MANUAL OF "" NORMAL HISTOLOGY ADAPTED FOR THE USE OF MEDICAL STUDENTS IN THE CLASS ROOM AND IN THE LABORATORY BY TILGHMAN BRICE MARDEN, A.B., M.D. HI Professor of Histology, Bacteriology, and Biology at the Baltimore Medical College. Press of A, Hoen & Co. Baltimore, Md. Copyright, 1896, by T. B. Marden. PREFACE. In the preparation of the present Manual, the author has endeavored to supply a want which he considers has been experi- enced by many of our Medical Students: a text-book upon Histology which, although concise in description shall still be sufficiently minute to furnish a clear and comprehensive idea of the subject. The following pages represent an effort to condense the description of the structure of the various portions of the human body in such a manner that they may be readily grasped and permanently retained by the student, and to furnish him with the means, in the form of experiments, by the aid of which he may be able to verify such description and impress upon his memory mental photographs of the microscopical appearance of the various tissues and organs, so permanent and distinct that time and future occupations shall fail to erase them. Although the Manual is not intended by the author to be regarded as a complete and exhaustive treatise on Histology, he feels confident that it will give to the student such a thorough knowledge of the essential facts of the science that he will be able with ease to study and comprehend such matters of histo- logical interest as may, from the elementary character of the work, have been necessarily omitted, or those subjects connected therewith which he may be called upon to study later in his advanced college course or professional career. As Embryology has now been added as a separate depart- ment to the college curriculum, the consideration of the develop- ment of the tissues and organs of the body has been omitted, except in a single instance, that of the development of bone. Except in the occasional instance where he has taken advan- tage of the excellent illustrations of other duly acknowledged authors, and in those instances where he has attempted to repre- sent by means of diagrams, all the illustrations are faithful representations of specimens examined by the author, and from which drawings were prepared by him expressly for the Manual. In presenting this work to the public, the author takes advan- tage of the opportunity to express his appreciation of the cordial reception extended to his Lecture Notes by the members of his former classes as it is largely due to that reception that he was encouraged to prepare the present Manual. He also extends his thanks to the Bausch and Lomb Opt. Co., of Rochester, New York, for their courtesy extended in the contribution of the cut used in Fig. 5. Baltimore, September 10th, 1896. T. B. M. Preface to the Second Edition. After ten years of additional experience, the author reiterates what he has stated in the preface to the first edition, and has become convinced that this Manual will suffice to lay a good foundation upon which the superstructure of medicine can be erected. He extends his thanks to the members of the class in His- tology for the courtesy extended in allowing the use of their specimens for some of the illustrations. Very little change has been made in the text as compared with that of the first edition, although additions have been made to the chapter on the Blood, and the structure of the prostate gland has been inserted. T. B. M. Baltimore, March 21st, 1906. CONTENTS. CHAPTER I. Introductory Pages 1 to 9 CHAPTER II. The; BloodPages 10 to 17 CHAPTER HI. EpitheliumPages 18 to 25 CHAPTER IV. Supporting TissuesPages 26 to 44 CHAPTER V. Muscular Tissue Pages 45 to 49 CHAPTER VI. Nervous Tissue Pages 50 to 58 CHAPTER VII. The Blood Vessels Pages 59 to 64 CHAPTER VIII. The Lymph Channels and the MembranesPages 65 to 68 CHAPTER IX. The Alimentary Canal and its AppendagesPages 69 to 108 CHAPTER X. The Aggregations oe Lymphoid Tissue Pages 109 to 116 CHAPTER XI. The Respiratory OrgansPages 117 to 122 CHAPTER XII. The Skin and its Appendages Pages 123 to 131 CHAPTER XIII. The Urinary OrgansPages 132 to 142 CHAPTER XIV. The Generative Organs of the MadePages 143 to 152 CHAPTER XV. The Reproductive Organs of the FemalePages 153 to 160 CHAPTER XVI. The Mammary Gland, The Thyroid Gland, and The Supra- renal BodyPages 161 to 167 CHAPTER XVII. The EyePages 168 to 176 CHAPTER XVIII. The Organ of Hearing Pages 177 to 181 CHAPTER XIX. The Organ of SmellPages 182 to 184 CHAPTER XX. The Nervous SystemPages 185 to 196 AppendixPages 197 to 211 IndexPages 213 to 233 MANUAL OF NORMAL HISTOLOGY. 1 CHAPTER I. INTRODUCTORY. Histology (Gr. loros, a tissue ; Xoyos, a discourse) is the branch of morphology which treats of the minute structure of tissues. As the minute structure of tissues is studied with the aid of the microscope (Gr. /xtxpos, small; o-kottcw, to view), this branch of science is commonly known as " microscopical anatomy." The study of the structure of normal tissues is " normal his- tology ," to distinguish it from the study of diseased tissues, or " pathological histology." As tissues may be animal or vege- table, there are two kinds of histology, termed respectively, "animal" and "vegetal." Animal histology may be divided into human, and comparative ; the former being the study of the structure of the tissues which occur in the human body. As the structure of the human tissues and organs in many instances is shown as well, and often better, by the corresponding tissues and organs of lower forms of animal life, the structure of the human tissues and organs, in such instances, can be demon- strated from corresponding tissues and organs of animals. Although the tissues and organs of the body are numerous, there are four groups of tissues which singly, or collectively, comprise all the structures of the body ; hence the four groups of tissues are known as the elementary tissues. The elementary groups of tissues are : Epithelial tissue. Supporting, more commonly known as connective, tissue. Muscular tissue. Nervous tissue. A tissue consists of two essential portions, a cellular and an intercellular. The intercellular portion may present variations which depend upon the location of, and the function to be per- formed by, the tissue. In some tissues the intercellular substance is a liquid (blood and lymph); in others it is solid, tough, and elastic (elastic connective tissue); or solid and hard (bone), etc. 2 MANUAL OF NORMAL HISTOLOGY. The proportion between the cellular and the intercellular sub- stances varies ; in some instances there is a preponderance of the former; in other instances of the latter. In the embryo the former is the most important and most abundant, while in the adult usually the reverse is true. Although the intercellular substance varies between wide limits, the cellular elements of one tissue are very similar to those of another, the main differ- ence being one in shape. A cell is a mass of protoplasm containing a nucleus, and enclosed by a limiting membrane, or cell wall. Protoplasm, sometimes termed cytoplasm, consists of two portions, spongioplasm and hyaloplasm. The spongioplasm exists as a fine fibrillar network; the hyaloplasm, sometimes spoken of as paraplasm, as a clear semi-fluid substance in the meshes of the network. In the protoplasm of some cells the network of the spongioplasm can readily be seen (liver-cells), while in other cells the spongioplasm exists as small granular particles disseminated throughout the protoplasm (colorless corpuscles of the blood), the hyalo- plasm being between the neighbor- ing particles. Protoplasm may contain fat, pigment, glycogen, etc. In some portion,usually the central, of the mass of protoplasm there is an oval or round dense area known as the nucleus, which is also com- posed of a fibrillar network, and a semi-fluid substance contained in the meshes of the network. The fibrillar network of the nucleus is termed the intranuclear network; the constituent fibrillae, owing to the fact that they stain readily with certain aniline dyes, are said to be chromatic (Gr. KpGtpa, color), the substance of which they are composed being known as chromatin. The semi-fluid sub- stance in the meshes of the network is termed the nuclear matrix, or nucleoplasm, which, owing to the fact that it does not stain with certain aniline dyes, is said to be achromatic, the substance of which it is composed being known as achromatin Attached to the intranuclear network, there is a collection of chromatic Fig. 1. A cell from the growing tip of an onion. a, cell wall; b, spongioplasm; c, hya- loplasm; d, nuclear membrane; e, intranuclear network; f, nuclear ma- trix; n, nucleolus. MANUAL OF NORMAL HISTOLOGY. 3 substance known as the nucleolus. In a nucleus there may be more than one nucleolus. The nucleus is separated from the surrounding protoplasm by a membrane known as the nuclear membrane, which, owing to the facts that it stains similar to the intranuclear network, and is attached to or continuous with it, may be considered as being composed of the same kind of sub- stance (chromatin) as that which composes the fibrillae of the network. In some cells there may be more than one nucleus, in which cases the cells are known as polynuclear cells. At the periphery of the protoplasm, the protoplasm appears more dense, or, which is more probable, the spongioplasm, besides forming the network of the protoplasm, extends around the periphery of the mass of protoplasm, thus forming a limiting membrane or cell wall. Any peripheral condensation of protoplasm, no matter how slight, should be regarded as a cell wall. In some cells the limiting membrane is pliable, elastic, and thin, so thin that it can only be seen after much difficulty. Due to the limiting membrane being of such a structure, the shape of the cells may change, due to pressure from within the cell. In other cells the limiting membrane is dense, thus giving to the cells definite shapes. The shape of a cell which has a dense cell wall depends upon the pressure from without the cell. If the pressure within such a cell increases to any great extent, the cell wall is liable to rupture (goblet cells). If the spongioplasm exist as granules instead of a network, the granules at the periphery come in con- tact with one another thereby causing the periphery to be more dense than the rest of the protoplasm. This is noticeable in the case of the colorless corpuscles of the blood. A cell during its life history may undergo certain modification, and become an atypical cell, as in the case of the colored cor- puscle of the blood, which, in the early part of its life history, has the structure of a typical cell, but at a later period loses its nucleus. Another instance of an atypical cell would be where a cell never, during its life history, possesses all the essential structures of a typical cell, as in the case of the low form of uni- cellular organisms,theprotamoeba, which is similar to theproteus animalcule, commonly known as the amoeba, except that it has not a nucleus. A cell has certain functions known as vital, which are assimi- lation, elimination, growth, irritability, motion, and reproduction. 4 manual of normal histology. Assimilation is the act by which living bodies appropriate and transform into their own substance matters with which they may be placed in contact (Dunglison's Medical Dictionary). The matters thus acquired may be utilized for the nutrition of the cell; or stored up, as such or after certain modification, for future use. Elimination is the process by which the cell ejects the stored up substances when needed, and the products formed by the katabolic changes which are continually going on in a living cell. Growth is the natural sequence to the nutrition acquired by the cell during the process of assimilation. Irritability is the function by means of which a cell responds to stimulation from within the cell, or from without. This func- tion is highly developed in the cells of the nervous system. Motion is the process by means of which the portions of a cell are capable of changing their relation. This process, going on within a cell, may cause change in the shape or position of a cell. This function is highly developed in the muscle cells. In some cases the changes in shape of the cell allow7 the cell to pass from one place to another, producing movements similar to those produced by the proteus animalcule (amoeba); hence in such instances the movements are termed amoeboid movements. Reproduction is the function by which living bodies produce bodies similar to themselves. (Dunglison.) It may be brought about in one of tw7o ways : direct division, and indirect division. Direct division is where the nucleus simply divides into twro equal parts, followed by a similar division of the protoplasm, each division of the protoplasm enclosing a division of the nucleus, thus forming tw7o daughter cells. Indirect division is w7here the nucleus divides after a series of changes has taken place within it. The series of changes is spoken of collectively as karyokinesis. (Schleicher.) The process is also known as mitotic (Gr. p-tros, a web), the direct division being amitotic. The cycle of changes w7hich take place in karyokinesis may be briefly summarized as follows : I. The intranuclear network appears to consist of one fibrilla, which is closely coiled, giving the close skein stage (Fig. 2, a.) II. The skein becomes less compact, the fibrilla being arranged as a loose coil, giving the loose skein stage (£). At about this time MANUAL OF NORMAL HISTOLOGY. 5 the nuclear membrane disappears, and also the nucleolus, and in Cells from the growing tip of an onion, showing stages of karyokinesis. Fig. 2. a, close skein; b, loose skein; c. rosette; d, aster; <?, cleavage;./-, diaster; _g, di-rosette, and daughter nuclei; /?, daughter cells. the achromatic substance striations (fibres) appear, which start from a central point in each polar field, diverge and become con- tinuous with those of the opposite side, forming the achromatic spindle (Fig. 4, AY III. The loosely arranged skein becomes arranged around a central clear space, giving the rosette stage (c). IV. The filament now breaks into small portions, usually V-shaped, known as chromosomes, which are arranged with their apices toward the central clear space, giving an appear- ance somewhat similar to that of a star; hence this stage is known as the aster stage (<Z). V. Each of the chromosomes cleaves longitudinally, giving two V-shaped portions. This is known as the stage of cleavage (Fig. 4, AY VI. The chromosomes pass to the central particle of each'polar field, along the fibres of the achromatic spindle, one chromosome of each pair formed in the previous stage going to each central particle. This is known as the stage of metakinesis (Fig. 4, BY Fig. 3. Cells from the epidermis of a salamander. d, aster; f diaster; g, daughter nuclei. 6 MANUAL OF NORMAL HISTOLOGY. VII. The chromosomes at each polar field arrange themselves around the central particle, giving a star-like appearance at each pole of the nucleus. This is known as the diaster stage (/). VIII. The asters pass through the rosette, loose skein and A Polar radialton. -(Cytaster) attraction sphere central... particle' chromatin. -loop cleft Longctutjdinally cell substance' Polar radiation central..--'" particle' B Diagrams (after Rabi) showing the achromatic spindle (A) and the stage of metakinesis (2?). Fig. 4. close skein stages, respectively known as di-rosette, di-loose skein, di-close skein, and become daughter nuclei ((g). The protoplasm divides, while the asters are passing through the intervening stages to become resting nuclei, so that by the time that the asters have become daughter nuclei the protoplasm has divided, and two daughter cells have been formed (/z). The student after having procured the apparatus, as required for laboratory work, should examine carefully the staining dishes, slides, cover-slips, teasing needles, section lifter, etc. He should then take the microscope to which he has been assigned from its case and carefully examine its various parts: the foot (A) or base of the stand, by means of which the instrument rests firmly upon MANUAL OF NORMAL HISTOLOGY. 7 the table; the pillar (A), which is immovably attached perpendicu- lar to the foot; the arm (0, which is attached to the pillar by means of a hinge joint, (T) ,thus allowing the instrument to be bent at an angle; thesZzg<?(0 .which is attached firmly to the arm contain- ing in its centre an opening through which light reflected by the mirror (0 can pass; the iris diaphragm (0,by means of which the amount of light allowed to pass through its opening to that of the stage is regulated; the clips (2V), by means of which the slides Fig. 5. A, foot or base of stand; B, pillar; C, arm; Z), main tube; E, triple nose-piece; F, objec- tive lens; G, eye-piece or ocular lens; H, draw tube; J, rack; K, pinion; L, fine ad- justment screw; N, clip for holding slide upon the stage; O, mirror; P, mirror attach- ment arm; Q, substage attachment consisting of Abbe condenser and iris diaphragm; E, screw for lowering or raising the substage attachment; 5", stage; T, hinge joint. B B, Continental Microscope (Bausch and Lomb Opt. Co.) are held firmly on the stage; the main tribe (Z?), in the upper end of which telescopes the draw tube (77); the upper end of the draw tube, into which fits the ocular lens (0; the lower end of the main tube, into which is screwed the objective lens (F) or the nose-piece (E)-, the rack (7) and pinion (A') arrangement of the coarse adjust- ment screw, by means of which the lower end of the main tube (carrying the objective lens) is raised from or lowered toward the 8 MANUAL OF NORMAL HISTOLOGY. stage; the fine adjustment screw (A), by means of which the instru- ment is focused on the specimen; the screw (A), by means of which the diaphragm is lowered from or raised to the stage; the mirror- bar (P), by means of which the mirror may be regulated in order to reflect the light. He should then take the box or boxes con- taining the lenses from the microscope case, and examine and compare the lenses, noticing the eye-pieces (or oculars) and objec- tives, the number on each lens. He should at all times remember that the lower the number on the lens the lower the magnifying power. If the lens be designated by a fraction, the lower the numerical value of the fraction the higher the magnifying power. (N. B.-The student should appreciate the value of a microscope, and handle it as gently and take as much pride in its care as if it were his own property. When he starts to work in the laboratory he should take the instrument and its attachments from the case, examine carefully, and if anything be missing or injured notify one of the demonstrators. While using the instrument, he should not jam the objective lens against the stage or specimen, or roughly use the fine adjustment screw. Before leaving the lab- oratory he should remove the lenses from the instrument and replace them, as well as the microscope, in their respective cases. When using slides and cover-slips, he should be careful to have them clean. He should have a good sketch-book, in which he should sketch what he sees through the microscope. He should constantly bear in mind that in order to derive the most benefit from a course in practical histology one must be patient, exact, careful, and use clean apparatus.) After having studied the construction of the microscope, become familiar with its use by performingthe following experi- ments: Experiment 1. On a clean slide put a drop of water, in which place a few fibres of linen, and examine with the low power. Sketch the fibres as they appear. Look for air bubbles; if any be found sketch them. Endeavor to look through the micro- scope with the left eye, keeping the right eye open and looking upon the paper upon which you sketch. As you thus look, sketch the image as it appears to be seen upon the paper. eA 2. As in Exp. 1, prepare a few fibres of silk thread, examine with the low power, and sketch. Then remove the slide from the stage of the microscope, and carefully tease apart the fibres with teasing needles; cover with a cover-slip and examine, first with the low power, then with the high, sketching what is seen under each power. Exp. 3. On another slide put a drop of a strong solution of sodium chloride (table salt). Allow it to dry, then cover with a cover-slip and examine with both powers, low and high, and sketch the crystals as seen. Repeat the experiment using a MANUAL OF NORMAL HISTOLOGY. 9 weak solution of sodium chloride. Heating gently over the flame of a Bunsen burner or of an alcohol lamp will facilitate drying. Exp. 4. In the same manner as in Exp. 3, prepare, examine, and sketch crystals of potassium bichromate. Exp. 5. In order to measure specimens or portions of speci- mens a scale should be prepared as follows: Place a stage micrometer (Gr. auk/oos, small; to measure) (which is a slide upon which are ruled straight lines yVtf and tvo o' inch apart, or yy and yjjy mm. apart) upon the stage of the microscope, and with the left eye to the instrument and the right eye looking at a plain card on the desk near the foot of the microscope, examine with the high power. As the lines appear projected on the card, with a sharp-pointed pencil mark their apparent distance from one another, and rule later with ink. On the card, besides the distance of the lines apart, put the number of the eye-piece, that of the objective, and the length of the tube. The scale thus prepared should be frequently used during the course, care being taken that, when measuring objects, the eye- piece, the objective and the length of the tube be the same as when the scale was prepared. Exp. 6. On a slide put a small drop of milk, and cover with a cover-slip. Examine, measure, and sketch several oil globules, under high power. Exp. 7. If during the previous experiments you have been unable to observe air bubbles, put a drop of saliva on a slide, cover and examine. Sketch several air bubbles. Exp. 8. Examine a stained and mounted specimen of an onion tip, or of the larva of a salamander, or of a newt. Study and sketch a cell illustrating the typical structure of a cell. Exp. 9. In the same specimen as used in Exp. 8, look for and sketch cells showing the different stages of karyokinesis. 10 MANUAL OF NORMAL HISTOLOGY. CHAPTER H. THE BLOOD. The blood is a tissue, in which the cellular and the intercellu- lar substances are of equal importance; but as the intercellular substance is a liquid, the liquor sanguinis or plasma, it presents no characteristics when viewed with the microscope. Hence the histology of the blood consists of the study of its cellular elements, the corpuscles. The corpuscles of the blood are three in variety : The colored corpuscles. The colorless corpuscles. The blood plaques. The colored corpuscle, commonly known as the red cor- puscle, is a small biconcave disc, the average diameter of which is 7.7 m* or inch, and it is about one-sixth as thick as its diameter. Its surface view appears round; its edge view appears larger at the periphery than at the centre, giving an appearance somewhat similar to the variety of pastry known as "lady-finger." It consists of a pale yellow-colored mass of modified protoplasm, enclosed by a limiting membrane or cell wall, and does not possess a nucleus. The structure of the pro- toplasm of a colored corpuscle is still a debated question. The theory commonly held, and which has not been replaced, is that there is a highly elastic and pliable, apparently homogeneous network, termed the stroma, holding within its meshes the coloring matter, haemaglobin. Haemaglobin consists of color- less substance known as globulin containing a pigment termed hematin which is a dark brownish red amorphous substance containg all the iron of haemoglobin. If hematin be treated with hydrochloric acid a crystalline substance termed hemin or hydrochlorate of hematin, (Teichmann's crystals) is formed. As this occurs even with small quantities of old dried blood it is of of a millimeter. MANUAL OF NORMAL HISTOLOGY. 11 great importance in medico-legal cases. Special attention is called to a substance termed haematoidin which occurs as crystals in old blood-clots retained within the body, as in some cases the crys- tals can be seen in prepared sections of some of the organs of the body especially if the organs had been congested before death of the person or animal from whom the organ had been obtained. Singly the corpuscles appear pale yellow in color, while in balk they appear red. Although a colored corpuscle does not possess a nucleus, on examination an error of supposing it to contain a nucleus might arise due to the peculiar shape of the corpuscle The surface of the corpuscle being concave, when the microscope is focused on the centre the peripheral portion is not in focus; the centre appears bright, the periphery dark (Fig. 6, <5). On the other hand, when the instrument is focused on the periphery the central portion is not in focus; the periphery appears bright, the centre dark (Fig. 6, a). Thus the colored corpuscle appears to possess a nucleus due to an error of refraction. The colored corpuscle in its early stages of development, possesses a nucleus which it loses before it enters the circulation, and becomes a "metamorphosed" or atypical cell. In blood, soon after it is drawn from the body, the colored cor- puscles are attracted to each other, their concave surfaces coming in con- tact, giving an appearance similar to that of a roll of coin. This is known as the rouleaux condition (Fig. 7), which is physical, occuring only under abnormal circumstances, such as having the blood outside the vessel. A similar condi- tion can be produced by putting small pieces of cork, which have previously been covered with oil, into water. After a short space of time the rouleaux break apart, and the corpuscles float about singly. The colored corpuscle is elastic or pliable, as can be seen on examining a fresh specimen of blood. The cor- puscles may be observed to be squeezed through spaces left be- tween neighboring masses of cells (Fig. 8, a); or its elasticity can be observed on examining the circulating blood in a The colored corpuscle. a, periphery in focus; b, centre in focus. Fig. 6. Colored Corpuscles. a, rouleaux; b, edge view of a single corpuscle. Fig. 7. 12 MANUAL OF NORMAL HISTOLOGY. capillary network, when a corpuscle may be seen to be caught at the junction of two capillaries, part extending into one capillary, while another portion extends into the other capillary; ora corpuscle maybe seen to be squeezed along a capillary,the diam- eter of which is less than that of the corpuscle. The colored corpuscles are very numerous, as estimated by means of the haema- cytometer (Gr. ut/za blood; kvtos cell; p.erpov to measure), being about five million to the cubic millimeter in man, and about four million five hundred thousand in woman. The colorless corpuscle, also known as the white cor- puscle or leucocyte (Gr. Xevxos, white ; kvtos, cell), although found in'the blood, is not restricted to it, and may be found in other tissues of the body, especially in the lymphoid structures. It consists of a gelatinous, more or less granular mass of proto- plasm, in which is imbedded a nucleus, and sometimes more than one nucleus. A leucocyte which contains one nucleus is termed a mononuclear, and one containing two or more nuclei as a polynuclear corpuscle. The leucocyte is a living mass of protoplasm, and is enclosed by a slight condensation of the peripheral portion of the proto- plasm, which may be considered as a cell wall.* The limiting membrane, probably formed by granules of spongio- plasm in close contact, is thin, and allows the corpuscle to assume various shapes due to the movements of the enclosed protoplasm. (See Chapter I.) The leucocyte possesses the power of movement to a high degree. At rest it is round (Fig. 10, a); in motion it assumes various shapes (Fig. 10, £), thrusting out Fig. 8. Fig. 9. Showing elasticity of colored corpuscles. One corpuscle (a) being squeezed, by the current in a freshly prepared specimen of human blood, between two others (b' and b) after being squeezed through the narrow space, it again as- sumes its normal shape. Crenated colored corpuscle Fig. 10. Leucocytes of a freshly drawn specimen of blood. a, at rest; b, in motion. *The author hesitates in asserting that the colorless corpuscle of the blood has a limiting membrane on account of the authorities who assert that it has not. Owing to his own obser- vations, after using various stains he finds that the periphery stains darker than the rest of the protoplasm, hence concludes that the cell has a limiting membrane composed of the granules of the spongioplasm arranged in one layer or more, the granules being in close contact. MANUAL OF NORMAL HISTOLOGY. 13 arm-like projections, pseudopodia (Gr. false; ?ro8es feet), resembling in its movements those of an amoeba; hence the movements are termed amoeboid. The leucocytes are larger than the colored corpuscles, their average diameter being or tAtt inch, but fewer in number, the proportion being about one leucocyte to from three hundred and fifty to five hundred colored corpuscles. The proportion of leucocytes in the blood increases during digestion; diminishes during a fast. As a rule, they are more numerous in venous than in arterial blood. Hemorrhage increases the proportion of the colorless corpuscles to the colored. If freshly-drawn blood be mixed with a few torulae, and the preparation be kept warm by means of a warming stage, the leucocytes thrust out arm-like processes, termed preudopodia, which enclose the torulae. In this manner it is supposed that the colorless corpuscles have the power of taking up substances, and carrying them to be utilized or eliminated. This power of swallowing gives to the leucocytes, which act so, the name phagocytes (Gr. to devour; kvtos, cell). The leucocytes, owing to their ability to perform amoeboid movements, are capable of passing out from the blood vessels into the tissues, and vice versa, and are then known as wandering cells, and may be appropriately termed planetocytes (Gr. -n-XavyTos, wandering; xvros, cell). The human leucocyte acts like an amoeba under favorable conditions, being most active at 38° to 40° C., sluggish at 20° C. Its move- ments are accelerated by an alkaline or neutral medium; retarded and stopped by an acid medium. ""CLASSIFICATION OF THE LEUCOCYTES. The leucocytes of normal blood may be divided into the following types : * In order to understand the classification of the leucocytes, it is necessary to know something about the predilection of certain granules of the protoplasm for certain stains. The dyes which are used for staining blood may be classed under three heads, acid, basic and neutral. Acid Dyes are those which have an acid reaction, examples of which are Orange G., Acid Fuchsin, and Eosin. The granules of the protoplasm which take up the acid dyes are said to be Eosinophilic or Oxyphilic. Basic Dyes are those which have an alkaline reaction, examples of which are Methylene Blue, Methyl Green and Dahlia. The granules which take up the basic dyes are said to be Basophilic. When one of the basic dyes is added to an acid dye a neutralization occurs, a precipitate is formed which will stain structures not distinctly colored by either of the dyes which have been brought together. The granules of the protoplasm which stain with this neutral stain are said to be Neutrophilic or Amphophilic. The neutral color obtained as just mentioned is soluble in an excess of the acid dye ; therefore, if care be taken, a staining fluid can be obtained which would have three color values-acid, basic and neutral. Methyl green con- tains two extra radicals which can unite with acid or acid dyes. This is the principle involved in making up Ehrlich's triacid stain, in which one radical of methyl green unites with orange G., the other with acid fuchsin. 14 MANUAL OF NORMAL HISTOLOGY. Lymphocytes.-Forming about 22 to 25 per cent, of the leucocytes, and varying in size from about 7.5 p to 14 p. The smaller ones are known as small lymphocytes, while the larger ones are known as the large lymphocytes. The nucleus nearly fills the cell. Large mononuclear cells.-Forming about 1 per cent, of the leucocytes, and varying in size from about 14 p to 20 p. They possess each an oval nucleus and quite a broad rim of protoplasm. By some they are classed as large lymphocytes. Transitional cells.-Forming about 2 to 4 per cent, of the leucocytes, and are about the size of the preceding type. The nucleus tends to assume a horseshoe shape. Polymorphonuclear neutrophile cells.-Forming about 65 to 75 per cent, of the leucocytes, and are about 10 m in diam- eter. The nucleus may be of an irregular form, usually S shaped, or may consist of several oval portions connected together by delicate chromatic threads. In some cases it is impossible to observe any chromatin filaments connecting the oval portions, thus presenting an appearance of several nuclei, giving a poly- nuclear type of leucocyte. In the protoplasm there are small neutrophile granules. Fosinophile cells, occurring in small numbers, about 2 to 4 per cent, of the leucocytes, and are very similar to the pre- ceding type in size and shape of the nucleus. They are the most actively amoeboid of all the leucocytes and are character-' ized by the presence in the protoplasm of large, coarse granules, which stain readily with the acid dyes, as acid fuchsin and eosin. Basophile cells, being also known as Mast cells, are very few in number, being about .5 per cent, of the leucocytes. They are about the size of the colored corpuscle, and contain in the protoplasm irregular shaped granules, which stain readily with basic dyes, as methylene blue, methyl green and dahlia. The blood plaques of Bizzozero, the third variety of blood corpuscles, are flat, circular colorless particles 2 p to 3 p in diam- eter, or about one-third the diameter of the colored corpuscle, and are present in the proportion of about 1 to 30 colored cor- puscles. These corpusclescan most readily be observed in blood circulating in a capillary network, but may be observed in drawn blood, especially if the blood be drawn into a preserv- ing fluid containing sodium sulphate or osmic acid. If a drop of blood be allowed to coagulate, on microscopical examination a network of fibrin can be observed. Fig. 11. Leucocytes (stained with Wright's stain.) a, Polymorphonuclear cell; b, small lymphocyte; c, large lym- phocyte ; d, transitional cell; e, blood plaques. Fig. 12. A, a specimen of human blood stained with haematoxylin and eosin ; B, a specimen of frog's blood stained in the same way. a, human colored corpuscles ; a1, colored corpuscles of frog showing nuclei; b, transitional leucocytes; c, large mono- nuclear cell; d, polynuclear cell; e, eosinophile ; /, small lymphocyte. Fig. 48. A portion of an injected specimen of voluntary muscle. a, low power; b, high power; a1, artery which ramifies be- tween the muscle fibres (m). Fig. 97. Portion of a transverse section of a cat's small intestine, the arteries of which have been injected, showing the arrange- ment of the vessels in the different coats. z/, villi; /, tunica propria ; m, muscularis mucosae; 5, submu- cosa ; r, circular layer of muscular coat; a, connective tissue between the two layers of muscular coat; b, longitudinal layer of muscular coat; <?, serous coat. Fig. 124. Portion of a section of an injected lung of a dog, showing capillary network between the alveoli. PLATE FIG. 97 FIG. 124 MANUAL OF NORMAL HISTOLOGY. 15 THE ACTION OF REAGENTS ON THE BLOOD CORPUSCLES. After freshly-drawn blood has been kept on a slide for a short space of time the colored corpuscles become shrunken or shriveled up, giving an appearance known as crenated. This condition may also be brought about by passing a stream of air under the cover slip, or by treating blood with a solution of sodium chloride. ' causes it to swell, lose its discoidal form and become spherical. At the same time the coloring matter passes out, leaving an almost trans- , parent limiting membrane, the 1 ' ghost ' ' of the corpuscle. ' the amoeboid movements cease, the processes of the cell are retracted, the cell becoming spherical. The protoplasm becomes more granular, the granules exhibiting the Brownian movements due to being suspended in a liquid of less den- sity than that of the plasma. The nucleus appears clear or slightly granular. Swelling of the cell may be so great as to cause rupture. on the colored corpuscle, acts similar to water. on the colorless corpuscle, the protoplasm becomes clear, and the nucleus more pronounced. ' weak solution-the coloring matter escapes and coagulates, adhering to the limiting membrane. strong solution-the coloring matter coagulates within the corpuscle, and presents the appearance as if the corpuscle pos- sesses a nucleus. ' causes crenation of colored corpuscles. . no effect on colorless corpuscles, causes marked crenation of the colored corpuscles. . causes slight shrinkage of the colorless corpuscles. weak solution... strong solution on the colored corpuscle.. on the colorless corpuscle Tannic acid, on the colored corpuscle '■ Acetic acid.. Sodium chloride. Water 16 MANUAL OF NORMAL HISTOLOGY. The coloring matter of the colored corpuscle may also be driven out of the corpuscle by heating the blood to a temperature of about 60° C. ; by freezing and thawing the blood ; by chloro- form or ether vapor, and by introducing the serum of one animal into the blood of another, which is probably due to a difference in density or alkalinity. Experiment 10. After having cleaned a slide and a cover-slip, prick with a sharp-pointed needle the end of a finger, or the lobe of an ear. Press the cover-slip against the bleeding point, and quickly put upon the slide, so that the drop of blood will be be- tween the cover-slip and the slide Examine with the high power. (a) Notice the numerous colored corpuscles ; the color of a single corpuscle. Sketch a colored corpuscle seen flat, and one seen in profile. Measure two or three. (b) Focus on the periphery of a colored corpuscle, then on its centre, and sketch. (c) Notice and sketch rouleaux, (d) Look for colorless corpuscles, and notice the scarcity of, and the difficulty experienced in finding them. (e) Compare a colorless corpuscle with a colored one, noticing the difference in size and color. Measure two. (f) Look for crenated colored corpuscles and blood plaques. The best results can be obtained by using the r? objective. Exp. 11. A fresh specimen of blood should be obtained, as in Exp. 10, the cover-slip taken off, and the specimen laid aside for ten minutes, then examined. Notice and sketch a portion of the network of fibrin. Exp. 12. Stain a specimen of blood by Ehrlich's, Jenner's, or Wright's method (see appendix). Look for colored corpuscles, the different types of leucocytes, and blood plaques, and sketch several when found. Notice the darker-stained rim at the periphery of the protoplasm of the leucocytes. Sketch. Exp. 13. Stain, mount, and preserve a specimen of blood as follows : Obtain a fresh specimen of blood on a cover-slip as in Exp. 10, and put the cover-slip against another slip, so that the blood will be between the slips. Press them firmly together, and gently draw apart, and pass them through the following process : 1. Put into alcohol (95 per cent.) for thirty seconds. 2. Transfer to haematoxylin for two to three minutes. 3. Rinse in distilled water. 4. Then into eosin for two minutes. 5. Rinse in distilled water. 6. Transfer to alcohol (95 per cent.) for one minute. 7. Blot with bibulous paper. 8. Put on a drop of balsam, and gently lower the slip upon the slide, and label. MANUAL OF NORMAL HISTOLOGY. 17 Sketch several of the colored and colorless corpuscles. Look for an eosinophile. If the specimen be not colored enough, it may be left a longer length of time in either or both stains, as the time required for proper staining depends upon the strength of the staining solu- tions used. Exp. 14. A fresh specimen of blood should be examined on a warming stage (using an oil-immersion objective lens), and the ameboid movements of the colorless corpuscles closely observed. Sketch various shapes which you see. Instead of human blood, the blood of a frog can be used without the need of a warming stage. Exp. 15. Estimate the number of colored and colorless cor- puscles in a cubic millimeter by means of a haemacytometer* under the supervision of one of the demonstrators. Exp. 16. Notice and sketch the effects produced on the cor- puscles of the blood by a solution of sodium chloride; by water; by acetic acid; by tannic acid (weak and strong solutions.) *A description of the haemacj'tometer and its use is given in the appendix. 18 MANUAL OF NORMAL HISTOLOGY. CHAPTER HI. EPITHELIUM. Covering the exterior of the body and those surfaces (mucous membranes) which are directly or indirectly continuous with the exterior, there is a tissue termed epithelium. This tissue is com- posed principally of cells, which rest on a condensed portion of the underlying connective tissue, which condensed portion is termed the membranapropria, or basement membrane. The intercellular portion of the tissue is very scanty, consisting of cement sub- stance sufficient to hold the cells together. Epithelium pos- sesses no blood vessels, its nourishment being obtained by absorp- tion of nutritive material by the cells from the neighboring tissue. Nerves have been demonstrated between the epithelial cells, but it is as yet doubtful whether they terminate between or within the cells. When the epithelium consists of a single layer of cells it is termed simple epithelium; when it consists of several layers it is termed stratified epithelium. Of each kind there are two varie- ties depending upon the shape of the cells, which are squamous (L. squama, a scale) and columnar. Of each variety there may be modified forms, giving modified epithelium. The classification of epithelium: (squamous 1 columnar. Simple Stratified ( squamous 1 columnar. Modified transitional epithelium goblet cells, ciliated ephiehelium. { cuboidal I rod I neuro I glandular MANUAL OF NORMAL HISTOLOGY. , 19 Simple squamous epithelium.-This type occurs as a single layer of scale-like cells, each cell being flat, polygonal in shape, possessing a cell wall and a nucleus. When viewed in their undisturbed relation, they present an appearance similar to that presented by a pavement; hence this type of epithelium is sometimes termed pavement or tessellated. This type of epithelium occurs only in a few localities, the chief of which are the alveoli of the lungs and the Malpighian bodies of the kidneys. Stratified squamous epithe- lium.-This type of epithelium is composed of several layers or strata, the topmost consisting of squamous cells. The lowest stratum, that resting upon the basement membrane, is composed of cells which are irregular cuboidal in shape. There is a gradual change in shape from the cu- boidal to the squamous in the successive strata passing from the lowest layer to the free sur- face. Depending upon the surrounding conditions, the topmost layers may be com- posed of cells containing proto- plasm and nuclei, or of cells which have lost their nuclei, and whose protoplasm has been converted into a horny-like material, termed keratin, the cells appearing as horny threads. The former type of stratified squamous epithelium occurs as a covering to those surfaces which are kept moist by secretions, as in the mouth, oesopha- gus, vagina, etc. The latter type occurs where the tissue is exposed to the atmosphere, as on the skin. Stratified squa- mous epithelium occurs more widely distributed in the body Fig. 14. Surface view of stratfied squamous epithelium of a frog's skin, show- ing the tessellated arrangement and a stoma (s). 20 MANUAL OF NORMAL HISTOLOGY. than the simple squamous variety, its chief localities being on the lining membrane of the mouth, oesopha- gus, and vagina and on the skin. Simple columnar EP ITHKLIU M.-This type occurs as a single layer of cells resembling in shape small cylinders or columns. Each cell has a distinct nucleus, cell wall, and reticular protoplasm. On the free border of some of the columnar cells there is a striation, the striations running for a short dis- tance perpendicular to the free border, giving a striated border or cubical ar seam. The cells of the small intestine have the striated border. Probably the striae have an impor- tant bearing on the physio- logical process of absorp- tion, and are little canals leading from the free surface of the cell to its interior, dividing the border into cubical masses of proto- .plasm. The chief localities where simple columnar epithelium occurs are the stomach and the intestines. Stratified columnar epithelium.- This type consists of several layers or strata of cells, the topmost of which is composed of columnar-shaped cells; the lower layers of irregular polygonal-shaped cells. This variety occurs in few localities, the chief of which being the vas deferens. Modified epithelium usually occurs as modifications of simple or stratified columnar epithelium : Fig. 15- Stratified squamous epithelium of a specimen of human vagina. a, uppermost layer consisting of flat cells; c, lowest layer consisting of cuboidal shaped cells: b, the in- tervening strata consisting of irregular shaped cells; rf, basement membrane. Fig. 16. Simple columnar epithelicem of the intestine of a • rabbit. a, isolated cells obtained bv teasing; b, a layer of cells in situ; s, striated border or cubicular seam. Fig. 17. Stratified columnar epithe- lium of the vas deferens of a dog.' a, uppermost layer of cells (columnar); c, lowest layer (cuboidal); b, middle layer (irreg- ular). MANUAL OF NORMAL HISTOLOGY. 21 There is a type of stratified epithelium known as tran- sitional epithelium, on account of the cells of the lower layers rapidly assuming the form of the cells of the top- most layer. The topmost layer consists of cells which are flat with depressions in their under surface to fit over the large ends of the pear-shaped cells of the next layer. This type of epithe- lium appears to be a modification of stratified columnar epithelium, in which some of the cells of the columnar layer (pear-shaped) ex- tend out and become flattened against the remaining pear-shaped cells, the under surface of the flat- tened cells becoming molded over the upper ends of the cells of the underlying layer. This type is found in the ureter, bladder, and the prostatic portion of the urethra. Ciliated epithelium in the human body is a modified form of simple or stratified columnar epithelium. The ciliated simple col- zcmnar type is found in few localities, the chief of which being the ventricles of the brain, the central canal of the spinal cord, and the oviducts. The ciliated stratified columnar type is found in the trachea and the epididymis. The cilia are protoplasmic projections from the free border of the cell, being about twenty to each cell, The length of the cilia varies, de- pending upon the locality of the cells. In the epididymis, the cilia are longer than those of the trachea. The cilia possess the power of movement. The movements are of two kinds : a primary or sudden, and a secondary, which is the gradual return of the cilia to their original position. One cilium moves ; the motion is taken up by the next cilium, and so on, giving a resemblance to a field of wheat as a flaw of wind passes over it. The cilia act most readily at the temperature of the body, and act sluggish if the temperature be gradually lowered, ceasing to act Fig. 18. Transitional epithelium of the bladder of a rabbit. a, uppermost layer consisting of large flattened cells; b, middle layer com- posed of pear shaped cells; c, cuboidal shaped cells resting upon a basement membrane making up the lowest layer. Fig. 19. Ciliated epithelial cells isolated by teasing from the trachea of a rabbit. a, columnar shaped cells; c, cilia; g, goblet cells expelling mucus. 22 MANUAL OF NORMAL HISTOLOGY. at 0° C. Their action is increased if the temperature be raised to42°-46° C., and influ- enced by the presence of oxygen. Among the waste products formed during their activity is carbon dioxide. Nar- cotic reagents, as chlo- roform and ether, cause their movements to be come sluggish. Poisons, such as nicotine, when constantly applied to the cilia, retard their movements and eventually cause their cessation and death. Goblet CELLS are modified forms of culumnar cells, and may occur in simple columnar epithelium (intestines) or in the top- most layer of stratified columnar epithelium (trachea). The goblet cells originally exist as columnar-shaped cells whose pro- toplasm contains mucigen. The cell absorbs water, which acts on the mu- cigen, forming mucin, which causes a swelling of the protoplasm to such an extent that the cell wall ruptures. The rupture takes place at the free border of the cell, that being the place of least resistance. The rupture of the cell wall allows the mucin to escape, the cell remaining somewhat goblet-shaped, with its protoplasm and nucleus in the portion of the cell near the basement membrane. There are other forms of modified epithelium, such as the cuboidal, which is composed of a layer of cube-shaped cells, modified forms of columnar cells; rod epithe- lium, which are columnar-shaped cells, striated at their outer border; "glandular epithelium," and "neuro- epithelium," which are modified for the purpose of performing special functions. Fig. 20 Ciliated stratified columnar epithelium. A, of the trachea of cat; B. of the epididymis of a rat; a, columnar shaped cells; c, ciliated border; g, goblet cell. Fig. 21. Rod epithelium. a, of a convoluted tubule of the kidney; b, of a duct of salivary gland. Specialized epithelium. Fig. 22. a, glandular epithelium of an acinus of a mucous gland; b, neuro-epi- thelium of a taste bud of the tongue of a rabbit. MANUAL OF NORMAL HISTOLOGY. 