ANATOM Y 
DESCRIPTIVE AND APPLIED 
BY 
HENRY GRAY, F.R.S. 
FELLOW OF THE ROYAL COLLEGE OF SURGEONS; LECTURER ON ANATOMY AT ST. GEORGE'S 
HOSPITAL MEDICAL SCHOOL, LONDON 
A NEW AMERICAN 
FROM THE EIGHTEENTH ENGLISH EDITION 
THOROUGHLY REVISED AND RE-EDITED 
WITH THE BASLE ANATOMICAL NOMENCLATURE 
IN ENGLISH 
BY 
ROBERT HOWDEN, M.A., M.B., C.M. 
PROFESSOR OF ANATOMY IN THE UNIVERSITY OF DURHAM, ENGLAND 
PART I 
HISTOLOGY 
EMBRYOLOGY 
OSTEOLOGY 
LEA & FEB I GER 
PHILADELPHIA AND NEW YORK 
1913 Entered according to the Act of Congress, in the year 1913, by 
LEA & FEBIGER 
in the Office of the Librarian of Congress. All rights reserved. DESCRIPTIVE AND APPLIED ANATOMY. 
HISTOLOGY. 
THE ANIMAL CELL (Fig. 1). 
A LL the tissues and organs of the body originate from a microscopic structure 
(the fertilized ovum), which consists of a soft jelly-like material enclosed in a 
membrane and containing a vesicle or small spherical body inside which are one 
or more denser spots. This may be regarded as a complete cell. All the solid 
tissues consist largely of cells essentially similar to it in nature but differing in 
external form. 
Centrosome consisting of cen- 
trosphere enclosing two cen- 
trioles 
Cell wall 
Nucleolus 
Nuclear 
membrane 
Net-knot of chromatin form- 
ing a pseudo-nucleolus 
Chromatin network 
Vacuole- 
Cell-inclusions (paraplasm) 
Fig. 1.-Diagram of a cell. (Modified from Wilson.) 
In the higher organisms a cell may be defined as "a nucleated mass of proto- 
plasm of microscopic size." Its two essentials, therefore, are: a soft jelly-like 
material, similar to that found in the ovum, and usually styled protoplasm, and a 
small spherical body imbedded in it, and termed a nucleus. Some of the unicellular 
protozoa contain no nuclei but granular particles which, like true nuclei, stain with 
basic dyes. The other constituents of the ovum, viz., its limiting membrane and 
the denser spot contained in the nucleus, called the nucleolus, are not essential to 
the type cell, and in fact many cells exist without them. 
Protoplasm (cytoplasm) is a material probably of variable constitution during 
life, but yielding on its disintegration bodies chiefly of proteid nature. Lecithin 
and cholesterin are constantly found in it, as well as inorganic salts, chief among 
which are the phosphates and chlorides of potassium, sodium, and calcium. It is 
of a semifluid viscid consistence, and in the living condition appears to be homo- 34 
HISTOLOGY 
geneous and structureless. When, however, cells have been "fixed" by reagents 
a fibrillar or granular appearance can often be made out under a high power of the 
microscope. The fibrils are usually arranged in a network or reticulum, to which 
the term spongioplasm is applied, the clear substance in the meshes being termed 
hyaloplasm. A granular appearance is often caused by the knots of the network; 
but, in addition to these, protoplasm frequently contains true granules, some of 
which are proteid in nature and probably essential constituents; others are fat, 
glycogen, or pigment granules, and are regarded as adventitious material taken in 
from without, and hence are styled cell-inclusions or paraplasm. The size and shape 
of the meshes of the spongioplasm vary in different cells and in different parts of 
the same cell. The relative amounts of spongioplasm and hyaloplasm also vary 
in different cells, the latter preponderating in the young cell and the former in- 
creasing at the expense of the hyaloplasm as the cell grows. The peripheral layer 
of a cell is in all cases modified, either by the formation of a definite cell membrane 
as in the ovum, or more frequently in the case of animal cells, by a transformation, 
probably chemical in nature, which is only recognizable by the fact that the surface 
of the cell behaves as a semipermeable membrane. 
Nucleus.-The nucleus is a minute body, imbedded in the protoplasm, and 
usually of a spherical or oval form, its size having little relation to that of the cell. 
It is surrounded by a well-defined wall, the nuclear membrane; this encloses the 
nuclear substance {nuclear matrix), which is composed of a homogeneous material 
or karyoplasm containing a network or karyomitome. The former is probably of 
the same nature as the hyaloplasm of the cell, but the latter, which forms also the 
wall of the nucleus, differs from the spongioplasm of the cell substance. It con- 
sists of fibres or filaments arranged in a reticular manner. These filaments are 
composed of a homogeneous material known as linin, which stains with acid dyes 
and contains embedded in its substance particles which have a strong affinity 
for basic dyes. These basiphil granules have been named chromatin or basichromatin 
and owe their staining properties to the presence of nucleic acid. 
Within the nuclear matrix are one or more highly refracting bodies, termed 
nucleoli, connected with the nuclear membrane by the nuclear filaments. They 
are regarded as being of two kinds. Some are mere local condensations (" net- 
knots") of the chromatin; these are irregular in shape and are termed pseudo- 
nucleoli ; others are distinct bodies differing from the pseudo-nucleoli both in nature 
and chemical composition; they may be termed true nucleoli, and are usually found 
in resting cells. The true nucleoli are oxyphil, i. e., they stain with acid dyes. 
Most living cells contain, in addition to their protoplasm and nucleus, a small 
particle which usually lies near the nucleus and is termed the centrosome. In the 
middle of the centrosome is a minute body called the centriole, and surrounding this 
is a clear spherical mass known as the centrosphere. The protoplasm surround- 
ing the centrosphere is frequently arranged in radiating fibrillar rows of granules, 
forming what is termed the attraction sphere. 
Reproduction of Cells.-Reproduction of cells is effected either by direct or by 
indirect division. In reproduction by direct division the nucleus becomes constricted 
in its centre, assuming an hour-glass shape, and then divides into two. This is fol- 
lowed by a cleavage or division of the whole protoplasmic mass of the cell; and thus 
two daughter cells are formed, each containing a nucleus. These daughter cells are 
at first smaller than the original mother cell; but they grow, and the process 
may be repeated in them, so that multiplication may take place rapidly. Indirect 
divsion or karyokinesis (karyomitosis) has been observed in all the tissues-genera- 
tive cells, epithelial tissue, connective tissue, muscular tissue, and nerve tissue. 
It is possible that cell division may always take place by the indirect method, and 
that in those cases in which direct division has been described the intermediate stages 
may not have been seen, owing to the process occurring more rapidly than usual. THE ANIMAL CELL 
35 
The process of indirect cell division is characterized by a series of complex 
changes in the nucleus, leading to its subdivision; this is followed by cleavage 
of the cell protoplasm. Starting with the nucleus in the quiescent or resting stage, 
these changes may be briefly grouped under the four following phases (Fig. 2). 
Fig. 2.-Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic 
> division. (Schafer.) I to IV, prophase; V and VI, metaphase; VII and VIII, anaphase. 
1. Prophase.-The nuclear network of chromatin filaments assumes the form 
of a twisted skein or spirem, while the nuclear membrane and nucleolus disappear. 
The convoluted skein of chromatin divides into a definite number of V-shaped 
segments or chromosomes. The number of chromosomes varies in different animals, 
but is constant for all the cells in an animal of any given species; in man the number 
is given by Flemming and Duesberg as twenty-four.1 Coincidently with or pre- 
ceding these changes the centriole, which usually lies by the side of the nucleus, 
undergoes subdivision, and the two resulting centrioles, each surrounded by a 
centrosphere, are seen to be connected by a spindle of delicate achromatic fibres 
1 Dr. J. Duesberg, Anat. Anz., Band xxviii, S. 475. 36 
HISTOLOGY 
the achromatic spindle. The centrioles move away from each other-one toward 
either extremity of the nucleus-and the fibrils of the achromatic spindle are cor- 
respondingly lengthened. A line encircling the spindle midway between its ex- 
tremities or poles is named the equator, and around this the V-shaped chromosomes 
arrange themselves in the form of a star, thus constituting the mother star or 
monaster. 
2. Metaphase. - Each V-shaped chromosome now undergoes longitudinal 
cleavage into two equal parts or daughter chromosomes, the cleavage commencing 
at the apex of the V and extending along its divergent limbs. The daughter 
chromosomes, thus separated, travel in opposite directions along the fibrils of 
the achromatic spindle toward the centrioles, around which they group themselves, 
and thus two star-like figures are formed, one at either pole of the achromatic 
spindle. This constitutes the diaster. 
3. Anaphase.-The daughter chromosomes now arrange themselves into a 
skein or spirem, and eventually form the network of chromatin which is character- 
istic of the resting nucleus. The nuclear membrane and nucleolus are also differ- 
entiated during this phase. The cell protoplasm begins to appear constricted 
around the equator of the achromatic spindle, where double rows of granules are 
also sometimes seen. The constriction deepens and the original cell gradually 
becomes divided. 
4. Telophase.-In this stage the cell is completely divided into two new cells, 
each with its own nucleus and centrosome, which assume the ordinary positions 
occupied by such structures in the resting stage. 
EPITHELIUM. 
All the surfaces of the body-the external surface of the skin, the internal 
surfaces of the digestive, respiratory, and genito-urinary tracts, the closed serous 
cavities, the inner coats of the vessels, the acini and ducts of all secreting and ex- 
creting glands, the ventricles of the brain and the central canal of the medulla 
spinalis-are covered by one or more layers of simple cells, called epithelium or 
epithelial cells. These cells are also present in the terminal parts of the organs 
of special sense, and in some other structures, such as the hypophysis cerebri 
and the thyroid gland. They serve various purposes, in some cases forming a 
protective layer, in others acting as agents in secretion and excretion, and again 
in others being concerned in the elaboration of the organs of special sense. Thus, 
in the skin, the main purpose served by the epithelium (here called the epidermis) is 
that of protection. As the surface is worn away by the agency of friction new cells 
are supplied, and thus the true skin and the vessels and nerves which it contains 
are defended from damage. In the gastro-intestinal mucous membrane and its 
glands, the epithelial cells appear to be the principal agents in preparing the diges- 
tive secretions, and in selecting and modifying materials for absorption. In other 
situations (as the nose, fauces, and respiratory passages) an important office of 
the epithelial cells appears to be to maintain an equable temperature by the 
moisture with which they keep the surface always slightly lubricated. In the 
serous cavities they also keep the opposed layers moist, and thus facilitate their 
movements on each other. Finally, in all internal parts, they ensure a perfectly 
smooth surface. 
Epithelium consists of one or more layers of cells usually supported on a base- 
ment membrane and united together by an interstitial cement substance which 
appears to be similar in chemical composition to the matrix or ground substance 
of the connective tissues. It is naturally grouped into two classes according as 
to whether there is a single layer of cells (simple epithelium), or more than one 
(stratified epithelium and transitional epithelium). EPITHELIUM 
37 
Simple Epithelium.-The different varieties of simple epithelium are squamous 
or pavement, columnar, glandular, and ciliated. 
Simple Squamous or Pavement Epithelium (Fig. 3) is composed of flat, nucleated 
scales of different shapes, usually polygonal, and varying in size. These cells fit 
together by their edges, like the tiles of a mosiac pavement. The nucleus is gen- 
erally flattened, but may be spheroidal; the flattening depends upon the thinness 
of the cell. The protoplasm of the cell presents a fine reticulum or honey-combed 
network, which gives to the cell the appearance of granulation. This kind of epi- 
thelium forms the lining lof the air-sacs of the lungs. The so-called endothelium, 
which covers the serous membranes, and which lines the heart, bloodvessels, and 
lymphatics, is also of the pavement type, being composed of a single layer of 
flattened transparent squamous cells, joined edge to edge in such a manner as 
to form a membrane of cells. 
Fig. 3.-Simple pavement epithelium. 
Fig. 4.-Columnar epithelial cells of the rabbit's intes- 
tine. (Schafer.) str, striated border; n, nucleus. 
Columnar or Cylindrical Epithelium (Fig. 4) is formed of cylindrical or rod-shaped 
cells set together so as to form a complete layer, resembling, when viewed in pro- 
file, a palisade. The cells have a prismatic figure, flattened from mutual pressure, 
and are set upright on the surface on which they are supported. Their protoplasm 
is always more or less reticulated, and fine longitudinal strise may be seen in it; 
the nucleus of each is oval in shape and contains an intranuclear network. In 
the case of the intestinal villi, the outer free border of each of these cells is dis- 
tinctly marked off from the rest of the protoplasm, and contains well-defined 
vertical striations. Columnar epithelium covers the mucous membrane and 
nearly the whole gastro-intestinal tract and its glands, the greater part of the 
male urethra, the ductus deferens, the prostate, the bulbo-urethral glands of 
Cowper, and the vestibular glands of Bartholin. In a modified form it also 
covers the ovary. 
Goblet or chalice cells are modified columnar cells. The goblet cell appears to 
be formed by an alteration in shape of a columnar cell (ciliated or otherwise) con- 
sequent on the formation of granules, which consist of a substance called mucigen, 
in the interior of the cell. This distends the upper part of the cell, while the nucleus 
is pressed down toward its deep part, until the cell bursts and the mucus is dis- 
charged on to the surface of the mucous membrane (Fig. 5), the cell then assuming 
the shape of an open cup or chalice. 
Glandular Epithelium (Fig. 6) is composed of polyhedral, columnar, or cubical 
cells. As in other forms of epithelial cells, the protoplasm shows a fine reticulum, 
which gives to the cells the appearance of granulation. Granular cells are found 
in the terminal recesses of secreting glands, and the protoplasm of the cells usually 
contains the materials which the cells secrete. 
Ciliated Epithelium (Fig. 7) generally inclines to the columnar shape. It is dis- 
tinguished by the presence of minute processes, like hairs or eyelashes (cilia) 
standing up from the free surface. The cilia (Fig. 8) at their points of attachment 38 
HISTOLOGY 
to the free border of the cell possess small nodular enlargements (basal knobs of 
Engelmann); within the cell they converge, and according to some authorities meet 
at or near the attraction sphere. If the cells be examined during life or immediately 
on removal from the living body (for which in the human subject the removal 
of a nasal polypus offers a convenient opportunity) in a weak solution of salt, 
the cilia will be seen in lashing motion; and if the cells be separated, they will often 
be seen to be moved about in the field by this ciliary action. 
Fig. 6.-Isolated liver cells of rabbit. X 500. 
Fig. 5.-Goblet cells of frog. X 500. 
Fro. 7.-Ciliated epithelium from trachea of kitten. X 255. 
Basal knobs 
Fig. 8.-Isolated ciliated cell (semidiagrammatic). 
Fig. 9.-Stratified epithelium from the cesophagus. 
The situations in which ciliated epithelium is found in the human body are: 
the respiratory tract from the nose downward to the smallest ramifications of 
the bronchial tubes, except the lower part of the pharynx and the surfaces of 
the vocal folds; the tympanic cavity and auditory tube; the uterine tube and the 
body of the uterus; the vasa efferentia, coni vasculosi and the first part of the 
ductus deferens; the ventricles of the brain and the central canal of the medulla 
spinalis. EPITHELIUM 
39 
Stratified Epithelium (Fig. 9)<-Stratified epithelium consists of several layers 
of cells varying greatly in shape. The cells of the deepest layer are for the most 
part columnar, and are placed vertically on the basement membrane; above these 
are several layers of polyhedral cells, which as they approach the surface become 
more and more compressed, until the superficial ones are found to consist of flat- 
tened scales (Fig. 10), the margins of which overlap one another so as to present 
an imbricated appearance. The protoplasm of the superficial cells is completely 
converted into a horny substance termed keratin. An intermediate body, eleidin, 
is often present in the deeper layers of this superficial portion; it exists in the form 
of coarse granules, and is especially well seen in the stratum granulosum of the 
epidermis (Fig. 11). The most superficial layers lose their nuclei, die, and are 
thrown or worn off. 
Fig. 10.-Epithelial cells from the oral cavity of man. 
X 350. a, large; b, middle sized; c. the same with two nuclei. 
Stratum, 
corneum 
Stratum 
lucidum 
Stratum 
granulosum 
Prickle-cells 
of stratum • 
Malpighii 
Fig. 11.-Portion of epidermis from a section of the skin of the finger. (Ranvier.) 
The cells of the deeper layers of stratified squamous epithelium are called prickle 
cells; they possess short, fine fibrils, which pass from their margins to those of 
neighboring cells, serving to connect them together. They are not closely joined 
together by cement-substance, but are separated from each other by intercellular 
channels, across which the fibrils may be seen bridging. When a cell is isolated, 
it appears to be covered over with a number of short spines, in consequence of the 
fibrils being broken through. These cells were first described by Max Schultze 
and Virchow, and it was believed by them that the cells were dovetailed together. 
Martyn subsequently showed that this was not the case and that the prickles were 
attached to each other by their apices; and Delepine believes the prickles to be 
parts of fibrils forming internuclear bundles between the nuclei of the cells of an 
epithelium in a state of active growth. 40 
HISTOLOGY 
Stratified epithelium is found in the skin, in the conjunctiva, in the mucous 
membrane of the nose, excepting the olfactory portion, and in the mucous membrane 
of the mouth, lower part of the pharynx, and oesophagus. 
Transitional Epithelium.-Transitional epithelium occurs in the ureters and 
urinary bladder. Here the cells of the most superficial layer are large and flat- 
tened, with depressions on their under 
surfaces, to fit on to the rounded ends 
of the cells of the second layer, which 
are pear-shaped, the apices touching the 
basement membrane. Between the 
tapering points of the cells of the second 
layer is a third variety of cells of smaller 
size than those of the other two layers 
(Fig. 12). 
Fig. 12.-Transitional epithelium. 
CONNECTIVE TISSUES. 
The term connective tissue includes a number of tissues which support and con- 
nect the other tissues of the body; they are composed of cells separated from 
one another by an intercellular material. The connective tissues may differ con- 
siderably from each other in appearance, but they present many points of relation- 
ship, and are, moreover, developed from the same layer of the embryo, the meso- 
derm. They are divided into three great groups: (1) the connective tissues proper, 
(2) cartilage, and (3) bone. The circulating fluids, although functionally and prob- 
ably developmentally different from the others, are regarded by some histologists 
as a form of connective tissue, and are dealt with therefore in this section. 
The Connective Tissues Proper.-Several varieties of connective tissue are 
recognized: (1) Areolar tissue. (2) White fibrous tissue. (3) Yellow elastic tissue. 
(4) Mucous tissue. (5) Retiform tissue. They are all composed of a homogeneous 
matrix, in which are imbedded cells and fibres-the latter of two kinds, white, 
and yellow or elastic. The distinction between the different varieties depends 
upon the relative preponderance of one or other kind of fibre, of cells, or of 
matrix. 
Areolar Tissue.-This is so called because its meshes can be easily distended 
with air or fluid and thus separated into areolae or spaces, which open freely into 
each other. Such spaces, however, do not exist in the natural condition of the body, 
the whole tissue forming one unbroken membrane composed of a number of inter- 
lacing fibres. The chief use of areolar tissue is to bind parts together, while by 
the laxity of its fibres, and the permeability of its areolae, it allows them to move 
on each other, and affords a ready exit for inflammatory and other effused fluids. 
It is quite the most extensively distributed of all the tissues. It is found beneath 
the skin in a continuous layer all over the body, connecting it to the subjacent parts. 
In the same way it is situated beneath the mucous and serous membranes. It is 
also found between muscles, vessels, and nerves, forming investing sheaths for 
them, and connecting them with surrounding structures. In addition to this it 
is present in the interior of organs, binding together the various lobes and lobules of 
the compound glands, the various coats of the hollow viscera, the fibres of muscles, 
etc., and thus forms the most important connecting medium of the various struc- 
tures or organs of which the body is made up. In many parts the areolae or inter- 
spaces of areolar tissue are occupied by fat cells, constituting adipose tissue, which 
will presently be described. 
Areolar tissue presents to the naked eye an appearance somewhat like spun 
silk. When stretched out, it is seen to consist of delicate soft elastic threads CONNECTIVE TISSUES 
41 
interlacing with each other in every direction, and forming a network of extreme 
delicacy. When examined under the microscope (Fig. 13) it is found to be com- 
posed of white fibres and yellow elastic fibres intercrossing in all directions, and 
united together by a homogeneous cement or ground substance, the matrix, 
showing cell-spaces wherein lie the connective tissue corpuscles; these contain the 
protoplasm out of which the whole is developed and regenerated. 
Plasma cell 
White 
'fibres 
Elastic, 
fibres 
Fibrillated 
cell 
Lamellar cell 
Fig. 13.-Subcutaneous tissue from a young rabbit. Highly magnified. (Schafer.) 
The white fibres are arranged in wavy bands or bundles of minute transparent 
homogeneous filaments or fibrillae. The bundles have a tendency to split up 
longitudinally or send off slips to join neighboring bundles, and receive others 
in return, but the individual fibres are unbranched, and never join other fibres. 
The yellow elastic fibres have well-defined outlines and are considerably larger 
in size than the white fibrillae, but vary much, being from 1 to 6^ in diameter. 
They form bold and wide curves, branch, and freely anastomose with each other; 
they are homogeneous in appearance, and tend to curl up, especially at their 
broken ends. 
The cells of areolar tissue are of four principal kinds: (1) Flattened lamellar 
cells, which may be either branched or unbranched. The branched lamellar cells 
are composed of clear cytoplasm, and contain oval nuclei; the processes of these 
cells may unite so as to form an open network, as in the cornea. The unbranched 
cells are joined edge to edge like the cells of an epithelium; the " tendon cells," pres- 
ently to be described, are examples of this variety. (2) Clasmatocytes, large irregular 
cells characterized by the presence of granules or vacuoles in their protoplasm, 
and containing oval nuclei. (3) Granule cells {Mastzellen), which are ovoid or 
spheroidal in shape. They are formed of a soft protoplasm, containing granules 
which are basiphil in character. (4) Plasma cells of Waldeyer, usually spheroidal 
and distinguished by containing a vacuolated protoplasm. The vacuoles are filled 42 
HISTOLOGY 
with fluid, and the protoplasm between the spaces is clear, with occasionally a few 
scattered basiphil granules. 
In addition to these four typical forms of connective-tissue corpuscles, areolar 
tissue may be seen to possess wandering cells, i. e., leucocytes which have emigrated 
from the neighboring vessels; in some instances, as in the choroid coat of the eye, 
cells filled with granules of pigment (pigment cells) are found. 
The cells lie in spaces in the ground substance between the bundles of fibres, 
and these spaces may be brought into view by treating the tissue with nitrate of 
silver and exposing it to the light. This will color the ground substance and leave 
the cell-spaces unstained. 
Adipose Tissue.-In almost all parts of the body the ordinary areolar tissue 
contains a variable quantity of fat. The principal situations where it is not found 
are the subcutaneous tissue of the eyelids, of the penis and scrotum, of the labia 
minora; within the cavity of the cranium; and in the lungs, except near their 
roots. The distribution of adipose tissue is not uniform; in some parts it is in 
great abundance, as in the subcutaneous tissue, especially of the abdomen, around 
the kidneys, and in some other situations. Lastly, fat enters largely into the for- 
mation of the marrow of bones. 
Fig. 14.-Adipose tissue. Highly magnified, a, star-like appearance, from crystallization of fatty acids. 
Adipose tissue consists of small vesicles, fat cells, lodged in the meshes of areolar 
tissue. Fat cells (Fig. 14) vary in size, but are of about the average diameter of 
50/z; each consists of an exceedingly delicate protoplasmic membrane, filled with 
fatty matter, which is liquid during life, but becomes solidified after death. They 
are round or spherical where they have not been subjected to pressure; otherwise 
they assume a more or less polygonal outline. A nucleus is always present under 
the cell membrane and can be easily demonstrated by staining with hematoxylin; 
in the natural condition it is so compressed by the contained oily matter as to be 
scarcely recognizable. The fat cells are contained in clusters in the areolae of fine 
connective tissue, and are held together mainly by the network of capillary blood- 
vessels which is distributed to them. 
Chemically the oily material in the cells is composed of the fats, olein, palmitin, 
and stearin, which are glycerin compounds with fatty acids. Sometimes fat 
crystals form in the cells after death (Fig. 14, a). By boiling the tissue in ether or 
strong alcohol the fat may be extracted from the vesicles, leaving them empty 
and shrunken. 
Fat may be first detected in the human embryo about the fourteenth week. 
The fat cells are formed by the transformation of connective-tissue corpuscles. CONNECTIVE TISSUES 
43 
Small droplets of oil are formed in the protoplasm, and these coalesce to produce a 
larger drop, which increases until it distends the corpuscles, the remaining proto- 
plasm and the nucleus being displaced toward the periphery of the cell (Fig. 15). 
Fig. 15.-Development of fat. (Klein and Noble Smith ) 
a, minute artery; v, minute vein; c, capillary bloodvessels 
in the course of formation; they are not yet completely hol- 
lowed out, there being still left in them protoplasmic septa; 
the ground substance, containing numerous nucleated cells, 
some of which are more distinctly branched and flattened 
than others, and appear therefore more spindle-shaped. 
Fig. 16.-White fibres of areolar tissue. X 400. 
(Sharpey.) 
Tendon 
cells ' 
»Fig. 17.-Tendon of mouse's tail, stained 
with [logwood, showing chains of cells be- 
tween\the tendon bundles. (From Quain's 
"Anatomy." E. A. Schafer.) 
Fig. 18.-Transverse section of tendon of rat. X 120. 
White Fibrous Tissue (Fig. 16) is a true connecting structure, and serves three 
purposes in the animal economy. In the form of ligaments it binds bones together; 
in the form of tendons it connects muscles to bones or other structures; and it 
constitutes investing or protecting structures to various organs in the form of 
membranes. Examples of such membranes are to be found in the muscular fasciee 
or sheaths, the periosteum, and the perichondrium; the investments of the various 
glands (such as the tunica albuginea testis, the capsule of the kidney, etc.); the 
investing sheaths of the nerves (epineurium), and of various organs, as the penis 
and the eye. In white fibrous tissue, as its name implies, the white fibres predomi- 44 
HISTOLOGY 
nate; the matrix is apparent only as a cement-substance, the yellow elastic fibres 
are comparatively few, while the tissue cells are arranged in a special manner. 
It presents to the naked eye the appearance of silvery white glistening fibres, 
covered over with a quantity of loose flocculent tissue which binds the fibres 
together and carries the bloodvessels. It is not possessed of any elasticity, and only 
the very slightest extensibility; it is exceedingly strong, so that upon the applica- 
tion of any external violence, a bone with which it is connected may fracture 
before the fibrous tissue gives way. In ligaments and tendons the bundles of fibres 
run parallel with each other; in membranes they intersect one another. The cells 
found in white fibrous tissue are often called tendon cells. They are situated on 
the surfaces of groups of bundles and are quadrangular in shape, arranged in rows, 
in single file, each cell being separated from its neighbors by a narrow line of cement- 
substance. The nucleus is generally situated at one end of the cell, the nucleus 
of the adjoining cell being in close proximity to it 
(Fig. 17). The tendon cells have wing-like processes 
which pass between the bundles of fibres, giving a stel- 
late appearance in transverse section (Fig. 18). Upon 
the addition of acetic acid white fibrous tissue swells 
up into a glassy looking indistinguishable mass. When 
boiled in water it is converted almost completely 
into gelatin, the white fibres being composed of the 
albuminoid collagen, which is often regarded as the 
anhydride of gelatin. 
Yellow Elastic Tissue.-In certain parts of the body a 
tissue is found which when viewed in mass is of a 
yellowish color, and is possessed of great elasticity, so 
that it is capable of considerable extension, and when 
the extending force is withdrawn returns at once to its 
original condition. This \syellow elastic tissue; it may 
be regarded as a connective tissue in which the yellow 
elastic fibres have developed to the practical exclusion 
of the other elements. It is found in the ligamenta 
flava, in the vocal folds, in the mucous membrane of the trachea and bronchi, 
in the coats of the bloodvessels, especially the larger arteries, and to a very 
considerable extent in the hyothyroid, cricothyroid, and stylohyoid ligaments. 
It is also found in the ligamentum nuchae of the lower animals (Fig. 19). In 
some parts where the fibres are broad and large and the network close, the tissue 
presents the appearance of a membrane, with gaps or perforations corresponding 
to the intervening spaces. This is to be found in the inner coat of the arteries, 
and to it the name of fenestrated membrane has been given by Henle. The yellow 
elastic fibres remain unaltered by acetic acid; chemically they are composed of 
the albuminoid body elastin. 
Mucous Tissue.-Mucous tissue exists chiefly in the "jelly of Wharton," which 
forms the bulk of the umbilical cord, but is also found in other situations in the 
fetus, chiefly as a stage in the development of connective tissue. It consists of a 
matrix, largely made up of mucin, in which are nucleated cells with branching 
and anastomosing processes (Fig. 20). Few fibres are seen in typical mucous tissue, 
although at birth the umbilical cord shows a considerable development of fibres. 
In the adult the vitreous humor of the eye is a persistent form of mucous tissue, 
in which there are no fibres, and from which the cells have disappeared, leaving- 
only the mucinous ground substance. 
Retiform or Reticular Tissue (Fig. 21) is found extensively in many parts of the 
body, constituting the framework of some organs and entering into the construc- 
tion of many mucous membranes. It is a variety of connective tissue, in which 
Fig. 19.-Elastic fibres. X 200. 
(Sharpey.) CONNECTIVE TISSUES 
45 
the intercellular or gound substance has, in great measure, disappeared, and is 
replaced by fluid. It is apparently composed almost entirely of extremely fine 
bundles of white fibrous tissue, forming an intricate network, and chemically it 
yields gelatin. The fibres are covered and concealed in places by flattened branched 
connective tissue cells. In many situations the interstices of the network are filled 
with rounded lymph-corpuscles, and the tissue is then termed lymphoid or adenoid 
tissue. 
Fig. 20.-Mucous tissue from the umbilical cord of the human fetus of four months. 
Fig. 21.-Retiform tissue, from a lymph gland. 
Basement Membranes, formerly described as homogeneous membranes, are in 
most cases really a form of connective tissue. They constitute the supporting 
membrane, or membrana propria, on which is placed the epithelium of mucous 
membranes or secreting glands, and they are also found in other situations. By 46 
HISTOLOGY 
means of staining with nitrate ot silver they may be shown to consist usually of 
flattened cells in close apposition, and joined together by their edges, thus forming 
an example of an epithelioid arrangement of connective tissue cells. In some 
situations the cells, instead of adhering by their edges, give off branching processes 
which join with similar processes of other cells, and so form a network rather than 
a continuous membrane. Some basement membranes are composed of elastic 
tissue, as in the cornea, others are merely condensed matrix. 
Vessels and Nerves of Connective Tissue.-The bloodvessels of connective tissue 
are very few-that is to say, there are few actually destined for the tissue itself, 
although many vessels carrying blood to other structures may permeate one of its 
forms, the areolar tissue. In white fibrous tissue the bloodvessels usually run 
parallel to the longitudinal bundles and between them, sending transverse com- 
municating branches across; in some forms, as in the periosteum and dura mater 
they are fairly numerous. In yellow elastic tissue, the bloodvessels also run 
between the fibres, and do not penetrate them. Lymphatic vessels are very numer- 
ous in most forms of connective tissue, especially in the areolar tissue beneath the 
skin and the mucous and serous surfaces. They are also found in abundance in 
the sheaths of tendons, as well as in the tendons themselves. Nerves are to be 
found in the white fibrous tissue, where they end in a special manner; but it is 
doubtful whether any nerves end in areolar tissue; at all events, they have not 
yet been demonstrated, and the tissue is possessed of very little sensibility. 
Pigment.-In various parts of the body pigment is found; most frequently in 
epithelial cells and in the cells of connective tissue. Pigmented epithelial cells 
are found in the external layer of the retina, on the posterior surface of the iris, 
in the olfactory region of the nose, and in 
the membranous labyrinth of the ear. Pig- 
ment is likewise found in the cells of the 
deeper layers of the cuticle and in the hairs; 
in the skin of the colored races it is abun- 
dantly present, but in the white races it is 
well-marked only in the areolse around the 
nipples and in irregular colored patches. 
In the connective tissue cells pigment is 
frequently met with in the lower verte- 
brates. In man it is found in the choroid 
coat of the eye (Fig. 22), and in the iris 
of all but the light blue eyes and the albino. 
It is also occasionally met with in the cells 
of retiform tissue and in the pia mater of 
the upper part of the medulla spinalis. The 
cells are characterized by their large size 
and by branched processes, which are also 
filled with granules. In the retina the pro- 
cesses of the cells can be withdrawn or protruded under the influence of light in 
order to protect the delicate rods and cones. The pigment (melanin) consists of 
dark brown or black granules of very small size closely packed together within 
the cells, but not invading the nucleus. Occasionally the pigment is yellow, 
and when occurring in the cells of the cuticle constitutes "freckles." In the 
retina another variety of pigment occurs, known as rhodopsin or visual purple, 
which is bleached on exposure to light. 
Fig. 22.-Pigment cells from the choroid coat of the 
eyeball. 
Applied Anatomy.-Abnormal pigmentation of the skin may be congenital, when it often takes 
the form of dark brown or black nevi {moles), scattered over a greater or smaller area of the 
body. It may also result from the prolonged consumption of various drugs, particularly of 
salts of silver or arsenic, being most marked wherever the skin is exposed to the action of light. CONNECTIVE TISSUES 
47 
Progressive darkening or bronzing of the skin is also highly suggestive of Addison's disease, which 
commonly follows destruction or tuberculosis of the suprarenal glands; it is then most obvious 
in regions where the skin is normally pigmented or is subjected to pressure or irritation from the 
clothes. Pigmentation is also associated with certain disorders of the skin, of the female genitalia, 
and of the thyroid gland, and with the later stages of wasting diseases such as cancer and phthisis. 
It does not yield to any medical treatment as a rule. 
Development of Connective Tissue.-Connective tissue is developed from cells of the meso- 
derm. These cells multiply and form a syncytium containing many nuclei. Later the proto- 
plasm increases rapidly in amount, and in the vicinity of each nucleus is differentiated into two 
parts: (1) a portion surrounding the nucleus and forming ultimately the cytoplasm of the con- 
nective tissue cell; (2) an outlying portion in which fibrillation takes place. Both the white and 
the yellow elastic fibres are laid down in the same manner. 
Cartilage.-Cartilage is a non-vascular structure which is found in various 
parts of the body-in adult life chiefly in the joints, in the parietes of the thorax, 
and in various tubes, such as the trachea and bronchi, nose, and ears, which require 
to be kept permanently open. In the fetus, at an early period, the greater part 
of the skeleton is cartilaginous; as this cartilage is afterward replaced by bone, 
it is called temporary, in contradistinction to that which remains unossified during 
the whole of life, and is called permanent. 
Cartilage is divided, according to its minute structure, into hyaline cartilage, 
white fibrocartilage, and yellow or elastic fibrocartilage. Besides these varieties 
met with in the adult human subject, there is a variety called cellular cartilage, 
which consists entirely, or almost entirely, of cells, separated from each other by 
their capsules only, which in this kind of cartilage are extremely well-marked. 
Cellular cartilage is found in the external ears of rats, mice, and some other animals, 
and is present in the notochord of the human embryo, but is not found in any 
other human structure. The various cartilages in the body are also classified, 
according to their functions and positions, into articular, interarticular, costal, 
and membraniform. 
Hyaline Cartilage.-Hyaline cartilage consists of a gristly mass of a firm consist- 
ence, but of considerable elasticity and pearly bluish color. Except where it coats 
the articular ends of bones, it is covered externally by a fibrous membrane, the 
perichondrium, from the vessels of 
which it imbibes its nutritive 
fluids, being itself destitute of 
bloodvessels. It contains no 
nerves. Its intimate structure is 
very simple. If a thin slice be 
examined under the microscope, it 
will be found to consist of cells of 
a rounded or bluntly angular 
form, lying in groups of two or 
more in a granular or almost 
homogeneous matrix (Fig. 23). 
The cells, when arranged in groups of two or more, have generally straight outlines 
where they are in contact with each other, and in the rest of their circumference 
are rounded. They consist of clear translucent protoplasm in which fine inter- 
lacing filaments and minute granules are sometimes present; imbedded in this 
are one or two round nuclei, having the usual intranuclear network. The cells 
are contained in cavities in the matrix, called cartilage lacunse; around these the 
matrix is arranged in concentric lines, as if it had been formed in successive 
portions around the cartilage cells. This constitutes the so-called capsule of the 
space. Each lacuna is generally occupied by a single cell, but during the division 
of the cells it may contain two, four, or eight cells. 
The matrix is transparent and apparently without structure, or else presents a 
Fig. 23.-Human cartilage cells from the cricoid cartilage. 
X 350 48 
HISTOLOGY 
dimly granular appearance, like ground glass. Some observers have shown that 
the matrix of hyaline cartilage, and especially of the articular variety, after pro- 
longed maceration, can be broken up into fine fibrils. These fibrils are probably 
of the same nature, chemically, as the white fibres of connective tissue. It is 
believed by some histologists that the matrix is permeated by a number of fine 
channels, which connect the lacunae with each other, and that these canals com- 
municate with the lymphatics of the perichondrium, and thus the structure 
is permeated by a current of nutrient fluid. 
Articular cartilage, costal cartilage, and temporary cartilage are all of the hyaline 
variety. They present differences in the size, shape, and arrangement of their 
cells. 
In Articular Cartilage (Fig. 24), which shows no tendency to ossification, the 
matrix is finely granular; the cells and nuclei are small, and are disposed parallel 
to the surface in the superficial part, while nearer to the bone they are arranged in 
vertical rows. Articular cartilages have a tendency to split in a vertical direction; 
in disease this tendency becomes very manifest. The free surface of articular 
cartilage, where it is exposed to friction, is not covered by perichondrium, although 
a layer of connective tissue continuous with that of the synovial membrane can be 
Superficial flattened cells 
Vertical rows of cells 
Calcified matrix 
Bone 
Fig. 25.-Costal cartilage from a man, aged 
seventy-six years, showing the development of 
fibrous structure in the matrix. In several por- 
tions of the specimen two or three generations of 
cells are seen enclosed in a parent cell wall. 
Highly magnified. 
Fig. 24.-Vertical section of articular cartilage. 
traced in the adult over a small part of its circumference, and here the cartilage 
cells are more or less branched and pass insensibly into the branched connective 
tissue corpuscles of the synovial membrane. Articular cartilage forms a thin 
incrustation upon the joint surfaces of the bones, and its elasticity enables it to 
break the force of concussions, while its smoothness affords ease and freedom of 
movement. It varies in thickness according to the shape of the articular surface 
on which it lies; where this is convex the cartilage is thickest at the centre, the 
reverse being the case on concave articular surfaces. It appears to derive its 
nutriment partly from the vessels of the neighboring synovial membrane and 
partly from those of the bone upon which it is implanted. Toynbee has shown 
that the minute vessels of the cancellous tissue as they approach the articular 
lamella dilate and form arches, and then return into the substance of the bone. 
In Costal Cartilage the cells and nuclei are large, and the matrix has a tendency 
to fibrous striation, especially in old age (Fig. 25). In the thickest parts of the 
costal cartilages a few large vascular channels may be detected. This appears, CONNECTIVE TISSUES 
49 
at first sight, to be an exception to the statement that cartilage is a non-vascular 
tissue, but is not so really, for the vessels give no branches to the cartilage sub- 
stance itself, and the channels may rather be looked upon as involutions of the 
perichondrium. The xiphoid process and the cartilages of the nose, larynx, and 
trachea (except the epiglottis and corniculate cartilages of the larynx, which are 
composed of elastic fibrocartilage) resemble the costal cartilages in microscopic 
characteristics. The arytenoid cartilage of the larynx shows a transition from 
hyaline cartilage at its base to elastic cartilage at the apex. 
The hyaline cartilages, especially in adult and advanced life, are prone to calcify 
-that is to say, to have their matrix permeated by calcium salts without any 
appearance of true bone. The process of calcification occurs frequently, in such 
cartilages as those of the trachea and in the costal cartilages, where it may be 
succeeded by conversion into true bone. 
White Fibrocartilage.-White fibrocartilage consists of a mixture of white fibrous 
tissue and cartilaginous tissue in various proportions; to the former of these con- 
stituents it owes its flexibility and 
toughness, and to the latter its 
elasticity. When examined under 
the microscope it is found to be 
made up of fibrous connective 
tissue arranged in bundles, with 
cartilage cells between the bundles; 
the cells to a certain extent re- 
semble tendon cells, but may be 
distinguished from them by being 
surrounded by a concentrically 
striated area of cartilage matrix 
and by being less flattened (Fig. 
26). The white fibrocartilages ad- 
mit of arrangement into four 
groups-inter articular, connecting, 
circumferential, and stratiform. 
1. The Interarticular Fibrocartilages (menisci) are flattened fibrocartilaginous 
plates, of a round, oval, triangular, or sickle-like form, interposed between the 
articular cartilages of certain joints. They are free on both surfaces, usually 
thinner toward the centre than at the circumference, and held in position by the 
attachment of their margins and extremities to the surrounding ligaments. The 
synovial membranes of the joints are prolonged over them. They are found 
in the temporomandibular, sternoclavicular, acromioclavicular, wrist, and knee 
joints-i. e., in those joints which are most exposed to violent concussion and 
subject to frequent movement. Their uses are to obliterate the intervals between 
opposed surfaces in their various motions; to increase the depths of the articular 
surfaces and give ease to the gliding movements; to moderate the effects of great 
pressure and deaden the intensity of the shocks to which the parts may be sub- 
jected. Humphry has pointed out that these interarticular fibrocartilages serve 
an important purpose in increasing the varieties of movement in a joint. Thus 
in the knee joint there are two kinds of motion, viz., angular movement and rota- 
tion, although it is a hinge joint, in which, as a rule, only one variety of motion 
is permitted; the former movement takes place between the condyles of the femur 
and the interarticular cartilages, the latter between the cartilages and the head 
of the tibia. So, also, in the temporomandibular joint, the movements of opening 
and shutting the mouth take place between the fibrocartilage and the mandible, 
the grinding movement between the mandibular fossa and the fibrocartilage, the 
latter moving with the mandible. 
Fig. 26.-White fibrocartilage from an intervertebral 
fibrocartilage. 50 
HISTOLOGY 
2. The Connecting Fibrocartilages are interposed between the bony surfaces of 
those joints which admit of only slight mobility, as between the bodies of the 
vertebrae. They form disks which are closely adherent to the opposed surfaces. 
Each disk is composed of concentric rings of fibrous tissue, with cartilaginous 
laminae interposed, the former tissue predominating toward the circumference, 
the latter toward the centre. 
3. The Circumferential Fibrocartilages consist of rims of fibrocartilage, which 
surround the margins of some of the articular cavities, e. g., the glenoidal labrum 
of the hip, and of the shoulder; they serve to deepen the articular cavities and to 
protect their edges. 
4. The Stratiform Fibrocartilages are those which form a thin coating to osseous 
grooves through which the tendons of certain muscles glide. Small masses of fibro- 
cartilage are also developed in the tendons of some muscles, where they glide 
over bones, as in the tendons of the Peronaeus longus and Tibialis posterior. 
Yellow or Elastic Fibrocartilage is found in the human body in the auricles of the 
external ear, the auditory tubes, the corniculate cartilages of the larynx, and the 
epiglottis. It consists of cartilage 
cells and a matrix, the latter being 
pervaded by a network of yellow 
elastic fibres, branching and anas- 
tomosing in all directions, except 
immediately around each cell, where 
there is a variable amount of non- 
fibrillated hyaline, intercellular sub- 
stance (Fig. 27). The fibres resem- 
ble those of yellow elastic tissue, 
both in appearance and in being- 
unaffected by acetic acid; and ac- 
cording to Rollett their continuity 
with the elastic fibres of the neigh- 
boring tissue is demonstrable. 
The distinguishing feature of 
cartilage chemically is that it yields 
on boiling a substance called chon- 
drin, very similar to gelatin, but 
differing from it in several of its 
reactions. It is now believed that 
chondrin is not a simple body, but 
a mixture of gelatin with mucinoid substances, chief among which, perhaps, is a 
compound termed chondro-mucoid. 
Bone.-Structure and Physical Properties.-Bone is one of the hardest structures 
of the animal body; it possesses also a certain degree of toughness and elasticity. 
Its color, in a fresh state, is pinkish-white externally, and deep red within. On 
examining a section of any bone, it is seen to be composed of two kinds of tissue, 
one of which is dense in texture, like ivory, and is termed compact tissue; the other 
consists of slender fibres and lamellae, which join to form a reticular structure; 
this, from its resemblance to lattice-work, is called cancellous tissue. The compact 
tissue is always placed on the exterior of the bone, the cancellous in the interior. 
The relative quantity of these two kinds of tissue varies in different bones, and 
in different parts of the same bone, according as strength or lightness is requisite. 
Close examination of the compact tissue shows it to be extremely porous, so that 
the difference in structure between it and the cancellous tissue depends merely 
upon the different amount of solid matter, and the size and number of spaces in 
each; the cavities are small in the compact tissue and the solid matter between 
Cartilage cell 
Hyalme matrix 
Yellow elastic 
fibres 
Fig. 27.-Yellow or elastic fibrocartilage from epiglottis of cat. CONNECTIVE TISSUES 
51 
them abundant, while in the cancellous tissue the spaces are large and the solid 
matter is in smaller quantity. 
Bone during life is permeated by vessels, and is enclosed, except where it is 
coated with articular cartilage, in a fibrous membrane, the periosteum, by means 
of which many of these vessels reach the hard tissue. If the periosteum be stripped 
from the surface of the living bone, small bleeding points are seen which mark the 
entrance of the periosteal vessels; and on section during life every part of the 
bone exudes blood from the minute vessels which ramify in it. The interior of 
each of the long bones of the limbs presents a cylindrical cavity filled with marrow 
and lined by a highly vascular areolar structure, called the medullary membrane 
or internal periosteum. 
Periosteum.-The periosteum adheres to the surface of each of the bones in 
nearly every part, but not to cartilaginous extremities. When strong tendons or 
ligaments are attached to a bone, the periosteum is incorporated with them. It 
consists of two layers closely united together, the outer one formed chiefly of 
connective tissue, containing occasionally a few fat cells; the inner one, of elastic 
fibres of the finer kind, forming dense membranous networks, which can be again 
separated into several layers. In young bones the periosteum is thick and very 
vascular, and is intimately connected at either end of the bone with the epiphysial 
cartilage, but less closely with the body of the bone, from which it is separated by 
a layer of soft tissue, containing a number of granular corpuscles or osteoblasts, by 
which ossification proceeds on the exterior of the young bone. Later in life the 
periosteum is thinner and less vascular, and the osteoblasts are converted into an 
epithelioid layer on the deep surface of the periosteum. The periosteum serves 
as a nidus for the ramification of the vessels previous to their distribution in the 
bone; hence the liability of bone to exfoliation or necrosis when denuded of this 
membrane by injury or disease. Fine nerves and lymphatics, which generally 
accompany the arteries, may also be demonstrated in the periosteum. 
Marrow.-The marrow not only fills up the cylindrical cavities in the bodies of 
the long bones, but also occupies the spaces of the cancellous tissue and extends 
into the larger bony canals (Haversian canals) which contain the bloodvessels. 
It differs in composition in different bones. In the bodies of the long bones the 
marrow is of a yellow color, and contains, in 100 parts, 96 of fat, 1 of areolar tissue 
and vessels, and 3 of fluid with extractive matter; it consists of a basis of connective 
tissue supporting numerous bloodvessels and cells, most of which are fat cells 
but some are "marrow cells," such as occur in the red marrow to be immediately 
described. In the flat and short bones, in the articular ends of the long bones, 
in the bodies of the vertebrse, in the cranial diploe, and in the sternum and ribs 
the marrow is of a red color, and contains, in 100 parts, 75 of water, and 25 of solid 
matter consisting of cell-globulin, nucleoprotein, extractives, salts, and only a 
small proportion of fat. The red marrow consists of a small quantity of connective 
tissue, bloodvessels, and numerous cells (Fig. 28), some few of which are fat cells, 
but the great majority are roundish nucleated cells, the true "marrow cells" 
of Kolliker. These marrow cells proper, or myelocytes, resemble in appearance 
lymphoid corpuscles, and like them are amoeboid; they generally have a hyaline 
protoplasm, though some show granules either oxyphil or basiphil in reaction. 
A number of eosinophil cells are also present. Among the marrow cells may be 
seen smaller cells, which possess a slightly pinkish hue; these are the erythroblasts 
or normoblasts, from which the red corpuscles of the adult are derived, and which 
may be regarded as descendants of the nucleated colored corpuscles of the embryo. 
Giant cells (myeloplaxes, osteoclasts}, large, multinucleated, protoplasmic masses, 
are also to be found in both sorts of adult marrow, but more particularly in red 
marrow. They were believed by Kolliker to be concerned in the absorption of 
bone matrix, and hence the name which he gave to them-osteoclasts. They 52 
HISTOLOGY 
excavate in the bone small shallow pits or cavities, which are named Howship's 
foveolae, and in these they are found lying. 
Vessels and Nerves of Bone.-The bloodvessels of bone are very numerous. Those 
of the compact tissue are derived from a close and dense network of vessels ramify- 
ing in the periosteum. From this membrane vessels pass into the minute orifices 
in the compact tissue, and run through the canals which traverse its substance. 
The cancellous tissue is supplied in a similar way, but by less numerous and larger 
vessels, which, perforating the outer compact tissue, are distributed to the cavities 
of the spongy portion of the bone. In the long bones, numerous apertures may 
be seen at the ends near the articular surfaces; some of these give passage to the 
arteries of the larger set of vessels referred to; but the most numerous and largest 
apertures are for some of the veins of the cancellous tissue, which emerge apart 
from the arteries. The marrow in the body of a long bone is supplied by one 
large artery (or sometimes more), which enters the bone at the nutrient foramen 
Normoblast with dividing nucleus 
Myelocyte 
Eosinophil 
cell 
Erythrocyte 
Normoblasts 
Myelocyte 
dividing 
Myeloplaxe -■ 
Myelocyte 
Myelocyte 
Fat' 
■ Fat 
Fig. 28.-Human bone marrow. Highly magnified. 
(situated in most cases near the centre of the body), and perforates obliquely the 
compact structure. The medullary or nutrient artery, usually accompanied by one 
or two veins, sends branches upward and downward, which ramify in the medul- 
lary membrane, and give twigs to the adjoining canals. The ramifications of this 
vessel anastomose with the arteries of the cancellous and compact tissues. In most 
of the flat, and in many of the short spongy bones, one or more large apertures are 
observed, which transmit to the central parts of the bone vessels corresponding to 
the nutrient arteries and veins. The veins emerge from the long bones in three 
places (Kolliker): (1) one or two large veins accompany the artery; (2) numerous 
large and small veins emerge at the articular extremities; (3) many small veins 
pass out of the compact substance. In the flat cranial bones the veins are large, 
very numerous, and run in tortuous canals in the diploic tissue, the sides of the 
canals being formed by thin lamellae of bone, perforated here and there for the 
passage of branches from the adjacent cancelli. The same condition is also 
found in all cancellous tissue, the veins being enclosed and supported by osseous CONNECTIVE TISSUES 
53 
material, and having exceedingly thin coats. When a bone is divided, the vessels 
remain patulous, and do not contract in the canals in which they are contained. 
Lymphatic vessels, in addition to those found in the periosteum, have been traced 
by Cruikshank into the substance of bone, and Klein describes them as running in 
the Haversian canals. Nerves are distributed freely to the periosteum, and accom- 
pany the nutrient arteries into the interior of the bone. They are said by Kolliker 
to be most numerous in the articular extremities of the long bones, in the vertebrae, 
and in the larger flat bones. 
Minute Anatomy.-A transverse section of dense bone may be cut with a saw 
and ground down until it is sufficiently thin. 
If this be examined with a rather low power the bone will be seen to be mapped 
out into a number of circular districts each consisting of a central hole surrounded 
by a number of concentric rings. These districts are termed Haversian systems; 
the central hole is an Haversian canal, and the rings are layers of bony tissue 
arranged concentrically around the central canal, and termed lamellae. More- 
over, on closer examination it will be found that between these lamellae, and 
therefore also arranged concentrically around the central canal, are a number of 
Fig. 29.-Transverse section of compact tissue of bone. Magnified. (Sharpey.) 
little dark spots, the lacunae, and that these lacunae are connected with each other 
and with the central Haversian canal by a number of fine dark lines, which radiate 
like the spokes of a wheel and are called canaliculi. Filling in the irregular intervals 
which are left between these circular systems are other lamellae, with their lacunae 
and canaliculi running in various directions, but more or less curved (Fig. 29); 
they are termed interstitial lamellae. Again, other lamellae, found on the surface 
of the bone, are arranged parallel to its circumference; they are termed circum- 
ferential, or by some authors primary or fundamental lamellae, to distinguish them 
from those laid down around the axes of the Haversian canals, which are then 
termed secondary or special lamellae. 
The Haversian canals, seen in a transverse section of bone as round holes at or 
about the centre of each Haversian system, may be demonstrated to be true canals 
if a longitudinal section be made (Fig. 30). It will then be seen that the canals 
run parallel with the longitudinal axis of the bone for a short distance and then 
branch and communicate. They vary considerably in size, some being as much as 
0.12 mm. in diameter; the average size is, however, about 0.05 mm. Near the 
medullary cavity the canals are larger than those near the surface of the bone. 54 
HISTOLOGY 
Each canal contains one or two bloodvessels, with a small quantity of delicate 
connective tissue and some nerve filaments. In the larger ones there are also 
lymphatic vessels, and cells with branching processes which communicate, through 
the canalculi, with the branched processes of certain bone cells in the substance 
of the bone, those canals near the surface of the bone open upon it by minute 
orifices, and those near the medullary cavity open in the same way into this space, 
so that the whole of the bone is permeated by a system of bloodvessels running 
through the bony canals in the centres of the Haversian systems. 
The lamellae are thin plates of bony tissue 
encircling the central canal, and may be com- 
pared, for the sake of illustration, to a number 
of sheets of paper pasted one over another 
around a central hollow cylinder. After 
macerating a piece of bone in dilute mineral 
acid, these lamellae may be stripped off in a 
Fig. 30.-Section parallel to the surface 
from the body of the femur. X 100. a, Haver- 
sian canals; b, lacunae seen from the side; c, 
others seen from the surface in lamellse, which 
are cut horizontally. 
Fig. 31.-Perforating fibres, human parietal bone, decalcified. 
(H. Muller.) a, perforating fibres in situ; b, fibres drawn out of 
their sockets; c, sockets. 
longitudinal direction as thin films. If one of these be examined with a high power 
of the microscope, it will be found to be composed of a finely reticular structure, 
made up of very slender transparent fibres, decussating obliquely; and coalescing 
at the points of intersection; these fibres are composed of fine fibrils identical with 
those of white connective tissue. The intercellular matrix between the fibres is 
impregnated by calcareous deposit which the acid dissolves. In many places the 
various lamellae may be seen to be held together by tapering fibres, which run 
obliquely through them, pinning or bolting them together; they were first de- 
scribed by Sharpey, and were named by him perforating fibres (Fig. 31). 
The Lacunae are situated between the lamellae, and consist of a number of oblong 
spaces. In an ordinary microscopic section, viewed by transmitted light, they 
appear as fusiform opaque spots. Each lacuna is occupied during life by a branched 
cell, termed a bone-cell or bone-corpuscle, the processes from which extend into the 
canaliculi (Fig. 32). 
The Canaliculi are exceedingly minute channels, crossing the lamellae and con- 
necting the lacunae with neighboring lacunae and also with the Haversian canal. 
From the Haversian canal a number of canaliculi are given off, which radiate from 
it, and open into the first set of lacunae between the first and second lamellae. 
From these lacunae a second set of canaliculi is given off; these run outward to the CONNECTIVE TISSUES 
55 
next senes of lacunae, and so on until the periphery of the Haversian system is 
reached; here the canaliculi given off from the last series of lacunae do not communi- 
cate with the lacunae of neighboring Haversian systems, but after passing outward 
for a short distance form loops and return to their own lacunae. Thus every 
part of an Haversian system is supplied with nutrient fluids derived from the 
vessels in the Haversian canal and distributed through the canaliculi and lacunae. 
The bone cells are contained in the lacunae, 
which, however, they do not completely fill. 
They are flattened nucleated branched cells, 
homologous with those of connective tissue; the 
branches, especially in young bones, pass into 
the canaliculi from the lacunae. 
In thin plates of bone (as in the walls of 
the spaces of cancellous tissue) the Haversian 
canals are absent, and the canaliculi open into 
the spaces of the cancellous tissue (medullary 
spaces), which thus have the same function as 
the Haversian canals. 
Chemical Composition.-Bone consists of an 
animal and an earthy part intimately com- 
bined together. 
Fig. 32y- Nucleated bone cells and their 
processes, contained in the bone lacunae and 
their canaliculi respectively. From a section 
through the vertebra of an adult mouse. 
(Klein and Noble Smith.) 
Ha versian canal 
Bone corpuscle 
Bone corpuscle 
between inter- 
stitial lamellae 
Fig. 33.-Transverse section of body of human fibula, decalcified. X 250. 
The animal part may be obtained by immersing a bone for a considerable time 
in dilute mineral acid, after which process the bone comes out exactly the same 
shape as before, but perfectly flexible, so that a long bone (one of the ribs, for 
example) can easily be tied in a knot. If now a transverse section is made 
(Fig. 33) the same general arrangement of the Haversian canals, lamellae, lacunae, 
and canaliculi is seen. 
The earthy part may be separately obtained by calcination, by which the 
animal matter is completely burnt out. The bone will still retain its original 
form, but it will be white and brittle, will have lost about one-third of its original 
weight, and will crumble down with the slightest force. The earthy matter is 
composed chiefly of calcium phosphate, forming about 66.7 per cent, of the weight 56 
HISTOLOGY 
of the bone; it confers on bone its hardness and rigidity, while the animal matter 
(ossein) determines its tenacity. 
Ossification.-Some bones are preceded by membrane, such as those forming 
the roof and sides of the skull; others, such as the bones of the limbs, are preceded 
by rods of cartilage. Hence two kinds of ossification are described: the intra- 
membranous and the intracartilaginous. 
Intramembranous Ossification.-In the case of bones which are developed 
in membrane, no cartilaginous mould precedes the appearance of the bony tissue. 
The membrane which occupies the place of the future bone is of the nature of con- 
nective tissue, and ultimately forms the periosteum; it is composed of fibres and 
granular cells in a matrix. The peripheral portion is more fibrous, while, in the 
interior the cells or osteoblasts predominate; the whole tissue is richly supplied with 
bloodvessels. At the outset of the process of bone formation a little network 
of spicules is noticed radiating from the point or centre of ossification. These 
rays consist at their growing points of a network of fine clear fibres and granular 
corpuscles with an intervening ground substance (Fig. 34). The fibres are termed 
Osteogenetic 
fibres 
Union of 
adjacent " 
spicules 
Calcified deposit 
between the fibres 
Osteoblasts 
Bony spicules 
Fig. 34.-Part of the growing edge of the developing parietal bone of a fetal cat. (After J. Lawrence.) 
osteogenetic fibres, and are made up of fine fibrils differing little from those of white 
fibrous tissue. The membrane soon assumes a dark and granular appearance from 
the deposition of calcareous granules in the fibres and in the intervening matrix, 
and in the calcified material some of the granular corpuscles or osteoblasts are 
enclosed. By the fusion of the calcareous granules the tissue again assumes a 
more transparent appearance, but the fibres are no longer so distinctly seen. 
The involved osteoblasts form the corpuscles of the future bone, the spaces in 
which they are enclosed constituting the lacunae. As the osteogenetic fibres grow 
out to the periphery they continue to calcify, and give rise to fresh bone spicules. 
