue and elastic fibers; while in the smallest arteries, just above the capillaries, the elastic fibers are wanting, and the connective tissue of which the coat is composed becomes more nearly homogeneous the nearer it approaches the capillaries, and is grad- ually reduced to a thin membranous envelope, which finally disappears. Some arteries have extremely thin walls in propor- tion to their size; this is especially the case in those situated in the cavity of the cranium and vertebral canal, the difference depending on the thinness of the external and middle coats. The arteries, in their distribution throughout the body, are included in thin fibro-areolar investments, which form their sheaths. The vessel is loosely con- nected with its sheath by delicate areolar tissue; and the sheath usually encloses the accompanying veins, and sometimes h nerve. Some arteries, as those in the cranium, are not included in sheaths. All the larger arteries, like the other organs of the body, are supplied with bloodvessels. These nutrient vessels, called the vasa vasorum, arise from a branch of the artery, or from a neighbor- ing vessel, at some considerable distance from the point at which they are distributed; they ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external coat, but do not, in man, penetrate the other coats; in some of the larger mammals a few vessels have been traced into the middle coat. Minute veins return the blood from these vessels; they empty themselves into the vein or veins accompanying the artery. Lymphatic vessels are also present in the outer coat. Arteries are also supplied with nerves, which are derived from the sympathetic, but may pass through the cerebrospinal nerves. They form intricate plexuses upon the surfaces of the larger trunks, and run along the smaller arteries as single filaments, or bundles of filaments which twist around the vessel and unite with each other in a plexiform manner. The branches derived from these plexuses penetrate the external coat and are distributed principally to the muscular tissue of the middle coat, and thus regulate, by causing the contraction and relaxation of this tissue the amount of blood sent to any part. The Capillaries.—The smaller arterial branches (excepting those of the cavernous structure of the sexual organs, of the splenic pulp, and of the placenta) terminate in net-works of vessels which pervade nearly every tissue of the body. These vessels, from their minute size, are termed capillaries. They are interposed between the smallest branches of the arteries and the commenc- ing veins, constituting a net-work, the branches of which maintain the same diameter throughout; the meshes of the net-work are more uniform in shape and size than those formed by the anasto- moses of the small arteries and veins. The diameters of the capillaries vary in the different tissues of the body, the usual size being about 8/i. The smallest are those of the brain and the mucous membrane of the intestines; and the largest those of the skin and the marrow of bone, where they are stated to be as large as in diameter. The form of the capillary net varies in the different tissues, the meshes being generally rounded or elongated. The rounded form of mesh is most common, and prevails where there is a dense network, as in the lungs, in most glands and mucous membranes, and in the cutis; the meshes are not of an absolutely circular outline, but more or less angular, sometimes nearly quadrangular, or polygonal, or more often irregular. Fia. 449.—Small artery and vein, pia mater of sheep. X 250. Surface view above the inter- rupted line; longitudinal section below. Artery in red; vein in blue, 500 ANGIOLOGY Elongated, meshes are observed in the muscles and nerves, the meshes resembling parallelograms in form, the long axis of the mesh running parallel with the long axis of the nerve or muscle. Sometimes the capillaries have a looped arrangement; a single vessel projecting from the common net-work and returning after forming one or more loops, as in the papillae of the tongue and skin. The number of the capillaries and the size of the meshes determine the degree of vascularity of a part. The closest network and the smallest interspaces are found in the lungs and in the choroid coat of the eye. In these situations the interspaces are smaller than the capillary vessels themselves. In the intertubular plexus of the kidney, in the conjunctiva, and in the cutis, the interspaces are from three to four times as large as the capillaries which form them; and in the brain from eight to ten times as large as the capillaries in their long diameters, and from four to six times as large in their transverse diameters. In the adventitia of arteries the width of the meshes is ten times that of the capillary vessels. As a general rule, the more active the func- tion of the organ, the closer is its capillary net and the larger its supply of blood; the meshes of the network are very narrow in all growing parts, in the glands, and in the mucous membranes, wider in bones and ligaments which are comparatively inactive; bloodvessels are nearly alto- gether absent in tendons, in which very little organic change occurs after their formation. In the liver the capillaries take a more or less radial course toward the intralobular vein, and their walls are incomplete, so that the blood comes into direct contact with the liver cells. These vessels in the liver are not true capillaries but "sinusoids;” they are developed by the growth of columns of liver cells into the blood spaces of the embryonic organ. Endothelial and sub- endothelial layer of . inner coat Elastic layer Innermost layers of middle coat Outermost layers of middle coat Innermost part of outer coat Outermost part of outer coat Fig. 450.—Section of a medium-sized artery. (After Grunstein.) Structure.—The wall of a capillary consists of a fine transparent endothelial layer, composed of cells joined edge to edge by an interstitial cement substance, and continuous with the endo- thelial cells which line the arteries and veins. When stained with nitrate of silver the edges which bound the epithelial cells are brought into view (Fig. 451). These cells are of large size and of an irregular polygonal or lanceolate shape, each containing an oval nucleus which may be dis- played by carmine or hematoxylin. Between their edges, at various points of their meeting, roundish dark spots are sometimes seen, which have been described as stomata, though they are closed by intercellular substance. They have been believed to be the situations through which the colorless corpuscles of the blood, when migrating from the bloodvessels, emerge; but this view, though probable, is not universally accepted. Kolossow describes these cells as having a rather more complex structure. He states that STRUCTURE OF VEINS 501 each consists of two parts, oi hyaline ground plates, and of a protoplasmic granular part, in which is imbedded the nucleus, on the outside of the ground plates. The hyaline' internal coat of the capillaries does not form a complete membrane, but consists of “plates” which are inelastic, and though in contact with each other are not continuous; when therefore the capillaries are sub- jected to intravascular pressure, the plates become separated from each other; the protoplasmic portions of the cells, on the other hand, are united together. In some organs, e. g., the glomeruli of the kidneys, intercellular cement cannot be demonstrated in the capillary wall and the cells are believed to form a syncytium. In many situations a delicate sheath or envelope of branched nucleated connective tissue cells is found around the simple capillary tube, particularly in the larger ones; and in other places, especially in the glands, the capillaries are invested with retiform connective tissue. Sinusoids—In certain organs, viz., the heart, the liver, the suprarenal and parathyroid glands, the glomus caroticum and glomus coccygeum, the smallest bloodvessels present various differences from true capillaries. They are wider, with an irregular lumen, and have no connective tissue covering, their endothelial cells being in direct contact with the cells of the organ. Moreover, they are either arterial or venous and not intermediate as are the true capillaries. These vessels have been called sinusoids by Minot. They are formed by columns of cells or trabeculae pushing their way into a large bloodvessel or blood space and carrying its endothe- lium before them; at the same time the wall of the vessel or space grows out between the cell columns. Structure of Veins.—The veins, like the arteries, are com- posed of three coats: internal, middle, and external; and these coats are, with the necessary modifications, analogous to the coats of the arteries; the internal being the endo- thelial, the middle the muscular, and the external the connective tissue or areolar (Fig. 452). The main differ- ence between the veins and the arteries is in the compara- tive weakness of the middle coat in the former. In the smallest veins the three coats are hardly to be dis- tinguished (Fig. 449). The endothelium is supported on a membrane separable into two layers, the outer of which is the thicker, and consists of a delicate, nucleated mem- brane (adventitia), while the inner is composed of a network of longitudinal elastic fibers (media). In the veins next above these in size (0.4 mm. in diameter), according to Kolliker, a connective tissue layer containing numerous muscle fibers circularly disposed can be traced, forming the middle coat, while the elastic and connective tissue elements of the outer coat become more distinctly perceptible. In the middle-sized veins the typical structure of these vessels becomes clear. The endothelium is of the same character as in the arteries, but its cells are more oval and less fusiform. It is supported by a connective tissue layer, consisting of a delicate net-work of branched cells, and external to this is a layer of elastic fibers disposed in the form of a net-work in place of the definite fenestrated membrane seen in the arteries. This constitutes the internal coat. The middle coat is composed of a thick layer of con- nective tissue with elastic fibers, intermixed, in some veins, with a transverse layer of muscular tissue. The white fibrous element is in considerable excess, and the elastic fibers are in much smaller proportion in the veins than in the arteries. The outer coat consists, as in the arteries, of areolar tissue, with longitudinal elastic fibers. In the largest veins the outer coat is from two to five times thicker than the middle coat, and contains a large number of longitudinal muscular fibers. These are most distinct in the inferior vena cava, especially at the termination of this vein in the heart, in the trunks of the hepatic veins, in all the large trunks of the portal vein, and in the external iliac, renal, and azygos veins. In the renal and portal veins they extend through the whole thickness of the outer coat, but in the other veins mentioned a layer of con- nective and elastic tissue is found external to the muscular fibers. All the large veins which open into the heart are covered for a short distance with a layer of striped muscular tissue continued on to them from the heart. Muscular tissue is wanting: (1) in the veins of the maternal part of the placenta; (2) in the venous sinuses of the dura mater and the veins of the pia mater of );he brain and medulla spinalis; (3) in the veins of the retina; (4) in the veins of the cancellous tissue of bones; (5) in the venous spaces of the corpora cavernosa. The veins of the above-men- tioned parts consist of an internal endothelial lining supported on one or more layers of areolar tissue. Most veins are provided with valves which serve to prevent the reflux of the blood. Each valve is formed by a reduplication of the inner coat, strengthened by connective tissue and elastic Pig. 451.—Capillaries from the .mesen- tery of a guinea-pig, after treatment with solution of nitrate of silver, a. Cells. b. Their nuclei. 502 ANGIOLOGY fibers, and is covered on both surfaces with endothelium, the arrangement of which differs on the two surfaces. On the surface of the valve next the wall of the vein the cells are arranged transversely; while on the other surface, over which the current of blood flows, the cells are arranged longitudinally in the direction of the current. Most commonly two such valves are found placed opposite one another, more especially in the smaller veins or in the larger trunks at the point where they are joined by smaller branches; occasionally there are three and some- times only one. The valves are semilunar. They are attached by their convex edges to the wall of the vein; the concave margins are free, directed in the course of the venous current, and lie in close apposition with the wall of the vein as long as the current of blood takes its natural course; if, however, any regurgitation takes place, the valves become distended, their opposed edges are brought into contact, and the current is interrupted. The wall of the vein on the cardiac side of the point of attachment of each valve is expanded into a pouch or sinus, which gives to the vessel, when injected or distended with blood, a knotted appearance. The valves are very numerous in the veins of the extremities, especially of the lower extremities, these vessels Endothelium ~ Elastic layer Middle coat Outer coat having to conduct the blood against the force of gravity. They are absent in the very small veins, i. e., those less than 2 mm. in diameter, also in the vense cava), hepatic, renal, uterine, and ovarian veins. A few valves are found in each spermatic vein, and one also at its point of junc- tion with the renal vein or inferior vena cava respectively. The cerebral and spinal veins, the veins of the cancellated tissue of bone, the pulmonary veins, and the umbilical vein and its branches, are also destitute of valves. A few valves are occasionally found in the azygos and intercostal veins. Rudimentary valves are found in the tributaries of the portal venous system. The veins, like the arteries, are supplied with nutrient vessels, vasa vasorum. Nerves also are distributed to them in the same manner as to the arteries, but in much less abundance. Fig. 452.—Section of a medium-sized vein. THE BLOOD. The blood is an opaque, rather viscid fluid, of a bright red or scarlet color when it flows from the arteries, of a dark red or purple color when it flows from the veins. It is salt to the taste, and has a peculiar faint odor and an alkaline reaction. Its specific gravity is about 1.06, and its temperature is generally about 37° C., though varying slightly in different parts of the body. THE BLOOD 503 General Composition of the Blood.—Blood consists of a faintly yellow fluid, the plasma or liquor sanguinis, in which are suspended numerous minute particles, the blood corpuscles, the majority of which are colored and give to the blood its red tint. If a drop of blood be placed in a thin layer on a glass slide and examined under the microscope, a number of these corpuscles will be seen floating in the plasma. The Blood Corpuscles are of three kinds: (1) colored cor- puscles or erythrocytes; (2) color- less corpuscles or leucocytes; (3) blood platelets. 1. Colored or red corpuscles (ierythrocytes), when examined under the microscope, are seen to be circular disks, biconcave in profile. The disk has no nucleus, but, in consequence of its bicon- cave shape, presents, according to the alterations of focus under an ordinary high power, a central part, sometimes bright, sometimes dark, which has the appearance of a nucleus (Fig. 453, a). It is to the aggregation of the red corpuscles that the blood owes its red hue, although when examined by transmitted light their color appears to be only a faint reddish yellow. The corpuscles vary slightly in size even in the same drop of blood, but the average diameter is about and the thickness about 2/j.. Besides these there are found certain smaller corpuscles of about one-half of the size just indicated; these are termed microcytes, and are very scarce in normal blood; in diseased con- ditions '{e. g., anemia), however, they are more numerous. The number of red corpuscles in the blood is enormous; between 4,000,000 and 5,000,000 are con- tained in a cubic millimetre. Power states that the red corpuscles of an adult would present an aggregate surface of about 3000 square yards. If the web of a living frog’s foot be spread out and examined under the micro- scope the blood is seen to flow in a continuous stream through the vessels, and the corpuscles show no tendency to adhere to each other or to the wall of the vessel. Doubtless the same is the case in the human body; but when human blood is drawn and examined on a slide without reagents the corpuscles tend to collect into heaps like rouleaux of coins (Fig. 453, b). It has been suggested that this phenomenon may be explained by alteration in surface tension. During life the red corpuscles may be seen to change their shape under pressure so as to adapt themselves, to some extent, to the size of the vessel. They are, however, highly elastic, and speedily recover their shape when the pressure is removed. They are readily influenced by the medium in which they are placed. In water they swell up, lose their shape, and become globular (endosmosis) (Fig. 453, c). Subsequently the hemoglobin is dissolved out, and the envelope can barely be distinguished as a faint circular outline. Solutions of salt or sugar, denser than the plasma, give them a stellate or crenated appearance (exosmosis) (Fig. 453, d), but the usual shape may be restored by diluting the solution to the same tonicity as the plasma. The crenated outline may be produced as the first effect of the passage of an elec- tric shock: subsequently, if sufficiently strong, the shock ruptures the envelope. A solution of salt, isotonic with the plasma, merely separates the blood corpuscles mechanically, without changing their shape. Two views are held with regard to Fig. 453.—Human red blood corpuscles. Highly magnified, a. Seen from the surface, b. Seen in profile and forming rouleaux, c. Rendered spherical by water, d. Rendered crenate by salt solution. * A micromillimetre (M ) is 1/1000 of a millimetre or 1/25000 of an inch. 504 ANGIOLOGY the structure of the erythrocytes. The older view, that of Rollett, supposes that the corpuscle consists of a sponge work or stroma permeated by a solution of hemo- globin. Schafer, on the other hand, believes that the hemoglobin solution is con- tained within an envelope or membrane, and the facts stated above with regard to the osmotic behavior of the erythrocyte support this belief. The envelope consists mainly of lecithin, cholesterin, and nucleoprotein. The colorless corpuscles or leucocytes are of various sizes, some no larger, others smaller, than the red corpuscles, In human blood, however, the majority are rather larger than the red corpuscles, and measure about 10/x in diameter. On the average from 7000 to 12,000 leucocytes are found in each cubic millimetre of blood. Fig. 454.—Varieties of leucocytes found in human blood. Highly magnified. They consist of minute masses of nucleated protoplasm, and exhibit several varieties, which are differentiated from each other chiefly by the occurrence or non-occurrence of granules in their protoplasm, and by the staining reactions of these granules when present (Fig. 454). (1) The most numerous (60 per cent.) and important are irregular in shape, possessed of the power of ameboid movement, and are characterized by nuclei which often consist of two or three parts (multi- partite) connected together by fine threads of chromatin. The protoplasm is clear, and contains a number of very fine granules, which stain with acid dyes, such as eosin, or with neutral dyes, and are therefore called oxyphil or neutrophil (Fig. 454, P). These cells are termed the polymorphonuclear leucocytes. (2) A second variety comprises from 1 to 4 per cent, of the leucocytes; they are larger than the previous kind, and are made up of coarsely granular protoplasm, the granules being highly retractile and grouped around single nuclei of horse-shoe shape (Fig. 454, E). The granules stain deeply with eosin, and the cells are there- fore often termed eosinophil corpuscles. (3) The third variety is called the hyaline cell or macrocyte (Fig. 454, II). This is usually about the same size as the eosino- phil cell, and, when at rest, is spherical in shape and contains a single round or oval nucleus. The protoplasm is free from granules, but is not quite transparent, having the appearance of ground glass. (4) The fourth kind of colorless corpuscle is designated the lymphocyte (Fig. 454, L), because it is identical with the cell derived from the lymph glands or other lymphoid tissue. It is the smallest of the leuco- cytes, and consists chiefly of a spheroidal nucleus with a very little surrounding protoplasm of a homogeneous nature; it is regarded as the immature form of the DEVELOPMENT OF THE VASCULAR SYSTEM 505 hyaiine cell. The third and fourth varieties together constitute from 20 to 30 per cent, of the colorless corpuscles, but of these two varieties the lymphocytes are by far the more numerous. Leucocytes having in their protoplasm granules which stain with basic dyes (basophil) have been described as occurring in human blood, but they are rarely found except in disease. The colorless corpuscles are very various in shape in living blood (Fig. 455), because many of them have the power of constantly changing their form by pro- truding finger-shaped or filamentous processes of their substance, by which they move and take up granules from the surrounding medium. In locomotion the corpuscle pushes out a process of its substance—a pseudopodium, as it is called Fig. 455.—Human colorless blood corpuscle, showing its successive changes of outline within ten minutes when kept moist on a warm stage. (Schofield.) —and then shifts the rest of the body into it. In the same way when any granule or particle comes in its way the corpuscle wraps a pseudopodium around it, and then withdraws the pseudopodium with the contained particle into its own substance. By means of these ameboid properties the cells have the power of wandering or emigrating from the bloodvessels by penetrating their walls and thus finding their way into the extravascular spaces. A chemical investigation of the proto- plasm of the leucocytes shows the presence of nucleoprotein and of a globulin. The occurrence of small amounts of fat, lecithin, and glycogen may also be demonstrated. The blood platelets (Fig. 456) are discoid or irregularly shaped, colorless, retractile bodies, much smaller than the red corpuscles. Each contains a central chromatin mass resembling a nucleus. Blood platelets possess the power of ameboid move- ment. When blood is shed they rapidly disintegrate and form granular masses, setting free prothrombin and the substance called by Howell thromboplastin. It is doubtful whether they exist normally in circu- lating blood. DEVELOPMENT OF THE VASCULAR SYSTEM. Bloodvessels first make their appearance in sev- eral scattered vascular areas which are developed simultaneously between the entoderm and the meso- derm of the yolk-sac, i. e., outside the body of the embryo. Here a new type of cell, the angioblast or vasoformative cell, is differentiated from the mesoderm. These cells as they divide form small, dense syncytial masses which soon join with similar masses by means of fine processes to form plexuses. These plexuses increase both by division and growth of its cells and by the addition of new angioblasts which differentiate from the mesoderm. Within these solid plexuses and also within the isolated masses of angioblasts vacuoles appear through liquefaction of the central part of the syncytium into plasma. The lumen of the bloodvessels thus formed is probably intracellular. The flattened cells at the periphery form the endothelium. The nucleated red blood corpuscles develop either from small masses of the original angioblast left attached to the inner wall of the lumen or directly from the flat endothelial cells. In either case the syncytial mass thus Fig. 456.—Blood platelets. Highly magnified. (After Kopsch.) 506 ANGIOLOGY formed projects from and is attached to the wall of the vessel. Such a mass is known as a blood island and hemoglobin gradually accumulates within it. Later the cells on the surface round up, giving the mass a mulberry-like appearance. Then the red blood cells break loose and are carried away in the plasma. Such free blood cells continue to divide. The term blood island was originally used for the syncytial masses of angioblasts found in the area vasculosa, but it is probably best to limit the term to the masses within the lumen from which the red blood cells arise as Sabin1 has done. Blood islands have been seen in the area vasculosa in the omphalomesenteric vein and arteries, and in the dorsal aorta. The differentiation of angioblasts from the mesoderm occurs not only in the area vasculosa but within the embryo and probably most of the larger bloodvessels are developed in situ in this manner. This process of the differentiation of angioblasts from the mesoderm probably ceases in different regions of the embryo at different periods and after its cessation new vessels are formed by sprouts from vessels already laid down in the form of capillary plexuses. The first rudiment of the heart appears as a pair of tubular vessels which are developed in the splanchnopleure of the peri- cardial area (Fig. 457). These are named the primitive aortae, and a direct continuity is soon established between them and the vessels of the yolk-sac. Each receives anteriorly a vein—the vitelline vein—from the yolk-sac, and is prolonged backward on the lateral aspect of the noto- chord under the name of the dorsal aorta. The dorsal aortae give branches to the yolk-sac, and are continued backward through the body-stalk as the umbilical arteries to the villi of the chorion. Eternod2 describes the circulation in an embryo which he estimated to be about thirteen days old (Fig. 458). The rudiment of the heart is situated immediately below the fore-gut and consists of a short stem. It gives off two vessels, the primi- tive aortae, which run backward, one on either side of the notochord, and then pass into the body-stalk along which they are carried to the chorion. From the chorionic villi the blood is returned by a pair of umbilical veins which unite in the body-stalk to form a single vessel and subsequently encircle the mouth of the yolk-sac and open into the heart. At the junction of the yolk-sac and body-stalk each vein is joined by a branch from the vascular plexus of the yolk-sac. From his observations it seems that, in the human embryo, the chorionic circulation is established before that on the yolk-sac. By the forward growth and flexure of the head the pericardial area and the anterior portions of the primitive aortae are folded backward on the ventral aspect of the fore-gut, and the original relation of the somatopleure and splanchnopleure layers of the pericardial area is reversed. Each primitive aorta now consists of a ventral and a dorsal part connected anteriorly by an arch (Fig. 459); these three parts are named respectively the anterior ventral aorta, the dorsal aorta, and the first cephalic arch. The vitelline veins which enter the embryo through the Fig. 457.—Transverse section through the region of the heart in a rabbit embryo of nine days. X 80. (Kolliker.) j, j. Jugular veins, ao. Aorta, ph. Pharynx, som. Somatopleure. bl. Proamnion. ect. Ectoderm, ent. Entoderm, p. Pericardium, spl. Splanchno- pleure. ah. Outer wall of heart, ih. Endothelial lining of heart, e'. Septum between heart tubes. 1 Anatomical Record, 1917, vol. xiii, p. 199. 2 Anat. Anzeiger, 1899, vol. xv. DEVELOPMENT OF THE VASCULAR SYSTEM 507 anterior wall of the umbilical orifice are now continuous with the posterior ends of the anterior ventral aorta. With the formation of the tail-fold the posterior parts of the primitive aortse are carried forward in a ventral direction to form the pos- terior ventral aortse and primary caudal arches.1 In the pericardial region the two primitive aortse grow together, and fuse to form a single tubular heart (Fig. 460), the posterior end of which receives the two vitelline veins, while from its anterior end the two anterior ventral aortse emerge.2 The first cephalic arches pass through the mandibular arches, and behind them five additional pairs subsequently develop, so that altogether six pairs of aortic arches are formed; the fifth arches are very transitory vessels connecting the ventral aortse with the dorsal ends of the sixth arches. By the rhythmical contraction of the tubular heart the blood is forced through the aortse and bloodvessels of the vascular area, from which it is returned to the heart by the vitelline veins. This constitutes the vitelline circulation (Fig. 459), and by means of it nutri- ment is absorbed from the yolk (vitellus.) The vitelline veins at first open separately into the poste- rior end of the tubular heart, but after a time their terminal por- tions fuse to form a single ves- sel. The vitelline veins ulti- mately drain the blood from the digestive tube, and are modified to form the portal vein. This is caused by the growth of the liver, which interrupts their direct continuity with the heart; and the blood returned by them cir- culates through the liver before reaching the heart. With the atrophy of the yolk- sac the vitelline circulation di- minishes and ultimately ceases, while an increasing amount of blood is carried through the um- bilical arteries to the villi of the chorion. Subsequently, as the non-placental chorionic villi atro- phy, their vessels disappear; and then the umbilical arteries con- vey the whole of their contents to the placenta, whence it is re- turned to the heart by the umbilical veins. In this manner the placental circu- lation is established, and by means of it nutritive materials are absorbed from, and waste products given up to the maternal blood. The umbilical veins, like the vitelline, undergo interruption in the developing liver, and the blood returned by them passes through this organ before reaching the heart. Ultimately the right umbilical vein shrivels up and disappears. During the occurrence of these changes great alterations take place in the primitive heart and bloodvessels. Heart-tubes Umbilical vein Umbilical vein Neurenteric canal Allantoic diverticulum Body-stalh Fig. 458.—Diagram of the vascular channels in a human embryo of the second week. (After Eternod.) The red lines are the dorsal aortae continued into the umbilical arteries. The red dotted lines are the ventral aortae, and the blue dotted lines the vitelline veins. 1 Young and Robinson, Journal of Anatomy and Physiology, vol. xxxii. 2 In most fishes and in the amphibia the heart originates as a single median tube. 508 ANGIOLOGY Further Development of the Heart.—Between the endothelial lining and the outer wall of the heart there exists for a time an intricate trabecular network of mesodermal tissue from which, at a later stage, the musculi papillares, chordae tendineae, and trabeculae carneae are developed. The simple tubular heart,.already Dorsal aorta Primitive jugular vein Amnion Cardinal vein Dorsal aorta Belly-stalk Chorionic villi- Fig. 459.—Human embryo of about fourteen days, with yolk-sac. (After His.) described, becomes elongated and bent on itself so as to form an S-shaped loop, the anterior part bending to the right and the posterior part to the left (Fig. 460). The intermediate portion arches transversely from left to right, and then turns sharply forward into the anterior part of the loop. Slight constrictions make their appearance in the tube and divide it from behind forward into five parts, viz.: Fore-brain Optic vesicle Bulbus cordis Atrium Ventricle Vitelline vein Fig. 460.—Head of chick embryo of about thirty-eight hours’ incubation, viewed from the ventral surface. X 26 (Duval.) (1) the sinus venosus; (2) the primitive atrium; (3) the primitive ventricle; (4) the bulbus cordis, and (5) the truncus arteriosus (Figs. 461, 462). The constriction between the atrium and ventricle constitutes the atrial canal, and indicates the site of the future atrioventricular valves. DEVELOPMENT OF THE VASCULAR SYSTEM 509 The sinus venosus is at first situated in the septum transversum (a layer of mesoderm in which the liver and the central tendon of the diaphragm are devel- oped) behind the primitive atrium, and is formed by the union of the vitelline veins. The veins or ducts of Cuvier from the body of the embryo and the umbilical veins from the placenta subsequently open into it (Fig. 463). The sinus is at first place transversely, and opens by a median aperture into the primitive atrium. Bulb us cordis /entricle- Atrium — Sinus venosus- Fig. 461.—Diagram to illustrate the simple tubular condition of the heart. (Drawn from Ecker-Ziegler model.) Vitelline veins* Fig. 462.—Heart of human embryo of about fourteen days. (From model by His.) Soon, however, it assumes an oblique position, and becomes crescentic in form; its right half or horn increases more rapidly than the left, and the opening into the atrium now communicates with the right portion of the atrial cavity. The right horn and transverse portion of the sinus ultimately become incorporated with and form a part of the adult right atrium, the line of union between it and the auricula being indicated in the interior of the atrium by a vertical crest, the crista terminalis of His. The left horn, which ultimately receives only the left duct of Cuvier, Maxillary process Stomodeum Mandibular arch Bulbus cordis Ventricle Atrium Duct of Cuvier Cardinal vein Bile-duct Umbilical vein Fig. 463.—Heart of human embryo of about fifteen days. (Reconstruction by His.) persists as the coronary sinus (Fig. 464). The vitelline and umbilical veins are soon replaced by a single vessel, the inferior vena cava, and the three veins (inferior vena cava and right and left Cuvierian ducts) open into the dorsal aspect of the atrium by a common slit-like aperture (Fig. 465). The upper part of this aperture repre- sents the opening of the permanent superior vena cava, the lower that of the inferior vena cava, and the intermediate part the orifice of the coronary sinus. The slit- 510 A NG10 LOGY like aperture lies obliquely, and is guarded by two halves, the right and left venous valves; above the opening these unite with each other and are continuous with a Left duct of Cuvier Opening into atrium Right duct of Cuvier Fig. 464.—Dorsal surface of heart of human embryo of thirty-five days. (From model by His ) Septum spurium Opening of sinus venosus Left venous valve Septum primum Right venous valve Spina vestibuli-' Posterior endocardial cushion Atrial canal' Fig. 465.—Interior of dorsal half of heart from a human embryo of about thirty days. (From model by His.) Septum, inferius fold named the septum spurium; below the opening they fuse to form a triangular thickening—the spina vestibuli. The right venous valve is retained; a small DEVELOPMENT OF THE VASCULAR SYSTEM septum, the sinus septum, grows from the posterior wall of the sinus venosus to fuse with the valve and divide it into two parts—an upper, the valve of the inferior vena cava, and a lower, the valve of the coronary sinus (Fig. 468). The extreme upper portion of the right venous valve, together with the septum spurium, form Right atrium Bulbus cordis Left atrium Atrial canal Ventricle Fig. 466.—Heart showing expansion of the atria. (Drawn from Ecker-Zeigler model.) the crista terminalis already mentioned. The upper and middle thirds of the left venous valve disappear; the lower third is continued into the spina vestibuli, and later fuses with the septum secundum of the atria and takes part in the forma- tion of the limbus fossae oval is. Opening of coronary sinus Septum secundum Septum spurium Left atrioventricular opening Right venous valuer Septum intermedium Right atrioventricular opening Septum inferius Fig. 467.—Interior of dorsal half of heart of human embryo of about thirty-five days. (From model by His.) The atrial canal is at first a short straight tube connecting the atrial with the ventricular portion of the heart, but its growth is relatively slow, and it becomes overlapped by the atria and ventricles so that its position on the surface of the heart is indicated only by an annular constriction (Fig. 466). Its lumen is reduced to a 512 ANGIOLOGY transverse slit, and two thickenings appear, one on its dorsal and another on its ventral wall. These thickenings, or endocardial cushions (Fig. 465) as they are termed, project into the canal, and, meeting in the middle line, unite to form the septum intermedium which divides the canal into two channels, the future right and left atrioventricular orifices. The primitive atrium grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria. The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum (Fig. 465), which grows downward into the cavity. For a time the atria communicate with each other by an opening, the ostium primum of Born, below the free margin of the septum. This opening is closed by the union of the septum primum with the septum inter- medium, and the communication between the atria is reestablished through an opening which is developed in the upper part of the septum primum; this opening is known as the foramen ovale (ostium secundum of Born) and persists until birth. Left duct of Cuvier Foramen ovale Probe in aorta Aortic septum Septum intermedium Septum inferius Opening of coronary sinus Fig. 468.—Same heart as in Fig. 467, opened on right side. (From model by His.) A second septum, the septum secundum (Figs. 467, 468), semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale. Shortly after birth it fuses with the primary septum, and by this means the foramen ovale is closed, but sometimes the fusion is incomplete and the upper part of the foramen remains patent. The limbus fossae ovalis denotes the free margin of the septum secundum. Issuing from each lung is a pair of pulmonary veins; each pair unites to form a single vessel, and these in turn join in a common trunk which opens into the left atrium. Subsequently the common trunk and the two vessels forming it expand and form the vestibule or greater part of the atrium, the expansion reaching as far as the openings of the four vessels, so that in the adult all four veins open separately into the left atrium. The primitive ventricle becomes divided by a septum, the septum inferius or ventricular septum (Figs. 465, 466, 467), wdiich growls upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow. Its dorsal part increases more rapidly than its ventral portion, and fuses with the dorsal part of the septum intermedium. For a time an interventricular foramen DEVELOPMENT OF THE VASCULAR SYSTEM 513 exists above its ventral portion (Fig. 468), but this foramen is ultimately closed by the fusion of the aortic septum with the ventricular septum. Fig. 469.—Diagrams to illustrate the transformation of the bulbus cordis. (Keith.) Ao. Truncus arteriosus, Au. Atrium. B. Bulbus cordis. RV. Right ventricle. IF. Left ventricle. P. Pulmonary artery. When the heart assumes its S-shaped form the bulbus cordis lies ventral to and in front of the primitive ventricle. The adjacent walls of the bulbus cordis and ventricle approximate, fuse, and finally disappear, and the bulbus cordis now Aortic septum Aortic septum Pulmonary artery v Aorta Common atrio- . ventricular aperture Left atrio- ventricular ' orifice Right atrio- ventricular orifice Right ventricle Right ventricle Septum inferius Left ventricle Septum inferius Left ventricle Fig. 470.—Diagrams to show the development of the septum of the aortic bulb and of the ventricles. (Born.) communicates freely with the right ventricle, while the junction of the bulbus with the truncus arteriosus is brought directly ventral to and applied to the atrial canal. By the upgrowth of the ventricular septum the bulbus cordis is in great measure Aorta Aorta Aorta Pulmonary artery Pulmo- nary artery Pulmonary artery Fig. 471.—Transverse sections through the aortic bulb to show the growth of the aortic septum. The lowest section is on the left, the highest on the right of the figure. (After His.) separated from the left ventricle, but remains an integral part of the right ventricle, of which it forms the infundibulum (Fig. 469). 514 ANGIOLOGY The truncus arteriosus and bulbus cordis are divided by the aortic septum (Fig. 470). This makes its appearance in three portions. (1) Two distal ridge-like thickenings project into the lumen of the tube; these increase in size, and ultimately meet and fuse to form a septum, which takes a spiral course toward the proximal end of the truncus arteriosus. It divides the distal part of the truncus into two vessels, the aorta and pulmonary artery, which lie side by side above, but near the heart the pulmonary artery is in front of the aorta. (2) Four endocardial cushions appear in the proximal part of the truncus arteriosus in the region of the future semilunar valves; the manner in which these are related to the aortic septum is described below. (3) Two endocardial thickenings—anterior and posterior— Third aortic arch Second aortic arch First aortic arch Auditory vesicle Primitive jugular vein Fourth aortic arch Olfactory pit Sixth aortic arch Dorsal aorta Maxillary process First branchial groove Mandibular arch Bulbus cordis Cardinal vein ~~Atrium - Ventricle Duct of Cuvier Digestive tube Vitelline vein Yolk-sac Hind-gut Allantois Umbilical artery Umbilical vein Fig. 472.—Profile view of a human embryo estimated at twenty or twenty-one days old. (After His.) develop in the bulbus cordis and unite to form a short septum; this joins above with the aortic septum and below with the ventricular septum. The septum grows down into the ventricle as an oblique partition, which ultimately blends with the ven- tricular septum in such a way as to bring the bulbus cordis into communication with the pulmonary artery, and through the latter with the sixth pair of aortic arches; while the left ventricle is brought into continuity with the aorta, which communicates with the remaining aortic arches. The Valves of the Heart.—The atrioventricular valves are developed in relation to the atrial canal. By the upward expansion of the bases of the ventricles the canal becomes invaginated into the ventricular cavities. The invaginated margin forms the rudiments of the lateral cusps of the atrioventricular valves; the mesial or DEVELOPMENT OF THE VASCULAR SYSTEM 515 septal cusps of the valves are developed as downward prolongations of the septum intermedium (Fig. 467). The aortic and pulmonary semilunar valves are formed from four endocardial thickenings—an anterior, a posterior, and two lateral— which appear at the proximal end of the truncus arteriosus. As the aortic septum grows downward it divides each of the lateral thickenings into two, thus giving rise to six thickenings—the rudiments of the semilunar valves—three at the aortic and three at the pulmonary orifice (Fig. 471). Further Development of the Arteries.—Recent observations show that practi- cally none of the main vessels of the adult arise as such in the embryo. In the site of each vessel a capillary network forms, and by the enlargement of definite paths in this the larger arteries and veins are developed. The branches of the main arteries are not always simple modifications of the vessels of the capillary network, but may arise as new outgrowths from the enlarged stem. External carotid Ventral aorta Internal carotid Common carotid Aortic arch Right subclavian artery Ductus arteriosus Right pulmonary artery Vertebral artery Subclavian artery Trunk of pulmonary artery Left 'pulmonary artery Fig. 473.—Scheme of the aortic arches and their destination. (Modified from Kollmann.) It has been seen (page 506) that each primitive aorta consists of a ventral and a dorsal part which are continuous through the first aortic arch. I he dorsal aortse at first run backward separately on either side of the notochord, but about the third week they fuse from about the level of the fourth thoracic to that of the fourth lumbar segment to form a single trunk, the descending aorta. Ihe first aortic arches run through the mandibular arches, and behind them five additional pairs are developed within the visceral arches; so that, in all, six pairs of aortic arches are formed (Figs. 472, 473). The first and second arches pass between the ventral and dorsal aortse, while the others arise at first by a common trunk from the truncus arteriosus, but end separately in the dorsal aortse. As the neck elongates, the ventral aortse are drawn out, and the third and fourth arches arise directly from these vessels. _ . In fishes these arches persist and give off branches to the gills, in which the blood is oxygenated. In mammals some of them remain as permanent structures, while others disappear or become obliterated (Fig. 473). 516 ANGIOLOGY The Anterior Ventral Aortse.—These persist on both sides. The right forms (a) the innominate artery, (b) the right common and external carotid arteries. The left gives rise to (a) the short portion of the aortic arch, which reaches from the origin of the innominate artery to that of the left common carotid artery; (6) the left common and external carotid arteries. The Aortic Arches.—The first and second arches disappear early, but the dorsal end of the second gives origin to the stapedial artery (Fig. 474), a vessel which atrophies in man but persists in some mammals. It passes through the ring of the stapes and divides into supraorbital, infraorbital, and mandibular branches which follow the three divisions of the trigeminal nerve. The infraorbital and man- Post, cerebral a. Ant. cerebral d. Supraorbital br. of stapedial a. Trigeminal nerve- Maxillary nerve Stapedial a, Infraorbital a.~ Mandibular nerve Mandibular a.. Ext. max. a.- Lingual a.- ■Int. carotid a. Slip, thyroid a.- Common carotid a.- Aortic arch Pulmonary arch Pulmonary art. Dorsal aorta Fig. 474.—Diagram showing the origins of the main branches of the carotid arteries. (Founded on Tandler.) dibular arise from a common stem, the terminal part of which anastomoses with the external carotid. On the obliteration of the stapedial artery this anastomosis enlarges and forms the internal maxillary artery, and the branches of the stapedial artery are now branches of this vessel. The common stem of the infraorbital and mandibular branches passes between the two roots of the auriculotemporal nerve and becomes the middle meningeal artery; the original supraorbital branch of the stapedial is represented by the orbital twigs of the middle meningeal. The third aortic arch constitutes the commencement of the internal carotid artery, and is therefore named the carotid arch. The fourth right arch forms the right sub- clavian as far as the origin of its internal mammary branch; while the fourth left arch constitutes the arch of the aorta between the origin of the left carotid artery DEVELOPMENT OF THE VASCULAR SYSTEM 517 and the termination of the ductus arteriosus. The fifth arch disappears on both sides. The sixth right arch disappears; the sixth left arch gives off the pulmonary arteries and forms the ductus arteriosus; this duct remains pervious during the whole of fetal life, but is obliterated a few days after birth. His showed that in the early embryo the right and left arches each gives a branch to the lungs, but that later both pulmonary arteries take origin from the left arch. The Dorsal Aortse. In front of the third aortic arches the dorsal aortse persist and form the continuations of the internal carotid arteries; these arteries pass to the brain and each divides into an anterior and a posterior branch, the former giving off the ophthalmic and the anterior and middle cerebral arteries, while the latter turns back and joins the cerebral part of the vertebral artery. Behind the third arch the right dorsal aorta disappears as far as the point where the two dorsal aortse fuse to form the descending aorta. The part of the left dorsal aorta between the third and fourth arches disappears, while the remainder persists to form the descending part of the arch of the aorta. A constriction, the aortic isthmus, is sometimes seen in the aorta between the origin of the left subclavian and the attachment of the ductus arteriosus. Sometimes the right subclavian artery arises from the aortic arch distal to the origin of the left subclavian and passes upward and to the right behind the trachea and esophagus. This condition may be explained by the persistence of the right dorsal aorta and the obliteration of the fourth right arch. In birds the fourth right arch forms the arch of the aorta; in reptiles the fourth arch on both sides persists and gives rise to the double aortic arch in these animals. The heart originally lies on the ventral aspect of the pharynx, immediately behind the stomodeum. With the elongation of the neck and the development of the lungs it recedes within the thorax, and, as a consequence, the anterior ventral aortse are drawn out and the original position of the fourth and fifth arches is greatly modified. Thus, on the right side the fourth recedes to the root of the neck, while on the left side it is withdrawn within the thorax. The recurrent nerves originally pass to the larynx under the sixth pair of arches, and are there- fore pulled backward with the descent of these structures, so that in the adult the left nerve hooks around the ligamentum arteriosum; owing to the disappearance of the fifth and the sixth right arches the right nerve hooks around that immediately above them, i. e., the commencement of the subclavian artery. Segmental arteries arise from the primitive dorsal aortse and course between successive segments. The seventh segmental artery is of special interest, since it forms the lower end of the vertebral artery and, when the forelimb bud appears, sends a branch to it (the subclavian artery). From the seventh segmental arteries the entire left subclavian and the greater part of the right subclavian are formed. The second pair of segmental arteries accompany the hypoglossal nerves to the brain and are named the hypoglossal arteries. Each sends forward a branch which forms the cerebral part of the vertebral artery and anastomoses with the posterior branch of the internal carotid. The two vertebrals unite on the ventral surface of the hind-brain to form the basilar artery. Later the hypoglossal artery atrophies and the vertebral is connected with the first segmental artery. The cervical part of the vertebral is developed from a longitudinal anastomosis between the first seven segmental arteries, so that the seventh of these ultimately becomes the source of the artery. As a result of the growth of the upper limb the subclavian artery increases greatly in size and the vertebral then appears to spring from it. Recent observations show that several segmental arteries contribute branches to the upper limb-bud and form in it a free capillary anastomosis. Of these branches, only one, viz., that derived from the seventh segmental artery, persists to form the subclavian artery. The subclavian artery is prolonged into the limb under the names of the axillary and brachial arteries, and these together constitute the 518 ANGIOLOGY arterial stem for the upper arm, the direct continuation of this stem in the forearm is the volar interosseous artery. A branch which accompanies the median nerve soon increases in size and forms the main vessel (median artery) of the forearm, while the volar interosseous diminishes. Later the radial and ulnar arteries are developed as branches of the brachial part of the stem and coincidently with their enlargement the median artery recedes; occasionally it persists as a vessel of some considerable size and then accompanies the median nerve into the palm of the hand. The primary arterial stem for the lower limb is formed by the inferior gluteal (sciatic) artery, which accompanies the sciatic nerve along the posterior aspect of the thigh to the back of the knee, whence it is continued as the peroneal artery. This arrangement exists in reptiles and amphibians. The femoral artery arises later as a branch of the common iliac, and, passing down the front and medial side of the thigh to the bend of the knee, joins the inferior gluteal artery. The femoral quickly enlarges, and, coincidently with this, the part of the inferior gluteal immediately above the knee undergoes atrophy. The anterior and posterior tibial arteries are branches of the main arterial stem. Anterior detached portions of umbilical veins Venae revehentes Stomach Ductus venosus Venae advehentes Pancreas Bile-duct -Liver Obliterated portions of venous rings Bight umbilical vein Left umbilical vein Portal vein Duodenum V itelline veins Fig. 475.—The liver and the veins in connection with it, of a human embryo, twenty-four or twenty-five days old, as seen from the ventral surface. (After His.) Further Development of the Veins.—The formation of the great veins of the embryo may be best considered by dividing them into two groups, visceral and parietal. The Visceral Veins.—The visceral veins are the two vitelline or omphalomesenteric veins bringing the blood from the yolk-sac, and the two umbilical veins returning the blood from the placenta; these four veins open close together into the sinus venosus. The Vitelline Veins run upward at first in front, and subsequently on either side of the intestinal canal. They unite on the ventral aspect of the canal, and beyond this are connected to one another by two anastomotic branches, one on the dorsal, and the other on the ventral aspect of the duodenal portion of the intestine, which is thus encircled by two venous rings (Fig. 475); into the middle or dorsal anastomosis the superior mesenteric vein opens. The portions of the veins above the upper ring become interrupted by the developing liver and broken up by it into DEVELOPMENT OF THE VASCULAR SYSTEM 519 a plexus of small capillary-like vessels termed sinusoids (Minot). The branches com eying the blood to this plexus are named the venae advehentes, and become the branches of the portal vein; while the vessels draining the plexus into the sinus venosusjire termed the venae revehentes, and form the future hepatic veins (Figs. 4t5, 476). Ultimately the left vena revehens no longer communicates directly with the sinus venosus, but opens into the right vena revehens. The persistent part of the upper venous ring, above the opening of the superior mes- enteric vein, forms the trunk of the portal vein. Right primitive jugular vein Right cardinal vein Left primitive jugular vein Left cardinal vein Right duct of Cuvier Sinus venosus Left duct of Cuvier Right hepatic vein Left hepatic vein Portal vein Left umbilical vein Portal vein Right umbilical vein Left umbilical vein Umbilical cord- Fia. 476.—Human embryo with heart and anterior body-wall removed to show the sinus venosus and its tributaries. (After His.) The two Umbilical Veins fuse early to form a single trunk in the body-stalk, but remain separate within the embryo and pass forward to the sinus venosus in the side walls of the body. Like the vitelline veins, their direct connection with the sinus venosus becomes interrupted by the developing liver, and thus at this stage the whole of the blood from the yolk-sac and placenta passes through the substance of the liver before it reaches the heart. The right umbilical and right vitelline veins shrivel and disappear; the left umbilical, on the other hand, becomes enlarged and opens into the upper venous ring of the vitelline veins; with the atrophy of the yolk-sac the left vitelline vein also undergoes atrophy and disappears. Finally a direct branch is established between this ring and the right hepatic vein; this branch is named the ductus venosus, and, enlarging rapidly, it forms a wide channel through which most of the blood, returned from the placenta, is carried direct to the heart without passing through the liver. A small proportion of the blood from the placenta is, however, conveyed from the left umbilical vein to the liver through the left vena advehens. The left umbilical 520 ANGIOLOGY vein and the ductus venosus undergo atrophy and obliteration after birth, and form respectively the ligamentum teres and ligamentum venosum of the liver. The Parietal Veins.—The first indication of a parietal, system consists in the appearance of two short transverse veins, the ducts of Cuvier, which open, one on either side, into the sinus venosus. Each of these ducts receives an ascending and descending vein. The ascending veins return the blood from the parietes of the trunk and from the Wolffian bodies, and are called cardinal veins. The descending veins return the blood from the head, and are called primitive jugular veins (Fig. 477). The blood from the lower limbs is collected by the right and left iliac and hypogastric veins, which, in the earlier stages of development, open into the corresponding right and left cardinal veins; later, a transverse branch (the left common iliac vein) is developed between the lower parts of the two cardinal veins (Fig. 479), and through this the blood is carried into the right cardinal vein. The portion of the left cardinal vein below the left renal vein atrophies and dis- appears up to the point of entrance of the left spermatic vein; the portion above Sinus venosus J—Internal jugular Primitive jugular —External jugular Subclavian Subclavian ~Duct of Cuvier -Duct of Cuvier V itelline Left cardinal Umbilical Ductus venosus Cardinal Subcardinal Renal Renal Subcardinal External iliac External iliac -Hypogastric Hypogastric Fig. 477.—Scheme of arrangement of parietal veins. Fig. 478.—Scheme showing early stages of development of the inferior vena cava. the left renal vein persists as the hemiazygos and accessory hemiazygos veins and the lower portion of the highest left intercostal vein. The right cardinal vein which now receives the blood from both lower extremities, forms a large venous trunk along the posterior abdominal wall; up to the level of the renal veins it forms the lower part of the inferior vena cava. Above the level of the renal veins the right cardinal vein persists as the azygos vein and receives the right intercostal veins, while the hemiazygos veins are brought into communication with it by the development of transverse branches in front of the vertebral column (Figs. 479, 480) Inferior Vena Cava.—The development of the inferior vena cava is associated with the formation of two veins, the subcardinal veins (Figs. 477, 478). These lie parallel to, and on the ventral aspect of, the cardinal veins, and originate as longitudinal anastomosing channels which link up the tributaries from the mes- entery to the cardinal veins; they communicate with the cardinal veins above and below, and also by a series of transverse branches. The two subcardinals are for a time connected with each other in front of the aorta by cross branches, but these disappear and are replaced by a single transverse channel at the level where the DEVELOPMENT OF THE VASCULAR SYSTEM 521 renal veins join the cardinals, and at the same level a cross communication is established on either side between the cardinal and subeardinal (Fig. 478). The portion of the right subcardinal behind this cross communication disappears, while Left innominate ■Internal jugular “External jugular Right innominate Superior vena cava ■Duct of Cuvier Left cardinal Prerenal part of inferior vena cava Left suprarenal Left renal Postrenal part of inferior vena cava Left common iliac External iliac Fig. 479.—Diagram showing development of main cross branches between jugulars and between cardinals. Hypogastric that in front, i. e., the prerenal part, forms a connection with the ductus venosus at the point of opening of the hepatic veins, and, rapidly enlarging, receives the Left innominate Internal jugular External jugular Subclavian Right innominate _ Highest left intercostal Ligament of left vena cava Superior vena cava _ Azygos vein - Oblique vein of left atrium Coronary sinus Accessory hemiazygos vein -Hemiazygos vein Prerenal part of inferior vena cava -Left suprarenal -Left renal —Left internal spermatic Left common iliac External iliac Hypogastric blood from the postrenal part of the right cardinal through the cross communica- tion referred to. In this manner a single trunk, the inferior vena cava (Fig. 480), is formed, and consists of the proximal part of the ductus venosus, the prerenal part Fig. 480.—Diagram showing completion of development of the parietal veins. 522 ANGIOLOGY of the right subcardinal vein, the postrenal part of the right cardinal vein, and the cross branch which joins these two veins. The left subcardinal disappears, except the part immediately in front of the renal vein, which is retained as the left supra- renal vein. The spermatic (or ovarian) vein opens into the postrenal part of the corresponding cardinal vein. This portion of the right cardinal, as already explained, forms the lower part of the inferior vena cava, so that the right spermatic opens directly into that vessel. The postrenal segment of the left cardinal dis- appears, with the exception of the portion between the spermatic and renal vein, which is retained as the terminal part of the left spermatic vein. In consequence of the atrophy of the Wolffian bodies the cardinal veins diminish in size; the primitive jugular veins, on the other hand, become enlarged, owing to the rapid development of the head and brain. They are further augmented by receiving the veins (subclavian) from the upper extremities, and so come to form the chief veins of the Cuvierian ducts; these ducts gradually assume an almost vertical position in consequence of the descent of the heart into the thorax. The right and left Cuvierian ducts are originally of the same diameter, and are frequently termed the right and left superior venae cavae. By the development of a transverse branch, the left innominate vein between the two primitive jugular veins, the blood is carried across from the left to the right primitive jugular (Figs. 479, 480). The portion of the right primitive jugular vein between the left innominate and the azygos vein forms the upper part of the superior vena cava of the adult; the lower part of this vessel, i. e., below the entrance of the azygos vein, is formed by the right Cuvierian duct. Below the origin of the transverse branch the left primitive jugular vein and left Cuvierian duct atrophy, the former constituting the upper part of the highest left intercostal vein, while the latter is represented by the ligament of the left vena cava, vestigial fold of Marshall, and the oblique vein of the left atrium, oblique vein of Marshall (Fig. 480). Both right and left superior venae cavae are present in some animals, and are occasionally found in the adult human being. The oblique vein of the left atrium passes downward across the back of the left atrium to open into the coronary sinus, which, as already indicated, represents the persistent left horn of the sinus venosus. Venous Sinuses of the Dura Mater.1—The primary arrangement for drainage of the capillaries of the head (Figs. 481, 488) consists of a primary head vein which starts in the region of the midbrain and runs caudalward along the side of the brain tube to terminate at the duct of Cuvier. The primary head vein drains three plexuses of capillaries: the anterior dural plexus, the middle dural plexus and the posterior dural plexus. The growth of the cartilaginous capsule of the ear and the growth and alteration in form of the brain bring about changes in this primary arrangement (Figs. 483-488). Owing to the growth of the otic capsule and middle ear the course of the primary head vein becomes unfavorable and a segment of it becomes obliterated. To make the necessary adjustment an anastomosis is estab- lished above the otic capsule (Fig. 483) and the middle plexus drains into the poste- rior plexus. Then the anteror plexus fuses with the middle plexus (Fig. 484) and drains through it and the newly estabished channel, dorsal to the otic capsule. All that remains of the primary head vein is the cardinal portion or internal jugular and the part in the region of the trigeminal nerve which may be called the cavernous sinus. Into it drain the orbital veins. The drainage from the cavernous sinus is now upward through the original trunk of the middle plexus, which is now the superior petrosal sinus, into the newly established dorsal channel. This dorsal channel is the transverse sinus (Figs. 485-488). The inferior petrosal sinus appears later (Fig. 486). From the anterior plexus a sagittal plexus extends forward from which develops the superior sagittal sinus (Figs. 484-488). The straight sinus is Streeter, Am. Jour. Anat., 1915, vol. xviii. DEVELOPMENT OF THE VASCULAR SYSTEM 523 formed in the ventral part of the sagittal plexus. As the hemispheres extend back- ward these sinuses elongate by incorporating the more caudal loops of the plexus. The anterior part of the sinus is completed first. PLEXUS. MEDIALIS PLEXUS MEDIALIS >A TRIGEMINUS, RLEXUS ANT V. CAPITIS PRIMA PLEXUS V. CAPITIS PRIMA PLEXUS ' POST. PLEXUS POST 481 482 PLEXUS MEDIALIS PLEXUS ANT ' RLEXUS ANT , PLEXUS POST. Plexus 6agittalis ,SIN. TRANS. PLEXUS POST. SIN. PETROS. I SUP. — /foramen /jugulars V OPTHAL.. PARS SIGMOia SIN. CAVERNOSUS / _V. JUG INT. , 483 484 SIN. RECTUS SIN. i SAGITTALIS SUP\ SIN. RECTUS PLEXUS ANT. Sin, sagittaus sup. PLEXUS ANT. SIN. TRANSVERSUS SIN. TRANSVERSUS Sigmoid. SIGMOID. V. OPTHAL.' V. OPTHAL. SIN. CAVERN. _ v. JUG. NT SIN. CAVERNOSUS SIN. PETROS. INF. 485 486 SIN. SAGITTALIS SUP! SIN. SAGITTALIS SUF». (SIN. SAGITTALIS i INP. . SIN- RECTUS .CONFLUEN9 SINUUM , SIN. RECTU9 V.PPTHAL. l SIN. TRANS. V. OPTHAL, -CONFLUEN9 SINUUM ySlN. CAVERN/ Is PETROS. INF/ LPARS SIGMOID^ SIN. CAVERN/ S. PETROS. INF/ '•SIN. TRANS. S. PETROS. SUP. S. PETROS. SUP. PARS SIGMOID. V. JUG INT. 487 -V. JUG. INT 488 Figs. 481 to 488.—Profile drawings of the dural veins showing principal stages in their development in human embryos from 4 mm. to birth. It is of particular interest to notice their adaptation to the growth and changes in the form of the central nervous system. Fig. 481,4 mm.; Fig. 482, 14 mm.; Fig. 483, 18 mm.; Fig. 484, 21 mm Fig. 485 35 mm.; Fig. 486, 50 mm. crown-rump length; Fig. 487, 80 mm. crown-rump length; Fig. 488, adult. ( j 524 ANGIOLOGY The external jugular vein at first drains the region behind the ear (posterior auricular) and enters the primitive jugular as a lateral tributary. A group of veins from the face and lingual region converge to form a common vein, the linguo-facial,1 which also terminates in the primitive jugular. Later, cross communications develop between the external jugular and the linguo-facial, with the result that the posterior group of facial veins is transferred to the external jugular. THE THORACIC CAVITY. The heart and lungs are situated in the thorax, the walls of which afford them protection. The heart lies between the two lungs, and is enclosed within a fibrous bag, the pericardium, while each lung is invested by a serous membrane, the pleura. The skeleton of the thorax, and the shape and boundaries of the cavity, have already been described (page 117). The Cavity of the Thorax.—The capacity of the cavity of the thorax does not correspond with its apparent size externally, because (1) the space enclosed by the lower ribs is occupied by some of the abdominal viscera; and (2) the cavity extends above the anterior parts of the first ribs into the neck. The size of the thoracic cavity is constantly varying during life with the movements of the ribs and diaphragm, and with the degree of distention of the abdominal viscera. From the collapsed state of the lungs as seen when the thorax is opened in the dead body, it would appear as if the viscera only partly filled the cavity, but during life there is no vacant space, that which is seen after death being filled up by the expanded lungs. The Upper Opening of the Thorax.—The parts which pass through the upper opening of the thorax are, from before backward, in or near the middle line, the Sternohyoideus and Sternothyreoideus muscles, the remains of the thymus, the inferior thyroid veins, the trachea, esophagus, thoracic duct, and the Longus colli muscles; at the sides, the innominate artery, the left common carotid, left subclavian and internal mammary arteries and the costocervical trunks, the innominate veins, the vagus, cardiac, phrenic, and sympathetic nerves, the greater parts of the anterior divisions of the first thoracic nerves, and the recurrent nerve of the left side. The apex of each lung, covered by the pleura, also projects through this aperture, a little above the level of the sternal end of the first rib. The Lower Opening of the Thorax.—The lower opening of the thorax is wider transversely than from before backward. It slopes obliquely downward and back- ward, so that the thoracic cavity is much deeper behind than in front. The dia- phragm (see page 404) closes the opening ahd forms the floor of the thorax. The floor is flatter at the center than at the sides, and higher on the right side than on the left; in the dead body the right side reaches the level of the upper border of the fifth costal cartilage, while the left extends only to the corresponding part of the sixth costal cartilage. From the highest point on each side the floor slopes suddenly downward to the costal and vertebral attachments of the diaphragm; this slope is more marked behind than in front, so that only a narrow space is left between the diaphragm and the posterior wall of the thorax. THE PERICARDIUM. The pericardium (Fig. 489) is a conical fibro-serous sac, in which the heart and the roots of the great vessels are contained. It is placed behind the sternum and the cartilages of the third, fourth, fifth, sixth, and seventh ribs of the left side, in the mediastinal cavity. Lewis, American Journa of Anatomy, February, 1909, No. 1, vol. ix. THE PERICARDIUM 525 In front, it is separated from the anterior wall of the thorax, in the greater part of its extent, by the lungs and pleurae; but a small area, somewhat variable in size, and usually corresponding with the left half of the lower portion of the body of the sternum and the medial ends of the cartilages of the fourth and fifth ribs of the left side, comes into direct relationship with the chest wall. The lower extrem- ity of the thymus, in the child, is in contact with the front of the upper part of the pericardium. Behind, it rests upon the bronchi, the esophagus, the descending thoracic aorta, and the posterior part of the mediastinal surface of each lung. Laterally, it is covered by the pleurae, and is in relation with the mediastinal sur- faces of the lungs; the phrenic nerve, with its accompanying vessels, descends between the pericardium and.pleura on either side. Jl. subclavian a. JR. common carotid a. L. common carotid a. L. subclavian a. Cut edges of serous 'pericardium Sup. vena cava L. pulmonary veins R. pulmonary veins Fig. 489.—Posterior wall of the pericardial sac, showing the lines of reflection of the serous pericardium on the great vessels. Structure of the Pericardium.—Although the pericardium is usually described as a single sac, an examination of its structure shows that it consists essentially of two sacs intimately connecte with one another, but totally different in structure, the outer sac, known as t e rous peri cardium, consists of fibrous tissue. The inner sac, or serous pericardium, is a delicate mem- brane which lies within the fibrous sac and lines its walls; it is composed of a sing e ayer o 526 ANGIOLOGY flattened cells resting on loose connective tissue. The heart invaginates the wall of the serous sac from above and behind, and practically obliterates its cavity, the space being merely a potential one. The fibrous pericardium forms a flask-shaped bag, the neck of which is closed by its fusion with the external coats of the great vessels, while its base is attached to the central tendon and to the muscular fibers of the left side of the diaphragm. In some of the lower mammals the base is either completely separated from the diaphragm or joined to it by some loose areolar tissue; in man much of its diaphragmatic attachment consists of loose fibrous tissue which can be readily broken down, but over a small area the central tendon of the diaphragm and the pericardium are completely fused. Above, the fibrous pericardium not only blends with the external coats of the great vessels, but is continuous with the pretracheal layer of the deep cervical fascia. By means of these upper and lower connections it is securely anchored within the thoracic cavity. It is also attached to the posterior surface of the sternum by the superior and inferior stemopericardiac ligaments; the upper passing to the manubrium, and the lower to the xiphoid process. The vessels receiving fibrous prolongations from this membrane are: the aorta, the superior vena cava, the right and left pulmonary arteries, and the four pulmonary veins. The inferior vena cava enters the pericardium through the central tendon of the diaphragm, and receives no covering from the fibrous layer. The serous pericardium is, as already stated, a closed sac which lines the fibrous pericardium and is invaginated by the heart; it therefore consists of a visceral and a parietal portion. The visceral portion, or epicardium, covers the heart and the great vessels, and from the latter is continuous with the parietal layer which lines the fibrous pericardium. The portion which covers the vessels is arranged in the form of two tubes. The aorta and pulmonary artery are enclosed in one tube, the arterial mesocardium. The superior and inferior venae cavae and the four pulmonary veins are enclosed in a second tube, the venous mesocardium, the attachment of which to the parietal layer presents the shape of an inverted U. The cul-de-sac enclosed between the limbs of the II lies behind the left atrium and is known as the oblique sinus, while the passage between the venous and arterial mesocardia—i. e., between the aorta and pulmonary artery in front and the atria behind—is termed the transverse sinus. The Ligament of the Left Vena Cava.—Between the left pulmonary artery and subjacent pulmonary vein is a triangular fold of the serous pericardium; it, is known as the ligament of the left vena cava (vestigial fold of Marshall). It is formed by the duplicature of the serous layer over the remnant of the lower part of the left superior vena cava (duct of Cuvier), which becomes obliterated during fetal life, and remains as a fibrous band stretching from the highest left inter- costal vein to the left atrium, where it is continuous with a small vein, the vein of the left atrium (oblique vein of Marshall), which opens into the coronary sinus. The arteries of the pericardium are derived from the internal mammary and its musculo- phrenic branch, and from the descending thoracic aorta. The nerves of the percardium are derived from the vagus and phrenic nerves, and the sympa- thetic trunks. THE HEART (COR). The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium (Fig. 490). It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane. Size.—The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women. Component Parts.—As has already been stated (page 497), the heart is sub- divided by septa into right and left halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium, the lower the ventricle. The heart therefore consists of four chambers, viz., right and left atria, and right and left ventricles. The division of the heart into four cavities is indicated on its surface by grooves. The atria are separated from the ventricles by the coronary sulcus (auriculo- THE HEART 527 ventricular groove?); this contains the trunks of the nutrient vessels of the heart, and is deficient in front, where it is crossed by the root of the pulmonary artery. The interatrial groove, separating the two atria, is scarcely marked on the posterior surface, while anteriorly it is hidden by the pulmonary artery and aorta. The \ entrides are separated by two grooves, one of which, the anterior longitudinal sulcus, is situated on the sternocostal surface of the heart, close to its left margin, the other posterior longitudinal sulcus, on the diaphragmatic surface near the right margin; these grooves extend from the base of the ventricular portion to a notch, the incisura apicis cordis, on the acute margin of the heart just to the right of the apex. Cut edge of 'pericardium, Left auricula Fig. 490.—Front view of heart and lungs. The base (basis cordis) (Fig. 491), directed upward, backward, and to the right, is separated from the fifth, sixth, seventh, and eighth thoracic vertebrae by the esophagus, aorta, and thoracic duct. It is formed mainly by the left atrium, and, to a small extent, by the back part of the right atrium. Somewhat quadri- lateral in form, it is in relation above with the bifurcation of the pulmonary artery, and is bounded below by the posterior part of the coronary sulcus, containing the coronary sinus. On the right it is limited by the sulcus terminalis of the right atrium, and on the left by the ligament of the left vena cava and the oblique vein of the left atrium. The four pulmonary veins, two on either side, open into the left atrium, while the superior vena cava opens into the upper, and the anterior vena cava into the lower, part of the right atrium. The Apex (apex cordis).—The apex is directed downward, forward, and to the left, and is overlapped by the left lung and pleura: it lies behind the fifth left intercostal space, 8 to 9 cm. from the mid-sternal line, or about 4 cm. below and 2 mm. to the medial side of the left mammary papilla. 528 ANGIOLOGY The sternocostal surface (Fig. 492) is directed forward, upward, and to the left. Its lower part is convex, formed chiefly by the right ventricle, and traversed near its left margin by the anterior longitudinal sulcus. Its upper part is separated from the lower by the coronary sulcus, and is formed by the atria; it presents a deep concavity (Fig. 494), occupied by the ascending aorta and the pulmonary artery. The diaphragmatic surface (Fig. 491), directed downward and slightly backward, is formed by the ventricles, and rests upon the central tendon and a small part of the left muscular portion of the diaphragm. It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus. The right margin of the heart is long, and is formed by the right atrium above and the right ventricle below. The atrial portion is rounded and almost vertical; it is situated behind the third, fourth, and fifth right costal cartilages about Azygos vein Left pulmonary veins < Right pulmonary veins Oblique vein ofleftctrium Great cardiac vein Left marginal vein Small cardiac vein Posterior vein of left ventricle Fig. 491.—Base and diaphragmatic surface of heart. Middle cardiac vein 1.25 cm. from the margin of the sternum. The ventricular portion, thin and sharp, is named the acute margin; it is nearly horizontal, and extends from the sternal end of the sixth right costal cartilage to the apex of the heart. The left or obtuse margin is shorter, full, and rounded: it is formed mainly by the left ventricle, but to a slight extent, above, by the left atrium. It extends from a point in the second left intercostal space, about 2.5 mm. from the sternal margin, obliquely downward, with a convexity to the left, to the apex of the heart. Right Atrium (atrium dextrum; right auricle).—The right atrium is. larger than the left, but its walls are somewhat thinner, measuring about 2 mm.; its cavity is capable of containing about 57 c.c. It consists of two parts: a principal cavity, or sinus venarum, situated posteriorly, and an anterior, smaller portion, the auricula. Sinus Venarum (sinus venosus).—The sinus venarum is the large quadrangular cavity placed between the two venae cavae. Its walls, which are extremely thin, THE HEART 529 are connected below with the right ventricle, and medially with the left atrium, but are free in the rest of their extent. Auricula (auricula dextra; right auricular appendix).—The auricula is a small conical muscular pouch, the margins of which present a dentated edge. It projects from the upper and front part of the sinus forward and toward the left side, over- lapping the root of the aorta. Ant. desc. branch of left coronary artery Right coronary artery Fig. 492.—Sternocostal surface of heart. The separation of the auricula from the sinus venarum is indicated externally by a groove, the terminal sulcus, which extends from the front of the superior vena cava to the front of the inferior vena cava, and represents the line of union of the sinus venosus of the embryo with the primitive atrium. On the inner wall of the atrium the separation is marked by a vertical, smooth, muscular ridge, the terminal crest. Behind the crest the internal surface of the atrium is smooth, while in front of it the muscular fibers of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati. Its interior (Fig. 493) presents the following parts for examination: Superior vena cava. Inferior vena cava. Coronary sinus. Foramina venarum minimarum. Atrioventricular. Openings Valves Valve of the inferior vena cava. Valve of the coronary sinus. Fossa ovalis. Limbus fossae ovalis. Intervenous tubercle. Musculi pectinati. Crista terminalis. The superior vena cava returns the blood from the upper half of the body, and opens into the upper and back part of the atrium, the direction of its orifice being downward and forward. Its opening has no valve. 530 ANGIOLOGY The inferior vena cava, larger than the superior, returns the blood from the lower half of the body, and opens into the lowest part of the atrium, near the atrial septum, its orifice being directed upward and backward, and guarded by a rudimentary valve, the valve of the inferior vena cava (Eustachian valve). The blood entering the atrium through the superior vena cava is directed downward and forward, i. e., toward the atrioventricular orifice, while that entering through the inferior vena cava is directed upward and backward, toward the atrial septum. This is the normal direction of the two currents in fetal life. The coronary sinus opens into the atrium, between the orifice of the inferior vena cava and the atrioventricular opening. It returns blood from the substance of the heart and is protected by a semicircular valve, the valve of the coronary sinus (valve of Thebesius). Pulmonary valve Ant. cusp of tricuspid ' valve Opening of sup. vena cava Chordce tendinece Crista terminalis Atrial septum Papillary ' muscles Limbus fossce ovalis Opening of coronary sinus Opening of inf. vena cava Valve of inf. vena cava Valve of coronary sinus Fig. 493.—Interior of right side of heart. The foramina venarum minimarum (foramina Thebesii) are the orifices of minute veins (venae cordis minimce), which return blood directly from the muscular sub- stance of the heart. The atrioventricular opening (tricuspid orifice) is the large oval aperture of com- munication between the atrium and the ventricle; it will be described with the right ventricle. The valve of the inferior vena cava (valvula venae cavoe inferioris [Eustachii]; Eustachian valve) is situated in front of the orifice of the inferior vena cava. It is semilunar in form, its convex margin being attached to the anterior margin of the orifice; its concave margin, which is free, ends in two cornua, of which the left is continuous with the anterior edge of the limbus fossae ovalis while the right is lost on the wall of the atrium. The valve is formed by a duplicature of the lining membrane of the atrium, containing a few muscular fibers. In the fetus this valve is of large size, and serves to direct the blood from the inferior vena cava, through the foramen ovale, into the left atrium. In the adidt it occa- sionally persists, and may assist in preventing the reflux of blood into the inferior vena cava; more commonly it is small, and may present a cribriform or filamentous appearance; sometimes it is altogether wanting. THE HEART 531 The valve of the coronary sinus (valvula sinus coronarii [ Thebesii]; Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the coronary sinus. It prevents the regurgitation of blood into the sinus during the contraction of the atrium. This valve may be double or it may be cribriform. The fossa ovalis is an oval depression on the septal wall of the atrium, and corre- sponds to the situation of the foramen ovale in the fetus. It is situated at the lower part of the septum, above and to the left of the orifice of the inferior vena cava. The limbus fossae ovalis (annulus ovalis) is the prominent oval margin of the fossa ovalis. It is most distinct above and at the sides of the fossa; below, it is deficient. A small slit-like valvular opening is occasionally found, at the upper margin of the fossa, leading upward beneath the limbus, into the left atrium; it is the remains of the fetal aperture between the two atria. The intervenous tubercle (tuberculum intervenosum; tubercle of Lower) is a small projection on the posterior wall of the atrium, above the fossa ovalis. It is distinct in the hearts of quadrupeds, but in man is scarcely visible. It was supposed by Lower to direct the blood from the superior vena cava toward the atrioventricular opening. Right Ventricle (ventriculus dexter).—The right ventricle is triangular in form, and extends from the right atrium to near the apex of the heart. Its antero- superior surface is rounded and convex, and forms the larger part of the sterno- costal surface of the heart. Its under surface is flattened, rests upon the dia- phragm, and forms a small part of the diaphragmatic surface of the heart. Its posterior wall is formed by the ventricular septum, which bulges into the right ventricle, so that a transverse section of the cavity presents a semilunar outline. Its upper and left angle forms a conical pouch, the conus arteriosus, from which the pulmonary artery arises. A tendinous band, which may be named the tendon of the conus arteriosus, extends upward from the right atrioventricular fibrous ring and connects the posterior surface of the conus arteriosus to the aorta. The wall of the right ventricle is thinner than that of the left, the proportion between them being as 1 to 3; it is thickest at the base, and gradually becomes thinner toward the apex. The cavity equals in size that of the left ventricle, and is capable of containing about 85 c.c. Its interior (Fig. 493) presents the following parts for examination: Right atrioventricular. Pulmonary artery. Tricuspid. .Pulmonary. . Opemngs Trabeculae carneae. Valves Chordae tendinese. The right atrioventricular orifice is the large oval aperture of communication between the right atrium and ventricle. Situated at the base of the ventricle, it measures about 4 cm. in diameter and is surrounded by a fibrous ring, covered by the lining membrane of the heart; it is considerably larger than the correspond- ing aperture on the left side, being sufficient to admit the ends of four fingers It is guarded by the tricuspid valve. The opening of the pulmonary artery is circular in form, and situated at the summit of the conus arteriosus, close to the ventricular septum. It is placed above and to the left of the atrioventricular opening, and is guarded by the pulmonary semilunar valves. The tricuspid valve (valvula tricuspidalis) (Figs. 493, 495) consists of three some- what triangular cusps or segments. The largest cusp is interposed between the atrioventricular orifice and the conus arteriosus and is termed the anterior or infundib- ular cusp. A second, the posterior or marginal cusp, is in relation to the right margin of the ventricle, and a third, the medial or septal cusp, to the ventricular septum. They are formed by duplicatures of the lining membrane of the heart, strengthened 532 ANGIOLOGY by intervening layers of fibrous tissue: their central parts are thick and strong, their marginal portions thin and translucent, and in the angles between the latter small intermediate segments are sometimes seen. Their bases are attached to a fibrous ring surrounding the atrioventricular orifice and are also joined to each other so as to form a continuous annular membrane, while their apices project into the ventricular cavity. Their atrial surfaces, directed toward the blood current from the atrium, are smooth; their ventricular surfaces, directed toward the wall of the ventricle, are rough and irregular, and, together with the apices and margins of the cusps, give attachment to a number of delicate tendinous cords, the chordae tendineae. Bight auricula _Right atrium Left auricula Left 'pulmonary veins Right 'pulmonary veins Fig. 494.—Heart seen from above. Fig. 495.—Base of ventricles exposed by removal of the atria. • The trabeculae cameae icolumnoe carnece) are rounded or irregular muscular columns which project from the whole of the inner surface of the ventricle, with the exception of the conus arteriosus. They are of three kinds: some are attached along their entire length on one side and merely form prominent ridges, others are fixed at their extremities but free in the middle, while a third set (musculi papillares) are continuous by their bases with the wall of the ventricle, while their apices give origin to the chordae tendineae which pass to be attached to the seg- ments of the tricuspid valve. There are two papillary muscles, anterior and pos- terior: of these, the anterior is the larger, and its chordae tendineae are connected with the anterior and posterior cusps of the valve: the posterior papillary muscle sometimes consists of tvro or three parts; its chordae tendineae are connected vTith the posterior and medial cusps. In addition to these, some chordae tendineae spring directly from the ventricular septum, or from small papillary eminences on it, and pass to the anterior and medial cusps. A muscular band, w-ell-marked in sheep and some other animals, frequently extends from the base of the anterior papillary muscle to the ventricular septum. From its attachments it may assist in preventing overdistension of the ventricle, and so has been named the moderator band. The pulmonary semilunar valves (Fig. 494) are three in number, two in front and one behind, formed by duplicatures of the lining membrane, strengthened by fibrous tissue. They are attached, by their convex margins, to the v-all of the artery, at its junction with the ventricle, their free borders being directed upward into the lumen of the vessel. The free and attached margins of each are strength- THE HEART 533 ened by tendinous fibers, and the former presents, at its middle, a thickened nodule 0corpus Arantii). From this nodule tendinous fibers radiate through the segment to its attached margin, but are absent from two narrow crescentic portions, the lunulae, placed one on either side of the nodule immediately adjoining the free margin. Between the semilunar valves and the wall of the pulmonary artery are three pouches or sinuses (sinuses of Valsalva). Left Atrium (atrium sinistum; left auricle).—The left atrium is rather smaller than the right, but its walls are thicker, measuring about 3 mm.; it consists, like the right, of two parts, a principal cavity and an auricula. The principal cavity is cuboidal in form, and concealed, in front, by the pul- monary artery and aorta; in front and to the right it is separated from the right atrium by the atrial septum; opening into it on either side are the two pulmonary veins. Auricula (auricula sinistra; left auricular appendix).—The auricula is somewhat constricted at its junction with the principal cavity; it is longer, narrower, and more curved than that of the right side, and its margins are more deeply indented. It is directed forward and toward the right and overlaps the root of the pulmonary artery. Fig. 496.—Interior of left side of heart. The interior of the left atrium (Fig. 496) presents the following parts for examination: Openings of the four pulmonary veins. Left atrioventricular opening. Musculi pectinati. The pulmonary veins, four in number, open into the upper part of the posterior surface of the left atrium—two on either side of its middle line: they are not provided with valves. The two left veins frequently end by a common opening. The left atrioventricular opening is the aperture between the left atrium and ventricle, and is rather smaller than the corresponding opening on the right side. 534 A NG10 LOGY The musculi pectinati, fewer and smaller than in the right auricula, are confined to the inner surface of the auricula. On the atrial septum may be seen a lunated impression, bounded below by a crescentic ridge, the concavity of which is turned upward. The depression is just above the fossa ovalis of the right atrium. Left Ventricle (ventriculus sinister).—The left ventricle is longer and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart. Its wTalls are about three times as thick as those of the right ventricle. Its interior (Fig. 496) presents the following parts for examination: Openings Left atrioventricular. Aortic. Valves Bicuspid or Mitral. Aortic. Trabeculae carneae. Chordse tendineae. The left atrioventricular opening (-mitral orifice) is placed below and to the left of the aortic orifice. It is a little smaller than the corresponding aperture of the opposite side, admitting only two fingers. It is surrounded by a dense fibrous ring, covered by the lining membrane of the heart, and is guarded by the bicuspid or mitral valve. Aortic sinus Left post, valve Nodulus Lunula Origins of coronary arteries Eight post, valve Ant. valve Fig. 497.—Aorta laid open to show the semilunar valves. The aortic opening is a circular aperture, in front and to the right of the atrio- ventricular, from which it is separated by the anterior cusp of the bicuspid valve. Its orifice is guarded by the aortic semilunar valves. The portion of the ventricle immediately below the aortic orifice is termed the aortic vestibule, and possesses fibrous instead of muscular walls. The bicuspid or mitral valve (valvula bicuspidalis [metralis]) (Figs. 495, 496) is attached to the circumference of the left atrioventricular orifice in the same way that the tricuspid valve is on the opposite side. It consists of two triangular cusps, formed by duplicatures of the lining membrane, strengthened by fibrous tissue, and containing a few muscular fibers. The cusps are of unequal size, and are larger, thicker, and stronger than those of the tricuspid valve. The larger cusp is placed in front and to the right between the atrioventricular and aortic orifices, and is known as the anterior or aortic cusp; the smaller or posterior cusp is placed behind and to the left of the opening. Two smaller cusps are usually found at the angles of junction of the larger. The cusps of the bicuspid valve are furnished with chordae tendineae, which are attached in a manner similar to those on the right side; they are, however, thicker, stronger, and less numerous. THE HEART 535 The aortic semilunar valves (Figs. 494, 497.) are three in number, and surround the orifice of the aorta; two are posterior (right and left) and one anterior. They are similar in structure, and in their mode of attachment, to the pulmonary semi- lunar valves, but are larger, thicker, and stronger; the lunulae are more distinct, and the noduli or corpora Arantii thicker and more prominent. Opposite the valves the aorta presents slight dilatations, the aortic sinuses {sinuses of Valsalva), which are larger than those at the origin of the pulmonary artery. The trabeculae carnese are of three kinds, like those upon the right side, but they are more numerous, and present a dense interlacement, especially at the apex, and upon the posterior wall of the ventricle. The musculi papillares are two in number, one being connected to the anterior, the other to the posterior wall; they are of large size, and end in rounded extremities from which the chordae tendineae arise. The chordae tendineae from each papillary muscle are connected to both cusps of the bicuspid valve. -Left auricula Inferior vena cava - Aortic valve Membranous septum Musculi, pectinati Papillary muscles Anterior papillary muscle Fig. 498.—Section of the heart showing the ventricular septum. Ventricular Septum (septum ventriculorum; interventricular septum) (Fig. 498).— The ventricular septum is directed obliquely backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci. The greater portion of it is thick and muscular and constitutes the muscular ventricular septum, but its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum. An abnormal communication may exist between the ventricles at this part owing to defective development of the membranous septum. Structure.—The heart consists of muscular fibers, and of fibrous rings which serve for their attachment. It is covered by the visceral layer of the serous pericardium (epicardium), and lined by the endocardium. Between these two membranes is the muscular wall or myocardium. The endocardium is a thin, smooth membrane which lines and gives the glistening appear- 536 ANGIOLOGY ance to the inner surface of the heart; it assists in forming the valves by its reduplications, and is continuous with the lining membrane of the large bloodvessels. It consists of connective tissue and elastic fibers, and is attached to the muscular structure by loose elastic tissue which contains bloodvessels and nerves; its free surface is covered by endothelial cells. The fibrous rings surround the atrioventricular and arterial orifices, and are stronger upon the left than on the right side of the heart. The atrioventricular rings serve for the attachment of the muscular fibers of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves. The left atrioventricular ring is closely connected, by its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the trigonum fibrosum, which represents the os cordis seen in the heart of some of the larger animals, as the ox and elephant. Lastly, there is the tendinous band, already referred to, the posterior surface of the conus arteriosus. The fibrous rings surrounding the arterial orifices serve for the attachment of the great vessels and semilunar valves. Each ring receives, by its ventricular margin, the attachment of some of the muscular fibers of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed. The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium internally. From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves. The middle coat of the artery in this situation is thin, and the vessel is dilated to form the sinuses of the aorta and pulmonary artery. A Fig. 500.—Purkinje’s fibers from the sheep’s heart. A. In longitudinal section. B. In transverse section. Fig. 499.—Anastomosing muscular fibers of the heart seen in a longitudinal section. On the right the limits of the separate cells with their nuclei are exhibited somewhat dia- grammatically. Cardiac Muscular Tissue.