23 ENDOTHELIUM. Endothelium is a tissue similar to simple squamous epithelium, but occurs as a lining to the cavities which are not continuous with the exterior of the body. It is found lining the serous cavities, blood-vessels and lym- phatics. It consists of a layer of flat poly- gonal-shaped cells, held together by cement sub- stance. In the cement substance are small openings, known as sto- mata, and collections of cement, known as pseu- do-stomata, or stigmata. Stomata arc not re- stricted to endothelium, as they may exist in epithelium, and may be found in the cement substance between the cells on the surface of the skin of a frog (Fig. 14), and between the cells (simple squamous epithelium) lining the alveoli of the lungs (Fig. 24). Therefore, the main difference between endothelium and simple squamous epithelium is one of location, the former existing as a lining to cavities not exposed to the atmosphere (serous cavities and vessels); the latter as a lining to some of the surfaces which are in com- munication with the exterior of the body. Experiment 17. Put a drop of saliva on a clean slide, cover, and examine. Look for the squamous cells. When found, notice the distinct cell wall, the nucleus, and the protoplasm. Measure and sketch several. If any be found united together, sketch them. Look for salivary corpuscles, and notice the Endothelium from mesentery of a cat. c, endothelial cell; n, nucleus; s, stoma; j1, stigma; jf, rim of small granular cells around the stoma. Fig. 23. Several alveoli of the lung of a kitten which has been stained with silver ni- trate, showing the outlines of the simple squamous cells in which are stomata (r) and stigmata (r1). Fig. 24. 24 MANUAL OF NORMAL HISTOLOGY. similarity which exits between them and the colorless corpuscles of the blood. Notice the air bubbles. Allow a drop of eosin to run under the cover-silp, and examine the specimen again. Exp. 18* Examine a strip of skin which has been peeled from the body of a frog, stained with haematoxylin or carmine, and mounted. Notice the pavement-like arrangement of the cells. Eook for stomata. Sketch. Exp. 19. Stain with haematoxylin, and mount a section of mucous membrane of the vagina cut perpendicular to the surface, or one of the tongue, or of the oesophagus. Examine with the high power and notice the cells arranged in layers or strata. Notice the gradual change in shape from the cuboidal to the flat, as you examine the successive layers from the basement mem- brane to the surface. Notice that the cells on the surface possess nuclei and protoplasm. Sketch. Exp. 20. Examine a section of human skin cut perpendicular to the surface, stained and mounted. Notice the difference between the topmost layers and those of the specimen used in Exp. 19. Exp. 21. Upon a clean slide put a drop of glycerin, and into it put the scraping from the inner lining of a small piece of a rabbit's intestine which has been in a solution of potassium bichromate for twenty-four hours. With teasing needles tease apart the scrapings ; add a drop of haematoxylin, and examine. Notice the simple columnar cells held together and singly. Measure and sketch. Cement the cover-glass and label. For a temporary mount the scrapings may be put into a drop of water or normal salt solution on a slide, covered and examined. Exp. 22. In the same manner as in Exp. 21, prepare simple columnar epithelium from a frog's intestine. Examine and sketch. Exp. 23. Examine the scrapings from the lining of a rabbit's bladder obtained as in Exp. 21. Examine and sketch some of the pear-shaped and surface cells. Exp. 24. Examine a stained section of a rabbit's bladder or ureter, the section having been cut perpendicular to the surface. Sketch the transitional epithelium as seen in situ. Exp. 25. Examine a stained transverse section of the trachea, epididymis, or Fallopian tube. As in Exp. 21, prepare scrap- ings from a cat's trachea. Eook for ciliated and goblet cells. Sketch. Exp. 26. Examine the scrapings from the tongue of a living frog which have been teased apart in a drop of a dilute solution of potassium bichromate on a slide- Look for cilia in action, *The methods for preparing specimens are given in the appendix. MANUAL OF NORMAL HISTOLOGY. 25 and notice that the ciliated cells are squamous and not columnar, as in the human body. Exp. 27. Examine a stained transverse section of the trachea or of the small intestine. Look for and sketch goblet cells. Exp. 28. A piece of the frog's mesentery should be rinsed in distilled water, then treated with a 1 per cent, solution of silver nitrate, rinsed again, put into alcohol and exposed to the sun- light. When of a brown color, it should be removed from the alcohol, carefully spread upon a clean slide and mounted with balsam. Examine for endothelial cells. Notice that the cement substance is stained brown, showing the outlines of the cells. Look for stomata and stigmata. Sketch. 26 MANUAL OF NORMAL HISTOLOGY. CHAPTER IV. SUPPORTING TISSUES. In progressive evolution, as we pass from the study of the uni- cellular organisms to that of the higher classes of animals, we find certain tissues set apart for the performance of definite func- tions. There is one set of tissues for the purpose of assimila- tion, another for elimination, another for motion, etc. To bind the various sets of tissues together, furnishing a means of con- nection and support, there is a set of tissues termed by some connective ; by others, supporting. To avoid the confusion which might arise by giving to a set of tissues, and a subdivision of the set, the same name, in this work the term supporting is applied to the set of tissues, reserving the term connective for a subdivision of the set. The supporting tissues may be arranged in five classes: 1. Connective tissue. 2. Anomalous connective tissue. 3. Cartilage. 4. Bone. 5. Dentine. These tissues are derived from the mesoblast of the embryo, and have a genetic relation; i. e., as a rule, cartilage replaces connective tissue, which in turn is replaced by bone. This rela- tion can be better seen by observing analogous structures in different animals. In the human subject the tendo Achilles is composed of connective tissue; in the frog it is composed of cartilage; in fowls the tendons of the leg muscles are composed of bone. In these tissues the cellular elements are more or less similar, while the intercellular substance varies. In the supporting tissues of the embryo the cellular elements are numerous and can be easily observed, while the intercellular substance is scanty. As the tissues pass on to their adult forms, the cellular elements become less conspicuous; while the intercellular substance be- MANUAL OF NORMAL HISTOLOGY. 27 comes greater in amount and more conspicuous, so that in the adult forms of the supporting tissues the intercellular substance is more abundant and seems to be of more importance than the cellular. Depending upon the requirements of the tissues, the intercellular substance may be tough, elastic, resistant or hard. CONNECTIVE TISSUE. This variety of supporting tissue is widely distributed through- out the body, and consists of cells termed connective tissue cor- puscles, and an intercellular substance composed of fibres. Connective tissue is arranged into five varieties : White fibrous. Yellow fibrous or elastic tissue. Areolar. Adipose. Retiform. White fibrous connective tissue occurs chiefly in tendons. It is composed of parallel bundles of fibres. The fibres are composed of smaller fibres termed fibrillae, which are held together by cement sub- stance. A fibrilla appears as a fine, delicate, wavy line, is 0.5 Mo 1 or to Tjinriyinch in diam- eter, and does not branch. Although a fibrilla does not branch, it may appear to branch; the fibrilla in such a case extends from one fibre into a neighboring one. Between the fibres are the connective tissue cor- puscles, which appear flat on surface view, and appear to possess projections when seen on edge view ; the projections of the cells and the cells separate the neighboring fibres from one another. On cross-section a tendon would be seen to be composed of bundles of fibres, fasciculi, each fasciculus composed of fibres between which are the connective tissue corpuscles, and each fibre composed of fibrillae between which is cement sub- White fibrous tissue from a tendon of rat's tail, a, obtained by teasing in dilute salt solution; b, by staining; c, connective tissue corpuscles; f, fibrillae. Fig. 25. 28 MANUAL OF NORMAL HISTOLOGY. stance. Between the fasciculi is'areolar connective tissue. The white fibrous tissue yields gelatin on boiling. When treated with acetic acid the fibres become swol- len and indistinct. White fibrous tissue is tough, inelastic, opaque and glistening white. Yellow fibrous tissue, some- times termed elastic tissue, is found chiefly in the ligaments. It also occurs in blood-vessels, being well marked in the large arteries. It consists of bundles of fibres; the bundles and the component fibres branch. The bundles of fibres are smaller than those of the white variety. The fibres are composed of smaller fibres, the fibrillae, which, as compared with the fibrillae of the white fibrous tissue, are larger, being to -jkSit inch a. transverse section of white fibrous connective tissue from a specimen of the skin of the finger; f, areolar con- nective tissue surrounding a bundle or fasciculus (b) of fibres; c, connec- tivetissue corpuscles of white fibrous tissue, dividing off the fibrillae into fibres. Fig. 26. Fig. 27. Yellow fibrous tissue from the ligamentum nuchae of an ox. a, a fresh specimen teased apart showing the fibrillae; b. branching fibrillae; c, a transverse section of ligamentum nuchae showing cross sections of the fibrillae (d),- f, net work of areolar connective tissue; w, nucleus of connective tissue corpuscle. in diameter ; have more distinct outlines ; possess pronounced curves, and branch. On transverse section each fibrilla can be distinctly seen. This variety of tissue is tough, elastic and of a yellowish color, and contains an albuminoid substance termed elastin. MANUAL OF NORMAL HISTOLOGY. 29 Elastic tissue (yellow-fibrous), in some instances, instead of being disposed in bundles, forms a network, in which are small spaces, giving a fenestrated membrane. If there be no spaces left between the fibres, a membrane is formed, such as Descemet's membrane of the eye. Areolar tissue consists of white and yellow fibroustissue, the former predominating. The fibrillae, instead of being arranged in parallel bundles, run in all directions, form- ing a delicate, close-meshed network. In the network some of the fibrillae may be collected together form- ing fibres. Connective tis- sue corpuscles exist in the network, occupying irregu- lar-shaped spaces between the fibrillae. Adipose tissue is areolar tissue, in which the connective tis- sue corpuscles have been invaded by fat. Small globules of fat are deposited in the protoplasm of the connective tissue corpuscles and coalesce, the amount increasing to such an extent that the protoplasm and the nucleus are ■pushed toward the cell wall. If the tis- sue be treated with ether the fat will be dissolved, and the protoplasm and nu- cleus of each cell will be seen as a layer closely applied to the cell wall. Retiform tissue is similar to areolar tissue, except that the fibrillae form a loose network instead of a close one. Fig. 28. Areolar connective tissue obtained from the subcutaneous tissue of a cat, stained J.; with haematoxylin. a, bundle of white fibrous tissue; b. net- work of fibrillae; c. connective tissue corpuscle; e, elastic fibres. Fig. 29 Adipose tissue from the mesentery of a cat. a, fat cells; a', fat crystals; b, fat cells more highly mag- nified showing protoplasm and nucleus pushed to the cell wall; f, areolar tissue network containing con- nective tissue corpuscles. 30 MANUAL OF NORMAL HISTOLOGY. ANOMALOUS CONNECTIVE TISSUE Anomalous connective tissue is connec- tive tissue which, while passing from the embryonal to the adult form, becomes arrested in its development, or has diverged from the normal mode of development. There are three varieties : Embryonal connective tissue of an embryo-pig. c, connective tissue corpuscle; a. capillary containing blood corpuscles. Fig. 30. Myxomatous. Vitreous. Adenoid. Vitreous tissue (L. vitrum, glass) starts as a mass of cells, which secrete an albuminous intercellular substance, and then disappear. As the structure of this tissue cannot be seen with the microscope, it is said to have no histological structure. It occurs as the vitreous humor of the eye. Myxomatous (Gr. mucous; like), or mucoid tissue, starts as a mass of cells, which secrete a mucous-like intercellu- lar substance, and branch, the branches joining neighboring branches. The tissue consists of a network of branching cells, between which is a mucous-like secretion, and is found in the umbilical cord as the "jelly of Wharton." Adenoid (Gr. a gland) tissue consists of cells which send out projections, which join and form a network. In many instances the cells cannot be recognized, and appear as en- largements on the fibres of the network. Lymphoid tissue is adenoid tissue in the meshes of the network of which there are lymph corpuscles. Experiment 29. Take a tendon from the tail of a recently-killed rat, and notice that it is composed of bundles of fibres. Tease apart a fibre in a normal solution of sodium chloride on a slide, being careful while teasing to tease the fibre lengthwise, and Fig. 31. Myxomatous tissue obtained from a human umbilical cord. A portion of splenic pulp showing adenoid tissue (a) and lymphoid tissue (6). Fig. 32. MANUAL OF NORMAL HISTOLOGY. 31 examine with the high power. Notice the wavy fabrillae. Notice that they do not branch. Sketch. Exp. 30. Take a fresh fibre and place it into a normal solution of sodium chloride for about fifteen minutes, then transfer to alcohol (95 per cent.) for ten minutes, water for one minute, haematoxylin for three minutes, water for thirty seconds, alco- hol (95 per cent.) five minutes. Carefully place the fibre upon a slide, put upon it a drop of balsam, and cover. Look for and sketch the connective tissue corpuscles. Exp. 31. Tease apart in a drop of normal saline solution on a slide a piece of the ligamentum nuchae of an ox. Notice the difficulty experienced in teasing it apart, and the elasticity of the fibres and fibrillae. Examine with the high power, and notice the distinct outlines and curves of the fibrillae. Look for branched fibrillae and cross-striations on the fibrillae. Sketch. Exp. 32. Examine and sketch a stained cross-section of the ligamentum nuchae. Notice the shape of the sections of the fibrillae, and the network of areolar tissue containing connective tissue corpuscles, between, and holding together, the fibrillae. Sketch. If a cross section of the ligamentum nuchae is not available, cross sections of yellow fibrous tissue can be observed in stained sections of the spleen (or lymph glands). Exp. 33. From a recently-killed animal obtain a small piece of the mesentery and spread upon a clean slide. Moisten with normal saline solution, cover and examine with the high power. Notice the membraneous structure of areolar tissue. Look for yellow fibrous tissue. Sketch. Keep the specimen for Exp. 35. Exp. 34. Stain another piece of mesentery with silver nitrate, mount and examine. Notice the irregular shaped clear spaces for the connective tissue corpuscles in the brown-stained mem- branous network. Exp. 35. Look for adipose tissue in the specimen used in Exp. 33. Measure the fat cells and sketch. Exp. 36. Examine a piece of adipose tissue which has been in ether for twenty-four hours, and then stained with haematoxylin. Notice the cells with the protoplasm and the nucleus arranged as a layer against the cell wall. Sketch. Exp. 37. Sketch a portion of retiform tissue as seen in a stained and mounted section of the spleen. Exp 38. Stain with haematoxylin and mount a transverse sec- tion of the umbilical cord. Examine and sketch the jelly of Wharton. Exp. 39. Examine the specimen used in Exp. 37 for adenoid tissue. Sketch. 32 MANUAL OF NORMAL HISTOLOGY. CARTILAGE. Cartilage is a more dense form of supporting tissue than the connective tissues. It is opaque, of a bluish-white appearance in thick slices, transparent in thin slices. It may be easily cut,and is flexible, firm and somewhat elastic. When allowed to dry it loses about three-fifths of its weight, showing that about 60 per cent, is water. In the embryo, cartilage is widely distributed. That which is replaced by bone as the embryo advances in its life history is termed temporary cartilage, and that which is not replaced by bone is termed permanent cartilage. In the embryo, cartilage consists of cells in contact with each other ; but as the cartilage passes on to the adult form the cartilage cells increase in number and deposit the intercellular substance, so that in adult cartilage the cells and the intercellular substance are of equal importance. Cartilage is usually covered by a membrane termed the perichondrium, which is tough and vascular, afford- ing protection and nourishment to the cartilage. Depending upon the structure of the intercellular substance, cartilage is divided into three varieties : Hyaline Cartilage. White fibro-cartilage. Yellow fibro-cartilage. Hyaline (Gr. vaXtws, glassy) cartilage occurs more widely distributed throughout the body than either of the other varieties, its chief localities being on the ends of bones, as articular and costal, in the nose and the trachea. It consists of cells imbedded in an intercellular substance termed the matrix. The matrix appears as a homogeneous substance, which has a glassy appear- ance, and in some instances appears to be fibrillated. The cells possess distinct cell walls, protoplasm, nuclei, and nucleoli. The cell is separated from the matrix by a capsule. The spaces in the matrix lined by the capsules are termed lacunae, which are occu- pied by the cells. In living or fresh cartilage, the cells fill the lacunae, while in prepared specimens they may not, due to the shrinkage of the cell caused by the reagents used during the preparation of the specimens. In a lacuna there may be one, two, three or four cells. One cell reproduces another, each of which reproduces another; thus at first there is one cell in the lacuna, then two, and finally four. After the cell has divided MANUAL OF NORMAL HISTOLOGY. 33 into two, one daughter cell may divide more rapidly than the other, which appears to explain how it is that a lacuna may contain three cells. The capsules form the matrix, new cap- sules being formed around the newly-formed cells. Although articular and costal cartilages belong to the hyaline variety, there are some differences be- tween them. Costal carti- lage has a perichondrium ; the articular has not. The cells of costal carti- lage, as a rule, are larger than those of articular cartilage, and sometimes may con- tain oil globules in the protoplasm. The outermost cells of costal cartilage do not form a continuous layer, while those of articular carti- lage do. The matrix of adult costal cartilage appears to be split up into rods or fibrillae, while of articular carti- lage it does not, although it may appear slightly fibrillated. The matrix of hyaline cartilage, in the aged, may become rigid and hard, due to a deposition of lime salts, the process being termed calcification, which is very different from ossification. White fibro-cartilage is similar to hyaline cartilage, except that the matrix has been invaded by white fibrous connective tissue. It is found as interarticular cartilage (the intervertebral discs, and interarticular cartilage of the tern- Fig. 33. A slice of articular cartilage showing cartilage cells (a) contained in lacuna (5); the matrix (c); and a lacuna (6') from which the cell was lost during the preparation of the specimen. Fig. 35. A portion of a section of the trachea showing hyaline cartilage. Fig. 34. A portion of a section of costal cartilage showing cells containing globules of fat. 34 MANUAL OF NORMAL HISTOLOGY. poro-maxillary articulation), and lining grooves on the surface of bones. Yellow fibro- CARTILAGE is similar to hyaline cartilage, except that the ma- trix has been invaded by yellow fibrous connective tissue. Its chief localities are the external ear and the epiglottis. Experiment 40. With a sharp razor moistened with saline solution cut several thin slices of articu- lar cartilage. Put them in normal saline solution on a slide, cover, and examine with the high power. Notice the cells singly and in groups. Look for empty lacunae. Sketch. Exp. 41. Compare stained-specimens of articular cartilage, preferably cut perpendicular to the surface, and of costal cartil- age cut transversely. Sketch both, showing main points of difference. Exp. 42. Stain and mount a section of an intervertebral disc. Examine with the high power, and notice the cells and the matrix. Notice especially the white fibrous tissue in the matrix. Sketch. Exp. 43. Examine a stained and mounted specimen of the ex- ternal ear or of the epiglottis. Notice and sketch the cells and the matrix containing yellow fibrous tissue. BONE. Bone, the hardest of the supporting tissues, is second in hard- ness of all the tissues of the body, enamel being the hardest. In the fresh condition it is covered by a membrane termed the periosteum, which covers the bones of the body except at their articular ends. In the fresh state it has a pinkish hue, due to the small blood-vessels which permeate its substance, and pos- sesses flexibility and elasticity. Dry bone is opaque, white, and somewhat brittle. Bone consists of a cellular portion, the bone corpuscles, and an intercellular substance. The intercellular Fig. 36. White fibro-cartilage from the intervertebral disc. c, cartilage cells; /, white fibrous connec- tive tissue. Fig. 37. Yellow fi bro-cartilage from the ear of a cat. c, cartilage cells; f, yellow fi- brous connective tissue. MANUAL OF NORMAL HISTOLOGY. 35 portion predominates and gives to bone its characteristic physi- cal properties, and consists of a foundation of organic matter, in which are deposited mineral salts, the chief of which is cal- cium phosphate. About one-third of bone is organic matter, the remaining two-thirds inorganic. The chemical composition of bone, according to Berzelius (Gray's "Anatomy"), is: Organic matter, ....... 33.30 Inorganic matter- Calcium phosphate, ..... 51.04 Calcium carbonate, . . . . .11.30 Calcium fluoride, ...... 2.00 Magnesium phosphate, . . . .1.16 Sodium carbonate and sodium chloride, . . 1.20 66.70 100.00 By allowing bone to remain in a dilute solution of a mineral acid, as hydrochloric or nitric, for twenty-four hours or longer, the mineral matters will be dissolved and the organic matter left. A bone treated in this manner will retain its original shape, but instead of being hard and resisting it will be flexible and elastic; so flexible that it can be tied into a knot, and when untied it assumes its original shape, due to its elasticity. If a bone be heated, without access of air to the bone, the organic matter will be decomposed; the mineral matter not affected. The bone thus treated retains its shape, but appears as a dark, honey- combed mass, which readily crumbles, breaking up into particles, which are hard and brittle. Thus it is evident that the characteristic properties of bone depend upon the organic and the inorganic substances present in a definite proportion. The intercellular substance is arranged in layers termed lamellae, and according to the arrangement of the lamellae bone is divided into two varieties, compact and cancellous. In the former variety the lamellae are arranged in layers closely applied to each other. In the latter variety the lamellae are arranged as a spongy-looking net work, in consequence of which this variety of bone is also termed spongy bone. Compact bone occurs in the shafts of the long bones and in the tables of the skull bones. Cancellous bone occurs to a small extent in the shafts of the 36 MANUAL OF NORMAL HISTOLOGY. long bones, in the heads of the long bones, in the skull bones between the tables, and in the centre of the ribs and inferior maxilla. On studying the structure of the shaft of a long bone it will be found to contain a canal running lengthwise in its centre, Fig. 38. A portion of a transverse section of the femur. a, an Haversian system; b, interstitial system; c, Haversian canals. termed the medullary canal. Encircling the canal are layers or lamellae of bone, their long axis parallel with the long axis of the bone. The system of lamellae thus formed is termed the peri- medullary system. Next to the perimedullary system of lamel- lae, there is a comparatively small amount of cancellous bone. At the periphery of the bone there are several layers of bone, termed the circumferential system of lamellae. The portion of bone between the circumferential system and the cancellous bone consists of two sets of lamellae, the Haversian and the interstitial MANUAL OF NORMAL HISTOLOGY. 37 systems. The Haversian systems consist of canals which run lengthwise of the bone and communicate with one another by means of branches, sur- rounded by lamellae of bone. The interstitial systems consist of lam- ellae which are more or less parallel to the lamellae of the circum- ferential system, and fill the interstices between neighboring Haversian systems. An Haversian sys- tem consists of a central canal, termed the Haver- sian canal, which, when seen in transverse sec- tion, appears as around opening. It varies in di- ameter from tthte to inch, and contains in living bone marrow, blood-vessels and nerves, but in prepared specimens of bone they usually appear dark, on account of containing dirt obtained during their preparation. Around the canal are concentrically arranged lamellae of bone, about six in number. Between the lamellae are small irregular-shaped cavities, termed lacunae, from which little canals, termed canaliculi, extend. The canaliculi of one lacuna branch and join those of neighboring la- cunae. The canaliculi of Fig. 39. A portion of a longitudinal section of the femur show- ing an Haversian canal cut lengthwise and dividing into branches. An Haversian system highly magnified showing the canal (c) surrounded by six lamellae, with lacunae (a) and canaliculi (6). Fig. 40. 38 MANUAL OF NORMAL HISTOLOGY. one Haversian system do not communicate with those of another. The lacunae nearest to the Haversian canal com- municate with it by means of canaliculi. In living bone the lacunae are occupied by the cellular elements of the tissue, the bone corpuscles, which send protoplasmic projections into the canaliculi. By means of this arrangement, the bone corpuscles nearest to the canal can absorb nourish- ment from the canal and transmit it through- out the Haversian system. Lacunae and canaliculi exist also in other systems, the perimedullary, circumferential, and inter- stitial. Cancellous bone consists of lamellae arranged in plates; between the lamellae of the plates there are lacunae, with their canaliculi. The plates join each other, enclosing irregular- shaped spaces. The periosteum is composed of fibrous tissue arranged in two layers - an outer as a dense network, and an inner as a loose network. In the periosteum blood-vessels ramify, the ramifica- tions extending into the substance of the bone to the Haversian canals. On the inner surface of the periosteum of young bones there is a layer of bone-forming cells termed osteoblasts. Some of the fibres of the periosteum extend for a short distance into the substance of the bone, and are termed the perforating fibres of Sharpey. Experiment 44. Examine with the unaided eye, a cross-sec- tion of a long bone. Notice the medullary canal in the centre, the zone of cancellous bone, the narrow, compact zone between the cancellous bone and the canal, and the mass of dense bone beyond the cancellous. Saw through the head of a long bone, and notice the sponge-like arrangment of the cancellous bone. Notice the weight of the piece sawed off, and compare it with the weight of compact bone. With a fresh bone, notice the yel- low marrow in the medullary canal, and the red marrow in the cancellous bone. Observe the pinkish hue of a fresh bone, and the periosteum. Exp. 45. Prepare a cross-section, and one longitudinal, of bone in the following manner: Saw as thin a section as possible, which rub on a fine file to the thickness of ordinary cardboard, and then rub on an oil stone until as thin as tissue paper, or until printed letters can easily be seen through it. Mount in A bone corpuscle. Fig. 41. MANUAL OF NORMAL HISTOLOGY. 39 glycerin, fixing the cover-slip with cement. If it be desired to mount the specimen in balsam instead of glycerin, after it has been rubbed to the proper thinness, put into a vessel containing dilute acetic acid for thirty seconds, then into alcohol (95 per cent.) for three minutes, then on the slide; cover with balsam and a cover-slip. The section can be stained by placing it, after having rubbed it down to desired thickness, into a solution of fuchsin for 24 hours; then after being rinsed with water, into dilute hydrochloric acid (1 per cent.) about five minutes; then after being rinsed again with water, it should be placed in 95 per cent, alcohol 2 minutes, dried with bibulous paper, and mounted with balsam and cover-slip. Exp. 46. In the specimen of a cross-section of bone, notice and sketch, under the low power, the systems which are seen. Sketch under high power an Haversian system, and measure two Haversian canals. Notice the lacunae and canaliculi. Sketch portions of the other systems. Exp. 47. Examine the longitudinal section of bone. Notice the Haversian canals running lengthwise, giving off branches. Notice the disposition of the lamellae and lacunae along the canals. Sketch. MARROW. Contained in the canals, medullary and Haversian, of compact bone, and in the enclosed spaces of cancellous bone, there is a substance termed marrow, of which there are two varieties, yellow and red. In the human subject the yellow variety occurs in the canals of compact bone, and the red variety in the spaces of cancellous bone. Yellow marrow contains fat, a small amount of connective tissue, and a few blood-vessels. It is of a pale yellow color, due to the presence of the fat, which is about 96 per cent, of the marrow, 3 per cent, of the remaining 4 per cent, being water. Red marrow consists of a loose network of connective tissue and capillaries, containing within its meshes connective tissue corpuscles, and three kinds of cells, which are the marrow cells, the giant cells, and the colored blood-corpuscle-forming cells. Fig. 42. Red marrow from the rib of a dog. a, myelocyte or marow cell; b, erythroblast; c, myeloplax or giant cell with a large irregular shaped nucleus; c', a myeloplax with several nuclei. 40 MANUAL OF NORMAL HISTOLOGY. The marrow cells or myelocytes are similar to the colorless corpuscles of the blood. cells, myeloplaxes (Gr. /xveXos, marrow ; *rXa£, piece) of Robin, are large, irregular-shaped masses, some of which contain several nuclei, while others contain one large irregular- shaped nucleus. The third kinds of cells, termed erythroblasts (Gr. cpvOpos, red; /JAaorew, to produce), from their similarity to the nucleated colored corpuscles of the embryo, are supposed to be cells which reproduce others to become colored blood-corpuscles (Neumann). Red marrow contains about 75 per cent, water and about 25 per cent, solids. Of the solids are albumin, salts, and fat. Experiment 48. Put a small piece of yellow marrow into a drop of normal saline solution on a slide, and tease it apart with teasing needles. Examine, and notice the numerous globules of fat, and the connective tissue reticulum. Exp. 49. In the same manner as in Exp. 48, prepare some red marrow obtained from a rib of a recently killed animal. Look for, sketch and measure the marrow cells, giant cells, and small nucleated cells. THE DEVELOPMENT OF BONE. All of the bones of the body are developed from cartilage, except the bones of the cranial vault, of the face and the inferior maxilla. Intracartilaginous or Endochondral Ossification. Cartilage does not become bone, but is removed and bone is formed in its stead. The cartilage which is to be ossified is of the hyaline variety, and, being embryonal, is composed of numerous cartilage cells and a small amount of cartilage matrix. Surrounding the cartilage there is a membrane termed the perichondrium, which consists of three layers-an outer dense fibrous, a middle loose fibrous (vascular), and an inner layer composed of bone-forming cells, the osteoblasts. An osteoblast is an irregular, generally quadrilateral-shaped, cell, of which the protoplasm appears granular, the nucleus oval. The cycle of changes which take place during ossification may be briefly summarized as follows : MANUAL OF NORMAL HISTOLOGY. 41 1. Stage of rearrangment of the cartilage cells.-The cartilage cells at the centre of ossification become larger, somewhat flattened and arranged in rows, the rows usually running parallel with the long axis of the cartilage (Fig. 44, b ). 2. State of vascularization.-Synchronous with the first stage, the periosteum sends inshoots into the cartilage, which consist of the inner and middle periosteal layers. The inshoots divide and subdivide, in consequence of which the cartilage is perme- ated by the vascular channels, and is said to be vascularized. A section of one of the channels would show that it contains capillaries, areolar tissue, leucocytes, and osteoblasts in the areolar tissue and lining the channel (Fig. 44, c). In the long bones, one of the channels permeate the central core of the shaft to become the future medullary canal. 3. Stage of granulariza- tion of the matrix.-After the cartilage cells have become enlarged and ar- ranged in rows the matrix becomes granular in ap- pearance (Fig. 44, d). 4. Stage of fibrillation of the matrix.-The matrix appears to become fibril- lated, the fibrillae enclosing the cells in quadrilateral shaped spaces 5. Stage of primary ar- eolae o f Sharpey. - The spaces formed in stage 4 become larger, the parti- tions thicker and the carti- lage cells appear to be degenerating. The spaces are now termed primary areolae (Fig. 44, e ). 6. Stage of irruption. - The vascular channels by this time having reached the primary areolae cause disintegration of some of the partitions and pass into the large spaces formed, which Fig. 43. A portion of developing bone from child's finger, a, cartilage; b, region of primary and secondary areolae; c, vascular channels containing besides blood corpuscles, osteoblasts; d, newly formed bone. 42 MANUAL OF NORMAL HISTOLOGY. are termed secondary areolae. A section of developing bone at this stage would show the remains of the fibrous partititions very similar in appearance to pieces of scroll work, and the spaces to contain blood corpuscles, osteoblasts and connective tissue (Fig. 44, /). Portion of the specimen used in Fig. 43, showing some of the stages in the development of bone from cartilage. Fig. 44. a, hyaline cartilage; b, state of rearrangement of the cartilage cells; c, stage of vasculariza- tion showing vascular channel with blood vessels (z>); rf, stage of granularization of the matrix; e, stage of primary areolae; f, stage of irruption; ,g. stage of ossification; h, newly formed bone showing bone corpuscles (i) and osteoblasts (o). MANUAL OF NORMAL HISTOLOGY. 43 7. Stage of ossification of the partitions.-Osteoblasts from the spaces penetrate into the remains of the fibrous partitions, form bone, and are caught between the lamellae to become bone cor- puscles (Fig. 44, g\ In this manner the remnants of the par- titions are ossified and exist in fully-developed bone as the inter- stitial systems. 8. Stage of formation of the Haversian and the perimedullary systems.-The osteoblasts arrange themselves as a layer between the contents of the canals and the trabeculae of bone formed in stage 7, and deposit successive layers or lamellae of bone, some of the cells becoming caught between the lamellae become bone corpuscles. In this way the Haversian and perimedullary sys- tems are formed (Fig. 44, K). Why the osteoblasts do not continue to lay down lamellae until no canal be left is not known. It may be due to the following factors: 1. Owing to the fact that many of the osteoblasts are left between the lamellae to become bone corpuscles, the number of osteoblasts is continually being diminished, the diminution be- ing in excess of the reproduction, if the cell reproduces while performing its function. 2. By the time the last lamella is deposited the remaining osteoblasts, if there be any, may be so weakened by their labor as to be unable to form more bone. 3. The increasing amount of pressure in the canals as they become smaller may become too great for the osteoblasts to overcome. In the long bone ossification, near the central core of the shaft, may pass through the seventh stage and stop, leaving a small area of cancellous bone. In the same way the cancellous bone in the extremities of long bones is formed. The bone grows lengthwise, by means of the cartilaginous plate between the shaft and the extremities of long bones (epiphyseal cartilage). During the endochondral ossification, ossification also goes on at the exterior of the bone termed periosteal. The osteoblasts of the perichondrium deposit lamellae of bone around the cir- cumference of the shaft, forming the circumferential system of lamellae. Intramembranous ossification is very similar to the sub- periosteal ossification. A membrane which is to become bone consists of two dense fibrous layers, between which is a loosely- 44 MANUAL OF NORMAL HISTOLOGY. arranged fibrous network. Among the fibres are osteoblasts which deposit lamellae, some of them becoming caught between the lamellae remain as bone corpuscles. In the dense layers compact bone is formed ; in the loose fibrous network cancellous bone is formed. The fully-developed bone consists of two tables of compact bone, between which is cancellous bone, the diploe. Experiment 50. Stain a decalcified section of a developing bone. Examine and sketch the different stages of ossification shown by the specimen. Dentine, the remaining variety of supporting tissue, will be considered in the article on the teeth. MANUAL OF NORMAL HISTOLOGY. 45 CHAPTER V. MUSCULAR TISSUE. Widely distributed throughout the body there is a set of tissues the function of which is to perform the various movements of the body. This set of tissues is known as muscle. There are two varieties of muscle : 1. The first variety includes the muscles which are under the control of the will, and are termed the voluntary muscles. 2. The other variety includes the muscles which are not under the control of the will, and are termed the involuntary muscles. Voluntary muscle-The chief muscles of this variety are the skeletal and the diaphragm. Enveloping a voluntary mus- cle there is a sheath compos- ed of areolar connective tis- sue termed the epimysium. The sheath sends in- shoots into the muscle, termed peri my sium, which divide the muscles into bundles of fibres termed the fas- ciculi. From the perimysium projections extend into the fas- ciculi, and divide them up into small, irregular-shaped usually quadrilateral, compartments, each of which is occupied by a muscle fibre. The inshoots from the perimysium are known collectively as endomysium. Fig. 45. A transverse section of voluntary muscle. a, epimysium ; b, perimysium; d, endomysium; c, connective tissue corpuscles; f, muscle fibre. 46 MANUAL OF NORMAL HISTOLOGY. An isolated muscle fibre (voluntary) is round, about one to one and one-half inch long and about inch in diameter. In a short muscle the fibres may be as long as the muscle, but in long muscles the fibres are dovetailed together to make the de- sired length. The fibre is a long cell, pointed at its ends, the protoplasm of which is modified in order to perform its function, which in contraction. The cell wall or fibre sheath is termed the sarcolemma. The nucleus is in the proto- plasm just beneath the sarcolemma. The protoplasm presents the appearance as if traversed transversely by alternating light and dark bands, from which appearance this variety of muscle is also termed cross-striated. muscle. Midway between the dark bands, each clear region is traversed by an inter- rupted granular-looking line, termed the intermediate disc, or the membrane of Krause. The portions of the light band between the intermediate discs and the dark bands are termed the lateral discs. The dark bands are com- posed of dark masses, with narrow, clear streaks be- tween them. The clear substance also occurs in the lateral discs and between the particles of which the membranes of Krause are composed. Running lengthwise of the fibre appear parallel streaks which indicate that the fibre is made up of fibrillae. In regard to the structure of the protoplasm of the muscle fibres, differ- ent theories have been advanced. According to Rollett's theory the dark- appearing portions of the protoplasm are contractile masses, parallel to each other and arranged lengthwise in the fibre. Fig. 46. Transverse section of a voluntary muscle fibre highly magni- fied showing areas of Cohnheim. Voluntary muscle fibres, from a fresh specimen teased apart, showing cross striation; longitud- inal fibrillation; nucleus (»,) and sarcolemma (s). Fig. 47. MANUAL OF NORMAL HISTOLOGY. 47 These masses are spindle-shaped and taper at their ends, ter- minating in enlargements. The enlargements constitute the membrane of Krause (the intermediate disc); the bodies of the masses of concractile substance constitute the dark bands. Filling up the spaces left between the contractile masses is a semi-fluid transparent substance, termed the sarcoplasm. It seems more probable that the fibre is made up of fibrillae separated from each other by a semi-fluid substance termed sarco- plasm, which fibrillae are made up of cubes of granular sub- stance termed contractile masses, separated from each other above and below by the transparent sarcoplasm. Midway between the cubical masses occur small granular particles which with those of the neighboring fibrillae make up the intermediate discs. Thus, according to either theory, the protoplasm appears to be composed of contractile fibrillae, corresponding to spongio- plasm, and a semi-fluid substance, sarcoplasm, corresponding to hyaloplasm. On cross-section of a fibre, dark areas are seen, which are separated by clear substance. The areas are the areas of Cohnheim, and correspond to cross-sections of the fibrillae, the intervening clear sub- stance corresponding to the sarcoplasm. The fibres of voluntary muscle do not branch, as a rule, an excep- tion being some of the fibres of the tongue. The tendons are continuous with the mus- cles, the sarcolemmae becom- ing blended with the fibrous tissue of the tendon, and the areolar tissue septa of mus- cle with those of the tendon. The blood supply to voluntary muscle is large. The arteri- oles penetrate the epimysium, extend into the muscle with the perimysium and termi- nate in the endomysium as a capillary network around the fibres. The veins arise from the capillary network and pass Fig. 49. Voluntary muscle fibres containing motor end plates. a, low power; b, high power. 48 manual of normal histology. from the muscle in the same manner as the arteries enter. The lymphatics arise in the clefts in the fibrous connective tissue of the endomysium, perimysium and epimysium. The nerves which go to voluntary muscle are of the medullated variety and terminate beneath the sarcolemma as motor end-plates. Involuntary muscle.-This variety occurs widely distributed throughout the body, existing in the alimentary canal, blood-vessels, ureters, bladder, uterus, etc. It consists of bundles of fibres held together b y means of areolar tissue and ramifying blood-ves- sels. The fibres are spindle-shaped cells, each having a cell wall composed of a delicate homogeneous sheath. In the protoplasm is an elongated nucleus the long axis of which is parallel with the long axis of the cell. The neighboring cells are held together by a small amount of cement substance. They are about tth) inch long and inch in diameter. In transverse sections of involuntary muscle the fibres appear usually as ir- regular quadrilateral shaped areas of varying size. The small areas appear homogeneous and rep- resent sections of the tapering ends of the fibres; the large areas have a dark spot in the centre and represent sections of the fibres through the nucleus. Cardiac muscle.-The muscle of the heart belongs to the involuntary variety of muscle, although in structure it resem- Fig. 51. A portion of the circular of the muscular coat of the small intestine of a cat, showing involuntary muscle fibres cut lengthwise in situ. Isolated involuntary mus- cle fibres obtained by teasing apart a portion of a piece of a rabbit's in- testine after having im- mersed it in Muller's fluid for twenty - four hours. Fig. 50. A portion of the longitudinal layer of the muscular coat of the small intes- tine of a cat, showing involuntary muscle fibres cut transversely. It will be noticed that some of the sections show nuclei while others do not. Fig. 52. MANUAL OF NORMAL HISTOLOGY. 49 hies the voluntary variety in some respects. The fibres are usually short, cross-striated and branched. The nucleus of a fibre is in the centre of the pro- toplasm. The fibres have not sarcolemmae. The blood-vessels to involun- tary muscle form a capillary network around the bundles of fibres. Lymphatics arise in the areolar tissue between the bun- dles. The nerves are of the non-medullated variety. They form a plexus between the layers of muscle, from which fibrillae extend between the bundles of fibres and possibly to the fibres. Experiment 51. Tease apart in a drop of normal saline solu- tion a small piece of a fresh skeletal muscle ; cover and examine. Look for fibres showing cross-striations and sarcolemmae. Notice the fibrillation lengthwise. Sketch. Exp. 52. Examine a longitudinal section of voluntary muscle, the specimen having been stained with haematoxylin and eosin. Look for cross-striations and nuclei. Sketch. Exp. 53. Examine a cross-section of voluntary muscle which has been stained as in Exp. 52. Notice the epimysium, peri- mysium, and endomysium, and the shape of the sections of fibres. Sketch. Measure two cross-sections of fibres. Exp. 54. Gently tease apart in a drop of glycerin on a slide a piece of voluntary muscle, the arteries of which have been injected. Examine with the low and then with the high power. Sketch. Exp. 55. Examine a prepared specimen of voluntary muscle, showing the termination of the nerve fibres in the muscle. Exp. 56. From a piece of intestine of a rabbit or frog, which has been in a dilute solution of potassium bichromate for twenty- four hours, tear off shreds, working from the outer surface. Tease apart in a drop of glycerin or weak saline solution on a slide ; cover and examine. Look for the spindle-shaped invol- untary muscle fibres; notice the nuclei. Sketch and measure. Exp. 57. Examine the specimen of the rabbit's bladder or ureter used in Exp. 24. Look for involuntary muscle fibres cut longitudinally and transversely. Sketch. Exp. 58. Tease apart a small piece of the heart muscle in a drop of glycerin on a slide. Add a drop of haematoxylin solu- tion, cover and examine. Look for cross striations, nuclei, and branching fibres. Sketch. Fig. 53. A portion of a section of the heart showing cardiac muscle fibres cut lengthwise (a) and transversely (c) held together by areolar connective tissue (£). 50 MANUAL OE NORMAL HISTOLOGY. CHAPTER VI. NERVOUS TISSUE. Nervous tissue consists of three parts : 1. Nerve cells for generating or modifying impulses. 2. Nerve fibres for conveying impulses. 3. Neuroglia and connective tissue framework. The NERVE cells are found in the gray matter and ganglia of the nervous system, and are from 10 m to 100 m in diameter. They consist of gran- ular-looking protoplasm, in which there is a distinct nucleus containing a nucleolus. The shape of the cells differ, depending upon their location. Some are spherical or angular, as in the spinal cord and cere- brum; others are stellate, as in the spinal cord; others, flash-shaped or pyriform, as in the cerebellum. The cells may have one or more protoplasmic projections. A cell which has only one projection is termed a unipolar; one which has two, a bipolar; one w i t h more than two, a multipolar cell. The pro- cesses are of two kinds, axis cylinder and branched. The former are termed the processes of Deiter, neuraxes, neurites, neuraxones, or axones. The process of a unipolar cell is an axis-cylinder process; of the bipolar, one is an axis cylinder, the other a branched process; of the multi- polar all are branched, except one, which is an axis-cylinder process. The branched processes 'known as dendrites form a communicating network. Fig. 54. Nerve-cells. .4,unipolar; /?, bipolar; C, multipolar; a. axis cylinder process; 6, branched processes. Fig. 55. A nerve cell from the cere- brum, termed a neurone. c, cell body; b, dendrite, with secondary dendrite branching off from it: a. telodendrion of main dendrite; e. a basal den- drite ; w, neuraxis. MANUAL OF NORMAL HISTOLOGY. 51 The entire nerve cell with its processes is termed a neurone, neura, or neurodendron. The terminal groups of branches of a dendrite or of a neuraxis are known as a telodendron. Each axis-cylinder process becomes the essential portion of a nerve fibre. The nerve fibres are of two varieties, medullated or white, and non- medullated or gray. The medullated or white nerve fibres vary in length, and are about inch in diameter. The fibre consists of a rod-shaped central portion termed the axis cylinder of Purkinje; a sheath around the axis cylinder termed the myelin or medul- lary sheath, or white sub- stance of Schwann, and a sheath around the medullary substance termed the primitive sheath, or neurilemma. The axis cylinder is a continuation of the axis-cylinder process of a nerve cell, and consists of a number of fibrillae termed the primitive fibiillae of Schultze, held together by a granular cement substance termed neuroplasm (Kolliker). Surrounding the axis-cylinder, according to Kiihne, there is a delicate sheath termed the axilemma. This sheath, if it exists, is probably a continuation of the limiting membrane of the nerve cell, from which the axis-cylinder is de- rived. The axis cylinder proceeds to the area to be supplied by it, and then divides into its primitive fibrillae. The medullary sheath, also known as the white sub- stance of Schwann, consists of a semi-fluid fatty sub- stance. At regular intervals (about -jk inch) along the fibre the medullary sheath is absent. These places where the medullary substance is not present are known as the nodes FiG. 56. Medullated nerve fibres from a fresh specimen teased apart in normal salt solution. a. axis cylinder ; tn, medullary sheath; n, node. A diagrammatic repre- sentation of a medul- lated nerve fibre. a, primitive sheath or neurilemma; d, me- dullary sheath or white substance of Schwann; c, axi- lemma (of Kiihne); d. nucleus; J, neuro- plasm(of Kblliker) \f, fibrillae(of Schultze); w, node (of Ranvier.) Fig. 57. A diagrammatic rep- resentation of a transverse section of a medulla ted nerve Fig. 58. a, neurilemma ; b, medullary sheath ; c , axilemma ; j , neuroplasm; f, fibrilla. 