Thus a network of bone is formed, the meshes of which contain the bloodvessels 
and a delicate connective tissue crowded with osteoblasts. The bony trabeculae 
thicken by the addition of fresh layers of bone formed by the osteoblasts on their 
surface, and the meshes are correspondingly encroached upon. Subsequently 
successive layers of bony tissue are deposited under the periosteum and around 
the larger vascular channels which become the Haversian canals, so that the bone 
increases much in thickness. CONNECTIVE TISSUES 
57 
Intercartilaginous Ossification.-Just before ossification begins the mass is 
entirely cartilaginous, and in a long bone, which may be taken as an example, the 
process commences in the centre and proceeds toward the extremities, which for 
some time remain cartilaginous. Subsequently a similar process commences in 
one or more places in those extremities and gradually extends through them. 
The extremities do not, however, become joined to the body of the bone by bony 
tissue until growth has ceased; between the body and either extremity a layer of 
cartilaginous tissue termed the epiphysial cartilage persists for a definite period. 
The first step in the ossification of 
the cartilage is that the cartilage cells, 
at the point where ossification is com- 
mencing and which is termed a centre 
of ossification, enlarge and arrange 
themselves in rows (Fig. 35). The 
matrix in which they are imbedded 
increases in quantity, so that the cells 
become further separated from each 
other. A deposit of calcareous material 
now takes place in this matrix, between 
the rows of cells, so that they become 
separated from each other by longi- 
tudinal columns of calcified matrix, 
presenting a granular and opaque ap- 
pearance. Here and there the matrix 
between two cells of the same row also 
becomes calcified, and transverse bars 
of calcified substance stretch across 
from one calcareous column to another. 
Thus there are longitudinal groups of 
the cartilage cells enclosed in oblong 
cavities, the walls of which are formed 
of calcified matrix which cuts off all 
nutrition from the cells; the cells, in 
consequence, atrophy, leaving spaces 
called the primary areolae. 
At the same time that this process 
is going on in the centre of the solid 
bar of cartilage, certain changes are 
taking place on its surface. This is 
covered by a very vascular membrane, 
the perichondrium, entirely similar to the 
embryonic connective tissue already 
described as constituting the basis of 
membrane bone; on the inner surface of this-that is to say, on the surface in 
contact with the cartilage-are gathered the formative cells, the osteoblasts. By 
the agency of these cells a thin layer of bony tissue is formed between the peri- 
chondrium and the cartilage, by the intramembranous mode of ossification just 
described. There are then, in this first stage of ossification, two processes going 
on simultaneously: in the centre of the cartilage the formation of a number of 
oblong spaces, formed of calcified matrix and containing the withered cartilage 
cells, and on the surface of the cartilage the formation of a layer of true mem- 
brane bone. The second stage consists in the prolongation into the cartilage of 
processes of the deeper or osteogenetic layer of the perichondrium, which has 
now become periosteum (Fig. 35, ir). The processes consist of bloodvessels and 
Fig. 35.-Section of fetal bone of cat. ir. Irruption 
of the subperiosteal tissue, p. Fibrous layer of the perios- 
teum. o. Layer of osteoblasts, im. Subperiosteal bony 
deposit. (From Quain's "Anatomy," E. A. Schafer.) 58 
HISTOLOGY 
cells-osteoblasts, or bone-formers, and osteoclasts, or bone-destroyers. The latter 
are similar to the giant cells (myeloplaxes) found in marrow, and they excavate 
passages through the new-formed bony layer by absorption, and pass through 
it into the calcified matrix (Fig. 36). Wherever these processes come in con- 
tact with the calcified walls of the primary areolae they absorb them, and thus 
cause a fusion of the original cavities and the formation of larger spaces, which 
are termed the secondary areolae or medullary spaces. These secondary spaces 
become filled with embryonic marrow, consisting of osteoblasts and vessels, derived, 
in the manner described above, from the 
osteogenetic layer of the periosteum (Fig. 36). 
Thus far there has been traced the forma- 
tion of enlarged spaces (secondary areolae), 
the perforated walls of which are still formed 
by calcified cartilage matrix, containing an 
embryonic marrow derived from the processes 
sent in from the osteogenetic layer of the 
periosteum, and consisting of bloodvessels and 
osteoblasts. The walls of these secondary 
areolae are at this time of only inconsiderable 
thickness, but they become thickened by the 
deposition of layers of true bone on their sur- 
face. This process takes place in the follow- 
ing manner: Some of the osteoblasts of the 
embryonic marrow, after undergoing rapid 
division, arrange themselves as an epithelioid 
layer on the surface of the wall of the space 
(Fig. 37). This layer of osteoblasts forms a 
bony stratum, and thus the wall of the space 
becomes gradually covered with a layer of 
Osteoclasis- 
Fig. 36.-Part of a longitudinal section of 
the developing femur of a rabbit, a. Flattened 
cartilage cells, b. Enlarged cartilage cells, c, 
d. Newly formed bone. e. Osteoblasts, f. 
Giant cells or osteoclasts. g, h. Shrunken 
cartilage cells. (From "Atlas of Histology," 
Klein and Noble Smith.) 
Osteoblasts 
Fig. 37.-Osteoblasts and osteoclasts on trabecula of lower jaw of 
calf embryo. (Kblliker.) 
true osseous substance in which some of the bone-forming cells are included as 
bone corpuscles. The next stage in the process consists in the removal of these 
primary bone spicules by the osteoclasts. One of these giant cells may be found 
lying in a Howship's foveola at the free end of each spicule. The removal of the 
primary spicules goes on pari passu with the formation of permanent bone by 
the periosteum, and in this way the medullary cavity of the body of the bone is 
formed. 
This series of changes has been gradually proceeding toward the end of the body 
of the bone, so that in the ossifying bone all the changes described above may 
be seen in different parts, from the true bone at the centre of the body to the hyaline 
cartilage at the extremities. CONNECTIVE TISSUES 
59 
While the ossification of the cartilaginous body is extending toward the articular 
ends, the cartilage immediately in advance of the osseous tissue continues to grow 
until the length of the adult bone is reached. 
During the period of growth the articular end, or epiphysis, remains for some 
time entirely cartilaginous, then a bony centre appears, and initiates in it the 
process of intracartilaginous ossification; but this process never extends to any 
great distance. The epiphysis remains separated from the body by a narrow 
cartilaginous layer for a definite time. This layer ultimately ossifies, the distinc- 
tion between body and epiphysis is obliterated, and the bone assumes its completed 
form and shape. The same remarks also apply to such processes of bone as are 
separately ossified, e. g., the trochanters of the femur. The bones therefore con- 
tinue to grow' until the body has acquired its full stature. They increase in length 
by ossification continuing to extend behind the epiphysial cartilage, which goes 
on growing in advance of the ossifying process. They increase in circumference 
by deposition of new bone, from the deeper layer of the periosteum, on their exter- 
nal surface, and at the same time an absorption takes place from within, by which 
the medullary cavities are increased. 
The permanent bone formed by the periosteum when first laid down is cancellous 
in structure. Later the osteoblasts contained in its spaces become arranged in 
the concentric layers characteristic of the Haversian systems, and are included 
as bone corpuscles. 
The number of ossific centres varies in different bones. In most of the short 
bones ossification commences at a single point near the centre, and proceeds toward 
the surface. In the long bones there is a central point of ossification for the body 
or diaphysis: and one or more for each extremity, the epiphysis. That for the 
body is the first to appear. The times of union of the epiphyses with the body 
vary inversely with the dates at which their ossifications began (with the exception 
of the fibula) and regulate the direction of the nutrient arteries of the bones. Thus, 
the nutrient arteries of the bones of the arm and forearm are directed toward 
the elbow, since the epiphyses at this joint become united to the bodies before 
those at the opposite extremities. In the lower limb, on the other hand, the 
nutrient arteries are directed away from the knee: that is, upward in the femur, 
downward in the tibia and fibula; and in them it is observed that the upper epiphysis 
of the femur, and the lower epiphyses of the tibia and fibula, unite first with the 
bodies. Where there is only one epiphysis, the nutrient artery is directed toward 
the other end of the bone; as toward the acromial end of the clavicle, toward the 
distal ends of the metacarpal bone of the thumb and the metatarsal bone of the 
great toe, and toward the proximal ends of the other metacarpal and metatarsal 
bones. 
Parsons1 groups epiphyses under three headings, viz.: (1) pressure epiphyses, 
appearing at the articular ends of the bones and transmitting "the weight of the 
body from bone to bone;" (2) traction epiphyses, associated with the insertion 
of muscles and "originally sesamoid structures though not necessarily sesamoid 
bones;" and (3) atavistic epiphyses, representing parts of the skeleton, which at 
one time formed separate bones, but which have lost their function, "and only 
appear as separate ossifications in early life." 
Applied Anatomy.-It has been stated above that the bones increase firstly in length by ossifi- 
cation continuing to extend in the epiphysial cartilage, which goes on growing in advance of the 
ossifying process; and secondly, in circumference by deposition of new bone from the deeper 
layer of the periosteum, on the external surface. 
A careful study of osseous development is of the very greatest utility in the proper understand- 
ing of bone disease; and, moreover, an accurate knowledge of the blood supply of a long bone 
1 Jour, of Anat, and Phys., vols. xxxviii, xxxix, and xlii. 60 
HISTOLOGY 
has also many important bearings. The outer portion of the compact tissue being supplied by 
periosteal vessels, which reach the bone through muscular attachments, it follows that where 
the muscular structures are well developed, and therefore amply supplied with blood, the perios- 
teum will also be well-nourished and the bones proportionately well-developed in girth; this is 
well seen in strong muscular men with well-marked ridges on the bones. Conversely, if the mus- 
cular development be poor, the bones are correspondingly thin and light, and if from any cause 
a limb has been paralyzed from early childhood, the whole of the bones of that extremity are 
remarkable for their extreme thinness-that is to say, the periosteal blood supply has been insuffi- 
cient to nourish that membrane, and consequently very little fresh osseous tissue has been added 
to the bones from the outside. 
The best example of this condition is seen in connection with the disease known as infantile 
paralysis, where a limb becomes paralyzed at a very early period of childhood, where the muscles 
become flaccid and atonic, and where the blood supply is in consequence very greatly diminished. 
In such cases, although the limb does continue to grow in length from the epiphysial lines, its 
length is considerably less than on the normal side, owing to the imperfect nutrition; but the 
most striking feature about all the long bones of the limb is their remarkable tenuity, little or no 
addition having been made to their circumferences. 
In cases where the periosteum has been separated from the compact tissue by extensive injury 
or inflammatory exudation, necrosis or death of the underlying portion of bone takes place owing 
to its blood supply having been cut off, and the dead portion or sequestrum has to be separated 
and subsequently cast off. 
Cases, however, occur where the inflammatory process affects the whole or a great portion 
of the diaphysis of a long bone, and here extensive death of the affected portion takes place, and 
the condition goes by the name of acute infective periostitis. Where this occurs the body of the 
bone dies very rapidly, especially if the single nutrient artery be thrombosed at the same time. 
The pus which has formed beneath the periosteum is set free by timely incision, or bursts on the 
surface; the periosteum then falls back on the necrosed diaphysis and rapidly forms a layer of 
new periosteal bone, surrounding the sequestrum. This layer is called the involucrum, and the 
openings in it through which the pus escapes the cloacae. When the inflammatory process affects 
mainly the medullary canal, the condition is spoken of as osteomyelitis, and the two conditions 
very frequently coexist, and then go by the name of acute infective necrosis of bone or acute 
diaphysitis. When the medullary cavity is filled with pus, septic thrombosis of the veins in the 
Haversian canals takes place, and there is a very great danger of septic emboli being displaced 
and carried into the general circulation, thus setting up a fatal pyemia. In fact, pyemia is more 
frequently due to septic bone conditions than to any other cause. 
In the pre-antiseptic days, pyemia frequently resulted from amputations, where the medullary 
canal of a long bone was opened by the saw cut. Osteomyelitis ensued, a$d if the patient sur- 
vived, a tubular sequestrum of the divided shaft subsequently separated. 
A proper knowledge of the epiphyses is of the utmost possible importance, and greatly simplifies 
many of the problems in the pathology of bone disease. 
Speaking generally, the long bones have at either end an epiphysis from the cartilage of which 
growth occurs, and hence the body of the bone increases in length from both ends. In every 
case, however, one epiphysis is the more active, and also continues in its activity for a longer 
time. This actively growing epiphysis is always the one from which the nutrient foramen in the 
diaphysis points, and it unites to the diaphysis at a later date. It follows, therefore, that the 
increase in length of a bone is largely dependent on this epiphysis, and hence anything which 
interferes with the growth from this epiphysial line at any time prior to the union of the epiphysis 
with the diaphysis must result in a cessation of growth in length of that bone. Thus when deal- 
ing with disease in the neighborhood of this actively growing epiphysis very great care should 
be taken not to excise or destroy its line of union with the diaphysis. These epiphyses are par- 
ticularly prone to become the seat of tuberculous disease, which especially tends to attack the 
soft, highly vascular cancellous tissue. 
Again, the actively growing epiphysial plate is the portion of a long bone which is in the vast 
majority of cases affected by tumor growth in bone, whether it be innocent or malignant, the 
former (e. g., osteoma) usually appearing about puberty, and the latter (e. g., sarcoma) usually 
toward the end of the active period of epiphysial growth. 
Epiphysial growth, moreover, has to be considered by the surgeon when he is about to ampu- 
tate in a child. If the amputation is being performed through a bone, the actively growing 
epiphysis of which is at the upper end, and which will continue to grow for several years (e. g., 
humerus and tibia), it will be necessary to make allowance for this and to cut the flaps long; 
as otherwise, owing to continued growth, the sawn end of the bone will ultimately project through 
the stump, and a condition known as "conical stump" will result. This requires removal of a 
further portion of the bone. 
An inflammatory condition termed acute epiphysitis also occurs, although it is not so frequent 
as the acute infective conditions of the diaphysis, owing to the freer blood supply of the epiphysis; THE CIRCULATING FLUIDS 
61 
in late years it has been shown that acute epiphysitis in children is very frequently the result 
of a pneumococcal infection, and it may pass on to complete separation of the epiphysis. In 
this connection it is worthy of note that some of the epiphysial lines lie entirely within the cap- 
sules of their corresponding joints, in other cases entirely without the capsules; and it must follow 
that in the former case epiphysial disease, acute or chronic, becomes, ipso facto, practically synony- 
mous with disease of that joint. The best examples of intra-articular epiphyses are those for the 
head of the femur and head of the humerus, and the vast majority of all cases of tuberculous disease 
of the hip start as a tuberculous epiphysitis about the intra-articular epiphysial plate of the femur; 
again cases of acute septic arthritis of the shoulder or hip joints generally have their origins in 
these intra-articular epiphysial lines, and often result in separation of the affected epiphysis. 
Those of the other class, or extra-articular epiphyses, when diseased, do not tend to involve the 
neighboring joint so readily; and it should be the surgeon's duty to keep the disease from involv- 
ing the joint. For example, the trochanteric epiphysis of the femur is extra-articular as regards 
the hip-joint, and the epiphysial line of the head of the tibia is well below the level of the knee- 
joint, and should a chronic tuberculous abscess form in the latter situation, it should be attacked 
from the outside before it has time to spread up and involve the cartilage of the head of the tibia. 
It is therefore of great surgical interest to note in every case the relations which the various 
epiphysial lines bear to their respective joint capsules. 
A knowledge of the exact periods when the epiphyses become joined to the shaft is often of 
great importance in medicolegal inquiries. It also aids the surgeon in the diagnosis of many of 
the injuries to which the joints are liable; for it not infrequently happens that, on the application 
of severe force to a joint, the epiphysis becomes separated from the diaphysis, and such injuries 
may be mistaken for fracture or dislocation. 
THE CIRCULATING FLUIDS. 
The circulating fluids of the body are the blood and the lymph. 
Blood.-The blood is an opaque, rather viscid fluid, of a bright red or scarlet 
color when it flows from the arteries, of a dark red or purple color when it flows 
from the veins. It is salt to the taste, and has a peculiar faint odor and an alkaline 
reaction. Its specific gravity is about 1.06, and its temperature is generally about 
37° C., though varying slightly in different parts of the body. 
General Composition of the Blood.-Blood consists of a faintly yellow fluid, the 
plasma or liquor sanguinis, in which are suspended numerous minute particles, 
the blood corpuscles, the majority of which are colored and give to the blood its 
red tint. If a drop of blood be placed in a thin layer on a glass slide and examined 
under the microscope, a number of these corpuscles will be seen floating in the 
plasma. 
The Blood Corpuscles are of 
three kinds: (1) colored cor- 
puscles or erythrocytes; (2) color- 
less corpuscles or leucocytes; (3) 
blood platelets. 
1. Colored or red corpuscles 
{erythrocytes), when examined 
under the microscope, are seen 
to be circular disks, biconcave in 
profile. The disk has no nucleus, 
but, in consequence of its bicon- 
cave shape, presents, according 
to the alterations of focus under 
an ordinary high power, a central 
part, sometimes bright, sometimes 
dark, which has the appearance of a nucleus (Fig. 38, a). It is to the aggregation 
of the red corpuscles that the blood owes its red hue, although when examined 
by transmitted light their color appears to be only a faint reddish yellow. The 
corpuscles vary slightly in size even in the same drop of blood, but the average 
Fig. 38.-Human red blood corpuscles. Highly magnified, a. 
Seen from the surface, b. Seen in profile and forming rouleaux, 
c. Rendered spherical by water, d. Rendered crenate by salt 
solution. 62 
HISTOLOGY 
diameter of each is about 7.5/z,1 and the thickness about 2/n Besides these there 
are found certain smaller corpuscles of about one-half of the size just indicated; 
these are termed microcytes, and are very scarce in normal blood; in diseased con- 
ditions (e. g., anemia), however, they are more numerous. The number of red 
corpuscles in the blood is enormous; between 4,000,000 and 5,000,000 are con- 
tained in a cubic millimetre. Power states that the red corpuscles of an adult 
would present an aggregate surface of about 3000 square yards. 
If the web of a living frog's foot be spread out and examined under the micro- 
scope the blood is seen to flow in a continuous stream through the vessels, and the 
corpuscles show no tendency to adhere to each other or to the wall of the vessel. 
Doubtless the same is the case in the human body; but when human blood is drawn 
and examined on a slide without reagents the corpuscles tend to collect into heaps 
like rouleaux of coins (Fig. 38, b). It has been suggested that this phenomenon 
may be explained by alteration in surface tension. During life the red corpuscles 
may be seen to change their shape under pressure so as to adapt themselves, to 
some extent, to the size of the vessel. They are, however, highly elastic, and 
speedily recover their shape when the pressure is removed. They are readily 
influenced by the medium in which they are placed. In water they swell up, lose 
their shape, and become globular (endosmosis) (Fig. 38, c). Subsequently the 
hemoglobin is dissolved out, and the envelope can barely be distinguished as a 
faint circular outline. Solutions of salt or sugar, denser than the plasma, give 
them a stellate or crenated appearance (exosmosis) (Fig. 38, d), but the usual 
shape may be restored by diluting the solution to the same tonicity as the plasma. 
The cremated outline may be produced as the first effect of the passage of an elec- 
tric shock: subsequently, if sufficiently strong, the shock ruptures the envelope. 
A solution of salt, isotonic with the plasma, merely separates the blood corpuscles 
mechanically, without changing their shape. Two views are held with regard to 
the structure of the erythrocytes. The older view, that of Rollett, supposes that 
the corpuscle consists of a sponge work or stroma permeated by a solution of hemo- 
globin. Schafer, on the other hand, believes that the hemoglobin solution is con- 
tained within an envelope or membrane, and the facts stated above with regard 
to the osmotic behavior of the erythrocyte support this belief. The envelope 
consists mainly of lecithin, cholesterin, and nucleoprotein. 
The colorless corpuscles or leucocytes are of various sizes, some no larger, others 
smaller, than the red corpuscles, In human blood, however, the majority are 
rather larger than the red corpuscles, and measure about 10/x in diameter. On the 
average from 7000 to 12,000 leucocytes are found in each cubic millimetre of 
blood. 
They consist of minute masses of nucleated protoplasm, and exhibit several 
varieties, which are differentiated from each other chiefly by the occurrence or 
non-occurrence of granules in their protoplasm, and by the staining reactions of 
these granules when present (Fig. 39). (1) The most numerous (60 per cent.) and 
important are irregular in shape, possessed of the power of amoeboid movement, 
and are characterized by nuclei which often consist of two or three parts (multi- 
partite) connected together by fine threads of chromatin. The protoplasm is 
clear, and contains a number of very fine granules, which stain with acid dyes, 
such as eosin, or with neutral dyes, and are therefore called oxyphil or neutrophil 
(Fig. 39, P). These cells are termed the polymorphonuclear leucocytes. (2) A 
second variety comprises from 1 to 4 per cent, of the leucocytes; they are larger 
than the previous kind, and are made up of coarsely granular protoplasm, the 
granules being highly refractile and grouped around single nuclei of horse-shoe 
shape (Fig. 39, E). The granules stain deeply with eosin, and the cells are there- 
1 A micromillimetre () is 1/1000 of a millimetre or 1/25000 of an inch. THE CIRCULATING FLUIDS 
63 
fore often termed eosinophil corpuscles. (3) The third variety is called the hyaline 
cell or macrocyte (Fig. 39, H). This is usually about the same size as the eosino- 
phil cell, and, when at rest, is spherical in shape and contains a single round or 
oval nucleus. The protoplasm is free from granules, but is not quite transparent, 
having the appearance of ground glass. (4) The fourth kind of colorless corpuscle 
is designated the lymphocyte (Fig. 39, L), because it is identical with the cell derived 
from the lymph glands or other lymphoid tissue. It is the smallest of the leuco- 
cytes, and consists chiefly of a spheroidal nucleus with a very little surrounding 
protoplasm of a homogeneous nature; it is regarded as the immature form of the 
Fig. 39.-Varieties of leucocytes found in human blood. Highly magnified. 
hyaline cell. The third and fourth varieties together constitute from 20 to 30 
per cent, of the colorless corpuscles, but of these two varieties the lymphocytes 
are by far the more numerous. Leucocytes having in their protoplasm granules 
which stain with basic dyes (basiphil) have been described as occurring in human 
blood, but they are rarely found except in disease. 
The colorless corpuscles are very various in shape in living blood (Fig. 40), 
because many of them have the power of constantly changing their form by pro- 
truding finger-shaped or filamentous processes of their substance, by which they 
move and take up granules from the surrounding medium. In locomotion the 
corpuscle pushes out a process of its substance-a pseudopodium, as it is called 
Fig. 40.-Human colorless blood corpuscle, showing its successive changes of outline within ten minutes when kept 
moist on a warm stage. (Schofield.) 
-and then shifts the rest of the body into it. In the same way when any granule 
or particle comes in its way the corpuscle wraps a pseudopodium around it, and then 
withdraws the pseudopodium with the contained particle into its own substance. 
By means of these amoeboid properties the cells have the power of wandering 
or emigrating from the bloodvessels by penetrating their walls and thus finding 
their way into the extravascular spaces. A chemical investigation of the proto- 
plasm of the leucocytes shows the presence of nucleoprotein and of a globulin. 
The occurrence of small amounts of fat, lecithin, and glycogen may also be 
demonstrated. 64 
HISTOLOGY 
The blood platelets (Fig. 41) are discoid or irregularly shaped, colorless, refractile 
bodies, much smaller than the red corpuscles. Each contains a central chromatin 
mass resembling a nucleus. Blood platelets possess the power of amoeboid move- 
ment. When blood is shed they rapidly disintegrate and form granular masses, 
setting free prothrombin and the substance called by Howell thromboplastin. It 
is doubtful whether they exist normally in circulating 
blood. 
Lymph.-Lymph is a transparent, colorless, or 
slightly yellow fluid, which is conveyed by a set of 
vessels, named lymphatics, into the blood. These 
vessels arise in nearly all parts of the body as lymph 
capillaries. They take up the fluid which has 
exuded from the blood capillaries for the nourish- 
ment of the tissue elements and return it into 
the veins. The greater number of these lymphatics 
empty themselves into one main duct, the thoracic 
duct, which passes upward along the front of the 
vertebral column and opens into the large veins on 
the left side of the root of the neck. The remainder 
empty themselves into a smaller duct which ends in 
the corresponding veins on the right side of the neck. 
Lymph is a watery fluid of specific gravity about 1.015; it closely resembles 
the blood plasma, but is more dilute. When it is examined under the microscope, 
leucocytes of the lymphocyte class are found floating in the transparent fluid; 
they are always increased in number after the passage of the lymph through 
lymphoid tissue, as in lymph glands. 
Fig. 41.-Blood platelets. Highly 
magnified. (After Kopsch.) 
THE MUSCULAR TISSUE. 
Muscular tissue is composed of bundles of reddish fibres endowed with the prop- 
erty of contractility. There are three varieties of muscle: (1) transversely striated 
fibres, which are for the most part under the control of the will, although some 
are not so, such as the muscles of the pharynx and upper part of the oesophagus. 
This variety is called skeletal, striped, or voluntary; (2) transversely striated cardiac 
fibres, which are not under the control of the will; (3) plain or unstriped fibres, 
which are involuntary and controlled by a different part of the nervous system 
from that which controls the activity of the voluntary muscles; such are the 
muscular walls of the stomach and intestine, of the uterus and bladder, of the 
bloodvessels, etc. 
Striped or Voluntary Muscle.-Striped or voluntary muscle is composed of bundles 
of fibres each enclosed in a delicate web called the perimysium in contradistinction 
to the sheath of areolar tissue which invests the entire muscle, the epimysium. 
The bundles are termed fasciculi; they are prismatic in shape, of different sizes 
in different muscles, and are for the most part placed parallel to one another, 
though they have a tendency to converge toward their tendinous attachments. 
Each fasciculus is made up of a strand of fibres, which also run parallel with each 
other, and are separated from one another by a delicate connective tissue derived 
from the perimysium and termed endomysium. This does not form the sheath 
of the fibres, but serves to support the bloodvessels and nerves ramifying between 
them. 
A muscular fibre may be said to consist of a soft contractile substance, enclosed 
in a tubular sheath named by Bowman the sarcolemma. The fibres are cylindrical 
or prismatic in shape (Fig. 42), and are of no great length, not exceeding, as a rule, 65 
THE MUSCULAR TISSUE 
40 mm. Their breadth varies in man from 0.01 to 0.1 mm. As a rule, the fibres 
do not divide or anastomose; but occasionally, especially in the tongue and facial 
muscles, they may be seen to divide into several branches. In the substance of 
the muscle, the fibres end by tapering extremities which are joined to the ends 
of other fibres by the sarcolemma. At the tendinous end of the muscle the sarco- 
lemma appears to blend with a small bundle of fibres, into which the tendon 
becomes subdivided, while the muscular substance ends abruptly and can be 
readily made to retract from the point of junction. The areolar tissue between 
the fibres appear to be prolonged more or less into the tendon, so as to form a kind 
of sheath around the tendon bundles for a longer or shorter distance. When 
muscular fibres are attached to skin or mucous membranes, their fibres become 
continuous with those of the areolar tissue. 
Fig. 42.-Transverse section of human striped muscle fibres. 
X 255. 
Fig. 43.-Striped muscle fibres from tongue of 
cat. X 250. 
The sarcolemma, or tubular sheath of the fibre, is a transparent, elastic, and 
apparently homogeneous membrane of considerable toughness, so that it some- 
times remains entire when the included substance is ruptured. On the internal 
surface of the sarcolemma in mammalia, and also in the substance of the fibre 
in frogs, elongated nuclei are seen, and in connection with these is a little granular 
protoplasm. 
Upon examination of a voluntary muscular fibre by transmitted light, it is 
found to be marked by alternate light and dark bands or striae, which pass trans- 
versely across the fibre (Fig. 43). When examined by polarized light the dark 
bands are found to be doubly refracting (anisotropic), while the clear stripes are 
singly refracting (isotropic). The dark and light bands are of nearly equal breadth, 
and alternate with great regularity; they vary in breadth from about 1 to 2/z. 
If the surface be carefully focussed, rows of granules will be detected at the points 
of junction of the dark and light bands, and very fine longitudinal lines may be 
seen running through the dark bands and joining these granules together. By 
treating the specimen with certain reagents (e. g., chloride of gold) fine lines may 
be seen running transversely between the granules and uniting them together. 
This appearance is believed to be due to a reticulum or network of interstitial 
substance lying between the contractile portions of the muscle. The longitudinal 
striation gives the fibre the appearance of being made up of a bundle of fibrils 
which have been termed sarcostyles or muscle columns, and if the fibre be hardened 
in alcohol, it can be broken up longitudinally and the sarcostyles separated from 
each other (Fig. 44.) The reticulum, with its longitudinal and transverse meshes, 
is called sarcoplasm. 66 
HISTOLOGY 
In a transverse section, the muscular fibre is seen to be divided into a number 
of areas, called the areas of Cohnheim, more or less polyhedral in shape and con- 
sisting of the transversely divided sarcostyles, surrounded by transparent sarco- 
plasm (Fig. 42). 
Upon closer examination, and by somewhat altering the focus, the appearances 
become more complicated, and are susceptible of various interpretations. The 
transverse striation, which in Fig. 
43 appears as a mere alternation of 
dark and light bands, is resolved 
into the appearance seen in Fig. 44, 
which shows a series of broad dark 
bands, separated by light bands, 
each of which is divided into two 
by a dark dotted line. This line is 
termed Dobie's line or Krause's mem- 
brane (Fig. 45, k), because it was 
believed by Krause to be an actual 
membrane, continuous with the sar- 
colemma, and dividing the light 
band into two compartments. In 
addition to the membrane of Krause, 
fine clear lines may be made out, 
with a sufficiently high power, cross- 
ing the centre of the dark band; 
these are known as the lines of Hensen 
(Fig. 45, H). 
Schafer has worked out the minute 
anatomy of muscular fibre, particu- 
larly in the wing muscles of insects, 
which are peculiarly adapted for this 
purpose on account of the large amount of interstitial sarcoplasm which sepa- 
rates the sarcostyles. In the following description that given by Schafer will be 
closely followed. 
Fig. 44.-A. Portion of a medium-sized human muscular 
fibre. Magnified nearly 800 diameters. B. Separated bundles 
of fibrils, equally magnified, a, a. Larger, and b, b, smaller 
collections, c. Still smaller, d, d. The smallest which could 
be detached. 
Fig. 45.-Diagram of a sarcomere. (After Schafer.) A. In moderately extended condition. B. In a contracted 
condition, k, k. Membranes of Krause. H. Line or plane of Hensen. S.E. Poriferous sarcous element. 
A sarcostyle may be said to be made up of successive portions, each of which 
is termed a sarcomere. The sarcomere is situated between two membranes of Krause 
and consists of (1) a central dark part, which forms a portion of the dark band 
of the whole fibre, and is named a sarcous element. This sarcous element really 
consists of two parts, superimposed one on the top of the other, and when the fibre 
is stretched these two parts become separated from each other at the line of Hensen THE MUSCULAR TISSUE 
67 
(Fig. 45, A). (2) On either side of this central dark portion is a clear layer, most 
visible when the fibre is extended; this is situated between the dark centre and the 
membrane of Krause, and when the sarcomeres are joined together to form the 
sarcostyle, constitutes the light band of the striated muscular fibre. 
When the sarcostyle is extended, the clear intervals are well-marked and plainly 
to be seen; when, on the other hand, the sarcostyle is contracted, that is to say, 
when the muscle is in a state of contraction, these clear portions are very small 
or they may have disappeared altogether (Fig. 45, B). When the sarcostyle is 
stretched to its full extent, not only is the clear portion well-marked, but the dark 
portion-the sarcous element-is separated into its two constituents along the 
line of Hensen. The sarcous element does not lie free in the sarcomere, for when 
the sarcostyle is stretched, so as to render the clear portion visible, very fine 
lines, which are probably septa, may be seen running through it from the sarcous 
element to the membrane of Krause. 
Schafer explains these phenomena in the following way: He considers that each 
sarcous element is made up of a number of longitudinal channels, which open 
into the clear part toward the membrane of Krause but are closed at the line of 
Hensen. When the muscular fibre is contracted the clear part of the muscular 
substance is driven into these channels or tubes, and is therefore hidden from 
sight, but at the same time it swells up the sarcous element and widens and shortens 
the sarcomere. When, on the other hand, the fibre is extended, this clear sub- 
stance is driven out of the tubes and collects between the sarcous element and 
the membrane of Krause, and gives the appearance of the light part between 
these two structures; by this means it elongates and narrows the sarcomere. 
If this view be true, it is a matter of great interest, and, as Schafer has shown, 
harmonizes the contraction of muscle with the amoeboid action of protoplasm. 
In an amoeboid cell, there is a framework of spongioplasm, which stains with 
hematoxylin and similar reagents, enclosing in its meshes a clear substance, hyalo- 
plasm, which will not stain with these reagents. Under stimulation the hyaloplasm 
passes into the pores of the spongioplasm; without stimulation it tends to pass 
out as in the formation of pseudopodia. In muscle there is the same thing, viz., 
a framework of spongioplasm staining with hematoxylin-the substance of the 
sarcous element-and this encloses a clear hyaloplasm, the clear substance of 
the sarcomere, which resists staining with this reagent. During contraction of the 
muscle-i. e., stimulation-this clear substance passes into the pores of the spongio- 
plasm; while during extension of the muscle-i. e., when there is no stimulation- 
it tends to pass out of the spongioplasm. 
In this way the contraction is brought about: under stimulation the proto- 
plasmic material (the clear substance of the sarcomere) recedes into the sarcous 
element, causing the sarcomere to widen out and shorten. The contraction of the 
muscle is merely the sum total of this widening out and shortening of these bodies. 
Vessels and Nerves of Striped Muscle.-The capillaries or striped muscle are 
very abundant, and form a sort of rectangular network, the branches of which run 
longitudinally in the endomysium between the muscular fibres, and are joined at 
short intervals by transverse anastomosing branches. In the red muscles of the 
rabbit dilatations occur on the transverse branches of the capillary network. The 
larger vascular channels, arteries and veins, are found only in the perimysium, 
between the muscular fasciculi. Nerves are profusely distributed to striped muscle. 
Their mode of termination is described on page 803. The existence of lymphatic 
vessels in striped muscle has not been ascertained, though they have been found in 
tendons and in the sheaths of the muscles. 
Unstriped, Plain, or Involuntary Muscle.-Unstriped, plain, or involuntary muscle 
is found in the following situations: in the lower half of the oesophagus and the 
whole of the remainder of the gastro-intestinal tube; in the trachea and bronchi; 68 
HISTOLOGY 
in the gall-bladder and common bile duct; m the large ducts of the salivary and 
pancreatic glands; in the pelvis and calices of the kidney, the ureter, bladder, 
and urethra; in the female sexual organs-viz., the ovary, the uterine tubes, the 
uterus (enormously developed in pregnancy), the vagina, the broad ligaments, and 
the corpora cavernosa of the clitoris; in the male sexual organs-viz., the dartos 
of the scrotum, the ductus deferens and epididymis, the vesiculee seminales, the 
prostate, and the corpora cavernosa of the penis and urethra; in the capsule and 
trabeculae of the spleen; in the mucous membranes, forming the muscularis mucosae; 
in the skin, forming the Arrectores pilorum, and also 
in the sweat glands; in the arteries, veins, and lym- 
phatics; in the iris and the ciliary muscle. 
Plain or unstriped muscle is made up of spindle- 
shaped cells, called contractile fibre cells, collected into 
bundles and held together by a cement substance (Fig. 
46). These bundles are further aggregated into larger 
fasciculi, or flattened bands, and bound together by 
ordinary connective tissue. 
The contractile fibre cells are elongated, spindle- 
shaped, nucleated cells of various sizes, averaging from 
40 to 80M in length, and 6 to 7/j. in breadth. On 
transverse section they are more or less polyhedral in 
shape, from mutual pressure. Each presents a faint 
longitudinal striation and consists of an elastic cell wall 
containing a central bundle of fibrillae, representing the 
contractile substance, and an oval or rod-like nucleus, 
which includes, within a membrane, a fine net-work 
communicating at the poles of the nucleus with the 
contractile fibres (Klein). The fibres are attached to 
one another by a certain amount of interstitial cement 
substance which reduces nitrate of silver, but in some 
regions, e. g., the muscular coats of the intestines, the 
muscle cells are also connected by " bridges" similar to 
those which occur in the prickle cells of the epidermis. 
Unstriped muscle, except the ciliary muscle, is not under 
the control of the will, neither is the contraction rapid 
nor does it, as a rule, involve the whole muscle, as is 
the case with the voluntary muscles. The membranes 
which are composed of unstriped muscle slowly contract 
in a part of their extent, generally under the influence 
of a mechanical stimulus, as that of distension or of 
cold; and then the contracted part slowly relaxes while 
another portion of the membrane takes up the contrac- 
tion. This peculiarity of action is most strongly marked 
in the intestines, constituting their vermicular motion. 
Cardiac Muscular Tissue.-The fibres of the heart differ very remarkably from 
those of other striped muscles. They are smaller by one-third, and their trans- 
verse striae are by no means so well-marked. They show faint longitudinal 
striation. The fibres are made up of distinct quadrangular cells, joined end to 
end so as to form a syncytium (Fig. 47). Each cell contains a clear oval nucleus, 
situated near its centre. The extremities of the cells have a tendency to branch 
or divide, the subdivisions uniting with offsets from other cells, and thus producing 
an anastomosis of the fibres. The connective tissue between the bundles of fibres 
is much less than in ordinary striped muscle, and no sarcolemma has been proved 
to exist. 
fig. 46- Muscle fibres from 
c^mpiete^c^n6' B.(SBroken cfii 
showing delicate external layer. THE NERVOUS TISSUE 
69 
Purkinje Fibres (Fig. 48).-Between the endocardium and the ordinary cardiac 
muscle are found, imbedded in a small amount of connective tissue, peculiar fibres 
known as Purkinje fibres. They are found in certain mammals and in birds, and 
can be best seen in the sheep's heart, where they form a considerable portion 
of the moderator band and also appear as gelatinous-looking strands on the inner 
walls of the atria and ventricles. They also occur in the human heart associated 
with the terminal distributions of the bundle of His (see p. 614). The fibres are 
very much larger in size than the cardiac cells and differ from them in several 
ways. In longitudinal section they are quadrilateral in shape, being about twice 
as long as they are broad. The central portion of each fibre contains one or more 
nuclei and is made up of granular protoplasm, with no indication of striations, 
while the peripheral portion is clear and has distinct transverse striations. The 
fibres are intimately connected with each other, possess no definite sarcolemma, 
and do not branch. 
Fig. 47.-Anastomosing muscular fibres of the heart seen 
in a longitudinal section. On the right the limits of the 
separate cells with their nuclei are exhibited somewhat dia- 
grammatically. 
Fig. 48.-Purkinje fibres from the sheep's heart. 
The Bundle of His (see p. 614) is composed of cells which differ from ordinary 
cardiac muscle cells in being more spindle-shaped. They are, moreover, more 
loosely arranged and have a richer vascular supply than the rest of the heart 
muscle. 
Development of Muscle Fibres.-Voluntary muscular fibres are developed from the mesoderm, 
the embryonic cells of which elongate, show multiplication of nuclei, and eventually become 
striated; the striation is first obvious at the side of the fibres, spreads around the circumference, 
and ultimately extends to the centre. The nuclei, at first situated centrally, gradually pass out 
to assume their final position immediately beneath the sarcolemma. In the case of involuntary 
muscle the mesodermal cell assumes a pointed shape at the extremities and becomes flattened, the 
nucleus also lengthening out to its permanent rod-like form. 
The nervous tissues of the body comprise the brain, the medulla spinalis or spinal 
cord, the cerebral, spinal,, and sympathetic nerves, and the ganglia connected with 
them. 
THE NERVOUS TISSUE. 70 
HISTOLOGY 
The nervous tissues are composed of nerve cells and their various processes, 
together with a supporting tissue called neuroglia, which, however, is found only 
in the brain and medulla spinalis. Certain long processes of the nerve cells are of 
special importance, and it is convenient to consider them apart from the cells; 
they are known as nerve fibres. 
To the naked eye a difference is obvious between certain portions of the brain 
and medulla spinalis, viz., the gray substance and the white substance. The gray 
substance is largely composed of nerve cells, while the white substance contains 
only their long processes, the nerve fibres. It is in the former that nervous impres- 
sions are received, stored, and transformed into efferent impulses, and by the latter 
that they are conducted. Hence the gray substance forms the essential constituent 
of all the ganglionic centres, both those in the isolated ganglia and those aggregated 
in the brain and medulla spinalis; while the white substance forms the bulk of the 
commissural portions of the nerve centres and the peripheral nerves. 
Fig. 49.-Neuroglia cells of brain shown by Golgi's method. (After Andriezen.) A. Cell with branched processes 
B. Spider cell with unbranched processes. 
Neuroglia.-Neuroglia, the peculiar ground substance in which are imbedded the 
true nervous constituents of the brain and medulla spinalis, consists of cells and 
fibres. Some of the cells are stellate in shape, with ill-defined cell body, and their 
fine processes become neuroglia fibres, which extend radially and unbranched 
(Fig. 49, B) among the nerve cells and fibres which they aid in supporting. Other 
cells give off fibres which branch repeatedly (Fig. 49, A). Some of the fibres start 
from the epithelial cells lining the ventricles of the brain and central canal of 
the medulla spinalis, and pass through the nervous tissue, branching repeatedly 
to end in slight enlargements on the pia mater. Thus, neuroglia is evidently a 
connective tissue in function but is not so in development; it is ectodermal in 
origin, whereas all connective tissues are mesodermal. 
Nerve Cells (Fig. 50).-Nerve cells are largely aggregated in the gray substance 
of the brain and medulla spinalis, but smaller collections of these cells also form 
the swellings, called ganglia, seen on many nerves. These latter are found chiefly 
upon the spinal and cerebral nerve roots and in connection with the sympathetic 
nerves. 
The nerve cells vary in shape and size, and have one or more processes. They 
may be divided for purposes of description into three groups, according to the 
number of processes which they possess: (1) Unipolar cells, which are found in 
the spinal ganglia; the single process, after a short course, divides in a T-shaped THE NERVOUS TISSUE 
71 
manner (Fig. 50, jE). (2) Bipolar cells, also found in the spinal ganglia (Fig. 51), 
when the cells are in an embryonic condition. They are best demonstrated in the 
spinal ganglia of fish. Sometimes the processes come off from opposite poles of 
Fig. 50.-Various forms of nerve cells. A. Pyramidal cell. B. Small multipolar cell, in which the axon quickly 
divides into numerous branches. C. Small fusiform cell. D and E. Ganglion cells (E shows T-shaped division of 
axon), ax. Axon. c. Capsule. 
-Axon 
Sheath of 
cell body 
-Nucleus 
Axon 
Nucleolus 
'Gell protoplasm 
Fig. 52.-Motor nerve cell from ventral horn of medulla 
spinalis of rabbit. (After Nissh) The angular and spindle- 
shaped Nissl bodies are well shown. 
the cell, and the cell then assumes a spindle 
shape; in other cells both processes emerge 
at the same point. In some cases where 
two fibres are apparently connected with a 
cell, one of the fibres is really derived from 
an adjoining nerve cell and is passing to 
end in a ramification around the ganglion 
cell, or, again, it may be coiled spirally 
around the nerve process which is issuing 
from the cell. (3) Multipolar cells, which 
are pyramidal or stellate in shape, and 
characterized by their large size and by the numerous processes which issue 
from them. The processes are of two kinds: one of them is termed the axis- 
cylinder process or axon because it becomes the axis-cylinder of a nerve fibre 
-Dendron 
-Myelin sheath 
Fig. 51.-Bipolar nerve cell from the spinal gan- 
glion of the pike. (After Kolliker.) 72 
HISTOLOGY 
(Figs. 52, 53, 54). The others are termed the protoplasmic processes or dendrons; 
they begin to divide and subdivide as soon as they emerge from the cell, and 
finally end in minute twigs and become lost among the other elements of the 
nervous tissue. 
The body of the nerve cell, known as the cyton, consists of a finely fibrillated 
protoplasmic material, of a reddish or yellowish-brown color, which occasionally 
presents patches of a deeper tint, caused by the aggregation of pigment granules 
at one side of the nucleus, as in the substantia nigra and locus caeruleus of the 
brain. The protoplasm also contains peculiar angular granules, which stain deeply 
~Axon 
Fig. 53.-Pyramidal cell from the cerebral cortex 
of a mouse. (After Ramon y Cajal.) 
Fig. 54.-Cell of Purkinje from the cerebellum. Golgi 
method. (Cajal.) a. Axon. b. Collateral, c and d. 
Dendrons. 
with basic dyes, such as methylene blue; these are known as Nissl's granules (Fig. 
52). They extend into the dendritic processes but not into the axis-cylinder; the 
small clear area at the point of exit of the axon is termed the cone of origin. These 
granules disappear {chromatolysis} during fatigue or after prolonged stimulation 
of the nerve fibres connected with the cells. They are supposed, to represent a 
store of nervous energy, and in various mental diseases are deficient or absent. 
The nucleus is, as a rule, a large, well-defined, spherical body, often presenting an 
intranuclear network, and containing a well-marked nucleolus. THE NERVOUS TISSUE 
73 
In addition to the protoplasmic network described above, each nerve cell may 
be shown to have delicate neurofibrils running through its substance (Fig. 55); 
these fibrils are continuous with the fibrils of the axon, and are believed to 
convey nerve impulses. Golgi has also described an extracellular network, which 
is probably a supporting structure. 
Nerve Fibres.-Nerve fibres are found universally in the peripheral nerves 
and in the white substance of the brain and medulla spinalis. They are of two 
kinds-viz., medullated or white fibres, and non-medullated or gray fibres. 
Fig. 55.-Nerve cells of kitten, showing neurofibrils. (Cajal.) a. Axon. b. Cyton. c. Nucleus, d. Neurofibrils. 
The medullated fibres form the white part of the brain and medulla spinalis, and 
also the greater part of every cerebral and spinal nerve, and give to these structures 
their opaque, white aspect. When perfectly fresh they appear to be homogeneous; 
but soon after removal from the body each fibre presents, when examined by trans- 
mitted light, a double outline or contour, as if consisting of two parts (Fig. 56). 
The central portion is named the axis-cylinder; around this is a sheath of fatty 
material, staining black with osmic acid, named the white substance of Schwann 
or medullary sheath, which gives to the fibre its double contour, and the whole 
is enclosed in a delicate membrane, the neurolemma, primitive sheath, or nucleated 
sheath of Schwann (Fig. 58). 
The axis-cylinder is the essential part of the nerve fibre, and is always present; 
the medullary sheath and the neurolemma are occasionally absent, expecially at 
the origin and termination of the nerve fibre. The axis-cylinder undergoes no 
interruption from its origin in the nerve centre to its peripheral termination, and 74 
HISTOLOGY 
must be regarded as a direct prolongation of a nerve cell. It constitutes about 
one-half or one-third of the nerve fibre, being greater in proportion in the fibres 
of the central organs than in those of the nerves. It is quite transparent, and is 
therefore indistinguishable in a perfectly fresh and natural state of the nerve. 
It is made up of exceedingly fine fibrils, which stain darkly with gold chloride 
Fig. 56.-Medullated nerve fibres. (Bidder 
and Volkmann.) 
Fig. 57.--Longitudinal and transverse sec- 
tions of medullated nerve fibre of frog, showing 
node of Ranvier, medullary, segments and fibrils 
of axis cylinder. Osmic acid. (Biedermann.) 
Fig. 58.-Diagram of medullated nerve fibres stained 
with osmic acid. X 425. (Schafer.) R. Nodes of Ran- 
vier. a. Neurolemma, c. Nucleus. 
(Fig. 57), and at its termination may be seen to break up into these fibrillae. The 
fibrillae have been termed the primitive fibrillae of Schultze. The axis-cylinder is 
said by some to be enveloped in a special reticular sheath, which separates it from 
the medullary sheath, and is composed of a substance called neurokeratin. The 
more common opinion is that this network or reticulum is contained in the white THE NERVOUS TISSUE 
75 
matter of Schwann, and by some it is believed to be produced by the action of 
the reagents employed to show it. 
The medullary sheath, or white matter of Schwann (Fig. 57), is regarded as being a 
fatty matter in a fluid state, which insulates and protects the essential part of the 
nerve-the axis-cylinder. It varies in thickness, in some forming a layer of extreme 
thinness, so as to be scarcely distinguishable, in others forming about one-half the 
nerve fibre. The variation in diameter of the nerve fibres (from 2 to 16/z) depends 
mainly upon the amount of the white substance, though the axis cylinder also 
varies within certain limits. The medullary sheath undergoes interruptions in its 
continuity at regular intervals, giving to the fibre the appearance of constriction 
at these points: these are known as the nodes of Ranvier (Figs. 57 and 58). The 
portion of nerve fibre between two nodes is called an internodal segment. The 
neurolemma or primitive sheath is not interrupted at the nodes, but passes over 
them as a continuous membrane. If the fibre be treated with silver nitrate the 
reagent penetrates the neurolemma at the nodes, and on exposure to light reduction 
takes place, giving rise to the appearance of black crosses, Ranvier's crosses, on the 
axis-cylinder. There may also be seen transverse lines beyond the nodes termed 
Frommann's 
lines 
Node of 
Ranvier 
Fig. 60.-A small nervous branch 
from the sympathetic of a mammal. 
a. Two medullated nerve fibres among 
a number of gray nerve fibres, b. 
Fig. 59.-Medullated nerve fibres stained with silver nitrate. 
Frommann's lines (Fig. 59); the significance of these is not understood. In addi- 
tion to these interruptions oblique clefts may be seen in the medullary sheath, 
subdividing it into irregular portions, which are termed medullary segments, or 
segments of Lantermann (Fig. 57); there is reason to believe that these clefts are 
artificially produced in the preparation of the specimens. Medullated nerve 
fibres, when examined in the fresh condition, frequently present a beaded or vari- 
cose appearance: this is due to manipulation and pressure causing the oily matter 
to collect into drops; and in consequence of the extreme delicacy of the primitive 
sheath, even slight pressure will cause the transudation of the fatty matter, which 
collects as drops of oil outside the membrane. 
The neurolemma or primitive sheath presents the appearance of a delicate, 
structureless membrane. Here and there beneath it, and situated in depressions 
in the white matter of Schwann, are nuclei surrounded by a small amount of 
protoplasm. The nuclei are oval and somewhat flattened, and bear a definite 
relation to the nodes of Ranvier, one nucleus generally lying in the centre of each 
internode. The primitive sheath is not present in all medullated nerve fibres, 
being absent in those fibres which are found in the brain and medulla spinalis. 76 
HISTOLOGY 
Wallerian Degeneration.-When nerve fibres are cut across, the central ends of the fibres 
degenerate as far as the first node of Ranvier; but the peripheral ends degenerate simultaneously 
throughout their whole length. The axons break up into fragments and become surrounded by 
drops of fatty substance which are formed from the breaking down of the medullary sheath. 
The nuclei of the primitive sheath proliferate, and finally absorption of the axons and fatty 
substance occurs. If the cut ends of the nerve be sutured together regeneration of the nerve 
fibres takes place by the downgrowth of axons from the central end of the nerve. At one time 
it was believed that the regeneration was peripheral in origin, but this has been disproved, the 
proliferated nuclei in the peripheral portions taking part merely in the formation of the so-called 
scaffolding along which the new axons pass. 
Non-medullated Fibres.-Most of the fibres of the sympathetic system, and 
some of the cerebrospinal, consist of the gray or gelatinous nerve fibres {fibres of 
Remak) (Fig. 60). Each of these consists of an axis-cylinder to which nuclei are 
applied at intervals. These nuclei are believed to be in connection with a delicate 
sheath corresponding with the neurolemma of the medullated nerve fibre. In 
external appearance the non-medullated nerve fibres are semitransparent and gray 
or yellowish gray. The individual fibres vary in size, generally averaging about 
half the size of the medullated fibres. EMBRYOLOGY. 
rpHE term Embryology, in its widest sense, is applied to the various changes 
which take place during the growth of an animal from the egg to the adult 
condition: it is, however, usually restricted to the phenomena which occur before 
birth. Embryology may be studied from two aspects: (1) that of ontogeny, which 
deals only with the development of the individual; and (2) that of phylogeny, 
which concerns itself with the evoluntionary history of the animal kingdom. 
In vertebrate animals the development of a new being can only take place when 
a female germ cell or ovum has been fertilized by a male germ cell or spermatozoon. 
The ovum is a nucleated cell, and all the complicated changes by which the various 
tissues and organs of the body are formed from it, after it has been fertilized, are 
the result of two general processes, viz., segmentation and differentiation of cells. 
Thus, the fertilized ovum undergoes repeated segmentation into a number of cells 
which at first closely resemble one another, but are, sooner or later, differentiated 
into two groups: (1) somatic cells, the function of which is to build up the various 
tissues of the body; and (2) germinal cells, which become imbedded in the sexual 
glands-the ovaries in the female and the testes in the male-and are destined for 
the perpetuation of the species. 
Having regard to the main purpose of this work, it is impossible, in the space 
available in this section, to describe fully, or illustrate adequately, all the phenom- 
ena which occur in the different stages of the development of the human body. 
Only the principal facts are given, and the student is referred for further details 
to one or other of the text-books1 on human embryology. 
THE OVUM. 
The ova are developed from the primitive germ cells which are imbedded in 
the substance of the ovaries. Each primitive germ cell gives rise, by repeated 
divisions, to a number of smaller cells termed oogonia, from which the ova or 
primary oocytes are developed. 
Human ova are extremely minute, measuring about 0.2 mm. in diameter, and 
are enclosed within the egg follicles of the ovaries; as a rule each follicle contains 
a single ovum, but sometimes two or more are present.2 By the enlargement and 
subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and 
conveyed by the uterine tube to the cavity of the uterus. Unless it be fertilized 
it undergoes no further development and is discharged from the uterus, but if 
fertilization take place it is retained within the uterus and is developed into a 
new being. 
In appearance and structure the ovum (Fig. 61) differs little from an ordinary 
cell, but distinctive names have been applied to its several parts; thus, the cell 
substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and 
the nucleolus as the germinal spot. The ovum is enclosed within a thick, trans- 
1 Manual of Human Embryology, Keibel and Mall; Handbuch der vergleichenden und experimentellen Entwickel- 
ungslehre der Wirbeltiere, Oskar Hertwig; Lehrbuch der Entwickelungsgeschichte, Bonnet; The Physiology of 
Reproduction, Marshall. 
2 See description of the ovary on a future page. 78 
EMBRYOLOGY 
parent envelope, the zona striata or zona pellucida, adhering to the outer surface 
of which are several layers of cells, derived from those of the follicle and collectively 
constituting the corona radiata. 
Yolk.-The yolk comprises (1) the cytoplasm of the ordinary animal cell with its 
spongioplasm and hyaloplasm; this is frequently termed the formative yolk; (2) 
the nutritive yolk or duetoplasm, which consists of numerous rounded granules of 
fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian 
ovum the nutritive yolk is extremely small in amount, and is of service in nourish- 
ing the embryo in the early stages of its development only, whereas in the egg 
of the bird there is sufficient to supply the chick with nutriment throughout 
Fig. 61.-Human ovum examined fresh in the liquor folliculi. (Waldeyer.) The zona pellucida is seen as a thick 
clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area 
and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. 
the whole period of incubation. The nutritive yolk not only varies in amount, 
but in its mode of distribution within the egg; thus, in some animals it is almost 
uniformly distributed throughout the cytoplasm; in some it is centrally placed and 
is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the 
ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole 
are present and lie in the immediate neighborhood of the nucleus. 
Germinal Vesicle.-The germinal vesicle or nucleus is a large spherical body 
which at first occupies a nearly central position, but becomes eccentric as the growth 
of the ovum proceeds. Its structure is that of an ordinary cell-nucleus, viz., it 
consists of a reticulum or karyomitome, the meshes of which are filled with THE OVUM 
79 
karyoplasm, while connected with, or imbedded in, the reticulum are a number 
of chromatin masses or chromosomes, which may present the appearance of a 
skein or may assume the form of rods or loops. The nucleus is enclosed by a 
delicate nuclear membrane, and contains in its interior a well-defined nucleolus 
or germinal spot. 
Coverings of the Ovum.-The zona striata or zona pellucida (Fig. 61) is a thick 
membrane, which, under the higher powers of the microscope, is seen to be radially 
striated. It persists for some time after fertilization has occurred, and may serve 
for protection during the earlier stages of segmentation. It is not yet determined 
whether the zona striata is a product of the cytoplasm of the ovum or of the cells 
of the corona radiata, or both. 
The corona radiata (Fig. 61) consists or two or three strata of cells; they are 
derived from the cells of the follicle, and adhere to the outer surface of the zona 
striata when the ovum is set free from the follicle; the cells are radially arranged 
around the zona, those of the innermost layer being columnar in shape. The 
cells of - the corona radiata soon disappear; in some animals they secrete, or 
are replaced by, a layer of adhesive protein, which may assist in protecting and 
nourishing the ovum. 
The phenomena attending the discharge of the ova from the follicles belong 
more to the ordinary functions of the ovary than to the general subject of embry- 
ology, and are therefore described with the anatomy of the ovaries.1 
Fig. 62.-Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In I the polar spindle 
(sp) has advanced to the surface of the egg. In II a small elevation (pb1) is formed which receives half of the spindle. 
In III the elevation is constricted off, forming the first polar body (pb1), and a second spindle is formed. In IV is 
seen a second elevation which in V has been constricted off as the second polar body (pb2). Out of the remainder of 
the spindle {f.pn in VI) the female pronucleus is developed. 
-Maturation of the Ovum.-Before an ovum can be fertilized it must undergo 
a process of maturation or ripening. This takes place previous to or immediately 
after its escape from the follicle, and consists essentially of an unequal subdivision 
of the ovum (Fig. 62) first into two and then into four cells. Three of the four 
cells are small, incapable of further development, and are termed polar bodies or 
polocytes, while the fourth is large, and constitutes the mature ovum. The process 
of maturation has not been observed in the human ovum, but has been carefully 
studied in the ova of some of the lower animals, to which the following description 
applies. 
It was pointed out on page 35 that the number of chromosomes found in the 
nucleus is constant for all the cells in an animal of any given species, and that in 
man the number is probably twenty-four. This applies not only to the somatic 
1 See description of the ovary on a future page. 80 
EMBRYOLOGY 
cells but to the primitive ova and their descendants. For the purpose of illustrating 
the process of maturation a species may be taken in which the number of nuclear 
chromosomes is four (Fig. 36). If an ovum from such be observed at the beginning 
of the maturation process it will be seen that the number of its chromosomes is 
apparently reduced to two. In reality, however, the number is doubled, since 
each chromosome consists of four granules grouped to form a tetrad. During the 
metaphase (see page 36) each tetrad divides into two dyads, which are equally 
distributed between the nuclei of the two cells formed by the first division of the 
ovum. One of the cells is almost as large as the original ovum, and is named 
the secondary oocyte; the other is small, and is termed the first polar body. The 
secondary oocyte now undergoes subdivision, during which each dyad divides and 
contributes a single chromosome to the nucleus of each of the two resulting cells. 
Primary oocyte 
Primary oocyte 
(commencing 
maturation) 
Secondary 
oocyte 
First 'polar 
body 
Mature 
ovum 
Polar bodies 
Fig. 63.-Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. 
This second division is also unequal, producing a large cell which constitutes the 
mature ovum, and a small cell, the second polar body. The first polar body fre- 
quently divides while the second is being formed, and as a final result four cells 
are produced, viz., the mature ovum and three polar bodies, each of which con- 
tains two chromosomes, i. e., one-half the number present in the nuclei of the 
somatic cells of members of the same species. The nucleus of the mature ovum 
is termed the female pronucleus. 