—The fibers of the heart differ very remarkably from those of other striped muscles. They are smaller by one-third, and their transverse striae are by no means so well-marked. They show faint longitudinal striation. The fibers are made up of distinct quad- rangular cells, joined end to end so as to form a syncytium (Fig. 499). Each cell contains a clear oval nucleus, situated near its center. The extremities of the cells have a tendency to branch or divide, the subdivisions uniting with offsets from other cells, and thus producing an anastomosis of the fibers. The connective tissue between the bundles of fibers is much less than in ordinary striped muscle, and no sarcolemma has been proved to exist. Purkinje Fibers (Fig. 500).—Between the endocardium and the ordinary cardiac muscle are found, imbedded in a small amount of connective tissue, peculiar fibers known as Purkinje fibers. They are found in certain mammals and in birds, and can be best seen in the sheep’s heart, where THE HEART 537 they form a considerable portion of the moderator band and also appear as gelatinous-looking strands on the inner walls of the atria and ventricles. They also occur in the human heart asso- ciated with the terminal distributions of the bundle of His. The fibers are very much larger in size than the cardiac cells and differ from them in several ways. In longitudinal section they are quadrilateral in shape, being about twice as long as they are broad. The central portion of each fiber contains one or more nuclei and is made up of granular protoplasm, with no indication of striations, while the peripheral portion is clear and has distinct transverse striations. The fibers are intimately connected with each other, possess no definite sarcolemma, and do not branch. The muscular structure of the heart consists of bands of fibers, which present an exceedingly intricate interlacement. They comprise (a) the fibers of the atria, (6) the fibers of the ventricles, and (c) the atrioventricular bundle of His. The fibers of the atria are arranged in two layers—a superficial, common to both cavities, and a deep, proper to each. The superficial fibers are most distinct on the front of the atria, across the bases of which they run in a transverse direction, forming a thin and incomplete layer. Some of these fibers run into the atrial septum. The deep fibers consist of looped and annular fibers. The looped fibers pass upward over each atrium, being attached by their two extremities to the corresponding atrioventricular ring, in front and behind. The annular fibers surround the auriculae, and form annular bands around the terminations of the veins and around the fossa ovalis. The fibers of the ventricles are arranged in a complex manner, and various accounts have been given of their course and connections; the following description is based on the work of McCallum.1 They consist of superficial and deep layers, all of which, with the exception of two, are inserted into the papillary muscles of the ventricles. The superficial layers consist of the following: (a) Fibers which spring from the tendon of the conus arteriosus and sweep downward and toward the left across the anterior longitudinal sulcus and around the apex of the heart, where they pass upward and inward to terminate in the papillary muscles of the left ventricle; those arising from the upper half of the tendon of the conus arteriosus pass to the anterior papillary muscle, those from the lower half to the posterior papillary muscle and the papillary muscles of the septum. (6) Fibers which arise from the right atrioventricular ring and run diagonally across the diaphragmatic surface of the right ventricle and around its right border on to its costosternal surface, where they dip beneath the fibers just described, and, crossing the anterior longitudinal sulcus, wind around the apex of the heart and end in the posterior papillary muscle of the left ventricle, (c) Fibers which spring from the left atrioventricular ring, and, crossing the posterior longitudinal sulcus, pass successively into the right ventricle and end in its papillary muscles. The deep layers are three in number; they arise in the papillary muscles of one ventricle and, curving in an S-shaped manner, turn in at the longitudinal sulcus and end in the papillary muscles of the other ventricle. The layer which is most superficial in the right ventricle lies next the lumen of the left, and vice versa. Those of the first layer almost encircle the right ventricle and, crossing in the septum to the left, unite with the superficial fibers from the right atrioventricular ring to form the posterior papillary muscle. Those of the second layer have a less extensive course in the wall of the right ventricle, and a correspondingly greater course in the left, where they join with the superficial fibers from the anterior half of the tendon of the conus arteriosus to form the papillary muscles of the septum. Those of the third layer pass almost entirely around the left ventricle and unite with the superficial fibers from the lower half of the tendon of the conus arteriosus to form the anterior papillary muscle. Besides the layers just described there are two bands which do not end in papillary muscles. One springs from the right atrioventricular ring and crosses in the atrioventricular septum; it then encircles the deep layers of the left ventricle and ends in the left atrioventricular ring. The second band is apparently confined to the left ventricle; it is attached to the left atrioventricular ring, and encircles the portion of the ventricle adjacent to the aortic orifice. The atrioventricular bundle of His (Fig. 501), is the only direct muscular connection knowmto exist between the atria and the ventricles. Its cells differ from ordinary cardiac muscle cells in being more spindle-shaped. They are, moreover, more loosely arranged and have a richer vascu- lar supply than the rest of the heart muscle. It arises in connection with two small collections of spindle-shaped cells, the sinoatrial and atrioventricular nodes. The sinoatrial node is situated on the anterior border of the opening of the superior vena cava; from its strands of fusiform fibers run under the endocardium of the wall of the atrium to the atrioventricular node. The atrioventricular node lies near the orifice of the coronary sinus in the annular and septal fibers of the right atrium; from it the atrioventricular bundle passes forward in the lower part of the membranous septum, and divides into right and left fasciculi. These run down in the right and left ventricles, one on either side of the ventricular septum, covered by endocardium. In the lower parts of the ventricles they break up into numerous strands which end in the papillary muscles and in the ventricular muscle generally. The greater portion of the atrioventricular bundle consists of narrow, somewhat fusiform fibers, but its terminal strands are composed of Purkinje fibers. 1 Johns Hopkins Hospital Reports, vo 538 ANGI0L0GY Dr. A. Morison1 has shown that in the sheep and pig the atrioventricular bundle “is a great avenue for the transmission of nerves from the auricular to the ventricular heart; large and numerous nerve trunks entering the bundle and coursing with it.” From these, branches pass off and form plexuses around groups of Purkinje cells, and from these plexuses fine fibrils go to innervate individual cells. Clinical and experimental evidence go to prove that this bundle conveys the impulse to sys- tolic contraction from the atrial septum to the ventricles. Fig. 501.—Schematic representation of the atrioventricular bundle of His. The bundle, represented in red originates near the orifice of the coronary sinus, undergoes slight enlargement to form a node, passes forward to the ventricular septum, and divides into two limbs. The ultimate distribution cannot be completely shown in this diagram. Vessels and Nerves.—The arteries supplying the heart are the right and left coronary from the aorta; the veins end in the right atrium. The lymphatics end in the thoracic and right lymphatic ducts. The nerves are derived from the cardiac plexus, which are formed partly from the vagi, and partly from the sympathetic trunks. They are freely distributed both on the surface and in the substance of the heart, the separate nerve filaments being furnished with small ganglia. The Cardiac Cycle and the Actions of the Valves.—By the contractions of the heart the blood is pumped through the arteries to all parts of the body. These contractions occur regularly and at the rate of about seventy per minute. Each wave of contraction or 'period, of activity is followed by a period of rest, the two periods constituting what is known as a cardiac cycle. Each cardiac cycle consists of three phases, which succeed each other as follows: (1) a short simultaneous contraction of both atria, termed the atrial systole, fol- 1 Journal of Anatomy and Physiology, vol. xlvi. PECULIARITIES IN THE VASCULAR SYSTEM OF THE FETUS 539 lowed, after a slight pause, by (2) a simultaneous, but more prolonged, contraction of both ventricles, named the ventricular systole, and (3) a period of rest, during which the wThole heart is relaxed. The atrial contraction commences around the venous openings, and sweeping over the atria forces their contents through the atrio- ventricular openings into the ventricles, regurgitation into the veins being pre- vented by the contraction of their muscular coats. When the ventricles contract, the tricuspid and bicuspid valves are closed, and prevent the passage of the blood back into the atria; the musculi papillares at the same time are shortened, and, pulling on the chordae tendinese, prevent the inversion of the valves into the atria. As soon as the pressure in the ventricles exceeds that in the pulmonary artery and aorta, the valves guarding the orifices of these vessels are opened and the blood is driven from the right ventricle into the pulmonary artery and from the left into the aorta. The moment the systole of the ventricles ceases, the pressure of the blood in the pulmonary artery and aorta closes the pulmonary and aortic semilunar valves to prevent regurgitation of blood into the ventricles, the valves remaining shut until reopened by the next ventricular systole. During the period of rest the tension of the tricuspid and bicuspid valves is relaxed, and blood is flowing from the veins into the atria, being aspirated by negative intrathoracic pressure, and slightly also from the atria into the ventricles. The average duration of a cardiac cycle is about yy of a second, made up as follows; Atrial systole, TV Ventricular systole, Ty. Total systole, Ty. Atrial diastole, yy. Ventricular diastole, Ty. Complete diastole, yfr. The rhythmical action of the heart is muscular in origin-—that is to say, the heart muscle itself possesses the inherent property of contraction apart from any nervous stimulation. The more embryonic the muscle the better is it able to initiate and propagate the contraction wave; this explains why the normal systole of the heart starts at the entrance of the veins, for there the muscle is most embryonic in nature. At the atrioventricular junction there is a slight pause in the wave of muscular contraction. To obviate this so far as possible a peculiar band of marked embryonic type passes across t|je junction and so carries on the contraction wave to the ventricles. This band, composed of special fibers, is the atrioventricular bundle of His (p. 537). The nerves, although not concerned in originating the contractions of the heart muscle, play an important role in regulating their force and frequency in order to subserve the physiological needs of the organism. The chief peculiarities of the, fetal heart are the direct communication between the atria through the foramen ovale, and the large size of the valve of the inferior vena cava. Among other peculiarities the following may be noted. (1) In early fetal life the heart lies immediately below the mandibular arch and is relatively large in size. As development proceeds it is gradually drawn within the thorax, but at first it lies in the middle line; toward the end of pregnancy it gradually becomes oblique in direction. (2) For a time the atrial portion exceeds the ventricular in size, and the walls of the ventricles are of equal thickness: toward the end of fetal life the ventricular portion becomes the larger and the wall of the left ventricle exceeds that of the right in thickness. (3) Its size is large as compared with that of the rest of the body, the proportion at the second month being 1 to 50, and at birth, 1 to 120, while in the adult the average is about 1 to 160. The foramen ovale, situated at the lower part of the atrial septum, forms a free communication between the atria until the end of fetal life. A septum (septum secundum) grows down from the upper wall of the atrium to the right of the primary PECULIARITIES IN THE VASCULAR SYSTEM OF THE FETUS. 540 ANGIOLOGY septum in which the foramen ovale is situated; shortly after birth it fuses with the primary septum and the foramen ovale is obliterated. The valve of the inferior vena cava serves to direct the blood from that vessel through the foramen ovale into the left atrium. The peculiarities in the arterial system of the fetus are the communication between the pulmonary artery and the aorta by means of the ductus arteriosus, and the continuation of the hypogastric arteries as the umbilical arteries to the placenta. The ductus arteriosus is a short tube, about 1.25 cm. in length at birth, and of the diameter of a goose-quill. In the early condition it forms the continuation of the pulmonary artery, and opens into the aorta, just beyond the origin of the left subclavian artery; and so conducts the greater amount of the blood from the right ventricle into the aorta. When the branches of the pulmonary artery have become larger relatively to the ductus arteriosus, the latter is chiefly connected to the left pulmonary artery. The hypogastric arteries run along the sides of the bladder and thence upward on the back of the anterior abdominal wall to the umbilicus; here they pass out of the abdomen and are continued as the umbilical arteries in the umbilical cord to the placenta. They convey the fetal blood to the placenta. The peculiarities in the venous system of the fetus are the communications established between the placenta and the liver and portal vein, through the umbil- ical vein; and between the umbilical vein and the inferior vena cava through the ductus venosus. Fetal Circulation (Fig. 502).—The fetal blood is returned from the placenta to the fetus by the umbilical vein. This vein enters the abdomen at the umbilicus, and passes upward along the free margin of the falciform ligament of the liver to the under surface of that organ, where it gives off two or three branches, one of large size to the left lobe, and others to the lobus quadratus and lobus caudatus. At the porta hepatis (transverse fissure of the liver) it divides into two branches: of these, the larger is joined by the portal vein, and enters the right lobe; the smaller is continued upward, under the name of the ductus venosus, and joins the inferior vena cava. The blood, therefore, which traverses the umbilical vein, passes to the inferior vena cava in three different ways. A considerable quantity circulates through the liver with the portal venous blood, before entering the inferior vena cava by the hepatic veins; some enters the liver directly, and is carried to the inferior cava by the hepatic veins; the remainder passes directly into the inferior vena cava through the ductus venosus. In the inferior vena cava, the blood carried by the ductus venosus and hepatic veins becomes mixed with that returning from the lower extremities and abdominal wall. It enters the right atrium, and, guided by the valve of the inferior vena cava, passes through the foramen ovale into the left atrium, where it mixes with a small quantity of blood returned from the lungs by the pulmonary veins. From the left atrium it passes into the left ventricle; and from the left ventricle into the aorta, by means of which it is distributed almost entirely to the head and upper extremities, a small quantity being probably carried into the descending aorta. From the head and upper extremities the blood is returned by the superior vena cava to the right atrium, where it mixes with a small portion of the blood from the inferior vena cava. From the right atrium it descends into the right ventricle, and thence passes into the pulmonary artery. The lungs of the fetus being inactive, only a small quantity of the blood of the pulmonary artery is distributed to them by the right and left pulmonary arteries, and returned by the pulmonary veins to the left atrium: the greater part passes through the ductus arteriosus into the aorta, where it mixes with a small quantity of the blood transmitted by the left ventricle into the aorta. Through this vessel it descends, and is in part distributed PECULIARITIES IN THE VASCULAR SYSTEM OF THE FETUS 541 to the lower extremities and the viscera of the abdomen and pelvis, but the greater amount is conveyed by the umbilical arteries to the placenta. From the preceding account of the circulation of the blood in the fetus the fol- lowing facts will be evident: (1) The placenta serves the purposes of nutrition Jjuotu* ~ArteriosuA -Hypogastric arteries Fig. 502.—Plan of the fetal circulation. In this plan the figured arrows represent the kind of blood, as well as the direction which it takes in the vessles. Thus—arterial blood is figured > - -> , venou , > , (arterial and venous) blood, > >. and excretion, receiving the impure blood from the fetus, and returning it purified and charged with additional nutritive material. (2) Nearly the whole of the blood of the umbilical vein traverses the liver before entering the inferior vena cava, hence the large size of the liver, especially at an early period of fetal life. (3) The right atrium is the point of meeting of a double current, the blood in the inferior 542 ANGIOLOGY vena cava being guided by the valve of this vessel into the left atrium, while that in the superior vena cava descends into the right ventricle. At an early period of fetal life it is highly probable that the two streams are quite distinct; for the inferior vena cava opens almost directly into the left atrium, and the valve of the inferior vena cava would exclude the current from the right ventricle. At a later period, as the separation between the two atria becomes more distinct, it seems probable that some mixture of the two streams must take place. (4) The pure blood carried from the placenta to the fetus by the umbilical vein, mixed with the blood from the portal vein and inferior vena cava, passes almost directly to the arch of the aorta, and is distributed by the branches of that vessel to the head and upper extremities. (5) The blood contained in the descending aorta, chiefly derived from that which has already circulated through the head and limbs, together with a small quantity from the left ventricle, is distributed to the abdomen and lower extremities. Changes in the Vascular System at Birth. —At birth, when respiration is estab- lished, an increased amount of blood from the pulmonary artery passes through the lungs, and the placental circulation is cut off. The foramen ovale is closed by about the tenth day after birth: the valvular fold above mentioned adheres to the margin of the foramen for the greater part of its circumference, but a slit-like opening is left between the two atria above, and this sometimes persists. The ductus arteriosus begins to contract immediately after respiration is estab- lished, and is completely closed from the fourth to the tenth day; it ultimately degenerates into an impervious cord, the ligamentum arteriosum, which connects the left pulmonary artery to the arch of the aorta. Of the hypogastric arteries, the parts extending from the sides of the bladder to the umbilicus become obliterated between the second and fifth days after birth, and project as fibrous cords, the lateral umbilical ligaments, toward the abdominal cavity, carrying on them folds of peritoneum. The umbilical vein and ductus venosus are completely obliterated between the second and fifth days after birth; the former becomes the ligamentum teres, the latter the ligamentum venosum, of the liver. BIBLIOGRAPHY. Bremer, J. L.: The Earliest Bloodvessels in Man, Am. Jour. Anat., 1914, xvi. Evans, H. M.: On the Development of the Aortse, Cardinal and Umbilical Veins and Other Bloodvessels of the Vertebrate Embryos from Capillaries, Anat. Rec., 1909, iii. Evans, H. M.: The Development of the Vascular System, Keibel and Mall, Manual of Human Embryology. His, W.: Anatomie Menschlichen Embryonen, Leipzig, 1880-85. MacCallum, J. B.: On the Muscular Architecture and Growth of the Ventricles of the Heart, Johns Hop. Hosp. Rep., 1900, ix. Mall, F. P.: A Study of the Structural Unit of the Liver, Am. Jour. Anat., 1906, v. Mall, F. P.: On the Muscular Architecture of the Ventricles of the Human Heart, Am. Jour. Anat., 1911, xi. Mall, F. P.: The Development of the Internal Mammary and Deep Epigastric Arteries in Man, Johns Hop. Hosp. Bulletin, 1898. Stockard, C. R.: A Study of Wandering Mesenchymal Cells on the Living Yolk Sac and Their Developmental Products: Chromatophores, Vascular Endothelium and Blood Cells, Am. Jour. Anat., 1915, xviii. Streeter, G. L.: The Development of the Venous Sinuses of the Dura Mater in the Human Embryo, Am. Jour. Anat., 1915, xviii. Thoma, It.: Text-book, of General Pathology and Pathological Anatomy, Translated by Bruce, London, 1896. THE ARTERIES. rpiIE distribution of the systematic arteries is like a highly ramified tree, the -L common trunk of which, formed by the aorta, commences at the left ventricle, while the smallest ramifications extend to the peripheral parts of the body and the contained organs. Arteries are found in all parts of the body, except in the hairs, nails, epidermis, cartilages, and cornea; the larger trunks usually occupy the most protected situations, running, in the limbs, along the flexor surface, where they are less exposed to injury. There is considerable variation in the mode of division of the arteries: occasion- ally a short trunk subdivides into several branches at the same point, as may be observed in the celiac artery and the thyrocervical trunk: the vessel may give off several branches in succession, and still continue as the main trunk, as is seen in the arteries of the limbs; or the division may be dichotomous, as, for instance, when the aorta divides into the two common iliacs. A branch of an artery is smaller than the trunk from which it arises; but if an artery divides into two branches, the combined sectional area of the two vessels is, in nearly every instance, somewhat greater than that of the trunk; and the combined sectional area of all the arterial branches greatly exceeds that of the aorta; so that the arteries collectively may be regarded as a cone, the apex of which corresponds to the aorta, and the base to the capillary system. The arteries, in their distribution, communicate with one another, forming what are called anastomoses, and these communications are very free between the large as well as between the smaller branches. The anastomosis between trunks of equal size is found where great activity of the circulation is requisite, as in the brain; here the two vertebral arteries unite to form the basilar, and the two ante- rior cerebral arteries are connected by a short communicating trunk; it is also found in the abdomen, where the intestinal arteries have very ample anastomoses between their larger branches. In the limbs the anastomoses are most numerous and of largest size around the joints, the branches of an artery above uniting with branches from the vessels below. These anastomoses are of considerable in- terest to the surgeon, as it is by their enlargement that a collateral circulation is established after the application of a ligature to an artery. The smaller branches of arteries anastomose more frequently than the larger; and between the smallest twigs these anastomoses become so numerous as to constitute a close network that pervades nearly every tissue of the body. Throughout the body generally the larger arterial branches pursue a fairly straight course, but in certain situations they are tortuous. Thus the external maxillary artery in its course over the face, and the arteries of the lips, are extremely tortuous to accommodate themselves to the movements of the parts. The uterine arteries are also tortuous, to accommodate themselves to the increase of size which the uterus undergoes during pregnancy. The Pulmonary Artery (A. Pulmonalis) (Figs. 503, 504) The pulmonary artery conveys the venous blood from the right ventricle of the heart to the lungs. It is a short, wide vessel, about 5 cm. in length and 3 cm. in (543) 544 ANGIOLOGY diameter, arising from the conus arteriosus of the right ventricle. It extends obliquely upward and backward, passing at first in front and then to the left Internal mammary vessels Transversuz thoracis Left 'phrenic nerve Pulmonary pleura Costal pleura Sympathetic trunk j Thoracic duct Vagus nerves Azygos vein Fig. 503.—Transverse section of thorax, showing relations of pulmonary artery. ENTRANCE OF "VENA AZYGOS BRANCH OF PUL- MONARY ARTERY Te ft j VENTRICLE LEFT ATRIUM Fig. 504.—Pulmonary vessels, seen in a dorsal view of the heart and lungs. The lungs have been pulled away from the median line, and a part of the right lung has been out away to display the air-ducts and bloodvessels. THE ASCENDING AORTA 545 of the ascending aorta, as far as the under surface of the aortic arch, where it divides, about the level of the fibrocartilage between the fifth and sixth thoracic vertebra}, into right and left branches of nearly equal size. Relations.—The whole of this vessel is contained within the pericardium. It is enclosed with the ascending aorta in a single tube of the visceral layer of the serous pericardium, which is con- tinued upward upon them from the base of the heart. The fibrous layer of the pericardium is gradually lost upon the external coats of the two branches of the artery. In front, the pulmonary artery is separated from the anterior end of the second left intercostal space by the pleura and left lung, in addition to the pericardium; it rests at first upon the ascending aorta, and higher up lies in front of the left atrium on a plane posterior to the ascending aorta. On either side of its origin is the auricula of the corresponding atrium and a coronary artery, the left coronary artery passing, in the first part of its course, behind the vessel. The superficial part of the cardiac plexus lies above its bifurcation, between it and the arch of the aorta. The right branch of the pulmonary artery {ramus dexter a. pulmonalis), longer and larger than the left, runs horizontally to the right, behind the ascending aorta and superior vena cava and in front of the right bronchus, to the root of the right lung, where it divides into two branches. The lower and larger of these goes to the middle and lower lobes of the lung; the upper and smaller is distributed to the upper lobe. The left branch of the pulmonary artery {ramus sinister a. pulmonalis), shorter and somewhat smaller than the right, passes horizontally in front of the descending aorta and left bronchus to the root of the left lung, where it divides into two branches, one for each lobe of the lung. Above, it is connected to the concavity of the aortic arch by the ligamentum arteriosum, on the left of which is the left recurrent nerve, and on the right the superficial part of the cardiac plexus. Below, it is joined to the upper left pul- monary vein by the ligament of the left vena cava. The terminal branches of the pulmonary arteries will be described with the anatomy of the lungs. THE AORTA. The aorta is the main trunk of a series of vessels which convey the oxygenated blood to the tissues of the body for their nutrition. It commences at the upper part of the left ventricle, where it is about 3 cm. in diameter, and after ascending for a short distance, arches backward and to the left side, over the root of the left lung; it then descends within the thorax on the left side of the vertebral column, passes into the abdominal cavity through the aortic hiatus in the diaphragm, and ends, considerably diminished in size (about 1.75 cm. in diameter), opposite the lower border of the fourth lumbar vertebra, by dividing into the right and left common iliac arteries. Hence it is described in several portions, viz., the ascending aorta, the arch of the aorta, and the descending aorta, which last is again divided into the thoracic and abdominal aortse. THE ASCENDING AORTA (AORTA ASCENDENS) (Fig. 505). The ascending aorta is about 5 cm. in length. It commences at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart’s axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm. behind the posterior surface of the sternum. At its origin it presents, opposite the segments of the aortic valve, three small dilatations called the aortic sinuses. At the union of the ascending aorta with the aortic arch the caliber of the vessel is increased, owing to a bulging of its right wall. This dilatation is termed the bulb of the aorta, and bn transverse section presents a some- 546 ANGIOLOGY what oval figure. The ascending aorta is contained within the pericardium, and is enclosed in a tube of the serous pericardium, common to it and the pulmonary artery. Relations.—The ascending aorta is covered at its commencement by the trunk of the pul- monary artery and the right auricula, and, higher up, is separated from the sternum by the pericardium, the right pleura, the anterior margin of the right lung, some loose areolar tissue, and the remains of the thymus; posteriorly, it rests upon the left atrium and right pulmonary artery. On the right side, it is in relation with the superior vena cava and right atrium, the former lying partly behind it; on the left side, with the pulmonary artery. Right vagus- Left vagus Recurrent nerve Left phrenic Thoracic duct ' Left auricula Left coronary Right - coronary Fig. 506.—Plan of the branches. Fig. 505.—The arch of the aorta, and its branches. Branches.—The only branches of the ascending aorta are the two coronary arteries which supply the heart; they arise near the commencement of the aorta immediately above the attached margins of the semilunar valves. The Coronary Arteries.—The Right Coronary Artery (a. coronaria [cordis] dextra) arises from the anterior aortic sinus. It passes at first between the conus arteriosus and the right auricula and then runs in the right portion of the coronary sulcus, coursing at first from the left to right and then on the diaphragmatic surface of the heart from right to left as far as the posterior longitudinal sulcus, down THE ARCH OF THE AORTA 547 which it is continued to the apex of the heart as the posterior descending branch. It gives off a large marginal branch which follows the acute margin of the heart and supplies branches to both surfaces of the right ventricle. It also gives tvrigs to the right atrium and to the part of the left ventricle vdiich adjoins the posterior longitudinal sulcus. The Left Coronary Artery (a. coronaria [cordis] sinistra), larger than the right, arises from the left posterior aortic sinus and divides into an anterior descending and a circumflex branch. The anterior descending branch passes at first behind the pulmonary artery and then comes forward between that vessel and the left auricula to reach the anterior longitudinal sulcus, along which it descends to the incisura apicis cordis; it gives branches to both ventricles. The circumflex branch follows the left part of the coronary sulcus, running first to the left and then to the right, reaching nearly as far as the posterior longitudinal sulcus; it gives branches to the left atrium and ventricle. There is a free anastomosis between the minute branches of the two coronary arteries in the substance of the heart. Peculiarities.—These vessels occasionally arise by a common trunk, or their number may be increased to three, the additional branch being of small size. More rarely, there are two addi- tional branches. THE ARCH OF THE AORTA (ARCUS TRANSVERSE AORTA) (Fig. 505). The arch of the aorta begins at the level of the upper border of the second sterno- costal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta. It thus forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 cm. below the superior border to the manubrium sterni. Relations.—The arch of the aorta is covered anteriorly by the pleurae and anterior margins of the lungs, and by the remains of the thymus. As the vessel runs backward its left side is in contact with the left lung and pleura. Passing downward on the left side of this part of the arch are four nerves; in order from before backward these are, the left phrenic, the lower of the superior cardiac branches of the left vagus, the superior cardiac branch of the left sympathetic, and the trunk of the left vagus. As the last nerve crosses the arch it gives off its recurrent branch, which hooks around below the vessel and then passes upward on its right side. The highest left inter- costal vein runs obliquely upward and forward on the left side of the arch, between the phrenic and vagus nerves. On the right are the deep part of the cardiac plexus, the left recurrent nerve, the esophagus, and the thoracic duct; the trachea lies behind and to the right of the vessel. Above are the innominate, left common carotid, and left subclavian arteries, which arise from the convexity of the arch and are crossed close to their origins by the left innominate vein. Below are the bifurcation of the pulmonary artery, the left bronchus, the ligamentum arteriosum, the superficial part of the cardiac plexus, and the left recurrent nerve. As already stated, the liga- mentum arteriosum connects the commencement of the left pulmonary artery to the aortic arch. Between the origin of the left subclavian artery and the attachment of the ductus arteriosus the lumen of the fetal aorta is considerably narrowed, forming what is termed the aortic isthmus, while immediately beyond the ductus arteriosus the vessel presents a fusiform dilation which His has named the aortic spindle—the point of junction of the two parts being marked in the concavity of the arch by an indentation or angle. These conditions persist, to some extent, in the adult, where His found that the average diameter of the spindle exceeded that of the isthmus by 3 mm. Distinct from this diffuse and moderate stenosis at the isthmus is the condition known as coarctation of the aorta, or marked stenosis often amounting to complete obliteration of its lumen, seen in adults and occurring at or near, oftenest a little below, the insertion of the ligamentum 548 ANGIOLOGY arteriosum into the aorta. According to Bonnet1 this coarctation is never found in the fetus or at birth, and is due to an abnormal extension of the peculiar tissue of the ductus into the aortic wall, which gives rise to a simultaneous stenosis of both vessels as it contracts after birth—the ductus is usually obliterated in these cases. An extensive collateral circulation is set up, by the costocervicals, internal mammaries, and the descending branches of the transverse cervical above the stenosis, and below it by the first four aortic intercostals, the pericardiaco-phrenics, and the superior and inferior epigastrics. > Peculiarities.-—The height to which the aorta rises in the thorax is usually about 2.5 cm. below the upper border of the sternum; but it may ascend nearly t9 the top of the bone. Occa- sionally it is found 4 cm., more rarely from 5 to 8 cm. below" this point. Sometimes the aorta arches over the root of the right lung (right aortic arch) instead of over that of the left, and passes down on the right side of the vertebral column, a condition which is found in birds. In such cases all the thoracic and abdominal viscera are transposed. Less frequently the aorta, after arching over the root of the right lung, is directed to its usual position on the left side of the vertebral column; this peculiarity is not accompanied by transposition of the viscera. The aorta occa- sionally divides, as in some quadrupeds, into an ascending and a descending trunk, the former of which is directed vertically upward, and subdivides into three branches, to supply the head and upper extremities. Sometimes the aorta subdivides near its origin into two branches, which soon reunite. In one of these cases the esophagus and trachea were found to pass through the interval between the two branches; this is the normal condition of the vessel in the reptilia. Branches (Figs. 505, 506).—The branches given off from the arch of the aorta are three in number: the innominate, the left common carotid, and the left subclavian. Peculiarities.—Position of the Branches.—The branches, instead of arising from the highest part of the arch, may spring from the commencement of the arch or upper part of the ascending aorta; or the distance between them at their origins may be increased or diminished, the most frequent change in this respect being the approximation of the left carotid toward the innominate artery. The number of the primary branches may be reduced to one, or more commonly two; the left carotid arising from the innominate artery; or (more rarely) the carotid and subclavian arteries of the left side arising from a left innominate artery. But the number may be increased to four, from the right carotid and subclavian arteries arising directly from the aorta, the innominate being absent. In most of these latter cases the right subclavian has been found to arise from the left end of the arch; in other cases it is the second or third branch given off, instead of the first. Another common form in which there are four primary branches is that in which the left vertebral artery arises from the arch of the aorta between the left carotid and subclavian arteries. Lastly, the number of trunks from the arch may be increased to five or six; in these instances, the external and internal carotids arise separately from the arch, the common carotid being absent on one or both sides. In some few cases six branches have been found, and this condition is associated with the origin of both vertebral arteries from the arch. Number Usual, Arrangement Different.—When the aorta arches over to the right side, the three branches have an arrangement the reverse of what is usual; the innominate artery is a left one, and the right carotid and subclavian arise separately. In other cases, where the aorta takes its usual course, the two carotids may be joined in a common trunk, and the subclavians arise separately from the arch, the right subclavian generally arising from the left end of the arch. In some instances other arteries spring from the arch of the aorta. Of these the most common are the bronchial, one or both, and the thyreoidea ima; but the internal mammary and the inferior thyroid have been seen to arise from this vessel. The Innominate Artery (A. Anonyma; Brachiocephalic Artery) (Fig. 505). The innominate artery is the largest branch of the arch of the aorta, and is from 4 to 5 cm. in length. It arises, on a level with the upper border of the second right costal cartilage, from the commencement of the arch of the aorta, on a plane anterior to the origin of the left carotid; it ascends obliquely upward, backward, and to the right to the level of the upper border of the right sternoclavicular articulation, where it divides into the right common carotid and right subclavian arteries. Relations.—Anteriorly, it is separated from the manubrium sterni by the Sternohyoideus and Sternothyreoideus, the remains of the thymus, the left innominate and right inferior thyroid veins which cross its root, and sometimes the superior cardiac branches of the right vagus. Posterior 1 Rev. de M6d., Paris, 1903. THE COMMON CAROTID ARTERY 549 to it is the trachea, which it crosses obliquely. On the right side are the right innominate vein, the superior vena cava, the right phrenic nerve, and the pleura; and on the left side, the remains of the thymus, the origin of the left common carotid artery, the inferior thyroid veins, and the trachea. Branches.—The innominate artery usually gives off no branches; but occasion- ally a small branch, the thyreoidea ima, arises from it. Sometimes it gives off a thymic or bronchial branch. The thyreoidea ima (a. thyreoidea ima) ascends in front of the trachea to the lower part of the thyroid gland, which it supplies. It varies greatly in size, and appears to compensate for deficiency or absence of one of the other thyroid vessels. It occasionally arises from the aorta, the right common carotid, the subclavian or the internal mammary. Point of Division.—The innominate artery sometimes divides above the level of the sterno- clavicular joint, less frequently below it. Position.—When the aortic arch is on the right side, the innominate is directed to the left side of the neck. Collateral Circulation.—Allan Burns demonstrated, on the dead subject, the possibility of the establishment of the collateral circulation after ligature of the innominate artery, by tying and dividing that artery. He then found that “Even coarse injection, impelled into the aorta, passed freely by the anastomosing branches into the arteries of the right arm, filling them and all the vessels of the head completely.”1 The branches by which this circulation would be carried on are very numerous; thus, all the communications across the middle line between the branches of the carotid arteries of opposite sides would be available for the supply of blood to the right side of the head and neck; while the anastomosis between the costocervical of the subclavian and the first aortic intercostal (see infra on the collateral circulation after obliteration of the thoracic aorta) would bring the blood, by a free and direct course, into the right subclavian. The numerous connections, also, between the intercostal arteries and the branches of the axillary and internal mammary arteries would, doubtless, assist in the supply of blood to the right arm, while the inferior epigastric from the external iliac would, by means of its anastomosis with the internal mammary, compensate for any deficiency in the vascularity of the wall of the chest. THE ARTERIES OF THE HEAD AND NECK. The principal arteries of supply to the head and neck are the two common carotids; they ascend in the neck and each divides into two branches, viz., (1) the external carotid, supplying the exterior of the head, the face, and the greater part of the neck; (2) the internal carotid, supplying to a great extent the parts within the cranial and orbital cavities. THE COMMON CAROTID ARTERY (A. CAROTIS COMMUNIS). The common carotid arteries differ in length and in their mode of origin. The right begins at the bifurcation of the innominate artery behind the sternoclavicular joint and is confined to the neck. The left springs from the highest part of the arch of the aorta to the left of, and on a plane posterior to the innominate artery, and therefore consists of a thoracic and a cervical portion. The thoracic portion of the left common carotid artery ascends from the arch of the aorta through the superior mediastinum to the level of the left sternoclavicular joint, where it is continuous with the cervical portion. Relations.—In front, it is separated from the manubrium sterni by the Sternohvoideus and Sternothyreoideus, the anterior portions of the left pleura and lung, the left innominate vein, and the remains of the thymus-; behind, it lies on the trachea, esophagus, left recurrent nerve, and thoracic duct. To its right side below is the innominate artery, and above, the trachea, the inferior thyroid veins, and the remains of the thymus; to its left side are the left vagus and phrenic nerves, left pleura, and lung. The left subclavian artery is posterior and slightly lateral to it. 1 Surgical Anatomy of the Head and Neck, p. 62. 550 ANGIOLOGY The cervical portions of the common carotids resemble each other so closely that one description will apply to both (Fig. 507). Each vessel passes obliquely upward, from behind the sternoclavicular articulation, to the level of the upper border of the thyroid cartilage, where it divides into the external and internal carotid arteries. Cricothyreoid artery Fig. 507.—Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. At the lower part of the neck the two common carotid arteries are separated from each other by a very narrow interval which contains the trachea; but at the upper part, the thyroid gland, the larynx and pharynx project forward between the two vessels. The common carotid artery is contained in a sheath, which is derived from the deep cervical fascia and encloses also the internal jugular vein and vagus nerve, the vein lying lateral to the artery, and the nerve between the artery and vein, on a plane posterior to both. On opening the sheath, each of these three structures is seen to have a separate fibrous investment. THE EXTERNAL CAROTID ARTERY 551 Relations.—At the lower part of the neck the common carotid artery is very deeply seated, being covered by the integument, superficial fascia, Platysma, and deep cervical fascia, the Sterno- cleidomastoideus, Sternohyoideus, Sternothyreoideus, and Omohyoideus; in the upper part of its course it is more superficial, being covered merely by the integument, the superficial fascia, Platysma, deep cervical fascia, and medial margin of the Sternocleidomastoideus. When the latter muscle is drawn backward, the artery is seen to be contained in a triangular space, the carotid triangle, bounded behind by the Sternocleidomastoideus, above by the Stylohyoideus and posterior belly of the Digastricus, and below by the superior belly of the Omohyoideus. This part of the artery is crossed obliquely, from its medial to its lateral side, by the sterno- cleidomastoid branch of the superior thyroid artery; it is also crossed by the superior and middle thyroid veins which end in the internal jugular; descending in front of its sheath is the descending branch of the hypoglossal nerve, this filament being joined by one or two branches from the cervical nerves, which cross the vessel obliquely. Sometimes the descending branch of the hypo- glossal nerve is contained within the sheath. The superior thyroid vein crosses the artery near its termination, and the middle thyroid vein a little below the level of the cricoid cartilage; the anterior jugular vein crosses the artery just above the clavicle, but is separated from it by the Sternohyoideus and Sternothyreoideus. Behind, the artery is separated from the transverse processes of the cervical vertebrae by the Longus colli and Longus capitis, the sympathetic trunk being interposed between it and the muscles. The inferior thyroid artery crosses behind the lower part of the vessel. Medially, it is in relation with the esophagus, trachea, and thyroid gland (which overlaps it), the inferior thyroid artery and recurrent nerve being interposed; higher up, with the larynx and pharynx. Lateral to the artery are the internal jugular vein and vagus nerve. At the lower part of the neck, the right recurrent nerve crosses obliquely behind the artery; the right internal jugular vein diverges from the artery, but the left approaches and often over- laps the lower part of the artery. Behind the angle of bifurcation of the common carotid artery is a reddish-brown oval body, known as the glomus caroticum (carotid body). It is similar in structure to the glomus coccygeum (icoccygeal body) which is situated on the middle sacral artery. Peculiarities as to Origin.—The right common carotid may arise above the level of the upper border of the sternoclavicular articulation; this variation occurs in about 12 per cent, of cases. In other cases the artery may arise as a separate branch from the arch of the aorta, or in con- junction with the left carotid. The left common carotid varies in its origin more than the right. In the majority of abnormal cases it arises with the innominate artery; if that artery is absent, the two carotids arise usually by a single trunk. It is rarely joined with the left subclavian, except in cases of transposition of the aortic arch. Peculiarities as to Point of Division.—In the majority of abnormal cases this occurs higher than usual, the artery dividing opposite or even above the hyoid bone; more rarely, it occurs below, opposite the middle of the larynx, or the lower border of the cricoid cartilage; one case is related by Morgagni, where the artery was only 4 cm. in length and divided at the root of the neck. Very rarely, the common carotid ascends in the neck without any subdivision, either the external or the internal carotid being wanting; and in a few cases the common carotid has been found to be absent, the external and internal carotids arising directly from the arch of the aorta. This peculiarity existed on both sides in some instances, on one side in others. Occasional Branches.—The common carotid usually gives off no branch previous to its bifurca- tion, but it occasionally gives origin to the superior thyroid or its laryngeal branch, the ascend- ing pharyngeal, the inferior thyroid, or, more rarely, the vertebral artery. Collateral Circulation.—After ligature of the common carotid, the collateral circulation can be perfectly established, by the free communication which exists between the carotid arteries of opposite sides, both without and within the cranium, and by enlargement of the branches of the subclavian artery on the side corresponding to that on which the vessel has been tied. The chief communications outside the skull take place between the superior and inferior thyroid arteries, and the profunda cervicis and ramus descendens of the occipital; the vertebral takes the place of the internal carotid within the cranium. The External Carotid Artery (A. Carotis Externa) (Fig. 507). The external carotid artery begins opposite the upper border of the thyroid cartilage, and, taking a slightly curved course, passes upward and forward, and then inclines backward to the space behind the neck of the mandible, where it divides into the superficial temporal and internal maxillary arteries. It rapidly diminishes in size in its course up the neck, owing to the number and large size of the branches given off from it. In the child, it is somewhat smaller than the internal carotid; but in the adult, the two vessels are of nearly equal size. At its 552 A NG10 LOGY origin, this artery is more superficial, and placed nearer the middle line than the internal carotid, and is contained within the carotid triangle. Relations.—The external carotid artery is covered by the skin, superficial fascia, Platysma, deep fascia, and anterior margin of the Sternocleidomastoideus; it is crossed by the hypoglossal nerve, by the lingual, ranine, common facial, and superior thyroid veins; and by the Digastricus and Stylohyoideus; higher up it passes deeply into the substance of the parotid gland, where it lies deep to the facial nerve and the junction of the temporal and internal maxillary veins. Medial to it are the hyoid bone, the wall of the pharynx, the superior laryngeal nerve, and a portion of the parotid gland. Lateral to it, in the lower part of its course, is the internal carotid artery. Posterior to it, near its origin, is the superior laryngeal nerve; and higher up, it is sepa- rated from the internal carotid by the Styloglossus and Stylopharyngeus, the glossopharyngeal nerve, the pharyngeal branch of the vagus, and part of the parotid gland. Branches.—The branches of the external carotid artery may be divided into four sets. Anterior. Superior Thyroid. Lingual. External Maxillary. Posterior. Occipital. Posterior Auricular. Ascending. Ascending Pharyngeal. Terminal. Superficial Temporal. Internal Maxillary. 1. The superior thyroid artery (a. thyreoidea superior) (Fig. 507) arises from the external carotid artery just below the level of the greater cornu of the hyoid bone and ends in the thyroid gland. Relations.—From its origin under the anterior border of the Sternocleidomastoideus it runs upward and forward for a short distance in the carotid triangle, where it is covered by the skin, Platysma, and fascia; it then arches downward beneath the Omohyoideus, Sternohyoideus, and Sternothyreoideus. To its medial side are the Constrictor pharyngis inferior and the external branch of the superior laryngeal nerve. Branches.—It distributes twigs to the adjacent muscles, and numerous branches to the thyroid gland, anastomosing with its fellow of the opposite side, and with the inferior thyroid arteries. The branches to the gland are generally two in number; one, the larger, supplies principally the anterior surface; on the isthmus of the gland it anastomoses with the corresponding artery of the opposite side: a second branch descends on the posterior surface of the gland and anastomoses with the inferior thyroid artery. Besides the arteries distributed to the muscles and to the thyroid gland, the branches of the superior thyroid are: Hyoid. Sternocleidomastoid. Superior Laryngeal. Cricothyroid. The Hyoid Branch (ramus hyoideus; infrahyoid branch) is small and runs along the lower border of the hyoid bone beneath the Thyreohyoideus and anastomoses with the vessel of the opposite side. The Sternocleidomastoid Branch (ramus sternocleidomastoideus; sternomastoid branch) runs downward and lateralward across the sheath of the common carotid artery, and supplies the Sternocleidomastoideus and neighboring muscles and integument; it frequently ari'ses as a separate branch from the external carotid. The Superior Laryngeal Artery (a. laryngea superior), larger than either of the preceding, accompanies the internal laryngeal branch of the superior laryngeal nerve, beneath the Thyreohyoideus; it pierces the hyothyroid membrane, and supplies the muscles, mucous membrane, and glands of the larynx, anastomosing with the branch from the opposite side. The Cricothyroid Branch (ramus cricothyreoideus) is small and runs transversely across the cricothyroid membrape, communicating with the artery of the opposite side. THE EXTERNAL CAROTID ARTERY 553 2. The lingual artery (a. lingualis) (Fig. 590) arises from the external carotid between the superior thyroid and external maxillary; it first runs obliquely upward and medialward to the greater cornu of the hyoid bone; it then curves downward and forward, forming a loop which is crossed by the hypoglossal nerve, and passing beneath the Digastricus and Stylohyoideus it runs horizontally forward, beneath the Hyoglossus, and finally, ascending almost perpendicularly to the tongue, turns forward on its lower surface as far as the tip, under the name of the profunda linguse. Relations.—Its first, or oblique, portion is superficial, and is contained within the carotid triangle; it rests upon the Constrictor pharyngis medius, and is covered by the Platysma and the fascia of the neck. Its second, or curved, portion also lies upon the Constrictor pharyngis medius, being covered at first by the tendon of the Digastricus and by the Stylohyoideus, and afterward by the Hyoglossus. Its third, or horizontal, portion lies between the Hyoglossus and Genioglossus. The fourth, or terminal part, under the name of the profunda linguse (ranine artery) runs along the under surface of the tongue to its tip; here it is superficial, being covered only by the mucous membrane; above it is the Longitudinalis inferior, and on the medial side the Genioglossus. The hypoglossal nerve crosses the first part of the lingual artery, but is sepa- rated from the second part by the Hyoglossus. Branches.—The branches of the lingual artery are: Hyoid. Dorsales linguae. Sublingual. Profunda linguse The Hyoid Branch (ramus hyoideus; suprahyoid branch) runs along the upper border of the hyoid bone, supplying the muscles attached to it and anastomosing with its fellow of the opposite side. The Arterise Dorsales Linguae (rami dorsales linguae) consist usually of two or three small branches which arise beneath the Hyoglossus; they ascend to the back part of the dorsum of the tongue, and supply the mucous membrane in this situa- tion, the glossopalatine arch, the tonsil, soft palate, and epiglottis; anastomosing with the vessels of the opposite side. The Sublingual Artery (a. sublingualis) arises at the anterior margin of the Hyo- glossus, and runs forward between the Genioglossus and Mylohyoideus to the sub- lingual gland. It supplies the gland and gives branches to the Mylohyoideus and neighboring muscles, and to the mucous membrane of the mouth and gums. One branch runs behind the alveolar process of the mandible in the substance of the gum to anastomose with a similar artery from the other side; another pierces the Mylohyoideus and anastomoses with the submental branch of the external maxillary artery. The Arteria Profunda Linguae (ranine artery; deep lirlgual artery) is the terminal portion of the lingual artery; it pursues a tortuous course and runs along the under surface of the tongue, below the Longitudinalis inferior, and above the mucous membrane; it lies on the lateral side of the Genioglossus, accompanied by the lingual nerve. At the tip of the tongue, it is said to anastomose with the artery of the opposite side, but this is denied by Hyrtl. In the mouth, these vessels are placed one on either side of the frenulum linguae. > 3. The external maxillary artery (a. maxillaris externa; facial artery) (Tig. 508), arises in the carotid triangle a little above the lingual artery and, sheltered by the ramus of the mandible, passes obliquely up beneath the Digastricus and Stylo- hyoideus, over which it arches to enter a groove on the posterior surface of the submaxillary gland. It then curves upward over the body of the mandible at the antero-inferior angle of the Masseter; passes forward and upward across the cheek to the angle of the mouth, then ascends along the side of the nose, and ends at the medial commissure of the eye, under the name of the angular artery. I his vessel, both in the neck and on the face, is remarkably tortuous: in the former 554 ANGIOLOGY situation, to accommodate itself to the movements of the pharynx in deglutition; and in the latter, to the movements of the mandible, lips, and cheeks. Relations.—In the neck, its origin is superficial, being covered by the integument, Platysma, and fascia; it then passes beneath the Digastricus and Stylohyoideus muscles and part of the submaxillary gland, and frequently beneath the hypoglossal nerve. It lies upon the Constrictores pharyngis medius and superior, the latter of which separates it, at the summit of its arch, from the lower and back part of the tonsil. On the face, where it passes over the body of the mandible, it is comparatively superficial, lying immediately beneath the Platysma. In its course over the face, it is covered by the integument, the fat of the cheek, and, near the angle of the mouth, by the Platysma, Risorius, and Zygomaticus. It rests on the Buccinator and Caninus, and passes either over or under the infraorbital head of the Quadratus labii superioris. The anterior facial vein lies lateral to the artery, and takes a more direct course across the face, where it is separated from the artery by a considerable interval. In the neck it lies superficial to the artery. The branches of the facial nerve cross the artery from behind forward. Angular Lateral nasal Septal Superior labial Inferior labial Fig. 508.—The arteries of the face and scalp.1 Branches.—The branches of the artery may be divided into two sets: those given off in the neck (cervical), and those on the face (facial). Cervical Branches. Ascending Palatine. Tonsillar. Glandular. Submental. Muscular. Facial Branches. Inferior Labial. Superior Labial. Lateral Nasal. Angular. Muscular. 1 The muscular tissue of the lips must be supposed to have been cut away, in order to show the course of the labial arteries. THE EXTERNAL CAROTID ARTERY 555 The Ascending Palatine Artery (a. palatina ascendens) (Fig. 513) arises close to the origin of the external maxillary artery and passes up between the Styloglossus and Stylopharyngeus to the side of the pharynx, along which it is continued between the Constrictor pharyngis superior and the Pterygoideus internus to near the base of the skull. It divides near the Levator veli palatini into two branches: one fol- lows the course of this muscle, and, winding over the upper border of the Constrictor pharyngis superior, supplies the soft palate and the palatine glands, anastomosing with its fellow of the opposite side and with the descending palatine branch of the internal maxillary artery; the other pierces the Constrictor pharyngis superior and supplies the palatine tonsil and auditory tube, anastomosing with the tonsillar and ascending pharyngeal arteries. The Tonsillar Branch (ramus tonsillaris) (Fig. 513) ascends between the Ptery- goideus internus and Styloglossus, and then along the side of the pharynx, perforating the Constrictor pharyngis superior, to ramify in the substance of the palatine tonsil and root of the tongue. The Glandular Branches (rami glandulares; submaxillary branches) consist of three or four large vessels, which supply the submaxillary gland, some being prolonged to the neighboring muscles, lymph glands, and integument. The Submental Artery (a. submentalis) the largest of the cervical branches, is given off from the facial artery just as that vessel quits the submaxillary gland: it runs forward upon the Mylohyoideus, just below the body of the mandible, and beneath the Digastricus. It supplies the surrounding muscles, and anastomoses with the sublingual artery and with the mylohyoid branch of the inferior alveolar; at the symphysis menti it turns upward over the border of the mandible and divides into a superficial and a deep branch. The superficial branch passes between the integument and Quadratus labii inferioris, and anastomoses with the inferior labial artery; the deep branch runs between the muscle and the bone, supplies the lip, and anastomoses with the inferior labial and mental arteries. Fig. 509—The labial coronary arteries, the glands of the lips, and the nerves of the right side seen from the posterior surface after removal of the mucous membrane The Inferior Labial Artery (a. labialis inferior; inferior coronary artery) arises near the angle of the mouth; it passes upward and forward beneath the Triangularis and, penetrating the Orbicularis oris, runs in a tortuous course along the edge of the lower lip between this muscle and the mucous membrane. It supplies the labial glands, the mucous membrane, and the muscles of the lower lip; and anas- tomoses with the artery of the opposite side, and with the mental branch of the inferior alveolar artery. The Superior Labial Artery (a. labialis superior; superior coronary artery) is larger and more tortuous than the inferior. It follows a similar course along the edge of the upper lip, lyingbetween the mucous membrane and the Orbicularis oris, and anastomoses with the artery of the opposite side. It supplies the upper lip, 556 ANGIOLOGY and gives off in its course two or three vessels which ascend to the nose; a septal branch ramifies on the nasal septum as far as the point of the nose, and an alar branch supplies the ala of the nose. The Lateral Nasal branch is derived from the external maxillary as that' vessel ascends along the side of the nose. It supplies the ala and dorsum of the nose, anas- tomosing with its fellow, with the septal and alar branches, with the dorsal nasal branch of the ophthalmic, and with the infraorbital branch of the internal maxillary. The Angular Artery (a. angularis) is the terminal part of the external maxillary; it ascends to the medial angle of the orbit, imbedded in the fibers of the angular head of the Quadratus labii superioris, and accompanied by the angular vein. On the cheek it distributes branches which anastomose with the infraorbital; after supplying the lacrimal sac and Orbicularis oculi, it ends by anastomosing with the dorsal nasal branch of the ophthalmic artery. The Muscular Branches in the neck are distributed to the Pterygoideus internus and Stylohyoideus, and on the face to the Masseter and Buccinator. The anastomoses of the external maxillary artery are very numerous, not only with the vessel of the opposite side, but, in the neck, with the sublingual branch of the lingual, with the ascending pharyngeal, and by its ascending palatine and tonsillar branches with the palatine branch of the internal maxillary; on the face, with the mental branch of the inferior alveolar as it emerges from the mental foramen, with the transverse facial branch of the superficial temporal, with the infraorbital branch of the internal maxillary, and with the dorsal nasal branch of the ophthalmic. Peculiarities.—The external maxillary artery not infrequently arises in common with the lingual. It varies in its size and in the extent to which it supplies the face; it occasionally ends as the submental, and not infrequently extends only as high as the angle of the mouth or nose. The deficiency is then compensated for by enlargement of one of the neighboring arteries. 4. The occipital artery (a. occipitalis) (Fig. 508) arises from the posterior part of the external carotid, opposite the external maxillary, near the lower margin of the posterior belly of the Digastricus, and ends in the posterior part of the scalp. Course and Relations.—At its origin, it is covered by the posterior belly of the Digastricus and. the Stylohyoideus, and the hypoglossal nerve winds around it from behind forward; higher up, it crosses the internal carotid artery, the internal jugular vein, and the vagus and accessory nerves. It next ascends to the interval between the transverse process of the atlas and the mastoid process of the temporal bone, and passes horizontally backward, grooving the surface of the latter bone, being covered by the Sternocleidomastoideus, Splenius capitis, Longissimus capitis, and Digastricus, and resting upon the Rectus capitis lateralis, the Obliquus superior, and Semi- spinalis capitis. It then changes its course and runs vertically upward, pierces the fascia con- necting the cranial attachment of the Trapezius with the Sternocleidomastoideus, and ascends in a tortuous course in the superficial fascia of the scalp, where it divides into numerous branches, which reach as high as the vertex of the skull and anastomose with the posterior auricular and superficial temporal arteries. Its terminal portion is accompanied by the greater occipital nerve. Branches.—The branches of the occipital artery are: Muscular. Sternocleidomastoid. Auricular. Meningeal. Descending. The Muscular Branches (rami musculares) supply the Digastricus, Stylohyoideus, Splenius, and Longissimus capitis. The Sternocleidomastoid Artery (a. sternocleidomastoidea; sternomastoid artery) generally arises from the occipital close to its commencement, but sometimes springs directly from the external carotid. It passes downward and backward over the hypoglossal nerve, and enters the substance of the muscle, in company with the accessory nerve. The Auricular Branch (ramus auricularis) supplies the back of the concha and frequently gives off a branch, which enters the skull through the mastoid foramen THE EXTERNAL CAROTID ARTERY 557 and supplies the dura mater, the diploe, and the mastoid cells; this latter branch sometimes arises from the occipital artery, and is then known as the mastoid branch. The Meningeal Branch (ramus meningeus; dural branch) ascends with the internal jugular vein, and enters the skull through the jugular foramen and condyloid canal, to supply the dura mater in the posterior fossa. The Descending Branch (ramus descendens; arteria princeps cervicis) (Fig. 513), the largest branch of the occipital, descends on the back of the neck, and divides into a superficial and deep portion. The superficial portion runs beneath the Splenius, giving off branches which pierce that muscle to supply the Trapezius and anastomose with the ascending branch of the transverse cervical: the deep portion runs down between the Semispinales capitis and colli, and anastomoses with the vertebral and -with the a. profunda cervicalis, a branch of the costocervical trunk. The anastomosis between these vessels assists in establishing the collateral circu- lation after ligature of the common carotid or subclavian artery. The terminal branches of the occipital artery are distributed to the back of the head: they are very tortuous, and lie between the integument and Occipitalis, anastomosing with the artery of the opposite side and with the posterior auricular and temporal arteries, and supplying the Occipitalis, the integument, and peri- cranium. One of the terminal branches may give off a meningeal twig which passes through the parietal foramen. 5. The posterior auricular artery (a. auricularis posterior) (Fig. 508) is small and arises from the external carotid, above the Digastricus and Stylohyoideus, opposite the apex of the styloid process. It ascends, under cover of the parotid gland, on the styloid process of the temporal bone, to the groove between the cartilage of the ear and the mastoid process, immediately above which it divides into its auricular and occipital branches. Branches.—Besides several small branches to the Digastricus, Stylohyoideus, and Sternocleidomastoideus, and to the parotid gland, this vessel gives off three branches: Stylomastoid. Auricular. Occipital. The Stylomastoid Artery (a. stylomastoidea) enters the stylomastoid foramen and supplies the tympanic cavity, the tympanic antrum and mastoid cells, and the semicircular canals. In the young subject a branch from this vessel forms, with the anterior tympanic artery from the internal maxillary, a vascular circle, which surrounds the tympanic membrane, and from which delicate vessels ramify on that membrane. It anastomoses with the superficial petrosal branch of the middle meningeal artery by a twig which enters the hiatus canalis facialis. The Auricular Branch (ramus auricularis) ascends behind the ear, beneath the Auricularis posterior, and is distributed to the back of the auricula, upon which it ramifies minutely, some branches curving around the margin of the cartilage, others perforating it, to supply the anterior surface. It anastomoses with the parietal and anterior auricular branches of the superficial temporal. The Occipital Branch (ramus occipitalis) passes backward, over the Sternocleido- mastoideus, to the scalp above and behind the ear. It supplies the Occipitalis and the scalp in this situation and anastomoses with the occipital artery. 6. The ascending pharyngeal artery (a. pharyngea ascendens) (Fig. 513), the smallest branch of the external carotid, is a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the Stylo- pharyngeus. It arises from the back part of the external carotid, near the com- mencement of that vessel, and ascends vertically between the internal carotid and the side of the pharynx, to the under surface of the base of the skull, lying on the Longus capitis. 558 ANGIOLOGY Branches.—Its branches are: Pharyngeal. Palatine. Pre vertebral. Inferior Tympanic. Posterior Meningeal The Pharyngeal Branches (rami pharyngei) are three or four in number. Two of these descend to supply the Constrictores pharyngis medius and inferior and the Stylopharyngeus, ramifying in their substance and in the mucous membrane lining them. The Palatine Branch varies in size, and may take the place of the ascending palatine branch of the facial artery, when that vessel is small. It passes inward upon the Constrictor pharyngis superior, sends ramifications to the soft palate and tonsil, and supplies a branch to the auditory tube. The Prevertebral Branches are numerous small vessels, which supply the Longi capitis and colli, the sympathetic trunk, the hypoglossal and vagus nerves, and the lymph glands; they anastomose with the ascending cervical artery. The Inferior Tympanic Artery (a. tympanica inferior) is a small branch which passes through a minute foramen in the petrous portion of the temporal bone, in company with the tympanic branch of the glossopharyngeal nerve, to supply the medial wall of the tympanic cavity and anastomose with the other tympanic arteries. The Meningeal Branches are several small vessels, which supply the dura mater. One, the posterior meningeal, enters the cranium through the jugular foramen; a second passes through the foramen lacerum; and occasionally a third through the canal for the hypoglossal nerve. 7. The superficial temporal artery (a. temporalis superficialis) (Fig. 508), the smaller of the two terminal branches of the external carotid, appears, from its direction, to be the continuation of that vessel. It begins in the substance of the parotid gland, behind the neck of the mandible, and crosses over the posterior root of the zygomatic process of the temporal bone; about 5 cm. above this process it divides into two branches, a frontal and a parietal. Relations.—As it crosses the zygomatic process, it is covered by the Auricularis anterior muscle, and by a dense fascia; it is crossed by the temporal and zygomatic branches of the facial nerve and one or two veins, and is accompanied by the auriculotemporal nerve, which lies immediately behind it. Branches.—Besides some twigs to the parotid gland, to the temporomandibular joint, and to the Masseter muscle, its branches are: Transverse Facial. Middle Temporal. Anterior Auricular. Frontal. Parietal. The Transverse Facial Artery (a. transversa faciei) is given off from the superficial temporal before that vessel quits the parotid gland; running forward through the substance of the gland, it passes transversely across the side of the face, between the parotid duct and the lower border of the zygomatic arch, and divides into numer- ous branches, which supply the parotid gland and duct, the Masseter, and the integument, and anastomose with the external maxillary, masseteric, buccinator, and infraorbital arteries. This vessel rests on the Masseter, and is accompanied by one or two branches of the facial nerve. The Middle Temporal Artery (a. temporalis media) arises immediately above the zygomatic arch, and, perforating the temporal fascia, gives branches to the Tem- poralis, anastomosing with the deep temporal branches of the internal maxillary. It occasionally gives off a zygomaticoorbital branch, which runs along the upper border of the zygomatic arch, between the two layers of the temporal fascia, to the lateral angle of the orbit. This branch, which may arise directly from the THE EXTERNAL CAROTID ARTERY 559 superficial temporal arterv, supplies the Orbicularis oculi, and anastomoses with the lacrimal and palpebral branches of the ophthalmic artery. The Anterior Auricular Branches (rami auriculares anteriores) are distributed to the anterior portion of the auricula, the lobule, and part of the external meatus, anastomosing with the posterior auricular. The Frontal Branch {ramus frontalis; anterior temporal) runs tortuously upward and forward to the forehead, supplying the muscles, integument, and pericranium in this region, and anastomosing with the supraorbital and frontal arteries. The Parietal Branch {ramus parietalis; posterior temporal) larger than the frontal, curves upward and backward on the side of the head, lying superficial to the tem- poral fascia, and anastomosing with its fellow of the opposite side, and with the posterior auricular and occipital arteries. < Incisor branch Fig. 510.—Plan of branches of internal maxillary artery. 8. The internal maxillary artery (a. maxillaris interna) (Fig. 510), the larger of the two terminal branches of the external carotid, arises behind the neck of the mandible, and is at first imbedded in the substance of the parotid gland; it passes forward between the ramus of the mandible and the sphenomandibular ligament, and then runs, either superficial or deep to the Pterygoideus externus, to the pterygopalatine fossa. It supplies the deep structures of the face, and may be divided into mandibular, pterygoid, and pterygopalatine portions. The first or mandibular portion passes horizontally forward, between the ramus of the mandible and the sphenomandibular ligament, where it lies parallel to and a little below the auriculotemporal nerve; it crosses the inferior alveolar nerve, and runs along the lower border of the Pterygoideus externus. The second or pterygoid portion runs obliquely forward and upward under cover of the ramus of the mandible and insertion of the Temporalis, on the superficial (very frequently on the deep) surface of the Pterygoideus externus; it then passes between the two heads of origin of this muscle and enters the fossa. The third or pterygopalatine portion lies in the pterygopalatine fossa in relation with the sphenopalatine ganglion. 560 ANGIOLOGY The branches of this vessel may be divided into three groups (Fig. 511), corre- sponding with its three divisions. Branches of the First or Mandibular Portions.— Anterior Tympanic. Deep Auricular. Middle Meningeal. Accessory Meningeal Inferior Alveolar The Anterior Tympanic Artery (a. tympanica anterior; tympanic artery) passes upward behind the temporomandibular articulation, enters the tympanic cavity through the petrotympanic fissure, and ramifies upon the tympanic membrane, forming a vascular circle around the membrane with the stylomastoid branch of the posterior auricular, and anastomosing with the artery of the pterygoid canal and with the caroticotympanic branch from the internal carotid. Sphenopalatine Post, deep temporal Desc. / pal Mid. meningeal Ant. deem temp.\ Ant. tympanic Pterygoid 'Access, menin- geal Post. sup. alveolar Deep A .auric Buccinator Masseteric Pterygoid External carotid Inferior alveolar Mylohyoid Fig. 511.—Plan of branches of internal maxillary artery. The Deep Auricular Artery (a. auricularis 'profunda) often arises in common with the preceding. It ascends in the substance of the parotid gland, behind the tem- poromandibular articulation, pierces the cartilaginous or bony wall of the external acoustic meatus, and supplies its cuticular lining and the outer surface of the tympanic membrane. It gives a branch to the temporomandibular joint. The Middle Meningeal Artery (a. meningea media; medidural artery) is the largest of the arteries which supply the dura mater. It ascends between the spheno- mandibular ligament and the Pterygoideus externus, and between the two roots of the auriculotemporal nerve to the foramen spinosum of the sphenoid bone, through which it enters the cranium; it then runs forward in a groove on the great wing of the sphenoid bone, and divides into two branches, anterior and posterior. The anterior branch, the larger, crosses the great wing of the sphenoid, reaches the groove, or canal, in the sphenoidal angle of the parietal bone, and then divides into branches which spread out between the dura mater and internal surface of the cranium, some passing upward as far as the vertex, and others backward to the occipital region. The posterior branch curves backward on the squama of the temporal bone, and, reaching the parietal some distance in front of its mastoid angle, divides into branches which supply the posterior part of the dura mater and THE EXTERNAL CAROTID ARTER Y 561 cranium. The branches of the middle meningeal artery are distributed partly to the dura mater, but chiefly to the bones; they anastomose with the arteries of the opposite side, and with the anterior and posterior meningeal. The middle meningeal on entering the cranium gives off the following branches: (1) Numerous small vessels supply the semilunar ganglion and the dura mater in this situation. (2) A superficial petrosal branch enters the hiatus of the facial canal, supplies the facial nerve, and anastomoses with the stylomastoid branch of the posterior auricular artery. (3) A superior tympanic artery runs in the canal for the Tensor tympani, and supplies this muscle and the lining membrane of the canal. (4) Orbital branches pass through the superior orbital fissure or through separate canals in the great wing of the sphenoid, to anastomose with the lacrimal or other branches of the ophthalmic artery. (5) Temporal branches pass through foramina in the great wing of the sphenoid, and anastomose in the temporal fossa with the deep temporal arteries. The Accessory Meningeal Branch (ramus meningeus accessorius; small meningeal or parvidural branch) is sometimes derived from the preceding. It enters the skull through the foramen ovale, and supplies the semilunar ganglion and dura mater. The Inferior Alveolar Artery (a. alveolaris inferior; inferior dental artery) descends with the inferior alveolar nerve to the mandibular foramen on the medial surface of the ramus of the mandible. It runs along the mandibular canal in the substance of the bone, accompanied by the nerve, and opposite the first premolar tooth divides into two branches, incisor and mental. The incisor branch is continued forward beneath the incisor teeth as far as the middle line, where it anastomoses with the artery of the opposite side; the mental branch escapes with the nerve at the mental foramen, supplies the chin, and anastomoses with the submental and inferior labial arteries. Near its origin the inferior alveolar artery gives off a lingual branch which descends with the lingual nerve and supplies the mucous membrane of the mouth. As the inferior alveolar artery enters the foramen, it gives off a mylohyoid branch which runs in the mylohyoid groove, and ramifies on the under surface of the Mylohyoideus.- The inferior alveolar artery and its incisor branch during their course through the substance of the bone give off a few twigs which are lost in the cancellous tissue, and a series of branches which correspond in number to the roots of the teeth: these enter the minute apertures at the extremities of the roots, and supply the pulp of the teeth. Branches of the Second or Pterygoid Portion.— Deep Temporal. Pterygoid. Masseteric. Buccinator. The Deep Temporal Branches, two in number, anterior and posterior, ascend between the Temporalis and the pericranium; they supply the muscle, and anasto- mose with the middle temporal artery; the anterior communicates with the lacrimal artery by means of small branches which perforate the zygomatic bone and great wing of the sphenoid. The Pterygoid Branches (rami pterygoidei), irregular in their number and origin, supply the Pterygoidei. The Masseteric Artery (a. masseterica) is small and passes lateralward through the mandibular notch to the deep surface of the Masseter. It supplies the muscle, and anastomoses with the masseteric branches of the external maxillary and with the transverse facial artery. The Buccinator Artery (a. buccinatoria; buccal artery) is small and runs obliquely forward, between the Pterygoideus internus and the insertion of the Temporalis, to the outer surface of the Buccinator, to which it is distributed, anastomosing with branches of the external maxillary and with the infraorbital. Branches of the Third or Pterygopalatine Portion.— Posterior Superior Alveolar. Infraorbital. Descending Palatine. Artery of the Pterygoid Canal. Pharyngeal. Sphenopalatine. 562 ANGIOLOGY The Posterior Superior Alveolar Artery (a. alveolaris superior posterior; alveolar or posterior dental artery) is given off from the internal maxillary, frequently in con- junction with the infraorbital just as the trunk of the vessel is passing into the pterygopalatine fossa. Descending upon the tuberosity of the maxilla, it divides into numerous branches, some of which enter the alveolar canals, to supply the molar and premolar teeth and the lining of the maxillary sinus, while others are continued forward on the alveolar process to supply the gums. The Infraorbital Artery (a. infraorbitalis) appears, from its direction, to be the continuation of the trunk of the internal maxillary, but often arises in conjunction with the posterior superior alveolar. It runs along the infraorbital groove and canal with the infraorbital nerve, and emerges on the face through the infraorbital foramen, beneath the infraorbital head of the Quadratus labii superioris. While in the canal, it gives off (a) orbital branches which assist in supplying the Rectus inferior and Obliquus inferior and the lacrimal sac, and (b) anterior superior alveolar branches which descend through the anterior alveolar canals to supply the upper incisor and canine teeth and the mucous membrane of the maxillary sinus. On the face, some branches pass upward to the medial angle of the orbit and the lacrimal sac, anastomosing with the angular branch of the external maxillary artery; others run toward the nose, anastomosing with the dorsal nasal branch of the ophthalmic; and others descend between the Quadratus labii superioris and the Caninus, and anastomose with the external maxillary, transverse facial, and buccinator arteries. The four remaining branches arise from that portion of the internal maxillary which is contained in the pterygopalatine fossa. The Descending Palatine Artery (a. palatina descendens) descends through the pterygopalatine canal with the anterior palatine branch of the sphenopalatine ganglion, and, emerging from the greater palatine foramen, runs forward in a groove on the medial side of the alveolar border of the hard palate to the incisive canal; the terminal branch of the artery passes upward through this canal to anastomose with the sphenopalatine artery. Branches are distributed to the gums, the palatine glands, and the mucous membrane of the roof of the mouth; while in the pterygo- palatine canal it gives off twigs which descend in the lesser palatine canals to supply the soft palate and palatine tonsil, anastomosing with the ascending palatine artery. The Artery of the Pterygoid Canal (a. canalis pterygoidei; Vidian artery) passes backward along the pterygoid canal with the corresponding nerve. It is distributed to the upper part of the pharynx and to the auditory tube, sending into the tympanic cavity a small branch which anastomoses with the other tympanic arteries. The Pharyngeal Branch is very small; it runs backward through the pharyngeal canal with the pharyngeal nerve, and is distributed to the upper part of the pharynx and to the auditory tube. The Sphenopalatine Artery (a. sphenopalatina; nasopalatine artery) passes through the sphenopalatine foramen into the cavity of the nose, at the back part of the superior meatus. Here it gives off its posterior lateral nasal branches which spread forward over the conchse and meatuses, anastomose with the ethmoidal arteries and the nasal branches of the descending palatine, and assist in supplying the frontal, maxillary, ethmoidal, and sphenoidal sinuses. Crossing the under surface of the sphenoid the sphenopalatine artery ends on the nasal septum as the posterior septal branches; these anastomose with the ethmoidal arteries and the septal branch of the superior labial; one branch descends in a groove on the vomer to the incisive canal and anastomoses with the descending palatine artery. THE TRIANGLES OF THE NECK (Fig. 512). The side of the neck presents a somewhat quadrilateral outline, limited, above, by the lower border of the body of the mandible, and an imaginary line extending THE TRIANGLES OF THE NECK 563 from the angle of the mandible to the mastoid process; below, by the upper border of the clavicle; in front, by the middle line of the neck; behind, by the anterior margin of the Trapezius. This space is subdivided into two large triangles by the Sternocleidomastoideus, which passes obliquely across the neck, from the sternum and clavicle below, to the mastoid process and occipital bone above. The triangular space in front of this muscle is called the anterior triangle; and that behind it, the posterior triangle. Anterior Triangle.—The anterior triangle is bounded, in front, by the middle line of the neck; behind, by the anterior margin of the Sternocleidomastoideus; its base, directed upward, is formed by the lower border of the body of the mandible, and a line extending from the angle of the mandible to the mastoid process; its apex is below, at the sternum. This space is subdivided into four smaller triangles by the Digastricus above, and the superior belly of the Omohyoideus below. These smaller triangles are named the inferior carotid, the superior carotid, the submaxillary, and the suprahyoid. Suprahyoid triangle Submaxillary triangle Superior carotid triangle Occipital triangle Inferior carotid triangle Subclavian triangle Fig. 512.—The triangles of the neck The Inferior Carotid, or Muscular Triangle, is bounded, in front, by the median line of the neck from the hyoid bone to the sternum; behind, by the anterior margin of the Sternocleidornastoideus; above, by the superior belly of the Omohyoideus. It is covered by the integument, superficial fascia, Platysma, and deep fascia, ramifying in which are some of the branches of the supraclavicular nerves. Be- neath these superficial structures are the Sternohyoideus and Sternothyreoideus, which, together with the anterior margin of the Sternocleidornastoideus, conceal the lower part of the common carotid artery.1 This vessel is enclosed within its sheath, together with the internal jugular vein and vagus nerve; the vein lies lateral to the artery on the right side of the neck, but overlaps it below on the left side; the nerve lies between the artery and vein, on a plane posterior to both. 1 Therefore the common carotid artery and internal jugular vein are not, strictly speaking, contained in tn angle, since they are covered by the Sternocleidornastoideus: that is to say, they lie under that muscle, which forms the posterior border of the triangle. But as they lie very close to the structures which are really contained in the triangle, and whose position it is essential to remember in operating on this part of the artery, it is expedient to study the relations of all these parts together. 564 ANGIOLOGY In front of the sheath are a few descending filaments from the ansa hypoglossi; behind the sheath are the inferior thyroid artery, the recurrent nerve, and the sym- pathetic trunk; and on its medial side, the esophagus, the trachea, the thyroid gland, and the lower part of the larynx. By cutting into the upper part of this space, and slightly displacing the Sternocleidomastoideus, the common carotid artery may be tied below the Omohyoideus. The Superior Carotid, or Carotid Triangle, is bounded, behind by the Sternocleido- mastoideus; below, by the superior belly of the Omohyoideus; and above, by the Stylohyoideus and the posterior belly of the Digastricus. It is covered by the integu- ment, superficial fascia, Platysma and deep fascia; ramifying in which are branches of the facial and cutaneous cervical nerves. Its floor is formed by parts of the Thyro- hyoideus, Hyoglossus, and the Constrictores pharyngis medius and inferior. This space when dissected is seen to contain the upper part of the common carotid artery, which bifurcates opposite the upper border of the thyroid cartilage into the external and internal carotid. These vessels are somewhat concealed from view by the anterior margin of the Sternocleidomastoideus, which overlaps them. The external and internal carotids lie side by side, the external being the more anterior of the two. The following branches of the external carotid are also met with in this space: the superior thyroid, running forward and downward; the lingual, directly forward; the external maxillary, forward and upward; the occipital, backward; and the ascending pharyngeal, directly upward on the medial side of the internal carotid. The veins met with are: the internal jugular, which lies on the lateral side of the common and internal carotid arteries; and veins corresponding to the above-mentioned branches of the external carotid—viz., the superior thyroid, the lingual, common facial, ascending pharyngeal, and sometimes the occipital— all of which end in the internal jugular. The nerves in this space are the following. In front of the sheath of the common carotid is the ramus descendens hypoglossi. The hypoglossal nerve crosses both the internal and external carotids above, curving around the origin of the occipital artery. Within the sheath, between the artery and vein, and behind both, is the vagus nerve; behind the sheath, the sym- pathetic trunk. On the lateral side of the vessels, the accessory nerve runs for a short distance before it pierces the Sternocleidomastoideus; and on the medial side of the external carotid, just below the hyoid bone, may be seen the internal branch of the superior laryngeal nerve; and, still more inferiorly, the external branch of the same nerve. The upper portion of the larynx and lower portion of the pharynx are also found in the front part of this space. The Submaxillary or Digastric Triangle corresponds to the region of the neck immediately beneath the body of the mandible. It is bounded, above, by the lower border of the body of the mandible, and a line drawn from its angle to the mastoid process; below, by the posterior belly of the Digastricus and the Stylohyoideus; in front, by the anterior belly of the Digastricus. It is covered by the integument, superficial fascia, Platysma, and deep fascia, ramifying in which are branches of the facial nerve and ascending filaments of the cutaneous cervical nerve. Its floor is formed by the Mylohyoideus, Hyoglossus, and Constrictor pharyngis superior. It is divided into an anterior and a posterior part by the stylomandibular ligament. The anterior part contains the submaxillary gland, superficial to which is the anterior facial vein, while imbedded in the gland is the external maxillary artery and its glandular branches; beneath the gland, on the surface of the Mylo- hyoideus, are the submental artery and the mylohyoid artery and nerve. The posterior part of this triangle contains the external carotid artery, ascending deeply in the substance of the parotid gland; this vessel lies here in front of, and super- ficial to, the internal carotid, being crossed by the facial nerve, and gives off in its course the posterior auricular, superficial temporal, and internal maxillary branches: more deeply are the internal carotid, the internal jugular vein, and the THE TRIANGLES OF THE NECK 565 vagus nerve, separated from the external carotid by the Styloglossus and Stylo- pharyngeus, and the glossopharyngeal nerve.1 The Suprahyoid Triangle is limited behind by the anterior belly of the Digastricus, in front by the middle line of the neck between the mandible and the hyoid bone; below, by the body of the hyoid bone; its floor is formed by the Mylohyoideus. It contains one or two lymph glands and some small veins; the latter unite to form the anterior jugular vein. Posterior Triangle.—The posterior triangle is bounded, in front, by the Sterno- cleidomastoideus; behind, by the anterior margin of the Trapezius; its base is formed by the middle third of the clavicle; its apex, by the occipital bone. The space is crossed, about 2.5 cm. above the clavicle, by the inferior belly of the Omo- hyoideus, which divides it into two triangles, an upper or occipital, and a lower or subclavian. The Occipital Triangle, the larger division of the posterior triangle, is bounded, in front, by the Sternocleidomastoideus; behind, by the Trapezius; below, by the Omohyoideus. Its floor is formed from above downward by the Splenius capitis, Levator scapulae, and the Scaleni medius and posterior. It is covered by the skin, the superficial and deep fasciae, and by the Platysma below. The accessory nerve is directed obliquely across the space from the Sternocleidomastoideus, which it pierces, to the under surface of the Trapezius; below, the supraclavicular nerves and the transverse cervical vessels and the upper part of the brachial plexus cross the space. A chain of lymph glands is also found running along the posterior border of the Sternocleidomastoideus, from the mastoid process to the root of the neck. The Subclavian Triangle, the smaller division of the posterior triangle, is bounded, above, by the inferior belly of the Omohyoideus; below, by the clavicle; its base is formed by the posterior border of the Sternocleidomastoideus. Its floor is formed by the first rib with the first digitation of the Serratus anterior. The size of the subclavian triangle varies with the extent of attachment of the clavicular portions of the Sternocleidomastoideus and Trapezius, and also with the height at which the Omohyoideus crosses the neck. Its height also varies according to the position of the arm, being diminished by raising the limb, on account of the ascent of the clavicle, and increased by drawing the arm downward, when that bone is depressed. This space is covered by the integument, the superficial and deep fasciae and the Platysma, and crossed by the supraclavicular nerves. Just above the level of the clavicle, the third portion of the subclavian artery curves lateralward and downward from the lateral margin of the Scalenus anterior, across the first rib, to the axilla, and this is the situation most commonly chosen for ligaturing the vessel. Some- times this vessel rises as high as 4 cm. above the clavicle; occasionally, it passes in front of the Scalenus anterior, or pierces the fibers of that muscle. The sub- clavian vein lies behind the clavicle, and is not usually seen in this space; but in some cases it rises as high as the artery, and has even been seen to pass with that vessel behind the Scalenus anterior. The brachial plexus of nerves lies above the artery, and in close contact with it. Passing transversely behind the clavicle are the transverse scapular vessels; and traversing its upper angle in the same direction, the transverse cervical artery and vein. The external jugular vein runs vertically downward behind the posterior border of the Sternocleidomastoideus, to terminate in the subclavian vein; it receives the transverse cervical and trans- verse scapular veins, which form a plexus in front of the artery, and occasionally a small vein which crosses the clavicle from the cephalic. The small nerve to the Subclavius also crosses this triangle about its middle, and some lymph glands are usually found in the space. 1 The remark made about the inferior carotid triangle applies also to this one. The structures enumerated as con- tained in its posterior part lie, strictly speaking, beneath the muscles which form the posterior boundary or t e r ' angle; but as it is very important to bear in mind their close relation to the parotid gland, all these parts are spoken of together. 566 ANGIOLOGY The Internal Carotid Artery (A. Carotis Interna) (Fig. 513). The internal carotid artery supplies the anterior part of the brain, the eye and its appendages, and sends branches to the forehead and nose. Its size, in the adult, is equal to that of the external carotid, though, in the child, it is larger than that First aortic intercostal Fig. 513.—The internal carotid and vertebral arteries. Right side. vessel. It is remarkable for the number of curvatures that it presents in different parts of its course. It occasionally has one or two flexures near the base of the skull, while in its passage through the carotid canal and along the side of the body of the sphenoid bone it describes a double curvature and resembles the italic letter S. THE INTERNAL CAROTID ARTERY 567 Course and Relations.