52 manual of normal histology. of Ranvier. The portions between the nodes are termed inter- nodes. In each portion of the medullary substance, about midway between the nodes, there is a nucleus. The primitive sheath, neurilemma, or nucleated sheath of Schwann, bears a relation to the nerve fibre similar to that borne by the sarcolemma to the muscle fibre. It is closely ap- plied to the medullary sheath, and consists of a thin membrane, on the internal surface of which there is a layer of endothelioid cells. At the nodes the neurilemma dips into the axis cylinder. In the nodes there exist collections of cement substance, which probably have some influence upon the nourishment of the axis cylinders. The medullated fibres may lose their medullary sheath and become non-medullated fibres. The non-meduleated, or gray fibres, the fibres of Remak, are essentially the same as the white fibres, except that they have not a medullary sheath. A gray fibre consists of an axis cylinder which is fibrillated lengthwise. Around the axis cylinder there is a sheath, in wdiich are oval-shaped nuclei. These fibres are smaller than the white variety, being about inch in diameter. The gray fibres branch, the medullated do not, except near their termination. These fibres are found making up the sympathetic system, very few existing in the cerebro- spinal system, while the other variety makes up the cerebro- spinal system of fibres. Holding the cells and fibres of the brain and spinal cord to- gether, there is a framework composed of connective tissue derived from the pia mater, and neuroglia. The neuroglia (Gr. verpov, nerve ; yAla, glue) consists of cells very similar in appearance to the lacunae of bone with their canaliculi. These cells are known as neuroglia cells. Their filament-like projec- tions intermingle and form a secondary network. The nerve trunks consist of nerve fibres collected together into bundles, which in turn make up the nerves. The nerves of the cerebro-spinal system are composed of the medullated variety of fibres. In many respects a nerve on cross-section resembles a cross-section of voluntary muscle. Surrounding the nerve there is an areolar connective tissue sheath termed the epineurium, which sends inshoots into the nerve, dividing it up into bundles of fibres, the inshoots being termed perineurium; the bundles of fibres, funiculi. From the MANUAL OF NORMAL HISTOLOGY. 53 perineurium projections termed the endoneurium extend into the funiculi, dividing them up into small compartments, which are occupied by the nerve fibres. The main points of difference between a cross-section of a nerve and one of voluntary muscle are shown by the fibres. In muscle the fibres are irregularly quadrilateral in shape ; in nerve they are usually round. The cross-section of a muscle fibre appears as a dense, solid mass, surrounded by the sarcolemma; that of a nerve fibre appears similar to a round cell, with its nucleus (axis cylinder) in the centre, with a clear zone (the medullary substance) between the nucleus and the cell wall (neurilemma). If the section of the nerve should pass through a node or a gray fibre, if there be any gray fibres in the nerve, only a dark spot, the cross-section of the axis cylinder, would be observed representing the fibre. As a funiculus nears its termination the fibres diverge from each other, each fibre receiving an extra sheath derived from the endo- and perineurium, which sheath is termed the sheath of Henle. The blood VESSELS-the vasa nervorum-pass into the epi- neurium, and send off branches into the peri- and endoneurium, forming a capillary network around the fibres, as in muscle. Lymphatics arise in the clefts in the fibrous tissue of the endo- meurium, join and communicate with the larger clefts in the epineurium, which in turn communicate with the clefts of the surrounding areolar tissue. The nerves which pass to the larger trunks, the nervi nervorum, pass into the epineurium, where, according to Horsley, they ter- minate in bulbous enlargements. Experiment 59. Stain and mount a cross-section of the spinal cord, preferably from an ox. Notice the gray matter and the white. In the gray matter, look for uni-, bi- and multipolar cells. Sketch and measure four of the cells. Exp. 60. In the white matter of the cord, look for cross-sections of nerves. Notice the numerous sections of medullated nerves. A transverse section of a nerve as ob- served in a section of the skin of the finger. a,epineurium; b. perineurium enclos- ing the funiculi or bundles of nerve fibres; c, endoneurium; n, nerve fibre cut transversely. Fro. 59. 54 MANUAL OU NORMAL HISTOLOGY. Notice the framework which holds the fibres together. Look for neuroglia cells. Sketch. Exp. 61. Stain with haematoxylin and eosin a transverse sec- tion of a large nerve. Examine and notice the points of resem- blance and the points of difference between it and muscle. Sketch. Exp. 62. From a recently-killed animal take a nerve, and tease apart lengthwise in a drop of normal saline solution. Cover and examine. Notice and sketch the axis cylinders, medullary sheaths, nodes and internodes. Exp. 63. Obtain a portion of a nerve which has been in a dilute solution of osmic acid (5 per cent.) for about thirty-six hours, and gently tease it apart in a drop of glycerin on a slide. Examine with the high power, and look for nuclei beneath the primitive sheath. Sketch. Cement the cover-slip on the slide. Ganglia occur on some of the cranial nerves, on the poste- rior roots of the spinal nerves, and as the sympathetic ganglia. The ganglia are nerve centres occurring on the nerves, and act as relays, aiding or modifying the impulses as they pass through them. A spinal ganglion consists of fibres and nerve cells. The nerve cells are usually near the surface of the ganglion, some being round, others unipolar, bipolar or multipolar. The processes extend from the cells to the nerve fibres which they join. Each cell has a nucleated cell wall,which is continued around the process as a sheath. The g a n g 1 i a ar- ranged as. a chain along each side of the vertebral column, which form the trunk of the sympa- thetic system, receive medul- lated fibres (rami commu- nicantes) from the spinal cord. From the ganglia non-medullated nerves pass A longitudinal section of a spinal ganglion. a, ganglion cells; a1, ganglion cells highly magnified; b, fibrous con- nective tissue; n, nerve fibres; v, blood vessels. Fig. 60. MANUAL OF NORMAL HISTOLOGY. 55 as the sympathetic nerves. In the sympathetic ganglia of the frog, pear-shaped cells have been observed which have, passing from their small end, two fibres, one medullated, the other non-medullated, from which it may be inferred that the medullated fibre enters the cell, loses it medullary sheath, and emerges as a non-medullated fibre. In this manner it is probable that the ganglia of the sympathetic trunk act upon the medullated fibres received from the spinal cord, in which case the sym- pathetic system would not be an independent one, but one derived from the cerebro-spinal system. Experiment 64. Stain and mount a longitudidal section of a spinal ganglion. Examine and notice the cells and nerve fibres. Try to find processes of the cells joining the nerve fibres. Sketch. THE PERIPHERAL NERVE TERMINATIONS. The terminations of the sensory nerves* may be simple or complex. The nerves may terminate as a fibrillar network from which fibrillae may pass to the cells to be supplied, terminating between or within the cells. There are some of the sensory nerves, especially those for the perception of the sensation of touch, which terminate in a special manner, the special endings being termed end- organs, the chief of which are : Tactile corpuscles. End-bulbs. Pacinian corpuscles. The tactile corpuscles, also termed the corpuscles of Meissner or of Wagner, occur in some of the papillae of the skin, and are most numerous in the localities where the sensation of touch is highly developed, as in the skin of the palmar surface of the fingers. The nerve fibre loses its medullary sheath, the axis cylinder divides, the fibrillae *The consideration of the termination of the nerves for the appreciation of the sensations of sight, hearing, smell and taste will be taken up with the corresponding organs which contain them. Ganglion cells from a transverse sec- tion of the gangli- onic commissure of an earthworm. Fig. 61. Fig. 62. A tactile corpuscle within a papilla of the skin of the hand. Chloride of gold preparation. (Ranvier.) a, varicose fibrillae; n, nerve fibre; f, fibrous tissue of the papilla. 56 MANUAL OF NORMAL HISTOLOGY. formed by the division continue and make numerous coils, giving an appearance somewhat similar to a pineapple. Upon the fibrillae small enlargements can be observed, which look like nuclei. The neurilemma of the fibre extends around the coiled mass as a capsule, which is in close contact writh the surrounding fibrous connective tissue. The end-bulbs are usually round or oval in shape, their chief localities being in the conjunctiva (the conjunctival end-bulbs) in the external genital organs (the genital corpuscles), and in the neighborhood of articular surfaces of joints (the articular Fig. 63. End-bulbs (after Krause), A, simple variety (conjunc- tival); B, compound va- riety (genital); a, vari- cose fibrillae; f. fibrous tissue; «, nerve fibres. corpuscles}. An end-bulb consists of a coiled net- work of fibrillae, derived from the axis cylinder of a medullated fibre, surrounded by a nucleated capsule. The fibrillae also appear to be nu- cleated. The Pacinian bodies, or cor- puscles of Vater, are found chiefly in the subcutane- ous tissue of the Fig. 64. A Pacinian corpuscle from the mesentery of a cat (after Ranvier). MANUAL OF NORMAL HISTOLOGY. 57 fingers and toes; occurring also in the mesentery, genital organs and joints. They are somewhat almond-shaped, and large enough to be seen with the unaided eye. The nerve going to form the corpuscle first loses its sheath of Henle, the perineural portion becoming arranged in layers or lamellae, the endoneural portion also as lamellae internal to the perineural lamellae. The primitive sheath blends with the inner lamellae of the endoneurium. The lamellae are about thirty in number, and appear to be nucleated. On entering the corpuscle, the medullary sheath becoming lost, the axis cylinder passes in the long axis of the corpuscle, and termi- nates near its smaller end in several fibrillae, which possess enlarge- ments. The mo- tor nerves to volunta- ry muscle end in the motor end- plates. The axis cylin- ders divide into fibril- lae, which have en- largements upon them. The sympathetic nerves (gray fibres) terminate in plexuses, which send off branches to the different parts to be supplied. At the junctions of the fibres of a plexus there are irregular- shaped collections of gray matter similar to that composing the axis cylinders. Experiment 65. Stain with haematoxylin and mount a section of skin from the palmar surface of a finger. Notice the papillae beneath the stratified squamous epithelium. In the papillae, look for tactile corpuscles. Sketch a tactile corpuscle under the high power. Fig. 65. Fig. 66. A Pacinian corpuscle observed in the subcutaneous tissue of the foot. A transverse section of a Paci- nian corpuscle observed in the subcutaneous tissue of the finger. 58 MANUAL OF NORMAL HISTOLOGY. Exp. 66. Look fpr small oval-shaped bodies in the mesentery of a cat. When one is found, remove it carefully and put into a dilute solution of osmic acid for twenty-four hours. Then put it into a drop of glycerin on a slide, around it place a hair; cover and examine, first with the low, then with the high power. Sketch the outlines of the Pacinian corpuscle under the low power. Under the high power sketch portions of the centre and the lamellae. manual of normal histology. 59 CHAPTER VII. the blood vessels. The blood is conveyed to and from the tissues and organs of the body by three sets of vessels-the arteries, capillaries, and veins. The arteries are the vessels which convey blood to the different parts of the body; the capillaries, the continuations of the arteries, form anastomosing networks in the tissues and organs of the body ; the veins, the vessels which convey the blood from the capillaries to the heart. An artery (Gr. air; to hold) received its name by the ancients, who believed that it was for the purpose to carry air, because after death it was found open and empty. It is composed of three tunics arranged around a central opening, the lumen: The tunica adventitia, or external coat. The tunica media, or middle coat. The tunica intima, or inner coat. The tunica adventitia consists of yellow fibrous tissue, most of the fibres running circularly around the vessel, a few running longitudinally. In addition to the yellow fibrous tissue there is a small amount of the white fibrous variety and connec- tive tissue corpuscles. The outer layers of this coat gradually blend with the areolar connective tissue which composes the sheath of the artery. Some of the yellow fibrous tissue of the adventitia in the larger-sized arteries is arranged as a distinct layer next to the middle coat, termed the external elastic mem- brane, which is seen in prepared specimens as a glistening con- voluted band. Also in the larger-sized arteries the longitudi- nally-disposed yellow fibres may be arranged in bundles. In some of the large arteries, as in the renal, some involuntary muscle fibres occur in this coat arranged in longitudinally- disposed bundles. In the large arteries the tunica adventitia is arranged in two zones, the inner of which consisting of dense 60 MANUAL OU NORMAL HISTOLOGY. elastic tissue, the outer of loosely-arranged white fibrous tissue in which there are some elastic fibres. The nourish- ing vessels, the vasa vaso- rum, of the large arteries run in the outer zone of the tunica adventitia. The tunica media con- sists of involuntary muscle fibres among which is some yellow fibrous connective tissue. In the small-sized arteries the involuntary muscle fibres are circularly disposed around the vessel, among which are a few scattered elastic fibres. As the artery increases in size more elastic tissue appears in the media, the amount of elastic tissue in the media being greater the larger the artery, so that in the aorta the media is composed almostentirely of elastic connective tissue. As a consequence the small arteries possess much contractile power and someelasticity,while the large arteries pos- sess much elasticity, and a small amount of con- tractility. Also in some of the large arteries some of the muscle fibres run longitudinally, in some instances collected into layers which may run internal to the circular layer, as in the subclavian, or external Fig. 67. A portion of a transverse section of a small artery. a, tunica adventitia; b, tunica media; c, internal elastic membrane; e. endothelial layer of the tunica intima. Fig. 68. A portion of a transverse section of the femoral artery of a rabbit. a, tunica adventitia containing circularly and longi- tudinally disposed elastic fibres; b, tunica media containing some elastic fibres among the muscle fibres, c, internal elastic membrane; d, subendothe- lial, and e, endothelial layersof tunica intima; c' ex- ternal elastic membrane. MANUAL OF NORMAL HISTOLOGY. 61 to the circular layer, as in the renal, or internal and external to the circular layer, as in the umbilical artery. The tunica intima consists of three layers : 1. The internal elastic membrane, which consists of yellow fibrous tissue, occurs as a dense layer next to the inner border of the media. The tissue is arranged as a closely woven membrane, in which are very small openings, forming a fenes- trated membrane (Henle). This layer of the intima appears in prepared speci- mens as a glistening con- voluted band. 2. Next to the internal elastic membrane there is a loose network of connec- tive tissue, indistinct in small vessels, distinct in large ones, known as the subendothelial layer. 3. Next to the suben- dothelial layer and lining the luman of the vessel there is a layer of nu- cleated, flat, elongated, irregular-shaped cells, ar- ranged with their long axis more or less parelled with the long axis of the vessel, termed the endothelial layer. As the arteries decrease in size their tunics become more distinct, and then as they approach the region to be nourished they gradually lose the adventitia, then the media, so that just before becoming capillaries they are termed arterioles, and consist of the intima surrounded by a few muscle fibres of the media. When the arterioles lose the muscle fibres the vessels are termed capillaries. Fig. 69. A portion of a transverse section of a (human) renal artery. a, outer zone of the tunica adventitia containing vasa vasorum; a', inner zone of the tunica adventitia containing bundles of involuntary muscle fibres longitudinally disposed; b, tunica media containing circularly disposed involun- tary muscle fibres and elastic tissue; c, internal elastic membrane; d, subendothelial, and e, en- dothelial layers of the tunica intima. 62 MANUAL OF NORMAL HISTOLOGY. The capillaries consist of a layer of endothelial cells, held to the surrounding tissue by the remains of the internal elastic membrane and sub- endothelial tissue having become blended with the surrounding tissue. The capillaries are about inch in diameter, and form anastomosing networks, and by virtue of their structure allow their con- tents to pass from the vessels into the tissues, and substances to pass from the tissues into their Fig. 70, A, a longitudinal section of an arteriole; B, a longitudinal section of a venule. interior (vide endothelium, Chapter III). The capil- laries of a network do not diminish in size, although in some networks, as of bone and the liver, the capillaries may be of greater diameter than those of other networks, as of the brain and muscle. The capillary network may be close-meshed, as of the lung, or wide-meshed, as of serous membranes and tendons. The capillaries passing from the network receive a covering of muscle fibres, then one of fibrous tissue, to become veins. A vein (L. veneo, to come) is so termed because it conveys the blood return- ing to the heart. It has three tunics, like an artery, but they are less distinct, and thinner than the corresponding tunics of an artery. In the connective tissue of an artery there is a preponderance A transverse section of a, small artery, v, small vein. Fig. 71. A portion of a tranverse section of a vein. a, tunica adventitia; b. tunica media; c, tunica intima; e. endothelial cells. Fig. 72. MANUAL OF NORMAL HISTOLOGY. 63 of yellow fibrous tissue, while of a vein there is a prepond- erance of the white fibrous variety, the elastic fibres being few in number. Consequently the veins are tough, but not elastic, and generally appear in prepared specimens more or less collapsed and filled with blood, due to their lack of elasticity and contractility. The adventitia consists of white fibrous tissue, among which is a small amount of the yellow variety. The media consists of involuntary muscle fibres, a large amount of white fibrous connective tissue and a few elastic fibres. In the small veins the muscle fibres are disposed circularly around the vessel, but in the larger veins, as in the arteries, longitudinally-disposed muscle fibres occur in the media, which may be collected into layers, in some veins internal to the circular layer, as in the femoral, in others external to the circular layer, as in the inferior vena cava and the hepatic. In some veins the muscular coat is almost entirely absent, as in the upper part of the inferior vena cava. In some veins, as those of the brain, spinal cord, bone and venous sinuses, there is no muscular coat. In many veins, especially in those of the lower extremity, in order to prevent regurgitation of the blood, there are reduplications of the intima, termed valves, which are pocket-shaped projections strengthened by fibrous tissue, and in some instances by muscle fibres, derived from the media. The valves are so arranged that the concavities are toward the heart. In the intima of a vein the internal elastic membrane is less distinct than in an artery, and the endothelial cells are less elongated than those of an artery, and are arranged with their long axis not paralied with the long axis of the vein, but oblique to it. Experiment 67. Stain with haematoxylin and eosin and mount a transverse section of a small artery. Examine with the low power and sketch the three tunics. With the aid of the high power sketch portions of the adventitia, media, and intima. Fig. 73. Portion of a transverse section of a medium sized vein. a tunica adventitia; b, tunica media; c, tunica intima. 64 MANUAL OF NORMAL HISTOLOGY. Exp. 68. Prepare as in Exp. 67 a transverse section of a large artery, as the femoral or the renal. Notice the elastic tissue in the media and the two zones of the adventitia. Look for cross-sections of longitudinal muscle fibres and of elastic fibres. Notice the vasa vasorum. Look for and study the three layers of the intima. Sketch. Exp. 69. Examine the specimen of the umbilical cord used in Exp. 38. Find artery, and look for the cross-sections of the longitudinal layers of involuntary muscle fibres, internal and external to the circular layer. Sketch. Exp. 70. Stain and mount a section of the aorta. Examine and notice the large amount of elastic fibres in the media. Sketch. Exp. 71. Stain with haematoxylin and eosin and mount a piece of areolar tissue, preferably the subcutaneous tissue. Look for small arteries (arterioles) and small veins cut longitudinally. Sketch. Exp. 72. Open lengthwise a small artery; cut away as much of the wall as possible without injuring the lining of the vessel. Stain the lining with silver nitrate and examine. Notice the dark brown lines marking out the boundaries of the endothelial cells. Sketch. Exp. 73. Stain and mount a transverse section of a vein. Ex- amine and compare with a section of an artery. Sketch. Exp. 74. Examine the mesentery or web of a living frog (curarized). Notice the blood circulating in the capillary net- work. Look for leucocytes within and outside the vessel. By careful examination leucocytes may be observed passing through the capillary walls. MANUAL OF NORMAL HISTOLOGY. 65 CHAPTER VIII. THE LYMPH CHANNELS AND THE MEMBRANES. The lymph channels may be regarded as extensions from the veins, as the larger-sized channels are similar in structure to, and terminate in, the veins. The lymph channels possess valves which are more numerous than those of the veins. They con- vey the lymph from the tissues to the veins. The lymph con- sists of a liquid, the liquor lymphae, and lymph corpuscles. The liquor lymphae is the liquor sanguinis, which has exuded from the capillary blood-vessels into the neighboring tissues. The lymph corpuscles are leucocytes which have passed from the capillary blood-vessels with the liquor sanguinis, and cor- puscles similar to the leucocytes (lymphocytes), which have been added to the lymph as it passes through the tissues. The class of leucocytes of the blood which have been termed lymphocytes may be regarded as lymph corpuscles which have passed into the blood-vessels. The lymph, after having given nourishment to, and taken up various substances from the tissues, passes into the venous system directly by means of the capillary blood-ves- sels, or indirectly by means of the lymphatic channels. The lymph channels arise as lymph spaces, which exist in the clefts in connective tissue, the interfascicular clefts. The clefts join one another and form lymph capillaries, which at first are lined by an incomplete layer of connective tissue corpuscles, but as the vessels become more distinct they are lined by a layer of endothelial cells. In some instances the interfascicular clefts in the fibrous tissue of blood-vessels, nerves and ducts join one another and form distinct enclosing canals in their outer coat, termed respectively perivascular (as in the liver), perineural (as in the brain and spinal cord), and periductular (as in the salivary glands) lymph channels. Into the interfascicular clefts of the fibrous tissue, beneath the endothelium of serous membranes, the excess of serous secretion passes, and is conveyed away by the lymphatic channels. In the small intestine the interfasci- 66 MANUAL OF NORMAL HISTOLOGY. cular clefts of the mucosa join to form club-shaped vessels termed lacteals, or chyliferous vessels, which, during absorption, con- tain a fluid similar in appearance to milk, which is due to the lymph containing a large amount of finely-divided fat globules. The lymph capillaries terminate in lymph vessels, which pos- sess, besides an intima, some involuntary muscle fibres. As the vessels become larger the muscular coat becomes more distinct, and they acquire an outer fibrous coat, which is com- posed chiefly of white fibrous connective tissue, so that in the largest-sized vessels there are three coats, as in the veins, but thinner than the corresponding coats of the veins. For example, a transverse section of the thoracic duct would exhibit three coats-an intima, media, and adventitia. The intima consists of an endothelial and a well-developed subendothelial layer, and an internal elastic membrane. The media consists of involun- tary muscle fibres circularly disposed, mixed with which is white fibrous connective tissue. The adventitia consists of white fibrous tissue, some elastic fibres, and a longitudinal layer of involuntary muscle near the media. The lymph channels, before reaching their termination, pass through lymphoid tissue, loosely arranged or collected into nodules or glands.* Serous membranes line the cavities which are not exposed to the exterior, such as the peritoneal, pericardial, and pleural. A serous membrane, besides lining the cavity, is reflected over the organs contained in the cavity, the portion lining the cavity being termed the parietal, that covering the organs the visceral layer. The serous membranes are strong, elastic, of a glistening white appearance, and consist of two portions, an endothelial and a subendothelial. The subendothelial layer consists of loosely arranged fibro-elastic tissue in which there may be some lymp- hoid tissue, which blends with the fibrous tissue of the subserous membrane. The endothelial portion consists of a single layer of flat, irregular-shaped cells, held together by cement substance. In the cement substance are small openings, stomata, and col- lections of cement substance, pseudo-stomata, or stigmata. The serous secretion is watery, and contains serum albumin. The excess of the secretion can readily pass through the stomata *The collections of lymphoid tissue will be considered in Chapter X. MANUAL OF NORMAL HISTOLOGY. 67 into the interfascicular clefts of the subendothelial tissue and be conveyed away by the lymphatic channels. The blood-vessels which go to the serous membranes form a capillary network in the subendothelial tissue. Synovial membranes are the membranes which cover the movable surfaces of joints and line the tendon-sheaths and bursae. They consist of connective tissue and the accompanying connective tissue corpuscles. To the synovial membranes there is no endothelial lining, although some of the connective tissue corpuscles may be found on the free border of the membranes. The outermost fibres of the connective tissue blend with the neighboring tissue. When the neighboring tissue is cartilage the fibres penetrate a portion of its matrix and form fibro- cartilage. The membrane may be thrown into folds, the Hav- ersian fringes, or into small elevations, the villi. The capillary blood-vessels are numerous in the synovial membranes. The synovial secretion is a glairy, viscid fluid, somewhat similar in appearance to the white portion of an uncooked egg. Mucous membranes occur on those surfaces which commu- nicate with the exterior of the body, consequently they are lined by epithelium. The mucous membranes are not continuous with serous membranes, except in one instance, which is at the begin- ning portion of the oviduct. A mucous membrane consists of two portions, an epithelial and a connective tissue portion termed the tunica propria. The epithelial portion varies according to the location of the membrane ; it is stratified squamous in the mouth, in the pharynx below the posterior nares and in the oesophagus ; simple columnar in the stomach and intestines ; ciliated in the trachea, upper portion of the pharynx, epididymis and oviduct. The tunica propria may occur as a thin or as a thick layer of con- nective tissue. The connective tissue of which it is composed consists of white and yellow fibres ; in some localities there is a preponderance of the former, in others a preponderance of the latter. The portion of the tunica propria nearest to the epithe- lium is condensed and is termed the membrana propria, or base- ment membrane. The tunica propria sometimes contains lym- phoid tissue in some instances loosely arranged, in other in- stances collected into nodules. Usually the connective tissue of the tunica gradually blends with the underlying connective tissue (submucous membrane), but in some instances it is separated 68 MANUAL OF NORMAL HISTOLOGY. from the submucous connective tissue by one or two layers of involuntary muscle fibres, forming a muscular layer to the mucous membrane, termed the muscularis mucosae. A mucous mem- brane, in order to give a greater surface, may be thrown into folds, as the valvulae conniventes of the small intestine ; into elevations, as the papillae of the tongue and the villi of the small intestine; or it may form depressions, forming glands. Glands are of different varieties, depending upon the simplicity or com- plexity of the depressions. If the depression is as a single tube, it is termed a simple tubular gland (Fig. 74, a). If the depress- ion gives off secondary tubular projections, it is termed a com- pound tubular gland (Fig. 74, d). If the de- pression is as a dilatation it is termed a simple sac- cular gland (Fig. 74, c). If the depression ter- minates in more than one saccule it is termed a compound saccular (or racemose, from its simi- larity in appearance to a bunch of grapes) gland (Fig. 74, d}. Experiment 75. Stain with silver nitrate a piece of omentum, and transfer it to the slide, being careful that it is not wrinkled, and mount in balsam. Examine and look for the endothelium of lymphatic vessels. Examine the endothelium of the serous membrane, looking especially for stomata and stigmata. Sketch. Exp. 76. Stain with silver nitrate and mount a piece of the central tendon of an animal's diaphragm. Look for lymphatic vessels. Sketch. Exp. 77. Stain with haematoxylin a transverse section of the thoracic duct, mount, and examine. Notice the similarity which exists between it and a transverse section of a vein. Sketch. Exp. 78. Examine the specimens mounted in Exps. 19 and 24, and study the structure of the mucous membrane. Sketch. Fig. 74. Diagrammatic representation of the general shape of the varieties of glands. a, simple tubular; b, compound tubular; c, simple sac- cular; rf, compound saccular or racemose. MANUAL OF NORMAL HISTOLOGY. 69 CHAPTER IX. THE ALIMENTARY CANAL AND ITS APPENDAGES. Food, before it can be utilized for the maintenance of the body, must be digested and absorbed into the blood. After the food has been taken into the mouth it is divided into small particles, the process being termed mastication, which is effected by means of the teeth. The teeth, are firmly retained within their sockets by means of the alveolar periosteum, which is reflected upon the roots of the teeth as a root membrane. Bach tooth is divided into three parts-a crown, a neck, and a root, according to some authori- ties ; into two parts-a crown and a root, by others, who regard the neck as a portion of the root. The crown is the portion of the tooth which projects beyond the gum. The crown of the tooth may exist as one elevation or cusp, two or more. If there be only one cusp the tooth is termed a cuspid, if two cusps a bicuspid, if three a tricuspid, etc., the number of cusps to one tooth usually not exceeding five. The neck of the tooth, or of the root of the tooth, is the portion which is embedded in the gum. At the junction of the neck with the crown there is a constriction termed the gingival line. The enamel above the line forms a ridge termed the basil ridge, or cingulum. The root is the portion of the tooth which is embedded in the alveolar process of the maxillary bone, or in the gum and alve- olar process, if the neck be considered as a portion of the root. It consists of a body continuous above as the neck, and termin- ating below in an apex in the lower jaw ; vice versa in the upper jaw. In the centre of the tooth, running lengthwise, there is a cavity termed the puep cavity, the portion of which contained in the crown is termed the pulp chamber, and the portion in the root the root canal. The pulp chamber at its upper portion in the lower teeth or the lower portion of the upper teeth terminates as a club-shaped cavity, with two or more projections, termed cornua, if the tooth has two or more cusps. The root canal is a continuation of the pulp chamber, and communicates with 70 MANUAL OF NORMAL HISTOLOGY. the subdental tissue by means of an opening in the apex of the fang. If the root should have more than one fang, there is a root canal in each. Fig. 75. Longitudinal Section of an incisor tooth (partly diagrammatic). a, enamel; b, interglobular spaces; c, dentine; e, crusta petrosa; f pulp cavity; rf, artery; v, vein, and n, nerve passing into pulp cavity through apical foramen; h. maxillary bone; i, pericementum; m, stratified squamous epithelium of gum. The dentine exists as a zone bounded internally by the pulp cavity, externally by the enamel of the crown and the crusta petrosa of the root. It consists of an organic substance in which are mineral salts, and through which pass canals, termed the dentinal canals. The dentinal canals extend in a radial manner from the pulp cavity to just beneath the enamel, terminating in MANUAL OF NORMAL HISTOLOGY. 71 irregular-shaped spaces, termed the interglobular spaces, the area containing the spaces being termed the interzonal layer. Just before reaching the interzonal layer the tubules usually divide into two branches. A dentinal tubule contains a fibrilla, which appears beaded, and is either derived from a nerve or from a cell contained in the pulp. Offshoots from the fibrilla extend into the dentine, permeating it as network. In chemical com- position dentine is very similar to bone, but there is more miner- al matter in dentine than in bone, the amount of organic matter in dentine being about 27 or 28 per cent.; of inorganic matter, which contains chiefly calcium phosphate, fluoride, carbonate and magnesium phosphate, about 72 or 73 percent. The enamel is found only on the crown of the tooth as a covering to the dentinal substance, and consists of hexagonal- shaped prisms closely packed together and usually perpendicu- lar to the zone of dentine. The prisms appear to be cross- striated, which is due to the minute canals which pass between the prisms and send branches into the prisms dividing them up into small cubical-shaped masses. In the deeper portion of the enamel the prisms appear to cross one another. The membrane of Nasmyth is a delicate membrane composed of keratose (horny) epithelial plates which occur on the surface of the enamel in the very young, usually becoming worn away as the child becomes older. In chemical composition enamel is some- what similar to bone, but in enamel the amount of mineral mat- ter is about 96 to 98 per cent., the chief salts being calcium phosphate, fluoride and carbonate. The CEMENTUM, or crusta petrosa, is found only on the root of the tooth as a covering to the dentinal substance. In struc- ture it resembles compact bone, but does not contain canals. The lamellae are disposed longitudinally around the fangs; be- tween the lamellae are lacunae, which possess numerous can- aliculi with well-marked branches. In chemical composition, as well as in structure, the cementum resembles bone more than either the dentine or enamel does. It contains about 30 per cent, organic matter and about 70 per cent, inorganic matter. The dental PULP is somewhat similar to the marrow of bone. It consists of a reticulum of areolar and lymphoid tissue, in which are blood-vessels, nerves, lymphatics, and cells. The cells include lymphoid and "medullary" cells. The medullary 72 MANUAL OF NORMAL HISTOLOGY. cells, somewhat similar to the myeloplaxes of marrow, are large protoplasmic masses, which contain usually four or five nuclei, and are generally arranged as a layer on the outer surface of the pulp, being the remains of the odontoblasts of young teeth. Into the dentinal canals the dentinal fibrillae extend from the pulp passing between the medullary cells. These fibrillae, giving off branches, reach the interglobular spaces, where they pro- bably communicate with the contents of the spaces, from which fibrillae extend into the enamel and into the canaliculi of the lacunae of the cementum. Whether the fibrillae are protoplas- mic projections from cells contained in the pulp, or nerve fibrils, is as yet an unsettled question. From the manner in which they stain when treated with chloride of gold, and their beaded appearance, they seem to be nerve fibrillae. The blood supply to the tooth is large. One or more arter- ioles enter the pulp cavity through the opening in the fang of the tooth, divide into capillaries in the pulp, then form one or more veins, which pass out in the same way as the arteries enter. The lymphatics arise in the clefts of the pulp, and pass out into the neighboring tissue, communicating with the channels of the tissue. The nerves which go to and enter the pulp cavity are of the medullated variety. They lose their medullary sheaths and their axis-cylinders divide into fibrillae, which are beaded in appearance. The ultimate distribution of the fibrillae is an un- settled question, but probaply they extend into the dentinal canals as the dentinal fibrillae to the various portions of the tooth. Experiment. 79. Prepare a longitudinal and a transverse section of a tooth in the same manner as you prepared the speci- men of bone. After having mounted them, examine. Notice the pulp cavity, dentine, enamel, and cementum. Sketch under the low power the outlines of the tooth ; under the high power portions of its structure. Exp. 80. Prepare a thin section of a tooth recently extracted, as in Exp. 79, and put it into a dilute solution of chromic acid (.5 per cent.) for forty-eight hours. Wash with distilled water and stain with haematoxylin. Examine and look especially for the dentinal fibrillae. Sketch. Exp. 81. Stain with haematoxylin a fresh specimen of denti- nal pulp. This may be done by putting the pulp in normal MANUAL OF NORMAL HISTOLOGY. 73 saline solution on a slide and adding the haematoxylin. Cover and examine. Look for the fibrous reticulum, lymphoid cells, nerves, and medullary cells. Sketch. THE SALIVARY GLANDS. The principal salivary glands are the submaxillary, parotid, and sublingual. The salivary glands are of the compound ra- cemose variety, each being formed by a duct leading from the mucous mem- brane of the mouth. The duct branches dichotomously, the branches subdivid- ing in the same man- ner, their ultimate branches terminat- ing in dilated blind pouches to form the lobules. Each lobule is formed by a number of small pouches termed acini, or alveoli. Areolar tissue forms a capsule to the gland, and sends inshoots, {trabeculae} into the gland, which subdivide it into lobes and separate the lobules from each other. The alveoli are oval in shape, and are of two kinds, mucous and serous, depend- ing upon the kind of secretion which they give. The mucous alveoli are so termed because they give a mucous secretion, which is of a ropy consistency and contains mucin. Each alveolus consists of a basement membrane upon which rests a layer of secreting cells. Each cell is conical in shape, arranged with its base on the basement membrane and apex toward the centre of the alveolus, and contains a clear- looking protoplasm. In the protoplasm near the basement Fig. 76. A section of submaxillary gland of a child (under low power). a, fibrous capsule ; b, trabeculae, dividing the gland into lobules; e, acini; d, ducts. 74 MANUAL OF NORMAL HISTOLOGY. membrane is the nucleus surrounded by a few granules. Between the cells there is a small amount of cement substance, of a hyaline appear- ance. In the peri- pheral portion of the alveolus, sometimes causing a bulging of the basement mem- brane, there is a cres- cent-shaped collection of dark granular- looking cells termed crescent of Gianuzzi, or demilune of Hei- denhain, the constitu- ent cells of which are termed the marginal cells. The serous aeveoli, so termed because they give a serous secretion which contains serum albumin, are smaller than the mucous alveoli. The cells of this type of alveolus possess a granular- looking protoplasm, the nucleus of which is in the centre of the cell. The cells nearly fill the alveoli, leaving a very small lumen per- ceptible. The ducts begin at the alveoli, the membrana propria of the alve- oli being continuous with that of the ducts. The duct, as it begins at the lobule, is lined by simple squamous epithelium, which, as the duct increases in size, is re- placed by a modified form of columnar epithelium termed rod epithelium. The rod epithelium occurs as a single layer of columnar shaped cells, each cell appearing to consist of two zones, the inner of which is granular and contains the nucleus; Fig. 77. A section of a salivary gland of an infant showing mucous alveoli. a, acinus; a', acini possessing crescents or demilunes; c, areolar connective tissue: d, transverse section of a duct; dr, longitudinal section of a duct. Fig. 78. A section of the parotid gland show- ing serous alveoli. a, acinus; d, duct; c, connective tissue. MANUAL OF NORMAL HISTOLOGY. 75 the outer zone appears to be striated, the striae or rods so arranged that an imaginary line continued in their long axis would pass through the centre of the duct, probably are little canals. Of the human being, the parotid gland is composed of serous alveoli, the sublingual of mucous alveoli, and the submaxillary of both varieties. The blood passes into the gland by means of arteries, which pierce the areolar tissue capsule and send branches along the tra- beculae, which terminate in a capillary network around the alveoli. Veins arise from the capillary network, and convey the blood from the gland. The lymphatic vessels arise in the fibrous tissue between the lobules and lobes, and communicate with those of the capsule, finally passing into the lymphatics of the neighboring tissues. The nerves of the salivary glands are composed of both varie- ties, medullated and non-medullated. The nerves follow the division of the ducts, and form a network around the alveoli. It is possible that the ultimate fibrillae pass through the base- ment membrane and terminate between or within the cells. Experiment 82. Stain with haematoxylin and eosin and mount a section of the human submaxillary or parotid gland and one of the sublingual. Examine and look for mucous and serous alveoli, crescents of Gianuzzi, and ducts. Sketch. THE TONGUE. The tongue is a muscular organ, covered by mucous mem- brane except at its points of attachment. The organ is divided into two lateral halves by a septum, or raphe, composed of con- nective tissue. The muscular tissue of which it is composed is of the voluntary variety, the fibres being arranged in bundles which run longitudinally, vertically, transversely and obliquely, some of the muscle fibres branching. Between the bundles of muscle fibres there is a loose network of areolar connective tissue, in which are blood-vessels, nerves, lymphatic vessels and glands. The glands of the tongue are of two kinds, mucous and serous. The mucous glands are of the compoud racemose type, are found in the submucous tissue, and are composed of mucous 76 MANUAL OF NORMAL HISTOLOGY. alveoli. The serous glands are found in the submucous tissue Fig. 79. A section of the tongue of a child. b, mucous membrane forming papillae; c, junction of the dorsal surface with the lateral border; a, artery; v, vein ; voluntary muscle cut in various sections; £', mucous gland; e, adipose tissue; /, fibrous tissue; d, a transverse section of a papilla. and between the bundles of muscle fibres. They are of the compound racemose type, and exist only in the posterior por- tion of the tongue, es- pecially in the region covered by the cir- cumvallate papillae, their ducts opening in the fossae which surround the papillae. The mucous mem- brane of the tongue is divided into two layers, epithelial and fibrous. The epithelial portion consists of stratified squamous epithelium, the lower Fig 80. The mucous membrane of the under surface of the tongue of a child. a, stratified squamous epithelium; c, tunica propria; b, microscopic papilla. MANUAL OF NORMAL HISTOLOGY. 77 border of which is thrown into depressions which fit over the papillae of the fibrous layer. The papillae of the tongue are of two kinds, the microscopic and macroscopic. The microscopic papillae are elevations of the outer portion of the fibrous tissue of the tunica propria. The macroscopic are elevations of the mucous membrane. The former variety occurs in all portions of the mucous mem- brane, while the latter occurs only on the dorsum of the tongue. The macroscopic papillae are of three varieties : 1. Conical, or fili- form. 2. Fungiform. 3. Circumvallate. The conical papillae are the most numerous of the papillae. They are conical in shape, the epithelium of which they are composed becomes keratose at the apex of each cone and pro- jects as filaments of a horny appearance. The Fungiform pa- pillae are bulbous- looking projections of the mucous membrane, consisting of a peripher- al portion composed of epithelium, and a central portion composed of fi- brous tissue, an exten- sion of the tunica pro- pria. At the base of the fungiform papilla there is a slight depress- ion of the mucous mem- brane, termed a fossa. Fig. 81. A portion of a section of the tongue of a rabbit (posterior region.) m, voluntary muscle cut longitudinally; m', voluntary mus- cle cut transversely; s, serous acini held together by fibrous tissue septa (/); v, vein; a, artery; n, nerve. Fig. 82. Filiform, or conical papilla, of the cat's tongue. a, horny threads due to the keratinization of the upper layers of cells of the mucous membrane (6); c, fibrous core derived from the tunica propria; d, a transverse section of one of the papillae. 78 MANUAL OF NORMAL HISTOLOGY. The circumvallate papillae are somewhat similar to the fungiform type. They are about ten in number, and are arranged in two rows, which converge and meet at the fora- men caecum of the tongue, forming a V-shaped arrangement, the divergence being toward the apex of the tongue. Each papilla is about inch transversely. Separating the rows of papillae from the vallum there is a depression in the mucous membrane, termed a fossa. The under surface of the epithelium appears corrugated, in order to fit over the papillae of the fibrous tissue which composes the central portion of each circumvallate papilla. T h e epithelial portion of the lateral boundaries of the papilla contains nerve endings for the appreciation of the sensation of taste, termed taste-buds. The taste- buds are not limited to the circumvallate papil- lae, as they may also be found in the epithelium scattered throughout the mucous membrane of the tongue, and in the mu- cous membrane of the soft palate and epiglottis. A taste-bud is an ovoid or pear- Fig. 83. A fungiform papilla from the tongue of a rabbit. a, stratified squamous epithelium; c connective tissue of the tunica propria. Fig, 84. Circumvallate papillae of a rabbit's tongue, a, stratified squamous epithelium ; b, taste-buds. MANUAL OF NORMAL HISTOLOGY. 79 shaped body, which communicates with the exterior by means of a small opening, the gustatory pore, on the surface of the tongue. It is composed of cells, neuro epithelial cells which evidently are cells of stratified squamous epithelium, which have been modified for their special function. The cells are of two kinds, gustatory and sustentacular. The gustatory cells are spindle-shaped, consisting of a body in which there is a large oval nucleus, and tapering ends, the distal of which extends into the gustatory pore; the proximal end is supposed to be continuous with a nerve fibrilla. The sustentacular cells are also spindle-shaped, but are broader than the cells of the other variety, and. probably become gustatory cells. The fibrous portion of the mucous membrane, the tunica propria, consists of white and yellow fibrous tissue, among which, especially at the posterior por- tion of the tongue is lymphoid tissue collected into nodules, or follicles. Beneath the tunica propria there is some fibrous tissue continuous with that of the tunica and with that which separates the bundles of muscle fibres from one another, termed the submu- cous layer. To the fibrous tissue of the submucous layer the muscle fibres of the tongue are inserted. Blood-vessels enter the tongue, and branch, the branches supplying the muscles and the fibrous tissue of the tunica propria. Lymphatic vessels arise in the clefts of the fibrous tissue, join, and form large channels which pass out with the blood-vessels. The nerves to the tongue are of the medullated variety, some of the fibres terminating in the muscle fibres as motor end-plates, others in the gustatory cells of the taste-buds. Experiment 83. Stain and mount a section of a rabbit's tongue, the section having been preferably obtained from the posterior portion. Examine and notice the papillae on the surface, the muscle fibres cut transversely, longitudinally and obliquely, the areolar tissue, blood-vessels, and nerves. Find a taste bud, and examine with the low and high powers. Sketch. Fig. 85. A taste-bud highly magnified. a, gustatory pore; g gustatory cell; 5, sustentacular cell; f tunica pro- pria containing medullated nerve fibres; e, stratified squamous epi- thelium. 