THE SPERMATOZOON. 
The spermatozoa or male germ cells are developed in the testes and are present 
in enormous numbers in the seminal fluid. Each consists of a small but greatly 
modified cell. The human spermatozoon possesses a head, a neck, a connecting 
piece or body, and a tail (Fig. 64). 
The head is oval or elliptical, but flattened, so that when viewed in profile 
it is pear-shaped. Its anterior two-thirds are covered by a layer of modified proto- THE SPERMATOZOON 
81 
plasm, which is named the head-cap. This, in some animals, e. g., the salamander, 
is prolonged into a barbed spear-like process or perforator, which probably facilitates 
the entrance of the spermatozoon into the ovum. The posterior part of the head 
exhibits an affinity for certain reagents, and presents a transversely striated appear- 
ance, being crossed by three or four dark bands. In some animals a central rod- 
like filament extends forward for about two-thirds of the length of the head, while 
in others a rounded body is seen near its centre. The head contains a mass of 
chromatin, and is generally regarded as the nucleus of the cell surrounded by a 
thin envelope. 
Head 
•Perforator 
Neck 
Connecting piece 
Head-cap 
Tail i 
Anterior centriole 
Posterior centriole 
■Spiral thread 
Mitochondria sheath 
Terminal disc 
End-piece 
Axial filament 
Fra. 64.-Human spermatozoon. Diagrammatic. A. Surface view. B. Profile view. In C the head, neck, 
and connecting piece are more highly magnified. 
The neck is less constricted in the human spermatozoon than in those of some 
of the lower animals. The anterior centriole, represented by two or three rounded 
particles, is situated at the junction of the head and neck, and behind it is a band 
of homogeneous substance. 
The connecting piece or body is rod-like, and is limited behind by a terminal 
disk. The posterior centriole is placed at the junction of the body and neck and, 
like the anterior, consists of two or three rounded particles. From this centriole 
an axial filament, surrounded by a sheath, runs backward through the body and 
tail. In the body the sheath of the axial filament is encircled by a spiral thread, 
around which is an envelope containing mitochondria granules, and termed the 
mitochondria sheath. 82 
EMBRYOLOGY 
The tail is of great length, and consists of the axial thread or filament, sur- 
rounded by its sheath, which may contain a spiral thread or may present a striated 
appearance. The terminal portion or end-piece of the tail consists of the axial 
filament only. 
Krause gives the length of the human spermatozoon as between 52^ and 62p, 
the head measuring 4 to 5^, the connecting piece 6/z, and the tail from 41 p to 52 p. 
By virtue of their tails, which act as propellers, the spermatozoa are capable of 
free movement, and if placed in favorable surroundings, e. g., in the female pas- 
sages, will retain their vitality and power of fertilizing for several days. In certain 
animals, e. g., bats, it has been proved that spermatozoa retained in the female 
passages for several months are capable of fertilizing. 
Primary oocyte 
Primary spermatocyte 
Secondary 
oocyte 
Secondary 
spermatocytes 
Mature 
ovum, 
Polar bodies 
Spermatids 
Fig. 65.-Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids 
(young spermatozoa). 
The spermatozoa are developed from the primitive germ cells which have become 
imbedded in the testes, and the stages of their development are very similar to those 
of the maturation of the ovum. The primary germ cells undergo division and 
produce a number of cells termed spermatogonia, and from these the primary 
spermatocytes are derived. Each primary spermatocyte divides into two secondary 
spermatocytes, and each secondary spermatocyte into two spermatids or young 
spermatozoa; from this it will be seen that a primary spermatocyte gives rise to 
four spermatozoa. On comparing this process with that of the maturation of the 
ovum (Fig. 65) it will be observed that the primary spermatocyte gives rise to 
two cells, the secondary spermatocytes, and the primary oocyte to two cells, the 
secondary oocyte and the first polar body. Again, the two secondary sperma- 
tocytes by their subdivision give origin to four spermatozoa, and the secondary 
oocyte and first polar body to four cells, the mature ovum and three polar bodies. 
In the development of the spermatozoa, as in the maturation of the ovum, there 
is a reduction of the nuclear chromosomes to one-half of those present in the 
primary spermatocyte. But here the similarity ends, for it must be noted that 
the four spermatozoa are of equal size, and each is capable of fertilizing a mature 
ovum, whereas the three polar bodies are not only very much smaller than the 
mature ovum but are incapable of further development, and may be regarded as 
abortive ova. 
FERTILIZATION OF THE OVUM. 
Fertilization consists in the union of the spermatozoon with the mature ovum 
(Fig. 66). Nothing is known regarding the fertilization of the human ovum, but FERTILIZATION OF THE OVUM 
83 
the various stages of the process have been studied in other mammals, and from 
the knowledge so obtained it is believed that fertilization of the human ovum takes 
place in the lateral or ampullary part of the uterine tube, and the ovum is then 
conveyed along the tube to the cavity of the uterus-a journey probably occupy- 
ing seven or eight days and during which the ovum loses its corona radiata and zona 
striata and undergoes segmentation. Sometimes the fertilized ovum is arrested 
in the uterine tube, and there undergoes development, giving rise to a tubal preg- 
nancy; or it may fall into the abdominal cavity and produce an abdominal preg- 
nancy. Occasionally the ovum is not expelled from the follicle when the latter 
ruptures, but is fertilized within the follicle and produces what is known as an 
ovarian pregnancy. Under normal conditions only one spermatozoon enters the 
Polar bodies- 
Female pronucleus 
Female pronucleus 
Male pronucleus 
Male pronucleus 
Female pronucleus 
Male pronucleus 
Fused pronuclei 
Segmentation 
nucleus 
Segmentation 
nucleus 
(commencing 
division) 
Fig. 66.-The process of fertilization in the ovum of a mouse. (After Sobotta.) 
yolk and takes part in the process of fertilization. At the point where the sperma- 
tozoon is about to pierce, the yolk is drawn out into a conical elevation, termed 
the cone of attraction. As soon as the spermatozoon has entered the yolk, the per- 
ipheral portion of the latter is transformed into a membrane, the vitelline membrane 
which prevents the passage of additional spermatozoa. Occasionally a second 
spermatozoon may enter the yolk, thus giving rise to a condition of polyspermy: 
when this occurs the ovum usually develops in an abnormal manner and gives rise 
to a monstrosity. Having pierced the yolk, the spermatozoon loses its tail, while 
its head and connecting piece assume the form of a nucleus containing a cluster of 
chromosomes. This constitutes the male pronucleus, and associated with it there are 
a centriole and centrosome. The male pronucleus passes more deeply into the yolk, 
and coincidently with this the granules of the cytoplasm surrounding it becomes 
radially arranged. The male and female pronuclei migrate toward each other, and, 84 
EMBRYOLOGY 
meeting near the centre of the yolk, fuse to form a new nucleus, the segmentation 
nucleus, which therefore contains both male and female nuclear substance; the 
former transmits the individualities of the male ancestors, the latter those of the 
female ancestors, to the future embryo. By the union of the male and female 
pronuclei the number of chromosomes, is restored to that which is present in the 
nuclei of the somatic cells. 
SEGMENTATION OF THE FERTILIZED OVUM. 
The early segmentation of the human ovum has not yet been observed, but 
judging from what is known to occur in other mammals it may be regarded as 
certain that the process starts immediately after the ovum has been fertilized, 
i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits 
the usual mitotic changes, and these are succeeded by a division of the ovum into 
two cells of nearly equal size.1 The process is repeated again and again, so that 
the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the 
result that a mass of cells is found within the zona striata, and to this mass the term 
Fig. 67.-First stages of segmentation of a mammalian ovum. Semidiagrammatic. (From a drawing by Allen 
Thomson.) z.p. Zona striata, p.gl. Polar bodies, a. Two-cell stage, b. Four-cell stage, c. Eight-cell stage. 
d, e. Morula stage. 
morula is applied (Fig. 67). The segmentation of the mammalian ovum may not 
take place in the regular sequence of two, four, eight, etc., since one of the two first 
formed cells may subdivide more rapidly than the other, giving rise to a three- 
or a five-cell stage. The cells of the morula are at first closely aggregated, but soon 
they become arranged into an outer or peripheral layer, the trophoblast, which 
does not contribute to the formation of the embryo proper, and an inner cell-mass, 
from which the embryo is developed. Fluid collects between the trophoblast 
and the greater part of the inner cell-mass, and thus the morula is converted into 
1 In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed through- 
out the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed 
holoblastic. In the ova of birds, reptiles, and fishes where the nutritive yolk forms by far the larger portion of the 
egg, the cleavage is limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic. Again, 
it has been observed, in some of the lower animals, that the pronuclei do not fuse but merely lie in apposition. At 
the commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the 
equator of the nuclear spindle and then divide; an equal number of male and female chromosomes travel to the opposite 
poles of the spindle, and thus the male and female pronuclei subscribe equal shares of chromatin to the nuclei of the 
two cells which result from the subdivision of the fertilized ovum. SEGMENTATION OF THE FERTILIZED OVUM 
85 
a vesicle, the blastodermic vesicle (Fig. 68). The inner cell-mass remains in con- 
tact, however, with the trophoblast at one pole of the ovum; this is named the 
embryomic pole, since it indicates the situation where the future embryo will be 
developed. The cells of the trophoblast become differentiated into two strata: an 
outer, termed the syncytium or syncytiotrophoblast, so named because it consists of 
a layer of protoplasm studded with nuclei, but showing no evidence of subdivision 
into cells; and an inner layer, the cytotrophoblast or layer of Langhans, in which 
Inner cell-mass 
Entoderm 
Blastodermic vesicle 
Trophoblast 
Fig. 68.-Blastodermic vesicle of Vespertilio murinus. (After van Beneden.) 
Inner cell-mass 
Trophoblast 
Embryonic ectoderm 
Entoderm 
Fig. 69.-Section through embryonic disk of Vespertilio murinus. (After van Beneden.) 
Amniotic cavity 
Syncyt io trophoblast 
Maternal bloodvessels 
Cytotrophoblast 
Embryonic ectoderm 
Entoderm 
Fig. 70.-Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. 
(After van Beneden,) 
the cell outlines are defined. As already stated, the cells of the trophoblast do not 
contribute to the formation of the embryo proper; they form the ectoderm of the 
chorion and play an important part in the development of the placenta. On the 
deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differ- 
entiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear 
between the remaining cells of the mass (Fig. 69), and by the enlargement and 
coalescence of these spaces a cavity, termed the amniotic cavity (Fig. 70), is gradually 86 
EMBRYOLOGY 
developed. The floor of this cavity is formed by the embryonic disk composed 
of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell- 
mass and lying in apposition with the entoderm. 
The Primitive Streak; Formation of the Mesoderm.-The embryonic disk 
becomes oval and then pear-shaped, the wider end being directed forward. Near 
the narrow, posterior end an opaque streak, the primitive 
streak (Figs. 71 and 72), makes its appearance and extends 
along the middle of the disk for about one-half of its 
length; at the anterior end of the streak there is a knob- 
like thickening termed Hensen's knot. A shallow groove, 
the primitive groove, appears on the surface of the streak, 
and the anterior end of this groove communicates by 
means of an aperture, the blastopore, with the yolk-sac. 
The primitive streak is produced by a thickening of the 
axial part of the ectoderm, the cells of which multiply, 
grow downward, and blend with those of the subjacent 
entoderm (Fig. 73). From the sides of the primitive streak 
a third layer of cells, the mesoderm, extends lateralward 
between the ectoderm and entoderm; the caudal end of 
the primitive streak forms the cloacal membrane. 
The extension of the mesoderm takes place throughout the whole of the embry- 
onic and extra-embryonic areas of the ovum, except in certain regions. One of 
these is seen immediately in front of the neural tube. Here the mesoderm extends 
forward in the form of two crescentic masses, which meet in the middle line so as 
Fig. 71.-Surface view of 
embryo of a rabbit. (After 
Kolliker.) arg. Embryonic 
disk. pr. Primitive streak. 
Yolk-sac 
Notochord 
Amnion 
Amnion 
Neurenteric canal 
Primitive streak 
Allantois in body-stalk 
Fig. 72.-Surface view of embryo of Hylobates concolor. (After Seienka.) The amnion has been opened to expose 
the embryonic disk. 
to enclose behind them an area which is devoid of mesoderm. Over this area the 
ectoderm and entoderm come into direct contact with each other and constitute 
a thin membrane, the buccopharyngeal membrane, which forms a septum between 
the primitive mouth and pharynx. In front of the buccopharyngeal area, where 
the lateral crescents of mesoderm fuse in the middle line, the pericardium is SEGMENTATION OF THE FERTILIZED OVUM 
87 
afterward developed, and this region is therefore designated the pericardial area. A 
second region where the mesoderm is absent, at least for a time, is that imme- 
diately in front of the pericardial area. This is termed the proamniotic area, and 
is the region where the proamnion is developed; in man, however, a proamnion is 
apparently never formed. A third region is at the hind end of the embryo where 
the ectoderm and entoderm come into apposition and form the cloacal membrane. 
Fig. 73.-Series of transverse sections through the embryonic disk of Tarsius. (After Hubrecht.) Section I passes 
through the disk, in front of Hensen's knot and shows only the ectoderm and entoderm. Sections II, III, and IV pass 
through Hensen's knot, which is seen in V tapering away into the primitive streak. In III, IV, and V the mesoderm 
is seen springing from the keel-like thickening of the ectoderm, which in III and IV is observed to be continuous into 
the entoderm. 
The blastoderm now consists of three layers, named from without inward: 
ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives 
rise to certain tissues of the body.1 
Ectoderm-The ectoderm consists of columnar cells, which are, however, somewhat 
flattened or cubical toward the margin of the embryonic disk. It forms the whole 
of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, 
sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose 
and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it 
also are derived the enamel of the teeth, and the anterior lobe of the hypophysis 
cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the 
neuro-epithelium of the sense organs. 
Entoderm.-The entoderm consists at first of flattened cells, which subsequently 
become columnar. It forms the epithelial lining of the whole of the digestive tube 
excepting part of the mouth and pharynx and the terminal part of the rectum 
1 The mode of formation of the germ layers in the human ovum has not yet been observed; in the youngest known 
human ovum (viz., that described by Bryce and Teacher), all three layers are already present and the mesoderm is 
split into its two layers. The extra-embryonic coelom is of considerable size, and scattered mesodermal strands are 
seen stretching between the mesoderm of the yolk-sac and that of the chorion. 88 
EMBRYOLOGY 
(which are lined by involutions of the ectoderm), the lining cells of all the glands 
which open into the digestive tube, including those of the liver and pancreas, 
the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, 
and air cells of the lungs, of the urinary bladder and part of the urethra, and that 
which lines the follicles of the thyroid gland and thymus. 
Mesoderm.-The mesoderm consists of loosely arranged branched cells sur- 
rounded by a considerable amount of intercellular fluid. From it the remaining 
tissues of the body are developed. The endothelial lining of the heart and blood- 
vessels and the blood corpuscles are, however, regarded by some as being of ento- 
dermal origin. 
Fig. 74.-A series of transverse sections through an embryo of the dog. (After Bonnet.) Section I is the most 
anterior. In V the neural plate is spread out nearly flat. The series shows the uprising of the neural folds to form the 
neural canal, a. Aortae. c. Intermediate cell mass. ect. Ectoderm, ent. Entoderm, h, h. Rudiments of endothelial 
heart tubes. In III, IV, and V the scattered cells represented between the entoderm and splanchnic layer of meso- 
derm are the vasoformative cells which give origin in front, according to Bonnet, to the heart tubes, h; l.p. Lateral 
plate still undivided in I, II, and III; in IV and V split into somatic (sm) and splanchnic (sp) layers of mesoderm. 
mes. Mesoderm, p. Pericardium, so. Primitive segment. 
As the mesoderm develops between the ectoderm and entoderm it is separated 
into lateral halves by the neural tube and notochord, presently to be described. A 
longitudinal groove appears on the dorsal surface of either half and divides it into 
a medial column, the paraxial mesoderm, lying on the side of the neural tube, and 
a lateral portion, the lateral mesoderm. The mesoderm in the floor of the groove 
connects the paraxial with the lateral mesoderm and is known as the intermediate 
cell-mass; in it the genito-urinary organs are developed. The lateral mesoderm 
splits into two layers, an outer or somatic, which becomes applied to the inner surface 
of the ectoderm, and with it forms the somatopleure; and an inner or splanchnic, 
which adheres to the entoderm, and with it forms the splanchnopleure (Fig. 74). 
The space between the two layers of the lateral mesoderm is termed the coelom. THE NEURAL GROOVE AND TUBE 
89 
THE NEURAL GROOVE AND TUBE. 
In front of the primitive streak two longitudinal ridges, caused by a folding up 
of the ectoderm, make their appearance, one on either side of the middle line 
(Fig. 74). These are named the neural folds; they commence some little distance 
behind the anterior end of the embryonic disk, where they are continuous with 
each other, and from there gradually extend backward, one on either side of the 
anterior end of the primitive streak. Between these folds is a shallow median 
groove, the neural groove (Figs. 74, 75). The groove gradually deepens as the neural 
folds become elevated, and ultimately the folds meet and coalesce in the middle line 
and convert the groove into a closed tube, the neural tube or canal (Fig. 76), the 
ectodermal wall of which forms the rudiment of the nervous system. By the 
coalescence of the neural folds over the anterior end of the primitive streak, the 
blastopore no longer opens on the surface but into the closed canal of the neural 
Yolk-sac 
Amnion 
Neural groove 
Neurenteric canal 
Primitive streak 
Body-stalk 
Fig. 75.-Human embryo-length, 2 mm. Dorsal view, with the amnion laid open. X 30. (After Graf Spee.) 
tube, and thus a transitory communication, the neurenteric canal, is established 
between the neural tube and the primitive digestive tube. The coalescence of the 
neural folds occurs first in the region of the hind-brain, and from there extends 
forward and backward; toward the end of the third week the front opening (anterior 
neuropore) of the tube finally closes at the anterior end of the future brain, and 
forms a recess which is in contact, for a time, with the overlying ectoderm; the 
hinder part of the neural groove presents for a time a rhomboidal shape, and to this 
expanded portion the term sinus rhomboidalis has been applied (Fig. 76). Before 
the neural groove is closed a ridge of ectodermal cells appears along the prominent 
margin of each neural fold; this is termed the neural crest or ganglion ridge, and from 
it the spinal and cerebral nerve ganglia and the ganglia of the sympathetic nervous 
system are developed. By the upward growth of the mesoderm the neural tube 
is ultimately separated from the overlying ectoderm. 
The cephalic end of the neural groove exhibits several dilatations, which, when 
the tube is closed, assume the form of three vesicles; these constitute the three 
primary cerebral vesicles, and correspond respectively to the future prosencephalon 90 
EMBRYOLOGY 
(fore-brain), mesencephalon (mid-brain), and rhombencephalon (hind-brain) (Fig. 
76). The walls of the vesicles are developed into the nervous tissue and neuroglia 
of the brain, and their cavities are modified to form its ventricles. The remainder 
of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall 
the nervous and neuroglial elements of the medulla spinalis are developed while 
the cavity persists as the central canal. 
Head fold of amnion partly 
covering the fore-brain 
Mid-brain 
Hind-brain 
Nerve ganglion 
Auditory vesicle 
Heart 
Vitelline vein 
Fourteenth primitive 
segment 
Paraxial mesoderm 
Neural fold 
Sinus rhomboidalis 
.Remains of primitive streak 
Fig. 76.-Chick embryo of thirty-three hours' incubation, viewed from the dorsal aspect. X 30. 
(From Duval's "Atlas d'Embryologie.") 
THE NOTOCHORD. 
The notochord (Fig. 77) consists of a rod of cells situated on the ventral aspect 
of the neural tube; it constitutes the foundation of the axial skeleton, since around 
it the segments of the vertebral column are formed. Its appearance synchronizes THE PRIMITIVE SEGMENTS 
91 
with that of the neural tube. On the ventral aspect of the neural groove an axial 
thickening of the entoderm takes place; this thickening assumes the appearance 
of a furrow-the chordal furrow-the margins of which come into contact, and so 
convert it into a solid rod of cells-the notochord-which is then separated from 
the entoderm. It extends throughout the entire length of the future vertebral 
Neural canal 
Primitive 
segment 
Wolffian 
duct 
Ectoderm 
Coelom 
o 7 
Somatic mesoderm 
Entoderm V 
Fig. 77.-Transverse section of a chick embryo of forty-five hours' incubation. (Balfour.) 
Notochord 
Aorta 
Splanchnic mesoderm 
column, and reaches as far as the anterior end of the mid-brain, where it ends in 
a hook-like extremity in the region of the future dorsum sellae of the sphenoid 
bone. It lies at first between the neural tube and the entoderm of the yolk-sac, 
but soon becomes separated from them by the mesoderm, which grows medial- 
ward and surrounds it. From the mesoderm 
surrounding the neural tube and notochord, 
the skull and vertebral column, and the 
membranes of the brain and medulla spinalis 
are developed. 
THE PRIMITIVE SEGMENTS. 
Toward the end of the second week 
transverse segmentation of the paraxial 
mesoderm begins, and it is converted into 
a series of well-defined, more or less cubical 
masses, the primitive segments (Figs. 76, 
77, 78), which occupy the entire length of 
the trunk on either side of the middle line 
from the occipital region of the head. Each 
Segment contains a central cavity-myoccel 
-which, however, is soon filled with angular 
and spindle-shaped cells. 
The primitive segments lie immediately 
under the ectoderm on the lateral aspect of 
the neural tube and notochord, and are con- 
nected to the lateral mesoderm by the inter- 
mediate cell-mass. Those of the trunk may 
be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, 
sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head 
are usually described as being four in number. In mammals primitive segments 
of the head can only be recognized in the occipital region, but a study of the 
lower vertebrates leads to the belief that they are present also in the anterior 
part of the head, and that altogether nine segments are represented in the 
cephalic region. 
Yolk-sac 
Cut edge of amnion 
Primitive segments 
Neural folds 
Neurenteric canal 
Fig. 78.-Dorsum of human embryo, 2.11 mm. in 
length. (After Eternod.) 92 
EMBRYOLOGY 
SEPARATION OF THE EMBRYO. 
The embryo increases rapidly in size, but the circumference of the embryonic 
disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of 
relatively slow growth and gradually comes to form a constriction between the 
embryo and the greater part of the yolk-sac. By means of this constriction, which 
corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within 
the embryo and constitutes the primitive digestive tube. 
The embryo increases more rapidly in length than in width, and its cephalic and 
caudal ends soon extend beyond the corresponding parts of the circumference of 
the embryonic disk and are bent in a ventral direction to form the cephalic and 
caudal folds respectively (Figs. 84 and 85). The cephalic fold is first formed, and 
Villi of chorion 
Chorion 
Amnion 
Mesoderm 
Embryonic disc 
Body-stalk 
Rudiment of heart 
Primitive streak 
'Allantois 
Yolk-sac 
- Entoderm 
Mesoderm 
- Bloodvessel 
Fig. 79.-Section through the embryo which is represented in Fig. 75. (After Graf Spee.) 
as the proamniotic area (page 87) lying immediately in front of the pericardial 
area (page 87) forms the anterior limit of the circumference of the embryonic 
disk, the forward growth of the head necessarily carries with it the posterior end 
of the pericardial area, so that this area and the buccopharyngeal membrane are 
folded back under the head of the embryo which now encloses a diverticulum of the 
yolk-sac named the fore-gut. The caudal end of the embryo is at first connected 
to the chorion by a band of mesoderm called the body-stalk, but with the formation 
of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the 
yolk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut 
and the hind-gut there exists for a time a wide opening into the yolk-sac, but the 
latter is gradually reduced to a small pear-shaped sac (sometimes termed the 
umbilical vesicle), and the channel of communication is at the same time narrowed 
and elongated to form a tube called the vitelline duct. DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 
93 
THE YOLK-SAC. 
The yolk-sac (Figs. 79 and 80) is situated on the ventral aspect of the embryo; 
it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with 
fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the 
embryo during the earlier stages of its existence. Blood is conveyed to the wall of 
the sac by the primitive aortse, and after circulating through a wide-meshed capil- 
lary plexus, is returned by the vitelline 
veins to the tubular heart of the em- 
bryo. This constitutes the vitelline 
eirculation, and by means of it nutri- 
tive material is absorbed from the 
yolk-sac and conveyed to the embryo. 
At the end of the fourth week the yolk- 
sac presents the appearance of a small 
pear-shaped vesicle (umbilical vesicle) 
opening into the digestive tube by a 
long narrow tube, the vitelline duct. 
The vesicle can be seen in the after- 
birth as a small, somewhat oval-shaped 
body whose diameter varies from 1 
mm. to 5 mm.; it is situated between 
the amnion and the chorion and may 
lie on or at a varying distance from 
the placenta. As a rule the duct 
undergoes complete obliteration during the seventh week, but in about three 
per cent, of cases its proximal part persists as a diverticulum from the small 
intestine, Meckel's diverticulum, which is situated about three or four feet above 
the ileocolic junction, and may be attached by a fibrous cord to the abdominal 
wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen 
opposite the site of attachment of the duct. 
Heart 
Mandibular arch- 
Hyoid arch- 
Fore-limb 
Maxillary process 
Eye, 
Hind-limb 
Fig. 80.-Human embryo from thirty-one to thirty-four 
days. (His.) 
DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA. 
The Allantois (Figs. 82 to 85).-The allantois arises as a tubular diverticulum 
of the posterior part of the yolk-sac; when the hind-gut is developed the allantois 
is carried backward with it and then opens into the cloaca or terminal part of the 
hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below 
and around the tail end of the embryo. The diverticulum is lined by entoderm 
and covered by mesoderm, and in the latter are carried the allantoic or umbilical 
vessels. 
In reptiles, birds, and many mammals the allantois becomes expanded into a 
vesicle which projects into the extra-embryonic coelom. If its further development 
be traced in the bird, it is seen to project to the right side of the embryo, and, 
gradually expanding, it spreads over its dorsal surface as a flattened sac between 
the amnion and the serosa, and extending in all directions, ultimately surrounds 
the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies 
immediately inside the shell membrane. Blood is carried to the allantoic sac by 
the two allantoic or umbilical arteries, which are continuous with the primitive 
aortse, and after circulating through the allantoic capillaries, is returned to the 
primitive heart by the two umbilical veins. In this way the allantoic circulation, 
which is of the utmost importance in connection with the respiration and nutrition 94 
EMBRYOLOGY 
of the chick, is established. Oxygen is taken from, and carbonic acid is given up 
to the atmosphere through the egg-shell, while nutritive materials are at the same 
time absorbed by the blood from the yolk. 
Amniotic cavity 
Body-stalk 
Amniotic cavity 
Allantois 
Yolk-sac 
Yolk-sac 
Chorion 
Chorion 
Fig. 81.-Diagram showing earliest observed stage 
of human ovum. 
Fig. 82.-Diagram illustrating early formation of 
allantois and differentiation of body-stalk. 
In man and other primates the nature of the allantois is entirely different from 
that just described. Here it exists merely as a narrow, tubular diverticulum of the 
hind-gut, and never assumes the form of a vesicle outside the embryo. With the 
formation of the amnion the embryo is, in most animals, entirely separated from 
the chorion, and is only again united to it when the allantoic mesoderm spreads 
over and becomes applied to its inner surface. The human embryo, on the other 
hand, as was pointed out by His, is never wholly separated from the chorion, its 
tail end being from the first connected with the chorion by means of a thick band 
of mesoderm, named the body-stalk (Bauchstiel); into this stalk the tube of the 
allantois extends (Fig. 79). 
Amniotic cavity 
Embryo 
Placental 
villi 
Body-stalk 
Placental 
villi 
Body-stalk 
Allantois 
Allantois 
Y olk-sac 
Heart 
Yolk-sac 
Chorion 
Fore.-gut 
Heart 
Amniotic cavity 
Embryo 
Fig. 83.-Diagram showing later stage of allan- 
toic development with commencing constriction 
of the yolk-sac. 
Fig. 84.-Diagram showing the expansion of amnion 
and delimitation of the umbilicus. 
The Amnion.-The amnion is a membranous sac which surrounds and protects 
the embryo. It is developed in reptiles, birds, and mammals, which are hence 
called "Amniota;" but not in amphibia and fishes, which are consequently termed 
" Anamnia." 
In the human embryo the earliest stages of the formation of the amnion have not 
been observed; in the youngest embryo which has been studied the amnion was 
already present as a closed sac (Figs. 81 and 88), and, as indicated on page 85, DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 
95 
appears in the inner cell-mass as a cavity. This cavity is roofed in by a single 
stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists 
of the prismatic ectoderm of the embryonic disk-the continuity between the 
roof and floor being established at 
the margin of the embryonic disk. 
Outside the amniotic ectoderm is 
a thin layer of mesoderm, which 
is continuous with that of the 
somatopleure and is connected by 
the body-stalk with the meso- 
dermal lining of the chorion. 
When first formed the amnion 
is in contact with the body of the 
embryo, but about the fourth or 
fifth week fluid (liquor amnii) be- 
gins to accumulate within it. This 
fluid increases in quantity and 
causes the amnion to expand and 
ultimately to adhere to the inner 
surface of the chorion, so that the 
extra-embryonic part of the coelom 
is obliterated. The liquor amnii 
increases in quantity up to the 
sixth or seventh month of preg- 
nancy, after which it diminishes 
somewhat; at the end of preg- 
nancy it amounts to about 1 litre. It allows of the free movements of the fetus 
during the later stages of pregnancy, and also protects it by diminishing the risk 
of injury from without. It contains less than 2 per cent, of solids, consisting of 
Placental villi 
Yolk-sac 
Umbilical cord 
Allantois 
Heart 
Digestive tube 
Amniotic cavity 
Embryo 
Fig. 85.-Diagram illustrating a later stage in the development 
of the umbilical cord. 
false amnion or serosa 
villv of 
tjwriorb 
amnion 
post.root 
gang!. 
neural 
canal 
notochord 
-muscle 
plate 
- card.dein 
primitive 
aorta 
Wolffian body 
and duct 
digestive tube 
coelom 
yolk-sac. 
Fig. 86.-Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic 
folds have nearly united in the middle line. (From Quain's Anatomy.) Ectoderm, blue; mesoderm, red; entoderm 
and notochord, black. 
urea and other extractives, inorganic salts, a small amount of protein, and frequently 
a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved 
by the fact that epidermal debris and hairs have been found among the contents of 
the fetal alimentary canal. 96 
EMBRYOLOGY 
In reptiles, birds, and many mammals the amnion is developed in the following 
manner: At the point of constriction where the primitive digestive tube of the 
embryo joins the yolk-sac a reflection of folding upward of the somatopleure takes 
place. This, the amniotic fold (Fig. 86), first makes its appearance at the cephalic 
extremity, and subsequently at the caudal end and sides of the embryo, and grad- 
ually rising more and more, its different parts meet and fuse over the dorsal aspect 
of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the 
edges of the amniotic fold, the two layers of the fold become completely separated, 
the inner forming the amnion, the outer the false amnion or serosa. The space 
between the amnion and the serosa constitutes the extra-embryonic coelom, and 
for a time communicates with the embryonic coelom. 
Somatic mesoderm 
Amniotic cavity 
Splanchnic 
mesoderm 
Amnion 
Neural groove 
Entoderm 
Neurenteric canal 
Vitelline veins1 
Body-stalk 
Fig. 87.-Model of human embryo 1.3 mm. long. (After Eternod.) 
The Umbilical Cord and Body-stalk.-The umbilical cord (Fig. 85) attaches 
the fetus to the placenta; its length at full time, as a rule, is about equal to the 
length of the fetus, i. e., about 50 cm., but it may be greatly diminished or increased. 
The rudiment of the umbilical cord is represented by the tissue which connects 
the rapidly growing embryo with the extra-embryonic area of the ovum. Included 
in this tissue are the body-stalk and the vitelline duct-the former containing the 
allantoic diverticulum and the umbilical vessels, the latter forming the communica- 
tion between the digestive tube and the yolk-sac. The body-stalk is the posterior 
segment of the embryonic area, and is attached to the chorion. It consists of a plate 
of mesoderm covered by thickened ectoderm on which a trace of the neural groove 
can be seen, indicating its continuity with the embryo. Running through its 
mesoderm are the two umbilical arteries and the two umbilical veins, together with 
the canal of the allantois-the last being lined by entoderm (Fig. 87). Its dorsal 
surface is covered by the amnion, while its ventral surface is bounded by the extra- 
embryonic coelom, and is in contact with the vitelline duct and yolk-sac. With 
the rapid elongation of the embryo and the formation of the tail fold, the body 
stalk comes to lie on the ventral surface of the embryo (Figs. 84 and 85), where 
its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral 
leaves of somatopleure then grow round on each side, and, meeting on the ventral DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 
97 
aspect of the allantois, enclose the vitelline duct and vessels, together with a part 
of the extra-embryonic coelom; the latter is ultimately obliterated. The cord is 
covered by a layer of ectoderm which is continuous with that of the amnion, and 
its various constitutents are enveloped by embryonic gelatinous tissue, jelly of 
Wharton. The vitelline vessels and duct, together with the right umbilical vein, 
undergo atrophy and disappear; and thus the cord, at birth, contains a pair of 
umbilical arteries and one (the left) umbilical vein. 
Fig. 88.-Section through ovum imbedded in the uterine decidua. Semidiagrammatic. (After Peters.) am. 
Amniotic cavity, b.c. Blood-clot. b.s. Body-stalk, ect. Embryonic ectoderm, ent. Entoderm, mes. Mesoderm. 
m.v. Maternal vessels, tr. Trophoblast, u.e. Uterine epithelium, u.g. Uterine glands, y.s. Yolk-sac. 
Implantation or Imbedding of the Ovum.-As described (page 82), fertilization 
of the ovum occurs in the lateral or ampullary end of the uterine tube and is 
immediately followed by segmentation. On reaching the cavity of the uterus the 
segmented ovum adheres like a parasite to the uterine mucous membrane, destroys 
the epithelium over the area of contact, and excavates for itself a cavity in the 
mucous membrane in which it becomes imbedded. In the ovum described by 
Bryce and Teacher1 the point of entrance was visible as a small gap closed by a 
mass of fibrin and leucocytes; in the ovum described by Peters2 the opening was 
covered by a mushroom-shaped mass of fibrin and blood-clot (Fig. 88), the narrow 
stalk of which plugged the aperture in the mucous membrane. Soon, however, 
all trace of the opening is lost and the ovum is then completely surrounded by the 
uterine mucous membrane. 
The structure actively concerned in the process of excavation is the trophoblast 
of the ovum, which possesses the power of dissolving and absorbing the uterine 
1 Contribution to the study of the early development and imbedding of the human ovum, 1908. 
2 Die Einbettung des menschlichen Eies, 1899. 
7 98 
EMBRYOLOGY 
tissues. The trophoblast proliferates rapidly and forms a network of branching 
processes which cover the entire ovum and invade and destroy the maternal 
tissues and open into the maternal bloodvessels, with the result that the spaces 
in the trophoblastic network are filled with maternal blood; these spaces com- 
municate freely with one another and become greatly distended and form the 
intervillous space. 
The Decidua.-Before the fertilized ovum reaches the uterus, the mucous 
membrane of the body of the uterus undergoes important changes and is then 
known as the decidua. The thickness 
and vascularity of the mucous mem- 
brane are greatly increased; its glands 
are elongated and open on its free 
surface by funnel-shaped orifices, 
while their deeper portions are tortu- 
ous and dilated into irregular spaces. 
The interglandular tissue is also in- 
creased in quantity, and is crowded 
with large round, oval, or polygonal 
cells, termed decidual cells. These 
changes are well advanced by the 
second month of pregnancy, when 
the mucous membrane consists of the 
following strata (Fig. 89): (1) stratum 
compactum, next the free surface; in 
this the uterine glands are only 
slightly expanded, and are lined by 
columnar cells; (2) stratum spongiosum, 
in which the gland tubes are greatly 
dilated and very tortuous, and are 
ultimately separated from one another 
by only a small amount of inter- 
glandular tissue, while their lining 
cells are flattened or cubical; (3) a 
thin unaltered or boundary layer, next 
the uterine muscular fibres, contain- 
ing the deepest parts of the uterine 
glands, which are not dilated, and 
are lined with columnar epithelium; 
it is from this epithelium that the 
epithelial lining of the uterus is re- 
generated after pregnancy. Distinc- 
tive names are applied to different 
portions of the decidua. The part 
which covers in the ovum is named the 
decidua capsularis; the portion which 
intervenes between the ovum and the 
uterine wall is named the decidua 
basalis or decidua placentalis; it is here 
that the placenta is subsequently 
developed. The part of the decidua which lines the remainder of the body of the 
uterus is known as the decidua vera or decidua parietalis. 
Coincidently with the growth of the embryo, the decidua capsularis is thinned 
and extended (Fig. 90) and the space between it and the decidua vera is gradually 
obliterated, so that by the third month of pregnancy the two are in contact. By 
Mucous membrane 
Muscular fibres 
Stratum compactum 
Stratum spongiosum 
Unaltered or 
boundary layer 
Muscular fibres 
Fig. 89.-Diagrammatic sections of the uterine mucous 
membrane: A. The non-pregnant uterus. B. The preg- 
nant uterus, showing the thickened mucous membrane 
and the altered condition of the uterine glands. (Kundrat 
and Engelmann.) DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 
99 
the fifth month of pregnancy the decidua capsularis has practically disappeared, 
while during the succeeding months the decidua vera also undergoes atrophy, 
owing to the increased pressure. The glands of the stratum compactum are oblit- 
erated, and their epithelium is lost, In the stratum spongiosum the glands are 
compressed and appear as slit-like fissures, while their epithelium undergoes degen- 
eration. In the unaltered or boundary layer, however, the glandular epithelium 
retains a columnar or cubical form. 
The Chorion (Figs. 80 to 85).-The chorion consists of two layers: an outer 
formed by the primitive ectoderm or trophoblast, and an inner by the somatic 
mesoderm; with this latter the amnion is in contact. The trophoblast is made 
up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer 
of Langhans, and an external layer of richly nucleated protoplasm devoid of cell 
boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms 
numerous processes, the chorionic villi, which invade and destroy the uterine 
Placental villi imbedded in the 
Decidua placentalis 
Uterine tube 
Allantois' 
Cavity of uterus 
Y olk-sac 
Umbilical cord 
with its con- 
tained vessels 
Cavity of amnion 
Decidua vera 
or parietalis 
Non-placental villi im- 
bedded in the decidua 
capsularis 
Plug of mucus in the 
cervix uteri 
Fig. 90.--Sectional plan of the gravid uterus in the third and fourth month. (Modified from Wagner.) 
decidua and at the same time absorb from it nutritive materials for the growth 
of the embryo. The chorionic villi are at first small and non-vascular, and consist 
of trophoblast only, but they increase in size and ramify, while the mesoderm, 
carrying branches of the umbilical vessels, grows into them, and in this way they 
are vascularized. Blood is carried to the villi by the branches of the umbilical 
arteries, and after circulating through the capillaries of the villi, is returned to 
the embryo by the umbilical veins. Until about the end of the second month 
of pregnancy the villi cover the entire chorion, and are almost uniform in size 
(Fig. 82), but after this they develop unequally. The greater part of the chorion 
is in contact with the decidua capsularis (Fig. 90), and over this portion the villi, 
with their contained vessels, undergo atrophy, so that by the fourth month scarcely 
a trace of them is left, and hence this part of the chorion becomes smooth, and is 
named the chorion laeve; as it takes no share in the formation of the placenta, it 
is also named the non-placental part of the chorion. On the other hand, the villi 
on that part of the chorion which is in contact with the decidua placentalis increase 100 
EMBRYOLOGY 
greatly in size and complexity, and hence this part is named the chorion frondosum 
(Fig. 85). 
The Placenta.-The placenta connects the fetus to the uterine wall, and is the 
organ by means of which the nutritive, respiratory, and excretory functions of the 
fetus are carried on. It is composed of fetal and maternal portions. 
Fetal Portion.--The fetal portion of the placenta consists of the villi of the 
chorion frondosum; these branch repeatedly, and increase enormously in size. 
These greatly ramified villi are sus- 
pended in the intervillous space, and 
are bathed in maternal blood, which 
is conveyed to the space by the uterine 
arteries and carried away by the uter- 
ine veins. A branch of an umbilical 
artery enters each villus and ends in 
a capillary plexus from which the 
blood is drained by a tributary of the 
umbilical vein. The vessels of the 
villus are surrounded by a thin layer 
of mesoderm consisting of gelatinous 
connective tissue, which is covered by 
two strata of ectodermal cells derived 
from the trophoblast: the deeper 
stratum, next the mesodermic tissue, 
represents the cytotrophoblast or layer 
of Langhans; the superficial, in contact 
with the maternal blood, the syncytiotrophoblast (Figs. 91 and 92). After the 
fifth month the two strata of cells are replaced by a single layer of somewhat 
flattened cells. 
Fig. 91.-Diagram to illustrate the first phase of the 
placenta. (After Peters.) b.l. Blood lacuna, ca. Maternal 
capillary, de. Decidua, mes. Mesoderm, sy. Syncytio- 
trophoblast. tr. Cytotrophoblast. 
Fig. 92.-Diagram to illustrate the second phase of the placenta. (After Peters.) The mesodermic core has now 
invaded the strands of the trophoblast, and is beginning to branch, ca. Maternal capillary, core. Core of villus. 
fib. Fibrinous material deposited at junction of trophoblast with decidua, mcp. Endothelium of maternal capillary 
mes. Mesoderm, sy. Syncytiotrophoblast. vs. Intervillous space. 
Maternal Portion.-The maternal portion of the placenta is formed by the 
decidua placentalis containing the intervillous space. As already explained, this 
space is produced by the enlargement and intercommunication of the spaces in 
the trophoblastic network. The changes involve the disappearance of the greater 
portion of the stratum compactum, but the deeper part of this layer persists and 
is condensed to form what is known as the basal plate. Between this plate and 
the uterine muscular fibres are the stratum spongiosum and the boundary layer; DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 
101 
through these and the basal plate the uterine arteries and veins pass to and from 
the intervillous space. The endothelial lining of the uterine vessels ceases at the 
point where they terminate in the intervillous space which is lined by the syncytio- 
trophoblast. Portions of the stratum compactum persist and are condensed to 
form a series of septa, which extend from the basal plate through the thickness 
of the placenta and subdivide it into the lobules or cotyledons seen on the uterine 
surface of the detached placenta. 
The fetal and maternal blood currents traverse the placenta, the former passing 
through the bloodvessels of the placental villi and the latter through the inter- 
villous space (Fig. 93). The two currents do not intermingle, being separated from 
each other by the delicate walls of the villi. Nevertheless, the fetal blood is able 
to absorb, through the walls of the villi, oxygen and nutritive materials from the 
maternal blood, and give up to the latter its waste products. The blood, so purified, 
is carried back to the fetus by the umbilical vein. It will thus be seen that the 
placenta not only establishes a mechan- 
ical connection between the mother 
and the fetus, but subserves for the 
latter the purposes of nutrition, respi- 
ration, and excretion. In favor of the 
view that the placenta possesses certain 
selective powers may be mentioned the 
fact that glucose is more plentiful in 
the maternal than in the fetal blood. 
It is interesting to note also that the 
proportion of iron, and of lime and 
potash, in the fetus is increased during 
the last months of pregnancy. Further, 
there is evidence that the maternal leu- 
cocytes may migrate into the fetal blood, 
since leucocytes are much more numer- 
ous in the blood of the umbilical vein 
than in that of the umbilical arteries. 
The placenta is usually attached 
near the fundus uteri, and more fre- 
quently on the posterior than on the 
anterior wall of the uterus. It may, 
however, occupy a lower position and, 
in rare cases, its site is close to the 
orificium internum uteri, which it may 
occlude, thus giving rise to the con- 
dition known as placenta praeoia. 
Separation of the Placenta.-After the child is born, the placenta and membranes 
are expelled from the uterus as the after-birth. The separation of the placenta from 
the uterine wall takes place through the stratum spongiosum, and necessarily 
causes rupture of the uterine vessels. The orifices of the torn vessels are, however, 
closed by the firm contraction of the uterine muscular fibres, and thus postpartum 
hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the 
proliferation and extension of the epithelium which lines the persistent portions 
of the uterine glands in the unaltered layer of the decidua. 
The expelled placenta appears as a discoid mass which weighs about 450 gm. 
and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., 
but this diminishes rapidly toward the circumference of the disk, which is continu- 
ous with the membranes. Its uterine surface is divided by a series of fissures into 
lobules or cotyledons, the fissures containing the remains of the septa which extended 
Amnion 
Chorion 
Umbilical 
artery 
Umbilical 
vein 
Uterine vein 
Uterine artery 
Fig. 93.-Scheme of placental circulation. 102 
EMBRYOLOGY 
between the maternal and fetal portions. Most of these septa end in irregular 
or pointed processes; others, especially those near the edge of the placenta, pass 
through its thickness and are attached to the chorion. In the early months these 
septa convey branches of the uterine arteries which open into the intervillous 
space on the surfaces of the septa. The fetal surface of the placenta is smooth, 
being closely invested by the amnion. Seen through the latter, the chorion presents 
a mottled appearance, consisting of gray, purple, or yellowish areas. The umbilical 
cord is usually attached near the centre of the placenta, but may be inserted any- 
where between the centre and the margin; in some cases it is inserted into the mem- 
branes, i. e., the velamentous insertion. From the attachment of the cord the larger 
branches of the umbilical vessels radiate under the amnion, the veins being deeper 
and larger than the arteries. The remains of the vitelline duct and yolk-sac may 
be sometimes observed beneath the amnion, close to the cord, the former as an 
attenuated thread, the latter as a minute sac. 
On section, the placenta presents a soft, spongy appearance, caused by the 
greatly branched villi; surrounding them is a varying amount of maternal blood 
giving the dark red color to the placenta. Many of the larger villi extend from 
the chorionic to the decidual surface, while others are attached to the septa which 
separate the cotyledons; but the great majority of the villi hang free in the inter- 
villous space. 
The further growth of the embryo will be best understood from a description of 
the principal facts relating to the development of the chief systems of which the 
body consists. 
DEVELOPMENT OF THE PARIETES. 
The Skeleton.-The skeleton is of mesodermal origin, and may be divided into 
(a) that of the trunk {axial skeleton), comprising the vertebral column, skull, ribs, 
and sternum, and (b) that of the limbs (appendicular skeleton). 
The Vertebral Column.-The notochord (Fig. 77) is a temporary structure and 
forms a central axis, around which the segments of the vertebral column are devel- 
oped.1 It is derived from the entoderm, and consists of a rod of cells, which lies 
on the ventral aspect of the neural tube and reaches from the anterior end of the 
mid-brain to the extremity of the tail. On either side of it is a column of paraxial 
mesoderm which becomes subdivided into a number of more or less cubical seg- 
ments, the primitive segments (Figs. 77 and 78). These are separated from one 
another by intersegmental septa and are arranged symmetrically on either side of 
the neural tube and notochord: to every segment a spinal nerve is distributed. 
At first each segment contains a central cavity, the myocoel, but this is soon filled 
with a core of angular and spindle-shaped cells. The cells of the segment become 
differentiated into three groups, which form respectively the cutis-plate or derma- 
tome, the muscle-plate or myotome, and the sclerotome (Fig. 94). The cutis-plate 
is placed on the lateral and dorsal aspect of the myocoel, and from it the true skin 
of the corresponding segment is derived; the muscle-plate is situated on the medial 
side of the cutis-plate and furnishes the muscles of the segment. The cells of the 
sclerotome are largely derived from those forming the core of the myocoel, and lie 
next the notochord. Fusion of the individual sclerotomes in an antero-posterior 
direction soon takes place, and thus a continuous strand of cells, the sclerotogenous 
layer, is formed along the ventro-lateral aspects of the neural tube. The cells of 
this layer proliferate rapidly, and extending medialward surround the notochord; 
at the same time they grow backward on the lateral aspects of the neural tube 
and eventually surround it, and thus the notochord and neural tube are enveloped 
1 In the amphioxus the notochord persists and forms the only representative of a skeleton in that animal. DEVELOPMENT OF THE PARIETES 
103 
by a continuous sheath of mesoderm, which is termed the membranous vertebral 
column. In this mesoderm the original segments are still distinguishable, but each 
is' now differentiated into 
two portions, an anterior, 
consisting of loosely arranged 
cells, and a posterior, of 
more condensed tissue (Fig. 
95, A and B). Between the 
two portions the rudiment 
of the intervertebral fibro- 
cartilage is laid down (Fig. 
95, C). Cells from the pos- 
terior mass grow into the 
intervals between the myo- 
tomes (Fig. 95, B and C) of 
the corresponding and suc- 
ceeding segments, and extend 
both dorsally and ventrally; 
the dorsal extensions sur- 
round the neural tube and 
represent the future verte- 
bral arch, while the ventral 
extend into the body-wall 
as the costal processes. The 
hinder part of the posterior 
mass joins the anterior mass 
of the succeeding segment 
to form the vertebral body. 
Each vertebral body is there- 
fore a composite of two segments, being formed from the posterior portion of 
one segment and the anterior part of that immediately behind it. The vertebral 
Fig. 94.-Transverse section of a human embryo of the third week 
to show the differentiation of the primitive segment. (Kollmann.) ao. 
Aorta, m.p. Muscle-plate, n.c. Neural canal, sc. Sclerotome, s.p. 
cutis-plate. 
Myotome. 
Anterior portion of sclerotome 
Intervertebral 
fbrocartilage 
Notochord 
Posterior portion of sclerotome 
Notochord 
Intermyolomic septum 
Costal process 
Centrum 
A 
B 
c 
Fig. 95.-Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent 
segments. 
and costal arches are derivatives of the posterior part of the segment in front 
of the intersegmental septum with which they are associated. 104 
EMBRYOLOGY 
This stage is succeeded by that of the cartilaginous vertebral column. In the 
fourth week two cartilaginous centres make their appearance, one on either side of 
the notochord; these extend around the notochord and form the body of the cartil- 
aginous vertebra. A second pair of cartilaginous foci appear in the lateral parts of 
the vertebral bow, and grow backward on either side of the neural tube to form 
the cartilaginous vertebral arch, and a separate cartilaginous centre appears for 
each costal process. By the eighth week the cartilaginous arch has fused with the 
body, and in the fourth month the two halves of the arch are joined on the dorsal 
aspect of the neural tube. The spinous process is developed from the junction of 
the two halves of the vertebral arch. The transverse process grows out from the 
vertebral arch behind the costal process. 
In the upper cervical vertebrae a band of mesodermal tissue connects the ends of 
the vertebral arches across the ventral surfaces of the intervertebral fibrocartilages. 
This is termed the hypochordal bar or brace; in all except the first it is transitory 
and disappears by fusing with the fibrocartilages. In the atlas, however, the entire 
bow persists and undergoes chondrification; it develops into the anterior arch of the 
bone, while the cartilage representing the body of the atlas forms the dens or 
odontoid process which fuses with the body of the second cervical vertebra. 
Anterior 
longitudinal 
ligament 
Posteriorlongitudinal 
ligament 
Cartilaginous end 
of vertebral body 
Nucleus pulposus 
Intervertebral fibro- 
cartilage 
Slight enlargement 
of notochord in 
the cartilaginous 
vertebral body 
Fig. 96.-Sagittal section through an intervertebral fibrocartilage and adjacent parts of two vertebrae of an advanced 
sheep's embryo. (Kolliker.) 
The portions of the notochord which are surrounded by the bodies of the verte- 
brae atrophy, and ultimately disappear, while those which lie in the centres of the 
intervertebral fibrocartilages undergo enlargement, and persist throughout life as 
the central nucleus pulposus of the fibrocartilages (Fig. 96). 
The Ribs.-The ribs are formed from the ventral or costal processes of the 
primitive vertebral bows, the processes extending between the muscle-plates. In 
the thoracic region of the vertebral column the costal processes grow lateralward to 
form a series of arches, the primitive costal arches. As already described, the 
transverse process grows out behind the vertebral end of each arch. It is at first 
connected to the costal process by continuous mesoderm, but this becomes differ- 
entiated later to form the costotransverse ligament; between the costal process 
and the tip of the transverse process the costotransverse joint is formed by 
absorption. The costal process becomes separated from the vertebral bow by the 
development of the costocentral joint. In the cervical vertebrae (Fig. 97) the trans- 
verse process forms the posterior boundary of the foramen transversarium, while 
the costal process corresponding to the head and neck of the rib fuses with the DEVELOPMENT OF THE PARIETES 
105 
body of the vertebra, and forms the antero-lateral boundary of the foramen. The 
distal portions of the primitive costal arches remain undeveloped; occasionally 
the arch of the seventh cervical vertebra undergoes greater development, and by 
the formation of costovertebral joints is separated oft* as a rib. In the lumbar 
region the distal portions of the primitive costal arches fail; the proximal portions 
fuse with the transverse processes to form the transverse processes of descriptive 
anatomy. Occasionally a movable rib is developed in connection with the first 
lumbar vertebra. In the sacral region costal processes are developed only in 
connection with the upper three, or it may be four, vertebrae; the processes of 
adjacent segments fuse with one another to form the lateral parts of the sacrum. 
The coccygeal vertebrae are devoid of costal processes. 
CERVICAL 
LUMBAR 
THORACIC 
SACRAL 
Fig. 97.-Diagrams showing the portions of the adult vertebra? derived respectively from the bodies, vertebral 
arches, and costal processes of the embryonic vertebrae. The bodies are represented in yellow, the vertebral arches 
in red, and the costal processes in blue. 
The Sternum.-The ventral ends of the ribs become united to one another by a 
longitudinal bar termed the sternal plate, and opposite the first seven pairs of ribs 
these sternal plates fuse in the middle line to form the manubrium and body of the 
sternum. The xiphoid process is formed by a backward extension of the sternal 
plates. 
The Skull.-Up to a certain stage the development of the skull corresponds with 
that of the vertebral column; but it is modified later in association with the expan- 
sion of the brain-vesicles, the formation of the organs of smell, sight, and hearing, 
and the development of the mouth and pharynx. 106 
EMBRYOLOGY 
I he notochord extends as far forward as the anterior end of the mid-brain, and 
becomes partly surrounded by mesoderm (Fig. 98). The posterior part of this meso- 
dermal investment corresponds with the basilar part of the occipital bone, and shows 
a subdivision into four segments, which are separated by the roots of the hypo- 
glossal nerve. The mesoderm then extends over the brain-vesicles, and thus the 
entire brain is enclosed by a mesodermal 
investment, which is termed the membran- 
ous cranium. From the inner layer of this 
the bones of the skull and the membranes 
of the brain are developed; from the outer 
layer the muscles, bloodvessels, true skin, 
and subcutaneous tissues of the scalp. In 
the shark and dog-fish this membranous 
cranium undergoes complete chondrifi- 
cation, and forms the cartilaginous skull 
or chondrocranium of these animals. In 
mammals, on the other hand, the process 
of chondrification is limited to the base 
of the skull-the roof and sides being 
covered in by membrane. Thus the bones 
of the base of the skull are preceded by 
cartilage, those of the roof and sides 
by membrane. The posterior part of the 
base of the skull is developed around 
the notochord, and exhibits a segmented 
condition analogous to that of the vertebral column, while the anterior part arises 
in front of the notochord and shows no regular segmentation. The base of the skull 
may therefore be divided into (a) a chordal or vertebral, and (6) a prechordal or 
pre vertebral portion. 
Fossa 
hypophyseos 
Mesoderm of base 
of skull 
Parachordal 
cartilage 
Notochord 
Anterior arch of atlas 
Notochord 
Body of axis 
Third cervical 
vertebra 
Fig. 98.-Sagittal section of cephalic end of noto- 
chord. (Keibel.) 
Situation of olfactory pit 
Situation of eyeball 
Ethmoid plate 
and nasal 
septum 
Olfactory organ 
Extension around 
olfactory organ 
Fossa 
hypophyseos 
Foramina for 
olfactory nerves 
Eyeball 
Trabecula 
cranii 
Fossa 
hypophyseos 
Situation of 
auditory 
vesicle 
Basilar plate 
Auditory vesicle 
Parachordal 
cartilage 
Notochord 
'Notochord 
Fig. 99.-Diagrams of the cartilaginous cranium. (Wiedersheim.) 
In the lower vertebrates two pairs of cartilages are developed, viz., a pair of 
parachordal cartilages, one on either side of the notochord; and a pair of pre- 
chordal cartilages, the trabeculae cranii, in front of the notochord (Fig. 99). The 
parachordal cartilages (Fig. 99) unite to form a basilar plate, from which the car- 
tilaginous part of the occipital bone and the basi-sphenoid are developed. On the 
lateral aspects of the parachordal cartilages the auditory vesicles are situated, DEVELOPMENT OF THE PARIETES 
107 
and the mesoderm enclosing them is soon converted into cartilage, forming the 
cartilaginous ear-capsules. These cartilaginous ear-capsules, which are of an oval 
shape, fuse with the sides of the basilar plate, and from them arise the petrous 
and mastoid portions of the temporal bones. The trabeculae cranii (Fig. 99) are 
two curved bars of cartilage which embrace the hypophysis cerebri; their posterior 
ends soon unite with the basilar plate, while their anterior ends join to form the 
ethmoidal plate, which extends forward between the fore-brain and the olfactory 
pits. Later the trabeculae meet and fuse below the hypophysis, forming the floor 
Crista galli 
Cribriform plate 
Small wing of sphenoid 
Optic foramen 
Great wing of 
sphenoid 
Meckel's cartilage 
Malleus- 
Sella turcica 
Incus 
Dorsum sellae 
Canal for facial 
nerve 
Int. acoustic meat. 
Jugular foramen 
Fossa subarcuata 
Ear capsule 
Ductus endol. 
Canal for hypoglossal nerve 
Foramen magnum 
Fig. 100.-Model of the chondrocranium of a human embryo, 8 cm. long. (Hertwig. The membrane bones are 
not represented. 
of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis 
from the stomodeum. The median part of the ethmoidal plate forms the bony 
and cartilaginous parts of the nasal septum. From the lateral margins of the 
trabeculae cranii three processes grow out on either side. The anterior forms the 
ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle 
gives rise to the small wing of the sphenoid, while from the posterior the great 
wing and lateral pterygoid plate of the sphenoid are developed (Figs. 100, 101). 
The bones of the vault are of membranous formation, and are termed dermal or 
covering bones. They are partly developed from the mesoderm of the membranous 108 
EMBRYOLOGY 
cranium, and partly from that which lies outside the entoderm of the fore- 
gut. They comprise the upper part of the occipital squama (interparietal), the 
squamee and tympanic parts of the temporals, the parietals, the frontal, the vomer, 
the medial pterygoid plates, and the bones of the face. Some of them remain 
distinct throughout life, e. g., parietal and frontal, while others join with the bones 
of the chondrocranium, e. g., interparietal, squamse of temporals, and medial 
pterygoid plates. 
Recent observations have shown that, in mammals, the basi-cranial cartilage, 
both in the chordal and prechordal regions of the base of the skull, is developed 
as a single plate which extends from behind forward. In man, however, its posterior 
part shows an indication of being developed from two chondrifying centres which 
fuse rapidly in front and below. The anterior and posterior thirds of the cartilage 
surround the notochord, but its middle third lies on the dorsal aspect of the noto- 
chord, which in this region is placed between the cartilage and the wall of the 
pharynx. 
Optic foramen 
Small wing of sphenoid 
Great wing of sphenoid 
Nasal 
capsule 
Canal for facial nerve 
Tegmen tymp. Incus 
Sept, 
nasi 
Maxilla 
Vomer' 
Palatine 
bone 
Mandible' 
Styloid process 
Meckel's cart. 