—In considering the course and relations of this vessel it may be divided into four portions: cervical, petrous, cavernous, and cerebral. Cervical Portion.—rlhis portion of the internal carotid begins at the bifurca- tion of the common carotid, opposite the upper border of the thyroid cartilage, and runs perpendicularly upward, in front of the transverse processes of the.upper three cervical vertebrae, to the carotid canal in the petrous portion of the temporal bone. It is comparatively superficial at its commencement, where it is contained in the carotid triangle, and lies behind and lateral to the external carotid, over- lapped by the Sternocleidomastoideus, and covered by the deep fascia, Platysma, and integument: it then passes beneath the parotid gland, being crossed by the hypoglossal nerve, the Digastricus and Stylohyoideus, and the occipital and pos- terior auricular arteries. Higher up, it is separated from the external carotid by the Styloglossus and Stylopharyngeus, the tip of the styloid process and the stylo- hyoid ligament, the glossopharyngeal nerve and the pharyngeal branch of the vagus. It is in relation, behind, with the Longus capitis, the superior cervical ganglion of the sympathetic trunk, and the superior laryngeal nerve; laterally, with the internal jugular vein and vagus nerve, the nerve lying on a plane posterior to the artery; medially, with the pharynx, superior laryngeal nerve, and ascending pharyngeal artery. At the base of the skull the glossopharyngeal, vagus, accessory, and hypo- glossal nerves lie between the artery and the internal jugular vein. Petrous Portion.—When the internal carotid artery enters the canal in the petrous portion of the temporal bone, it first ascends a short distance, then curves forward and medialward, and again ascends as it leaves the canal to enter the cavity of the skull between the lingula and petrosal process of the sphenoid. The artery lies at first in front of the cochlea and tympanic cavity; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age. Farther forward it is separated from the semilunar ganglion by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Fre- quently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from the bony wall of the carotid canal by a prolongation of dura mater, and is surrounded by a number of small veins and by filaments of the carotid plexus, derived from the ascending branch of the superior cervical ganglion of the sympathetic trunk. Cavernous Portion.—In this part of its course, the artery is situated between the layers of the dura mater forming the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the posterior clinoid process, then passes forward by the side of the body of the sphenoid bone, and again curves upward on the medial side of the anterior clinoid process, and perforates the dura mater forming the roof of the sinus. This portion of the artery is surrounded by filaments of the sympathetic nerve, and on its lateral side is the abducent nerve. Cerebral Portion.—Having perforated the dura mater on the medial side of the anterior clinoid process, the internal carotid passes between the optic and oculo- motor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure, where it gives off its terminal or cerebral branches. Peculiarities.—The length of the internal carotid varies according to the length of the neck, and also according to the point of bifurcation of the common carotid. It arises sometimes fiom the arch of the aorta; in such rare instances, this vessel has been found to be placed nearer t e middle line of the neck than the external carotid, as far upward as the larynx, when the latter vessel crossed the internal carotid. The course of the artery, instead of being straight, may be very tortuous. A few instances are recorded in which this vessel was altogether absent, in one of these the common carotid passed up the neck, and gave off the usual branches of the externa carotid; the cranial portion of the internal carotid was replaced by two branches of the interna maxillary, which entered the skull through the foramen rotundum and foramen ovale, and joine to form a single vessel. 568 ANGIOLOGY Branches.—The cervical portion of the internal carotid gives off no branches, Those from the other portions are: (( From the Petrous Portion Caroticotympanic. Artery of the Pterygoid Canal. Cavernous. Hypophyseal. ■ Semilunar. Anterior Meningeal. Ophthalmic. From the Cavernous Portion Anterior Cerebral. Middle Cerebral. Posterior Communicating. .Choroidal. From the Cerebral Portion 1. The caroticotympanic branch (ramus caroticotympanicus; tympanic branch) is small; it enters the tympanic cavity through a minute foramen in the carotid canal, and anastomoses with the anterior tympanic branch of the internal maxillary, and with the stylomastoid artery. 2. The artery of the pterygoid canal (a. canilis pterygoidei [Vidii]; Vidian artery) is a small, inconstant branch which passes into the pterygoid canal and anas- tomoses with a branch of the internal maxillary artery. 3. The cavernous branches are numerous small vessels which supply the hypophysis, the semilunar ganglion, and the walls of the cavernous and inferior petrosal sinuses. Some of them anastomose with branches of the middle meningeal. 4. The hypophyseal branches are one or two minute vessels supplying the hypophysis. 5. The semilunar branches are small vessels to the semilunar ganglion. 6. The anterior meningeal branch (a. meningea anterior) is a small branch which passes over the small wing of the sphenoid to supply the dura mater of the anterior cranial fossa; it anastomoses with the meningeal branch from the posterior eth- moidal artery. 7. The ophthalmic artery (a. ophthalmica) (Fig. 514) arises from the internal carotid, just as that vessel is emerging from the cavernous sinus, on the medial side of the anterior clinoid process, and enters the orbital cavity through the optic foramen, below and lateral to the optic nerve. It then passes over the nerve to reach the medial wall of the orbit, and thence horizontally forward, beneath the lower border of the Obliquus superior, and divides it into twm terminal branches, the frontal and dorsal nasal. As the artery crosses the optic nerve it is accompanied by the nasociliary nerve, and is separated from the frontal nerve by the Rectus superior and Levator palpebrse superioris. Branches.—The branches of the ophthalmic artery may be divided into an orbital group, distributed to the orbit and surrounding parts; and an ocular group, to the muscles and bulb of the eye. Orbital Group. Lacrimal. Supraorbital* Posterior Ethmoidal. Anterior Ethmoidal. Medial Palpebral. Frontal. Dorsal Nasal. Ocular Group. Central Artery of the Retina. Short Posterior Ciliary. Long Posterior Ciliary. Anterior Ciliary. Muscular. THE INTERNAL CAROTID ARTERY 569 The Lacrimal Artery (a. lacrimalis) arises close to the optic foramen, and is one of the largest branches derived from the ophthalmic: not infrequently it is given off before the artery enters the orbit. It accompanies the lacrimal nerve along the upper border of the Rectus lateralis, and supplies the lacrimal gland. Its terminal branches, escaping from the gland, are distributed to the eyelids and con- junctiva: of those supplying the eyelids, two are of considerable size and are named the lateral palpebral arteries; they run mediaiward in the upper and lower lids respectively and anastomose with the medial palpebral arteries, forming an arterial circle in this situation. The lacrimal artery give off one or two zygomatic branches, one of which passes through the zygomatico-temporal foramen, to reach the tem- poral fossa, and anastomoses with the deep temporal arteries; another appears on the cheek through the zygomatico-facial foramen, and anastomoses with the transverse facial. A recurrent branch passes backward through the lateral part of the superior orbital fissure to the dura mater, and anastomoses with a branch of the middle meningeal artery. The lacrimal artery is sometimes derived from one of the anterior branches of the middle meningeal artery. Dorsal nasal Medial palpebral Frontal Bwpraorbital Anterior ethmoidal - Posterior ethmoidal. Zygomatic branches of lacrimal Arteria centralis retinae Lacrimal Muscular Ophthalmic - Internal carotid Fig. 514.—The ophthalmic artery and its branches. The Supraorbital Artery (a. supraorbitalis) springs from the ophthalmic as that vessel is crossing over the optic nerve. It passes upward on the medial borders of the Rectus superior and Levator palpebrse, and meeting the supraorbital nerve accompanies it between the periosteum and Levator palpebrse to the supraorbital foramen; passing through this it divides into a superficial and a deep branch, which supply the integument, the muscles, and the pericranium of the forehead, anastomosing with the frontal, the frontal branch of the superficial temporal, and the artery of the opposite side. This artery in the orbit supplies the Rectus superior and the Levator palpebrse, and sends a branch across the pulley of the Obliquus superior, to supply the parts at the medial palpebral commissure. At the supra- orbital foramen it frequently transmits a branch to the diploe. 570 ANGIOLOGY The Ethmoidal Arteries are two in number: posterior and anterior. The posterior ethmoidal artery, the smaller, passes through the posterior ethmoidal canal, supplies the posterior ethmoidal cells, and, entering the cranium, gives off a meningeal branch to the dura mater, and nasal branches which descend into the nasal cavity through apertures in the cribriform plate, anastomosing with branches of the sphenopalatine. The anterior ethmoidal artery accompanies the nasociliary nerve through the anterior ethmoidal canal, supplies the anterior and middle ethmoidal cells and frontal sinus, and, entering the cranium, gives off a meningeal branch to the dura mater, and nasal branches; these latter descend into the nasal cavity through the slit by the side of the crista galli, and, running along the groove on the inner surface of the nasal bone, supply branches to the lateral wall and septum of the nose, and a terminal branch which appears on the dorsum of the nose between the nasal bone and the lateral cartilage. Fig. 515.—Bloodvessels of the eyelids, front view. 1, supraorbital artery and vein; 2, nasal artery; 3, angular artery, the terminal branch of 4, the facial artery; 5, suborbital •artery; 6, anterior branch of the superficial temporal artery; 6', malar branch of the transverse artery of the face; 7, lacrimal artery; 8, superior palpebral artery with 8', its external arch; 9, anastomoses of the superior palpebral with the superficial temporal and lacrimal; 10, inferior palpebral artery; 11, facial vein; 12, angular vein; 13, branch of the superficial temporal vein. (Testut.) The Medial Palpebral Arteries (aa. palpebrales mediates; internal palpebral arteries), two in number, superior and inferior, arise from the ophthalmic, opposite the pulley of the Obliquus superior; they leave the orbit to encircle the eyelids near their free margins, forming a superior and an inferior arch, -which lie between the Orbicularis oculi and the tarsi. The superior palpebral anastomoses, at the lateral angle of the orbit, with the zygomaticoorbital branch of the temporal artery and with the upper of the two lateral palpebral branches from the lacrimal artery; the inferior palpebral anastomoses, at the lateral angle of the orbit, with the lower of the two lateral palpebral branches from the lacrimal and with the transverse facial artery, and, at the medial part of the lid, with a branch from the angular artery. From this last anastomoses a branch passes to the nasolacrimal duct, ramifying in its mucous membrane, as far as the inferior meatus of the nasal cavity. The Frontal Artery (a. frontalis), one of the terminal branches of the ophthalmic, leaves the orbit at its medial angle with the supratrochlear nerve, and, ascending THE INTERNAL CAROTID ARTERY 571 on the forehead, supplies the integument, muscles, and pericranium, anastomosing with the supraorbital artery, and with the artery of the opposite side. The Dorsal Nasal Artery (a. dorsalis nasi; nasal artery), the other terminal branch of the ophthalmic, emerges from the orbit above the medial palpebral ligament, and, after giving a twig to the upper part of the lacrimal sae, divides into two branches, one of which crosses the root of the nose, and anastomoses with the angular artery, the other runs along the dorsum of the nose, supplies its outer surface; and anastomoses with the artery of the opposite side, and with the lateral nasal branch of the external maxillary. The Central Artery of the Retina (a. centralis retina?) is the first and one of the smallest branches of the ophthalmic artery. It runs for a short distance within the dural sheath of the optic nerve, but about 1.25 cm. behind the eyeball it pierces the nerve obliquely, and runs forward in the center of its substance to the retina. Its mode of distribution will be described with the anatomy of the eye. The Ciliary Arteries (aa. ciliares) are divisible into three groups, the long and short, posterior, and the anterior. The short posterior ciliary arteries from ,six to twelve in number, arise from the ophthalmic, or its branches; they pass forward around the optic nerve to the posterior part of the eyeball, pierce the sclera around the entrance of the nerve, and supply the choroid and ciliary processes. The long posterior ciliary arteries, two in number, pierce the posterior part of the sclera at some little distance from the optic nerve, and run forward, along either side of the eyeball, between the sclera and choroid, to the ciliary muscle, where they divide into two branches; these form an arterial circle, the circulus arteriosus major, around the circumference of the iris, from which numerous converging branches run, in the substance of the iris, to its pupillary margin, where they form a second arterial circle, the circulus arteriosus minor. The anterior ciliary arteries are derived from the muscular branches; they run to the front of the eyeball in company with the tendons of the Recti, form a vascular zone beneath the conjunctiva, and then pierce the sclera a short distance from the cornea and end in the circulus arteriosus major. The Muscular Branches, (rami musculares), two in number, superior and inferior, frequently spring from a common trunk. The superior, often wanting, supplies the Levator palpebrse superioris, Rectus superior, and Obliquus superior. The inferior, more constantly present, passes forward between the optic nerve and Rectus inferior, and is distributed to the Recti lateralis, medialis, and inferior, and the Obliquus inferior. This vessel gives off most of the anterior ciliary arteries. Addi- tional muscular branches are given off from the lacrimal and supraorbital arteries, or from the trunk of the ophthalmic. 8. The anterior cerebral artery (a. cerebri anterior) (Figs. 516, 517, 518) arises from the internal carotid, at the medial extremity of the lateral cerebral fissure. It passes forward and medialward across the anterior perforated substance, above the optic nerve, to the commencement of the longitudinal fissure. Here it comes into close relationship with the opposite artery, to which it is connected by a short trunk, the anterior communicating artery. From this point the two vessels run side by side in the longitudinal fissure, curve around the genu of the corpus callosum, and turning backward continue along the upper surface of the corpus callosum to its posterior part, wrhere they end by anastomosing with the posterior cerebral arteries. Branches.—In its course the anterior cerebral artery gives off the following branches: Antero-medial Ganglionic. Inferior. Anterior. Middle. Posterior. The Antero-medial Ganglionic Branches are a group of small arteries which arise at the commencement of the anterior cerebral artery; they pierce the anterior 572 ANGIOLOGY perforated substance and lamina terminalis, and supply the rostrum of the corpus callosum, the septum pellucidum, and the head of the caudate nucleus. The inferior branches, two or three in number, are distributed to the orbital surface of the frontal lobe, where they supply the olfactory lobe, gyrus rectus, and internal orbital gyrus. The anterior branches supply a part of the superior frontal gyrus, and send twigs over the edge of the hemisphere to the superior and middle frontal gyri and upper part of the anterior central gyrus. The middle branches supply the corpus callosum, the cingulate gyrus, the medial surface of the superior frontal gyrus, and the upper part of the anterior central gyrus. The posterior branches supply the precuneus and adjacent lateral surface of the hemisphere. Fig. 516.—The arteries of the base of the brain. The tempora pole of the cerebrum and a portion of the cerebellar hemisphere have been removed on the right side. The Anterior Communicating Artery (a. communicans anterior) connects the two anterior cerebral arteries across the commencement of the longitudinal fissure. Sometimes this vessel is wanting, the two arteries joining together to form a single trunk, which afterward divides; or it may be wdiolly, or partially, divided into two. Its length averages about 4 nun., but varies greatly. It gives off some of the antero-medial ganglionic vessels, but these are principally derived from the anterior cerebral. 9. The middle cerebral artery (a. cerebri media) (Figs. 516, 517), the largest branch of the internal carotid, runs at first lateralward in the lateral cerebral or Sylvian fissure and then backward and upward on the surface of the insula, where THE INTERNAL CAROTID ARTERY 573 it divides into a number of branches which are distributed to the lateral surface of the cerebral hemisphere. Branches.—The branches of this vessel are the: Antero-lateral Ganglionic. Ascending Parietal. Inferior Lateral Frontal. Parietotemporal. Ascending Frontal. Temporal. Fig. 517.—Outer surface of cerebral hemisphere, showing areas supplied by cerebral arteries, The Antero-lateral Ganglionic Branches, a group of small arteries which arise at the commencement of the middle cerebral artery, are arranged in two sets: one, the internal striate, passes upward through the inner segments of the lentiform nucleus, and supplies it, the caudate nucleus, and the internal capsule; the other, the external striate, ascends through the outer segment of the lentiform nucleus, and supplies the caudate nucleus and the thalamus. One artery of this group is of larger size than the rest, and is of special importance, as being the artery in the brain most frequently ruptured; it has been termed by Charcot the artery of cerebral hemorrhage. It ascends between the lentiform nucleus and the external capsule, and ends in the caudate nucleus. The inferior lateral frontal supplies Fig. 518.—Medial surface of cerebral hemisphere, showing areas supplied by cerebral arteries. the inferior frontal gyrus (Broca’s convolution) and the lateral part of the orbital surface of the frontal lobe. The ascending frontal supplies the anterior central gyrus. The ascending parietal is distributed to the posterior central gyrus and the lower part of the superior parietal lobule. The parietotemporal supplies the supra- marginal and angular gyri, and the posterior parts of the superior and middle temporal gyri. The temporal branches, two or three in number, are distributed to the lateral surface of the temporal lobe. 10. The posterior communicating artery (a. communicans posterior) (Fig. 516) runs backward from the internal carotid, and anastomoses with the posterior 574 ANGIOLOGY cerebral, a branch of the basilar. It varies in size, being sometimes small, and occa- sionally so large that the posterior cerebral may be considered as arising from the internal carotid rather than from the basilar. It is frequently larger on one side than on the other. From its posterior half are given off a number of small branches, the postero-medial ganglionic branches, which, with similar vessels from the posterior cerebral, pierce the posterior perforated substance and supply the medial surface of the thalami and the walls of the third ventricle. 11. The anterior choroidal (a. chorioidea; choroid artery) is a small but constant branch, which arises from the internal carotid, near the posterior communicating artery. Passing backward and lateralward between the temporal lobe and the cerebral peduncle, it enters the inferior horn of the lateral ventricle through the choroidal fissure and ends in the choroid plexus. It is distributed to the hippo- campus, fimbria, tela chorioidea of the third ventricle, and choroid plexus. Since the mode of distribution of thq vessels of the brain has an important bearing upon a considerable number of the pathological lesions which may occur in this part of the nervous system, it is im- portant to consider a little more in detail the manner in which the vessels are distributed. The cerebral arteries are derived from the internal carotid and vertebral, which at the base of the brain form a remarkable anasto- mosis known as the arterial circle of Willis. It is formed in front by the anterior cere- bral arteries, branches of the internal carotid, which are connected together by the anterior communicating; behind by the two posterior cerebral arteries, branches of the basilar, which are connected on either side with the internal carotid by the posterior commu- nicating (Figs. 516, 519). The parts of the brain included within this arterial circle are the lamina terminalis, the optic chiasma, the infundibulum, the tuber cinereum, the corpora mammillaria, and the posterior perforated substance. The three trunks which together supply each cerebral hemisphere arise from the arterial circle of Willis. From its anterior part proceed the two anterior cerebrals, from its antero-lateral parts the middle cerebrals, and from its posterior part the posterior cerebrals. Each of these prin- cipal arteries gives origin to two different systems of secondary vessels. One of these is named the ganglionic system, and the vessels belonging to it supply the thalami and corpora striata; the other is the cortical system, and its vessels ramify in the pia mater and supply the cortex and subjacent brain substance. These two systems do not communicate at any point of their peripheral distribution, but are entirely independent of each other, and there is between the parts supplied by the two systems a borderland of diminished nutritive activity, where, it is said, softening is especially liable to occur in the brains of old people. THE ARTERIES OF THE BRAIN. Int. carotid Ant. communicating Ant. cerebral Arterial circle Post com- municating Pontine Intemnl auditory Anterior Spinal Posterior inferior cerebellar Fig. 519.—Diagram of the arterial circulation at the base of the brain. A.L. Antero-lateral. A.M. Antero-medial. P.L. Postero-lateral. P.M. Postero- medial ganglionic branches. THE SUBCLAVIAN ARTERY 575 The Ganglionic System—All the vessels of this system are given off from the arterial circle of Willis, or from the vessels close to it. They form six principal groups: (I) the antero-medial group, derived from the anterior cerebrals and anterior communicating; (II) the postero-medial group, from the posterior cerebrals and posterior communicating; (III and IV) the right and left antero-lateral groups, from the middle cerebrals; and (V and VI) the right and left postero-lateral groups, from the posterior cerebrals, after they have wound around the cerebral peduncles. The vessels of this system are larger than those of the cortical system, and are what Cohnheim designated terminal arteries—that is to say, vessels which from their origin to their termination neither supply nor receive any anastomotic branch, so that, through any one of the vessels only a limited area of the thalamus or corpus striatum can be injected, and the injection cannot be driven beyond the area of the part supplied by the particular 'vessel which is the subject of the experiment. The Cortical Arterial System.—The vessels forming this system are the terminal branches of the anterior, middle, and posterior cerebral arteries. They divide and ramify in the substance of the pia mater, and give off branches which penetrate the brain cortex, perpendicularly. These branches are divisible into two classes, long and short. The long, or medullary arteries, pass through the gray substance and penetrate the subjacent white substance to the depth of 3 or 4 cm., without intercommunicating otherwise than by very fine capillaries, and thus constitute so many independent small systems. The short vessels are confined to the cortex, where they form with the long vessels a compact net-work in the middle zone of the gray substance, the outer and inner zones being sparingly supplied with blood. The vessels of the cortical arterial system are not so strictly ‘‘terminal” as those of the ganglionic system, but they approach this type very closely, so that injection of one area from the vessel of another area, though possible, is frequently very difficult, and is only effected through vessels of small caliber. As a result of this, obstruction of one of the main branches, or its divisions, may have the effect of producing softening in a limited area of the cortex. THE ARTERIES OF THE UPPER EXTREMITY. The artery which supplies the upper extremity continues as a single trunk from its commencement down to the elbow; but different portions of it have received different names, according to the regions through which they pass. That part of the vessel which extends from its origin to the outer border of the first rib is termed the subclavian; beyond this point to the lower border of the axilla it is named the axillary; and from the lower margin of the axillary space to the bend of the elbow it is termed brachial; here the trunk ends by dividing into two branches the radial and ulnar. THE SUBCLAVIAN ARTERY (A. SUBCLAVIA) (Fig. 520). On the right side the subclavian artery arises from the innominate artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta. The two vessels, therefore, in the first part of their course, differ in length, direction, and relation with neighboring structures. In order to facilitate the description, each subclavian artery is divided into three parts. The first portion extends from the origin of the vessel to the medial border of the Scalenus anterior; the second lies behind this muscle; and the third extends from the lateral margin of the muscle to the outer border of the first rib, where it becomes the axillary artery. The first portions of the two vessels require separate descriptions; the second and third parts of the two arteries are practically alike. 576 ANGIOLOGY First Part of the Right Subclavian Artery (Figs. 505, 520).—The first part of the right subclavian artery arises from the innominate artery, behind the upper part of the right sternoclavicular articulation, and passes upward and lateralward to the medial margin of the Scalenus anterior. It ascends a little above the clavicle, the extent to which it does so varying in different cases. Cricothyroid artery Fig. 520.—Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. Relations.—It is covered, in front, by the integument, superficial fascia, Platysma, deep fascia, the clavicular origin of the Sternocleidomastoideus, the Sternohyoideus, and Sternothyreoideus, and another layer of the deep fascia. It is crossed by the internal jugular and vertebral veins, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the sub- clavian loop of the sympathetic trunk which forms a ring around the vessel. The anterior jugular vein is directed lateralward in front of the artery, but is separated from it by the Sternohyoideus and Sternothyreoideus. Below and behind the artery is the pleura, which separates it from the apex of the lung; behind is the sympathetic trunk, the Longus colli and the first thoracic vertebra. The right recurrent nerve winds around the lower and back part of the vessel. THE SUBCLAVIAN ARTERY 577 First Part of the Left Subclavian Artery (Fig. 505).—The first part of the left subclavian artery arises from the arch of the aorta, behind the left common carotid, and at the level of the fourth thoracic vertebra ; it ascends in the superior medias- tinal cavity to the root of the neck and then arches lateralward to the medial border of the Scalenus anterior. Relations.—It is in relation, in front, with the vagus, cardiac, and phrenic nerves, which lie parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein, and is covered by the Sternothyreoideus, Sterno- hyoideus, and Sternocleidomastoideus; behind, it is in relation with the esophagus, thoracic duct, left recurrent nerve, inferior cervical ganglion of the sympathetic trunk, and Longus colli; higher up, however, the esophagus and thoracic duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to it are the esophagus, trachea, thoracic duct, and left recurrent nerve; lateral to it, the left pleura and lung. Second and Third Parts of the Subclavian Artery (Fig. 520).—The second portion of the subclavian artery lies behind the Scalenus anterior; it is very short, and forms the highest part of the arch described by the vessel. Relations.—It is covered, in front, by the skin, superficial fascia, Platysma, deep cervical fascia, Sternocleidomastoideus, and Scalenus anterior. On the right side of the neck the phrenic nerve is separated from the second part of the artery by the Scalenus anterior, while on the left side it crosses the first part of the artery close to the medial edge of the muscle. Behind the vessel are the pleura and the Scalenus medius; above, the brachial plexus of nerves; below, the pleura. The subclavian vein lies below and in front of the artery, separated from it by the Scalenus anterior. .The third portion of the subclavian artery runs downward and lateralward from the lateral margin of the Scalenus anterior to the outer border of the first rib, where it becomes the axillary artery. This is the most superficial portion of the vessel, and is contained in the subclavian triangle (see page 565). Relations.—It is covered, in front, by the skin, the superficial fascia, the Platysma, the supra- clavicular nerves, and the deep cervical fascia. The external jugular vein crosses its medial part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which frequently form a plexus in front of the artery. Behind the veins, the nerve to the Subclavius descends in front of the artery. The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels. The subclavian vein is in front of and at a slightly lower level than the artery. Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the Scalenus medius. Above and to its lateral side are the upper trunks of the brachial plexus and the Omohyoideus. Below, it rests on the upper surface of the first rib. Peculiarities.—The subclavian arteries vary in their origin, their course, and the height to which they rise in the neck. The origin of the right subclavian from the innominate takes place, in some cases, above the sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery may arise as a separate trunk from the arch of the aorta, and in such cases it may be either the first, second, third, or even the last branch derived from that vessel; in the majority, however, it is the first or last, rarely the second or third. When it is the first branch, it occupies the ordinary position of the innominate artery; when the second or third, it gains its usual position by passing behind the right carotid; and when the last branch, it arises from the left extremity of the arch, and passes obliquely toward the right side, usually behind the trachea, esophagus, and right carotid, sometimes between the esophagus and trachea, to the upper border of the first rib, whence it follows its ordinary course. In very rare instances, this vessel arises from the thoracic aorta, as low down as the fourth thoracic vertebra. Occasionally, it perforates the Scalenus anterior; more rarely it passes in front of that muscle. Sometimes the subclavian vein passes with the artery behind the Scalenus anterior. The artery may ascend as high as 4 cm. above the clavicle, or any intermediate point between this and the upper border of the bone, the right subclavian usually ascending higher than the left. The left subclavian is occasionally joined at its origin with the left carotid. The left subclavian artery is more deeply placed than the right in the first part of its course, and, as a rule, does not reach quite as high a level in the neck. The posterior border of the Sterno- cleidomastoideus corresponds pretty closely to the lateral border of the Scalenus anterior, so that the third portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the Sternocleidomastoideus. 578 ANGIOLOGY Collateral Circulation.—After ligature of the third part of the subclavian artery, the collateral circulation is established mainly by three sets of vessels, thus described in a dissection: 1. A posterior set, consisting of the transverse scapular and the descending ramus of the trans- verse cervical branches of the subclavian, anastomosing with the subscapular from the axillary. 2. A medial set, produced by the connection of the internal mammary on the one hand, with the highest intercostal and lateral thoracic arteries, and the branches from the subscapular on the other. 3. A middle or axillary set, consisting of a number of small vessels derived from branches of the subclavian, above, and, passing through the axilla, terminating either in the main trunk, or some of the branches of the axillary below. This last set presented most conspicuously the peculiar character of newly formed or, rather, dilated arteries, being excessively tortuous, and forming a complete plexus. The chief agent in the restoration of the axillary artery below the tumor was the subscapular artery, which communicated most freely with the internal mammary, transverse scapular and descending ramus of the transverse cervical branches of the subclavian, from all of which it received so great an influx of blood as to dilate it to three times its natural size.1 When a ligature is applied to the first part of the subclavian artery, the collateral circulation is carried on by: (1) the anastomosis between the superior and inferior thyroids; (2) the anastomosis of the two vertebrals; (3) the anastomosis of the internal mammary with the inferior epigastric and the aortic intercostals; (4) the costocervical anastomosing with the aortic intercostals; (5) the profunda cervicis anastomosing with the descending branch of the occipital; (6) the scapular branches of the thyrocervical trunk anastomosing with the branches of the axillary, and (7) the thoracic branches of the axillary anastomosing with the aortic intercostals. Branches.—The branches of the subclavian artery are: Vertebral. Thyrocervical. Internal mammary. Costocervical. On the left side all four branches generally arise from the first portion of the vessel; but on the right side (Fig. 520) the costocervical trunk usually springs from the second portion of the vessel. On both sides of the neck, the first three branches arise close together at the medial border of the Scalenus anterior; in the majority of cases, a free interval of from 1.25 to 2.5 cm. exists between the commencement of the artery and the origin of the nearest branch. 1. The vertebral artery (a. vertebralis) (Fig. 514), is the first branch of the sub- clavian, and arises from the upper and back part of the first portion of the vessel. It is surrounded by a plexus of nerve fibers derived from the inferior cervical ganglion of the sympathetic trunk, and ascends through the foramina in the transverse processes of the upper six cervical vertebrae;2 it then winds behind the superior articular process of the atlas and, entering the skull through the foramen magnum, unites, at the lower border of the pons, with the vessel of the opposite side to form the basilar artery. Relations.—The vertebral artery may be divided into four parts: The first part runs upward and backward between the Longus colli and the Scalenus anterior. In front of it are the internal jugular and vertebral veins, and it is crossed by the inferior thyroid artery; the left vertebral is crossed by the thoracic duct also. Behind it are the transverse process of the seventh cervical vertebra, the sympathetic trunk and its inferior cervical ganglion. The second part runs upward through the foramina in the transverse processes of the upper six cervical vertebrae, and is sur- rounded by branches from the inferior cervical sympathetic ganglion and by a plexus of veins which unite to form the vertebral vein at the lower part of the neck. It is situated in front of the trunks of the cervical nerves, and pursues an almost vertical course as far as the transverse process of the atlas, above which it runs upward and lateralward to the foramen in the trans- verse process of the atlas. The third part issues from the latter foramen on the medial side of the Rectus capitis lateralis, and curves backward behind the superior articular process of the atlas, the anterior ramus of the first cervical nerve being on its medial side; it then lies in the groove on the upper surface of the posterior arch of the atlas, and enters the vertebral canal by passing beneath the posterior atlantooccipital membrane. This part of the artery is covered by the Semispinalis capitis and is contained in the suboccipital triangle—a triangular space 1 Guy’s Hospital Reports, vol. i, 1836. Case of axillary aneurism, in which Aston Key had tied the subclavian artery on the lateral edge of the Scalenus anterior, twelve years previously. 2 The vertebral artery sometimes enters the foramen in the transverse process of the fifth vertebra, and has been seen entering that of the seventh vertebra. THE SUBCLAVIAN ARTERY 579 bounded by the Rectus capitis posterior major, the Obliquus superior, and the Obliquus inferior. The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas. 1 he fourth part pierces the dura mater and inclines medialward to the front of the medulla oblongata; it is placed between the hypoglossal nerve and the anterior root of the first cervical nerve and beneath the first digitation of the ligamentum denticulatum. At the lower border of the pons it unites with the vessel of the opposite side to form the basilar artery. Branches.—The branches of the vertebral artery may be divided into two sets: those given off in the neck, and those within the cranium. Cervical Branches. Spinal. Muscular. Cranial Branches. Meningeal. Posterior Spinal. Anterior Spinal. Posterior Inferior Cerebellar. Medullary. Spinal Branches (rami spinales) enter the vertebral canal through the interverte- bral foramina, and each divides into two branches. Of these, one passes along the roots of the nerves to supply the medulla spinalis and its membranes, anasto- mosing with the other arteries of the medulla spinalis; the other divides into an ascending and a descending branch, which unite with similar branches from the arteries above and below, so that two lateral anastomotic chains are formed on the posterior surfaces of the bodies of the vertebrae, near the attachment of the pedicles. From these anastomotic chains branches are supplied to the periosteum and the bodies of the vertebrae, and others form communications with similar branches from the opposite side; from these communications small twigs arise which join similar branches above and below, to form a central anastomotic chain on the posterior surface of the bodies of the vertebrae. Muscular Branches are given off to the deep muscles of the neck, where the vertebral artery curves around the articular process of the atlas. They anastomose with the occipital, and with the ascending and deep cervical arteries. The Meningeal Branch (ramus meningeus; posterior meningeal branch) springs from the vertebral opposite the foramen magnum, ramifies between the bone and dura mater in the cerebellar fossa, and supplies the falx cerebelli. It is fre- quently represented by one or two small branches. The Posterior Spinal Artery (a. spinalis posterior; dorsal spinal artery) arises from the vertebral, at the side of the medulla oblongata; passing backward, it descends on this structure, lying in front of the posterior roots of the spinal nerves, and is reinforced by a succession of small branches, which enter the vertebral canal through the intervertebral foramina; by means of these it is continued to the lower part of the medulla spinalis, and to the cauda equina. Branches from the posterior spinal arteries form a free anastomosis around the posterior roots of the spinal nerves, and communicate, by means of very tortuous transverse branches, with the vessels of the opposite side. Close to its origin each gives off an ascending branch, which ends at the side of the fourth ventricle. The Anterior Spinal Artery (a. spinalis anterior; ventral spinal artery) is a small branch, which arises near the termination of the vertebral, and, descending in front of the medulla oblongata, unites with its fellow of the opposite side at the level of the foramen magnum. One of these vessels is usually larger than the other, but occasionally they are about equal in size. The single trunk, thus formed, descends on the front of the medulla spinalis, and is reinforced by a succession of small branches which enter the vertebral canal through the intervertebral foramina; these branches are derived from the vertebral and the ascending cervical of the inferior thyroid in the neck; from the intercostals in the thorax; and from the lumbar, iliolumbar, and lateral sacral arteries in the abdomen and pelvis. They unite, by means of ascending and descending branches, to form a single 580 ANGIOLOGY anterior median artery, which extend as far as the lower part of the medulla spinalis, and is continued as a slender twig on the filum terminale. This vessel is placed in the pia mater along the anterior median fissure; it supplies that membrane, and the substance of the medulla spinalis, and sends off branches at its lower part to be distributed to the cauda equina. The Posterior Inferior Cerebellar Artery (a. cerebelli inferior posterior) (Fig. 516), the largest branch of the vertebral, winds backward around the upper part of the medulla oblongata, passing between the origins of the vagus and accessory nerves, over the inferior peduncle to the under surface of the cerebellum, where it divides into two branches. The medial branch is continued backward to the notch between the two hemispheres of the cerebellum; while the lateral supplies the under surface of the cerebellum, as far as its lateral border, where it anastomoses with the anterior inferior cerebellar and the superior cerebellar branches of the basilar artery. Branches from this artery supply the choroid plexus of the fourth ventricle. The Medullary Arteries (bulbar arteries) are several minute vessels which spring from the vertebral and its branches and are distributed to the medulla oblongata. The Basilar Artery (a. basilaris) (Fig. 516), so named from its position at the base of the skull, is a single trunk formed by the junction of the two vertebral arteries: it extends from the lower to the upper border of the pons, lying in its median groove, under cover of the arachnoid. It ends by dividing into the two posterior cerebral arteries. Its branches, on either side, are the following: Pontine. Internal Auditory. Anterior Inferior Cerebellar. Superior Cerebellar. Posterior Cerebral. The pontine branches (rami ad pontem; transverse branches) are a number of small vessels which come off at right angles from either side of the basilar artery and supply the pons and adjacent parts of the brain. The internal auditory artery (a. auditiva interna; auditory artery), a long slender branch, arises from near the middle of the artery; it accompanies the acoustic nerve through the internal acoustic meatus, and is distributed to the internal ear. The anterior inferior cerebellar artery (a. cerebelli inferior anterior) passes back- ward to be distributed to the anterior part of the under surface of the cerebellum, anastomosing with the posterior inferior cerebellar branch of the vertebral. The superior cerebellar artery (a. cerebelli superior) arises near the termination of the basilar. It passes lateralward, immediately below the oculomotor nerve, which separates it from the posterior cerebral artery, winds around the cerebral peduncle, close to the trochlear nerve, and, arriving at the upper surface of the cerebellum, divides into branches which ramify in the pia mater and anastomose with those of the inferior cerebellar arteries. Several branches are given to the pineal body, the anterior medullary velum, and the tela chorioidea of the third ventricle. The posterior cerebral artery (a. cerebri posterior) (Figs. 516, 517, 518) is larger than the preceding, from which it is separated near its origin by the oculomotor nerve. Passing lateralward, parallel to the superior cerebellar artery, and receiving the posterior communicating from the internal carotid, it winds around the cerebral peduncle, and reaches the tentorial surface of the occipital lobe of the cerebrum, where it breaks up into branches for the supply of the temporal and occipital lobes. The branches of the posterior cerebral artery are divided into two sets, ganglionic and cortical: Ganglionic Posterior-medial. Posterior Choroidal. Postero-lateral. Anterior Temporal. Posterior Temporal. Calcarine. Parietooccipital. Cortical THE SUBCLAVIAN ARTERY 581 Ganglionic.—The postero-medial ganglionic branches (Fig. 519) are a group of small arteries which arise at the commencement of the posterior cerebral artery; these, with similar branches from the posterior communicating, pierce the pos- terior perforated substance, and supply the medial surfaces of the thalami and the walls of the third ventricle. The posterior choroidal branches run forward beneath the splenium of the corpus callosum, and supply the tela chorioidea of the third ventricle and the choroid plexus. The postero-lateral ganglionic branches are small arteries which arise from the posterior cerebral artery after it has turned around the cerebral peduncle; they supply a considerable portion of the thalamus. Cortical.—The cortical branches are: the anterior temporal, distributed to the uncus and the anterior part of the fusiform gyrus; the posterior temporal, to the fusiform and the inferior temporal gyri; the calcarine, to the cuneus and gyrus lingualis and the back part of the convex surface of the occipital lobe; and the parietooccipital, to the cuneus and the precuneus. 2. The thyrocervical trunk (truncus thyreocervicalis; thyroid axis) (Fig. 520) is a short thick trunk, which arises from the front of the first portion of the subclavian artery, close to the medial border of the Scalenus anterior, and divides almost immediately into three branches, the inferior thyroid, transverse scapular, and trans- verse cervical. The Inferior Thyroid Artery (a. thyreoidea inferior) passes upward, in front of the vertebral artery and Longus colli; then turns medialward behind the carotid sheath and its contents, and also behind the sympathetic trunk, the middle cervical ganglion resting upon the vessel. Reaching the lower border of the thyroid gland it divides into two branches, which supply the postero-inferior parts of the gland, and anastomose with the superior thyroid, and with the corresponding artery of the opposite side. The recurrent nerve passes upward generally behind, but occa- sionally in front, of the artery. The branches of the inferior thyroid are: Inferior Laryngeal. Tracheal. Esophageal. Ascending Cervical. Muscular. The inferior laryngeal artery (a. laryngea inferior) ascends upon the trachea to the back part of the larynx under cover of the Constrictor pharyngis inferior, in company with the recurrent nerve, and supplies the muscles and mucous mem- brane of this part, anastomosing with the branch from the opposite side, and with the superior laryngeal branch of the superior thyroid artery. The tracheal branches (rami tracheales) are distributed upon the trachea, and anastomose below with the bronchial arteries. The esophageal branches (rami cesophagei) supply the esophagus, and anasto- mose with* the esophageal branches of the aorta. The ascending cervical artery (a. cervicalis ascendens) is a small branch which arises from the inferior thyroid as that vessel is passing behind the carotid sheath; it runs up on the anterior tubercles of the transverse processes of the cervical vertebrae in the interval between the Scalenus anterior and Longus capitis, lo the muscles of the neck it gives twigs which anastomose with branches of the ver- tebral, and it sends one or two spinal branches into the vertebral canal through the intervertebral foramina to be distributed to the medulla spinalis and its mem- branes, and to the bodies of the vertebrae, in the same manner as the spinal branches from the vertebral. It anastomoses with the ascending pharyngeal and occipital arteries. The muscular branches supply the depressors of the hyoid bone, and the Longus colli, Scalenus anterior, and Constrictor pharyngis inferior. 582 ANGIOLOGY The Transverse Scapular Artery (a. transversa scapulae; suprascapular artery) passes at first downward and lateralward across the Scalenus anterior and phrenic nerve, being covered by the Sternocleidomastoideus; it then crosses the subclavian artery and the brachial plexus, and runs behind and parallel with the clavicle and Subclavius, and beneath the inferior belly of the Omohyoideus, to the superior border of the scapula; it passes over the superior transverse ligament of the scapula which separates it from the suprascapular nerve, and enters the supraspinatous fossa (Fig. 521). In this situation it lies close to the bone, and rami- fies between it and the Supra- spinatus, to which it supplies branches. It then descends be- hind the neck of the scapula, through the great scapular notch and under cover of the inferior transverse ligament, to reach the infraspinatous fossa, where it anastomoses with the scapular circumflex and the descending branch of the transverse cervical. Besides distributing branches to the Sternocleidomastoideus, Subclavius, and neighboring muscles, it gives off a suprasternal branch, which crosses over the sternal end of the clavicle to the skin of the upper part of the chest; and an acromial branch, which pierces the Trapezius and supplies the skin over the acromion, anastomosing with the thoracoacromial artery. As the artery passes over the superior transverse ligament of the scapula, it sends a branch into the subscapular fossa, where it ramifies beneath the Sub- scapularis, and anastomoses with the subscapular artery and with the descending branch of the transverse cervical. It also sends articular branches to the acro- mioclavicular and shoulder-joints, and a nutrient artery to the clavicle. The Transverse Cervical Artery (a. transversa colli; transversalis colli artery) lies at a higher level than the transverse scapular; it passes transversely above the inferior belly of the Omohyoideus to the anterior margin of the Trapezius, beneath which it divides into an ascending and a descending branch. It crosses in front of the phrenic nerve and the Scaleni, and in front of or between the divisions of the brachial plexus, and is covered by the Platysma and Sternocleidomastoideus, and crossed by the Omohyoideus and Trapezius. The ascending branch (ramus ascendens; superficial cervical artery) ascends be- neath the anterior margin of the Trapezius, distributing branches to it, and to the neighboring muscles and lymph glands in the neck, and anastomosing with the superficial branch of the descending ramus of the occipital artery. The descending branch (ramus descendens; posterior scapular artery) (Fig. 521) passes beneath the Levator scapulae to the medial angle of the scapula, and then descends under the Rhomboidei along the vertebral border of that bone as far as the inferior angle. It supplies the Rhomboidei, Latissimus dorsi and Trapezius, and anastomoses with the transverse scapular and subscapular arteries, and with the posterior branches of some of the intercostal arteries. Desc. br. of transverse cervical Transverse scapular Acromial branch of thoracoacromial Anterior humeral circumflex Termination of subscapular Fig. 521.—The scapular and circumflex arteries. THE SUBCLAVIAN ARTERY 583 Peculiarities. The ascending branch of the transverse cervical frequently arises directly from the thyrocervical trunk; and the descending branch from the third, more rarely from the second, part of the subclavian. Thoraco-acromial artery Scalenus anterior - Common carotid artery Innominate artery Internal mammary artery Perforating branches Superior epigastric artery Musculophrenic artery Inferior epigastric artery External iliac artery Fig. 522.—The internal mammary artery and its branches. 3. The internal mammary artery (a. mammaria interna) (Fig. 522) arises from the under surface of the first portion of the subclavian, opposite the thyro- cervical trunk. It descends behind the cartilages of the upper six ribs at a distance 584 ANGIOLOGY of about 1.25 cm. from the margin of the sternum, and at the level of the sixth intercostal space divides into the musculophrenic and superior epigastric arteries. Relations.—It is directed at first downward, forward, and medialward behind the sternal end of the clavicle, the subclavian and internal jugular veins, and the first costal cartilage, and passes forward close to the lateral side of the innominate vein. As it enters the thorax the phrenic nerve crosses from its lateral to its medial side. Below the first costal cartilage it descends almost vertically to its point of bifurcation. It is covered in front by the cartilages of the upper six ribs and the intervening Intercostales interni and anterior intercostal membranes, and is crossed by the terminal portions of the upper six intercostal nerves. It rests on the pleura, as far as the third costal cartilage; below this level, upon the Transversus thoracis. It is accompanied by a pair of veins; these unite above to form a single vessel, which runs medial to the artery and ends in the corresponding innominate vein. Branches.—The branches of the internal mammary are: Pericardiacophrenic. Anterior Mediastinal. Pericardial. Sternal. Intercostal. Perforating. Musculophrenic. Superior Epigastric. The Pericardiacophrenic Artery (a. pericardiacophrenica; a. comes nervi phrenici) is a long slender branch, which accompanies the phrenic nerve, between the pleura and pericardium, to the diaphragm, to which it is distributed; it anastomoses with the musculophrenic and inferior phrenic arteries. The Anterior Mediastinal Arteries (aa. mediastinales anteriores; mediastinal arter- ies) are small vessels, distributed to the areolar tissue and lymph glands in the anterior mediastinal cavity, and to the remains of the thymus. The Pericardial Branches supply the upper part of the anterior surface of the pericardium; the lower part receives branches from the musculophrenic artery. The Sternal Branches (rami sternales) are distributed to the Transversus thoracis, and to the posterior surface of the sternum. The anterior mediastinal, pericardial, and sternal branches, together with some twigs from the pericardiacophrenic, anastomose with branches from the intercostal and bronchial arteries, and form a subpleural mediastinal plexus. The Intercostal Branches (rami intercostales; anterior intercostal arteries) supply the upper five or six intercostal spaces. Two in number in each space, these small vessels pass lateralward, one lying near the lower margin of the rib above, and the other near the upper margin of the rib below, and anastomose with the intercostal arteries from the aorta. They are at first situated between the pleura and the Intercostales interni, and then between the Intercostales interni and externi. They supply the Intercostales and, by branches which perforate the Intercostales externi, the Pectorales and the mamma. The Perforating Branches (rami perjorantes) correspond to the five or six inter- costal spaces. They pass forward through the intercostal spaces, and, curving lateralward, supply the Pectoralis major and the integument. Those which corre- spond to the second, third, and fourth spaces give branches to the mamma, and during lactation are of large size. The Musculophrenic Artery (a. musculophrenica) is directed obliquely downward and lateralward, behind the cartilages of the false ribs; it perforates the dia- phragm at the eighth or ninth costal cartilage, and ends, considerably reduced in size, opposite the last intercostal space. It gives off intercostal branches to the seventh, eighth, and ninth intercostal spaces; these diminish in size as the spaces decrease in length, and are distributed in a manner precisely similar to the intercostals from the internal mammary. The musculophrenic also gives branches to the lower part of the pericardium, and others which run backward to the dia- phragm, and downward to the abdominal muscles. THE AXILLA 585 The Superior Epigastric Artery (a. epigaslrica superior) continues in the original direction of the internal mammary; it descends through the interval between the costal and sternal attachments of the diaphragm, and enters the sheath of the Rectus abdominis, at first lying behind the muscle, and then perforating and sup- plying it, and anastomosing with the inferior epigastric artery from the external iliac. Branches perforate the anterior wall of the sheath of the Rectus, and supply the muscles of the abdomen and the integument, and a small branch passes in front of the xiphoid process and anastomoses with the artery of the opposite side. It also gives some twigs to the diaphragm, while from the artery of the right side small branches extend into the falciform ligament of the liver and anastomose with the hepatic artery. 4. The costocervical trunk (truncus costocervicalis; superior intercostal artery) (Tig. 513) arises from the upper and back part of the subclavian artery, behind the Scalenus anterior on the right side, and medial to that muscle on the left side. Passing backward, it gives off the profunda cervicalis, and, continuing as the highest intercostal artery, descends behind the pleura in front of the necks of the first and second ribs, and anastomoses wfith the first aortic intercostal. As it crosses the neck of the first rib it lies medial to the anterior division of the first thoracic nerve, and lateral to the first thoracic ganglion of the sympathetic trunk. In the first intercostal space, it gives off a branch which is distributed in a manner similar to the distribution of the aortic intercostals. The branch for the second intercostal space usually joins with one from the highest aortic intercostal artery. This branch is not constant, but is more commonly found on the right side; when absent, its place is supplied by an intercostal branch from the aorta. Each intercostal gives off a posterior branch which goes to the posterior vertebral muscles, and sends a small spinal branch through the corresponding intervertebral foramen to the medulla spinalis and its membranes. The Profunda Cervicalis (a. cervicalis profunda; deep cervical branch) arises, in most cases, from the costocervical trunk, and is analogous to the posterior branch of an aortic intercostal artery: occasionally it is a separate branch from the sub- clavian artery. Passing backward, above the eighth cervical nerve and between the transverse process of the seventh cervical vertebra and the neck of the first rib, it runs up the back of the neck, between the Semispinales capitis and colli, as high as the axis vertebra, supplying these and adjacent muscles, and anastomosing with the deep division of the descending branch of the occipital, and with branches of the vertebral. It gives off a spinal twig which enters the canal through the inter- vertebral foramen between the seventh cervical and first thoracic vertebrae. THE AXILLA. The axilla is a pyramidal space, situated between the upper lateral part of the chest and the medial side of the arm. Boundaries.—The apex, which is directed upward toward the root of the neck, corresponds to the interval between the outer border of the first rib, the superior border of the scapula, and the posterior surface of the clavicle, and through it the axillary vessels and nerves pass. The base, directed downward, is broad at the chest but narrow and pointed at the arm; it is formed by the integument and a thick layer of fascia, the axillary fascia, extending between the lower border of the Pectoralis major in front, and the lower border of the Latissimus dorsi behind. The anterior wall is formed by the Pectorales major and minor, the former covering the whole of this wall, the latter only its central part. The space between the upper border of the Pectoralis minor and the clavicle is occupied by the coracoclavicular fascia. The posterior wall, which extends somewhat lower than the anterior, is formed by the Subscapularis above, the Teres major and Latissimus dorsi below. 586 ANGIOLOGY On the medial side are the first four ribs with their corresponding Intercostales, and part of the Serratus anterior. On the lateral side, where the anterior and posterior walls converge, the space is narrow, and bounded by the humerus, the Coracobrachialis, and the Biceps brachii. Contents.—It contains the axillary vessels, and the brachial plexus of nerves, with their branches, some branches of the intercostal nerves, and a large number of lymph glands, together with a quantity of fat and loose areolar tissue. The axillary artery and vein, with the brachial plexus of nerves, extend obliquely along the lateral boundary of the axilla, from its apex to its base, and are placed much nearer to the anterior than to the posterior wall, the vein lying to the thoracic side of the artery and partially concealing it. At the forepart of the axilla, in contact with the Pectorales, are the thoracic branches of the axillary artery, and along the lower margin of the Pectoralis minor the lateral thoracic artery extends to the side of the chest. At the back part, in contact with the lower margin of the Sub- scapularis, are the subscapular vessels and nerves; winding around the lateral border of this muscle are the scapular circumflex vessels; and, close to the neck of the humerus, the posterior humeral circumflex vessels and the axillary nerve curve backward to the shoulder. Along the medial or thoracic side no vessel of any importance exists, the upper part of the space being crossed merely by a few small branches from the highest thoracic artery. There are some important nerves, however, in this situation, viz., the long thoracic nerve, descending on the surface of the Serratus anterior, to which it is distributed; and the intercostobrachial nerve, perforating the upper and anterior part of this wall, and passing across the axilla to the medial side of the arm. The position and arrangement of the lymph glands are described on pages 699 and 700. The Axillary Artery (A. Axillaris) (Fig. 523). The axillary artery, the continuation of the subclavian, commences at the outer border of the first rib, and ends at the lower border of the tendon of the Teres major, where it takes the name of brachial. Its direction varies with the position of the limb; thus the vessel is nearly straight when the arm is directed at right angles with the trunk, concave upward when the arm is elevated above this, and convex upward and lateralward when the arm lies by the side. At its origin the artery is very deeply situated, but near its termination is superficial, being covered only by the skin and fascia. To facilitate the description of the vessel it is divided into three portions; the first part lies above, the second behind, and the third below the Pectoralis minor. Relations.—The first portion of the axillary artery is covered anteriorly by the clavicular portion of the Pectoralis major and the coracoclavicular fascia, and is crossed by the lateral anterior thoracic nerve, and the thoracoacromial and cephalic veins; posterior to it are the first intercostal space, the corresponding Intercostalis externus, the first and second digitations of the Serratus anterior, and the long thoracic and medial anterior thoracic nerves, and the medial cord of the brachial plexus; on its lateral side is the brachial plexus, from -which it is separated by a little areolar tissue; on its medial, or thoracic side, is the axillary vein which overlaps the artery. It is enclosed, together with the axillary vein and the brachial plexus, in a fibrous sheath —the axillary sheath—continuous above with the deep cervical fascia. The second portion of the axillary artery is covered, anteriorly, by the Pectorales major and minor; posterior to it are the posterior cord of the brachial plexus, and some areolar tissue which intervenes between it and the Subscapularis; on the medial side is the axillary vein, separated from the artery by the medial cord of the brachial plexus and the medial anterior thoracic nerve; on the lateral side is the lateral cord of the brachial plexus. The brachial plexus thus surrounds the artery on three sides, and separates it from direct contact with the vein and adjacent muscles. The third portion of the axillary artery extends from the lower border of the Pectoralis minor to the lower border of the tendon of the Teres major. In front, it is covered by the lower part of the Pectoralis major above, but only by the integument and fascia below; behind, it is in rela- tion with the lower part of the Subscapularis, and the tendons of the Latissimus dorsi and Teres THE AXILLARY ARTERY 587 major; on its lateral side is the Coracobrachialis, and on its medial or thoracic side, the axillary vein. The nerves of the brachial plexus bear the following relations to this part of the artery: on the lateral side are the lateral head and the trunk of the median, and the musculocutaneous for a short distance; on the medial side the ulnar (between the vein and artery) and medial brachial cutaneous (to the medial side of the vein); in front are the medial head of the median and the medial antibrachial cutaneous, and behind, the radial and axillary, the latter only as far as the lower border of the SubscapUlaris. Collateral Circulation after Ligature of the Axillary Artery.—If the artery be tied above the origin of the thoracoacromial, the collateral circulation will be carried on by the same branches as after the ligature of the third part of the subclavian; if at a lower point, between the thoracoacromial and the subscapular, the latter vessel, by its free anastomosis with the trans- verse scapular and transverse cervical branches of the subclavian, will become the chief agent in carrying on the circulation; the lateral thoracic, if it be below the ligature, will materially contrib- ute by its anastomoses with the intercostal and internal mammary arteries. If the point included in the ligature is below the origin of the subscapular artery, it will most probably also be below the origins of the two humeral circumflex arteries. The chief agents in restoring the circulation will then be the subscapular and the two humeral circumflex arteries anastomosing with the a. profunda brachii. Anterior humeral . circumflex Fig. 523.—The axillary artery and its branches. Branches.—The branches of the axillary are: From first part, Highest Thoracic. Thoracoacromial. Lateral Thoracic. From second part From third part f Subscapular. [Posterior Plumeral Circumflex. [Anterior Humeral Circumflex. 1. The highest thoracic artery (a. ihoracalis suprema; superior thoracic artery) is a small vessel, which may arise from the thoracoacromial. Running forward and medialward along the upper border of the Rectoralis minor, it passes between it and the Pectoralis major to the side of the chest. It supplies branches to these 588 ANGIOLOGY muscles, and to the parietes of the thorax, and anastomoses with the internal mam- mary and intercostal arteries. 2. The thoracoacromial artery (a. thoracoacromialis; acromiothoracic artery; tho- racic axis) is a short trunk, which arises from the forepart of the axillary artery, its origin being generally overlapped by the upper edge of the Pectoralis minor Projecting forward to the upper border of this muscle, it pierces the coracoclavicular fascia and divides into four branches—pectoral, acromial, clavicular, and deltoid. The pectoral branch descends between the two Pectorales, and is distributed to them and to the mamma, anastomosing with the intercostal branches of the internal mammary and with the lateral thoracic. The acromial branch runs lateralward over the coracoid process and under the Deltoideus, to which it gives branches; it then pierces that muscle and ends on the acromion in an arterial network formed by branches from the transverse scapular, thoracoacromial, and posterior humeral circumflex arteries. The clavicular branch runs upward and medialward to the sternoclavicular joint, supplying this articulation, and the Subclavius. The deltoid (humeral) branch, often arising with the acromial, crosses over the Pectoralis minor and passes in the same groove as the cephalic vein, between the Pectoralis major and Deltoideus, and gives branches to both muscles. 3. The lateral thoracic artery (a. thoracalis lateralis; long thoracic artery; external mammary artery) follows the lower border of the Pectoralis minor to the side of the chest, supplying the Serratus anterior and the Pectoralis, and sending branches across the axilla to the axillary glands and Subscapularis; it anastomoses with the internal mammary, subscapular, and intercostal arteries, and with the pectoral branch of the thoracoacromial. In the female it supplies an external mammary branch which turns round the free edge of the Pectoralis major and supplies the mamma. 4. The subscapular artery (a. subscapularis) the largest branch of the axillary artery, arises at the lower border of the Subscapularis, which it follows to the in- ferior angle of the scapula, where it anastomoses with the lateral thoracic and intercostal arteries and with the descending branch of the transverse cervical, and ends in the neighboring muscles. About 4 cm. from its origin it gives off a branch, the scapular circumflex artery. The Scapular Circumflex Artery (a. circumflexa scapulae; dorsalis scapulae artery) is generally larger than the continuation of the sub- scapular. It curves around the axillary border of the scapula, traversing the space between the Subscapularis above, the Teres major below, and the long head of the Triceps laterally (Fig. 524); it enters the infra- spinatous fossa under cover of the Teres minor, and anasto- moses with the transverse scap- ular artery and the descending branch of the transverse cervical. In its course it gives off two branches: one (infrascapular) enters the subscapular fossa beneath the Subscapularis, which it supplies, anastomosing with the transverse scapular Desc. hr. of transverse cervical Transverse scapular Acromial branch of thoraco-acromial Anterior humeral circumflex s germination of subscapular Fig. 524.—The scapular and circumflex arteries. THE BRACHIAL ARTERY 589 artery and the descending branch of the transverse cervical; the other is continued along the axillary border of the scapula, between the Teres major and minor, and at the dorsal surface of the inferior angle anastomoses with the descending branch of the transverse cervical. In addition to these, small branches are dis- tributed to the back part of the Deltoideus and the long head of the Triceps brachii, anastomosing with an ascending branch of the a. profunda brachii. 5. The posterior humeral circumflex artery (a. circumflexa humeri posterior; pos- terior circumflex artery) (Fig. 524) arises from the axillary artery at the lower border of the Subscapularis, and runs backward with the axillary nerve through the quad- rangular space bounded by the Subscapularis and Teres minor above, the Teres major below, the long head of the Triceps brachii medially, and the surgical neck of the humerus laterally. It winds around the neck of the humerus and is dis- tributed to the Deltoideus and shoulder-joint, anastomosing with the anterior humeral circumflex and profunda brachii. 6. The anterior humeral circumflex artery (a. circumflexa humeri anterior; anterior circumflex artery) (Fig. 524), considerably smaller than the posterior, arises nearly opposite it, from the lateral side of the axillary artery. It runs horizontally, beneath the Coracobrachialis and short head of the Biceps brachii, in front of the neck of the humerus. On reaching the intertubercular sulcus, it gives off a branch which ascends in the sulcus to supply the head of the humerus and the shoulder-joint. The trunk of the vessel is then continued onward beneath the long head of the Biceps brachii and the Deltoideus, and anastomoses with the posterior humeral circumflex artery. Peculiarities.—The branches of the axillary artery vary considerably in different subjects. Occasionally the subscapular, humeral circumflex, and profunda arteries arise from a common trunk, and when this occurs the branches of the brachial plexus surround this trunk instead of the main vessel. Sometimes the axillary artery divides into the radial and ulnar arteries, and occasionally it gives origin to the volar interosseous artery of the forearm. The Brachial Artery (A. Brachialis) (Fig. 525). The brachial artery commences at the lower margin of the tendon of the Teres major, and, passing down the arm, ends about 1 cm. below the bend of the elbow, where it divides into the radial and ulnar arteries. At first the brachial artery lies medial to the humerus; but as it runs down the arm it gradually gets in front of the bone, and at the bend of the elbow it lies midway between its two epicondyles. Relations.—The artery is superficial throughout its entire extent, being covered, in jront, by the integument and the superficial and deep fasciae; the lacertus fibrosus (bicipital fascia) lies in front of it opposite the elbow and separates it from the vena mediana cubiti; the median nerve crosses from its lateral to its medial side opposite the insertion of the Coracobrachialis. Behind, it is separated from the long head of the Triceps brachii by the radial nerve and a. pro- funda brachii. It then lies upon the medial head of the Triceps brachii, next upon the insertion of the Coracobrachialis, and lastly on the Brachialis. Laterally, it is in relation above with the median nerve and the Coracobrachialis, below with the Biceps brachii, the two muscles over- lapping the artery to a considerable extent. Medially, its upper half is in relation with the medial antibrachial cutaneous and ulnar nerves, its lower half with the median nerve. The basilic vein lies on its medial side, but is separated from it in the lower part of the arm by the deep fascia. The artery is accompanied by two venae comitantes, which lie in close contact with it, and are connected together at intervals by short transverse branches. The Anticubital Fossa.—At the bend of the elbow the brachial artery sinks deeply into a triangular interval, the anticubital fossa. The base of the triangle is directed upward, and is represented by a line connecting the two epicondyles of the humerus; the sides are formed by the medial edge of the Brachioradialis and the lateral margin of the Pronator teres; the floor is formed by the Brachialis and Supinator. This space contains the brachial artery, with its accompanying veins; the radial and ulnar arteries; the median and radial nerves; and the tendon of the Biceps brachii. The brachial artery occupies the middle of the space, and 590 ANGIOLOGY divides opposite the neck of the radius into the radial and ulnar arteries; it is covered, in front, by the integument, the superficial fascia, and the vena mediana cubiti, the last being separated from the artery by the lacertus fibrosus. Behind it is the Brachialis which separates it from the elbow-joint. The median nerve lies close to the medial side of the artery, above, but is separated from it below by the ulnar head of the Pronator teres. The tendon of the Biceps brachii lies to the lateral side of the artery; the radial nerve is situated upon the Supinator, and concealed by the Brachioradialis. Peculiarities of the Brachial Artery as Regards its Course.—The brachial artery, accompanied by the median nerve, may leave the medial border of the Biceps brachii, and descend toward the medial epicondyle of the humerus; in such cases it usually passes behind the supracondylar process of the humerus, from which a fibrous arch is in most cases thrown over the artery; it then runs beneath or through the substance of the Pronator teres, to the bend of the elbow. This variation bears considerable analogy with the normal condition of the artery in some of the carnivora; it has been re- ferred to in the description of the hu- merus (p. 212). As Regards its Division.—Occasionally, the artery is divided for a short distance at its upper part into two trunks, which are united below. Frequently the artery divides at a higher level than usual, and the vessels concerned in this high division are three, viz., radial, ulnar, and inter- osseous. Most frequently the radial is given off high up, the other limb of the bifurcation consisting of the ulnar and interosseous; in some instances the ulnar arises above the ordinary level, and the radial and interosseous form the other limb of the division; occasionally the in- terosseous arises high up. Sometimes, long slender vessels, vasa aberrantia, connect the brachial or the axillary artery with one of the arteries of the forearm, or branches from them. These vessels usually join the radial. Varieties in Muscular Relations.—The brachial artery is occasionally concealed, in some part of its course, by muscular or tendinous slips derived from the Coracobrachialis, Biceps brachii, Brachialis, or Pronator teres. Collateral Circulation.—After the application of a ligature to the brachial artery in the upper third of the arm, the circulation is carried on by branches from the humeral circumflex and sub- scapular arteries anastomosing with ascending branches from the profunda brachii. If the artery be tied below the origin of the profunda brachii and superior ulnar collateral, the circula- tion is maintained by the branches of these two arteries anastomosing with the inferior ulnar collateral, the radial and ulnar recurrents, and the dorsal interosseous. Branches.—The branches of the brachial artery are: Med. antibrach. cutan. nerve Radial nerve A. profunda brachii Sup. ulnar collateral artery Inf. ulnar collateral artery Fig. 525.—The brachial artery. Profunda Brachii. Nutrient. Superior Ulnar Collateral. Inferior Ulnar Collateral. Muscular. THE BRACHIAL ARTERY 591 1. The arteria profunda brachii (superior profunda artery) is a large vessel which arises from the medial and back part of the brachial, just below the lower border of the Teres major. It follows closely the radial nerve, running at first backward between the medial and lateral heads of the Triceps brachii, then along the groove for the radial nerve, where it is covered by the lateral head of the Triceps brachii, to the lateral side of the arm; there it pierces the lateral intermuscular septum, and, descending between the Brachioradialis and the Brachialis to the front of the lateral epicondyle of the humerus, ends by anastomosing with the radial recur- rent artery. It gives branches to the Deltoideus and to the muscles between which it lies; it supplies an occasional nutrient artery which enters the humerus behind the deltoid tuberosity. A branch ascends between the long and lateral heads of the Triceps brachii to anastomose with the posterior humeral circumflex artery; a middle collateral branch descends in the middle head of the Triceps brachii and assists in forming the anastomosis above the olecranon; and, lastly, a radial collateral branch runs down behind the lateral intermuscular septum to the back of the lateral epicondyle of the humerus, where it anastomoses with the interosseous recurrent and the inferior ulnar collateral arteries. 2. The nutrient artery (a. nutricia humeri) of the body of the humerus arises about the middle of the arm and enters the nutrient canal near the insertion of the Coracobrachialis. A. profunda brachii ■ Sup. ulnar collateral Brachial Anterior branch of profunda Ini. ulnar collateral Radial collateral branch of 'profunda Anterior ulnar recurrent Radial recurrent Posterior ulnar recurrent Interosseous recurrent Interosseous Radial - TJlnar Dorsal interosseous Volar interosseous Fig. 526.—Diagram of the anastomosis around the elbow-joint. 3. The superior ulnar collateral artery (a. collateralis ulnans superior; inferior profunda artery), of small size, arises from the brachial a little below the middle of the arm; it frequently springs from the upper part of the a. profunda brachii. It pierces the medial intermuscular septum, and descends on the surface of the media) head of the Triceps* brachii to the space between the medial epicondyle and 592 ANGIOLOGY olecranon, accompanied by the ulnar nerve, and ends under the Flexor carpi ulnaris by anastomosing with the posterior ulnar recurrent, and inferior ulnar collateral. It sometimes sends a branch in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. 4. The inferior ulnar collateral artery (a. collaterals ulnaris inferior; anastomotica magna artery) arises about 5 cm. above the elbow. It passes medial ward upon the Brachialis, and piercing the medial intermuscular septum, winds around the back of the humerus between the Triceps brachii and the bone, forming, by its junction with the profunda brachii, an arch above the olecranon fossa. As the vessel lies on the Brachialis, it gives off branches which ascend to join the superior ulnar collateral: others descend in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. Behind the medial epicondyle a branch anastomoses with the superior ulnar collateral and posterior ulnar recurrent arteries. 5. The muscular branches (rami niusculares) three or four in number, are dis- tributed to the Coracobrachialis, Biceps brachii, and Brachialis. The Anastomosis Around the Elbow-joint (Fig. 526).—The vessels engaged in this anastomosis may be conveniently divided into those situated in front of and those behind the medial and lateral epicondyles of the humerus. The branches anastomosing in front of the medial epicondyle are: the anterior branch of the inferior ulnar collateral, the anterior ulnar recurrent, and the anterior branch of the superior ulnar collateral. Those behind the medial epicondyle are: the inferior ulnar collateral, the posterior ulnar recurrent, and the posterior branch of the supe- rior ulnar collateral. The branches anastomosing in front of the lateral epicondyle are: the radial recurrent and the terminal part of the profunda brachii. Those behind the lateral epicondyle (perhaps more properly described as being situated between the lateral epicondyle and the olecranon) are: the inferior ulnar collateral, the interosseous recurrent, and the radial collateral branch of the profunda brachii. There is also an arch of anastomosis above the olecranon, formed by the interosseous recurrent joining with the inferior ulnar collateral and posterior ulnar recurrent (Fig. 529). The Radial Artery (A. Radialis) (Fig. 527) The radial artery appears, from its direction, to be the continuation of the brachial, but it is smaller in caliber than the ulnar. It commences at the bifurcation of the brachial, just below the bend of the elbow, and passes along the radial side of the forearm to the wrist. It then winds backward, around the lateral side of the carpus, beneath the tendons of the Abductor pollicis longus and Extensores pollicis longus and brevis to the upper end of the space between the metacarpal bones of the thumb and index finger. Finally it passes forward between the two heads of the first Interosseous dorsalis, into the palm of the hand, where it crosses the metacarpal bones and at the ulnar side of the hand unites with the deep volar branch of the ulnar artery to form the deep volar arch. The radial artery therefore consists of three portions, one in the forearm, a second at the back of the wrist, and a third in the hand. Relations.—(a) In the forearm the artery extends from the neck of the radius to the forepart of the styloid process, being placed to the medial side of the body of the bone above, and in front of it below. Its upper part is overlapped by the fleshy belly of the Bracliioradialis; the rest of the artery is superficial, being covered by the integument and the superficial and deep fascia}. In its course downward, it lies upon the tendon of the Biceps brachii, the Supinator, the Pronator teres, the radial origin of the Flexor digitorum sublimis, the Flexor pollicis longus, the Pronator quadratus, and the lower end of the radius. In the upper third of its course it lies between the Brachioradialis and the Pronator teres; in the lower two-thirds, between the tendons of the Brachioradialis and Flexor carpi radialis. The superficial branch of the radial nerve is close to the lateral side of the artery in the middle third of its course; and some filaments of the lateral antibrachial cutaneous nerve run along the lower part of the artery as it winds around the wrist. The vessel is accompanied by a pair of venae comitantes throughout its whole course. THE RADIAL ARTERY 593 (b) At the wrist the artery reaches the back of the carpus by passing between the radial collateral ligament of the wrist and the tendons of the Abductor pollicis longus and Extensor pollicis brevis. Inferior ulnar collateral Radial recurrent - Radial recurrent _ Anterior ulnar recurrent Posterior ulnar recurrent Dorsal interosseous Muscular - Muscular Extensor pollicis - brevis Deep volar branch fof ulnar Volar radial carpal Superficial volar Superficial volar- Volar ulnar carpal Deep volar branch of ulnar A. volar is indicts radialis Fig. 528.—Ulnar and radial arteries. Deep view. It then descends on the navicular and greater multangular bones, and before disappearing be- tween the heads of the first Interosseus dorsalis is crossed by the tendon of the Extensor pollicis Fig. 527.—The radial and ulnar arteries. 594 ANGIOLOGY longus. In the interval between the two Extensores pollicis it is crossed by the digital rami of the superficial branch of the radial nerve which go to the thumb and index finger. (c) In the hand, it passes from the upper end of the first interosseous space, between the heads of the first Interosseus dorsalis, transversely across the palm between the Adductor pollicis obliquus and Adductor pollicis transversus, but sometimes piercing the latter muscle, to the base of the metacarpal bone of the little, finger, where it anastomoses with the deep volar branch from the ulnar artery, completing the deep volar arch (Fig. 528). Peculiarities.—The origin of the radial artery is, in nearly one case in eight, higher than usual; more often it arises from the axillary or upper part of the brhchial than from the lower part of the latter vessel. In the forearm it deviates less frequently from its normal position than the ulnar. It has been found lying on the deep fascia instead of beneath it. It has also been observed on the surface of the Brachioradialis, instead of under its medial border; and in turning around the wrist, it has been seen lying on, instead of beneath, the Extensor tendons of the thumb. Branches.—The branches of the radial artery may be divided into three groups, corresponding with the three regions in which the vessel is situated. In the Forearm. Radial Recurrent. Muscular. Volar Carpal. Superficial Volar. At the Wrist. Dorsal Carpal. First Dorsal Metacarpal. In the Hand. Princeps Pollicis. Volaris Indicis Radialis. Volar Metacarpal. Perforating. Recurrent. The radial recurrent artery (a. recurrens radialis) arises immediately below the elbow. It ascends between the branches of the radial nerve, lying on the Supinator and then between the Brachioradialis and Brachialis, supplying these muscles and the elbow-joint, and anastomosing with the terminal part of the profunda brachii. The muscular branches (rami musculares) are distributed to the muscles on the radial side of the forearm. The volar carpal branch (ramus carpeus volaris; anterior radial carpal artery) is a small vessel which arises near the lower border of the Pronator quadratus, and, running across the front of the carpus, anastomoses with the volar carpal branch of the ulnar artery. This anastomosis is joined by a branch from the volar interosseous above, and by recurrent branches from the deep volar arch below, thus forming a volar carpal net-work which supplies the articulations of the wrist and carpus. The superficial volar branch (ramus volaris superficialis; superficialis voice artery) arises from the radial artery, just where this vessel is about to wind around the lateral side of the wrist. Running forward, it passes through, occasionally over, the muscles of the ball of the thumb, which it supplies, and sometimes anastomoses with the terminal portion of the ulnar artery, completing the superficial volar arch. This vessel varies considerably in size: usually it is very small, and'ends in the muscles of the thumb; sometimes it is as large as the continuation of the radial The dorsal carpal branch (ramus carpeus dorsalis; posterior radial carpal artery) is a small vessel which arises beneath the Extensor tendons of the thumb; crossing the carpus transversely toward the medial border of the hand, it anastomoses with the dorsal carpal branch of the ulnar and with the volar and dorsal interosseous arteries to form a dorsal carpal network. From this network are given off three slender dorsal metacarpal arteries, which run downward on the second, third, and fourth Interossei dorsales and bifurcate into the dorsal digital branches for the supply of the adjacent sides of the middle, ring, and little fingers respectively, communicating with the proper volar digital branches of the superficial volar arch. Near their origins they anastomose with the deep volar arch by the superior perforating arteries, and near their points of bifurcation with the common volar digital vessels of the superficial volar arch by the inferior perforating arteries. THE ULNAR ARTERY 595 The first dorsal metacarpal arises just before the radial artery passes between the two heads of the first Interosseous dorsalis and divides almost immediately into two branches which supply the adjacent sides of the thumb and index finger; the radial side of the thumb receives a branch directly from the radial artery. The arteria princeps pollicis arises from the radial just as it turns medialward to the deep part of the hand; it descends between the first Interosseous dorsalis and Adductor pollicis obliquus, along the ulnar side of the metacarpal bone of the thumb to the base of the first phalanx, where it lies beneath the tendon of the Flexor pollicis longus and divides into two branches. These make their appear- ance between the medial and lateral insertions of the Adductor pollicis obliquus, and run along the sides of the thumb, forming on the volar surface of the last phalanx an arch, from which branches are distributed to the integument and subcutaneous tissue of the thumb. The arteria volaris indicis radialis (radialis indicis artery) arises close to the pre- ceding, descends between the first Interosseus dorsalis and Adductor pollicis trans- versus, and runs along the radial side of the index finger to its extremity, where it anastomoses with the proper digital artery, supplying the ulnar side of the finger. At the lower border of the Adductor pollicis transversus this vessel anastomoses with the princeps pollicis, and gives a communicating branch to the superficial volar arch. The a. princeps pollicis and a. volaris indicis radialis may spring from a common trunk termed the first volar metacarpal artery. The deep volar arch (arcus volaris profundus; deep palmar arch) (Fig. 528) is formed by the anastomosis of the terminal part of the radial artery with the deep volar branch of the ulnar. It lies upon the carpal extremities of the metacarpal bones and on the Interossei, being covered by the Adductor pollicis obliquus, the Flexor tendons of the fingers, and the Lumbricales. Alongside of it, but running in the opposite direction—that is to say, toward the radial side of the hand—is the deep branch of the ulnar nerve. The volar metacarpal arteries {aa. metacarpece volares; palmar interosseous arteries), three or four in number, arise from the convexity of the deep volar arch; they run distally upon the Interossei, and anastomose at the clefts of the fingers with the common digital branches of the superficial volar arch. The perforating branches (rami perfor antes), three in number, pass backward from the deep volar arch, through the second, third, and fourth interosseous spaces and between the heads of the corresponding Interossei dorsalis, to anastomose with the dorsal metacarpal arteries, The recurrent branches arise from the concavity of the deep volar arch. They ascend in front of the wrist, supply the intercarpal articulations, and end in the volar carpal network. The Ulnar Artery (A. Ulnaris) (Fig. 528). The ulnar artery, the larger of the two terminal branches of the brachial, begins a little below the bend of the elbow, and, passing obliquely downward, reaches the ulnar side of the forearm at a point about midway between the elbow and the wrist. It then runs along the ulnar border to the wrist, crosses the transverse carpal ligament on the radial side of the pisiform bone, and immediately beyond this bone divides into two branches, which enter into the formation of the superficial and deep volar arches. Relations.—(a) In the forearm.—In its upper half, it is deeply seated, being covered by the Pronator teres, Flexor carpi radialis, Palmaris longus, and tlexor digitorum sublimis; it lies upon the Brachialis and Flexor digitorum profundus. The median nerve is in relation with the medial side of the artery for about 2.5 cm. and then crosses the vessel, being separated from it by the ulnar head of the Pronator teres. In the lower half of the forearm it lies upon the Flexor digitorum profundus, being covered by the integument and the superficial and deep fasciae, 596 ANGIOLOGY and placed between the Flexor carpi ulnaris and Flexor digitorum sublimis. It is accompanied by two vena3 comitantes, and is overlapped in its middle third by the Flexor carpi ulnaris; the ulnar nerve lies on the medial side of the lower two-thirds of the artery, and the palmar cutaneous branch of the nerve descends on the lower part of the vessel to the palm of the hand. (6) At the wrist (Fig. 527) the ulnar artery is covered by the integument and the volar carpal ligament, and lies upon the transverse carpal ligament. On its medial side is the pisiform bone, and, somewhat behind the artery, the ulnar nerve. Peculiarities.—The ulnar artery varies in its origin in the proportion of about one in thirteen cases; it may arise about 5 to 7 cm. below the elbow, but more frequently higher, the brachial being more often the source of origin than the axillary. Variations in the position of this vessel are more common than in the radial. When its origin is normal, the course of the vessel is rarely changed. When it arises high up, it is almost invariably superficial to the Flexor muscles in the forearm, lying commonly beneath the fascia, more rarely between the fascia and integument. In a few cases, its position was subcutaneous in the upper part of the forearm, and subaponeurotic in the lower part. Branches.—The branches of the ulnar artery may be arranged in the following groups: Anterior Recurrent. Posterior Recurrent. Common Interosseous. Muscular. At the Wrist Volar Carpal. Dorsal Carpal. In the Forearm In the Hand Deep Volar. Superficial Volar Arch. The anterior ulnar recurrent artery (a. recurrentes ulnaris anterior) arises imme- diately below the elbow-joint, runs upward between the Brachialis and Pronator teres, supplies twigs to those muscles, and, in front of the medial epicondyle, anasto- moses with the superior and inferior ulnar collateral arteries. The posterior ulnar recurrent artery (a. recurrentes ulnaris posterior) is much larger, and arises somewhat lower than the preceding. It passes backward and medialward on the Flexor digitorum profundus, behind the Flexor digitorum sub- limis, and ascends behind the medial epicondyle of the humerus. In the interval between this process and the olecranon, it lies beneath the Flexor carpi ulnaris, and ascending between the heads of that muscle, in relation with the ulnar nerve, it supplies the neighboring muscles and the elbow-joint, and anastomoses with the superior and inferior ulnar collateral and the interosseous recurrent arteries (Fig. 529). The common interosseous artery (a. interossea communis) (Fig. 528), about 1 cm. in length, arises immediately below the tuberosity of the radius, and, passing backward to the upper border of the interosseous membrane, divides into two branches, the volar and dorsal interosseous arteries. The Volar Interosseous Artery (a. interossea volaris; anterior interosseous artery) (Fig. 528), passes down the forearm on the volar surface of the interosseous mem- brane. It is accompanied by the volar interosseous branch of the median nerve, and overlapped by the contiguous margins of the Flexor digitorum profundus and Flexor pollicis longus, giving off in this situation muscular branches, and the nutrient arteries of the radius and ulna. At the upper border of the Pronator quadratus it pierces the interosseous membrane and reaches the back of the forearm, where it anastomoses with the dorsal interosseous artery (Fig. 529). It then descends, in company with the terminal portion of the dorsal interosseous nerve, to the back of the wrist to join the dorsal carpal net-work. The volar interosseous artery gives off a slender branch, the arteria mediana, which accompanies the median nerve, and gives offsets to its substance; this artery is sometimes much enlarged, and runs with the nerve into the palm of the hand. Before it pierces the interosseous membrane the volar interosseous sends a branch downward behind the Pronator quadratus to join the volar carpal network. The Dorsal Interosseous Artery (a. interossea dorsalis; posterior interosseous artery) (Fig. 529) passes backward between the oblique cord and the upper border of the interosseous membrane. It appears between the contiguous borders of the Supinator THE ULNAR ARTERY 597 and the Abductor pollicis longus, and runs down the back of the forearm between the superficial and deep layers of muscles, to both of which it distributes branches. Where it lies upon the Abductor pollicis longus and the Extensor pollicis brevis, A. profunda brachii Inf. ulnar collateral Posterior ulnar recurrent Dorsal interosseous Termination of volar interosseous Dorsal ulnar carpal Dorsal radial carpal Radial \ 1st dorsal J metacarpal Fig. 529.