80 MANUAL OF NORMAL HISTOLOGY. Exp. 84. Prepare a section of the anterior portion of the tongue of a dog or rat, and notice the conical papillae. Sketch. The mucous membrane of the mouth is continuous ante- riorly at the outer border of the lips with the skin, posteriorly with the mucous membrane lining the fauces. It consists of two portions, an epithelial and a fibrous. The epi- thelial portion consists of stratified squamous epithelium. The fibrous portion or tunica propria consists of white and yellow fibrous tissue, densely arranged in the gums, not so densely in the lips, and least dense in the buccal mucous membrane. In Fig. 86. j, surface of skin; /?, hair follicle containing' a portion of a hair in the center; a, sebaceous gland; m,' voluntary muscle cut in various sections; £ anterior border showing continuity of the epithelium of the skin with that of the mouth (w); g, mucous gland with duct (rf); v, blood vessels; /, fibrous connective tissue. A longitudinal section of the upper lip (human). the tunica propria there are small mucous glands of the com- pound racemose variety, which communicate with the free surface by means of ducts which are lined near their orifices by stratified squamous epithelium. The tunica propria possesses papillae, MANUAL OF NORMAL HISTOLOGY. 81 which cause depressions in the lower border of the epithelial covering. The fibrous tissue of the tunica is intimately con- nected to the periosteum of the palate and maxillary bones. The mucous membrane lining the fauces is similar to the buccal mucous membrane, except that it contains a large amount of lymphoid tissue, which is collected into masses or nodules; on each side of the fauces there is an accumulation of lymphoidtissue, so great as to cause a protuberance of the mucous membrane, which is termed the tonsil. The tonsil primitively regarded, is a protuberance of the mucous membrane of the fauces, the tunica propria of which consists of lymphoid tissue loosely and densely arranged. It consists of three portions, epithelial, lymphoid, and fibrous. The Fig. 87. A portion of a section of a human tonsil. e, stratified squamous epithelium; f, fibrous tissue; w, lymphoid nodules; c, crypt, Epithelial portion consists of stratified squamous epithelium, covering the free surface of the tonsil, continuous with that lining the fauces. The epithelial covering may form depressions 82 MANUAL OF NORMAL HISTOLOGY. into the gland, which are termed the crypts of the tonsil, and are lined by stratified squamous epithelium. In some instances there may be as many as twelve crypts in one tonsil. The lymphoid portion consists of a close-meshed network of ade- noid tissue closely packed with lymphoid cells. The lymphoid tissue is collected into nodules, and is also diffused. In the glands which possess crypts the nodules are most numerous around the crypts. The fibrous portion corresponds with the tunica propria of the mucous membrane and the submucosa. It extends into the tonsil at its attached border and contains vessels and nerves. In the portion of the fibrous tissue beneath the epithelium there may be mucous glands. The lymphoid cells multiply rapidly, some of which become lymph corpuscles or leucocytes, while others penetrate the epithelial covering and enter the fauces as salivary corpuscles. The distribution of the blood and lymphatic vessels and the nerves is the same as in the mucous membrane elsewhere. Experiment 85. Stain and mount a section of a kitten's tonsil. Notice the epithelial, lymphoid, and fibrous portions. Look for salivary corpuscles along the free surface of the section, and notice the similarity between them and the leucocytes. Sketch. Exp. 86. Prepare a specimen of the human tonsil. Notice the crypts lined by stratified squamous epithelium and surrounded by lymphoid nodules. Sketch. THE PHARYNX. The pharynx is a musculo-membranous tube extending from the posterior nares and fauces to the oesophagus. It consists of three coats, mucous, fibrous, and muscular. The mucous coat is continuous above with that of the nares and fauces, below with that of the Eustachian tubes, larynx, and oesophagus. The epithelial portion of the mucous membrane is composed of two varieties of epithelium, that lining the upper portion down to the palate, and extending into the Eustachian tubes, is ciliated columnar (stratified); that lining the portion of the pharynx below the hard palate is stratified squamous. The tunica propria of the mucous membiane is composed of white and yellow fibrous tissue, in which there are mucous glands of the compound racemose type termed the pharyngeal glands. MANUAL OF NORMAL HISTOLOGY. 83 There is in the tunica a considerable quantity of lymphoid tissue, collected into nodules in the upper portion of the pharynx, one of which is especially large, and situated between the orifices of the Eustachian tubes, termed the pharyngeal tonsil. Beneath the mucous membrane there is a loosely-arranged area of fibrous tissue, which may be regarded as a submucous coat, although there is no line of demarcation between it and the tunica propria. The fibrous coat consists of densely-arranged fibrous tissue, termed the pharyngeal aponeurosis. Posteriorly it is much thicker than elsewhere, forming the raphe to which the constrictor muscles are attached. The muscuear coat consists of the voluntary variety of muscle. External to the muscular coat there is a sheath com- posed of areolar connective tissue, which connects the pharynx to the neighboring organs. The blood-vessels pierce the outer coats of the pharynx, giving off branches to the muscle fibres, reach the submucous tissue, and form a network from which branches supply the glands and the tunica propria. The lymph- atics arise in the interfascicular clefts of the fibrous tissue in the various coats. The nerves are of both varieties, and besides supplying the muscle fibres they form a subepithelial plexus. Experiment 87. Stain and mount a transverse section of the pharynx. Examine and notice the muscular tissue, the fibrous coat, and the mucous membrane. Took for lymphoid tissue and pharyngeal glands. Sketch. THE OESOPHAGUS. Extending from the lower end of the pharynx to the cardiac end of the stomach there is a musculo-membranous tube, termed the gullet, or oesophagus, which consists of a central opening surrounded by four tunics, or coats : Mucous coat, or tunica mucosa. Submucous coat, or tunica submucosa. Muscular coat. Fibrous coat. The mucosa, the innermost of the coats, is continuous with the corresponding coat of the pharynx. It is thrown into folds termed rugae, which disappear when the oesophagus is distended. It consists of three distinct layers : Epithelial, or inner layer. Tunica propria, or middle layer. Muscularis mucosae, or outer layer. 84 MANUAL OF NORMAL HISTOLOGY. The epithelial layer is composed of stratified squamous epi- thelium. The tunica propria consists of areolar and adenoid tissue. In the lower part of the oesophagus the muscularis mucosae consists of two layers of involuntary muscle, an inner layer composed of circularly disposed fibres, and an outer layer composed of longitudinally disposed fibres. In the upper part of the oesophagus the muscularis mucosae is not present but gradually makes its appearance in about the middle portion, and is quite distinct in the lower portion near the cardiac end of the stomach. Fig. 88. A portion of a transverse section of the oesophagus of a child (upper third). a, stratified squamous epithelium; c, tunica propria; m, rudimentary muscularis mucosae; b, a ruga; rf. submucosa containing blood-vessels, adipose tissue and oesophageal gland; e, inner layer andjg, outer layer of muscular coat; connective tissue; h, fibrous coat. The submucosa, sometimes termed the areolar or vascular coat, consists of an areolar connective tissue network in which MANUAL OF NORMAL HISTOLOGY. 85 ramify blood-vessels, lymphatics, and nerves. Mucous glands of the compound racemose variety, termed the oesophageal glands, occur in the submucosa. The acini of these glands are lined by modified columnar-shaped cells, the nuclei of which are near the basement membrane; the ducts are lined by cuboidal cells, except near the surface of the mucous membrane, where they are lined by an extension of the stratified squamous epithelium of the surface. The muscular coat consists of two layers of muscular tissue, an inner layer, composed of bundles of circularly-disposed fibres, and an outer layer, composed of bundles of longitudinally-dis- Fig. 89. A portion of a transverse section of the oesophagus of a dog (lower third). a, stratified squamous epithelium; c, tunica propria: m, muscularis mucosae (longitudinal and transverse sections of involuntary muscle); b, ruga; d, submucosa; e, inner layer, and g, outer layer of muscular coat; f, fibrous connective tissue; h, fibrous coat. posed fibres. Between the two layers there is a layer of areolar connective tissue continuous with the areolar tissue of the mus- cular layers, which in turn is continuous with the submucous and the fibrous coats. In the upper third of the oesophagus the 86 MANUAL OF NORMAL HISTOLOGY. muscle fibres are of the voluntary variety, in the lower third they are of the involuntary variety, and those of the middle third are of both varieties, there being a gradual diminution and dis- appearance of the voluntary variety, and a gradual appearance and increase of the involuntary variety from the upper to the lower third. The fibrous coat consists of yellow fibrous tissue mixed with a small amount of the white fibrous variety. The fibres are arranged circularly around the oesophagus, some of which are continuous with the areolar tissue of the muscular coat. External to the fibrous coat there is areolar connective tissue, which holds the oesophagus to the neighboring organs. The blood-vessels pierce the fibrous coat, and extend to the submucosa, giving off branches to the fibrous and muscular coats. In the submucous coat the vessels form an anastomosing net- work, branches from which supply nourishment to the tunica propria. The lymphatics arise in the fibrous tissue of the oesoph- ageal coats and accompany the veins from the oesophagus. The nerves are of both varieties, and after supplying the other coats form a subepithelial plexus in the mucosa. Experiment 88. Stain and mount a transvere section of the oesophagus. Examine and notice to which variety the muscular tissue belongs. Look for oesophageal glands and ducts. Notice the mucous membrane thrown into folds or rugae. Sketch. The stomach is a dilated portion of the alimentary canal, and THE STOMACH. A longitudinal section at the junction of the oesophagus and stomach of a cat, showing continuity of mucous membrane. a. epithelium of oesophagus; b, point of junction ; c, small patch of stratified squamous epi- thelium; j, glands; t, tunica propria; e, collection of lymphoid tissue (lenticular gland); m, muscularis mucosae. Fig. 90. MANUAL OF NORMAL HISTOLOGY. 87 has four coats, mucous, submucous, muscular and serous. The first three are contin- uous with the corre- sponding coats of the oesophagus, while the serous coat is anala- gous to the fibrous tunic of the oesoph- agus. The mucous MEMBRANE, the most important of the gas- tric coats, consists of three portions, the epithelial, the tunica propria, and the mus- cular. The epithelial portion consists of simple columnar epi- thelium, the cells of which hdve not a stri- ated border, resting upon a basement membrane,which dips into, or nearly to, the muscularis mucosae, forming the gastric glands. The gastric glands are of two kinds', named accord- ing to their principal locations, cardiac and pyloric glands. The cardiac glands are most nu- merous at the cardiac end of the stomach, although they may be found in all regions of the gastric mucous membrane except A portion of a longitudinal section of the cardiac end of the stomach (human). m, surface of mucous membrane showing simple colum- nar epithelium (<z) and mouths of cardiac glands (a1); b, tunica propria; c, longitudinal section and (c') trans- verse section of secreting tubule of cardiac gland; o, oxyntic cell; d, muscularis mucosae; j, submucosa; <?, inner layer (cut transversely) and g, outer layer (cut longitudinally) of the muscular coat, between which is the fibrous tissue (f)', i, endothelial layer of serous coat. Fig. 91. 88 MANUAL OF NORMAL HISTOLOGY. near the pylorus. They are compound tubular glands, arranged perpendicularly to the surface of the mucous membrane. Each gland, resembling in appearance a pair of trousers, consists of a mouth and two secreting tubules. The epithelium lining the mouth of the gland is of the simple columnar type, which Fig. 92. Glands of the stomach. A, cardiac gland; B, pyloric gland; a, epithelial surface of the gastric mucous membrane nt, mouth; e, secreting tubules; it, chief or peptic cells; c, oxyntic cell; d, lumen or canal becomes cuboidal at the beinning of the tubules. The tubule is long, reaching to, or nearly to, the muscularis mucosae, and has an irregular contour. It consists of a canal lined by secreting cells. The canal runs the length of the tubule, terminating below in a blind extremity, above in the mouth of the gland, the por- tion of the tubule at its junction with the mouth being termed MANUAL OF NORMAL HISTOLOGY. 89 the neck. Lining the canal there is a layer of cells of an irreg- ular quadrilateral shape, each cell containing a nucleus and granular protoplasm. These cells are termed central according to their location, chief or peptic cells on account of giving the ferment pepsin. Situated external to the central cells is the other variety, which consists of cells arranged, not in a continu- ous row, but at irregular intervals, thus causing the irregular contour of the tubules. These cells are ovoid in shape, each containing a nucleus and granular protoplasm, and are termed parietal according to their location, ovoid on account of their shape, and oxyntic (Gr. o£o$, acid) because they secrete the hydro- chloric acid of the gastric juice. Leading from the canal between two neighboring chief cells to an oxyntic cell, there may in some instances be a clear-looking area, which is probably a means of communication between the oxyntic cell and the lumen of the tubule. The pyloric glands are simple tubular glands, located prin- cipally at the pyloric end of the stomach, and lined by a layer of quadrilateral cells very similar in appearance to the central cells of the cardiac glands. The cells, owing to their similarity in appearance, and when treated with reagents, to the central cells of the cardiac glands, probably secrete pepsin. The pyloric glands do not contain oxyntic cells. Although usually the car- diac glands are compound tubular, and the pyloric simple tubu- lar, some of the cardiac glands may be simple tubular, and some of the pyloric compound tubular. The tunica propria of the mucosa consists of a network of areolar and lymphoid tissue between and around the gastric glands. Scattered about in the tunica propria, but most numer- ous at the pyloric end of the stomach, are collections or nodules of lymphoid tissue termed lenticular glands. The muscularis mucosae consist of two layers of involun- tary muscle, the inner of which is composed of fibres disposed circularly; the outer of fibres disposed longitudinally. The submucosa consists of a network of areolar connective tissue, in which ramify blood-vessels, lymphatics and nerves. The nerves form a sympathetic plexus, the plexus of Meissner. The muscular coat consists of involuntary muscle disposed in two layers, an inner circular and an outer longitudinal; at the fundus there is a third layer consisting of a few oblique fibres 90 MANUAL OF NORMAL HISTOLOGY. internal to the circular layer. Of the two layers the circular is much thicker than the longitudinal, and between them there is a layer of areolar tissue which contains, besides vessels, a sympa- Fig. 93. Portion of a longitudinal section at the junction of the pyloric end of the stomach with the duodenum, showing the mucous and submucous coats. p, pyloric gland; p,' pyloric gland of the compound tubular type; b, duodenal glands: b,' sections of ducts of the duodenal glands passing through the muscularis mucosae (m) to reach the submucous coat ( /') to form the glands (,e); s, surface of mucous membrane; t, tunica propria; a. aggregation of lymphoid tissue (lenticular gland). thetic nerve plexus, the plexus of Auerbach. At the pylorus the circular fibres become more numerous and form a sphincter, termed the sphincter pylori. The serous coat, the most external tunic, is a reflection from the peritoneum, and covers nearly the entire surface of the organ. In the empty condition of the stomach its mucous membrane is thrown into longitudinal folds, termed rugae. The blood-vessels pass to the stomach between the layers of the mesentery, penetrate the muscular coat, giving off branches to the bundles of muscle fibres and the areolar connective tissue MANUAL OF NORMAL HISTOLOGY. 91 between the layers of the muscular coat, and reach the submucosa, where they form a network, which supplies the tunica propria, glands, and muscularis mucosae. The lymphatics arise in the connective tissue of the gastric coats, and form larger channels which pass out with the blood- vessels. The nerves are of both varieties, the medullated nerves being derived from the pneumogastrics, the non-medullated from the solar plexus. The nerves form a plexus of non-medullated fibres between the layers of circular and longitudinal fibres of the mus- cular coat, termed the plexus of Auerbach, from which fibres pass to the submucosa and form a secondary plexus, termed the plexus of Meissner, the fibres of which are smaller than those of the former plexus. From the latter plexus branches pass between the bundles of fibres of the muscularis mucosae, to supply the glands and to form a subepithelial plexus. Experiment 89. Stain and mount a longitudinal section of the junction of the oesophagus with the stomach. Notice the cessa- tion of stratified squamous epithelium and the appearance of simple columnar epithelium, and tubular glands. Exp. 90. Stain and mount a transverse section of the cardiac end of the stomach. Examine and sketch, under the low power, the coats. Under the high power study the structure of the cardiac glands, the muscularis mucosae, and the layers of the muscular coat. Exp. 91. Stain and mount a longitudinal section of the pyloric end of the stomach. Study and sketch the pyloric and the len- ticular glands. Compare the appearance of the coats with the appearance of the corresponding coats of the specimen used in the foregoing experiment. THE SMALL INTESTINE. The small intestine has four coats, which are similar in nom- enclature and disposition to those of the stomach. The mucous coat is the most important of the coats of the small intestine, and consists of an epithelial portion, a tunica propria, and a muscularis mucosae. The epithelial portion con- sists of simple columnar epithelium, the outer border of the constituent cells being striated. The striated border, or cubicu- lar seam, has not been demonstrated to consist of small canals leading from the free surface for a short distance into the cell- protoplasm, but owing to the fact that the striae occur on an 92 MANUAL OF NORMAL HISTOLOGY. absorbing surface it seems probable that they aid absorption, and are little canals appearing as dark lines when viewed under a microscope. The tunica propria consists of a network com- A portion of a transverse section of the duodenum of a cat. v, villi; c' duct of duodenal gland; /, tunica propria; w, muscularis mucosae; 5, submucosa, containing a section of the ductus communis choledochus (rf) as it is passing through the coats of the duodenum to open on the surface of the mucous membrane along with the pancreatic duct, and a portion of a duodenal gland (.c); a, inner layer and c, outer layer of the muscular coat; b, connective tissue; e endothelial layer of serous coat. Fig. 94. posed of areolar and lymphoid tissue. The muscularis mucosae consist of two layers of involuntary muscle, the inner of which is composed of fibres disposed circularly around the intestine, the outer of longitudinally-disposed fibres. The mucous membrane contains the following important structures : Villi. Crypts of Lieberkuhn. Brunher's glands. Solitary follicles. Peyer's patches. Valvulae conniventes. MANUAL OF NORMAL HISTOLOGY. 93 The Villi are finger-like projections of the mucous mem- brane, which are very numerous (about four million, according to Krause), and give to the mucous membrane a velvety-like Portion of a transverse section of small intestine of a cat. Fig. 95. v, villi; c, crypt of Lieberkuhn; t. tunica propria; m. muscularis mucosae; s, submucous coat containing areolar connective tissue, blood-vessels, lymphatics and plexus of Meissner; a, inner layer of muscular coat, the fibres of which are cut longitudinally; e, areolar con- nective tissue, between the two layers of the muscular coat aud extending between the bundles of muscle fibres of the two layers, containing areolar connective tissue, blood- vessels, lymphatics and plexus of Auerbach; g, ganglion cells; d, serous coat. surface. They are most numerous and largest in the upper portion of the intestine, and become fewer and smaller in size the nearer they are to the lower end of the small intestine, their average length being about mm., their diameter about mm. 94 MANUAL OF NORMAL HISTOLOGY. A VILLUS consists of an epithelial covering of simple colum- nar-shaped cells with a striated border, among which are goblet cells; a club-shaped lymph radicle, termed a lacteal or chyliferous vessel, which is in its central portion; a capillary network, formed by afferent arterioles and forming the efferent veins; involuntary muscle fibres derived from the muscularis mucosae, which run lengthwise of the villus and are connected to the fibres of the network of connective tissue; a connective tissue network composed of areolar and lymphoid tissue. The crypts of Lieberkuhn, or simple follicles, are simple tubular glands extending perpendicularly from the surface of the mucous membrane to the muscularis mucosae. They occur in the mucous membrane between the villi, and are lined by simple A villus of specimen used for Fig. 95, highly magnified and partly diagrammatic Fig. 96. c, epithelial covering containing simple columnar cells with striated border and goblet cells (_g); f, tunica propria; muscular fibres derived from the muscularis mucosae: a, artery ; v. vein; c, lacteal or chyliferous vessel; ,g'. crypt of Lieberkuhn; f, epithelium of the gene- ral surface of mucous membrane of the intestine. columnar epithelium and goblet cells. Their function is to secrete the intestinal juice, the succus entericus. MANUAL OF NORMAL HISTOLOGY. 95 The valvulae conniventes are folds of the mucous mem- brane and part of the submucosa, and may be as much as two inches in length. The mucous membrane contains villi and crypts. They are not present in the beginning of the duodenum, appearing about two inches from the pyloric end of the stomach, becoming long and numerous in the lower portion of the duo- denum and upper portion of the jejunum. At about the middle of the jejunum they begin to decrease in number and size, dis- appearing in the lower portion of the ileum. Their functions are to retard the onward movement of the intestinal contents and to give a greater surface for absorption. The duodenal or Brunner's glands, are limited to the duo- denum and are tubular glands, which extend to the muscularis mucosae and in some instances into the submucosa, where the tubules become coiled upon themselves. They are lined by simple columnar-shaped cells. The solitary glands are collections of lymphoid tissue, round or oval in shape, occurring in the tunica propria of the Fig. 98. A portion of a longitudinal section of the jejunum of a cat, showing valvulae conniventes. v, valvulae conniventis possessing villi, crypts and lymphoid aggregations (solitary follicles); m, muscularis mucosae; f, submucosa, part of which extends into valvulae conniventes; a. inner layer (cut transversely) and c, outer layer, (cut longitudinally) of the muscular coat; b, fibrous tissue between the two layers of muscle; s, serous coat. intestines. They are most numerous in the ileum, sometimes causing a bulging of the free surface of the mucous membrane and encroaching upon the submucosa. They consist of an ade- 96 manual of normal histology. noid-tissue network, in the meshes of which are lymphoid cells and capillaries. The agminated glands, commonly termed Peyer's patches, are collections or aggregations of solitary glands, one patch containing, in some instances, as many as thirty solitary glands. Fig. 99. A portion of a transverse section of the ileum of a cat (low power). a, surface of mucous membrane possessing villi and crypts; b, submucosa containing agmi- nated gland, or Peyer's patch; c, inner layer, and d, outer layer of muscular coat. They are from one to four inches long, and are most numerous in the ileum. They are located in the mucous and submucous membranes of the small intestine, opposite to the amesenteric border. The submucosa consists of a loose network of areolar connec- tive tissue containing blood-vessels, lymphatics, and a plexus of nerves termed the plexus of Meissner. The muscular coat consists of involuntary muscle disposed in two layers, an inner circular and an outer longitudinal. The muscular coat is thicker in the upper portion of the small intes- tine than in the lower portion and is comparatively thin in the jejunum. Of the two layers, the inner is the thicker. Between the two layers there is a small amount of areolar tissue, which contains, besides vessels, a nerve plexus, the plexus of Auerbach. The serous coat is a reflection from the peritoneum, and envelopes the small intestine, excepting portions of the duo- denum and the amesenteric border. The blood-supply to the small intestine is abundant. The arteries enter between the layers of the mesentery, penetrate the muscular coat, giving off branches to the layers through which they pass, and reach the submucosa, where they form a network. {See Fig. 97, Colored Plate I.) MANUAL OF NORMAL HISTOLOGY. 97 From the network branches pass to supply the muscularis mu- cosae, tunica propria, crypts, duodenal glands, solitary glands, Fig. 100. Portion of a longitudinal section of the ileum of a cat (high power). e. epithelial lining of mucous membrane; c, crypt; v, villus; t, tunica propria; c', section of a crypt; m, muscularis mucosae; s, submucosa containing part of a Peyer's patch (a), portions of which extend through the muscularis mucosae and cause a bulging of the free surface (at d) of the mucous membrane; b, inner layer (cut transversely) and g, outer layer (cut longitudinally) of the muscular coat;./, areolar connective tissue between the two layers of muscular coat; h, serous coat. Peyer's patches and villi. Veins arise from the capillary net- works, and pass out in the same manner as the arteries enter. 98 MANUAL OF NORMAL HISTOLOGY. The lymphatics arise in the connective tissue of the intestine. The most important origin is in the lymphoid tissue of the tunica propria, in the solitary and agminated glands, and villi. The clefts in the lymphoid tissue of a villus are continuous or com- municate with the club-shaped lacteal in its centre. The nerves which pass to the small intestine are of the non- medullated variety, and are derived from the solar plexus of the sympathetic system. The fibres form a plexus between the two layers of the muscular coat, termed the plexus myentericus of Auerbach, from which fibres pass to the submucosa and form a secondary plexus, the plexus of Meissner, in which the fibres are smaller and the ganglia less numerous than in the former plexus. Experiment 92. Stain and mount a longitudinal section show- ing the junction of the pyloric end of stomach with the beginning portion of the duodenum. Notice the appearance of the Brunner's glands in the submucous coat. Exp. 93. Stain and mount a transverse section of the duo- denum. Examine and sketch the arrangement of the coats. Examine a villus and a crypt, measuring the length of each. Look for Brunner's glands in the submucous coat. Sketch. Exp. 94. Stain and mount a longitudinal section of the jeju- num. Notice the thickness of the coats as compared with the corresponding coats of specimen used in Exp. 93. Notice the valvulae conniventes ; the villi and crypts on their surface, and the fibrous core derived from the submucous coat. Look for solitary follicles. Sketch. Exp. 95. Stain and mount a longitudinal section of the lower portion of the ileum. Examine and study a Peyer's patch. Notice the difference between the villi and crypts when compared with those of the preceding specimen. Sketch. Exp. 96. Mount an injected section of the small intestines. Examine and study the disposition of the blood-vessels. Exp. 97. If a prepared specimen of the small intestine, show- ing one of the plexuses of nerves, be available, examine it and sketch. THE LARGE INTESTINE. The large intestine has four coats similar, in nomenclature and disposition, to those of the small intestine. The mucous membrane is covered by simple columnar epithelium, and pos- MANUAL OF NORMAL HISTOLOGY. 99 sesses a well-marked muscularis mucosae divided into two layers, an inner circular and an outer longitudinal. The mucous mem- A portion of a transverse section of the large intestine. Fig. 101. c, crypt of Lieberkuhn cut lengthwise: c', crypt cut transversely; /, tunica propria; m, muscularis mucosae; /, submucosa; a, solitary follicle; b, inner layer, and g. outer layer of muscular coat; s, areolar tissue between the two layers of the muscuiar coat; h, serous coat; e, depression between the rugae. brane differs from that of the small intestine in containing only the crypts of Lieberkuhn and the solitary glands. The crypts are very numerous and larger than those of the small intestine, and are lined by simple columnar-shaped cells, among which there are numerous goblet cells. .The solitary glands occur in 100 MANUAL OF NORMAL HISTOLOGY. the upper portion of the large intestine, being present in the submucous and mucous coats. The submucosa is similar to that of the small intestine. The muscular coat is composed of involuntary muscle disposed in two layers, an inner circular and an outer longitudinal, the fibres of the former layer increasing in number at the lower portion of the rectum to form the internal sphincter ani. The outer layer is composed of longitudinal fibres, which are arranged in bands ; the fibres in the caecum and colon being about one- half as long as the remaining coats, cause the sacculated appear- ance so characteristic of the caecum and colon. The puckering of the muscular coat causes a puckering of the serous coat; the pouches thus formed are filled with fat, forming the appendices epiploicae. Fig. 102. Portion of a transverse section of the vermiform appendix of a child. a, epithelial portion of the mucous membrane consisting of simple columnar cells and goblet (g) cells; b tunica propria; /, crypts of Lieberkuhn cut longitudinally, obliquely, and transversely; r, lymphoid tissue; c,' solitary follicle; rf, muscularis mucosae; j, submu- cous coat; i, adipose tissue; wi, inner layer, and m,' outer layer of muscular coat; e, serous coat. The lymphatic, blood and nerve supplies are similar to those of the small intestine. The vermiform appendix being a portion of the large intestine is made up in the same manner with a large amount of lymphoid MANUAL OF NORMAL HISTOLOGY. 101 tissue in the mucous coat; the lymphoid tissue in some cases being so great as to simulate an agminated gland. Fig. 103. Portion of a longitudinal section of the lower portion of the rectum (human) showing contin- uity of the mucous membrane of rectum with that of anus, and that of the anus with the skin just beyond. a, rectal mucous membrane; b, anal mucous membrane; c, skin. Experiment 98. Stain and mount a section (transverse) of the upper portion of the large intestine. Examine and notice the rugae of the mucous membrane, the crypts of Lieberkuhn, the goblet cells, and the outer layer of the muscular coat. Sketch. Exp. 99. Stain and mount a longitudinal section of the large intestine. Examine and look for a solitary gland. Sketch. Exp. 100. Stain and mount a transverse section of the vermi- form appendix. Notice the large amount of lymphoid tissue present in the mucous and submucous coats. Sketch. Exp. 101. Stain and mount a longitudinal section of rectum in the region of the anus. Notice the crypts in the rectum, the stratified squamous epithelium of the anus, and the layers of the skin beyond the anus. THE LIVER. The liver is a compound tubular gland, the excretory duct of which is the hepatic duct. The tubular arrangement, although not well shown by the human liver, is shown by the gland of some of the lower forms of animal life, especially the frog. It has twro coats, the outer of which is a reflection from the perito- neum termed the serous coat, the inner a fibrous coat. The serous coat forms a complete covering to the organ, being absent at the attachments of the ligaments and at the bottom of the fis- sures. The fibrous coat is composed of densely-arranged white and yellow fibrous tissue, the former variety predominating, and 102 MANUAL OF NORMAL HISTOLOGY. forms a complete covering beneath the serous coat. The fibrous coat sends projections, termed trabeculae, into the substance of the liver and accompanies the vessels entering the liver at the transverse fissure as a reticular capsule termed the capsule of Fig. 104. Portion of the liver of the pig to show the lobular arrangement, consisting of one lobule surrounded by portions of five others. a, intralobular vein; c, cords of liver cells radiating toward centre of lobule: e, intralobular capillaries; b, fibrous tissue of the interlobular spaces in which is a section of a portal canal (rf). Glisson. The capsule divides and subdivides, the divisions accompanying the branches of the vessels ; ultimately the cap- sular fibrous tissue blends with that of the trabeculae sent in from the periphery of the liver. In this manner the liver is divided up into smaller portions, termed lobules. The lobules are not well shown by the human liver, except in the very young child, but are well shown by the pig's liver. They vary from to Ttf inch in diameter, and appear polygonal (usually penta- gonal or hexagonal) in transverse section and quadrilateral in vertical section. In shape they resemble somewhat inverted truncated pyramids. The spaces between the lobules, the inter- lobular spaces, contain four sets of vessels, enclosed and held together by extensions of Glisson's capsule, which are : The branches of the portal vein, termed the interlobular veins. The branches of the hepatic artery, termed the interlobular arteries. Fig. 106. Diagrammatic representation of the liver. a, interlobular artery ; v, interlobular vein ; b, interlobular bile duct; c, intralobular capillaries ; d, bile capillaries ; e, group of liver cells; z, intralobular vein. Fig. 107. Portion of an injected liver of the cat, showing vessels of one lobule and of portions of two adjoining lobules. v, interlobular vein; i, intralobular vein; c, intralobular capillaries. PLATE II FIG. 106 FIG. 107 MANUAL OF NORMAL HISTOLOGY. 103 The branches of the hepatic duct, termed the interlobular ducts. The branches of the lymphatic vessels, termed the interlobular lymphatics. A lobule contains hepatic cells, blood capillaries, bile capilla- ries and a central vein. The hepatic cells vary in size, from to titoo inch in diameter, are polygonal in shape, and each one is composed of a mass of protoplasm in which is one and some- times two nuclei, each nu- cleus containing one or more nucleoli. The cells are enclosed by a thin cell wall, and are arranged in groups radiating from the centre of the lobule toward the periphery. The pro- toplasm of the liver cells contains some fat and gly- cogen. The bile capilla- ries arise between the liver cells, the walls of the ca- pillaries being formed by depressions in adjoining cells, join one another, and empty into the interlobular bile ducts. In the centre of the lobule there is a vein, termed the intralobular vein, toward which the blood capillaries, the intralobular capillaries, derived from the interlobular vein, con- verge. The intralobular vein runs in the centre of the lobule from the base towards its apex, receiving the intralobular capil- laries, and empties into a vein at the apex termed a sublob ar vein. The blood-vessels of the liver. The portal vein enters the liver at the transverse fissure and gives off branches, termed the interlobtilar veins, which pass between the lobules. From the Portion of a section of the human liver. a, liver cells; b, bile capillaries; c, intralobular (blood) capillaries containing colored corpuscles and leucocytes; d, group of liver cells enclosing a capillary. Fig. 105. Fig. 108. Diagrammatic representation of a vertical section of a lobule of the liver. C, intralobular capillaries; /, intralobular vein; .S', sub- lobular vein. 104 MANUAL OF NORMAL HISTOLOGY. interlobular veins capillaries, termed the intralobular capillaries, pass into the lobules, forming an anastomosing network; the vessels, converging toward the centre of each lobule, enclose the cords of liver-cells and empty into the central vein, termed an intralobular vein, which empties into a sublobular vein. The sublobular veins join to form the hepatic veins. The hepatic veins occur as channels in the substance of the liver, and not with the interlobular vessels, their walls, on account of being in close union with the liver-cells, remain open after death. The hepatic veins occur as three main channels, in addition to numer- ous small ones, all of which empty into the inferior vena cava. The hepatic ar- tery enters the liver at the trans- verse fissure, and divides into branches, some of which supply nou- rishment to the capsule of Glisson, and are termed vaginal branches; some supply the capsule of the liver, termed capsular branches; the others become in- terlobular arteries, which give off ca- pillaries, thez>z/<?r- lobular capillaries, which supply nourishment to the interlobular spaces and anas- tomose with the intralobular capillaries. Thus the intralobular capillaries contain blood brought to the liver by the portal vein and by the hepatic artery. The blood derived from the hepatic artery, after it reaches the intralobular capillaries, passes from the liver by means of the same channels which convey the blood derived from the portal vein. The hepatic duct. - The bile capillaries are formed by depressions in neighboring liver-cells, the wall of the capillaries Fig. 109. Schematic representation of the circulation through the liver. a, hepatic artery; v, portal vein; b, interlobular vein; rf, inter- lobular artery; c, intralobular capillaries; c/interlobular capillaries; rf, intralobular vein; J,sublobular vein; h, hepatic vein; <?, ascending vena cava. MANUAL OF NORMAL HISTOLOGY. 105 being portions of the cell walls of the liver-cells. The capillaries join and empty into an interlobular bile duct, which joins the other interlobular bile ducts to form the hepatic duct. The hepatic duct is formed by the union of two channels, one from the right lobe, the other from the left lobe of the liver, each being formed by the junction of the interlobular bile ducts of their respective lobes. It consists of three coats-an inner mucous, a middle muscular, and an outer fibrous. The mucous coat consists of a layer of columnar-shaped cells resting upon a basement membrane, beneath which there is a tunica propria. The middle coat consists of involuntary muscle fibres circularly disposed, among which there is some fibrous connective tissue. The outer coat consists of areolar connective tissue. The hepatic duct and its interlobular branches have numerous diverticula. The contents of an interlobular space are spoken of collectively as a portal canal. A portal canal consists of an interlobular artery, an interlobular vein, an interlobular bile duct, and lym- phatic vessels, all of which are surrounded by an extension of Glisson's capsule and held to- gether by projections from the capsule of each canal. It is common to find more than one of each in one canal. The nerves to the liver are of both varieties, the medullated being derived from the pneumogastrics and the right phrenic; the non-medul- lated from the hepatic plexus of the sympathetic system. The nerves ac- company the vessels into the liver and between the lobules, their termi- nation being unknown at the present time. The lymphatics of the liver are arranged in two sets, superficial, and deep. The superficial set arises in the capsule of the liver. The deep set arises in the connective Fig. 110. Transverse section of a bile duct. a, simple columnar epithel- ium ; b, involuntary mus- cle c, connective tissue. Fig. 111. 106 MANUAL OF NORMAL HISTOLOGY. tissue of the interlobular spaces, and probably around the intra- lobular capillaries as perivascular channels (Disse). The gall bladder consists of three coats similar to those of the hepatic duct. The inner or mucous coat is thrown into folds or rugae, which disappear when the bladder is distended. The middle coat con- tains beside dense fibrous tissue, invol- untary muscle fibres, some of which run longitudinally, others circularly. Experiment 102. Stain and mount a section of a pig's liver. Examine and notice the lobules, the interlobular and intra- lobular veins. Measure two lobules. Sketch. Exp. 103. Stain and mount a section of human or dog's liver. Examine and notice the lobular arrangement under the low power. Examine under the high power the liver-cells and the constituents of a portal canal. Measure three liver-cells. Sketch. Exp. 104. Mount a section of a liver the blood-vessels of which have been injected. Examine and sketch. Exp. 105. Mount and examine a section of a liver the bile capillaries of which have been previously injected. Sketch. A portion of a section of the gall bladder of a cat. a, rugae covered by simple columnar epithelium ; Z>, tunica propria; c, few fibres of involuntary fibres cut longitu- dinally; d, connective tissue containing a few trans- verse sections of involuntary muscle fibres. Fig. 112. THE PANCREAS. The pancreas (Gr. Har, all; Kp«i$, flesh) is a racemose gland, resembling in structure a salivary gland, and is appropriately termed by the Germans "the abdominal salivary gland." It has a connective tissue coat composed of loosely-arranged areo- lar tissue, in which there is some involuntary muscle fibres. The capsule sends trabeculae into the gland, which divide it into lobes and lobules, from which projections extend between the acini. The pancreatic duct, consisting of a fibrous tube lined by simple columnar cells, divides and subdivides, the ultimate branches terminating in dilated blind extremities which form the lobules. The dilated extremities have secondary dilatations termed acini. The columnar-shaped cells lining the pancreatic MANUAL OF NORMAL HISTOLOGY. 107 duct gradually become cuboidal in the branches, then squamous near the dilatations. The acini are more tubular than those of the salivary glands, and are lined by simple columnar epithelium which has become modified for the pur- pose of secreting the pancreatic juice. The protoplasm of the cells is divided into two zones, an outer homo- geneous o r faintly- striated zone which stains readily with carmine and contains the nucleus; an inner granular zone which does not stain readily with carmine. During the secretion of the pancreatic juice the granules, which are claimed to be zymogen, gradu- ally disappear, as a consequence of which the inner zone becomes nar- row and the outer zone broader. Dur- ing the periods of rest the granules accumulate in the inner zone which becomes broader, while the outer zone becomes nar- row. In the ducts, rod epithelium A portion of the pancreas of a cat (low power), serous coat; f, fibrous coat from which extend trabecu- lae (Z) which divide the gland into lobules; a, acini; b, body of Langerhans; d, interlobular duct; c, interacinal connective tissue. Fig. 113. Fig. 114. A portion of specimen of pancreas used in Fig. 113, more highly magnified. a, capillary blood vessel in the interacinal connective tissue (_/"); c. transverse section of an acinus; c', longitudinal section of an acinus; d interacinal duct; b, body of Lan- gerhans. 108 MANUAL OF NORMAL HISTOLOGY. does not occur. Scattered among the acini are round or oval masses of immature acini, which masses are termed the " bodies of Langerhans' The arteries are derived from the splenic, hepatic, and super- ior mesenteric arteries, and ramify in the areolar connective tissue capsule, sending branches between the lobules and the acini. The veins arise from the capillary network around the acini, and pass out in the same manner as the arteries enter, emptying into the splenic and superior mesenteric veins. The lymphatics arise between the acini, and pass through the interlobular and interlobar connective tissue to the capsule, whence they pass to the lumbar glands. The nerves are of the non-medullated variety, and are derived from the splenic plexus of the sympathetic system. They pass between the lobes and lobules, and probably terminate as a plexus around the acini. Experiment 106. Stain and mount a section of the human pancreas. Examine and compare it with a section of the parotid gland. Notice the loose arrangement, the more tubular acini, and the absence of rod epithelium. Took for the bodies of Langerhans and ducts. Sketch. Exp. 107. Examine a specimen of pancreas stained with car- mine. Notice the two zones of the cells composing the acini. Sketch. MANUAL OF NORMAL HISTOLOGY. 109 CHAPTER X. THE AGGREGATIONS OF LYMPHOID TISSUE. Lymphoid tissue may be arranged as a loose network ; or as aggregations, simple or complex. When loosely arranged it is termed diffuse lymphoid tissue, as is found in the tunica propria of the mucous membrane of the alimentary canal. The simplest type of the aggregations of lymphoid tissue occur as the lenticular glands of the stomach. The solitary glands of the intestine are aggregations of lymphoid tissue, usually oval in shape, the peripheral portion of each gland being more dense than the cen- tral portion. The glands are surrounded by a thin capsule of areolar tissue, and are permeated by blood capillaries and lym- phatic vessels as clefts in the tissue. When a varying number of these solitary glands are collected together an agminated gland, or Peyer's patch, is formed. When the solitary follicles are collected together with loosely-arranged lymphoid tissue a com- pound lymph follicle is formed. THE LYMPH GLANDS. The lymph glands are compound lymph follicles somewhat oval in shape. One portion of the surface of each gland is usu- ally less convex than the remainder, in which portion, especially of the large glands, there is a depression, termed the hilum, for the transmission of blood-vessels and the efferent lymph chan- nels. The gland has a distinct capsule, composed of white and yellow fibrous tissue among which are involuntary muscle fibres, connected externally with the areolar connective tissue which serves to connect the gland to the neighboring tissues. In the largest glands the yellow fibrous tissue of the capsule is arranged in alternating layers of longitudinally and circularly-disposed fibres. The capsule sends inshoots into the gland, which termi- nate in a loosely-arranged network. Some of the inshoots are collected into bands termed trabeculae. The substance of the gland is composed of a network of areolar and adenoid tissue, in 110 MANUAL OF NORMAL HISTOLOGY. which there are lymphoid cells and vessels. By the arrangement of the lymphoid tissue the gland is divided into a cortical and a Fig. 115. A longitudinal section of a lymph gland of a sheep. a, network of areolar and adipose tissue; t>, capsule containing circular and longitudinal fibres of connective tissue; e, trabecula; c. lymphoid nodule; i, lymph sinus; if, medul- lary cord; v, vein; I, lymph channel; g, hilum. medullary or central portion. The cortical portion encircles the gland, except at the hilum, and consists chiefly of dense col- lections of lymphoid tissue which are situated between the tra- beculae. The collections of lymphoid tissue are round or oval in shape, similar in appearance and structure to the solitary glands of the intestines. Between the nodules and the capsule of the gland and the trabeculae there is a narrow area in which is loosely arranged fibrous tissue containing lymphoid cells, termed a lymph sinus. MANUAL OF NORMAL HISTOLOGY. 