Handle, 
of 
malleus 
Fen. cochleae 
Cricoid cart. 
Canal for hypoglossal 
nerve 
Fig. 101.-The same model as shown in Fig. 100 from the left side. Certain of the membrane bones of the right side 
are represented in yellow. 
Thyroid cart. 
The Branchial or Visceral Arches and Pharyngeal Pouches.-In the lateral walls 
of the anterior part of the fore-gut five pharyngeal pouches appear (Fig. 104); each 
of the upper four pouches is prolonged into a dorsal and a ventral diverticulum. 
Over these pouches corresponding indentations of the ectoderm occur, forming what 
are known as the branchial or outer pharyngeal grooves. The intervening mesoderm 
is pressed aside and the ectoderm conies for a time into contact with the ento- 
dermal lining of the fore-gut, and the two layers unite along the floors of the 
grooves to form thin closing membranes between the fore-gut and the exterior. 
Later the mesoderm again penetrates between the entoderm and the ectoderm. 
In gill-bearing animals the closing membranes disappear, and the grooves become 
complete clefts, the gill-clefts, opening from the pharynx on to the exterior; perfor- 
ation, however, does not occur in birds or mammals. The grooves separate a 
series of rounded bars or arches, the branchial or visceral arches, in which thickening 
of the mesoderm takes place (Figs. 102 and 103). The dorsal ends of these arches 
are attached to the sides of the head, while the ventral extremities ultimately 
meet in the middle line of the neck. In all, six arches make their appearance, 109 
DEVELOPMENT OF THE PARIETES 
but of these only the first four are visible externally. The first arch is named the 
mandibular, and the second the hyoid; the others have no distinctive names. 
In each arch a cartilaginous bar, consisting of right and left halves, is developed, 
and with each of these there is one of the primitive aortic arches. 
Mid-brain 
Eye 
, Hind-brain 
Fore-brain 
Auditory vesicle 
Stomodeum. 
Visceral 
arches 
Mandibular arch 
Heart - 
Maxillary process 
Olfactory pit 
Amnion (cut) 
Mandibular arch 
Hyoid arch 
Third arch 
Body-stalk 
Fig. 102.-Embryo between eighteen and twenty-one 
days. (His.) 
Fig. 103.-Head end of human embryo, about the end 
of the fourth week. (From model by Peter.) 
The mandibular arch lies between the first branchial groove and the stomodeum; 
from it are developed the lower lip, the mandible, the muscles of mastication, 
and the anterior part of the tongue. Its cartilaginous bar is formed by what 
are known as Meckel's cartilages (right and left) (Fig. 105). The dorsal ends of 
these cartilages are connected with the ear- 
capsules and are ossified to form two of the 
bones of the middle ear, the malleus and 
incus; the ventral ends meet each other in 
the region of the symphysis menti, and are 
usually regarded as undergoing ossification 
to form that portion of the mandible which 
contains the incisor teeth. The intervening- 
part of the cartilage disappears; the portion 
immediately adjacent to the malleus and 
incus is replaced by fibrous membrane, which 
constitutes the spheno-mandibular ligament, 
while from the connective tissue covering 
the remainder of the cartilage the greater 
part of the mandible is ossified. From the 
dorsal ends of the mandibular arch a triangular process, the maxillary process, grows 
forward on either side and forms the cheek and lateral part of the upper lip. The 
second or hyoid arch assists in forming the side and front of the neck. From its 
cartilage are developed the styloid process, stylohyoid ligament, and lesser cornu 
of the hyoid bone. The cartilage of the third arch gives origin to the greater 
cornu of the hyoid bone. The ventral ends of the second and third arches unite 
with those of the opposite side, and form a transverse band, from which the body of 
Lateral tongue 
elevations 
Thyroid 
diverticulum 
Entrance to 
larynx 
Fig. 104.-Floor of pharynx of embryo shown in 
Fig. 103. 110 
EMBRYOLOGY 
the hyoid bone and the posterior part of the tongue are developed. The ventral 
portions of the cartilages of the fourth and fifth arches unite to form the thyroid 
cartilage; from the cartilages of the sixth arch the cricoid and arytenoid cartilages 
and the cartilages of the trachea are developed. The mandibular and hyoid 
arches grow more rapidly than those behind them, with the result that the latter 
Malleus 
Tympanic ring 
Mandible 
Meckels cartilage 
Incus 
Hyoid bone 
Fig. 105.-Head and neck of a human embryo eighteen weeks old, with Meckel's cartilage and hyoid bar exposed. 
(After Kolliker.) 
become, to a certain extent, telescoped within the former, and a deep depression, 
the sinus cervicalis, is formed on either side of the neck. This sinus is bounded in 
front by the hyoid arch, and behind by the thoracic wall; it is ultimately obliterated 
by the fusion of its walls. 
Membranous capsule over cerebral hemisphere 
Fronto-nasal process 
Lateral nasal process 
Eye 
Globular process 
Maxillary process 
Stomodeum 
Mandibular arch 
Hyomandibular cleft 
Fig. 106.-Under surface of the head of a human embryo about twenty-nine days old. (After His.) 
From the first branchial groove the concha auriculae and external acoustic 
meatus are developed, while around the groove there appear, on the mandibular 
and hyoid arches, a number of swellings from which the auricula or pinna is formed. 
The first pharyngeal pouch is prolonged dorsally to form the auditory tube and the 
tympanic cavity; the closing membrane between the mandibular and hyoid arches DEVELOPMENT OF THE PARIETES 
111 
is invaded by mesoderm, and forms the tympanic membrane. No traces of the 
second, third, and fourth branchial grooves persist. The inner part of the second 
pharyngeal pouch is named the sinus tonsillaris; in it the tonsil is developed, above 
which a trace of the sinus persists as the supratonsillar fossa. The fossa of Rosen- 
muller or lateral recess of the pharynx is by some regarded as a persistent part of 
the second pharyngeal pouch, but it is probably developed as a secondary forma- 
tion. From the third pharyngeal pouch the thymus arises as an entodermal diver- 
ticulum on either side, and from the fourth pouches small diverticula project and 
become incorporated with the thymus, but in man these diverticula probably 
never form true thymus tissue. The parathyroids also arise as diverticula from 
the third and fourth pouches. From the fifth pouches the ultimobranchial bodies 
originate and are enveloped by the lateral prolongations of the median thyroid 
rudiment; they do not, however, form true thyroid tissue, nor are any traces 
of them found in the human adult. 
Future apex of nose 
Future apex of nose 
Medial nasal process 
Medial nasal process 
■ Olfactory pit 
■Lateral nasal process 
Olfactory pit 
Lateral nasal process 
Globular process 
Maxillary process 
Globular process 
Maxillary process 
Stomodeum 
Roof of pharynx 
Mandibular arch 
Hypophyseal diverticulum 
Dorsal wall of pharynx 
Fig. 107.-Head end of human embryo of about thirty 
to thirty-one days. (From model by Peter.) 
Fig. 108.-Same embryo as shown in Fig. 107, with front 
wall of pharynx removed. 
The Nose and Face.--During the third week two areas of thickened ectoderm, the 
olfactory areas, appear immediately under the fore-brain in the anterior wall of the 
stomodeum, one on either side of a region termed the fronto-nasal process (Fig. 106). 
By the upgrowth of the surrounding parts these areas are converted into pits, 
the olfactory pits, which indent the fronto-nasal process and divide it into a 
medial and two lateral nasal processes (Fig. 107). The rounded lateral angles of 
the medial process constitute the globular processes of His. The olfactory pits form 
the rudiments of the nasal cavities, and from their ectodermal lining the epithe- 
lium of the nasal cavities, with the exception of that of the inferior meatuses, is 
derived. The globular processes are prolonged backward as plates, termed the nasal 
laminae: these laminae are at first some distance apart, but, gradually approach- 
ing, they ultimately fuse and form the nasal septum; the processes themselves 
meet in the middle line, and form the premaxillae and the philtrum or central 
part of the upper lip (Fig. 110). The depressed part of the medial nasal process 
between the globular processes forms the lower part of the nasal septum or 
columella; while above this is seen a prominent angle, which becomes the future 112 
EMBRYOLOGY 
apex (Figs. 107, 108), and still higher a flat area, the future bridge, of the nose. 
The lateral nasal processes form the alee of the nose. 
Continuous with the dorsal end of the mandibular arch, and growing forward 
from its cephalic border, is a triangular process, the maxillary process, the ventral 
extremity of which is separated from the mandibular arch by a > shaped notch 
(Fig. 106). The maxillary process forms the lateral wall and floor of the orbit, 
and in it are ossified the zygomatic bone and the greater part of the maxilla; it 
meets with the lateral nasal process, from which, however, it is separated for a 
time by a groove, the naso-optic furrow, that extend from the furrow encircling 
the eyeball to the olfactory pit. The maxillary processes ultimately fuse with the 
lateral nasal and globular processes, and form the lateral parts of the upper lip 
and the posterior boundaries of the nares (Figs. 109, 110). From the third to 
the fifth month the nares are filled by masses of epithelium, on the breaking down 
and disappearance of which the permanent openings are produced. The maxillary 
process also gives rise to the lower portion of the lateral wall of the nasal cavity. 
Lateral nasal pro- 
cess 
Globular processes 
Fig. 109.-Head of a human embryo of 
about eight weeks, in which the nose and 
mouth are formed. (His.) 
Fig. 110.-Diagram showing the regions of the adult face and neck 
related to the fronto-nasal process and the branchial arches. 
The roof of the nose and the remaining parts of the lateral wall, viz., the ethmoidal 
labyrinth, the inferior nasal concha, the lateral cartilage, and the lateral crus of 
the alar cartilage, are developed in the lateral nasal process. By the fusion of the 
maxillary and nasal processes in the roof of the stomodeum the primitive palate 
(Fig. Ill) is formed, and the olfactory pits extend backward above it. The pos- 
terior end of each pit is closed by an epithelial membrane, the bucconasal membrane, 
formed by the apposition of the nasal and stomodeal epithelium. By the rupture 
of these membranes the primitive choanee or openings between the olfactory pits 
and the stomodeum are established. The floor of the nasal cavity is completed 
by the development of a pair of shelf-like palatine processes which extend medial- 
ward from the maxillary processes (Figs. 112 and 113); these coalesce with each 
other in the middle line, and constitute the entire palate, except a small part in 
front which is formed by the premaxillary bones. Two apertures persist for a time 
between the palatine processes and the premaxillae and represent the permanent 
channels which in the lower animals connect the nose and mouth. The union of 
the parts which form the palate commences in front, the premaxillary and palatine 
processes joining in the eighth week, while the region of the future hard palate 
is completed by the ninth, and that of the soft palate by the eleventh week. By DEVELOPMENT OF THE PARIETES 
113 
the completion of the palate the permanent choanae are formed and are situated a 
considerable distance behind the primitive choanae. The deformity known as 
cleft palate results from a non-union of the palatine processes, and that of hare- 
lip through a non-union of the maxillary and globular processes (see page 299). 
The nasal cavity becomes divided by a vertical septum, which extends downward 
and backward from the medial nasal process and nasal laminae, and unites below 
with the palatine processes. Into this septum a plate of cartilage extends from 
Nares 
Primitive 
palate 
Nasal 
cavity 
Bucconasal 
membranes 
Fig. 111.-Primitive palate of a human embryo of thirty-seven to thirty-eight days. (From model by Peter.) 
On the left side the lateral wall of the nasal cavity has been removed. 
the under aspect of the ethmoid plate of the chodrocranium. The anterior part 
of this cartilaginous plate persists as the septal cartilage of the nose and the medial 
crus' of the alar cartilage, but the posterior and upper parts are replaced by the 
vomer and perpendicular plate of the ethmoid. On either side of the nasal septum, 
at its lower and anterior part, the ectoderm is invaginated to form a blind pouch 
or diverticulum, which extends backward and upward into the nasal septum and 
Globular process 
Mouth of olfactory 
pit, or naris 
Palatine process of 
globular process 
Lens 
Palatine part of 
maxillary process 
Ey& 
Maxillary process 
Pharynx 
Fig. 112.-The roof of the mouth of a human embryo, aged about two and a half months, showing the mode of 
formation of the palate. (His.) 
is supported by a curved plate of cartilage. These pouches form the rudiments of 
the vomero-nasal organs of Jacobson, which open below, close to the junction 
of the premaxillary and maxillary bones. 
The Limbs.-The limbs begin to make their appearance in the third week as 
small elevations or buds at the side of the trunk (Fig. 114). Prolongations from 
the muscle- and cutis-plates of several primitive segments extend into each bud, 
and carry with them the anterior divisions of the corresponding spinal nerves. 114 
EMBRYOLOGY 
The nerves supplying the limbs indicate the number of primitive segments which 
contribute to their formation-the upper limb being derived from seven, viz., 
fourth cervical to second thoracic inclusive, and the lower limb from ten, viz., 
twelfth thoracic to fourth sacral inclusive. The axial part of the mesoderm of 
the limb-bud becomes condensed and converted into its cartilaginous skeleton, 
and by the ossification of this the bones of the limbs are formed. By the sixth 
week the three chief divisions of the limbs are marked off by furrows-the upper 
into arm, forearm, and hand; the lower into thigh, leg, and foot (Fig. 115). The 
limbs are at first directed backward nearly parallel to the long axis of the trunk, 
and each presents two surfaces and two borders. Of the surfaces, one-the future 
flexor surface of the limb-is directed ventrally; the other, the extensor surface, 
dorsally; one border, the preaxial, looks forward toward the cephalic end of the 
embryo, and the other, the postaxial, backward toward the caudal end. The lateral 
epicondyle of the humerus, the radius, and the thumb lie along the preaxial border 
Lateral part of_ 
nasal capsule 
Cartilage of 
nasal septum 
Inferior concha 
I nferior meatus 
Vomeronasal 
organ of Jacobson 
Vomeronasal 
cartilage 
Inferior meatus 
Palatine process 
Cavity of mouth 
Fig. 113.-Frontal section of nasal cavities of a human embryo 28 mm. long. (Kollmann.) 
of the upper limb; and the medial epicondyle of the femur, the tibia, and the great 
toe along the corresponding border of the lower limb. The preaxial part is derived 
from the anterior segments, the postaxial from the posterior segments of the limb- 
bud; and this explains, to a large extent, the innervation of the adult limb, the 
nerves of the more anterior segments being distributed along the preaxial (radial 
or tibial), and those of the more posterior along the postaxial (ulnar or fibular) 
border of the limb. The limbs next undergo a rotation or torsion through an angle 
of 90° around their long axes the rotation being effected almost entirely at the 
limb girdles. In the upper limb the rotation is outward and forward; in the lower 
limb, inward and backward. As a consequence of this rotation the preaxial (radial) 
border of the fore-limb is directed lateralward, and the preaxial (tibial) border 
of the hind-limb is directed medialward; thus the flexor surface of the fore-limb 
is turned forward, and that of the hind-limb backward. DEVELOPMENT OF THE JOINTS 
115 
DEVELOPMENT OF THE JOINTS. 
The mesoderm from which the different parts of the skeleton are formed at 
first shows no differentiation into masses corresponding with the individual bones. 
Thus continuous cores of mesoderm form the axes of the limb-buds and a continu- 
ous column of mesoderm the future vertebral column. The first indications of the 
bones and joints are circumscribed condensations of the mesoderm; these condensed 
parts become chondrified and finally ossified to form the bones of the skeleton. 
The intervening non-condensed portions consist at first of undifferentiated meso- 
derm, which may develop in one of three directions. It may be converted into 
fibrous tissue as in the case of the skull bones, a synarthrodial joint being the 
result, or it may become partly cartilaginous, in which case an amphiarthrodial 
joint is formed. Again, it may become looser in texture and a cavity ultimately 
appear in its midst; the cells lining the sides of this cavity form a synovial mem- 
brane and thus a diarthrodial joint is developed. 
Heart 
Auricula 
Hyoid arch\ 
Fore-limb 
Maxillary process 
Mandibular arch' 
Eye 
Eye. 
Nose 
Fore-limb 
Digits 
Hind-limb 
Hind-limb 
Umbilical cord 
Fig. 114.-Human embryo from thirty-one to thirty- 
four days. (His.) 
Fig. 115.-Embryo of about six weeks. (His.) 
The tissue surrounding the original mesodermal core forms fibrous sheaths for 
the developing bones, i. e., periosteum and perichondrium, which are continued 
between the ends of the bones over the synovial membrane as the capsules of the 
joints. These capsules are not of uniform thickness, so that in them may be 
recognized especially strengthened band which are described as ligaments. This, 
however, is not the only method of formation of ligaments. In some cases by 
modification of, or derivations from, the tendons surrounding the joint, additional 
ligamentous bands are provided to further strengthen the articulations. 
In several of the movable joints the mesoderm which originally existed between 
the ends of the bones does not become completely absorbed-a portion of it 
persists and forms an articular disk. These disks may be intimately associated in 
their development with the muscles surrounding the joint, e. g., the menisci of the 
knee-joint, or with cartilaginous elements, representatives of skeletal structures, 
which are vestigial in human anatomy, e. g., the articular disk of the sterno- 
clavicular joint. 116 
EMBRYOLOGY 
DEVELOPMENT OF THE MUSCLES. 
The voluntary muscles are developed from the myotonies of the primitive 
segments. Portions of the myotomes retain their position on the sides of 
the neural tube, where they may remain distinct from each other and form 
the short muscles of the vertebral column, or fuse with corresponding portions 
of neighboring myotomes to form the Sacrospinales and their continuations. 
Other portions of the myotomes extend into the trunk wall, where again they 
may retain their segmental condition, as in the Intercostales, or may fuse with 
adjacent segments to form the flat muscles of the abdominal wall. Finally, por- 
tions of the myotomes wander into the limb-buds and there undergo fusions 
and alterations in form to produce the limb muscles. The original segmental 
character of the limb muscles is therefore lost, but their segmental nerve supplies 
are retained. Some of the limb muscles expand and migrate secondarily toward the 
mid-dorsal line, e. g., Trapezius and Latissimus dorsi, or toward the mid-ventral 
line, e. g., Pectoralis major. Again, muscles may migrate in a cephalic direction, 
e. g., the facial muscles which are derived from the hyoid arch, or in a caudal direc- 
tion, e. g., the Serratus anterior. In all cases the muscles carry with them the 
segmental nerves of the myotomes from which they were originally derived; two 
examples of this will suffice, viz., the Diaphragma, which is derived from the third 
and fourth and the Serratus anterior, from the fifth, sixth, and seventh cervical 
segments as is indicated by their nerves of supply. In man and the higher verte- 
brates many of the derivatives of the myotomes degenerate and are converted 
into aponeuroses, e. g., galea aponeurotica, and the aponeuroses of the abdominal 
muscles, or ligaments, e. g., sacrotuberous ligament and fibular collateral ligament 
of the knee. 
The involuntary muscles are derived from the splanchnopleure mesoderm. 
DEVELOPMENT OF THE SKIN, GLANDS, AND SOFT PARTS. 
The epidermis and its appendages, consisting of the hairs, nails, sebaceous and 
sweat glands, are developed from the ectoderm, while the corium or true skin 
is of mesodermal origin, being derived from the cutis-plates of the primitive seg- 
ments. About the fifth week the epidermis consists of two layers of cells, the deeper 
one corresponding to the rete mucosum. The subcutaneous fat appears about 
the fourth month, and the papillae of the true skin about the sixth. A considerable 
desquamation of epidermis takes place during fetal life, and this desquamated 
epidermis, mixed with sebaceous secretion, constitutes the vernix caseosa, with 
which the skin is smeared during the last three months of fetal life. The nails 
are formed at the third month, and begin to project from the epidermis about 
the sixth. The hairs appear between the third and fourth months in the form of 
solid downgrowths of the deeper layer of the epidermis, the growing extremities 
of which .become inverted by papillary projections from the corium. The central 
cells of the solid downgrowths undergo alteration to form the hair, while the 
peripheral cells are retained to form the lining cells of the hair-follicle. About the 
fifth month the fetal hairs (lanugo) appear, first on the head and then on the other 
parts; they drop off after birth, and give place to the permanent hairs. The cellular 
structures of the sudoriferous and sebaceous glands are formed from the ectoderm, 
while the connective tissue and bloodvessels are derived from the mesoderm. 
The mamma is also formed partly from mesoderm and partly from ectoderm- 
its bloodvessels and connective tissue being derived from the former, its cellular 
elements from the latter. Its first rudiment is seen about the third month, in the DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
117 
form of a number of small inward projections of the ectoderm, which invade the 
mesoderm; from these, secondary tracts of cellular elements radiate and sub- 
sequently give rise to the epithelium of the glandular follicles and ducts. The 
development of the follicles, however, remains imperfect, except in the parous 
female. 
DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS. 
The entire nervous system is of ectodermal origin, and its first rudiment is seen 
in the neural groove which extends along the dorsal aspect of the embryo (Fig. 
75). By the elevation and ultimate fusion of the neural folds, the groove is con- 
verted into the neural tube (Fig. 77). The anterior end of the neural tube becomes 
expanded to form the three primary brain-vesicles; the cavity of the tube is sub- 
sequently modified to form the ventricular cavities of the brain, and the central 
canal of the medulla spinalis; from the wall the nervous elements and the neuroglia 
of the brain and medulla spinalis are developed. 
■Roof-plate 
Oval bundle 
Posterior nerve root 
Central canal 
•Ependymal layer 
Mantle layer 
•Anterior nerve- roots 
■Marginal layer 
■Floor-plate 
Fig. 116.-Section of medulla spinalis of a four weeks' embryo. (His.) 
The Medulla Spinalis.-At first the wall of the neural tube is composed of a 
single layer of columnar ectodermal cells. Soon the side-walls become thickened, 
while the dorsal and ventral parts remain thin, and are named the roof- and floor- 
plates (Figs. 116, 118). A transverse section of the tube at this stage presents 
an oval outline, while its lumen has the appearance of a slit. The cells which 
constitute the wall of the tube proliferate rapidly, lose their cell-boundaries and 
form a syncytium. This syncytium consists at first of dense protoplasm with 
closely packed nuclei, but later it opens out and forms a looser meshwork with 
the cellular strands arranged in a radiating manner from the central canal. Three 
layers may now be defined-an internal or ependymal, an intermediate or mantle, 
and an external or marginal. The ependymal layer is ultimately converted into the 
ependyma of the central canal; the processes of its cells pass outward toward 
the periphery of the medulla spinalis. The marginal layer is devoid of nuclei, and 
later forms the supporting framework for the white funiculi of the medulla spinalis. 
The mantle layer represents the whole of the future gray columns of the medulla 118 
EMBRYOLOGY 
spinalis; in it the cells are differentiated into two sets, viz., (a) spongioblasts or 
young neuroglia cells, and (6) germinal cells, which are the parents of the neuroblasts 
or young nerve cells (Fig. 117). The spongioblasts are at first connected to one 
another by filaments of the syncytium; in these, fibrils are developed, so that as the 
Germinal cell 
Neuroblast 
Nuclei of spongioblasts 
Syncytium 
Fig. 117.-Transverse section of the medulla spinalis of a human embryo at the beginning of the fourth week. 
(After His.) The left edge of the figure corresponds to the lining of the central canal. 
neuroglial cells become defined they exhibit their characteristic mature appearance 
with multiple processes proceeding from each cell. The germinal cells are large, 
round or oval, and first make their appearance between the ependymal cells on 
the sides of the central canal. They increase rapidly in number, so that by the 
Roof-plate 
Fasciculus gracilis 
Posterior 
funiculus 
Alar lamina 
Oval bundle 
Fasciculus cuneatus. 
Posterior 
nerve-root 
Post, nerve-root 
Central canal 
Ependymal 
layer 
Lateral 
funiculus 
Lateral 
funiculus 
'Basal lamina 
■Central canal 
Anterior 
column 
Anterior 
nerve-root 
Anterior funiculus 
Floor-plate, 
A 
Anterior funiculus 
B 
Fig. 118.-Transverse sections through the medullae spinales of human embryos. A. Aged about four and a half 
weeks. B. Aged about three months. (His.) 
fourth week they form an almost continuous layer on each side of the tube. No 
germinal cells are found in the roof- or floor-plates; the roof-plate retains, in certain 
regions of the brain, its epithelial character; elsewhere, its cells become spongio- 
blasts. By subdivision the germinal cells give rise to the neuroblasts or young DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
119 
nerve cells, which migrate outward from the sides of the central canal into the 
mantle layer and neural crest, and at the same time become pear-shaped; the 
tapering part of the cell undergoes still further elongation, and forms the axis- 
cylinder of the cell. 
The lateral walls of the medulla spinalis continue to increase in thickness, and 
the canal widens out near its dorsal extremity, and assumes a somewhat lozenge- 
shaped appearance. The widest part of the canal serves to subdivide the lateral 
wall of the neural tube into a dorsal or alar, and a ventral or basal lamina (Fig. 118), 
a subdivision which extends forward into the brain. At a later stage the ventral 
part of the canal widens out, while the dorsal part is first reduced to a mere slit 
and then becomes obliterated by the approximation and fusion of its walls; the 
ventral part of the canal persists and forms the central canal of the adult medulla 
spinalis. The caudal end of the canal exhibits a conical expansion which is known 
as the terminal ventricle. 
The ventral part of the mantle layer becomes thickened, and on cross-section 
appears as a triangular patch between the marginal and ependymal layers. This 
thickening is the rudiment of the anterior column of gray substance, and contains 
many neuroblasts, the axis-cylinders of which pass out through the marginal layer 
and form the anterior roots of the spinal nerves (Figs. 116, 118). The thickening 
of the mantle layer gradually extends in a dorsal direction, and forms the posterior 
column of gray substance. The axons of many of the neuroblasts in the alar lamina 
run forward, and cross in the floor-plate to the opposite side of the medulla spinalis; 
these form the rudiment of the anterior white commissure. 
About the end of the fourth week nerve fibres begin to appear in the marginal 
layer. The first to develop are the short intersegmental fibres from the neuro- 
blasts in the mantle zone, and the fibres of the dorsal nerve roots which grow into 
the medulla spinalis from the cells of the spinal ganglia. By the sixth week these 
dorsal root fibres form a well-defined oval bundle in the peripheral part of the alar 
lamina; this bundle gradually increases in size, and spreading toward the middle 
line forms the rudiment of the posterior funiculus. The long intersegmental fibres 
begin to appear about the third month and the cerebrospinal fibres about the fifth 
month. All nerve fibres are at first destitute of medullary sheaths. Different 
groups of fibres receive their sheaths at different times-the dorsal and ventral 
nerve roots about the fifth month, the cerebrospinal fibres after the ninth month. 
By the growth of the anterior columns of gray substance, and by the increase 
in size of the anterior funiculi, a furrow is formed between the lateral halves of the 
cord anteriorly; this gradually deepens to form the anterior median fissure. The 
mode of formation of the posterior septum is somewhat uncertain. Many believe 
that it is produced by the growing together of the walls of the posterior part of the 
central canal and by the development from its ependymal cells of a septum of 
fibrillated tissue which separates the future funiculi graciles. 
Up to the third month of fetal life the medulla spinalis occupies the entire 
length of the vertebral canal, and the spinal nerves pass outward at right angles 
to the medulla spinalis. From this time onward, the vertebral column grows more 
rapidly than the medulla spinalis, and the latter, being fixed above through its 
continuity with the brain, gradually assumes a higher position within the canal. 
By the sixth month its lower end reaches only as far as the upper end of the sacrum; 
at birth it is on a level with the third lumbar vertebra, and in the adult, with the 
lower border of the first or upper border of the second lumbar vertebra. A delicate 
filament, the filum terminale, extends from its lower end as far as the coccyx. 
The Spinal Nerves.--Each spinal nerve is attached to the medulla spinalis by 
an anterior or ventral and a posterior or dorsal root. 
The fibres of the anterior roots are formed by the axons of the neuroblasts 
which lie in the ventral part of the mantle layer; these axons grow out through the 120 
EMBRYOLOGY 
overlying marginal layer and become grouped to form the anterior nerve root 
(Fig. 117). 
The fibres of the posterior roots are developed from the cells of the spinal ganglia. 
Before the neural groove is closed to form the neural tube a ridge of ectodermal 
cells, the ganglion ridge or neural crest (Fig. 119), appears along the prominent 
margin of each neural fold. When the folds meet in the middle line the two gan- 
glion ridges fuse and form a wedge-shaped area along the line of closure of the tube. 
The cells of this area proliferate rapidly opposite the primitive segments and then 
migrate in a lateral and ventral direction to the sides of the neural tube, where they 
ultimately form a series of oval-shaped masses, the future spinal ganglia. These 
ganglia are arranged symmetrically on the two sides of the neural tube and, except 
in the region of the tail, are equal in number to the primitive segments. The cells 
of the ganglia, like the cells of the mantle layer, are of two kinds, viz., spongio- 
blasts and neuroblasts. The spongioblasts develop into the neuroglial cells of the 
ganglia. The neuroblasts are at first round or oval in shape, but soon assume 
the form of spindles the extremities of which gradually elongate into central and 
peripheral processes. The central 
processes grow medialward and, be- 
coming connected with the neural 
tube, constitute the fibres of the 
posterior nerve roots, while the per- 
ipheral processes grow lateralward to 
mingle with the fibres of the anterior 
root in the spinal nerve. As de- 
velopment proceeds the original 
bipolar form of the cells changes; 
the two processes become approxi- 
mated until they ultimately arise 
from a single stem in a T-shaped 
manner. Only in the ganglia of the 
acoustic nerve is the bipolar form 
retained. More recent observers hold, 
however, that the T-form is derived 
from the branching of a single pro- 
cess which grows out from the cell. 
The anterior or ventral and the pos- 
terior or dorsal nerve roots join imme- 
diately beyond the spinal ganglion to form the spinal nerve, which then divides into 
anterior, posterior, and visceral divisions. The anterior and posterior divisions 
proceed directly to their areas of distribution without further association with 
ganglion cells (Fig. 120). The visceral divisions are distributed to the thoracic, 
abdominal, and pelvic viscera, to reach which they pass through the sympathetic 
trunk, and many of the fibres form arborizations around the ganglion cells of this 
trunk. Visceral branches are not given off from all the spinal nerves; they form 
two groups, viz., (a) thoracico-lumbar, from the first or second thoracic, to the 
second or third lumbar nerves; and (b) pelvic, from the second and third, or 
third and fourth sacral nerves. 
The Brain.--The brain is developed from the anterior end of the neural tube, 
which at an early period becomes expanded into three vesicles, the primary cerebral 
vesicles (Fig. 76). These are marked off from each other by intervening con- 
strictions, and are named the prosencephalon or fore-brain, the mesencephalon 
or mid-brain, and the rhombencephalon or hind-brain-the last being continuous 
with the medulla spinalis. As the result of unequal growth of these different 
parts three flexures are formed and the embryonic brain becomes bent on itself 
Fig. 119.-Two stages in the development of the neural 
crest in the human embryo. (Lenhossdk.) DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
121 
in a somewhat zigzag fashion; the two earliest flexures are concave ventrally 
and are associated with corresponding flexures of the whole head. The first flexure 
appears in the region of the mid-brain, and is named the ventral cephalic flexure 
(Fig. 125). By means of it the fore-brain is bent in a ventral direction around 
the anterior end of the notochord and fore-gut, with the result that the floor of 
the fore-brain comes to lie almost parallel with that of the hind-brain. This 
flexure causes the mid-brain to become, for a time, the most prominent part of 
Auditory vesicle 
Facial and acoustic Ns. 
Glossopharyngeal N. 
Trochlear N. 
Trigeminal N. 
Vagus N. 
Accessory N. 
Hypoglossal N. 
M esencephalon. 
Oculomotor N. 
Fr or iep's 
' ganglion 
J- Cervical 
Diencephalon- 
Cerebral 
hemisphere 
Phrenic N. 
Rhinencephalon 
I. Thoracic 
Heart 
Liver 
Vitelline loop 
Tail 
I. Coccygeal 
"I. Lumbar 
I. Sacral 
Fig. 120.-Reconstruction of peripheral nerves of a human embryo of 10.2 mm. (After His.) The abducent nerve 
is not labelled, but is seen passing forward to the eye under the mandibular and maxillary nerves. 
the brain, since its dorsal surface corresponds with the convexity of the curve. 
The second bend appears at the junction of the hind-brain and medulla spinalis. 
This is termed the cervical flexure (Fig. 127), and increases from the third to the 
end of the fifth week, when the hind-brain forms nearly a right angle with the 
medulla spinalis; after the fifth week erection of the head takes place and the cervi- 
cal flexure diminishes and disappears. The third bend is named the pontine flexure 
(Fig. 127), because it is found in the region of the future pons Varoli. It differs 122 
EMBRYOLOGY 
from the other two in that (a) its convexity is forward, and (b) it does not affect 
the head. The lateral walls of the brain-tube, like those of the medulla spinalis, 
are divided by internal furrows into alar or dorsal and basal or ventral laminae 
(Fig. 121). 
Roof-plate 
Alar lamina 
Furrow between 
alar and basal 
laminae 
Basal lamina 
Vagus nerve 
Floor-plate 
Hypoglossal nerve 
Fig. 121.-Diagram to illustrate the alar and 
basal laminae of brain vesicles. (His.) 
Fig. 122.-Transverse section of medulla oblongata of human 
embryo. X 32. (Kollmann.) 
The Rhombencephalon or Hind-brain.-The cavity of the hind-brain becomes 
the fourth ventricle. At the time when the ventral cephalic flexure makes its 
appearance, the length of the hind-brain exceeds the combined lengths of the other 
two vesicles. Immediately behind the mid-brain it exhibits a marked constriction, 
the isthmus rhombencephali (Fig. 125, Isthmus'), which is best seen when the brain is 
viewed from the dorsal aspect. From the isthmus the anterior medullary velum 
Roof-plate 
Alar lamina 
Rhombic lip 
Basal lamina 
Tractus 
solitarius 
Vagus nerve 
Hypoglossal nerve 
Floor-plate. 
Fig. 123.-Transverse section of medulla oblongata of human embryo. (After His.) 
and the brachia conjunctiva of the cerebellum are formed. It is customary to 
divide the rest of the hind-brain into two parts, viz., an upper, called the meten- 
cephalon, and a lower, the myelencephalon. The cerebellum is developed by a 
thickening of the roof, and the pons by a thickening in the floor and lateral walls 
of the metencephalon. The floor and lateral walls of the myelencephalon are DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
123 
thickened to form the medulla oblongata; its roof remains thin, and, retaining to 
a great extent its epithelial nature, is expanded in a lateral direction. Later, by 
the growth and backward extension of the cerebellum, the roof is folded inward 
toward the cavity of the fourth ventricle; it assists in completing the dorsal wall 
of this cavity, and is also invaginated to form the ependymal covering of its choroid 
plexuses. Above it is continuous with the posterior medullary velum; below, with 
the obex and ligulse. 
Taenia 
Optic stalk 
Rhombic lip 
V. N. Motor root 
V. N. Sensory root 
Ganglia of VII. and 
VIII. Ns. 
Obex 
Auditory vesicle 
Fig. 124.-Hind-brain of a human embryo of three 
months-viewed from behind and partly from left side. 
(From model by His.) 
Fig. 125.-Exterior of brain of human embryo of four 
and a half weeks. (From model by His.) 
The development of the medulla oblongata resembles that of the medulla spinalis, 
but at the same time exhibits one or two interesting modifications. On transverse 
section the myelencephalon at an early stage is seen to consist of two lateral walls, 
connected across the middle line by floor- and roof-plates (Figs. 122 and 123). 
Each lateral wall consists of an alar and a basal lamina, separated by an internal 
furrow, the remains of which are represented in the adult brain by the sulcus 
limitans on the rhomboid fossa. The contained cavity is more or less triangular 
in outline, the base being formed by the roof-plate, which is thin and greatly 
expanded transversely. Pear-shaped neuroblasts are developed in the alar and 
basal laminae, and their narrow stalks are elongated to form the axis-cylinders of 
the nerve fibres. Opposite the furrow or boundary between the alar and basal 
laminae a bundle of nerve fibres attaches itself to the outer surface of the alar 
lamina. This is named the tractus solitarius (Fig. 123), and is formed by the sensory 
fibres of the glossopharyngeal and vagus nerves. It is the homologue of the oval 
bundle seen in the medulla spinalis, and, like it, is developed by an ingrowth of 
fibres from the ganglia of the neural crest. At first it is applied to the outer surface 
of the alar lamina, but it soon becomes buried, owing to the growth over it of the 
neighboring parts. By the fifth week the dorsal part of the alar lamina bends 
in a lateral direction along its entire length, to form what is termed the rhombic 
lip (Figs. 123, 124). Within a few days this lip becomes applied to, and unites 124 
EMBRYOLOGY 
with, the outer surface of the main part of the alar lamina, and so covers in the 
tractus solitarius and also the spinal root of the trigeminal nerve; the nodulus 
and flocculus of the cerebellum are developed from the rhombic lip. 
Neuroblasts accumulate in the mantle layer; those in the basal lamina corre- 
spond with the cells in the anterior gray column of the medulla spinalis, and, like 
them, give origin to motor nerve fibres; in the medulla oblongata they are, however, 
arranged in groups or nuclei, instead of forming a continuous column. From the 
alar lamina and its rhombic lip, neuroblasts migrate into the basal lamina, and 
become aggregated to form the olivary nuclei, while many send their axis-cylinders 
through the floor-plate to the opposite side, and thus constitute the rudiment of 
the raphe of the medulla oblongata. By means of this thickening of the ventral 
portion, the motor nuclei are buried deeply in the interior, and, in the adult, are 
found close to the rhomboid fossa. This is still further accentuated: (a) by the 
development of the pyramids, which 
are formed about the fourth month 
by the downward growth of the 
motor fibres from the cerebral cortex; 
and (6) by the fibres which pass to 
and from the cerebellum. On the 
rhomboid fossa a series of six tem- 
porary furrows appears; these are 
termed the rhombic grooves. They 
bear a definite relationship to certain 
of the cerebral nerves; thus, from 
before backward the first and second 
grooves overlie the nucleus of the 
trigeminal; the third, the nucleus of 
the facial; the fourth, that of the ab- 
ducent; the fifth, that of the glosso- 
pharyngeal; and the sixth, that of 
the vagus. 
The pons is developed from the 
ventro-lateral wall of the meten- 
cephalon by a process similar to that 
which has been described for the 
medulla oblongata. 
The cerebellum is developed in 
the roof of the anterior part of 
the hind-brain (Figs. 124 to 129). 
The alar laminae of this region 
become thickened to form two 
lateral plates which soon fuse in the middle line and produce a thick lamina which 
roofs in the upper part of the cavity of the hind-brain vesicle; this constitutes 
the rudiment of the cerebellum, the outer surface of which is originally smooth 
and convex. The fissures of the cerebellum appear first in the vermis and floccular 
region, and traces of them are found during the third month; the fissures on the 
cerebellar hemispheres do not appear until the fifth month. The primitive fissures 
are not developed in the order of their relative size in the adult-thus the hori- 
zontal sulcus in the fifth month is merely a shallow groove. The best marked 
of the early fissures are: (a) the fissura prima between the developing culmen and 
declive, and (6) the fissura secunda between the future pyramid and uvula. The 
flocculus and nodule are developed from the rhombic lip, and are therefore recog- 
nizable as separate portions before any of the other cerebellar lobules. The 
groove produced by the bending over of the rhombic lip is here known as the 
Optic stalk 
Ganglia of VII. 
and VIII. Ns. 
Auditory vesicle 
Fig. 126.-Brain of human embryo of four and a half weeks, 
showing interior of fore-brain. (From model by Ris.) DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
125 
floccular fissure; when the two lateral walls fuse, the right and left floccular fissures 
join in the middle line and their central part becomes the post-nodular fissure. 
On the ventricular surface of the cerebellar lamina a transverse furrow, the 
incisura fastigii, appears, and deepens to form the tent-like recess of the roof of the 
fourth ventricle. The rudiment of the cerebellum at first projects in a dorsal 
direction; but, by the backward growth of the cerebrum, it is folded downward and 
somewhat flattened, and the thin roof-plate of the fourth ventricle, originally 
continuous with the posterior border of the cerebellum, is projected inward toward 
the cavity of the ventricle. 
The Mesencephalon or Mid-brain.-The mid-brain (Figs. 125 to 129) exists for a 
time as a thin-walled cavity of some size, and is separated from the isthmus rhom- 
encephali behind, and from the fore-brain in front, by slight constrictions. Its 
cavity becomes relatively reduced in diameter, and forms the cerebral aqueduct 
of the adult brain. Its basal laminae increase in thickness to form the cerebral 
peduncles, which are at first of small size, but rapidly enlarge after the fourth month. 
Ganglion habenulce 
Optic s'alk 
Hypophysis cerebri 
Fig. 127.-Exterior of brain of human embryo of five weeks. (From model by His.) 
The neuroblasts of these laminae are grouped in relation to the sides and floor 
of the cerebral aqueduct, and constitute the nuclei of the oculomotor and trochlear 
nerves, and of the mesencephalic root of the trigeminal nerve. By a similar 
thickening process its alar laminae are developed into the quadrigeminal lamina. 
The dorsal part of the wall for a time undergoes expansion, and presents an internal 
median furrow and a corresponding external ridge; these, however, disappear, 
and the latter is replaced by a groove. Subsequently two oblique furrows extend 
medialward and backward, and the thickened lamina is thus subdivided into the 
superior and inferior colliculi. 
The Prosencephalon or Fore-brain.-A transverse section of the early fore-brain 
shows the same parts as are displayed in similar sections of the medulla spinalis 
and medulla oblongata, viz., a pair of thick lateral walls connected by thin floor- 
and roof-plates. Moreover, each lateral wall exhibits a division into a dorsal or 
alar and a ventral or basal lamina separated internally by a furrow termed the sulcus 126 
EMBRYOLOGY 
of Monro. This sulcus ends anteriorly at the medial end of the optic stalk, and in 
the adult brain is retained as a slight groove extending backward from the inter- 
ventricular foramen to the cerebral aqueduct. 
At a very early period-in some animals before the closure of the cranial part of 
the neural tube-two lateral diverticula, the optic vesicles, appear, one on either 
side of the fore-brain; for a time they communicate with the cavity of the fore-brain 
by relatively wide openings. The peripheral parts of the vesicles expand, while 
the proximal parts are reduced to tubular stalks, the optic stalks. The optic vesicle 
gives rise to the retina and the epithelium on the back of the ciliary body and iris; 
the optic stalk is invaded by nerve fibres to form the optic nerve. The fore-brain 
then grows forward, and from the alar laminae of this front portion the cerebral 
hemispheres originate as diverticula which rapidly expand to form two large 
pouches, one on either side. The cavities of these diverticula are the rudiments of 
the lateral ventricles; they communicate with the median part of the fore-brain 
cavity by relatively wide openings, which ultimately form the interventricular 
Choroidal fissure 
Hypophysis, 
Recessus infundibuli 
Corpus mamiliare 
Tuber cinereum 
Pontine 
flexure 
Fig. 128.-Interior of brain of human embryo of five weeks. (From model by His.) 
Cervical flexure 
foramen. The median portion of the wall of the fore-brain vesicle consists of a 
thin lamina, the lamina terminalis (Figs. 129, 132), which stretches from the 
interventricular foramen to the recess at the base of the optic stalk. The 
anterior part of the fore-brain, including the rudiments of the cerebral hemi- 
spheres, is named the telencephalon, and its posterior portion is termed the 
diencephalon; both of these contribute to the formation of the third ventricle. 
The Diencephalon.-From the alar lamina of the diencephalon, the thalamus, 
metathalamus, and epithalamus are developed. The thalamus (Figs. 125 to 129) 
arises as a thickening which involves the anterior two-thirds of the alar lamina. 
The two thalami are visible, for a time, on the surface of the brain, but are subse- 
quently hidden by the cerebral hemispheres which grow backward over them. 
The thalami extend medialward and gradually narrow the cavity between them 
into a slit-like aperture which forms the greater part of the third ventricle; their 
medial surfaces ultimately adhere, in part, to each other, and the intermediate DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
127 
mass of the ventricle is developed across the area of contact. The metathalamus 
comprises the geniculate bodies which originate as slight outward bulgings of the 
alar lamina. In the adult the lateral geniculate body appears as an eminence on 
the lateral part of the posterior end of the thalamus, while the medial is situated 
on the lateral aspect of the mesencephalon. The epithalamus includes the pineal 
body, the posterior commissure, and the trigonum habenulae. The pineal body 
arises as an upward evagination of the roof-plate immediately in front of the mid- 
brain; this evagination becomes solid with the exception of its proximal part, 
which persists as the recessus pinealis. In lizards the pineal evagination is elongated 
into a stalk, and its peripheral extremity is expanded into a vesicle, in which a 
rudimentary lens and retina are formed; the stalk becomes solid and nerve fibres 
make their appearance in it, so that in these animals the pineal body forms a 
rudimentary eye. The posterior commissure is formed by the ingrowth of fibres 
into the depression behind and below the pineal evagination, and the trigonum 
habenulae is developed in front of the pineal recess. 
Choroidal fissure 
Rhinent'j^jhalon 
Lamina terminalis 
Corpus striatum 
Optic recess 
Chiasma 
Hypophysis 
Recessus infundibuli 
Fig. 129.-Median sagittal section of brain of human embryo of three months. (From model by His.) 
From the basal laminae of the diencephalon the pars mamillaria hypothalami 
is developed; this comprises the corpora mamillaria and the posterior part of the 
tuber cinereum. The corpora mamillaria arise as a single thickening, which 
becomes divided into two by a median furrow during the third month. 
The roof-plate of the diencephalon, in front of the pineal body, remains thin and 
epithelial in character, and is subsequently invaginated by the choroid plexuses 
of the third ventricle. 
The Telencephalon.-This consists of a median portion and two lateral diver- 
ticula. The median portion forms the anterior part of the cavity of the third 
ventricle, and is closed below and in front by the lamina terminalis. The lateral 
diverticula consist of outward pouchings of the alar laminae; the cavities represent 
the lateral ventricles, and their walls become thickened to form the nervous 128 
EMBRYOLOGY 
matter of the cerebral hemispheres. The roof-plate of the telencephalon remains 
thin, and is continuous in front with the lamina terminalis and behind with the 
roof-plate of the diencephalon. In the basal laminse and floor-plate the pars 
optica hypothalami is developed; this comprises the anterior part of the tuber 
cinereum, the infundibulum and posterior lobe of the hypophysis, and the optic 
chiasma. The anterior part of the tuber cinereum is derived from the posterior 
part of the floor of the telencephalon; the infundibulum and posterior lobe of the 
hypophysis arise as a downward diverticulum from the floor. The most dependent 
part of the diverticulum becomes solid and forms the posterior lobe of the hypo- 
physis; the anterior lobe of the hypophysis is developed from a diverticulum of the 
ectodermal lining of the stomodeum (page 166). The optic chiasma is formed 
by the meeting and partial decussation of the optic nerves, which subsequently 
grow backward as the optic tracts and end in the diencephalon. 
The cerebral hemispheres arise as diverticula of the alar laminae of the telen- 
cephalon (Figs. 125 to 129); they increase rapidly in size and ultimately overlap 
the structures developed from the mid- and hind-brains. This great expansion 
of the hemispheres is a char- 
acteristic feature of the brains 
of mammals, and attains its 
maximum development in 
the brain of man. Elliott- 
Smith divides each cerebral 
hemisphere into three funda- 
mental parts, viz., the rhinen- 
cephalon, the corpus striatum, 
and the neopallium. 
The rhinencephalon (Fig. 
130) represents the oldest 
part of the telencephalon, 
and forms almost the whole 
of the hemisphere in fishes, 
amphibians, and reptiles. In 
man it is feebly developed 
in comparison with the rest 
of the hemisphere, and com- 
prises the following parts, 
viz., the olfactory lobe (con- 
sisting of the olfactory tract and bulb and the trigonum olfactorium), the anterior 
perforated substance, the septum pellucidum, the subcallosal, supracallosal, and 
dentate gyri, the fornix, the hippocampus, and the uncus. The rhinencephalon 
appears as a longitudinal elevation, with a corresponding internal furrow, on the 
under surface of the hemisphere close to the lamina terminalis; it is separated 
from the lateral surface of the hemisphere by a furrow, the external rhinal fissure, 
and is continuous behind with that part of the hemisphere, which will ultimately 
form the anterior end of the temporal lobe. The elevation becomes divided by 
a groove into an anterior and a posterior part. The anterior grows forward as 
a hollow stalk the lumen of which is continuous with the anterior part of the ven- 
tricular cavity. During the third month the stalk becomes solid and forms the 
rudiment of the olfactory bulb and tract; a strand of gelatinous tissue in the interior 
of the bulb indicates the position of the original cavity. From the posterior part the 
anterior perforated substance and the pyriform lobe are developed; at the begin- 
ning of the fourth month the latter forms a curved elevation continuous behind 
with the medial surface of the temporal lobe, and consisting, from before backward, 
of the gyrus olfactorius lateralis, gyrus ambiens, and gyrus semilunaris, parts which 
Gyr. olf. lai. 
Gyr. olf. med. 
Gyr. ambiens 
Gyr. diagonalis 
Gyr. semilunaris 
Cerebellum 
Olive 
Fig. 130.-Inferior surface of brain of embryo at beginning of fourth 
month. (From Kollmann.) DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
129 
in the adult brain are represented by the lateral root of the olfactory tract and the 
uncus. The position and connections of the remaining portions of the rhinen- 
cephalon are described with the anatomy of the brain. 
The corpus striatum (Figs. 126 and 128) appears in the fourth week as a triangular 
thickening of the floor of the telencephalon between the optic recess and the 
interventicular foramen, and continuous behind with the thalamic part of the 
diencephalon. It increases in size, and by the second month is seen as a swelling 
in the floor of the future lateral ventricle; this swelling reaches as far as the posterior 
end of the primitive hemisphere, and wdien this part of the hemisphere grows 
backward and downward to form the temporal lobe, the posterior part of the corpus 
striatum is carried into the roof of the inferior horn of the ventricle, where it is 
seen as the tail of the caudate nucleus in the adult brain. During the fourth and 
fifth months the corpus striatum becomes incompletely subdivided by the fibres of 
the internal capsule into two masses, an inner, the caudate nucleus, and an outer, 
the lentiform nucleus. In front, the corpus striatum is continuous with the anterior 
perforated substance; laterally it is confluent for a time with that portion of the 
wall of the vesicle which is developed into the insula, but this continuity is sub- 
sequently interrupted by the fibres of the external capsule. 
Falx cerebri 
Edge of grey cortical 
substance 
Edge of white substance 
Hippocampal fissure 
Cs. Corpus striatum. Th. Thalamus. 
Fig. 131.-Diagrammatic coronal section of brain to show relations of neopallium. (After His.) Cs. Corpus striatum. 
Th. Thalamus. 
The neopallium (Fig. 131) forms the remaining, and by far the greater, part of the 
cerebral hemisphere. It consists, at an early stage, of a relatively large, more or 
less hemispherical cavity-the primitive lateral ventricle-enclosed by a thin wall 
from which the cortex of the hemisphere is developed. The vesicle expands in all 
directions, but more especially upward and backward, so that by the third month 
the hemispheres cover the diencephalon, by the sixth they overlap the mid-brain, 
and by the eighth the hind-brain. 
The median lamina uniting the two hemispheres does not share in their expan- 
sion, and thus the hemispheres are separated by a deep cleft, the forerunner of 
the longitudinal fissure, and this cleft is occupied by a septum of mesodermal 
tissue which constitutes the primitive falx cerebri. Coincidently with the expan- 130 
EMBRYOLOGY 
sion of the vesicle, its cavity is drawn out into three prolongations which represent 
the horns of the future lateral ventricle; the hinder end of the vesicle is carried down- 
ward and forward and forms the inferior horn; the posterior horn is produced 
somewhat later, in association with the backward growth of the occipital lobe of 
the hemisphere. The roof-plate of the primitive fore-brain remains thin and of an 
epithelial character; it is invaginated into the lateral ventricle along the medial 
wall of the hemisphere. This invagination constitutes the choroidal fissure, and 
extends from the interventricular foramen to the posterior end of the vesicle. Mes- 
odermal tissue, continuous with that of the primitive falx cerebri, and carrying 
bloodvessels with it, spreads between the two layers of the invaginated fold and 
forms the rudiment of the tela choroidea; the margins of the tela become highly 
vascular and form the choroid plexuses which for some months almost completely 
fill the ventricular cavities; the tela at the same time invaginates the epithelial 
roof of the diencephalon to form the choroid plexuses of the third ventricle. By 
the downward and forward growth of the posterior end of the vesicle to form the 
temporal lobe the choroidal fissure finally reaches from the interventricular fora- 
men to the extremity of the inferior horn of the ventricle. 
Choroidal fissure 
Gyrus dentatus 
Taenia thalami 
Thalamus 
Corpus callosum 
Post, commissure 
Septum pellucidum 
Anterior commissure 
Corpora quadrigemina 
Cerebral aqueduct 
Lamina terminals 
Cerebral peduncle 
Cerebellum 
Optic chiasmo. 
Rhinencephalon 
III. ventricle 
Pons 
Hypophysis 
IV. ventricle 
Medulla oblongata 
Parallel with but above and in front of the choroidal fissure the medial wall of 
the cerebral vesicle becomes folded outward and gives rise to the hippocampal 
fissure on the medial surface and to a corresponding elevation, the hippocampus, 
within the ventricular cavity. The gray or ganglionic covering of the wall of the 
vesicle ends at the inferior margin of the fissure is a thickened edge; beneath this 
the marginal or reticular layer (future white substance) is exposed and its lower 
thinned edge is continuous with the epithelial invagination covering the choroid 
plexus (Fig. 131). As a result of the later downward and forward growth of the 
temporal lobe the hippocampal fissure and the parts associated with it extend from 
the interventricular foramen to the end of the inferior horn of the ventricle. 
The thickened edge of gray substance becomes the gyrus dentatus, the fasciola 
cinerea and the supra- and subcallosal gyri, while the free edge of the white sub- 
stance forms the fimbria hippocampi and the body and crus of the fornix. The 
corpus callosum is developed within the arch of the hippocampal fissure, and the 
upper part of the fissure forms, in the adult brain, the callosal fissure on the medial 
surface of the hemisphere. 
Fig. 132.-Median sagittal section of brain of human embryo of four months. (Marchand.) DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
131 
The Commissures (Fig. 132).-The development of the posterior commissure 
has already been referred to (page 127). The great commisssures of the hemi- 
spheres, viz., the corpus callosum, the fornix, and anterior commissure, arise from 
the lamina terminalis. About the fourth month a small thickening appears in 
this lamina, immediately in front of the interventricular foramen. The lower 
part of this thickening is soon constricted off, and fibres appear in it to form 
the anterior commissure. The upper part continues to grow with the hemispheres, 
and is invaded by two sets of fibres. Transverse fibres, extending between the 
hemispheres, pass into its dorsal part, which is now differentiated as the corpus 
callosum (in rare cases the corpus callosum is not developed). Into the ventral 
part longitudinal fibres from the hippocampus pass to the lamina terminalis, and 
through that structure to the corpora mamillaria; these fibres constitute the fornix. 
A small portion, lying antero-inferiorly between the corpus callosum and fornix, 
is not invaded by the commissural fibres; it remains thin, and later a cavity, 
the cavity of the septum pellucidum, forms in its interior. 
Fissures and Sulci.-The outer surface of the cerebral hemisphere is at first smooth, 
but later it exhibits a number of elevations or convolutions, separated from each 
other by fissures and sulci, most of which 
make their appearance during the sixth 
or seventh months of fetal life. The 
term fissure is applied to such grooves as 
involve the entire thickness of the cere- 
bral wall, and thus produce correspond- 
ing eminences in the ventricular cavity, 
while the sulci affect only the superficial 
part of the wall, and therefore leave no 
impressions in the ventricle. The fissures 
comprise the choroidal and hippocampal 
already described, and two others, viz., 
the calcarine and collateral, which pro- 
duce the swellings known respectively 
as the calcar avis and the collateral 
eminence in the ventricular cavity. Of 
the sulci the following may be referred 
to, viz., the central sulcus (fissure of 
Rolando), which is developed in two 
parts; the intraparietal sulcus in four 
parts; and the cingulate sulcus in two 
or three parts. The lateral cerebral or Sylvian fissure differs from all the other 
fissures in its mode of development. It appears about the third month as a depres- 
sion, the Sylvian fossa, on the lateral surface of the hemisphere (Fig. 133); this 
fossa corresponds with the position of the corpus striatum, and its floor is moulded 
to form the insula. The intimate connection which exists between the cortex 
of the insula and the subjacent corpus striatum prevents this part of the hemis- 
phere wall from expanding at the same rate as the portions which surround it. 
The neighboring parts of the hemisphere therefore gradually grow over and cover 
in the insula, and constitute the temporal, parietal, frontal, and orbital opercula 
of the adult brain. The frontal and orbital opercula are the last to form, but by the 
end of the first year after birth the insula is completely submerged by the approxi- 
mation of the opercula. The fissures separating the opposed margins of the oper- 
cula constitute the composite lateral cerebral fissure. 
If a section across the wall of the hemisphere about the sixth week be examined 
microscopically it will be found to consist of a thin marginal or reticular layer, a 
thick ependymal layer, and a thin intervening mantle layer. Neuroblasts from the 
Parietal 
operculum 
Temporal operculum 
Frontal operculum 
Sylvian fossa 
Fig. 133.-Outer surface of cerebral hemisphere of 
human embryo of about five months. 132 
EMBRYOLOGY 
ependymal and mantle layers migrate into the deep part of the marginal layer and 
form the cells of the cerebral cortex. The nerve fibres which form the underlying 
white substance of the hemispheres consist at first of outgrowths from the cells of 
the corpora striata and thalami; later the fibres from the cells of the cortex are 
added. Medullation of these fibres begins about the time of birth and continues 
until puberty. 
A summary of the parts derived from the brain vesicles is given in the following 
table: 
Medulla oblongata 
Lower part of fourth 
ventricle. 
1. Myelencephalon 
Pons 
Cerebellum 
Intermediate part of fourth 
ventricle. 
Rhombencephalon 
or Hind-brain 
2. Metencephalon 
Anterior medullary velum 
Brachia conjunctiva 
cerebelli. 
Upper part of fourth 
ventricle. 
3. Isthmus rhomb- 
[ encephali 
Cerebral peduncles 
Lamina quadrigemina 
Cerebral aqueduct. 
Mesencephalon or Mid-brain 
Thalamus 
Metathalamus 
Epithalamus 
Pars mamillaria hypo- 
thalami 
Posterior part of third 
ventricle. 
1. Diencephalon 
Prosencephalon or 
Fore-brain 
Anterior part of third 
ventricle 
Pars optica hypo- 
thalami 
Cerebral hemispheres 
Lateral ventricles 
Interventricular foramen. 
2. Telencephalon 
The Cerebral Nerves.-With the exception of the olfactory, optic, and acoustic 
nerves, which will be especially considered, the cerebral nerves are developed in a 
similar manner to the spinal nerves (see page 119). The sensory or afferent nerves 
are derived from the cells of the ganglion rudiments of the neural crest. The cen- 
tral processes of these cells grow into the brain and form the roots of the nerves, 
while the peripheral processes extend outward and constitute their fibres of dis- 
tribution (Fig. 120). It has been seen, in considering the development of the 
medulla oblongata (page 123), that the tractus solitarius (Fig. 135), derived from 
the fibres which grow inward from the ganglion rudiments of the glossopharyn- 
geal and vagus nerves, is the homologue of the oval bundle in the cord which had 
its origin in the posterior nerve roots. The motor or efferent nerves arise as out- 
growths of the neuroblasts situated in the basal laminae of the mid- and hind- 
brain. While, however, the spinal motor nerve roots arise in one series from the 
basal lamina, the cerebral motor nerves are grouped into two sets, according as 
they spring from the medial or lateral parts of the basal lamina. To the former 
set belong the oculomotor, trochlear, abducent, and hypoglossal nerves; to the DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
133 
latter, the accessory and the motor fibres of the trigeminal, facial, glossopharyn- 
geal, vagus nerves (Figs. 134, 135). 