—Arteries of the back of the forearm and hand. it is accompanied by the dorsal interosseous nerve. At the lower part of the fore- arm it anastomoses with the termination of the volar interosseous artery, and with the dorsal carpal network. It gives off, near its origin, the interosseous recurrent artery, which ascends to the interval between the lateral epicondyle and olecranon, 598 ANGIOLOGY on or through the fibers of the Supinator, but beneath the Anconaeus, and anasto- moses with the radial collateral branch of the profunda brachii, the posterior ulnar recurrent and the inferior ulnar collateral. The muscular branches (rami musculares) are distributed to the muscles along the ulnar side of the forearm. The volar carpal branch (ramus carpeus volares; anterior ulnar carpal artery) is a small vessel which crosses the front of the carpus beneath the tendons of the Flexor digitorum profundus, and anastomoses with the corresponding branch of the radial artery. The dorsal carpal branch (ramus carpeus dorsalis; posterior idnar carpal artery) arises immediately above the pisiform bone, and winds backward beneath the tendon of the Flexor carpi ulnaris; it passes across the dorsal surface of the carpus beneath the Extensor tendons, to anastomose with a corresponding branch of the radial artery. Immediately after its origin, it gives off a small branch, which runs along the ulnar side of the fifth metacarpal bone, and supplies the ulnar side of the dorsal surface of the little finger. The deep volar branch (ramus volaris profundus; profunda branch) (Fig. 528) passes between the Abductor digiti quinti and Flexor digiti quinti brevis and through the origin of the Opponens digiti quinti; it anastomoses with the radial artery, and completes the deep volar arch. The superficial volar arch (arcus volaris superficialis; superficial palmar arch) (Fig. 527) is formed by the ulnar artery, and is usually completed by a branch from the a. volaris indicis radialis, but sometimes by the superficial volar or by a branch from the a. princeps pollicis of the radial artery. The arch passes across the palm, describing a curve, with its convexity downward. Relations.—The superficial volar arch is covered by the skin, the Pahnaris brevis, and the palmar aponeurosis. It lies upon the transverse carpal ligament, the Flexor digiti quinti brevis and Opponens digiti quinti, the tendons of the Flexor digitorum sublimis, the Lumbricales, and the divisions of the median and ulnar nerves. Three Common Volar Digital Arteries (aa. digitales volares communes; palmar digital arteries) (Fig. 527) arise from the convexity of the arch and proceed downward on the second, third, and fourth Lumbricales. Each receives the corresponding volar metacarpal artery and then divides into a pair of proper volar digital arteries (aa. digitales volares proprice; collateral digital arteries) which run along the con- tiguous sides of the index, middle, ring, and little fingers, behind the corresponding digital nerves; they anastomose freely in the subcutaneous tissue of the finger tips and by smaller branches near the interphalangeal joints. Each gives off a couple of dorsal branches which anastomose with the dorsal digital arteries, and supply the soft parts on the back of the second and third phalanges, including the matrix of the finger-nail. The proper volar digital artery for medial side of the little finger springs from the ulnar artery under cover of the Palmaris brevis. THE ARTERIES OF THE TRUNK. THE DESCENDING AORTA. The descending aorta is divided into two portions, the thoracic and abdominal, in correspondence with the two great cavities of the trunk in which it is situated. The Thoracic Aorta (Aorta Thoracalis) (Fig. 530). The thoracic aorta is contained in the posterior mediastinal cavity. It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth at the aortic THE THORACIC AORTA 599 hiatus in the diaphragm. At its commencement, it is situated on the left of the vertebral column; it approaches the median line as it descends; and, at its termina- tion, lies directly in front of the column. The vessel describes a curve which is concave forward, and as the branches given off from it are small, its diminution in size is inconsiderable. Highest intercostal artery Highest intercostal vein Rami communicantes Lig. arteriosum Fig. 530.—The thoracic aorta, viewed from the left side. Relations—It is in relation, anteriorly, from above downward, with the root of the left lung, the pericardium, the esophagus, and the diaphragm; posteriorly, with the vertebral column and the hemiazygos veins; on the right side, with the azygos vein and thoracic duct, on the / side, with the left pleura and lung. The esophagus, with its accompanying plexus of nerves lies on the right side of the aorta above; but at the lower part of the thorax it is placed m fro of the aorta, and, close to the diaphragm, is situated on its left sic e. . , Peculiarities.—The aorta is occasionally found to be obliterated at the junction. of with the thoracic aorta, just below the ductus arteriosus. Whether this is the result of disease or of congenital malformation, is immaterial to our present purpose; it affords an mterestmg opportunity of observing the resources of the collateral circulation. The course of the anastomos- 600 ANGIOLOGY ing vessels, by which the blood is brought from the upper to the lower part of the artery, will be found well described in an account of two cases in the Pathological Transactions, vols. viii and x. In the former, Sydney Jones thus sums up the detailed description of the anastomosing vessels: The principal communications by which the circulation was carried on were: (1) The internal mammary, anastomosing with the intercostal arteries, with the inferior phrenic of the abdominal aorta by means of the musculophrenic and pericardiacophrenic, and largely with the inferior epigastric. (2) The costocervical trunk, anastomosing anteriorly by means of a large branch with the first aortic intercostal, and posteriorly with the posterior branch of the same artery. (3) The inferior thyroid, by means of a branch about the size of an ordinary radial, forming a communication with the first aortic intercostal. (4) The transverse cervical, by means of very large communications with the posterior branches of the intercostals. (5) The branches (of the subclavian and axillary) going to the side of the chest were large, and anastomosed freely with the lateral branches of the intercostals. In the second case Wood describes the anastomoses in a somewhat similar manner, adding the remark that “the blood which was brought into the aorta through the anastomosis of the intercostal arteries appeared to be expended principally in supplying the abdomen and pelvis; while the supply to the lower extremities had passed through the internal mammary and epigastrics.” In a few cases an apparently double descending thoracic aorta has been found, the two vessels lying side by side, and eventually fusing to form a single tube in the lower part of the thorax or in the abdomen. One of them is the aorta, the other represents a dissecting aortic aneurism which has become canalized; opening above and below into the true aorta, and at first sight presenting the appearances of a proper bloodvessel. Branches of the Thoracic Aorta.— Pericardial. Bronchial. Esophageal. Mediastinal. Intercostal. Subcostal. Superior Phrenic. Visceral Parietal The pericardial branches (rami pericardiaci) consist of a few small vessels which are distributed to the posterior surface of the pericardium. The bronchial arteries (aa. bronchioles) vary in number, size, and origin. There is as a rule only one right bronchial artery, which arises from the first aortic inter- costal, or from the upper left bronchial artery. The left bronchial arteries are usually two in number, and arise from the thoracic aorta. The upper left bronchial arises opposite the fifth thoracic vertebra, the lower just below the level of the left bron- chus. Each vessel runs on the back part of its bronchus, dividing and subdividing along the bronchial tubes, supplying them, the areolar tissue of the lungs, the bronchial lymph glands, and the esophagus. The esophageal arteries (aa. cesophageee) four or five in number, arise from the front of the aorta, and pass obliquely downward to the esophagus, forming a chain of anastomoses along that tube, anastomosing with the esophageal branches of the inferior thyroid arteries above, and with ascending branches from the left inferior phrenic and left gastric arteries below. The mediastinal branches (rami mediastinales) are numerous small vessels which supply the lymph glands and loose areolar tissue in the posterior mediastinum. Intercostal Arteries (aa. intercostales).—There are usually nine pairs of aortic intercostal arteries. They arise from the back of the aorta, and a redistributed to the lower nine intercostal spaces, the first two spaces being supplied by the highest intercostal artery, a branch of the costocervical trunk of the subclavian. The right aortic intercostals are longer than the left, on account of the position of the aorta on the left side of the vertebral column; they pass across the bodies of the vertebrae behind the esophagus, thoracic duct, and vena azygos, and are covered by the right lung and pleura. The left aortic intercostals run backward on the sides of the vertebrae and are covered by the left lung and pleura; the upper two vessels are crossed by the highest left intercostal vein, the lower vessels by the hemiazygos veins. The further course of the intercostal arteries is practically the same on both sides. Opposite the heads of the ribs the sympathetic trunk THE THORACIC AORTA 601 passes downward in front of them, and the splanchnic nerves also descend in front by the lower arteries. Each artery then divides into an anterior and a posterior ramus. The Anterior Ramus crosses the corresponding intercostal space obliquely toward the angle of the upper rib, and thence is continued forward in the costal groove. It is placed at first between the pleura and the posterior intercostal membrane, then it pierces this membrane, and lies between it and the Intercostalis externus as far as the angle of the rib; from this onward it runs between the Intercostales externus and internus, and anastomoses in front with the intercostal branch of the internal mammary or musculophrenic. Each artery is accompanied by a vein and a nerve, the former being above and the latter below the artery, except in the upper spaces, where the nerve is at first above the artery. The first aortic intercostal artery anastomoses with the intercostal branch of the costocervical trunk, and may form the chief supply of the second intercostal space. The lower two intercostal arteries are continued anteriorly from the intercostal spaces into the abdominal wall, and anastomose with the subcostal, superior epigastric, and lumbar arteries. Branches.—The anterior rami give off the following branches: Collateral Intercostal. Muscular. Lateral Cutaneous. Mammary. The collateral intercostal branch comes off from the intercostal artery near the angle of the rib, and descends to the upper border of the rib below, along which it courses to anastomose with the intercostal branch of the internal mammary. Muscular branches are given to the Intercostales and Pectorales and to the Serratus anterior; they anastomose with the highest and lateral thoracic branches of the axillary artery. The lateral cutaneous branches accompany the lateral cutaneous branches of the thoracic nerves. Mammary branches are given off by the vessels in the third, fourth, and fifth spaces. They supply the mamma, and increase considerably in size during the period of lactation. The Posterior Ramus runs backward through a space which is bounded above and below by the necks of the ribs, medially by the body of a vertebra, and laterally by an anterior costotransverse ligament. It gives off a spinal branch which enters the vertebral canal through the intervertebral foramen and is distributed to the medulla spinalis and its membranes and the vertebrae. It then courses over the transverse process with the posterior division of the thoracic nerve, supplies branches to the muscles of the back and cutaneous branches which accompany the corresponding cutaneous branches of the posterior division of the nerve. The subcostal arteries, so named because they lie below the last ribs, constitute the lowest pair of branches derived from the thoracic aorta, and are in series with the intercostal arteries. Each passes along the lower border of the twelfth rib behind the kidney and in front of the Quadratus lumborum muscle, and is accom- panied by the twelfth thoracic nerve. It then pierces the posterior aponeurosis of the Transversus abdominis, and, passing forward between this muscle and the Obliquus internus, anastomoses with the superior epigastric, lower intercostal, and lumbar arteries. Each subcostal artery gives off a posterior branch which has a similar distribution to the posterior ramus of an intercostal artery. The superior phrenic branches are small and arise from the lower part of the thoracic aorta; they are distributed to the posterior part of the upper surface of the diaphragm, and anastomose with the musculophrenic and pericardiacophrenic arteries. A small aberrant artery is sometimes found arising from the right side of the tho- racic aorta near the origin of the right bronchial. It passes upward and to the right 602 ANGIOLOGY behind the trachea and the esophagus, and may anastomose with the highest right intercostal artery. It represents the remains of the right dorsal aorta, and in a small proportion of cases is enlarged to form the first part of the right subclavian artery. The Abdominal Aorta (Aorta Abdominalis) (Fig. 531). The abdominal aorta begins at the aortic hiatus of the diaphragm, in front of the lower border of the body of the last thoracic vertebra, and, descending in Inferior phrenic arteries Internal -spermatic vessels Fig. 531.—The abdominal aorta and its branches. front of the vertebral column, ends on the body of the fourth lumbar vertebra, commonly a little to the left of the middle line,1 by dividing into the two common iliac arteries. It diminishes rapidly in size, in consequence of the many large branches which it gives off. As it lies upon the bodies of the vertebrae, the curve which it describes is convex forward, the summit of the convexity corresponding to the third lumbar vertebra. 1 Lord Lister, having accurately examined 30 bodies in order to ascertain the exact point of termination of this vessel, found it “either absolutely, or almost absolutely, mesial in 15, while in 13 it deviated more or less to the left, and in 2 was slightly to the right. ” System of Surgery, edited by T. Holmes, 2d ed., v, 652. THE ABDOMINAL AORTA 603 Relations—The abdominal aorta is covered, anteriorly, by the lesser omentum and stomach, behind which are the branches of the celiac artery and the celiac plexus; below these, by the lienal vein, the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and aortic plexus. Posteriorly, it is separated from the lumbar vertebrae and intervertebral fibrocartilages by the anterior longitudinal ligament and left lumbar veins. On the right side it is in relation above with the azygos vein, cisterna chyli, thoracic duct, and the right crus of the diaphragm the last separating it from the upper part of the inferior vena cava, and from the right celiac ganglion; the inferior vena cava is in contact with the aorta below. On the left side are the left crus of the diaphragm, the left celiac ganglion, the ascending part of the duodenum, and some coils of the small intestine. Collateral Circulation.—The collateral circulation would be carried on by the anastomoses between the internal mammary and the inferior epigastric; by the free communication between the superior and inferior mesenteries, if the ligature were placed between these vessels; or by the anastomosis between the inferior mesenteric and the internal pudendal, when (as is more common) the point of ligature is below the origin of the inferior mesenteric; and possibly by the anastomoses of the lumbar arteries with the branches of the hypogastric. Branches.—The branches of the abdominal aorta may be divided into three sets: visceral, parietal, and terminal. Visceral Branches. Celiac. Superior Mesenteric. Inferior Mesenteric. Middle Suprarenals. Renals. Internal Spermatics. Ovarian (in the female). Parietal Branches. Inferior Phrenics. Lumbars. Middle Sacral. Terminal Branches. Common Iliacs. Of the visceral branches, the celiac artery and the superior and inferior mes- enteric arteries are unpaired, while the suprarenals, renals, internal spermatics, and ovarian are paired. Of the parietal branches the inferior phrenics and lumbars are paired; the middle sacral is unpaired. The terminal branches are paired. The celiac artery (a. coeliaca; celiac axis) (Figs. 532, 533) is a short thick trunk, about 1.25 cm. in length, which arises from the front of the aorta, just below the aortic hiatus of the diaphragm, and, passing nearly horizontally forward, divides into three large branches, the left gastric, the hepatic, and the splenic; it occasionally gives off one of the inferior phrenic arteries. Relations.—The celiac artery is covered by the lesser omentum. On the right side it is in relation with the right celiac ganglion and the caudate process of the liver; on the left side, with the left celiac ganglion and the cardiac end of the stomach. Below, it is in relation to the upper border of the pancreas, and the lienal vein. 1. The Left Gastric Artery (a. gastrica sinistra; gastric or coronary artery), the smallest of the three branches of the celiac artery, passes upward and to the left, posterior to the omental bursa, to the cardiac orifice of the stomach. Here it dis- tributes branches to the esophagus, which anastomose with the aortic esophageal arteries; others supply the cardiac part of the stomach, anastomosing with branches of the lienal artery. It then runs from left to right, along the lesser curvature of the stomach to the pylorus, between the layers of the lesser omentum; it gives branches to both surfaces of the stomach and anastomoses with the right gastric artery. 2. The Hepatic Artery (a. hepatica) in the adult is intermediate in size between the left gastric and lienal; in the fetus, it is the largest of the three branches of the celiac artery. It is first directed forward and to the right, to the upper margin of the superior part of the duodenum, forming the lower boundary of the epiploic foramen (foramen of Winslow). It then crosses the portal vein anteriorly and ascends between the layers of the lesser omentum, and in front of the epiploic fora- men, to the porta hepatis, where it divides into two branches, right and left, which supply the corresponding lobes of the liver, accompanying the ramifications of the 604 ANGIOLOGY portal vein and hepatic ducts. The hepatic artery, in its course along the right border of the lesser omentum, is in relation with the common bile-duct and portal vein, the duct lying to the right of the artery, and the vein behind. Its branches are: Right Gastric. Gastroduodenal vTdbtl Utl LtUU.t/llcll Right Gastroepiploic. Superior Pancreaticoduodenal. Cystic. Cystic artery Probe passed through epiploic foramen Fig. 532.—The celiac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed. The right gastric artery (a. gastrica dextra; pyloric artery) arises from the hepatic, above the pylorus, descends to the pyloric end of the stomach, and passes from right to left along its lesser curvature, supplying it with branches, and anastomosing with the left gastric artery. The gastroduodenal artery (a. gastroduodenalis) (Fig. 533) is a short but large branch, which descends, near the pylorus, between the superior part of the duo- denum and the neck of the pancreas, and divides at the lower border of the duodenum into two branches, the right gastroepiploic and the superior pancreaticoduodenal. Previous to its division it gives off two or three small branches to the pyloric end of the stomach and to the pancreas. The right gastroepiploic artery (a. gastroepiploica dextra) runs from right to left along the greater curvature of the stomach, between the layers of the greater omentum, anastomosing with the left gastroepiploic branch of the lienal artery. Except at the pylorus, where it is in contact with the stomach, it lies about a finger’s THE ABDOMINAL AORTA 605 breadth from the greater curvature, This vessel gives off numerous branches, some of which ascend to supply both surfaces of the stomach, while others descend to supply the greater omentum and anastomose with branches of the middle colic. The superior pancreaticoduodenal artery (a. pancreaticoduodenalis superior) descends between the contiguous margins of the duodenum and pancreas. It supplies both these organs, and anastomoses with the inferior pancreaticoduodenal branch of the superior mesenteric artery, and with the pancreatic branches of the lienal artery. Branches to greater omentum Fio. 533.—The celiac artery and its branches; the stomach has been raised and the peritoneum removed, The cystic artery (a. cystica) (Fig. 532), usually a branch of the right hepatic, passes downward and forward along the neck of the gall-bladder, and divides into two branches, one ot which ramifies on the free surface, the other on the attached surface of the gall-bladder. 3. The Lienal or Splenic Artery (a. lienalis), the largest branch of the celiac artery, is remarkable for the tortuosity of its course. It passes horizontally to the left side, behind the stomach and the omental bursa of the peritoneum, and along the upper border of the pancreas, accompanied by the lienal vein, which lies below it; it crosses in front of the upper part of the left kidney, and, on arriving near the spleen, divides into branches, some of which enter the hilus of that organ between the two layers of the phrenicolienal ligament to be distributed to the tissues of the spleen; some are given to the pancreas, while others pass to the greater curva- ture of the stomach between the layers of the gastrolienal ligament. Its branches are: Pancreatic. Short Gastric. Left Gastroepiploic. 606 ANGIOLOGY The pancreatic branches (rami pancreatici) are numerous small vessels derived from the lienal as it runs behind the upper border of the pancreas, supplying its body and tail. One of these, larger than the rest, is sometimes given off near the tail of the pancreas; it runs from left to right near the posterior surface of the gland, following the course of the pancreatic duct, and is called the arteria pancreatica magna. These vessels anastomose with the pancreatic branches of the pancreatico- duodenal and superior mesenteric arteries. Fig. 534.—The superior mesenteric artery and its branches. The short gastric arteries (aa. gastricce breves; vasa brevia) consist of from five to seven small branches, which arise from the end of the lienal artery, and from its terminal divisions. They pass from left to right, between the layers of the gastro- lienal ligament, and are distributed to the greater curvature of the stomach, anasto- mosing with branches of the left gastric and left gastroepiploic arteries. The left gastroepiploic artery (a. gastroepiploica sinistra) the largest branch of the lienal, runs from left to right about a finger’s breadth or more from the greater curvature of the stomach, between the layers of the greater omentum, and anasto- moses with the right gastroepiploic. In its course it distributes several ascending branches to both surfaces of the stomach; others descend to supply the greater omentum and anastomose with branches of the middle colic. The superior mesenteric artery (a. mesenterica superior) (Fig. 534) is a large THE ABDOMINAL AORTA 607 vessel which supplies the whole length of the small intestine, except the superior part of the duodenum; it also supplies the cecum and the ascending part of the colon and about one-half of the transverse part of the colon. It arises from the front of the aorta, about 1.25 cm. below the celiac artery, and is crossed at its origin by the lienal vein and the neck of the pancreas. It passes downward and forward, anterior to the processus uncinatus of the head of the pancreas and inferior part of the duodenum, and descends between the layers of the mesentery to the right iliac fossa, where, considerably diminished in size, it anastomoses with one of its own branches, viz., the ileocolic. In its course it crosses in front of the inferior vena cava, the right ureter and Psoas major, and forms an arch, the convexity of which is directed forward and downward to the left side, the concavity backward and upward to the right. It is accompanied by the superior mesenteric vein, which lies to its right side, and it is surrounded by the superior mesent.eric plexus of nerves. Branches.—Its branches are: Inferior Pancreaticoduodenal. Intestinal. Ileocolic. Right Colic. Middle Colic. The Inferior Pancreaticoduodenal Artery (a. pancreaticoduodenalis inferior) is given off from the superior mesenteric or from its first intestinal branch, opposite the upper border of the inferior part of the duodenum. It courses to the right between the head of the pancreas and duodenum, and then ascends to anastomose with the superior pancreaticoduodenal artery. It distributes branches to the head of the pancreas and to the descending and inferior parts of the duodenum. The Intestinal Arteries (aa. intestinales; rasa intestini tenuis) arise from the convex side of the superior mesenteric artery. They are usually from twelve to fifteen in number, and are distributed to the jejunum and ileum. They run nearly parallel with one another between the layers of the mesentery, each vessel dividing into two branches, which unite with adjacent branches, forming a series of arches, the convexities of which are directed toward the intestine (Fig. 535). From this first set of arches branches arise, which unite with similar branches from above and below and thus a second series of arches is formed; from the lower branches of the artery, a third, a fourth, or even a fifth series of arches may be formed, diminishing in size the nearer they approach the intestine. In the short, upper part of the mesen- tery only one set of arches exists, but as the depth of the mesentery increases, second, third, fourth, or even fifth groups are developed. From the terminal arches numerous small straight vessels arise which encircle the intestine, upon which they are distributed, ramifying between its coats. From the intestinal arteries small branches are given off to the lymph glands and other structures between the layers of the mesentery. The Ileocolic Artery (a. ileocolica) is the lowest branch arising from the concavity of the superior mesenteric artery. It passes downward and to the right behind the peritoneum toward the right iliac fossa, where it divides into a superior and an inferior branch; the inferior anastomoses with the end of the superior mesenteric artery, the superior with the right colic artery. The inferior branch of the ileocolic runs toward the upper border of the ileo- colic junction and supplies the following branches (Fig. 536): (a) colic, which pass upward on the ascending colon; (b) anterior and posterior cecal, which are distributed to the front and back of the cecum; (c) an appendicular artery, which descends behind the termination of the ileum and enters the mesen- teriole of the vermiform process; it runs near the free margin of this mesenteriole and ends in branches wThich supply the vermiform process; and (d) ileal, w'hich run upward and to the left on the lower part of the ileum, and anastomose with the termination of the superior mesenteric. 608 ANG10L0GY Fig. 535.—Loop of small intestine showing distribution of intestinal arteries (From a preparation byMrHamilton Drummond.) The vessels were injected while the gut was in situ; the gut was then removed, and an rr-ray photog ap taken. - Terminal part of ileocolic Cecal branches - Ileal branches Appendicular artery Fig. 536.—Arteries of cecum and vermiform process. THE ABDOMINAL AORTA 609 The Right Colic Artery (a. colica dextra) arises from about the middle of the con- cavity of the superior mesenteric artery, or from a stem common to it and the ileo- colic. It passes to the right behind the peritoneum, and in front of the right internal spermatic or ovarian vessels, the right ureter and the Psoas major, toward the middle of the ascending colon; sometimes the vessel lies at a higher level, and crosses the descending part of the duodenum and the lower end of the right kidney. At the colon it divides into a descending branch, which anastomoses with the ileocolic, and an ascending branch, which anastomoses with the middle colic. These branches form arches, from the convexity of which vessels are distributed to the ascending colon. Middle Hemorrhoidal Inferior Hemorrhoidal Fig. 537.—The inferior mesenteric artery and its branches. The Middle Colic Artery (a. colica media) arises from the superior mesenteric just below the pancreas and, passing downward and forward between the layers of the transverse mesocolon, divides into two branches, right and left; the former anastomoses with the right colic; the latter with the left colic, a branch of the in- ferior mesenteric. The arches thus formed are placed about two fingers’ breadth from the transverse colon, to which they distribute branches. The inferior mesenteric artery (a. mesenterica inferior) (Fig. 537) supplies the left half of the transverse part of the colon, the whole of the descending and iliac parts of the colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric, and arises from the aorta, about 3 or 4 cm. 610 ANGIOLOGY above its division into the common iliacs and close to the lower border of the inferior part of the duodenum. It passes downward posterior to the peritoneum, lying at first anterior to and then on the left side of the aorta. It crosses the left common iliac artery and is continued into the lesser pelvis under the name of the superior hemorrhoidal artery, which descends between the two layers of the sigmoid mesocolon and ends on the upper part of the rectum. Branches.—Its branches are: Left Colic. Sigmoid. Superior Hemorrhoidal. The Left Colic Artery (a. colica sinistra) runs to the left behind the peritoneum and in front of the Psoas major, and after a short, but variable, course divides into an ascending and a descending branch; the stem of the artery or its branches cross the left ureter and left internal spermatic vessels. The ascending branch crosses in front of the left kidney and ends, between the two layers of the transverse mesocolon, by anastomosing with the middle colic artery; the descending branch anastomoses with the highest sigmoid artery. From the arches formed by these anastomoses branches are distributed to the descending colon and the left part of the transverse colon. The Sigmoid Arteries (aa. sigmoideoe) (Fig. 538), two or three in number, run obliquely downward and to the left behind the peritoneum and in front of the Psoas major, ureter, and internal spermatic vessels. Their branches supply the lower part of the descending colon, the iliac colon, and the sigmoid or pelvic colon; anasto- mosing above with the left colic, and below with the superior hemorrhoidal artery. The Superior Hemorrhoidal Artery (a. hcemorrhoidalis superior) (Fig. 538), the continuation of the inferior mesenteric, descends into the pelvis between the layers of the mesentery of the sigmoid colon, crossing, in its course, the left common iliac vessels. It divides, opposite the third sacral vertebra, into two branches, which descend one on either side of the rectum, and about 10 or 12 cm. from the anus break up into several small branches. These pierce the muscular coat of the bowel and run downward, as straight vessels, placed at regular intervals from each other in the wall of the gut between its muscular and mucous coats, to the level of the Sphincter ani internus; here they form a series of loops around the lower end of the rectum, and communicate with the middle hemorrhoidal branches of the hypogastric, and with the inferior hemorrhoidal branches of the internal pudendal. The middle suprarenal arteries (aa. suprarenales media; middle capsular arteries; suprarenal arteries) are two small vessels which arise, one from either side of the aorta, opposite the superior mesenteric artery. They pass lateralward and slightly upward, over the crura of the diaphragm, to the suprarenal glands, where they anastomose with suprarenal branches of the inferior phrenic and renal arteries. In the fetus these arteries are of large size. The renal arteries (aa. renales) (Fig. 531), are two large trunks, which arise from the side of the aorta, immediately below the superior mesenteric artery. Each is directed across the crus of the diaphragm, so as to form nearly a right angle with the aorta. The right is longer than the left, on account of the position of the aorta; it passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum. The left is somewhat higher than the right; it lies behind the left renal vein, the body of the pancreas and the lienal vein, and is crossed by the inferior mesenteric vein. Before reaching the hilus of the kidney, each artery divides into four or five branches; the greater number of these lie between the renal vein and ureter, the vein being in front, the ureter behind, but one or more branches are usually situated behind the ureter. Each vessel gives off some small inferior suprarenal branches to the suprarenal gland, the ureter, and the surrounding cellular tissue and muscles. One or two accessory renal arteries are frequently found, more especially on the left side THE ABDOMINAL AORTA 611 the\ usually arise from the aorta, and may come off above or below the main artery, the former being the more common position. Instead of entering the kidney at the hilus, they usually pierce the upper or lower part of the gland. internal spermatic arteries (aa. spermaticce internee; spermatic arteries) (Fig. 531) are distributed to the testes. They are two slender vessels of consid- erable length, and arise from the front of the aorta a little below the renal arteries. Fach passes obliquely downward and lateralward behind the peritoneum, resting on the Psoas major, the right spermatic lying in front of the inferior vena cava and behind the middle colic and ileocolic arteries and the terminal part of the ileum, the left behind the left colic and sigmoid arteries and the iliac colon. Each crosses obliquely over the ureter and the lower part of the external iliac artery Middle . Hemorrhoidal} Artery Fig. 538.—Sigmoid colon and rectum, showing distribution of branches of inferior mesenteric artery and their anastomoses. (From a preparation by Mr. Hamilton Drummond.) Prepared in same manner as Fig. 535. to reach the abdominal inguinal ring, through which it passes, and accompanies the other constituents of the spermatic cord along the inguinal canal to the scrotum, where it becomes tortuous, and divides into several branches. Two or three of these accompany the ductus deferens, and supply the epididymis, anasto- mosing with the artery of the ductus deferens; others pierce the back part of the tunica albuginea, and supply the substance of the testis. The internal spermatic artery supplies one or two small branches to the ureter, and in the inguinal canal gives one or two twigs to the Cremaster. The ovarian arteries (aa. ovaricoe) are the corresponding arteries in the female to the internal spermatic in the male. They supply the ovaries, are shorter than the internal spermatics, and do not pass out of the abdominal cavity. The origin and course of the first part of each artery are the same as those of the internal 612 ANGIOLOGY spermatic, but on arriving at the upper opening of the lesser pelvis the ovarian artery passes inward, between the two layers of the ovariopelvic ligament and of the broad ligament of the uterus, to be distributed to the ovary. Small branches are given to the ureter and the uterine tube, and one passes on to the side of the uterus, and unites with the uterine artery. Other offsets are continued on the round ligament of the uterus, through the inguinal canal, to the integument of the labium majus and groin. At an early period of fetal life, when the testes or ovaries lie by the side of the vertebral column, below the kidneys, the internal spermatic or ovarian arteries are short; but with the descent of these organs into the scrotum or lesser pelvis, the arteries are gradually lengthened. The inferior phrenic arteries (aa. phrenicce inferiores) (Fig. 531) are two small vessels, which supply the diaphragm but present much variety in their origin. They may arise separately from the front of the aorta, immediately above the celiac artery, or by a common trunk, which may spring either from the aorta or from the celiac artery. Sometimes one is derived from the aorta, and the other from one of the renal arteries; they rarely arise as separate vessels from the aorta. They diverge from one another across the crura of the diaphragm, and then run ob- liquely upward and lateralward upon its under surface. The left phrenic passes behind the esophagus, and runs forward on the left side of the esophageal hiatus. The right phrenic passes behind the inferior vena cava, and along the right side of the foramen which transmits that vein. Near the back part of the central tendon each vessel divides into a medial and a lateral branch. The medial branch curves forward, and anastomoses with its of the opposite side, and with the musculophrenic and pericardiacophrenic arteries. The lateral branch passes toward the side of the thorax, and anastomoses with the lower intercostal arteries, and with the musculophrenic. The lateral branch of the right phrenic gives off a few vessels to the inferior vena cava; and the left one, some branches to the esophagus. Each vessel gives off superior suprarenal branches to the suprarenal gland of its own side. The spleen and the liver also receive a few twigs from the left and right vessels respectively. The lumbar arteries (aa. lumbales) are in series with the intercostals. They are usually four in number on either side, and arise from the back of the aorta, opposite the bodies of the upper four lumbar vertebrae. A fifth pair, small in size, is occasionally present: they arise from the middle sacral artery. They run lateral- ward and backward on the bodies of the lumbar vertebrae, behind the sympathetic trunk, to the intervals between the adjacent transverse processes, and are then continued into the abdominal wall. The arteries of the right side pass behind the inferior vena cava, and the upper two on each side run behind the corresponding crus of the diaphragm. The arteries of both sides pass beneath the tendinous arches which give origin to the Psoas major, and are then continued behind this muscle and the lumbar plexus. They now cross the Quadratus lumborum, the upper three arteries running behind, the last usually in front of the muscle. At the lateral border of the Quadratus lumborum they pierce the posterior aponeurosis of the Transversus abdominis and are carried forward between this muscle and the Obliquus interims. They anastomose with the lower intercostal, the subcostal, the iliolumbar, the deep iliac circumflex, and the inferior epigastric arteries. Branches.—In the interval between the adjacent transverse processes each lumbar artery gives off a posterior ramus which is continued backward between the trans- verse processes and is distributed to the muscles and skin of the back; it furnishes a spinal branch which enters the vertebral canal and is distributed in a manner similar to the spinal branches of the posterior rami of the intercostal arteries (page 601). Muscular branches are supplied from each lumbar artery and from its posterior ramus to the neighboring muscles. THE COMMON ILIAC ARTERIES 613 The middle sacral artery (a. sacralis media) (Fig. 531) is a small vessel, which arises from the back of the aorta, a little above its bifurcation. It descends in the middle line in front of the fourth and fifth lumbar vertebrae, the sacrum and coccyx, and ends in the glomus coccygeUm (coccygeal gland). From it, minute branches are said to pass to the posterior surface of the rectum. On the last lumbar vertebra it anastomoses with the lumbar branch of the iliolumbar artery; in front of the sacrum it anastomoses with the lateral sacral arteries, and sends offsets into the anterior sacral foramina. It is crossed by the left common iliac Vein, and is accompanied by a pair of venae comitantes; these unite to form a single vessel, which opens into the left common iliac vein. Middle sacral Sup. hemorrhoidal Fio. 539.—The arteries of the pelvis. THE COMMON ILIAC ARTERIES (AA. ILIAC.® COMMUNES) (Figs. 531, 539) The abdominal aorta divides, on the left side of the body of the fourth lumbar vertebra, into the two common iliac arteries. Each is about 5 cm. in length. Ihey diverge from the termination of the aorta, pass downward and lateralward, and divide, opposite the intervertebral fibrocartilage between the last lumbar vertebra and the sacrum, into two branches, the external iliac and hypogastric arteries, the former supplies the lower extremity; the latter, the viscera and parietes of the pelvis. 614 ANGIOLOGY The right common iliac artery (Fig. 589) is somewhat longer than the left, and passes more obliquely across the body of the last lumbar vertebra. In front of it are the peritoneum, the small intestines, branches of the sympathetic nerves, and, at its point of division, the ureter. Behind, it is separated from the bodies of the fourth and fifth lumbar vertebrae, and the intervening fibrocartilage, by the terminations of the two common iliac veins and the commencement of the inferior vena cava. Laterally, it is in relation, above, with the inferior vena cava and the right common iliac vein; and, below, with the Psoas major. Medial to it, above, is the left common iliac vein. The left common iliac artery is in relation, in front, with the peritoneum, the small intestines, branches of the sympathetic nerves, and the superior hemorrhoidal artery; and is crossed at its point of bifurcation by the ureter. It rests on the bodies of the fourth and fifth lumbar vertebrae, and the intervening fibrocartilage. The left common iliac vein lies partly medial to, and partly behind the artery; laterally, the artery is in relation with the Psoas major. Branches.—The common iliac arteries give off small branches to the peritoneum, Psoas major, ureters, and the surrounding areolar tissue, and occasionally give origin to the iliolumbar, or accessory renal arteries. Peculiarities.—The point of origin varies according to the bifurcation of the aorta. In three- fourths of a large number of cases, the aorta bifurcated either upon the fourth lumbar vertebra, or upon the fibrocartilage between it and the fifth; the bifurcation being, in one case out of nine, below, and in one out of eleven, above this point. In about 80 per cent, of the cases the aorta bifurcated within 1.25 cm. above or below the level of the crest of the ilium; more frequently below than above. The point of division is subject to great variety. In two-thirds of a large number of cases it was between the last lumbar vertebra and the upper border of the sacrum; being above that point in one case out of eight, and below it in one case out of six. The left common iliac artery divides lower down more frequently than the right. The relative lengths, also, of the two common iliac arteries vary. The right common iliac was the longer in sixty-three cases; the left in fifty-two; while they were equal in fifty-three. The 'ength of the arteries varied, in five-sevenths of the cases examined, from 3.5 to 7.5 cm.; in about half of the remaining cases the artery was longer, and in the other half, shorter; the minimum length being less than 1.25 cm., the maximum, 11 cm. In rare instances, the right common iliac has been found wanting, the external iliac and hypogastric arising directly from the aorta. Collateral Circulation.—The principal agents in carrying on the collateral circulation after the application of a ligature to the common iliac are: the anastomoses of the hemorrhoidal branches of the hypogastric with the superior hemorrhoidal from the inferior mesenteric; of the uterine, ovarian, and vesical arteries of the opposite sides; of the lateral sacral with the middle sacral artery; of the inferior epigastric with the internal mammary, inferior intercostal, and lumbar arteries; of the deep iliac circumflex with the lumbar arteries; of the iliolumbar with the last lumbar artery; of the obturator artery, by means of its pubic branch, with the vessel of the opposite side and with the inferior epigastric. The Hypogastric Artery (A. Hypogastrica; Internal Iliac Artery) (Fig. 539). The hypogastric artery supplies the walls and viscera of the pelvis, the buttock, the generative organs, and the medial side of the thigh. It is a short, thick vessel, smaller than the external iliac, and about 4 cm. in length. It arises at the bifur- cation of the common iliac, opposite the lumbosacral articulation, and, passing downward to the upper margin of the greater sciatic foramen, divides into two large trunks, an anterior and a posterior. Relations.—It is in relation in front with the ureter; behind, with the internal iliac vein, the lumbosacral trunk, and the Piriformis muscle; laterally, near its origin, with the external iliac vein, which lies between it and the Psoas major muscle; lower down, with the obturator nerve. In the fetus, the hypogastric artery is twice as large as the external iliac, and is the direct continuation of the common iliac. It ascends along the side of the bladder, and runs upward on the back of the anterior wall of the abdomen to the umbilicus, converging toward its fellow of the opposite side. Having passed through THE HYPOGASTRIC ARTERY 615 the umbilical opening, the two arteries, now termed umbilical, enter the umbilical cord, where they are coiled around the umbilical vein, and ultimately ramify in the placenta. At birth, when the placental circulation ceases, the pelvic portion only of the artery remains patent and constitutes the hypogastric and the first part of the superior vesical artery of the adult; the remainder of the vessel is converted into a solid fibrous cord, the lateral umbilical ligament (obliterated hypogastric artery) which extends from the pelvis to the umbilicus. Peculiarities as Regards Length.—In two-thirds of a large number of cases, the length of the hypogastric varied between 2.25 and 3.4 cm.; in the remaining third it was more frequently longer than shorter, the maximum length being about 7 cm. the minimum about 1 cm. The lengths of the common iliac and hypogastric arteries bear an inverse proportion to each other, the hypogastric artery being long when the common iliac is short, and vice versa. As Regards its Place of Division.—The place of division of the hypogastric varies between the upper margin of the sacrum and the upper border of the greater sciatic foramen. The right and left hypogastric arteries in a series of cases often differed in length, but neither seemed constantly to exceed the other. Collateral Circulation.—The circulation after ligature of the hypogastric artery is carried on by the anastomoses of the uterine and ovarian arteries; of the vesical arteries of the two sides; of the hemorrhoidal branches of the hypogastric with those from the inferior mesenteric; of the obturator artery, by means of its pubic branch, with the vessel of the opposite side, and with the inferior epigastric and medial femoral circumflex; of the circumflex and perforating branches of the profunda femoriswith the inferior gluteal; of the superior gluteal with the posterior branches of the lateral sacral arteries; of the iliolumbar with the last lumbar; of the lateral sacral with the middle sacral; and of the iliac circumflex with the iliolumbar and superior gluteal.1 Branches.—The branches of the hypogastric artery are: From the Anterior Trunk. Superior Vesical. Middle Vesical. Inferior Vesical. Middle Hemorrhoidal. Obturator. Internal Pudendal. Inferior Gluteal. From the Posterior Trunk. Iliolumbar. Lateral Sacral. Superior Gluteal. Uterine Vaginal -In the Female. The superior vesical artery {a. vesicalis superior) supplies numerous branches to the upper part of the bladder. From one of these a slender vessel, the artery to the ductus deferens, takes origin and accompanies the duct in its course to the testis, where it anastomoses with the internal spermatic artery. Other branches supply the ureter. The first part of the superior vesical artery represents the terminal section of the pervious portion of the fetal hypogastric artery. The middle vesical artery (a. vesicalis medialis), usually a branch of the superior, is distributed to the fundus of the bladder and the vesiculse seminales. The inferior vesical artery (a. vesicalis inferior) frequently arises in common with the middle hemorrhoidal, and is distributed to the fundus of the bladder, the prostate, and the vesiculse seminales. The branches to the prostate communicate with the corresponding vessels of the opposite side. The middle hemorrhoidal artery (a. hcemorrhoidalis media) usually arises with the preceding vessel. It is distributed to the rectum, anastomosing with the inferior vesical and with the superior and inferior hemorrhoidal arteries. It gives offsets to the vesiculse seminales and prostate. The uterine artery (a. uterina) (Fig. 540) springs from the anterior division of 1 For a description of a case in which Owen made a dissection ten years after ligature of the hypogastric artery, see Med.-Chir. Trans., vol. xvi. 616 ANGIOLOGY the hypogastric and runs medial ward on the Levator ani and toward the cervix uteri; about 2 cm. from the cervix it crosses above and in front of the ureter, to which it supplies a small branch. Reaching the side of the uterus it ascends in a tortuous manner between the two layers of the broad ligament to the junction of the uterine tube and uterus. It then runs lateral ward toward the hilus of the ovary, and ends by joining with the ovarian artery. It supplies branches to the cervix uteri and others which descend on the vagina; the latter anastomose with branches of the vaginal arteries and form with them two median longitudinal vessels—the azygos arteries of the vagina—one of which runs down in front of and the other behind the vagina. It supplies numerous branches to the body of the uterus, and from its terminal portion twigs are distributed to the uterine tube and the round ligament of the uterus. The vaginal artery (a. vaginalis) usually corresponds to the inferior vesical in the male; it descends upon the vagina, supplying its mucous membrane, and sends branches to the bulb of the vestibule, the fundus of the bladder, and the contiguous part of the rectum. It assists in forming the azygos arteries of the vagina, and is frequently represented by two or three branches. Branches to fundus Branches to tiibe Branch to round ligament Round ligament of uterus ' Uterine artery ■ Arteries of cervix Vaginal arteries Fig. 540.—The arteries of the internal organs of generation of the female, seen from behind. (After Hyrtl.) The obturator artery (a. obturatoria) passes forward and downward on the lateral wall of the pelvis, to the upper part of the obturator foramen, and, escaping from the pelvic cavity through the obturator canal, it divides into an anterior and a posterior branch. In the pelvic cavity this vessel is in relation, laterally, with the obturator fascia; medially, with the ureter, ductus deferens, and peritoneum; while a little below it is the obturator nerve. Branches.—Inside the pelvis the obturator artery gives off iliac branches to the iliac fossa, which supply the bone and the Iliacus, and anastomose with the ilio- lumbar artery; a vesical branch, which runs backward to supply the bladder; and a pubic branch, which is given off from the vessel just before it leaves the pelvic cavity. The pubic branch ascends upon the back of the pubis, communicating THE HYPOGASTRIC ARTERY 617 with the corresponding vessel of the opposite side, and with the inferior epigastric artery. Outside the pelvis, the obturator artery divides at the upper margin of the obtur- ator foramen, into an anterior and a posterior branch which encircle the foramen under cover of the Obturator externus. The anterior branch runs forward on the outer surface of the obturator mem- brane and then curves downward along the anterior margin of the foramen. It distributes branches to the Obturator externus, Pectineus, Adductores, and Gracilis, and anastomoses with the posterior branch and with the medial femoral circum- flex artery. The posterior branch follows the posterior margin of the foramen and turns for- ward on the inferior ramus of the ischium, where it anastomoses with the anterior branch. It gives twigs to the muscles attached to the ischial tuberosity and anas- tomoses with the inferior gluteal. It also supplies an articular branch which enters the hip-joint through the acetabular notch, ramifies in the fat at the bottom of the acetabulum’ and sends a twig along the ligamentum teres to the head of the femur. Peculiarities.—The obturator artery sometimes arises from the main stem or from the posterior trunk of the hypogastric, or it may spring from the superior gluteal artery; occasionally it arises from the external iliac. In about two out of every seven cases it springs from the inferior epi- gastric and descends almost vertically to the upper part of the obturator foramen. The artery in this course usually lies in contact with the external iliac vein, and on the lateral side of the femoral ring (Fig. 541 A); in such cases it would not be endangered in the operation for strangulated femoral hernia. Occasionally, however, it curves along the free margin of the lacunar ligament (Fig. 541 i?), and if in such circumstances a femoral hernia occurred, the vessel would almost completely encircle the neck of the hernial sac, and would be in great danger of being wounded if an operation were performed for strangulation. The internal pudendal artery (a. pudenda interna; internal pudic artery) is the smaller of the two terminal branches of the anterior trunk of the hypogastric, and supplies the external organs of generation. Though the course of the artery is the same in the two sexes, the vessel is smaller in the female than in the male, and the distribution of its branches somewhat different. The description of its arrange- ment in the male will first be given, and subsequently the differences which it presents in the female will be mentioned. The internal pudendal artery in the male passes downward and outward to the lower border of the greater sciatic foramen, and emerges from the pelvis between the Piriformis and Coccygeus; it then crosses the ischial spine, and enters the peri- neum through the lesser sciatic foramen. The artery now crosses the Obturator internus, along the lateral wall of the ischiorectal fossa, being situated about 4 cm. above the lower margin of the ischial tuberosity. It gradually approaches the margin of the inferior ramus of the ischium and passes forward between the two layers of the fascia of the urogenital diaphragm; it then runs forward along the medial margin of the inferior ramus of the pubis, and about 1.25 cm. behind the pubic arcuate ligament it pierces the inferior fascia of the urogenital diaphragm and divides into the dorsal and deep arteries of the penis. Fig. 541.—Variations in origin and course of obturator artery 618 ANGIOLOGY Relations.—Within the pelvis, it lies in front of the Piriformis muscle, the sacral plexus of nerves, and the inferior gluteal artery. As it crosses the ischial spine, it is covered by the Glutaeus maximus and overlapped by the sacrotuberous ligament. Here the pudendal nerve lies to the medial side and the nerve to the Obturator internus to the lateral side of the vessel. In the peri- neum it lies on the lateral wall of the ischiorectal fossa, in a canal (Alcock’s canal) formed by the splitting of the obturator fascia. It is accompanied by a pair of vena) comitantes and the pudendal nerve. Peculiarities.—The internal pudendal artery is sometimes smaller than usual, or fails to give off one or two of its usual branches; in such cases the deficiency is supplied by branches derived from an additional vessel, the accessory pudendal, which generally arises from the internal pudendal artery before its exit from the greater sciatic foramen. It passes forward along the lower part of the bladder and across the side of the prostate to the root of the penis, where it perforates the urogenital diaphragm, and gives off the branches usually derived from the internal pudendal artery. The deficiency most frequently met with is that in which the internal pudendal ends as the artery of the urethral bulb, the dorsal and deep arteries of the penis being derived from the accessory pudendal. The internal pudendal artery may also end as the perineal, the artery of the urethral bulb being derived, with the other two branches, from the accessory vessel. Occasionally the accessory pudendal artery is derived from one of the other branches of the hypogastric artery, most frequently the inferior vesical or the obturator. Branches.—The branches of the internal pudendal artery (Figs. 542, 543) are: Muscular. Inferior Hemorrhoidal. Perineal. Artery of the Urethral Bulb. Urethral. Deep Artery of the Penis. Dorsal Artery of the Penis. Posterior scrotal arteries Sacrot.uberous ligament Posterior scrotal nerves Pudendal nerve Internal pudendal artery Fig. 542.—The superficial branches of the internal pudendal artery. The Muscular Branches consist of two sets: one given off in the pelvis; the other, as the vessel crosses the ischial spine. The former consists of several small offsets which supply the Levator ani, the Obturator interims, the Piriformis, and the Coccygeus. The branches given off outside the pelvis are distributed to the adjacent parts of the Glutieus maximus and external rotator muscles. They anastomose with branches of the inferior gluteal artery. THE HYPOGASTRIC ARTERY 619 The Inferior Hemorrhoidal Artery (a. hcemorrhoidalis inferior) arises from the internal pudendal as it passes above the ischial tuberosity. Piercing the wall of Alcock’s canal it divides into two or three branches which cross the ischiorectal fossa, and are distributed to the muscles and integument of the anal region, and send offshoots around the lower edge of the Glutseus maximus to the skin of the buttock. They anastomose w-ith the corresponding vessels of the opposite side, with the superior and middle hemorrhoidal, and with the perineal artery. The Perineal Artery (a. perinei; superficial perineal artery) arises from the internal pudendal, in front of the preceding branches, and turns upward, crossing either over or under the Trans versus perimei superficialis, and runs forward, parallel to the pubic arch, in the interspace between the Bulbocavernosus and Ischiocaver- nosus, both of which it supplies, and finally divides into several posterior scrotal branches which are distributed to the skin and dartos tunic of the scrotum. As it crosses the Transversus perintei superficialis it gives off the transverse perineal artery which runs transversely on the cutaneous surface of the muscle, and anasto- moses with the corresponding vessel of the opposite side and with the perineal and inferior hemorrhoidal arteries. It supplies the Transversus perinsei super- ficialis and the structures between the anus and the urethral bulb. Deep artei~y of penis Dorsal artery of penis Artery of urethral bulb Internal pudendal artery Bulbo-urethral gland Fig. 543.—The deeper branches of the internal pudendal artery. The Artery of the Urethral Bulb (a. bulbi urethrai) is a short vessel of large caliber which arises from the internal pudendal between the twro layers of fascia of the uro- genital diaphragm; it passes medialward, pierces the inferior fascia of the urogenital diaphragm, and gives off branches which ramify in the bulb of the urethra and in the posterior part of the corpus cavernosum urethrse. It gives off a small branch to the bulbo-urethral gland. The Urethral Artery (a. urethralis) arises a short distance in front of the artery of the urethral bulb. It runs forward and medialwrard, pierces the inferior fascia of the urogenital diaphragm and enters the corpus cavernosum urethrae, in which it is continued forward to the glans penis. 620 ANGIOLOGY The Deep Artery of the Penis (a. profunda penis; artery to the corpus cavernosum), one of the terminal branches of the internal pudendal, arises from that vessel while it is situated between the twro fasciae of the urogenital diaphragm; it pierces the inferior fascia, and, entering the crus penis obliquely, runs forward in the center of the corpus cavernosum penis, to which its branches are distributed. The Dorsal Artery of the Penis (a. dorsalis penis) ascends between the crus penis and the pubic symphysis, and, piercing the inferior fascia of the urogenital dia- phragm, passes between the two layers of the suspensory ligament of the penis, and runs forward on the dorsum of the penis to the glans, where it divides into two branches, which supply the glans and prepuce. On the penis, it lies between the dorsal nerve and deep dorsal vein, the former being on its lateral side. It supplies the integument and fibrous sheath of the corpus cavernosum penis, sending branches through the sheath to anastomose with the preceding vessel. The internal pudendal artery in the female is smaller than in the male. Its origin and course are similar, and there is considerable analogy in the distribution of its branches. The perineal artery supplies the labia pudendi; the artery of the bulb supplies the bulbus vestibuli and the erectile tissue of the vagina; the deep artery of the clitoris supplies the corpus cavernosum clitoridis; and the dorsal artery of the clitoris supplies the dorsum of that organ, and ends in the glans and prepuce of the clitoris. The inferior gluteal artery (a. glutcea inferior; sciatic artery) (Fig. 544), the larger of the two terminal branches of the anterior trunk of the hypogastric, is distributed chiefly to the buttock and back of the thigh. It passes down on the sacral plexus of nerves and the Piriformis, behind the internal pudendal artery, to the lower part of the greater sciatic foramen, through wdiich it escapes from the pelvis between the Piriformis and Coccygeus. It then descends in the interval between the greater trochanter of the femur and tuberosity of the ischium, accom- panied by the sciatic and posterior femoral cutaneous nerves, and covered by the Glutseus maximus, and is continued down the back of the thigh, supplying the skin, and anastomosing with branches of the perforating arteries. Inside the pelvis it distributes branches to the Piriformis, Coccygeus, and Levator ani; some branches which supply the fat around the rectum, and occasionally take the place of the middle hemorrhoidal artery; and vesical branches to the fundus of the bladder, vesiculse seminales, and prostate. Outside the pelvis it gives off the following branches: Muscular. Coccygeal. Comitans Nervi Ischiadici. Anastomotic. Articular. Cutaneous. The Muscular Branches supply the Glutseus maximus, anastomosing with the superior gluteal artery in the substance of the muscle; the external rotators, anastomosing with the internal pudendal artery; and the muscles attached to the tuberosity of the ischium, anastomosing with the posterior branch of the obturator and the medial femoral circumflex arteries. The Coccygeal Branches run medialward, pierce the sacrotuberous ligament, and supply the Glutaius maximus, the integument, and other structures on the back of the coccyx. * The Arteria Comitans Nervi Ischiadici is a long, slender vessel, which accom- panies the sciatic nerve for a short distance; it then penetrates it, and runs in its substance to the lower part of the thigh. The Anastomotic is directed downward across the external rotators, and assists in forming the so-called crucial anastomosis by joining with the first perforating and medial and lateral femoral circumflex arteries. The Articular Branch, generally derived from the anastomotic, is distributed to the capsule of the hip-joint. THE HYPOGASTRIC ARTERY 621 The Cutaneous Branches are distributed to the skin of the buttock and back of the thigh. The iliolumbar artery (a. iliolumbalis) a branch of the posterior trunk of the hypogastric, turns upward behind the obturator nerve and the external iliac vessels, to the medial border of the Psoas major, behind which it divides into a lumbar and an iliac branch. The Lumbar Branch (ramus lumbalis) supplies the Psoas major and Quadratus lumborum, anastomoses with the last lumbar artery, and sends a small spinal branch through the intervertebral foramen between the last lumbar vertebra and the sacrum, into the vertebral canal, to supply the cauda equina. The Iliac Branch (ramus iliacus) descends to supply the Iliacus; some offsets, running between the muscle and the bone, anastomose with the iliac branches of the ob- turator; one of these enters an oblique canal to supply the bone, while others run along the crest of the ilium, distributing branches to the gluteal and abdominal muscles, and anastomosing in their course with the superior gluteal, iliac circumflex, and lateral femoral circumflex arteries. The lateral sacral arteries (act. sacrales laterales) (Fig. 539) arise from the posterior division of the hypogastric; there are usually two, a superior and an inferior. The superior, of large size, passes mediahvard, and, after anastomos- ing with branches from the middle sacral, enters the first or second anterior sacral foramen, supplies branches to the contents of the sacral canal, and, escaping by the corresponding posterior sacral fora- men, is distributed to the skin and muscles on the dorsum of the sacrum, anastomosing with the superior gluteal. The inferior runs obliquely across the front of the Piriformis and the sacral nerves to the medial side of the anterior sacral foramina, de- scends on the front of the sacrum, and anastomoses over the coccyx with the middle sacral and opposite lateral sacral artery. In its course it gives off branches, which enter the anterior sacral foramina; these, after supplying the contents of the sacral canal, escapes by the posterior-sacral foramina, and are distributed to the muscles and skm on the dorsal surface of the sacrum, anastomosing with the gluteal arteiies. Termination of medial femoral circumflex First perforating Second perforating . Third perforating Termination of prof unda Superior muscular Lateral superior - genicular Medial superior genicular Sural Fio. 544.—The arteries of the gluteal and posterior femoral regions. 622 ANGIOLOGY The superior gluteal artery (a. glutcea superior; gluteal artery) (Fig. 544) is the largest branch of the hypogastric, and appears to be the continuation of the pos- terior division of that vessel. It is a short artery which runs backward between the lumbosacral trunk and the first sacral nerve, and, passing out of the pelvis above the upper border of the Piriformis, immediately divides into a superficial and a deep branch. Within the pelvis it gives off a few branches to the Iliacus, Piriformis, and Obturator internus, and just previous to quitting that cavity, a nutrient artery which enters the ilium. The superficial branch enters the deep surface of the Glutaeus maximus, and divides into numerous branches, some of which supply the muscle and anastomose with the inferior gluteal, while others perforate its tendinous origin, and supply the integument covering the posterior surface of the sacrum, anastomosing with the posterior branches of the lateral sacral arteries. The deep branch lies under the Glutaeus medius and almost immediately sub- divides into two. Of these, the superior division, continuing the original course of the vessel, passes along the upper border of the Glutaeus minimus to the anterior superior spine of the ilium, anastomosing with the deep iliac circumflex artery and the ascending branch of the lateral femoral circumflex artery. The inferior division crosses the Glutaeus minimus obliquely to the greater trochanter, distributing branches to the Glutaei and anastomoses with the lateral femoral circumflex artery. Some branches pierce the Glutaeus minimus and supply the hip-joint. The External Iliac Artery (A. Iliaca Externa) (Fig. 539). The external iliac artery is larger than the hypogastric, and passes obliquely downward and lateralward along the medial border of the Psoas major, from the bifurcation of the common iliac to a point beneath the inguinal ligament, midway between the anterior superior spine of the ilium and the symphysis pubis, where it enters the thigh and becomes the femoral artery. Relations.—In front and medially, the artery is in relation with the peritoneum, subperitoneal areolar tissue, the termination of the ileum and frequently the vermiform process on the right side, and the sigmoid colon on the left, and a thin layer of fascia, derived from the iliac fascia, which surrounds the artery and vein. At its origin it is crossed by the ovarian vessels in the female, and occasionally by the ureter. The internal spermatic vessels lie for some distance upon it near its termination, and it is crossed in this situation by the external spermatic branch of the genitofemoral nerve and the deep iliac circumflex vein; the ductus deferens in the male, and the round ligament of the uterus in the female, curve down across its medial side. Behind, it is in relation with the medial border of the Psoas major, from which it is separated by the iliac fascia. At the upper part of its course, the external iliac vein lies partly behind it, but lower down lies entirely to its medial side. Laterally, it rests against the Psoas major, from which it is separated by the iliac fascia. Numerous lymphatic vessels and lymph glands lie on the front and on the medial side of the vessel. Collateral Circulation.—The principal anastomoses in carrying on the collateral circulation, after the application of a ligature to the external iliac, are: the iliolumbar with the iliac circum- flex; the superior gluteal with the lateral femoral circumflex; the obturator with the medial femoral circumflex; the inferior gluteal with the first perforating and circumflex branches of the profunda artery; and the internal pudendal with the external pudendal. When the obturator arises from the inferior epigastric, it is supplied with blood by branches, from either the hypogastric, the lateral sacral, or the internal pudendal. The inferior epigastric receives its supply from the internal mammary and lower intercostal arteries, and from the hypogastric by the anastomoses of its branches with the obturator.1 Branches.—Besides several small branches to the Psoas major and the neighbor- ing lymph glands, the external iliac gives off two branches of considerable size: Inferior Epigastric. Deep Iliac Circumflex. 1 Sir Astley Cooper describes in Guy’s Hospital Reports, vol. i, the dissection of a limb eighteen years after successful ligature of the external iliac artery. THE FEMORAL ARTERY 623 The inferior epigastric artery (a. epigastrica inferior; deep epigastric artery) (Fig. 547) arises from the external iliac, immediately above the inguinal ligament. It curves forward in the subperitoneal tissue, and then ascends obliquely along the medial margin of the abdominal inguinal ring; continuing its course upward, it pierces the transversalis fascia, and, passing in front of the linea semicircularis, ascends between the Rectus abdominis and the posterior lamella of its sheath. It finally divides into numerous branches, which anastomose, above the umbilicus, with the superior epigastric branch of the internal mammary and with the lower intercostal arteries (Fig. 522). As the inferior epigastric artery passes obliquely upward from its origin it lies along the lower and medial margins of the abdominal inguinal ring, and behind the commencement of the spermatic cord. The ductus deferens, as it leaves the spermatic cord in the male, and the round ligament of the uterus in the female, winds around the lateral and posterior aspects of the artery. Branches.—The branches of the vessel are: the external spermatic artery {cremasteric artery), which accompanies the spermatic cord, and supplies the Cremaster and other coverings of the cord, anastomosing with the internal spermatic artery (in the female it is very small and accompanies the round ligament); a pubic branch which runs along the inguinal ligament, and then descends along the medial margin of the femoral ring to the back of the pubis, and there anastomoses with the pubic branch of the obturator artery; muscular branches, some of which are distributed to the abdominal muscles and peritoneum, anastomosing with the iliac circumflex and lumbar arteries; branches which perforate the tendon of the Obliquus externus, and supply the integument, anastomosing with branches of the super- ficial epigastric. Peculiarities.—The origin of the inferior epigastric may take place from any part of the external iliac between the inguinal ligament and a point 6 cm. above it; or it may arise below this ligament, from the femoral. It frequently springs from the external iliac, by a common trunk with the obturator. Sometimes it arises from the obturator, the latter vessel being furnished by the hypogastric, or it may be formed of two branches, one derived from the external iliac, the other from the hypogastric. The deep iliac circumflex artery (a. circumflexa ilium profunda) arises from the lateral aspect of the external iliac nearly opposite the inferior epigastric artery. It ascends obliquely lateralward behind the inguinal ligament, contained in a fibrous sheath formed by the junction of the transversalis fascia and iliac fascia, to the anterior superior iliac spine, where it anastomoses with the ascending branch of the lateral femoral circumflex artery. It then pierces the transversalis fascia and passes along the inner lip of the crest of the ilium to about its middle, where it perforates the Transversus, and runs backward between that muscle and the Obliquus internus, to anastomose with the iliolumbar and superior gluteal arteries. Opposite the anterior superior spine of the ilium it gives off a large branch, which ascends between the Obliquus internus and Transversus muscles, supplying them, and anastomosing with the lumbar and inferior epigastric arteries. THE ARTERIES OF THE LOWER EXTREMITY. The artery which supplies the greater part of the lower extremity is the direct continuation of the external iliac. It runs as a single trunk from the inguinal ligament to the lower border of the Popliteus, where it divides into two branches, the anterior and posterior tibial. The upper part of the main trunk is named the femoral, the lower part the popliteal. THE FEMORAL ARTERY (A. FEMORALIS) (Figs. 549, 550). The femoral artery begins immediately behind the inguinal ligament, midway between the anterior superior spine of the ilium and the symphysis pubis, and 624 ANGIOLOGY Fig. 545.—Femoral sheath laid open to show its three compartments. Lai. fem. cutan. nerve Femoral nerve Lumbo-tnguinal nerve Femoral artery Femoral sheath Femoral vein Femoral ring Lacunar ligament Fig. 546.—Structures passing behind the inguinal ligament. THE FEMORAL ARTERY 625 passes down the front and medial side of the thigh. It ends at the junction of the middle with the lower third of the thigh, where it passes through an opening in the Adductor magnus to become the popliteal artery. The vessel, at the upper part of the thigh, lies in front of the hip-joint; in the lower part of its course it lies to the medial side of the body of the femur, and between these two parts, where it crosses the angle between the head and body, the vessel is some distance from the bone. The first 4 cm. of the vessel is enclosed, together with the femoral vein, in a fibrous sheath—the femoral sheath. In the upper third of the thigh the femoral artery is contained in the femoral triangle (Scarpa’s triangle), and in the middle third of the thigh, in the adductor canal (Hunter’s canal). The femoral sheath (crural sheath) (Figs. 545, 546) is formed by a prolongation downward, behind the inguinal ligament, of the fascise which line the abdomen, the transversalis fascia being continued down in front of the femoral vessels and the iliac fascia behind them. The sheath assumes the form of a short funnel, the wide end of which is directed upward, while the lower, narrow end fuses with the Fig. 547—The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side. fascial investment of the vessels, about 4 cm. below the inguinal ligament. It is strengthened in front by a band termed the deep crural arch (page 419). T he lateral wall of the sheath is vertical and is perforated by the lumboinguinal ne^"e’ the medial wall is directed obliquely downward and lateralward, and is pierced by the great saphenous vein and by some lymphatic vessels. Ihe sheath is divided by two vertical partitions which stretch between its anterior and posterior walls. The lateral compartment contains the femoral artery, and the intermediate t e femoral vein, while the medial and smallest compartment is named the femora canal, and contains some lymphatic vessels and a lymph gland imbedded m a sma amount of areolar tissue. The femoral canal is conical and measures about 1. 5 cm. in length. Its base, directed upward and named the femoral ring, is o\a m form, its long diameter being directed transversely and measuring about 1.25 cm. The femoral ring (Figs. 546, 547) is bounded in front by the inguinal ligament, behind by the Pectineus covered by the pectineal fascia, medially by the crescentic base of the lacunar ligament, and laterally by the fibrous septum on the media side of the femoral vein. The spermatic cord in the male and the round ligament 626 ANGIOLOGY of the uterus in the female lie immediately above the anterior margin of the ring, while the inferior epigastric vessels are close to its upper and lateral angle. The femoral ring is closed by a somewhat condensed portion of the extraperitoneal fatty tissue, named the septum femorale (crural septum), the abdominal surface of which supports a small lymph gland and is covered by the parietal layer of the peritoneum. The septum femorale is pierced by numerous lymphatic vessels passing from the deep inguinal to the external iliac lymph glands, and the parietal peritoneum immediately above it presents a slight depression named the femoral fossa. SUPERFICIAL CI R- _ CUMFLEX ILIAC SUPERFICIAL- EPIGASTRIC SUPERFICIAL EXTERNAL "PUDIC COMMON FEMORAL' DEEP EXTERNAL PUDIC INTERNAL CIRCUM FLEX EXTERNAL CIRCUMFLEX FEMORAL PROFUNDA DESCENDING RAMUS OF EXTERNAL CIRCUMFLEX FIRST PERFORATING SUPERFICIAL "FEMORAL SECOND PERFORATING THIRD 'PERFORATING ANASTOMOTICA MAGNA SUPERIOR INTERNAL ARTICU LAR -BRANCH OF i POPLITEAL SUPERIOR EXTER- NAL ARTICULAR BRANCH OF* POPLITEAL | Fig. 518.—Scheme of the femoral artery. The femoral triangle (trigonum femorale; Scarpa’s triangle) (Fig. 549) corre- sponds to the depression seen immediately below the fold of the groin. Its apex is directed downward, and the sides are formed laterally by the medial margin of the Sartorius, medially by the medial margin of the Adductor longus, and above by the inguinal ligament. The floor of the space is formed from its lateral to its medial side by the Iliacus, Psoas major, Pectineus, in some cases a small part of THE FEMORAL ARTERY 627 the Adductor brevis, and the Adductor longus; and it is divided into two nearly equal parts by the femoral vessels, which extend from near the middle of its base to its apex: the artery giving off in this situation its superficial and profunda branches, the vein receiving the deep femoral and great saphenous tributaries. On the lateral side of the femoral artery is the femoral nerve dividing into its branches. Besides the vessels and nerves, this space contains some fat and lymphatics. The adductor canal (canalis adductorius; Hunter’s canal) is an aponeurotic tunnel in the middle third of the thigh, extending from the apex of the femoral triangle to the opening in the Adductor magnus. It is bounded, in front and later- ally, by the Vastus medialis; behind by the Adductores longus and magnus; and is covered in by a strong aponeurosis which extends from the Vastus medialis, across the femoral vessels to the Adductores longus and magnus; lying on the aponeurosis is the Sartorius muscle. The canal contains the femoral artery and vein, the saphenous nerve, and the nerve to the Vastus medialis. Superficial iliac circumflex vessels Femoral nerve Superficial epigastric vessels Superficial external pudendal vessels Deep external pudendal vessels Great saphenous vein Fig. 549.—The left femoral triangle. Relations of the Femoral Artery—In the femoral triangle (Fig. 549) the artery is superficial. In front of it are the skin and superficial fascia, the superficial subinguinal lymph glands, the superficial iliac circumflex vein, the superficial layer of the fascia lata and the anterior par o the femoral sheath. The lumboinguinal nerve courses for a short distance within the lateral compartment of the femoral sheath, and lies at first in front and then lateral to the artery. car the apex of the femoral triangle the medial branch of the anterior femoral cutaneous nerve crosses the artery from its lateral to its medial side. 628 ANGIOLOGY Behind the artery are the posterior part of the femoral sheath, the pectineal fascia, the medial part of the tendon of the Psoas major, the Pectineus and the Adductor longus. The artery is separated from the capsule of the hip-joint by the tendon of the Psoas major, from the Pectineus by the femoral vein and profunda vessels, and from the Adductor longus by the femoral vein. The nerve to the Pectineus passes medialward behind the artery. On the lateral side of the artery, but separated from it by some fibers of the Psoas major, is the femoral nerve. The femoral vein is on the medial side of the upper part of the artery, but is behind the vessel in the lower part of the femoral triangle. Scrotum - Saphenous nerve Highest genicular Lateral sup. genicular Musculo-arlicular hr. of highest genicular Medial sup. genicular Lateral inf. genicular Medial inf. genicular Anterior tibial recurrent Fig. 550.—The femoral artery. In the adductor canal (Fig. 550) the femoral artery is more deeply situated, being covered by the integument, the superficial and deep fasciae, the Sartorius and the fibrous roof of the canal; the saphenous nerve crosses from its lateral to its medial side. Behind the artery are the Adduc- THE FEMORAL ARTERY 629 tores longus and magnus; in front and lateral to it is the Vastus medialis. The femoral vein lies posterior to the upper part, and lateral to the lower part of the artery. Peculiarities.—Several cases are recorded in which the femoral artery divided into two trunks below the origin of the profunda, and became reunited near the opening in the Adductor magnus, so as to form a single popliteal artery. One occurred in a patient who was operated upon for popliteal aneurism. A few cases have been recorded in which the femoral artery was absent, its place being supplied by the inferior gluteal artery which accompanied the sciatic nerve to the popliteal fossa. The external iliac in these cases was small, and terminated in the profunda. The femoral vein is occasionally placed along the medial side of the artery throughout the entire extent of the femoral trangle; or it may be split so that a large vein is placed on either side of the artery for a greater or lesser distance. Collateral Circulation.—After ligature of the femoral artery, the main channels for carrying on the circulation are the anastomoses between—(1) the superior and inferior gluteal branches of the hypogastric with the medial and lateral femoral circumflex and first perforating branches of the profunda femoris; (2) the obturator branch of the hypogastric with the medial femoral circumflex of the profunda; (3) the internal pudendal of the hypogastric with the superficial and deep external pudendal of the femoral; (4) the deep iliac circumflex of the external iliac with the lateral femoral circumflex of the profunda and the superficial iliac circumflex of the femoral, and (5) the inferior gluteal of the hypogastric with the perforating branches of the profunda. Branches.—The branches of the femoral artery are: Superficial Epigastric. Superficial Iliac Circumflex. Superficial External Pudendal. Deep External Pudendal. Muscular. Profunda Femoris. The superficial epigastric artery (a. epigastrica superficialis) arises from the front of the femoral artery about 1 cm. below the inguinal ligament, and, passing through the femoral sheath and the fascia cribrosa, turns upward in front of the inguinal ligament, and ascends between the two layers of the superficial fascia of the abdominal wall nearly as far as the umbilicus. It distributes branches to the superficial subinguinal lymph glands, the superficial fascia, and the integument; it anastomoses with branches of the inferior epigastric, and with its fellow of the opposite side. The superficial iliac circumflex artery (a. circumflexa ilium superficialis), the smallest of the cutaneous branches, arises close to the preceding, and, piercing the fascia lata, runs lateralward, parallel with the inguinal ligament, as far as the crest of the ilium; it divides into branches which supply the integument of the groin, the superficial fascia, and the superficial subinguinal lymph glands, anas- tomosing with the deep iliac circumflex, the superior gluteal and lateral femoral circumflex arteries. The superficial external pudendal artery (a. pudenda externa superdcialis; superficial external pudic artery) arises from the medial side of the femoral artery, close to the preceding vessels, and, after piercing the femoral sheath and fascia cribrosa, courses medialward, across the spermatic cord (or round ligament in the female), to be distributed to the integument on the lower part of the abdomen, the penis and scrotum in the male, and the labium majus in the female, anasto- mosing with branches of the internal pudendal. The deep external pudendal artery (a. pudenda externa profunda; deep external pudic artery), more deeply seated than the preceding, passes medialward. across the Pectineus and the Adductor longus muscles; it is covered by the fascia lata, which it pierces at the medial side of the thigh, and is distributed, in the male, to the integument of the scrotum and perineum, in the female to the labium majus, its branches anastomose with the scrotal (or labial) branches of the perineal artery. Muscular branches (rami musculares) are supplied by the femoral artery to the Sartorius, Vastus medialis, and Adductores. The profunda femoris artery (a. profunda femoris; deep femoral artery) (rig. 550) is a large vessel arising from the lateral and back part of the femoral artery, Highest Genicular. 630 ANGIOLOGY from 2 to 5 cm. below the inguinal ligament. At first it lies lateral to the femoral artery; it then runs behind it and the femoral vein to the medial side of the femur, and, passing downward behind the Adductor longus, ends at the lowTer third of the thigh in a small branch, wrhich pierces the Adductor magnus, and is distributed on the back of the thigh to the hamstring muscles. The terminal part of the pro- funda is sometimes named the fourth perforating artery. Relations.—Behind it, from above downward, are the Iliacus, Pectineus, Adductor brevis, and Adductor magnus. In front it is separated from the femoral artery by the femoral and pro- funda veins above and by the Adductor longus below. Laterally, the origin of the Vastus medialis intervenes between it and the femur. Peculiarities.—This vessel sometimes arises from the medial side, and, more rarely, from the back of the femoral artery; but a more important peculiarity, from a surgical point of view, is that relating to the height at which the vessel arises. In three-fourths of a large number of cases it arose from 2.25 to 5 cm. below the inguinal ligament; in a few cases the distance was less than 2.25 cm.; more rarely, opposite the ligament; and in one case above the inguinal ligament, from the external iliac. Occasionally the distance between the origin of the vessel and the inguinal ligament exceeds 5 cm. Branches.—The profunda gives off the following branches: Lateral Femoral Circumflex. Medial Femoral Circumflex. Perforating. Muscular. The Lateral Femoral Circumflex Artery (a. circumflexa femoris lateralis; external circumflex artery) arises from the lateral side of the profunda, passes horizontally between the divisions of the femoral nerve, and behind the Sartorius and Rectus femoris, and divides into ascending, transverse, and descending branches. The ascending branch passes upward, beneath the Tensor fasciae latae, to the lateral aspect of the hip, and anastomoses with the terminal branches of the superior gluteal and deep iliac circumflex arteries. The descending branch runs downward, behind the Rectus femoris, upon the Vastus lateralis, to which it gives offsets; one long branch descends in the muscle as far as the knee, and anastomoses with the superior lateral genicular branch of the popliteal artery. It is accompanied by the branch of the femoral nerve to the Vastus lateralis. The transverse branch, the smallest, passes laterahvard over the Vastus inter- medius, pierces the Vastus lateralis, and winds around the femur, just below the greater trochanter, anastomosing on the back of the thigh with the medial femoral circumflex, inferior gluteal, and first perforating arteries. The Medial Femoral Circumflex Artery (a. circumflexa femoris medialis; internal circumflex artery) arises from the medial and posterior aspect of the profunda, and winds around the medial side of the femur, passing first between the Pectineus and Psoas major, and then between the Obturator externus and the Adductor brevis. At the upper border of the Adductor brevis it gives off two branches: one is distributed to the Adductores, the Gracilis, and Obturator externus, and anastomoses with the obturator artery; the other descends beneath the Adductor brevis, to supply it and the Adductor magnus; the continuation of the vessel passes backward and divides into superficial, deep, and acetabular branches. The superficial branch appears between the Quadratus femoris and upper border of the Adductor magnus, and anastomoses wuth the inferior gluteal, lateral femoral circumflex, and first perforating arteries (crucial anastomosis). The deep branch runs obliquely upward upon the tendon of the Obturator externus and in front of the Quadratus femoris towrard the trochanteric fossa, where it anastomoses with twigs from the gluteal arteries. The acetabular branch arises opposite the acetabular notch and enters the hip-joint beneath the transverse ligament in com- pany with an articular branch from the obturator artery; it supplies the fat in the bottom of the acetabulum, and is continued along the round ligament to the head of the femur. THE POPLITEAL FOSSA 631 I he Perforating Arteries (Tig. 544), usually three in number, are so named because they perforate the tendon of the Adductor magnus to reach the back of the thigh, dhey pass backward close to the linea aspera of the femur under cover of small tendinous arches in the muscle. The first is given off above the Adductor brevis, the second in front of that muscle, and the third immediately below it. The first perforating artery (a. perforans prima) passes backward between the Pec- tineus and Adductor brevis (sometimes it perforates the latter); it then pierces the Adductor magnus close to the linea aspera. It gives branches to the Adductores brevis and magnus, Biceps femoris, and Glutseus maximus, and anastomoses with the inferior gluteal, medial and lateral femoral circumflex and second perforating arteries. The second perforating artery (a. perforans secunda), larger than the first, pierces the tendons of the Adductores brevis and magnus, and divides into ascending and descending branches, which supply the posterior femoral muscles, anasto- mosing with the first and third perforating. The second artery frequently arises in common with the first. The nutrient artery of the femur is usually given off from the second perforating artery; when two nutrient arteries exist, they usually spring from the first and third perforating vessels. The third perforating artery (a. perforans tertia) is given off below the Adductor brevis; it pierces the Adductor magnus, and divides into branches which supply the posterior femoral muscles; anastomosing above with the higher perforating arteries, and below with the terminal branches of the profunda and the muscular branches of the popliteal. The nutrient artery of the femur may arise from this branch. The termination of the profunda artery, already described, is sometimes termed the fourth perforating artery. Numerous muscular branches arise from the profunda; some of these end in the Adductores, others pierce the Adductor magnus, give branches to the hamstrings, and anastomose with the medial femoral circumflex artery and with the superior muscular branches of the popliteal. The highest genicular artery (a. genu suprema; anastomotica magna artery) (Fig. 550) arises from the femoral just before it passes through the opening in the tendon of the Adductor magnus, and immediately divides into a saphenous and a musculo-articular branch. The saphenous branch pierces the aponeurotic covering of the adductor canal, and accompanies the saphenous nerve to the medial side of the knee. It passes between the Sartorius and Gracilis, and, piercing the fascia lata, is distributed to the integument of the upper and medial part of the leg, anastomosing with the medial inferior genicular artery. The musculo-articular branch descends in the substance of the \ astus medialis, and in front of the tendon of the Adductor magnus, to the medial side of the knee, where it anastomoses with the medial superior genicular artery and anterior recur- rent tibial artery. A branch from this vessel crosses above the patellar surface of the femur, forming an anastomotic arch with the lateral superior genicular artery, and supplying branches to the knee-joint. THE POPLITEAL FOSSA (Fig. 551). Boundaries.—The popliteal fossa or space is a lozenge-shaped space, at the back of the knee-joint. Laterally it is bounded by the Biceps femoris above, and by the Plantaris and the lateral head of the Gastrocnemius below; medially it is limited by the Semitendinous and Semimembranosus above, and by the medial head of the Gastrocnemius below. The floor is formed by the popliteal surface of the femur, the oblique popliteal ligament of the knee-joint, the upper end of the tibia, and the fascia covering the Popliteus; the fossa is covered in by the fascia lata. 632 ANGIOLOGY Contents.—The popliteal fossa contains the popliteal vessels, the tibial and the common peroneal nerves, the termination of the small saphenous vein, the lower part of the posterior femoral cutaneous nerve, the articular branch from the obtur- ator nerve, a few small lymph glands, and a considerable quantity of fat. The tibial nerve descends through the middle of the fossa, lying under the deep fascia and cross- ing the vessels posteriorly from the lateral to the medial side. The common peroneal nerve descends on the lateral side of the upper part of the fossa, close to the tendon of the Biceps femoris. On the floor of the fossa are the popliteal vessels, the vein being superficial to the artery and united to it by dense areolar tissue; the vein is a thick-walled vessel, and lies at first lateral to the artery, and then crosses it posteriorly to gain its medial side below; sometimes it is double, the artery lying between the two veins, which are usually connected by short transverse branches. The articular branch from the obturator nerve descends upon the artery to the knee-joint. The popliteal lymph glands, six or seven in number, are imbedded in the fat; one lies beneath the popliteal fascia near the termi- nation of the external saphenous vein, another between the popliteal artery and the back of the knee-joint, while the others are placed at the sides of the popliteal vessel. Arising from the artery, and pass- ing off from it at right angles, are its genic- ular branches. Sural arteries The Popliteal Artery (A. Poplitea) (Fig. 551). The popliteal artery is the continuation of the femoral, and courses through the poplit- eal fossa. It extends from the opening in the Adductor magnus, at the junction of the middle and lower thirds of the thigh, down- ward and lateralward to the intercondyloid fossa of the femur, and then vertically down- ward to the lower border of the Popliteus, where it divides into anterior and posterior tibial arteries. Relations.—In front of the artery from above downward are the popliteal surface of the femur (which is separated from the vessel by some fat), the back of the knee-joint, and the fascia cover- ing the Popliteus. Behind, it is overlapped by the Semimembranosus above, and is covered by the Gastrocnemius and Plantaris below. In the middle part of its course the artery is separated from the integument and fasciae by a quantity of fat, and is Perf. branch of peroneal Medial calcaneal Fio. 551.—The popliteal, posterior tibial, and peroneal arteries. THE POPLITEAL ARTERY 633 crossed from the lateral to the medial side by the tibial nerve and the popliteal vein, the vein being between the nerve and the artery and closely adherent to the latter. On its lateral side, above, are the Biceps femoris, the tibial nerve, the popliteal vein, and the lateral condyle of the femur, below, the Plantaris and the lateral head of the Gastrocnemius. On its medial side, above, are the Semimembranosus and the medial condyle of the femur; below, the tibial nerve, the popliteal vein, and the medial head of the Gastrocnemius. The relations of the popliteal lymph glands to the artery are described above. Peculiarities in Point of Division.—Occasionally the popliteal artery divides into its terminal branches opposite the knee-joint. The anterior tibial under these circumstances usually passes in front of the Popliteus. Unusual Branches. The artery sometimes divides into the anterior tibial and peroneal, the posterior tibial being wanting, or very small. Occasionally it divides into three branches, the anterior and posterior tibial, and peroneal. Branches.