111 The medullary portion consists of loosely-arranged lymph- oid tissue, among which are dense collections of the tissue of irregular shapes termed medullary cords, and ramifying trabe- culae and vessels. The areolar connective tissue surrounding the capsule of the gland is loosely arranged, containing distinct irregular-shaped spaces. The lymph passes through the spaces of the areolar tissue, through the capsule of the gland into the lymph sinuses, whence it passes through the lymphoid tissue of the gland. The lymph in this manner filters through the lymphoid tissue and is drawn toward the hilum to the efferent lymph channels by means of the negative pressure at the hilum caused by the efferent vessels. Its onward course is aided by the contraction of the involuntary muscle fibres contained in the capsule and in the trabeculae of the gland. The blood-vessels enter the gland at its periphery, including the hilum, some of which pass into the substance of the gland enclosed by trabeculae ; others pass directly into the lymphoid tissue. The blood passes by means of arterioles into the sinuses of the cortical and medullary portions, and is carried from the gland by veins which arise in the medullary portion and pass out through the hilum. The nerves to the glands are medullated and non-medullated, the ultimate distribution of which is not known. Experiment 108. Stain, mount, and examine a section of a lymph gland, preferably of a sheep. Sketch, under both powers, portions of the capsule, trabeculae, cortical and medullary regions. # THE SPLEEN. The spleen is a compound lymph follicle, and is very similar in structure to the lymph glands. It has two coats, the outer of which, the serous coat, is a reflection from the peritoneum ; the inner is a fibrous coat, composed of white and yellow fibrous tissue containing involuntary muscle fibres. The fibrous coat sends in trabeculae, which by their ultimate ramifications form a network. The splenic substance is composed of lymphoid tissue arranged as a loose network termed the splenic pulp, and as dense aggregations termed the Malpighian corpuscles. 112 MANUAL OF NORMAL HISTOLOGY. The splenic pulp consists of a network formed by the rami- fications of the trabeculae and adenoid tissue. The junctions of the fibres of the adenoid tissue appear large, sometimes nucle- ated, and have been termed sustentacular cells. In the network there are numerous blood-vessels, lymphoid cells, leucocytes, and colored corpuscles of the blood. Some of the leucocytes and lymphoid cells contain pigment which has been derived from the disintegrated colored corpuscles of the blood. Fig. 116. Portion of a section of the human spleen. c, fibrous capsule; t, trabecula; n, nucleus of involuntary muscle fibre; a, Malpighian cor- puscle; p, splenic pulp; v, blood-vessels; b, blood corpuscles; transverse section of a trabecula. The Malpighian corpuscles of the spleen are dense collec- tions of lymphoid tissue, very similar to the corresponding col- lections in the lymph glands, which may be found throughout the spleen, but are most numerous in its peripheral portion. They ensheath one or more arterioles, are most dense at their periphery, and are surrounded by delicate capsules. The blood-vessels of the spleen are of great importance. The splenic artery enters the spleen at its hilum and divides into MANUAL OF NORMAL HISTOLOGY. 113 numerous branches, some of which are enclosed by trabeculae, while others pass directly into the splenic substance. The arte- rioles become continuous with spaces in the splenic pulp formed by the connective tissue, some of them having previously passed through the Malpighian corpuscles. The walls of the arterioles blend with the fibrous tissue of the network; as a consequence of which the blood flows into the spaces termed sinuses, of the splenic pulp, thus facilitating the disintegration of the enfeebled colored corpuscles of the blood and the addition of lymph cor- puscles, to become leucocytes, to the blood. The blood, after slowly filtering through the lymph- oid tissue, is carried away by veins, which begin in the same manner as the arteries terminate, join, and pass through the hilum as the splenic vein. The lymphatics occur as a plexus in the capsule of the spleen, which is continuous with clefts in the trabe- culae, sheaths of the arteries, and the spaces of the lymphoid tissue. The clefts join and pass as lymphatic vessels from the spleen through the hilum. The flow of the lymph from the periphery of the spleen to the hilum is brought about by the contraction of the involuntary muscle fibres contained in the capsule and the trabeculae, and by the negative pressure at the hilum caused by the efferent vessels. The nerves of the spleen are of both varieties, the medullated fibres being derived from the right pneumogastric nerve, the non-medullated from the semilunar ganglion of the sympathetic system. Fig. 117. Portion of specimen used for fig. 116-more highly magnified, a, Malpighian corpuscle; c, lymphoid cells; b. arteriole; p, splenic pulp; Z, transverse section of a trabecula containing sections of elastic and involuntary muscle fibres; t,' a tra- becula with an artery contained within it. 114 MANUAL OF NORMAL HISTOLOGY. Experiment 109. Stain and mount a section of the spleen. Examine and notice the trabeculae cut longitudinally, obliquely, and transversely ; the Malpighian corpuscles ; splenic pulp; and blood-vessels. Sketch the general arrangement under the low power, and the individual portions under the high power. Measure a Malpighian corpuscle. Exp. 110. Mount and examine an injected section of the spleen of a pig or of a cat. Notice the numerous blood-vessels. Sketch. THE THYMUS BODY. The thymus body or gland, during its early stages of develop- ment, is epithelial in structure, while in its later stages it is lymphoid. It reaches its highest development about the second year of extra-uterine life, then it undergoes retrograde metamorphosis, and dis- appears at the age of puberty (eighteen to twenty-one years ). It consists of two lateral lobes, each of which is composed of lobules. The lobes are enclosed by a capsule, composed of connective tissue con- taining some involun- tary muscle fibres,which sends trabeculae into the gland to divide it into lobules. The trabeculae enclosing the lobules send projections into the lobules, dividing them into small irreg- ular-shaped spaces. The irregular-shaped spaces thus formed contain lymphoid tissue, and some of the remains of the embry- onal epithelial structure. The lymphoid tissue is more densely arranged at the periphery of the lobule than at the centre, thus forming a densely arranged cortical zone enclosing a loosely arranged medullary portion. As the gland degenerates the cen- tral portion appears to be the first part affected , consequently Fig. 118. A portion of the thymus gland of a child. /", fibrous capsule; t, trabecula; c, cortical portion, and m, medullary portion of a lobule. In the me- dullary portion there are three concentric corpuscles, and blood-vessels. MANUAL OF NORMAL HISTOLOGY. 115 the contrast between the medullary and cortical substance becomes more marked as degeneration progresses. The epithel- ial structures which occur in the lymphoid tissue are termed the concentric corpuscles or the cor- puscles of Hassel, are round or oval in shape, and consist of an outer zone concentrically striated, arranged around one or more centrally disposed structures resembling somewhat in appearance epithelial cells. The arteries enter the lobes, and divide into branches, which accom- pany the trabeculae into the lobules and divisions of the lobules. The arterioles pass into the lymphoid tis- sue and form sinuses, from which veins arise and pass from the gland in the same manner as the arteries enter. Fig. 119. Concentric corpuscles of Hassel highly magnified. Fig. 120. A, thymus gland cut tangen tai to the surface; Z, trabeculae; Z, lymphoid cells; c, concentric corpuscles; v, blood-vessels; C, concentric corpuscles under high power. The lymphatics are numerous in the lymphoid tissue, whence they pass to join those in the trabeculae. From the trabeculae 116 MANUAL OF NORMAL HISTOLOGY. they pass to the capsule, and become connected with those of the surrounding tissues. The nerves are derived from the pneu- mogastric nerves and the sympathetic system.* Experiment 110. Stain with haematoxylin and eosin and mount a section of the thymus gland. Examine and notice the lobules, trabeculae, blood-vessels, lymphoid tissue, and the cor- puscles of Hassel. Sketch. ♦The tonsil represents an aggregation of lymphoid tissue, and has been considered in Chapter IX. MANUAL OF NORMAL HISTOLOGY. 117 CHAPTER XI. THE RESPIRATORY ORGANS. THE LARYNX. The larynx is a cartilaginous box-shaped organ composed of cartilages, which are held together by ligaments, moved by muscles, and lined by mucous membrane. The cartilages are of the hyaline and yellow fibrous variety, those of the former variety being the thyroid, the cricoid, and the two arytenoids ; those of the latter variety being the epiglottis, the two cuneiform and the two corniculae laryngis. Lining the laryngeal surfaces of the cartilages there is mucous membrane, which is reflected over the vocal cords. The epithelium of the mucous mem- brane is of the ciliated stratified columnar variety below the false vocal chords. Above the false vocal chords the epithelial lining of the anterior surface of the larynx is composed of ciliated stratified columnar epithelium, while that lining the poster- ior surface is of the stratified squamous variety continuous with that of the pharynx. The ciliated epithelium ceases on the under surface of the epiglottis, and the stratified squamous epithelium begins, covering a portion of its under surface and its entire upper surface. In the mucous membrane there are numerous mucous glands. Connecting the mucous membrane to the cartilages there is fibrous tissue arranged as a submu- cous layer. The fibrous tissue adjoining the cartilage is arranged as a dense layer, and is composed chiefly of the yellow fibrous variety. The ligaments of the larynx consist of yellow fibrous tissue arranged in bands. The muscles of the larynx are of the voluntary variety. Experiment 111. Stain and mount a section of the epiglottis. Examine and notice the epithelium, the tunica propria of the mucous membrane, the acini of the mucous glands, and the cartilage. Sketch. 118 MANUAL OF NORMAL HISTOLOGY. THE TRACHEA. The trachea (Gr. Tpaxda, tumultuous) is a tube continuous with the lower end of the larynx, consisting of cartilage, fibrous tissue, involuntary muscle, and mucous membrane, which are disposed in three coats : Mucous. Submucous. Fibro- cartilaginous. The mucous coat consists of an epithelial portion and a tunica propria. The epithelium is of the ciliated stratified col- umnar variety, among the cells of the outer layer of which are numerous goblet cells. The/wwzra propria consists of white and yellow fibrous tissue containing some lymphoid tissue, and is disposed in two zones, the inner of which is loosely arranged, the outer densely arranged. In the tunica propria ramify blood- vessels, lymphatics and nerves. The submucous coat consists of a loose network of areolar connective tissue, in which blood-vessels, lymphatics, nerves, and glands exists. The glands, termed the tracheal glands, are of the racemose type, being most numerous at the posterior por- tion of the trachea, and are mucous in variety. The fibro-cartilaginous coat, so termed because it is composed of fibrous tissue and cartilage, consists of incomplete cartilaginous rings enclosed in' a fibrous sheath. The cartilage of the trachea is disposed in C-shaped rings, the open portion being at the posterior portion of the trachea, and is of the hya- line variety, the outer surface of which, being invaded by yellow fibrous tissue, becomes yellow fibro-cartilage. The fibrous por- tion of the coat consists chiefly of yellow fibrous tissue, forming an enveloping sheath to the cartilage. It forms a thick layer at the posterior portion of the trachea between the ends of the in- complete rings of cartilage, and also extends between the rings. At the posterior portion of the trachea there is some involuntary muscle fibres disposed in two layers, one containing transverse fibres; the other, longitudinal fibres. The transverse fibres form a continuous layer between the ends of the incomplete cartilaginous rings. The longitudinal fibres are external to the MANUAL OF NORMAL HISTOLOGY. 119 transverse fibres, and are not so well marked. Areolar tissue serves to connect the trachea with the neighboring structures. The blood supply to the tra- chea is derived from the infe- rior thyroid arteries. The vessels penetrate the coats to reach the submucosa, where they ramify, the branches surrounding the glands and supplying the tunica pro- pria. The lymphatics arise in the clefts of the connective tissue contained in the coats of the trachea. The nerves are of both varieties, the me- dullated fibres being derived from the pneumogastric, the non-medullated from the cav- ernous plexus of the sym- pathetic system. Experiment 112. Stain and mount a section of the trachea. Examine and notice the ciliated epithelium, tunica propria, cartilage, tracheal glands, and fibrous tissue. Sketch. Fig. 121, A transverse section of the trachea of the cat. a, ciliated stratified columnar epithelium ; g, goblet cell ; b, tunica propria; c, a layer of elastic fibres cut transversely; d, submucosa containing part of a tracheal gland; e, inner layer, aud e', outer layer of fibrous tissue en- sheathing the hyaline cartilage (_/"); v, blood vessels. THE BRONCHIAL TUBES. The trachea divides into two tubes, termed bronchi, which are similar in structure to the trachea. The bronchi divide, the divisions subdividing, the ultimate divisions, termed bronchioles, terminating in dilated extremities termed infundibula. There is a gradual change in structure of the bronchial tubes from the bronchi to the infundibula. The epithelium gradually changes from the ciliated stratified columnar variety to the ciliated sim- ple columnar, to the non-ciliated simple columnar to the 120 MANUAL OF NORMAL HISTOLOGY. cuboidal and to the squamous, the squamous variety lining the terminal bronchioles and infundibula, car til age gradually changes from cartilaginous rings in the bronchi to cartilaginous plates in the bronchioles. In the terminal bronchi- oles there is no cartilage. As the tubes decrease in size involuntary muscle fibres occur in the outer border of the tunica pro- pria, forming a musculavis mucosae, becoming more marked as the cartilage diminishes in amount, ap- pearing to take the place of the elastic fibres of the outer zone of the tunica propria. The bronchioles consist of fibrous tissue and involuntary muscle fibres, and are lined by simple squamous epithel- ium. The bronchioles continue to divide until the divisions are of a di- ameter of about A to 3V inch, then become dilated, forming the lung substance. Portion of a section of the lung showing bronchial tube. a, epithelial lining of mucous membrane consisting of ciliated simple columnar epithelium ; b, duct of bronchial gland; m, layer of involuntary muscle fibres; jg, bronchial gland in submucosa; c, cartilage plate; e, alveoli; /, bronchial artery; d, pulmonary artery; v. pulmonary vein. Fig. 122. THE LUNG. The substance of the lung consists of the dilated terminations of the bronchioles, and areolar tissue containing blood-vessels, lymphatics and nerves. The terminations of the bronchioles, termed infundibula, intercellular passages, or air sacs, are pouch-like dilations, which have secondary dilations termed air cells or alveoli. The lung, consequently, may be regarded as a manual of normal histology. 121 racemose gland, the ducts of which are the bronchial tubes which terminate in the main duct, the trachea. Fig. 123. e, epithelial (cuboidal) lining of a bronchiole; tn, involuntary muscular fibres; g, bronchial lymph gland; c, alveoli of lung showing lining epithelium (simple squamous); c' alveolus in which are some of the detached epithelial cells; f, fibrous septum, between the aveoli, in which the blood capillaries are located; b, small blood vessel containing corpuscles; a, bronchial artery; v, bronchial vein. Portion of a section of human lung. The alveoli, or air cells, are small pouch-like distensions, which normally are filled with air, varying in size from to tts- inch in diameter. They consist of fibro-elastic tissue, lined by simple squamous epithelium. Between the alveoli is connec- tive tissue, composed of white and yellow fibres, in which ramify the blood-vessels. Covering the lung there is a serous coat, termed the visceral layer of the pleura. The blood supply of the lung.-The lung has two sets of blood-vessels, the pulmonary and the bronchial. The pulmonary artery conveys impure blood from the right ventricle of the heart to the lung. The vessel enters the 122 MANUAL OF NORMAL HISTOLOGY. lung with, but external to, the bronchus, dividing as the bronchus divides and subdivides, and terminates as an anasto- mosing network of capillaries between and around the infundi- bula and alveoli. The blood in this manner is brought into close relation to the air contained within the alveoli, and after being aerated returns to the heart by means of the pulmonary veins. (See Fig. 124, Plate I.) The bronchial artery is derived from the throacic aorta, and conveys pure blood to the lung substance for its nourish- ment. Its branches form a capillary network to supply the tissue of the bronchioles and of the lung, some of the blood pass- ing from the tissue by the bronchial vein and some by the pul- monary vein. The lymphatics of the lung are arranged in two sets, one set arising in the connective tissue of the lung, the other set in the mucous membrane of the bronchioles. Of the first set there are two sources, one just beneath the visceral layer of the pleura, the other in the clefts in the fibrous tissue between the infundibula. The two sets communicate and terminate in the bronchial lymph glands. The nerves are derived from the pulmonary plexuses which are formed by the pneumogastric nerves and branches from the sympathetic system. The fibres possess ganglia, and accompany the branching bronchial tubes. Experiment 113. Stain and mount a section of the lung. Examine and notice the alveoli, the fibrous septa between the alveoli, and sections of bronchioles, and blood-vessels. Look for the lining cells of the alveoli and of the bronchioles. Sketch. If the section include a bronchial tube, study its structure and sketch it. Exp. 114. Stain a section of the lung with silver nitrate. Look for the outlines of the lining cells; also stomata and stigmata. Exp. 115. Mount a section of an injected lung. Examine and notice the capillary network around the alveoli. Exp. 116. Open the thorax of a curarized or pithed frog, being careful not to injure the lungs. Notice the lungs distended with air; the air sacs and the capillary network of vessels. If necessary use an ordinary hand lens. MANUAL OF NORMAL HISTOLOGY. 123 CHAPTER XII. The skin is divided into two zones, an outer zone, termed the cuticle or epidermis; an inner zone, termed the dermis, cutis vera (true skin), orcorium. The epidermis is composed of stratified squamous epithelium, modified to withstand the influence of the atmosphere and violence, acting as a covering for the protection of the underlying dermis. On account of the modification of the epithelium, the epidermis is divided into layers or strata. The dermis also is divided into strata, the division depending upon the disposition of the component fibrous tissue. The strata of the skin are : Epidermis- Stratum corneum. Stratum lucidum. Stratum granulosum. Stratum Malpighi. Dermis- Stratum papillare. Stratum reticulare. The stratum corneum consists of the superficial layers of the stratified squamous epithelium, the cells of which have lost their nuclei and their protoplasm has been converted into or to keratin. The stratum appears as if it were composed of horny- like fibres. The stratum lucidum consists of a layer of cells which have lost their nuclei and whose protoplasm has become con- verted into eleidin, a substance closely allied to keratin. The stratum granulosum consists of irregular-shaped cells the outlines and nuclei of which can be readily observed, and whose protoplasm contains numerous dark granules. The stratum Malpighi or retemucosum, consists of several layers of cells, the lowest layer being composed of irregular cuboidal-shaped cells, the cells of the succeeding layers becom- THE SKIN AND ITS APPENDAGES. 124 MANUAL OF NORMAL HISTOLOGY. ing more flat as they approach the stratum granulosum. In the protoplasm of the cells of this stratum there are pigment gran- ules which give the characteristic hue to the colored races of mankind. Extending between the neighboring cells there are bridge-like projections, which give to the cells a bristling appear- ance ; hence the cells are termed prickle cells. The lower border of the stratum Malpighi is thrown into depressions to fit over corresponding elevations of the dermis. The cells of the lower layers of the epidermis reproduce, the cells thus formed pushing those of the other layers nearer to the surface. The cells as they approach the surface become flatter, and their protoplasm gradually changes to eleidin, then to kera- tin. The outer layers of the stratum cor- neum are continually being thrown or rub- bed off, constituting a physiological desqua- mation. The dermis con- sists of connective tissue, in which are white and yellow fibres, arranged in two strata, the strat- um papillare and the stratum reticulare. The STRATUM PAPIL- LARE consists of dense connective tis- sue arranged as eleva- tions termed papillae, which fit into the de- pressions in the under surface of the epi- dermis. The papillae are about yw inch long and inch in diameter at their base, Fig. 125. A portion of a section of the skin of the heel cut vertical to the free surface. a, upper portion of stratum corneum showing keratinized fibrous remains of superficial epithelial cells, and por- tions of duct of sudoriferous gland; b, lower layer of stratum corneum showing outlines of the cells; c, strat- um lucidum; d, stratum granulosum; e, stratum Mal- pighi composed of prickle cells; /'.stratum papillare containing blood vessels; jf. stratumreticulareshowing portion of a duct of sudoriferous gland, and transverse sections of elastic fibres. MANUAL OF NORMAL HISTOLOGY. 125 and contain capillary blood-vessels. In some of the papillae, especially of the portions of the skin destined for the apprecia- tion of the sense of touch, there are tactile corpuscles. The STRATUM RETICU- LARIS is a loose network of white and yellow fibrous tissue, in which are blood-vessels, lymphatics, and nerves,and in some localities of the body, as the scrot- um, penis and the nipple of the mam- mary gland, invol- untary muscle fibres. The fibres of the stratum reticulare blend with those of the subcutaneous tissue. The two zones of the skin vary in thickness in different parts of the body. The subcutaneous tissue consists of a loose network of yellow and white fibrous tissue, the former predominating. Fat occurs in the subcutaneous tissue, sometimes as a distinct layer termed the panniculus adiposus. In the subcutaneous tissue of some localities, as of the penis, eyelids and labia minora, there is no fat. THE APPENDAGES OF THE SKIN. The appendages of the skin are the nails, the hairs, and the cutaneous glands. A nail consists of an exposed portion, termed the body, which ends anteriorly as a free edge; and of an unexposed por- Fig. 126. Portion of a section of skin of finger cut vertical to the surface. a, stratum corneum; b, stratum lucidum; c, stratum granu- losum; d, stratum Malpighi; e, stratum papillare; f, strat- um reticulare; S, portions of sudiferous gland; h, sub- cutaneous tissue; i, transverse section of a Pacinian cor- puscle; jf. adipose tissue; n, transverse section of a medul- lated nerve. 126 MANUAL OF NORMAL HISTOLOGY. tion, termed the root, which is covered by an overhanging portion, termed the nail fold, of the nail groove in the skin. The portion of the skin beneath the nail is termed the matrix, or nail bed. The portion of the matrix beneath the body of the nail is arranged in vascular and sensitive longitudinal folds. A portion of a longitudinal section of a child's finger showing the nail. f, nail fold; c, nail groove in which is located the root of the nail; n, body of nail; a, body- matrix; b, skin of end of finger. Fig. 127. Beneath the root of the nail the papillae of the matrix are small and less vascular than those of the body-matrix, causing the root to appear more opaque than the body of the nail. The opacity may extend beyond the nail groove, as in the nail of the thumb, producing a semilunar white area termed the lunula. The nail is essentially a highly-developed stratum lucidum, the outer layer of which is slightly keratinized. The nail is attached, except at its free border, to the nail-bed, but only grows at its root. The nail-bed consists of the Malpighian stratum of the epidermis. The nail consists of three layers, the lowest of which is composed of cells similar to the topmost cells of the stratum Malpighi, the middle layer of the stratum lucidum, and the topmost layer of slightly keratinized cells. The hairs are appendages of the skin, and, like the nails, are modifications of the epidermis. They are found on nearly all surfaces which are covered by the skin, being absent on the palms of the hands, soles of the feet and anterior portion of the THE HAIRS. MANUAL OF NORMAL HISTOLOGY. 127 penis. In some localities the hairs are extremely short, as on the upper surface of the eyelids and on the forehead, while in other regions they may be long and numerous, as on the free border of the eyelids, the scalp, external genital organs, etc. Portion of a vertical section of the scalp. Fig. 128. a, stratum corneum; b, stratum Malpighii; c, stratum papillate; d, stratum reticulare; j, portion of a sebaceous gland; s' portion of a sebaceous gland with its duct extending to a hair follicle; e, hair follicle containing a portion of a hair; f, hair bulb fitting over a papilla of the dermis of the hair follicle; g, sudoriferous gland; A, adipose tissue. A hair consists of two portions, a shaft and a rw/. The shaft is the portion which projects beyond the surface of the body, the root the portion below the surface. The lower end of the root is enlarged forming the hair bulb, which is indented on its lower surface to fit over a papilla of the dermis. The root is enclosed by a modification of the epidermis and dermis, termed the hair follicle, which is narrow at the surface, and broad at the lower portion of the root. The hair consists of three portions, the external of which is termed the hair cuticle, the middle the fibrous cells, and the central portion of the medulla or pith. The hair cuticle consists of irregular-shaped cells, arranged as a single layer. The fibrous cells form a layer just beneath the 128 MANUAL OF NORMAL HISTOLOGY. hair cuticle, appearing as long fibrous-looking cells. The me- dulla, or pith, is composed of irregular-shaped granular-looking cells which contain air vesicles and eleidin. The medulla is not present in all hairs. The color of hair depends upon the number of minute air vesicles and the amount of pigment contained in the cells of the medulla and of the fibrous layer. As a rule, the greater the amount of pigment the darker the hair, and the greater the number of air vesicles the lighter the hair. The hair follicle consists of modified epidermis and der- mis. It consists of an outer fibrous and an inner epithelial por- tion. The fibrous portion is a modification of the dermis, and consists of three layers, an outer layer composed of connective tissue, chiefly of the yellow fibrous variety, the fibres of which are disposed lengthwise of the follicles; a middle layer, com- posed of connective tissue, the fibres of which run circularly around the follicle, and an inner layer, composed of a circularly- disposed hyaline membrane, corresponding to a membrana pro- pria, termed the glassy membrane. In the middle layer of the fibrous portion of the follicles, in the regions where involuntary- muscle fibres occur in the dermis, involuntary muscle fibres exist. Next to the glassy mem- brane comes the epithelial portion, which is subdi- vided into an outer and an inner root sheath. The outer root sheath is composed of several layers of cells, which are similar to stratified squamous epi- thelium, and corresponds to the stratum Malpighi of the skin, the cuboidal cells resting upon the glassy membrane. The inner root sheath is composed of three layers. The layer nearest to the outer root sheath is composed of elongated non-nucleated cells, and is termed Henle's layer. The middle layer is composed of one or more rows of polyhedral nucleated cells, and is termed A transverse section of a hair and its follicle. a, outer layer, and b, inner layer of the fibrous portion of the follicle; c, glassy membrane; d, outer root sheath; e, Henle's layer; f, Hux- ley's layer; g. cuticular layer. Fig. 129. MANUAL OF NORMAL HISTOLOGY. 129 Huxley's layer. The third layer, the layer nearest to the cuticle of the hair, is composed of cells similar to, and closely connected to those of, the cuticle of the hair. Some of the involuntary muscle fibres of the corium extend to the hair follicle, forming an arrector pili. The contraction of the ar- rectores pilorum produces an erection of the hairs and a papillary appear- ance of the skin around the roots of the hairs, givingthe condition termed cutis anserina (goose skin). The geands of the skin are of two varieties, the sebaceous and the sudori- ferous. The sebaceozis glands are found in connection with the hairs, but may be found in localities which do not possess hairs. They are racemose glands situated in the corium and open usually in the upper portion of the hair follicle. The acini are lined by several layers of polyhedral cells undergoing fatty metamorphosis to produce the sebum. The duct is lined by cuboidal-shaped cells. The sebum is an oily liquid at the tem- perature of the body, which becomes of the consistency of tallow on ex- posure to the atmosphere. It con- tains oil globules and debris derived from the disintegration of the cells lining the acini. The sudoriferous glands commonly termed the sweat glands, are of the simple tubular type, and extend from the free surface of the skin to the lower portion of the stratum reticulare, in some instances into the subcutaneous tissue. Bach tube becomes Portion of a longitudinal section of the anterior border of the upper eye lid, a, stratum corneum; b, stratum Malpighi; o, transverse sections of hair follicles; m, or- bicularis muscle; e, eye lashes; sebaceous gland; a?, duct of Meibomian gland Gg"); c, epithe- lium of conjunctiva;/", fibrous connective tissue. Fig. 130. Fig. 131. Portion of a sebaceous gland of the scalp. a, acinus; c, a secreting cell; /, fibroustissue; d, duct. 130 MANUAL OF NORMAL HISTOLOGY. coiled upon itself, the coiled portion being termed the gland, and the portion leading to the surface the duct. The tube is sur- rounded by the connec- tive tissue and involun- tary muscle fibres of the stratum reticulare. The glandular portion is enclosed in a capsule formed by the fibrous tissue of the stratum reticulare, or of the sub- cutaneous tissue and consists of the coiled portion of the tubule, which consists of three layers besides the en- sheathing capsule of connective tissue and in- voluntary muscle fibres. The outermost layer is the basement membrane. The middle layer appears as round or quadrilateral-shaped cells, each of which contains a nucleus, which have been termed involuntary muscle fibres, but appear more like cuboidal-shaped cells than transverse sections of involuntary muscle fibres. The inner layer is composed of a row of columnar-shaped cells arranged around a central opening. The portion of the duct near the gland is lined by several layers of cuboidal-shaped cells, but as the duct approaches the surface the cuboidal-shaped cells gradually are replaced by a layer of simple squamous cells, which in turn dis- appear in the epidermis, so that the portion of the duct which passes through the stratum corneum is represented by a cork- screw-shaped opening without a distinct lining. The secretion is a fluid which sometimes contains degenerated epithelial cells. The blood-vessels of the skin.-The arteries enter the subcuta- neous tissue and ramify ; some of the branches extend to and form capillary networks around the glands and hair follicles ; others supply the dermis and extend into the papillae of the dermis. The veins arise from the capillary networks and pass into the subcutaneous tissue, terminating in the cutaneous branches of the veins. Portion of a sudoriferous gland of the section used in figure 128. f, fibrous connective tissue containing involuntary muscle fibres, forming a network which holds the portions of the glands together; b, outer layer of cells; c. inner layer of cells lining the canal (a); v, blood vessels. Fig. 132. MANUAL OF NORMAL HISTOLOGY. 131 The lymphatics arise in the corium, join those of the subcuta- neous tissue, and pass away from the skin in the cutaneous lymphatic channels. The nerves of the skin, after reaching the subcutaneous tissue, divide, the fibres extending to the glands, involuntary muscle fibres, and to the corium where a plexus is formed, from which fibres pass into some of the papillae to become tactile corpuscles, while others pass into the epidermis to terminate between the cells. In the subcutaneous tissue of some portions of the body, some of the nerve fibres terminate as Pacinian corpuscles. Experiment 117. Stain and mount a vertical section of the skin of a finger. Examine and notice the strata of the epidermis and of the dermis. Look for Pacinian and tactile corpuscles. Sketch. Exp. 118. Stain and mount a section of skin which is cov- ered with hair, as that of the human scalp or of an animal's ear. Examine and study the structure of a hair, of a hair follicle, and of a sebaceous gland. Sketch. Exp. 119. Stain and mount a vertical section of the skin from the sole of a human foot. Examine and study the structure of the sudoriferous glands and of the subcutaneous tissue. Sketch. Exp. 120. Stain and mount a longitudinal section of the tip of an infant's finger. Notice and sketch the nail, nail fold, nail groove, etc. 132 MANUAL OF NORMAL HISTOLOGY. CHAPTER XIII. THE URINARY ORGANS. THE KIDNEY. The kidney is a compound tubular gland, the excretory duct of which is termed the ureter. Its shape is similar to that of a bean, and about the middle-third of its concave border there is a slit-like opening, termed the hilum, through.which the ureter, blood-vessels, lymphatics, and nerves pass. The kidney has two coats, an outer dense fibrous and an inner muscular coat, the latter consisting of an incomplete layer of involuntary muscle fi- bres. The fibrous coat is tough, smooth and firm, forming a complete covering to the organ, and extending through the hilum to line a central cavity in the kidney, termed the sinus. The fibrous coat is covered externally by a dense mass of adipose tissue, and sends ramifying projections into the substance of the kidney which meet corresponding pro- jections from the fibrous lining of the sinus. In this manner the kidney is divided up into lobules, the number of which varies between eight and eighteen. Al- though the lobular arrangement of the adult human kidney can not readily be recognized, it can easily be recognized in the kidney of a human foetus or of an animal such as the sheep. Fig. 133. The appearance of a kidney which has been cut in half. c, cortical zone; m, medullary zone; p, Malpighian pyramid; b, column of Ber- tini ; e, medullary rays, or pyramids of Ferrein; d, mammilla or apex of Mal- pighian pyramid; j, sinus; A, hilum; a, renal artery; i, calyx of ureter (w). MANUAL OF NORMAL HISTOLOGY. 133 The kidney substance is arranged around a central cavity, the sinus, being absent at one portion corresponding to the hilum, and is divided into two well-marked zones, the outer of which is termed the cortical, the inner the medullary portion. The medullary portion is composed chiefly of conical masses of a pale reddish striated appearance, termed the pyramids of Malpighi, of which there are from eight to eighteen, the num- ber depending upon the number of lobules into which the kidney is divided. The pyramids are arranged with their bases toward the cortical zone, their apices toward and projecting into the sinus. The apex of each Malpighian pyramid is nipple-shaped, and is termed a mammilla, or papilla. Between the pyramids of Malpighi there are columnar-shaped extensions of the cortical substance, termed the columns of Bertini. The cortical zone is about one-half as wide as the medulla, and has a bright reddish-brown granular appearance. The cor- tical zone, besides forming a zone beyond the medulla, sends projections between the Malpighian pyramids, the columns of Bertini. The portions of the cortical zone which extend over the bases of the Malpighian pyramids are termed the cortical arches. Into the cortical arches extend pyramidal projections from the Malpighian pyramids, termed the medullary rays, or the pyramids of Ferrein. The sinus of the kidney contains the dilated portion of the ureter, termed the pelvis, in the same manner as a bag would be held in the hand, with the open end projecting from the hand. The pelvis divides into several divi- sions, generally four, termed infundibula, which in turn divide, each subdivision of which, termed a calyx, encloses the apex of a Malpighian pyramid. The substance of the kidney consists of uriniferous tubules, blood-vessels, lymphatics, nerves, and a connective tissue net- work termed the stroma. The uriniferous tubules begin in the cortical substance of the kidney, and each one after following a tortuous course opens on the surface of a mammilla into a calyx. A uriniferous tubule begins as a funnel-shaped envelope in the cortical substance of the columns of Bertini or of the cor- tical zone, termed the capsule of Bowman, or Malpighian capstde; on leaving the capsule it becomes slightly constricted, the constriction being termed the neck. The tubule now 134 MANUAL OF NORMAL HISTOLOGY. becomes convoluted, thus forming what is termed the prox- imal convoluted tubule, after which it follows an irregular or spiral course toward a Malpighian pyramid, and is termed Fig. 134. Portion of section of kidney of Guinea-pig. f, fibrous coat; m. Malpighian body; t, sections of uriniferous tubules; a, pyramid of Fer- rein; b, Malpighian pyramid; d, column of Bertini; e, mammilla; c, oblique section of arteria propria renalis, and v, one of vena propria renalis; g, loops of Henle. the spiral tubule of Schachowa. The tubule now enters the base of a Malpighian pyramid, its lumen becomes smaller, and it extends down a variable distance toward the apex of the pyra- mid, as the descending limb of Henle's loop, bends upon itself, forming the loop of Henle, and passes toward the cortex, parallel with the descending limb, as the ascending limb of Henle's loop. It then enters the cortical substance as an irregular or zig-zag tubule, and again becomes convoluted, forming the distal convo- luted tubule which terminates in a curved collecting tubule. The curved collecting tubule joins a straight collecting tubule, which passes through a Malpighian pyramid to open on the surface of its mammilla. MANUAL OF NORMAL HISTOLOGY. 135 The straight collecting tubules begin at the apex of the mam- milla, about sixteen or eighteen in number, divide and subdivide Fig. 135. A diagrammatic representation of an uriniferous tubule, with lining epithelium. c, capsule of Bowman; a, neck; b, proximal convoluted tubule; d, spiral tubule of Scha- chowa; e, descending limb of Henle's loop; f, the loop; g, ascending limb of the loop; h, zig-zag tubule; i, distal convoluted tubule; n, curved collecting tubule; straight collect- ing tubule. 136 MANUAL OF NORMAL HISTOLOGY. dichotomously, the branches becoming more numerous the farther they are from the mammilla, and form a Malpighian pyramid. Most of the subdivisions cease on reaching the cortical arch, while others extend into the cortical arch, forming the medullary rays., or pyramids of Ferrein. The structure of a uriniferous tubule is simple, consisting of a basement membrane on which rests a single layer of epithelium.* The shape of the epithelial cells varies in different portions of the tubule. In the capsule of Bowman and the neck it is of the simple squamous variety. In the proximal convoluted tubule and the spiral tubule of Schachowa it is composed of polyhedral-shaped vertically stri- ated cells, a nucleus being in the centre of each, and the indi- vidual cells recognizable with great difficulty. The descending limb of Henle's loop is lined by simple squamous cells; the loop, and ascending limb by striated cuboidal cells; the zig-zag tubule by striated cuboidal cells ; the distal convoluted tubule by cells similar to those of the proximal convoluted tubule, but more distinct; the curved collecting tubule by cuboidal-shaped cells, and the straight collecting tubule by cuboidal and columnar- shaped cells. The portions of the straight collecting tubules near the apex of the pyramid are sometimes termed the tubes of Bellini. The blood VESSELS of the kidney.-The renal artery passes through the hilum into the sinus, external to the pelvis of the ureter, and divides into four or five branches, which, after giving off branches for the nutrition of the neighboring tissues, divide into the main branches of the kidney, the arteriaepropriae renales. The arteriae propriae renales pass into the spaces between the Malpighian pyramids, there being at least two to each pyramid, and extend through the columns of Bertini to the bases of the pyramids. Bach arteria propria renalis arches over the base of the pyramid as an arterial arch to anastomose with its fellow of the opposite side. During its passage through the column of Bertini the artery gives off branches to the capsule of Bowman contained in the column. At the base of the Malpighian pyramid the arteria propria renalis gives off two sets of branches. One set, the arteriae interlobulares, extends toward the periphery of *It is worthy of notice that most of the cells are striated, the striae running toward the lumen of the tubule, which suggests that thev are little canals which aid the cells in extract- ing the constituents of urine from the blood. Fig. 136. A diagrammatic representation of the kidney, showing the blood vessels. a, arteria propria renalis; a.a., arterial arch; i.a., interlobular artery; s, stellate plexus ; a.v., afferent vessel; g, glomeru- lus ; e.v., efferent vessel; p, plexus around convoluted tubules; a1, arteria recta ; px, plexus in Malpighian pyramid ; 7/1, vena recta ; z>.a., venous arch ; i.v., interlobular vein ; v, vena propria renalis ; c, capsule of Bowman ; p.c.t., proximal convoluted tubule; s.t., spiral tubule; d, descending limb of the loop ; e, the loop ; /, ascending limb of the loop; g, zig- zag tubule ; d.c.t., distal convoluted tubule ; h, curved collect- ing and s.c.t., straight collecting tubule ; ex, calyx. Portion of a human kidney injected with Prussian blue and stained with carmine. a, arteria propria renalis ; i, arteria interlobularis ; a1, afferent vessel; <?, efferent vessel; r, convoluted tubule ; />, plexus around convoluted tubules; o, Malpighian body showing a portion of the glomerulus, and the simple squamous epithel- ium of the capsule ; 5, spiral tubule ; /, stroma ; g, glomeru- lus ; b, straight collecting tubule; 7z, loop of Henle; d, descending limb; j, ascending limb; px, plexus in Malpighian pyramid ; u, vena propria renalis. Fig. 137. Plate ill. MANUAL OF NORMAL HISTOLOGY. 137 the kidney to terminate in a capillary plexus, termed the stellate plexus, just beneath the coats of the organ. In their course toward the periphery, the interlobular arteries give off branches to the capsules of Bowman, each branch passing to a capsule as an afferent vessel, becomes coiled upon itself in the space enclosed by the capsule, the coiled vessel being termed a glomerulus. A glomerulus and the enclosing capsule of Bowman compose a Malpighian body of the kidney. The vessel, after having formed a glomerulus, emerges as the efferent vessel, and forms a capillary network around the proximal convoluted tubule. The capillary network thus formed anastomoses with the networks formed by other efferent vessels, the combined network enclosing all por- tions of the tubules which are contained in the cortical portion of the kidney. The other set of branches from the arterial arch, termed the arteriae rectae, arise at right angles to the arch, and pass into the Malpighian pyramids. The arteriae rectae of each pyramid terminate as a plexus at its apex for the nourish- ment of the contents of the pyramid. The veins have three sources, one at the stellate plexus, another at the apex of each Malpighian pyramid, the third at the plexus enclosing the con- voluted tubules. The vein which arises from the stellate plexus is termed a venainterlobularis, and follows a course parallel to the course followed by the corresponding interlobular artery. After receiving the veins which arise from the capillary networks surrounding the convoluted tubules the interlobular vein empties into a venous arch at the base of a Malpighian pyramid, which also receives the veins, the venae rectae, arising from the plexus at the apex of the pyramid. The venous arch, on reaching a column of Bertini, bends and follows a course parallel to the corresponding arteria propria renalis, being termed the vena propria renalis. The venae propriae renales join, and receive veins from the neighboring tissue, forming the renal vein, which passes from the kidney through the hilum. The stroma of the kidney consists of a fine interlacing net- work of areolar tissue (derived from the fibrous coat) which holds the other structures together. The nerves are of the non-medullated variety, derived from the renal plexus. They are about fifteen in number, and enter the kidney through the hilum. 138 MANUAL OF NORMAL HISTOLOGY. The lymphatics arise beneath the capsule, and between the uriniferous tubules and blood-vessels. They pass from the kidney through the hilum and terminate in the lumbar lymph glands. Experiment 121. Examine the kidney of a human foetus and notice the lobulation. Exp. 122. Examine a kidney which has been cut longitudi- nally into halves. Notice the cortical zone, the Malpighian pyramids, the columns of Bertini, the pelvis of the ureter, the sinus, and the hilum. Exp. 123. Stain and mount a section of the kidney. Examine with the low power, and notice the difference between the corti- cal and medullary portions. Under the high power look for and examine the Malpighian bodies, the sections of the tubules, the coats of the kidney, and the blood-vessels. Endeavor to recog- nize the different divisions of the uriniferous tubules. Sketch. Exp. 124. Mount a section of an injected kidney. Examine and notice the glomeruli, the afferent and efferent vessels, por- tions of the capillary networks, the interlobular arteries, the arteriae rectae, and the arteriae propriae renales. Sketch. Exp. 125. If the kidney of an ox be accessible, endeavor to Study and tease out the different portions of a uriniferous tubule. Sketch. THE URETER. The ureter is a fibro-muscular tube, beginning at the pelvis in the sinus of the kidney, and extending to the bladder. It con- sists of two coats, mucous and submucous. The mucous coat consists of three portions, epithelial, tunica propria, and muscularis mucosae. The epithelial portion con- sists of transitional epithelium which extends into the calices above and is continuous with the epithelium of the bladder below. The tunica propria is composed of areolar tissue in which cap- illary blood-vessels ramify and lymphatics arise. The muscularis mucosae is a distinct band of involuntary muscle (hence has been termed the muscular coat of the ureter) continuous above with that of the covering of the kidney, below with that of the bladder. It becomes more distinct as the ureter approaches the bladder, consisting in its upper portion of circu- MANUAL OF NORMAL HISTOLOGY. 139 lar fibres, containing a few longitudinal ones internal to the circular fibres ; and near the bladder consisting of circular fibres, Fig. 138. A transverse section of the human ureter. a, lumen; e, transitional epithelium ; c, circular layer of involuntary muscle with some longitudinal fibres (6): d, outer layer of longitudinally disposed involuntary muscle fibres ; f, fibrous coat containing blood vessels, adipose tissue, nerves and lymphatics. internal and external to which are longitudinal fibres, thus appearing as three layers. The fibrous tissue of the covering of the kidney continues on the ureter, and becomes its submucous coat, and besides contain- ing ramifying blood-vessels, serves as a means of connection between the ureter and the neighboring structures. Experiment 126. Stain and mount a transverse section of the ureter. Examine and sketch. Notice the rugae. THE BLADDER. The bladder consists of three coats. The outer coat is fibrous, and is continuous with that of the ureter, external to which in some regions of the bladder there is a reflection from the peri- 140 MANUAL OF NORMAL HISTOLOGY. toneum, forming a serous coat. The middle coat of the bladder is muscular, and consists of involuntary muscle fibres. The muscle fibres being continuous with those of the ureter have a tendency to be dis- posed in three layers, a middle circular and an inner and outer longitudinal; but as the fibres spread out in the wall of the bladder they become so intertwined that the division into three layers is not very dis- tinct. At the lower end of the bladder the circu- lar fibres increase in number and form a sphincter, the sphincter vesicae. The inner coat is a mucous membrane, which is covered by transi- tional epithelium, and the tunica propria of which contains mu- cous glands and lym- phoid nodules. The arteries to the ureter and to the blad- der ramify in the fib- rous coat of each, the branches extending to the tunica propria, where they terminate in a capillary plexus. The veins arise and pass from the organs in the same manner as the arteries pass to them. The lymphatics arise in the fibrous tissue of the coats and accompany the blood-vessels from the Fig. 139. A portion of a section of the human urinary bladder. e, transitional epithelium; /.tunica propria; m, involuntary muscle fibres most of which are circularly disposed; a, ob- lique sections of bundles of involuntary muscle fibres; b, circulary disposed fibres which, with the preceding two layers, make up the inner layer of the muscular coat; c, middle layer, and ,g, external layer of muscular coat; d, areolar and adipose tissue; f, serous coat. MANUAL OF NORMAL HISTOLOGY. 