The Sympathetic System.-The ganglion cells of the sympathetic system are 
derived from the cells of the neural crests. As these crests move forward along 
the sides of the neural tube and become segmented off to form the spinal ganglia, 
certain cells detach themselves from 
the ventral margins of the crests 
and migrate toward the sides of the 
aorta, where some of them are 
grouped to form the ganglia of the 
sympathetic trunks, while others 
undergo a further migration and 
form the ganglia of the prevertebral 
and visceral plexuses. The ciliary, 
sphenopalatine, otic, and submax- 
illary ganglia which are found on 
the branches of the trigeminal nerve 
are formed by groups of cells which 
have migrated from the part of 
the neural crest which gives rise 
to the semilunar ganglion. Some 
of the cells of the ciliary ganglion 
are said to migrate from the 
neural tube along the oculomotor 
nerve. 
Chromaffin Organs.-The tissue from which the sympathetic ganglia are formed 
is at first a syncytium of cells termed sympatho-chromaffin cells, but later two 
kinds of cells become differentiated from it; the smaller cells (sympathoblasts) 
are transformed into the sympathetic nerve cells, the larger become chromaffin 
cells, and, separating from the others, accumulate to form the chromaffin organs. 
■Roof-plate 
Alar lamina 
Furrow between 
alar and basal 
lamince 
-Basal lamina 
Vagus nerve 
Fig. 134.-Transverse section of medulla oblongata of 
human embryo. X 32. (Kollmann.) 
s Hypoglossal nerve 
Floor-plate 
Roof-plate 
Alar lamina - 
Rhombic lip 
Basal lamina 
Tr actus 
solitarius 
Vagus nerve 
Hypoglossal nerve 
Floor-plate 
Fig. 135.-Transverse section of medulla oblongata of human embryo. (After His.) 
In the gangliated trunk of the sympathetic the chromaffin bodies are situated in 
depressions in the ganglia. In connection with certain, but not all, of the secondary 
plexuses of the sympathetic system chromaffin organs are found; the largest mem- 
bers of this series are the aortic bodies, which lie along the sides of the abdominal 
aorta between the superior mesenteric and common iliac arteries; to this group 134 
EMBRYOLOGY 
belong also the carotid skeins. After birth the chromaffin organs degenerate 
and can no longer be isolated by gross dissection, but chromaffin tissue can be 
recognized with the microscope in the sites originally occupied by them. 
The Suprarenal Glands.-Each suprarenal gland consists of a cortical portion 
derived from the coelomic epithelium and a medullary portion originally composed 
of sympatho-chromaffin tissue. The cortical portion is first recognizable about 
Pigmented layer of retina 
Cavity of fore-brain 
Invagination of 
ectoderm to form ■ 
lens rudiment 
Margin of optic cup 
Nervous layer of retina 
Optic vesicle 
Fig. 136.-Transverse section of head of chick embryo of forty-eight hours' incubation. (Duval.) 
the beginning of the fourth week as a series of buds from the coelomic cells at the root 
of the mesentery. Later it becomes completely separated from the coelomic 
epithelium and forms a suprarenal ridge projecting into the coelom between the 
mesonephros and the root of the mesentery. Into this cortical portion cells from 
the neighboring masses of sympatho-chromaffin tissue migrate along the line of 
its central vein to reach and form the medullary portion of the gland. 
The Nose.-The development of 
the nose has already been con- 
sidered (pagesill, 112). 
The olfactory nerves are developed 
from the cells of the ectoderm which 
lines the olfactory pits; these cells 
undergo proliferation and give rise 
to what are termed the olfactory 
cells of the nose. The axons of the 
olfactory cells grow into the over- 
lying olfactory bulb and form the 
olfactory nerves. 
The Eye.-The eyes begin to 
develop as a pair of diverticula 
from the lateral aspects of the fore- 
brain. These diverticula make their 
appearance before the closure of the 
anterior end of the neural tube; 
after the closure of the tube they are 
known as the optic vesicles. They project toward the sides of the head, and the 
peripheral part of each expands to form a hollow bulb, while the proximal part 
remains narrow and constitutes the optic stalk (Figs. 136, 137). The ectoderm 
overlying the bulb becomes thickened, invaginated, and finally severed from the 
ectodermal covering of the head as a vesicle of cells, the lens vesicle, which con- 
stitutes the rudiment of the crystalline lens. The outer wall of the bulb becomes 
thickened and invaginated, and the bulb is thus converted into a cup, the optic cup, 
Cavity of fore-brain 
Pigmented layer 
of retina 
Ectoderm 
Lens 
Nervous layer of 
retina 
Fig. 137.-Transverse section of head of chick embryo of 
fifty-two hours' incubation. (Duval.) 
Optic stalk DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
135 
consisting of two strata of cells (Fig. 137). These two strata are continuous with 
each other at the cup margin, which ultimately overlaps the front of the lens and 
reaches as far forward as the future aperture of the pupil. The invagination is not 
limited to the outer wall of the bulb, but involves also its postero-inferior surface 
and extends in the form of a groove for some distance along the optic stalk, so that, 
for a time, a gap or fissure, the choroidal fissure, exists in the lower part of the 
cup (Fig. 138). Through the groove and fissure the mesoderm extends into the 
optic stalk and cup, and in this mesoderm a bloodvessel is developed; during the 
seventh week the groove and fissure are closed and the vessel forms the central 
artery of the retina. Sometimes the choroidal fissure persists, and when this 
occurs the choroid and iris in the region of the fissure remain undeveloped, giving 
rise to the condition known as coloboma of the choroid or iris. 
Telencephalon 
Edge of optic cup 
Thalamencephalon 
Choroidal fissure 
Optic stalk 
Arteria centralis 
retinae 
Fig. 138.-Optic cup and choroidal fissure seen from below, from a human embryo of about four weeks. 
(Kollmann.) 
The retina is developed from the optic cup. The outer stratum of the cup 
persists as a single layer of cells which assume a columnar shape, acquire pigment, 
and form the pigmented layer of the retina; the pigment first appears in the cells 
near the edge of the cup. The cells of the inner stratum proliferate and form a 
layer of considerable thickness from which the nervous elements and the susten- 
tacular fibres of the retina, together with a portion of the vitreous body, are 
developed. In that portion of the cup which overlaps the lens the inner stratum is 
not differentiated into nervous elements, but forms a layer of columnar cells which 
is applied to the pigmented layer, and these two strata form the pars ciliaris and 
pars iridica retinae. 
The cells of the inner or retinal layer of the optic cup become differentiated into spongioblasts 
and germinal cells, and the latter by their subdivisions give rise to neuroblasts. From the spongio- 
blasts the sustentacular fibres of Muller, the outer and inner limiting membranes, together with 
the groundwork of the molecular layers of the retina are formed. The neuroblasts become 
arranged to form the ganglionic and nuclear layers. The layer of rods and cones is first developed 
in the central part of the optic cup, and from there gradually extends toward the cup margin. 
All the layers of the retina are completed by the eighth month of fetal life. 
The optic stalk is converted into the optic nerve by the obliteration of its cavity 
and the growth of nerve fibres into it. Most of these fibres are centripetal, and 
grow backward into the optic stalk from the nerve cells of the retina, but a few 
extend in the opposite direction and are derived from nerve cells in the brain. The 
fibres of the optic nerve receive their medullary sheaths about the tenth week after 136 
EMBRYOLOGY 
birth. The optic chiasma is formed by the meeting and partial decussation of the 
fibres of the two optic nerves. Behind the chiasma the fibres grow backward as 
the optic tracts to the thalami and mesencephalon. 
The crystalline lens is developed from the lens vesicle, which recedes within the 
margin of the cup, and becomes separated from the overlying ectoderm by mes- 
oderm. The cells forming the posterior wall of the vesicle lengthen and are con- 
verted into the lens fibres, which grow forward and fill up the cavity of the vesicle 
(Fig. 139). The cells forming the anterior wall retain their cellular character, and 
form the epithelium on the anterior surface of the adult lens. By the second month 
the lens is invested by a vascular mesodermal capsule, the capsula vasculosa lentis; 
the bloodvessels supplying the posterior part of this capsule are derived from the 
hyaloid artery; those for the anterior part from the anterior ciliary arteries; the 
portion of the capsule which covers the front of the lens is named the pupillary 
Rudiment of choroid 
Rectus muscle - 
Optic nerve 
Eyelid 
Lens 
Pigmented layer 
Vitreous body 
{shrunken) 
Retina 
-Cornea 
Membrana pupillaris 
-Eyelid 
Iris 
Fig. 139.-Horizontal section through the eye of an eighteen days' embryo rabbit. X 30. (Kolliker.) 
Pars ciliaris and pars iridica retinae 
membrane. By the sixth month all the vessels of the capsule are atrophied except 
the hyaloid artery, which disappears during the ninth month; the position of this 
artery is indicated in the adult by the hyaloid canal, which reaches from the optic 
disk to the posterior surface of the lens. With the loss of its bloodvessels the cap- 
sula vasculosa lentis disappears, but sometimes the pupillary membrane persists 
at birth, giving rise to the condition termed congenital atresia of the pupil. 
The vitreous body is developed between the lens and the optic cup. The lens 
rudiment and the optic vesicle are at first in contact with each other, but after the 
closure of the lens vesicle and the formation of the optic cup the former withdraws 
itself from the retinal layer of the cup; the two, however, remain connected by a net- 
work of delicate protoplasmic processes. This network, derived partly from the cells 
of the lens and partly from those of the retinal layer of the cup, constitutes the 
primitive vitreous body (Figs. 140, 141). At first these protoplasmic processes 
spring from the whole of the retinal layer of the cup, but later are limited to the DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
137 
ciliary region, where by a process of condensation they appear to form the zonula 
ciliaris. The mesoderm which enters the cup through the choroidal fissure and 
around the equator of the lens becomes intimately united with this reticular tissue, 
and contributes to form the vitreous body, which is therefore derived partly from 
the ectoderm and partly from the mesoderm. 
Upper eyelid 
Pigmented 
layer of 
retina 
Mesodermal 
part of 
vitreous body 
Rudiment 
of sclera 
Mesoderm 
Ectodermal 
part of 
vitreous body 
Nervous layer 
of retina 
Fig. 140.-Sagittal section of eye of human embryo of six weeks. (Kollmann.) 
The anterior chamber of the eye appears as a cleft in the mesoderm separating 
the lens from the overlying ectoderm. The layer of mesoderm in front of the cleft 
forms the substantia propria of the cornea, that behind the cleft the stroma of the 
iris and the pupillary membrane. The fibres of the ciliary muscle are derived from 
the mesoderm, but those of the Sphincter and Dilatator pupillae are of ectodermal 
origin, being developed from the cells of the pupillary part of the optic cup. 
The sclera and choroid are derived from the mesoderm surrounding the optic cup. 
The eyelids are formed as small cutaneous folds (Figs. 139, 140), which about 
the middle of the third month come together and unite in front of the cornea. 
They remain united until about the end of the sixth month. 
The lacrimal sac and nasolacrimal duct result from a thickening of the ectoderm 
in the groove, nasobptic furrows, between the lateral nasal and maxillary processes. 
This thickening forms a solid cord of cells which sinks into the mesoderm; during 
the third month the central cells of the cord break down, and a lumen, the naso- 
lacrimal duct, is established. The lacrimal ducts arise as buds from the upper part 138 
EMBRYOLOGY 
of the cord of cells and secondarily establish openings (puncta lacrimalia) on the 
margins of the lids. The epithelium of the cornea and conjunctiva, and that which 
lines the ducts and alveoli of the lacrimal gland, are of ectodermal origin, as are 
also the eyelashes and the lining cells of the glands which open on the lid-margins. 
Lens 
Blood-vessel 
Primitive 
vitreous 
body 
Retina 
Outer layer of 
optic cup 
Fig 141.-Section of developing eye of trout. (Szily.) 
The Ear.-The first rudiment of the internal ear appears shortly after that of 
the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the 
region of the hind-brain. The auditory plate becomes depressed and converted 
into the auditory pit (Fig. 142). The mouth of the pit is then closed, and thus a shut 
sac, the auditory vesicle, is formed (Fig. 143); from it the epithelial lining of the 
Cavity of hind-brain 
Hind-brain 
Auditory pit 
Auditory 
vesicle 
Ectoderm 
Notochord 
Fig. 142.-Section through the head of a human 
embryo, about twelve days old, in the region of the 
hind brain. (Kollmann.) 
Fig. 143.-Section through hind brain and audi- 
tory vesiclesof an embryo more advanced than that 
of Fig. 142. (After His.) 
membranous labyrinth is derived. The vesicle becomes pear-shaped, and the neck 
of the flask is obliterated (Fig. 144). From the vesicle certain diverticula are given 
off which form the various parts of the membranous labyrinth. One from the 
middle part forms the ductus and saccus endolymphaticus, another from the 
anterior end gradually elongates, and, forming a tube coiled on itself, becomes the DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 
139 
cochlear duct, the vestibular extremity of which is subsequently constricted to form 
the canalis reuniens. Three others appear as disk-like evaginations on the surface 
of the vesicle; the central parts of the walls of the disks coalesce and disappear, 
while the peripheral portions persist to form the semicircular ducts; of these the 
Saccus 
endolymphaticus 
Lateral semicircular 
duct 
Ductus endo- 
lymphaticus 
Auditory vesicle 
Superior semi- 
circular duct ' 
Posterior semi- 
circular duct 
Fig. 144.-Left auditory vesicle of a human 
embryo of four weeks, seen from the outer 
surface. (W. His, Jr.) 
Fig. 145.-Left auditory vesicle of a human embryo of five 
weeks, seen from the outer surface. (W. His, Jr.) 
Rudiment of cochlear duct 
superior is the first and the lateral the last to be completed (Figs. 145, 146). The 
central part of the vesicle represents the membranous vestibule, and is subdivided 
by a constriction into a smaller ventral part, the saccule, and a larger dorsal and 
posterior part, the utricle. This subdivision is effected by a fold which extends 
D uctus endolymphaticus 
Superior semi- 
circular duct 
Utricle 
Saccule 
Ganglion 
cochleare 
Lateral semi- 
circular duct 
.Ductus cochlearis 
Fig. 146.-Transverse section through head of fetal sheep, in the region of the labyrinth. X 30. (After Boettcher.) 
deeply into the proximal part of the ductus endolymphaticus, with the result that 
the utricle and saccule ultimately communicate with each other by means of a 
Y-shaped canal. The saccule opens into the cochlear duct, through the canalis 
reuniens, and the semicircular ducts communicate with the utricle (Fig. 147). 140 
EMBRYOLOGY 
The mesodermal tissue surrounding the various parts of the epithelial labyrinth 
is converted into a cartilaginous ear-capsule, and this is finally ossified to form the 
bony labyrinth. Between the cartilaginous capsule and the epithelial structures 
is a stratum of mesodermal tissue which is differentiated into three layers, viz., 
Canalis 
reuniens 
Fig. 147.-Left membranous labyrinth of a human embryo of 30 mm. (From model by W. His, Jr.) 
an outer, forming the periosteal lining of the bony labyrinth; an inner, in direct 
contact with the epithelial structures; and an intermediate, consisting of gelatinous 
tissue: by the absorption of this latter tissue the perilymphatic spaces are developed. 
The modiolus and osseous spiral lamina of the cochlea are not preformed in cartil- 
age but are ossified directly from connective tissue. 
Cochlear nerve 
Scala 
vestibuli 
Ganglion spirale 
Embryonic connective 
tissue 
Vestibular 
membrane 
Embryonic 
connective tissue 
Limbus spiralis 
Cochlear duct 
Scala tympani 
Ligamentum spirals 
Epithelium of the spiral 
organ of Corti 
Fig. 148.-Transverse section of the cochlear duct of a fetal cat. (After Boettcher and Ayres.) 
The middle ear and auditory tube are developed from the first pharyngeal pouch. 
The entodermal lining of the dorsal end of this pouch is in contact with the ecto- 
derm of the corresponding pharyngeal groove; by the extension of the mesoderm 
between these two layers the tympanic membrane is formed. During the sixth or DEVELOPMENT OF THE VASCULAR SYSTEM 
141 
seventh month the tympanic antrum appears as an upward and backward expan- 
sion of the tympanic cavity. With regard to the exact mode of development of 
the ossicles of the middle ear there is some difference of opinion. The view generally 
held is that the incus and malleus are developed from the proximal end of the 
mandibular (Meckel's) cartilage (Fig. 105) and that the stapes is formed from the 
proximal end of the second arch. The malleus, with the exception of its anterior 
process, is ossified from a single centre which appears near the neck of the bone; 
the anterior process is ossified separately in membrane and joins the main part 
of the bone about the sixth month of fetal life. The incus is ossified from one centre 
which appears in the upper part of its long crus and ultimately extends into its 
lenticular process. The stapes first appears as a ring {annulus stapedius) encircling 
a small vessel, the stapedial artery, which subsequently undergoes atrophy; it is 
ossified from a single centre which appears in its base. 
The external acoustic meatus is developed from the first branchial groove. The 
lower part of this groove extends inward as a funnel-shaped tube (primary meatus) 
from which the cartilaginous portion and a small part of the roof of the osseous 
portion of the meatus are developed. From the lower part of the funnel-sliaped 
tube an epithelial lamina extends downward 
and inward along the inferior wall of the 
primitive tympanic cavity; by the splitting of 
this lamina the inner part of the meatus (sec- 
ondary meatus) is produced, while the inner 
portion of the lamina forms the cutaneous 
stratum of the tympanic membrane. The 
auricula or pinna is developed by the gradual 
differentiation of six tubercles (Fig. 149) which 
appear around the margin of the first branchial 
groove. Two tubercles appear on the posterior 
edge of the mandibular arch; these represent 
the rudiments of the tragus and crus helicis. 
Three are found on the hyoid arch, and indi- 
cate, from below upward, the lobule, antitragus, 
and antihelix. One arises above the groove, 
and grows downward behind the antitragus 
and antihelix; from it and its downward pro- 
longation the upper part of the helix and the 
cauda helicis are developed (Figs. 150, 151). 
Some observers, however, maintain that the lowest tubercle on the hyoid arch 
becomes the antitragus, and that the lobule is developed later as an independent 
formation. The rudiment of the acoustic nerve appears about the end of the third 
week as a group of ganglion cells closely applied to the cephalic edge of the audi- 
tory vesicle. Whether these cells are derived from the ectoderm adjoining the 
auditory vesicle, or have migrated from the wall of the neural tube, is as yet un- 
certain. Each cell gives off a proximal fibre which passes into the neural tube, 
and a distal which is distributed to the epithelial cells of the auditory vesicle. 
Mandibular arch 
Maxillary process 
Fig. 149.-Tubercles from which the different 
parts of the auricula are developed. (His.) 
1, 2. Tubercles on mandibular arch. 3. Tuber- 
cle above cleft. 3, c. Prolongation of 3 down- 
ward. 4, 5, 6. Tubercles on hyoid arch. o.v. 
Auditory vesicle. 
DEVELOPMENT OF THE VASCULAR SYSTEM 
Bloodvessels first make their appearance in several scattered vascular areas 
(Fig. 152) which are developed simultaneously between the entoderm and the meso- 
derm of the yolk-sac, i. e., outside the body of the embryo.1 Here the cells become 
1 No definite statement can be made as to whether the earliest vessels are derived from the entoderm of the yolk- 
sac or from the mesoderm overlying it; the most recent view favors the entoderm as the original source of the blood 
corpuscles and endothelium of the vessels. 142 
EMBRYOLOGY 
arranged into solid strands or cords which join to form a close-meshed network, the 
area vasculosa, which covers the whole yolk-sac. The peripheral cells of these 
Helix 
Crus helicis 
Helix 
Antihelix 
Crus helicis 
Antihelix 
Tragus 
Antitragus 
Antitragus 
Mandible. 
Lobule 
Tragus 
Mandible 
Lobule 
Fig. 150.-Left auriculae of human embryos estimated at thirty-five and thirty-eight days respectively.' 
(After His.) 
strands become flattened and joined to each other by their edges to form the endo- 
thelium of the walls of the primitive bloodvessels. Fluid collects within the strands 
and converts them into tubes, and the more 
centrally situated cells of the cell-cords are thus 
pushed to the sides of the vessels and appear as 
masses of loosely arranged cells projecting toward 
the lumen of the tube. These masses are termed 
blood islands (Fig. 153); their cells are detached 
to form the blood corpuscles. The earliest blood- 
vessels, therefore, are formed at several separate 
centres; from the walls of these vessels buds grow 
out, become vascularized and converted into new 
vessels, and join with those of neighboring areas 
to form a close meshwork. It is uncertain whether 
the vessels within the body of the embryo are ex- 
tensions from this network (His) or whether they 
are of new formation. Most observers agree, 
however, that, after the aortse have appeared, 
no other independent vessels are laid down, i. e., all new vessels are derived from 
preexisting ones. 
Helix 
■Antihelix 
■Crus helicis 
Antitragus 
Lobule 
Tragus 
Fig. 151.-Auricula in a more advanced 
stage of development than those repre- 
sented in Fig. 150. 
Mandible 
Mesoderm 
Blood island 
Mesoderm 
Vascular cells 
Entoderm 
Endothelial wall 
of vessel 
Entoderm 
Fig. 152.-Section through vascular area to show differ- 
entiation of primitive vascular cells. Diagrammatic. 
Fig. 153.-Section through developing bloodvessel. 
Diagrammatic. 
The red and the colorless corpuscles of the blood are all derived from the nucleated 
cells of the blood islands-mes amoeboid cells of Minot-and the earliest blood 
corpuscles are thus all nucleated; they are also capable of subdivision and of DEVELOPMENT OF THE VASCULAR SYSTEM 
143 
executing amoeboid movements. Some of these cells acquire coloring matter 
(hemoglobin); their nuclei disintegrate and are expelled and the non-nucleated red 
corpuscles result. Other mesam- 
oeboid cells retain their nuclei; 
some remain in the blood as 
the leucocytes; others wander 
out into the tissues, particularly 
into the liver, lymphoid tissues, 
and marrow of the bones, where 
they form specialized masses 
from which the corpuscles of 
the blood are regenerated. From 
the mesamoeboid cells five chief 
forms are derived: (1) erythro- 
cytes, (2) lymphocytes, (3) finely 
granular or neutrophil leuco- 
cytes, (4) coarsely granular or 
eosinophil leucocytes, (5) degen- 
erating or basiphil leucocytes. 
The first rudiment of the heart 
appears as a pair of tubular 
vessels which are developed in 
the splanchnopleure of the peri- 
cardial area (Fig. 154). These 
are named the primitive aortas, 
and a direct continuity is soon 
established between them and 
the vessels of the yolk-sac. Each 
receives anteriorly a vein-the 
vitelline vein-from the yolk-sac, 
and is prolonged backward on 
the lateral aspect of the noto- 
chord under the name of the 
dorsal aorta. The dorsal aortae 
give branches to the yolk-sac, 
and are continued backward 
through the body-stalk as the 
umbilical arteries to the villi of 
the chorion. 
Eternod1 describes the circu- 
lation in an embryo which he 
estimated to be about thirteen 
days old (Fig. 155). The rudi- 
ment of the heart is situated 
immediately below the fore-gut 
and consists of a short stem. It 
gives off two vessels, the primi- 
tive aortae, which run backward, 
one on either side of the noto- 
chord, and then pass into the 
body-stalk along which they are carried to the chorion. From the chorionic villi 
the blood is returned by a pair of umbilical veins which unite in the body-stalk 
Fig. 154.-Transverse section through the region of the heart in 
a rabbit embryo of nine days. X 80. (Kolliker.) j, j. Jugular 
veins, ao. Aorta, ph. Pharynx, som. Somatopleure. bl. Proamnion. 
ect. Ectoderm, ent. Entoderm, p. Pericardium, spl. Splanchno- 
pleure. ah. Outer wall of heart, ih. Endothelial lining of heart, e'. 
Septum between heart tubes. 
Heart-tubes 
Umbilical 
vein 
Umbilical 
vein 
Neur enteric 
canal 
Allantoic 
diverticulum 
Body-stalk- 
Fig. 155.-Diagram of the vascular channels in a human embryo 
of the second week. (After Eternod.) The red lines are the dorsal 
aortse continued into the umbilical arteries. The red dotted lines 
are the ventral aortse, and the blue dotted lines the vitelline veins. 
Anat. Anzeiger, 1899, vol. xv. 144 
EMBRYOLOGY 
to form a single vessel and subsequently encircle the mouth of the yolk-sac and 
open into the heart. At the junction of the yolk-sac and body-stalk each vein 
is joined by a branch from the vascular plexus of the yolk-sac. From his 
observations it seems that, in the human embryo, the chorionic circulation is 
established before that on the yolk-sac. 
Dorsal aorta 
Primitive •jugular 
vein 
Amnion 
Cardinal vein 
Dorsal aorta 
Body-stalk 
Chorionic villi- 
Fig. 156.-Human embryo of about fourteen days old with yolk-sac. (After His.) 
By the forward growth and flexure of the head the pericardial area and the 
anterior portions of the primitive aortse are folded backward on the ventral aspect 
of the fore-gut, and the original relation of the somatopleure and splanchnopleure 
Fore-brain 
Optic vesicle 
Bulbus cordis 
A trium 
Ventricle 
Vitelline vein 
Fig. 157.-Head of chick embryo of about thirty-eight hours' incubation, viewed from the ventral surface. X 26,. 
(Duval.) 
layers of the pericardial area is reversed. Each primitive aorta now consists of 
a ventral and a dorsal part connected anteriorly by an arch (Fig. 156); these three 
parts are named respectively the anterior ventral aorta, the dorsal aorta, and the 
first cephalic arch. The vitelline veins which enter the embryo through the DEVELOPMENT OF THE VASCULAR SYSTEM 
145 
anterior wall of the umbilical orifice are now continuous with the posterior ends of 
the anterior ventral aorta. With the formation of the tail-fold the posterior parts 
of the primitive aortae are carried forward in a ventral direction to form the pos- 
terior ventral aortae and primary caudal arches.1 In the pericardial region the two 
primitive aortae grow together, and fuse to form a single tubular heart (Fig. 157), 
the posterior end of which receives the two vitelline veins, while from its anterior 
end the two anterior ventral aortae emerge.2 The first cephalic arches pass through 
the mandibular arches, and behind them five additional pairs subsequently develop, 
so that altogether six pairs of aortic arches are formed; the fifth arches are very 
transitory vessels connecting the ventral aortae with the dorsal ends of the sixth 
arches. By the rhythmical contraction of the tubular heart the blood is forced 
through the aortae and bloodvessels of the vascular area, from which it is returned 
to the heart by the vitelline veins. This constitutes the vitelline circulation (Fig. 
156), and by means of it nutriment is absorbed from the yolk vitellus. 
The vitelline veins at first open separately into the posterior end of the tubular 
heart, but after a time their terminal portions fuse to form a single vessel. The 
vitelline veins ultimately drain the blood from the digestive tube, and are modified 
to form the portal vein. This is caused by the growth of the liver, which interrupts 
their direct continuity with the heart; and the blood returned by them circulates 
through the . liver before reaching the heart. 
With the atrophy of the yolk-sac the vitelline circulation diminishes and ulti- 
mately ceases, while an increasing amount of blood is carried through the umbilical 
arteries to the villi of the chorion. Subsequently, as the non-placental chorionic 
villi atrophy, their vessels disappear; and then the umbilical arteries convey the 
whole of their contents to the placenta, whence it is returned to the heart by the 
umbilical veins. In this manner the placental circulation is established, and by 
means of it nutritive materials are absorbed from, and waste products given up to, 
the maternal blood. 
The umbilical veins, like the vitelline, undergo interruption in the developing 
liver, and the blood returned by them passes through this organ before reaching 
the heart. Ultimately the right umbilical vein shrivels up and disappears, as will 
be explained later (page 156). 
During the occurrence of these changes great alterations take place in the 
primitive heart and bloodvessels. 
Further Development of the Heart.-Between the endothelial lining and the 
outer wall of the heart there exists for a time an intricate trabecular network of 
mesodermal tissue from which, at a later stage, the musculi papillares, chordae 
tendineae, and trabeculae carneae are developed. The simple tubular heart, already 
described, becomes elongated and bent on itself so as to form an S-shaped loop, 
the anterior part bending to the right and the posterior part to the left (Fig. 157). 
The intermediate portion arches transversely from left to right, and then turns 
sharply forward into the anterior part of the loop. Slight constrictions make their 
appearance in the tube and divide it from behind forward into five parts, viz.: 
(1) the sinus venosus; (2) the primitive atrium; (3) the primitive ventricle; (4) the 
bulbus cordis, and (5) the truncus arteriosus (Figs. 158, 159). The constriction 
between the atrium and ventricle constitutes the atrial canal, and indicates the site 
of the future atrioventricular valves. 
The sinus venosus is at first situated in the septum transversum (a layer of 
mesoderm in which the liver and the central tendon of the Diaphragma are devel- 
oped) behind the primitive atrium, and is formed by the union of the vitelline 
veins. The veins or ducts of Cuvier from the body of the embryo and the umbilical 
veins from the placenta subsequently open into it (Fig. 160). The sinus is at first 
1 Young and Robinson, Journal of Anatomy and Physiology, vol. xxxii. 
2 In most fishes and in the amphibia the heart originates as a single median tube. 146 
EMBRYOLOGY 
place transversely, and opens by a median aperture into the primitive atrium. 
Soon, however, it assumes an oblique position, and becomes crescentic in form; its 
right half or horn increases more rapidly than the left, and the opening into the 
atrium now communicates with the right portion of the atrial cavity. The right 
horn and transverse portion of the sinus ultimately become incorporated with and 
form a part of the adult right atrium, the line of union between it and the auricula 
Bulbus cordis 
Ventricle- 
Atrium - 
Sinus venosus- 
Vitelline veins' 
Fig. 158.-Diagram to illustrate the simple tubular 
condition of the heart. (Drawn from Ecker-Ziegler 
model.) 
Fig. 159.-Heart of human embryo of about fourteen 
days. (From model by His.) 
being indicated in the interior of the atrium by a vertical crest, the crista terminalis 
of His. The left horn, which ultimately receives only the left duct of Cuvier, 
persists as the coronary sinus (Fig. 161). The vitelline and umbilical veins are soon 
replaced by a single vessel, the inferior vena cava, and the three veins (inferior vena 
cava and right and left Cuvierian ducts) open into the dorsal aspect of the atrium 
by a common slit-like aperture (Fig. 162). The upper part of this aperture repre- 
sents the opening of the permanent superior vena cava, the lower that of the inferior 
Maxillary process 
Stomodeum 
Mandibular arch 
Bulbus cordis 
Duct of Cuvier 
Ventricle 
Atrium 
Bile-duct 
Cardinal vein 
Umbilical vein 
Fig. 160.-Heart of human embryo of about fifteen days. (Reconstruction by His.) 
vena cava, and the intermediate part the orifice of the coronary sinus. The slit- 
like aperture lies obliquely, and is guarded by two halves, the right and left venous 
valves; above the opening these unite with each other and are continuous with a 
fold named the septum spurium; below the opening they fuse to form a triangular 
thickening-the spina vestibuli. The right venous valve is retained; a small 
septum, the sinus septum, grows from the posterior wall of the sinus venosus to fuse 147 
DEVELOPMENT OF THE VASCULAR SYSTEAI 
with the valve and divide it into two parts-an upper, the valve of the inferior 
vena cava, and a lower, the valve of the coronary sinus (Fig. 165). The extreme 
Left duct of 
Cuvier 
Opening into 
atrium 
Right duct of 
Cuvier 
Fig. 161.-Dorsal surface of heart of human embryo of thirty-five days. (From model by His.) 
Septum spurium 
Opening of sinus vcnosus 
Left venous valve 
Septum primum 
Right venous 
valve 
Spina vestibuli 
Posterior endocardial 
cushion 
Atrial canal ' 
Septum inferius 
Fig. 162.-Interior of dorsal half of heart from a human embryo of about thirty days. (From model by His.) 
upper portion of the right venous valve, together with the septum spurium, form 
the crista terminalis already mentioned. The upper and middle thirds of the left 148 
EMBRYOLOGY 
venous valve disappear; the lower third is continued into the spina vestibuli, 
and later fuses with the septum secundum of the atria and takes part in the forma- 
tion of the limbus fossae ovalis. 
Right atrium 
Bulbus cordis 
- Left atrium 
Atrial canal 
Ventricle 
Fig. 163.-Heart showing expansion of the atria. (Drawn from Ecker-Zeigler model.) 
The atrial canal is at first a short straight tube connecting the atrial with the 
ventricular portion of the heart, but its growth is relatively slow, and it becomes 
overlapped by the atria and ventricles so that its position on the surface of the heart 
is indicated only by an annular constriction (Fig. 163). Its lumen is reduced to a 
transverse slit, and two thickenings appear, one on its dorsal and another on its 
Septum secundum 
Opening of coronary sinus 
Septum spurium 
Spina vestibuli fused with 
septum primum 
Left atr io ventr icular 
opening 
Right atrioventricular 
opening 
Right venous valve 
Septum intermedium 
Fig. 164.-Interior of dorsal half of heart of human embryo of about thirty-five days. (From model by His.) 
Septum inferius 
ventral wall. These thickenings, or endocardial cushions (Fig. 162) as they are 
termed, project into the canal, and, meeting in the middle line, unite to form the 
septum intermedium which divides the canal into two channels, the future right and 
left atrioventricular orifices. DEVELOPMENT OF THE VASCULAR SYSTEM 
149 
The primitive atrium grows rapidly and partially encircles the bulbus cordis; 
the groove against which the bulbus cordis lies is the first indication of a division 
into right and left atria. The cavity of the primitive atrium becomes subdivided 
into right and left chambers by a septum, the septum primum (Fig. 162), which 
grows downward into the cavity. For a time the atria communicates with each 
other by an opening, the ostium primum of Born, below the free margin of the septum. 
This opening is closed by the union of the septum primum with the septum inter- 
medium, and the communication between the atria is reestablished through an 
opening which is developed in the upper part of the septum primum; this opening 
is known as the foramen ovale (ostium secundum of Born) and persists until birth. 
A second septum, the septum secundum (Figs. 164, 165), semilunar in shape, grows 
downward from the upper wall of the atrium immediately to the right of the 
primary septum and foramen ovale. Shortly after birth it fuses with the primary 
septum, and by this means the foramen ovale is closed, but sometimes the fusion 
is incomplete and the upper part of the foramen remains patent. The limbus fossae 
Left duct of Cuvier 
-Foramen ovale 
Probe in aorta 
Aortic septum 
Septum 
intermedium 
Septum 
inferius 
Opening of coronary 
sinus 
Fig. 165.-Same heart as in Fig. 164, opened on right side. (From model by His.) 
ovalis denotes the free margin of the septum secundum. Issuing from each lung 
is a pair of pulmonary veins; each pair unites to form a single vessel, and these in 
turn join in a common trunk which opens into the left atrium. Subsequently 
the common trunk and the two vessels forming it expand and form the vestibule 
or greater part of the atrium, the expansion reaching as far as the openings of the 
four vessels, so that in the adult all four veins open separately into the left atrium. 
The primitive ventricle becomes divided by a septum, the septum inferius or 
ventricular septum (Figs. 162, 164, 165), which grows upward from the lower part 
of the ventricle, its position being indicated on the surface of the heart by a furrow. 
Its dorsal part increases more rapidly than its ventral portion, and fuses with the 
dorsal part of the septum intermedium. For a time an interventricular foramen 
exists above its ventral portion (Fig. 165), but this foramen is ultimately closed by 
the fusion of the aortic septum with the ventricular septum. 
When the heart assumes its S-shaped form the bulbus cordis lies ventral to and 
in front of the primitive ventricle. The adjacent walls of the bulbus cordis and 
ventricle approximate, fuse, and finally disappear, and the bulbus cordis now 150 
EMBRYOLOGY 
communicates freely with the right ventricle, while the junction of the bulbus with 
the truncus arteriosus is brought directly ventral to and applied to the atrial canal. 
Fig. 166.-Diagrams to illustrate the transformation of the bulbus cordis. (Keith.) Ao. Truncus arteriosus. 
Au. Atrium. B. Bulbus cordis. RV. Right ventricle. LV. Left ventricle. P. Pulmonary artery. 
By the upgrowth of the ventricular septum the bulbus cordis is in great measure 
separated from the left ventricle, but remains an integral part of the right ventricle, 
of which it forms the infundibulum (Fig. 166). 
Aortic septum 
Aortic septum 
Common atrio- 
ventricular aperture 
Pulmonary 
artery x 
Aorta 
Right atrio- 
ventricular 
orifice 
Left atrio- 
ventricular 
' orifice 
Right 
ventricle 
Septum 
inferius 
Left 
ventricle 
Right 
ventricle 
Septum inferius 
Left 
ventricle 
Fig. 167.-Diagrams to show the development of the septum of the aortic bulb and of the ventricles. (Born.) 
The truncus arteriosus and bulbus cordis are divided by the aortic septum (Fig. 
167). This makes its appearance in three portions. (1) Two distal ridge-like 
Aorta 
Aorta 
Aorta 
Pulmonary artery 
Pulmo- 
nary artery 
Pulmonary artery 
Fig. 168.-Transverse sections through the aortic bulb to show the growth of the aortic septum. The lowest 
section is on the left, the highest on the right of the figure. (After His.) 
thickenings project into the lumen of the tube; these increase in size, and ultimately 
meet and fuse to form a septum, which takes a spiral course toward the proximal DEVELOPMENT OF THE VASCULAR SYSTEM 
151 
end of the truncus arteriosus. It divides the distal part of the truncus into two 
vessels, the aorta and pulmonary artery, which lie side by side above, but near 
the heart the pulmonary artery is in front of the aorta. (2) Four endocardial 
cushions appear in the proximal part of the truncus arteriosus in the region of the 
future semilunar valves; the manner in which these are related to the aortic septum 
is described below. (3) Two endocardial thickenings-anterior and posterior- 
develop in the bulbus cordis and unite to form a short septum; this joins above with 
the aortic septum and below with the ventricular septum. The septum grows down 
into the ventricle as an oblique partition, which ultimately blends with the ven- 
tricular septum in such a way as to bring the bulbus cordis into communication 
with the pulmonary artery, and through the latter with the sixth pair of aortic 
arches; while the left ventricle is brought into continuity with the aorta, which 
communicates with the remaining aortic arches. 
Second aortic arch 
First aortic arch 
Third aortic arch 
Auditory vesicle 
Primitive jugular vein 
Fourth aortic arch 
Sixth aortic arch 
Olfactory pit 
Dorsal aorta 
Maxillary process 
First branchial groove 
Mandibular arch 
Cardinal vein 
-Atrium 
Eulbus cordis 
-Duct of Cuvier 
Ventricle 
Digestive tube 
Vitelline vein 
Yolk-sac 
Hind-gut 
Allantois 
Umbilical artery 
Umbilical vein 
Fig. 169.-Profile view of a human embryo estimated at twenty or twenty-one days old. (After His.) 
The Valves of the Heart.-The atrioventricular valves are developed in relation to 
the atrial canal. By the upward expansion of the bases of the ventricles the canal 
becomes invaginated into the ventricular cavities. The invaginated margin forms 
the rudiments of the lateral cusps of the atrioventricular valves; the mesial or 
septal cusps of the valves are developed as downward prolongations of the septum 
intermedium (Fig. 164). The aortic and pulmonary semilunar valves are formed 
from four endocardial thickenings-an anterior, a posterior, and two lateral- 152 
EMBRYOLOGY 
which appear at the proximal end of the truncus arteriosus. As the aortic septum 
grows downward it divides each of the lateral thickenings into two, thus giving 
rise to six thickenings-the rudiments of the semilunar valves-three at the aortic 
and three at the pulmonary orifice (Fig. 168). 
Further Development of the Arteries.-Recent observations show that practi- 
cally none of the main vessels of the adult arise as such in the embryo. In the site 
of each vessel a capillary network forms, and by the enlargement of definite paths 
in this the larger arteries and veins are developed. The branches of the main 
arteries are not always simple modifications of the vessels of the capillary network, 
but may arise as new outgrowths from the enlarged stem. 
External carotid 
Ventral aorta 
-Internal carotid 
•Common carotid 
Hight subclavian 
artery 
Aortic arch 
■Ductus arteriosus 
Right pulmonary 
artery 
■ Vertebral artery 
Trunk of pulmonary 
artery 
J Subclavian artery 
Left pulmonary artery 
Fig. 170.-Scheme of the aortic arches and their destination. (Modified from Kollmann.) 
It has been seen (page 145) that each primitive aorta consists of a ventral and 
a dorsal part which are continuous through the first aortic arch. The dorsal aortse 
at first run backward separately on either side of the notochord, but about the 
third week they fuse from about the level of the fourth thoracic to that of the fourth 
lumbar segment to form a single trunk, the descending aorta. The first aortic 
arches run through the mandibular arches, and behind them five additional pairs 
are developed within the visceral arches; so that, in all, six pairs of aortic arches 
are formed (Figs. 169, 170). The first and second arches pass between the ventral 
and dorsal aortse, while the others arise at first by a common trunk from the truncus 
arteriosus, but end separately in the dorsal aortse. As the neck elongates, the 
ventral aortse are drawn out, and the third and fourth arches arise directly from 
these vessels. 
In fishes these arches persist and give off branches to the gills, in which the 
blood is oxygenated. In mammals some of them remain as permanent structures, 
while others disappear or become obliterated (Fig. 170). 
The Anterior Ventral Aortse.-These persist on both sides. The right forms (a) 
the innominate artery, (b) the right common and external carotid arteries. The 
left gives rise to (a) the short portion of the aortic arch, which reaches from the DEVELOPMENT OF THE VASCULAR SYSTEM 
153 
origin of the innominate artery to that of the left common carotid artery; (6) the 
left common and external carotid arteries. 
The Aortic Arches.-The first and second arches disappear early, but the dorsal 
end of the second gives origin to the stapedial artery (Fig. 171), a vessel which 
atrophies in man but persists in some mammals. It passes through the ring of the 
stapes and divides into supraorbital, infraorbital, and mandibular branches which 
follow the three divisions of the trigeminal nerve. The infraorbital and man- 
dibular arise from a common stem, the terminal part of which anastomoses with 
Post, cerebral a. 
Ant. cerebral ar 
Supraorbital br. 
of stapedial a. ' 
Trigeminal nerve- 
Maxillary nerve 
Stapedial a. 
Infraorbital a. 
Mandibular nerve- 
Mandibular a.. 
Ext. max. a. 
Lingual a. 
■Int. carotid a. 
Sup. thyroid a. 
Common carotid a.- 
Aortic arch 
Pulmonary arch 
Pulmonary art. 
Dorsal aorta 
Fig. 171.-Diagram showing the origins of the main branches of the carotid arteries. (Founded on Tandler.) 
the external carotid. On the obliteration of the stapedial artery this anastomosis 
enlarges and forms the internal maxillary artery, and the branches of the stapedial 
artery are now branches of this vessel. The common stem of the infraorbital and 
mandibular branches passes between the two roots of the auriculotemporal nerve 
and becomes the middle meningeal artery; the original supraorbital branch of the 
stapedial is represented by the orbital twigs of the middle meningeal. The third 
aortic arch constitutes the commencement of the internal carotid artery, and is 
therefore named the carotid arch. The fourth right arch forms the right sub- 
clavian as far as the origin of its internal mammary branch; while the fourth left 
arch constitutes the arch of the aorta between the origin of the left carotid artery 
and the termination of the ductus arteriosus. The fifth arch disappears on both 
sides. The sixth right arch disappears; the sixth left arch gives off the pulmonary 154 
EMBRYOLOGY 
arteries and forms the ductus arteriosus; this duct remains pervious during the 
whole of fetal life, but is obliterated a few days after birth. His showed that in the 
early embryo the right and left arches each gives a branch to the lungs, but that 
later both pulmonary arteries take origin from the left arch. 
The Dorsal Aortae.-In front of the third aortic arches the dorsal aortse persist 
and form the continuations of the internal carotid arteries; these arteries pass to the 
brain and each divides into an anterior and a posterior branch, the former giving- 
off the ophthalmic and the anterior and middle cerebral arteries, while the latter 
turns back and joins the cerebral part of the vertebral artery. Behind the third 
arch the right dorsal aorta disappears as far as the point where the two dorsal 
aortae fuse to form the descending aorta. The part of the left dorsal aorta between 
the third and fourth arches disappears, while the remainder persists to form 
the descending part of the arch of the aorta. A constriction, the aortic isthmus, is 
sometimes seen in the aorta between the origin of the left subclavian and the 
attachment of the ductus arteriosus. 
Sometimes the right subclavian artery arises from the aortic arch distal to the 
origin of the left subclavian and passes upward and to the right behind the trachea 
and oesophagus. This condition may be explained by the persistence of the right 
dorsal aorta and the obliteration of the fourth right arch. 
In birds the fourth right arch forms the arch of the aorta; in reptiles the fourth 
arch on both sides persists and gives rise to the double aortic arch in these animals. 
The heart originally lies, on the ventral aspect of the pharynx, immediately 
behind the stomodeum. With the elongations of the neck and the development 
of the lungs it recedes within the thorax, and, as a consequence, the anterior 
ventral aortse are drawn out and the original position of the fourth and fifth arches 
is greatly modified. Thus, on the right side the fourth recedes to the root of the 
neck, while on the left side it is withdrawn within the thorax. The recurrent 
nerves originally pass to the larynx under the sixth pair of arches, and are there- 
fore pulled backward with the descent of these structures, so that in the adult the 
left nerve hooks around the ligamentum arteriosum; owing to the disappearance of 
the fifth and the sixth right arches the right nerve hooks around that immediately 
above them, i. e., the commencement of the subclavian artery. Segmental arteries 
arise from the primitive dorsal aortee and course between successive segments. 
The seventh segmental artery is of special interest, since it forms the lower end of 
the vertebral artery and, when the forelimb bud appears, sends a branch to it 
(the subclavian artery). From the seventh segmental arteries the entire left 
subclavian and the greater part of the right subclavian are formed. The second 
pair of segmental arteries accompany the hypoglossal nerves to the brain and are 
named the hypoglossal arteries. Each sends forward a branch which forms the 
cerebral part of the vertebral artery and anastomoses with the posterior branch 
of the internal carotid. The two vertebrals unite on the ventral surface of the 
hind-brain to form the basilar artery. Later the hypoglossal artery atrophies 
and the vertebral is connected with the first segmental artery. The cervical part 
of the vertebral is developed from a longitudinal anastomosis between the first 
seven segmental arteries, so that the seventh of these ultimately becomes the source 
of the artery. As a result of the growth of the upper limb the subclavian artery 
increases greatly in size and the vertebral then appears to spring from it. 
Recent observations show that several segmental arteries contribute branches to 
the upper limb-bud and form in it a free capillary anastomosis. Of these branches, 
only one, viz., that derived from the seventh segmental artery, persists to form 
the subclavian artery. The subclavian artery is prolonged into the limb under 
the names of the axillary and brachial arteries, and these together constitute the 
arterial stem for the upper arm, the direct continuation of this stem in the forearm 
is the volar interosseous artery. A branch which accompanies the median nerve DEVELOPMENT OF THE VASCULAR SYSTEM 
155 
soon increases in size and forms the main vessel (median artery) of the forearm, 
while the volar interosseous diminishes. Later the radial and ulnar arteries are 
developed as branches of the brachial part of the stem and coincidently with their 
enlargement the median artery recedes; occasionally it persists as a vessel of some 
considerable size and then accompanies the median nerve into the palm of the hand. 
The primary arterial stem for the lower limb is formed by the inferior gluteal 
(sciatic) artery, which accompanies the sciatic nerve along the posterior aspect of 
the thigh to the back of the knee, whence it is continued as the peroneal artery. 
This arrangement exists in reptiles and amphibians. The femoral artery arises 
later as a branch of the common iliac, and, passing down the front and medial 
side of the thigh to the bend of the knee, joins the inferior gluteal artery. The 
femoral quickly enlarges, and, coincidently with this, the part of the inferior gluteal 
immediately above the knee undergoes atrophy. The anterior and posterior tibial 
arteries are branches of the main arterial stem. 
Anterior detached portions 
of umbilical veins 
Venae revehentes 
Stomach 
V enae advehentes 
Ductus venosus 
Pancreas 
Bile-duct - 
Liver 
Obliterated portions 
of venous rings 
Right umbilical vein- 
Left umbilical vein 
Portal vein 
Vitelline 
veins 
Fig. 172.-The liver and the veins in connection with it, of a human embryo, twenty-four or twenty-five days old; 
as seen from the ventral surface. (After His.) 
Duodenum 
Further Development of the Veins.-The formation of the great veins of the 
embryo may be best considered by dividing them into two groups, visceral and 
parietal. 
The Visceral Veins.-The visceral veins are the two vitelline or omphalomesenteric 
veins bringing the blood from the yolk-sac, and the two umbilical veins returning 
the blood from the placenta; these four veins open close together into the sinus 
venosus. 
The Vitelline Veins run upward at first in front, and subsequently on either 
side of the intestinal canal. They unite on the ventral aspect of the canal, and 
beyond this are connected to one another by two anastomotic branches, one on the 
dorsal, and the other on the ventral aspect of the duodenal portion of the intestine, 
which is thus encircled by two venous rings (Fig. 172); into the middle or dorsal 
anastomosis the superior mesenteric vein opens. The portions of the veins above 
the upper ring become interrupted by the developing liver and broken up by it into 
a plexus of small capillary-like vessels termed sinusoids (Minot). The branches 
conveying the blood to this plexus are named the venae advehentes, and become 156 
EMBRYOLOGY 
the branches of the portal vein; while the vessels draining the plexus into the 
sinus venosus are termed the venae revehentes, and form the future hepatic veins 
(Figs. 172, 173). Ultimately the left vena revehens no longer communicates 
directly with the sinus venosus, but opens into the right vena revehens. The 
persistent part of the upper venous ring, above the opening of the superior mes- 
enteric vein, forms the trunk of the portal vein. 
Right primitive jugular vein 
Left primitive 
jugular vein 
Right cardinal vein 
Right duct of Cuvier 
Left cardinal vein 
Sinus venosus 
Left duct of Cuvier 
Right hepatic vein 
Left hepatic vein 
Portal vein 
Left umbilical vein 
Portal vein 
Right umbilical vein 
Left umbilical vein 
Umbilical cord- 
Fig. 173.-Human embryo with heart and anterior body-wall removed to show the sinus venosus and its tributaries. 
(After His.) 
The two Umbilical Veins fuse early to form a single trunk in the body-stalk, 
but remain separate within the embryo and pass forward to the sinus venosus 
in the side walls of the body. Like the vitelline veins, their direct connection 
with the sinus venosus becomes interrupted by the developing liver, and thus at 
this stage the whole of the blood from the yolk-sac and placenta passes through 
the substance of the liver before it reaches the heart. The right umbilical and 
right vitelline veins shrivel and disappear; the left umbilical, on the other hand, 
becomes enlarged and opens into the upper venous ring of the vitelline veins; with 
the atrophy of the yolk-sac the left vitelline vein also undergoes atrophy and 
disappears. Finally a direct branch is established between this ring and the right 
hepatic vein; this branch is named the ductus venosus, and, enlarging rapidly, 
it forms a wide channel through which most of the blood, returned from the 
placenta, is carried direct to the heart without passing through the liver. A small 
proportion of the blood from the placenta is, however, conveyed from the left 
umbilical vein to the liver through the left vena advehens. The left umbilical 
vein and the ductus venosus undergo atrophy and obliteration after birth, and 
form respectively the ligamentum teres and ligamentum venosum of the liver. DEVELOPMENT OF THE VASCULAR SYSTEM 
157 
The Parietal Veins.-The first indication of a parietal system consists in the 
appearance of two short transverse veins, the ducts of Cuvier, which open, one 
on either side, into the sinus venosus. Each of these ducts receives an ascending 
and descending vein. The ascending veins return the blood from the parietes 
of the trunk and from the Wolffian bodies, and are called cardinal veins. The 
descending veins return the blood from the head, and are called primitive jugular 
veins (Fig. 174). The blood from the lower limbs is collected by the right and 
left iliac and hypogastric veins, which, in the earlier stages of development, open 
into the corresponding right and left cardinal veins; later, a transverse branch (the 
left common iliac vein) is developed between the lower parts of the two cardinal 
veins (Fig. 176), and through this the blood is carried into the right cardinal vein. 
The portion of the left cardinal vein below the left renal vein atrophies and dis- 
appears up to the point of entrance of the left spermatic vein; the portion above 
the left renal vein persists as the hemiazygos and accessory hemiazygos veins 
and the lower portion of the highest left intercostal vein. The right cardinal vein 
Sinus venosus 
Internal jugular 
Primitive jugular 
External jugular 
Subclavian 
Subclavian 
Duct of Cuvier 
Duct of Cuvier 
Vitelline 
Left cardinal 
Umbilical 
Cardinal 
Ductus venosus 
Renal 
Subcardinal 
Renal 
Subcardinal 
External iliac 
External iliac 
Hypogastric 
Hypogastric 
Fig. 174.-Scheme of arrangement of parietal 
veins. 
Fig. 175.-Scheme showing early stages of 
development of the inferior vena cava. 
which now receives the blood from both lower extremities, forms a large venous 
trunk along the posterior abdominal wall; up to the level of the renal veins it 
forms the lower part of the inferior vena cava. Above the level of the renal veins 
the right cardinal vein persists as the azygos vein and receives the right intercostal 
veins, while the hemiazygos veins are brought into communication with it by the 
development of transverse branches in front of the vertebral column (Figs. 176, 177) 
Inferior Vena Cava.-The development of the inferior vena cava is associated 
with the formation of two veins, the subcardinal veins (Figs. 174, 175). These 
lie parallel to, and on the ventral aspect of, the cardinal veins, and originate as 
longitudinal anastomosing channels which link up the tributaries from the mes- 
entery to the cardinal veins; they communicate with the cardinal veins above and 
below, and also by a series of transverse branches. The two subcardinals are for 
a time connected with each other in front of the aorta by cross branches, but these 
disappear and are replaced by a single transverse channel at the level where the 
renal veins join the cardinals, and at the same level a cross communication is 158 
EMBRYOLOGY 
established on either side between the cardinal and subcardinal (Fig. 175). The 
portion of the right subcardinal behind this cross communication disappears, while 
that in front, i. e., the prerenal part, forms a connection with the ductus venosus 
Left innominate 
•Internal jugular 
•External jugular 
Right innominate 
Duct of Cuvier 
Superior vena cava 
Left cardinal 
Prerenal part of 
inferior vena cava 
Left suprarenal 
Left renal 
Postrenal part of 
inferior vena cava 
Left common iliac 
External iliac 
Hypogastric 
Fig. 176.-Diagram showing development of main cross branches between jugulars and between cardinals. 
at the point of opening of the hepatic veins, and, rapidly enlarging, receives the 
blood from the postrenal part of the right cardinal through the cross communica- 
Left innominate 
Internal jugular 
External jugular 
Right innominate 
Subclavian 
Highest left intercostal 
Superior vena cava 
Ligament of left vena cava 
Azygos vein 
Oblique vein of left atrium 
Coronary sin-us 
Accessory hemiazygos vein 
Prerenal part of 
inferior vena cava 
Hemiazygos vein 
Left suprarenal 
Left renal 
Left internal spermatic 
Left common iliac 
External iliac 
Fig. 177.-Diagram showing completion of development of the parietal veins. 
Il ypogastric 
tion referred to. In this manner a single trunk, the inferior vena cava (Fig. 177), is 
formed, and consists of the proximal part of the ductus venosus, the prerenal part 
of the right subcardinal vein, the postrenal part of the right cardinal vein, and the DEVELOPMENT OF THE VASCULAR SYSTEM 
159 
cross branch which joins these two veins. The left subcardinal disappears, except 
the part immediately in front of the renal vein, which is retained as the left supra- 
renal vein. The spermatic (or ovarian) vein opens into the postrenal part of 
the corresponding cardinal vein. This portion of the right cardinal, as already 
explained, forms the lower part of the inferior vena cava, so that the right spermatic 
opens directly into that vessel. The postrenal segment of the left cardinal dis- 
appears, with the exception of the portion between the spermatic and renal vein, 
which is retained as the terminal part of the left spermatic vein. 
In consequence of the atro- 
phy of the Wolffian bodies the 
cardinal veins diminish in size; 
the primitive jugular veins, 
on the other hand, become 
enlarged, owing to the rapid 
development of the head and 
brain. They are further aug- 
mented by receiving the veins 
(subclavian) from the upper ex- 
tremities, and so come to form 
the chief veins of the Cuvierian ducts; these ducts gradually assume an almost 
vertical position in consequence of the descent of the heart into the thorax. The 
right and left Cuvierian ducts are originally of the same diameter, and are frequently 
termed the right and left superior venae cavse. By the development of a transverse 
branch, the left innominate vein between the two primitive jugular veins, the 
blood is carried across from the left to the right primitive jugular (Figs. 176, 177). 
The portion of the right primitive jugular vein between the left innominate and 
the azygos vein forms the upper part of the superior vena cava of the adult; the 
lower part of this vessel, i. e., below the entrance of the azygos vein, is formed by 
the right Cuvierian duct. Below the origin of the transverse branch the left 
Auditory vesicle 
Primitive 
jugular vein 
Vena capitis medialis 
Trigeminal nerve 
Ophthalmic vein 
Vena capitis 
lateralis 
Superior sagittal 
sinus 
Fig. 178.-Diagram of veins of head of an embryo four weeks old. 
(After Mall.) 
Auditory 
vesicle 
Middle 
cerebral 
vein 
Anterior cerebral vein 
Torcular Her ophili 
Posterior 
cerebral vein 
Superior sagittal 
sinus 
Jugular vein- 
Trigeminal nerve 
Fig. 179.-Diagram of veins of head of an embryo five weeks old. (After Mall.) 
Vena capitis lateralis 
Ophthalmic vein 
primitive jugular vein and left Cuvierian duct atrophy, the former constituting 
the upper part of the highest left intercostal vein, while the latter is represented 
by the ligament of the left vena cava, vestigial fold of Marshall, and the oblique 
vein of the left atrium, oblique vein of Marshall (Fig. 177). Both right and left 
superior vense cavse are present in some animals, and are occasionally found in the 
adult human being. The oblique vein of the left atrium passes downward across 
the back of the left atrium to open into the coronary sinus, which, as already 
indicated, represents the persistent left horn of the sinus venosus. 
The primitive jugular veins drain the blood from the brain, and their proximal 
parts form the internal jugular veins. The distal portion of each has been named 
the vena capitis medialis (Fig. 178); it runs on the medial side of the auditory 160 
EMBRYOLOGY 
vesicle and cerebral nerve roots, and the portion of it situated in the neighborhood 
of the trigeminal nerve becomes the cavernous sinus. The greater part of the vena 
capitis medialis is replaced, however, by the vena capitis lateralis (Fig. 179), which 
is developed on the lateral aspect of the cerebral nerves from the trigeminal to the 
hypoglossal. This vein receives three principal tributaries, viz., the anterior 
cerebral vein from the eye, fore-brain, and mid-brain, the middle cerebral vein 
Middle cerebral vein 
Torcular Herophili 
Posterior cerebral vein 
Superior sagittal sinus 
Vena capitis 
lateralis 
Auditory 
vesicle 
Trigeminal 
nerve 
Ophthalmic 
vein 
Anterior 
cerebral vein 
Fig. 180.-Diagram of veins of head at the beginning of the third month. (After Mall.) 
from the cerebellum, and the posterior cerebral vein from the lower part of the hind- 
brain. At this stage, therefore, practically the whole of the blood from the brain 
is drained into the vena capitis lateralis, which leaves the skull in company with 
the facial nerve and opens into the internal jugular vein. The terminal branches 
of the two anterior cerebral veins anastomose in the middle line and thus form the 
Straight sinus 
Torcular Herophili 
Inferior sagittal sinus 
Great cerebral vein 
Superior petrosal 
sinus 
Superior sagittal sinus 
Transverse sinus 
Middle cerebral vein 
Anterior cerebral vein 
Sphenoparietal sinus 
Auditory vesicle 
Inferior petrosal sinus 
Trigeminal nerve 
Ophthalmic vein 
Fig. 181.-Diagram of veins of head of an older embryo. (After Mall.) 
superior sagittal sinus (Fig. 180). By the backward growth of the cerebral hemis- 
pheres this sinus comes to anastomose with the middle and posterior cerebral veins, 
the latter of which leaves the skull through the jugular foramen; this last anastomo- 
sis forms the greater part of the transverse sinus. The vena capitis lateralis under- 
goes atrophy; the middle cerebral vein forms the superior petrosal sinus (Fig. 