—The branches of the popliteal artery are: Muscular Superior Sural. Lateral Superior Genicular. Middle Genicular. Medial Inferior Genicular. Lateral Inferior Genicular. Cutaneous. Medial Superior Genicular The superior muscular branches, two or three in number, arise from the upper part of the artery, and are distributed to the lower parts of the Adductor magnus and hamstring muscles, anastomosing with the terminal part of the profunda femoris. The sural arteries (aa. surales; inferior muscular arteries) are two large branches, which are distributed to the Gastrocnemius, Soleus, and Plantaris. They arise from the popliteal artery opposite the knee-joint. The cutaneous branches arise either from the popliteal artery or from some of its branches; they descend between the two heads of the Gastrocnemius, and, piercing the deep fascia, are distributed to the skin of the back of the leg. One branch usually accompanies the small saphenous vein. The superior genicular arteries (aa. genu superiores; superior articular arteries) (Figs. 550, 551), two in number, arise one on either side of the popliteal, and wind around the femur immediately above its condyles to the front of the knee-joint. The medial superior genicular runs in front of the Semimembranosus and Semitendinosus, above the medial head of the Gastrocnemius, and passes beneath the tendon of the Adductor magnus. It divides into two branches, one of which supplies the Vastus medialis, anastomosing with the highest genicular and medial inferior genicular arteries; the other ramifies close to the surface of the femur, supplying it and the knee-joint, and anastomosing with the lateral superior genicular artery. The medial superior genicular artery is frequently of small size, a condition, which is associated with an increase in the size of the highest genicular. The lateral superior genicular passes above the lateral condyle of the femur, beneath the tendon of the Biceps femoris, and divides into a superficial and a deep branch; the superficial branch supplies the Vastus lateralis, and anastomoses with the descending branch of the lateral femoral circumflex and the lateral inferior genicular arteries; the deep branch supplies the lower part of the femur and knee-joint, and forms an anasto- motic arch across the front of the bone with the highest genicular and the medial inferior genicular arteries. The middle genicular artery (a. genu media; azygos articular artery) is a small branch, arising opposite the back of the knee-joint. It pierces the oblique popliteal ligament, and supplies the ligaments and synovial membrane in the interior of the articulation. # The inferior genicular arteries (aa. genu inferiores; inferior articular arteries) (hfigs. 550, 551), two in number, arise from the popliteal beneath the Gastrocnemius. I he medial inferior genicular first descends along the upper margin of the Topliteus, to which it gives branches; it then passes below the medial condyle of the tibia, beneath 634 ANGIOLOGY the tibial collateral ligament, at the anterior border of which it ascends to the front and medial side of the joint, to supply the upper end of the tibia and the articula- tion of the knee, anastomosing with the lateral inferior and medial superior genic- ular arteries. The lateral inferior genicular runs lateralward above the head of the fibula to the front of the knee-joint, passing in its course beneath the lateral head of the Gastrocnemius, the fibular collateral ligament, and the tendon of the Biceps femoris. It ends by dividing into branches, which anastomose with the medial inferior and lateral superior genicular arteries, and with the anterior recurrent tibial artery. » Highest genicular Descending branch of lateral femoral circumflex Musculo-articular branch of highest genicular Saphenous branch of highest genicular Medial superior genicular Lateral superior genicular Lateral inferior genicular Medial inferior genicular Fibular Anterior recurrent tibial Anterior tibial Fig. 552.—Circumpatellar anastomosis. The Anastomosis Around the Knee-joint (Fig. 552).—Around and above the patella, and on the contiguous ends of the femur and tibia, is an intricate net-work of vessels forming a superficial and a deep plexus. The superficial plexus is situated between the fascia and skin around about the patella, and forms three wrell-defined arches: one, above the upper border of the patella, in the loose connective tissue over the Quadriceps femoris; the other two, below the level of the patella, are situated in the fat behind the ligamentum patellae. The deep plexus, which forms a close net-work of vessels, lies on the lower end of the femur and upper end of the tibia around their articular surfaces, and sends numerous offsets into the interior of the joint. The arteries which form this plexus are the two medial and the two lateral genicular branches of the popliteal, the highest genicular, the descending branch of the lateral femoral circumflex, and the anterior recurrent tibial. The Anterior Tibial Artery (A. Tibialis Anterior) (Fig. 553). The anterior tibial artery commences at the bifurcation of the popliteal, at the lower border of the Popliteus, passes forward between the two heads of the Tibialis THE ANTERIOR TIBIAL ARTERY 635 posterior, and through the aperture above the upper border of the interosseous membrane, to the deep part of the front of the leg: it here lies close to the medial side of the neck of the fibula. It then descends on the anterior surface of the inter- osseous membrane, gradually approaching the tibia; at the lower part of the leg it lies on this bone, and then on the front of the ankle-joint, where it is more superficial, and becomes the dorsalis pedis. Relations.—In the upper two-thirds of its extent, the anterior tibial artery rests upon the inter- osseous membrane; in the lower third, upon the front of the tibia, and the anterior ligament of the ankle-joint. In the upper third of its course, it lies between the Tibialis anterior and Extensor digitorum longus; in the middle third between the Tibialis anterior and Extensor hallucis longus. At the ankle it is crossed from the lateral to the medial side by the tendon of the Extensor hallucis longus, and lies between it and the first tendon of the Extensor digitorum longus. It is covered in the upper two-thirds of its course, by the muscles which lie on either side of it, and by the deep fascia; in the lower third, by the integument and fascia, and the transverse and cruciate crural ligaments. The anterior tibial artery is accompanied by a pair of vena; comitantes which lie one on either side of the artery; the deep peroneal nerve, coursing around the lateral side of the neck of the fibula, comes into relation with the lateral side of the artery shortly after it has reached the front of the leg; about the middle of the leg the nerve is in front of the artery; at the lower part it is generally again on the lateral side. Peculiarities in Size.—This vessel may be diminished in size, may be deficient to a greater or less extent, or may be entirely wanting, its place being supplied by perforating branches from the posterior tibial, or by the perforating branch of the peroneal artery. Course.—The artery occasionally deviates toward the fibular side of the leg, regaining its usual position at the front of the ankle. In rare instances the vessel has been found to approach the surface in the middle of the leg, being covered merely by the integument and fascia below that point. Branches.—The branches of the anterior tibial artery are: Posterior Tibial Recurrent. Fibular. Anterior Tibial Recurrent. Muscular. Anterior Medial Malleolar. Anterior Lateral Malleolar. The posterior tibial recurrent artery (a. recurrens tibialis posterior) an inconstant branch, is given off from the anterior tibial before that vessel passes through the interosseous space. It ascends in front of the Popliteus, which it supplies, and anastomoses with the inferior genicular branches of the popliteal artery, giving an offset to the tibiofibular joint. The fibular artery is sometimes derived from the anterior tibial, sometimes irom the posterior tibial. It passes lateralward, around the neck of the fibula, through the Soleus, which it supplies, and ends in the substance of the Peroneus longus. The anterior tibial recurrent artery (a. recurrens tibialis anterior) arises from the anterior tibial, as soon as that vessel has passed through the interosseous space; it ascends in the Tibialis anterior, ramifies on the front and sides of the knee-joint, and assists in the formation of the patellar plexus by anastomosing with the genicular branches of the popliteal, and with the highest genicular artery. The muscular branches (rami musculares) are numerous; they are distributed to the muscles which lie on either side of the vessel, some piercing the deep fascia to supply the integument, others passing through the interosseous membrane, and anastomosing with branches of the posterior tibial and peroneal arteries. The anterior medial malleolar artery (a. malleolar is. anterior medialis; internal malleolar artery) arises about 5 cm. above the ankle-joint, and passes behind the tendons of the Extensor hallucis longus and Tibialis anterior, to the medial side of the ankle, upon which it ramifies, anastomosing with branches of the posterior tibial and medial plantar arteries and with the medial calcaneal from the posterior tibial. The anterior lateral malleolar artery (a. malleolaris anterior lateralis;. exter- nal malleolar artery) passes beneath the tendons of the Extensor digitorum 636 ANGIOLOGY longus and Peronseus tertius and supplies the lateral side of the ankle, anas- tomosing with the perforating branch of the peroneal artery, and with ascend- ing twigs from the lateral tarsal artery. The arteries around the ankle-joint anastomose freely with one another and form net-works below the corre- sponding malleoli. The medial malleolar net-work is formed by the anterior medial malleolar branch of the anterior tibial, the medial tarsal branches of the dorsalis pedis, the posterior medial malleolar and medial calcaneal branches of the posterior tibial and branches from the medial plantar artery. The lateral malleolar net-work is formed by the anterior lateral malleolar branch of the anterior tibial, the lateral tarsal branch of the dorsalis pedis, the per- forating and the lateral calcaneal branches of the peroneal, and twigs from the lateral plantar artery. Lateral inferior genicular Medial inferior genicular Anterior tibial recurrent The Arteria Dorsalis Pedis (Dorsalis Pedis Artery) (Fig. 553). The arteria dorsalis pedis, the contin- uation of the anterior tibial, passes for- ward from the ankle-joint along the tibial side of the dorsum of the foot to the proximal part of the first inter- metatarsal space, where it divides into two branches, the first dorsal metatarsal and the deep plantar. Relations.—This vessel, in its course for- ward, rests upon the front of the articular capsule of the ankle-joint, the talus, navic- ular, and second cuneiform bones, and the ligaments connecting them, being covered by the integument, fascia and cruciate ligament, and crossed near its termination by the first tendon of the Extensor digitorum brevis. On its tibial side is the tendon of the Extensor hallucis longus; on its fibular side, the first tendon of the Extensor digitorum longus, and the termination of the deep peroneal nerve. It is accompanied by two veins. Peculiarities in Size.—The dorsal artery of the foot may be larger than usual, to com- pensate for a deficient plantar artery; or its terminal branches to the toes may be absent, the toes then being supplied by the medial plantar; or its place may be taken altogether by a large perforating branch of the peroneal artery. Position.—This artery frequently curves lateralward, lying lateral to the line between the middle of the ankle and the back part of the first interosseous space. Perf. hr. of _ peroneal Ant. med. malleolar Ant. lat. malleolar Deep plantar Pig. 553.—Anterior tibial and dorsalis pedis arteries. THE POSTERIOR TIBIAL ARTERY 637 Branches.—The branches of the arteria dorsalis pedis are: Lateral Tarsal. Medial Tarsal. Arcuate. First Dorsal Metatarsal. Deep Plantar. The lateral tarsal artery (a. tarsea lateralis; tarsal artery) arises from the dorsalis pedis, as that vessel crosses the navicular bone; it passes in an arched direction lateralward, lying upon the tarsal bones, and covered by the Extensor digitorum brevis; it supplies this muscle and the articulations of the tarsus, and anastomoses with branches of the arcuate, anterior lateral malleolar and lateral plantar arteries, and with the perforating branch of the peroneal artery. The medial tarsal arteries (aa. tarsece mediates) are two or three small branches which ramify on the medial borderof the foot and join the medial malleolar net-work. The arcuate artery (a. arcuata; metatarsal artery) arises a little anterior to the lateral tarsal artery; it passes lateralward, over the bases of the metatarsal bones, beneath the tendons of the Extensor digitorum brevis, its direction being influenced by its point of origin; and it anastomoses with the lateral tarsal and lateral plantar arteries. This vessel gives off the second, third, and fourth dorsal metatarsal arteries, which run forward upon the corresponding Interossei dorsales; in the clefts between the toes, each divides into two dorsal digital branches for the adjoining toes. At the proximal parts of the interosseous spaces these vessels receive the posterior perforating branches from the plantar arch, and at the distal parts of the spaces they are joined by the anterior perforating branches, from the plantar metatarsal arteries. The fourth dorsal metatarsal artery gives off a branch which supplies the lateral side of the fifth toe. The first dorsal metatarsal artery (a. dorsalis hallucis) runs forward on the first Interosseous dorsalis, and at the cleft between the first and second toes divides into two branches, one of which passes beneath the tendon of the Extensor hallucis longus, and is distributed to the medial border of the great toe; the other bifurcates to supply the adjoining sides of the great and second toes. The deep plantar artery (ramus plantaris profundus; communicating artery) descends into the sole of the foot, between the two heads of the first Interosseous dorsalis, and unites with the termination of the lateral plantar artery, to complete the plantar arch. It sends a branch along the medial side of the great toe, and is continued forward along the first interosseous space as the first plantar metatarsal artery, which bifurcates for the supply of the adjacent sides of the great and second toes. The Posterior Tibial Artery (A. Tibialis Posterior) (Fig. 551). The posterior tibial artery begins at the lower border of the Popliteus, opposite the interval between the tibia and fibula; it extends obliquely downward, and, as it descends, it approaches the tibial side of the leg, lying behind the tibia, and in the lower part of its course is situated midway between the medial malleolus and the medial process of the calcaneal tuberosity. Here it divides beneath the origin of the Adductor hallucis into the medial and lateral plantar arteries. Relations.—The posterior tibial artery lies successively upon the 1 ibialis posterior, the Flexor digitorum longus, the tibia, and the back of the ankle-joint. It is covered by the deep trans- verse fascia of the leg, which separates it above from the Gastrocnemius and Soleus; at its termi- nation it is covered by the Abductor hallucis. In the lower third of the leg, where it is more superficial, it is covered only by the integument and fascia, and runs parallel with the medial border of the tendo calcaneus. It is accompanied by two veins, and by the tibial nerve, which lies at first to the medial side of the artery, but soon crosses it posteriorly, and is in the greater part of its course on its lateral side. Behind the medial malleolus, the tendons, bloodvessels, and nerve are arranged, under co\er of the laciniate ligament, in the following order from the medial to the lateral side. (1) the 638 ANGIQLOGY tendons of the Tibialis posterior and Flexor digitorum longus, lying in the same groove, behind the malleolus, the former being the more medial. Next is the posterior tibial artery, with a vein on either side of it; and lateral to the vessels is the tibial nerve; about 1.25 cm. nearer the heel is the tendon of the Flexor hallucis longus. Peculiarities in Size.—The posterior tibial is not infrequently smaller than usual, or absent, its place being supplied by a large peroneal artery, which either joins the small posterior tibial artery, or continues alone to the sole of the foot. Branches.—The branches of the posterior tibial artery are: Peroneal. Nutrient. Muscular. Posterior Medial Malleolar. Communicating. Medial Calcaneal. The peroneal artery (a. peroncea) is deeply seated on the back of the fibular side of the leg. It arises from the posterior tibial, about 2.5 cm. below the lower border of the Popliteus, passes obliquely toward the fibula, and then descends along the medial side of that bone, contained in a fibrous canal between the Tibialis posterior and the Flexor hallucis longus, or in the substance of the latter muscle. It then runs behind the tibiofibular syndesmosis and divides into lateral calcaneal branches which ramify on the lateral and posterior surfaces of the calcaneus. It is covered, in the upper part of its course, by the Soleus and deep transverse fascia of the leg; below, by the Flexor hallucis longus. Peculiarities in Origin.—The peroneal artery may arise 7 or 8 cm. below the Popliteus, or from the posterior tibial high up, or even from the popliteal. Its size is more frequently increased than diminished; and then it either reinforces the posterior tibial by its junction with it, or altogether takes the place of the posterior tibial in the lower part of the leg and foot, the latter vessel only existing as a short muscular branch. In those rare cases where the peroneal artery is smaller than usual, a branch from the posterior tibial supplies its place; and a branch from the anterior tibial compensates for the diminished anterior peroneal artery. In one case the peroneal artery was entirely wanting. Branches.—The branches of the peroneal are: Muscular. Nutrient. Perforating. Communicating. Lateral Calcaneal. Muscular Branches.—The peroneal artery, in its course, gives off branches to the Soleus, Tibialis posterior, Flexor hallucis longus, and Peronei. The Nutrient Artery (a. nutricia fibulae) supplies the fibula, and is directed downward. The Perforating Branch (ramus perforans; anterior peroneal artery) pierces the interosseous membrane, about 5 cm. above the lateral malleolus, to reach the front of the leg, where it anastomoses with the anterior lateral malleolar; it then passes down in front of the tibiofibular syndesmosis, gives branches to the tarsus, and anastomoses with the lateral tarsal. The perforating branch is sometimes enlarged, and takes the place of the dorsalis pedis artery. The Communicating Branch (ramus communicans) is given off from the peroneal about 2.5 cm. from its lower end, and joins the communicating branch of the posterior tibial. The Lateral Calcaneal (ramus calcaneus lateralis; external calcaneal) are the ter- minal branches of the peroneal artery; they pass to the lateral side of the heel, and communicate with the lateral malleolar and, on the back of the heel, with the medial calcaneal arteries. The nutrient artery (a. nutricia tibiae) of the tibia arises from the posterior tibial, near its origin, and after supplying a few muscular branches enters the nutrient canal of the bone, which it traverses obliquely from above downward. This is the largest nutrient artery of bone in the body. THE POSTERIOR TIBIAL ARTERY 639 The muscular branches of the posterior tibial are distributed to the Soleus and deep muscles along the back of the leg. The posterior medial malleolar artery (a. malleolaris posterior medialis; internal malleolar artery) is a small branch which winds around the tibial malleolus and ends in the medial malleolar net-work. The communicating branch (ramus communicans) runs transversely across the back of the tibia, about 5 cm. above its lower end, beneath the Flexor hallucis longus, and joins the communicating branch of the peroneal. The medial calcaneal (rami calcanei mediates; internal calcaneal) are several large arteries which arise from the posterior tibial just before its division; they pierce the laciniate ligament and are distributed to the fat and integument behind the tendo calcaneus and about the heel, and to the muscles on the tibial side of the sole, anastomosing with the peroneal and medial malleolar and, on the back of the heel, with the lateral calcaneal arteries. Deep plantar 1st plantar meiatarsal Fig. 554.—The plantar arteries. Superficial view. Fig. 555.—The plantar arteries. Deep view. The medial plantar artery (a. plantaris medialis; internal plantar artery). (Figs. 554 and 555), much smaller than the lateral, passes forward along the medial side of the foot. It is at first situated above the Abductor hallucis, and then between it and the Flexor digitorum brevis, both of which it supplies. At the base of the first metatarsal bone, where it is much diminished in size, it passes along the medial border of the first toe, anastomosing with the first dorsal metatarsal artery. Small superficial digital branches accompany the digital branches of the medial plantar nerve and join the plantar metatarsal arteries of the first three spaces. The lateral plantar artery (a. plantaris lateralis; external plantar artery), much larger than the medial, passes obliquely lateralward and forward to the base of the fifth metatarsal bone. It then turns medialward to the interval between the bases of the first and second metatarsal bones, where it unites with the deep plantar branch of the dorsalis pedis artery, thus completing the plantar arch. As this artery passes lateralward, it is first placed between the calcaneus and Abductor hallucis, 640 ANGIOLOGY and then between the Flexor digitorum brevis and Quadratus plantse; as it runs forward to the base of the little toe it lies more superficially between the Flexor digitorum brevis and Abductor digiti quinti, covered by the plantar aponeurosis and integument. The remaining portion of the vessel is deeply situated; it extends from the base of the fifth metatarsal bone to the proximal part of the first inter- osseous space, and forms the plantar arch; it is convex forward, lies below the bases of the second, third, and fourth metatarsal bones and the corresponding Interossei, and upon the oblique part of the Adductor hallucis. Branches.—The plantar arch, besides distributing numerous branches to the muscles, integument, and fasciae in the sole, gives off the following branches: Perforating. Plantar Metatarsal. The Perforating Branches (rami perforantes) are three in number; they ascend through the proximal parts of the second, third, and fourth interosseous spaces, between the heads of the Interossei dorsales, and anastomose with the dorsal metatarsal arteries. The Plantar Metatarsal Arteries (aa. metatarsece plantares; digital branches) are four in number, and run forward between the metatarsal bones and in contact with the Interossei. Each divides into a pair of plantar digital arteries which sup- ply the adjacent sides of the toes. Near their points of division each sends upward an anterior perforating branch to join the corresponding dorsal metatarsal artery. The first plantar metatarsal artery (arteria princeps hallucis) springs from the junc- tion between the lateral plantar and deep plantar arteries and sends a digital branch to the medial side of the first toe. The digital branch for the lateral side of the fifth toe arise from the lateral plantar artery near the base of the fifth metatarsal bone. BIBLIOGRAPHY. Bean, R. B.: A Composite Study of the Subclavian Artery in Man, Am. Jour. Anat., 1905, iv. Bremer, J. L.: On the Origin of the Renal Artery in Mammals and its Anomalies, Am. Jour. Anat., 1915, xviii. Broman, Ivar: Ueber die Entwickelung “ Wanderung, ” und Variation der Bauchaortenzweige bei den Wirbeltieren, Ergebnisse der Anat. u. Entwick., 1906, xvi. Eaton, P. B.: The Celiac Axis, Anat. Rec., 1917, xiii. Henle, J.: Anatomie des Menschen. Hitzrot, J. M.: A Composite Study of the Axillary Artery in Man, Johns Hop. Hosp. Bull., 1901, xii. Lipshittz, B. B.: Studies on the Blood Vascular Tree. I. A Composite Study of the Femoral Artery, Anat. Rec., 1916, x. Poirier et Charpy: Traite d’Anatomie Humaine. Quain’s Anatomy. THE VEINS. THE Veins convey the blood from the capillaries of the different parts of the body to the heart. They consist of two distinct sets of vessels, the pulmonary and systemic. The Pulmonary Veins, unlike other veins, contain arterial blood, which they return from the lungs to the left atrium of the heart. The Systemic Veins return the venous blood from the body generally to the right atrium of the heart. The Portal Vein, an appendage to the systemic venous system, is confined to the abdominal cavity, and returns the venous blood from the spleen and the viscera of digestion to the liver. This vessel ramifies in the substance of the liver and there breaks up into a minute network of capillary-like vessels, from which the blood is conveyed by the hepatic veins to the inferior vena cava. The veins commence by minute plexuses which receive the blood from the capil- laries. The branches arising from these plexuses unite together into trunks, and these, in their passage toward the heart, constantly increase in size as they receive tributaries, or join other veins. The veins are larger and altogether more numerous than the arteries; hence, the entire capacity of the venous system is much greater than that of the arterial; the capacity of the pulmonary veins, however, only slightly exceeds that of the pulmonary arteries. The veins are cylindrical like the arteries; their walls, howTever, are thin and they collapse when the vessels are empty, and the uniformity of their surfaces is interrupted at intervals by slight constrictions, which indicate the existence of valves in their interior. They com- municate very freely with one another, especially in certain regions of the body; and these communications exist between the larger trunks as well as between the smaller branches. Thus, between the venous sinuses of the cranium, and between the veins of the neck, where obstruction would be attended with imminent danger to the cerebral venous system, large and frequent anastomoses are found. The same free communication exists between the veins throughout the whole extent of the vertebral canal, and between the veins composing the various venous plexuses in the abdomen and pelvis, e. g., the spermatic, uterine, vesical, and pudendal. The systemic venous channels are subdivided into three sets, viz., superficial and deep veins, and venous sinuses. The Superficial Veins (cutaneous veins) are found between the layers of the superficial fascia immediately beneath the skin; they return the blood from these structures, and communicate with the deep veins by perforating the deep fascia. The Deep Veins accompany the arteries, and are usually enclosed in the same sheaths with those vessels. With the smaller arteries as the radial, ulnar, brachial, tibial, peroneal—they exist generally in pairs, one lying on each side of the vessel, and are called venae comitantes. The larger arteries such as the axillary, sub- clavian, popliteal, and femoral—have usually only one accompanying vein. . In certain organs of the body, however, the deep veins do not accompany the arteries; for instance, the veins in the skull and vertebral canal, the hepatic veins ip the liver, and the larger veins returning blood from the bones. Venous Sinuses are found only in the interior of the skull, and consist of canals formed by a separation of the two layers of the dura mater; their outer coat con- sists of fibrous tissue, their inner of an endothelial layer continuous with the lining membrane of the veins. 641 642 ANGIOLOGY THE PULMONARY VEINS (VENjE PULMONALES). The pulmonary veins return the arterialized blood from the lungs to the left atrium of the heart. They are four in number, two from each lung, and are desti- tute of valves. The commence in a capillary net-work upon the walls of the air sacs, where they are continuous with the capillary ramifications of the pulmonary artery, and, joining together, form one vessel for each lobule. These vessels uniting successively, form a single trunk for each lobe, three for the right, and two for the left lung. The vein from the middle lobe of the right lung generally unites with that from the upper lobe, so that ultimately two trunks from each lung are formed; they perforate the fibrous layer of the pericardium and open separately into the upper and back part of the left atrium. Occasionally the three veins on the right side remain separate. Not infrequently the two left pulmonary veins end by a common opening. At the root of the lung, the superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the hilus of the lung and on a plane posterior to the upper vein. Behind the pulmonary artery is the bronchus. Within the pericardium, their anterior surfaces are invested by the serous layer of this membrane. The right pulmonary veins pass behind the right atrium and superior vena cava; the left in front of the descending thoracic aorta. THE SYSTEMIC VEINS. The systemic veins may be arranged into three groups: (1) The veins of the heart. (2) The veins of the upper extremities, head, neck, and thorax, which end in the superior vena cava. (3) The veins of the lower extremities, abdomen, and pelvis, which end in the inferior vena cava. THE VEINS OF THE HEART (VV. Cordis) (Fig. 556). Coronary Sinus (sinus coronarius).—Most of the veins of the heart open into the coronary sinus. This is a wide venous channel about 2.25 cm. in length situated in the posterior part of the coronary sulcus, and covered by muscular fibers from the left atrium. It ends in the right atrium between the opening of the inferior vena cava and the atrioventricular aperture, its orifice being guarded by a semilunar valve, the valve of the coronary sinus (valve of Thebesius). Tributaries.—Its tributaries are the great, small, and middle cardiac veins, the posterior vein of the left ventricle, and the oblique vein of the left atrium, all of which, except the last, are provided with valves at their orifices. 1. The Great Cardiac Vein (v. cordis magna; left coronary vein) begins at the apex of the heart and ascends along the anterior longitudinal sulcus to the base of the ventricles. It then curves to the left in the coronary sulcus, and reaching the back of the heart, opens into the left extremity of the coronary sinus. It receives tributaries from the left atrium and from both ventricles: one, the left marginal vein, is of considerable size, and ascends along the left margin of the heart. 2. The Small Cardiac Vein (v. cordis parva; right coronary vein) runs in the coronary sulcus between the right atrium and ventricle, and opens into the right extremity of the coronary sinus. It receives blood from the back of the right atrium and ventricle; the right marginal vein ascends along the right margin of the heart and joins it in the coronary sulcus, or opens directly into the right atrium. THE VEINS OF THE HEAD AND NECK 643 3. The Middle Cardiac Vein (v. cordis media) commences at the apex of the heart, ascends in the posterior longitudinal sulcus, and ends in the coronary sinus near its right extremity. 4. 1 he Posterior Vein of the Left Ventricle (v. posterior ventriculi sinistri) runs on the diaphragmatic surface of the left ventricle to the coronary sinus, but may end in the great cardiac vein. 5. The Oblique Vein of the Left Atrium (v. obliqua atrii sinistri [Marshalli]; oblique vein of Marshall) .is a small vessel which descends obliquely on the back of the left atrium and ends in the coronary sinus near its left extremity; it is continuous above with the ligament of the left vena cava (lig. venae cavce sinistrce; vestigial fold of Marshall), and the two structures form the remnant of the left Cuvierian duct. Azygos vein Left pulmonary veins Bight 'pulmonary veins Oblique vein of left atrium Great cardiac vein Left marginal vein Small cardiac vein Posterior vein of left ventricle Middle cardiac vein Fiq. 556.—Base and diaphragmatic surface of heart. The following cardiac veins do not end in the coronary sinus: (1) the anterior cardiac veins, comprising three or four small vessels which collect blood from the front of the right ventricle and open into the right atrium; the right marginal vein frequently opens into the right atrium, and is therefore sometimes regarded as belonging to this group; (2) the smallest cardiac veins (veins of Ihebesius), con- sisting of a number of minute veins which arise in the muscular wall of the heart; the majority open into the atria, but a few end in the ventricles. THE VEINS OF THE HEAD AND NECK. The veins of the head and neck may be subdivided into three groups: (1) The veins of the exterior of the head and face. {2) T he veins of the neck. (3) The diploic veins, the veins of the brain, and the venous sinuses of the dura mater. 644 ANGIOLOGY The Veins of the Exterior of the Head and Face (Fig. 557). The veins of the exterior of the head and face are Frontal. Supraorbital. Angular. Anterior Facial. Superficial Temporal Internal Maxillary. Posterior Facial. Posterior Auricular. Occipital Frontal Communicating branch with ophthalmic vein Angular Lingual Pharyngeal Superior thyroid Fig. 557.—Veins of the head and neck. The frontal vein (v. frontalis) begins on the forehead in a venous plexus which communicates with the frontal branches of the superficial temporal vein. The veins converge to form a single trunk, which runs downward near the middle line of the forehead parallel with the vein of the opposite side. The two veins are joined, at the root of the nose, by a transverse branch, called the nasal arch, which receives some small veins from the dorsum of the nose. At the root of the nose the veins diverge, and, each at the medial angle of the orbit, joins the supraorbital vein, to THE VEINS OF THE EXTERIOR OF THE HEAD AND FACE 645 form the angular vein. Occasionally the frontal veins join to form a single trunk, which bifurcates at the root of the nose into the two angular veins. The supraorbital vein (v. supraorbitalis) begins on the forehead where it com- municates with the frontal branch of the superficial temporal vein. It runs down- ward superficial to the Frontalis muscle, and joins the frontal vein at the medial angle of the orbit to form the angular vein. Previous to its junction with the frontal vein, it sends through the supraorbital notch into the orbit a branch which com- municates with the ophthalmic vein; as this vessel passes through the notch, it receives the frontal diploic vein through a foramen at the bottom of the notch. The angular vein (v. angularis) formed by the junction of the frontal and supra- orbital veins, runs obliquely downward, on the side of the root of the nose, to the level of the lower margin of the orbit, where it becomes the anterior facial vein. It receives the veins of the ala nasi, and communicates wdth the superior ophthalmic vein through the nasofrontal vein, thus establishing an important anastomosis between the anterior facial vein and the cavernous sinus. The anterior facial vein (v. facialis anterior; facial vein) commences at the side of the root of the nose, and is a direct continuation of the angular vein. It lies behind the external maxillary (facial) artery and follows a less tortuous course. It runs obliquely downward and backward, beneath the Zygomaticus and zygo- matic head of the Quadratus labii superioris, descends along the anterior border and then on the superficial surface of the Masseter, crosses over the body of the mandible, and passes obliquely backward, beneath the Platysma and cervical fascia, superficial to the submaxillary gland, the Digastricus and Stylohyoideus. It unites with the posterior facial vein to form the common facial vein, which crosses the external carotid artery and enters the internal jugular vein at a vari- able point below the hyoid bone. From near its termination a communicating branch often runs down the anterior border of the Sternocleidomastoideus to join the lower part of the anterior jugular vein. The facial vein has no valves, and its walls are not so flaccid as most superficial veins. Tributaries.—The anterior facial vein receives a branch of considerable size, the deep facial vein, from the pterygoid venous plexus. It is also joined by the superior and inferior palpebral, the superior and inferior labial, the buccinator and the masseteric veins. Below the mandible it receives the submental, palatine, and submaxillary veins, and, generally, the vena comitans of the hypoglossal nerve. The superficial temporal vein (v. temporalis superficialis) begins on the side and vertex of the skull in a plexus which communicates with the frontal and supra- orbital veins, with the corresponding vein of the opposite side, and with the pos- terior auricular and occipital veins. From this net-work frontal and parietal branches arise, and unite above the zygomatic arch to form the trunk of the vein, which is joined in this situation by the middle temporal vein, from the substance of the Tem- poralis. It then crosses the posterior root of the zygomatic arch, enters the sub- stance of the parotid gland, and unites with the internal maxillary vein to form the posterior facial vein. Tributaries.—The superficial temporal vein receives in its course some parotid veins, articular veins from the temporomandibular joint, anterior auricular veins from the auricula, and the transverse facial from the side of the face. I he middle temporal vein receives the orbital vein, which is formed by some lateral palpebral branches, and passes backward between the layers of the temporal fascia to join the superficial temporal vein. . . The pterygoid plexus (plexus pterygoideus) is of considerable size, and is situated between the Temporalis and Pterygoideus externus, and partly between the two Pterygoidei. It receives tributaries corresponding with the branches of the internal maxillary artery. Thus it receives the sphenopalatine, the middle meningeal, the deep temporal, the pterygoid, masseteric, buccinator, alveolar, and some palatine 646 ANGIOLOGY veins, and a branch which communicates with the ophthalmic vein through the inferior orbital fissure. This plexus communicates freely with the anterior facial vein; it also communicates with the cavernous sinus, by branches through the foramen Vesalii, foramen ovale, and foramen lacerum. The internal maxillary vein (v. maxillaris interna) is a short trunk which accom- panies the first part of the internal maxillary artery. It is formed by a confluence of the veins of the pterygoid plexus, and passes backward between the spheno- mandibular ligament and the neck of the mandible, and unites with the temporal vein to form the posterior facial vein. The posterior facial vein (v. facialis posterior; temporomaxillary rein), formed by the union of the superficial temporal and internal maxillary veins, descends in the substance of the parotid gland, superficial to the external carotid artery but beneath the facial nerve, between the ramus of the mandible and the Sternocleido- mastoideus muscle. It divides into two branches, an anterior, which passes forward and unites with the anterior facial vein to form the common facial vein and a pos- terior, which is joined by the posterior auricular vein and becomes the external jugular vein. The posterior auricular vein (r. auricularis posterior) begins upon the side of the head, in a plexus which communicates with the tributaries of the occipital, and superficial temporal veins. It descends behind the auricula, and joins the posterior division of the posterior facial vein to form the external jugular. It receive the stylomastoid vein, and some tributaries from the cranial surface of the auricula. The occipital vein (v. occipitalis) begins in a plexus at the back part of the vertex of the skull, From the plexus emerges a single vessel, which pierces the cranial attachment of the Trapezius and, dipping into the suboccipital triangle, joins the deep cervical and vertebral veins. Occasionally it follows the course of the occipital artery and ends in the internal jugular; in other instances, it joins the posterior auricular and through it opens into the external jugular. The parietal emissary vein connects it with the superior sagittal sinus; and as it passes across the mastoid portion of the temporal bone, it receives the mastoid emissary vein which connects it with the transverse sinus. The occipital diploic vein sometimes joins it. The Veins of the Neck (Fig. 558). The veins of the neck, which return the blood from the head and face, are: External Jugular. Posterior External Jugular. Anterior Jugular. Internal Jugular. Vertebral. The external jugular vein (y. jugularis externa) receives the greater part of the blood from the exterior of the cranium and the deep parts of the face, being formed by the junction of the posterior division of the posterior facial with the posterior auricular vein. It commences in the substance of the parotid gland, on a level with the angle of the mandible, and runs perpendicularly down the neck, in the direction of a line drawn from the angle of the mandible to the middle of the clavicle at the posterior border of the Sternocleidomastoideus. In its course it crosses the Sternocleidomastoideus obliquely, and in the subclavian triangle perforates the deep fascia, and ends in the subclavian vein, lateral to or in front of the Scalenus anterior. It is separated from the Sternocleidomastoideus by the investing layer of the deep cervical fascia, and is covered by the Platysma, the superficial fascia, and the integument; it crosses the cutaneous cervical nerve, and its upper half runs parallel with the great auricular nerve. The external jugular vein varies in size, bearing an inverse proportion to the other veins of the neck, it is occasionally THE VEINS OF THE NECK 647 double. It is provided with two pairs of valves, the lower pair being placed at its entrance into the subclavian vein, the upper in most cases about 4 cm. above the clavicle. The portion of vein between the two sets of valves is often dilated, and is termed the sinus. These valves do not prevent the regurgitation of the blood, or the passage of injection from below upward. Tributaries.—This vein receives the occipital occasionally, the posterior external jugular, and, near its termination, the transverse cervical, transverse scapular, and anterior jugular veins; in the substance of the parotid, a large branch of commu- nication from the internal jugular joins it. Ext. carotid artery Fig. 558.—The veins of the neck, viewed from in front. Subclavian vein The posterior external jugular vein (v. jugularis posterior) begins in the occipital region and returns the blood from the skin and superficial muscles m the upper anc back part of the neck, lying between the Splenius and Trapezius. It runs down the back part of the neck, and opens into the external jugular vein just below the middle of its course. . v 7 , , The anterior jugular vein (v. jugularis anterior) begins near the hyoid bone by the confluence of several superficial veins from the submaxillary region It descends between the median line and the anterior border of the Sternocleidomastoideus, and, at the lower part of the neck, passes beneath that muscle to open into the ter- mination of the external jugular, or, in some instances, into e su c a,\lan ven (Figs. 557, 558). It varies considerably in size, bearing usually an inverse propor- 648 ANGIOLOGY tion to the external jugular; most frequently there are two anterior jugulars, a right and left; but sometimes only one. Its tributaries are some laryngeal veins, and occasionally a small thyroid vein. Just above the sternum the two anterior jugular veins communicate by a transverse trunk, the venous jugular arch, which receive tributaries from the inferior thyroid veins; each also communicates with the internal jugular. There are no valves in this vein. The internal jugular vein (v. jugularis interna) collects the blood from the brain, from the superficial parts of the face, and from the neck. It is directly continuous with the transverse sinus, and begins in the posterior compartment of the jugular foramen, at the base of the skull. At its origin it is somewhat dilated, and this dilatation is called the superior bulb. It runs down the side of the neck in a vertical direction, lying at first lateral to the internal carotid artery, and then lateral to the common carotid, and at the root of the neck unites with the subclavian vein to form the innominate vein; a little above its termination is a second dilatation, the inferior bulb. Above, it lies upon the Rectus capitis lateralis, behind the internal carotid artery and the nerves passing through the jugular foramen; lower down, the vein and artery lie upon the same plane, the glossopharyngeal and hypoglossal nerves passing forward between them; the vagus descends between and behind the vein and the artery in the same sheath, and the accessory runs obliquely backward, superficial or deep to the vein. At the root of the neck the right internal jugular vein is placed at a little distance from the common carotid artery, and LINGUAE ARTERY. DORSALIS LINGUAL VEIN - VEINS OF DORSUM OF- TONGUE I HYPOGLOSSAL NERVE Fig. 559.—Veins of the tongue. The hypoglossal nerve has been displaced downward in this preparation. crosses the first part of the subclavian artery, while the left internal jugular vein usually overlaps the common carotid artery. The left vein is generally smaller than the right, and each contains a pair of valves, which are placed about 2.5 cm. above the termination of the vessel. Tributaries.—This vein receives in its course the inferior petrosal sinus, the common facial, lingual, pharyngeal, superior and middle thyroid veins, and sometimes the occipital. The thoracic duct on the left side and the right lymphatic duct on the right side open into the angle of union of the internal jugular and subclavian veins. The Inferior Petrosal Sinus (sinus yetrosus inferior) leaves the skull through the anterior part of the jugular foramen, and joins the superior bulb of the internal jugular vein. The Lingual Veins (vv. linguales) begin on the dorsum, sides, and under surface of the tongue, and, passing backward along the course of the lingual artery, end in the internal jugular vein. The vena comitans of the hypoglossal nerve (ranine THE VEINS OF THE NECK 649 vein), a branch of considerable size, begins below the tip of the tongue, and may join the lingual; generally, however, it passes backward on the Hyoglossus, and joins the common facial. The Pharyngeal Veins (yv. pharyngeoe) begin in the pharyngeal plexus on the outer surface of the pharynx, and, after receiving some posterior meningeal veins and the vein of the pterygoid canal, end in the internal jugular. They occasionally open into the facial, lingual, or superior thyroid vein. The Superior Thyroid Vein (v. thyreoidea superioris) (Fig. 560) begins in the sub- stance and on the surface of the thyroid gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein. It receives the superior laryngeal and cricothyroid veins. The Middle Thyroid Vein (Figs. 561, 562) collects the blood from the lower part of the thyroid gland, and after being joined by some veins from the larynx and trachea, ends in the lower part of the internal jugular vein. The common facial and occipital veins have been described. External carotid artery Superior thyroid artery Superior thyroid vein Middle thyroid vein Vagus nerve Fig. 560.—The veins of the thyroid gland. The vertebral vein (v. vertebralis) is formed in the suboccipital triangle, from numerous small tributaries which spring from the internal vertebral venous plexuses and issue from the vertebral canal above the posterior arch of the a^|as- unite with small veins from the deep muscles at the upper part of the back of the neck, and form a vessel which enters the foramen in the transverse process of the atlas, and descends, forming a dense plexus around the vertebral artery, in the canal formed by the foramina transversaria of the cervical vertebrae.. 1 his plexus ends in a single trunk, which emerges from the foramen transversanum o the sixth cervical vertebra, and opens at the root of the neck into the back part of the innominate vein near its origin, its mouth being guarded by a pair of valves. On the right side, it crosses the first part of the subclavian artery. 650 ANGIOLOGY Tributaries.—The vertebral vein communicates with the transverse sinus by vein which passes through the condyloid canal, when that canal exists. It Fig. 561.—Diagram showing common arrangement of thyroid veins. (Kocher.) SUPERIOR THYROID- ARTERY CRICO- THYROID- MUSCLE STERNO- THYROID MUSCLE MIDDLE THYROID- VEIN INFERIOR THYROID VEIN INFERIOR THYROID VEIN Fig. 562.—The-fascia and middle thyroid veins. The veins here designated the inferior thyroid are called by Kocher tho thyroidea ima. receives branches from the occipital vein and from the prevertebral muscles, from the internal and external vertebral venous plexuses, .from the anterior vertebral THE DIPLOIC VEINS 651 and the deep cervical veins; close to its termination it is sometimes joined by the first intercostal vein. The Anterior Vertebral Vein commences in a plexus around the transverse pro- cesses of the upper cervical vertebrae, descends in company with the ascending cenical artery between the bcalenus anterior and Longus capitis muscles, and opens into the terminal part of the vertebral vein. VERTEBRAL- POSTERIOR EXTERNAL- JUGULAR -VERTEBRAL POSTERIOR DEEP, CERVICAL _ ASCENDING ’cervical Fig. 563.—The vertebral vein. The Deep Cervical Vein (v. cervicalis profunda; posterior vertebral or posterior deep cervical vein) accompanies its artery between the Semispinales capitis and colli. It begins in the suboccipital region by communicating branches from the occipital vein and by small veins from the deep muscles at the back of the neck. It receives tributaries from the plexuses around the spinous processes of the cer- vical vertebrae, and terminates in the lower part of the vertebral vein. The diploic veins occupy channels in the diploe of the cranial bones. They are large and exhibit at irregular intervals pouch-like dilatations; their walls are thin, and formed of endothelium resting upon a layer of elastic tissue. So long as the cranial bones are separable from one another, these veins are confined to the particular bones; but when the sutures are obliterated, they unite with each other, and increase in size. They communicate with the meningeal veins and the sinuses of the dura mater, and with the veins of the pericranium. They consist of (1) the frontal, which opens into the supraorbital vein and the superior sagittal sinus; (2) the anterior temporal, which is confined chiefly to the frontal bone, and .opens into the sphenoparietal sinus and into one of the deep temporal veins, through an aperture in the great wing of the sphenoid; (3) the posterior temporal, which is situated in the parietal bone, and ends in the transverse sinus, through an aperture at the mastoid angle of the parietal bone or through the The Diploic Veins (Venae Diploicae) (Fig. 564). 652 ANGIOLOGY mastoid foramen; and (4) the occipital, the largest of the four, which is confined to the occipital bone, and opens either externally into the occipital vein, or inter- nally into the transverse sinus or into the confluence of the sinuses (torcular Herophili). Fia. 564.—Veins of the diploe as displayed by the removal of the outer table of the skull. The Veins of the Brain. The veins of the brain possess no valves, and their walls, owing to the absence of muscular tissue, are extremely thin. They pierce the arachnoid membrane and the inner or meningeal layer of the dura mater, and open into the cranial venous sinuses. They may be divided into two sets, cerebral and cerebellar. The cerebral veins (yv. cerebri) are divisible into external and internal groups according as they drain the outer surfaces or the inner parts of the hemispheres. The external veins are the superior, inferior, and middle cerebral. The Superior Cerebral Veins (yv. cerebri superiores), eight to twelve in number, drain the superior, lateral, and medial surfaces of the hemispheres, and are mainly lodged in the sulci between the gyri, but some run across the gyri. They open into the superior sagittal sinus; the anterior veins runs nearly at right angles to the sinus; the posterior and larger veins are directed obliquely forward and open into the sinus in a direction more or less opposed to the current of the blood contained within it. The Middle Cerebral Vein (v. cerebri media; superficial Sylvian vein) begins on the lateral surface of the hemisphere, and, running along the lateral cerebral fissure, ends in the cavernous or the sphenoparietal sinus. It is connected (a) with the superior sagittal sinus by the great anastomotic vein of Trolard, which opens into one of the superior cerebral veins; (b) with the transverse sinus by the posterior anasto- motic vein of Labbe, which courses over the temporal lobe. The Inferior Cerebral Veins (vv. cerebri inferiores), of small size, drain the under surfaces of the hemispheres. Those on the orbital surface of the frontal lobe join the superior cerebral veins, and through these open into the superior sagittal sinus; those of the temporal lobe anastomose with the middle cerebral and basal veins, and join the cavernous, sphenoparietal, and superior petrosal sinuses. THE VEINS OF THE BRAIN 653 The basal vein is formed at the anterior perforated substance by the union of (a) a small anterior cerebral vein which accompanies the anterior cerebral artery, (6) the deep middle cerebral vein (deep Sylvian vein), which receives tributaries from the insula and neighboring gyri, and runs in the lower part of the lateral cerebral fissure, and (c) the inferior striate veins, which leave the corpus striatum through the anterior perforated substance. The basal vein passes backward around the cerebral peduncle, and ends in the internal cerebral vein (vein of Galen); it receives tributaries from the interpeduncular fossa, the inferior horn of the lateral ventricle, the hippocampal gyrus, and the mid-brain. The Internal Cerebral Veins (vv. cerebri internee; veins of Galen; deep cerebral veins) drain the deep parts of the hemisphere and are two in number; each is formed near the interventricular foramen by the union of the terminal and choroid veins. They run backward parallel with one another, between the layers of the tela chorioidea of the third ventricle, and beneath the splenium of the corpus callosum, where they unite to form a short trunk, the great cerebral vein; just before their union each receives the corresponding basal vein. The terminal vein (v. terminalis; vena corporis striati) commences in the groove between the corpus striatum and thalamus, receives numerous veins from both of these parts, and unites behind the crus fornicis with the choroid vein, to form one of the internal cerebral veins. The choroid vein runs along the whole length of the choroid plexus, and receives veins from the hippocampus, the fornix, and the corpus callosum. ANT. OF FORNIX' “nucleus OF MONRO CHOROID rVEIN MEDIAN PLEXUS^ -VELUM CHOROID “PLEXUS VELAR, VEINS GREAT CEREBRAL VEIN Fig. 565.—Velum interpositum. The Great Cerebral Vein (v. cerebri magna [Galeni\; great vein of Galen) (Fig. 565), formed by the union of the two internal cerebral veins, is a short median trunk which curves backward and upward around the splenium of the corpus callosum and ends in the anterior extremity of the straight sinus. The cerebellar veins are placed on the surface of the cerebellum, and are dis- posed in two sets, superior and inferior. The superior cerebellar veins (vv. cerebelli superiores) pass partly forward and medialward, across the superior vermis, to en in the straight sinus and the internal cerebral veins, partly lateralward to the trans- verse and superior petrosal sinuses. The inferior cerebellar veins (vv. cerebelli mje- riores) of large size, end in the transverse, superior petrosal, and occipital sinuses. 654 ANGIOLOGY The Sinuses of the Dura Mater (Sinus Durse Matris). Ophthalmic Veins and Emissary Veins. The sinuses of the dura mater are venous channels which drain the blood from the brain; they are devoid of valves, and are situated between the two layers of the dura mater and lined by endothelium continuous with that which lines the veins. They may be divided into two groups: (1) a postero-superior, at the upper and back part of the skull, and (2) an antero-inferior, at the base of the skull. The postero-superior group comprises the Superior Sagittal. Inferior Sagittal. Straight. Two Transverse. Occipital. Dural vein Superior sagittal smus Venous lacuna Venous lacuna ' Fia. 506. —■ Superior sagittal sinus laid open after remova of the skull cap. The chordae Willisii are clearly seen. The venous lacunae are also well shown; from two of them probes are passed into the superior sagittal sinus. (Poirier and Charpy.) The superior sagittal sinus (sinus sagittalis superior; superior longitudinal sinus) (Figs. 566, 567) occupies the attached or convex margin of the falx cerebri. Com- mencing at the foramen cecum, through which it receives a vein from the nasal cavity, it runs from before backward, grooving the inner surface of the frontal, the adjacent margins of the two parietals, and the superior division of the cruciate eminence of the occipital; near the internal occipital protuberance it deviates to one or other side (usually the right), and is continued as the corresponding trans- verse sinus. It is triangular in section, narrow in front, and gradually increases in size as it passes backward. Its inner surface presents the openings of the superior cerebral veins, which run, for the most part, obliquely forward, and open chiefly at the back part of the sinus, their orifices being concealed by fibrous folds; numerous THE SINUSES OF THE DURA MATER 655 fibrous bands {chordce Willisii) extend transversely across the inferior angle of the sinus; and, lastly, small openings communicate with irregularly shaped venous spaces {venous lacunae) in the dura mater near the sinus. There are usually three lacume on either side of the sinus: a small frontal, a large parietal, and an occipital, intermediate in size between the other two (Sargent1). Most of the cerebral veins from the outer surface of the hemisphere open into these lacunae, and numer- ous arachnoid granulations {Pacchionian bodies) project into them from below. The superior sagittal sinus receives the superior cerebral veins, veins from the diploe and dura mater, and, near the posterior extremity of the sagittal suture, veins from the pericranium, which pass through the parietal foramina. The numerous communications exist between this sinus and the veins of the nose, scalp, and diploe. Olfactory tract Great cerebral vein Glossopharyngeal nerve Ophthalmic artery Optic nerves Vagus nerve Accessory nerve Diaphragma sellce Acoustic nerve Facial nerve Oculomotor nerves Trochlear nerve Fig. 567.—Dura mater and its processes exposed by removing part of the right half of the skull, and the brain. Abducent nerve Trigeminal nerve The inferior sagittal sinus {sinus sagittalis inferior; inferior longitudinal sinus) (Fig. 567) is contained in the posterior half or two-thirds of the free margin of the falx cerebri. It is of a cylindrical form, increases m size as it passes backward, an ends in the straight sinus. It receives several veins from the falx cerebri, and occasionally a few from the medial surfaces of the hemispheres. . , The straight sinus {sinus rectus; tentorial sinus) (bigs. 567, 5 ) is si ua e the line of junction of the falx cerebri with the tentorium cere e i. is riangu ar 1 Journal of Anatomy and Physiology, vol. xlv. 656 ANGIOLOGY in section, increases in size as it proceeds backward, and runs downward and back- ward from the end of the inferior sagittal sinus to the transverse sinus of the oppo- -Foramen cecum Torcular herophtti. Fig. 568.—Sagittal section of the skull, showing the sinuses of the dura. Optic nerve Internal carotid artery Diaphragma sellce Oculomotor nerve Attached margin of tentorium Free margin of tentorium Conjtuence of the sinuses Fig. 569.—Tentorium cerebelli from above. site side to that into which the superior sagittal sinus is prolonged. Its terminal part communicates by a cross branch with the confluence of the sinuses. Besides THE SINUSES OF THE DURA MATER 657 the inferior sagittal sinus, it receives the great cerebral vein {great vein of Galen) and the superior cerebellar veins. A few transverse bands cross its interior. The transverse sinuses {sinus transversals; lateral sinuses) (Figs. 569, 570) are of large size and begin at the internal occipital protuberance; one, generally the right, being the direct continuation of the superior sagittal sinus, the other of the straight sinus. Each transverse sinus passes lateralward and forward, describing a slight curve with its convexity upward, to the base of the petrous portion of the temporal bone, and lies, in this part of its course, in the attached margin of the tentorium cerebelli; it then leaves the tentorium and curves downward and Levator palpebrce Rectus superior Sup. oph- 'thalmic vein Sphenoparietal sinus Vertebral artery End of straight sinus Superior sagittal sinus Fig. 570.—The sinuses at the base of the skull. medialward to reach the jugular foramen, where it ends in the internal jugular vein. In its course it rests upon the squama of the occipital, the mastoid angle of the parietal, the mastoid part of the temporal, and, just before its termination, the jugular process of the occipital; the portion which occupies the groo\e on the mastoid part of the temporal is sotnetimes termed the sigmoid sinus. Ihe trans- verse sinuses are frequently of unequal size, that formed by the superior sagitta sinus being the larger; they increase in size as they proceed from behind forward. On transverse section the horizontal portion exhibits a prismatic, the curve portion a semicylindrical form. They receive the blood from the superior petrosa 658 ANGIOLOGY sinuses at the base of the petrous portion of the temporal bone; they communicate with the veins of the pericranium by means of the mastoid and condyloid emissary veins; and they receive some of the inferior cerebral and inferior cerebellar veins, and some veins from the diploe. The petrosquamous sinus, when present, runs backward along the junction of the squama and petrous portion of the temporal, and opens into the transverse sinus. The occipital sinus (sinus occipitalis) (Fig. 570) is the smallest of the cranial sinuses. It is situated in the attached margin of the falx cerebelli, and is generally single, but occasionally there are two. It commences around the margin of the for- amen magnum by several small venous channels, one of which joins the terminal part of the transverse sinus; it communicates with the posterior internal vertebral venous plexuses and ends in the confluence of the sinuses. The Confluence of the Sinuses (confluens sinuum; torcular Herophili) is the term applied to the dilated extremity of the superior sagittal sinus. It is of irregular form, and is lodged on one side (generally the right) of the internal occipital pro- tuberance. From it the transverse sinus of the same side is derived. It receives also the blood from the occipital sinus, and is connected across the middle line with the commencement of the transverse sinus of the opposite side. The antero-inferior group of sinuses comprises the Two Cavernous. Two Intercavernous Two Superior Petrosal. Two Inferior Petrosal. Basilar Plexus. The cavernous sinuses (sinus cavernosus) (Figs. 570, 571) are so named because they present a reticulated structure, due to their being traversed by numerous inter- lacing filaments. They are of irregular form, larger behind than in front, and are placed one on either side of the body of the sphenoid bone, extending from the superior orbital fissure to the apex of the petrous portion of the temporal bone. Each opens be- hind into the petrosal sinuses. On the medial wall of each sinus is the internal carotid artery, accompanied by filaments of the carotid plexus; near the artery is the abducent nerve; on the lateral wall are the oculomotor and trochlear nerves, and the oph- _ thalmic and maxillary divisions of the trigeminal nerve (Fig. 571). These structures are separated from the blood flowing along the sinus by the lining membrane of the sinus. The cavernous sinus receives the superior ophthalmic vein through the superior orbital fissure, some of the cerebral veins, and also the small sphenoparietal sinus, which courses along the under surface of the small wing of the sphenoid. It communicates with the transverse sinus by means of the superior petrosal sinus; with the internal jugular vein through the inferior petrosal sinus and a plexus of veins on the inter- nal carotid artery; with the pterygoid venous plexus through the foramen Vesalii, foramen ovale, and foramen lacerum, and With the angular vein through the ophthalmic vein. The two sinuses also communicate with each' other by means of the anterior and posterior intercavernous sinuses. The ophthalmic veins (Fig. 572), two in number, superior and inferior, are devoid of valves. Internal carotid artery Cavernous sinus Oculomotor nerve Trochlear nerve Ophthalmic nerve Abducent nerve Maxillary nerve Pig. 571.—Oblique section through the cavernous sinus. THE SINUSES OF THE DURA MATER 659 The Superior Ophthalmic Vein (v. ophthalmica superior) begins at the inner angle of the orbit in a vein named the nasofrontal which communicates anteriorly with the angular vein; it pursues the same course as the ophthalmic artery, and receives tributaries corresponding to the branches of that vessel. Forming a short single trunk, it passes between the two heads of the Rectus lateralis and through the medial part of the superior orbital fissure, and ends in the cavernous sinus. The Inferior Ophthalmic Vein (v. ophthalmica inferior) begins in a venous net-work at the forepart of the floor and medial wall of the orbit; it receives some veins from the Rectus inferior, Obliquus inferior, lacrimal sac and eyelids, runs backward in the lower part of the orbit and divides into two branches. One of these passes through the inferior orbital fissure and joins the pterygoid venous plexus, while the other enters the cranium through the superior orbital fissure and ends in the cavernous sinus, either by a separate opening, or more frequently in common with the superior ophthalmic vein. Superior ophthalmic Cavernous sinus Inferior ophthalmic Fig. 572.—Veins of orbit. (Poirier and Charpy.) The intercavernous sinuses (sini intercavernosi) (Fig. 570) are two in number, an anterior and a posterior, and connect the two cavernous sinuses across the middle line. The anterior passes in front of the hypophysis cerebri, the posterior behind it, and they form with the cavernous sinuses a venous circle (circular sinus) around the hypophysis. The anterior one is usually the larger of the two, and one or other is occasionally absent. # The superior petrosal sinus (sinus petrosus superior) (Fig. 570) small and narrow, connects the cavernous with the transverse sinus.. It runs lateral ward, and back- ward, from the posterior end of the cavernous sinus, over the trigeminal nerve, and lies in the attached margin of the tentorium cerebelli and in the superior petrosal sulcus of the temporal bone; it joins the transverse sinus where the latter curves downward on the inner surface of the mastoid part of the temporal. It receives some cerebellar and inferior cerebral veins, and veins from the tympanic CBiVity The inferior petrosal sinus {sinus petrosus inferior) (I ig. 570) is situated in the inferior petrosal sulcus formed by the junction of the petrous part o t le tempora with the basilar part of the occipital. It begins in the postero-mfenor part of the cavernous sinus, and, passing through the anterior part of the jugu ar oramen, ends in the superior bulb of the internal jugular vein. I he inferior petrosal smus ANGIOLOGY receives the internal auditory veins and also veins from the medulla oblongata, pons, and under surface of the cerebellum. The exact relation of the parts to one another in the jugular foramen is as follows: the inferior petrosal sinus lies medially and anteriorly with the meningeal branch of the ascending pharyngeal artery, and is directed obliquely downward and back- ward; the transverse sinus is situated at the lateral and back part of the foramen with a meningeal branch of the occipital artery, and between the two sinuses are the glossopharyngeal, vagus, and accessory nerves. These three sets of structures are divided from each other by two processes of fibrous tissue. The junction of the inferior petrosal sinus with the internal jugular vein takes place on the lateral aspect of the nerves. The basilar plexus (plexus basilaris; transverse or basilar sinus) (Fig. 571) con- sists of several interlacing venous channels between the layers of the dura mater over the basilar part of the occipital bone, and serves to connect the two inferior petrosal sinuses. It communicates with the anterior vertebral venous plexus. Emissary Veins (emissaria).—The emissary veins pass through apertures in the cranial wall and establish communication between the sinuses inside the skull and the veins external to it. Some are always present, others only occasionally so. The principal emissary veins are the following: (1) A mastoid emissary vein, usually present, runs through the mastoid foramen and unites the transverse sinus with the posterior auricular or with the occipital vein. (2) A parietal emissary vein passes through the parietal foramen and connects the superior sagittal sinus with the veins of the scalp. (3) A net-work of minute veins (rete canalis hypoglossi) traverses the hypoglossal canal and joins the transverse sinus with the vertebral vein and deep veins of the neck. (4) An inconstant condyloid emissary vein passes through the condyloid canal and connects the transverse sinus with the deep veins of the neck. (5) A net-work of veins (rete foraminis ovalis) unites the cavernous sinus with the pterygoid plexus through the foramen ovale. (6) Two or three small veins run through the foramen lacerum and connect the cavernous sinus with the pterygoid plexus. (7) The emissary vein of the foramen of Vesalius connects the same parts. (8) An internal carotid plexus of veins traverses the carotid canal and unites the cavernous sinus with the internal jugular vein. (9) A vein is trans- mitted through the foramen cecum and connects the superior sagittal sinus with the veins of the nasal cavity. THE VEINS OF THE UPPER EXTREMITY AND THORAX. The veins of the upper extremity are divided into two sets, superficial and deep; the two sets anastomose frequently with each other. The superficial veins are placed immediately beneath the integument between the two layers of superficial fascia. The deep veins accompany the arteries, and constitute the vense comi- tantes of those vessels. Both sets are provided with valves, which are more numerous in the deep than in the superficial veins. The Superficial Veins of the Upper Extremity. The superficial veins of the upper extremity are the digital, metacarpal, cephalic, basilic, median. Digital Veins.—The dorsal digital veins pass along the sides of the fingers and are joined to one another by oblique communicating branches. Those from the adjacent sides of the fingers unite to form three dorsal metacarpal veins (Fig. 573), which end in a dorsal venous net-work opposite the middle of the meta- carpus. The radial part of the net-work is joined by the dorsal digital vein from the radial side of the index finger and by the dorsal digital veins of the thumb, and is prolonged upward as the cephalic vein. The ulnar part of the net-work receives THE SUPERFICIAL VEINS OF THE UPPER EXTREMITY 661 the dorsal digital vein of the ulnar side of the little finger and is continued upward as the basilic vein. A communicating branch frequently connects the dorsal venous network with the cephalic vein about the middle of the forearm. The volar digital veins on each finger are connected to the dorsal digital veins by oblique intercapitular veins. They drain into a venous plexus which is situated over the thenar and hypothenar eminences and across the front of the wrist. Basilic Cephalic Dorsal venom network Dorsal metacarpals Venous arch Fig. 573.—The veins on the dorsum of the hand. (Bourgery.) The cephalic vein (Fig. 574) begins in the radial part of the dorsal venous net- work and winds upward around the radial border of the forearm, receiving tri m- taries from both surfaces. Below the front of the elbow it gives off the vena mediana cubiti (median basilic vein), which receives a communicating branch from t e eep veins of the forearm and passes across to join the basilic vein, ihe cep la ic vein then ascends in front of the elbow in the groove between the Brachioradialis and the Biceps brachii. It crosses superficial to the musculocutaneous nerve and ascends in the groove along the lateral border of the Biceps brachii. In the upper third of the arm it passes between the Pectoralis major and Deltoideus, where it is accom 662 ANGIOLOGY panied by the deltoid branch of the thoracoacromial artery. It pierces the coraco- clavicular fascia and, crossing the axillary artery, ends in the axillary vein just below the clavicle. Sometimes it communicates with the external jugular vein by a branch which ascends in front of the clavicle. The accessory cephalic vein (v. cephalica accessoria) arises either from a small tributory plexus on the back of the forearm or from the ulnar side of the dorsal venous net-work; it joins the cephalic be- low the elbow. In some cases the accessory cephalic springs from the cephalic above the wrist and joins it again higher up. A large oblique branch frequently con- nects the basilic and cephalic veins on the back of the forearm. The basilic vein (v. basilica) (Fig. 574) begins in the ulnar part of the dorsal venous network. It runs up the posterior surface of the ulnar side of the forearm and inclines forward to the anterior surface below the elbow, where it is joined by the vena mediana cubiti. It ascends obliquely in the groove between the Biceps brachii and Pronator teres and crosses the brachial artery, from which it is separated by thelacertus fibrosus; filaments of the medial antibrachial cutaneous nerve pass both in front of and behind this portion of the vein. It then runs upward along the medial border of the Biceps brachii, perforates the deep fascia a little below the middle of the arm, and, ascending on the medial side of the brachial artery to the lower border of the Teres major, is continued onward as the axillary vein. The median antibrachial vein (v. mediana antibrachii) drains the venous plexus on the volar surface of the hand. It ascends on the ulnar side of the front of the fore- arm and ends in the basilic vein or in the vena mediana cubiti; in a small proportion of cases it divides into two branches, one of which joins the basilic, the other the cephalic, below the elbow. Cephalic vein- -Basilic vein Lateral antibrachial cutaneous nerve _ Vena mediana cubiti Accessory _ cephalic vein ■Basilic vein Medial anti- . brachial cutane- ous nerve Cephalic vein - Median anti- brachial vein Fig. 574.—The superficial veins of the upper extremity. THE DEEP VEINS OF THE UPPER EXTREMITY 663 The Deep Veins of the Upper Extremity. The deep veins follow the course of the arteries, forming their venae comitantes. They are generally arranged in pairs, and are situated one on either side of the corresponding artery, and connected at intervals by short transverse branches. Deep Veins of the Hand.—The superficial and deep volar arterial arches are each accompanied by a pair of vense comitantes which constitute respectively the superficial and deep volar venous arches, and receive the veins corresponding to the branches of the arterial arches; thus the common volar digital veins, formed by the union of the proper volar digital veins, open into the superficial, and the volar metacarpal veins into the deep volar venous arches. The dorsal metacarpal veins receive perforating branches from the volar metacarpal veins and end in the radial veins and in the superficial veins on the dorsum of the wrist. The deep veins of the fore- arm are the venae comitantes of the radial and ulnar veins and constitute respectively the upward continuations of the deep and superficial volar venous arches; they unite in front of the elbow to form the brachial veins. The radial veins are smaller than the ulnar and receive the dorsal meta- carpal veins. The ulnar veins receive tributaries from the deep volar venous arches and communicate with the super- ficial veins at the wrist; near the elbow they receive the volar and dorsal interosseous veins and send a large communicat- ing branch (profunda vein) to the vena mediana cubiti. The brachial veins (vv. brachiales) are placed one on either side of the brachial artery, receiving tributaries corresponding with the branches given off from that vessel; near the lower margin of the Subscapularis, they join the axillary vein; the medial one frequently joins the basilic vein. These deep veins have numerous anastomoses, not only with each other, but also with the superficial veins. The axillary vein (v. axillaris) begins at the lower border of the Teres major, as the continuation of the basilic vein, increases in size as it ascends, and ends at the outer border of the first rib as the subclavian vein. Near the lower border of the Subscapularis it receives the brachial veins and, close to its termination, the cephalic vein; its other tributaries correspond with the branches of the axillary artery. It lies on the medial side of the artery, which it partly overlaps; between the two vessels are the medial cord of the brachial plexus, the median, the ulnar, VENAE COMITES "OF BRACHIAL ARTERY ANASTOMOSIS -OF RADIAL AND ULNAR interosseous RADIAL DEEP "VEINS ULNAR DEEP VEINS Fig. 575.—The deep veins of the upper extremity. 664 ANGIOLOGY and the medial anterior thoracic nerves. It is provided with a pair of valves oppo- site the lower border of the Subscapularis; valves are also found at the ends of the cephalic and subscapular veins. The subclavian vein (v. snbclavia), the continuation of the axillary, extends from the outer border of the first rib to the sternal end of the clavicle, where it unites with the internal jugular to form the innominate vein. It is in relation, in front, with the clavicle and Subclavius; behind and above, with the subclavian artery, from which it is separated medially by the Scalenus anterior and the phrenic nerve. Below, it rests in a depression on the first rib and upon the pleura. It is usually provided with a pair of valves, which are situated about 2.5 cm. from its termination. AXILLARY ARTERY MEDIAN NERVE ANTERIOR ' CIRCUMFLEX MUSCULO- CUTANEUS NERVE COSTOAXILLARY SUBSCAPULAR LONG THORACIC COSTOAXILLARY Fig. 576.—The veins of the right axilla, viewed from in front. The subclavian vein occasionally rises in the neck to a level with the third part of the subclavian artery, and occasionally passes with this vessel behind the Scalenus anterior. Tributaries.—This vein receives the external jugular vein, sometimes the anterior jugular vein, and occasionally a small branch, which ascends in front of the clavicle, from the cephalic. At its angle of junction with the internal jugular, the left subclavian vein receives the thoracic duct, and the right subclavian vein the right lymphatic duct. The Veins of the Thorax (Fig. 577) The innominate veins (vv. anonymce; brachiocephalic veins) are two large trunks, placed one on either side of the root of the neck, and formed by the union of the internal jugular and subclavian veins of the corresponding side; they are devoid of valves. The Right Innominate Vein (v. anonyma dextra) is a short vessel, about 2.5 cm. in length, which begins behind the sternal end of the clavicle, and, passing almost vertically downward, joins with the left innominate vein just below the cartilage THE VEINS OF THE THORAX of the first rib, close to the right border of the sternum, to form the superior vena cava. It lies in front and to the right of the innominate artery; on its right side 665 Anterior jugular Superior thyroid - Middle thyroid ■External jugular Internal t mammary Inferior phrenic - Suprarenal Suprarenal- Fig. 577.—The venae cavae and azygos veins, with their tributaries. are the phrenic nerve and the pleura, which are interposed between it and the apex of the lung. This vein, at its commencement, receives the right vertebral vein; and, 666 ANGIOLOGY lower down, the right internal mammary and right inferior thyroid veins, and some- times the vein from the first intercostal space. The Left Innominate Vein (v. anonyma sinistra), about 6 cm. in length, begins behind the sternal end of the clavicle and runs obliquely downward and to the right behind the upper half of the manubrium sterni to the sternal end of the first right costal cartilage, where it unites with the right innominate vein to form the superior vena cava. It is separated from the manubrium sterni by the Sterno- hyoideus and Sternothvreoideus, the thymus or its remains, and some loose areolar tissue. Behind it are the three large arteries, innominate, left common carotid, and left subclavian, arising from the aortic arch, together with the vagus and phrenic nerves. The left innominate vein may occupy a higher level, crossing the jugular notch and lying directly in front of the trachea. Tributaries.—Its tributaries are the left vertebral, left internal mammary, left inferior thyroid, and the left highest intercostal veins, and occasionally some thymic and pericardiac veins. * Peculiarities.—Sometimes the innominate veins open separately into the right atrium; in such cases the right vein takes the ordinary course of the superior vena cava; the left vein— left superior vena cava, as it is then termed—which may communicate by a small branch with the right one, passes in front of the root of the left lung, and, turning to the back of the heart, ends in the right atrium. This occasional condition in the adult is due to the persistence of the early fetal condition, and is the normal state of things in birds and some mammalia. The internal mammary veins (vv. mammaries internee) are venae comitantes to the lower half of the internal mammary artery, and receive tributaries corre- sponding to the branches of the artery. They then unite to form a single trunk, which runs up on the medial side of the artery and ends in the corresponding innominate vein. The superior phrenic vein, i. e., the vein accompanying the peri- cardiacophrenic artery, usually opens into the internal mammary vein. The inferior thyroid veins (vv. thyreoidece inferiores) two, frequently three or four, in number, arise in the venous plexus on the thyroid gland, communicating with the middle and superior thyroid veins. They form a plexus in front of the trachea, behind the Sternothyreoidei. From this plexus, a left vein descends and joins the left innominate trunk, and a right vein passes obliquely downward and to the right across the innominate artery to open into the right innominate vein, just at its junction with the superior vena cava; sometimes the right and left veins open by a common trunk in the latter situation. These veins receive esophageal tracheal, and inferior laryngeal veins, and are provided with valves at their terminations in the innominate veins. The highest intercostal vein (v. intercostalis suprema; superior intercostal veins) (right and left) drain the blood from the upper three or four intercostal spaces. The right vein (v. intercostalis suprema dexira) passes downward and opens into the vena azygos; the left vein (v. intercostalis suprema sinistra) runs across the arch of the aorta and the origins of the left subclavian and left common carotid arteries and opens into the left innominate vein. It usually receives the left bronchial vein, and sometimes the left superior phrenic vein, and communicates below with the accessory hemiazygos vein. The superior vena cava (v. cava superior) drains the blood from the upper half of the body. It measures about 7 cm. in length, and is formed by the junction of the two innominate veins. It begins immediately below the cartilage of the right first rib close to the sternum, and, descending vertically behind the first and second intercostal spaces, ends in the upper part of the right atrium opposite the upper border of the third right costal cartilage: the lower half of the vessel is within the pericardium. In its course it describes a slight curve, the convexity of which is to the right side. THE VEINS OF THE VERTEBRAL COLUMN 667 . Relations.—In front are the anterior margins of the right lung and pleura with the pericardium intervening below, these separate it from the first and second intercostal spaces and from the second and third right costal cartilages; behind it are the root of the right lung and the right vagus nerve. On its right side are the phrenic nerve and right pleura; on its left side, the com- mencement of the innominate artery and the ascending aorta, the latter overlapping it. Just before it pierces the pericardium, it receives the azygos vein and several small veins from the pericardium and other contents of the mediastinal cavity. The portion contained within the pericardium is covered, in front and laterally, by the serous layer of the membrane. The superior vena cava has no valves. The azygos vein (v. azygos; vena azygos major) begins opposite the first or second lumbar vertebra, by a branch, the ascending lumbar vein (page 678); sometimes by a branch from the right renal vein, or from the inferior vena cava. It enters the thorax through the aortic hiatus in the diaphragm, and passes along the right side of the vertebral column to the fourth thoracic vertebra, where it arches forward over the root of the right lung, and ends in the superior vena cava, just before that vessel pierces the pericardium. In the aortic hiatus, it lies with the thoracic duct on the right side of the aorta; in the thorax it lies upon the intercostal arteries, on the right side of the aorta and thoracic duct, and is partly covered by pleura. Tributaries.—It receives the right subcostal and intercostal veins, the upper three or four of these latter opening by a common stem, the highest superior intercostal vein. It receives the hemiazygos veins, several esophageal, mediastinal, and peri- cardial veins, and, near its termination, the right bronchial vein. A few imperfect valves are found in the azygos vein; but its tributaries are provided with complete valves. The intercostal veins on the left side, below the upper three intercostal spaces, usually form two trunks, named the hemiazygos and accessory hemiazygos veins. The Hemiazygos Vein (v. hemiazygos; vena azygos minor inferior) begins in the left ascending lumbar or renal vein. It enters the thorax, through the left crus of the diaphragm, and, ascending on the left side of the vertebral column, as high as the ninth thoracic vertebra, passes across the column, behind the aorta, esoph- agus, and thoracic duct, to end in the azygos vein. It receives the lower four or five intercostal veins and the subcostal vein of the left side, and some esophageal and mediastinal veins. The Accessory Hemiazygos Vein (v. hemiazygos accessoria; vena azygos minor supe- rior) descends on the left side of the vertebral column, and varies inversely in size with the highest left intercostal vein. It receives veins from the three or four intercostal spaces between the highest left intercostal vein and highest tributary of the hemiazygos; the left bronchial vein sometimes opens into it. It either crosses the body of the eighth thoracic vertebra to join the azygos vein or ends in the hemiazygos. When this vein is small, or altogether wanting, the left highest intercostal vein may extend as low as the fifth or sixth intercostal space. In obstruction of the superior vena cava, the azygos and hemiazygos veins are one of the principal means by which the venous circulation is carried on, connecting as they do the superior and inferior venae cavae, and communicating with the common iliac veinf by the ascending lumbar veins and with many of the tributaries of the inferior vena cava. The Bronchial Veins (vv. bronchioles) return the blood from the larger bronchi, and from the structures at the roots of the lungs; that of the right side opens into the azygos vein, near its termination; that of the left side, into the highest left inter- costal or the accessory hemiazygos vein. A considerable quantity of the blood which is carried to the lungs through the bronchial arteries is returned to the left side of the heart through the pulmonary veins. The Veins of the Vertebral Column (Figs. 578, 579). The veins which drain the blood from the vertebral column, the neighboring muscles, and the meninges of the medulla spinalis form intricate plexuses extending 668 ANGIOLOGY along the entire length of the column; these plexuses may be divided into two groups, external and internal, according to their positions inside or outside the vertebral canal. The plexuses of the two groups anastomose freely with each other and end in the intervertebral veins. The external vertebral venous plexuses (plexus venosi vertebrates externi; extra- spinal veins) best marked in the cervical region, consist of anterior and posterior plexuses which anastomose freely with each other. The anterior external plexuses lie in front of the bodies of the vertebrae, communicate with the basivertebral and intervertebral veins, and receive tributaries from the vertebral bodies. The pos- terior external plexuses are placed partly on the posterior surfaces of the vertebral arches and their processes, and partly between the deep dorsal muscles. They are best developed in the cervical region, and there anastomose with the vertebral, occipital, and deep cervical veins. The internal vertebral venous plexuses (plexus venosi vertebrales interni; intra- spinal veins) lie within the vertebral canal between the dura mater and the verte- brae, and receive tributaries from the bones and from the medulla spinalis. They Posterior external plexuses Posterior external plexus Anterior external vlexus Fig. 578.—Transverse section of a thoracic vertebra, showing the vertebral venous plexuses. Fig. 579.—Median sagittal section of two thoracic verte- brae, showing the vertebral venous plexuses. form a closer net-work than the external plexuses, and, running mainly in a vertical direction, form four longitudinal veins, two in front and two behind; they therefore may be divided into anterior and posterior groups. The anterior internal plexuses consist of large veins which lie on the posterior surfaces of the vertebral bodies and intervertebral fibrocartilages on either side of the posterior longitudinal ligament; under cover of this ligament they are connected by transverse branches into which the basivertebral veins open. The posterior internal plexuses are placed, one on either side of the middle line in front of the vertebral arches and ligamenta flava, and anastomose by veins passing through those ligaments with the posterior exter- nal plexuses. The anterior and posterior plexuses communicate freely with one another by a series of venous rings (retia venosa vertebrarum), one opposite each vertebra. Around the foramen magnum they form an intricate net-work which opens into the vertebral veins and is connected above with the occipital sinus, the basilar plexus, the condyloid emissary vein, and the rete canalis hypoglossi. The basivertebral veins (vv. basivertebrales) emerge from the foramina on the posterior surfaces of the vertebral bodies. They are contained in large, tortuous THE SUPERFICIAL VEINS OF THE LOWER EXTREMITY 669 channels in the substance of the bones, similar in every respect to those found in the diploe of the cranial bones. They communicate through small openings on the front and sides of the bodies of the vertebrae with the anterior external vertebral plexuses, and converge behind to the principal canal, which is sometimes double toward its posterior part, and open by valved orifices into the transverse branches which unite the anterior internal vertebral plexuses. They become greatly enlarged in advanced age. The intervertebral veins (vv. intervertebrales) accompany the spinal nerves through the intervertebral foramina; they receive the veins from the medulla spinalis, drain the internal and external vertebral plexuses and end in the vertebral, intercostal, lumbar, and lateral sacral veins, their orifices being provided with valves. The veins of the medulla spinalis (vv. spinales; veins of the spinal cord) are situated in the pia mater and form a minute, tortuous, venous plexus. They emerge chiefly from the median fissures of the medulla spinalis and are largest in the lumbar region. In this plexus there are (1) two median longitudinal veins, one in front of the anterior fissure, and the other behind the posterior sulcus of the cord, and (2) four lateral longitudinal veins which run behind the nerve roots. They end in the intervertebral veins. Near the base of the skull they unite, and form two or three small trunks, which communicate with the vertebral veins, and then end in the inferior cerebellar veins, or in the inferior petrosal sinuses. THE VEINS OF THE LOWER EXTREMITY, ABDOMEN, AND PELVIS. The veins of the lower extremity are subdivided, like those of the upper, into two sets, superficial and deep; the superficial veins are placed beneath the integument between the twro layers of superficial fascia; the deep veins accompany the arteries. Both sets of veins are provided writh valves, which are more numerous in the deep than in the superficial set. Valves are also more numerous in the veins of the lowrer than in those of the upper limb. The Superficial Veins of the Lower Extremity. The superficial veins of the lower extremity are the great and small saphenous veins and their tributaries. On the dorsum of the foot the dorsal digital veins receive, in the clefts between the toes, the intercapitular veins from the plantar cutaneous venous arch and join to form short common digital veins which unite across the distal ends of the metatarsal bones in a dorsal venous arch. Proximal to this arch is an irregular venous net- work which receives tributaries from the deep veins and is joined at the sides of the foot by a medial and a lateral marginal vein, formed mainly by the union of branches from the superficial parts of the sole of the foot. On the sole of the foot the superficial veins form a plantar cutaneous venous arch which extends across the roots of the toes and opens at the sides of the foot into the medial and lateral marginal veins. Proximal to this arch is a plantar cutaneous venous net-work which is especially dense in the fat beneath the heel; this net-work communicates with the cutaneous venous arch and with the deep veins, but is chiefly drained into the medial and lateral marginal veins. The great saphenous vein (v. saphena magna; internal or long saphenous vein) (Fig. 581), the longest vein in the body, begins in the medial marginal \ ein of the dorsum of the foot and ends in the femoral vein about 3 cm. below the inguinal ligament. It ascends in front of the tibial malleolus and along the medial side o the leg in relation with the saphenous nerve. It runs upw ard behind the media 670 ANGIOLOGY condyles of the tibia and femur and along the medial side of the thigh and, passing through the fossa ovalis, ends in the femoral vein. Tributaries.-—At the ankle it receives branches from the sole of the foot through the medial marginal vein; in the leg it anastomoses freely with the small saphenous vein, communicates with the anterior and posterior tibial veins and receives many cutaneous veins; in the thigh it communicates with the femoral vein and receives numerous tributaries; those from the medial and posterior parts of the thigh frequently unite to form a large accessory saphenous vein which joins the main vein at a variable level. Near the fossa ovalis (Fig. 580) it is joined by the super- ficial epigastric, superficial iliac circumflex, and superficial external pudendal veins. A vein, named the thoracoepigastric, runs along the lateral aspect of the trunk between the superficial epigastric vein below and the lateral thoracic vein above and establishes an important communication between the femoral and axillary veins. Pig. 580.—The great saphenous vein and its tributaries at the fossa ovalis. The valves in the great saphenous vein vary from ten to twenty in number; they are more numerous in the leg than in the thigh. The small saphenous vein (v. saphena parva; external or short saphenous vein) (Fig. 582) begins behind the lateral malleolus as a continuation of the lateral marginal vein; it first ascends along the lateral margin of the tendocalcaneus, and then crosses it to reach the middle of the back of the leg. Running directly upward, it perforates the deep fascia in the lower part of the popliteal fossa, and ends in the popliteal vein, between the heads of the Gastrocnemius. It comrnu- THE DEEP VEINS OF THE LOWER EXTREMITY 671 nicates with the deep veins on the dorsum of the foot, and receives numerous large tributaries from the back of the leg. Before it pierces the deep fascia, it gives off a branch which runs upward and forward to join the great saphenous vein. The small saphenous vein possesses from nine to twelve valves, one of which is always found near its termination in the popliteal vein. In the lower third of the leg the small saphenous vein is in close relation with the sural nerve, in the upper two-thirds with the medial sural cutaneous nerve. The Deep Veins of the Lower Extremity. The deep veins of the lower extremity accom- pany the arteries and their branches; they possess numerous valves. Fig. 581.—The great saphenous vein and its tributaries. Fig. 582.—The small saphenous vein. The plantar digital veins (w. digitales plantares) arise from plexuses. on the plantar surfaces of the digits, and, after sending intercapitular vems to join the 672 ANGIOLOGY dorsal digital veins, unite to form four metatarsal veins; these run backward in the metatarsal spaces, communicate, by means of perforating veins, with the veins on the dorsum of the foot, and unite to form the deep plantar venous arch which lies alongside the plantar arterial arch. From the deep plantar venous arch the medial and lateral plantar veins run backward close to the corresponding arteries and, after communicating with the great and small saphenous veins, unite behind the medial malleolus to form the posterior tibial veins. The posterior tibial veins (vv. tibiales posteriores) accompany the posterior tibial artery, and are joined by the peroneal veins. The anterior tibial veins (vv. tibiales anteriores) are the upward continuation of the vense comitantes of the dorsalis pedis artery. They leave the front of the leg by passing between the tibia and fibula, over the interosseous membrane, and unite with the posterior tibial, to form the popliteal vein. The Popliteal Vein (v. poplitea) (Fig. 583) is formed by the junction of the anterior and posterior tibial veins at the lower border of the Popliteus; it ascends through the popliteal fossa to the aperture in the Adductor mag- nus, where it becomes the femoral vein. In the lower part of its course it is placed medial to the artery; between the heads of the Gastrocnemius it is super- ficial to that vessel; but above the knee-joint, it is close to its lateral side. It receives tributaries corresponding to the branches of the popliteal artery, and it also receives the small saphenous vein. The valves in the popliteal vein are usually four in number. The femoral vein (a. femoralis) accompanies the femoral artery through the upper two-thirds of the thigh. In the lower part of its course it lies lateral to the artery; higher up, it is behind it; and at the inguinal ligament, it lies on its medial side, and on the same plane. It receives numerous muscular tributaries, and about 4 cm. below the inguinal ligament is joined by the v. profunda femoris; near its termination it is joined by the great saphenous vein. The valves in the femoral vein are three in number. The Deep Femoral Vein (v. profunda femoris).receives tributaries corresponding to the perforating branches of the profunda artery, and through these establishes communications with the popliteal vein below and the inferior gluteal vein above. It also receives the medial and lateral femoral circum- flex veins. Fig. 583.