141 organs. The nerves to the ureter are of the non-medullated variety, while those of the bladder are of both varieties. (The bladder may be regarded as composed of a mucous and a sub- mucous membrane, similar to the ureter.) Experiment 127. Stain, mount and examine a vertical sec- tion of the bladder. Notice the coats, the involuntary muscle fibres, and the transitional epithelium. Sketch. Notice the rugae. THE URETHRA. The urethra, the membranous tube which leads from the bladder to the exterior, consists of a mucous membrane supple- mented by a submucous tissue. The mucous membrane is continuous with that of the bladder, and is lined by epithelium, which varies in character according to the location. In the Prostatic portion of the urethra the epithelium is similar to that of the vesical mucous membrane, being of the transitional variety ; in the membranous portion it is of the stratified colum- nar variety; while in the penile portion it is of the stratified columnar variety to the fossa navicularis, where it becomes of the stratified squamous variety, which is continuous with the stratified squamous epithelium covering the free surface of the penis. In the female the urethra is lined by stratified squamous epithelium, which is continuous with that lining the vagina. Beneath the epithelium of the mucous membrane of the urethra there is a tunica propria, which is composed of white and yellow fibrous tissue and a variable amount of lymphoid tissue. The tunica propria is beset with papillae, which are most numerous near the external opening of the urethra, the meatus urinarius. The submucous tissue consists of white and yellow fibrous tissue, in which there are mucous glands or follicles, termed the glands of Uttre, which open by means of ducts on the free sur- face of the mucous membrane. The submucous tissue contains involuntary muscle fibres throughout portions of the urethra, which are continuous with those of the bladder. In the prostatic portion the muscle is arranged in two layers, an inner longitudi- nal, continuous with the internal longitudinal layer of the mus- cular coat of the bladder, and an outer circular continuous with the corresponding layer of the bladder. The muscle fibres gradually diminish in the membranous, disappearing in the 142 MANUAL OF NORMAL HISTOLOGY. penile portion, becoming replaced by fibrous tissue. On the membranous portion there are also some voluntary muscle fibres, which are derived from the compressor zirethrae muscle. Experiment 128. Stain and mount a transverse section of the penis, preferably of an infant. Examine and look for the ure- thral opening. Sketch the section of the urethra, and designate, by the lining epithelium, which portion it is. MANUAL OF NORMAL HISTOLOGY. 143 CHAPTER XIV. THE GENERATIVE ORGANS OF THE MALE. THE TESTICLE. The testicle is a compound tubular gland, oval in shape, con- vex on its anterior border, and somewhat flattened laterally and posteriorly. It has two coats, the outer of which is serous, and the inner is fibrous. The serous coat is a reflection from the peritoneum, termed the tunica vaginalis propria, and covers the entire organ, ex- cept at its anterior border. The fibrous coat is a dense cover- ing composed of white fibrous connective tis- sue of a glistening white appearance, and is termed the tunica albuginea. The inner portion of the tunica albuginea is loosely arranged , rich in blood-vessels, and is termed the tunica vas- culosa testis. At the posterior border of the gland the tunica albu- ginea forms a dense vertical mass, termed the mediastinum testis, or the corpus Fig. 140. A, testicle; B, portion of globus major of epididymis; C, epididymus; a,tunica albuginea testis; b. section of con- voluted or tortuous tubule; c, vasum efferentium con- taining spermatozoa; d, adipose tissue. Section of testicle of rat. 144 MANUAL OF NORMAL HISTOLOGY. Highmori. From the mediastinum fibrous septa extend to the periphery of the organ, which become connected with the fibrous coat and divide the gland into lobules, termed the lobuli testis. The number of lobules in one testicle is about three hundred. Bach lobule is conical in shape, with its base at the periphery, its apex at the mediastinum, and contains one or more of the secreting tubules, termed the tubuli seminiferi. Bach tubule is divided into three portions: (a) the convoluted or tortuous portion, which makes up the bulk of the lobule, being most tortuous at the base of the lobule and becoming less tortuous toward the apex, assuming (b) a straight course near the apex, termed the vasum rectum, which passes into the medi- astinum and joins other vasa recta to form (c) an anastomosing network in the mediatinum termed the rete testis. The tubules are held together by a loose network of fibrous tissue, the spaces of which network are lined by endothelioid cells (connective tis- sue cells) and appear to be lymph spaces. On examining stained sections of the testicle groups of cells are sometimes observed in the intertubular spaces. These groups of cells have caused some uncertainty in the minds of investigators, and various reasons have been assigned accounting for their presence. After care- fully examining various sections of the testicle the author con- cludes that the groups of cells in the intertubular spaces are merely tangental sections of portions of the tortuous tubules of a different plane than the one in which the sections have been cut. The tubules consist of a basement membrane, upon which rest modified epithelial cells. The epithelial cells of the tortuous portion of the tubule are arranged in several layers, the layer resting upon the basement membrane being composed of cuboidal- shaped cells, the other layers of spherical-shaped cells. The spherical-shaped cells produce the spermatozoa, and are termed spermatoblasts. The spermatoblasts may be observed in differ- ent stages of spermatogenesis, the cells first becoming pyriform, with the large end toward the lumen of the tubule, and the nucleus in the narrow end. The nucleated narrow end becomes the head of a spermatozoon ; the large end, the body and the tail. The epithelium of the vasum rectum consists of a single layer of low cuboidal cells, which represent a transition between the cells of the lowest layer in the tortuous portion of the tubule and the cells lining the tubules of the rete testis. The tubules MANUAL OF NORMAL HISTOLOGY. 145 of the rete testis appear as communicating clefts in the fibrous tissue of the me- diastinum, which clefts are lined by a layer of flat cells. A t the upper border of the me- diastinum the tu- bules leave the testicle, and are termed the vasa efferentia. There are about fifteen vasa efferentia, each of which con- sists of a single tube, which be- comes convoluted, forming a conical-looking mass, and consists of a basement membrane lined by simple ciliated cuboidal-shaped cells, which represent a transition between the flat cells of the rete testis and the ciliated stratified columnar epithelium of the epididymis. In some instances an additional layer of flat cells can be observed next to the basement membrane. The vasa effe- rentia are surrounded by a vascular fibrous network, forming the coni vasculosi. The vascular cones are arranged with their apices toward the mediastum, and their bases form the globus major of the epididymis. The vasa efferentia, after forming the glo- bus major of the epididymis, open into a single duct, termed the epididy- mis (Gr. «rt, upon ; testicle), which passes in a tortuons manner from the upper border of the testicle to the lower border, where it forms a convoluted mass, termed globus minor of the epi- didymis, and continues as the vas deferens. In some instances, Portions of three sections of the tortuous portion of a seminifer- ous tubule showing different stages of spermatogenesis. j, spermatozoa; f, the intertubular fibrous tissue containing blood-vessels, and a group of polygonal-shaped cells (c). Fig. 141. Fig. 142. Sections of vasa efferentia of speci- men used in fig. 140. a, ciliated epithelium; f, fibrous connective tissue; J, spermato- zoa. 146 MANUAL OF NORMAL HISTOLOGY. a tube termed the vas aberrans (Haller) extends from the lower portion of the epididymis or from the beginning portion of the vas deferens, terminating as a blind extremity. It is similar in structure to the vas deferens. The epididymis consists of three coats, a mucous, a muscular and a fibrous. The mucous coat consists of an epithelial por- tion composed of ciliated stratified columnar epithelium, and a small amount of areolar connective tissue as a tunica propria. The muscular coat consists of a thin layer of involuntary muscle fibres. The fi- brous coat con- sists of white fibrous connec- tive tissue the fibres of which are chiefly dis- posed longitu- dinally. Ex- ternal to the fibrous coat there is a layer of areolar tissue containing some adipose tissue, blood- vessels, lymph- aticsandnerves, enclosed by a band of circu- larly disposed white fibrous tissue analo- gous in appear- ance and struc- ture to the tunica albugi- nea of the testis. The vas deferens is a tube which has three distinct coats. The inner, or mucous, coat is lined by stratified columnar epi- thelium. Beyond the. basement membrane there is a small Fig. 143. t, lumen; b. ciliated stratified columnar epithelium; e, tunica pro- pria; d, circularly disposed muscle fibres; f bundles of white fibrous connective tissue; g, fibrous tissue containing- blood- vessels, adipose tissue, nerves, lymphatics: h, fibrous coat; a, artery; v. vein. Transverse section of the epididymis of a rat. MANUAL OF NORMAL HISTOLOGY. 147 amount of fibrous tissue, the tunica propria, which connects it with the muscular coat. The middle, or muscular, coat consists of involuntary muscle fibres disposed in three layers, a middle Fig. 144. a, stratified columnar epithelium; b, tunica propria; c, internal, d, middle, and e. external layers of the muscular coat; f, fibrous coat. A transverse section of the vas deferens. circular, and an inner and outer longitudinal. The outer, or fibrous, coat is composed chiefly of white fibrous tissue contain- ing adipose tissue, vessels and nerves. The mucous coat of prepared specimens appears to be thrown into longitudinal folds, or rugae. Experiment 130. Stain and mount a section of the testicle. Examine and sketch several sections of the seminiferous tubules, the intertubular tissue, septa, and tunica albuginea. Exp. 131. Stain and mount a section of a rat's testicle. Notice the same portions as in the preceding experiment. Took for spermatozoa in the sections of the tubules and also the cells in different stages of spermatogenesis. Took for vasa efferentia outside of the tunica albuginea. Sketch. Exp. 132. Stain and mount a transverse section of the epidi- dymis. Examine and notice the lining epithelium. Took for involuntary muscle fibres. Sketch. 148 MANUAL OF NORMAL HISTOLOGY. Exp. 133. Stain and mount a transverse section of the vas deferens. Examine and sketch the three coats. THE VESICULAE SEMINALES. The vesiculae seminales, the two pouch-like reservoirs for the semen, consist each of a coiled tube of varying diameter, which has pouch-like diverticula extending from it. Each vesicle is composed of three coats, an inner, or mucous, coat, lined by stratified columnar epithelium ; a middle, or muscular, coat, composed of involuntary muscle fibres disposed in three layers, the internal and external of which are composed of fibres arranged longitudinally, while the middle layer is composed of circularly- disposed fibres ; and an outer, or fibrous, coat, derived from the neighboring fascia (the recto-vesicle), which holds the coils and the diverticula of the tube in a mass. The continuation of the vas deferens, after its junction with the tube of the vesicula seminalis, is termed the ejaculatory duct. Each ejaculatory duct terminates in the prostatic portion of the urethra, and consists of three thin coats. The outer, or fibrous, and the inner, or mucous coats, are similar to the cor- responding coats of the vas deferens with the exception that the epithelium is of the simple columnar variety instead of the strat- ified type. The middle, or muscular, coat is composed of two layers of involuntary muscle, very poorly developed, the outer of which is composed of circularly, the inner of longitudinally- disposed fibres. THE PENIS. The penis, the organ of the male adapted for the purpose of copulation, consists of specially-arranged fibrous tissue covered by skin. Through it, lengthwise, passes the urethra for the transmission of the seminal fluid, as well as the urine, to the exterior of the body. The skin of the penis is remarkable on account of its thin- ness, dark color, looseness, and not containg fat in its subcuta- neous tissue. It is continuous at the root of the penis with the skin of the pubes and scrotum. Anteriorly it projects over the glans penis as the prepuce, the free border of the prepuce being connected by means of mucous membrane to the constricted por- tion behind the glans penis, termed the neck, or cervix penis. MANUAL OF NORMAL HISTOLOGY. 149 The glans penis is covered by mucous membrane, the epithelium of which is of the stratified squamous variety continuous with that lining the terminal portion of the urethra. The mucous membrane which covers the glans penis does not contain seba- ceous glands, but does contain sensitive papillae. In the mucous membrane behind the corona glandis, and in that which forms the fraenum preputii, there are small sebaceous glands, termed the glandulae Tysonii odoriferae, which secrete a sebaceous substance which emits a peculiar characteristic odor. The main substance of the penis consists of fibrous tissue, disposed in three cylindrical masses, two of which are on the same level, the other below the two, the three collections thus disposed presenting an appearance similar to that presented by a " double-barrel shotgun, with ramrod below." The two upper masses are termed the corpora cavernosa., the lower mass the corpus spongiosum. The corpora cavernosa are covered by a sheath composed Fig. 145. A transverse section of the penis of a child. a, dorsal artery of penis; f, septum pectiniforme; b, longitudinally disposed fibres, and d, circularly disposed fibres of connective tissue of the sheaths to the corpora cavernosa (c); s, corpus spongiosum containing a transverse section of the urethra in its centre. 150 MANUAL OF NORMAL HISTOLOGY. of white and yellow fibrous tissue disposed in two layers, the outer of which is composed of longitudinal fibres arranged as a sheath common to both of the corpora; the inner composed of circular fibres disposed as a sheath to each of the corpora. Where the circular layers blend together between the corpora cavernosa an incomplete septum is formed, termed the septum pectiniforme. The fibrous sheath sends inshoots into the corpora, which ramify and form a network with wide, irregular - shaped spaces between the fibres. The inshoots consist of white and highly developed yellow fibrous tissue, among which are involuntary muscle fibres. This tissue is termed erectile tissue. The corpus spongiosum is similar in structure to the corpora cavernosa, except that its fibrous sheath is thinner but more elastic than that of the corpora cavernosa. In its sheath and in the tissue surrounding the spongy portion of the urethra (which is contained in the corpus spongiosum) there are usually some involuntary muscle fibres derived from the muscular tissue con- tained in the wall of the membranous portion of the urethra. The tissue around the corpora is fibrous connective tissue, which contains numerous blood-vessels, lymphatics, and nerves. The arteries entering the penis ramify in the fibrous tissue, branches extending into the erectile tissue to terminate in sin- uses. The walls of the arterioles blend with the septa of the erectile tissue, as a consequence of which the blood passes into the spaces. Veins arise in the same manner as the arteries ter- minate, and convey the blood from the penis. The nerves of the penis are of both varieties, the medullated fibres being derived from the internal pudic nerve, the non-medullated from the hypogastric plexus of the sympathetic system. Some of the nerves terminate as Pacinian corpuscles, others as genital cor- puscles. The lymphatic vessels consist of two sets. The super- ficial set arises in the skin of the penis and in the mucous Fig.146. A portion of corpus cavernosum of speci- men used in fig. 145, showing erectile tissue. j, blood sinus; f, fibrous bands containing involuntary muscle fibres; a, artery. MANUAL OF NORMAL HISTOLOGY. 151 membrane of the glans and cervix, and passes to the inguinal glands. The deep set arises in and around the corpora and join the lymphatics of the pelvis. Experiment 134. Examine the specimen of the penis used in Exp. 128. Notice the arrangement of the corpora, the section of the urethra contained in the corpus spongiosum, the erectile tissue, the section of mucous membrane, or of skin, at the peri- phery of the section, and the numerous blood-vessels. Sketch. THE PROSTATE GLAND. In close proximity to the neck of the bladder and somewhat encircling the prostatic portion of the urethra there is a gland which secretes a thin, glairy fluid having a slightly acid reaction, which seems to be for the purpose of diluting the fluid coming from the testes. This gland is known as the prostate body or gland. The prostate gland is a compound racemose gland possessing numerous excretory ducts, varying between twelve and thirty in number. It has two coats somewhat blended together, an outer fibrous and an inner muscular. The inner, composed of invol- untary muscle fibres, accom- panies the fibrous inshoots or trabeculae into the gland as they extend in and divide the gland up into lobules. The ducts start at the free surface of the mucous membrane of the prostatic portion of the urethra and at first are lined by the same kind of epithe- lium as that lining this portion of the urethra, transitional epithelium, but very soon the transitional variety is dis- placed by the simple columnar type, which continues on as the ducts divide and subdivide to terminate in acini. The acini or alveoli are the terminal dilatations of the ducts and are Fig. 147. Portion of a section of the human prostate gland. f, fibrous coat containing involuntary muscle fibres; a, acinus; b, trabecula. 152 MANUAL OF NORMAL HISTOLOGY. lined by low form of simple columnar epithelium modified so as to give the secretion characteristic to the gland. Sometimes what appears to be an additional layer of cells can be observed next to the basement membrane. The acini are held together by the fibrous tissue network derived from the trabeculae which contains a comparatively large amount of involuntary muscle. In the alveoli, especially of old men, peculiar concentricly arranged bodies termed corpora amylaceae are sometimes found. The arteries are derived from the vesical, hemorrhoidal, and pudic arteries, and accompany the trabeculae into the gland finally terminating as a capillary network around and between the acini. Veins arise from the capillary network and pass out in the same way as the arteries enter. The lymphatics arise in the interfascicular clefts of the fibrous tissue, join one another and pass to the neighboring lymph glands. The nerves, consisting of medullated and non-medullated fibres, pass along in the trabeculae to the acini and form a plexus beneath the glandular epithelium. Experiment 135. Stain and mount a section of the prostate gland. Notice the irregular outline of the acini; the lining epi- thelium ; the involuntary muscle fibres between the acini, as well as in the trabeculae and on the surface of the gland. Look for the concentric bodies. Sketch. MANUAL OF NORMAL HISTOLOGY. 153 CHAPTER XV. THE REPRODUCTIVE ORGANS OF THE FEMALE. THE OVARY. The ovary is an oval-shaped organ corresponding in the female to the testicle of the male. It has a serous coat, formed by a reflection of the peritoneum, which differs from other serous membranes in having a dull gray instead of a glistening white appearance, and a layer of short columnar-shaped cells, known as the germinal epithelium, instead of a layer of flat endothelial cells. The substance of the ovary consists of a stroma, Graafian vesicles, and corpora lutea. The stroma consists of a network of connective tissue, among the fibres of which are spindle-shaped cells similar in appearance to connective tissue corpuscles. The portion of the stroma just beneath the serous covering of the organ is more dense than the rest of the stroma, and is termed the tunica albu- ginea of the ovary, which is not a distinct coat like that of the testicle. In the stroma are the Graafian vesicles, corpora lutea and numerous blood-vessels. The Graafian vesicles are usually round, and contain the ova. The ova are derived from the germinal epithelium. Each epi- thelial cell which is to become an ovum, while passing from the periphery of the gland toward the centre, assumes a covering of cells, which probably is formed by the spindle-shaped cells of the stroma, the covering cells reproducing rapidly, so that, in the fully-developed vesicle, the ovum is surrounded by a covering of cells which is continuous with several layers of cells applied to the fibrous covering of the vesicle. A fluid secretion of the cells accumulates in the vesicle. The vesicles are most nume- rous, but immature, in the outer portion of the stroma, just beneath the tunica albuginea. A mature Graafian vesicle is surrounded by an envelope of the stroma, termed the theca folliculi. The theca folliculi 154 MANUAL OF NORMAL HISTOLOGY. consists of two layers, an outer dense layer containing a few blood-vessels, termed the tunica fibrosa, an inner layer the fibrous tissue of which is as a loose network rich in blood-vessels, termed the tu- nica vasculosa. Next to the tu- nica vasculosa there are cells arranged in several layers, forming the membrana gra- nulosa. The cells which are continuous with the membrana granulosa, and surround the ovum, form a membrane termed the dis- cus proligerus. In some cases the discus pro- ligerus is sepa- rated from the membrana granulosa, except at one place of attachment, the space thus formed being occupied by a liquid secretion of the cells, the liquor folliculi. The ovum is sur- rounded by the cells of the discus proligerus ; those near the ovum become arranged perpendicularly to the ovum, giving the zona radiata. Next to the zona radiata, and nearer to the ovum, there is a membrane which, on account of its transparency, is termed the zona pellucida. It appears to be composed of cells of the discus proligerus which have lost their nuclei and have become more or less flattened against the true cell wall of the ovum. The limiting membrane or cell wall of the ovum is termed the vitelline membrane, and is closely applied to the inner surface of the zona pellucida. It can be observed if during the preparation of a specimen of an ovary, the membrane shrinks from the zona pellucida (Fig. 150). Enclosed by the vitelline Fig. 148. Section of ovary of cat. e, germinal epithelium; a, one of the germinal epithelial cells passing inward to become an ovum; b. area of young Graafian follicles; j, stroma containing spindle-shaped fibres, an artery and a vein (v); c, region of advanced Graafian follicles. MANUAL OF NORMAL HISTOLOGY 155 membrane is the protoplasm of the ovum, which is termed the vitellus, and consists principally of oil globules. In the proto- A Graafian follicle (high power). Fig. 149. a, theca folliculi; b, discus proligerus; c, membrana granulosa;cavity occupied by liquor folliculi; o, ovum. plasm there is a nucleus termed the geminal vesicle, in which is a nucleolus termed the germinal spot. In some Graafian vesicles there may be more than one ovum. After the Graafian ves- icle becomes mature it gradu- ally approaches the periphery of the ovary, ruptures, and the ovum, with some of the cells of the discus proligerus, especially the zona pellucida and radiata, adhering to it, is discharged from the ovary. The remains of the vesicle undergo metamorpho- sis to become a corpus luteum. Fig. 150. a, zona radiata; b, zona pellucida; m, vi- telline membrane shrunken from zona pellucida; c, germinal vesicle; germi- nal spot; v, vitellus. Ovum greatly magnified. 156 MANUAL OF NORMAL HISTOLOGY. The corpora lutea are yellowish-looking masses formed by the Graafian vesicles after they have discharged their ova. They are of two kinds, the true and the false corpora. A true corpus luteum is one formed by the remains of a vesicle which has discharged an ovum which becomes fecundated. The false corpus luteuni is one formed by the ruptured vesicle which has discharged an ovum which does not become fecundated. When the vesicle ruptures, the ruptured blood-vessels of the theca folliculi pour blood into the now partially-collapsed vesi- cle. The cells of the membrana granulosa increase in number, and the escaped blood is gradually absorbed, leav- ing behind some of the pigment of the colored corpuscles, so that the vesicle is now filled with cells derived from the membrana granulosa and pigment, and has a yellow color due to the latter. Newly formed connective tissue, containing embry- onic connective tissue, corpuscles and capillaries, makes its appearance between the cells. The tissue thus formed by contracting causes a destruction of the cells, until they even- tually disappear. Finally the fibrous tissue contracts, and the vesicle becomes like a cicatrix, yellow in color, due to the pig- ment obtained from the blood, and is known as a corpus luteum. The pigment gradually disappears. The true corpora lutea differ from the false in being larger, in undergoing the retrograde changes more slowly, and in retaining the pigment longer. The Graafian vesicles are very numerous, "the entire number con- tained within the two ovaries of a child being estimated at over seventy thousand" (Piersol). The Graafian vesicles mature at regular intervals (about every twenty-eight days), the ova pass- ing to the uterus by means of the oviducts to be retained by the uterus if fecundated, or thrown off by the uterus, if not fecun- dated, in the menstrual discharge. The vesicles continue to mature from the age of puberty to the age at which the meno- pause occurs, which usually is at forty-five years. Portion of corpus luteuni. Fig. 151. a, blood-vessel; b, newly formed fibrous tissue; c cells derived from membrana granulosa. MANUAL OF NORMAL HISTOLOGY. 157 The ovarian artery enters the ovary at its attached border and ramifies in the stroma, the branches extending to the periphery and Graafian vesicles. The veins arise in the stroma and pass out to the pampiniform plexus of veins. The lymphatics arise in the clefts of the fibrous tissue in the stroma and walls of the vesicles. The nerves are derived from the pelvic and ovarian plexuses, and supply the stroma and the walls of the vesicles. Experiment 136. Stain and mount a section of a cat's ovary. Examine and study the structure of the germinal epithelium, the stroma, Graafian vesicles, and corpora lutea. Notice the large number of young vesicles just beneath the epithelium. Sketch. THE OVIDUCT The oviduct, or Fallopian tube, has three coats, a serous, a muscular, and a mucous. The serous coat is a reflection from the peritoneum. The muscu- lar coat consists of two layers of involuntary muscle fibres, an external longitudinal and an internal circular. The mucous coat is continuous with the peritoneum at the fimbriated extremity of the tube and with the mucous membrane of the uterus at its uterine extremity. The epi- thelium lining the tube is of the ciliated simple columnar variety. The tunica propria of the mucous membrane is composed of white and yellow fibrous tissue. The mucous membrane is thrown into numerous folds, especially at the fimbriated extremity of the tube. Experiment 137. Stain and mount a transverse section of the oviduct. Examine and sketch the coats under both powers. Portion of a transverse section of the oviduct of a cat. a, serous coat; b, outer or longitudinal layer of involuntary muscle; c, inner or circular layer of involuntary muscle; d, tunica pro- pria ; f, fold of mucous membrane lined by ciliated columnar epithelium; e. lumen. Fig. 152. 158 MANUAL OF NORMAL HISTOLOGY. THE UTERUS. The uterus is composed of three coats, a serous, a muscular, and a mucous. The serous coat is a reflection from the peritoneum, and does not cover the entire uterus. The muscu- lar coATis com- posed of bundles of involuntary muscle fibres which run in va- rious directions and can not be divided into dis- tinct layers, but for convenience are arranged in three, an outer, a middle, and an inner. The outer layer, termed the stratum serosum, is composed of involuntary muscle fibres, disposed in cir- cular and longi- tudinal bundles, which are con- tinued into the structures at- tached to the uterus, i. e., the oviducts and ligaments. The middle layer, termed the stratum vasculosum, on account of the numerous blood-vessels therein contained, is composed of involuntary muscle fibres running in all directions. The inner layer, termed the stratum mucosum, is composed of fibres disposed in all directions, those most inter- Fig. 153. Portion of a section of the uterus of a cat. a, uterine gland; a,' transverse section of uterine gland; b, tunica propria; c inner layer, d, middle layer, and e, outer layer of the muscular coat; f, serous coat. MANUAL OF NORMAL HISTOLOGY. 159 nal being disposed chiefly in a circular manner, and may be regarded as a highly developed muscularis mucosae. The mucous coat consists of a tunica propria, upon which rests the epithelium which is of the ciliated simple columnar variety. The basement membrane, with its lining epithelium, extends from the general surface of the mucous membrane as tubular (simple and compound) glands, termed the uterine glands, to and sometimes among the fibres of the inner layer of the muscular coat. The mu- cous membrane of the cervix uteri is lined on its upper portion by epithelium similar to that of the mucous mem- brane of the body of the ute- rus, but in the lower portion of the cervix the epithelium is of the stratified squamous variety, continuous with that lining the vagina. Besides the uterine glands, there are in the cervical mucous mem- brane mucous follicles which give the characteristic white glairy mucous secretion of the cervix uteri. When reten- tion of the secretion occurs, the ovtda Nabothi are formed. The arteries to the uterus are derived from the ovarian and uterine arteries. They pass beneath the serous coat into the muscular coat and ramify, some of the branches formed supplying the muscle fibres of the muscular coat, while others pass to and ramify in the tunica propria of the mucous membrane. The arterioles terminate in irregular-shaped spaces, the walls of which become blended with the connective tissue between the bundles of muscle fibres. In this manner the blood flows directly into Fig. 154. a, epithelial lining of mucous membrane; b, tu- nica propria, containing uterine glands; a,' transverse section of uterine gland; c, the so- called inner layer of the muscular coat analo- gous to a muscularis mucosae; d, portion of the so-called middle layer of muscular coat. Portion of a section of the human uterus. 160 MANUAL OF NORMAL HISTOLOGY. the spaces in the connective tissue, termed the uterine sinuses. The veins begin in the muscular coat in the same manner as the arteries terminate. The lymphatics arise in the interfascicular clefts of the tunica propria and of the intermuscular connective tissue, and join to form channels in the subendothelial tissue of the serous coat. The nerves of the uterus consist of both varieties, the medul- lated fibres being derived from the lower sacral nerves ; the non- medullated fibres from the hypogastric and ovarian plexuses of the sympathetic. Experiment 138. Stain, mount and examine, a transverse sec- tion of the human uterus. Notice the muscular tissue, blood- vessels, mucous membrane, and glands. Sketch. MANUAL OF NORMAL HISTOLOGY. 161 CHAPTER XVI. THE MAMMARY GRAND, THE THYROID GRAND, AND THE SUPRARENAR BODY. THE MAMMARY GRAND. Each mamma is composed of about fifteen racemose glands, which are enclosed by a fibrous capsule. The excretory tubes, termed the tubuli lactiferi or galactophori, begin as small orifices on the nipple of the mamma, and extend into the substance of the gland. Near its origin each tubule becomes dilated, forming a small reservoir termed an ampulla, for the accumula- tion of milk between the periods of suckling. After forming an ampulla, the tube continues into the mamma, dividing and sub- dividing, the terminal branches terminating in clusters of saccular acini. The cluster of acini formed by each terminal tubule constitutes a lobule, and the lobules formed by each lac- tiferous duct constitute a lobe. The lobes, lobules, and acini are held together by connective tissue septa derived from the fibrous capsule of the mamma, and ramifying blood-vessels contained in the septa. The septa, besides con- taining connective tissue some of which is adipose, contain involuntary muscle fibres. The acini are pouch-like dilatations which are lined by a layer of granular-looking cuboidal-shaped Fig. 155. Portion of a section of human mammary gland (low power). d, galactophorous duct; a, acinus; b, a lobule; c, trabecula. 162 MANUAL OF NORMAL HISTOLOGY. cells. During lactation the cells increase in number, and their protoplasm becomes invaded by oil-globules. The oil-globules are at first small and gradually increase in size, the increase being so great as to push the nucleus and the remaining proto- plasm to the cell wall (as in the conversion of the cells of areolar tissue into fat cells of adipose tissue), and finally the pressure within the cell becomes so great that the cell wall ruptures at the point of least resistance, and the oil-globules are discharged into the lumen of the acinus, thence into the tubule. The ter- minal tubules are lined by a layer of low cuboidal-shaped cells, which gradually are replaced by a layer of columnar-shaped cells, which are in turn replaced by stratified squamous epithe- lium at the orifice, continuous with that of the epidermis. The basement membrane of the tu- bules is supplemented by invol- untary muscle fibres derived from the corium of the skin of the nipple. In the beginning of lactation the flow of milk is preceded by colostrum, which consists of a liquid containing oil globules, epithelial cells termed the colostral corpuscles, and the debris formed by the disintegration of some of the cells contained in the acini. The nipple of the mamma may be regarded as a macro- scopic papilla of the skin. It is covered by stratified squa- mous epithelium rich in pig- ment. Beneath the epithelium there is a mass of fibro-elastic tissue which contains the lac- tiferous tubules, blood-vessels, and involuntary muscle fibres, and corresponds to the corium of the skin. The involuntary muscle fibres, by their contraction, cause erection of the nipple. The areola around the base of the nipple is darkly pigmented, becoming more so during pregnancy, and contains sudoriferous and sebaceous glands. The subcu- Fig. 156. Portion of a mammary gland (high power). t, galactophorous duct, the coat of which contains transverse sections of elastic fibres and involuntary muscle fibres; a, acini containing cells in various stages of milk production; j, interacinal septa. MANUAL OF NORMAL HISTOLOGY. 163 taneous tissue of the nipple and of the areola is remarkable on account of not containing fat. The arteries to the mamma are derived from the thoracic branches of the axillary, the intercos- tals, and the internal mammary. They pass through the fibrous capsule of the gland, and send branches to the lobes and lobules which form capillary networks between the acini. Veins arise from the capillaries and pass from the gland in the same manner as the artery enters, to terminate in the axillary and internal mammary veins. The lymphatics arise in the inter- fascicular clefts of the septa and of the capsule, and are closely connected with the axillary lymph glands. The nerves of the mamma are of both varieties, the medullated variety supplying especially the skin covering the gland, some of the medullated fibres extending to the areola and nipple terminate in Pacinian corpuscles, others in tactile corpuscles which give the sensitiveness to those regions. Experiment 139. Stain, mount and examine a section of the mamma. Notice under the low power the fibrous septa, sections of acini and duct, and blood-vessels. Under the high power, look for the lining cells of the acini and involuntary muscle fibres in the septa. Sketch. Portions of acini of mammary gland highly magnified. Fig. 157. c, lining cells of an acinus; f, fat globules; a, interacinal connec- tive tissue. THE THYROID GLAND. The thyroid gland is commonly classed among the respiratory organs on account of its location. It is a compound tubular gland during its early stages of development, the duct of which communicates with the primitive pharynx, but as its develop- ment proceeds the duct becomes obliterated, so that in its adult form it consists of closed acini held together by connective tissue and ramifying blood-vessels. The adult gland is surrounded by a capsule composed of are- olar connective tissue continuous with that of the neighboring structures. The fibrous capsule sends projections into the gland, 164 MANUAL OF NORMAL HISTOLOGY. which extend between the lobes, lobules, and acini. The acini are usually round or oval in shape, and are composed of a base- ment membrane upon which rests a layer of cuboidal or short columnar-shaped cells. Within the acini there is a yellowish, viscid, semi- liquid material termed the colloid substance, which is secreted by the cells lining the acini, the yellow color of which being obtained from the disintegrated col- oredcorpuscles of the blood. There are also present in prepared sections between the acini collections of cells which are some of the lin- ing cells of acini of a dif- ferent plane than that in which the sections have been cut. Between the neighboring acini there is fibrous tissue, derived from the capsule of the gland, which contains some invol- untary muscle fibres, and numerous connective tissue corpuscles sometimes ap- plied as a layer lining the interfascicular clefts. The clefts in the interacinal septa join each other and form channels between the lobules, which chan- nels communicate with large channels contained in the fibrous capsule. In the clefts and channels are leucocytes, lymphoid cells, and colored blood-corpuscles. The colored corpuscles of the blood may be observed in different stages of disintegration. The arteries of the gland enter its fibrous capsule and branch, the branches passing into the gland with the fibrous inshoots from the capsule, reach the interacinal septa, and terminate in capillaries. The walls of the capillaries blend with the fibrous tissue of the septa, thus allowing the blood to flow directly into Fig. 158. Portion of the thyroid gland. f, fibrous coat with artery (a), veins (z/), and spaces containing blood (d); g-, lining cells of the acinus; d, interacinal connective tissue; <?, interacinal group of cells. MANUAL OF NORMAL HISTOLOGY. 165 the interfascicular clefts. Veins arise in the same manner as the arteries terminate, and pass along the septa to the capsule, and from the gland. The lymphatics arise in the septa in the same manner as the veins, and in the fibrous capsule ; the chan- nels formed communicate with the collections of lymphoid sub- stance within, and the lymphatic channels without, the capsule. The nerves which pass to the gland are of both varieties. Besides innervating the blood-vessels,their terminations,although not known, probably extend between the acini to form a plexus beneath the basement membranes of the acini. In accordance with the structure of the gland, and the myxoe- dematous condition of the tissues of the body which follow its extirpation, it appears to the author that the thyroid gland is a blood-elaborating gland, which acts as follows : The lining cells of the acini cause disintegration of some of the colored corpus- cles of the blood, and act upon the plasma which passes through them in such a manner that its mucin-forming power is dimin- ished ; the plasma containing pigment derived from the disinte- grated colored corpuscles, composing the colloid substance, passes from the acini to be carried off by the veins, or the lymphatic channels. Experiment 140. Stain, mount and examine a section of the thyroid gland. Took for and study the appearance 'of the lobules, acini, interacinal septa, blood-vessels, fibrous capsule, the colloid material contained in the acini, and the lining epi- thelial cells. Sketch. THE SUPRARENAL BODY. The suprarenal body is usually classed as one of the ductless glands, although some investigators claim that it is a portion of the nervous system * It is a pyramidal or "cocked-hat" shaped organ, situated above and anterior to the superior border of the kidney. It is enclosed by a fibrous capsule which sends projections (trabecu- lae) into the substance of the organ, dividing it up into smaller portions. The substance of the suprarenal body consists of a *The author considers the suprarenal body as a blood elaborating gland, aiding the spleen tw its function. The blood coming to the gland filters through the network formed by the trabeculae and their lateral projections, and is modified during its passage from the peri- phery toward the medullary portion. Probably some of the cells, which so closely resemble lymphoid cells, take up the pigment derived by the disintegration of the colored blood- corpuscles and become colored corpuscles. 166 MANUAL OF NORMAL HISTOLOGY. dense area termed the cortical portion., enclosing a less dense area termed the central or medullary portion. The cortical portion consists of three zones, formed by the trabeculae and their branches, termed the zona glomerulosa, the zona fasciculata, and the -"V zona reticularis. The zona glomerulosa, the XI most external zone, consists i of irregular oval or round compartments formed by the * trabeculae, containing brush- , like extensions from the en- closing trabeculae, cells which are similar in appear- r ance to lymphoid cells, col- I ored blood-corpuscles, and pigment. The zona fasciculata, the middle zone, consists of long compartments, formed by the trabeculae which radiate to- ward the central portion of the organ, containing irreg- u 1 a r quadrilateral - shaped spaces in which are cells similar to lymphoid cells, colored blood-corpuscles,and fig. 159. pigment. Vertical section of suprarenal gland. ,. , . , a. fibrous coat external to which is adipose tis- The ZOna reticularis, the sue; b. zona glomerulosa; c, zona fasciculata; 7onp adioininv the medlillarv d. zona reticularis; e, medullary substance aujutiiing me meuunarj of°censsinUSeS' connective tissue> portion of the organ, consists of irregular-shaped spaces formed by the trabeculae, and containing elements similar to those of the other zones. The medullary portion of the suprarenal body consists of irregular-shaped compartments, containing elements similar to those of the cortical substance, between which are irregular- shaped sinus-like spaces from which the veins arise. The arteries which pass to the suprarenal body are derived from the aorta, the phrenic, and the renal. They ramify in the Fig. 159. a, fibrous coat external to which is adipose tis- sue; b. zona glomerulosa; c, zona fasciculata; d, zona reticularis; e, medullary substance containing blood sinuses, connective tissue, and groups of cells. Vertical section of suprarenal gland. MANUAL OF NORMAL HISTOLOGY. 167 fibrous capsule of the organ, some of the branches forming a capillary network in it, while others accompany the trabeculae into the substance of the organ and form a capillary network. The blood is collected in the venous sinuses of the medullary portion, and carried from the organ by the suprarenal vein, which empties into the inferior vena cava or into the renal vein. The lymphatic vessels arise in the interfascicular clefts of the capsule and trabeculae and empty into the lumbar glands. The nerves are of the non-medullated variety and form a plexus in the medullary portion of the suprarenal body, the fibres of which possess numerous minute ganglia. Experiment 141. Stain, mount and examine a section of the suprarenal body. Notice the arrangement of the cortical portion into zones. Examine the structure of the cells Examine the medullary portion, and notice the venous sinuses. Sketch the general outlines under the low power, and portions of the corti- cal and medullary regions under the high power. Exp. 142. Stain and mount a section of a suprarenal gland which has been injected. Notice the capillary network between and around the groups of cells of the cortical zone. Sketch. 168 manual of normal histology. CHAPTER XVII. THE EYE. The eye, the organ which contains the pheripheral termina- tions of the optic nerve, consists of three coats enclosing a central cavity which contains refracting media. The tunics or coats of the eye are three, the sclera, the choroidea, and the retina. The sclerotic (Gr. hard) coat, the outer tunic of the eye, is divided into two portions, a posterior portion (about five- sixths of the sclera) termed the sclera propria, and an anterior portion (the remaining one-sixth) termed the cornea. The sclera propria is surrounded by a membrane lined by endothelioid cells termed the tunica vaginalis oculi, and consists of interlacing bundles of white fibrous tissue and elastic fibres, and connective tissue corpuscles. Its inner surface is composed of loosely-arranged fibrous tissue which contains pigment, and is termed the lamina fusca. Externally the sclera propria blends with the conjunctiva. At the posterior portion of the eye the sclera becomes cribiform, the fibres of the optic nerve passing through the openings. The central opening of the cribiform lamina, termed the porus opticus, is larger than the others, and transmits the arteria centralis retinae. The Cornea is transparent, and consists of four layers : 1. The outermost layer is composed of stratified squamous epithelium continuous with that of the conjunctiva. 2. The next layer is fibrous, and is the proper substance of the cornea. It consists of bundles of transparent fibres continuous with those of the sclera propria, arranged as laminae. The outer border of the layer being more densely arranged than the remaining portion, has been termed the anterior elastic lamina (Bowman), or anterior limiting layer (Reichert). The remainder of the fibrous layer of the cornea is loosely arranged, the bundles of fibres running transversely and occasionally branching en- THE SCLERA. MANUAL OF NORMAL HISTOLOGY. 169 close elongated interfascicular spaces, termed the corneal spaces, which contain connective tissue corpuscles, termed the corneal corpuscles. 3. Covering the inner border of the fibrous layer there is a thin, transparent, highly-elastic membrane termed the membrane of Descemet, the posterior limiting membrane, or the posterior elastic membrane. 4. Lining the membrane of Descemet there is a layer of flat endothelioid. cells. Fig. 160. stratified squamous epithelium; f, fibrous portion of cornea; s, corneal space; d, mem- brane of Descemet; a, endothelioid layer of cornea; f', fibrous tissue of sclerotic coat; i, iris; b, lymph channels (Fontana); m, ciliary muscle; m', ring muscle of Muller; c, ciliary body; g, lens capsule; h, lens fibres; R, retina; a. c., anterior chamber; p.c., posterior chamber; v. c., vitreous chamber. Portion of a section of the eye of a guinea-pig (low power). At the junction of the cornea and the sclera propria the fibres of which the posterior elastic membrane is composed, continue into the iris as the ligamentum pectinatum. The fibres of the ligament enclose spaces termed the spaces of Fontana, at the circumference of the iris, which communicate with a large cir- cular canal in the sclera propria near its junction with the cornea, which canal is termed the canal of Schlemm or the sinus circu- laris iridis. The endothelioid cells lining the internal surface of the cornea continue on to line the corneal surface of the iris. 170 MANUAL OF NORMAL HISTOLOGY. THE CHOROIDEA. The choroid coat is the vascular coat of the eye, and lies in- ternal to the sclera propria. At the junction of the cornea and the sclera propria the choroid coat hangs as a curtain (iris), per- forated at a point to the nasal side of its centre by an opening (pupil). It is composed of three layers: 1. The layer nearest to the sclera consists of loosely-arranged fibrous tissue composed of white and yellow fibres ; connective tissue corpuscles which contain pigment; and lymph corpuscles. The outer surface of the layer is lined by endothelioid cells. The layer is termed the lamina suprachoroidea, and is separated from the lamina fusca of the sclera by a space termed the subscleral space. 2. The middle layer is termed the vascular layer, and is com- posed of white and yellow fibrous tissue, among which are blood-vessels and pigmented connective tissue corpuscles. In the outer portion of the layer the blood-vessels are large, and the veins often assume a tortuous course and are termed the venae vorticosae. The inner portion of the layer contains the capillary networks, and is sometimes termed the choriocapillaris or the tunica Ruyschiana. 3. The inner layer is a hyaline homogeneous layer, termed the lamina vitrea, which is closely applied to the retina. THE IRIS. The iris is composed of the following structures : 1. The anterior surface is lined by a layer of endothelioid cells similar to and continuous with the layer of cells lining the inter- nal surface of the cornea. In dark-colored eyes these cells con- tain pigment. 2. A stroma which consists of an interlacing network of fibrous tissue, among which are blood-vessels, and connective tissue corpuscles which contain pigment in dark-colored eyes. The fibres are chiefly arranged radially toward the pupil, some being circularly disposed around it. 3. Muscle fibres of the involuntary variety. Around the pupil the fibres are arranged in a circular manner, forming the sphincter of the pupil. The remaining fibres are arranged radi- MANUAL OF NORMAL HISTOLOGY. 