181). The inferior petrosal sinus is a later formation. The external jugular vein DEVELOPMENT OF THE VASCULAR SYSTEM 
161 
at first drains the region behind the ear (posterior auricular) and enters the primi- 
tive jugular as a lateral tributary. A group of veins from the face and lingual region 
converge to form a common vein, the linguo-facial,1 which also terminates in the 
primitive jugular. Later, cross communications develop between the external 
jugular and the linguo-facial, with the result that the posterior group of facial 
veins is transferred to the external jugular. 
Peculiarities of the Fetal Heart.-In early fetal life the heart is placed directly 
under the head and is relatively of large size. Later it assumes its position in the 
thorax, but lies at first in the middle line; toward the end of pregnancy it gradu- 
ally becomes oblique in direction. The atrial portion is at first larger than the 
ventricular part, and the two atria communicate freely through the foramen ovale. 
In consequence of the communication through the ductus arteriosus, between the 
pulmonary artery and the aorta, the contents of the right ventricle are mainly 
carried into the latter vessel instead of to the lungs, and hence the wall of the 
right ventricle is as thick as that of the left. At the end of fetal life, however, 
the left ventricle is thicker than the right, a difference which becomes more and 
more emphasized after birth. 
The fetal circulation and the changes which take place in the circulation after 
birth are described on pages 616 to 618. 
Left innominate 
Internal jugular 
Jugular lymph-sac 
External jugular 
Right innominate 
8'iperior vena cava 
Duct of Cuvier 
Left cardinal 
Prerenal part of 
inferior vena cava 
Left suprarenal 
Left renal 
Retro-peritoneal 
lymph-sac 
Postrenal part of 
inferior vena cava 
Cisterna chyli 
Posterior lymph-sac 
Left common iliac 
External iliac 
Hypogastric 
Fig. 182.-Scheme showing relative positions of primary lymph sacs based on the description given by 
Florence Sabin. 
The Lymphatic Vessels.-The lymphatic system begins as a series of sacs2 at 
the points of junction of certain of the embryonic veins. These lymph-sacs are 
developed by the confluence of numerous venous capillaries, which at first lose 
their connections with the venous system, but subsequently, on the formation of 
the sacs, regain them. The lymphatic system is therefore developmentally an 
offshoot of the venous system, and the lining walls of its vessels are always 
endothelial. 
In the human embryo the lymph sacs from which the lymphatic vessels are 
derived are six in number; two paired, the jugular and the posterior lymph-sacs; 
and two unpaired, the retroperitoneal and the cisterna chyli. In lower mammals 
1 Lewis, American Journal of Anatomy, February, 1909, No. 1, vol. ix. 
2 Sabin, ibid. 162 
EMBRYOLOGY 
an additional pair, subclavian, is present, but in the human embryo these are 
merely extensions of the jugular sacs. 
The position of the sacs is as follows: (1) jugular sac, the first to appear, at 
the junction of the subclavian vein with the primitive jugular; (2) posterior sac, 
at the junction of the iliac vein with the cardinal; (3) retroperitoneal, in the root 
of the mesentery near the suprarenal glands; (4) cisterna chyli, opposite the third 
and fourth lumbar vertebrae (Fig. 182). From the lymph-sacs the lymphatic 
vessels bud out along fixed lines corresponding more or less closely to the course 
of the embryonic bloodvessels. Both in the body-wall and in the wall of the 
intestine,1 the deeper plexuses are the first to be developed; by continued growth 
of these the vessels in the superficial layers are gradually formed. The thoracic 
duct is probably formed from anastomosing outgrowths from the jugular sac and 
cisterna chyli. At its connection with the cisterna chyli it is at first double, but 
the two vessels soon join. 
All the lymph-sacs except the cisterna chyli are, at a later stage, divided up by 
slender connective tissue bridges and transformed into groups of lymph glands. 
The lower portion of the cisterna chyli is similarly converted, but its upper portion 
remains as the adult cisterna. 
A m ni on 
Neural canal 
Allantois 
Hind-gut 
Vitelline duct 
Fore-gut 
Notochord 
Heart 
Yolk-sac 
Fig. 183.-Diagram of a sagittal section of a mammalian embryo. Very early. (After Quain.) 
DEVELOPMENT OF THE DIGESTIVE AND RESPIRATORY APPARATUS 
The Digestive Tube.-As already indicated (page 92), the primitive digestive 
tube consists of two parts, viz.: (1) the fore-gut, within the cephalic flexure, and 
dorsal to the heart; and (2) the hind-gut, within the caudal flexure (Figs. 183, 184). 
Between these is the wide opening of the yolk-sac, which is gradually narrowed 
and reduced to a small foramen leading into the vitelline duct. At first the fore- 
gut and hind-gut end blindly. The anterior end of the fore-gut is separated from 
1 Heuer, American Journal of Anatomy, vol. ix, No, 1, February, 1909. DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
163 
the stomodeum by the buccopharyngeal membrane (Fig. 184); the hind-gut ends 
in the cloaca, which is closed by the cloacal membrane. 
The Mouth.-The mouth is developed partly from the stomodeum, and partly 
from the floor of the anterior portion of the fore-gut. By the growth of the head 
end of the embryo, and the formation of the cephalic flexure, the, pericardial area 
and the buccopharyngeal membrane come to lie on the ventral surface of the 
embryo. With the further expansion of the brain, and the forward bulging of the 
pericardium, the buccopharyngeal membrane is depressed between these two 
prominences. This depression constitutes the stomodeum (Fig. 184). It is lined 
by ectoderm, and is separated from the anterior end of the fore-gut by the bucco- 
pharyngeal membrane. This membrane is devoid of mesoderm, being formed 
by the apposition of the stomodeal ectoderm with the fore-gut entoderm; at the 
end of the third week it disappears, and thus a communication is established 
Thalamencephalon 
Mid-brain 
Optic vesicle 
B uccopharyngeal 
membrane 
Stomodeum 
Pharynx 
Auditory pit 
V entricle 
Bulbus cordis 
Liver 
Stomach 
Y olk-sac 
Cloaca 
Hind-gut 
Body-stalk' 
Allantois 
Umbilical artery 
Umbilical vein 
Fig. 184.-Human embryo about fifteen days old. Brain and heart represented from right side. Digestive tube and 
yolk sac in median section. (After His.) 
between the mouth and the future pharynx. No trace of the membrane is found 
in the adult; and the communication just mentioned must not be confused with the 
permanent isthmus faucium. The lips, teeth, and gums are formed from the walls 
of the stomodeum, but the tongue is developed in the floor of the pharynx. 
The visceral arches extend in a ventral direction between the stomodeum and 
the pericardium; and with the completion of the mandibular arch and the formation 
of the maxillary processes, the mouth assumes the appearance of a pentagonal 
orifice. The orifice is bounded in front by the fronto-nasal process, behind by the 
mandibular arch, and laterally by the maxillary processes (Fig. 185). With the 
inward growth and fusion of the palatine processes (Figs. 112, 113), the stomodeum 
is divided into an upper nasal, and a lower buccal part. Along the free margins 
of the processes bounding the mouth cavity a shallow groove appears; this is 
termed the primary labial groove, and from the bottom of it a downgrowth of 164 
EMBRYOLOGY 
ectoderm takes place into the underlying mesoderm. The central cells of the 
ectodermal downgrowth degenerate and a secondary labial groove is formed; by 
the deepening of this, the lips and cheeks are separated from the alveolar processes 
of the maxillae and mandible. 
The Salivary Glands.-The salivary glands arise as buds from the epithelial 
lining of the mouth; the parotid appears during the fourth week in the angle 
between the maxillary process and the 
mandibular arch; the submaxillary ap- 
pears in the sixth week, and the sublin- 
gual during the ninth week in the hollow 
between the tongue and the mandibular 
arch. 
The Tongue (Figs. 186 to 188).-The 
tongue is developed in the floor of the 
pharynx, and consists of an anterior or 
buccal and a posterior or pharyngeal part 
which are separated in the adult by the 
V-shaped sulcus terminalis. During the 
third week there appears, immediately 
behind the ventral ends of the two halves 
of the mandibular arch, a rounded 
swelling named the tuberculum impar, 
which was described by His as un- 
dergoing enlargement to form the 
buccal part of the tongue. More re- 
cent researches, however, show that 
this part of the tongue is mainly, if 
not entirely, developed from a pair 
of lateral swellings which rise from 
the inner surface of the mandibular arch and meet in the middle line. The tuber- 
culum impar is said to form the central part of the tongue immediately in front 
of the foramen cecum, but Hammar insists that it is purely a transitory structure 
and forms no part of the adult tongue. From the ventral ends of the fourth arch 
Future apex of nose 
Medial nasal process 
Olfactory pit 
Lateral nasal process 
Globular process 
Maxillary process 
S tomodeum 
Mandibular arch 
Fig. 185.-Head end of human embryo of about thirty 
to thirty-one days. (From model by Peter.) 
Lateral tongue 
swellings 
Thyroid 
diverticulum 
Lateral tongue swellings 
Entrance to 
larynx 
Entrance to 
larynx 
Arytenoid 
swellings 
Fig. 186.-Floor of pharynx of human embryo 
about twenty-six days old. (From model by 
Peter.) 
Fig. 187.-Floor of pharynx of human embryo 
of about the end of the fourth week. (From 
model by Peter.) 
there arises a second and larger elevation, in the centre of which is a median groove 
or furrow. This elevation was named by His the furcula, and is at first separated 
from the tuberculum impar by a depression, but later by a ridge, the copula, 
formed by the forward growth and fusion of the ventral ends of the second and 
third arches. The posterior or pharyngeal part of the tongue is developed from DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
165 
the copula, which extends forward in the form of a V, so as to embrace between its 
two limbs the buccal part of the tongue. At the apex of the V a pit-like invagination 
occurs, to form the thyroid gland, and this depression is represented in the adult 
by the foramen cecum of the tongue. In the adult the union of the anterior and 
posterior parts of the tongue is marked by the V-shaped sulcus terminalis, the 
apex of which is at the foramen cecum, while the two limbs run lateralward and 
forward, parallel to, but a little behind, the vallate papillae. 
The Thyroid Gland.-The thyroid gland is developed from a median diverticulum 
(Fig. 189), which appears about the fourth week on the summit of the tuberculum 
impar, but later is found in the furrow immediately behind the tuberculum (Fig. 
186). It grows downward and backward as a tubular duct, which bifurcates and 
subsequently subdivides into a series of cellular cords, from which the isthmus 
and lateral lobes of the thyroid gland are developed. As already stated (page 111), 
the ultimobranchial bodies from the fifth pharyngeal pouches are enveloped by 
the lateral lobes of the thyroid gland; they undergo atrophy and do not form true 
thyroid tissue. The connection of the diverticulum with the pharynx is termed 
the thyroglossal duct; its continuity is subsequently interrupted, and it undergoes 
degeneration, its upper end being represented by the foramen cecum of the tongue, 
and its lower by the pyramidal lobe of the thyroid gland. 
Thyroid gland 
Parathyroids 
Thymus 
Arytenoid 
swellings 
Thymus 
Fig. 188.-Floor of pharynx of human embryo about thirty 
days old. (From model by Peter.) 
Fig. 189.-Scheme showing development of bran- 
chial epithelal bodies. (Modified from Kohn.) I, 
II, III, IV. Branchial pouches. 
Ultimo-branchial body 
The Palatine Tonsils.-The palatine tonsils are developed from the dorsal angles 
of the second branchial pouches. The entoderm which lines these pouches grows 
in the form of a number of solid buds into the surrounding mesoderm. These 
buds become hollowed out by the degeneration and casting off of their central cells, 
and by this means the tonsillar crypts are formed. Lymphoid cells accumulate 
around the crypts, and become grouped to form the lymphoid follicles; the latter, 
however, are not well-defined until after birth. 
The Thymus.-The thymus appears in the form of two flask-shaped entodermal 
diverticula, which arise, one on either side, from the third branchial pouch (Fig. 
189), and extend lateralward and backward into the surrounding mesoderm in 
front of the ventral aortse. Here they meet and become joined to one another by 
connective tissue, but there is never any fusion of the thymus tissue proper. The 
pharyngeal opening of each diverticulum is soon obliterated, but the neck of the 
flask persists for some time as a cellular cord. By further proliferation of the cells 
lining the flask, buds of cells are formed, which become surrounded and isolated 166 
EMBRYOLOGY 
by the invading mesoderm. In the latter, numerous lymphoid cells make their 
appearance, and are aggregated to form lymphoid follicles. These lymphoid 
cells are probably derivatives of the entodermal cells which lined the original 
diverticula and their subdivisions. Additional portions of thymus tissue are 
sometimes developed from the fourth branchial pouches. Thymus continues 
to grow until the time of puberty and then begins to atrophy. 
The Parathyroid Bodies.-The parathyroid bodies are developed as outgrowths 
from the third and fourth branchial pouches (Fig. 189). 
A pair of diverticula arise 
from the fifth branchial 
pouch and form what are 
termed the ultimobranchial 
bodies (Fig. 189): these fuse 
with the thyroid gland, but 
probably contribute no true 
thyroid tissue. 
The Hypophysis Cerebri.- 
This in the adult consists of 
a large anterior, and a small 
posterior, lobe: the former 
is derived from the ecto- 
derm of the stomodeum, the 
latter from the floor of the 
fore-brain. About the fourth 
week there appears a pouch- 
like diverticulum of the ecto- 
dermal lining of the roof of 
the stomodeum. This diver- 
ticulum, pouch of Rathke 
(Fig. 190), is the rudiment of 
the anterior lobe of the hypo- 
physis ; it extends upward in 
front of the cephalic end of 
the notochord and the rem- 
nant of the buccopharyngeal 
membrane and comes into 
contact with the under sur- 
face of the fore-brain. It is 
then constricted off to form 
a closed vesicle, but remains 
for a time connected to the 
ectoderm of the stomodeum 
by a solid cord of cells. Masses 
of epithelial cells form on 
either side and in the front 
wall of the vesicle, and by the growth between these of a stroma from the mesoderm 
the development of the anterior lobe is completed. The upwardly directed hypo- 
physeal involution becomes applied to the antero-lateral aspect of a downwardly 
directed diverticulum from the base of the fore-brain (page 128). This divertic- 
ulum constitutes the future infundibulum in the floor of the third ventricle 
while its inferior extremity becomes modified to form the posterior lobe of the 
hypophysis. In some of the lower animals the posterior lobe contains nerve cell$ 
and nerve fibres, but in man and the higher vertebrates these are replaced by 
connective tissue. A canal, craniopharyngeal canal, is sometimes found extending 
Fig. 190.-Vertical sections of the heads of early embryos of the rab- 
bit. Magnified. (From Mihalkovics.) A. From an embryo 5 mm. 
long. B. From an embryo 6 mm. long. C. Vertical section of the 
anterior end of the notochord and hypophysis, etc., from an embryo 16 
mm. long. In A the buccopharyngeal membrane is still present. In B 
it is in the process of disappearing, and the stomodeum now communi- 
cates with the primitive pharynx, am. Amnion, c. Fore-brain, ch. 
Notochord, f. Anterior extremity of fore-gut, i. h. Heart, if. Infun- 
dibulum. m. Wall of brain cavity, me. Mid-brain, mo. Hind-brain. 
p. Original position of hypophyseal diverticulum, py. ph. Pharynx. 
sp.e. Sphenoethmoidal, be. Central, sp.o. Sphenooccipital parts of basis 
cranii. tha. Thalamus. DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
167 
from the anterior part of the fossa hypophyseos of the sphenoid bone to the under 
surface of the skull, and marks the original position of Rathke's pouch; while at 
Notochord 
Rathke's pouch 
Mandibular 
arch 
Lung diverticulum 
Stomach 
Liver 
Opening into 
yolk-sac 
Allantois 
Postallantoic part 
of hind-gut 
Wolffian duct 
Lung diverticulum 
Thyroid gland 
(Esophagus 
Mandibular arch 
Notochord 
Rathke's pouch 
Stomach 
Pancreas ■ 
Bile-duct 
Vitelline duct' 
Allantois 
Postallantoic part 
of hind-gut 
-Wolffian duct 
Fig. 191.-Sketches in profile of two stages in the development of the human digestive tube. (His.) 
A X 30. B X 20. 
the junction of the septum of the nose with the palate traces of the stomodeal 
end are occasionally present (Frazer). 168 
EMBRYOLOGY 
The Further Development of the Digestive Tube.-The upper part of the fore-gut 
becomes dilated to form the pharynx (Fig. 184), in relation to which the branchial 
arches are developed (see page 108); the succeeding part remains tubular, and with 
the descent of the stomach is elongated to form the oesophagus. About the fourth 
week a fusiform dilatation, the future stomach, makes its appearance, and beyond 
this the gut opens freely into the yolk-sac (Fig. 191, A and B). The opening is at 
first wide, but is gradually narrowed into a tubular stalk, the yolk-stalk or vitelline 
duct. Between the stomach and the mouth of the yolk-sac the liver diverticulum 
appears. From the stomach to the rectum the alimentary canal is attached to the 
notochord by a band of mesoderm, from which the common mesentery of the gut 
is subsequently developed. The stomach has an additional attachment, viz., to 
the ventral abdominal wall as far as the umbilicus by the septum transversum. 
The cephalic portion of the septum takes part in the formation of the Diaphragma, 
while the caudal portion into which the liver grows forms the ventral mesogastrium 
(Fig. 193). The stomach undergoes a further dilatation, and its two curvatures 
can be recognized (Figs. 191, B, and 192), the greater directed toward the vertebral 
Trachea 
(Esophagus 
Lung 
- Trachea 
Lung 
Stomach 
(Esophagus 
Pancreas 
Bile-duct- 
Stomach 
Bile-duct 
Pancreas 
rCecum 
M-shaped loop of 
small intestine 
Cloaca 
Vitelline duct 
Cloaca 
Fig. 192.-Front view of two successive stages in the development of the digestive tube. (His.) 
column and the lesser toward the anterior wall of the abdomen, while its two 
surfaces look to the right and left respectively. Behind the stomach the gut 
undergoes great elongation, and forms a V-shaped loop which projects downward 
and forward; from the bend or angle of the loop the vitelline duct passes to the 
umbilicus (Fig. 193). For a time a considerable part of the loop extends beyond 
the abdominal cavity into the umbilical cord, but by the end of the third month 
it is withdrawn within the cavity. With the lengthening of the tube, the mesoderm, 
which attaches it to the future vertebral column and carries the bloodvessels for 
the supply of the gut, is thinned and drawn out to form the posterior common 
mesentery. The portion of this mesentery attached to the greater curvature of 
the stomach is named the dorsal mesogastrium, and the part which suspends the 
colon is termed the mesocolon (Fig. 194). About the sixth week a diverticulum 
of the gut appears just behind the opening of the vitelline duct, and indicates 
the future cecum and vermiform process. The part of the loop on the distal side 
of the cecal diverticulum increases in diameter and forms the future ascending 
and transverse portions of the large intestine. Until the fifth month the cecal 
diverticulum has a uniform calibre, but from this time onward its distal part DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
169 
remains rudimentary and forms the vermiform process, while its proximal part 
expands to form the cecum. Changes also take place in the shape and position 
of the stomach. Its dorsal part or greater curvature, to which the dorsal meso- 
Septum transversum 
Aorta 
Liver 
Falciform ligament of liver 
Dorsal mesogastrium 
Lesser omentum 
Stomach 
Umbilical vein 
Intestinal V-shaped loop 
Mesentery 
Umbilical cord 
~Colon 
Fig. 193.-The primitive mesentery of a six weeks' human embryo, half schematic. (Kollmann.) 
gastrium is attached, grows much more rapidly than its ventral part or lesser 
curvature to which the ventral mesogastrium is fixed. Further, the greater curva- 
ture is carried downward and to the left, so that the right surface of the stomach is 
Aorta 
Ventral mesogastrium 
Spleen 
Dorsal 
mesogastrium 
Caeliac artery 
Pancreas 
Duodenum 
Superior mesenteric 
artery 
Mesentery 
Cecum' 
Inferior mesenteric artery 
Fig. 194.-Abdominal part of digestive tube and its attachment to the primitive or common mesentery. Human 
embryo of six weeks. (After Toldt.) 
Hind-gut 
now directed backward and the left surface forward (Fig. 195), a change in position 
which explains why the left vagus nerve is found on the front, and the right vagus 
on the back of the stomach. The dorsal mesogastrium being attached to the greater 170 
EMBRYOLOGY 
curvature must necessarily follow its movements, and hence it becomes greatly 
elongated and drawn lateralward and ventralward from the vertebral column, 
and, as in the case of the stomach, the right surfaces of both the dorsal and ventral 
mesogastria are now directed backward, and the left forward. In this way a pouch, 
the bursa omentalis, is formed behind the stomach, and this increases in size as 
the digestive tube undergoes further development; the entrance to the pouch 
constitutes the future foramen epiploicum or foramen of Winslow. The duodenum 
is developed from that part of the tube which immediately succeeds the stomach; 
it undergoes little elongation, being more or less fixed in position by the liver and 
8th cervical nerve 
IsZ thoracic 
vertebra 
Pericardium 
Lung 
Liver 
Suprarenal 
gland 
Stomach 
12th thoracic 
nerve 
Mesonephros 
Kidney 
5th lumbar 
nerve 
Bladder 
Small 
intestine 
Cecum 
Great 
intestine 
Wolffian duct 
Ureter 
Fig. 195.-Reconstruction of a human embryo of 17 mm. (After Mall.) 
pancreas, which arise as diverticula from it. The duodenum is at first suspended 
by a mesentery, and projects forward in the form of a loop. The loop and its mes- 
entery are subsequently displaced by the transverse colon, so that the right surface 
of the duodenal mesentery is directed backward, and, adhering to the parietal 
peritoneum, is lost. The remainder of the digestive tube becomes greatly elongated, 
and as a consequence the tube is coiled on itself, and this elongation demands a 
corresponding increase in the width of the intestinal attachment of the mesentery, 
which becomes folded. 
At this stage the small and large intestines are attached to the vertebral column 171 
DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
by a common mesentery, the coils of the small intestine falling to the right of the 
middle line, while the large intestine lies on the left side.1 
The gut is now rotated upon itself, so that the large intestine is carried over in 
front of the small intestine, and the cecum is placed immediately below the liver; 
about the sixth month the cecum descends into the right iliac fossa, and the large 
intestine forms an arch consisting of the ascending, transverse, and descending 
portions of the colon-the transverse portion crossing in front of the duodenum 
and lying just below the greater curvature of the stomach; within this arch the 
coils of the small intestine are disposed (Fig. 197). Sometimes the downward 
progress of the cecum is arrested, so that in the adult it may be found lying imme- 
diately below the liver instead of in the right iliac region. 
Meso- 
gastrium 
Mesogastrium 
Greater 
curvature 
of stomach 
Greater 
curvature of 
stomach 
Bile duct 
Duodenum 
Greater omentum 
Duodenum 
Mesentery 
Greater 
omentum 
Point where 
intestinal 
loops cross 
each other 
Cecum 
Point where 
intestinal 
loops cross 
each other 
Mesocolon 
Mesocolon 
Small 
intestine 
Large 
intestine 
Vermiform 
process 
Cecum 
Large intestine 
Small intestine 
Vitelline duct 
Mesentery 
Vitelline duct 
Rectum 
. Rectum 
Fig. 196.-Diagrams to illustrate two stages in the development of the digestive tube and its mesentery. 
The arrow indicates the entrance to the bursa omentalis. 
Further changes take place in the bursa omentalis and in the common mesentery, 
and give rise to the peritoneal relations seen in the adult. The bursa omentalis, 
which at first reaches only as far as the greater curvature of the stomach, grows 
downward to form the greater omentum, and this downward extension lies in front 
of the transverse colon and the coils of the small intestine (Fig. 198). Above, before 
the pleuro-peritoneal opening is closed, the bursa omentalis sends up a diverticulum 
on either side of the oesophagus; the left diverticulum soon disappears, but the right 
is constricted off and persists in most adults as a small sac lying within the thorax 
on the right side of the lower end of the oesophagus. The anterior layer of the 
transverse mesocolon is at first distinct from the posterior layer of the greater 
omentum, but ultimately the two blend, and hence the greater omentum appears 
as if attached to the transverse colon (Fig. 199). The mesenteries of the ascending 
and descending parts of the colon disappear in the majority of cases, while that of 
the small intestine assumes the oblique attachment characteristic of its adult 
condition. 
1 Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross from the 
right to the left side of the vertebra! column, but lies entirely on the right side of the median plane, where it is continued 
into the jejunum; the arteries to the small intestine (aa. intestinales') also arise from the right instead of the left side 
of the superior mesenteric artery. 172 
EMBRYOLOGY 
The lesser omentum is formed, as indicated above, by a thinning of the meso- 
derm or ventral mesogastrium, which attaches the stomach and duodenum to the 
anterior abdominal wall. By the subsequent growth of the liver this leaf of 
mesoderm is divided into two parts, viz., the lesser omentum between the stomach 
and liver, and the falciform and coronary ligaments between the liver and the 
abdominal wall and Diaphragma (Fig. 198). 
The Rectum and Anal Canal.-The hind-gut is at first prolonged backward into 
the body-stalk as the tube of the allantois; but, with the growth and flexure of the 
tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried 
forward to the ventral aspect of the body, and consequently a bend is formed at the 
junction of the hind-gut and allantois. This bend becomes dilated into a pouch, 
which constitutes the entodermal cloaca; into its dorsal part the hind-gut opens, 
and from its ventral part the allantois passes forward. At a later stage the Wolffian 
and Mullerian ducts open into its ventral portion. The cloaca is, for a time, shut 
Ventral 
mesogastrium 
Liver- 
Bursa 
omentalis 
Umbilical vein- 
Border of 
ventral 
mesogastrium' 
Pancreas 
Dorsal 
'mesogastrium 
Duodenum 
Greater 
omentum 
Stomach 
Transverse 
' mesocolon 
Transverse 
colon 
Fig. 197.--Final disposition of the 
intestines and their vascular relations. 
(Jonnesco.) A. Aorta. H. Hepatic 
artery. M, Col. Branches of superior 
mesenteric artery, m, m'. Branches 
of inferior mesenteric artery. S. 
Splenic artery. 
Fig. 198.-Schematic figure of the bursa omentalis, etc. Human 
embryo of eight weeks. (Kollmann.) 
off from the anterior by a membrane, the cloacal membrane, formed by the apposi- 
tion of the ectoderm and entoderm, and reaching, at first, as far forward as the 
future umbilicus. Behind the umbilicus, however, the mesoderm subsequently 
extends to form the lower part of the abdominal wall and symphysis pubis. By 
the growth of the surrounding tissues the cloacal membrane comes to lie at the 
bottom of a depression, which is lined by ectoderm and named the ectodermal 
cloaca (Fig. 200). 
The entodermal cloaca is divided into a dorsal and a ventral part by means of a 
partition, the urorectal septum (Fig. 201), which grows downward from the ridge 
separating the allantoic from the cloacal opening of the intestine and ultimately 
fuses with the cloacal membrane and divides it into an anal and a urogenital part. 
The dorsal part of the cloaca forms the rectum, and the anterior part of the uro- 
genital sinus and bladder. For a time a communication named the cloacal duct 
exists between the two parts of the cloaca below the urorectal septum; this duct DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
173 
occasionally persists as a passage between the rectum and urethra. The anal 
canal is formed by an invagination of the ectoderm behind the urorectal septum. 
Diaphragma 
Diaphragma 
Liver 
Liver 
Lesser omentum 
Bursa omentalis. 
Stomach- 
Greater omentum 
Lesser omentum 
Bursa omentalis 
Pancrea s 
Stomach 
Pancreas 
Transverse mesocolon 
Greater omentum 
Obliterated part of wesogcLstrium 
Duodenum 
Transverse colon 
Transverse colon 
Mesentery 
■Small intestine 
Small intestine 
Duodenum 
Fig. 199.-Diagrams to illustrate the development of the greater omentum and transverse mesocolon. 
Mesentery 
Wolffian duct 
Wolffian duct 
Bladder 
Ectodermal cloaca 
Rectum 
Septum 
Cloacal membrane 
Notochord 
Fig. 200.-Tail end of human embryo from fifteen to 
eighteen days old. (From model by Keibel.) 
Fig. 201.-Cloaca of human embryo from 
twenty-five to twenty-seven days old. (From 
model by Keibel.) 
Wolffian duct 
Ureter, 
Symphysis pubis 
Mullerian duct 
Bladder x 
Glans penis 
Urethra 
Vertebral column 
Fig. 202.-Tail end of human embryo, from eight and a half to nine weeks old. (From model by Keibel.) 174 
EMBRYOLOGY 
This invagination is termed the proctodoeum, and it meets with the entoderm of the 
hind-gut and forms with it the anal membrane. By the absorption of this membrane 
the anal canal becomes continuous with the rectum (Fig. 202). A small part of the 
hind-gut projects backward beyond the anal membrane; it is named the post-anal 
gut (Fig. 200), and usually becomes obliterated and disappears.1 
The Liver.-The liver arises in the form of a diverticulum or hollow outgrowth 
from the ventral surface of that portion of the gut which afterward becomes the 
descending part of the duodenum (Figs. 191, 203). This diverticulum is lined by 
entoderm, and grows upward and forward into the septum transversum, a mass 
of mesoderm between the vitelline duct and the pericardial cavity, and there gives 
off two solid buds of cells which represent the right and the left lobes of the liver. 
The solid buds of cells grow into columns or cylinders, termed the hepatic cylinders, 
which branch and anastomose to form a close meshwork. This network invades 
the vitelline and umbilical veins, and breaks up these vessels into a series of capil- 
lary-like vessels termed sinusoids (Minot), which ramify in the meshes of the cellular 
network and ultimately form the venous capillaries of the liver. By the continued 
Truncus arteriosus 
Pericardial cavity 
Dorsal mesocardium 
Anterior wall of 
pericardium' ■ 
Atrium 
Lower wall of 
pericardium ■ 
Cuvierian duct 
Umbilical vein 
Liver 
Vitelline vein 
Bile duct 
Communication 
between pericardial 
and peritoneal cavities 
Vitelline duct- 
Peritoneal cavity 
Fig. 203.-Liver with the septum transversum. Human embryo 3 mm. long. (After model and figure by His.) 
growth and ramification of the hepatic cylinders the mass of the liver is gradually 
formed. The original diverticulum from the duodenum forms the common bile- 
duct, and from this the cystic duct and gall-bladder arise as a solid outgrowth which 
later acquires a lumen. The opening of the common duct is at first in the ventral 
wall of the duodenum; later, owing to the rotation of the gut, the opening is carried 
to the left and then dorsalward to the position it occupies in the adult. 
As the liver undergoes enlargement, both it and the ventral mesogastrium of 
the fore-gut are gradually differentiated from the septum transversum; and from 
the under surface of the latter the liver projects downward into the abdominal 
cavity. By the growth of the liver the ventral mesogastrium is divided into two 
parts, of which the anterior forms the falciform and coronary ligaments, and the 
posterior the lesser omentum. About the third month the liver almost fills the 
abdominal cavity, and its left lobe is nearly as large as its right. From this period 
1 Consult, in this connection, the following article: "A Contribution to the Morphology of the Human Urino- 
genital Tract," by D. Berry Hart, M.D., F.R.C.P.E., Journal of Anatomy and Physiology, April, 1901, vol. xxxv. DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
175 
the relative development of the liver is less active, more especially that of the left 
lobe, which actually undergoes some degeneration and becomes smaller than the 
right; but up to the end of fetal life the liver remains relatively larger than in 
the adult. 
The Pancreas (Figs. 204, 205).-The pancreas is developed in two parts, a 
dorsal and a ventral. The former arises as a diverticulum from the dorsal aspect 
of the duodenum a short distance above the hepatic diverticulum, and, growing 
upward and backward into the dorsal mesogastrium, forms a part of the head and 
uncinate process and the whole of the body and tail of the pancreas. The ventral 
Accessory pancreatic duct 
Dorsal pancreas 
Accessory pancreatic duct 
Dorsal pancreas 
Pancreatic duct 
Ventral pancreas 
Ventral pancreas 
Bile duct 
Bile duct 
Fig. 205.-Pancreas of a human embryo at end of 
sixth week. (Kollmann.) 
Pancreatic duct 
Fig. 204.-Pancreas of a human embryo of five 
weeks. (Kollmann.) 
part appears in the form of a diverticulum from the primitive bile-duct and forms 
the remainder of the head and uncinate process of the pancreas. The duct of the 
dorsal part (accessory pancreatic duct) therefore opens independently into the 
duodenum, while that of the ventral part (pancreatic duct) opens with the common 
bile-duct. About the sixth week the two parts of the pancreas meet and fuse 
and a communication is established between their ducts. After this has occurred 
the terminal part of the accessory duct, i. e., the part between the duodenum and 
the point of meeting of the two ducts, undergoes little or no enlargement, while 
Lesser 
omentum 
Liver 
Stomach 
Liver 
Left suprarenal 
gland 
Right suprarenal 
gland 
Fig. 206.-Schematic and enlarged cross-section through the body of a human embryo in the region of the 
mesogastrium. Beginning of third month. (Toldt.) 
the pancreatic duct increases, in size and forms, the main duct of the gland. The 
opening of the accessory duct into the duodenum is sometimes obliterated, and 
even when it remains patent it is probable that the whole of the pancreatic secretion 
is conveyed through the pancreatic duct. 
At first the pancreas is directed upward and backward between the two layers 
of the dorsal mesogastrium, which give to it a complete peritoneal investment, 
and its surfaces look to the right and left. With the change in the position of the 
stomach the dorsal mesogastrium is drawn downward and to the left, and the right 
side of the pancreas is directed backward and the left forward (Fig. 206). The 176 
EMBRYOLOGY 
right surface becomes applied to the posterior abdominal wall, and the peritoneum 
which covered it undergoes absorption (Fig. 207); and thus, in the adult, the gland 
appears to lie behind the peritoneal cavity. 
Stomach 
Lesser 
omentum 
Liver 
Liver 
Right suprarenal gland 
Left suprarenal gland 
Fig. 207.-Section through same region as in Fig. 206, at end of third month. (Toldt.) 
The Spleen (Fig. 194).-Although the spleen belongs to the group of ductless 
glands, its development may be conveniently referred to here. It appears about 
the fifth week as a localized thickening of the mesoderm in the dorsal mesogastrium 
above the tail of the pancreas. With the change in position of the stomach the 
spleen is carried to the left, and comes to lie behind the stomach and in contact 
with the left kidney. The part of the dorsal mesogastrium which intervened 
between the spleen and the greater curvature of the stomach forms the gastro- 
splenic ligament. 
Mouth of olfactory pit 
Median part of fronto- 
nasal process 
Eye. 
Processus globulari 
Maxillary process 
Hypophysis 
Mandibular arch 
1st branchial pouch 
Future tympanic 
membrane 
Sinus cervicalis 
Hyoid arch 
Laryngo-tracheal tube 
Third arch 
Lung 
Fig. 208.-The head and neck of a human embryo thirty-two days old, seen from the ventral surface. The floor of 
the mouth and pharynx have been removed. (His.) 
Fourth arch 
The Respiratory Organs.-The rudiment of the respiratory organs appear 
as a median longitudinal groove in the ventral wall of the pharynx. The groove 
deepens and its lips fuse to form a septum which grows from below upward and 
converts the groove into a tube, the laryngo-tracheal tube (Fig. 208), the cephalic 
end of which opens into the pharynx by a slit-like aperture formed by the persistent 
anterior part of the groove. The tube is lined by entoderm from which the epithe- 
lial lining of the respiratory tract is developed. The cephalic part of the tube DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 
177 
becomes the larynx, and its next succeeding part the trachea, while from its caudal 
end two lateral outgrowths, the right and left lung buds, arise, and from them the 
bronchi and lungs are developed. The first rudiment of the larynx consists of two 
arytenoid swellings, which appear, one on either side of the cephalic end of the laryngo- 
tracheal groove, and are continuous in front of the groove with a transverse ridge 
(furcula of His) which lies between the ventral ends of the third branchial arches 
and from which the epiglottis is subsequently developed (Figs. 187, 188). After 
the separation of the trachea from the oesophagus, the arytenoid swellings come 
into contact with one another and with the back of the epiglottis, and the entrance 
to the larynx assumes the form of a T-shaped cleft, the margins of the cleft adhere 
to one another and the laryngeal entrance is for a time occluded. The mesodermal 
wall of the tube becomes condensed to form the cartilages of the larynx and trachea. 
The arytenoid swellings are differentiated into the arytenoid and corniculate car- 
tilages, and the folds joining them to the epiglottis form the aryepiglottic folds 
in which the cuneiform cartilages are developed as derivatives of the epiglottis. 
The thyroid cartilage appears as two lateral plates, each chondrified from two 
centres and united in the mid-ventral line by membrane in which an additional 
centre of chondrification develops. The cricoid cartilage arises from two cartil- 
aginous centres, which soon unite ventrally and gradually extend and ultimately 
fuse on the dorsal aspect of the tube. 
J. Ernest Frazer1 has made an important investigation on the development of the larynx, 
and the following are his main conclusions: 
The opening of the pulmonary diverticulum lies between the two fifth arch masses and behind 
a "central mass" in the middle line-the proximal end of the diverticulum is compressed between 
the fifth arch masses. The fifth arch is joined by the fourth to form a "lateral mass" on each 
side of the opening, and these "lateral masses" grow forward and overlap the central mass and 
so form a secondary transverse cavity, which is really a part of the cavity of the pharynx. The 
two parts of the cavity of the larynx are separated in the adult by a line drawn back along the 
vocal fold and then upward along the border of the arytenoid eminence to the interarytenoid 
notch. The arytenoid and cricoid are developed in the fifth arch mass. The thyroid is primarily 
a fourth arch derivative, and if it has a fifth arch element this is a later addition. The epiglottis 
is derived from the "central mass," and has a third arch element in its oral and upper aspect; 
the arch value of the "central mass" is doubtful. 
Fig. 209.-Lung buds from a human embryo of 
about four weeks, showing commencing lobulations. 
(His.) 
Fig. 210.-Lungs of a human embryo more 
advanced in development. (His.) 
The right and left lung buds grow out behind the ducts of Cuvier, and are at 
first symmetrical, but their ends soon become tabulated, three lobules appearing 
on the right, and two on the left; these subdivisions are the early indications of the 
corresponding tabes of the lungs (Figs. 209, 210). The buds undergo further sub- 
division and ramification, and ultimately end in minute expanded extremities- 
the infundibula of the lung. After the sixth month the air-sacs begin to make their 
appearance on the infundibula in the form of minute pouches. The pulmonary 
arteries are derived from the sixth aortic arches. During the course of their 
development the lungs migrate in a caudal direction, so that by the time of birth 
1 Journal of Anatomy and Physiology, vol. xliv. 178 
EMBRYOLOGY 
the bifurcation of the trachea is opposite the fourth thoracic vertebra. As the 
lungs grow they project into that part of the coelom which will ultimately form the 
pleural cavities, and the superficial layer of the mesoderm enveloping the lung 
rudiment expands on the growing lung and is converted into the pulmonary pleura. 
DEVELOPMENT OF THE BODY CAVITIES. 
In the human embryo described by Peters the mesoderm outside the embryonic 
disk is split into two layers enclosing an extra-embryonic coelom; there is no trace 
of an intra-embryonic coelom. At a later stage four cavities are formed within the 
embryo, viz., one on either side within the mesoderm of the pericardial area, and 
one in either lateral mass of the general mesoderm. All these are at first independent 
of each other and of the extra-embryonic coelom, but later they become continuous. 
The two cavities in the general mesoderm unite on the ventral aspect of the gut 
and form the pleuro-peritoneal cavity, which becomes continuous with the remains 
of the extra-embryonic coelom around the umbilicus; the two cavities in the peri- 
cardial area rapidly join to form a single pericardial cavity, and from this two lateral 
Pleural cavity 
Mesentery 
Lung^ 
Mesoderm 
surrounding 
duct of Cuvier 
Pl euro- pericardial 
opening 
'Dorsal mesocardium 
-Heart 
Pericardium 
Fig. 211.-Figure obtained by combining several successive sections of a human embryo of about the fourth week 
(From Kollmann.) The upper arrow is in the pleuroperitoneal opening, the lower in the pleuropericardial. 
diverticula extend caudalward to open into the pleuro-peritoneal cavity (Fig. 211). 
Between the two latter diverticula is a mass of mesoderm containing the ducts 
of Cuvier, and this is continuous ventrally with the mesoderm in which the umbili- 
cal veins are passing to the sinus venosus. A septum of mesoderm thus extends 
across the body of the embryo. It is attached in front to the body-wall between 
the pericardium and umbilicus; behind to the body-wall at the level of the second 
cervical segment; laterally it is deficient where the pericardial and pleuro-peri- 
toneal cavities communicate, while it is perforated in the middle line by the fore- 
gut. This partition is termed the septum transversum, and is at first a bulky plate 
of tissue. As development proceeds the dorsal end of the septum is carried grad- 
ually caudalward, and when it reaches the fifth cervical segment muscular tissue 
with the phrenic nerve grow into it. It continues to recede, however, until it 
reaches the position of the adult Diaphragma on the bodies of the upper lumbar 
vertebrae. As already described (page 174), the liver buds grow into the septum 
transversum and undergo development there. 
The lung buds meantime have grown out from the fore-gut, and project laterally 
into the forepart of the pleuro-peritoneal cavity; the developing stomach and liver DEVELOPMENT OF THE BODY CAVITIES 
179 
are imbedded in the septum trans versum; caudal to this the intestines project into 
the back part of the pleuro-peritoneal cavity (Fig. 212). Owing to the descent of 
the dorsal end of the septum transversum the lung buds come to lie above the 
Left due of Cuvier 
(Esophagus 
Right duct of Cuvier 
Mesoderm 
surrounding duct 
Pleuro-pericardial 
opening 
■Ridge growing across 
opening 
Dorsal mesentery 
Omental bursa 
Peritoneal recess 
Stomach 
Fig. 212.-Upper part of ccelom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) 
septurn and thus pleural and peritoneal portions of the pleuro-peritoneal cavity 
(still, however, in free communication with one another) may be recognized; the 
pericardial cavity opens into the pleural part. 
The ultimate separation of the permanent cavities from one another is effected 
by the growth of a ridge of tissue on either side from the mesoderm surrounding 
Aorta 
Pleural cavity 
Lung 
(Esophagus 
Inferior vena cava 
Body-wall 
Pericardium 
the duct of Cuvier (Figs. 211, 212). The front part of this ridge grows across and 
obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- 
peritoneal opening. 
Fig. 213.-Diagram of transverse section through rabbit embryo. (After Keith.) 180 
EMBRYOLOGY 
With the continued growth of the lungs the pleural cavities are pushed forward 
in the body-wall toward the ventral median line, thus separating the pericardium 
from the lateral thoracic walls (Fig. 213). The further development of the peritoneal 
cavity has been described with the development of the digestive tube (page 168 
et seq.). 
Sterno-costal part of 
Diaphragma 
Central tendon of Diaphragma 
Inferior vena cava 
Spleen 
(Esophagus 
Vertebral part of Diaphragma 
Suprarenal gland 
Colon 
Posterior 'mediastinal cavity 
-Aorta 
Eleventh rib 
Twelfth rib 
Spino-costal hiatus 
Left pleura 
Right pleura 
Fig. 214.-The thoracic aspect of the Diaphragma of a newly born child in which the communication between the 
peritoneum and pleura has not been closed on the left side; the position of the opening is marked on the right side by 
the spinocostal hiatus. (After Keith.) 
DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS. 
The urinary and generative organs are developed from the intermediate cell- 
mass which is situated between the primitive segments and the lateral plates of 
mesoderm. The permanent organs of the adult are preceded by a set of structures 
which are purely embryonic, and which with the exception of the ducts disappear 
almost entirely before the end of fetal life. These embryonic structures are on 
either side; the pronephros, the mesonephros, the metanephros, and the Wolffian and 
Mullerian ducts. The pronephros disappears very early; the structural elements 
of the mesonephros mostly degenerate, but in their place is developed the genital 
gland in association with which the Wolffian duct remains as the duct of the male 
genital gland, the Mullerian as that of the female; some of the tubules of the 
metanephros form part of the permanent kidney. 
The Pronephros and Wolffian Duct.-In the outer part of the intermediate 
cell-mass, immediately under the ectoderm, in the region from the fifth cervical to 
the third thoracic segments, a series of short evaginations from each segment grow 
dorsalward and extend caudalward, fusing successively from before backward to 
form the pronephric duct. This continues to grow caudalward until it opens into 
the ventral part of the cloaca; beyond the pronephros it is termed the Wolffian duct. 
The original evaginations form a series of transverse tubules each of which com- 
municates by means of a funnel-shaped ciliated opening with the coelomic cavity, 
and in the course of each duct a glomerulus also is developed. Secondary glo- 
meruli are formed ventral to each of the others, and the complete group constitutes 
the pronephros. The pronephros undergoes rapid atrophy and disappears. 
The Mesonephros, Mullerian Duct, and Genital Gland.-On the medial side of 
the Wolffian duct, from the sixth cervical to the third lumbar segments, a series 
of tubules, the Wolffian tubules (Fig. 215), is developed; at a later stage in develop- 
ment they increase in number by outgrowths from the original tubules. These 
tubules first appear as solid masses of cells, which later become hollowed in the DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 
181 
centre; one end grows toward and finally opens into the Wolffian duct, the other 
dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus. 
The tubules collectively constitute the mesonephros or Wolffian body (Figs. 195, 
216). By the fifth or sixth week this body forms an elongated spindle-shaped 
structure, termed the urogenital fold (Fig. 215), which projects into the coelomic 
cavity at the side of the dorsal mesentery, reaching from the septum transversum 
Wolffian duct 
Mullerian duct 
Stroma 
of ovary 
Wolffian tubules 
Genital 
ridge 
Primitive 
ova 
Body-wall 
Mesentery 
Fig. 215.-Section of the urogenital fold of a chick embryo of the fourth day. (Waldeyer.) 
in front to the fifth lumbar segment behind; in this fold the reproductive glands are 
developed. The Wolffian bodies persist and form the permanent kidneys in fishes 
and amphibians, but in reptiles, birds, and mammals, they atrophy and for the 
most part disappear coincidently with the development of the permanent kidneys. 
The atrophy begins during the sixth or seventh week and rapidly proceeds, so that 
by the beginning of the fifth month only the ducts and a few of the tubules remain. 
In the male the Wolffian duct persists, 
and forms the tube of the epididymis, the 
ductus deferens and the ejaculatory duct, 
while the seminal vesicle arises during the 
third month as a lateral diverticulum from 
its hinder end. A large part of the head 
end of the mesonephros atrophies and dis- 
appears; of the remainder the anterior 
tubules form the efferent ducts of the 
testis; while the posterior tubules are 
represented by the ductuli aberrantes, 
and by the paradidymis, which is some- 
times found in front of the spermatic 
cord above the head of the epididvmis 
(Fig. 219, C). 
In the female the Wolffian bodies and ducts atrophy. The remains of the 
Wolffian tubules are represented by the epodphoron or organ of Rosenmuller, and 
the paroophoron, two small collections of rudimentary blind tubules which are 
situated in the mesosalpinx (Fig. 217). The lower part of the Wolffian duct 
Fig. 216.-Enlarged view from the front of the 
left Wolffian body before the establishment of the 
distinction of sex. (From Farre, after Kobelt.) a, 
a, b, c, d. Tubular structure of the Wolffian body. 
e. Wolffian duct. f. Its upper extremity, g. Its 
termination in x, the urogenital sinus, h. The duct 
of Muller, i. Its upper, funnel-shaped extremity. 
k. Its lower end, terminating in the urogenital sinus. 
I. The genital gland. 182 
EMBRYOLOGY 
disappears, while the upper part persists as the longitudinal duct of the epodphoron 
or duct of Gartner1 (Fig. 219, B). 
The Mullerian Ducts.-Shortly after the formation of the Wolffian ducts a 
second pair of ducts is developed; these are named the Mullerian ducts. Each 
arises on the lateral aspect of the corresponding Wolffian duct as a tubular inva- 
gination of the cells lining the coelom (Fig. 215). The orifice of the invagination 
Fig. 217.-Broad ligament of adult, showing epoophoron. (From Farre, after Kobelt.) a, a. Epoophoron formed 
from the upper part of the Wolffian body. b. Remains of the uppermost tubes sometimes forming appendices, c. Middle 
set of tubes, d. Some lower atrophied tubes, e. Atrophied remains of the Wolffian duct. f. The terminal bulb or 
hydatid, h. The uterine tube, originally the duct of Muller, i. Appendix attached to the extremity. I. The ovary. 
remains patent, and undergoes enlargement and modification to form the abdomi- 
nal ostium of the uterine tube. The ducts pass backward lateral to the Wolffian 
ducts, but toward the posterior end of the embryo they cross to the medial side 
of these ducts, and thus come to lie side by side between and behind the latter- 
the four ducts forming what is termed the genital cord (Fig. 218). The Mullerian 
ducts end in an epithelial elevation, the Mullerian eminence, on the ventral part of 
the cloaca between the orifices of the Wolffian 
ducts; ata later date they open into the cloaca 
in this situation. 
In the male' the Mullerian ducts atrophy, 
but traces of their anterior ends are repre- 
sented by the appendices testis (hydatids of 
Morgagni), while their terminal fused portions 
form the utriculus in the floor of the prostatic 
portion of the urethra (Fig. 219, C). 
In the female the Mullerian ducts persist 
and undergo further development. The por- 
tions which lie in the genital core fuse to form 
the uterus and vagina; the parts in front of 
this cord remain separate, and each forms 
the corresponding uterine tube-the abdomi- 
nal ostium of which is developed from the 
anterior extremity of the original tubular in- 
vagination from the coelom (Fig. 219, B). The 
usion of the Mullerian ducts begins in the third month, and the septum formed 
>y their fused medial walls disappears from below upward, and thus the cavities 
Mullerian ducts 
Mullerian 
eminence 
Fig. 218.-Urogenital sinus of female human 
embryo of eight and a half to nine weeks old. 
(From model by Keibel) 
1 Berry Hart (op. cit.) has described the Wolffian ducts as ending at the site of the future hymen in bulbous enlarge- 
ments, which he has named the Wolffian bulbs; and states that the hymen is formed by these bulbs, "aided by a special 
involution from below of the cells lining the urogenital sinus." He further believes that "the lower third of the vagina 
is due to the coalescence of the upper portion of the urogenital sinus and the lower ends of the Wolffian ducts," and 
that "the epithelial lining of the vagina is derived from the Wolffian bulbs." He also regards the colliculus seminalis 
of the male urethra as being formed from the lower part of the Wolffian ducts. DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 
183 
Fig. 219.-Diagrams to show the develop- 
ment of male and female generative organs 
from a common type. (Allen Thomson.) 
A.-Diagram of the primitive urogenital 
organs in the embryo previous to sexual dis- 
tinction. 3. Ureter. 4. Urinary bladder. 5. 
Urachus, cl. Cloaca, cp. Elevation which be- 
comes clitoris or penis, i. Lower part of the 
intestine. Is. Fold of integument from which 
the labia majora or scrotum are formed. 
m, m. Right and left Mullerian ducts uniting 
together and running with the Wolffian ducts 
in gc, the genital cord. ot. The genital ridge 
from which either the ovary or testis is 
formed, ug. Sinus urogenitalis. W. Left 
Wolffian body, w, w. Right and left Wolffian 
ducts. 
B.-Diagram of the female type of sexual 
organs. C. Greater vestibular gland, and 
immediately above it the urethra, cc. Corpus 
cavernosum clitoridis. dG. Remains of the 
left Wolffian duct, such as give rise to the 
duct of Gartner, represented by dotted lines; 
that of the right side is marked w. f. The 
abdominal opening of the left uterine tube. 
g. Round ligament, corresponding to guber- 
naculum. h. Situation of the hymen, i. Lower 
pait of the intestine. I. Labium major, n. 
Labium minus, o. The left ovary, po. Epo- 
ophoron. sc. Corpus cavernosum urethrae, u. 
Uterus. The uterine tube of the right side 
is marked m. v. Vulva, va. Vagina. W. 
Scattered remains of Wolffian tubes near it 
(paroophoron of Waldeyer). 
C.-Diagram of the male type of sexual 
organs. C. Bulbo-urethral gland of one side. 
cp. Corpora cavernosa penis cut short, e. 
Caput epididymis, g. The gubernaculum. 
i. Lower part of the intestine, m. Mullerian 
duct, the upper part of which remains as 
the hydatid of Morgagni; the lower part, 
represented by a dotted line descending to 
the prostatic utricle, constitutes the occa- 
sionally existing cornu and tube of the uterus 
masculinus. pr. The prostate, s. Scrotum. 
sp. Corpus cavernosum urethrae, t. Testis 
in the place of its original formation, t', 
together with the dotted lines above, indi- 
cates the direction in which the testis and 
epididymis descend from the abdomen into 
the scrotum, vd. Ductus deferens, vh. Ductus 
aberrans. vs. The vesicula seminalis. W. 
Scattered remains of the Wolffian body, con- 
stituting the organ of Giraldes, or the para- 
didymis of Waldeyer. 184 
EMBRYOLOGY 
of the vagina and uterus are produced. About the fifth month an annular con- 
striction marks the position of the neck of the uterus, and after the sixth month 
the walls of the uterus begin to thicken. For a time the vagina is represented by a 
solid rod of epithelial cells. A ring-like outgrowth of this epithelium occurs at 
the lower end of the uterus and marks the future vaginal fornices; about the fifth 
or sixth month the lumen of the vagina is produced by the breaking down of the 
central cells of the epithelium. The hymen represents the remains of the Mullerian 
eminence. 
Genital Glands.-The first appearance of the genital gland is essentially the 
same in the two sexes, and consists in a thickening of the epithelial layer which 
lines the peritoneal cavity on the medial side of the urogenital fold (Fig. 215). 
The thick plate of epithelium extends deeply, pushing before it the mesoderm and 
forming a distinct projection. This is termed the genital ridge (Fig. 215), and from 
it the testis in the male and the ovary in the female are developed. At first the 
mesonephros and genital ridge are suspended by a common mesentery, but as the 
embryo grows the genital ridge gradually becomes pinched off from the mesone- 
phros, with which it is at first continuous, 
though it still remains connected to the 
remnant of this body by a fold of peri- 
toneum, the mesorchium or mesovarium 
(Fig. 220). About the seventh week the 
distinction of sex in the genital ridge 
begins to be perceptible. 
The Ovary.-The ovary, thus formed 
from the genital ridge, is at first a mass 
of cells derived from the coelomic epi- 
thelium; later the mass is differentiated 
into a central part or medulla (Fig. 221) 
covered by a surface layer, the germinal 
epithelium. Between the cells of the 
germinal epithelium a number of larger 
cells, the primitive ova, are found, and 
these are carried into the subjacent 
stroma by bud-like ingrowths (genital 
cords) of the germinal epithelium (Fig. 
222). The surface epithelium ultimately 
forms the permanent epithelial covering 
of this organ; it soon loses its connection 
with the central mass, and a tunica albuginea develops between them. The ova 
are chiefly derived from the cells of the central mass; these are separated from 
one another by the growth of connective tissue in an irregular manner; each ovum 
assumes a covering of connective tissue (follicle) cells, and in this way the rudi- 
ments of the ovarian follicles are formed (Fig. 222). According to Beard the primi- 
tive ova are early set apart during the segmentation of the ovum and migrate into 
the germinal ridge. 
Wolffian body 
Mullerian duct 
Wolffian duct 
Medulla spinalis 
Spinal ganglion 
Notochord 
Sympathetic ganglion 
Inferior vena cava 
Common iliac artery 
" Ureter 
Mesovarium 
Intestine 
■ Bladder 
Umbilical artery 
Fig. 220.-Transverse section of human embryo eight and 
a half to nine weeks old. (From model by Keibel.) 
Waldeyer taught that the primitive germ cells are derived from the "germinal epithelium," 
covering the genital ridge. Beard,1 on the other hand, maintains that in the skate they are not 
derived from this epithelium, but are probably formed during the later stages of cell cleavage, 
before there is any trace of an embryo; and a similar view was advanced by Nussbaum as to their 
origin in amphibia. Beard says: "At the close of segmentation many of the future germ cells 
lie in the segmentation cavity just beneath the site of the future embryo, and there is no doubt 
they subsequently wander into it." The germ cells, "after they enter the resting phase, are 
'Journal of Anatomy and Physiology, vol. xxxviii. DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 
185 
sharply marked off from the cells of the embryo by entire absence of mitoses among them." 
They can be further recognized by their irregular form and amoeboid processes, and by the fact 
Uterine, tube 
■ Epoophoron 
Germinal epithelium 
• Pete 
Medulla 
Mesonephros 
Plica peritonalis 
tuboe 
Uterine tube 
Fig 221.-Longitudinal section of ovary of cat embryo of 9.4 cm. long. Schematic. (After Coert.) 
that their cytoplasm has no affinity for ordinary stains, but assumes a brownish tinge when treated 
by osmic acid. The path along which they travel into the embryo is a very definite one, viz., 
"from the yolk sac upward between the splanchnopleure and gut in the hinder portion of the 
Genital cord 
Germinal 
epithelium 
Primitive ova 
Cell-nest 
Blood-vessel 
Ovarian follicle 
Fig. 222.-Section of the ovary of a newly born child. (Waldeyer.) 
embryo." This pathway, named by Beard the germinal path, "leads them directly to the posi- 
tion which they ought finally to take up in the 'germinal ridge' or nidus." A considerable number 186 
EMBRYOLOGY 
apparently never reach their proper destination, since "vagrant germ cells are found in all sorts 
of places, but more particularly on the mesentery." Some of these may possibly find their way 
into the germinal ridge; some probably undergo atrophy, while others may persist and become 
the seat of dermoid tumors. 
The Testis.-The testis is developed in much the same way as the ovary. Like 
the ovary, in its earliest stages it consists of a central mass of epithelium covered 
by a surface epithelium. In the central mass a series of cords appear (Fig. 223), 
and the periphery of the mass is converted into the tunica albuginea, thus excluding 
the surface epithelium from any part in the formation of the tissue of the testis. 
The cords of the central mass run together toward the future hilus and form a 
network which ultimately becomes the rete testis. From the cords the seminiferous 
tubules are developed, and between them connective tissue septa extend. The 
seminiferous tubules become connected with outgrowths from the Wolffian body, 
which, as before mentioned, form the efferent ducts of the testis. 
Descent of the Testes.-The testes, at an early period of fetal life, are placed 
at the back part of the abdominal cavity, behind the peritoneum, and each is 
attached by a peritoneal fold, the 
mesorchium, to the mesonephros. 