—The popliteal vein. The external iliac vein (v. iliaca externa), the upward continuation of the femoral vein, begins behind the inguinal ligament, and, passing upward along the brim of the lesser pelvis, ends opposite the sacroiliac articulation, by uniting with the hypogastric vein to form the common iliac vein. On the right side, it lies at first medial to the artery: but, as it passes upward, gradually inclines behind it. On the left side, it lies altogether on the medial side of the artery. It frequently contains one, sometimes two, valves. Tributaries.—The external iliac vein receives the inferior epigastric, deep iliac circumflex, and pubic veins. The Inferior Epigastric Vein (v. epigastric a inferior; deep epigastric vein) is formed The Veins of the Abdomen and Pelvis (Figs. 585, 586, 587). THE VEINS OF THE ABDOMEN AND PELVIS 673 by the union of the venae comitantes of the inferior epigastric *artery, which com- municate above with the superior epigastric vein; it joins the external iliac about 1.25 cm. above the inguinal ligament. The Deep Iliac Circumflex Vein (v. circumflexa ilium profunda) is formed by the union of the venae comitantes of the deep iliac circumflex artery, and joins the external iliac vein about 2 cm. above the inguinal ligament. The Pubic Vein communicates with the obturator vein in the obturator foramen, and ascends on the back of the pubis to the external iliac vein. The hypogastric vein (v. hypogastrica; internal iliac vein) begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the hypogastric artery and, at the brim of the pelvis, joins with the external iliac to form the common iliac vein. UMBILiCUS SUPERFICIAL EPIGASTRIC SUPERFICIAL EXTERNAL CIRCUMFLEX SUPERFICIAL INTERNAL CIRCUMFLEX SUPERFICIAL EXTERNAL/ PUDIC, Fig. 584.—The femoral vein and its tributaries. Tributaries.—With the exception of the fetal umbilical vein which passes upward and backward from the umbilicus to the liver, and the iliolumbar vein w ic usua y joins the common iliac vein, the tributaries of the hypogastric vein correspon with the branches of the hypogastric artery. It receives (a) the gluteal, internal pudendal, and obturator veins, which have their origins outside the pelvis; (b) the lateral sacral veins, which lie in front of the sacrum; and (c) the middle hemorrhoidal vesical, uterine, and vaginal veins, which originate in venous plexuses connected with the pelvic viscera. 674 ANGIOLOGY 1. The Superior -Gluteal Veins (vv. glutaeoe superior es; gluteal veins) are venae comitantes of the superior gluteal artery; they receive tributaries from the buttock corresponding with the branches of the artery, and enter the pelvis through the greater sciatic foramen, above the Piriformis, and frequently unite before ending in the hypogastric vein. Third lumbar Spermatic . Superior hemorrhoidal Deep iliac ~ circumflex Obturator - Hemorrhoidal plexus Middle ’ hemorrhoidal Prostatic plexus Inferior hemorrhoidal Deep dorsal vein of penis Scrotal Fig. 585.—The veins of the right half of the male pelvis. Vesical plexus Internal pudendal 2. The Inferior Gluteal Veins (vv. glutaeoe inferiores; sciatic veins), or venae comi- tantes of the inferior gluteal artery, begin on the upper part of the back of the thigh, where they anastomose with the medial femoral circumflex and first perfo- rating veins. They enter the pelvis through the lower part of the greater sciatic foramen and join to form a single stem which opens into the lower part of the hypo- gastric vein. 3. The Internal Pudendal Veins (internal pudic veins) are the venae comitantes of the internal pudendal artery. They begin in the deep veins of the penis which issue from the corpus cavernosum penis, accompany the internal pudendal artery, and unite to form a single vessel, which ends in the hypogastric vein. They receive the veins from the urethral bulb, and the perineal and inferior hemorrhoidal veins. THE VEINS OF THE ABDOMEN AND PELVIS 675 CIRCUMFLEX "ILIAC DEEP "EPIGASTRIC LATERAL^ SACRAL M I DDIE SACRAL Fig. 586.—The iliac veins. SUPERIOR HEMORRHOIDAL .MIDDLE SACRA . MIDDLE^ hemorrhoidal' IN FERlOR_ H EM OR R HOI DAL Fig. 587.—Scheme of the anastomosis of the veins of the rectum. 676 ANGIOLOGY The deep dorsal vein of the penis communicates with the internal pudendal veins, but ends mainly in the pudendal plexus. 4. The Obturator Vein (v. obturatoria) begins in the upper portion of the adductor region of the thigh and enters the pelvis through the upper part of the obturator foramen. It runs backward and upward on the lateral wall of the pelvis below the obturator artery, and then passes between the ureter and the hypogastric artery, to end in the hypogastric vein. 5. The Lateral Sacral Veins (m. sacrales laterales) accompany the lateral sacral arteries on the anterior surface of the sacrum and end in the hypogastric vein. 6. The Middle Hemorrhoidal Vein (v. hcemorrhoidalis media) takes origin in the hemorrhoidal plexus and receives tributaries from the bladder, prostate, and seminal vesicle; it runs lateralward on the pelvic surface of the Levator ani to end in the hypogastric vein. The hemorrhoidal plexus (;plexus hcemorrhoidalis) surrounds the rectum, and communicates in front with the vesical plexus in the male, and the uterovaginal plexus in the female. It consists of two parts, an internal in the submucosa, and an external outside the muscular coat. The internal plexus presents a series of dilated pouches which are arranged in a circle around the tube, immediately above the anal orifice, and are connected by transverse branches. The lower part of the external plexus is drained by the inferior hemorrhoidal veins into the internal pudendal vein; the middle part by the middle hemorrhoidal vein which joins the hypogastric vein; and the upper part by the superior hemor- rhoidal vein which forms the commencement of the inferior mesenteric vein, a tributary of the portal vein. A free communication between the portal and sys- temic venous systems is established through the hemorrhoidal plexus. The veins of the hemorrhoidal plexus are contained in very loose, connective tissue, so that they get less support from surrounding structures than most other veins, and are less capable of resisting increased blood-pressure. The pudendal plexus (plexus pudendalis; vesicoprostatic plexus) lies behind the arcuate pubic ligament and the lower part of the symphysis pubis, and in front of the bladder and prostate. Its chief tributary is the deep dorsal vein of the penis, but it also receives branches from the front of the bladder and prostate. It com- municates with the vesical plexus and with the internal pudendal vein and drains into the vesical and hypogastric veins. The prostatic veins form a well-marked prostatic plexus which lies partly in the fascial sheath of the prostate and partly between the sheath and the prostatic capsule. It communicates with the pudendal and vesical plexuses. The vesical plexus (plexus vesicalis) envelops the lower part of the bladder and the base of the prostate and communicates with the pudendal and prostatic plexuses. It is drained, by means of several vesical veins, into the hypogastric veins. The Dorsal Veins of the Penis (vv. dorsales penis) are two in number, a superficial and a deep. The superficial vein drains the prepuce and skin of the penis, and, running backward in the subcutaneous tissue, inclines to the right or left, and opens into the corresponding superficial external pudendal vein, a tributary of the great saphenous vein. The deep vein lies beneath the deep fascia of the penis; it receives the blood from the glans penis and corpora cavernosa penis and courses backward in the middle line between the dorsal arteries; near the root of the penis it passes between the two parts of the suspensory ligament and then through an aperture between the arcuate pubic ligament and the transverse ligament of the pelvis, and divides into two branches, which enter the pudendal plexus. The deep vein also communicates below the symphysis pubis with the internal pudendal vein. The uterine plexuses lie along the sides and superior angles of the uterus between the two layers of the broad ligament, and communicate with the ovarian and vaginal plexuses. They are drained by a pair of uterine veins on either side: these THE VEINS OF THE ABDOMEN AND PELVIS- 677 arise from the lower part of the plexuses, opposite the external orifice of the uterus, and open into the corresponding hypogastric vein. I he vaginal plexuses are placed at the sides of the vagina; they communicate with the uterine, vesical, and hemorrhoidal plexuses, and are drained by the vaginal veins, one on either side, into the hypogastric veins. The common iliac yeins (vv. iliacce communes) are formed by the union of the external iliac and hypogastric veins, in front of the sacroiliac artic- ulation; passing obliquely upward toward the right side, they end upon the fifth lumbar vertebra, by uniting with each other at an acute angle to form the inferior vena cava. The right common iliac is shorter than the left, nearly vertical in its di- rection, and ascends behind and then lateral to its corresponding artery. The left common iliac, longer than the right and more oblique in its '* course, is at first situated on the medial side of the corresponding artery, and then behind the right common iliac. Each common iliac receives the iliolumbar, and sometimes the lateral sacral veins. The left receives, in addition, the middle sacral vein. No valves are found in these veins. The Middle Sacral Veins (vv. sacrales mediates) accompany the corresponding artery along the front of the sacrum, and join to form a single vein, which ends in the left common iliac vein; sometimes in the angle of junction of the two iliac veins. SUPERFICIAL DOR- SAL VEIN CORPUS CAVER nosum; DORSAL ARTERY .DEEP DORSAL VEIN SUPERFICIAL FASCIA SKIN- AREOLAR " TISSUE CAVERNOUS... ARTERV DEEP FASCIA BULBO-CAVERNOUS ARTERY, — ANTERIOR BRANCH CORPUS SPONGIOSUM URETHRA Pig. 588.—The penis in transverse section, showing the bloodvessels. TUBAL VESSELS ANASTOMOSIS OF UTERINE AND OVARIAN ARTERIES FALLOPIAN TUfBE HELICINE BRANCHES UTERINE VENOUS PLEXUS/ UTERO- SACRAL I /LIGA- / MENT “ROUND LIGAMENT URETER UTERINE/ veins' fUTERI N E ARTERY VAGINAL VENOUS PLEXUS ■'SUPERIOR VAGINAL ARTERIES OS UTERI* VAGINA CUT OPEN BEHIND Fig. 589.—Vessels of the uterus and its appendages, rear view. Peculiarities.—The left common'iliac vein, instead of joining with the right in its usual posi- tion, occasionally ascends on the left side of the aorta as high as the kidney, where, after receiving the left renal vein, it crosses over the aorta, and then joins with the right vein to form the vena cava. In these cases, the two common iliacs are connected by a small communicating branc at the spot where they are usually united. The inferior vena cava (v. cava inferior) (Fig. 577), returns to the heart the blood from the parts below the diaphragm. It is formed by the junction of the two common iliac veins, on the right side of the fifth lumbar vertebra. It ascends a ong 678 ANGIOLOGY the front of the vertebral column, on the right side of the aorta, and, having reached the liver, is continued in a groove on its posterior surface. It then perforates the diaphragm between the median and right portions of its central tendon; it subsequently inclines forward and medialward for about 2.5 cm., and, piercing the fibrous pericardium, passes behind the serous pericardium to open into the lower and back part of the right atrium. In front of its atrial orifice is a semilunar valve, termed the valve of the inferior vena cava: this is rudimentary in the adult, but is of large size and exercises an important function in the fetus (see page 540). Relations.—The abdominal portion of the inferior vena cava is in relation in front, from below upward, with the right common iliac artery, the mesentery, the right internal spermatic artery, the inferior part of the duodenum, the pancreas, the common bile duct, the portal vein, and the posterior surface of the liver; the last partly overlaps and occasionally completely surrounds it; behind, with the vertebral column, the right Psoas major, the right crus of the diaphragm, the right inferior phrenic, suprarenal, renal and lumbar arteries, right sympathetic trunk and right celiac ganglion, and the medial part of the right suprarenal gland; on the right side, with the right kidney and ureter; on the left side, with the aorta, right crus of the diaphragm, and the caudate lobe of the liver. The thoracic portion is only about 2.5 cm. in length, and is situated partly inside and partly outside the pericardial sac. The extrapericardial part is separated from the right pleura and lung by a fibrous band, named the right phrenicopericardiac ligament. This ligament, often feebly marked, is attached below to the margin of the vena-caval opening in the diaphragm, and above to the pericardium in front of and behind the root of the right lung. The intrapericardiac part is very short, and is covered antero-laterally by the serous layer of the pericardium. Peculiarities.—In Position.—This vessel is sometimes placed on the left side of the aorta, aa high as the left renal vein, and, after receiving this vein, crosses over to its usual position on the right side; or it may be placed altogether on the left side of the aorta, and in such a case the abdominal and thoracic viscera, together with the great vessels, are all transposed. Point of Termination.—Occasionally the inferior vena cava joins the azygos vein, which is then of large size. In such cases, the superior vena cava receives the whole of the blood from the body before transmitting it to the right atrium, except the blood from the hepatic veins, which passes directly into the right atrium. Tributaries.—The inferior vena cava receives the following veins: Lumbar. Right Spermatic or Ovarian. Renal. Suprarenal. Inferior Phrenic. Hepatic. The Lumbar Veins (vv. lumbales) four in number on each side, collect the blood by dorsal tributaries from the muscles and integument of the loins, and by abdomi- nal tributaries from the walls of the abdomen, where they communicate with the epigastric veins. At the vertebral column, they receive veins from the vertebral plexuses, and then pass forward, around the sides of the bodies of the vertebrae, beneath the Psoas major, and end in the back part of the inferior cava. The left lumbar veins are longer than the right, and pass behind the aorta. The lumbar veins are connected together by a longitudinal vein which passes in front of the transverse processes of the lumbar vertebrae, and is called the ascending lumbar; it forms the most frequent origin of the corresponding azygos or hemiazygos vein, and serves to connect the common iliac, iliolumbar, and azygos or hemiazygos veins of its own side of the body. The Spermatic Veins (vv. sperviaticce) (Fig. 590) emerge from.the back of the testis, and receive tributaries from the epididymis; they unite and form a convo- luted plexus, called the pampiniform plexus, which constitutes the greater mass of the spermatic cord; the vessels composing this plexus are very numerous, and ascend along the cord, in front of the ductus deferens. Below the subcutaneous inguinal ring they unite to form three or four veins, which pass along the inguinal canal, and, entering the abdomen through the abdominal inguinal ring, coalesce to form two veins, which ascend on the Psoas major, behind the peritoneum, lying one on either side of the internal spermatic artery. These unite to form a single vein, which opens on the right side into the inferior vena cava, at an acute angle; on the left side into the left renal vein, at a right angle. The spermatic veins THE VEINS OF THE ABDOMEN AND PELVIS 679 are provided with valves.1 The left spermatic vein passes behind the iliac colon, and is thus exposed to pressure from the contents of that part of the bowel. The Ovarian Veins {vv. ovaricce) correspond with the spermatic in the male; they form a plexus in the broad ligament near the ovary and uterine tube, and communi- cate with the uterine plexus. They end in the same way as the spermatic veins in the male. Valves are occasionally found in these veins. Like the uterine veins, they become much enlarged during pregnancy. The Renal Veins (vv. renales) are of large size, and placed in front of the renal arteries. The left is longer than the right, and passes in front of the aorta, just below the origin of the superior mesenteric artery. It receives t le left spermatic and left inferior phrenic veins, and, generally, the left suprarenal vein. It opens into the inferior vena cava at a slightly higher level than the right. The Suprarenal Veins {vv. suprarenales) are two in number: the right ends m the inferior vena cava; the left, in the left renal or left inferior phrenic vein. . The Inferior Phrenic Veins (vv. phrenicce inferiores) follow the course of the inferior phrenic arteries; the right ends in the inferior vena cava; the left is often repre- sented by two branches, one of which ends in the left renal or suprarenal v ein, while the other passes in front of the esophageal hiatus in the diaphragm and opens into the inferior vena cava. Fig. 590.—Spermatic veins. 1 Rivington has pointed out that valves are usually found at the orifices bo**)vrSv-e 1 present in When no valves exist at the opening of the left spermatic vein into the the left renal vein within 6 mm from the orifice of the spermatic vein.—Journal of Anatomy and l fiysioiogy, vu, 680 ANGIOLOGY The Hepatic Veins (vv. hepaticce) commence in the substance of the liver, in the terminations of the portal vein and hepatic artery, and are arranged in two groups, upper and lower. The upper group usually consists of three large veins, which converge toward the posterior surface of the liver, and open into the inferior vena cava, while that vessel is situated in the groove on the back part of the liver. The veins of the lower group vary in number, and are of small size; they come from the right and caudate lobes. The hepatic veins run singly, and are in direct contact with the hepatic tissue. They are destitute of valves. Fig. 591.—The portal vein and its tributaries. THE PORTAL SYSTEM OF VEINS (Fig. 591). The portal system includes all the veins which drain the blood from the abdominal part of the digestive tube (with the exception of the lower part of the rectum) and from the spleen, pancreas, and gall-bladder. From these viscera the blood is conveyed to the liver by the portal vein. In the liver this vein ramifies like an artery and ends in capillary-like vessels termed sinusoids, from which the blood is THE PORTAL SYSTEM OF VEINS 681 conveyed to the inferior vena cava by the hepatic veins. From this it will be seen that the blood of the portal system passes through two sets of minute vessels, viz., (a) the capillaries of the digestive tube, spleen, pancreas, and gall-bladder; and (b) the sinusoids of the liver. In the adult the portal vein and its tributaries are destitute of valves; in the fetus and for a short time after birth valves can be demonstrated in the tributaries of the portal vein; as a rule they soon atrophy and disappear, but in some subj'ects they persist in a degenerate form. The portal vein (vena portce) is about 8 cm. in length, and is formed at the level of the second lumbar vertebra by the j"unction of the superior mesenteric and lienal veins, the union of these veins taking place in front of the inferior vena cava and behind the neck of the pancreas. It passes upward behind the superior part of the duodenum and then ascends in the right border of the lesser omentum to the right extremity of the porta hepatis, where it divides into a right and a left branch, which accompany the corresponding branches of the hepatic artery into the sub- stance of the liver. In the lesser omentum it is placed behind and between the common bile duct and the hepatic artery, the former lying to the right of the latter. It is surrounded by the hepatic plexus of nerves, and is accompanied by numerous lymphatic vessels and some lymph glands. The right branch of the portal vein enters the right lobe of the liver, but before doing so generally receives the cystic vein. The left branch, longer but of smaller caliber than the right, crosses the left sagittal fossa, gives branches to the caudate lobe, and then enters the left lobe of the liver. As it crosses the left sagittal fossa it is j'oined in front by a fibrous cord, the ligamentum teres (obliterated umbilical vein),.and is united to the inferior vena cava by a second fibrous cord, the ligamentum venosum (obliterated ductus venosus). Tributaries.—The tributaries of the portal vein are: Lienal. Superior Mesenteric. Coronary. Pyloric, Cystic. Parumbilical. The Lienal Vein (v. lienalis; splenic vein) commences by five or six large branches which return the blood from the spleen. These unite to form a single vessel, which passes from left to right, grooving the upper and back part of the pancreas, below the lineal artery, and ends behind the neck of the pancreas by uniting at a right angle with the superior mesenteric to form the portal vein. The lienal vein is of large size, but is not tortuous like the artery. Tributaries.—The lineal vein receives the short gastric veins, the left gastro- epiploic vein, the pancreatic veins, and the inferior mesenteric veins. The short gastric veins (vv. gastricce breves), fourot five in number, drain the fundus and left part of the greater curvature of the stomach, and pass between the two layers of the gastrolienal ligament to end in the lienal vein or in one of its large tributaries. The left gastroepiploic vein (v. gastroepiploic a sinistra) receives branches from the antero-superior and postero-inferior surfaces of the stomach and from the greater omentum; it runs from right to left along the greater curvature of the stomach and ends in the commencement of the lienal vein. . The pancreatic veins (vv. pancreaticee) consist of several small vessels which dram the body and tail of the pancreas, and open into the trunk of the lienal vein. The inferior mesenteric vein (v. mesenterica inferior) returns blood from the rectum and the sigmoid, and descending parts of the colon.. It begins in the rectum as the superior hemorrhoidal vein, which has its origin in the hemorrhoidal plexus, and through this plexus communicates with the middle and inferior hemor- rhoidal veins. The superior hemorrhoidal vein leaves the lesser peh is and crosses the left common iliac vessels with the superior hemorrhoidal artery and is con- tinued upward as the inferior mesenteric vein. This vein lies to the left ot its artery, and ascends behind the peritoneum and in front of the left 1 soas major, 682 ANGIOLOGY it then passes behind the body of the pancreas and opens into the lienal vein; sometimes it ends in the angle of union of the lienal and superior mesenteric veins. Tributaries.—The inferior mesenteric vein receives the sigmoid veins from the sigmoid colon and iliac colon, and the left colic vein from the descending colon and left colic flexure. The Superior Mesenteric Vein (v. mesenterica superior) returns the blood from the small intestine, from the cecum, and from the ascending and transverse portions of the colon. It begins in the right iliac fossa by the union of the veins which drain the terminal part of the ileum, the cecum, and vermiform process, and ascends between the two layers of the mesentery on the right side of the superior mes- enteric artery. In its upward course it passes in front of the right ureter, the inferior vena cava, the inferior part of the duodenum, and the lower portion of the head of the pancreas. Behind the neck of the paflcreas it unites with the lienal vein to form the portal vein. Tributaries.—Besides the tributaries which correspond with the branches of the superior mesenteric artery, viz., the intestinal, ileocolic, right colic, and middle colic veins, the superior mesenteric vein is joined by the right gastroepiploic and pan- creaticoduodenal veins. The right gastroepiploic vein (v. gastroepiploica dextra) receives branches from the greater omentum and from the lower parts of the antero-superior and postero- inferior surfaces of the stomach; it runs from left to right along the greater curva- ture of the stomach between the two layers of the greater omentum. The pancreaticoduodenal veins (vv. pancreaticoduodenales) accompany their corre- sponding arteries; the lower of the two frequently joins the right gastroepiploic vein. The Coronary Vein (v. coronaria ventriculi; gastric vein) derives tributaries from both surfaces of the stomach; it runs from right to left along the lesser curvature of the stomach, between the two layers of the lesser omentum, to the esophageal opening of the stomach, where it receives some esophageal veins. It then turns backward and passes from left to right behind the omental bursa and ends in the portal vein. The Pyloric Vein is of small size, and runs from left to right along the pyloric portion of the lesser curvature of the stomach, between the two layers of the lesser omentum, to end in the portal vein. The Cystic Vein (v. cystica) drains the blood from the gall-bladder, and, accom- panying the cystic duct, usually ends in the right branch of the portal vein. Parumbilical Veins (vv. parumbilicales).—In the course of the ligamentum teres of the liver and of the middle umbilical ligament, small veins (parumbilical) are found which establish an anastomosis between the veins of the anterior abdominal wall and the portal, hypogastric, and iliac veins. The best marked of these small veins is one which commences at the umbilicus and runs backward and upward in, or on the surface of, the ligamentum teres between the layers of the falciform ligament to end in the left portal vein. Collateral venous circulation to relieve portal obstruction in the liver may be effected by communications between (a) the gastric veins and the esophageal veins which often project as a varicose bunch into the stomach, emptying themselves into the hemiazygos vein; (b) the veins of the colon and duodenum and the left renal vein; (c) the accessory portal system of Sappey, branches of which pass in the round and falciform ligaments (particularly the latter) to unite with the epigastric and internal mammary veins, and through the diaphragmatic veins with the azygos; a single large vein, shown to be a parumbilical vein, may pass from the hilus of the liver by the round ligament to the umbilicus, producing there a bunch of prominent varicose veins known as the caput 'medusae; (d) the veins of Retzius, which connect the intestinal veins with the inferior vena cava and its retroperitoneal branches; (e) the inferior mesenteric veins, and the hemorrhoidal veins that open into the hypogastrics; (/) very rarely the ductus venosus remains patent, affording a direct connection between the portal vein and the inferior vena cava. THE LYMPHATIC SYSTEM. rpHE lymphatic system consists (1) of complex capillary networks which collect the lymph in the various organs and tissues; (2) of an elaborate system of collecting vessels which conduct the lymph from the capillaries to the large veins of the neck at the junction of the internal jugular and subclavian veins, where the lymph is poured into the blood stream; and (3) lymph glands or nodes which are inter- spaced in the pathways of the collecting vessels filtering the lymph as it passes through them and contributing lymphocytes to it. The lymphatic capillaries and collecting vessels are lined throughout by a continuous layer of endothelial cells, forming thus a closed system. The lymphatic vessels of the small intestine receive the special designation of lacteals or chyliferous vessels; they differ in no respect from the lymphatic vessels generally excepting that during the process of digestion they contain a milk-white fluid, the chyle. Left innominate Internal jugular Jugular lymph-sac External jugular Right innominate Superior vena cava Duct of Cuvier Left cardinal Prerenal part of inferior vena cava Left suprarenal Left renal Retro-peritoneal Postrenal part of inferior vena cava lymph-sac Cisterna chyli Posterior lymph-sac Left common iliac External iliac Fig. 592.—Scheme showing relative positions of primary lymph sacs based on the description given by Florence Sabin. Hypogastric The Development of the Lymphatic Vessels.—-The lymphatic system begins as a series of sacs1 at the points of junction of certain of the embryonic veins. lese lymph-sacs are developed by the confluence of numerous venous capillaries, w ic 1 at first lose their connections with the venous system, but subsequently, on t ie formation of the sacs, regain them. The lymphatic system is therefore deve op- mentally an offshoot of the venous system, and the lining walls of its vessels are In the human embryo the lymph sacs from which the lymphatic vessels are i sabin, Am. Jour. Anat., 1909, vol. ix; Johns Hopkins Hospital Reports, 1913. 684 ANGIOLOGY derived are six in number; two paired, the jugular and the posterior lymph-sacs; and two unpaired, the retroperitoneal and the cisterna chyli. In lower mammals an additional pair, subclavian, is present, but in the human embryo these are merely extensions of the jugular sacs. The position of the sacs is as follows: (1) jugular sac, the first to appear, at the junction of the subclavian vein with the primitive jugular; (2) posterior sac, at the junction of the iliac vein with the cardinal; (3) retroperitoneal, in the root of the mesentery near the suprarenal glands; (4) cisterna chyli, opposite the third and fourth lumbar vertebrae (Fig. 592). From the lymph-sacs the lymphatic vessels bud out along fixed lines corresponding more or less closely to the course of the embryonic bloodvessels. Both in the body-wall and in the wall of the intestine, the deeper plexuses are the first to be developed; by continued growth of these the vessels in the superficial layers are gradually formed. The thoracic duct is probably formed from anastomosing outgrowths from the jugular sac and cisterna chyli. At its connection with the cisterna chyli it is at first double, but the two vessels soon join. All the lymph-sacs except the cisterna chyli are, at a later stage, divided up by slender connective tissue bridges and transformed into groups of lymph glands. The lower portion of the cisterna chyli is similarly converted, but its upper portion remains as the adult cisterna. Lymphatic Capillaries.—The complex capillary plexuses which consist of a single layer of thin flat endothelial cells lie in the connective-tissue spaces in the various regions of the body to which they are distributed and are bathed by the intercellular tissue fluids. Two views are at present held as to the mode in which the lymph is formed: one being by the physical processes of filtration, diffusion, and osmosis, and the other, that in addition to these physical processes the endothelial cells have an active secretory function. The colorless liquid lymph has about the same composition as the blood plasma. It contains many lymphocytes and fre- quently red blood corpuscles. Granules and bacteria are also taken up by the lymph from the connective-tissue spaces, partly by the action of lymphocytes which pass into the lymph between the endothelial cells and partly by the direct passage of the granules through the endothelial cells. The lymphatic capillary plexuses vary greatly in form; the anastomoses are usually numerous; blind ends or cul-de-sacs are especially common in the intestinal villi, the dermal papillae and the filiform papillae of the tongue. The plexuses are often in two layers: a superficial and a deep, the superficial being of smaller caliber than the deep. The caliber, however, varies greatly in a given plexus from a few micromillimeters to one millimeter. The capillaries are without valves. Distribution.—The Skin.—Lymphatic capillaries are abundant in the dermis where they form superficial and deep plexuses, the former sending blind ends into the dermal papillae. The plexuses are especially rich over the palmar surface of the hands and fingers and over the plantar surface of the feet and toes. The epidermis is without capillaries. The conjunctiva has an especially rich plexus. The subcutaneous tissue is without capillaries. The tendons of striated muscle and muscle sheaths are richly supplied. In muscle, however, their existence is still disputed. The periosteum of bone is richly supplied and they have been described in the Haversian canals. They are absent in cartilage and probably in bone marrow. The joint capsules are richly supplied with lymphatic capillaries, they do not, however, open into the joint cavities. Beneath the mesothelium lining of the pleural, peritoneal and pericardial cavities are rich plexuses; they do not open into these cavities. The alimentary canal is supplied with rich plexuses beneath the epithelium, often as a superficial plexus in the niucosa and a deeper submucosal plexus. Cul-de-sacs LYMPHATIC CAPILLARIES 685 extend into the filiform papillae of the tongue and the villi of the small intestine. lost1 portions of the alimentary canal covered by peritoneum, have in addition a subserous h mphatic capillary plexus beneath the mesothelium. Fig. 593.—Lymph capillaries of the human conjunctiva: a, conjunctiva cornea:: 6, conjunctiva sclerotic®, X 40 dia. (Teichmann.) Fig. 594.—Lymph capillaries from the human scrotum, showing also transition from capillaries to the collecting vessels o, a. X 20 dia. (Teichmann.) The salivary glands are supplied with lymphatic capillaries. The liver has a rich subserous plexus in the capsule and also extensive plexuses which accompany the hepatic artery and portal vein. I he lymphatic capillaries have not been followed into the liver lobules. The lymph from the liver forms a 686 ANGIOLOGY large part of that which flows through the thoracic duct. The gall-bladder and bile ducts have rich subepithelial plexuses and the former a subserous plexus. I he spleen ha,s a rich subserous set and a capsular set of lymphatic capillaries. Their presence in the parenchyma is uncertain. Fig. 595.—Lymph capillaries of the cutis from the inner border of the sole of the human foot, a, a, outer layer b, b, inner layer. X 30 dia. (Teichmann.) The nasal cavity has extensive capillary plexuses in the mucosa and submucosa. The trachea and bronchi have plexuses in the mucosa and submucosa but the smaller bronchi have only a single layer. The capillaries do not extend to the air-cells. The plexuses around the smaller bronchi connect with the rich subserous plexus of the lungs in places where the veins reach the surface. Fig. 596.—Vertical section through human tongue; a, a, blind lymph capillaries in the filiform papillae with the under- lying lymphatic plexus. X 45. (Teichmann.) Lymphatics have been described in the thyroid gland and in the thymus. The adrenal has a superficial plexus divided into two layers, one in the loose tissue about the gland and the other beneath the capsule. Capillaries have also been described within the parenchyma. STRUCTURE OF LYMPHATIC VESSELS 687 The kidney is supplied with a coarse subserous plexus and a deeper plexus of finer capillaries in the capsule. Lymphatics have been described within the sub- stance of the kidney surrounding the tubules. The urinary bladder has a rich plexus of lymphatic capillaries just beneath the epithelial lining, also a subserous set which anastomoses with the former through the muscle layer. The submucous plexus is continuous with the submucous plexus of the urethra. The prostate has a rich lymphatic plexus surrounding the gland and a wide- meshed subcapsular plexus. The testis has a rich superficial plexus beneath the tunica albuginea. The pres- ence of deep lymphatics is disputed. The uterus is provided with a subserous plexus, the deeper lymphatics are uncertain. Subepithelial plexuses are found in the vagina. The ovary has a rich superficial plexus and a deep interstitial plexus. The heart has a rich subserous plexus beneath the epicardium. Lymphatic capillaries have also been described beneath the endocardium and throughout the muscle. Lymphatic capillaries are probably absent in the central nervous system, the meninges, the eyeball (except the conjunctiva), the orbit, the internal ear, within striated muscle, the liver lobule, the spleen pulp and kidney parenchyma. They are entirely absent in cartilage. In many places further investigation is needed. Lymphatic Vessels.—The lymphatic vessels are exceedingly delicate, and their coats are so transparent that the fluid they contain is readily seen through them. They are interrupted at intervals by constrictions, which give them a knotted or beaded appearance; these constrictions correspond to the situations of valves in their interior. Lymphatic vessels have been found in nearly every texture and organ of the body which contains bloodvessels. Such non-vascular structures as cartilage, the nails, cuticle, and hair have none, but these with exceptions it is probable that eventually all parts will be found to be permeated by these vessels. Structure of Lymphatic Vessels.—The larger lymphatic vessels are each composed of three coats. The internal coat is thin, transparent, slightly elastic, and consists of a layer of elongated endothelial cells with wavy margins by which the contiguous cells are dovetailed into one another; the cells are supported on an elastic membrane. The middle coat is composed of smooth muscular and fine elastic fibers, disposed in a transverse direction. The external coat consists of connective tissue, intermixed with smooth muscular fibers longitudinally or obliquely disposed; it forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures. In the smaller vessels there are no muscular or elastic fibers, and the wall consists only of a connective-tissue coat, lined by endothelium. The thoracic duct has a more complex structure than the other lymphatic vessels; it presents a distinct subendothelial layer of branched corpuscles, similar to that found in the arteries; in the middle coat there is, in addition to the muscular and elastic fibers, a layer of connective tissue with its fibers arranged longitudinally. The lymphatic vessels are supplied by nutrient vessels, which are distributed to their outer and middle coats; and here also have been traced many non-medullated nerves in the form of a fine plexus of fibrils. The valves of the lymphatic vessels are formed of thin layers of fibrous tissue covered on both surfaces by endothelium which presents the same arrangement as on the valves of veins (p. 501). In form the valves are semilunar; they are attached by their convex edges to the wall of the vessel, the concave edges being free and directed along the course of the contained current. Usually two such valves, of equal size, are found opposite one another; but occasionally excep- tions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may be of small size and the other increased in proportion. In the lymphatic vessels the valves are placed at much shorter intervals than in the veins. They are most numerous near the lymph glands, and are found more frequently in the lymphatic vessels of the neck and upper extremity than in those of the lower extremity. The wall of the lymphatic vessel immediately above the point of attachment of each segment of a valve is expanded into a pouch or sinus which gives to these vessels, when distended, the knotted or beaded appearance already referred to. Valves are wanting in the vessels composing the plexi- form net-work in which the lymphatic vessels usually originate on the surface of the body. 688 ANGIOLOGY Lympn Glands (lyrnyhoglandulce).—The lymph glands are small oval or bean- shaped bodies, situated in the course of lymphatic and lacteal vessels so that the lymph and chyle pass through them on their way to the blood. Each generally presents on one side a slight depression—the hilus—through which the bloodvessels enter and leave the interior. The efferent lymphatic vessel also emerges from the gland at this spot, while the afferent vessels enter the organ at different parts of the periphery. On section (Fig. 597) a lymph gland displays two different struc- tures: an external, of lighter color—the cortical; and an internal, darker—the medullary. The cortical structure does not form a complete investment, but is deficient at the hilus, where the medullary portion reaches the surface of the gland; so that the efferent vessel is derived directly from the medullary structures, while the afferent vessels empty themselves into the cortical substance. Lymphoid tissue in cortex Svbcapsular lymph-path Lymph-path in medulla Fig. 597.—Section of small lymph gland of rabbit. X 100. Structure of Lymph Glands.—A lymph gland consists of (1) a fibrous envelope, or capsule, from which a frame-work of processes (trabeculae) proceeds inward, imperfectly dividing the gland into open spaces freely communicating with each other; (2) a quantity of lymphoid tissue occupying these spaces without completely filling them; (3) a free supply of bloodvessels, which are supported in the trabeculae; and (4) the afferent and efferent vessels communicating through the lymph paths in the substance of the gland. The nerves passing into the hilus are few in number and are chiefly distributed to the bloodvessels supplying the gland. The capsule is composed of connective tissue with some plain muscle fibers, and from its internal surface are given off a number of membranous processes or trabeculae, consisting, in man, of connective tissue, with a small admixture of plain muscle fibers; but in many of the lower animals composed almost entirely of involuntary muscle. They pass inward, radiating toward the center of the gland, for a certain distance—that is to say, for about one-third or one-fourth of the space between the circumference and the center of the gland. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the gland into a number of compart- ments (so-called follicles), but in man this arrangement is not obvious. The larger trabeculae springing from the capsule break up into finer bands, and these interlace to form a mesh-work in the central or medullary portion of the gland. In these spaces formed by the interlacing trabeculae is contained the proper gland substance or lymphoid tissue. The gland pulp does not, however, completely fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout. This is termed the lymph path STRUCTURE OF LYMPH GLANDS 689 or lymph sihus (Fig. 597). Running across it are a number of finer trabeculae of retiform con- nective tissue, the fibers of which are, for the most part, covered by ramifying cells. On account of the peculiar arrangement of the frame-work of the organ, the gland pulp in the cortical portion is disposed in the form of nodules, and in the medullary part in the form of rounded cords. It consists of ordinary lymphoid tissue (Fig. 598), being made up of a delicate net-work of retiform tissue, which is continuous with that in the lymph paths, but marked off from it by a closer reticulation; it is probable, moreover, that the reticular tissue of the gland pulp and the lymph paths is continuous with that of the trabeculee, and ultimately with that of the capsule of the gland. In its meshes, in the nodules and cords of lymphoid tissue, are closely packed lymph corpuscles. The gland pulp is traversed by a dense plexus of capillary bloodvessels. The nodules or follicles in the cortical portion of the gland frequently show, in their centers, areas where karyokinetic figures indicate a division of the lymph corpuscles. These areas are termed germ centers. The cells composing them have more abundant protoplasm than the peripheral cells. The afferent vessels, as stated above, enter at all parts of the periphery of the gland, and after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. In doing this they lose all their coats except their endothelial lining, which is continuous with a layer of similar cells lining the lymph paths. In like manner the efferent vessel commences from the lymph sinuses of the medullary portion. The stream of lymph carried to the gland by the afferent vessels thus passes through the plexus in the capsule to the lymph Fig. 598.—Lymph gland tissue. Highly magnified, a, Trabeculae, b. Small artery in substance of same, c. Lymph paths, d. Lymph corpuscles, e. Capillary plexus. paths of the cortical portion, where it is exposed to the action of the gland pulp; flowing through these it enters the paths or sinuses of the medullary portion, and finally emerges from the hilus by means of the efferent vessel. The stream of lymph in its passage through the lymph sinuses is much retarded by the presence of the reticulum, hence morphological elements, either normal or morbid, are easily arrested and deposited in the sinuses. Many lymph corpuscles pass with the efferent lymph stream to join the general blood stream. Ihe arteries of the gland enter at the hilus, and either go at once to the gland pulp, to break up into a capillary plexus, or else run along the trabeculae, partly to supply them and partly running across the lymph paths, to assist in forming the capillary plexus of the gland pulp. This plexus traverses the lymphoid tissue, but does not enter into the lymph sinuses. From it the veins commence and emerge from the organ at the same place as that at which the arteries enter. The lymphatic vessels are arranged into a superficial and a deep set. On the surface of the body the superficial lymphatic vessels are placed immediately beneath the integument, accompanying the superficial veins; they join the deep lymphatic vessels in certain situations by perforating the deep fascia. In the interior of the body they lie in the submucous areolar tissue, throughout the whole length of the digestive, respiratory, and genitourinary tracts; and in the subserous tissue of the thoracic and abdominal walls. Plexiform netw orks of minute lym- phatic vessels are found interspersed among the proper elements and bloodvesse s of the several tissues; the vessels composing the net-work, as well as the meshes 690 ANGIOLOGY between them, are much larger than those of the capillary plexus. From these net-works small vessels emerge, which pass, either to a neighboring gland, or to join some larger lymphatic trunk. The deep lymphatic vessels, fewer in number, but larger than the superficial, accompany the deep bloodvessels. Their mode of origin is probably similar to that of the superficial vessels. The lymphatic vessels of any part or organ exceed the veins in number, but in size they are much smaller. Their anastomoses also, especially those of the large trunks, are more frequent, and are effected by vessels equal in diameter to those which they connect, the con- tinuous trunks retaining the same diameter. Hemolymph nodes or glands and hemal nodes which are so abundant in some mammals are probably not present in man. Lymph.—Lymph, found only in the closed lymphatic vessels, is a transparent, colorless, or slightly yellow, watery fluid of specific gravity about 1.015; it closely resembles the blood plasma, but is more dilute. When it is examined under the microscope, leucocytes of the lymphocyte class are found floating in the transparent fluid; they are always increased in number after the passage of the lymph through lymphoid tissue, as in lymph glands. Lymph should be distinguished from “ tissue fluid”1 which is found outside the lymphatic vessels in the tissue spaces. THE THORACIC DUCT. The thoracic duct (ductus thoracicus) (Fig. 599) conveys the greater part of the lymph and chyle into the blood. It is the common trunk of all the lymphatic vessels of the body, excepting those on the right side of the head, neck, and thorax, and right upper extremity, the right lung, right side of the heart, and the convex surface of the liver. In the adult it varies in length from 38 to 45 cm. and extends from the second lumbar vertebra to the root of the neck. It begins in the abdomen by a triangular dilatation, the cisterna chyli, which is situated on the front of the body of the second lumbar vertebra, to the right side of and behind the aorta, by the side of the right crus of the diaphragm. It enters the thorax through the aortic hiatus of the diaphragm, and ascends through the posterior mediastinal cavity between the aorta and azygos vein. Behind it in this region are the vertebral column, the right intercostal arteries, and the hemiazygos veins as they cross to open into the azygos vein; in front of it are the diaphragm, esophagus, and peri- cardium, the last being separated from it by a recess of the right pleural cavity. Opposite the fifth thoracic vertebra, it inclines toward the left side, enters the supe- rior mediastinal cavity, and ascends behind the aortic arch and the thoracic part of the left subclavian artery and between the left side of the esophagus and the left pleura, to the upper orifice of the thorax. Passing into the neck it forms an arch which rises about 3 or 4 cm. above the clavicle and crosses anterior to the subclavian artery, the vertebral artery and vein, and the thyrocervical trunk or its branches. It also passes in front of the phrenic nerve and the medial border of the Scalenus anterior, but is separated from these two structures by the pre- vertebral fascia. In front of it are the left common carotid artery, vagus nerve, and internal jugular vein; it ends by opening into the angle of junction of the left subclavian vein with the left internal jugular vein. The thoracic duct, at its com- mencement, is about equal in diameter to a goose-quill, but it diminishes consid- erably in caliber in the middle of the thorax, and is again dilated just before its termination. It is generally flexuous, and constricted at intervals so as to present a varicose appearance. Not infrequently it divides in the middle of its course into two vessels of unequal size which soon reunite, or into several branches which form 1 Sabin, Harvey Lecture, Series ix, New York, 1915-16. THE THORACIC DUCT 691 a plexiform interlacement. It occasionally divides at its upper part into two branches, right and left; the left ending in the usual manner, while the right opens into the right subclavian vein, in connection with the right lymphatic duct. The thoracic duct has several valves; at its termination it is pro- vided with a pair, the free borders of which are turned toward the vein, so as to prevent the passage of venous blood into the duct. The cisterna chyli (receptaculum chyli) (Fig. 600) receives the two lumbar lymphatic trunks, right and left, and the intestinal lymphatic trunk. The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph glands. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kid- neys and suprarenal glands and the deep lymphatics of the greater part of the abdominal wall. The intes- tinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver. Tributaries.—Opening into the commencement of the thoracic duct, on either side, is a descending trunk from the posterior intercostal lymph glands of the lower six or seven in- tercostal spaces. In the thorax the duct is joined, on either side, by a trunk which drains the upper lumbar lymph glands and pierces the crus of the diaphragm. It also receives the efferents from the posterior mediastinal lymph glands and from the posterior intercostal lymph glands of the upper six left spaces. In the neck it is joined by the left jugular and left subclavian trunks, and sometimes by the left broncho- mediastinal trunk; the last-named, however, usually opens indepen- dently into the junction of the left subclavian and internal jugular veins. The right lymphatic duct (ductus lymphaticus dexter) (Fig. 601), about 1.25 cm. in length, courses along the medial border of the Scalenus anterior at the root of the neck and ends in the right subclavian vein, at its angle of junction with the right internal jugular vein. Its orifice is guarded by two semilunar valves, which prev ent the passage of venous blood into the duct. Right lymphatic duct y Posterior intercostal 1 glands J Lumbar glands r Fig. 599.—The thoracic and right lymphatic ducts. 692 ANGIOLOGY Tributaries.—The right lymphatic duct receives the lymph from the right side of the head and neck through the right jugular trunk; from the right upper extremity through the right subclavian trunk; from the right side of the thorax, right lung, Fig. 600.—Modes of origin of thoracic duct. (Poirier and Charpy.) a. Thoracic duct. a'. Cistema chyli. 5, c Efferent trunks from lateral aortic glands, d. An efferent vessel which pierces the left crus of the diaphragm, c. f. Lateral aortic glands, h. Retroaortic glands, i. Intestinal trunk, j. Descending branch from intercostal lymphatics. right side of the heart, and part of the convex surface of the liver, through the right bronchomediastinal trunk. These three collecting trunks frequently open separately in the angle of union of the two veins. Fig. 601.—Terminal collecting trunks of right side. (Poirier and Charpy.) a. Jugular trunk. 6. Subclavian trunk, c. Bronchomediastinal trunk, d. Right lymphatic trunk, e. Gland of internal mammary chain. /. Gland of deep cervical chain. THE LYMPHATICS OF THE HEAD, FACE, AND NECK. The Lymph Glands of the Head (Fig. 602). The lymph glands of the head are arranged in the following groups: Occipital. Posterior Auricular. Anterior Auricular. Parotid. Facial. Deep Facial. Lingual. Retropharyngeal. The occipital glands (lymphoglandulce occipitales), one to three in number, are placed on the back of the head close to the margin of the Trapezius and resting on the insertion of the Semispinalis capitis. Their afferent vessels drain the occipi- tal region of the scalp, while their efferents pass to the superior deep cervical glands. THE LYMPH GLANDS OF THE HEAD ie posterior auricular glands (lymphoglandulce auriculares; mastoid glands), usually tw o m number, are situated on the mastoid insertion of the Sternocleido- mastoideus, beneath the Auricularis posterior. Their afferent vessels drain the posterior part of the temporoparietal region, the upper part of the cranial surface of the auricula or pinna,. and the back of the external acoustic meatus; their efferents pass to the superior deep cervical glands. 693 •Maxillary glands Posterior auricular - glands Parotid glands Occipital glands ■Buccinator glands Supramandibular glands Superficial cervical glands .Suibmaxillary glands 'Submental glands Superior deep cervical glands .Inferior deep cervical glands Fig. 602.—Superficial lymph glands and lymphatic vessels of head and neck. The anterior auricular glands (lymphoglandulce auriculares anteriores; superficial parotid or preauricular glands), from one to three in number, lie immediately in front of the tragus. Their afferents drain the lateral surface of the auricula and the skin of the adjacent part of the temporal region; their efferents pass to the superior deep cervical glands. The parotid glands (lymphoglandulce parotidece), form two groups in relation with the parotid salivary gland, viz., a group imbedded in the substance of the gland, and a group of subparotid glands lying on the lateral wTall of the pharynx. Occa- sionally small glands are found in the subcutaneous tissue over the parotid gland. Their afferent vessels drain the root of the nose, the eyelids, the frontotemporal region, the external acoustic meatus and the tympanic cavity, possibly also the posterior parts of the palate and the floor of the nasal cavity. The efferents of these glands pass to the superior deep cervical glands. The afferents of the sub- 694 ANGIOLOGY parotid glands drain the nasal part of the pharynx and the posterior parts of the nasal cavities; their efferents pass to the superior deep cervical glands. The facial glands comprise three groups: (a) infraorbital or maxillary, scattered over the infraorbital region from the groove between the nose and cheek to the zygomatic arch; (b) buccinator, one or more placed on the Buccinator opposite the angle of the mouth; (c) supramandibular, on the outer surface of the mandible, in front of the Masseter and in contact with the external maxillary artery and anterior facial vein. Their efferent vessels drain the eyelids, the conjunctiva, and the skin and mucous membrane of the nose and cheek; their efferents pass to the submaxillary glands. The deep facial glands (lymphoglandulce faciales profunda; internal maxillary glands) are placed beneath the ramus of the mandible, on the outer surface of the Pterygoideus externus, in relation to the internal maxillary artery. Their afferent vessels drain the temporal and infratemporal fossae and the nasal part of the pharynx their efferents pass to the superior deep cervical glands. The lingual glands (lymphoglandulce linguales) are two or three small nodules lying on the Hyoglossus and under the Genioglossus. They form merely glandular substations in the course of the lymphatic vessels of the tongue. Retropharyngeal glands Afferent vessels of I retropharyngeal glands Afferent vessel to deep cervical glands Glandular nodule Gland of deep cervical chain Efferent vessels of retro- pharyngeal glands Pig. 603.—Lymphatics of pharynx. (Poirier and Charpy. The retropharyngeal glands (Fig. 603), from one to three in number, lie in the buccopharyngeal fascia, behind the upper part of the pharynx and in front of the arch of the atlas, being separated, however, from the latter by the Longus capitis. Their afferents drain the nasal cavities, the nasal part of the pharynx, and the auditory tubes; their efferents pass to the superior deep cervical glands. The lymphatic vessels of the scalp are divisible into (a) those of the frontal region, which terminate in the anterior auricular and parotid glands; (b) those of the temporoparietal region, which end in the parotid and posterior auricular glands; and (c) those of the occipital region, which terminate partly in the occipital glands and partly in a trunk which runs down along the posterior border of the Sternocleidomastoideus to end in the inferior deep cervical glands. The lymphatic vessels of the auricula and external acoustic meatus are also divisible into three groups: (a) an anterior, from the lateral surface of the auricula and anterior wall of the meatus to the anterior auricular glands; (6) a posterior, from the margin of the auricula, the upper part of its cranial surface, the internal surface THE LYMPH GLANDS OF THE HEAD 695 and posterior wall of the meatus to the posterior auricular and superior deep cervical glands, (o') an inferior, from the floor of the meatus and from the lobule of the auric- ula to the superficial and superior deep cervical glands. 1 he lymphatic vessels of the face (Fig. 604) are more numerous than those of the scalp. 1 hose from the eyelids and conjunctiva terminate partly in the submaxillary but mainly in the parotid glands. The vessels from the posterior part of the cheek also pass to the parotid glands, while those from the anterior portion of the cheek, the side of the nose, the upper lip, and the lateral portions of the lower lip end in the submaxillary glands. The deeper vessels from the temporal and infratemporal fossse pass to the deep facial and superior deep cervical glands. The deeper vessels of the cheek and lips end, like the superficial, in the submaxillary glands. Both superficial and deep vessels of the central part of the lower lip run to the submental glands. Parotid glands Facial glands Submaxillary glands Superficial cervi cal glands Deep cervical glands Fig. 604.—The lymphatics of the face. (After Kiittner.) Lymphatic Vessels of the Nasal Cavities.—Those from the anterior parts of the nasal cavities communicate with the vessels of the integument of the nose and end in the submaxillary glands; those from the posterior two-thirds of the nasal cavities and from the accessory air sinuses pass partly to the retropharyngeal and partly to the superior deep cervical glands. Lymphatic Vessels of the Mouth.—The vessels of the gums pass to the submaxillary glands; those of the hard palate are continuous in front with those of the upper gum, but pass backward to pierce the Constrictor pharyngis superior and end in the superior deep cervical and subparotid glands; those of the soft palate pass backward and lateralward and end partly in the retropharyngeal and subparotid, and partly in the superior deep cervical glands. The vessels of the anterior part of the floor of the mouth pass either directly to the inferior glands of the superior deep cervical group, or indirectly through the submental glands; from the rest of the floor of the mouth the vessels pass to the submaxillary and superior deep cervical glands. The lymphatic vessels of the palatine tonsil, usually three to five in number, pierce the buccopharyngeal fascia and constrictor pharyngis superior and pass 696 ANGIOLOGY between the Stylohyoideus and internal jugular vein to the uppermost of the superior deep cervical glands. They end in a gland which lies at the side of the posterior belly of the Digastricus, on the internal jugular vein; occasionally one or two additional vessels run to small glands on the lateral side of the vein under cover of the Sternocleidomastoideus. Vessels from root of tongue Vessels from margin of tongue Vessels from apex Principal gland of tongue Submental gland Trunks from * margin of tongue Interrupting nodule Central trunk Supra-omohyoid gland Fig. 605.—Lymphatics of the tongue. (Poirier.) The lymphatic vessels of the tongue (Fig. 605) are drained chiefly into the deep cervical glands lying between the posterior belly of the Digastricus and the superior belly of the Omohyoideus; one gland situated at the bifurcation of the common carotid artery is so intimately associated with these vessels that it is known as the principal gland of the tongue. The lymphatic vessels of the tongue may be divided into four groups: (1) apical, from the tip of the tongue to the suprahyoid glands and principal gland of the tongue; (2) lateral, from the margin of the tongue— some of these pierce the Mylohyoideus to end in the submaxillary glands, others pass down on the Hvoglossus to the superior deep cervical glands; (3) basal, from the region of the vallate papillae to the superior deep cervical glands; and (4) median, a few of which perforate the Mylohyoideus to reach the submaxillary glands, while the majority turn around the posterior border of the muscle to enter the superior deep cervical glands. THE LYMPH GLANDS OF THE NECK 697 The lymph glands of the neck include the following groups: The Lymph Glands of the Neck. Submaxillary* Submental. Superficial Cervical. Anterior Cervical. The submaxiTlary glands (lymphoglandulce submaxillares) (Fig. 604), three to six in number, are placed beneath the body of the mandible in the submaxillary triangle, and rest on the superficial surface of the submaxillary salivary gland. One gland, the middle gland of Stahr, which lies on the external maxillary artery as it turns over the mandible, is the most constant of the series; small lymph glands are sometimes found on the deep surface of the submaxillary salivary glands. The afferents of the submaxillary glands drain the medial palpebral commissure, the cheek, the side of the nose, the upper lip, the lateral part of the lower lip, the gums, and the anterior part of the margin of the tongue; efferent vessels from the facial and submental glands also enter the submaxillary glands. Their efferent vessels pass to the superior deep cervical glands. The submental or suprahyoid glands are situated between the anterior bellies of the Digastrici. Their afferents drain the central portions of the lower lip and floor of the mouth and the apex of the tongue; their efferents pass partly to the submaxillary glands and partly to a gland of the deep cervical group situated on the internal jugular vein at the level of the cricoid cartilage. The superficial cervical glands (lymphoglandulce cervicales superficiales) lie in close relationship with the external jugular vein as it emerges from the parotid gland, and, therefore, superficial to the Sternocleidomastoideus. Their afferents drain the lower parts of the auricula and parotid region, while their efferents pass around the anterior margin of the Sternocleidomastoideus to join the superior deep cervical glands. The anterior cervical glands form an irregular and inconstant group on the front of the larynx and trachea. They may be divided into (a) a superficial set, placed on the anterior jugular vein; (6) a deeper set, which is further subdivided into prelaryngeal, on the middle cricothyroid ligament, and pretracheal, on the front of the trachea. This deeper set drains the lower part of the larynx, the thyroid gland, and the upper part of the trachea; its efferents pass to the lowest of the superior deep cervical glands. The deep cervical glands (lymphoglandulce cervicales profundee) (Figs. 602, 605) are numerous and of large size: they form a chain along the carotid sheath, lying by the side of the pharynx, esophagus, and trachea, and extending from the base of the skull to the root of the neck. They are usually described in two groups: (1) the superior deep cervical glands lying under the Sternocleidomastoideus in close relation with the accessory nerve and the internal jugular vein, some of the glands lying in front of and others behind the vessel; (2) the inferior deep cervical glands extending beyond the posterior margin of the Sternocleidomastoideus into the supraclavicular triangle, where they are closely related to the brachial plexus and subclavian vein. A few minute paratracheal glands are situated along- side the recurrent nerves on the lateral aspects of the trachea and esophagus. The superior deep cervical glands drain the occipital portion of the scalp, the auricula, the back of the neck, a considerable part of the tongue, the larynx, thyroid gland, trachea, nasal part of the pharynx, nasal cavities, palate, and esophagus. They receive also the efferent vessels from all the other glands of the head and neck, except those from the inferior deep cervical glands. The inferior deep cervical glands drain the back of the scalp and neck, the superficial pectoral region, part of the arm (see page 701), and, occasionally, part of the superior surface of the Deep Cervical. 698 ANGIOLOGY liver, In addition, they receive vessels from the superior deep cervical glands. The efferents of the superior deep cervical glands pass partly to the inferior deep cervical glands and partly to a trunk which unites with the efferent vessel of the inferior deep cervical glands and forms the jugular trunk. On the right side, this trunk ends in the junction of the internal jugular and subclavian veins; on the left side it joins the thoracic duct. Deltoideo. pectoral glands Axillary glands - Supratrochlear gland Fig. 606.—The superficial lymph glands and lymphatic vessels of the upper extremity. The lymphatic vessels of the skin and muscles of the neck pass to the deep cervical glands. From the upper part of the pharynx the lymphatic vessels pass to the retro- pharyngeal, from the lower part to the deep cervical glands. From the larynx two sets of vessels arise, an upper and a lower. The vessels of the upper set pierce the hyothyroid membrane and join the superior deep cervical glands. Of the lower set, some pierce the conus elasticus and join the pretracheal and pre- laryngeal glands; others run between the cricoid and first tracheal ring and enter the inferior deep cervical glands. The lymphatic vessels of the thyroid gland con- sist of two sets, an upper, which accompanies the superior thyroid artery and enters the superior deep cervical glands, and a lower, which runs partly to the pretracheal THE LYMPH GLANDS OF THE UPPER EXTREMITY 699 glands and partly to the small paratracheal glands which accompany the recurrent nerves. These latter glands receive also the lymphatic vessels from the cervical portion of the trachea. THE LYMPHATICS OF THE UPPER EXTREMITY. The Lymph Glands of the Upper Extremity (Fig. 606). The lymph glands of the upper extremity are divided into two sets, superficial and deep. The superficial lymph glands are few and of small size. One or two supra- trochlear glands are placed above the medial epicondyle of the humerus, medial to the basilic vein. Their afferents drain the middle, ring, and little fingers, the medial portion of the hand, and the superficial area over the ulnar side of the fore- arm; these vessels are, however, in free communication with the other lymphatic vessels of the forearm. Their efferents accompany the basilic vein and join the deeper vessels. One or two deltoideopectoral glands are found beside the cephalic vein, between the Pectoralis major and Deltoideus, immediately below the clavicle. They are situated in the course of the external collecting trunks of the arm. Lateral group Deltoideopectoral glands Subclavicular group Central group Subscapular group ■ Mammary lymphatic ending in subclavicular glands Pectoral group ■Mammary collecting trunks Pectoral group J Subareolar 'plexus Cutaneous collecting trunk from the thoracic wall Cutaneous collecting trunks Collecting trunks passing to internal mammary glands Fig. 607.—Lymphatics of the mamma, and the axillary glands (semidiagrammatic). (Poirier and Charpy.) The deep lymph glands are chiefly grouped in the axilla, although a few may be found in the forearm, in the course of the radial, ulnar, and interosseous v essels, and in the arm along the medial side of the brachial artery. The Axillary Glands (lymphoglanduloe axillares) (big. 607) are of large size, vary from twenty to thirty in number, and may be arranged in the following groups. 1. A lateral group of from four to six glands lies in relation to the medial and posterior aspects of the axillary vein; the afferents of these glands drain the w o e arm with the exception of that portion whose vessels accompany the cephalic 700 ANGIOLOGY vein. The efferent vessels pass partly to the central and subclavicular groups of axillary glands and partly to the inferior deep cervical glands. 2. An anterior or pectoral group consists of four or five glands along the lower border of the Pectoralis minor, in relation with the lateral thoracic artery. Their afferents drain the skin and muscles of the anterior and lateral thoracic walls, and the central and lateral parts of the namma; their efferents pass partly to the central and partly to the subclavicular groups of axillary glands. 3. A posterior or subscapular group of six or seven glands is placed along the lower margin of the posterior wall of the axilla in the course of the subscapular artery. The afferents of this group drain the skin and muscles of the lower part of the back of the neck and of the posterior thoracic wall; their efferents pass to the central group of axillary glands. 4. A central or intermediate group of three or four large glands is imbedded in the adipose tissue near the base of the axilla. Its afferents are the efferent vessels of all the preceding groups of axillary glands; its efferents pass to the subclavicular group. 5. A medial or subclavicular group of six to twelve glands is situated partly posterior to the upper portion of the Pectoralis minor and partly above the upper border of this muscle. Its only direct territorial afferents are those wThich accompany the cephalic vein and one which drains the upper peripheral part of the mamma, but it receives the efferents of all the other axillary glands. The efferent vessels of the subclavicular group unite to form the subclavian trunk, which opens either directly into the junction of the internal jugular and subclavian veins or into the jugular lymphatic trunk; on the left side it may end in the thoracic duct. A few efferents from the subclavicular glands usually pass to the inferior deep cervical glands. The Lymphatic Vessels of the Upper Extremity. The lymphatic vessels of the upper extremity are divided into two sets, superficial and deep. The superficial lymphatic vessels commence (Fig. 608) in the lymphatic plexus which everywhere pervades the skin; the meshes of the plexus are much finer in the palm and on the flexor aspect of the digits than else- where. The digital plexuses are drained by a pair of vessels Which run on the sides of each digit, and incline backward to reach the dorsum of the hand. From the dense plexus of the palm, vessels pass in different direc- tions, viz., upward toward the wrist, downward to join the digital vessels, medialward to join the vessels on the ulnar border of the hand, and lateralward to those on the thumb. Several vessels from the central part of the plexus unite to Fig. 608.—Lymphatic vessels of the dorsal surface of the hand. (Sappey.) THE LYMPH GLANDS OF THE LOWER EXTREMITY 701 form a trunk, which passes around the metacarpal bone of the index finger to join the vessels on the back of that digit and on the back of the thumb. Running upward in front of and behind the wrist, the lymphatic vessels are collected into radial, median, and ulnar groups, which accompany respectively the cephalic, median, and basilic veins in the forearm. A few of the ulnar lymphatics end in the supratrochlear glands, but the majority pass directly to the lateral group of axillary glands. Some of the radial vessels are collected into a trunk which ascends with the cephalic vein to the deltoideopectoral glands; the efferents from this group pass either to the subclavicular axillary glands or to the inferior cervical glands. The deep lymphatic vessels accompany the deep bloodvessels. In the fore- arm, they consist of four sets, corresponding with the radial, ulnar, volar, and dorsal interosseous arteries; they communicate at intervals with the superficial lymphatics, and some of them end in the glands which are occasionally found beside the arteries. In their course upward, a few end in the glands which lie upon the brachial artery; but most of them pass to the lateral group of axillary glands. Tibial nerve Popliteal vein Popliteal artery Common peronceal nerve Gland at side of popliteal vessels Gland on back of knee joint Gland at termination of small saph. vein Fig. 609.—Lymph glands of popliteal fossa. (Poirier and Charpy.) THE LYMPHATICS OF THE LOWER EXTREMITY The Lymph Glands of the Lower Extremity. The lymph glands of the lower extremity consist of the anterior tibial gland and the popliteal and inguinal glands. ... . , . The anterior tibial gland (lymphoglandula tibialis anterior) is small and lr\c°n- stant. It lies on the interosseous membrane in relation to the upper part of the anterior tibial vessels, and constitutes a substation in the course o t e an erior tibial lymphatic trunks. . „ „ . , The popliteal glands (lymphoglandulce popliteal) (Fig. 609), small in size and some six or seven in number, are imbedded in the fat contained in the popliteal 702 ANGIOLOGY fossa. One lies immediately beneath the popliteal fascia, near the terminal part of the small saphenous vein, and drains the region from which this vein derives its tributaries. Another is placed between the popliteal artery and the posterior surface of the knee-joint; it receives the lymphatic vessels from the knee-joint together with those which accompany the genicular arteries. The others lie at the sides of the popliteal vessels, and receive as efferents the trunks which accompany the anterior and posterior tibial vessels. The effer- ents of the popliteal glands pass almost entirely alongside the femoral vessels to the deep inguinal glands, but a few may accompany the great saphenous vein, and end in the glands of the superficial subinguinal group. The inguinal glands (lymphoglandulce inguinales) (Fig. 610), from twrelve to twenty in number, are situated at the upper part of the femoral triangle. They may be divided into two groups by a horizontal line at the level of the termi- nation of the great saphenous vein; those lying above this line are termed the superficial inguinal glands, and those below it the subinguinal glands, the latter group consisting of a superficial and a deep set. The Superficial Inguinal Glands form a chain immediately below the inguinal ligament. They receive as afferents lym- phatic vessels from the integument of the penis, scrotum, perineum, buttock, and abdominal wall below the level of the umbilicus. The Superficial Subinguinal Glands (lymphoglandulce subinguinales super- ficiales) are placed on either side of the upper part of the great saphenous vein; their efferents consist chiefly of the superficial lymphatic vessels of the lower extremity; but they also receive some of the vessels which drain the in- tegument of the penis, scrotum, peri- neum, and buttock. The Deep Subinguinal Glands (lympho- glandules subinguinales profundoe) vary from one to three in number, and are placed under the fascia lata, on the medial side of the femoral vein. When Superficial inguinal glands Superficial subinguinal glands Fig. 610.—The superficial lymph glands and lymphatic vessels of the lower extremity. THE LYMPH GLANDS OF THE ABDOMEN AND PELVIS 703 three are present, the lowest is situated just below the junction of the great saphe- nous and femoral veins, the middle in the femoral canal, and the highest in the lateral part of the femoral ring. The middle one is the most inconstant of the three, but the highest, the gland of Cloquet or Rosenmiiller, is also frequently absent. They receive as afterents the deep lymphatic trunks which accompany the femoral vessels, the lymphatics from the glans penis vel clitoridis, and also some of the efferents from the superficial subinguinal glands. The Lymphatic Vessels of the Lower Extremity. The lymphatic vessels of the lower extremity consist of two sets, superficial and deep, and in their distribution correspond closely with the veins. The superficial lymphatic vessels lie in the superficial fascia, and are divisible into two groups: a medial, which follow's the course of the great saphenous vein, and a lateral, which accompanies the small saphenous vein. The vessels of the medial group (Fig. 610) are larger and more numerous than those of the lateral group, and commence on the tibial side and dorsum of the foot; they ascend both in front of and behind the medial malleolus, run up the leg with the great saphe- nous vein, pass with it behind the medial condyle of the femur, and accompany it to the groin, where they end in the subinguinal group of superficial glands. The vessels of the lateral group arise from the fibular side of the foot; some ascend in front of the leg, and, just below the knee, cross the tibia to join the lymphatics on the medial side of the thigh; others pass behind the lateral malleolus, and, accompanying the small saphenous vein, enter the popliteal glands. The deep lymphatic vessels are few in number, and accompany the deep blood- vessels. In the leg, they consist of three sets, the anterior tibial, posterior tibial, and peroneal, which accompany the corresponding bloodvessels, two or three with each artery; they enter the popliteal lymph glands. The deep lymphatic vessels of the gluteal and ischial regions follow the course of the corresponding bloodvessels. Those accompanying the superior gluteal vessels end in a gland which lies on the intrapelvic portion of the superior gluteal artery near the upper border of the greater sciatic foramen. Those following the inferior gluteal vessels traverse one or two small glands which lie below the Piriformis muscle, and end in the hypogastric glands. THE LYMPHATICS OF THE ABDOMEN AND PELVIS. The Lymph Glands of the Abdomen and Pelvis. The lymph glands of the abdomen and pelvis may be divided, from their situa- tions, into (a) parietal, lying behind the peritoneum and in close association with the larger bloodvessels; and (b) visceral, which are found in relation to the visceral arteries. The parietal glands (Figs. 611, 612) include the following groups: External Iliac. Common Iliac. Epigastric. Iliac Circumflex. Hypogastric. Sacral. 'Lateral Aortic. Preaortic. JRetroaortic. Lumbar The External Iliac Glands, from eight to ten in number, lie along the external iliac vessels. They are arranged in three groups, one on the lateral, another on the medial, and a third on the anterior aspect of the vessels; the third group is, however, sometimes absent. Their principal afferents are derived from the inguinal and subinguinal glands, the deep lymphatics of the abdominal wall below the umbili- cus and of the adductor region of the thigh, and the lymphatics from the glans 704 ANGIOLOGY penis vel clitoridis, the membranous urethra, the prostate, the fundus of the bladder, the cervix uteri, and upper part of the vagina. The Common Iliac Glands, four to six in number, are grouped behind and on the * sides of the common iliac artery, one or two being placed below the bifurcation of the aorta, in front of the fifth lumbar vertebra. They drain chiefly the hypo- gastric and external iliac glands, and their efferents pass to the lateral aortic glands. The Epigastric Glands (lymphoglandulce epigastricce), three or four in number, are placed alongside the lower portion of the inferior epigastric vessels. Left lateral aortic Right lateral aortic Common iliac Gland in front of sacral promontory Common iliac Common iliac - External iliac External iliac Obturator nerve Obturator artery External iliac Obturator artery Obturator gland Fig. 611.—The parietal lymph glands of the pelvis. (Cun6o and Marcille.) The Iliac Circumflex Glands, two to four in number, are situated along the course of the deep iliac circumflex vessels; they are sometimes absent. The Hypogastric Glands (lymphoglandulce hypogastricce; internal iliac gland) (Fig. 612) surround the hypogastric vessels, and receive the lymphatics corre- sponding to the distribution of the branches of the hypogastric artery, i. e., they receive lymphatics from all the pelvic viscera, from the deeper parts of the perineum, including the membranous and cavernous portions of the urethra, and from the buttock and back of the thigh. An obturator gland is sometimes seen in the upper part of the obturator foramen. The Sacral Glands are placed in the concavity of the sacrum, in relation to the THE LYMPH GLANDS OF THE ABDOMEN AND PELVIS 705 middle and lateral sacral arteries; they receive lymphatics from the rectum and posterior wall of the pelvis. The efferents of the hypogastric group end in the common iliac glands. The Lumbar Glands (lymphoglandulce lumbales) are very numerous, and consist of right and left lateral aortic, preaortic, and retroaortic groups. The right lateral aortic glands are situated partly in front of the inferior vena cava, near the termination of the renal vein, and partly behind it on the origin of the Psoas major, and on the right crus of the diaphragm. The left lateral aortic glands form a chain on the left side of the abdominal aorta in front of the origin of the Psoas major and left crus of the diaphragm. The glands on either side receive (a) the efferents of the common iliac glands, (6) the lymphatics from the testis in the male and from the ovary, uterine tube, and body of the uterus in the Hypogastric Gland in front of - Sacral promontory Lateral sacral External iliac glands Hypogastric Satellite trunk of internal puden- dal vessels. Trunk of middle hcemorrhoidal vessels. Internal lymphatics of bladder Lymphatic from glans penis Lymphatics of bladder Prostatic collecting trunk Urethral collecting trunks Glandular nodule in front of symphysis Fig. 612.—Iliopelvic glands (lateral view). (CunSo and Marcille.) Prostatic collecting trv.nk female; (c) the lymphatics from the kidney and suprarenal gland, and (d) the lymphatics draining the lateral abdominal muscles and accompany mg the um ar veins. Most of the efferent vessels of the lateral aortic glands converge to form the right and left lumbar trunks which join the cisterna chyh, but some enter the pre- and retroaortic glands, and others pierce the crura of the diaphragm to join the lower end of the thoracic duct. The preaortic glands he in front of the aorta, and may be divided into celiac, superior mesenteric, and inferior mesenteric groups, arranged around the origins of the corresponding arteries. T ey receive a ew vessels from the lateral aortic glands, but their principal afferents are derived from the viscera supplied bv the three arteries with which they are associated borne of their efferents pass*to the retroaortic glands, but the majority unite to form the intestinal trunk, which enters the cisterna cliyli. The retroaortic glands are placed 706 ANGIOLOGY below the cisterna chyli, on the bodies of the third and fourth lumbar vertebrae. They receive lymphatic trunks from the lateral and preaortic glands, wdiile their efferents end in the cisterna chyli. The Lymphatic Vessels of the Abdomen and Pelvis. The lymphatic vessels of the walls of the abdomen and pelvis may be divided into two sets, superficial and deep. The superficial vessels follow the course of the superficial bloodvessels and converge to the superficial inguinal glands; those derived from the integument of the front of the abdomen below the umbilicus follow the course of the superficial epigastric vessels, and those from the sides of the lumbar part of the abdominal wall pass along the crest of the ilium, with the superficial iliac circumflex vessels. The superficial lymphatic vessels of the gluteal region turn horizontally around the buttock, and join the superficial inguinal and subinguinal glands. The deep vessels run alongside the principal bloodvessels. Those of the parietes of the pelvis, which accompany the superior and inferior gluteal, and obturator vessels, follow the course of the hypogastric artery, and ultimately join the lateral aortic glands. Lymphatic Vessels of the Perineum and External Genitals.—The lymphatic vessels of the perineum, of the integument of the penis, and of the scrotum (or vulva), follow the course of the external pudendal vessels, and end in the superficial ingui- nal and subinguinal glands. Those of the glans penis vel clitoridis terminate partly in the deep subinguinal glands and partly in the external iliac glands. The visceral glands are associated with the branches of the celiac, superior and inferior mesenteric arteries. Those related to the branches of the celiac artery form three sets, gastric, hepatic, and pancreaticolienal. The Gastric Glands (Figs. 613, 614) consist of two sets, superior and inferior. The Superior Gastric Glands (lymphoglandidae gastricce superiores) accompany the left gastric artery and are divisible into three groups, viz.: (a) upper, on the stem of the artery; (h) lower, accompanying the descending branches of the artery along the cardiac half of the lesser curvature of the stomach, between the two layers of the lesser omentum; and (c) paracardial outlying members of the gastric glands, disposed in a manner comparable to a chain of beads around the neck of the stomach (Jamieson and Dobson1). They receive their afferents from the stomach; their efferents pass to the celiac group of preaortic glands. The Inferior Gastric Glands (lymphoglandulce gastricce inferiores; right gastro- epiploic gland), four to seven in number, lie between the two layers of the greater omentum along the pyloric half of the greater curvature of the stomach, and may be regarded as an outlying group of the hepatic glands. The Hepatic Glands (lymphoglandulae hepaticce) (Fig. 613), consist of the follow- ing groups: (a) hepatic, on the stem of the hepatic artery, and extending upward along the common bile duct, between the two layers of the lesser omentum, as far as the porta hepatis; the cystic gland, a member of this group, is placed near the neck of the gall-bladder; (b) subpyloric, four or five in number, in close relation to the bifurcation of the gastroduodenal artery, in the angle between the superior and descending parts of the duodenum; an outlying member of this group is some- times found above the duodenum on the right gastric (pyloric) artery. The glands of the hepatic chain receive afferents from the stomach, duodenum, liver, gall- bladder, and pancreas; their efferents join the celiac group of preaortic glands. The Pancreaticolienal Glands (lymphoglandulce pancreaticolienales; splenic glands) (Fig. 614) accompany the lienal (splenic) artery, and are situated in rela- tion to the posterior surface and upper border of the pancreas; one or two members 1 Lancet, April 20 and 27, 1907. THE LYMPHATIC VESSELS OF THE ABDOMEN AND PELVIS 707 Superior gastric glands Paracardial glands Hepatic glands Svbpylonc glands Pancreaticolienal glands Inferior gastric glands Fig. 613.—Lymphatics of stomach, etc. (Jamieson and Dobson.) Subpylonc glands Fig. 614.—Lymphatics of stomach, etc. The stomach has been turned upward. (Jamieson and Dobson.) 708 ANGIOLOGY of this group are found in the gastrolienal ligament (Jamieson and Dobson, op. cii.’ Their afferents are derived from the stomach, spleen, and pancreas, their eft'erenl join the celiac group of preaortic glands. Duodenum Upper group of ileocolic glands Lower group of ileocolic glands Cecum Vermiform process Fig. 615.—The lymphatics of cecum and vermiform process from the front. (Jamieson and Dobson.) Upper group of ileocolic glands Lower group of ileocolic glands Fig. 616.—The lymphatics of cecum and vermiform process from behind. (Jamieson and Dobson.) Vermiform 'process Cecum THE LYMPHATIC VESSELS OF ABDOMEN AND PELVIS The superior mesenteric glands may be divided into three principal groups* mesenteric, ileocolic, and mesocolic. h p The Mesenteric Glands (lympho glandules mesenteries?) lie between the lavers of the mesentery. They vary from one hundred to one hundred and fifty in number and may be grouped into three sets, viz.: one lying close to the wall of the small intestine, among the terminal twigs of the superior mesenteric arterv; a second in relation to the loops and primary branches of the vessels; and a”third along the trunk of the artery. 6 The Ileocolic glands (Figs. 615, 616), from ten to twenty in number, form a chain around the ileocolic artery, but show a tendency to subdivision into two groups, one near the duodenum and another on the lower part of the trunk of the artery! 709 Inferior mesenteric glands Fig. 617.—Lymphatics of colon. (Jamieson and Dobson.) Where the vessel divides into its terminal branches the chain is broken up into sev- eral groups, viz.: (a) ileal, in relation to the ileal branch of the artery; (b) anterior ileocolic, usually of three glands, in the ileocolic fold, near the wall of the cecum; (c) posterior ileocolic, mostly placed in the angle between the ileum and the colon, but partly lying behind the cecum at its junction with the ascending colon; (d) a single gland, between the layers of the mesenteriole of the vermiform process; (e) right colic, along the medial side of the ascending colon. TheMesocolic Glands (lymphoglandulce mesocolicce) are numerous, and lie between the layers of the transverse mesocolon, in close relation to the transverse colon; they are best developed in the neighborhood of the right and left colic flexures. One or two small glands are occasionally seen along the trunk of the right colic artery and others are found in relation to the trunk and branches of the middle colic artery. 710 ANGIOLOGY The superior mesenteric glands receive afferents from the jejunum, ileum, cecum, vermiform process, and the ascending and transverse parts of the colon; their efferents pass to the preaortic glands. The inferior mesenteric glands (Fig. 617) consist of: (a) small glands on the branches of the left colic and sigmoid arteries; (6) a group in the sigmoid mesocolon, around the superior hemorrhoidal artery; and ( contain filaments from all the primary nervous trunks which form the plexus, in the formation also of smaller plexuses at the periphery of the body there is a tree interchange of the funiculi and primitive fibers. In each case, however, the individual fibers remain separate and distinct. It is probable that through this interchange of fibers, every branch passing off from a plexus has a more extensive connection with the spinal cord than if it had proceeded to its distribution without forming connections with other nerves. Consequently the parts supplied by these nerves have more extended relations with the nervous centers; by this means, also, groups of muscles may be associated ior combined action. 729 Ejpineurium Perineurium Fig. 636.—Transverse section of human tibial nerve. The sympathetic nerves are constructed in the same manner as the cerebrospinal nerves, but consist mainly of non-medullated fibers, collected in funiculi and enclosed in sheaths of connective tissue. There is, however, in these nerves a certain admix- ture of medullated fibers. The number of the latter varies in different nerves, and may be estimated by the color of the nerve. Those branches of the sympathetic, which present a well-marked gray color, are composed chiefly of non-medullated nerve fibers, intermixed with a few medullated fibers; while those of a white color contain many of the latter fibers, and few of the former. The cerebrospinal and sympathetic nerve fibers convey various impressions. The sensory nerves, called also centripetal or afferent nerves, transmit to the nervous centers impressions made upon the peripheral extremities of the nerves, and in this way the mind, through the medium of the brain, becomes conscious of external objects. The centrifugal or efferent nerves transmit impressions from the nervous centers to the parts to which the nerves are distributed, these impressions either exciting muscular contraction or influencing the processes of nutrition, growth, and secretion. Origins and Terminations of Nerves.—By the expression “the terminations of nerve fibers” is signified their connections with the nerve centers and with the parts 730 NEUROLOGY they supply. The former are sometimes called their origins or central terminations; the latter their peripheral terminations. Origins of Nerves.—The origin in some cases is single—that is to say, the whole nerve emerges from the nervous center by a single root; in other instances the nerve arises by two or more roots which come off from different parts of the nerve center, sometimes widely apart from each other, and it often happens, when a nerve arises in this way by two roots, that the functions of these two roots are different; as, for example, in the spinal nerves, each of which arises by two roots, the anterior of which is motor, and the posterior sensory. The point where the nerve root or roots emerge from the surface of the nervous center is named the superficial or apparent origin, but the fibers of the nerve can be traced for a certain distance into the substance of the nervous center to some portion of the gray matter, which constitutes the deep or real origin of the nerve. The centrifugal or efferent nerve fibers originate in the nerve cells of the gray substance, the axis-cylinder processes of these cells being prolonged to form the fibers. In the case of the centripetal or afferent nerves the fibers grow inward either from nerve cells in the organs of special sense, e. g., the retina, or from nerve cells in the ganglia. Having entered the nerve center they branch and send their ultimate twigs among the cells, without, however, uniting with them. Peripheral Terminations of Nerves.—Nerve fibers terminate peripherally in various ways, and these may l?e conveniently studied in the sensory and motor nerves respectively. The terminations of the sensory nerves are dealt with in the section on Sense Organs. Motor nerves can be traced into either unstriped or striped muscular fibers. In the unstriped or involuntary muscles the nerves are derived from the sympathetic, and are composed mainly of non-medullated fibers. Near their terminations they divide into numerous branches, which communicate and form intimate plexuses. At the junction of the branches small triangular nuclear bodies (ganglion cells) are situated. From these plexuses minute branches are given off which divide and break up into the ultimate fibrillse of which the nerves are composed. These fibrillse course between the involuntary muscle cells, and, according to Elischer, terminate on the surfaces of the cells, opposite the nuclei, in minute swellings. In the striped or voluntary muscle the nerves supplying the muscular fibers are derived from the cerebrospinal nerves, and are composed maiiffy of medullated fibers. The nerve, after entering the sheath of the muscle, breaks up into fibers or bundles of fibers, which form plexuses, and gradually divide until, as a rule, a single nerve fiber enters a single muscular fiber. Sometimes, however, if the muscular fiber be long, more than one nerve fiber enters it. Within the muscular fiber the nerve terminates in a special expansion, called by Kill me, who first accurately described it, a motor end-plate (Fig. 637). The nerve fiber, on approaching the mus- cular fiber, suddenly loses its medullary sheath, the neurolemma becomes continuous with the sarcolemma of the muscle, and only the axis-cylinder enters the muscular fiber. There it at once spreads out, ramifying like the roots of a tree, immediately beneath the sarcolemma, and becomes imbedded in a layer of granular matter, containing a number of clear, oblong nuclei, the whole constituting an end-plate from which the contractile wave of the muscular fiber is said to start. Ganglia are small aggregations of nerve cells. They are found on the posterior roots of the spinal nerves; on the sensory roots of the trigeminal, facial, glosso- pharyngeal, and vagus nerves, and on the acoustic nerves. They are also found in connection with the sympathetic nerves. On section they are seen to consist of a reddish-gray substance, traversed by numerous white nerve fibers; they vary con- siderably in form and size; the largest are found in the cavity of the abdomen; the smallest, not visible to the naked eye, exist in considerable numbers upon the nerves distributed to the different viscera. Each ganglion is invested by a smooth STRUCTURE OF THE NERVOUS SYSTEM 731 aiul firm,, closely adhering, membranous envelope, consisting of dense areolar tissue, this sheath is continuous with the perineurium of the nerves, and sends numerous processes into the interior to support the bloodvessels supplying the substance of the ganglion. Fig. 637.