171 ally toward the pupil from the circumference of the iris, and are termed the dilators of the pupil. 4. The posterior surface of the iris is covered by a thick stratum of pigmented cells which are derived from the pigmented layer of the retina. Owing to the purple color of the layer it is termed the uvea. THE CILIARY MUSCLE. The ciliary muscle (Bowman) consists of involuntary muscle fibres disposed in two sets. One set arises at the junction of the sclera propria and the cornea, intimately related with the peri- pheral termination of the dilator fibres of the pupil, and extend posteriorly to terminate in the choroid coat, near the ciliary pro- cesses. The other set is disposed circularly around the circum- ference of the iris, and is termed the ring muscle of Muller. THE CILIARY PROCESSES. The ciliary processes are fringe like projections of the chor- oidea consisting of the middle layer and the lamina vitrea. They are very numerous, being about seventy in number in one eye, and are rich in blood-vessels and pigmented connective tis- sue corpuscles. Their outer borders corresponding to the lamina vitrea are not pigmented. The fibrous tissue of which they are composed gradually blend with the fibres of the suspensory ligament of the lens. THE RETINA. The retina, the internal tunic of the eye, lines the posterior portion of the eye, extending forward to the ciliary processes, where it terminates as a serrated free border, termed the ora serrata. The retina contains the termination of the optic nerve, and is capable of responding to visual impressions throughout its extent, except at the point of entrance of the arteria centralis retinae (which in reality is due to the absence of the retina at that point). The posterior portion of the retina responds more readily than the anterior portion, one spot being more sensitive than the remainder, which is situated at the centre of the retina and is termed the yellow spot or the macula lutea of Sommer- ring, in the centre of which there is a depression termed the fovea centralis. 172 MANUAL OF NORMAL HISTOLOGY. The retina may be divided into ten layers : 1. The pigmented layer, the layer next to the choroid coat, consists of a layer of hexagonal columnar-shaped nucleated cells. The cells are pigmented and send filamentous projections between the constituents of the next layer. 2. The layer of rods and cones. This layer consists of the cells which receive the visual impressions. The cells are of two kinds, rods and cones. Each rod is divided into two segments, an outer and an inner. The outer segment is columnar or rod- shaped, and is transversely striated, appearing to be composed of flat discs superimposed upon each other. The inner segment is slightly broader than the outer segment for a distance about equal to the length of the outer segment, then tapers to form a narrow fibre, which soon becomes enlarged to enclose the rod nucleus, then becoming narrow again continues to the outer molecular layer. The outer border of the inner segment is striated lengthwise, while the portion between the outer border and the point at which it tapers is granular. A cone is similar to a rod, except that the outer segment is conical and shorter than the corresponding segment of the rod, and that the portions of the inner segment are broader than the corresponding por- tions of the inner segment of the rod. The cones appear to be capable of causing more accurate vision than the rods. They are most numerous in the fovea centralis, least numerous or absent in the anterior portion of the retina. 3. The membrana limitans externa is composed of fibres derived from the fibres of Muller, from which fibrous projections extend between the rods and cones. This membrane is situated on a level with the beginning of the tapering portion of the inner segments of the rods and cones. 4. The outer nuclear layer is composed of the nucleated portions of the rods and cones. They are of two kinds, termed the rod-granules and the cone-granules. A rod-granule is spindle-shaped, and consists of a nucleus and two tapering ends, the distal end being continuous with a rod, while the proximal end becomes varicose and terminates in an enlargement at the border of the next layer. A cone-granule is similar to a rod- granule, except that its nucleus and the tapering ends are broader than the corresponding portions of the rod-granule. 5. The outer molecular layer is a thin layer composed of a fine fibrillar network, among which are small granular MANUAL OF NORMAL HISTOLOGY. 173 bodies which probably are nuclei. The fibrillae of which the network is composed are de- rived from proximal ends of the rod- and cone-granules, and from the fibres of Muller. 6. The Inner nuclear layer is composed of three kinds of cells : (a) Bipolar cells, one process of each cell extending to the outer mole- cular layer, probably com- municating with a rod or a cone, while the other process extends to the inner molecular layer, (b) Multipolar cells, the processes of each cell ex- tend into one of the molecular layers, (c) Cells connected with or contained in the fibres of Muller. 7. THE INNER MOLECULAR layer is thicker than the outer molecular layer, and contains ramifying fibrillae, among which are granular- looking nuclei. 8. The vesicular layer consists of a single row of large bipolar ganglionic or nerve-cells. The proximal process of each cell is connected to a fibre of the next layer, while the distal process ramifies, the ramifications passing into the inner molecular layer. 9. The fibrous layer is composed of nerve fibres derived from the optic nerve. The fibres lose their medullary sheaths during their passage through the lamina cribrosa of the sclera, and probably send a primitive fibrilla to join the proximal pro- cess of each cell of the vesicular layer. 10. The membrana linitans interna is formed by the fibres of Muller, and separates the retina from the capsule of the vitreous humor of the eye. Fig. 162. The retina of the eye (partly diagrammatic). a, pigmented layer; b, layer of rods and cones: c, outer nuclear layer; d, outer molecular layer; e, inner nuclear layer; f, inner mole- cular layer; g, vesicular layer; h, fibrous layer; z, external limiting membrane; m, fibre of Muller. 174 MANUAL OF NORMAL HISTOLOGY. The layers of the retina are held together by a connective tissue network, the fibres of which are termed the fibres of Muller. They commence at the inner border of the retina (adjacent to the vitreous body) as bases of cones, the joined bases forming the internal limiting membrane of the retina. The fibres extend into and between the portions of the various retinal layers, terminating as the external limiting membrane. In the inner nuclear layer of the retina the fibres of Muller appear to be nucleated, giving the cellular appearance mentioned. As the retina extends anteriorly toward the ora serrata, it gradually diminishes in thickness and sensitiveness. The cones gradually diminish in number and disappear, then disappear the rods, then the vesicular, fibrous and recticular layers. The radial fibres of Muller become more distinct. The pigmented layer continues on to the ciliary processes as the pars ciliaris, and on the posterior surface of the iris as the pars iridica retinae. THE LENS. The lens is situated immediately behind the pupil, and is the most important of the refracting media. It is enclosed by a capsule which is a transparent elastic membrane, the portion covering the anterior surface of the lens being about twice as thick as the portion covering the posterior surface. The capsule is lined by a layer of low columnar-shaped cells., except at its posterior portion. By some authors the layer of cells is con- sidered as a portion of the lens substance and not as a portion of the capsule. At irregular intervals small spaces may be ob- served between the cells and the membrane of the capsules, termed the supraepithelial spaces. Between the epithelial cells and the lens-substance there is a distinct space termed the sub- epithelial space. The lens substance is a biconvex mass, and consists of fibres arranged in lamellae which run concentrically around the centre of the lens. The central portion of the lens being more dense than the peripheral portion, is termed its nucleus. The fibres are formed by the epithelial cells lining the capsule, and in their early stages of development contain distinct nuclei, which disappear as the fibres become older. On transverse sec- tion, the fibres appear as sections of prisms with polygonal- shaped bases. The suspensory ligament of the lens, or zonula of Zinn, is composed of ligamentous fibres which arise from the fringe-like MANUAL OF NORMAL HISTOLOGY. 175 folds of the ciliary processes and from the depressions between the folds, and are inserted in the equatorial portion of the lens- capsule, some of the fibres extending into its anterior portion. The lens, with its capsule and suspensory ligament, divides the interior of the eye into two unequal portions. The anterior por- tion is occupied by the aqueous humor, the posterior portion by the vitreous body or humor. The anterior portion is subdivided into two chambers by the iris, the anterior of which, termed the anterior chamber, is bounded by the posterior surface of the cornea and the anterior surface of the iris; the posterior of which termed the posterior chamber, is bounded anteriorly by the posterior surface of the iris, posteriorly by the anterior portion of the lens-capsule. The chambers communicate through the pupil, and contain the aqueous humor, which consists of water containing a small amount of salts, the chief of which is sodium chloride. The posterior portion of the interior of the eye is occupied by the vitreous body, which consists of mucoid tissue in its early stages of development ; of water, salts, and wandering cells in its adult condition, the mucoid cells having disappeared. The anterior surface of the body is depressed to accommodate the posterior surface of the lens. Enclosing the vitreous body, ex- cept at its anterior surface, there is a transparent homogeneous membrane, termed the hyaloid membrane, which becomes fibrous as it nears and blends with the zonula of Zinn. The arteries of the eye, derived from the ophthalmic artery, are divided into two sets retinal and ciliary, which are distinct from each other except at the point of entrance of the optic nerve, where they communicate by means of a few anastomosing branches. The retinal SET are branches from the retinal artery, and supply nourishment to the retina. One of the branches pierces the vitreous humor of the embryo, termed the hyaloid artery, which disappears later, and is represented by a few fibres in the adult humor. The ciliary SET is subdivided into three groups, short, long, and anterior. The short ciliary arteries arise from the ophthalmic artery and surround the optic nerve as it enters the eye. They pass through the sclerotic coat into the choroid, which it supplies in addition to the ciliary processes. 176 MANUAL OF NORMAL HISTOLOGY. 2. The long ciliary arteries, of which there are two, pass through the sclera, each passing between the sclerotic and choroid coats on one side of the eye, to the ciliary muscle, and encircle the periphery of the iris, forming the large arterial circle from which branches pass radially toward the pupil and form a smaller circle among the fibres of the sphincter of the pupil. 3. The anterior ciliary arteries, derived from the muscular branches of the ophthalmic artery, pass through the sclera pro- pria near its junction with the cornea, and terminate in the large arterial circle of the iris. The lymphatics arise in the clefts between the fibrous tissue of the various structures of the eye, as the corneal and scleral spaces ; the canal of Petit (the triangular-shaped circular canal bounded anteriorly by the suspensory ligament of the lens pos- teriorly by the vitreous humor, internally by a portion of the lens-capsule); the subscleral space; the interfascicular clefts of the choroidea, ciliary processes, ciliary muscle, and iris; the perivascular spaces ; the hyaloid canal ; and the perineural spaces of the optic nerve. The excess of aqueous humor passes from the anterior chamber into the spaces of Fontana. The lymphatics join and form larger channels, which pass from the eye along with the optic nerve. The nerves of the eye, other than the optic, are termed the long and the short ciliary nerves. The long ciliary nerves are derived from the nasal branch of the ophthalmic nerve, and after receiving the short ciliary nerves derived from the ophthalmic ganglion, pierce the sclerotic coat near to the optic nerve, and accompany the ciliary arteries to be distributed to the ciliary muscle and the iris. Experiment 143. Stain, mount and examine a longitudinal section of the eye, preferably of a small animal as the rat or guinea-pig. Notice and sketch, under the low power, the gen- eral appearance and arrangement of the different portions. Under the high power, examine and sketch portions of the cornea, sclera, choroidea, ciliary processes, iris, and lens with its capsule. Exp. 144. Stain and mount a section of the head of an em- bryo (pig or kitten), the section having been cut so as to include the eye. Notice the lids still closed, and the various parts as in Exp. 143. Notice the lens fibres, and the cells on anterior border of lens. Exp. 145. If a prepared specimen of the retina can be ob- tained, examine it and notice the different layers. Sketch under the high power several rods and cones. Fig. 161. Section of the eye of an embryonal pig, stained with haema- toxylin and eosin. e, stratified squamous epithelium of eyelid ; a, place of adhesion of the eyelids; b1, body substance of eyelid; e\ stratified squamous epithelium of cornea ; /, fibrous portion of cornea ; b, region showing continuity of the epithelium of cornea with that of the under surface of the eyelid ; a.c., anterior chamber of the eye ; L, lens; d, epithelium of anterior border of lens ; v.c., vitreous chamber ; R, retina ; n, optic nerve ; Z1, fibrous tissue which has not differentiated into sclerotic and choroid coats S and C; m, one of the eye muscles ; c, cartilage of the orbital process of the frontal bone ; pigmented layer between R and C. PLATE IV. FIG. 161 MANUAL OF NORMAL HISTOLOGY. 177 CHAPTER XVIII. THE ORGAN OF HEARING. The organ of hearing consists of three portions, the external ear, the middle ear or tympanum, and the internal ear or labyrinth. The external Ear consists of two portions, an expanded portion termed the pinna and a canal termed the external auditory meatus. The pinna, commonly termed the ear, is composed of carti- lage, connective tissue and muscle, and is covered by skin. The cartilage is a thin layer of the yellow fibrous variety, which follows the general outlines of the pinna, but is not present in the lobule of the pinna. It is incompletely divided into seg- ments, which are held together by bands of yellow fibrous tissue termed ligaments. The connective tissue consists chiefly of the yellow fibrous variety, that of the lobule being adipose. The muscular tissue is of the voluntary variety, and differs in amount in different pinnae. The skin which covers the pinna is thin, and possesses sebaceous glands and short hairs. The external auditory meatus is a canal, formed by the auditory process of the temporal bone and cartilage, lined by an invagination of the skin. The cartilaginous portion forms nearly one-half the length of the canal, and is continuous with and similar to the cartilage of the pinna. The osseous portion of the wall of the canal is composed of an inner and an outer layer of compact bone enclosing a layer of the cancellous variety. The skin lining the meatus is thin and closely united to the cartilaginous and osseous portions of the canal-wall. It extends to and is reflected upon the membrana tympani. Near the orifice of the meatus it is covered by long hairs, and contains sebaceous glands. The ceruminous glands are compound tubular glands which extend from the surface of the skin into the sub- cutaneous tissue of the cartilaginous portion of the canal. 178 MANUAL OF NORMAL HISTOLOGY. THE TYMPANUM. The tympanum, or middle ear, is separated from the external auditory meatus by a membranous structure termed the mem- branum tympa.ni, which consists of three layers: a middle fibrous layer composed of white and yellow fibrous tissue, some of the fibres being arranged radially from the centre, others circumfer- entially; an external layer, the reflection of the skin of the external auditory meatus; an inner layer, which is a portion of the mucous membrane which lines the tympanum. Covering the foramen rotundum there is a secondary tympanic membrane similar in structure to the membranum tympani, consisting of three layers: a middle fibrous; an external layer (tympanic sur- face) composed of mucous membrane continuous with that of the tympanic cavity; an internal layer composed of endothelioid cells. The mucous membrane lining the tympanum consists of a tunica propria and an epithelial portion. The epithelium is of the ciliated cuboidal variety in the lower portion of the tym- panum near the opening of the Eustachian tube and non-ciliated in the remaining portions of the tympanum. The mucous mem- brane extends into the mastoid cells, where it is lined by non- ciliated epithelium. THE INTERNAL EAR. The internal ear, termed the labyrinth on account of its com- plexity, consists of a membranous sac (lining the irregular hollowed-out cavity in the petrous portion of the temporal bone, termed the osseous labyrinth) and structures contained in the sac, together forming the the membranous labyrinth. The membranous labyrinth is connected to the osseous canals by fibrous projections, the spaces left between the membranous and osseous labyrinths being filled by the perilymph. The wall of the membranous labyrinth consists of two por- tions, an outer fibrous portion and an inner hyaline portion lined by a layer of cells which secrete the endolymph. The membranous labyrinth is composed of a vestibule, three semicircular canals and the cochleal canal. The vestibule consists of two portions termed the utricle and the saccule. The semicircular canals are membranous tubes suspended in the osseous semicircular canals, the inner border of which is papillated, with dilated ampullae nearly filling the osseous ampullae. MANUAL OF NORMAL HISTOLOGY. 179 The cochlea is conical in shape, having a columnar projec- tion termed the modiolus or columella extending from the centre of its base nearly to its apex. Projecting from the circumfer- ence of the modiolus there is a lamina of bone which passes spirally from the lower portion to its termination, termed the lamina spiralis. The lamina projects about half way across to the membranous wall. The terminal edge of the lamina is con- nected to the membranous wall by a fibrous projection from it, Diagrammatic representation of a portion of the human cochlea. Fig. 163. a, ligamentum spirale; c. lamina spiralis; b. membrane of Reissner; e, basilar mem- brane; d c., canal of the cochlea; s.t , scala tympani; j v., scala vestibule; /. mem- brana tectoria; f, spiral groove; C. organ of Corti; z, internal ciliated epithelium; •/', external ciliated epithelium; d, canal or tunnel of Corti; n. nerve fibres. which consequently is spirally arranged, and is termed the ligamentum spirale. In this manner two canals are formed, the upper of which is termed the scala vestibuli, the lower the scala tympani. The upper canal is subdivided by a membrane, termed the membrane of Reissner, which extends from the liga- mentum spirale to the edge of the lamina spiralis, the triangular- shaped canal thus formed being termed the scala media or canalis cochleae. 180 MANUAL OF NORMAL HISTOLOGY. The canalis spiralis modioli (Rosenthal) is a spiral canal which winds around the modiolus at the junction of the lamina spiralis with the modiolus. The connective tissue of the upper surface of the lamina spiralis becomes thickened near the termination of the lamina, which is termed the limbus laminae spiralis and terminates as a groove termed the spiral groove. The liga- mentum spirale is composed of fibrous tissue derived from the endosteum of the bony wall of the cochlea. As the ligamentum spirale approaches the lower border of the spiral groove the upper border becomes more dense and hyaline and is termed the basilar membrane, upon which rests a layer of cuboidal-shaped cells. Extending from the upper surface of the lamina, arising between the attachment of Reissner's membrane and the termi- nation of the limbus, to the wall of the cochlea, there is a delicate membrane termed the membrana tectoria or the membrane of Corti. The canal formed between Corti's membrane and the basilar membrane is termed the ductus cochlearis or ductus auditorius, in which is contained the organ of Corti. The organ of Corti consists of cells peculiarly arranged: The rods of Corti are attached to the basilar membrane, and are divided into an inner and an outer row. The bases of the cells of the inner row are separated from the bases of the cells of the outer row, and the cells of one row lean toward and meet the corresponding ones of the other row, thus forming an arch which encloses a canal termed the zona ar- cuata, which ascends through the length of the cochlea. The inner rods are more narrow and numerous than the outer, and are somewhat ulna- shaped. In the angular corners of the zona arcuata at the base of the cells there is usually a row of granular cells. To the inner side of the inner rods there is a layer of cells columnar in shape and ciliated at their free borders termed the inner hair cells, next to which the cells are cuboidal and continue as a The organ of Corti (partly diagrammatic). e, protoplasmic cells; t, tunnell of Corti; o. outer rod, and /.inner rod of Corti; b, basilar membrane; a, inner hair cell; c, outer hair cells; J, epithelium of spiral groove; d, reticular lamina. Fig. 164. MANUAL OF NORMAL HISTOLOGY. 181 lining to the sulcus spiralis. The upper portion of the outer rods have been compared in appearance to the neck, head and bill of a swan. External to the outer rods there is a layer of ciliated columnar-shaped cells termed the oiiter hair cells, beyond which there are cells which are non-ciliated and cuboidal in shape. The cells gradually become endothelioid on the ligamentum spirale. Extending over the outer hair cells there is a reticular lamina or membrane of Kolliker, which appears to arise from the upper border of the inner rods and receive the projection (phalangeal process) from the outer rods. The membrane is composed of several rows of "fiddle-shaped" fibres termed phalanges. In the membrane there are small openings through which the cilia of the outer hair cells project. The membrane of Corti, or membrana tectoria, is above but not in contact with the reticular lamina. The internal auditory artery divides into two branches, coch- lear and vestibular. The cochlear artery divides into branches which enter the modiolus and terminate as capillaries in the lamina spiralis. The vestibular artery supplies the membranous labyrinth. Veins arise from the capillary networks and termi- nate in the superior petrosal sinus. The auditory nerve divides into two branches, cochlear and vestibular. The vestibular nerves supply the membranous labyrinth. The cochlear nerve divides into branches which pass into the modiolus, thence into the spiral lamina to the organs of Corti. Experiment 146. Stain, mount and examine a section of the pinna. Notice the skin, cartilage, yellow fibrous tissue and muscular tissue. Sketch. Exp. 147. Stain, mount and examine a vertical section of a decalcified cochlea. Notice the modiolus, lamina spiralis, liga- mentum spirale, and the organ of Corti. Sketch. 182 MANUAL OF NORMAL HISTOLOGY. CHAPTER XIX. THE ORGAN OF SMELL. The organ of smell, besides containing the peripheral termi- nations of the olfactory nerve, is the beginning portion of the respiratory tract. It consists of two portions, the nose and the nasal fossae. The nose is a pyramidal-shaped projection covered by skin, and is composed of an osseous and cartilaginous framework lined by mucous membrane and covered by muscle and con- nective tissue. The osseous portion of the framework is composed of the nasal bones and the nasal processes of the superior maxillae, which are similar to the other bones of the face in consisting of an internal and an external layer of compact bone enclosing can- cellous bone. The cartilaginous portion consists of cartilages one of which, that of the septum, is of the white fibro-variety, the others being of the hyaline variety. The muscular tissue is situated external to the framework and is of the voluntary variety. The connective tissue is scanty, consists of the areolar variety, and is most abundant in the lobe of the nose. The skin is continuous with the skin of the cheeks, superior lip and forehead, and with the mucous membrane lining the nose at the nostrils. It is thin throughout most of its extent, the thicker portions being on the alae nasi and tip, and contains numerous sebaceous glands. It contains hairs which are of considerable length at the nostrils. The mucous membrane of the nose is lined by stratified squamous epithelium. The nasal fossae are lined by mucous membrane which is intimately connected to the periosteum and the perichondrium of the bones and cartilages over which it lies. It is continuous anteriorly with the mucous membrane of the nose, and pos- MANUAL OF NORMAL HISTOLOGY. 183 teriorly with the mucous membrane of the pharynx. The mucous membrane consists of two portions, the tunica propria and the epithelium. The tunica propria consists of fibrous tissue, in which there may be some adenoid tissue, and contains muco-serous glands termed Bowman's glands. The epit helium of the mucous membrane lining the nasal fossae is of the modi- fied stratified columnar variety, which differs in the respiratory and olfactory regions. The respiratory region, which is the lower portion of the fossae, is lined by epithelium similar to the variety lining the trachea, ciliated stratified columnar variety containing goblet cells. The olfactory region, the upper por- tion of the fossae, is lined by stratified columnar epithelium, some of the cells of which have been modified in order to receive and transmit odors, becoming neuro-epithelial cells. The cells of the olfactory region of the mucous membrane are of three varieties: (a) Sustentacular cells, which are columnar-shaped and form an outer layer, the free border of the cells forming the membrana limitans olfactoria. The protoplasm of the cells contain pigment of a yellow color. The lower portion of each cell extends into the lower strata, as a fila- mentous projection which in some in- stances branch. (b) Olfactory cells which are spindle- shaped, each consisting of an enlarge- ment which contains the nucleus, and two tapering ends, the distal of which extends between neighboring susten- tacular cells and terminates at the free surface of the mucous membrane as a single extremity, and in some animals as several extremities similar in appear- ance to cilia: the proximal end passes through the lower stratum of cells to become connected with a fibrilla of the olfactory nerve. (c) A stratum of cells, consisting of one or more layers rest- ing upon the basement membrane, the cells being polygonal in shape and probably produce cells to replace the other varieties when required. Fig. 165. a, lowest layer of epithelial por- tion consisting of cuboidal- shaped cells; c, sustentacular cells; o, olfactory cells; n, nerve fibre; fibrous tissue; g, gland of Bowman. Olfactory mucous membrane. 184 MANUAL OF NORMAL HISTOLOGY. The arteries to the nose form a close-meshed network in the tunica propria of the mucous membrane. The veins arising from the capillaries are numerous, large and sinus-like. The nerves of the organ of smell are of the medullated variety, most of which innervate the component parts of the organ; while one, the olfactory, is the nerve specialized for the sense of smell. The olfactory nerve is distributed to the mucous membrane of the upper portion of the septum and of the inner surface of the superior and middle turbinated bones, its ultimate fibrillae being continuous with the olfactory cells. Experiment 148. Stain, mount and examine a section of the nose. Notice the skin, cartilage, and lining epithelium. Sketch. Exp. 149. Stain, mount and examine a section of a decalcified superior turbinated bone. Notice the mucous membrane with its lining epithelium, and the structure of the bone. Sketch. MANUAL OF NORMAL HISTOLOGY. 185 CHAPTER XX. THE NERVOUS SYSTEM. The membranes -The spinal cord and the brain are envel- oped by three membranes: the dura mater, the arachnoidea, and the pia mater. The dura mater is the outermost of the three membranes, and consists of a network formed by white and yellow fibrous tissue and a few blood-vessels. Its outer surface is closely con- nected to the inner surface of the skull bones forming an internal periosteum; and loosely to the inner periosteum of the vertebrae by means of connective tissue extensions. Its inner surface is lined by a layer of endothelioid cells. The arachnoid (Gr. a spider's web) membrane is non-vascular and composed of white fibrous tissue. Both of its surfaces are lined by endothelioid cells. Between it and the dura mater there is a space termed the szibdural space, while the space which exists between it and the inner membrane is termed the subarachnoideal space. This membrane is attached to the dura externally, and to the pia mater internally, by filamentous bands of connective tissue. The pia mater, the innermost of the membranes, is com- posed of white and yellow fibrous tissue in which ramify blood- vessels. It is divided into two layers the outer of which is dense and covered by a layer of endothelioid cells; the inner of which is loosely arranged and extends into the fissures and depressions of the spinal cord and the brain, terminating as a reticulum in the cerebro-spinal substance. The spinal cord is suspended in the vertebral canal by means of the ligamenta denticulata, each of which is situated between the origins of the anterior and posterior roots of the spinal nerves, attached to the pia mater internally, the dura mater externally. 186 MANUAL OF NORMAL HISTOLOGY. THE SPINAL CORD. The spinal cord is composed of white and gray matter, the former occurring as a covering external to the latter. Extending from the anterior median (longitudinal) line there is a fissure termed the anterior median fissure. In the corresponding pos- terior median line there is a slight depression, from the bottom of which extends an areolar connective tissue septum, the depres- sion and the septum being termed the posterior median fissure. The fissures extend into the cord for a variable distance, tending to divide it into two lateral halves. The portion of the cord between the internal terminations of the fissures is termed a commissure, and connects as .a bridge the two lateral halves. Fig. 166. A transverse section of the spinal cord, the right half of which is diagrammatic, while the left half represents half of a section of the cord of a dog, under the low power. A, anterior portion of cord (anterior median fissure); d, dura mater; s, subdural space; a, arachnoid membrane; s.' subarachnoidal space; p, pia mater: P. posterior median fissure; ,/i ligamentum denticulatum; a. c., anterior cornu: c. s. c., central spinal canal; p. c., pos- terior cornu; D P. T,, direct pyramidal tract; A. P. Z.. anterior root zone; c, anterior root fibres; Af. L., mixed lateral tract; D. C. T., descending cerebellar tract; Z>. C:, direct or dorsal cerebellar tract; C. P. pyramidal tract; A,' antero-lateral cerebellar tract; G, column of Goll; P, column of Burdach, The commissure is composed of white and gray matter, the former consists of transverse fibres situated anteriorly and is termed the white commissure, the latter is situated posterior to MANUAL OF NORMAL HISTOLOGY. 187 the white commissure and is termed the gray commissure. In the centre of the gray commissure is the central canal which is lined by a layer of ciliated columnar-shaped cells. Each lateral half of the cord contains a crescent-shaped mass of gray matter, the convex border of which is toward, and con- nected by means of the gray commissure to, the convex border of the other. The posterior cornu of the crescent reaches nearly to the surface of the cord, is narrow throughout most of its length, becoming broader at its outer extremity, the broad por- tion being termed the caput cornu. The anterior cornu is broad and does not extend near to the surface. From each cornu fibres extend to form the respective roots of the spinal nerves. By means of the cornu and the root-forming fibres the white matter of each half of the cord is divided into three columns : anterior, lateral, and posterior. The white matter of the cord consists of medullated nerve- fibres held together by the network formed by the neuroglia and the inshoots from the pia mater, and disposed in bundles termed . tracts. The anterior col- umn is divided into two tracts, the direct pyramidal (Tiirck's) and the ante- rior root zone; the poste- rior column into two, the column of Goll and the column of Burdach; the lateral column into five, the crossed pyramidal, the descending cerebellar, the direct cerebellar, the ante- ro-lateral cerebellar (Gower's), and the mixed lateral. According to the degen- erative method of experi- mentation the direct pyramidal, the crossed pyramidal and the descending cerebellar are descending tracts; the posterior median (Goll), the direct cerebellar, and the antero- lateral (Gower's) are ascending tracts. Fig. 167. Portion of the spinal cord (high power). 4. gray matter showing c, nerve cells, and a. neu- rogliacells; B, white matter showing cross sections of nerves (»); C, central spinal canal showing cil- iated epithelium. 188 MANUAL OF NORMAL HISTOLOGY. The gray matter of the cord consists of nerve-cells and their processes, held together by neuroglia. The nerve-cells are distributed throughout the gray matter, some of which are col- lected into groups. The groups are : 1. Several groups of large multipolar cells situated in the an- terior cornu, the axis cylinder processes of which form the ante- rior roots of the spinal nerves. 2. A group of large cells situated in the inner portion of the base of the posterior cornu, the axis cylinder processes of which pass into the direct cerebellar tract of the white matter of the cord. This group of cells is termed Clark's column. 3. A group of cells situated in a projection from the outer side of the body-of the crescent termed the lateral cornu, w'hich group is termed the intermedia-lateral tract. Experiment 150. Stain, mount and examine a transverse section of the spinal cord. Under the low power, sketch the outlines of the white and gray matters. Under the high power, sketch the central canal, nerve-cells, and sections of nerve-fibres. THE MEDULLA OBLONGATA. The medulla consists of gray and white matters which are continuous with the corresponding matters of the cord. It is divided into lateral halves by an incomplete septum. The white matter of each half of the medula is arranged in four columns: the anterior pyramid, the lateral tract, the restiform body, and the posterior pyramid. The fibres of the anterior pyramid are continuations of those of the direct pyramidal tract of the corresponding side of the cord and of the crossed pyramidal tract of the opposite side of the cord. After receiving fibres from the lateral tract of the medulla, the fibres of the pyramid are distributed to the cerebrum and to the cerebellum. Those which pass to the cerebrum are arranged in two sets, the inner of which passes as a distinct bundle internal to the olivary body, while the outer encloses the olivary body, from which it receives fibres, to become the olivary fasciculus. The fibres which pass to the cerebellum run as a bundle below and external to the olivary body to blend with the restiform body. The fibres of the lateral tract are continuations of fibres of the lateral tract of the corresponding side of the cord. Some of MANUAL OF NORMAL HISTOLOGY. 189 them pass to the anterior pyramid of the opposite side of the medulla, some pass beneath the olivary body to aid in forming the fasciculus teres, others join the restiform body and pass to the cerebellum. The olivary body is composed of gray and white matter, the former, termed the corpus dentatum of the olivary body, exists as a capsule open at its upper extremity, while the latter consists of medullated fibres passing into or from the interior of the cap- sule which aid in forming the olivary fasciculus. The restiform body is composed of fibres which are continuous with those of the column of Burbach (fasciculus cuneatus). It blends with fibres from the anterior pyramid and lateral tract of the medulla. It enters the pons and divides into two sets of fibres, one of which accompanies the posterior pyramid to the cerebrum, while the other passes to the cerebellum as its inferior peduncle. The posterior pyramid (the fasciculus gracilis) is a continuation of the column of Goll and is closely applied to the restiform body. After receiving fibres from the restiform body it passes to the cerebrum. The gray matter of the lower portion of the medulla is continuous with that of the cord and, like it, is arranged as two lateral crescents joined by a gray commissure which contains in its centre the central canal. The central canal as it extends up- ward becomes wider and lozenge-shaped to become the fourth ventricle. The anterior cornu of each crescent as it extends upward becomes larger and penetrated by the decussating fibres from the crossed pyramidal tract of the cord. The decussating fibres divide the cornu into two portions. The portion which is divided off by the fibres is termed the lateral nucleus of gray matter, while the portion which is penetrated by the fibres is termed the formatio reticularis of the medulla and consists of gray and white matter. The posterior cornua as they extend upward diverge, the caput of each becomes larger and appears as a mass of gray matter near the surface which is termed a tubercle of Rolando, while the remaining portion of the cornu blends with the gray commissure to aid in forming the boundary of the cen- tral canal and later the floor of the fourth ventricle. As the central canal expands to become the fourth ventricle, portions of the gray matter which forms its wall extend on each side into 190 MANUAL OF NORMAL HISTOLOGY. the posterior pyramid and the restiform body forming the nucleus gracilis of the pyramid and the nucleus cuneatus of the restiform body (fasciculus cuneatus). The fourth ventricle is a continuation of the central canal of the cord, and its peculiar shape is due to masses of fibres which form its boundaries. Its floor contains a longitudinal median depression which terminates below in the calamus scriptorius. Situated in the upper portion of the floor there is an eminence on each side of the median depression, termed the fasciculus teres, which consists of gray and white matter. Most of the cells of the floor of the fourth ventricle are collected into groups from which arise cranial nerves. The groups in the lower portion of the floor give origin to the hypoglossal and the spinal accessory nerves. The next group, which is situated near the upper extremity of the calamus scriptorius, gives origin to the vagus. The next group gives origin to the glosso-pharyngeal; while the group near the upper end of the floor gives origin to the auditory nerve. Pass- ing across the floor of the ventricle from the median depression are the transverse white striae, some of which pass into the audi- tory nerve. Passing from the anterior median fissure of the medulla white fibres, termed arciform fibres, extend transversely on the anterior surface of the medulla. The internal surface of the fourth ventricle is lined by ciliated columnar-shaped cells, resting upon a basement membrane termed the ependyma. THE PONS VAROLH. The pons is divided into two lateral halves by an incomplete septum which is continuous with the septum of the medulla. Each half is composed of white and gray matter. The white matter is composed of medullated fibres some of which pass transversely, while the others pass longitudinally. The trans- verse fibres are arranged in two sets, superficial and deep, the former of which is on the anterior surface of the pons and is composed of fibres derived from the middle peduncles of the cerebellum, the fibres of one peduncle being continuous in the vertical median line of the pons with those of the other. The deep transverse fibres are derived from the middle peduncles of the cerebellum, among which are fibres which pass from the superior olivary fasciculus of one side of the pons to the acces- sory auditory nucleus of the other side. The longitudinal MANUAL OF NORMAL HISTOLOGY. 191 fibres of the pons are derived from the medulla and pass across the deep transverse fibres, at right angles to them, to the cere- brum. The irregular-shaped spaces formed by the crossing of the longitudinal and deep transverse fibres contain gray matter, forming the formatio recticularis pontis. Longitudinal fibres: 1. The fibres from the anterior pyramid pass through the pons to form the crusta of the crus cerebri. 2. The olivary fasciculus divides into two bundles, one of which passes to the corpora quadrigemina, while the other blends with the fibres of the lateral tract of the medulla. 3. The fibres from the lateral tract and posterior pyramid of the medulla, after receiving fibres from the olivary fasciculus and restiform body, become mixed with gray matter forming the fasciculus teres of the fourth ventricle, whence they continue upward to aid in the formation of the tegmentum of the crus cerebri. The formatio reticularis of the medulla, after sending off a portion to form the olivary body, extends into the pons, becom- ing continuous with the formatio reticularis pontis. THE CEREBELLUM. The cerebellum is composed of white and gray matters. The white matter consists of two kinds of fibres, the peduncular and the fibrae propriae. The peduncular fibres arise from the cortical gray matter of the cerebellum and extend from each cerebellar hemisphere to the cerebrum, to each other, and to the medulla. They are divided into three sets termed peduncles: 1. The superior peduncle (processus e cerebello ad testes) is composed of fibres, some of which arise from the cerebellar cor- tex, others from the corpus dentatum cerebelli. It passes inward and forward to the cerebrum, forming in its course the antero-lateral boundary of the fourth ventricle, to pass beneath the testes of the corpora quadrigemina. Some of the fibres of the peduncle continue in the corresponding half of the cerebrum, while the internal fibres decussate with internal fibres of the superior peduncle from the other cerebellar hemisphere to pass into the cerebral hemisphere of the other side. 192 MANUAL OF NORMAL HISTOLOGY. 2. The middle peduncle (processus ad pontem) is composed of fibres which arise from the cortex of each cerebellar hemisphere and pass through the pons as its transverse fibres, becoming continuous at the median septum pontis. 3. The inferior peduncle (processus ad medullam) is composed of fibres which connect the cerebellum with the medulla oblon- gata. The fibres arise in the cortical substance of a cerebellar hemisphere and form the restiform body which in its course forms the postero-lateral boundary of the fourth ventricle. The fibrae propriae of the cerebellum are of two kinds, com- missural and arcuate. The commissural fibres pass from the cortical substance of one cerebellar hemisphere to that of the other. The arcuate fibres connect one region of the cortical substance to another region in the same hemisphere. The gray matter of the cerebellum exists as a cortical and a central portion. The central portion, termed the corpus den- Fig. 168. sulcus; a, outer layer of gray matter; b, cells of Purkinje; c, inner layer of gray matter d, white substance of cerebellum. Portion of the cerebellum (slightly magnified). tatum cerebelli, is similar in structure to the corpus dentatum of the olivary body. The cortical portion exists as a covering to the projections of white matter, which, with the projections, give the characteristic " arbor vitae" appearance. It is divided into three zones; an external granular, a middle vesicular, an internal granular. MANUAL OF NORMAL HISTOLOGY. 193 The external granular-looking zone is composed of a fine fibrillar network, some of the fibrillae being derived from the inshoots from the pia mater, others from neuroglia-cells and others from the cells of the vesicular zone below. Among the fibres there are numerous granular-looking masses usually round in shape which apparently are nuclei of neuroglia- and nerve- cells the processes of which aid in forming the reticular network. The middle or vesicular zone con- sists of large flask - shaped cells, termed the cells of Purkinje, arranged with their large part toward the inter- nal zone and their tapering end toward the external zone. The outer end of each cell divides, the divisions sub- dividing, the ramifications aiding in the formation of the network of the outer zone. The inner larger portion of each cell sends out a filamentous projection into the inner zone which is probably continuous with a nerve fibre of the white matter of the cerebellum. The inner granular-looking zone rests upon the white matter of the cerebellum and appears similar to the outer zone, consisting of large and small granular-looking bodies, some of which apparently are nuclei of ganglionic cells, others of neurog- lia cells, held together by the network formed by their processes. Experiment 151. Stain and mount a section of the cerebellum. Examine with the low power and notice the "arbor vitae" appearance. Under the high power, sketch several cells of Purkinje, with their processes. THE CEREBRUM. The cerebrum is composed of white and gray matter, the latter occurring as a covering to the convolutions and sulci of the Fig. 169. A portion of the specimen used in fig. 168 (under high power). a, pia mater; b, outer molecular layer; c, cell of Purkinje; d, in- ner molecular layer; e, stellate cells (neuroglia ); /, fibrous por- tion or white matter. 194 MANUAL OF NORMAL HISTOLOGY. hemispheres, as collections in the white matter, and lining the ventricles. The cortical gray matter consists of nerve-cells usually pyramidal in shape, and neuroglia cells, held together by a network formed by inshoots from the pia mater and ramifying processes of the cells. It is usually disposed in five layers. 1. The superficial layer is similar in appearance to the outer granular layer of the cerebellum, consisting of round masses which appear to be nuclei of neuroglia cells held together by the fibrillar network. 2. The second layer consists of nerve-cells usually pyramidal in shape very similar in appearance to spear-heads. The processes from the angles of the cells branch and form a fibrillar network, while the process arising from the side of the cells (corresponding to the shaft of a spear), being an axis cylinder pro- cess, extends through the lower layers to become continuous with a nerve fibre of the white matter. 3. The third layer is composed of structures similar to those of the previous layer except that the nerve-cells are larger. 4. The fourth layer consists of structures similar to those of the two previous layers and represents a transition between the third layer and the fifth. Among the cells medulated nerve fibres occur. 5. The fifth layer, the layer bordering upon the white matter, is composed of round or spindle-shaped cells, among which are numerous medullated nerve fibres. The collections of gray matter termed the basal ganglia are: the corpus striatum, the corpora quadrigemina, the optic thalamus, the locus niger, and the corpora geniculata. Fig. 170. Portion of a section of the cerebrum cut verticle to the surface (stained with chloride of gold). a.piamater; b, molecular layer: c,layer of small pyramidal-shaped cells show- ing a telodendrion; d, large pyramidal cells; e. large and small pyramidal cells; f, irregular-shaped cells; g, white matter of cerebrum. MANUAL OF NORMAL HISTOLOGY. 195 The corpus striatum consists of two collections of gray matter, separated by a bundle of medullated nerve fibres termed the internal capsule. The intraventricular collection is termed the nucleus caudatus ; the extraventricular collection the nucleus lenticularis. They consist of large and small multipolar cells among which pass medullated fibres. The optic thalamus is composed of multipolar and fusiform cells arranged in two masses, an inner and an outer nucleus, separated by an incomplete vertical septum. Internally it is separated from the corpus striatum by the internal capsule. The corpora quadrigemina consists of four bodies arranged as two pairs, one of each pair being on each side of the median line of the cerebrum. The anterior pair, termed the nates, consist of multipolar cells among which pass the fibres of the optic nerve. The superficial covering of each natis is termed the stratum zonale and consists of medullated nerve fibres. The portion immediately beneath the stratum zonale is termed the stratum cinerum and occurs as a dense mass of gray matter con- taining multipolar nerve-cells resting upon the underlying fibres of the optic nerve The next portion, termed the stratum opticzim. consists of gray matter through which pass fibres to form the optic nerve. The lowest layer with the corresponding layer of the other natis forms the central nucleus which forms the floor of the aqueduct of Sylvius, its multipolar cells being grouped to- gether to give origin to the third, fourth, and fifth cranial nerves. The posterior pair of the corpora quadrigemina, termed the testes, are composed of gray matter containing multipolar nerve- cells and surrounded by medullated nerve fibres. The corpora geniculata.