From the front of the mesonephros 
a fold of peritoneum termed the 
inguinal fold grows forward to meet 
and fuse with a peritoneal fold, 
the inguinal crest, which grows 
backward from the antero-lateral 
abdominal wall. The testis thus ac- 
quires an indirect connection with 
the anterior abdominal wall; and at 
the same time a portion of the peri- 
toneal cavity lateral to these fused 
folds is marked off as the future 
saccus vaginalis. In the inguinal 
crest a peculiar structure, the guber- 
naculum testis, makes its appearance. 
This is at first a slender band, ex- 
tending from that part of the skin 
of the groin which afterward forms 
the scrotum through the inguinal 
canal to the body and epididymis of the testis. As development advances, the 
peritoneum enclosing the gubernaculum forms two folds, one above the testis 
and the other below it. The one above the testis is the plica vascularis, and con- 
tains ultimately the internal spermatic vessels; the one below, the plica guber- 
natrix, contains the lower part of the gubernaculum, which has now grown into 
a thick cord; it ends below at the abdominal inguinal ring in a tube of peritoneum, 
the saccus vaginalis, which protrudes itself down the inguinal canal. By the fifth 
month the lower part of the gubernaculum has become a thick cord, while the 
upper part has disappeared. The lower part now consists of a central core of 
unstriped muscle fibre, and outside this of a firm layer of striped elements, con- 
nected, behind the peritoneum, with the abdominal wall. As the scrotum develops, 
the main portion of the lower end of the gubernaculum is carried, with the skin 
to which it is attached, to the bottom of this pouch; other bands are carried to 
the medial side of the thigh and to the perineum. The tube of peritoneum con- 
stituting the saccus vaginalis projects itself downward into the inguinal canal, 
and emerges at the cutaneous inguinal ring, pushing before it a part of the Obliquus 
internus and the aponeurosis of the Obliquus externus, which form respectively 
Epithelium 
Tunica 
albuginea 
■Interstitial 
1x11 
Supporting 
cell 
Genital 
cell 
Fig. 223.-Section of a genital cord of the testis of a human 
embryo 3.5 cm. long. (Felix and Buhler.) DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 
187 
the Cremaster muscle and the intercrural fascia. It forms a gradually elongating 
pouch, which eventually reaches the bottom of the scrotum, and behind this pouch 
the testis is drawn by the growth of the body of the fetus, for the gubernaculum 
does not grow commensurately with the growth of other parts, and therefore 
the testis, being attached by the gubernaculum to the bottom of the scrotum, 
is prevented from rising as the body grows, and is drawn first into the inguinal 
canal and eventually into the scrotum. It seems certain also that the guber- 
nacular cord becomes shortened as development proceeds, and this assists in caus- 
ing the testis to reach the bottom of the scrotum. By the end of the eighth month 
the testis has reached the scrotum, preceded by the saccus vaginalis, which com- 
municates by its upper extremity with the peritoneal cavity. Just before birth 
the upper part of the saccus vaginalis usually becomes closed, and this obliteration 
extends gradually downward to within a short distance of the testis. The process 
of peritoneum surrounding the testis is now entirely cut off from the general peri- 
toneal cavity and constitutes the tunica vaginalis. 
Descent of the Ovaries.-In the female there is also a gubernaculum, which 
effects a considerable change in the position of the ovary, though not so extensive 
a change as in that of the testis. The gubernaculum in the female lies in contact 
with the fundus of the uterus and contracts adhesions to this organ, and thus 
the ovary is prevented from descending below this level. The part of the guber- 
naculum between the ovary and the uterus becomes ultimately the proper ligament 
of the ovary, while the part between the uterus and the labium majus forms the 
round ligament of the uterus. A pouch of peritoneum analogous to the saccus 
vaginalis in the male accompanies it along the inguinal canal: it is called the canal 
of Nuck. In rare cases the gubernaculum may fail to contract adhesions to the 
uterus, and then the ovary descends through the inguinal canal into the labium 
majus, and under these circumstances its position resembles that of the testis. 
Wolffian duct 
Allantois 
Kidney diverticulum 
Umbilical cord 
Rectum 
Umbilical vessels 
Hind-gut 
Notochord 
Fig. 224.-Tail end of human embryo twenty- 
five to twenty-nine days old. (From model by Keibel.) 
Fig. 225.-Tail end of human embryo thirty-two 
to thirty-three days old. (From model by Keibel.) 
The Metanephros and the Permanent Kidney.-The rudiments of the perma- 
nent kidneys make their appearance about the end of the first or the beginning 
of the second month. Each kidney has a two-fold origin, part arising from the 
metanephros, and part as a diverticulum from the hind-end of the Wolffian duct, 
close to where the latter opens into the cloaca (Figs. 224, 225). The metanephros 
arises in the intermediate cell mass, caudal to the mesonephros, which it resembles 
in structure. The diverticulum from the Wolffian duct grows dorsalward and 
forward along the posterior abdominal wall, where its blind extremity expands 
and subsequently divides into several buds, which form the rudiments of the 
pelvis and calices of the kidney; by continued growth and subdivision it gives 
rise to the collecting tubules of the kidney. The proximal portion of the diver- 
ticulum becomes the ureter. The secretory tubules are developed from the 188 
EMBRYOLOGY 
metanephros, which is moulded over the growing end of the diverticulum from the 
Wolffian duct. The tubules of the metanephros, unlike those of the pronephros 
and mesonephros, do not open into the Wolffian duct. One end expands to form 
a glomerulus, while the rest of the tubule rapidly elongates to form the convoluted 
and straight tubules, the loops of Henle, and the connecting tubules; these last 
join and establish communications 
with the collecting tubules derived 
from the ultimate ramifications of the 
diverticulum from the Wolffian duct. 
The mesoderm around the tubules be- 
comes condensed to form the connec- 
tive tissue of the kidney. The ureter 
opens at first into the hind-end of the 
Wolffian duct; after the sixth week it 
separates from the Wolffian duct, and 
opens independently into the part of 
the cloaca which ultimately becomes 
the bladder (Figs. 226, 227). 
The secretory tubules of the kid- 
ney become arranged into pyramidal 
masses or lobules, and the lobulated 
condition of the kidneys exists for 
some time after birth, while traces of 
it may be found even in the adult. The kidney of the ox and many other animals 
remains lobulated throughout life. 
The Urinary Bladder.-The bladder is formed partly from the entodermal 
cloaca and partly from the ends of the Wolffian ducts; the allantois takes no share 
in its formation. After the separation of the rectum from the dorsal part of the 
Ureter 
MiUlerian duct 
Wolffian duct 
Symphysis pubis 
Bladder 
Glans penis 
Urethra 
Vertebral column 
Fig. 226.-Tail end of human embryo; from eight and a 
half to nine weeks old. (From model by Keibel.) 
Wolffian duct 
Hind-gut 
•Outer zone 
Inner zone 
of kidney 
Bladder 
Pelvis of kidney 
Urogenital 
membrane" 
Cloaca 
Fig. 227.-Primitive kidney and bladder, from a reconstruction. (After Schreiner.) 
cloaca (p. 172), the ventral part becomes subdivided into three portions: (1) an 
anterior vesico-urethral portion, continuous with the allantois-into this portion the 
Wolffian ducts open; (2) an intermediate narrow channel, the pelvic portion; and 
(3) a posterior phallic portion, closed externally by the urogenital membrane (Fig. 
227). The second and third parts together constitute the urogenital sinus. The DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 
189 
vesico-urethral portion absorbs the ends of the Wolffian ducts and the associated 
ends of the renal diverticula, and these give rise to the trigone of the bladder and 
part of the prostatic urethra. The remainder of the vesico-urethral portion forms 
the body of the bladder and part of the prostatic urethra; its apex is prolonged to 
the umbilicus as a narrow canal, which later is obliterated and becomes the medial 
umbilical ligament (urachus). 
Umbilical cord 
'Genital tubercle 
Genital tubercle 
■Hind-limb 
- Cloaca 
Labium majus 
Labium minus 
Urogenital 
membrane 
- Tail 
Glans clitoridis 
Glans penis 
Scrotal swelling 
Edge of groove on phallus 
Labium majus 
Labizim minus 
Opening of 
urogenital sinus 
Opening of urogenital sinus 
Anus 
Perineum 
Perineum 
Anus 
Glans penis 
Prepuce 
Glans clitoridis 
Cavernous urethra 
Labium majus 
Labium minus 
Scrotum 
Vestibule 
Vaginal orifice 
Raphe 
Anus 
Anus 
Fig. 228.-Stages in the development of the external sexual organs in the male and female. (Drawn from the 
Ecker-Ziegler models.) 
The Prostate.-The prostate originally consists of two separate portions, each 
of which arises as a series of diverticular buds from the epithelial lining of the uro- 
genital sinus and vesico-urethral part of the cloaca, between the third and fourth 
months. These buds become tubular, and form the glandular substance of the two 
lobes, which ultimately meet and fuse behind the urethra and also extend on to its 
ventral aspect. The isthmus or middle lobe is formed as an extension of the lateral 190 
EMBRYOLOGY 
lobes between the common ejaculatory ducts and the bladder. Skene's ducts in the 
female urethra are regarded as the homologues of the prostatic glands. 
The bulbo-urethral glands of Cowper in the male, and greater vestibular glands 
of Bartholin in the female, also arise as diverticula from the epithelial lining of the 
urogenital sinus. 
The External Organs of Generation (Fig. 228).-As already stated (page 172), 
the cloacal membrane, composed of ectoderm and entoderm, originally reaches from 
the umbilicus to the tail. The mesoderm extends to the mid ventral line for some 
distance behind the umbilicus, and forms the lower part of the abdominal wall; 
it ends below in a prominent swelling, the cloacal tubercle. Behind this tubercle 
the urogenital part of the cloacal membrane separates the ingrowing sheets of 
mesoderm. 
The first rudiment of the penis (or clitoris) is a structure termed the phallus; it 
is derived from the phallic portion of the cloaca which has extended on to the 
end and sides of the under surface of the cloacal tubercle. The terminal part of 
the phallus representing the future glans becomes solid; the remainder, which 
is hollow, is converted into a longitudinal groove by the absorption of the 
urogenital membrane. 
In the female a deep groove forms around the phallus and separates it from the 
rest of the cloacal tubercle, which is now termed the genital tubercle. The sides of 
the genital tubercle grow backward as the genital swellings, which ultimately form 
the labia majora; the tubercle itself becomes the mons pubis. The labia minora 
arise by the continued growth of the lips of the groove on the under surface of the 
phallus; the remainder of the phallus forms the clitoris. 
In the male the early changes are similar, but the pelvic portion of the cloaca 
undergoes much greater development, pushing before it the phallic portion. The 
genital swellings extend around between the pelvic portion and the anus, and form a 
scrotal area; during the changes associated with the descent of the testes this area 
is drawn out to form the scrotal sacs. The penis is developed from the phallus. 
As in the female, the urogenital membrane undergoes absorption, forming a channel 
on the under surface of the phallus; this channel extends only as far forward as the 
corona glandis. 
The corpora cavernosa of the penis (or clitoris) and of the urethra arise from the 
mesodermal tissue in the phallus; they are at first dense structures, but later 
vascular spaces appear in them, and they gradually become cavernous. 
The prepuce in both sexes is formed by the growth of a solid plate of ectoderm 
into the superficial part of the phallus; on coronal section this plate presents the 
shape of a horseshoe. By the breaking down of its more centrally situated cells 
the plate is split into two lamellae, and a cutaneous fold, the prepuce, is liberated 
and forms a hood over the glans. "Adherent prepuce is not an adhesion really, 
but a hindered central desquamation" (Berry Hart, op. citf. 
The Urethra.-As already described, in both sexes the phallic portion of the 
cloaca extends on to the under surface of the cloacal tubercle as far forward as the 
apex. At the apex the walls of the phallic portion come together and fuse, the 
lumen is obliterated, and a solid plate, the urethral plate, is formed. The remainder 
of the phallic portion is for a time tubular, and then, by the absorption of the 
urogenital membrane, it establishes a communication with the exterior; this open- 
ing is the primitive urogenital ostium, and it extends forward to the corona glandis. 
In the female this condition is largely retained; the portion of the groove on the 
clitoris broadens out while the body of the clitoris enlarges, and thus the adult 
urethral opening is situated behind the base of the clitoris. 
In the male, by the greater growth of the pelvic portion of the cloaca a longer 
urethra is formed, and the primitive ostium is carried forward with the phallus, 
but it still ends at the corona glandis. Later it closes from behind forward. Mean- FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 
191 
while the urethral plate of the glans breaks down centrally to form a median 
groove continuous with the primitive ostium. This groove also closes from behind 
forward, so that the external urethral opening is shifted forward to the end of 
the glans. 
THE FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH. 
First Week.-During this period the ovum is in the uterine tube. Having been fertilized in 
the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the 
uterus. Peters1 described a specimen, the age of which he reckoned as from three to four days. 
It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua 
capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum 
was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside this 
was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous 
villous processes-some consisting of trophoblast only, others possessing a core of mesoderm- 
projected from the surface of the ovum into the surrounding decidua. Inside this sac the rudi- 
ment of the embryo was found in the form of a patch of ectoderm, covered by a small but com- 
pletely closed amnion. It possessed a minute yolk-sac and was surrounded by mesoderm, which 
was connected by a band to that lining the trophoblast (Fig. 88).2 
Il eart 
Amnion 
' Body-stalk 
Fig. 229.-Human embryo about fifteen days old. (His.) 
Chorion 
Second Week.-By the end of this week the ovum has increased considerably in size, and the 
majority of its villi are vascularized. The embryo has assumed a definite form, and its cephalic 
and caudal extremities are easily distinguished. The neural folds are partly united. The embryo 
is more completely separated from the yolk-sac, and the paraxial mesoderm is being divided into 
the primitive segments (Fig. 229). 
Third Week.-By the end of the third week the embryo is strongly curved, and the primitive 
segments number about thirty. The primary divisions of the brain are visible, and the optic 
and auditory vesicles are formed. Four branchial grooves are present: the stomodeum is well- 
marked, and the buccopharyngeal membrane has disappeared. The rudiments of the limbs 
are seen as short buds, and the Wolffian bodies are visible (Fig. 230). 
Fourth Week.-The embryo is markedly curved on itself, and when viewed in profile is almost 
circular in outline. The cerebral hemispheres appear as hollow buds, and the elevations which 
form the rudiments of the auricula are visible. The limbs now appear as oval flattened projec- 
tions (Fig. 231). 
Fifth Week.-The embryo is less curved and the head is relatively of large size. Differentiation 
of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloacal 
tubercle is evident (Fig. 232). 
1 Die Einbettung des menschlichen Eies, 1899. 
2 Bryce and Teacher {Early Development and Imbedding of the Human Ovum, 1908) have described an ovum which 
they regard as thirteen to fourteen days old. In it the two vesicles, the amnion and yolk-sac, were present, but there 
was no trace of a layer of embryonic ectoderm. They are of opinion that the age of Peters' ovum has been understated, 
and estimate it as between thirteen and one-half and fourteen and one-half days. 192 
EMBRYOLOGY 
Sixth Week.-The curvature of the embryo is further diminished. The branchial grooves- 
except the first--have disappeared, and the rudiments of the fingers and toes can be recognized 
(Fig. 233). 
Mid-brain 
, Hind-brain 
Auditory vesicle 
Fore-bram- 
Stomodeum- 
Visceral 
arches 
Mandibular arch' 
Heart - 
■Ammon (cut} 
Body-stalk 
Fig. 230.-Human embryo between eighteen and twenty-one days old. (His.) 
Seventh and Eighth Weeks.-The flexure of the head is gradually reduced and the neck is 
somewhat lengthened. The upper lip is completed and the nose is more prominent. The nostrils 
are directed forward and the palate is not completely developed. The eyelids are present in the 
shape of folds above and below the eye, and the different parts of the auricula are distinguish- 
able. By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 
234). 
Heart 
Fore-limb 
Mandibular arch 
Hyoid arch 
Maxillary process _ 
Eye 
Olfactory pit 
Chorion 
Hind-limb 
Fig. 231.-Human embryo, twenty-seven to thirty days old. (His.) 
Third Month.-The head is extended and the neck is lengthened. The eyelids meet and fuse, 
remaining closed until the end of the sixth month. The limbs are well-developed and nails appear 
on the digits. The external generative organs are so far differentiated that it is possible to dis- 
tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs 
be included it is from 9 to 10 cm. 
Fourth Month.-The loop of gut which projected into the umbilical cord is withdrawn within 
the fetus. The hairs begin to make their appearance. There is a general increase in size so that 
by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included 
it is from 16 to 20 cm. FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 
193 
Fifth Month.-It is during this month that the first movements of the fetus are usually ob- 
served. The eruption of hair on the head commences, and the vernix caseosa begins to be deposited. 
By the end of this month the total length of the fetus, including the legs, is from 25 to 27 cm. 
Heart 
Mandibular arch- 
Hyoid arch 
Fore-limb 
Maxillary process 
Eye 
Hind-limb 
Fig. 232.-Human embryo, thirty-one to thirty-four days old. (His.) 
Sixth Month.-The body is covered by fine hairs {lanugo) and the deposit of vernix caseosa 
is considerable. The papilte of the skin are developed and the free border of the nail projects 
from the corium of the dermis. Measured from vertex to heels, the total length of the fetus 
at the end of this month is from 30 to 32 cm. 
, Auricula 
Eye~ 
Noser 
-Fore-limb 
Digits 
_ Hind-limb 
Umbilical cord 
Pig. 233.-Human embryo of about six weeks. 
(His.) 
Fig. 234.-Human embryo about eight and a half 
weeks old. (His.) 
Seventh Month.-The pupillary membrane atrophies and the eyelids are open. The testis 
descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the 
end of the seventh month is from 35 to 36 cm. The weight is a little over three pounds. 
13 194 
EMBRYOLOGY 
Eighth Month.-The skin assumes a pink color and is now entirely coated with vernix caseosa, 
and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable 
extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, 
at the end of the eighth month is about 40 cm., and the weight varies between four and one-half 
and five and one-half pounds. 
Ninth Month.-The lanugo has largely disappeared from the trunk. The umbilicus is almost 
in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from 
six and one-half to eight pounds, and measures from head to heels about 50 cm. OSTEOLOGY. 
rpHE general framework of the body is built up mainly of a series of bones, 
J- supplemented, however, in certain regions by pieces of cartilage; the bony 
part of the framework constitutes the skeleton. 
In comparative anatomy the term skeleton has a wider application, since in 
some of the lower animals hard, protecting and supporting structures are developed 
in association with the integumentary system. In such animals the skeleton 
is described as consisting of an internal or deep skeleton, the endoskeleton, and 
an external or superficial, the exoskeleton. In the human subject the exoskeleton 
is extremely rudimentary, its only important representatives being the nails 
and the enamel of the teeth. The term skeleton is, therefore, confined to the 
endoskeleton, and this is divisible into an axial part, which includes that of the 
head and trunk, and an appendicular part, which comprises that of the extremities 
or limbs. 
In the skeleton of the adult there are 206 distinct bones, as follows:- 
Axial 
[ Vertebral column 
Skull 
. 26 
. 22 
Skeleton 
Hyoid bone ... 
[ Ribs and sternum 
1 
. 25 
- 74 
Appendicular 1 
Upper extremities . 
. 64 
Skeleton ) 
Lower extremities 
. 62 
- 126 
Auditory ossicles 
6 
Total 
206 
The patellae are included in this enumeration, but the smaller sesamoid bones 
are not reckoned. 
Bones are divisible into four classes: Long, Short, Flat, and Irregular. 
Long Bones.-The long bones are found in the limbs, and each consists of a body 
or shaft and two extremities. The body, or diaphysis is cylindrical, with a central 
cavity termed the medullary canal; the wall consists of dense, compact tissue 
of considerable thickness in the middle part of the body, but becoming thinner 
toward the extremities; within the medullary canal is some cancellous tissue, 
scanty in the middle of the body but greater in amount toward the ends. The 
extremities are generally expanded, for the purposes of articulation and to afford 
broad surfaces for muscular attachment. They are usually developed from sep- 
arate centres of ossification termed epiphyses, and consist of cancellous tissue 
surrounded by thin compact bone. The medullary canal and the spaces in the 
cancellous tissue are filled with marrow. The long bones are not straight, but 
curved, the curve generally taking place in tw'o planes, thus affording greater 
strength to the bone. The bones belonging to this class are: the clavicle, humerus, 
radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges. 196 
OSTEOLOGY 
Short Bones.-Where a part of the skeleton is intended for strength and com- 
pactness combined with limited movement, it is constructed of a number of short 
bones, as in the carpus and tarsus. These consist of cancellous tissue covered 
by a thin crust of compact substance. The patellae, together with the other 
sesamoid bones, are by some regarded as short bones. 
Flat Bones.-Where the principal requirement is either extensive protection or 
the provision of broad surfaces for muscular attachment, the bones are expanded 
into broad, flat plates, as in the skull and the scapula. These bones are composed 
of two thin layers of compact tissue enclosing between them a variable quantity 
of cancellous tissue. In the cranial bones, the layers of compact tissue are famili- 
arly known as the tables of the skull; the outer one is thick and tough; the inner 
is thin, dense, and brittle, and hence is termed the vitreous table. The intervening 
cancellous tissue is called the diploe, and this, in certain regions of the skull, 
becomes absorbed so as to leave spaces filled with air {air-sinuses} between 
the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, 
vomer, scapula, os coxae {hip bone}, sternum, ribs, and, according to some, the 
patella. 
Irregular Bones.-The irregular bones are such as, from their peculiar form, 
cannot be grouped under the preceding heads. They consist of cancellous tissue 
enclosed within a thin layer of compact bone. The irregular bones are: the 
vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, 
palatine, inferior nasal concha, and hyoid. 
Surfaces of Bones.-If the surface of a bone be examined, certain eminences 
and depressions are seen. These eminences and depressions are of two kinds: 
articular and non-articular. Well-marked examples of articular eminences are 
found in the heads of the humerus and femur; and of articular depressions in the 
glenoid cavity of the scapula, and the acetabulum of the hip bone. Non-articular 
eminences are designated according to their form. Thus, a broad, rough, uneven 
elevation is called a tuberosity, protuberance, or process, a small, rough prominence, 
a tubercle; a sharp, slender pointed eminence, a spine; a narrow, rough elevation, 
running some way along the surface, a ridge, crest, or line. Non-articular depres- 
sions are also of variable form, and are described as fossae, pits, depressions, grooves, 
furrows, fissures, notches, etc, These non-articular eminences and depressions serve 
to increase the extent of surface for the attachment of ligaments and muscles, 
and are usually well-marked in proportion to the muscularity of the subject; 
the grooves, fissures, and notches transmit tendons, vessels, or nerves. 
The minute structure, growth, and composition of bone are described on 
pages 50 to 59. 
THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS; SPINAL 
COLUMN). 
The vertebral column is a flexuous and flexible column, formed of a series of 
bones called vertebrse. 
The vertebrse are thirty-three in number, and are grouped under the names 
cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they 
occupy; there are seven in the cervical region, twelve in the thoracic, five in the 
lumbar, five in the sacral, and four in the coccygeal. 
This number is sometimes increased by an additional vertebra in one region, 
or it may be diminished in one region, the deficiency being supplied by an addi- 
tional vertebra in another. The number of cervical vertebrae is, however, very 
rarely increased or diminished. 
The vertebrae in the upper three regions of the column remain distinct through- 
out life, and are known as true or movable vertebrae; those of the sacral and GENERAL CHARACTERISTICS OF A VERTEBRA 
197 
coccygeal regions, on the other hand, are termed false or fixed vertebrae, because 
they are united with one another in the adult to form two bones-five forming 
the upper bone or sacrum, and four the terminal bone or coccyx. 
With the exception of the first and second cervical, the true or movable vertebrae 
present certain common characteristics which are best studied by examining one 
from the middle of the thoracic region. 
GENERAL CHARACTERISTICS OF A VERTEBRA. 
A typical vertebra consists of two essential parts-viz., an anterior segment, the 
body, and a posterior part, the vertebral or neural arch; these enclose a foramen, 
the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair 
of laminae, and supports seven processes-viz., four articular, two transverse, and 
one spinous. 
When the vertebrae are articulated with each other the bodies form a strong 
pillar for the support of the head and trunk, and the vertebral foramina constitute 
a canal for the protection of the medulla spinalis (spinal cord), while between 
every pair of vertebrae are two apertures, the intervertebral foramina, one on 
either side, for the transmission of the spinal nerves and vessels. 
Body (corpus vertebrae) .-The body is the largest part of a vertebra, and is 
more or less cylindrical in shape. Its upper and lower surfaces are flattened and 
rough, and give attachment to the intervertebral fibrocartilages, and each presents 
a rim around its circumference. In front, the body is convex from side to side 
and concave from above downward. Behind, it is flat from above downward 
and slightly concave from side to side. Its anterior surface presents a few small 
apertures, for the passage of nutrient vessels; on the posterior surface is a single 
large, irregular aperture, or occasionally more than one, for the exit of the basi- 
vertebral veins from the body of the vertebra. 
Pedicles (radices arci vertebrae).-The pedicles are two short, thick processes, 
which project backward, one on either side, from the upper part of the body, 
at the junction of its posterior and lateral surfaces. The concavities above and 
below the pedicles are named the vertebral notches; and when the vertebrae are 
articulated, the notches of each contiguous pair of bones form the intervertebral 
foramina, already referred to. 
Laminae.-The laminae are two broad plates directed backward and medialward 
from the pedicles. They fuse in the middle line posteriorly, and so complete the 
posterior boundary of the vertebral foramen. Their upper borders and the 
lower parts of their anterior surfaces are rough for the attachment of the 
ligamenta flava. 
Processes.-Spinous Process (processus spinosus).--The spinous process is 
directed backward and downward from the junction of the laminae, and serves 
for the attachment of muscles and ligaments. 
Articular Processes.-The articular processes, two superior and two inferior, 
spring from the junctions of the pedicles and laminae. The superior project 
upward, and their articular surfaces are directed more or less backward; the 
inferior project downward, and their surfaces look more or less forward. 
Transverse Processes (processus transversi).-The transverse processes, two in 
number, project one at either side from the point where the lamina joins the 
pedicle, between the superior and inferior articular processes. They serve for 
the attachment of muscles and ligaments. 
Structure of a Vertebra (Fig. 235).-The body is composed of cancellous tissue, covered by 
a thin coating of compact bone; the latter is perforated by numerous orifices, some of large size 198 
OSTEOLOGY 
for the passage of vessels; the interior of the bone is traversed by one or two large canals, for the 
reception of ;yeins,^hic® converge toward a single large, irregular aperture, or several small 
apertures, at the posterior part of the 
body. The arch and processes pro- 
jecting from it have thick coverings 
of compact tissue. 
The Cervical Vertebrae (Verte 
brae Cervicales). 
The cervical vertebrae (Fig. 
236) are the smallest of the true 
vertebrae, and can be readily 
distinguished from those of the 
thoracic or lumbar regions by 
the presence of a foramen in 
each transverse process. The 
first, second, and seventh present exceptional features and must be separately 
described; the following characteristics are common to the remaining four. 
The body is small, and broader from side to side than from before backward 
The anterior and posterior surfaces are flattened and of equal depth; the former 
is placed on a lower level than the latter, and its inferior border is prolonged 
downward, so as to overlap the upper and forepart of the vertebra below. The 
upper surface is concave transversely, and presents a projecting lip on either side; 
the lower surface is concave from before backward, convex from side to side, and 
presents laterally shallow concavities which receive the corresponding projecting 
lips of the subjacent vertebra. The pedicles are directed lateralward and backward, 
Fig. 235.-Sagittal section of a lumbar vertebra. 
Anterior tubercle of 
transverse process 
transversarium 
Foramen 
Transverse process 
Posterior tubercle of- 
transverse process 
Superior articular 
process 
Inferior articular 
process 
Spinous 
process 
Fig. 236.-A cervical vertebra. 
and are attached to the body midway between its upper and lower borders, so that 
the superior vertebral notch is as deep as the inferior, but it is, at the same time, 
narrower. The laminae are narrow, and thinner above than below; the vertebral 
foramen is large, and of a triangular form. The spinous process is short and bifid, 
the two divisions being often of unequal size. The superior and inferior articular 
processes on either side are fused to form an articular pillar, which projects lateral- 
ward from the junction of the pedicle and lamina. The articular facets are flat 
and of an oval form: the superior look backward, upward, and slightly medial- 
ward: the inferior forward, downward, and slightly lateralward. The transverse 
processes are each pierced by the foramen transversarium, which, in the upper six 
vertebrae, gives passage to the vertebral artery and vein and a plexus of sympa- THE CERVICAL VERTEBRAE 
199 
thetic nerves. Each process consists of an anterior and a posterior part. The 
anterior portion is the homologue of the rib in the thoracic region, and is there- 
fore named the costal process or costal element: it arises from the side of the body, 
is directed lateralward in front of the foramen, and ends in a tubercle, the tuber- 
culum anterius. The posterior part, the true transverse process, springs from the 
vertebral arch behind the foramen, and is directed forward and lateralward; it 
ends in a flattened vertical tubercle, the tuberculum posterius. These two parts 
are joined, outside the foramen, by a bar of bone which exhibits a deep sulcus 
on its upper surface for the passage of the corresponding spinal nerve.1 
Chassaignac first pointed out that the common carotid artery can be easily compressed against 
the anterior tubercle of the transverse process of the sixth cervical vertebra, and therefore this 
tubercle is named the tuberculum caroticum or Chassaignac's tubercle. It also constitutes an im- 
portant guide to the vertebral artery which enters the foramen transversarium of this vertebra. 
Anterior tubercle 
Outline of section of odontoid 
process 
Outline of section of trans, 
verse atlantal ligament 
Foramen 
transver- 
sarium 
T ransverse 
process 
Groove for vertebral artery 
and first cervical nerve 
Posterior tubercle 
Fig. 237.-First cervical vertebra, or atlas. 
First Cervical Vertebra.-The first cervical vertebra (Fig. 237) is named the 
atlas because it supports the globe of the head. Its chief peculiarity is that it has 
no body, and this is due to the fact that the body of the atlas has fused with that 
of the next vertebra. Its other peculiarities are that it has no spinous process, 
is ring-like, and consists of an anterior and a posterior arch and two lateral masses. 
The anterior arch forms about one-fifth of the ring: its anterior surface is convex, 
and presents at its centre the anterior tubercle for the attachment of the Longus 
colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular 
facet (fovea dentis), for articulation with the odontoid process (dens) of the axis. 
The upper and lower borders respectively give attachment to the anterior atlanto- 
occipital membrane and the anterior atlantoaxial ligament; the former connects 
it with the occipital bone above, and the latter with the axis below. The posterior 
arch forms about two-fifths of the circumference of the ring: it ends behind in the 
posterior tubercle, which is the rudiment of a spinous process and gives origin to 
the Recti capitis posteriores minores. The diminutive size of this process pre- 
vents any interference with the movements between the atlas and the skull. 
The posterior part of the arch presents above and behind a rounded edge for 
the attachment of the posterior atlan to occipital membrane, while immediately 
behind each superior articular process is a groove (sulcus arteriae vertebralis), 
sometimes converted into a foramen by a delicate bony spiculum which arches 
backward from the posterior end of the superior articular process. This groove 
represents the superior vertebral notch, and serves for the transmission of the 
vertebral artery, which, after ascending through the foramen in the transverse 
1 The costal element of a cervical vertebra not only includes the portion which springs from the side of the body, but 
the anterior and posterior tubercles and the bar of bone which connects them (Fig. 97). 200 
OSTEOLOGY 
process, winds around the lateral mass in a direction backward and medialward; it 
also transmits the suboccipital (first spinal) nerve. On the under surface of the 
posterior arch, behind the articular facets, are two shallow grooves, the inferior 
vertebral notches. The lower border gives attachment to the posterior atlanto- 
axial ligament, which connects it with the axis. The lateral masses are the most 
bulky and solid parts of the atlas, in order to support -the weight of the head. 
Each carries two articular facets, a superior and an inferior. The superior facets 
are of large size, oval, concave, and approach each other in front, but diverge 
behind: they are directed upward, medialward, and a little backward, each forming 
a cup for the corresponding condyle of the occipital bone, and are admirably 
adapted to the nodding movements of the head. Not infrequently they are 
partially subdivided by indentations which encroach upon their margins. The 
inferior articular facets are circular in form, flattened or slightly convex and directed 
downward and medialward, articulating with the axis, and permitting the rotatory 
movements of the head. Just below the medial margin of each superior facet is 
a small tubercle, for the attachment of the transverse atlantal ligament which 
stretches across the ring of the atlas and divides the vertebral foramen into two 
unequal parts-the anterior or- smaller receiving the odontoid process of the axis, 
the posterior transmitting the medulla spinalis and its membranes. This part 
of the vertebral canal is of considerable size, much greater than is required for the 
accommodation of the medulla spinalis, and hence lateral displacement of the 
atlas may occur without compression of this structure. The transverse processes 
are large; they project lateralward and downward from the lateral masses, and 
serve for the attachment of muscles which assist in rotating the head. They 
are long, and their anterior and posterior tubercles are fused into one mass; the 
foramen transversarium is directed from below, upward and backward. 
Odontoid process 
Rough surface for alar ligament 
Articular facet for 
anterior arch of atlas 
Groove for transverse atlantal ligament 
Spinous process 
Body 
Transverse process 
Inferior articular process 
Fig. 238.-Second cervical vertebra, epistropheus, or axis. 
Second Cervical Vertebra.--The second cervical vertebra (Fig. 238) is named 
the epistropheus or axis because it forms the pivot upon which the first vertebra, 
carrying the head, rotates. The most distinctive characteristic of this bone is 
the strong odontoid process which rises perpendicularly from the upper surface 
of the body. The body is deeper in front than behind, and prolonged downward 
anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- 
sents in front a median longitudinal ridge, separating two lateral depressions for 
the attachment of the Longus colli muscles. Its under surface is concave from 
before backward and covex from side to side. The dens or odontoid process exhibits 
a slight constriction or neck, where it joins the body. On its anterior surface 
is an oval or nearly circular facet for articulation with that on the anterior arch THE THORACIC VERTEBRAE 
201 
of the atlas. On the back of the neck, and frequently extending on to its lateral 
surfaces, is a shallow groove for the transverse atlantal ligament which retains 
the process in position. The apex is pointed, and gives attachment to the middle 
alar ligament; below the apex the process is somewhat enlarged, and presents 
on either side a rough impression for the attachment of the lateral alar ligament; 
these ligaments connect the process to the occipital bone. The internal structure 
of the odontoid process is more compact than that of the body. The pedicles 
are broad and strong, especially in front, where they coalesce with the sides of 
the body and the root of the odontoid process. They are covered above by the 
superior articular surfaces. The laminae are thick and strong, and the vertebral 
foramen large, but smaller than that of the atlas. The transverse processes are 
very small, and each ends in a single tubercle; each is perforated by the foramen 
transversarium, which is directed obliquely upward and lateralward. The superior 
articular surfaces are round, slightly convex, directed upward and lateralward, 
and are supported on the body, 
pedicles, and transverse processes. 
The inferior articular surfaces have 
the same direction as those of the 
other cervical vertebrae. The supe- 
rior vertebral notches are very shal- 
low, and lie behind the articular 
processes; the inferior lie in front 
of the articular processes, as in the 
other cervical vertebrae. The spinous 
process is large, very strong, deeply 
channelled on its under surface, 
and presents a bifid, tuberculated 
extremity. 
The Seventh Cervical Vertebra 
(Fig. 239).-The most distinctive 
characteristic of this vertebra is 
the existence of a long and promi- 
nent spinous process, hence the 
name vertebra prominens. This pro- 
cess is thick, nearly horizontal in 
direction, not bifurcated, but ter- 
minating in a tubercle to which the lower end of the ligamentum nuchae is 
attached. The transverse processes are of considerable size, their posterior roots 
are large and prominent, while the anterior are small and faintly marked; the 
upper surface of each has usually a shallow' sulcus for the eighth spinal nerve, 
and its extremity seldom presents more than a trace of bifurcation. The foramen 
transversarium may be as large as that in the other cervical vertebrae, but is 
generally smaller on one or both sides; occasionally it is double, sometimes it is 
absent. On the left side it occasionally gives passage to the vertebral artery; 
more frequently the vertebral vein traverses it on both sides; but the usual 
arrangement is for both artery and vein to pass in front of the transverse pro- 
cess, and not through the foramen. Sometimes the anterior root of the trans- 
verse process attains a large size and exists as a separate bone, wThich is known 
as a cervical rib. 
Fig. 239.-Seventh cervical vertebra. 
Spinous process 
The Thoracic Vertebrae (Vertebrae Thoracales). 
The thoracic vertebree (Fig. 240) are intermediate in size between those of 
the cervical and lumbar regions; they increase in size from above downward the 202 
OSTEOLOGY 
upper vertebrae being much smaller than those in the lower part of the region. 
They are distinguished by the presence of facets on the sides of the bodies for 
articulation with the heads of the ribs, and facets on the transverse processes of 
all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. 
The bodies in the middle of the thoracic region are heart-shaped, and as broad 
in the antero-posterior as in the transverse direction. At the ends of the thoracic 
region they resemble respectively those of the cervical and lumbar vertebrae. 
They are slightly thicker behind than in front, flat above and below, convex from 
side to side in front, deeply concave behind, and slightly constricted laterally 
and in front. They present, on either side, two costal demi-facets, one above, 
near the root of the pedicle, the other below, in front of the inferior vertebral 
notch; these are covered with cartilage in the recent state, and, when the vertebrae 
are articulated with one another, form, with the intervening intervertebral fibro- 
cartilages, oval surfaces for the reception of the heads of the ribs. The pedicles 
are directed backward and slightly upward, and the inferior vertebral notches 
are of large size, and deeper than in any other region of the vertebral column. 
Superior articular process 
Demi-facet for head of rib 
Facet for articular part 
of tubercle of rib 
Demi-facet for head of rib 
Inferior articular process 
Fig. 240.-A thoracic vertebra. 
The laminae are broad, thick, and imbricated-that is to say, they overlap those 
of subjacent vertebrae like tiles on a roof. The vertebral foramen is small, and of 
a circular form. The spinous process is long, triangular on coronal section, directed 
obliquely downward, and ends in a tuberculated extremity. These processes 
overlap from the fifth to the eighth, but are less oblique in direction above and 
below.1 The superior articular processes are thin plates of bone projecting upward 
from the junctions of the pedicles and laminae; their articular facets are practi- 
cally flat, and are directed backward and a little lateral ward and upward. The 
inferior articular processes are fused to a considerable extent with the laminae, 
and project but slightly beyond their lower borders; their facets are directed 
forward and a little medialward and downward. The transverse processes arise 
from the arch behind the superior articular processes and pedicles; they are thick, 
strong, and of considerable length, directed obliquely backward and lateralward, 
1 In quadrupeds the majority of the spinous processes of the thoracic vertebrae project upward and backward, while 
those of the lumbar region are directed upward and forward. The change in inclination is effected in one of the lower 
thoracic vertebrae, the spine of which points almost directly upward. This vertebra is known as the anticlinal, and 
in man its representative is the eleventh thoracic. THE THORACIC VERTEBRAE 
203 
and each ends in a clubbed extremity, on the front of which is a small, concave 
surface, for articulation with the tubercle of a rib. 
The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certain 
peculiarities, and must be specially considered (Fig. 2-11). 
An entire facet above ; 
a demi-facet below 
' A demi-facet above 
One entire facet 
One. entire facet. 
No facet on trans, proc, 
which is rudimentary 
One, entire facet. 
No facet on trans- 
verse process. 
I nfer. artic. process 
convex and turned 
laterahvards 
Fig. 241.-Peculiar thoracic vertebrae. 
The First Thoracic Vertebra has, on either side of the body, an entire articular 
facet for the head of the first rib, and a demi-facet for the upper half of the head 
of the second rib. The body is like that of a cervical vertebra, being broad trans- 
versely; its upper surface is concave, and lipped on either side. The superior 
articular surfaces are directed upward and backward; the spinous process is thick, 
long, and almost horizontal. The transverse processes are long, and the upper 
vertebral notches are deeper than those of the other thoracic vertebrae. 204 
OSTEOLOGY 
The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- 
jects however, it has two demi-facets on either side; when this occurs the tenth 
has only demi-facets at the upper part. 
The Tenth Thoracic Vertebra has (except in the cases just mentioned) an entire 
articular facet on either side, which is placed partly on the lateral surface of the 
pedicle. 
In the Eleventh Thoracic Vertebra the body approaches in its form and size 
to that of the lumbar vertebrae. The articular facets for the heads of the ribs 
are of large size, and placed chiefly on the pedicles, which are thicker and stronger 
in this and the next vertebra than in any other part of the thoracic region. The 
spinous process is short, and nearly horizontal in direction. The transverse processes 
are very short, tuberculated at their extremities, and have no articular facets. 
The Twelfth Thoracic Vertebra has the same general characteristics as the 
eleventh, but may be distinguished from it by its inferior articular surfaces being 
convex and directed lateralward, like those of the lumbar vertebrae; by the general 
form of the body, laminae, and spinous process, in which it resembles the lumbar 
vertebrae; and by each transverse process being subdivided into three elevations, 
the superior, inferior, and lateral tubercles: the superior and inferior correspond 
to the mamillary and accessory processes of the lumbar vertebrae. Traces of 
similar elevations are found on the transverse processes of the tenth and eleventh 
thoracic vertebrae. 
Superior articular process 
Fig. 242.-A lumbar vertebra seen from the side. 
The Lumbar Vertebrae (Vertebrae Lumbales). 
The lumbar vertebrae (Figs. 242 and 243) are the largest segments of the movable 
part of the vertebral column, and can be distinguished by the absence of a foramen 
in the transverse process, and by the absence of facets on the sides of the body. 
The body is large, wider from side to side than from before backward, and a 
little thicker in front than behind. It is flattened or slightly concave above and 
below, concave behind, and deeply constricted in front and at the sides. The 
pedicles are very strong, directed backward from the upper part of the body; 
consequently, the inferior vertebral notches are of considerable depth. The 
laminae are broad, short, and strong; the vertebral foramen is triangular, larger 
than in the thoracic, but smaller than in the cervical region. The spinous process 
is thick, broad, and somewhat quadrilateral; it projects backward and ends in 
a rough, uneven border, thickest below where it is occasionally notched. The 
superior and inferior articular processes are well-defined, projecting respectively 
upward and downward from the junctions of pedicles and laminae. The facets THE SACRAL AND COCCYGEAL VERTEBRA 
205 
on the superior processes are concave, and look backward and medialward; those 
on the inferior are convex, and are directed forward and lateralward. The former 
are wider apart than the latter, since in the articulated column the inferior articular 
processes are embraced by the superior processes of the subjacent vertebra. The 
transverse processes are long, slender, and horizontal in the upper three lumbar 
vertebrae; they incline a little upward in the lower two. In the upper three verte- 
brae they arise from the junctions of the pedicles and laminae, but in the lower 
two they are set farther forward and spring from the pedicles and posterior parts 
of the bodies. They are situated in front of the articular processes instead of behind 
them as in the thoracic vertebrae, and are homologous with the ribs. Of the three 
tubercles noticed in connection with the transverse processes of the lower thoracic 
Inferior articular 
process 
Transverse process 
Alamillary process 
Accessory process 
Superior articular 
process 
Fig. 243.-A lumbar vertebra viewed obliquely from above. 
vertebrae, the superior one is connected in the lumbar region with the back part 
of the superior articular process, and is named the mamillary process; the inferior 
is situated at the back part of the base of the transverse process, and is called the 
accessory process (Fig. 243). Although in man these are comparatively small, 
in some animals they attain considerable size, and serve to lock the vertebrae 
more closely together. 
The Fifth Lumbar Vertebra is characterized by its body being much deeper 
in front than behind, which accords with the prominence of the sacrovertebral 
articulation; by the smaller size of its spinous process; by the wide interval between 
the inferior articular processes; and by the thickness of its transverse processes, 
which spring from the body as well as from the pedicles. 
The Sacral and Coccygeal Vertebrae. 
The sacral and coccygeal vertebrae consist at an early period of life of nine 
separate segments which are united in the adult, so as to form two bones, five 
entering into the formation of the sacrum, four into that of the coccyx. Some- 
times the coccyx consists of five bones; occasionally the number is reduced to 
three. 206 
OSTEOLOGY 
The Sacrum {os sacrum').-The sacrum is a large, triangular bone, situated 
in the lower part of the vertebral column and at the upper and back part of the 
pelvic cavity, where it is inserted like a wedge between the two hip bones; its 
upper part or base articulates with the last lumbar vertebra, its apex with the 
coccyx. It is curved upon itself and placed very obliquely, its base projecting 
forward and forming the prominent sacrovertebral angle when articulated with 
the last dumbar vertebra; its central part is projected backward, so as to give 
increased capacity to the pelvic cavity. The sacrum is rather narrower at the 
level of the second segment than at the level of the third. It presents for examina- 
tion a pelvic, a dorsal, and two lateral surfaces, a base, an apex, and a central 
canal. 
Promontory 
Fig. 244.-Sacrum, pelvic surface. 
Pelvic Surface (facies pelvina).-The pelvic surface (Fig. 244) is concave from 
above downward, and slightly so from side to side. Its middle part is crossed 
by four transverse ridges, the positions of which correspond with the original 
planes of separation between the five segments of the bone. The portions of bone 
intervening between the ridges are the bodies of the sacral vertebrae. The body 
of the first segment is of large size, and in form resembles that of a lumbar vertebra; 
the succeeding ones diminish from above downward, are flattened from before 
backward, and curved so as to accommodate themselves to the form of the sacrum, 
being concave in front, convex behind. At the ends of the ridges are seen the 
anterior sacral foramina, four in number on either side, somewhat rounded in form 
diminishing in size from above downward, and directed lateralward and forward; 
they give exit to the anterior divisions of the sacral nerves and entrance to the 
lateral sacral arteries. Lateral to these foramina are the lateral parts of the sacrum, 
each consisting of five separate segments at an early period of life; in the adult, THE SACRAL AND COCCYGEAL VERTEBRAE 
207 
these are blended with the bodies and with each other. Each lateral part is tra- 
versed by four broad, shallow grooves, which lodge the anterior divisions of the 
sacral nerves, and are separated by prominent ridges of bone which give origin 
to the Piriformis muscle. 
If a sagittal section be made through the centre of the sacrum (Fig. 246), the 
bodies are seen to be united at their circumferences by bone, wide intervals being 
left centrally, which, in the recent state, are filled by the intervertebral fibro- 
cartilages. In some bones this union is more complete between the lower than 
the upper segments. 
Latissimus 
dorsi 
Sacrospinalis 
Sacrospinalis 
Upper half of fifth 
'posterior sacral foramen 
Fig. 245.-Sacrum, dorsal surface. 
Dorsal Surface (facies dorsalis).-The dorsal surfa.ce (Fig. 245) is convex and 
narrower than the pelvic. In the middle line it displays a crest, the middle sacral 
crest, surmounted by three or four tubercles, the rudimentary spinous processes 
of the upper three or four sacral vertebrae. On either side of the middle sacral 
crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, 
the floor of the groove being formed by the united laminae of the corresponding- 
vertebrae. The laminae of the fifth sacral vertebra, and sometimes those of the 
fourth, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior 
wall of the sacral canal. On the lateral aspect of the sacral groove is a linear 
series of tubercles produced by the fusion of the articular processes which together 
form the indistinct sacral articular crests. The articular processes of the first 
sacral vertebra are large and oval in shape; their facets are concave from side to 
side, look backward and medialward, and articulate with the facets on the inferior 
processes of the fifth lumbar vertebra. The tubercles which represent the inferior 
articular processes of the fifth sacral vertebra are prolonged downward as rounded 
processes, which are named the sacral cornua, and are connected to. the cornua 208 
OSTEOLOGY 
of the coccyx. Lateral to the articular processes are the four posterior sacral 
foramina; they are smaller in size and less regular in form than the anterior, and 
transmit the posterior divisions of the sacral nerves. On the lateral side of the 
posterior sacral foramina is a series of tubercles, which represent the transverse 
processes of the sacral vertebrae, and form the lateral crests of the sacrum. The 
transverse tubercles of the first.sacral vertebra are large and very distinct; they, 
together with the transverse tubercles of the second vertebra, give attachment 
to the horizontal parts of the posterior sacroiliac ligaments; those of the third 
vertebra give attachment to the oblique fasciculi of the posterior sacroiliac liga- 
ments; and those of the fourth and fifth to the sacrotuberous ligaments. 
Lateral Surface.-The lateral surface is broad above, but narrowed into a thin 
edge below. The upper half presents in front an ear-shaped surface, the auricular 
surface for articulation with the ilium. Behind it is a rough surface, the sacral 
tuberosity, on which are three deep and uneven impressions, for the attachment 
of the posterior sacroiliac ligament. The lower half is thin, and ends in a pro- 
jection called the inferior lateral angle; medial to this angle is a notch, which is 
converted into a foramen by the transverse process of the first piece of the coccyx, 
and transmits the anterior division of the fifth sacral nerve. The thin lower half 
of the lateral surface gives attachment to the sacrotuberous and sacrospinous 
ligaments, to some fibres of the Glutaeus maximus behind, and to the Coccygeus 
in front. 
Base (basis oss. sacri).-The base of the sacrum, which is broad and expanded, 
is directed upward and forward. In the middle is a large oval articular surface, 
the upper surface of the body of the first sacral vertebra, which is connected with 
the under surface of the body of the last lumbar vertebra by an intervertebral 
fibrocartilage. Behind this is the large triangular orifice of the sacral canal, which 
is completed by the laminae and spinous process of the first sacral vertebra. The 
superior articular processes project from it on either side; they are oval, concave, 
directed backward and medialward, like the superior articular processes of a lumbar 
vertebra. They are attached to the body of the first sacral vertebra and to the 
alee by short thick pedicles; on the upper surface of each pedicle is-a vertebral 
notch, which forms the lower part of the foramen between the last lumbar and first 
sacral vertebrae. On either side of the body is a large triangular surface, which 
supports the Psoas major and the lumbosacral trunk, and in the articulated 
pelvis is continuous with the iliac fossa. This is called the ala; it is slightly concave 
from side to side, convex from before backward, and gives attachment to a few 
of the fibres of the Iliacus. The posterior fourth of the ala represents the transverse 
process, and its anterior three-fourths the costal process of the first sacral segment. 
Apex (apex oss. sacri).-The apex is directed downward, and presents an oval 
facet for articulation with the coccyx. 
Vertebral Canal (canalis sacralis; sacral canal).-The vertebral canal (Fig. 246) 
runs throughout the greater part of the bone; above, it is triangular in form; 
below, its posterior wall is incomplete, from the non-development of the laminae 
and spinous processes. It lodges the sacral nerves, and its walls are perforated by 
the anterior and posterior sacral foramina through which these nerves pass out. 
Structure.--The sacrum consists of cancellous tissue enveloped by a thin layer of compact bone. 
Articulations.-The sacrum articulates with four bones; the last lumbar vertebra above, the 
coccyx below, and the hip bone on either side. 
Differences in the Sacrum of the Male and Female.-In the female the sacrum is shorter and 
wider than in the male; the lower half forms a greater angle with the upper; the upper half is 
nearly straight, the lower half presenting the greatest amount of curvature. The bone is also 
directed more obliquely backward; this increases the size of the pelvic cavity and renders the 
sacrovertebral angle more prominent. In the male the curvature is more evenly distributed 
over the whole length of the bone, and is altogether greater than in the female. THE SACRAL AND COCCYGEAL VERTEBRA 
209 
Variations.-The sacrum, in some cases, consists of six pieces; occasionally the number is 
reduced to four. Sometimes the uppermost transverse tubercles are not joined to the rest of the 
ala on one or both sides, or the sacral canal may be open throughout a considerable part of its 
length, in consequence of the imperfect development of the laminae and spinous processes. The 
sacrum, also, varies considerably with respect to its degree of curvature. 
Cornua 
Rudim. 
Trans, 
prac. 
Anterior Surface 
Posterior surface 
Fig. 246.-Median sagittal section of the sacrum. 
Fig. 247.-Coccyx. 
The Coccyx {os coccygis).-The coccyx (Fig. 247) is usually formed of four 
rudimentary vertebrae; the number may however be increased to five or diminished 
to three. In each of the first three segments may be traced a rudimentary body 
and articular and transverse processes; the last piece (sometimes the third) is a 
mere nodule of bone. All the segments are destitute of pedicles, laminae, and 
spinous processes. The first is the largest; it resembles the lowest sacral vertebra, 
and often exists as a separate piece; the last three diminish in size from above 
downward, and are usually fused with one another. Owing to the gradual diminu- 
tion in the size of the segments, the coccyx is triangular in form, and presents 
for examination an anterior and a posterior surface, two borders, a base, and an 
apex. 
Surfaces.-The anterior surface is slightly concave, and marked with three trans- 
verse grooves which indicate the junctions of the different segments. It gives 
attachment to the anterior sacrococcygeal ligament and the Levatores ani, and 
supports part of the rectum. The posterior surface is convex, marked by transverse 
grooves similar to those on the anterior surface, and presents on either side a linear 
row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. 
Of these, the superior pair are large, and are called the coccygeal cornua; thev 210 
OSTEOLOGY 
project upward, and articulate with the cornua of the sacrum, and on either side 
complete the foramen for the transmission of the posterior division of the fifth 
sacral nerve. 
Borders.-The lateral borders are thin, and exhibit a series of small eminences, 
which represent the transverse processes of the coccygeal vertebrse. Of these, 
the first is the largest; it is flattened from before backward, and often ascends 
to join the lower part of the thin lateral edge of the sacrum, thus completing the 
foramen for the transmission of the anterior division of the fifth sacral nerve; 
the others diminish in size from above downward, and are often wanting. The 
borders of the coccyx are narrow, and give attachment on either side to the sacro- 
tuberous and sacrospinous ligaments, to the Coccygeus in front of the ligaments, 
and to the Glutaeus ma^imus behind them. 
Base.-The base presents an oval surface for articulation with the sacrum. 
Apex.-The apex is rounded, and has attached to it the tendon of the Sphincter 
ani externus. It may be bifid, and is sometimes deflected to one or other side. 
Ossification of the Vertebral Column.-Each vertebra is ossified from three primary centres 
(Fig. 248), two for the vertebral arch and one for the body.1 Ossification of the vertebral arches 
begins in the upper cervical vertebrae about the seventh or eighth week of fetal fife, and gradually 
extends down the column. The ossific granules first appear in the situations where the transverse 
processes afterward project, and spread backward to the spinous process forward into the pedicles, 
and lateralward into the transverse and articular processes. Ossification of the bodies begins 
about the eighth week in the lower thoracic region, and subsequently extends upward and down- 
ward along the column. The centre for the body does not give rise to the whole of the body of 
the adult vertebra, the postero-lateral portions of which are ossified by extensions from the verte- 
bral arch centres. The body of the vertebra during the first few years of life shows, therefore, 
two synchondroses, neurocentral synchondroses, traversing it along the planes of junction of 
the three centres (Fig. 249). In the thoracic region, the facets for the heads of the ribs lie behind 
the neurocentral synchondroses and are ossified from the centres for the vertebral arch. At 
birth the vertebra consists of three pieces, the body and the halves of the vertebral arch. During 
the first year the halves of the arch unite behind, union taking place first in the lumbar region 
and then extending upward through the thoracic and cervical regions. About the third year 
the bodies of the upper cervical vertebrae are joined to the arches on either side; in the lower 
lumbar vertebrae the union is not completed until the sixth year. Before puberty, no other 
changes occur, excepting a gradual increase of these primary centres, the upper and under sur- 
faces of the bodies and the ends of the transverse and spinous processes being cartilaginous. 
About the sixteenth year (Fig. 249), five secondary centres appear, one for the tip of each trans- 
verse process, one for the extremity of the spinous process, one for the upper and one for the 
lower surface of the body (Fig. 250). These fuse with the rest of the bone about the age of 
twenty-five. 
Exceptions to this mode of development occur in the first, second, and seventh cervical verte- 
brae, and in the lumbar vertebrae. 
Atlas.-The atlas is usually ossified from three centres (Fig. 251). Of these, one appears in 
each lateral mass about the seventh week of fetal life, and extends backward; at birth, these 
portions of bone are separated from one another behind by a narrow interval filled with cartilage. 
Between the third and fourth years they unite either directly or through the medium of a separate 
centre developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a 
separate centre appears about the end of the first year after birth, and joins the lateral masses 
from the sixth to the eighth year--the lines of union extending across the anterior portions of 
the superior articular facets. Occasionally there is no separate centre, the anterior arch being 
formed by the forward extension and ultimate junction of the two lateral masses; sometimes 
this arch is ossified from two centres, one on either side of the middle line. 
Epistropheus or Axis.-The axis is ossified from five primary and two secondary centres (Fig. 
252). The body and vertebral arch are ossified in the same manner as the corresponding parts 
in the other vertebrae, viz., one centre for the body, and two for the vertebral arch. The centres 
for the arch appear about the seventh or eighth week of fetal life, that for the body about the 
fourth or fifth month. The dens or odontoid process consists originally of a continuation upward 
of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month 
of fetal life, two centres make their appearance in the base of this process: they are placed 
laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval 
1 A vertebra is occasionally found in which the body consists of two lateral portions-a condition which proves that 
the body is sometimes ossified from two primary centres, one on either side of the middle line. THE SACRAL AND COCCYGEAL VERTEBRA 
211 
between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece 
of cartilage. The base of the process is separated from the body by a cartilaginous disk, which 
gradually becomes ossified at its cir- 
cumference, but remains cartilaginous 
in its centre until advanced age. In 
this cartilage, rudiments of the lower 
epiphysial lamella of the atlas and the 
upper epiphysial lamella of the axis 
may sometimes be found. The apex 
of the odontoid process has a separate 
centre which appears in the second and 
joins about the twelfth year; this is the 
upper epiphysial lamella of the atlas. 
In addition to these there is a secondary 
centre for a thin epiphysial plate on 
the under surface of the body of the 
bone. 
Fig. 248.-Ossification of a vertebra 
By 3 primary centres 
1 for body (8th week) 
1 for each vertebral arch (1th or 8th week) 
Fig. 249. 
By 3 secondary centres 
Neurocentral 
synchondrosis 
1 for each 
trans, process 
IQth year 
Additional centres 
for costal elements* 
At birth 
1 for spinous process (Idth year) 
By 2 additional plates 
Fig. 250. 
Fig. 254 
1 for upper surface 
of body 
1 for under surface 
of body 
16/A year 
Fig. 251.-Atlas. 
1 for anter. arch (end of 1st year) 
At 4| yrs 
.1 for each 
lateral mass 
1th week 
By 7 centres 
Fig. 252.-Axis. 
2nd year 
Fig. 255 
6th month 
1 for each vertebral arch Qth 
or 8th week) 
Exceptional cases 
Two epiphysial plates 
for each lateral surface * 
1 for body (4th month) 
1 for wider surface of body 
Fig. 253.-Lumbar vertebra. 
At 
25th year 
2 additional centres for mamillary processes 
Fig. 256.-Ossification of the sacrum. 
The Seventh Cervical Vertebra.-The anterior or costal part of the transverse process of this 
vertebra is sometimes ossified from a separate centre which appears about the sixth month of 212 
OSTEOLOGY 
fetal life, and joins the body and posterior part of the transverse process between the fifth and 
sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened 
lateralward and forward, constitutes what is known as a cervical rib. Separate ossific centres 
have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. 
Lumbar Vertebrae.-The lumbar vertebrae (Fig. 253) have each two additional centres, for 
the mamillary processes. The transverse process of the first lumbar is sometimes developed as 
a separate piece, which may remain permanently ununited with the rest of the bone, thus form- 
ing a lumbar rib-a peculiarity, however, rarely met with. 