—Muscular fibers of Lacerta viridis with the terminations of nerves, a. Seen in profile. P, P. The nerve end-plates. S, S. The base of the plate, consisting of a granular mass with nuclei, b. The same as seen in looking at a perfectly fresh fiber, the nervous ends being probably still excitable. (The forms of the variously divided plate can hardly be represented in a woodcut by sufficiently delicate and pale contours to reproduce correctly what is seen in nature.) c. The same as seen two hours after death from poisoning by curare. In structure all ganglia are essentially similar, consisting of the same structural elements—viz., nerve cells and nerve fibers. Each nerve cell has a nucleated sheath which is continuous with the neurolemma of the nerve fiber with which the cell is connected. The nerve cells in the ganglia of the spinal nerves (Fig. 638) are pyri- form in shape, and have each a single process. A short distance from the cell and while still within the ganglion this process divides in a T-shaped manner, one limb of the cross-bar turning into the medulla spinalis, the other limb passing out- Pm. 638.—Transverse section of spinal ganglion of rabbit. A. Ganglion. X 30. a. Large clear nerve cell. b. Small deeply staining nerve cell. c. Nuclei of capsule. X 250. The lines in the center point to the corresponding cells in the ganglion. ward to the periphery. In the sympathetic ganglia (Fig. 639) the nerve cells are multipolar and each has one axis-cylinder process and several dendrons; the axon emerges from the ganglion as a non-medullated nerve fiber. Similar cells are found in the ganglia connected with the trigeminal nerve, and these ganglia are therefore 732 NEUROLOGY regarded as the cranial portions of the sympathetic system. The sympathetic nervous system includes those portions of the nervous mechanism in which a medul- lated nerve fiber from the central system passes to a ganglion, sympathetic or peripheral, from which fibers, usually non-medullated, are distributed to such structures, e. g., bloodvessels, as are not under voluntary control. The spinal and sympathetic ganglia differ somewhat in the size and disposition of the cells and in the number of nerve fibers entering and leaving them. In the spinal ganglia (Fig. 638) the nerve cells are much larger and for the most part collected in groups near the periphery, while the fibers, which are mostly medullated, traverse the central portion of the ganglion; whereas in the sympathetic ganglia (Fig. 639) the cells are smaller and distributed in irregular groups throughout the whole ganglion; the fibers also are irregularly scattered; some of the entering ones are medullated, while many of those leaving the ganglion are non-medullated. Neuron Theory.—The nerve cell and its processes collectively con- stitute what is termed a neuron, and Waldeyer formulated the theory that the nervous system is built up of numerous neurons, “ anatomically and genetically independent of one another.” According to this theory (neuron theory) the processes of one neuron only come into con- tact, and are never in direct con- rtinuity, with those of other neu- rons; while impulses are transmitted from one nerve cell to another through these points of contact, the synapses. The synapse or synaptic membrane seems to allow nervous impulses to pass in one direction only, namely, from the terminals of the axis-cylinder to the dendrons. This theory is based on the following facts, viz.: (1) embryonic nerve cells or neuroblasts are entirely distinct from one another; (2) when nervous tissues are stained by the Golgi method no continuity is seen even between neighboring neurons; and (3) when degenerative changes occur in nervous tissue, either as the result of disease or experiment, they never spread from one neuron to another, but are limited to the individual neurons, or groups of neurons, primarily affected. It must, however, be added that within the past few years the validity of the neuron theory has been called in question by certain eminent histol- ogists, who maintain that by the employment of more delicate histological methods, minute fibrils can be followed from one nerve cell into another. Their existence, however, in the living is open to question. Mott and Marinesco made careful examinations of living cells, using even the ultramicroscope and agree that neither Nissel bodies nor neurofibrils are present in the living state. For the present we may look upon the neurons as the units or structural elements of the nervous system. All the neurons are present at birth which are present in the adult, their division ceases before birth; they are not all functionally active at birth, but gradually assume functional activity. There is no indication of any regeneration after the destruction of the cell-body of any individual neuron. Fasciculi, tracts or fiber systems are groups of axons having homologous origin and homologous distribution (as regards their collaterals, subdivisions and ter- minals) and are often named in accordance with their origin and termination, the Nerve-cells of ganglion Fig. 639.—Transverse section of sympathetic ganglion of cat. ,4.. Ganglion. X 50. a. A nerve cell. X 250. DEVELOPMENT OF THE NERVOUS SYSTEM 733 name of the nucleus or the location of the cell body from which the axon or fiber arises preceding that of the nucleus or location of its termination. A given topo- graphical area seldom represents a pure tract, as in most cases fibers of different systems are mixed. DEVELOPMENT OF THE NERVOUS SYSTEM. The entire nervous system is of ectodermal origin, and its first rudiment is seen in the neural groove w-hich extends along the dorsal aspect of the embryo (Fig. 17). By the elevation and ultimate fusion of the neural folds, the groove is con- verted into the neural tube (Fig. 19). The anterior end of the neural tube becomes expanded to form the three primary brain-vesicles; the cavity of the tube is sub- sequently modified to form the ventricular cavities of the brain, and the central canal of the medulla spinalis; from the wall the nervous elements and the neuroglia of the brain and medulla spinalis are developed. -Roof-plate Oval bundle Posterior nerve root Central canal •Ependymal layer Mantle layer ■Anterior nerve roots ■Marginal layer Fig. 640.—Section of medulla spinalis of a four weeks’ embryo. (His.) Floor-plate The Medulla Spinalis.-—At first the wall of the neural tube is composed of a single layer of columnar ectodermal cells. Soon the side-walls become thickened, while the dorsal and ventral parts remain thin, and are named the roof- and floor- plates (Figs. 640, 642, 643). A transverse section of the tube at this stage presents an oval outline, while its lumen has the appearance of a slit, ihe cells, which constitute the wall of the tube proliferate rapidly, lose their cell-boundaries and form a syncytium. This syncytium consists at first of dense protoplasm with closely packed nuclei, but later it opens out and forms a looser meshwork with the cellular strands arranged in a radiating manner from the central canal. Three layers may now be defined—an internal or ependymal, an intermediate or mantle, and an external or marginal. The ependymal layer is ultimately converted into the ependyma of the central canal; the processes of its cells, pass outward toward the periphery of the medulla spinalis. The marginal layer is de\oid of nuclei, and later forms the supporting framework for the white funiculi of the medulla spinalis. The mantle layer represents the wrhole of the future gray columns of the medulla spinalis; in it the cells are differentiated into two sets, viz., (a) spongioblasts or young neuroglia cells, and (6) germinal cells, which are the parents ol the neuroblasts 734 NEUROLOGY or young nerve cells (Fig. 641). The spongioblasts are at first connected to one another by filaments of the syncytium: in these, fibrils are developed, so that as the neuroglial cells become defined they exhibit their characteristic mature appearance with multiple processes proceeding from each cell. The germinal cells are large, Germinal cell Neuroblast Nuclei of spongioblasts Syncytium Fig. 641.—Transverse section of the medulla spinalis of a human embryo at the beginning of the fourth week. (After His.) The left edge of the figure corresponds to the lining of the central canal. round or oval, and first make their appearance between the ependymal cells on the sides of the central canal. They increase rapidly in number, so that by the fourth week they form an almost continuous layer on each side of the tube. No germinal cells are found in the roof- or floor-plates; the roof-plate retains, in certain Roof-plate Alar lamina Fasciculus gracilis Posterior funiculus Oval bundle Fasciculus cuneatus J Posterior nerve-root Post, nerve-root Central canal Lateral funiculus Lateral funiculus Ependymal layer ! Basal lamina Central canal Anterior column y Anterior nerve-root Anterior funiculus Floor-plate Anterior funiculus Figs. 642, 643.—Transverse sections through the medullar' spinales of human embryos. (His.) Fig. 642, aged about four and a half weeks. Fig. 643, aged about three months. regions of the brain, its epithelial character; elsewhere, its cells become spongio- blasts. By subdivision the germinal cells give rise to the neuroblasts or young nerve cells, which migrate outward from the sides of the central canal into the mantle layer and neural crest, and at the same time become pear-shaped; the DEVELOPMENT OF THE NERVOUS SYSTEM tapering part ot the cell undergoes still further elongation, and forms the axis- cylinder of the cell. 1 he lateral w alls ot the medulla spinalis continue to increase in thickness, and the canal w idens out near its dorsal extremity, and assumes a somewhat lozenge- shaped appearance. The widest part of the canal serves to subdivide the lateral wall of the neural tube into a dorsal or alar, and a ventral or basal lamina (Figs. 642, 643), a subdivision which extends forward into the brain. At a later stage the ventral part of the canal widens out, while the dorsal part is first reduced to a mere slit and then becomes obliterated by the approximation and fusion of its walls; the ventral part of the canal persists and forms the central canal of the adult medulla spinalis. 4 he caudal end of the canal exhibits a conical expansion which is known as the terminal ventricle. I he ventral part of the mantle layer becomes thickened, and on cross-section appears as a triangular patch between the marginal and ependymal layers. This thickening is the rudiment of the anterior column of gray substance, and contains many neuroblasts, the axis-cylinders of which pass out through the marginal layer and form the anterior roots of the spinal nerves (Figs. 640,642,643). The thickening of the mantle layer gradually extends in a dorsal direction, and forms the posterior column of gray substance. The axons of many of the neuroblasts in the alar lamina run forward, and cross in the floor-plate to the opposite side of the medulla spinalis; these form the rudiment of the anterior white commissure. About the end of the fourth week nerve fibers begin to appear in the marginal layer. The first to develop are the short intersegmental fibers from the neuro- blasts in the mantle zone, and the fibers of the dorsal nerve roots which grow into the medulla spinalis from the cells of the spinal ganglia. By the sixth week these dorsal root fibers form a well-defined oval bundle in the peripheral part of the alar lamina; this bundle gradually increases in size, and spreading toward the middle line forms the rudiment of the posterior funiculus. The long intersegmental fibers begin to appear about the third month and the cerebrospinal fibers about the fifth month. All nerve fibers are at first destitute of medullary sheaths. Different groups of fibers receive their sheaths at different times—the dorsal and ventral nerve roots about the fifth month, the cerebrospinal fibers after the ninth month. By the growth of the anterior columns of gray substance, and by the increase in size of the anterior funiculi, a furrow is formed between the lateral halves of the cord anteriorly; this gradually deepens to form the anterior median fissure. The mode of formation of the posterior septum is somewhat uncertain. Many believe that it is produced by the growing together of the walls of the posterior part of the central canal and by the development from its ependymal cells of a septum of fibrillated tissue which separates the future funiculi graciles. Up to the third month of fetal life the medulla spinalis occupies the entire length of the vertebral canal, and the spinal nerves pass outward at right angles to the medulla spinalis. From this time onward, the vertebral column grows more rapidly than the medulla spinalis, and the latter, being fixed above through its continuity with the brain, gradually assumes a higher position within the canal. By the sixth month its lower end reaches only as far as the upper end of the sacrum; at birth it is on a level with the third lumbar vertebra, and in the adult with the lower border of the first or upper border of the second lumbar vertebra. A delicate filament, the filum terminale, extends from its lower end as far as the coccyx. The Spinal Nerves.—Each spinal nerve is attached to the medulla spinalis by an anterior or ventral and a posterior or dorsal root. The fibers of the anterior roots are formed by the axons of the neuroblasts which lie in the ventral part of the mantle layer; these axons grow out through the overlying marginal layer and become grouped to form the anterior nerve root (Fig. 641). 735 736 NEUROLOGY The fibers of the posterior roots are developed from the cells of the spinal ganglia. Before the neural groove is closed to form the neural tube a ridge of ectodermal cells, the ganglion ridge or neural crest (Fig. 644), appears along the prominent margin of each neural fold. When the folds meet in the middle line the two gan- glion ridges fuse and form a wedge-shaped area along the line of closure of the tube. The cells of this area proliferate rapidly opposite the primitive segments and then migrate in a lateral and ventral direction to the sides of the neural tube, where they ultimately form a series of oval-shaped masses, the future spinal ganglia. These ganglia are arranged symmetrically on the two sides of the neural tube and, except in the region of the tail, are equal in number to the primitive segments. The cells of the ganglia, like the cells of the mantle layer, are of two kinds, viz., spongio- blasts and neuroblasts. The spongioblasts develop into the neuroglial cells of the ganglia. The neuroblasts are at first round or oval in shape, but soon assume the form of spindles the extremities of which gradually elongate into central and • peripheral processes. The central processes grow medialward and, be- coming connected with the neural tube, constitute the fibers of the posterior nerve roots, while the per- ipheral processes grow lateralward to mingle with the fibers of the anterior root in the spinal nerve. As de- velopment proceeds the original bipolar form of the cells changes; the two processes become approxi- mated until they ultimately arise from a single stem in a T-shaped manner. Only in the ganglia of the acoustic nerve is the bipolar form retained. More recent observers hold, however, that the T-form is derived from the branching of a single pro- cess which grows out from the cell. The anterior or ventral and the pos- terior or dorsal nerve roots join imme- diately beyond the spinal ganglion to form the spinal nerve, which then divides into anterior, posterior, and visceral divisions. The anterior and posterior divisions proceed directly to their areas of distribution without further association with ganglion cells (Fig. 645). The visceral divisions are distributed to the thoracic, abdominal, and pelvic viscera, to reach which they pass through the sympathetic trunk, and many of the fibers form arborizations around the ganglion cells of this trunk. \ isceral branches are not given off from all the spinal nerves; they form two groups, viz., (a) thoracico-lumbar, from the first or second thoracic, to the second or third lumbar nerves; and (6) pelvic, from the second and third, or third and fourth sacral nerves. , The Brain.—The brain is developed from the anterior end of the neural tube, which at an early period becomes expanded into three vesicles, the primary cerebral vesicles (Fig. 18). These are marked off from each other by intervening con- strictions, and are named the fore-brain or prosencephalon, the mid-brain or mesencephalon, and the hind-brain or rhombencephalon—the last being continuous with the medulla spinalis. As the result of unequal growth of these different parts three flexures are formed and the embryonic brain becomes bent on itself in a somewhat zigzag fashion; the two earliest flexures are concave ventrally and are associated with corresponding flexures of the whole head. The first flexure Fig. 044.—Two stages in the development of the neural • crest in the human embryo. (Lenhossek.) DEVELOPMENT OF THE NERVOUS SYSTEM 737 appears in the region of the mid-brain, and is named the ventral cephalic flexure (Fig. 650). By means of it the fore-brain is bent in a ventral direction around the anterior end of the notochord and fore-gut, with the result that the floor of the fore-brain comes to lie almost parallel with that of the hind-brain. This flexure causes the mid-brain to become, for a time, the most prominent part of the brain, since its dorsal surface corresponds with the convexity of the curve. Auditory vesicle Facial and acoustic Ns. Trigeminal N. Glossopharyngeal N. Vagus N. Trochlear N. Accessory N. Hypoglossal N. Mesencephalon. Oculomotor N. Frorieps ’ ganglion 1- Cervical Diencephalon - Cerebral hemisphere Phrenic N. I. Thoracic Rhinencephaion Heart Liver Vitelline loop Tail I. Coccygeal T. Lumbar Fro. 645—Reconstruction of periphera nerves^offa humangembryo maxillMynerve^06114 is not labelled, but is seen passing forward to tne eye I. Sacral The second bend appears at the junction of the hind-brain and medulla spinalis. This is termed the cervical flexure (Fig. 652), and increases from the third to the end of the fifth week, when the hind-bram forms nearly a right angle with the medulla spinalis; after the fifth week erection of the head takes place and the cervi- cal flexure diminishes and disappears. The third bend is named the pontine flexure (Fig. 652), because it is found in the region of the future pons \ aroli. from the other two in that (a) its convexity is forward, and (b) it does not affect 738 NEUROLOGY the head. The lateral walls of the brain-tube, like those of the medulla spinalis, are divided by internal furrows into alar or dorsal and basal or ventral laminae (Fig. 646). The Hind-brain or Rhombencephalon.—The cavity of the hind-brain becomes the fourth ventricle. At the time when the ventral cephalic flexure makes its Roof-plate Alar lamina Furrow between alar and basal laminae Basal lamina . Hypoglossal nerve Vagus nerve Fig. 646.—Diagram to illustrate the alar and basal laminse of brain vesicles. (His.) Fig. 647.—Transverse section of medulla oblongata of human embryo. X 32. (Kollmann.) Floor-plate appearance, the length of the hind-brain exceeds the combined lengths of the other two vesicles. Immediately behind the mid-brain it exhibits a marked constriction, the isthmus rhombencephali (Fig. 650, Isthmus), which is best seen when the brain is viewed from the dorsal aspect. From the isthmus the anterior medullary velum and the superior peduncle of the cerebellum are formed. It is customary to Roof.plate Basal lamina Alar lamina- Rhombic lip Tractus solitarius Vagus nerve Hypoglossal nerve Floor-plate Fig. 648.—Transverse section of medulla oblongata of human embryo. (After His.) divide the rest of the hind-brain into two parts, viz., an upper, called the meten- cephalon, and a lower, the myelencephalon. The cerebellum is developed by a thickening of the roof, and the pons by a thickening in the floor and lateral walls of the metencephalon. The floor and lateral walls of the myelencephalon are thickened to form the medulla oblongata; its roof remains thin, and, retaining to DEVELOPMENT OF THE NERVOUS SYSTEM 739 a great extent its epithelial nature, is expanded in a lateral direction. Later, by the growth and backward extension of the cerebellum, the roof is folded inward toward the cavity of the fourth ventricle; it assists in completing the dorsal wall of this cavity, and is also invaginated to form the ependymal covering of its choroid plexuses. Above it is continuous with the posterior medullary velum; below, with the obex and ligulse. The development of the medulla oblongata resembles that of the medulla spinalis, but at the same time exhibits one or two interesting modifications. On transverse section the myelencephalon at an early stage is seen to consist of twTo lateral walls, connected across the middle line by floor- and roof-plates (Figs. 647 and 648). Each lateral wall consists of an alar and a basal lamina, separated by an internal furrow, the remains of which are represented in the adult brain by the sulcus limitans on the rhomboid fossa. The contained cavity is more or less triangular Tania Optic stalk Rhombic lip V. N. Motor root ■ V. N. Sensory root Ganqlia of VII. and VIII. Ns. Obex -Auditory vesicle Fig. 649.—Hind-brain of a human embryo of three months—viewed from behind and partly from left side. (From model by His.) Fig. 650.—Exterior of brain of human embryo of four and a half weeks. (From model by His.) in outline, the base being formed by the roof-plate, which is thin and greatly expanded transversely. Pear-shaped neuroblasts are developed in the alar and basal laminae, and their narrow stalks are elongated to form the axis-cylinders of the nerve fibers. Opposite the furrow or boundary between the alar and basal laminae a bundle of nerve fibers attaches itself to the outer surface of the alar lamina. This is named the tractus solitarius (Fig. 648), and is formed by the sensory fibers of the glossopharyngeal and vagus nerves. It is the homologue of the oval bundle seen in the medulla spinalis, and, like it, is developed by an ingrowth o fibers from the ganglia of the neural crest. At first it is applied to the outer surface of the alar lamina, but it soon becomes buried, owing to the growth over it of the neighboring parts. By the fifth week the dorsal part of the alar lamina ben s in a lateral direction along its entire length, to form what is termed the rhombic lip (Figs. 648, 649). Within a few days this lip becomes applied to, and unites 740 NEUROLOGY with, the outer surface of the main part of the alar lamina, and so covers in the tractus solitarius and also the spinal root of the trigeminal nerve; the nodulus and flocculus of the cerebellum are developed from the rhombic lip. Neuroblasts accumulate in the mantle layer; those in the basal lamina corre- spond with the cells in the anterior gray column of the medulla spinalis, and, like them, give origin to motor nerve fibers; in the medulla oblongata they are, however, arranged in groups or nuclei, instead of forming a continuous column. From the alar lamina and its rhombic lip, neuroblasts migrate into the basal lamina, and become aggregated to form the olivary nuclei, while many send their axis-cylinders through the floor-plate to the opposite side, and thus constitute the rudiment of the raphe of the medulla oblongata. By means of this thickening of the ventral portion, the motor nuclei are buried deeply in the interior, and, in the adult, are found close to the rhomboid fossa. This is still further accentuated: (a) by the development of the pyramids, which are formed about the fourth month by the downward growth of the motor fibers from the cerebral cortex; and (6) by the fibers which pass to and from the cerebellum. On the rhomboid fossa a series of six tem- porary furrows appears; these are termed the rhombic grooves. They bear a definite relationship to certain of the cranial nerves; thus, from before backward the first and second grooves overlie the nucleus of the trigeminal; the third, th'e nucleus of the facial; the fourth, that of the ab- ducent; the fifth, that of the glosso- pharyngeal; and the sixth, that of the vagus. The pons is developed from the ventro-lateral wall of the meten- cephalon by a process similar to that which has been described for the medulla oblongata. The cerebellum is developed in the roof of the anterior part of the hind-brain (Figs. 649 to 654). The alar laminae of this region become thickened to form two lateral plates which soon fuse in the middle line and produce a thick lamina which roofs in the upper part of the cavity of the hind-brain vesicle; this constitutes the rudiment of the cerebellum, the outer surface of which is originally smooth and convex. The fissures of the cerebellum appear first in the vermis and floccular region, and traces of them are found during the third month; the fissures on the cerebellar hemispheres do not appear until the fifth month. The primitive fissures are not developed in the order of their relative size in the adult—thus the hori- zontal sulcus in the fifth month is merely a shallow groove. The best marked of the early fissures are: (a) the fissura prima between the developing culmen and declive, and (b) the fissura secunda between the future pyramid and uvula. The flocculus and nodule are developed from the rhombic lip, and are therefore recog- nizable as separate portions before any of the other cerebellar lobules. The groove produced by the bending over of the rhombic lip is here known as the Optic stalk ' Ganglia of VII. and VIII. Ns. Auditory vesicle - Fig. 651—Brain of human embryo of four and a half weeks, showing interior of fore-brain. (From model by His.) DEVELOPMENT OF THE NERVOUS SYSTEM 741 floccular fissure; when the two lateral walls fuse, the right and left floccular fissures join in the middle line and their central part becomes the post-nodular fissure. On the ventricular surface of the cerebellar lamina a transverse furrow, the incisura fastigii, appears, and deepens to form the tent-like recess of the roof of the fourth ventricle. The rudiment of the cerebellum at first projects in a dorsal direction; but, by the backward growth of the cerebrum, it is folded downward and somewhat flattened, and the thin roof-plate of the fourth ventricle, originally continuous with the posterior border of the cerebellum, is projected inward toward the cavity of the ventricle. The Mid-brain or Mesencephalon.—The mid-brain (Figs. 650 to 654) exists for a time as a thin-walled cavity of some size, and is separated from the isthmus rhomb- encephali behind, and from the fore-brain in front, by slight constrictions. Its cavity becomes relatively reduced in diameter, and forms the cerebral aqueduct of the adult brain. Its basal laminae increase in thickness to form the cerebral peduncles, which are at first of small size, but rapidly enlarge after the fourth month. Ganglion habenulce Optic s'allc Hypophysis cerebri Fig. 652.—Exterior of brain of human embryo of five weeks. (From model by His.) The neuroblasts of these laminae are grouped in relation to the sides and floor of the cerebral aqueduct, and constitute the nuclei of the oculomotor and trochlear nerves, and of the mesencephalic root of the trigeminal nerve. By a similar thickening process its alar laminae are developed into the quadrigeminal lamina. The dorsal part of the wall for a time undergoes expansion, and presents an internal median furrow and a corresponding external ridge; these, however, disappear, and the latter is replaced by a groove. Subsequently two oblique furrows extend medialward and backward, and the thickened lamina is thus subdivided into e superior and inferior colliculi. . . „ , . The Fore-brain or Prosencephalon.—A transverse section of the ear y ore rain shows the same parts as are displayed in similar sections of the me u a spma is and medulla oblongata, viz., a pair of thick lateral walls connec ey in oor and roof-plates. Moreover, each lateral wall exhibits a division m o a c orsa or alar and a ventral or basal lamina separated internally by a furrow terme e su cus 742 NEUROLOGY of Monro. This sulcus ends anteriorly at the medial end of the optic stalk, and in the adult brain is retained as a slight groove extending backward from the inter- ventricular foramen to the cerebral aqueduct. At a very early period—in some animals before the closure of the cranial part of the neural tube—two lateral diverticula, the optic vesicles, appear, one on either side of the fore-brain; for a time they communicate with the cavity of the fore-brain by relatively wide openings. The peripheral parts of the vesicles expand, while the proximal parts are reduced to tubular stalks, the optic stalks. The optic vesicle gives rise to the retina and the epithelium on the back of the ciliary body and iris; the optic stalk is invaded by nerve fibers to form the optic nerve. The fore-brain then grows forward, and from the alar laminae of this front portion the cerebral hemispheres originate as diverticula which rapidly expand to form two large pouches, one on either side. The cavities of these diverticula are the rudiments of the lateral ventricles; they communicate with the median part of the fore-brain cavity by relatively wide openings, which ultimately form the interventricular Choroidal fissure Hypophysis/ Recessus infundibuli' Tuber cinereum' Corpus mamiliare/ Pontine flexure Fig. 653.—Interior of brain of human embryo of five weeks. (From model by His.) Cervical flexure foramen. The median portion of the wall of the fore-brain vesicle consists of a thin lamina, the lamina terminalis (Figs. 654, 657), which stretches from the interventricular foramen to the recess at the base of the optic stalk. The anterior part of the fore-brain, including the rudiments of the cerebral hemi- spheres, is named the telencephalon, and its posterior portion is termed the diencephalon; both of these contribute to the formation of the third ventricle. The Diencephalon.—From the alar lamina of the diencephalon, the thalamus, metathalamus, and epithalamus are developed. The thalamus (Figs. 650 to 654) arises as a thickening which involves the anterior two-thirds of the alar lamina. The two thalami are visible, for a time, on the surface of the brain, but are subse- quently hidden by the cerebral hemispheres which grow backward over them. The thalami extend medialward and gradually narrow the cavity between them into a slit-like aperture which forms the greater part of the third ventricle; their medial surfaces ultimately adhere, in part, to each other, and the intermediate DEVELOPMENT OF THE NERVOUS SYSTEM mass of the ventricle is developed across the area of contact. The metathalamus comprises the geniculate bodies which originate as slight outward bulgings of the alar lamina. In the adult the lateral geniculate body appears as an eminence on the lateral part of the posterior end of the thalamus, while the medial is situated on the lateral aspect of the mid-brain. The epithalamus includes the pineal body, the posterior commissure, and the trigonum habenulte. The pineal body arises as an upward the evagination of roof-plate immediately in front of the mid- brain, this evagination becomes solid with the exception of its proximal part, which persists as the recessus pinealis. In lizards the pineal evagination is elongated into a stalk, and its peripheral extremity is expanded into a vesicle, in which a rudimentary lens and retina are formed; the stalk becomes solid and nerve fibers make their appearance in it, so that in these animals the pineal body forms a rudimentary eye. The posterior commissure is formed by the ingrowth of fibers into the depression behind and below the pineal evagination, and the trigonum habenulae is developed in front of the pineal recess. 743 Choroidal fissure Lamina terminal,is Rhinencephalon , Corpus striatum Optic recess/ Chiasma Hypophysis Recessus infundibuli Fio. 654.—Median sagittal section of brain of human embryo of three months. (From model by His.) From the basal laminae of the diencephalon the pars mamillaris hypothalami is developed; this comprises the corpora mamillaria and the posterior part of the tuber cinereum. The corpora mamillaria arise as a single thickening, which becomes divided into two by a median furrow during the third month. The roof-plate of the diencephalon, in front of the pineal body, remains thin and epithelial in character, and is subsequently invaginated by the choroid plexuses of the third ventricle. The Telencephalon.—This consists of a median portion and two lateral diver- ticula. The median portion forms the anterior part of the cavity of the third ventricle, and is closed below and in front by the lamina terminalis. Ihe lateral diverticula consist of outward pouchings of the alar laminae; the cavities represent the lateral ventricles, and their walls become thickened to form the nervous 744 NEUROLOGY matter of the cerebral hemispheres. The roof-plate of the telencephalon remains thin, and is continuous in front with the lamina terminalis and behind with the roof-plate of the diencephalon. In the basal laminae and floor-plate the pars optica hypothalami is developed; this comprises the anterior part of the tuber cinereum, the infundibulum and posterior lobe of the hypophysis, and the optic chiasma. The anterior part of the tuber cinereum is derived from the posterior part of the floor of the telencephalon; the infundibulum and posterior lobe of the hypophysis arise as a downward diverticulum from the floor. The most depen- dent part of the diverticulum becomes solid and forms the posterior lobe of the hypophysis; the anterior lobe of the hypophysis is developed from a diverticulum of the ectodermal lining of the stomodeum. The optic chiasma is formed by the meeting and partial decussation of the optic nerves, which subsequently grow backward as the optic tracts and end in the diencephalon. The cerebral hemispheres arise as diverticula of the alar laminae of the telen- cephalon (Figs. 650 to 654); they increase rapidly in size and ultimately overlap the structures developed from the mid- and hind-brains. This great expansion of the hemispheres is a char- acteristic feature of the brains of mammals, and attains its maximum development in the brain of man. Elliott- Smith divides each cerebral hemisphere into three funda- mental parts, viz., the rhinen- cephalon, the corpus striatum, and the neopallium. The rhinencephalon (Fig. 655) represents the oldest part of the telencephalon, and forms almost the whole of the hemisphere in fishes, amphibians, and reptiles. In man it is feebly developed in comparison with the rest of the hemisphere, and com- prises the following parts, viz., the olfactory lobe (con- sisting of the olfactory tract and bulb and the trigonum olfactorium), the anterior perforated substance, the septum pellucidum, the subcallosal, supracallosal, and dentate gyri, the fornix, the hippocampus, and the uncus. The rhinencephalon appears as a longitudinal elevation, with a corresponding internal furrow, on the under surface of the hemisphere-close to the lamina terminalis; it is separated from the lateral surface of the hemisphere by a furrow, the external rhinal fissure, and is continuous behind with that part of the hemisphere, which will ultimately form the anterior end of the temporal lobe. The elevation becomes divided by a groove into an anterior and a posterior part. The anterior grows forward as a hollow stalk the lumen of which is continuous with the anterior part of the ven- tricular cavity. During the third month the stalk becomes solid and forms the rudiment of the olfactory bulb and tract; a strand of gelatinous tissue in the interior of the bulb indicates the position of the original cavity. From the posterior part the anterior perforated substance and the pyriform lobe are developed; at the begin- ning of the fourth month the latter forms a curved elevation continuous behind with the medial surface of the temporal lobe, and consisting, from before backward, of the gyrus olfactorius lateralis, gyrus ambiens, and gyrus semilunaris, parts which Gyr. olf. med. Gyr. olf. lat. Gyr. ambiens Gyr. diagonalis Gyr. semilunaris Cerebellum Olive Fig. 655.—Inferior surface of brain of embryo at beginning of fourth month. (From Kollmann.) DEVELOPMENT OF THE NERVOUS SYSTEM 745 in the adult brain are represented by the lateral root of the olfactory tract and the uncus. The position and connections of the remaining portions of the rhinen- cephalon are described with the anatomy of the brain. The corpus striatum (Figs. 651 and 653) appears in the fourth week as a triangular thickening of the floor of the telencephalon between the optic recess and the interventricular foramen, and continuous behind with the thalamic part of the diencephalon. It increases in size, and by the second month is seen as a swelling in the floor of the future lateral ventricle; this swelling reaches as far as the posterior end of the primitive hemisphere, and when this part of the hemisphere grows backward and downward to form the temporal lobe, the posterior part of the corpus striatum is carried into the roof of the inferior horn of the ventricle, where it is seen as the tail of the caudate nucleus in the adult brain. During the fourth and fifth months the corpus striatum becomes incompletely subdivided by the fibers of the internal capsule into two masses, an inner, the caudate nucleus, and an outer, the lentiform nucleus. In front, the corpus striatum is continuous with the anterior perforated substance; laterally it is confluent for a time with that portion of the wall of the vesicle which is developed into the insula, but this continuity is sub- sequently interrupted by the fibers of the external capsule. Falx cerebri ' Edge of white substance Hippocampal fissure Edge of grey cortical substance Fig. 656.—Diagrammatic coronal section of brain to show relations of neopallium. (After His.) Cs. Corpus striatum Th. Thalamus. Cs. Corpus striatum. Th. Thalamus. The neopallium (Fig. 656) forms the remaining, and by far the greater, part of the cerebral hemisphere. It consists, at an early stage, of a relatively large, more or less hemispherical cavity—the primitive lateral ventricle enclosed by a thin wall from which the cortex of the hemisphere is developed. I he vesicle expands in all directions, but more especially upward and backward, so that by the third month the hemispheres cover the diencephalon, by the sixth they overlap the mid-bram, and by the eighth the hind-brain. # . The median lamina uniting the two hemispheres does not share in their expan- sion, and thus the hemispheres are separated by a deep cleft, the forerunner o the longitudinal fissure, and this cleft is occupied by a septum of mesoderma tissue which constitutes the primitive falx cerebri. Coincidently v\ ith the expan- sion of the vesicle, its cavity is drawn out into three prolongations which represent 746 NEUROLOGY the horns of the future lateral ventricle; the hinder end of the vesicle is carried down- ward and forward and forms the inferior horn; the posterior horn is produced somewhat later, in association with the backward growth of the occipital lobe of the hemisphere. The roof-plate of the primitive fore-brain remains thin and of an epithelial character; it is invaginated into the lateral ventricle along the medial wall of the hemisphere. This invagination constitutes the choroidal fissure, and extends from the interventricular foramen to the posterior end of the vesicle. Meso- dermal tissue, continuous with that of the primitive falx cerebri, and carrying bloodvessels with it, spreads between the two layers of the invaginated fold and forms the rudiment of the tela choroidea; the margins of the tela become highly vascular and form the choroid plexuses which for some months almost completely fill the ventricular cavities; the tela at the same time invaginates the epithelial roof of the diencephalon to form the choroid plexuses of the third ventricle. By the downward and forward growth of the posterior end of the vesicle to form the temporal lobe the choroidal fissure finally reaches from the interventricular fora- men to the extremity of the inferior horn of the ventricle. Gyrus dentatus Choroidal fissure Tcenia thalami Thalamus Corpus callosum Post, commissure Septum pellucidum Corpora quadrigemina Cerebral aqueduct Lamina terminalis Anterior commissure Cerebral 'peduncle Optic chiasma- Phinencephalon Cerebellum Hypophysis IV. ventricle III. ventricle Pons Medulla oblongata Fig. 657.—Median sagittal section of brain of human embryo of four months. (Marchand.) Parallel with but above and in front of the choroidal fissure the medial wall of the cerebral vesicle becomes folded outward and gives rise to the hippocampal fissure on the medial surface and to a corresponding elevation, the hippocampus, within the ventricular cavity. The gray or ganglionic covering of the Vail of the vesicle ends at the inferior margin of the fissure is a thickened edge; beneath this the marginal or reticular layer (future white substance) is exposed and its lower thinned edge is continuous with the epithelial invagination covering the choroid plexus (Fig. 656). As a result of the later downward and forward growth of the temporal lobe the hippocampal fissure and the parts associated with it extend from the interventricular foramen to the end of the inferior horn of the ventricle. The thickened edge of gray substance becomes the gyrus dentatus, the fasciola cinerea and the supra- and subcallosal gyri, while the free edge of the white sub- stance forms the fimbria hippocampi and the body and crus of the fornix. The corpus callosum is developed within the arch of the hippocampal fissure, and the upper part of the fissure forms, in the adult brain, the callosal fissure on the medial surface of the hemisphere. The Commissures (Fig. 657).—The development of the posterior commissure has already b.een referred to (page 743). The great commisssures of the hemi- DEVELOPMENT OF THE NERVOUS SYSTEM 747 spheres, viz., the corpus callosum, the fornix, and anterior commissures, arise from the lamina terminalis. About the fourth month a small thickening appears in this lamina, immediately in front of the interventricular foramen. The lower part of this thickening is soon constricted off, and fibers appear in it to form the anterior commissure. The upper part continues to grow with the hemispheres, and is invaded by two sets of fibers. Transverse fibers, extending between the hemispheres, pass into its dorsal part, which is now differentiated as the corpus callosum (in rare cases the corpus callosum is not developed). Into the ventral part longitudinal fibers from the hippocampus pass to the lamina terminalis, and through that structure to the corpora mamillaria; these fibers constitute the fornix. A small portion, lying antero-inferiorly between the corpus callosum and fornix, is not invaded by the commissural fibers; it remains thin, and later a cavity, the cavity of the septum pellucidum, forms in its interior. Fissures and Sulci.—The outer surface of the cerebral hemisphere is at first smooth, but later it exhibits a number of elevations or convolutions, separated from each other by fissures and sulci, most of which make their appearance during the sixth or seventh months of fetal life. The term fissure is applied to such grooves as involve the entire thickness of the cere- bral wall, and thus produce correspond- ing eminences in the ventricular cavity, while the sulci affect only the superficial part of the wall, and therefore leave no impressions in the ventricle. The fissures comprise the choroidal and hippocampal already described, and two others, viz., the calcarine and collateral, which pro- duce the swellings known respectively as the calcar avis and the collateral eminence in the ventricular cavity. Of the sulci the following may be referred to, viz., the central sulcus (fissure of Rolando), which is developed in two parts; the intraparietal sulcus in four parts; and the cingulate sulcus in two or three parts. The lateral cerebral or Sylvian fissure differs from all the other fissures in its mode of development. It appears about the third month as a depres- sion, the Sylvian fossa, on the lateral surface of the hemisphere (Fig. 658); this fossa corresponds with the position of the corpus striatum, and its floor is moulded to form the insula. The intimate connection which exists between the cortex of the insula and the subjacent corpus striatum prevents, this part of the hemi- sphere wall from expanding at the same rate as the portions which surround it. The neighboring parts of the hemisphere therefore gradually grow over and cover in the insula, and constitute the temporal, parietal, frontal, and orbital opercula of the adult brain. The frontal and orbital opercula are the last to form, but by the end of the first year after birth the insula is completely submerged by the approxi- mation of the opercula. The fissures separating the opposed margins of the oper- cula constitute the composite lateral cerebral fissure. If a section across the wall of the hemisphere about the.sixth week be examined microscopically it will be found to consist of a thin marginal or reticular layer, a thick ependymal layer, and a thin intervening mantle layer. Neuroblasts from the ependymal and mantle layers migrate into the deep part of the marginal layer and form the cells of the cerebral cortex. The nerve fibers which form the underlying white substance of the hemispheres consist at first of outgrowths from the cells of Parietal operculum Temporal operculum Sylvian fossa Frontal operculum Fig. 658.—Outer surface of cerebral hemisphere of human embryo of about five months. 748 NEUROLOGY the corpora striata and thalami; later the fibers from the cells of the cortex are added. Medullation of these fibers begins about the time of birth and continues until puberty. A summary of the parts derived from the brain vesicles is given in the following table: Medulla oblongata 1. Myelencephalon Lower part of fourth ventricle. Pons Hind-brain or 2. Meteneephalon Cerebellum Intermediate part of fourth Rhombencephalon 3. Isthmus rhomb- encephali ventricle. Anterior medullary velum Brachia conjunctiva cerebelli. Upper part of fourth ventricle. Cerebral peduncles Mid-brain or Mesencephalon . . . . < Lamina quadrigemina Cerebral aqueduct. - Thalamus Metathalamus Epithalamus 1. Diencephalon < Pars mamillaris hypo- thalami Posterior part of third Fore-brain or ventricle. Prosencephalon Anterior part of third ventricle . Pars optica hypo- 2. Telencephalon thalami Cerebral hemispheres Lateral ventricles Interventricular foramen. The Cranial Nerves.—With the exception of the olfactory, optic, and acoustic nerves, which will be especially considered, the cranial nerves are developed in a similar manner to the spinal nerves (see page 735). The sensory or afferent nerves are derived from the cells of the ganglion rudiments of the neural crest. The central processes of these cells grow into the brain and form the roots of the nerves, while the peripheral pro- cesses extend outward and consti- tute their fibers of distribution (Fig. 645). It has been seen, in considering the development of the medulla oblongata (page 739), that the tractus solitarius (Fig. 660), de- rived from the fibers which grow inward from the ganglion rudiments of the glossopharyngeal and vagus nerves, is the homologue of the oval bundle in the cord which had -Boof-plate Alar lamina Furrow between alar and basal lamince -Basal lamina Vagus nerve Floor-plate Hypoglossal nerve Fig. 659.—Transverse section of medulla oblongata of human embryo. X 32. (Kollmann ) THE MEDULLA SPINALIS OR SPINAL CORD its origin in the posterior nerve roots. The motor or efferent nerves arise as out- growths ot the neuro blasts situated in the basal laminae of the mid- and hind- brain. While, however, the spinal motor nerve roots arise in one series from the basal lamina, the cranial motor nerves are grouped into two sets, according as they spring from the medial or lateral parts of the basal lamina. To the former set belong the oculomotor, trochlear, abducent, and hypoglossal nerves; to the latter, the accessory and the motor fibers of the trigeminal, facial, glossopharyn- geal, vagus nerves (Figs. 659, 660). 749 Roof-plate Alar lamina— Basal lamina Rhombic lip Tr actus solitarius Vagus nerve Hypoglossal nervo Fig. 660.—Transverse section of medulla oblongata of human embryo. (After His.) Floor-plate THE MEDULLA SPINALIS OR SPINAL CORD. The medulla spinalis or spinal cord forms the elongated, nearly cylindrical, part of the central nervous system which occupies the upper two-thirds of the vertebral canal. Its average length in the male is about 45 cm., in the female from 42 to 43 cm., while its weight amounts to about 30 gms. It extends from the level of the upper border of the atlas to that of the lower border of the first, or upper border of the second, lumbar vertebra. Above, it is continuous with the brain; below, it ends in a conical extremity, the conus medullaris, from the apex of which a delicate filament, the filum terminale, descends as far as the first segment of the coccyx (Fig. 661). The position of the medulla spinalis varies with the movements of the vertebral column, its lower extremity being drawn slightly upward when the column is flexed. It also varies at different periods of life; up to the third month of fetal life the medulla spinalis is as long as the vertebral canal, but from this stage onward the vertebral column elongates more rapidly than the medulla spinalis, so that by the end of the fifth month the medulla spinalis terminates at the base of the sacrum, and at birth about the third lumbar vertebra. The medulla spinalis does not fill the part of the vertebral canal in which it lies; it is ensheathed by three protective membranes, separated from each other by two concentric spaces. The three membranes are named from without inward, the dura mater, the arachnoid, and the pia mater. The dura mater is a strong, fibrous membrane which forms a wide, tubular sheath; this sheath extends below the ter- mination of the medulla spinalis and ends in a pointed cul-de-sac at the level of the lower border of the second sacral vertebra. The dura mater is separated from the wall of the vertebral canal by the epidural cavity, which contains a quantity of loose areolar tissue and a plexus of veins; between the dura mater and the subjacent arachnoid is a capillary interval, the subdural cavity, which contains a small quan- tity of fluid, probably of the nature of lymph. The arachnoid is a thin, transparent 750 NEUROLOGY sheath, separated from the pia mater by a comparatively wide interval, the sub- arachnoid cavity, which is filled with cerebrospinal fluid. The pia mater closely invests the medulla spinalis and sends delicate septa into its substance; a narrow band, the ligamentum denticulatum, extends along each of its lateral surfaces and is attached by a series of pointed processes to the inner surface of the dura mater. Thirty-one pairs of spinal nerves spring from the medulla spinalis, each nerve having an anterior or ventral, and a posterior or dorsal root, the latter being dis- tinguished by the presence of an oval swelling, the spinal ganglion, which contains numerous nerve cells. Each root consists of several bundles of nerve fibers, and at its attachment extends for some distance along the side of the medulla spinalis. The pairs of spinal nerves are grouped as follows: cervical 8, thoracic 12, lumbar 5, sacral 5, coccygeal 1, and, for convenience of description, the medulla spinalis is divided into cervical, thoracic, lumbar and sacral regions, corre- sponding with the attachments of the different groups of nerves. Although no trace of transverse segmen- tation is visible on the surface of the medulla spinalis, it is convenient to regard it as being built up of a series of superimposed spinal segments or neuromeres, each of which has a length equivalent to the extent of attach- ment of a pair of spinal nerves. Since the ex- tent of attachment of the successive pairs of nerves varies in different parts, it follows that the spinal segments are of varying lengths; thus, in the cervical region they average about 13 mm., in the mid-thoracic region about 26 mm., while in the lumbar and sacral regions they diminish rapidly from about 15 mm. at the level of the first pair of lumbar nerves to about 4 mm. opposite the attachments of the lower sacral nerves. As a consequence of the relative inequality in the rates of growth of the medulla spinalis and vertebral column, the nerve roots, which in the early embryo passed transversely out- ward to reach their respective intervertebral foramina, become more and more oblique in direction from above downward, so that the lumbar and sacral nerves descend almost vertically to reach their points of exit. From the appearance these nerves present at their attachment to the medulla spinalis and from their great length they are collectively termed the cauda equina (Fig. 662). The filum terminate is a delicate filament, about 20 cm. in length, prolonged downward from the apex of the conus medullaris. It consists of two parts, an upper and a lower. The upper part, or filum terminate internum, measures about 15 cm. in length and reaches as far as the lower border of the second sacral vertebra. It is contained within the tubular sheath of dura mater, and is surrounded by the nerves forming the cauda equina, from which it can be readily recognized by its bluish-white color. The lower part, or filum terminate externum, is closely invested Fig. 661.—Sagittal section of vertebral canal to show the lower end of the medulla spinalis and the filum terminale. (Testut.) Li, Lv. First and fifth lumbar vertebrae. Sii. Second sacral vertebra. 1. Dura mater. 2. Lower part of tube of dura mater. 3. Lower extremity of medulla spinalis. 4. Intradural, and 5, Extra- dural portions of filum terminale. 6. Attach- ment of filum terminale to first segment of coccyx. THE MEDULLA SPINALIS OR SPINAL CORD by, and is adherent to, the dura mater; it extends downward from the apex of the tubular sheath and is attached to the back of the first segment of the coccyx. The filum terminale consists mainly of fibrous tissue, continuous above with that of the pia mater. Adhering to its outer surface, however, are a few strands of nerve fibers which probably represent rudimentary second and third coccygeal nerves; further, the central canal of the medulla spinalis extends downward into it for 5 or 6 cm. Enlargements.—The medulla spinalis is not quite cylindrical, being slightly flattened from before backward; it also Decussation of the pyramids Postero- intermediate sulcus Anterior median fissure Cervical enlargement Posterior median sulcus Postero- lateral sulcus -Dura mater Conus medullaris Posterior nerveroots Filum ierminale Lumbar enlargement ■ Conus Filum - Fig. 662.—Cauda equina and filum terminale seen from behind. The dura mater has been opened ana spread out, and the arachnoid has been removed. Fto. 663.—Diagrams of the medulla spinalis. Ventral aspect Dorsal aspect 752 NEUROLOGY presents two swellings or enlargements, an upper or cervical, and a lower or lumbar (Fig. 663). The cervical enlargement is the more pronounced, and corresponds with the attach- ments of the large nerves which supply the upper limbs. It extends from about the third cervical to the second thoracic vertebra, its maximum circumference (about 38 mm.) being on a level with the attachment of the sixth pair of cervical nerves. The lumbar enlargement gives attachment to the nerves which supply the lower limbs. It commences about the level of the ninth thoracic vertebra, and reaches its maximum circumference, of about 33 mm., opposite the last thoracic vertebra, below which it tapers rapidly into the conus medullaris. Fissures and Sulci (Fig. 664).—An anterior median fissure and a posterior median sulcus incompletely divide the medulla spinalis into two symmetrical parts, which are joined across the middle line by a commissural band of nervous matter. Posterior median sulcus Posterior median septum Posterior nerve roots .Postero-lateral sulcus Posterior : column Format io 'reticularis Lateral column Anterior column Fig. 664.—Transverse section of the medulla spinalis in the mid-thoracic region. Anterior nerve roots Anterior median fissure The Anterior Median Fissure (fissura mediana anterior) has an average depth of about 3 mm., but this is increased in the lower part of the medulla spinalis. It contains a double fold of pia mater, and its floor is formed by a transverse band of white substance, the anterior white commissure, which is perforated by blood- vessels on their way to or from the central part of the medulla spinalis. The Posterior Median Sulcus (sulcus medianus posterior) is very shallow; from it a septum of neuroglia reaches rather more than half-way into the substance of the medulla spinalis; this septum varies in depth from 4 to 6 mm., but diminishes considerably in the lower part of the medulla spinalis. On either side of the posterior median sulcus, and at a short distance from it, the posterior nerve roots are attached along a vertical furrow named the postero- lateral sulcus. The portion of the medulla spinalis which lies between this and the posterior median sulcus is named the posterior funiculus. In the cervical and upper thoracic regions this funiculus presents a longitudinal furrow, the postero-inter- mediate sulcus; this marks the position of a septum which extends into the posterior funiculus and subdivides it into two fasciculi—a medial, named the fasciculus gracilis (tract of Goll); and a lateral, the fasciculus cuneatus (tract of Burdach) THE MEDULLA SPINALIS OR SPINAL CORD (Fig. 6/2). The portion of the medulla spinalis which lies in front of the postero- lateral sulcus is termed the antero-lateral region. The anterior nerve roots, unlike the posterior, are not attached in linear series, and their position of exit is not marked by a sulcus. I hey arise by separate bundles which spring from the anterior column of gra\ substance and, passing forward through the white substance, emerge o\ er an area of some slight width. The most lateral of these bundles is generally taken as a dividing line which separates the antero-lateral region into two parts, \iz., an anterior funiculus, between the anterior median fissure and the most lateral of the anterior nerve roots; and a lateral funiculus, between the exit of these roots and the postero-lateral sulcus. In the upper part of the cervical region a series of nerve roots passes outward through the lateral funiculus of the medulla spinalis; these unite to form the spinal portion of the accessory nerve, which runs upward and enters the cranial cavity through the foramen magnum. 753 White matter. Gray matter. Entire section. Fig. 665.—Curves showing the sectional area at different levels of the cord. The ordinates show the area in sq. mm. (Donaldson and Davis.) The Internal Structure of the Medulla Spinalis.—On examining a transverse section of the medulla spinalis (Fig. 664) it is seen to consist of gray and white nervous substance, the former being enclosed within the latter. Gray Substance (,substantia grisea centralis).-—The gray substance consists of two symmetrical portions, one in each half of the medulla spinalis: these are joined across the middle line by a transverse commissure of gray substance, through which runs a minute canal, the central canal, just visible to the naked eye. In a transverse section each half of the gray substance is shaped like a comma or crescent, the concavity of which is directed laterally; and these, together with the intervening gray commissure, present the appearance of the letter H. An imaginary coronal plane through the central canal serves to divide each crescent into an anterior or ventral, and a posterior or dorsal column. The Anterior Column (columna anterior; anterior cornu), directed forward, is broad and of a rounded or quadrangular shape. Its posterior part is termed the base, and its anterior part the head, but these are not differentiated from each other by any well-defined constriction. It is separated from the surface of the medulla spinalis by a layer of white substance w7hich is traversed by the bundles of the anterior nerve roots. In the thoracic region, the postero-lateral part of the anterior column projects lateralward as a triangular field, which is named the lateral column {columna lateralis; lateral cornu). The Posterior Column {columna 'posterior; posterior cornu) is long and slender, and is directed backward and lateralward: it reaches almost as far as the postero- lateral sulcus, from which it is separated by a thin layer of white substance, the tract of Lissauer. It consists of a base, directly continuous writh the base of the anterior horn, and a neck or slightly constricted portion, which is succeeded by an oval or fusiform area, termed the head, of which the apex approaches the postero- lateral sulcus. The apex is capped by a b -shaped or crescentic mass of trans- lucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando, which 754 NEUROLOGY contains both neuroglia cells, and small nerve cells. Between the anterior and posterior columns the gray substance extends as a series of processes into the lateral funiculus, to form a net-work called the for- matio reticularis. The quantity of gray substance, as well as the form which it presents on transverse section, varies mark- edly at different levels. In the thoracic region it is small, not only in amount but relatively to the sur- rounding white substance. In the cervical and lum- bar enlargements it is greatly increased: in the latter, and especially in the conus medullaris, its proportion to the white substance is greatest (Fig. 665). In the cervical region its posterior column is compara- tively narrow, while its anterior is broad and ex- panded; in the thoracic region, both columns are attenuated, and the lateral column is evident; in the lumbar enlargement, both are expanded; while in the conus medullaris the gray substance assumes the form of two oval masses, one in each half of the cord, connected together by a broad gray commissure. The Central Canal (canalis centralis) runs through- out the entire length of the medulla spinalis. The portion of gray substance in front of the canal is named the anterior gray commissure; that behind it, the posterior gray commissure. The former is thin, and is in contact anteriorly with the anterior white commissure: it contains a couple of longitudinal veins, one on either side of the middle line. The posterior gray commissure reaches from the central canal to the posterior median septum, and is thin- nest in the thoracic region, and thickest in the conus medullaris. The central canal is continued upward through the lower part of the medulla oblongata, and opens into the fourth ventricle of the brain; below, it reaches for a short distance into the filum termi- nale. In the lower part of the conus medullaris it exhibits a fusiform dilatation, the terminal ventricle; this has a vertical measurement of from 8 to 10 mm., is triangular on cross-section with its base directed forward, and tends to undergo obliteration after the age of forty years. Throughout the cervical and thoracic regions the central canal is situated in the anterior third of the medulla spinalis; in the lumbar enlargement it is near the middle, and in the conus medullaris it approaches the posterior surface. It is filled with cerebrospinal fluid, and lined by ciliated, columnar epithelium, outside of which is an encircling band of gelatinous substance, the substantia gelatinosa centralis. This gelatinous substance consists mainly of neuroglia, but contains a few nerve cells and fibers; it is traversed by processes from the deep ends of the columnar ciliated cells which line the central canal (Fig. 667). Cl C2. C,5. C.8, Th.2. Th.8. Th.12 L.3. S.2. Coc. Fio. 666.—Transverse sections of the medulla spinalis at different levels. THE MEDULLA SPINALIS OR SPINAL CORD 755 Structure of the Gray Substance. The gray substance consists of numerous nerve cells and nerve fibers held together by neuroglia. Throughout the greater part of the gray substance the neuroglia presents the appearance of a sponge-like net- work, but around the central canal and on the apices of the posterior columns it consists of the gelatinous substance already referred to. The nerve cells are multipolar, and vary greatly in size and shape. They consist of (1) motor cells of large size, v hich are situated in the anterior horn, and are especially numerous in the cervical and lumbar enlargements; the axons of most of these cells pass out to form the anterior nerve roots, but before leaving the white substance they fre- quently give off collaterals, which reenter and ramify in the gray substance.1 (2) Cells of small or medium size, whose axons pass into the white matter, where some pursue an ascending, and others a descending course, but most of them divide in a T-shape manner into descending and ascend- ing processes. They give off col- laterals which enter and ramify in the gray substance, and the termi- nations of the axons behave in a similar manner. The lengths of these axons vary greatly: some are short and pass only between adjoining spinal segments, while others are longer and connect more Collateral Ascending Descending Neuroglial cells / ■Arborisation Ependymal cells Fig. 668.—Cells of medulla spinalis. (Poirier.) Diagram showing in longitudinal section the intersegmental neurons of the medulla spinalis. The gray and white parts corre- spond respectively to the gray and white substance of the medulla spinalis. Fig. 667.—Section of central canal of medulla spinalis, showing ependymal and neuroglial cells, (v. Lenhossek.) distant segments. These cells and their processes constitute a series of association or intersegmental neurons (Fig. 668), which link together the dillerent parts of the medulla spinalis. The axons of most of these cells are confined to that side of the medulla spinalis in which the nerve cells are situated, but some cross to the opposite side through the anterior commissure, and are termed crossed commissural fibers. Some of these latter end directly in the gray substance, while others enter the white substance, and ascend or descend in it for varying distances, before finally terminating in the gray substance. (3) C ells of the type II of Golgi, limited for the 1 Lcnhossek and Cajal found that in the chick embryo the axons of a few of these nerve cells'Passed backwardThough the posterior column, and emerged as the motor fibers of the posterior nerve roots. These fibers are said to control the peristaltic movements of the intestine. Their presence, in man, has not yet been determined. 756 NEUROLOGY most part to the posterior column, are found also in the substantia gelatinosa of Rolando; their axons are short and entirely confined to the gray substance, in which Fasciculus gracilisi, Fasciculus cuneatus Lissauer's fasciculus- Dorsal spinocerebellar . fasciculus Dorsal nucleus Ventral ~spinocerebellar fasciculus Posterior ~ spinothalamic fasciculus -Spinotectal fasciculus Ventral spinothalamic fasciculus * lo. 669.—Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fasciculi. they break up into numerous fine filaments. Most of the nerve cells are arranged in longitudinal columns, and appear as groups on transverse section (Figs. 669,670,671). Lateral cerebrospinal fasciculus Rubrospinal fasciculus -Tectospinal fasciculus -Vestibulospinal fasciculus Fig. 670.—Diagram showing possible connection of long descending fibers from higher centers with the motor cells of the ventral column through association fibers. Nerve Cells in the Anterior Column.—The nerve cells in the anterior column are arranged in columns of varying length. The longest occupies the medial part of the anterior column, and is named the antero medial column: it is well marked in C4, C5, again from C8 to L4, it disappears in L5 and SI but is well marked in THE MEDULLA SPINALIS OR SPINAL CORD 757 S2, S3 and S4 (Bruce).1 Behind it is a dorso-medial column of small cells, which is not represented in L5, SI, S2 nor below S4. Its axons probably pass into the dorsal rami of the spinal nerves to supply the dorsal musculature of the spinal column. In the cervical and lumbar enlargements, where the anterior column is expanded in a lateral direc- tion, the following additional col- umns are present, viz.: (a) antero- lateral, which consists of two groups, one in C 4, C 5, C 6 the other in C 6, C 7, C 8 in the cervical enlargement and of a group from L2 to S2 in the lumbo-sacral enlargement; (b) postero-lateral, in the lower five cer- vical, lower four lumbar, and upper three sacral segments; (c) post-postero- lateral, in the last cervical, first tho- racic, and upper three sacral seg- ments; and (d) a central, in the lower four lumbar and upper two sacral segments. These cell groups are evi- dently related to the nerve roots of the brachial and sacral plexuses and supply fibers to the muscles of the arm and leg. Throughout the base of the anterior column are scattered solitary cells, the axons of some of which form crossed commissural fibers, while others constitute the motor fibers of the posterior nerve roots. (See footnote, page 755.) Nerve Cells in the Lateral Column. —These form a column which is best marked where the lateral gray column is differentiated, viz., in the thoracic region;2 but it can be traced throughout the entire length of the medulla spinalis in the form of groups of small cells which are situ- ated in the anterior part of the formatio reticularis. In the upper part of the cervical region and lower part of the medulla oblongata as well as in the third and fourth sac- ral segments this column is again differentiated. In the medulla it is known as the lateral nucleus. The cells of this column are fusiform or star-shaped, and of a medium size: the axons of some of them pass into C. VII Lateral column' Postero- lateral ' column ' Dorso-medial column Antero-lateral column _ A nlero-medial column Dorsal nucleu, TH. VI Lateral column- Anterior column'' L. I Postero- lateral column Antero-medial column Antero-laterall column Central column S. I Postero-lateral_ column Central column 1 Topographical Atlas of the Spinal Cord, 1901. 2 According to Bruce and Pirie (B. M. J., N°y®ni" her 17, 1906) this column extends from the middle of the eighth cervical segment to the lower part of the second lumbar or the upper part of the third lumbar segment. Fig. 671.—Transverse sections of the medulla spinalis a,t different levels to show the arrangement of the principal cel) columns. 758 NEUROLOGY the anterior nerve roots, by which they are carried to the sympathetic nerves: they constitute the white rami and are sympathetic or visceral efferent fibers; they are also known as preganglionic fibers of the sympathetic system; the axons of others pass into the anterior and lateral funiculi, where they become longitudinal. Nerve Cells in the Posterior Column.—1. The dorsal nucleus (nucleus dorsalis; col- umn of Clarke) occupies the medial part of the base of the posterior column, and appears on the transverse section as a well-defined oval area. It begins below at the level of the second or third lumbar nerve, and reaches its maximum size opposite the twelfth thoracic nerve. Above the level of the ninth thoracic nerve its size diminishes, and the column ends opposite the last cervical or first thoracic nerve. It is represented, however, in the other regions by scattered cells, which become aggregated to form a cervical nucleus opposite the third cervical nerve, and a sacral nucleus in the middle and lower part of the sacral region. Its cells are of medium size, and of an oval or pyriform shape; their axons pass into the peripheral part of the lateral funiculus of the same side, and there ascend, prob- ably in dorsal spinocerebellar (direct cerebellar) fasciculus. 2. The nerve cells in the substantia gelatinosa of Rolando are arranged in three zones: a posterior or margi- nal, of large angular or fusiform cells; an intermediate, of small fusiform cells; and an anterior, of star-shaped cells. The axons of these cells pass into the lateral and posterior funiculi, and there assume a vertical course. In the anterior zone some Golgi cells are found whose short axons ramify in the gray substance. 3. Solitary cells of varying form and size are scattered throughout the posterior column. Some of these are grouped to form the posterior basal column in the base of the posterior column, lateral to the dorsal nucleus; the posterior basal column is well-marked in the gorilla (Waldeyer), but is ill-defined in man. The axons of its cells pass partly to the posterior and lateral funiculi of the same side, and partly through the anterior white commissure to the lateral funiculus of the opposite side. Golgi cells, type II, located in this region send axons to the lateral and ventral columns. A few star-shaped or fusiform nerve cells of varying size are found in the sub- stantia gelatinosa centralis. Their axons pass into the lateral funiculus of the same, or of the opposite side. The nerve fibers in the gray substance form a dense interlacement of minute fibrils among the nerve cells. This interlacement is formed partly of axons which pass from the cells in the gray substance to enter the white funiculi or nerve roots; partly of the axons of Golgi’s cells which ramify only in the gray substance; and partly of collaterals from the nerve fibers in the white funiculi which, as already stated, enter the gray substance and ramify within it. White Substance (substantia alba).—The white substance of the medulla spinalis consists of medullated nerve fibers imbedded in a spongelike net-work of neuroglia, and is arranged in three funiculi: anterior, lateral, and posterior. The anterior funiculus lies between the anterior median fissure and the most lateral of the ante- rior nerve roots: the lateral funiculus between these nerve roots and the postero- lateral sulcus; and the posterior funiculus between the postero-lateral and the pos- terior median sulci (Fig. 672). The fibers vary greatly in thickness, the smallest being found in the fasciculus gracilis, the tract of Lissauer, and inner part of the lateral funiculus; while the largest are situated in the anterior funiculus, and in the peripheral part of the lateral funiculus. Some of the nerve fibers assume a more or less transverse direction, as for example those which cross from side to side in the anterior white commissure, but the majority pursue a longitudinal course and are divisible into (1) those connecting the medulla spinalis with the brain and conveying impulses to or from the latter, and (2) those which are confined to the medulla spinalis and link together its different segments, i. e., intersegmental or association fibers. THE MEDULLA SPINALIS OR SPINAL CORD 759 Nerve Fasciculi. The longitudinal fibers are grouped into more or less definite bundles or fasciculi, these are not recognizable from each other in the normal state, and their existence has been determined by the following methods; (1) A. Waller disco\ ered that if a bundle of nerve fibers be cut, the portions of the fibers which are separated from their cells rapidly degenerate and become atrophied, while the cells and the parts of the fibers connected with them undergo little alter- ation. I his is knov n as Wallerian degeneration. Similarly, if a group of nerve cells be destroyed, the fibers arising from them undergo degeneration. Thus, if the motor cells of the cerebral cortex be destroyed, or if the fibers arising from these cells be severed, a descending degeneration from the seat of injury takes place in the fibers. In the same manner, if a spinal ganglion be destroyed, or the fibers v hich pass from it into the medulla spinalis be cut, an ascending degenera- tion v ill extend along these fibers. (2) Pathological changes, especially in man, ha^e gi\en important information by causing ascending and descending degenera- Fasciculus gracilis- (Gollff Septomarginal fasciculus pomma fasciculus Fasciculus cuneatus_ (Burdach) . 4Posterior proper fasciculus Lissauer's fasciculus Lateral proper j Lateral cerebrospinal fasciculus Dorsal spinocerebellar fasciculus (Flechsig) Rubrospinal fasciculus (Monakow) Ventro spinocerebellar fasciculus (Gowers) Tectospinal fasciculus Posterior , spinothalamic fasciculus Vestibulospinal fasciculus Spinotectal fasciculus Anterior spinothalamic fasciculus Anterior cerebrospinal fasciculus 'Sulcomarginal fasciculus 'Anterior proper fasciculus Fig. 672.—Diagram of the principal fasciculi of the spinal cord. tions. (3) By tracing the development of the nervous system, it has been observed that at first the nerve fibers are merely naked axis-cylinders, and that they do not all acquire their medullary sheaths at the same time; hence the fibers can be grouped into different bundles according to the dates at which they receive their medullary sheaths. (4) Various methods of staining nervous tissue are of great value in tracing the course and mode of termination of the axis-cylinder processes. Fasciculi in the Anterior Funiculus.— Descending Fasciculi.—The anterior cerebro- spinal (fasciculus cerebrospinalis anterior; direct pyramidal tract), which is usually small, but varies inversely in size with the lateral cerebrospinal fasciculus. It lies close to the anterior median fissure, and is present only in the upper part of the medulla spinalis; gradually diminishing in size as it descends, it ends about the middle of the thoracic region. It consists of descending fibers which arise 1 Somewhat later a change, termed chromatolysis, takes place in the nerve cells, and consists of a breaking down and an ultimate disappearance of the Nissl bodies. Further, the body of the cell is swollen, the nucleus displaced toward the periphery, and the part of the axon still attached to the altered cell is diminished in size and somewhat atrophied. Under favorable conditions the cell is capable of reassuming its normal appearance, and its axon may grow again. 760 NEUROLOGY from cells in the motor area of the cerebral hemisphere of the same side; and which, as they run downward in the medulla spinalis, cross in succession through the anterior white commissure to the opposite side, where they end, either directly or indirectly, by arborizing around the motor cells in the anterior column. A few of its fibers are said to pass to the lateral column of the same side and to the gray matter at the base of the posterior column. They conduct voluntary motor impulses from the precentral gyrus to the motor centers of the cord. The vestibulospinal fasciculus, situated chiefly in the marginal part of the funiculus and mainly derived from the cells of Deiters’ nucleus, of the same and the opposite side, i. e., the chief terminal nucleus of the vestibular nerve. Fibers are also contributed to this fasciculus from scattered cells of the articular formation of the medulla oblongata, the pons and the mid-brain (tegmentum). The other terminal nuclei of the vestibular nerve also contribute fibers. In the brain stem these fibers form part of the median longitudinal bundle. The fasciculus can be traced to the sacral region. Its terminals and collaterals end either directly or indirectly among the motor cells of the anterior column. This fasciculus is probably concerned with equilibratory reflexes. The tectospinal fasciculus, situated partly in the anterior and partly in the lateral funiculus, is mainly derived from the opposite superior colliculus of the mid-brain. The fibers from the superior colliculus cross the median raphe in the fountain decussation of Meynert and descend as the ventral longitudinal bundle in the reticular formation of the brain-stem. Its collaterals and terminals end either directly or indirectly among the motor cells of the anterior column of the same side. Since the superior colliculus is an important visual reflex center, the tectospinal fasciculus is probably concerned with visual reflexes. Ascending Fasciculi.—The ventral spinothalamic fasciculus, situated in the marginal part of the funiculus and intermingled more or less with the vestibulo- spinal fasciculus, is derived from cells in the posterior column or intermediate gray matter of the opposite side. Their axons cross in the anterior commissure. This is a somewhat doubtful fasciculus and its fibers are supposed to end in the thalamus and to conduct certain of the touch impulses. The remaining fibers of the anterior funiculus constitute what is termed the anterior proper fasciculus (fasciculus anterior proprius; anterior basis bundle). It consists of (a) longitudinal intersegmental fibers which arise from cells in the gray substance, more especially from those of the medial group of the anterior column, and, after a longer or shorter course, reenter the gray substance; (6) fibers which cross in the anterior white commissure from the gray substance of the opposite side. Fasciculi in the Lateral Funiculus. — 1. Descending Fasciculi. —{a) The lateral cerebrospinal fasciculus (fasciculus cerebrospinalis lateralis; crossed pyramidal tract) extends throughout the entire length of the medulla spinalis, and on trans- verse section appears as an oval area in front of the posterior column and medial to the cerebellospinal. Its fibers arise from cells in the motor area of the cerebral hemisphere of the opposite side. They pass downward in company with those of the anterior cerebrospinal fasciculus through the same side of the brain as that from which they originate, but they cross to the opposite side in the medulla oblon- gata and descend in the lateral funiculus of the medulla spinalis. It is probable1 that the fibers of the anterior and lateral cerebrospinal fasciculi are not related in this direct manner with the cells of the anterior column, but ter- minate by arborizing around the cells at the base of the posterior column and the cells of Clarke’s column, which in turn link them to the motor cells in the anterior column, usually of several segments of the cord. In consequence of these interposed 1 Schafer, Proc. Physiolog. Soc., 1899. THE MEDULLA SPINALIS OR SPINAL CORD 761 neurons the fibers of the cerebrospinal fasciculi correspond not to individual muscles, but to associated groups of muscles. The anterior and lateral cerebrospinal fasciculi constitute the motor fasciculi of the medulla spinalis and have their origins in the motor cells of the cerebral cortex. They descend through the internal capsule of the cerebrum, traverse the cerebral peduncles and pons and enter the pyramid of the medulla oblongata. In the lower part of the latter about two-thirds of them cross the middle line and run downward in the lateral funiculus as the lateral cerebrospinal fasciculus, while the remaining fibers do not cross the middle line, but are continued into the same side of the medulla spinalis, where they form the anterior cerebrospinal fasciculus. The fibers of the latter, however, cross the middle line in the anterior white com- missure, and thus all the motor fibers from one side of the brain ultimately reach the opposite side of the medulla spinalis. The proportion of fibers which cross in the medulla oblongata is not a constant one, and thus the anterior and lateral cerebrospinal fasciculi vary inversely in size. Sometimes the former is absent, and in such cases it may be presumed that the decussation of the motor fibers in the medulla oblongata has been complete. The fibers of these two fasciculi do not acquire their medullary sheaths until after birth. In some animals the motor fibers are situated in the posterior funiculus. (b) The rubrospinal fasciculus (Monakow) (prepyramidal tract), lies on the ventral aspect of the lateral cerebrospinal fasciculus and on transverse section appears as a somewhat triangular area. Its fibers descend from the mid-brain, where they have their origin in the red nucleus of the tegmentum of the opposite side. Its terminals and collaterals end either directly or indirectly in relation with the motor cells of the anterior column. The rubrospinal fasciculus is supposed to be concerned with cerebellar reflexes since its afferent fibers which pass through the superior peduncle send many collaterals and terminals to the red nucleus. (c) The olivospinal fasciculus (Helweg) arises in the vicinity of the inferior olivary nucleus in the medulla oblongata, and is seen only in the cervical region of the medulla spinalis, where it forms a small triangular area at the periphery, close to the most lateral of the anterior nerve roots. Its exact origin and its mode of ending have not yet been definitely made out. 2. Ascending Fasciculi—(a) The dorsal spinocerebellar fasciculus (fasciculus cerebellospinalis; direct cerebellar tract of Flechsig) is situated at the periphery of the posterior part of the lateral funiculus, and on transverse section appears as a flattened band reaching as far forward as a line drawn transversely through the central canal. Medially, it is in contact with the lateral cerebrospinal fasciculus, behind, with the fasciculus of Lissauer. It begins about the level of the second or third lumbar nerve, and increasing in size as it ascends, passes to the vermis of the cerebellum through the inferior peduncle. Its fibers are generally regarded as being formed by the axons of the cells of the dorsal nucleus (Clarke s column)] they receive their medullary sheaths about the sixth or seventh month of fetal life. Its fibers are supposed to conduct impulses of unconscious muscle sense. The superficial antero-lateral fasciculus (tract of Gowers) consists of four fasciculi, the ventral spinocerebellar, the lateral spinothalamic, the spinotectal and the ventral spinothalamic. (b) The ventral spinocerebellar fasciculus (Gowers) skirts the periphery of the lateral funiculus in front of the dorsal spinocerebellar fasciculus. . In transverse section it is shaped somewhat like a comma, the expanded end of which lies in front of the dorsal spinocerebellar fasciculus while the tail reaches forward into the anterior funiculus. Its fibers come from the same but mostly from the opposite side of the medulla spinalis and cross both in the anterior white commissure and in the gray commissure; they are probably derived from the cells of the dorsal nucleus and from other cells of the posterior column and the intermediate poition 762 NEUROLOGY of the gray matter. The ventral spinocerebellar fasciculus begins about the level of the third pair of lumbar nerves, and can be followed into the medulla oblongata and pons almost to the level of the inferior colliculus where it crosses over the superior peduncle and then passes backward along its medial border to reach the vermis of the cerebellum. In the pons it lies along the lateral edge of the lateral lemniscus. Some of its fibers join the dorsal spinocerebellar fasciculus at the level of the inferior peduncle and pass with them into the cerebellum. Other fibers are said to continue upward in the dorso-lateral part of the tegmentum of the mid-brain probably as far as the thalamus. (c) The lateral spinothalamic fasciculus is supposed to come from cells in the dorsal column and the intermediate gray matter whose axons cross in the anterior com- missure to the opposite lateral funiculus where they pass upward on the medial side of the ventral spinocerebellar fasciculus; on reaching the medulla oblongata they continue in the formatio reticularis near the median fillet and probably ter- minate in the ventro-lateral region of the thalamus. It is supposed to conduct impulses of pain and temperature. The lateral and ventral spinothalamic fasciculi are sometimes termed the secondary sensory fasciculus or spinal lemniscus. (d) The spinotectal fasciculus is supposed to arise in the dorsal column and terminate in the (inferior ?) and superior colliculi. It is situated ventral to the lateral spinothalamic fasciculus, but its fibers are more or less intermingled with it. It is also known as the spino-quadrigeminal system of Mott. In the brain-stem the fibers run lateral from the inferior olive, ventro-lateral from the superior olive, then ventro-medial from the spinal tract of the trigeminal; the fibers come to lie in the medial portion of the lateral lemniscus. (■e) The fasciculus of Lissauer is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots. It consists of fine fibers which do not receive their medullary sheaths until toward the close of fetal life. It is usually regarded as being formed by some of the fibers of the posterior nerve roots, which ascend for a short distance in the tract and then enter the posterior column, but since its fibers are myelinated later than those of the posterior nerve roots, and do not undergo degeneration in locomotor ataxia, they are probably intersegmental in character. In addition the fasciculus or tract of Lissauer contains great numbers of fine non-medullated fibers derived mostly from the dorsal roots but partly endogenous in origin. These fibers are intimately related to the substantia gelatinosa which is probably the terminal nucleus. The non-medullated fibers ascend or descend for short distances not exceeding one or two segments, but most of them enter the substantia gelatinosa at or near the level of their origin. Ransom1 suggests that these non-medullated fibers and the substantia gelatinosa are concerned with the reflexes associated with pain impulses. (/) The lateral proper fasciculus (fasciculus lateralis proprius; lateral basis bundle) constitutes the remainder of the lateral column, and is continuous in frontvwith the anterior proper fasciculus. It consists chiefly of intersegmental fibers which arise from cells in the gray substance, and, after a longer or shorter course, reenter the gray substance and ramify in it. Some of its fibers are, however, continued upward into the brain under the name of the medial longitudinal fasciculus. Fasciculi in the Posterior Funiculus.—This funiculus comprises two main fasciculi, viz., the fasciculus gracilis, and the fasciculus cuneatus. These are separated from each other in the cervical and upper thoracic regions by the postero-intermediate septum, and consist mainly of ascending fibers derived from the posterior nerve roots. The fasciculus gracilis (tract of Goll) is wedge-shaped on transverse section, and lies next the posterior median septum, its base being at the surface of the medulla 1 Ransom, Am. Jour. Anat., 1914; Brain, 1915. THE MEDULLA SPINALIS OR SPINAL CORD 763 spinalis, and its apex directed toward the posterior gray commissure. It increases in size from below upward, and consists of long thin fibers which are derived from the posterior nerve roots, and ascend as far as the medulla oblongata, where they end in the nucleus gracilis. The fasciculus cuneatus (tract of Burdach) is triangular on transverse section, and lies between the fasciculus gracilis and the posterior column, its base corre- sponding with the surface of the medulla spinalis. Its fibers, larger than those of Descending comma fasciculus Posterior column First thoracic nerve D Dorsal 'peripheral hand Posterior column C Oval area of Flechsig. Posterior column Lumbar nerves B Triangular fasciculus Sacral nerves posterior column A Fig. 673.—Formation of the fasciculus gracilis. (Poirier.) Medulla spinalis viewed from behind. To the left, the fasciculus gracilis is shaded. To the right, the drawing shows that the fasciculus gracilis is formed by the long fibers of the posterior roots, and that in this tract the sacral nerves lie next the median plane, the lumbar to their lateral side, and the thoracic still more laterally. Fig 674.—Descending fibers in the posterior funicuii, shown at different levels. (After Testut.) A In the conus medullaris. B. In the lumbar region. C. In the lower thoracic region. D. In the upper thoracic region. the fasciculus gracilis, are mostly derived from the same source, \iz., e pos enor nerve roots. Some ascend for only a short distance in the tract, en (jrinS the gray matter, come into close relationship with the cells o t e orsa nuc eus, while others can be traced as far as the medulla oblongata, where they en in le gracile and cuneate nuclei. , . , , The fasciculus gracilis and fasciculus cuneatus conduct 1) impulses of conscious muscle sense, neurons of the second order from the nucleus gi.it 1 is ant nuc eus cuneatusj pass in the median lemniscus to the thalamus and neurons o e nr 764 NEUROLOGY order from the thalamus to the cerebral cortex; (2) impulses of unconscious muscle sense, via neurons of the second order from the nucleus gracilis and nucleus cuneatus pass in the internal and external arcuate fibers of the medulla oblongata to the inferior peduncle and through it to the cerebellum; (3) impulses of tactile discrimina- tion, via neurons of the second order from the nucleus cuneatus and nucleus gracilis pass in the median lemniscus to the thalamus, neurons of the third order pass from the thalamus to the cortex. The Posterior Proper Fasciculus (;posterior ground bundle; posterior basis bundle) arises from cells in the posterior column; their axons bifurcate into ascending and descending branches which occupy the ventral part of the funiculus close to the gray column. They are intersegmental and run for varying distances sending off collaterals and terminals to the gray matter. Some descending fibers occupy different parts at different levels. In the cer- vical and upper thoracic regions they appear as a comma-shaped fasciculus in the lateral part of the fasciculus cuneatus, the blunt end of the comma being directed toward the posterior gray commissure; in the lower thoracic region they form a dorsal peripheral band on the posterior surface of the funiculus; in the lumbar region, they are situated by the side of the posterior median septum, and appear on section as a semi-elliptical bundle, which, together with the corresponding bundle of the opposite side, forms the oval area of Flechsig; while in the conus medullaris they assume the form of a triangular strand in the postero-medial part of the fasciculus gracilis. These descending fibers are mainly intersegmental in character and derived from cells in the posterior column, but some consist of the descending branches of the posterior nerve roots. The comma-shaped fasciculus was supposed to belong to the second category, but against this view is the fact that it does not undergo descending degeneration when the posterior nerve roots are destroyed. Roots of the Spinal Nerves.—As already stated, each spinal nerve possesses two roots, an anterior and a posterior, which are attached to the surface of the medulla spinalis opposite the corresponding column of gray substance (Fig. 675); their fibers become medullated about the fifth month of fetal life. The Anterior Nerve Root (radix anterior) consists of efferent fibers, which are the axons of the nerve cells in the ventral part of the anterior and lateral columns. A short distance from their origins, these axons are invested by medul- lary sheaths and, passing forward, emerge in two or three irregular rows over an area which meas- ures about 3 mm. in width. The Posterior Root (radix pos- terior) comprises some six or eight fasciculi, attached in linear series along the postero-lateral sulcus. It consists of afferent fibers which arise from the nerve cells in a spinal ganglion. Each ganglion cell gives off a single fiber which divides in a T-shaped manner into two processes, medial and lateral. The lateral processes extend to the sensory end-organs of the skin, muscles, tendons, joints, etc. (somatic receptors), and to the sensory end-organs of the viscera (visceral Lateral column Ant. med. fissure- Anterior column'' Posterior column Posterior root Anterior root.. Spinal ganglion Spinal nerve Posterior division Fig. 675.—A spinal nerve with its anterior and posterior roots. THE MEDULLA SPINALIS OR SPINAL CORD 765 receptors). The medial processes of the ganglion cells grow into the medulla spinalis as the posterior roots of the spinal nerves. The posterior nerve root enters the medulla spinalis in three chief bundles, medial, intermediate, and lateral. The medial strand passes directly into the fas- ciculus cuneatus: it consists of coarse fibers, which acquire their medullary sheaths about the fifth month of intrauterine life; the intermediate strand consists of coarse fibers, which enter the gelatinous substance of Rolando; the lateral is composed of fine fibers, which assume a longitudinal direction in the tract of Lissauer, and do not acquire their medullary sheaths until after birth. In addition to these medullated fibers there are great numbers of non-medullated fibers which enter with the lateral bundle. They are more numerous than the myelinated fibers. They arise from the small cells of the spinal ganglia by T-shaped axons similar to the myelinated. They are distributed with the peripheral nerves chiefly to the skin, only a few are found in the nerves to the muscles.1 Having entered the medulla spinalis, all the fibers of the posterior nerve roots divide into ascending and descending branches, and these in their turn give off collaterals w’hich enter the gray substance (Fig. 676). The de- scending fibers are short, and soon enter the gray substance. The ascending fibers are grouped into long, short, and intermedi- ate: the long fibers ascend in the fasciculus cuneatus and fas- ciculus gracilis as far as the me- dulla oblongata, where they end by arborizing around the cells of the cuneate and gracile nuclei; the short fibers run upward for a distance of only 5 or 6 mm. and enter the gray substance; while the intermediate fibers, after a somewhat longer course, have a similar destination. All fibers entering the gray sub- stance end by arborizing around its nerve cells or the dendrites of cells, those of intermediate length being especially associated with the cells of the dorsal nu- cleus. . . The long fibers of the posterior nerve roots pursue an oblique course upward, being situated at first in the lateral part of the fasciculus cuneatus: higher up, they occupy the middle of this fasciculus, having been displaced by the accession of other entering fibers; while still higher, they ascend in the fasciculus gracilis. The upper cervical fibers do not reach this fasciculus, but are entirely confined to the fascic- ulus cuneatus. The localization of these fibers is very precise:, the sacral nerves lie in the medial part of the fasciculus gracilis and near its periphery, the lumbar nerves lateral to them, the thoracic nerves still more laterally; while the cemcal nerves are confined to the fasciculus cuneatus (big. 673). Fig. 676.—Posterior roots entering medulla spinalis and dividing into ascending and descending branches. (Van Gehuchten.) a. Stem fiber, b, b. Ascending and descending limbs of bifurcation. c. Collateral arising from stem fiber. 1 Ransom, Brain, 1915, 38. 766 NEUROLOGY THE ENCEPHALON OR BRAIN. General Considerations and Divisions.—The brain, is contained within the cranium, and constitutes the upper, greatly expanded part of the central nervous system. In its early embryonic condition it consists of three hollow vesicles, termed the hind-brain or rhombencephalon, the mid-brain or mesencephalon, and the fore-brain or prosencephalon; and the parts derived from each of these can be recognized in the adult (Fig. 677). Thus in the process of de- velopment the wall of the hind- brain undergoes modification to form the medulla oblongata, the pons, and cerebellum, while its cavity is expanded to form the fourth ventricle. The mid-brain forms only a small part of the adult brain; its cavity becomes the cerebral aqueduct (aqueduct of Cerebral peduncle Superior peduncle Middle peduncle Inferior peduncle Medulla oblongata Fig. 677.