-The external corpus appears laminated, and consists of alternating thick layers of gray, and thin layers of white, matter. The cells of the gray matter are multipolar and pigmented. The internal corpus does not appear laminated and consists of gray matter, the nerve-cells of which are small, fusiform and not pigmented. The white matter of the cerebrum is composed of medullated nerve fibres which are devoid of neurilemmae. The fibres are divided into three sets : peduncular. which include the fibres derived from the pons Varolii contained in the crura cerebri; commissural, which consists of fibres which connect portions of 196 MANUAL OF NORMAL HISTOLOGY. one hemisphere with those of the other; collateral or arcuate, which consists of fibres which connect portions of a hemisphere together. Each crus cerebri is composed of three portions: an upper, a middle and a lower. The middle portion, termed the locus niger, acts as a septum between the other two portions and con- sists of small pigmented multipolar cells. The upper portion, termed the tegmentum, consists chiefly of a continuation of the formatio reticularis pontis and fibres derived from the superior peduncle of the cerebellum. The lower portion, termed the crusta, consists of fibres derived from the anterior pyramid of the medulla oblongata which pass as the internal capsule to the cortex cerebri. The fibres continuing from the internal capsule and the other fibres of the peduncular set spread out in a fan-shaped manner to pass to the cortex. The fourth ventricle continues as a small canal, the Sylvan aqueduct, into the cerebrum, where it spreads out to form the third and the lateral ventricles. Commissures.-The anterior commissure is composed of medullated fibres which perforate the corpus striatum of each side to extend to the cortex cerebri. The posterior commissure is composed of medullated fibres which connect together the optic thalami posteriorly. The middle commissure is composed of gray matter which connects the inner portions of the optic thalami to each other. Experiment 152 Stain, mount and examine a section of the cerebrum, the section having been cut perpendicular to the sur- face. Look for the various layers of the cortical gray matter, and sketch, under the high power, portions of each layer. MANUAL OF NORMAL HISTOLOGY. 197 APPENDIX. Specimens of the tissues and organs may be obtained from the body and examined in some instance without previous prep- aration (as blood and connective tissue), in other instances only after they have been prepared for examination. The prepara- tion of the specimens usually consists of the following processes: 1. Fixation.-The tissue or organ is obtained as quickly as possible after the death of the animal and cut into small pieces, about one-half inch long, one-quarter inch wide and one-quarter inch thick, which are placed into a solution adapted for fixing the component parts of the specimen and preserving them from undergoing disintegration or putrefaction. 2. Dehydration.-After the constituent portions of the speci- men have been properly fixed, the specimen is then dehydrated by means of alcohol. 3. Embedding.-The dehydrated specimen is prepared for embedding; the embedding material used may be either paraffin or celloidin. 4. Cutting.-The embedded specimen is then cut with either a razor or a microtome (Gr. p-utpos, small; Te/zvw, to cut), prefer- ably the latter. 5. Staining.-The sections may be caused to adhere to slides by means of some adhesive material, such as "albumin fixative," and then stained; or they may be stained before being placed upon slides. 6. Clarifying.-After the sections have been properly stained the embedding material is either removed from them or clarified, and they then are mounted in Canada balsam or dammar upon slides, covered with cover-slips and labeled. If the sections are to be fixed upon the slides before being stained, the slides are smeared with a thin layer of some trans- parent adhesive substance, such as "albumin fixative," in which the sections are placed; the sections are then treated in the same manner as in the method used for staining and mounting sec- 198 MANUAL OF NORMAL HISTOLOGY. tions before they are placed upon slides, with the exception that the solutions are placed upon the sections, instead of placing the sections into the solutions. If the sections are to be stained before being placed upon the slides they are passed through the reagents (see table) contained in staining dishes, clarified and mounted upon slides. If it be desired to stain a specimen in bulk before it is embed- ded, it is fixed, dehydrated, stained, embedded and then cut into sections, which may be clarified and mounted. When it is desired to examine a specimen which has not been previously prepared, it is placed on a slide upon which has been put a few drops of a normal solution of sodium chloride (tem- porary mounting) or of glycerin. When mounted in the latter the cover-slip is cemented to the slide and the specimen is then labeled and kept. In some instances when sections of a specimen are desired in a short time the specimen is fixed and sections are cut, the speci- men being caused to adhere to the specimen-holder of the micro- tome by means of water which has been made to freeze around it; or it may be held by a piece of an organ which, when previ- ously hardened, has sufficient firmness (as a piece of the liver). FIXING MEDIA. The fixing media are used for the purpose of fixing the com- ponent parts of a specimen as soon as possible after it has been taken from the body, in order that post mortem changes may not take place. The chief ones are : Formol (formalin, formalose, or formaldehyde), which is per- haps the best general fixing medium. It is the aldehyde of the first member of the marsh gas series of hydrocarbon, methane : fit Formol, 2 to 5 per cent. Water, 98 to 95 per cent. Alcohol (ethyl alcohol) which is a generally used fixing medium. The specimen may be passed through solutions of alcohol in water of different percentage, passing from the lower to the higher; or it may be placed at once into a 95 per cent, solution of alcohol in water. manual of normal histology. 199 Muller's fluid. H Potassium bichromate, 2.5 parts. Sodium sulphate (Glauber's salt), 1 part. Water, 100 parts. Flemming's solution, which is a fixing medium especially adapted for nuclear structures : H Chromic acid (1 per cent, solution), 15 c. c. Osmic acid (2 per cent, solution), 4 c. c. Glacial acetic acid, 1 c. c. Sometimes diluting with two to five times its bulk of water will give better results. Picro-sulphuric acid, which is a fixing medium especially adapted for embryos : lx Picric acid (saturated aqueous solution), 500 parts. Sulphuric acid (concentrated), 1 part. STAINING SOLUTIONS. Haemotoxylin. Delafield's- U Saturated solution of haematoxylin in absolute alcohol, 4 c. c. Saturated solution of ammonia-alum in water, 150 c. c. After allowing the mixture to stand for eight days exposed to the sunlight, filter and add : Glycerin, 25 c. c. Absolute alcohol, 25 c. c. To stain with this solution, add a small amount of it to an equal amount of water. Ehrlich' s- Haematoxylin crystals, 2 grms. Absolute alcohol, 100 c. c. After the crystals have been dissolved, add : Water, 100 c. c. Glycerin, 100 c. c. Glacial acetic acid, 10 c. c. 200 MANUAL OF NORMAL HISTOLOGY. Carmine. Ji or ax-Ca rm ine- E Borax, 4 grms. Carmine, 3 grms. Warm water, 100 c. c. After the borax and carmine have been dissolved by the water, add : Alcohol (70 per cent.), 100 c. c. Decant as needed. Picro-carmine (Ranvier)- To a saturated solution of picric acid add an ammoniacal solution of carmine until a precipitate appears. Evaporate slowly (on a water bath) to about one-fifth its volume, and filter. Evaporate the filtrate to dryness. The powder thus obtained should be dissolved in water as needed, the strength of the solu- tion usually being 5 per cent. Safranin is an important stain, its importance depending chiefly upon its power of staining the chromatin filaments of nuclei : Safranin, 3 parts. Alcohol (70 per cent.), 100 parts. The solution may be diluted with alcohol or made stronger by adding more safranin as desired. Eosin is generally used as a .2 to 2 per cent, solution of the powder in water. Methyl-green- Methyl-green, 1 grm. Distilled water, 100 c. c. After the methyl-green has dissolved, add 25 c. c. absolute alcohol. Silver nitrate.-The fresh piece of tissue which is to be stained is rinsed in distilled water and then placed into a one- half to 1 percent, solution of silver nitrate in distilled water for five to fifteen minutes. It is then rinsed again in distilled water and exposed (in distilled water) to the action of sunlight. When sufficiently stained it should be thoroughly rinsed in a normal solution of sodium chloride and mounted in glycerin ; or in bal- sam after having been dehydrated. Sections of embedded speci- mens may be stained in the same manner, but before being mounted they should be dehydrated and clarified. This stain MANUAL OF NORMAL HISTOLOGY. 201 affects especially cement substance, and therefore useful for staining endothelium and fibrous connective tissue. Chloride of gold.-Specimens may be stained with the chloride of gold (one-half to 1 per cent, solution in distilled water) in the same manner with silver nitrate. Weigert's haematoxylin method is especially adapted for staining portions of the central nervous The specimen, after having been hardened or fixed in Muller's fluid and em- bedded in celloidin, is immersed in a saturated solution of neutral cupric acetate which has been diluted with an equal volume of water, in which it is kept for about twenty-four hours at a tem- perature of 35° to 45° C. The following solutions having been prepared : A- Lithium carbonate (sat. aq. sol.), 1 part. Water, 90 parts. B- Haematoxylin crystals, 1 part. Absolute alcohol, 10 parts. and the specimen having been cut into sections, the sections are placed into a mixture of A and B (equal quantities) for a length of time sufficient for them to be properly stained, usually one to four hours. After having been properly stained, the sections are dehydrated, clarified and mounted. SPECIAL METHODS FOR STAINING BLOOD. Ehrlich's triacid or neutrophile stain: Saturated solution of orange G., 13-14 c. c. Saturated solution of acid fuchsin, 6-7 c. c. Water, 15 c. c. Alcohol, 15 c. c. Saturated solution of methyl green, 12.5 c. c. Alcohol, 10 c. c. Glycerin, 10 c. c. The blood having been obtained upon a clean slide or cover- slip, should be gently heated until the blood is "fixed." Place in stain 1 to 5 minutes. Rinse in distilled water. Dry with bibulous paper, and mount with balsam ; or put on a drop of cedar oil and examine with objective. 202 MANUAL OF NORMAL HISTOLOGY. The nuclei are stained green ; the eosinophile and neutrophile granules, red; the basophile granules are usually not stained; the colored corpuscles appear pale yellow or red. Jenner's stain : Equal quantities of a 1.2 per cent, aqueous solution of eosin and of a 1 per cent, aqueous solution of methylene blue are thoroughly mixed and allowed to stand for 24 hours. The precipitate is filtered off, washed thoroughly with distilled water, dried in the air without heating. For use dissolve % grm. of the dry powder in 100 c. c. of pure methyl alcohol. Into this is placed the slide or cover-slip containing the smear of blood which has been allowed to dry without the aid of heat, and allowed to remain 1 to 3 minutes. It is then rinsed in distilled water until the film has a pale pink color (5 to 10 seconds). Allow specimen to dry in the air and mount. The colored corpuscles stain a terra-cotta color ; the nuclei are blue ; the blood plaques purple ; the neutrophile and eosinophile granules red ; the basophile granules and cell bodies blue. Wright's chromatin stain : To a 5 per cent, solution of sodium bicarbonate in distilled water, add 1 per cent, by weight of powdered methylene blue. The mixture, having been put into a flask, is steamed in an Arnold sterilizer for one hour from the time the temperature reaches 100° C. It is then taken from the sterilizer and allowed to cool. It is then poured gently into a dish or flask and to it is added 1 to 1000 aqueous solution of eosin until the blue color changes to purple and the mixture has a yellowish metallic looking scum on its surface (requiring about 500 c. c. of the eosin solution to 100 of the alkaline methylene blue). The pre- cipitate formed is collected on a filter and allowed to dry with- out washing or heating. When dry a saturated solution in methyl alcohol is made (.3 grm. will saturate 100 c. c. methyl alcohol in a few minutes). After filtering, add to 80 c. c. of the filtrate, 20 c. c. of methyl alcohol. The stain thus prepared should be kept in tightly stoppered bottles. The blood smeared slide or cover-slip is allowed to dry and is placed into the stain for one minute. The slide or cover-slip is then removed and upon it is dropped water until a metallic-like scum forms on the surface of the mixture, and a reddish tint developes at the margins. The preparation is then left for from MANUAL OF NORMAL HISTOLOGY. 203 3 to 10 minutes. Then the specimen is washed with distilled water, until the thin portions of the film appear pale yellow or a faint pink. The specimen is then dried with bibulous paper and mounted with balsam or examined with cedar oil and yy objective. The colored corpuscles should be pink ; nuclei red or may be blue ; cell bodies blue. The chromatin network of the nucleus and nucleoli stained with this stain can be distinctly seen. EMBEDDING. In order that specimens can be cut into sections of suitable thinness they should be permeated by and embedded in some substance which, when it has set, gives firmness to the specimens and is not injurious to the cutting edge of the knife used in sec- tioning. The substances generally used are two, paraffin and celloidin. Paraffin method. The dehydrated specimen is placed into chloroform or turpentine 2 to 10 hours. Then into a saturated solution of paraffin, in chloroform or in turpentine, 2 to 4 hours. Into melted soft paraffin 3 hours. Hard paraffin should be slowly melted on a water bath and poured into a mold, into which the specimen is lifted from the soft paraffin (using a warm section-lifter) and arranged in any position desired. When the surface of the paraffin appears to possess a thin film upon its surface, cold water should be run around and then over the mold. (A very efficient mold is formed by placing two right-angle- shaped pieces of metal (one-quarter inch deep) upon a glass plate so placed that they form a parallelogram. By adjusting the pieces of metal, molds of various sizes can be obtained.) Celloidin method. The dehydrated specimen is placed into a mixture of equal parts of absolute alcohol and ether 12-24 hours. It is then transferred to a thin solution of celloidin in equal parts of absolute alcohol and ether 12-24 hours. Then it is placed into a thick solution of celloidin (in ether and absolute alcohol, equal parts) 24 hours. 204 MANUAL OF NORMAL HISTOLOGY. The surface of a cork (the size of the cork depending upon the size of the specimen) having been smeared with a thin layer of the thick celloidin solution, the specimen is lifted to the cork and arranged in the position desired, and upon it a few drops of the thick celloidin is placed. When the surface of the celloidin becomes converted into a film, the cork is placed into a vessel containing alcohol (80 per cent.), in which it is kept until needed for sectioning. On account of the tendency of the cork, with specimen upon it, to float on the surface of the alcohol, the author has ceased using it, and has been using instead pieces of "fibre" that is used in electrical works for insulating purposes. The pieces sink to the bottom of the jar of alcohol, thereby keeping the specimen immersed. The surface of the pieces of "fibre" should be roughened, so as to cause better adhesion of the celloidin. SECTIONING. Specimens may be cut into sections by means of a razor held in the hand or (which is more advisable) by means of a "micro- tome." If the specimen be embedded in paraffin, the paraffin should be carefully trimmed off to the end of the specimen at which the sectioning is to begin, the end being made rectangular in shape. The specimen is placed in the specimen-holder of the microtome (supposing that the microtome is to be used) and the knife should be so arranged that the cutting edge is at an angle with the specimen if single sections be desired, parallel with the specimen if serial sections be desired. As the sections are cut they should be kept from curling by means of a fine camel-hair brush, the brush being placed upon the edge of each section as it slides upon the knife. If the specimen be embedded in celloidin, it should be placed into the specimen-holder of the microtome and continually kept flooded with alcohol (85 per cent.). The knife should be arranged at an angle and kept continually flooded also with alcohol (85 per cent.). The sections, as cut, should be placed into a vessel which contains alcohol (85 per cent.) or a mixture of equal parts of alcohol (95 per cent.), glycerin and ether. The sections should be kept in the vessel until needed for mounting. MANUAL OF NORMAL HISTOLOGY. 205 In some instances when sections of a specimen are desired without previously embedding the specimen in paraffin or cel- loidin, the specimen is fixed and then covered with water, which is then frozen by means of a freezing apparatus. The freezing may be done by means of an "ether spray" or by means of liquified carbon dioxide, which is allowed to assume the gaseous form beneath a metal plate upon which the specimen rests. In either case the specimen rests upon a metal plate so constructed that it can be held by the specimen-holder of the microtome. Clarifying Reagents. The embedding material surrounding and contained in the sections should be removed or clarified in order that it may not obscure the portions of the sections. The reagents which may be used are: benzole, xylol, turpentine, creosote, oil of cloves, oil of bergamot, or other essential oils. Generally if the sections be embedded in paraffin, use xylol or turpentine; if embedded in celloidin, use creosote (which clarifies the celloidin) or oil of cloves (which dissolves the celloidin). Memnting Reagents. Sections or thin specimens can be mounted in glycerin, balsam or dammar. Glycerin is used as a mounting medium when the sections or specimens are to be mounted without having been previously embedded; when used, the cover-slip should be made adherent to the slide by means of some form of cement, as zinc white, gold size, etc. Balsam is the generally used mounting medium, as a solution in xylol. After the mounting medium has been placed upon the section the cover-slip should be placed on it, care being taken that no air be allowed to remain under the cover-slip. One end of the cover-slip should be placed at one edge of the section in contact with the balsam and the slip gradually lowered by means of a teasing needle. After the sections have been mounted the slides should be placed in a horizontal position for several days, then cleaned with alcohol or xylol, labeled and stored away to be examined when desired. 206 MANUAL OF NORMAE HISTOLOGY. INJECTING MEDIA. Injecting media are used for the purpose of injecting capillary blood-vessels. Carmine-gelatin- I : Liquor ammonia, 8 parts. Carmine, 4 parts. After being allowed to stand one-half to one hour, add : Distilled water, 50 parts. II : Gelatin mass, prepared by adding to about ten parts of pure gelatin a sufficient amount of water to cover it, and allowing the mixture to stand until the water is absorbed by the gelatin. Filter preparation I and place the filtrate in an evaporating dish on a water bath, and add to it, while hot, preparation II slowly, continually stirring the contents of the evaporating dish. Then add drop by drop a dilute solution of acetic acid until the prepa- ration is slightly acid in reaction. Prussian blue gelatin may be prepared in the same manner, using instead of preparation I a solution of Prussian blue (9 per cent, solution in water). Whichever medium is used it should be used before it has been allowed to set, and should be injected into the vessel going to the region to be injected. The injection should take place as soon after death of the animal as possible, or while the animal is under the influence of chloroform. The haemacytometer consists of a glass slide which con- tains a quadrilateral rectangular depression of uniform depth, the floor of which is divided into squares by parallel lines cross- ing othei' parallel lines at right angles. Accompanying the slide there is at least one cover-slip, a graduated pipette and sometimes a puncturing needle. The depth of the depression is usually one-tenth of a milli- meter. The sides of the squares into which the floor of the depression is divided are one-twentieth of a millimeter long. Therefore each space, the base of which is represented by one of the previously-mentioned squares, has a capacity of one four- thousanths of a cubic millimeter rnm. X mm. X jo mm.). MANUAL OF NORMAL HISTOLOGY. 207 The method for using the instrument is as follows : With a puncturing needle which has been cleansed immedi- ately before using, puncture the tip of a finger or the the lobe of the ear, the surface used having been thoroughly cleansed. Place the point of the pipette into the oozing blood and draw (by suction) the blood into the pipette until it reaches the point marked .5 c. c. The point of the pipette should then be cleansed with a cloth which has been soaked in a solution of sodium sul- phate (10 per cent.) and placed into a vessel containing sodium sulphate (10 per cent, aqueous solution); a dilute solution of acetic acid if only the colorless corpuscles are to be counted ; the sodium sulphate solution to which a few drops of a 1 per cent, solution of gentian violet has been added ; or a dilute solu- tion of acid methylene blue. Whichever solution is used, it is drawn into the pipette to the point marked 101 c. c. and the pipette is then gently shaken. It will readily be understood that the bulb of the pipette contains 100 c. c. of the mixture, of which .5 c. c. is blood, giving .5 per cent, solution of blood. About one-third of the contents is now driven from the pipette and then a drop is forced from the pipette into the depression on the slide. After the drop has been covered with a cover-slip the slide is placed upon the stage of the microscope. After suf- ficient time has elapsed (about ten minutes) for the corpuscles to settle on the floor of the depression, the specimen is examined. The corpuscles contained in a large number of areas, usually about fifty (the larger the number of areas counted the more reliable will be the result), are carefully counted. The number of corpuscles divided by the number of areas counted gives the average number contained in one area, which, as stated above, has a capacity of c. mm. The average number of corpuscles of the diluted blood con- tained in c. mm. multiplied by 4000 gives the average number of corpuscles contained in one cubic millimeter. The average number of corpuscles of the diluted blood con- tained in a cubic millimeter multiplied by the quotient obtained by dividing 100 by the amount of blood originally drawn into the pipette (.5 c. c.) will give the average number of corpuscles contained in a cubic millimeter of blood. Average number contained in one area : X 4000 X -1!- (or 200)= Average number contained in one cubic millimeter. 208 MANUAL OF NORMAL HISTOLOGY. (The student should carefully note the dimensions of the divi- sions of the depression as etched on the slide, and if different from the dimensions mentioned in the foregoing description, which applies to the Zeiss haemacytometer, he should calculate accordingly.) Method for staining cut sections with haematoxylin and eosin. 1. Receive the specimen in water. 2. Place it into haematoxylin stain for about 5 minutes. 3. Rinse in water. 4. Acid alcohol % to 3 minutes, depending upon the strength of the stain and of the acid alcohol. 5. Rinse in water. 6. Ammonia water % to 3 minutes, or until specimen turns to the desired blue color. 7. Rinse in water. 8. Eosin 2 to 5 minutes. 9. Rinse in water. 10. Alcohol 95 per cent, for 1% minute. 11. Creosote 1 to 3 minutes. 12. Rift specimen on to the slide being careful not to get the specimen wrinkled or folded. 13. Press with bibulous paper in order to dry. 14. Put a drop of balsam upon the specimen, and upon that the cover-slip, and finally label. [see TABLE ON PAGES 210 AND 211]. 210 MANUAL OF NORMAL HISTOLOGY. r " ' > ....... Fixing. Formol. Alcohol. Muller's Fluid. Picro-Sulphuric Acid. Flemming's Solution. 1- 12 to 24 hours. 2- Graded Alcohols. 30 per cent., J hour. 50 " 1 *• 60 2 " 70 " 12 " 80 " 12 " 95 " 12 " or transfer direct from formol to alcohol (95 per cent.) for 24 to 36 hours. 1-Graded alcohols. 30 per cent., J hour. 50 " 1 " 60 2 " • 70 " 12 " 80 *' 12 " 95 " 12 " or 1-Place the fresh tissue at once into alcohol (95 per cent.) for 24 to 48 hours. 1- 1 to 6 weeks, changing the fluid,at first daily, or when it becomes turbid. 2- Running water, 4 to 10 hours. 3- Graded alcohols. 1- 5 to 24 hours. 2- Graded alcohols. 1- Small pieces of the tis- sue, 2 to 5 mm thick should be placed in about 4 c.c. of the solution, 24to 36 hours. 2- Wash in running water 1 to 3 hours. 3- Distilled water 5 min- utes. 4- Graded alcohols. Dehydrating.. Absolute Alcohol, 4 to 24 Hours. /- Embedding.. In Paraffin. In Celloidin. Chloroform or turpentine 2 to 10 hours. Chloroform and paraffin) or > 2 to 4 hours. Turpentine and paraffin J Soft paraffin 3 hours. Hard paraffin (in a mold.) Alcohol and ether 24 hours. Thin solution of celloidin 12 to 24 hours. Thick solution of celloidin 12 to 24 hours. Place on a cork, and after the celloidin has become firm put into alcohol (80 per cent.) until needed. FRESH TISSUE. MANUAL OF NORMAL HISTOLOGY. 211 Sectioning Cut Sections with a Microtome (or razor). r Haematoxylin. | Eosin. Safranin. Borax-carmine. PlCRO-CARMINE. 1-3 to 5 minutes. 1 1-1 to 5 minutes. 1-5 to 30 minutes. 1-1 to 3 minutes. 1-1 to 15 minutes. Staining... ... 2- Rinse quickly, but 2-Rinse in distilled water, thoroughly, in distilled , water. | 3-Distilled water, 5 min- If overstained, rinse in utes. acidulated alcohol until excessive stain is re-| 4-Graded alcohol, moved. (Acidulated alcohol: alco- hol (70 per cent.) contain- | ing 1 percent, nitricacid.) ' 3- Graded alcohols. 2- Wash quickly in dis- tilled water. 3- Alcohol 95 per cent., 5 minutes. 4- A b s o 1 u t e alcohol, 1 minute. 2- Rinse quickly in dis- tilled 3- If overstained, place into acidulated alcohol until excessive stain is removed. 2- Rinse in 70 per cent, alcohol. 3- Absolute alcohol, 1 to 2 minutes. To prevent absolute alco- hol from dissolving out all the yellow color from the specimen, put a small crystal of picric acid into the alcohol. Dehydrating .. Absolute Alcohol, 1 to 5 Minutes. f- Clarifying. If Section is Embedded in Paraffin. If Section is Embedded in Celloidin. Turpentine, xylol, or oil of bergamot, 5 to 10 minutes. Oil of cloves, creosote, or xylol, 5 to 10 minutes. Mounting. Put upon a slide, press with bibulous paper, put upon it a drop of balsam, then the cover-slip. Labeling. Label. INDEX. A Page. Achilles, tendon of 26 Achromatic spindle 5, 6 Achromatin >. 2 Acid dyes 13 Adenoid tissue 30, 109, 112 Adipose tissue , 27, 28, 29 Agminated glands 92, 96, 109 Air-cells .120, 121 Air-sacs 120 Alcohol 198 Amitotic division of cells 4 Amoeba 3, 13 Amoeboid movements 4, 12, 14 Amphophilic granules ............................................ 13 Ampullae.? 161 Anal mucous membrane 101 Anatomy, microscopical 1 Animal histology . 1 Anomalous connective tissue 30 Aorta, structure of 60 Apical foramen 70 Appendages of the skin 125 Appendices epiploicae 100 Appendix 197 " vermiform , 100 Aqueduct of Sylvius 195, 196 Arachnoid membrane 185 Areas of Cohnheim 47 Areola 162 Areolae, primary 41 ' ' secondary 42 Areolar tissue 27 Arrector pili 129 Arteria centralis retinae 168 Arteriae interlobulares > 136 ' ' propriae renales 136 * ' rectae 137 Arterioles , 61 Artery, bronchial 121 ciliary 175 " hepatic 102 " hyaloid 175 ' ' interlobular 102 " renal 59, 61, 136 " subclavian 60 " tunics of -. 59 " umbilical 61 Articular cartilage 32 ' ' corpuscles 56 214 irtDEX. Page. Assimilation 3, 26 Aster 5 Atypical cell3, 11 Axilemma 51 Axis-cylinder51, 52, 53 " " processes50, 51 Axones 50 B Basement membrane18, 67 Basic dyes13, 14 Basophile cells 14 " granules 13 Bellini, tubes of 136 Bile capillaries103, 104 " duct103, 104 Bipolar cells 50 Bizzozero, plaques of 14 Bladder, gall 106 * ' urinary 139 Blood 10 " action of reagents upon 15 ' ' corpuscles 10 " fibrin 17 ' ' plaques 14 " plasma 10 ' ' staining of 16 Bodies of Langerhans 108 Body, Malpighian 137 * ' olivary 189 " restif orm 189 " suprarenal 165 " vitreous 175 Bone 26, 34 " cancellous35, 36, 38, 44 " circumferential lamellae 36, 38, 43 " compact 35, 44 ' ' composition of 35 " corpuscles34, 38, 43, 44 ' ' development of • 40 " Haversian lamellae 36 " interstitial lamellae36, 43 " marrow37, 39 " periosteum of 35 " spongy 35 " varieties of 35 Bowman, capsule of 133 " glands of 183 Bronchi 119 Bronchioles 119 Brunner's glands92, 95 Bursae 67 c Calamus scriptorius 190 Calcification 33 Calyx 133 INDEX. 215 Page. Canal, alimentary 69 " cochleal 178 " dentinal 70, 72 " Haversian 37, 38, 39 " medullary 35 " portal 105 " root < 69 " of Schlemm 169 " semicircular 178 Canaliculi 37, 38, 52, 71 Canalis spiralis modioli : 180 Capillaries, bile 103, 104 blood 59, 61, 62 ' ' interlobular 104 intralobular 103, 104 lymph 65, 66 Capsule of Bowman . 133 " " Glisson 102, 104, 105 " internal 195, 196 " of the lens 174 Caput cornu 187 Cardiac glands 87, 88 " muscle 49 Carmine : 200 " gelatin 206 Cartilage 26, 32 " articular 32 " cells 32, 40 " costal 32, 33 ' ' embryonal 40 " epiphyseal 43 " fibro- 32 " hyaline 32, 40 1 ' lacunae of 32 " matrix of 32, 40 " permanent 32 ' ' temporary 32 ' ' varieties of 32 Cavity, pulp 69 Cell, definition of 2 " structure " 2 " -division, direct 4 indirect 4 " -wall 2, 3, 11 Celloidin method of embedding specimens 203 Cells, atypical 3, 11 " basophile 14 * ' bipolar 50 " cartilage 32 ' ' central 89 " chief 89 ' ' daughter 6 " giant 89 " goblet 3, 18, 21, 94, 99, 183 " gustatory 79 " hepatic 103 " lymphoid 112 " marginal 74 " marrow 39 " mast 14 216 Page. Cells, medullary 71 " mononuclear 2, 14 " nerve 50, 54 " neuroglia.... ,... 52 " olfactory 183 " ovoid 89 ' ' oxyntic 89 " parietal 89 " peptic 89 " polynuclear 3 " prickle 124 " of Purkinje 193 " sustentacular 79, 112, 183 Cement substance 23, 27, 48, 51, 52, 66, 74 Cementum 71 Cerebellum, the 191 fibrae propriae of 191, 192 " gray matter of -. 192, 193 peduncles of 191, 192 white matter of 191 Cerebro-spinal system 52, 55, 185 Cerebrum 193 Ceruminous glands 177 Cervix penis 148 ' ' uteri 159 Choriocapillaris 170 Choroidea 170 Chromatin 2, 3, 14 Chromosomes 5 Chyliferous vessels 66, 94 Cilia 21 Ciliary processes 171 Cingulum 69 Circumvallate papillae 76, 77, 78 Clarifying reagents 205 " specimens 197, 205 Cleavage 5 Close-skein 4 Cochlea 179 Cohnheim, areas of 47 Colloid substance 164 Colostrum 162 Column of Bertini 133 Columnar epithelium 20 Commissures of the brain 196 Compact bone 35, 44 Compressor urethrae 142 Coni vasculosi 145 Conical papillae 77 Conjunctival end bulb 56 Connective tissue 1, 26, 27 " adenoid 36, 109, 112 " adipose 27/29 " anomalous 26, 30 " areolar , 27, 28, 29 " embryonal 30 " " fibres 27 " fibrous 27, 28 " myxomatous 30 " retiform 27, 29 " varieties of 27 INDEX. INDEX. 217 Page. Contractile masses 46 Cord, spinal 186 Cords, medullary Ill Cornea 168 Cornua of spinal cord 187 " " pulp cavity 69 Corona glandis 149 Corpora amylacea 152 " cavernosa 149 " quadrigemina 195 Corpus dentatum 189 " Highmori 143 " luteum 153, 155, 156 " spongiosum 149, 150 " striatum 195 Corpuscles, articular 56 blood 10 bone 34, 38 colostral 162 concentric 115 connective tissue 65, 67 corneal 169 crenated 12, 15 genital 56 of Hassel 115 lymph 30 Malpighian Ill, 112 Pacinian 55, 56, 131 salivary 23, 82 tactile 55, 125, 131 of Vater 56 " Wagner 55 Costal cartilage 32 Cranial nerves, origin of 190, 195 Crescents of Gianuzzi 74 Crus cerebri 196 Crusta 196 " petrosa 71 Crypts of Lieberkuhn 99 " " tonsil 82 Cubicular seam 20 Cuticle 123 Cutis anserina 129 " vera 123 D Dahlia 13, 14 Daughter cells 6 nuclei 6 Dehydration 197 Delafield's haematoxylin 199 Demilunes of Heidenhain 74 Dendrites 50, 51 Dental pulp : 71 Dentinal canals 70, 72 Dentine * 26, 44, 70, 71 Dermis 123 Descemet's membrane 29, 169 Development of bone 40 218 INDEX. Page. Diaster 6 Diploe 44 Direct cell-division.... 4 Discs, intermediate 46 " intervertebral 33 " lateral 46 Discus proligerus 154 Duct, ejaculatory 148 " galactophorous 161 " hepatic 103, 104 ' ' thoracic : 66 Ductus auditorius 180 * ' cochlearis 180 " communis choledochus 92 Duodenum, glands of 95 Dura mater 185 Dyes 13, 14 E Ear, the 177 " blood vessels of 181 " cartilage of 34 " glands of .■ 177 " nerves of 181 Ehrlich's stain for blood 13, 201 Ejaculatory duct 148 Elastic tissue 60 Eleidin 123 Elementary tissues 1 Elimination 3, 4, 26 Embedding 197, 203 Embryonal cartilage 40 connective tissue 30 Enamel 34, 71 End-bulbs 55 Endolymph 178 Endomysium 45, 47, 48 Endoneurium 53, 57 End-organs 55 Endothelium 23 End-plates, motor 48, 57, 79 Eosin ..13, 14, 200 Eosinophile 14,, 17 Eosinophilic granules 13 Ependyma 190 Epidermis 123 Epididymis 145 Epimysium 45, 47, 48 Epineurium 52 Epiglottis 34 Epiphyseal cartilage 43 Epithelium 18 ciliated 21 classification of 18 columnar 20 cuboidal 22 germinal 153 glandular 22 modified 20 INDEX. 219 Page. Epithelium of mucous membranes 67 neuro- 22, 79 pavement 19 rod..... 22 " simple 18 specialized 22 " stratified 18 squamous 19 tessellated 19 ' ' transitional 18, 21 " varieties of 18 Erythroblasts 39, 40 External auditory meatus 177 " elastic membrane 59 Eye 168 " blood vessels of 175 " chambers of ? 175 " choroidea of 170 " ciliary processes of 171 " cornea of 168 " lymphatics of 176 " nerves of.... 176 " retina of 171 " sclera of 168 " tunics of 168 " vitreous body of 30, 175 F Fallopian tube 157 Fasciculi 27, 45 Fasciculus, cuneatus 189 gracilis 189 olivary 188 " teres 188, 190 Fat 29, 39, 40 , 66, 100, 103 Fauces 81 Fenestrated membrane 29, 61 Ferrein, pyramids of 133 Fibres, arciform 190 " of Mueller 172, 174 " of Sharpey ; 38 Fibrillae 27, 46, 57, 71 " primitive 51 Fibrin 14 Fibro-cartilage 32 Fixation of tissues 197, 198 Flemming's solution 199 Follicle, hair 127, 128 Foramen caecum 78 Formatio reticularis 189, 191 Formol... 198 Fossa navicularis 141 Fossae, nasal 183 Fourth ventricle 189 Fovea centralis 171 Fraenum preputii 149 Fuchsin 13, 14 Fungiform papillae 77 Funiculi.... 52, 53 220 INDEX. G Page. Galactophorous duct 161 Gall-bladder , 106 Ganglia 54 Gastric glands 87 Generative organs of female 153 " of male 143 Genital corpuscles 56 Germinal epithelium 153 vesicle 155 Giant cells 39 Gingival line 69 Glands, agminated 92 " of Bowman 183 " Brunner's 95 ' ' cardiac 87 " ceruminous . 177 ' ' duodenal 95 " epithelium of 18, 22 ' ' gastric 87 " lenticular 89, 109 " of Lieberkuhn 95 " of Littre 141 ' ' lymph 109 " mammary 161 " oesophageal , 85 " parotid 73, 75 " pharyngeal 87 " pyloric 87, 88, 89 ' ' racemose 68 " saccular , 68 ' ' of the skin 129 " solitary 99 " sudoriferous 129 " thymus 114 " thyroid 163 " tubular 68 " uterine 159 " varieties of 68 Glisson, capsule of 102, 104, 105 Globulin 10 Glycogen 103 Glandulae Tysonii odoriferae 149 Glans penis 148 Glomerulus . 137 Goblet cells 3, 18, 21, 22, 94, 99, 183 Gold chloride ' 201 Graafian vesicles. 153 Granule stains 13 Groove, spiral 180 Growth 3. 4, 26 Gullet 83 Gustatory cells 79 pore 4 79 H Haemacytometer 206 Haemaglobin 10 Haematoidin 10 INDEX. 221 Page. Haematoxylin 199 Hair 126, 127 Hassel, corpuscles of 115 Haversian canals . 37, 38, 39 fringes 67 systems 36, 37, 38, 43 Heart-muscle . 87 Heidenhain, demilunes of 74 Hematin 10 Hemin 10 Henle, fenestrated membrane of 61 " layer of 128 " loop of 134 " sheath of 53, 57 Histology, definition of 1 Huxley's layer 129 Hyaloplasm 2 I Ileum 95, 96 Indirect cell-division 4 Infundibula 119, 120, 133 Injecting media 206 Interarticular cartilage 33 Intercellular substance 1, 34 Interfascicular clefts 65, 67 Interglobular spaces 71 Interlobular arteries . 102, 104 bile-ducts 103, 105 capillaries , 104 lymphatics 103 " spaces 102, 104 veins 102 Intermediate discs 46, 47 Internal elastic membrane 61, 66 Internodes 52 Intervertebral cartilage 33 Interzonal layer of tooth 71 Interstitial lamellae 36, 37 38, 43 Intestine, large 100 small v 91 Intranuclear network 2 Iris, the 170 Irritability 3 J Jelly of Wharton 30 Jenner's blood-stain 202 K Karyokinesis, stages of 4, 5 Keratin ; 19, 123 Kidney 132 " blood-vessels of ,136 ' * coats of 13£ " columns of Bertini 133 222 Page. Kidney, cortical portion of 133 " cortical arches of 133 " hilum of 132 ' ' lobules of 132 " lymphatics of 138 ' ' mammilla of 133 ' ' medullary portion of 133 " nerves of 137 " papillae of 133 " pyramids of Ferrein 133 " pyramids of Malpighi 133 " sinus of 132 Krause, membrane of 46, 47 Kiihe, axilemma of 51 L Labyrinth 177, 178 Lacteal vessels 66, 94 Lacunae of bone 37, 38, 52, 71 " of cartilage 32, 33 Lamellae of bone . 35, 36 Lamina cribiformis 168 " fusca 168 " spiralis 179 " suprachoroidea 170 " vitrea 170 Langerhans, bodies of 108 Larynx 117 Lateral discs 46 Layers of the retina 172 Lens of the eye ,........................................................ 174 Lenticular glands 89, 109 Leucocytes 12, 13, 14 classification of 13, 14 Lieberkiihn, crypts of 95 Ligament, suspensory 174 Ligaments 28 Ligamentum denticulatum 185 nuchae 31 pectinatum 169 spirale ...... 179 Limiting membrane. '. 2, 3 Liquor folliculi 154 " lymphae 65 " sanguinis 10 Littre, glands of 141 Liver, the 101 " bile-capillaries of 103, 104 " bile-ducts of 103, 104 " blood vessels of 102 " cells 103 ' ' coats of 101 " Glisson's capsule of 102 ' lobules of 102, 106 " of pig 102 Lobuli testis 144 Locus niger 196 Loop of Henle 134 Loose-skein 4 INDEX. INDEX. 223 Page. Lung, the 120 ' ' air-cells of 120 " air-sacs of 120 " alveoli of 19, 120, 121 " blood vessels of 121 " infundibula of 119, 120 ' ' lymphatics of 122 " nerves of 122 Lunula 126 Lymph 65 " capillaries 65, 66 " channels 65, 67 " corpuscles . 30, 65 ' ' sinus 110 ' ' spaces 65 Lymph gland 109 " cortical portion of 110 " hilum of 109 " medullary portion 110, 111 Lymphocytes 14, 65 Lymphoid aggregations . 109 tissue 36, 66, 109 M Macula lutea 171 Malpighian body 19, 137 capsule 133 corpuscle 113 pyramid 133 stratum 123, 124 Mammary gland 161 " acini of 161 ' ' ampulla of 161 ' ' blood vessels of 163 " colostrum of 162 " lymphatics of 163 " nerves of ...... 163 " nipple of 162 " tubules of ~ 161 Mammilla 135 Marrow .37, 39 ' ' cells 39 " red 39 " yellow 39 Mast cells 14 Mastication 69 Matrix, cartilage 32 " nail 126 ' ' nuclear 2 Meatus, external auditory 177 " urinarius 141 Mediastinum testis 143 Medulla oblongata 188 Medullary cords Ill canal 35 cells 71 rays 133 sheath 55, 57 Meissner, corpuscles of 55 224 Page. Meissner, plexus of 98 Membrana granulosa 154 limitans olfactoria 183 propria 18, 67 " tectoria 180 Membrane, arachnoid i 185 basement 18, 19 basilar . 180 of Corti 180 of Descemet 29, 169 ' * external elastic 59 fenestrated 29 glassy 128 hyaloid 175 internal elastic 61, 66 of Kolliker 183 " of Krause 46, 47 " limiting 2, 3, 12, 23 mucous 18, 67 of Nasmyth 71 nuclear 3, 5 of Reissner 179 root 70 serous 65, 66 synovial 67 Membranes, the 65 Membranum tympani 178 Mesoblast 26 Metakinesis 5, 6 Methylene blue 13, 14 Methyl green 13, 14, 200 Micrometer 9 Micromillimeter (M) 10 Microscope 6, 7, 8 Microscopical Anatomy 1 Modiolus 179 Motor end-plates 48, 57, 79 Mouth, the \ 19, 20 Mucigen 22 Mucin 22, 73 Mucous alveoli 73, 75 Muller, ring muscle of 171 " fibres of 172, 173, 174 Muller's fluid 199 Muscle 45 * ' cardiac 49 " ciliary 171 " involuntary 59, 60, 63, 66, 68 " ring 171 " voluntary 45, 53 Muscularis mucosae 68 Myelin 51 Myelocytes 40 Myeloplaxes of Robin 40, 72 Myxomatous tissue 30 N Nails 125 Nasal mucous membrane 183 Nasmyth, membrane of 71 INDEX. INDEX. 225 Page. Nates of Brain ' 195 Nerve 50 " cells 50, 54 ciliary 176 " fibres 50 ' ' ganglia 54 " terminations 55 " trunks 52 Nervi nervorum 53 Nervous system 52 " tissue 1, 50 Neura 51 Neuraxes 50 Neuraxones 50 Neurilemma 51, 53, 56 Neurites.... 50 Neurodendron 51 Neuroglia 50, 52 Neurone 51 Neuroplasm ; 51 Neutrophilic granules 13, 14 Nipple, the 162 Nodes of Ranvier 51, 52 Nose, the 182 Nuclear matrix 2 " membrane 3, 5 Nucleolus 3, 5 Nucleoplasm 2 Nucleus, structures of 2 " candatus 195 " cuneatus 190 ' ' gracilis 190 " lateral ;........ 189 " of the lens 174 " lenticularis 195 o Odontoblasts 72 Oesophagus .' 83 epithelium of 19, 20 glands of 85 Oil globules 33, 129, 155, 162 Olivary body 189 " fasciculus 188 Optic thalamus 195 Ora serrata 171 Orange G 13 Organ of Corti 180 Ossification, endochondral 40, 43 intramembranous 43 periosteal •> 43 Osteoblasts 38, 40, 41, 42, 43, 44 Ovary, the 153 " blood-vessels of 157 " coats of 153 " corpus luteum of 153, 155 " follicles of 153 " germinal epithelium of 153 " lymphatics of 157 226 Page. Ovary, nerves of 157 " stroma of 153 Oviduct, the 67, 157 Ovoid cells . 89 Ovula Nabothi 159 Ovum 154 Oxyntic cells 89 Oxyphilic granules 13 P* Pacinian corpuscles 55, 56, 131 Pancreas, the 106 " acini of ' 106 " duct of 106, 107 Panniculus adiposus < 125 Papillae 68 " circumvallate 76, 77, 78 " conical 77 " fungiform 77 " of the skin 55, 124 Parafin method of embedding specimens 203 Paraplasm 2 Parietal cells 89 Parotid gland 73, 75 Pars ciliaris 174 " iridica retinae 174 Penis, the 148 ' ' blood vessels of 150 " corpora cavernosa of 149 " corpus spongiosum of 149, 150 ' ' erectile tissue of 150 " glands of 149 " lymphatics of 150 " nerves of 150 " skin of 148 Pepsin 89 Pericementum 70 Perichondrium 32 Periductular lymph channels 65 Perilymph 178 Perimedullary lamellae... 36, .38, 43 Perimysium 45, 47, 48 Perineural lymph channels 65 Perineurium 52 Periosteum 38 Peripheral nerve-endings 55 Perivascular lymph channels ......65, 106 Peyer's patches 92, 96, 97, 109 Phagocytes 13 Pharynx, the ~ 82 aponeurosis of ....................................... 83 glands of 87 raph6of 83 Pia mater 185 Picro-sulphuric acid 199 Pigment granules of skin 124 Pinna of the ear 177 Plasma, the 10 INDEX. ....92, 96, 97, 109 INDEX. 227 Page. Planetocytes . 13 Plaques of the blood 14 Plexus of Auerbach 90, 91, 93, 96, 98 " of Meissner 89, 91, 93, 96, 98 stellate 137 sympathetic 57 Polymorphonuclear leucocytes 14 Polynuclear cells 3 Pons Varolii 190 Portal canal .'. 105 " vein 102, 103 Porus opticus 168 Prepuce, the 148 Primitive fibrillae 51 " sheath 51, 52, 57 Prickle cells 124 Processes of Deiter 50 Prostate gland 151 Protamoeba 3 Proteus animalcule. 3 Protoplasm 2, 12 Prussian blue gelatin 206 Pseudopodia 13 Pseudo-stomata 66 Pulp, dental 69 " splenic Ill, 112, 113 Pupil of the eye 170 Purkinje, axis cylinders of 51, 52 cells of 193 Pyloric glands 87, 88, 89 Pyramids of Ferrein 133 of Malpighi 133 R Racemose gland 68 Rami communicantes 54 Ranvier, nodes of 51, 52 Reissner's membrane 179 Remak, fibres of 52 Reproduction 3, 4 Reproductive organs of female 153 " " " male 143 Respiratory organs 117 Restiform body 189 Rete mucosum 123 " testis 144 Retiform tissue 27, 28 Retina, the 171 Rod epithelium 74, 107 Rods of Corti 180 Rollett's theory 46 Root canal 69 ' ' membrane 69 Rosette 5 Roleaux 11 Rugae of oesophagus 83 " " gall-bladder 106 " " stomach 90 " " vas deferens 147 228 INDEX. S Page. Saccular glands 68 Saccule 178 Sacs, air ....... 120 Safranin 200 Salivary corpuscles 23, 82 Salivary glands 73, 106 " acini of 73 " " alveoli of 73 " " duct of * 74 " " lobules of 73 Sarcolemma.. r..46, 49, 53 Sarcoplasm 47 Scala media 179 " tympani 179 " vestibuli 179 Schachowa, tubule of 134 Schlemm, canal of 169 Schultz, fibrillae of 51 Schwann, white substance of 51, 53 Sclera propria 168 Seam, cubicular 20 Sebaceous gland 129 Sebum 129 Secondary areolae 42 Section Cutting 197, 204 Semicircular canals 178 Sensory nerves 55 Septum pectiniforme 150 Serous alveoli 73, 74, 75 " membranes 66 Sharpey, fibres of ' 38 '1 primary areolae of 41 Sheath of Henle 53, 57 " medullary 55, 57 " primitive 52 Silver nitrate staining 25, 200 Simple epithelium 18 Sinus circularis iridis 169 Skin 123 " appendages of 125 " arrector pili of 129 " blood vessels of 130 " glands of 129 " layers of 123 " lymphatics of 131 " nerves of 131 " strata of 123, 124, 125 Solitary follicles 92, 95 " gland 99, 109 Space, subarachnoideal, 185 " subdural 185 " subscleral 170 Spaces, corneal 169 " of Fontana 169 " interlobular 105 " subepithelial 174 " supraepithelial 174 Spindle, achromatic 5, 6 INDEX. 229 Page. Spermatoblasts v 144 Spermatogenesis 144 Spermatozoa 144 Sphincter ani 99 of pupil 170 pylori 90 vesicae 140 Spinal cord, the 186 " " anterior median fissure of 186 " " central canal of 187 " " columns of 187 " " commissures of 186 " " posterior median fissure of 186 " " tracts of 187 Spleen, the Ill " blood vessels of 113 " coats of Ill " hilum of 112 " lymphatics of . 113 " Malpighian corpuscles of 113 " nerves of 113 " pulp of Ill, 112, 113 " trabeculae of Ill, 113 Spongioplasm 2, 12 Spongy-bone 35 Squamous epithelium 18 Stage-micrometer 9 Stages of karyokinesis 4, 5 Stain, Ehrlich's 13, 201 Staining of specimens 197 " with haematoxylin and eosin 208 Stigmata 23, 66 Stomach .* 86 " blood vessels of . 90 " coats of 86, 87 ' ' glands of 89 ' ' lymphatics of 90 " nerves of 90 Stomata 23 Strata of the skin 123, 124, 125 Stratified epithelium 18 Stratum cinerum 195 " mucosum ■. 158 " opticum 195 " serosum 158 " vasculosum 158 ' ' zonale 195 Striated border 20 Stroma of blood corpuscles > 10 " " kidney 133, 137 " " ovary 153 Subarachnoideal space 185 Subcutaneous tissue 125 Sublingual gland 73, 75 Sublobular vein 103, 104 Submaxillary gland . 73 Succus entericus 94 Sudoriferous gland 129, 130 Suprarenal gland . 165 Supporting tissues 1, 26, 34 230 INDEX. 1'age. Suspensory ligament 174 Sustentacular cells79, 112, 183 Sweat glands 129 Sylvius, aqueduct of 195 Synovial membranes 67 Sympathetic system52, 55 T Table for preparation of specimens210, 211 Tactile corpuscles55, 125, 131 Taste-buds 78 Teeth, the 69 " cementum of 71 " crusta petrosa of 71 " dentinal canals of70, 72 " dentine of26, 44, 71 " enamel of34, 71 " interglobular spaces ofa 71 " interzonal layer of 71 " membrane of Nasmyth of71 " odontoblasts of 72 " pulp of 69 Tegmentum 196 Teichmann's crystals 10 Telodendron 51 Temporary cartilage 32 Tendo Achilles 26 Tendons 47 Testes of the brain 195 Testicle 143 " coats of 143 " coni vasculosi of 145 ' ' mediastenum of 143 " seminiferous tubules of 144 " spermatoblasts of 144 " vasa efferentia of 145 " vasa recta of 144 Theca folliculi 153 Thoracic duct 66 Thymus gland 114 " blood vessels of 115 " concentric corpuscles of 115 " lobes of 114 " lobules of 114 " lymphatics of 115 " nerves of 116 " trabeculae of 114 Thyroid gland 163 " acini of 164 ' ' blood vessels of 164 " colloid substance of 164 " lymphatics of 165 " nerves of 165 Tissue, adenoid 30 ' * adipose 27 " anomalous connective• 30 " areolar 27 " connective1, 26 INDEX. 231 Page. Tissue, epithelial 1, 18 ' ' erectile 150 ' ' lymphoid 36 " muscular 1, 45 ' ' myxomatous 30 " nervous 1, 50 ' ' retiform 27 " subcutaneous 125 " supporting 1, 26 " vitreous 30 " white fibrous 27 " yellow fibrous 27 Tissues, classification of 1 " component parts of 1 ' ' elementary 1 " supporting 1, 26 Tongue, the 75 " glands of 75 " mucous membrane of 75, 76, 79 " papillae of 77 " raphe of 75 Tonsil, the 81 • ' ' crypts of 82 ' ' pharyngeal 83 Trachea, the 118 " blood vessels of 119 " cartilage of 118 " coats of . 118 " glands of 118 " lymphathic of 119 " nerves of . 119 Tracts of spinal cord 187 Transitional cells 14 Tube, Fallopian .' 157 Tubercule of Rolando 189 Tubular glands 68 Tubule, uriniferous 133 Tubuli galactophori ; 161 ' ' lactiferi 161 ' ' seminiferi 144 Tunica, adventitia 59, 63 " albuginea 143, 153 " fibrosa 154 " intima 59, 61, 63, 66 " media 59, 63 propria 67 " Ruyschiana... 170 " vaginalis 143, 168 " vasculosa 143, 154 Tympanum, the 178 u Umbilical artery 61 cord 30 Unipolar cell 50 Ureter, the 133, 138 " blood vessels of 140 " calyx of 133, 138 " coats of .- 138 232 Page Ureter, epithelium of 138 " infundibula of 133 " lymphatics of 14# 1 * muscular tissue of 138 " nerves of -141 " pelvis of 133 Urethra, the 141 epithelium of ? 141 Urinary organs 132 Uriniferous tubule 133 " epithelium of 136 Urinary bladder, the 139 ' ' blood vessels of 140 " coats of 139, 140 " epithelium of 140 " lymphatics of 140 " nerves of 141 Uterus, the 158 " bloodvessels of 159 " cervix of 159 " coats of 158 " epithelium of 159 ' ' glands of 159 " lymphatics of 160 " muscle of 158 " nerves of 160 " sinuses 160 Utricle 178 Uvea, the 171 V Vagina, epithelium of 19, 20 Vallum of tongue 78 Valves 63, 65 Valvulae conniventes 68, 92, 95 Vas aberrans 146 " deferens 145, 146, 147 Vasa efferentia 145 " nervorum 53 " vasorum 60 Vasum rectum 144 Vater, corpuscles of 56 Vegetal histology 1 Vein, central 103 " femoral 63 " hepatic 63 " interlobular 102, 103 " intralobular 103, 104 " portal 102, 103 " structure of 59, 62, 63, 65 " sublobular 103, 104 Venae interlobulares 137 " propriae renales 137 " rectae 137 " vorticosae 170 Vermiform appendix 100 Vesicle germinal 155 " Graafian 153 Vesiculae seminales ; 148 INDEX. INDEX 233 Page. Vessel, afferent 137 " efferent 137 Vessels, blood 59 " chyliferous 66, 94 ' ' lymphatic 65 Vestibule, the 178 Villi 67, 68, 92, 93, 94, 95 Vital functions of a cell 3 Vitelline membrane 154 Vitellus 155 Vitreous humor 30, 175 Voluntary muscle 45 w Wagner, corpuscles of 55 Wandering cells { 13 Weigert's haematoxylin method 201 Wharton, jelly of 30 White fibro-cartilage 32, 33 " fibroustissue 27, 28, 59, 60, 63 Wright's blood stain 202 Yellow fibro-cartilage 32, 34 " fibroustissue 27, 28, 34, 59, 60, 61, 63 z Zona arcuata 180 " fasciculata , 166 " glomerulosa 166 " pellucida..... 154 " radiata 154 " reticularis 166 Zonula of Zinn 174 Zymogen 107