—Scheme showing the connections of the several parts of the brain. (After Schwalbe.) BASAL OF FCRE-BRAIN CORPORA 'quadrigemina RE D NUCLEUS" SUBSTANTIA N IGRA- PONTILE NUCLEI^ TT RETICULAR GANGLIONIC MASS WITH CRANIAL- NEHVE NUCLEI OLIVE- CENTRAL GRAY (FLOOR OF FOURTH VENTRICLE AND AROUND AQUEDUCT) -CENTRAL GRAY OF I. SPINAL CORD Fig. 678.—Schematic representation of the chief ganglionic categories (I to V). THE HIND-BRAIN OR RHOMBENCEPHALON 767 Sylvius), which serves as a tubular communication between the third and fourth ventricles; while its walls are thickened to form the corpora quadrigemina and cerebral peduncles. The fore-brain undergoes great modification: its anterior part or telencephalon expands laterally in the form of two hollow vesicles, the cavities of which become the lateral ventricles, while the surrounding walls form the cere- bral hemispheres and their commissures; the cavity of the posterior part or dien- cephalon forms the greater part of the third ventricle, and from its walls are devel- oped most of the structures which bound that cavity. THE HIND-BRAIN OR RHOMBENCEPHALON. The hind-brain or rhombencephalon occupies the posterior fossa of the cranial cavity and lies below a fold of dura mater, the tentorium cerebelli. It consists of (a) the myelencephalon, comprising the medulla oblongata and the lower part of the fourth ventricle; (6) the metencephalon, consisting of the pons, cerebellum, and the intermediate part of the fourth ventricle; and (c) the isthmus rhomben- cephali, a constricted portion immediately adjoining the mid-brain and includ- ing the superior peduncles of the cerebellum, the anterior medullary velum, and the upper part of the fourth ventricle. The Medulla Oblongata (spinal bulb).—The medulla oblongata extends from the lower margin of the pons to a plane passing transversely below the pyram- idal decussation and above the first pair of cervical nerves; this plane corre- sponds with the upper border of the atlas behind, and the middle of the odontoid process of the axis in front; at this level the medulla oblongata is continuous with the medulla spinalis. Its anterior surface is separated from the basilar part of the occipital bone and the upper part of the odontoid process by the membranes of the brain and the occipitoaxial -ligaments. Its posterior surface is received into the fossa between the hemispheres of the cerebellum, and the upper portion of it forms the lower part of the floor of the fourth ventricle. The medulla oblongata is pyramidal in shape, its broad extremity being directed upward toward the pons, while its narrow, lower end is continuous with the medulla spinalis. It measures about 3 cm. in length, about 2 cm. in breadth at its widest part, and about 1.25 cm. in thickness. The central canal of the medulla spinalis is prolonged into its lower half, and then opens into the cavity of the fourth ven- tricle; the medulla oblongata may therefore be divided into a lower closed part containing the central canal, and an upper open part corresponding with the lower portion of the fourth ventricle. The Anterior Median Fissure (fissura mediana anterior; ventral or ventromedian fissure) contains a fold of pia mater, and extends along the entire length of the medulla oblongata: it ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum. Its lower part is interrupted by bundles of fibers which cross obliquely from one side to the other, and constitute the pyram- idal decussation. Some fibers, termed the anterior external arcuate fibers, emerge from the fissure above this decussation and curve lateralward and upward over the surface of the medulla oblongata to join the inferior peduncle. The Posterior Median Fissure (fissura mediana posterior; dorsal or dorsomedian fissure) is a narrow groove; and exists only in the closed part of the medulla oblon- gata; it becomes gradually shallower from below upward, and finally ends about the middle of the medulla oblongata, where the central canal expands into the cavity of the fourth ventricle. These two fissures divide the closed part of the medulla oblongata into sym- metrical halves, each presenting elongated eminences which, on surface view, are continuous with the funiculi of the medulla spinalis. In the open part the halves are separated by the anterior median fissure, and by a median raphe which 768 NEUROLOGY extends from the bottom of the fissure to the floor of the fourth ventricle. Further, certain of the cranial nerves pass through the substance of the medulla oblongata, and are attached to its surface in series with the roots of the spinal nerves; thus, the fibers of the hypoglossal nerve represent the upward continuation of the anterior nerve roots, and emerge in linear series from a furrow termed the antero-lateral sulcus. Similarly, the accessory, vagus, and glossopharyngeal nerves correspond with the posterior nerve roots, and are attached to the bottom of a sulcus named the postero-lateral sulcus. Advantage is taken of this arrangement to sub- divide each half of the medulla oblongata into three districts, anterior, middle, and posterior. Although these three districts appear to be directly continuous with the corresponding funiculi of the medulla spinalis, they do not necessarily contain the same fibers, since some of the fasciculi of the medulla spinalis end in the medulla oblongata, while others alter their course in passing through it. The anterior district (Fig. 679) is named the pyramid (pyramis medulloe oblongatcp) and lies between the anterior median fissure and the antero-lateral sulcus. Its upper end is slightly constricted, and between it and the pons the fibers of the abducent nerve emerge; a little below the pons it becomes enlarged and prominent, and finally tapers into the anterior funiculus of the medulla spinalis, with which, at first sight, it ap- pears to be directly continuous. The two pyramids contain the motor fibers which pass from the brain to the medulla oblongata and medulla spinalis, corticobulbar and corticospinal fibers. When these pyramidal fibers are traced down- Brachium ) pontis cerebelli Fig. 680.—Decussation of pyramids. Scheme showing pas- sage of various fasciculi from medulla spinalis to medulla ob- longata. (Testut.) a. Pons. b. Medulla oblongata, c. Decussation of the pyramids, d. Section of cervical part of medulla spinalis. 1. Anterior cerebrospinal fasciculus (in red). 2. Lateral cerebrospinal fasciculus (in red). 3. Sensory tract (fasciculi gracilis et cuneatus) (in blue). 3'. Gracile and cuneate nuclei. 4. Antero-lateral proper fasciculus (in dotted line). 5. Pyramid. 6. Lemniscus. 7. Medial longi- tudinal fasciculus. 8. Ventral spinocerebellar fasciculus (in blue). 9. Dorsal spinocerebellar fasciculus (in yellow). Fig. 679.—Medulla oblongata and pons. Anterior surface. ward it is found that some two-thirds or more of them leave the pyramids in successive bundles, and decussate in the anterior median fissure, forming what is termed the pyramidal decussation. Having crossed the middle line, they pass down in the posterior part of the lateral funiculus as the lateral cerebrospinal fascic- THE HIND-BRAIN OR RHOMBENCEPHALON 769 ulus. The remaining fibers—u e., those which occupy the lateral part of the p\ ramid—do not cross the middle line, but are carried downward as the anterior cerebrospinal fasciculus (Fig. 680) into the anterior funiculus of the same side. . The greater part of the anterior proper fasciculus of the medulla spinalis is con- tinued upward through the medulla oblongata under the name of the medial longitudinal fasciculus. SupeHor brachium Inferior brachium Lateral geniculate body Medial geniculate body Pineal body Pulvinar Optic tract Optic commissure Superior colliculi - Inferior colliculi - Lateral lemniscus - Frenulum veli. Trochlear nerve - Oculomotor nerve Superior peduncte- Middle peduncle- Rhomboid fossa. ■ Trigeminal nerve Acoustic nerve Facial nerve - Abducent nerve Glossopharyngeal and vagus nerves • Clava Hypoglossal nerve Accessory nerve The lateral district (Fig. 681) is limited in front by the antero-lateral sulcus and the roots of the hypoglossal nerve, and behind by the postero-lateral sulcus and the roots of the accessory, vagus, and glossopharyngeal nerves. Its upper part consists of a prominent oval mass which is named the olive, while its lower part is of the same width as the lateral funiculus of the medulla spinalis, and appears on the surface to be a direct continuation of it. As a matter of fact, only a portion of the lateral funiculus is continued upward into this district, for the lateral cerebro- spinal fasciculus passes into the pyramid of the opposite side, and the dorsal spinocerebellar fasciculus is carried into the inferior peduncle in the posterior district. The ventral spinocerebellar fasciculus is continued upward on the lateral surface of the medulla oblongata in the same relative position it occupies in the spinal cord until it passes under cover of the external arcuate fibers. It passes beneath these fibers just dorsal to the olive and ventral to the roots of the vagus and glossopharyngeal nerves; it continues upward through the pons along the dorso-lateral edge of the lateral lemniscus. The remainder of the lateral funiculus consists chiefly of the lateral proper fasciculus. Most of these fibers dip beneath the olive and disappear from the surface; but a small strand remains superficial to the olive. In a depression at the upper end of this strand is the acoustic nerve. The olive (oliva; olivary body) is situated lateral to the pyramid, from which it is separated by the antero-lateral sulcus, and the fibers of the hypoglossal nerve. Behind, it is separated from the postero-lateral sulcus by the ventral spinocerebellar fasciculus. In the depression between the upper end of the olive and the pons lies the acoustic nerve. It measures about 1.25 cm. in length, and between its upper Fig. 681.—Hind- and mid-brains; postero-lateral view. 770 NEUROLOGY Superior colliculus - Inferior colliculus Ventral spinocere- bellar fasciculus Fig. 682.—Superficial dissection of brain-stem. Lateral view. THE HIND-BRAIN OR RHOMBENCEPHALON 771 Stria terminalis -Nucleus amygdalae Lateral geniculate' Superior colliculus External arcuate fibers Dorsal external ' arcuate fibers Cochlear nucleus ..Pyramidal tract Fig. 683.—Dissection of brain-stem. Lateral view. 772 NEUROLOGY Stria terminalis' Medial geniculate Cortico-tectal. fibers Superior colliculus - Inferior colliculus - Dorsal external arcuate fibers Pyramidal de- cussation Fig. 684.—Deep dissection of brain-stem. Lateral view. THE HIND-BRAIN OR RHOMBENCEPHALON 773 Anterior com- missure Substantia nigra Medial geniculate Superior colliculus. Inferior colliculus Ventral spinocere- bellar fas. Olivo-cerebellar fasciculus Ftg. 685.—Deep dissection of brain-stem. Lateral view. 774 NEUROLOGY end and the pons there is a slight depression to which the roots of the facial nerve are attached. The external arcuate fibers wind across the lower part of the pyra- mid and olive and enter the inferior peduncle. The posterior district (Fig. 686) lies behind the postero-lateral sulcus and the roots of the accessory, vagus, and the glossopharyngeal nerves, and, like the lateral district, is divisible into a lower and an upper portion. Trochlear nerve Cerebral peduncle Trigeminal nerve - Superior peduncle Facial nerve Middle peduncle Inferior peduncle Acoustic nerve Glossopharyngeal nerve Accessory nerve (cerebral part) Vagus nerve Hypoglossal nerve Accessory nerve (spinal part) Occipital bone Vertebral artery Post, roots of first cervical nerve Clava Medulla spinalis - Fasciculus cuneatus Fasciculus gracilis Dura mater (laid open) ' Fig. 686.—Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ. The lower part is limited behind by the posterior median fissure, and consists of the fasciculus gracilis and the fasciculus cuneatus. The fasciculus gracilis is placed parallel to and along the side of the posterior median fissure, and separated from the fasciculus cuneatus by the postero-intermediate sulcus and septum. The gracile and cuneate fasciculi are at first vertical in direction; but at the lower part of the rhomboid fossa they diverge from the middle line in a V-shaped manner, and each presents an elongated swelling. That on the fasciculus gracilis is named the clava, and is produced by a subjacent nucleus of gray matter, the nucleus gracilis; that on the fasciculus cuneatus is termed the cuneate tubercle, and is like- wise caused by a gray nucleus, named the nucleus cuneatus. The fibers of these fasciculi terminate by arborizing around the cells in their respective nuclei. A third elevation, produced by the substantia gelatinosa of Rolando, is present in the lower part of the posterior district of the medulla oblongata. It lies on the THE HIND-BRAIN OR RHOMBENCEPHALON 775 lateral aspect of the fasciculus cuneatus, and is separated from the surface of the medulla oblongata by a band of nerve fibers which form the spinal tract (spinal root) of the trigeminal nerve. Narrow below, this elevation gradually expands above, and ends, about 1.25 cm. below the pons, in a tubercle, the tubercle of Rolando (tuber cinereum). The upper part of the posterior district of the medulla oblongata is occupied by the inferior peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves. The inferior peduncles connect the medulla spinalis and medulla oblongata with the cerebellum, and are sometimes named the restiform bodies. As they pass upward, they diverge from each other, and assist in forming the lower part of the lateral boundaries of the fourth ventricle; higher up, they are directed backward, each passing to the corresponding cerebellar hemisphere. Near their entrance, into the cerebellum they are crossed by several strands of fibers, which run to the median sulcus of the rhomboid fossa, and are named the striae medullares. The inferior peduncle appears to be the upward continuation of the fasciculus gra- cilis and fasciculus cuneatus; this, however, is not so, as the fibers of these fasciculi end in the gracile and cuneate nuclei. The constitution of the inferior peduncle will be subsequently discussed. Caudal to the striae medullares the inferior peduncle is partly covered by the corpus pontobulbare (Essick1), a thin mass of cells and fibers extending from the pons between the origin of the VII and VIII cranial nerves. Internal Structure of the Medulla Oblongata.—Although the external form of the medulla oblongata bears a certain resemblance to that of the upper part of the medulla spinalis, its internal structure differs widely from that of the latter, and this for the following principal reasons: (1) certain fasciculi which extend from the medulla spinalis to the brain, and vice versa, undergo a rearrangement in their passage through the medulla oblongata; (2) others which exist in the medulla spin- alis end in the medulla oblongata; (3) new fasciculi originate in the gray substance of the medulla oblongata and pass to different parts of the brain; (4) the gray substance, which in the medulla spinalis forms a continuous H-shaped column, becomes greatly modified and subdivided in the medulla oblongata, where also new masses of gray substance are added; (5) on account of the opening out of the central canal of the medulla spinalis, certain parts of the gray substance, which in the medulla spinalis were more or less centrally situated, are displayed in the rhomboid fossa; (6) the medulla oblongata is intimately associated with many of the cranial nerves, some arising from, and others ending in, nuclei within its substance. The Cerebrospinal Fasciculi.—The downward course of these fasciculi from the pyramids of the medulla oblongata and their partial decussation have already been described (page 761). In crossing to reach the lateral funiculus of the oppo- site side, the fibers of the lateral cerebrospinal fasciculi extend backward through the anterior columns, and separate the head of each of these columns from its base (Figs. 687, 688). The base retains its position in relation to the ventral aspect of the central canal, and, when the latter opens into the fourth ventricle, appears in the rhomboid fossa close to the middle line, where it forms the nuclei of the hypoglossal and abducent nerves; while above the level of the ventricle it exists as the nuclei of the trochlear and oculomotor nerves in relation to the floor of the cerebral aqueduct. The head of the column is pushed lateralward and forms the nucleus ambiguus, which gives origin from below upward to the cranial part of the accessory and the motor fibers of the vagus and glossopharyngeal, and still higher to the motor fibers of the facial and trigeminal nerves. 1 Essick, Am. Jour. Anat., 1907 776 NEUROLOGY The fasciculus gracilis and fasciculus cuneatus constitute the posterior sensory fasciculi of the medulla spinalis; they are prolonged upward into the lower part Fig. 687.—Section of the medulla oblongata through the lower part of the decussation of the pyramids. (Tes- tut.) 1. Anterior median fissure. 2. Posterior median sulcus. 3. Anterior column (in red), with 3', anterior root. 4. Posterior column (in blue), with 4', posterior roots. 5. Lateral cerebrospinal fasciculus. 6. Posterior funiculus. The red arrow, a, o', indicates the course the lateral cerebrospinal fasciculus takes at the level of the decussation of the pyramids; the blue arrow, b, b', indi- cates the course which the sensory fibers take. Fig. 688.—Section of the medulla oblongata at the level of the decussation of the pyramids. (Testut.) 1 Anterior median fissure. 2. Posterior median sulcus. 3. Motor roots. 4. Sensory roots. 5 Base of the anterior column, from which the head (5') has been detached by the lateral cerebrospinal fasciculus. 6. Decussation of the lateral cerebrospinal fasciculus. 7. Posterior columns (in blue). 8. Gracile nucleus. N. V. N. VI Nn. VII, VIII- Decussation Fig. 689.—Superficial dissection of brain-stem. Ventral view. of the medulla oblongata, where they end respectively in the nucleus gracilis and nucleus cuneatus. These two nuclei are continuous with the central gray substance THE HIND-BRAIN OR RHOMBENCEPHALON 777 o the medulla spinalis, and may be regarded as dorsal projections of this, each being covered superficially by the fibers of the corresponding fasciculus. On transverse section (Fig. 694) the nucleus gracilis appears as a single, more or less quadrangular mass, while the nucleus cuneatus consists of two parts: a larger somewhat triangular, medial nucleus, composed of small or medium-sized cells, and a smaller lateral nucleus containing large cells. Decussation of superior pe- - duncle Nucleus of I lateral lemniscus Decussation of lemniscus Internal arcu- ate fibers Fig. 690.—Deep dissection of brain-stem. Ventral view. The fibers of the fasciculus gracilis and fasciculus cuneatus end by arborizing around the cells of these nuclei (Fig. 692). From the cells of the nuclei new fibers arise; some of these are continued as the posterior external arcuate fibers into the inferior peduncle, and through it to the cerebellum, but most of them pass forward through the neck of the posterior column, thus cutting off its head from its base (Fig. 693). Curving forward, they decussate in the middle line with the correspond- ing fibers of the opposite side, and run upward immediately behind the cerebro- spinal fibers, as a flattened band, named the lemniscus or fillet. The decussation of these sensory fibers is situated above that of the motor fibers, and is named the decussation of the lemniscus or sensory decussation. The lemniscus is joined by the spinothalamic fasciculus (page 762), the fibers of which are derived from the cells of the gray substance of the opposite side of the medulla spinalis. The base of the posterior column at first lies on the dorsal aspect of the central canal, but when the latter opens into the fourth ventricle, it appears in the lateral part of the rhomboid fossa. It forms the terminal nuclei of the sensory fibers of 778 NEUROLOGY the vagus and glossopharyngeal nerves, and is associated with the vestibular part of the acoustic nerve and the sensory root of the facial nerve. Still higher, it forms a mass of pigmented cells—the locus caeruleus—in which some of the sensory fibers of the trigeminal nerve appear to end. The head of the posterior column forms a long nucleus, in which the fibers of the spinal tract of the trigeminal nerve largely end. Stria terminalis Auditory radiation. Medial geniculate Inferior colliculus Nucleus incertus N. V -Lateral lemniscus Vestibular nucleus Inferior peduncle Cochlear nucleus Dorsal external arcuate fibers Nucleus cinerea External arcuate fibers Nucleus cuneatus Nucleus gracilis- Nucleus spinal tract, trigem- inal Fig. 691.—Dissection of brain-stem. Dorsal view. The nuclear masses are taken from model by Weed, Carnegie Publication, No. 19. The dorsal spinocerebellar fasciculus (fasciculus cerebellospinalis; direct cerebellar tract) leaves the lateral district of the medulla oblongata; most of its fibers are carried backward into the inferior peduncle of the same side, and through it are conveyed to the cerebellum; but some run upward with the fibers of the lemniscus, and, reaching the inferior colliculus, undergo decussation, and are carried to the cerebellum through the superior peduncle. The proper fasciculi (basis bundles) of the anterior and lateral funiculi largely consist of intersegmental fibers, which link together the different segments of the medulla spinalis; they assist in the production of the formatio reticularis of the medulla oblongata, and many of them are accumulated into a fasciculus which runs up close to the median raphe between the lemniscus and the rhomboid fossa; THE HIND-BRAIN OR RHOMBENCEPHALON 779 this strand is named the medial longitudinal fasciculus, and will be again re- ferred to. Gray Substance of the Medulla Oblongata (Figs. 694, 695).—In addition to the gracile and cuneate nuclei, there are several other nuclei to be considered. Some of these are traceable from the gray substance of the medulla spinalis, while others are unrepresented in it. 1. The hypoglossal nucleus is derived from the base of the anterior column; m the lower closed part of the medulla oblongata it is situated on the ventro- lateral aspect of the central canal; but in the upper part it approaches the rhomboid fossa, where it lies close to the middle line, under an eminence named the trigonum hypoglossi (Fig. 709). Numerous fibers corinect the two nuclei, both nuclei send long dendrons across the midline to the opposite nucleus; commis- sure fibers also connect them. The nucleus measures about 2 cm. in length, and con- Fig. 692.—Superior terminations of the posterior fas- ciculi of the medulla spinalis. (Testut.) 1. Posterior median sulcus. 2. Fasciculus gracilis. 3. Fasciculus cuneatus. 4. Gracile nucleus. 5. Cuneate nucleus. 6, 6', 6". Sensory fibers forming the lemniscus. 7. Sen- sory decussation. 8. Cerebellar fibers uncrossed (in black). 9. Cerebellar fibers crossed (in black). Fig. 693.—Transverse section passing through the sensory decussation. (Schematic.) (Testut.) 1. Ante- rior median fissure. 2. Posterior median sulcus. 3, 3. Head and base of anterior column (in red). 4. Hypo- glossal nerve. 5. Bases of posterior columns. 6. Gracile nucleus. 7. Cuneate nucleus. 8, 8. Lemniscus. 9. Sensory decussation. 10. Cerebrospinal fasciculus sists of large multipolar nerve cells, similar to those in the anterior column of the spinal cord, whose axons constitute the roots of the hypoglossal nerve. These nerve roots leave the ventral side of the nucleus, pass forward between the white reticular formation and the gray reticular formation, some between the inferior olivary nucleus and the medial accessory olivary nucleus, and emerge from the antero-lateral sulcus. 2. The nucleus ambiguus (Figs. 696, 697), the somatic motor nucleus of the glosso- pharyngeal, vagus and cranial portion of the accessory nerves, is the continuation into the medulla oblongata of the dorso-lateral cell group of the anterior column of the spinal cord. Its large multipolar cells are like those in the anterior column of the cord; they form a slender column in the deep part of the formatio reticularis grisea about midway between the dorsal accessory olive and the nucleus of the spinal tract of the trigeminal. It extends from the level of the decussation of the median fillet to the upper end of the medulla oblongata. Its fibers first pass back- ward toward the floor of the fourth ventricle and then curve rather abruptly lateralward and ventrally to join the fibers from the dorsal nucleus. NEUROLOGY 780 3. The dorsal nucleus (Figs. 696, 698), nucleus ala cinerea, often called the sensory nucleus or the terminal nucleus of the sensory fibers of the glossopharyngeal Ligvla 4 Nucleus of medial eminence Hypo- glossal nucleus Vagus nuclei Nucleus gracilis Nucleus cuneatus Inferior peduncle Formatio reticularis grisea Raplie Spinal trad of trigeminal nerve Vagus nerve Formatio reticularis Alba Arcuate fibers Accessory olivary nuclei Inferior olivary nucleus Hypoglossal nerve Anterior median fissure Fig. 694.—Section of the medulla oblongata at about the middle of the oiive. (Schwalbe.) Nucleus intercalate Ligula Nucleus of vagus Medial longitudinal fasciculus Hypoglossal nucleus Fourth ventricle Fasciculus solitarius Descending root of vestibular nerve Hestiform body Nucleus lateralis Spinal tract of tri- geminal nerve - Nucleus anibiguus Vagus nerve _Dorsal accessory ~ olivary nucleus Inferior olivary nucleus .Hypoglossal nerve Cerebrospinal fasciculus Medial accessory olivary nucleus Fig. 695.—Transverse section of medulla oblongata below the middle of the olive. Lemniscus Nucleus arcuatus and vagus nerves, is probably a mixed nucleus and contains not only the terminations of the sympathetic afferent or sensory fibers and the cells connected with them but contains also cells which give rise to sympathetic efferent or preganglionic fibers. THE HIND-BRAIN OR RHOMBENCEPHALON 781 These preganglionic fibers terminate in sympathetic ganglia from which the impulses are carried by other neurons. The cells of the dorsal nucleus are spindle-shaped, like those of the posterior column of the spinal cord, and the nucleus is usually considered as representing the base of the posterior column. It measures about 2 cm. in length, and in the lower, closed part of the medulla oblongata is situated behind the hypoglossal nucleus; whereas in the upper, open part it lies lateral to that nucleus, and corresponds to an eminence, named the ala cinerea (trigonum vagi), in the rhomboid fossa. 4. The nuclei of the cochlear and vestibular nerves are described on page 788. 5. The olivary nuclei (Fig. 694) are three in number on either side of the middle line, viz., the inferior olivary nucleus, and the medial and dorsal accessory olivary nu- clei; they consist of small, round, yellowish cells and numerous fine nerve fibers, (a) The inferior oli- vary nucleus is the largest, and is situated within the olive. It con- sists of a gray folded lamina ar- ranged in the form of an incom- plete capsule, opening medially by an aperture called the hilum; emerging from the hilum are num- erous fibers which collectively constitute the peduncle of the olive. The axons, olivocerebellar fibers, which leave the olivary nucleus pass out through the hilum and decussate with those from the opposite olive in the raphe, then as internal arcuate fibers they pass partly through and partly around the opposite olive and enter the inferior peduncle to be distributed to the cerebellar hemisphere of the opposite side from which they arise. The fibers are smaller than the internal arcuate fibers connected with the median lem- niscus. Fibers passing in the op- posite direction from the cerebel- lum to the olivary nucleus are often described but their existence is doubtful. Much uncertainty also pviyfq in rprarrl to the ronnpotions of the olive and the spinal cord. Important connections between the cerebrum and the olive of the same side exist but the exact pathway is unknown. Many collaterals from the reticular formation and from the pyramids enter the inferior olivary nucleus. Removal of one cerebellar hemisphere is followed by atrophy of the opposite olivary nucleus. (b) The medial accessory olivary nucleus lies between the inferior olivary nucleus and the pyramid, and forms a curved lamina, the con- cavity of which is directed laterally. The fibers of the hypoglossal nerve, as they DT. Mnn" VYHI Nucleus ambiguus (IX and X) IX and X IE" , Nucleus of solitary tract Fig 696 —The cranial nerve nuclei schematically represented; dorsal'view. Motor nuclei in red; sensory in blue. (The olfactory and optic centers are not repre8ented) 782 NEUROLOGY traverse the medulla, pass between the medial accessory and the inferior olivary nuclei, (c) The dorsal accessory olivary nucleus is the smallest, and appears on transverse section as a curved lamina behind the inferior olivary nucleus. G. The nucleus arcuatus is described below with the anterior external arcuate fibers. Inferior Peduncle (restiform body).—The position of the inferior peduncles has already been described (page 775). Each comprises: (1) Fibers from the dorsal spinocerebellar fasciculus, which ascends from the lateral funiculus of the medulla spinalis. (2) The olivocerebellar fibers from the opposite olivary nucleus. (3) Internal arcuate fibers from the gracile and cuneate nuclei of the opposite side; these fibers form the deeper and larger part of the inferior peduncle. --V' v (Motor root) -xn N ucleus ambiguus IX and X Cervical nerves Fig. 697.—Nuclei of origin of cranial motor nerves schematically represented; lateral view. (4) The anterior external arcuate fibers vary as to their prominence in different cases: in some they form an almost continuous layer covering the pyramid and olive, while in others they are barely visible on the surface. They arise from the cells of the gracile and cuneate nuclei, and passing forward through the formatio reticu- laris, decussate in the middle line. Most of them reach the surface by way of the anterior median fissure, and arch backward over the pyramid. Reinforced by others which emerge between the pyramid and olive, they pass backward over the olive and lateral district of the medulla oblongata, and enter the inferior peduncle. They thus connect the cerebellum with the gracile and cuneate nuclei of the opposite side. As the fibers arch across the pyramid, they enclose a small nucleus which lies in front of and medial to the pyramid. This is named the nucleus arcuatus, and is serially continuous above with the nuclei pontis in the pons; it contains small fusiform cells, around which some of the arcuate fibers end, and from which others arise. THE HIND-BRAIN OR RHOMBENCEPHALON 783 (5) The posterior external arcuate fibers also take origin in the gracile and cuneate nuclei; they pass to the inferior peduncle of the same side. It is uncertain whether Semilunar gang. Sensory root of V Sensory root of VII; Fig. 698.—Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view. The olfactory and optic centers are not represented. Fig 699.—Diagram showing the "oiivS nudeus!'vdtlfth^ 2. Anterior median fissure 3. fourth ventricle 4. peduncles, seen from in front. 9. Posterior external ?roou"«“bi°r io. LSrSbX, ii. “v™5 »»»•*«><«'■ «■ nucleus. 13. Nucleus arcuatus. 14. Vagus. 15. Hypoglossal. 784 NEUROLOGY fibers are continued directly from the gracile and cuneate fasciculi into the inferior peduncle. (6) Fibers from the terminal sensory nuclei of the cranial nerves, especially the vestibular. Some of the fibers of the vestibular nerve are thought to continue directly into the cerebellum. (7) Fibers from the ventral spinocerebellar fasciculus. (8) The existence of fibers from the cerebellum (cerebellobulbar, cerebelloolivarv, and cerebellospinal) to the medulla and spinal cord is very uncertain. Fig. 700.—-The formatio reticularis of the medulla oblongata, shown by a transverse section passing through the middle of the olive. (Testut.) 1. Anterior median fissure. 2. Fourth ventricle. 3. Formatio reticularis, with 3', its internal part (reticularis alba), and 3", its external part (reticularis grisea). 4. Raph6. 5. Pyramid. 6. Lemniscus. 7. Inferior olivary nucleus with the two accessory olivary nuclei. 8. Hypoglossal nerve, -with 8', its nucleus of origin. 9. Vagus nerve, with 9', its nucleus of termination. 10. Lateral dorsal acoustic nucleus. 11. Nucleus ambiguus (nucleus of origin of motor fibers of glossopharyngeal, vagus, and cerebral portion of spinal accessory). 12. Gracile nucleus. . 13. Cuneate nucleus. 14. Head of posterior column, with 14', the lower sensory root of trigeminal nerve. 15. Fasciculus solitarius. 16. Anterior external arcuate fibers, with 16', the nucleus arcuatus. 17. Nucleus lateralis 18. Nucleus of fasciculus teres. 19. Ligula. Formatio Reticularis (Fig. 700).—This term is applied to the coarse reticulum which occupies the anterior and lateral districts of the medulla oblongata. It is situated behind the pyramid and olive, extending laterally as far as the inferior peduncles, and dorsally to within a short distance of the rhomboid fossa. The reticulum is caused by the intersection of bundles of fibers running at right angles to each other, some being longitudinal, others more or less transverse in direction. The formatio reticularis presents a different appearance in the anterior district from what it does in the lateral; in the former, there is an almost entire absence of nerve cells, and hence this part is known as the reticularis alba; whereas in the lateral district nerve cells are numerous, and as a consequence it presents a gray appear- ance, and is termed the reticularis grisea. In the substance of the formatio reticularis are two small nuclei of gray matter: one, the inferior central nucleus (nucleus of Roller), near the dorsal aspect of the hilus of the inferior olivary nucleus; the other, the nucleus lateralis, between the olive and the spinal tract of the trigeminal nerve. In the reticularis alba the longitudinal fibers form two well-defined fasciculi, viz.: (1) the lemniscus, which lies close to the raphe, immediately behind the fibers of the pyramid; and (2) the medial longitudinal fasciculus, which is continued upward from the anterior and lateral proper fasciculi of the medulla spinalis, and, THE HIND-BRAIN OR RHOMBENCEPHALON 785 in the upper part of the medulla oblongata, lies between the lemniscus and the gray substance of the rhomboid fossa. The longitudinal fibers in the reticularis grisea are derived from the lateral funiculus of the medulla spinalis after the lateral cerebrospinal fasciculus has passed over to the opposite side, and the dorsal spino- cerebellar fasciculus has entered the inferior peduncle. They form indeterminate fibers, with the exception of a bundle named the fasciculus solitarius, which is made up of descending fibers of the vagus and glossopharyngeal nerves. The transverse fibers of the formatio reticularis are the arcuate fibers already described (page 782). The Pons (pons Varoli).—The pons or forepart of the hind-brain is situ- ated in front of the cerebellum. From its superior surface the cerebral peduncles emerge, one on either side of the middle line. Curving around each peduncle, close to the upper surface of the pons, a thin white band, the taenia pontis, is frequently seen; it enters the cerebellum between the middle and superior peduncles. Behind and below, the pons is continuous with the medulla oblongata, but is separated from it in front by a furrow in which the abducent, facial, and acoustic nerves appear. Its ventral or anterior surface (pars basilaris pontis) is very prominent, markedly convex from side to side, less so from above downward. It consists of transverse fibers arched like a bridge across the middle line, and gathered on either side into a compact mass which forms the middle peduncle. It rests upon the clivus of the sphenoidal bone, and is limited above and below by well-defined borders. In the middle line is the sulcus basilaris for the lodgement of the basilar artery; this sulcus is bounded on either side by an eminence caused by the descent of the cerebrospinal fibers through the substance of the pons. Outside these eminences, near the upper border of the pons, the trigeminal nerves make their exit, each consisting of a smaller, medial, motor root, and a larger, lateral, sensory root; vertical lines drawn immediately beyond the trigeminal nerves, may be taken as the boundaries between the ventral surface of the pons and the middle cerebellar peduncle. Its dorsal or posterior surface (pars dorsalis pontis), triangular in shape, is hidden by the cerebellum, and is bounded laterally by the superior peduncle; it forms the upper part of the rhomboid fossa, with which it will be described. Structure (Fig. 701).—Transverse sections of the pons show it to be composed of two parts which differ in appearance and structure: thus, the basilar or ventral portion consists for the most part of fibers arranged in transverse and longitudinal bundles, together with a small amount of gray substance; while the dorsal tegmental portion is a continuation of the reticular formation of the medulla oblongata, and most of its constituents are continued into the tegmenta of the cerebral peduncles. The basilar part of the pons consists of—(a) superficial and deep transverse fibers, (b) longitudinal fasciculi, and (e) some small nuclei of gray substance, termed the nuclei pontis which give rise to the transverse fibers. The superficial transverse fibers (fibres pontis superficiales) constitute a rather thick layer on the ventral surface of the pons, and are collected into a large rounded bundle on either side of the middle line. This bundle, with the addition of some transverse fibers from the deeper part of the pons, forms the greater part of the brachium pontis. The deep transverse fibers (fibres pontis profunda;) partly intersect and partly lie on the dorsal aspect of the cerebrospinal fibers. They course to the lateral border of the pons, and form part of the middle peduncle; the further connections of this brachium will be discussed with the anatomy of the cerebellum. The longitudinal fasciculi (fasciculi longitudinales) are derived from the cerebral peduncles, and enter the upper surface of the pons. I hey stream downward on either side of the middle line in larger or smaller bundles, separated from each other by the deep transverse fibers; these longitudinal bundles cause a forward 786 NE UROLOGY projection of the superficial transverse fibers, and thus give rise to the eminences on the anterior surface. Some of these fibers end in, or give off collateral to, the nuclei pontis. An important pathway is thus formed between the cerebral cortex and the cerebellum, the first neuron having its cell body in the cortex and sending its axon through the internal capsule and cerebral peduncle to form synapses either by terminals or collaterals with cell bodies situated in the nuclei pontis. Axons from these cells form the transverse fibers which pass through the middle peduncle info the cerebellum. Others after decussating, terminate either directly or indi- rectly in the motor nuclei of the trigeminal, abducent, facial, and hypoglossal nerves; but most of them are carried through the pons, and at its lower surface are collected into the pyramids of the medulla. The fibers which end in the motor nuclei of the cranial nerves are derived from the cells of the cerebral cortex, and bear the same relation to the motor cells of the cranial nerves that the cerebro- Ant. med. velum White stratum Superior peduncle Gray stratum Fourth ventricle Mesencephalic root V. - Nn. mes. root- Med. long, fas.- Formatio reticularis- Lateral lemniscus Medial _ lemniscus , TransverseJ fibers I Cerebrospinal fasciculi Trigeminal- Raphe Fig. 701.—Coronal section of the pons, at its upper part. spinal fibers bear to the motor cells in the anterior column of the medulla spinalis. Probably none of the collaterals or terminals of the cerebrospinal and cerebro- bulbar fibers end directly in the motor nuclei of the spinal and cranial nerves, one or more association neurons are probably interpolated in the pathway. The nuclei pontis are serially continuous with the arcuate nuclei in the medulla, and consist of small groups of multipolar nerve cells which are scattered between the bundles of transverse fibers. The dorsal or tegmental part of the pons is chiefly composed of an upward con- tinuation of the reticular formation and gray substance of the medulla oblongata. It consists of transverse and longitudinal fibers and also contains important gray nuclei, and is subdivided by a median raphe, which, however, does not extend into the basilar part, being obliterated by the transverse fibers. The transverse fibers in the lower part of the pons are collected into a distinct strand, named the THE HIND-BRAIN OR RHOMBENCEPHALON 787 trapezoid body. This consists of fibers which arise from the cells of the cochlear nucleus, and will be referred to in connection with the cochlear division of the acoustic nerve. In the substance of the trapezoid body is a collection of nerve cells, which constitutes the trapezoid nucleus. The longitudinal fibers, wdiich are continuous with those of the medulla oblongata, are mostly collected into two fasciculi on either side. One of these lies between the trapezoid body and the reticular formation, and forms the upward prolongation of the lemniscus; the second is situated near the floor of the fourth ventricle, and is the medial longitudinal fasciculus. Other longitudinal fibers, more diffusely distributed, arise from the cells of the gray substance of the pons. The rest of the dorsal part of the pons is a continuation upward of the formatio reticularis of the medulla oblongata, and, like it, presents the appearance of a net- work, in the meshes of which are numerous nerve cells. Besides these scattered nerve cells, there are some larger masses of gray substance, viz., the superior olivary nucleus and the nuclei of the trigeminal, abducent, facial, and acoustic nerves (Fig. 696). 1. The superior olivary nucleus (nucleus olivaris superior) is a small mass of gray substance situated on the dorsal surface of the lateral part of the trapezoid body. Rudimentary in man, but well developed in certain animals, it exhibits the same structure as the inferior olivary nucleus, and is situated immediately above it. Some of the fibers of the trapezoid body end by arborizing around the cells of this nucleus, while others arise from these cells. 2. The nuclei of the trigeminal nerve (nuclei n. trigemini) in the pons are two in number: a motor and a sensory. The motor nucleus is situated in the upper part of the pons, close to its posterior surface and along the line of the lateral margin of the fourth ventricle. It is serially homologous with the nucleus ambiguus and the dorso-lateral cell group of the anterior column of the spinal cord. The axis-cylinder processes of its cells form a portion of the motor root of the trigeminal nerve: the remaining fibers of the motor root of this nerve consist of a fasciculus which arises from the gray substance of the floor of the cerebral aqueduct, and hence is named the mesencephalic root. It is not altogether clear whether the mesencephalic root is motor or sensory. The sensory nucleus is lateral to the motor one, and beneath the superior peduncle. Some of the sensory fibers of the trigeminal nerve end in this nucleus; but the greater number descend, under the name of the spinal tract of the trigeminal nerve, to end in the substantia gelatinosa of Rolando. The roots, motor and sensory, of the trigeminal nerve pass through the substance of the pons and emerge near the upper margin of its anterior surface. 3. The nucleus of the abducent nerve (nucleus n. abducentis) is a circular mass of gray substance situated close to the floor of the fourth ventricle, above the striae medullares and subjacent to the medial eminence: it lies a little lateral to the ascending part of the facial nerve. The fibers of the abducent nerve pass forward through the entire thickness of the pons on the medial side of the superior olivary nucleus, and between the lateral fasciculi of the cerebrospinal fibers, and emerge in the furrow between the lower border of the pons and the pyramid of the medulla oblongata. 4. The nucleus of the facial nerve (nucleus n. fascialis) is situated deeply in the reticular formation of the pons, on the dorsal aspect of the superior olivary nucleus, and the roots of the nerve derived from it pursue a remarkably tortuous course in the substance of the pons. At first they pass backward and medialward until they reach the rhomboid fossa, close to the median sulcus, where they are collected into a round bundle; this passes upward and forward, producing an elevation, the colliculus facialis, in the rhomboid fossa, and then takes a sharp bend, and arches lateral ward through the substance of the pons to emerge at its lower border in the interval between the olive and the inferior peduncle of the medulla oblongata. 788 NEUROLOGY 5. The nucleus of the cochlear nerve consists of: (a) the lateral cochlear nucleus, corresponding to the tuberculum acusticum on the dorso-lateral surface of the inferior peduncle; and (6) the ventral or accessory cochlear nucleus, placed between the two divisions of the nerve, on the ventral aspect of the inferior peduncle. The nuclei of the vestibular nerve, (a) The medial (dorsal or chief vestibular nucleus), corresponding to the lower part of the area acustica in the rhomboid fossa; the caudal end of this nucleus is sometimes termed the descending or spinal vestibular nucleus. (b) The lateral or nucleus of Deiters, consisting of large cells and situated in the lateral angle of the rhomboid fossa; the dorso-lateral part of this nucleus is sometimes termed the nucleus of Bechterew. The fibers of the vestibular nerve enter the medulla oblongata on the medial side of those of the cochlear, and pass between the inferior peduncle and the spinal tract of the trigeminal. They then divide into ascending and descending fibers. The latter end by arborizing around the cells of the medial nucleus, which is situ- ated in the area acustica of the rhomboid fossa. The ascending fibers either end in the same manner or in the lateral nucleus, which is situated lateral to the area acustica and farther from the ventricular floor. Some of the axons of the cells of the lateral nucleus, and possibly also of the medial nucleus, are continued upward through the inferior peduncle to the roof nuclei of the opposite side of the cere- bellum, to which also other fibers of the vestibular root are prolonged without interruption in the nuclei of the medulla oblongata. A second set of fibers from the medial and lateral nuclei end partly in the tegmentum, while the remainder ascend in the medial longitudinal fasciculus to arborize around the cells of the nuclei of the oculomotor nerve. The Cerebellum.—The cerebellum constitutes the largest part of the hind- brain. It lies behind the pons and medulla oblongata; between its central portion and these structures is the cavity of the fourth ventricle. It rests on the inferior occipital fossae, while above it is the tentorium cerebelli, a fold of dura mater which separates it from the tentorial surface of the cerebrum. It is somewhat oval in form, but constricted medially and flattened from above downward, its greatest diameter being from side to side. Its surface is not convoluted like that of the cerebrum, but is traversed by numerous curved furrows or sulci, which vary in depth at different parts, and separate the laminae of which it is composed. Its average weight in the male is about 150 gms. In the adult the propor- tion between the cerebellum and cerebrum is about 1 to 8, in the infant about 1 to 20. Lobes of the Cerebellum.—The cerebellum consists of three parts, a median and twro lateral, which are continuous with each other, and are substantially the same in structure. The median portion is constricted, and is called the vermis, from its annulated appearance which it'owes to the transverse ridges and furrows upon it; the lateral expanded portions are named the hemispheres. On the upper surface of the cerebellum the vermis is elevated above the level of the hemispheres, but on the under surface it is sunk almost out of sight in the bottom of a deep depres- sion between them; this depression is called the vallecula cerebelli, and lodges the posterior part of the medulla oblongata. The part of the vermis on the upper surface of the cerebellum is named the superior vermis; that on the lower surface, the inferior vermis. The hemispheres are separated below and behind by a deep notch, the posterior cerebellar notch, and in front by a broader shallower notch, the anterior cerebellar notch. The anterior notch lies close to the pons and upper part of the medulla, and its superior edge encircles the inferior colliculi and the superior cerebellar peduncle. The posterior notch contains the upper part of the falx cerebelli, a fold of dura mater. The cerebellum is characterized by a laminated or foliated appearance; it is marked by deep, somewhat curved fissures, which extend for a considerable dis- THE HIND-BRAIN OR RHOMBENCEPHALON 789 tance into its substance, and divide it into a series of layers or leaves. The largest and deepest fissure is named the horizontal sulcus. It commences in front of the pons, and passes horizontally around the free margin of the hemisphere to the middle line behind, and divides the cerebellum into an upper and a lower portion. Several secondary but deep fissures separate the cerebellum into lobes, and these are further subdivided by shallower sulci, which separate the individual folia or laminae from each other. Sections across the laminae show that the folia, though differing in appearance from the convolutions of the cerebrum, are analogous to them, inasmuch as they consist of central white substance covered by gray substance. The cerebellum is connected to the cerebrum, pons, and medulla oblongata; to the cerebrum by the superior peduncle, to the pons by the middle peduncle, and to the medulla oblongata by the inferior peduncles. Ala lobuli centralis Lobulus centralis Postcentral fissure Prceclival fits sure Postclival fissure Horizontal sulcus Clivus monticuli Fig. 702.—Upper surface of the cerebellum. (Schafer.) The upper surface of the cerebellum (Fig. 702) is elevated in the middle and sloped toward the circumference, the hemispheres being connected together by the supe- rior vermis, which assumes the form of a raised median ridge, most prominent in front, but not sharply defined from the hemispheres. The superior vermis is subdivided from before backward into the lingula, the lobulus centralis, the mon- ticulus and the folium vermis, and each of these, with the exception of the lingula, is continuous with the corresponding parts of the hemispheres—the lobulus centralis with the alee, the monticulus with the quadrangular lobules, and the folium vermis with the superior semilunar lobules. The lingula (lingula cerebelli) is a small tongue-shaped process, consisting of four or five folia; it lies in front of the lobulus centralis, and is concealed by it. Anteriorly, it rests on the dorsal surface of the anterior medullary velum, and its white substance is continuous with that of the velum. The Lobulus Centralis and Alse.—The lobulus centralis is a small square lobule, situated in the anterior cerebellar notch. It overlaps the lingula, from which it is separated by the precentral fissure; laterally, it extends along the upper and anterior part of each hemisphere, where it forms a wing-like prolongation, the ala lobuli centralis. The Monticulus and Quadrangular Lobules.—The monticulus is the largest part of the superior vermis. Anteriorly, it overlaps the lobulus centralis, from which it is separated by the postcentral fissure; laterally, it is continuous with the quad- rangular lobule in the hemispheres. It is divided by the preclival fissure into an 790 NEUROLOGY anterior, raised part, the culmen or summit, and a posterior sloped part, the clivus; the quadrangular lobule is similarly divided. The culmen and the anterior parts of the quadrangular lobules form the lobus culminis; the clivus and the posterior parts, the lobus clivi. The Folium Vermis and Superior Semilunar Lobule.—The folium vermis (folium cacuminis; cacuminal lobe) is a short, narrow, concealed band at the posterior extremity of the vermis, consisting apparently of a single folium, but in reality marked on its upper and under surfaces by secondary fissures. Laterally, it expands in either hemisphere into a considerable lobule, the superior semilunar lobule (lobulus semilunaris superior; postero-swperior lobules), which occupies the posterior third of the upper surface of the hemisphere, and is bounded below by the horizontal sulcus. The superior semilunar lobules and the folium vermis form the lobus semilunaris. Ant. medullary velum Lobulus centralis Ala lobuli centralis Flocculus Postnodular fissure Horizontal sulcus Fig. 703.—Under surface of the cerebellum, (Schafer. Tuber vermis The under surface of the cerebellum (Fig. 703) presents, in the middle line, the inferior vermis, buried in the vallecula, and separated from the hemisphere on either side by a deep groove, the sulcus valleculae. Here, as on the upper surface, there are deep fissures, dividing it into separate segments or lobules; but the arrangement is more complicated, and the relation of the segments of the vermis to those of the hemispheres is less clearly marked. The inferior vermis is subdivided from before backward, into (1) the nodule, (2) the uvula, (3) the pyramid, and (4) the tuber vermis; the corresponding parts on the hemispheres are (1) the flocculus, (2) the tonsilla cerebelli, (3) the biventral lobule, and (4) the inferior semilunar lobule. The three main fissures are (1) the postnodular fissure, which runs transversely across the vermis, between the nodule and the uvula. In the hemispheres this fissure passes in front of the tonsil, crosses between the flocculus in front and the biventral lobule behind, and joins the anterior end of the horizontal sulcus. (2) The pre- pyramidal fissure crosses the vermis between the uvula in front and the pyramid behind, then curves forward between the tonsil and the biventral lobe, to join the postnodular fissure. (3) The postpyramidal fissure passes across the vermis between the pyramid and the tuber vermis, and, in the hemispheres, courses behind the tonsil and biventral lobules, and then along the lateral border of the biventral lobule to the postnodular sulcus; in the hemisphere it forms the anterior boundary of the inferior semilunar lobule. The Nodule and Flocculus.—The nodule {nodulus vermis; nodular lobe), or anterior end of the inferior vermis, abuts against the roof of the fourth ventricle, and can THE HIND-BRAIN OR RHOMBENCEPHALON 791 onb be distinctly seen after the cerebellum has been separated from the medulla oblongata and pons. On either side of the nodule is a thin layer of white sub- stance, named the posterior medullary velum. It is semilunar in form, its convex border being continuous with the white substance of the cerebellum; it extends on either side as far as the flocculus. The flocculus is a prominent, irregular lobule, situated in front of the biventral lobule, between it and the middle cere- bellar peduncle. It is subdivided into a few small laminae, and is connected to the inferior medullary velum by its central white core. The flocculi, together with the posterior medullary velum and nodule, constitute the lobus noduli. The Uvula and Tonsilla.—The uvula (uvula vermis; uvular lobe) forms a consid- erable portion of the inferior vermis; it is separated on either side from the tonsil by the sulcus valleculse, at the bottom of which it is connected to the tonsil by a ridge of gray matter, indented on its surface by shallow furrows, and hence called the furrowed band. The tonsilla (tonsilla cerebelli; amygdaline nucleus) is a rounded mass, situated in the hemispheres. Each lies in a deep fossa, termed the bird’s nest (nidus avis), between the uvula and the biventral lobule. The uvula and ton- sillse form the lobus uvulae. The Pyramid and Biventral lobules constitute the lobus pyramidis. The pyramid is a conical projection, forming the largest prominence of the inferior vermis. It is separated from the hemispheres by the sulcus valleculae, across which it is connected to the biventral lobule by an indistinct gray band, analogous to the furrowed band already described. The biventral lobule is triangular in shape; its apex points backward, and is joined by the gray band to the pyramid. The lateral border is separated from the inferior semilunar lobule by the postpyramidal fissure. The base is directed forward, and is on a line with the anterior border of the tonsil, and is separated from the flocculus by the postnodular fissure. The Tuber Vermis (tuber valvidce) and the Inferior Semilunar Lobule (lobulus semi- lunaris inferior; postero-superior lobule) collectively form the lobus tuberus (tuberce lobe). The tuber vermis, the most posterior division of the inferior vermis, is of small size, and laterally spreads out into the large inferior semilunar lobules, which comprise at least two-thirds of the inferior surface of the hemisphere. Internal Structure of the Cerebellum.—The cerebellum consists of white and gray substance. White Substance.—If a sagittal section (Fig. 704) be made through either hemi- sphere, the interior will be found to consist of a central stem of white substance, in the middle of which is a gray mass, the dentate nucleus. From the surface of this central white stem a series of plates is prolonged; these are covered with gray substance and form the laminae. In consequence of the main branches from the central stem dividing and subdividing, a characteristic appearance, named the arbor vitae, is presented. If the sagittal section be made through the middle of the vermis, it will be found that the central stem divides into a vertical and a hor- izontal branch. The vertical branch passes upward to the culmen monticuli, where it subdivides freely, one of its ramifications passing forward and upward to the central lobule. The horizontal branch passes backward to the folium vermis, greatly diminished in size in consequence of having given off large secondary branches; one, from its upper surface, ascends to the clivus monticuli; the others descend, and enter the lobes in the inferior vermis, viz., the tuber vermis, the pyramid, the uvula, and the nodule. The white substance of the cerebellum includes two sets of nerve fibers: (1) projection fibers, (2) fibrse propriae. Projection Fibers.—The cerebellum is connected to the other parts of the brain by three large bundles of projection fibers, viz., to the cerebrum by the superior peduncle, to the pons by the middle peduncle, and to the medulla oblongata by the inferior peduncles (Fig. 705). 792 NEUROLOGY The superior cerebellar peduncles (brachia conjunctiva), two in number, emerge from the upper and medial part of the white substance of the hemispheres and are placed under cover of the upper part of the cerebellum. They are joined to each other across the middle line by the anterior medullary velum, and can be followed Ala lobuli centralis Lingula Superior peduncle Horizontal sulcus Nodule Fourth ventricle Fig. 704.—Sagittal section of the cerebellum, near the junction of the vermis with the hemisphere. (Schafer.) Superior peduncle Inferior peduncle Middle peduncle Trigeminal _ nerve Acoustic nerve- Pyramid - Olive' Fig. 705.—Dissection showing the projection fibers of the cerebellum. (After E. B. Jamieson.) Inferior peduncle upward as far as the inferior colliculi, under which they disappear. Below, they form the upper lateral boundaries of the fourth ventricle, but as they ascend they converge on the dorsal aspect of the ventricle and thus assist in roofing it in. The fibers of the superior peduncle are mainly derived from the cells of the THE HIND-BRAIN OR RHOMBENCEPHALON 793 dentate nucleus of the cerebellum and emerge from the hilus of this nucleus; a few arise from the cells of the smaller gray nuclei in the cerebellar white sub- stance, and others from the cells of the cerebellar cortex. They are continued upward beneath the corpora quadrigemina, and the fibers of the two peduncles under- go a complete decussation ventral to the Sylvian aqueduct. Having crossed the middle line they divide into ascending and descending groups of fibers, the former ending in the red nucleus, the thalamus, and the nucleus of the oculomotor nerve, while the descending fibers can be traced as far as the dorsal part of the pons; Cajal believes them to be continued into the anterior funiculus of the medulla spinalis. As already stated (page 762), the majority of the fibers of the ventral spino- cerebellar fasciculus of the medulla spinalis pass to the cerebellum, which they reach by way of the superior peduncle. The middle cerebellar peduncles (brachia pontis) (Fig. 705) are composed entirely of centripetal fibers, wdiich arise from the cells of the nuclei pontis of the opposite side and end in the cerebellar cortex; the fibers are arranged in three fasciculi, superior, inferior, and deep. The superior fasciculus, the most superficial, is derived from the upper transverse fibers of the pons; it is directed backward and lateral ward superficial to the other two fasciculi, and is distributed mainly to the lobules on the inferior surface of the cerebellar hemisphere and to the parts of the superior surface adjoining the posterior and lateral margins. The inferior fasciculus is formed by the lowrest transverse fibers of the pons; it passes under cover of the superior fasciculus and is continued downward and backward more or less parallel with it, to be distributed to the folia on the under surface close to the vermis. The deep fasciculus comprises most of the deep transverse fibers of the pons. It is at first covered by the superior and inferior fasciculi, but crosses obliquely and appears on the medial side of the superior, from which it receives a bundle; its fibers spread out and pass to the upper anterior cerebellar folia. The fibers of this fasciculus cover those of the restiform body.1 The inferior cerebellar peduncles (restiform bodies) pass at first upward and lateral- wrard, forming part of the lateral walls of the fourth ventricle, and then bend abruptly backward to enter the cerebellum between the superior and middle peduncles. Each contains the following fasciculi: (1) the dorsal spinocerebellar fasciculus of the medulla spinalis, which ends mainly in the superior vermis; (2) fibers from the gracile and cuneate nuclei of the same and of the opposite sides; (3) fibers from the opposite olivary nuclei; (4) crossed and uncrossed fibers from the reticular formation of the medulla oblongata; (5) vestibular fibers, derived partly from the vestibular division of the acoustic nerve and partly from the nuclei in which this division ends-r-these fibers occupy the medial segment of the inferior peduncle and divide into ascending and descending groups of fibers, the ascending fibers partly end in the roof nucleus of the opposite side of the cerebellum; (6) cerebellobulbar fibers which come from the opposite roof nucleus and probably from the dentate nucleus, and are said to end in the nucleus of Deiters and in the formatio reticularis of the medulla oblongata; (7) some fibers from the ventral spinocerebellar fasciculus are said to join the dorsal spinocerebellar fasciculus. The anterior medullary velum (velum medullare anterius; valve of Vieussens; superior medullary velum) is a thin, transparent lamina of white substance, which stretches between the superior peduncle; on the dorsal surface of its lower half the folia and lingula are prolonged. It forms, together with the superior peduncle, the roof of the upper part of the fourth ventricle; it is narrow above, where it passes beneath the inferior colliculi, and broader below, where it is continuous with the white substance of the superior vermis. A slightly elevated ridge, the frsenulum 1 See article by E. B. Jamieson, Journal of Anatomy and Physiology, vol. xliv. 794 NEUROLOGY veli, descends upon its upper part from between the inferior colliculi, and on either side of this the trochlear nerve emerges. The posterior medullary velum (velum medullare posterius; inferior medullary velum) is a thin layer of white substance, prolonged from the white center of the cerebellum, above and on either side of the nodule; it forms a part of the roof of the fourth ventricle. Somewhat semilunar in shape, its convex edge is continuous with the white substance of the cerebellum, while its thin concave margin is apparently free; in reality, however, it is continuous with the epithelium of the ventricle, which is prolonged downward from the posterior medullary velum to the ligulse. The two medullary vela are in contact with each other along their line of emer- gence from the white substance of the cerebellum; and this line of contact forms the summit of the roof of the fourth ventricle, which, in a vertical section through the cavity, appears as a pointed angle. The Fibrse Propriae of the cerebellum are of two kinds: (1) commissural fibers, which cross the middle line at the anterior and posterior parts of the vermis and connect the opposite halves of the cerebellum; (2) arcuate or association fibers, which connect adjacent laminae with each other. Gray Substance.—The gray substance of the cerebellum is found in two situations: (1) on the surface, forming the cortex; (2) as independent masses in the anterior. (1) The gray substance of the cortex presents a characteristic foliated appearance, due to the series of laminae which are given off from the central white substance; these in their turn give off secondary laminae, which are covered by gray substance. Externally, the cortex is covered by pia mater; internally is the medullary center, consisting mainly of nerve fibers. Microscopic Appearance of the Cortex (Fig. 706).—The cortex consists of two layers, viz., an external gray molecular layer, and an internal rust-colored nuclear layer; between these is an incomplete stratum of cells which are characteristic of the cerebellum, viz., the cells of Purkinje. The external gray or molecular layer consists of fibers and cells. The nerve fibers are delicate fibrillse, and are derived from the following sources: (a) the dendrites and axon collaterals of Purkinje’s cells; (b) fibers from cells in the nuclear layer; (c) fibers from the central white substance of the cerebellum; (d) fibers derived from cells in the molecular layer itself. In addition to these are other fibers, which have a vertical direction, and are the processes of large neuroglia cells, situated in the nuclear layer. They pass outward to the periphery of the gray matter, where they expand into little conical enlargements which form a sort of limiting membrane beneath the pia mater, analogous to the membrana limitans interna in the retina, formed by the sustentacular fibers of Muller. The cells of the molecular layer are small, and are arranged in two strata, an outer and an inner. They all possess branched axons; those of the inner layer are termed basket cells; they run for some distance parallel with the surface of the folium—giving off collaterals which pass in a vertical direction toward the bodies of Purkinje’s cells, around which they become enlarged, and form basket-like net-works. The cells of Purkinje form a single stratum of large, flask-shaped cells at the junction of the molecular and nuclear layers, their bases resting against the latter; in fishes and reptiles they are arranged in several layers. The jcells are flattened in a direction transverse to the long axis of the folium, and thus appear broad in sections carried across the folium, and fusiform in sections parallel to the long axis of the folium. From the neck of the flask one or more dendrites arise and pass into the molecular layer, where they subdivide and form an extremely rich arbores- cence, the various subdivisions of the dendrites being covered by lateral spine- like processes. This arborescence is not circular, but, like the cell, is flattened at right angles to the long axis of the folium; in other words, it does not resemble THE HIND-BRAIN OR RHOMBENCEPHALON 795 a round bush, but has been aptly compared by Obersteiner to the branches of a fruit tree trained against a trellis or a wall. Hence, in sections carried across the folium the arborescence is broad and expanded; whereas in those which are parallel to the long axis of the folium, the arborescence, like the cell itself, is seen in profile, and is limited to a narrow area. Irom the bottom of the flask-shaped cell the axon arises; this passes through the nuclear layer, and, becoming medullated, is continued as a nerve fiber in the subjacent white substance. As this axon traverses the granular layer it gives off fine collaterals, some of which run back into the molecular layer. Cell of Purkinje ) Molecular layer Golgi cell Axons of granule cells cut trans- versely layer Granule cells Small cell of molecular- layer Basket cell~ Axon of cell of Purkinje Neuroglia cell Moss fiber Tendril fiber Fig. 706.—Transverse section of a cerebellar folium. after Cajal and Kolliker.) The internal rust-colored or nuclear layer (Fig. 706) is characterized by containing numerous small nerve cells of a reddish-brown color, together with many nerve fibrils. Most of the cells are nearly spherical and provided with short dendrites which spread out in a spider-like manner in the nuclear layer, dheir axons pass outward into the molecular layer, and, bifurcating at right angles, run for some distance parallel with the surface. In the outer part of the nuclear layer are some larger cells, of the type II of Golgi. Their axons undergo frequent division as soon as they leave the nerve cells, and pass into the nuclear layer; while their dendrites ramify chiefly in the molecular layer. 796 NEUROLOGY Finally, in the gray substance of the cerebellar cortex there are fibers which come from the white center and penetrate the cortex. The cell-origin of these fibers is unknown, though it is believed that it is probably in the gray substance of the medulla spinalis. Some of these fibers end in the nuclear layer by dividing into numerous branches, on which are to be seen peculiar moss-like appendages; hence they have been termed by Ramon y Cajal the moss fibers; they form an arborescence around the cells of the nuclear layer and are said to come from fibers in the inferior peduncle. Other fibers, the clinging or tendril fibers, derived from the medullary center can be traced into the molecular layer, where their branches cling around the dendrites of Purkinje’s cells. They are said to come from fibers of the middle peduncle. (2) The independent centers of gray substance in the cerebellum are four in number on either side: one is of large size, and is known as the nucleus dentatus; the other three, much smaller, are situated near the middle of the cerebellum, and are known as the nucleus emboliformis, nucleus globosus, and nucleus fastigii. Nucleus dentatus Superior peduncle Corpora quadrigemina Fig. 707.—Sagittal section through right cerebellar hemisphere. The right olive has also been cut sagitally. Inferior olivary nucleus The nucleus dentatus (Fig. 707) is situated a little to the medial side of the center of the stem of the white substance of the hemisphere. It consists of an irregularly folded lamina, of a grayish-yellow color, containing white fibers, and presenting on its antero-medial aspect an opening, the hilus, from which most of the fibers of the superior peduncle emerge (page 792). The nucleus emboliformis lies immediately to the medial side of the nucleus dentatus, and partly covering its hilus. The nucleus globosus is an elongated mass, directed antero-posteriorly, and placed medial to preceding. The nucleus fastigii is somewdiat larger than the other two, and is situated close to the middle line at the anterior end of the superior vermis, and immediately over the roof of the fourth ventricle, from which it is separated by a thin layer of white substance. The cerebellum is concerned with the coordination of movements necessary in equilibration, locomotion and prehension. In it terminate pathways conducting impulses of muscle sense, tendon sense, joint sense and equilibratory disturbances. With the exception of the ventral spinocerebellar fasciculus these impulses enter through the inferior peduncle. The reflex arc is completed by fibers in the superior peduncle which pass to the red nucleus and the thalamus and thence by additional neurons (rubrospinal tract) to the motor centers. The exact functions of its different parts are still quite uncertain, owing to the contradictory nature of the evidence furnished by (1) ablation experiments upon animals,-and (2) clinical observations in man of the effects produced by abscesses or tumors affecting different portions of the organ. THE HIND-BRAIN OR RHOMBENCEPHALON 797 The Fourth Ventricle (ventriculus quartus).—The fourth ventricle, or cavity of the hind-brain, is situated in front of the cerebellum and behind the pons and upper half of the medulla oblongata. Developmentally considered, the fourth ventricle consists of three parts: a superior belonging to the isthmus rhombencephali, an intermediate, to the metencephalon, and an inferior, to the myelencephalon. It is lined by ciliated epithelium, and is continuous below with the central canal of the medulla oblongata;1 above, it communicates, by means of a passage termed the cerebral aqueduct, with the cavity of the third ventricle. It presents four angles, and possesses a roof or dorsal wall, a floor or ventral wall, and lateral boundaries. Angles.—The superior angle is on a level with the upper border of the pons, and is continuous with the lower end of the cerebral aqueduct. The inferior angle is on a level with the lower end of the olive, and opens into the central canal of the medulla oblongata. Each lateral angle corresponds with the point of meeting of the brachia and inferior peduncle. A little below the lateral angles, on a level with the strife medullares, the ventricular cavity is prolonged outward in the form of two narrow lateral recesses, one on either side; these are situated between the inferior peduncles and the flocculi, and reach as far as the attachments of the glosso- pharyngeal and vagus nerves. Lateral Boundaries.—The lower part of each lateral boundary is constituted by the clava, the fasciculus cuneatus, and the inferior peduncle; the upper part by the middle and the superior peduncle. Roof or Dorsal Wall (Fig. 708).—The upper portion of the roof is formed by the superior peduncle and the anterior medullary velum; the lower portion, by the posterior medullary velum, the epithelial lining of the ventricle covered by the tela chorioidea inferior, the taeniae of the fourth ventricle, and the obex. The superior peduncle (page 792), on emerging from the central white sub- stance of the cerebellum, pass upward and forward, forming at first the lateral boundaries of the upper part of the cavity; on approaching the inferior colliculi, they converge, and their medial portions overlap the cavity and form part of its roof. The anterior medullary velum (page 793) fills in the angular interval between the superior peduncle, and is continuous behind with the central white sub- stance of the cerebellum; it is covered on its dorsal surface by the lingula of the superior vermis. The posterior medullary velum (page 794) is continued downward and forward from the central white substance of the cerebellum in front of the nodule and tonsils, and ends interiorly in a thin, concave, somewhat ragged margin. Below this margin the roof is devoid of nervous matter except in the immediate vicinity of the lower lateral boundaries of the ventricle, where two narrow white bands, the taeniae of the fourth ventricle (ligulce), appear; these bands meet over the inferior angle of the ventricle in a thin triangular lamina, the obex. I he non-nervous part of the roof is formed by the epithelial lining of the ventricle, which is prolonged downward as a thin membrane, from the deep surface of the posterior medullary velum to the corresponding surface of the obex and taeniae, and thence on to the floor of the ventricular cavity; it is covered and strengthened by a portion of the pia mater, which is named the tela chorioidea of the fourth ventricle. The taeniae of the fourth ventricle (;tcenia ventriculi quarti; ligula) are two narrow bands of white matter, one on either side, which complete the lower part of the roo of the cavity. Each consists of a vertical and a horizontal part. The vertical part is continuous below the obex with the clava, to which it is adherent by its latera 1 J. T. Wilson (Journal of Anatomy and Physiology, vol. xl) has pointed out t a - presented by the fetal oblongata, immediately below its entrance into the fourth ventricle, retains the - P medulla spinalis, and that it is marked by dorso- and ventro-lateral sulci. 798 NEUROLOGY border. The horizontal portion extends transversely across the inferior peduncle, below the strife medullares, and roofs in the lower and posterior part of the lateral recess; it is attached by its lower margin to the inferior peduncle, and partly encloses the choroid plexus, which, however, projects beyond it like a cluster of grapes; and hence this part of the tsenia has been termed the cornucopia (Bochdalek). The obex is a thin, triangular, gray lamina, which roofs in the lower angle of the ventricle and is attached by its lateral margins to the clavse. The tela chorioidea of the fourth ventricle is the name applied to the triangular fold of pia mater which is carried upward between the cerebellum and the medulla oblongata. It consists of two layers, which are continuous with each other in front, and are more or less adherent throughout. The posterior layer covers the antero-inferior surface of the cere- bellum, while the anterior is applied to the structures which form the lower part of the roof of the ventricle, and is continuous interiorly with the pia mater on the inferior peduncles and closed part of the medulla. Corpora quadrigemina Cerebral peduncle Anterior medullary velum Ependymal lining of ventricle Posterior medullary velum Choroid plexus Cisterna cerebellomedullaris of subarachnoid cavity Central canal Cisterna pontis of subarachnoid cavity Fig. 708.—Scheme of roof of fourth ventricle. The arrow is in the foramen of Majendie. Choroid Plexuses.—These consist of two highly vascular inflexions of the tela chorioidea, which invaginate the lower part of the roof of the ventricle and are everywhere covered by the epithelial lining of the cavity. Each consists of a ver- tical and a horizontal portion: the former lies close to the middle line, and the latter passes into the lateral recess and projects beyond its apex. The vertical parts of the plexuses are distinct from each other, but the horizontal portions are joined in the middle line; and hence the entire structure presents the form of the letter T, the vertical limb of which, however, is double. Openings in the Eoof.—In the roof of the fourth ventricle there are three openings, a medial and two lateral: the medial aperture (foramen Majendii), is situated imme- diately above the inferior angle of the ventricle; the lateral apertures, (foramina of Luschka are found at the extremities of the lateral recesses. By means of these three openings the ventricle communicates with the subarachnoid cavity, and the cerebrospinal fluid can circulate from the one to the other. Rhomboid Fossa (fossa rhomboidea; “floor” of the fourth ventricle) (Fig. 709).— The anterior part of the fourth ventricle is named, from its shape, the rhomboid fossa, and its anterior wall, formed by the back of the pons and medulla oblongata, constitutes the floor of the fourth ventricle. It is covered by a thin layer of gray THE HIND-BRAIN OR RHOMBENCEPHALON 799 substance continuous with that of the medulla spinalis; superficial to this is a thin lamina of neuroglia which constitutes the ependyma of the ventricle and supports a layer of ciliated epithelium. The fossa consists of three parts, superior, inter- mediate, and inferior. The superior part is triangular in shape and limited laterally by the superior cerebellar peduncle; its apex, directed upwrard, is continuous with the cerebral aqueduct; its base it represented by an imaginary line at the level of the upper ends of the superior foveae. The intermediate part extends from this level to that of the horizontal portions of the taeniae of the ventricle; it is narrow above where it is limited laterally by the middle peduncle, but wddens below and is pro- longed into the lateral recesses of the ventricle. The inferior part is triangular, and its downwardly directed apex, named the calamus scriptorius, is continuous with the central canal of the closed part of the medulla oblongata. —Frenulum veli -Trochlear nerve Tcenia pontiss Ant. medullary velum Superior peduncle Nucleus dentatus Superior fovea Colliculus facialis Striae medullares Trigonum hypoglossi Area acustica- Taenia of fourth ventricle Ala drierea Funiculus separans Area postrema Glava \ Obex Fig. 709.—Rhomfeoid fossa. The rhomboid fossa is divided into symmetrical halves by a median sulcus which reaches from the upper to the lower angles of the fossa and is deeper below than above. On either side of this sulcus is an elevation, the medial eminence, bounded laterally by a sulcus, the sulcus limitans. In the superior part of the fossa the medial eminence has a width equal to that of the corresponding half of the fossa, but opposite the superior fovea it forms an elongated swelling, the colliculus facialis, which overlies the nucleus of the abducent nerve, and is, in part at least, produced by the ascending portion of the root of the facial nerve. In the inferior part of the fossa the medial eminence assumes the form of a triangular area, the trigonum hypoglossi. When examined under water with a lens this trigone is seen to consist of a medial and a lateral area separated by a series of oblique furrows, the medial area corresponds with the upper part of the nucleus of the hypoglossal nerve, the lateral with a small nucleus, the nucleus intercalatus. The sulcus limitans forms the lateral boundary of the medial eminence. In the superior part of the rhomboid fossa it corresponds with the lateral limit of t le 800 NEUROLOGY fossa and presents a bluish-gray area, the locus cseruleus, which owes its color to an underlying patch of deeply pigmented nerve cells, termed the substantia ferruginea. At the level of the colliculus facialis the sulcus limitans widens into a flattened depression, the superior fovea, and in the inferior part of the fossa appears as a distinct dimple, the inferior fovea. Lateral to the fovese is a rounded elevation named the area acustica, which extends into the lateral recess and there forms a feebly marked swelling, the tuberculum acusticum. Winding around the inferior peduncle and crossing the area acustica and the medial eminence are a number of white strands, the striae medullares, which form a portion of the cochlear division of the acoustic nerve and disappear into the median sulcus. Below the inferior fovea, and between the trigonum hypoglossi and the lower part of the area acustica is a triangular dark field, the ala cinerea, which corresponds to the sensory nucleus of the vagus and glossopharyngeal nerves. The end of the ala cinerea is crossed by a narrow translucent ridge, the funiculus separans, and between this funiculus and the clava, is a small tongue-shaped area, the area postrema. On section it is seen that the funiculus separans is formed by a strip of thickened ependyma, and the area postrema by loose, highly vascular, neuroglial tissue con- taining nerve cells of moderate size. THE MID-BRAIN OR MESENCEPHALON. The mid-brain or mesencephalon (Fig. 681) is the short, constricted portion which connects the pons and cerebellum with the thalamencephalon and cerebral hemi- spheres. It is directed upward and for- ward, and consists of (1) a ventro- lateral portion, composed of a pair of cylindrical bodies, named the cerebral peduncles; (2) a dorsal portion, consist- ing of four rounded eminences, named the corpora quadrigemina; and (3) an intervening passage or tunnel, the cere- bral aqueduct, which represents the original cavity of the mid-brain and connects the third with the fourth ven- tricle (Fig. 710). The cerebral peduncles (pedunculus cerebri; crus cerebri) are two cylindrical masses situated at the base of the brain, and largely hidden by the temporal lobes of the cerebrum, which must be drawn aside or removed in order to expose them. They emerge from the upper surface of the pons, one on either side of the middle line, and, diverging as they pass upward and forward, dis- appear into the substance of the cere- bral hemispheres. The depressed area between the crura is termed the inter- peduncular fossa, and consists of a layer of grayish substance, the posterior perforated substance, which is pierced by small apertures for the transmission of bloodvessels; its lower part lies on the ventral aspect of the medial portions of the tegmenta, and contains a nucleus named the interpeduncular ganglion (page 802); its upper part assists in forming the floor of the third ventricle. The ventral sur- Fig. 710.—Coronal section through mid-brain. (Sche- matic.) (Testut.) 1. Corpora quadrigemina. 2. Cere- bral aqueduct. 3. Central gray stratum. 4. Interpedun- cular space. 5. Sulcus lateralis, b. Substantia nigra. 7. Red nucleus of tegmentum. 8. Oculomotor nerve, with 8', its nucleus of origin, a. Lemniscus (in blue) with o' the medial lemniscus and a" the lateral lemniscus, b. Medial longitudinal fasciculus, c. Raph6. d. Temporo- pontine fibers, e. Portion of medial lemniscus, which runs to the lentiform nucleus and insula, f. Cerebrospinal fibers, gr. Frontopontine fibers. THE MID-BRAIN OR MESENCEPHALON 801 face of each peduncle is crossed from the medial to the lateral side by the superior cerebellar and posterior cerebral arteries; its lateral surface is in relation to the gyrus hippocampi of the cerebral hemisphere and is crossed from behind forward by the trochlear nerve. Close to the point of disappearance of the peduncle into the cerebral hemisphere, the optic tract winds forward around its ventro-lateral Inferior colliculi _Cerebral aqueduct Nucleus of oculomotor nerve Lateral lemniscus - Medial longitudinal fasciculus ■Medial lemniscus Raphe. Fig. 711.—Transverse section of mid-brain at level of inferior colliculi. surface. The medial surface of the peduncle forms the lateral boundary of the interpeduncular fossa, and is marked by a longitudinal furrow, the oculo- motor sulcus, from which the roots of the oculomotor nerve emerge. On the lateral surface of each peduncle there is a second longitudinal furrow, termed the lateral sulcus; the fibers of the lateral lemniscus come to the surface in this sulcus, and pass backward and upward, to disappear under the inferior colliculus. Superior colliculi Cerelrral aqueduct Nucleus of oculomotor nerve Medial longitudinal fasciculus Fig. 712.—Transverse section of mid-brain at level of superior colliculi. Structure of the Cerebral Peduncles (Figs. 711, 712).—On transverse section, each peduncle is seen to consist of a dorsal and a ventral part, separated by a deeply pigmented lamina of gray substance, termed the substantia nigra. Ihe dorsal part NEUROLOGY 802 is named the tegmentum; the ventral, the base or crusta; the two bases are separated from each other, but the tegmenta are joined in the median plane by a forward prolongation of the raphe of the pons. Laterally, the tegmenta are free; dorsally, they blend with the corpora quadrigemina. The base (basis pedunculi; crusta or pes) is semilunar on transverse section, and consists almost entirely of longitudinal bundles of efferent fibers, which arise from the cells of the cerebral cortex and are grouped into three principal sets, viz., cerebrospinal, frontopontine, and temporopontine (Fig. 710). The cerebrospinal fibers, derived from the cells of the motor area of the cerebral cortex, occupy the middle three-fifths of the base; they are continued partly to the nuclei of the motor cranial nerves, but mainly into the pyramids of the medulla oblongata. The frontopontine fibers are situated in the medial fifth of the base; they arise from the cells of the frontal lobe and end in the nuclei of the pons. The temporopontine fibers are lateral to the cerebrospinal fibers; they originate in the temporal lobe and end in the nuclei pontis.1 The substantia nigra (intercalatum) is a layer of gray substance containing numerous deeply pigmented, multipolar nerve cells. It is semilunar on transverse section, its concavity being directed toward the tegmentum; from its convexity, prolongations extend between the fibers of the base of the peduncle. Thicker medially than laterally, it reaches from the oculomotor sulcus to,the lateral sulcus, and extends from the upper surface of the pons to the subthalamic region; its medial part is traversed by the fibers of the oculomotor nerve as these stream for- ward to reach the oculomotor sulcus. The connections of the cells of the substantia nigra have not been definitely established. It receives collaterals from the medial lemniscus and the pyramidal bundles. Bechterew is of the opinion that the fibers from the motor area of the cerebral cortex form synapses with cells whose axons pass to the motor nucleus of the trigeminal nerve and serve for the coordination of the muscles of mastication. The tegmentum is continuous below with the reticular formation of the pons, and, like it, consists of longitudinal and transverse fibers, together with a consider- able amount of gray substance. The principal gray masses of the tegmentum are the red nucleus and the interpeduncular ganglion; of its fibers the chief longi- tudinal tracts are the superior peduncle, the medial longitudinal fasciculus, and the lemniscus. Gray Substance.—The red nucleus is situated in the anterior part of the teg- mentum, and is continued upward into the posterior part of the subthalamic region. In sections at the level of the superior colliculus it appears as a circular mass which is traversed by the fibers of the oculomotor nerve. It receives many terminals and collaterals from the superior cerebellar peduncle also collaterals from the ventral longitudinal bundle, from Gudden’s bundle and the median lemniscus. The axons of its larger cells cross the middle line and are continued downward into the lateral funiculus of the medulla spinalis as the rubrospinal tract (page 761); those of its smaller cells end mainly in the thalamus. The rubrospinal tract forms an important part of the pathway from the cerebellum to the lower motor centers. The interpeduncular ganglion is a median collection of nerve cells situated in the ventral part of the tegmentum. The fibers of the fasciculus retroflexus of Meynert, which have their origin in the cells of the ganglion habenulae (page 812), end in it. Besides the two nuclei mentioned, there are small collections of cells which form the dorsal and ventral nuclei and the central nucleus or nucleus of the raphe. 1 A band of fibers, the tractua peduncularis transverSus, is sometimes seen emerging from in front of the superior collic- it passes around the ventral aspect of the peduncle about midway between the pons and the optic tract, and dips into the oculomotor sulcus. This band is a constant structure in many mammals, but is only present in about 30 per cent, of human brains. Since it undergoes atrophy after enucleation of the eyeballs, it may be considered as forming a path for visual sensations. THE MID-BRAIN OR MESENCEPHALON 803 White Substance. (1) The origin and course of the superior peduncle have already been described (page 792). (2) The medial (posterior) longitudinal fasciculus is continuous below with the proper fasciculi of the anterior and lateral funiculi of the medulla spinalis. In the medulla oblongata and pons it runs close to the middle line, near the floor of the fourth ventricle; in the mid-brain it is situated on the ventral aspect of the cerebral aqueduct, below the nuclei of the oculomotor and trochlear nerves. Its connections are imperfectly known, but it consists largely of ascend- ing and descending intersegmental or association fibers, which connect the nuclei of the hind-brain and mid-brain to each other. Many of the fibers arise in Deiters’s nucleus (lateral vestibular nucleus) and divide into ascending and descend- ing branches which send terminals and collaterals to the motor nuclei of the cranial and spinal nerves. Its spinal portion is located in the anterior funiculus and is known as the vestibulospinal fasciculus. Other fibers pass to the median longitudinal bundle from cells in the reticular formation of the medulla, pons and mid-brain and also from certain large cells in the terminal nucleus of the trigeminal nerve. According to Edinger it extends to the so-called nucleus of the posterior longi- tudinal bundle in the hypothalamic region, but this is uncertain and the fibers above the nucleus of the oculomotor are smaller in diameter than the rest of the bundle. According to Held fibers from the posterior commissure can be traced into the posterior longitudinal bundle, and according to the same author many of the descending fibers arise in the superior colliculus, and, after decussating in the middle line, end in the motor nuclei of the pons and medulla oblongata. These fibers from the superior colliculus probably pass into the ventral longitudinal bundle. Fibers are said to pass through the medial longitudinal fasciculus from the nucleus of the abducent nerve into the oculomotor nerve of the opposite side, and through this nerve to the Rectus medialis oculi. Fraser, however, denies the exist- ence of such fibers. Again, fibers are said to be prolonged through this fasciculus from the nucleus of the oculomotor nerve into the facial nerve, and are distributed to the Orbicularis oculi, the Corrugator, and the Frontalis.1 The ventral longitudinal bundle consists for the most part of the tectospinal fas- ciculus, and arises from the superior colliculus, the fibers arch ventrally around the central gray matter and cross the midline in the fountain-decussation of Meynert. They then descend in the tegmentum, part of them passing through the red nucleus ventral to the medial longitudinal bundle. In the medulla oblongata and spinal cord its fibers are more or less intermingled with the medial longitudinal bundle and the rubrospinal tract. It descends in the adjoining region of the ventral and lateral funiculi. Collaterals and terminals are given off to the red nucleus and probably other nuclei of the brain stem and to the anterior column of the spinal cord. It is probably concerned in optic reflexes. (3) The medial lemniscus or medial fillet (Fig. 713).—The fibers of the medial lemniscus take origin in the gracile and cuneate nuclei of the medulla oblongata, and as internal arcuate fibers they cross to the opposite side in the sensory decussa- tion (page 777). They then pass in the interolivary stratum upward through the medulla oblongata, in which they are situated behind the cerebrospinal fibers and between the olives. In the pons and lower part of the mid-brain it occupies the ventral part of the reticular formation and tegmentum close to the raphe, while above it gradually shifts to the dorso-lateral part of the tegmentum in the angle between the red nucleus and the substantia nigra. In the pons it assumes a flattened ribbon-like appearance, and is placed dorsal to the trapezium. As the lemniscus ascends, it receives additional fibers from the terminal sensory nuclei of the*nranial i A. Bruce and J. H. Harvey Pirrie, “On tire Origin of the Facial Nerve,” Review of Neurology and Psychiatry. December, 1908, No. 12, vol. vi, produce weighty evidence against the view that the facial nerve derives nbers irom the nucleus of the oculomotor nerve. 804 NEUROLOGY nerVes of the opposite side. Many of the fibers which arise from the terminal sensory nuclei of the cranial nerves pass upward in the formatio reticularis as a separate bundle, known as the central tract of the cranial nerves, to the thalamus. Many fibers either terminate in or send off collaterals to the gray matter of the medulla, the pons, and the mid-brain. Large numbers of fibers pass to or from the substantia nigra. Many collaterals enter the red nucleus and other fibers are said to run to the superior colliculus. The great bulk of the fibers, however, enter the ventro-lateral portion of the thalamus, give off collaterals to the posterior semi- lunar nucleus and then terminate in the principal sensory nucleus of the thalamus. .. Corpora quadrigemina _ Superior olivary nucleus - Cochlear nucleus Sensory cerebral nuclei Nucleus gracilis Nucleus cuneatus In the cerebral peduncle, a few of its fibers pass upward in the lateral part of the base of the peduncle, on the dorsal aspect of the temporopontine fibers, and reach the lentiform nucleus and the insula. The greater part of the medial lemniscus, on the other hand, is prolonged through the tegmentum, and most of its fibers end in the thalamus; probably some are continued directly through the occipital part of the internal capsule to the cerebral cortex. From the cells of the thalamus a relay of fibers is prolonged to the cerebral cortex. 1 he medial lemniscus may be considered as the upward continuation of the posterior funiculus of the spinal cord and to convey conscious impulses of muscle .sense and tactile discrimination. Fig. 713.—Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red. THE MID-BRAIN OR MESENCEPHALON 805 mp1|i",l I™*™1 01 thnamj? tract.the ,cranial nerves is closely associated with the medial lemniscus The fibers of the spinothalamic fasciculi are continued from the tecnnentnrn ‘t " '“t PaSSfS T™"1 in the ret!cular formation and the tegmentum to the thalamus along the dorsal side of the median lemniscus. It recen es fibers from the opposite terminal sensory nuclei of the vagus, glossopharyn- geal, facial, trigeminal and probably the vestibular nerves. Many of the secondary sensory fibers of the trigeminal cross the raphe from its terminal nucleus and pass upward to the thalamus by a more or less separate but closely associated pathway known as the central tract of the trigeminal nerve which also lies on the dorsal aspect of the lemnis- cus. These two tracts give off collaterals to the posterior semilunar nucleus of the thalamus and terminate in the anterior semilunar nucleus of the ventro-lateral region of the thalamus sending collaterals into the zona incerta. The fibers of the rubrospinal tract (