Sacrum (Figs. 254 to 257).-The body of each sacral vertebra is ossified from a primary centre 
and two epiphysial plates, one for its upper and another for its under surface, while each vertebral 
arch is ossified from two centres. 
The anterior portions of the lateral parts have six additional centres, two for each of the first 
three vertebrae; these represent the costal elements, and make their appearance above and lateral 
to the anterior sacral foramina (Figs. 254, 255). 
On each lateral surface two epiphysial plates are developed (Figs. 256, 257): one for the auric- 
ular surface, and another for the remaining part of the thin lateral edge of the bone.1 
Periods of Ossification.-About the eighth or ninth week of fetal life, ossification of the 
central part of the body of the first sacral vertebra commences, and is rapidly followed by deposit 
of ossific matter in the second and third; 
ossification does not commence in the 
bodies of the lower two segments until 
between the fifth and eighth months of 
fetal life. Between the sixth and eighth 
months ossification of the vertebral arches 
takes place; and about the same time the 
costal centres for the lateral parts make 
their appearance. The junctions of the 
vertebral arches with the bodies take place 
in the lower vertebrae as early as the 
second year, but are not effected in the 
uppermost until the fifth or sixth year. 
About the sixteenth year the epiphysial 
plates for the upper and under surfaces of the bodies are formed; and between the eighteenth and 
twentieth years, those for the lateral surfaces make their appearance. The bodies of the sacral 
vertebrae are, during early life, separated from each other by intervertebral fibrocartilages, but 
about the eighteenth year the two lowest segments become united by bone, and the process of 
bony union gradually extends upward, with the result that between the twenty-fifth and thirtieth 
years of life all the segments are united. On examining a sagittal section of the sacrum, the situa- 
tions of the intervertebral fibrocartilages are indicated by a series of oval cavities (Fig. 246). 
Coccyx.-The coccyx is ossified from four centres, one for each segment. The ossific nuclei 
make their appearance in the following order: in the first segment between the first and fourth 
years; in the second between the fifth and tenth years; in the third between the tenth and fifteenth 
years; in the fourth between the ourteenth and twentieth years. As age advances, the segments 
unite with one another, the union between the first and second segments being freq ently delayed 
until after the age of twenty-five or thirty. At a late period of life, especially in females, the coccyx 
often fuses with the sacrum. 
Centre for 
neural arch. 
Centre for 
neural arch. 
Costal 
dementi 
Costal 
element. 
Lateral 
epiphysis. 
Centre for 
body. 
Lateral 
epiphysis. 
Fig. 257.-Base of young sacrum. 
THE VERTEBRAL COLUMN AS A WHOLE. 
The vertebral column is situated in the median line, as the posterior part of the 
trunk; its average length in the male is about 71 cm. Of this length the cervical 
part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the 
sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length. 
Curves.-Viewed laterally (Fig. 258), the vertebral column presents several 
curves, which correspond to the different regions of the column, and are called 
cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins 
1 The ends of the spinous processes of the upper three sacral vertebra; are sometimes developed from separate epi- 
physes, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be 
seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mamillary pro- 
cesses of the first sacral vertebra; twelve-six on either side-in connection with the costal elements (two each for the 
first and second and one each for the third and fourth) and eight for the transverse processes-four on either side- 
one each for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of 
the sacrum is formed by the extension and union of the third and fourth "costal" and fourth and fifth "transverse" 
epiphyses. THE VERTEBRAL COLUMN AS A WHOLE 
213 
at the apex of the odontoid process, and 
ends at the middle of the second thoracic 
vertebra; it is the least marked of all the 
curves. The thoracic curve, concave for- 
ward, begins at the middle of the second 
and ends at the middle of the twelfth tho- 
racic vertebra. Its most prominent point 
behind corresponds to the spinous process 
of the seventh thoracic vertebra. The 
lumbar curve is more marked in the female 
than in the male; it begins at the middle of 
the last thoracic vertebra, and ends at the 
sacrovertebral angle. It is convex ante- 
riorly, the convexity of the lower three 
vertebrae being much greater than that of 
the upper two. The pelvic curve begins 
at the sacrovertebral articulation, and ends 
at the point of the coccyx; its concavity 
is directed downward and forward. The 
thoracic and pelvic curves are termed 
primary curves, because they alone are 
present during fetal life. The cervical 
and lumbar curves are compensatory or 
secondary, and are developed after birth, 
the former when the child is able to hold 
up its head (at three or four months), and 
to sit upright (at nine months), the latter 
at twelve or eighteen months, when the 
child begins to walk. 
The vertebral column has also a slight 
lateral curvature, the convexity of which is 
directed toward the right side. This may 
be produced by muscular action, most 
persons using the right arm in preference 
to the left, especially in making long-con- 
tinued efforts, when the body is curved 
to the right side. In support of this ex- 
planation it has been found that in one 
or two individuals who were left-handed, 
the convexity was to the left side. By others 
this curvature is regarded as being produced 
by the aortic arch and upper part of the 
descending thoracic aorta-a view which is 
supported by the fact that in cases where 
the viscera are transposed and the aorta is 
on the right side, the convexity of the 
curve is directed to the left side. 
Surfaces. - Anterior Surface. - When 
viewed from in front, the width of the bodies 
of the vertebrae is seen to increase from the 
second cervical to the first thoracic; there 
is then a slight diminution in the next 
three vertebrae; below this there is again 
a gradual and progressive increase in width 
1st cervical 
or Atlas 
2nd cervical 
or Axis 
1st thoracic 
1st lumbar 
Fig. 258.-Lateral view of the vertebral column. 214 
OSTEOLOGY 
as low as the sacrovertebral angle. From this point there is a rapid diminution, 
to the apex of the coccyx. 
Posterior Surface.-The posterior surface of the vertebral column presents in 
the median line the spinous processes. In the cervical region (with the exception 
of the second and seventh vertebrae) these are short and horizontal, with bifid 
extremities. In the upper part of the thoracic region they are directed obliquely 
downward; in the middle they are almost vertical, and in the lower part they are 
nearly horizontal. In the lumbar region they are nearly horizontal. The spinous 
processes are separated by considerable intervals in the lumbar region, by narrower 
intervals in the neck, and are closely approximated in the middle of the thoracic 
region. Occasionally one of these processes deviates a little from the median line 
-a fact to be remembered in practice, as irregularities of this sort are attendant 
also on fractures or displacements of the vertebral column. On either side of the 
spinous processes is the vertebral groove formed by the laminae in the cervical and 
lumbar regions, where it is shallow, and by the laminae and transverse processes 
in the thoracic region, where it is deep and broad; these grooves lodge the deep 
muscles of the back. Lateral to the vertebral grooves are the articular processes, 
and still more laterally the transverse processes. In the thoracic region, the trans- 
verse processes stand backward, on a plane, considerably behind that of the same 
processes in the cervical and lumbar regions. In the cervical region, the transverse 
processes are placed in front of the articular processes, lateral to the pedicles and 
between the intervertebral foramina. In the thoracic region they are posterior 
to the pedicles, intervertebral foramina, and articular processes. In the lumbar 
region they are in front of the articular processes, but behind the intervertebral 
foramina. 
Lateral Surfaces.--The lateral surfaces are separated from the posterior surface 
by the articular processes in the cervical and lumbar regions, and by the transverse 
processes in the thoracic region. They present, in front, the sides of the bodies 
of the vertebrae, marked in the thoracic region by the facets for articulation with 
the heads of the ribs. More posteriorly are the intervertebral foramina, formed 
by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical 
and upper part of the thoracic regions, and gradually increasing in size to the last 
lumbar. They transmit the spinal nerves and are situated between the transverse 
processes in the cervical region, and in front of them in the thoracic and lumbar 
regions. 
Base.-The base of that portion of the vertebral column which is made up of 
the twenty-four movable vertebrae is formed by the under surface of the body 
of the fifth lumbar vertebrae; and the summit, by the upper surface of the atlas. 
Vertebral Canal.-The vertebral canal follows the different curves of the column; 
it is large and triangular in those parts of the column which enjoy the greatest 
freedom of movement, viz., the cervical and lumbar regions; and is small and 
rounded in the thoracic region, where motion is more limited. 
Applied Anatomy.-Occasionally the coalescence of the laminae is not completed, and conse- 
quently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal 
membranes (dura mater and arachnoid), and generally of the medulla spinalis itself, takes place, 
constituting the malformation known as spina bifida. This condition is most common in the 
lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout 
the whole length of the canal may remain incomplete. 
The construction of the movable part of the vertebral column of a number of pieces, securely 
connected together and enjoying only a slight degree of movement between any two individual 
pieces, but permitting of a very considerable range as a whole, allows a sufficient degree of mobility 
without any material diminution of strength. The many joints of which the column is composed, 
together with the very varied movements to which it is subjected, render it liable to sprains; 
but, so closely are the individual vertebrae articulated that these sprains are rarely severe, and 
an amount of violence sufficiently great to produce tearing of the ligaments would tend rather 
to cause a dislocation or fracture. The further safety of the column and its slight liability to THE VERTEBRAL COLUMN AS A WHOLE 
215 
injury are provided for by its disposition in curves instead of in a straight line. For it is an elastic 
column, and must bend before it breaks; under these circumstances, being made up of three curves, 
it represents three columns, and greater force is required to produce bending of a short column 
than of a longer one that is equal to it in breadth and material. Again, the safety of the column 
is largely provided for by the presence between the bodies of the intervertebral fibrocartilages, 
which act as buffers in counteracting the effects of violent jars or shocks. 
Fracture dislocation of the vertebral column may be caused by direct or indirect violence. 
Fractures from indirect violence are the more common, and here the bodies of the vertebrae are 
compressed, while the arches are torn asunder; in fracture from direct violence, on the other 
hand, the arches are compressed and the bodies of the vertebrae separated from each other. It 
will therefore be seen that in both classes of injury the medulla spinalis is the part least likely to 
be injured, and may escape damage even where there has been considerable lesion of the bony 
framework. When a fracture dislocation is produced by indirect violence, the displacement is 
almost always the same; the upper segment being driven forward on the lower, so that the medulla 
spinalis is compressed between the body of the vertebra below and the arch of the vertebra above. 
Diseases of the Vertebral Column.-Spinal caries, or tuberculous disease affecting the cancellous 
tissue of the bodies of the vertebrae, is a very common condition. When the bodies, having been 
destroyed, begin to fall together, the spinous processes are necessarily thrown backward and 
stand out prominently, especially if the disease affect the thoracic region, which is most commonly 
the case. The condition then goes by the name of angular curvature, and great rigidity of the 
muscles in the affected region accompanies it. Pressure, by the inflammatory thickenings of the 
disease, is apt to involve the spinal nerves in the affected region, giving rise to peripheral pains, 
and if the disease be in the lower thoracic vertebrae the pains are referred to the epigastric or 
umbilical regions, and often the chief thing complained of is "belly ache." Chronic abscess forma- 
tion in spinal caries is very frequent, and it nearly always forms in front of the vertebral bodies. 
When the disease is in the lower thoracic region, the abscess usually tracks down behind the 
Diaphragma and enters the Psoas sheath, forming the well-known psoas abscess, which may present 
above the inguinal ligament, or may pass beneath it into the thigh. In other cases the abscess 
takes a backward course between the transverse processes and presents as a thoracic or lumbar 
abscess; if the disease affect the cervical region of the vertebral column, a post-pharyngeal abscess 
results. 
Lateral curvature of the vertebral column is a common affection in girls who are outgrowing their 
strength and who sit or stand long at lessons, and is due to the uneven transmission of weight 
down the column. In addition to the lateral displacement of the spinous processes there is a 
marked rotation of the bodies of the vertebrae, the displacement of which is far in excess of that 
of the spinous processes. When the curve is severe and the bones have actually become distorted, 
the condition is past cure. 
Kyphosis is an affection in which there is an increase in the normal thoracic curve, and is due 
to bending forward of the upper part of the body carrying the weight of the head. It is seen 
in rickety children, in rapidly growing adolescents, in senile conditions, and in certain diseases, 
such as osteoarthritis and osteitis deformans. In the senile kyphosis often met with in aged 
laborers, the head is firmly fixed and bent forward and downward on to the chest, and the vertebral 
column is curved and rigid. The ribs are immobilized, the chest is flattened antero-posteriorly, 
and breathing becomes almost entirely abdominal. Postmortem, bony ankylosis of the ligaments 
and capsules of the intervertebral joints is found, with ossification of the ligamenta flava, inter- 
spinal and other ligaments. 
It may be noted that in marked cases of spinal deformity the trachea and aorta follow closely 
along the line of a spinal curvature occurring in their vicinity, whereas the oesophagus between 
the tracheal bifurcation and the stomach often passes like a bowstring across the concavity of 
the curve. 
Lordosis, on the other hand, is an exaggeration of the normal lumbar curve, the trunk being 
thrown backward. This is always a compensatory curve, and occurs when, from any cause such 
as pregnancy or tumors, the abdomen is enlarged. It is more strongly marked in cases of disease 
of the hip-joint where the joint is permanently retained in a flexed position, so that in order to 
bring the foot down to the ground the pelvis has to be tilted forward, and this is accomplished by 
an increase of the normal lumbar curve. 
Laminectomy.-The operation of laminectomy is performed in cases of pressure on the medulla 
spinalis, where the continuity of the nerve tracts has not been completely destroyed. It consists 
of cutting down on and removing the laminae and spinous processes in the affected region, so as 
to relieve the medulla spinalis from pressure; but it is useless in cases of complete destruction 
of this structure. Laminectomy is chiefly performed (1) for fracture dislocation; (2) for localized 
pressure in cases of spinal caries, the object here being to remove the laminae against which the 
medulla spinalis is pressed by the inflammatory mass; and (3) for the removal of tumors growing 
inside the vertebral canal and compressing the medulla spinalis. If such cases be taken early, 
very satisfactory results are obtained. 216 
OSTEOLOGY 
THE THORAX. 
The skeleton of the thorax or chest is an osseo-cartilaginous cage, containing 
and protecting the principal organs of respiration and circulation. It is conical 
in shape, being narrow above and broad below, flattened from before backward, 
and longer behind than in front. It is somewhat reniform on transverse section 
on account of the projection of the vertebral bodies into the cavity. 
Boundaries.-The posterior surface is formed by the twelve thoracic vertebrae 
and the posterior parts of the ribs. It is convex from above downward, and pre- 
sents on either side of the middle line a deep groove, in consequence of the lateral 
and backward direction which the ribs take from their vertebral extremities to 
their angles. The anterior surface, formed by the sternum and costal cartilages, 
is flattened or slightly convex, and inclined from above downward and forward. 
The lateral surfaces are convex; they are formed by the ribs, separated from 
each other by the intercostal spaces, eleven in number, which are occupied by 
the Intercostal muscles and membranes. 
The upper opening of the thorax is reniform in shape, being broader from side 
to side than from before backward. It is formed by the first thoracic vertebra 
behind, the upper margin of the sternum in front, and the first rib on either side. 
It slopes downward and forward, so that the anterior part of the opening is on a 
lower level than the posterior. Its antero-posterior diameter is about 5 cm., and 
its transverse diameter about 10 cm. The lower opening is formed by the twelfth 
thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front 
by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on 
either side and form an angle, the subcostal angle, into the apex of which the 
xiphoid process projects. The lower opening is wider transversely than from 
before backward, and slopes obliquely downward and backward, it is closed by 
the Diaphragma which forms the floor of the thorax. 
The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 2. 
The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part 
of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower 
part of the body of the second. 4. The upper ribs are more movable, and so allow a greater 
enlargement of the upper part of the thorax. 
The Sternum (Breast Bone). 
The sternum (Figs. 259 to 261) is an elongated, flattened bone, forming the 
middle portion of the anterior wall of the thorax. Its upper end supports the 
clavicles, and its margins articulate with the cartilages of the first seven pairs 
of ribs. It consists of three parts, named from above downward, the manubrium, 
the body or gladiolus, and the xiphoid process; in early life the body consists of four 
segments or sternebrce. In its natural position the inclination of the bone is oblique 
from above, downward and forward. It is slightly convex in front and concave 
behind; broad above, becoming narrowed at the point where the manubrium joins 
the body, after which it again widens a little to below the middle of the body, 
and then narrows to its lower extremity. Its average length in the adult is about 
17 cm., and is rather greater in the male than in the female. 
Manubrium (manubrium sterni).-The manubrium is of a somewhat quad- 
rangular form, broad and thick above, narrow below at its junction with the body. 
Surfaces.-Its anterior surface, co'nvex from side to side, concave from above 
downward, is smooth, and affords attachment on either side to the sternal origins 
of the Pectoralis major and Sternocleidomastoideus. In well-marked bones the 
ridges limiting the attachments of these muscles are very distinct. Its posterior THE STERNUM 
217 
surface, concave and smooth, affords attachment on either side to the Sterno- 
hyoideus and Sternothyreoideus. 
Borders.-The superior border is the thickest and presents at its centre the jugular 
or presternal notch; on either side of the notch is an oval articular surface, directed 
upward, backward, and lateralward, for articulation with the sternal end of the 
STERNOCLEIDOMASTOIDEUS 
SUBCLAVIUS 
Fig. 259.-Anterior surface of sternum and costal cartilages. 
clavicle. The inferior border, oval and rough, is covered in a recent state with a 
thin layer of cartilage, for articulation with the body. The lateral borders are each 
marked above by a depression for the first costal cartilage, and below by a small 
facet, which, with a similar facet on the upper angle of the body, forms a notch 
for the reception of the costal cartilage of the second rib. Between the depression 218 
OSTEOLOGY 
for the first costal cartilage and the demi-facet for the second is a narrow, curved 
edge, which slopes from above downward and medialward. 
Body {corpus sterni; gladiolus).-The body, considerably longer, narrower, and 
thinner than the manubrium, attains its greatest breadth close to the lower end. 
Surfaces.-Its anterior surface is nearly flat, directed upward and forward, 
and marked by three transverse ridges which cross the bone opposite the third, 
fourth, and fifth articular depressions.1 It affords attachment on either side to 
the sternal origin of the Pectoralis major. At the junction of the third and fourth 
pieces of the body is occasionally seen an orifice, the sternal foramen, of varying 
size and form. The posterior surface, slightly concave, is also marked by three 
transverse lines, less distinct, however, than those in front; from its lower part, 
on either side, the Transversus thoracis takes origin. 
For Isf 
costal 
cartilage 
Articular surface 
for clavicle 
Depression for 
lsi costal cartilage 
Manubrium 
Sternal 
angle 
Demifacets for 2nd costal 
cartilage 
Facet for 3rd costal cartilage 
Body 
Facet for Aih costal cartilage 
Facet for 5th costal cartilage 
- Facet for 6th costal cartilage 
Facet for 7th costal cartilage 
Xiphoid process 
Xiphoid process 
Fig. 260.-Posterior surface of sternum. 
Fig. 261.-Lateral border of sternum. 
Borders.-The superior border is oval and articulates with the manubrium, the 
junction of the two forming the sternal angle {angulus Ludovici2). The inferior 
border is narrow, and articulates with the xiphoid process. Each lateral border 
(Fig. 261), at its superior angle, has a small facet, which with a similar facet on 
the manubrium, forms a cavity for the cartilage of the second rib; below this 
are four angular depressions which receive the cartilages of the third, fourth, 
fifth, and sixth ribs, while the inferior angle has a small facet, which, with a cor- 
responding one on the xiphoid process, forms a notch for the cartilage of the seventh 
rib. These articular depressions are separated by a series of curved interarticular 
intervals, which diminish in length from above downward, and correspond to 
1 Paterson (The Human Sternum, 1904), who examined 524 specimens, points out that these ridges are altogether 
absent in 26.7 per cent.; that in 69 per cent, a ridge exists opposite the third costal attachment; in 39 per cent, opposite 
the fourth; and in 4 per cent, only, opposite the fifth. 
2 Named after the French surgeon Antoine Louis, 1723-1792. The Latin name angulus Ludovici is not infrequently 
mistranslated into English as "the angle of Ludwig." THE STERNUM 
219 
1 for manubrium 
6th month 
Time 
of 
appearance 
4 for body 
7 th month 
1st year after birth 
1 for xiphoid 
process 
5th to 18th year 
Fig. 262.-Ossification of the sternum. 
Rarely unite, except in old age 
Time 
of 
union 
Between puberty and the 25th year 
Soon after puberty 
Partly cartilaginous to advanced life 
Fig. 263 
for first piece, two or more centres 
for second piece, usually one 
In 
number of 
centres 
for third 
2, placed laterally 
for fourth 
for fifth 
Fig. 264.-Peculiarities. 
In 
mode, of 
union 
Arrest of ossification of lateral pieces, 
producing ; 
-Sternal fissure, and 
Sternal foramen 
Fig. 265 220 
OSTEOLOGY 
the intercostal spaces. Most of the cartilages belonging to the true ribs, as will 
be seen from the foregoing description, articulate with the sternum at the lines 
of junction of its primitive component segments. This is well seen in many of 
the lower animals, where the parts of the bone remain ununited longer than in 
man. 
Xiphoid Process (processus xiphoideus; ensiform or xiphoid appendix).-The 
xiphoid process is the smallest of the three pieces: it is thin and elongated, 
cartilaginous in structure in youth, but more or less ossified at its upper part in 
the adult. 
Surfaces.-Its anterior surface affords attachment on either side to the anterior 
costoxiphoid ligament and a small part of the Rectus abdominis; its posterior sur- 
face, to the posterior costoxiphoid ligament and to some of the fibres of the Dia- 
phragma and Transversus thoracis, its lateral borders, to the aponeuroses of the 
abdominal muscles. Above, it articulates with the lower end of the body, and 
on the front of each superior angle presents a facet for part of the cartilage of the 
seventh rib; below, by its pointed extremity, it gives attachment to the linea 
alba. The xiphoid process varies much in form; it may be broad and thin, pointed, 
bifid, perforated, curved, or deflected considerably to one or other side. 
Structure.-The sternum is composed of highly vascular cancellous tissue, covered by a thin 
layer of compact bone which is thickest in the manubrium between the articular facets for the 
clavicles. 
Ossification.-The sternum originally consists of two cartilaginous bars, situated one on either 
side of the median plane and connected with the cartilages of the upper nine ribs of its own side. 
These two bars fuse with each other along the middle line to form the cartilaginous sternum which 
is ossified from six centres: one for the manubrium, four for the body, and one for the xiphoid 
process (Fig. 262). The ossific centres appear in the intervals between the articular depressions 
for the costal cartilages, in the following order: in the manubrium and first piece of the body, 
during the sixth month; in the second and third pieces of the body, during the seventh month of 
fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between 
the fifth and eighteenth years. The centres make their appearance at the upper parts of the seg- 
ments, and proceed gradually downward.1 To these may be added the occasional existence of 
two small episternal centres, which make their appearance one on either side of the jugular notch; 
they are probably vestiges of the episternal bone of the monotremata and lizards. Occasionally 
some of the segments are formed from more than one centre, the number and position of which 
vary (Fig. 264). Thus, the first piece may have two, three, or even six centres. When two are 
present, they are generally situated one above the other, the upper being the larger; the second 
piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two 
centres placed laterally, the irregular union of which explains the rare occurrence of the sternal 
foramen (Fig. 265), or of the vertical fissure which occasionally intersects this part of the bone; 
these conditions are further explained by the manner in which the cartilaginous sternum is formed. 
Union of the various centres of the body begins about puberty, and proceeds from below upward 
(Fig. 263); by the age of twenty-five they are all united. The xiphoid process may become joined 
to the body before the age of thirty, but this occurs more frequently after forty; on the other 
hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally 
joined to the body by bone. When this takes place, however, the bony tissue is generally only 
superficial, the central portion of the intervening cartilage remaining unossified. 
Articulations.-The sternum articulates on either side with the clavicle and upper seven costal 
cartilages. 
The Ribs (Costae). 
The ribs are elastic arches of bone, which form a large part of the thoracic 
skeleton. They are twelve in number on either side; but this number may be 
increased by the development of a cervical or lumbar rib, or may be diminished 
to eleven. The first seven are connected behind with the vertebral column, and in 
front, through the intervention of the costal cartilages, with the sternum (Fig. 
259); they are called true or vertebro-sternal ribs.2 The remaining five are false 
1 Out of 141 sterna between the time of birth and the age of sixteen years, Paterson (op. cit.) found the fourth or 
lowest centre for the body present only in thirty-eight cases-i. e., 26.9 per cent. 
2 Sometimes the eighth rib cartilage articulates with the sternum; this condition occurs more frequently on the 
right than on the left side. THE RIBS 
221 
ribs; of these, the first three have their cartilages attached to the cartilage of the 
rib above (vertebro-chondral): the last two are free at their anterior extremities 
Non-articular part of tubercle 
Angle 
Articular part of tubercle 
and are termed floating or vertebral ribs. The 
ribs vary in their direction, the upper ones 
being less oblique than the lower; the obliquity 
reaches its maximum at the ninth rib, and 
gradually decreases from that rib to the 
twelfth. The ribs are situated one below the 
other in such a manner that spaces called 
intercostal spaces are left between them. The 
length of each space corresponds to that of 
the adjacent ribs and their cartilages; the 
breadth is greater in front than behind, and 
between the upper than the lower ribs. The 
ribs increase in length from the first to the 
seventh, below which they diminish to the 
twelfth. In breadth they decrease from above 
downward; in the upper ten the greatest 
breadth is at the sternal extremity. 
Common Characteristics of the Ribs (Figs. 
266, 267).-A rib from the middle of the 
series should be taken in order to study the 
common characteristics of these bones. 
Each rib has two extremities, a posterior or 
vertebral, and an anterior or sternal, and an 
intervening portion-the body or shaft. 
Posterior Extremity.-The posterior or verte- 
bral extremity presents for examination a head, 
neck, and tubercle. 
The head is marked by a kidney-shaped 
articular surface, divided by a horizontal 
crest into two facets for articulation with 
the depression formed by the junction of 
the bodies of two contiguous thoracic verte- 
brae; the upper facet is the smaller; to the 
crest is attached the interarticular ligament. 
The neck is the flattened portion which 
extends lateralward from the head; it is 
about 2.5 cm. long, and is placed in front of 
the transverse process of the lower of the two 
vertebrae with which the head articulates. Its 
anterior surface is flat and smooth, its posterior 
rough for the attachment of the ligament of the 
Costal groove 
-Body 
Fig. 266.-A central rib of the left side. 
Inferior aspect. 222 
OSTEOLOGY 
neck, and perforated by numerous foramina. Of its two borders the superior presents 
a rough crest (crista colli costae) for the attachment of the anterior costotransverse 
ligament; its inferior border is rounded. On the posterior surface at the junction 
of the neck and body, and nearer the lower than the upper border, is an eminence 
-the tubercle; it consists of an articular and a non-articular portion. The articular 
portion, the lower and more medial of the two, presents a small, oval surface for 
articulation with the end of the transverse process of the lower of the two vertebrae 
to which the head is connected. The non-articzdar portion is a rough elevation, 
and affords attachment to the ligament of the tubercle. The tubercle is much more 
prominent in the upper than in the lower ribs. 
Body.-The body or shaft is thin and flat, with two surfaces, an external and an 
internal; and two borders, a superior and an inferior. The external surface is convex, 
smooth, and marked, a little in front of the tubercle, by a prominent line, directed 
downward and lateralward; this gives attachment to a tendon of the Iliocostalis, 
and is called the angle. At this point the rib is bent in two directions, and at the 
same time twisted on its long axis. If the rib be laid upon its lower border, the 
portion of the body in front of the angle rests upon this border, while the portion 
behind the angle is bent medialward and at the same time tilted upward; as the 
Demifacet for vertebra 
Interarticular crest 
Demifacet for vertebra 
Articular part of tubercle 
Non-articular part of tubercle 
Costal groove 
Fig. 267.-A central rib of the left side, viewed from behind. 
result of the twisting, the external surface, behind the angle, looks downward, 
and in front of the angle, slightly upward. The distance between the angle and the 
tubercle is progressively greater from the second to the tenth ribs. The portion 
between the angle and the tubercle is rounded, rough, and irregular, and serves 
for the attachment of the Longissimus dorsi. The external surface presents, 
toward its sternal end, an oblique line, the anterior angle. The internal surface 
is concave, smooth, directed a little upward behind the angle, a little downward 
in front of it, and is marked by a ridge which commences at the lower extremity 
of the head; this ridge is strongly marked as far as the angle, and gradually becomes 
lost at the junction of the anterior and middle thirds of the bone. Between it 
and the inferior border is a groove, the costal groove, for the intercostal vessels 
and nerve. At the back part of the bone, this groove belongs to the inferior border, 
but just in front of the angle, where it is deepest and broadest, it is on the internal 
surface. The superior edge of the groove is rounded and serves for the attach- 
ment of an Intercostalis interims; the inferior edge corresponds to the lower 
margin of the rib, and gives attachment to an Intercostalis externus. Within 
the groove are seen the orifices of numerous small foramina for nutrient vessels THE RIBS 
223 
which traverse the shaft obliquely from before backward. The superior border, 
thick and rounded, is marked by an external and an internal lip, more distinct 
behind than in front, which serve for the attachment of Intercostales externus 
and internus. The inferior border is thin, and has attached to it an Intercostalis 
externus. 
Anterior Extremity.-The anterior or sternal extremity is flattened, and presents a 
porous, oval, concave depression, into which the costal cartilage is received. 
Fig. 268 
Fig. 269 
First digitation 
ofSerratus anterior 
Angle- 
Fig. 270 
Single articular facet 
Fig. 271 
Single articular facet 
Fig. 272 
Single articular facet 
Figs. 268 to 272.-Peculiar ribs. 
Peculiar Ribs.--The first, second, tenth, eleventh, and twelfth ribs present 
certain variations from the common characteristics described above, and require 
special consideration. 
First Rib.-The first rib (Fig. 268) is the most curved and usually the shortest 
of all the ribs; it is broad and flat, its surfaces looking upward and downward, 
and its borders inward and outward. The head is small, rounded, and possesses 224 
OSTEOLOGY 
only a single articular facet, for articulation with the body of the first thoracic 
vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, 
is placed on the outer border. There is no angle, but at the tubercle the rib is 
slightly bent, with the convexity upward, so that the head of the bone is directed 
downward. The upper surface of the body is marked by two shallow grooves, 
separated from each other by a slight ridge prolonged internally into a tubercle, 
the scalene tubercle, for the attachment of the Scalenus anterior; the anterior 
groove transmits the subclavian vein, the posterior the subclavian artery and 
the lowest trunk of the brachial plexus.1 Behind the posterior groove is a rough 
area for the attachment of the Scalenus medius. The under surface is smooth, 
and destitute of a costal groove. The outer border is convex, thick, and rounded, 
and at its posterior part gives attachment to the first digitation of the Serratus 
anterior; the inner border is concave, thin, and sharp, and marked about its centre 
by the scalene tubercle. The anterior extremity is larger and thicker than that 
of any of the other ribs. 
Second Rib.-The second rib (Fig. 269) is much longer than the first, but has a 
very similar curvature. The non-articular portion of the tubercle is occasionally 
only feebly marked. The angle is slight, and situated close to the tubercle. The 
body is not twisted, so that both ends touch any plane surface upon which it may 
be laid; but there is a bend, with its convexity upward, similar to, though smaller 
than that found in the first rib. The body is not flattened horizontally like that 
of the first rib. Its external surface is convex, and looks upward and a little outward; 
near the middle of it is a rough eminence for the origin of the lower part of the 
first and the whole of the second digitation of the Serratus anterior; behind and 
above this is attached the Scalenus posterior. The internal surface, smooth, and 
concave, is directed downward and a little inward: on its posterior part there is 
a short costal groove. 
Tenth Rib.-The tenth rib (Fig. 270) has only a single articular facet on its head. 
Eleventh and Twelfth Ribs.-The eleventh and twelfth ribs (Figs. 271 and 272) 
have each a single articular facet on the head, which is of rather large size; they 
have no necks or tubercles, and are pointed at their anterior ends. The eleventh 
has a slight angle and a shallow costal groove. The twelfth has neither; it is much 
shorter than the eleventh, and its head is inclined slightly downward. Sometimes 
the twelfth rib is even shorter than the first. 
Structure.-The ribs consist of highly vascular cancellous tissue, enclosed in a thin layer of 
compact bone. 
Ossification.-Each rib, with the exception of the last two, is ossified from four centres; a 
primary centre for the body, and three epiphysial centres, one for the head and one each for the 
articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only 
two centres, those for the tubercles being wanting. Ossification begins near the angle toward the 
end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses 
for the head and tubercle make their appearance between the sixteenth and twentieth years, and 
are united to the body about the twenty-fifth year. Fawcett2 states that "in all probability there 
is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib. 
The Costal Cartilages (Cartilagines Costales). 
The costal cartilages (Fig. 259) are bars of hyaline cartilage which serve to 
prolong the ribs forward and contribute very materially to the elasticity of the 
walls of the thorax. The first seven pairs are connected with the sternum; the 
next three are each articulated with the lower border of the cartilage of the pre- 
ceding rib; the last two have pointed extremities, which end in the wall of the 
abdomen. Like the ribs, the costal cartilages vary in their length, breadth, and 
'Anat. Anzeiger, 1910, Band xxxvi. 
2 Journal of Anatomy and Physiology, vol. xlv. THE COSTAL CARTILAGES 
225 
direction. They increase in length from the first to the seventh, then gradually 
decrease to the twelfth. Their breadth, as well as that of the intervals between 
them, diminishes from the first to the last. They are broad at their attachments 
to the ribs, and taper toward their sternal extremities, excepting the first two, 
which are of the same breadth throughout, and the sixth, seventh, and eighth, 
which are enlarged where their margins are in contact. They also vary in direc- 
tion: the first descends a little, the second is horizontal, the third ascends slightly, 
while the others are angular, following the course of the ribs for a short distance, 
and then ascending to the sternum or preceding cartilage. Each costal cartilage 
presents two surfaces, two borders, and two extremities. 
Surfaces.-The anterior surface is convex, and looks forward and upward: that 
of the first gives attachment to the costoclavicular ligament and the Subclavius 
muscle; those of the first six or seven at their sternal ends, to the Pectoralis major. 
The others are covered by, and give partial attachment to, some of the flat muscles 
of the abdomen. The posterior surface is concave, and directed backward and 
downward; that of the first gives attachment to the Sternothyroideus, those of 
the third to the sixth inclusive to the Transversus thoracis, and the six or seven 
inferior ones to the Transversus abdominis and the Diaphragma. 
Borders.-Of the two borders the superior is concave, the inferior convex; they 
afford attachment to the Intercostales interni: the upper border of the sixth gives 
attachment also to the Pectoralis major. The inferior borders of the sixth, seventh, 
eighth, and ninth cartilages present heel-like projections at the points of greatest 
convexity. These projections carry smooth oblong facets which articulate respec- 
tively with facets on slight projections from the upper borders of the seventh, 
eighth, ninth, and tenth cartilages. 
Extremities.-The lateral end of each cartilage is continuous with the osseous 
tissue of the rib to which it belongs. The medial end of the first is continuous 
with the sternum; the medial ends of the six succeeding ones are rounded and are 
received into shallow concavities on the lateral margins of the sternum. The 
medial ends of the eighth, ninth, and tenth costal cartilages are pointed, and are 
connected each with the cartilage immediately above. Those of the eleventh and 
twelfth are pointed and free. In old age the costal cartilages are prone to undergo 
superficial ossification. 
Applied Anatomy.-Fracture of the sternum is by no means common, owing, no doubt, to the 
elasticity of the ribs and their cartilages which support it like so many springs. The fracture 
usually occurs in the upper half of the body. Dislocation of the body from the manubrium may 
take place, and is sometimes described as a fracture. 
The bone is frequently the seat of gummatous tumors and not uncommonly is affected with 
caries. 
The ribs are frequently broken, though from their connections and shape they are able to 
withstand great force, yielding under the injury and recovering themselves like a spring. The 
middle ribs are the most liable to fracture. The first and to a less extent the second, being pro- 
tected by the clavicle, are rarely fractured; and the eleventh and twelfth on account of their 
loose and floating condition enjoy a like immunity. The fracture generally occurs from indirect 
violence, from forcible compression of the chest wall, and the bone then gives way at its weakest 
part, i. e., just in front of the angle. But the ribs may also be broken by direct violence, in which 
case the bone is driven inward at the point struck. Fracture of the ribs is frequently complicated 
with some injury to the viscera contained within the thorax or upper part of the abdominal cavity; 
this is most likely to occur in fractures from direct violence. 
Fracture of the costal cartilages or separation of the cartilages from the ribs, may also take 
place, though they are comparatively rare injuries. In workmen the pressure of tools may dis- 
place the xiphoid process inward. 
The ribs are frequently the seat of tuberculous disease, with the formation of a chronic abscess 
in the chest wall. This may not immediately overlie the carious portion of rib, as the pus is 
often directed a considerable distance along the costal groove before appearing beneath the 
integument. 
Resection of a portion of a rib is often required in order to give efficient drainage to an empyema; 
this is referred to in the description of the respiratory organs. 226 
OSTEOLOGY 
Cervical ribs derived from the seventh cervical vertebra (page 201) are of not infrequent occur- 
rence, and are important clinically because they may give rise to obscure nervous or vascular 
symptoms. The cervical rib may be a mere epiphysis articulating only with the transverse process 
of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or 
without a body. It extends lateralward, or forward and lateralward, into the posterior triangle 
of the neck, where it may terminate in a free end or may join the first thoracic rib, the first costal 
cartilage, or the sternum.1' It varies much in shape, size, direction, and mobility. If it reach 
far enough forward, part of the brachial plexus and the subclavian artery and vein cross over 
it, and are apt to suffer compression in so doing. Pressure on the artery may obstruct the circula- 
tion so much that arterial thrombosis results, causing gangrene of the finger tips. Pressure on 
the nerves is commoner, and affects the eighth cervical and first thoracic nerves, causing paralysis 
of the muscles they supply, and neuralgic pains and paresthesia in the area of skin to which they 
are distributed: no oculopupillary changes are to be found. If these symptoms be severe, removal 
of the rib or as much of it as causes pressure on the vessels and nerves is called for. The operation 
is not free from difficulty, and has been followed by paralysis of the muscles and by subclavian 
aneurism, due to injuries inflicted in the course of the operation. 
The thorax is frequently found to be altered in shape in certain diseases. 
In rickets, the ends of the ribs, where they join the costal cartilages, become enlarged, giving 
rise to the so-called "rickety rosary," which in mild cases is only found on the internal surface 
of the thorax. Lateral to these enlargements the softened ribs sink in, so as to present a groove 
passing downward and lateralward on either side of the sternum. This bone is forced forward 
by the bending of the ribs, and the antero-posterior diameter of the chest is increased. The ribs 
affected are the second to the eighth, the lower ones being prevented from falling in by the pres- 
ence of the liver, stomach, and spleen; and when the abdomen is distended, as it often is in rickets, 
the lower ribs may be pushed outward, causing a transverse groove (Harrison's sulcus) just 
above the costal arch. This deformity or forward projection of the sternum, often asymmetrical, 
is known as pigeon breast, and may be taken as evidence of active or old rickets except in cases 
of primary spinal curvature. In many instances it is associated in children with obstruction in 
the upper air passages, due to enlarged tonsils or adenoid growths. In some rickety children or 
adults, and also in others who give no history or further evidence of having had rickets, an opposite 
condition obtains. The lower part of the sternum and often the xiphoid process as well are deeply 
depressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. 
This is known as funnel breast (German, Trichterbrust'); it never appears to produce the least 
disturbance of any of the vital functions. The phthisical chest is often long and narrow, and with 
great obliquity of the ribs and projection of the scapute In pulmonary emphysema the chest is 
enlarged in all its diameters, and presents on section an almost circular outline. It has received 
the name of the barrel-shaped chest. In severe cases of lateral curvature of the vertebral column 
the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebrae 
which takes place in this disease, the ribs opposite the convexity of the dorsal curve become 
extremely convex behind, being thrown out and bulging, and at the same time flattened in front, 
so that the two ends of the same rib are almost parallel. Coincidently with this the ribs on the 
opposite side, on the concavity of the curve, are sunk and depressed behind, and bulging and 
convex in front. 
It is commonly said that in tuberculosis of the lungs the chest is characteristically "flat," 
that is to say, that the ratio of its antero-posterior to its transverse diameter is less than the 
normal. But by careful measurement in a large number of cases, Woods Hutchinson has shown 
that this is not so. Taking the transverse diameter of the chest at the nipple level as = 100, he 
finds that in the normal adult man between the ages of twenty and forty-four the antero-posterior 
diameter = 71. In 82 phthisical subjects it was =79.5, and in 30 "flat-chested" persons was = 
80. He explains the error as an optical illusion, due to rolling forward of the shoulders in the 
"flat chested;" the back is seen to be correspondingly rounded and protuberant, while the forward 
position of the shoulders and clavicles lends an appearance of flattening to the chest. 
More or less shrinkage of one side of the thorax is often seen as a consequence of adhesive 
pleurisy, in which the pulmonary and parietal pleura; adhere closely to one another and the lung 
becomes collapsed and fibrosed. If this process be at all complete, great deformity of the chest 
results, the ribs on the affected side falling in, together with obliteration of the intercostal spaces; 
the contents of the mediastinal cavity are pulled over toward the affected side, the other lung 
becomes emphysematous compensatorily. The vertebral column becomes scoliotic, with the 
concavity of the curve toward the affected side. 
THE SKULL. 
The skull is supported on the summit of the vertebral column, and is of an 
oval shape, wider behind than in front. It is composed of a series of flattened 
1 W. Thorburn, The Medical Chronicle, Manchester, 1907, 4th series, xiv, No. 3. 227 
THE OCCIPITAL BONE 
or irregular bones which, with one exception (the mandible), are immovably 
jointed together. It is divisible into two parts: (1) the cranium, which lodges 
and protects the brain, consists of eight bones, and (2) the skeleton of the face, 
of fourteen, as follows: 
Occipital. 
Two Parietals. 
Frontal. 
Cranium, 8 bones 
Two Temporals. 
Sphenoidal. 
Ethmoidal. 
Skull, 22 bones 
Two Nasals. 
Two Maxillae. 
Face, 14 bones 
Two Lacrimals. 
Two Zygomatics. 
Two Palatines. 
Two Inferior Nasal Conchae. 
Vomer. 
Mandible. 
In the Basle nomenclature, certain bones developed in association with the nasal 
capsule, viz., the inferior nasal conchse, the lacrimals, the nasals, and the vomer, 
are grouped as cranial and not as facial bones. 
The hyoid bone, situated at the root of the tongue and attached to the base 
of the skull by ligaments, is described in this section. 
THE CRANIAL BONES (OSSA CRANII). 
The Occipital Bone (Os Occipitale). 
The occipital bone (Figs. 273, 274), situated at the back and lower part of the 
cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval 
aperture, the foramen magnum, through which the cranial cavity communicate 
with the vertebral canal. 
The curved, expanded plate behind the foramen magnum is named the squama; 
the thick, somewhat quadrilateral piece in front of the foramen is called the 
basilar part, whilst on either side of the foramen is the lateral portion. 
The Squama {squama occipitalis).-The squama, situated above and behind 
the foramen magnum, is curved from above downward and from side to side. 
Surfaces.-The external surface is convex and presents midway between the 
summit of the bone and the foramen magnum a prominence, the external occipital 
protuberance. Extending lateralward from this on either side are two curved 
lines, one a little above the other. The upper, often faintly marked, is named 
the highest nuchal line, and to it the galea aponeurotica is attached. The lower 
is termed the superior nuchal line. That part of the squama which lies above 
the highest nuchal lines is named the planum occipitale, and is covered by the 
Occipitalis muscle; that below, termed the planum nuchale, is rough and irregular 
for the attachment of several muscles. From the external occipital protuberance 
a ridge or crest, the mediannuchalline, often faintly marked, descends to the fora- 
men magnum, and affords attachment to the ligamentum nuchae; running from 
the middle of this line across either half of the nuchal plane is the inferior nuchal 
line. Several muscles are attached to the outer surface of the squama, thus: 
the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion 228 
OSTEOLOGY 
to the Sternocleidomastoideus and Splenius capitis: into the surface between 
the superior and inferior nuchal lines the Semispinalis capitis and the Obliquus 
capitis superior are inserted, while the inferior nuchal line and the area below 
it receive the insertions of the Recti capitis posteriores major and minor. The 
posterior atlantooccipital membrane is attached around the postero-lateral part 
of the foramen magnum, just outside the margin of the foramen. 
Highest 
nuchal line 
Hypoglossal canal 
- Constrictor pharyngis 
superior 
Fig. 273.-Occipital bone. Outer surface. 
The internal surface is deeply concave and divided into four fossae by a cruciate 
eminence. The upper two fossae are triangular and lodge the occipital lobes of 
the cerebrum; the lower two are quadrilateral and accommodate the hemispheres 
of the cerebellum. At the point of intersection of the four divisions of the cruciate 
eminence is the internal occipital protuberance. From this protuberance the upper 
division of the cruciate eminence runs to the superior angle of the bone, and on 
one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges 
the hinder part of the superior sagittal sinus; to the margins of this sulcus the falx 
cerebri is attached. The lower division of the cruciate eminence is prominent, 
and is named the internal occipital crest; it bifurcates near the foramen magnum 
and gives attachment to the falx cerebelli; in the attached margin of this falx 
is the occipital sinus, which is sometimes duplicated. In the upper part of the 
internal occipital crest, a small depression is sometimes distinguishable; it is 
termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. 
Transverse grooves, one on either side, extend from the internal occipital protuber- 
ance to the lateral angles of the bone; those grooves accommodate the transverse 
sinuses, and their prominent margins give attachment to the tentorium cerebelli. 
The groove on the right side is usually larger than that on the left, and is THE OCCIPITAL BONE 
229 
continuous with that for the superior sagittal sinus. Exceptions to this condition 
are, however, not infrequent; the left may be larger than the right or the two 
may be almost equal in size. The angle of union of the superior sagittal and trans- 
verse sinuses is named the confluence of the sinuses (torcular Herophili1), and its 
position is indicated by a depression situated on one or other side of the 
protuberance. 
Hypoglossal 
z canals \ 
Fig. 274.-Occipital bone. Inner surface. 
Lateral Parts (pars lateralis).-The lateral parts are situated at the sides of 
the foramen magnum; on their under surfaces are the condyles for articulation 
with the superior facets of the atlas. The condyles are oval or reniform in shape, 
and their anterior extremities, directed forward and medialward, are closer together 
than their posterior, and encroach on the basilar portion of the bone; the posterior 
extremities extend back to the level of the middle of the foramen magnum. The 
articular surfaces of the condyles are convex from before backward and from 
side to side, and look downward and lateralward. To their margins are attached 
the capsules of the atlantobccipital articulations, and on the medial side of each 
is a rough impression or tubercle for the alar ligament. At the base of either 
condyle the bone is tunnelled by a short canal, the hypoglossal canal (anterior 
condyloid foramen). This begins on the cranial surface of the bone immediately 
above the foramen magnum, and is directed lateralward and forward above the 
1 The columns of blood coming in different directions were supposed to be pressed together at this point (.torcular, 
a wine press). 230 
OSTEOLOGY 
condyle. It may be partially or completely divided into two by a spicule of bone; 
it gives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal 
branch of the ascending pharyngeal artery. Behind either condyle is a depression, 
the condyloid fossa, which receives the posterior margin of the superior facet of 
the atlas when the head is bent backward; the floor of this fossa is sometimes 
perforated by the condyloid canal, through which an emissary vein passes from the 
transverse sinus. Extending lateralward from the posterior half of the condyle 
is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular 
notch, which, in the articulated skull, forms the posterior part of the jugular fora- 
men. The jugular notch may be divided into two by a bony spicule, the intra- 
jugular process, which projects lateralward above the hypoglossal canal. The 
under surface of the jugular process is rough, and gives attachment to the Rectus 
capitis lateralis muscle and the lateral atlantooccipital ligament; from this 
surface an eminence, the paramastoid process, sometimes projects downward, and 
may be of sufficient length to reach, and articulate with, the transverse process 
of the atlas. Laterally the jugular process presents a rough quadrilateral or tri- 
angular area which is joined to the jugular surface of the temporal bone by a plate 
of cartilage; after the age of twenty-five this plate tends to ossify. 
The upper surface of the lateral part presents an oval eminence, the jugular 
tubercle, which overlies the hypoglossal canal and is sometimes crossed by an 
oblique groove for the glossopharyngeal, vagus, and accessory nerves. On the 
upper surface of the jugular process is a deep groove which curves medialward 
and forward and is continuous with the jugular notch. This groove lodges the 
terminal part of the transverse sinus, and opening into it, close to its medial 
margin, is the orifice of the condyloid canal. 
Basilar Part (pars basilaris).-The basilar part extends forward and upward 
from the foramen magnum, and presents in front an area more or less quadrilateral 
in outline. In the young skull this area is rough and uneven, and is joined to the 
body of the sphenoid by a plate of cartilage. By the twenty-fifth year this cartil- 
aginous plate is ossified, and the occipital and sphenoid form a continuous bone. 
Surfaces.-On its lower surface, about 1 cm. in front of the foramen magnum, 
is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. 
On either side of the middle line the Longus capitis and Rectus capitis anterior 
are inserted, and immediately in front of the foramen magnum the anterior 
atlantooccipital membrane is attached. 
The upper surface presents a broad, shallow groove which inclines upward 
and forward from the foramen magnum; it supports the medulla oblongata, and 
near the margin of the foramen magnum gives attachment to the membrana 
tectoria. On the lateral margins of this surface are faint grooves for the inferior 
petrosal sinuses. 
Foramen Magnum.-The foramen magnum is a large oval aperture with its long 
diameter antero-posterior; it is wider behind than in front where it is encroached 
upon by the condyles. It transmits the medulla oblongata and its membranes, 
the accessory nerves, the vertebral arteries, the anterior and posterior spinal 
arteries, and the membrana tectoria and alar ligaments. 
Angles.-The superior angle of the occipital bone articulates with the occipital 
angles of the parietal bones and, in the fetal skull, corresponds in position with the 
posterior fontanelle. The inferior angle is fused with the body of the sphenoid. 
The lateral angles are situated at the extremities of the grooves for the transverse 
sinuses: each is received into the interval between the mastoid angle of the parietal 
and the mastoid part of the temporal. 
Borders.-The superior borders extend from the superior to the lateral angles: 
they are deeply serrated for articulation with the occipital borders of the parietals, 
and form bv this union the lambdoidal suture. The inferior borders extend from THE PARIETAL BONE 
231 
the lateral angles to the inferior angle; the upper half of each articulates with 
the mastoid portion of the corresponding temporal, the lower half with the petrous 
part of the same bone. These two portions of the inferior border are separated 
from one another by the jugular process, the notch on the anterior surface of which 
forms the posterior part of the jugular foramen. 
Structure.-The occipital, like the other cranial bones, consists of two compact lamellae, called 
the outer and inner tables, between which is the cancellous tissue or diploe; the bone is especially 
thick at the ridges, protuberances, condyles, and anterior part of the basilar part; in the inferior 
fossae it is thin, semitransparent, and destitute of diploe. 
Ossification (Fig. 275).-The planum occipitale of the squama is developed in membrane, 
and may remain separate throughout life when it constitutes the interparietal bone; the rest of 
the bone is developed in cartilage. The number 
of nuclei for the planum occipitale is usually 
given as four, two appearing near the middle Une 
about the second month, and two some little 
distance from the middle line about the third 
month of fetal life. The planum nuchale of the 
squama is ossified from two centres, which ap- 
pear about the seventh week of fetal life and soon 
unite to form a single piece. Union of the upper 
and lower portions of the squama takes place in 
the third month of fetal life. An occasional centre 
(Kerckring) appears in the posterior margin of the 
foramen magnum during the fifth month; this 
forms a separate ossicle (sometimes double) which 
unites with the rest of the squama before birth. 
Each of the lateral parts begins to ossify from a 
single centre during the eighth week of fetal life. 
The basilar portion is ossified from two centres, 
one in front of the other; these appear about the 
sixth week of fetal life and rapidly coalesce. Mall1 
states that the planum occipitale is ossified from 
two centres and the basilar portion from one. 
About the fourth year the squama and the two 
lateral portions unite, and about the sixth year 
the bone consists of a single piece. Between the 
eighteenth and twenty-fifth years the occipital and sphenoid become united, forming a single 
bone. 
Articulations.-The occipital articulates with six bones: the two parietals, the two temporals, 
the sphenoid, and the atlas. 
Planum 
occipitale 
Planum 
nuchale 
Kerckring's 
centre 
_ Lateral 
part 
Basilar part 
Fig. 275.-Occipital bone at birth. 
The Parietal Bone (Os Parietale). 
The parietal bones form, by their union, the sides and roof of the cranium. Each 
bone is irregularly quadrilateral in form, and has two surfaces, four borders, 
and four angles. 
Surfaces.-The external surface (Fig. 276) is convex, smooth, and marked near 
the centre by an eminence, the parietal eminence (tuber parietale), which indicates 
the point where ossification commenced. Crossing the middle of the bone in an 
arched direction are two curved lines, the superior and inferior temporal lines; the 
former gives attachment to the temporal fascia, and the latter indicates the upper 
limit of the muscular origin of the Temporalis. Above these lines the bone is 
covered by the galea aponeurotica; below them it forms part of the temporal 
fossa, and affords attachment to the Temporalis muscle. At the back part and 
close to the upper or sagittal border is the parietal foramen, which transmits a 
vein to the superior sagittal sinus, and sometimes a small branch of the occipital 
artery; it is not constantly present, and its size varies considerably. 
1 American Journal of Anatomy, 1906, vol. v. 232 
OSTEOLOGY 
The internal surface (Fig. 277) is concave; it presents depressions corresponding 
to the cerebral convolutions, and numerous furrows for the ramifications of the 
middle meningeal vessel;1 the latter run upward and backward from the sphenoidal 
angle, and from the central and posterior part of the squamous border. Along 
the upper margin is a shallow groove, which, together with that on the opposite 
parietal, forms a channel, the sagittal sulcus, for the superior sagittal sinus; the 
edges of the sulcus afford attachment to the falx cerebri. Near the groove are 
several depressions, best marked in the skulls of old persons, for the arachnoid 
granulations (Pacchionian bodies'). In the groove is the internal opening of the 
parietal foramen when that aperture exists. 
Articulates with opposite parietal bone 
Articulates 
with 
frontal 
bone 
Articulates 
with 
occipita 
bone 
With 
temporal squama 
With sphenoid 
With mastoid 'portion of 
temporal bone 
Fig. 276.-Left parietal bone. Outer surface. 
Borders.-The sagittal border, the longest and thickest, is dentated and articu- 
lates with its fellow of the opposite side, forming the sagittal suture. The squamous 
border is divided into three parts: of these, the anterior is thin and pointed, bevelled 
at the expense of the outer surface, and overlapped by the tip of the great wing 
of the sphenoid; the middle portion is arched, bevelled at the expense of the outer 
surface, and overlapped by the squama of the temporal; the posterior part is thick 
and serrated for articulation with the mastoid portion of the temporal. The 
frontal border is deeply serrated, and bevelled at the expense of the outer surface 
above and of the inner below; it articulates with the frontal bone, forming one- 
half of the coronal suture. The occipital border, deeply denticulated, articulates 
with the occipital, forming one-half of the lambdoidal suture. 
1 Journal of Anatomy and Physiology, 1912, vol. xlvi. THE FRONTAL BONE 
233 
Angles.-The frontal angle is practically a right angle, and corresponds with 
the point of meeting of the sagittal and coronal sutures; this point is named the 
bregma; in the fetal skull and for about a year and a half after birth this region is 
membranous, and is called the anterior fontanelle. The sphenoidal angle, thin 
and acute, is received into the interval between the frontal bone and the great 
wing of the sphenoid. Its inner surface is marked by a deep groove, sometimes 
a canal, for the anterior divisions of the middle meningeal artery. The occipital 
angle is rounded and corresponds with the point of meeting of the sagittal and 
lambdoidal sutures-a point which is termed the lambda; in the fetus this part 
of the skull is membranous, and is called the posterior fontanelle. The mastoid 
angle is truncated; it articulates with the occipital bone and with the mastoid 
portion of the temporal, and presents on its inner surface a broad, shallow groove 
which lodges part of the transverse sinus. The point of meeting of this angle 
with the occipital and the mastoid part of the temporal is named the asterion. 
Occipital 
angle 
Frontal 
' angle 
Mastoid 
angle 
Sphenoidal angle 
Fig. 277.-Left parietal bone. Inner surface. 
Ossification.-The parietal bone is ossified in membrane from a single centre, which appears 
at the parietal eminence about the eighth week of fetal life. Ossification gradually extends in 
a radial manner from the centre toward the margins of the bone; the angles are consequently 
the parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone 
is divided into two parts, upper and lower, by an antero-posterior suture. 
Articulations.-The parietal articulates with five bones: the opposite parietal, the occipital, 
frontal, temporal, and sphenoid. 
The Frontal Bone (Os Frontale). 
The frontal bone resembles a cockle-shell in form, and consists of two portions 
-a vertical portion, the squama, corresponding with the region of the forehead; 234 
OSTEOLOGY 
and an orbital or horizontal portion, which enters into the formation of the roofs 
of the orbital and nasal cavities. 
Squama (squama frontalis) .-Surfaces.-The external surface (Fig. 278) of this 
portion is convex and usually exhibits, in the lower part of the middle line, the 
remains of the frontal or metopic suture; in infancy this suture divides the bone into 
two, a condition which may persist throughout life. On either side of this suture, 
about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal emi- 
nence (tuber frontale). These eminences vary in size in different individuals, are 
occasionally unsymmetrical, and are especially prominent in young skulls; the sur- 
face of the bone above them is smooth, and covered by the galea aponeurotica. 
Below the frontal eminences, and separated from them by a shallow groove, are 
two arched elevations, the superciliary arches; these are prominent medially, and 
Orbicularis oculi 
Nasal part 
Zygomatic 
process 
spine 
Fig. 278.-Frontal bone. Outer surface. 
Frontal 
are joined to one another by a smooth elevation named the glabella. They are 
larger in the male than in the female, and their degree of prominence depends 
to some extent on the size of the frontal air sinuses;1 prominent ridges are, how- 
ever, occasionally associated with small air sinuses. Beneath each superciliary 
arch is a curved and prominent margin, the supraorbital margin, which forms the 
upper boundary of the base of the orbit, and separates the squama from the orbital 
portion of the bone. The lateral part of this margin is sharp and prominent, 
affording to the eye, in that situation, considerable protection from injury; the 
medial part is rounded. At the junction of its medial and intermediate thirds is 
1 Some confusion is occasioned to students commencing the study of anatomy by the name "sinus" having been 
given to two different kinds of space connected with the skull. It may be as well, therefore, to state here that the 
"sinuses" in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous 
channels which convey the blood from the brain, while the "sinuses" external to the cranial cavity (the frontal, 
sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves; they communicate with the nasal 
cavities and contain air. THE FRONTAL BONE 
235 
a notch, sometimes converted into a foramen, the supraorbital notch or foramen, 
which transmits the supraorbital vessels and nerve. A small aperture in the upper 
part of the notch transmits a vein from the diploe to join the supraorbital vein. 
The supraorbital margin ends laterally in the zygomatic process, which is strong 
and prominent, and articulates with the zygomatic bone. Running upward and 
backward from this process is a well-marked line, the temporal line, which divides 
into the upper and lower temporal lines, continuous, in the articulated skull, with 
the corresponding lines on the parietal bone. The area below and behind the tem- 
poral line forms the anterior part of the temporal fossa, and gives origin to the 
Temporalis muscle. Between the supraorbital margins the squama projects down- 
ward to a level below that of the zygomatic processes; this portion is known as the 
nasal part and presents a rough, uneven interval, the nasal notch, which articulates 
on either side of the middle line with the nasal bone, and laterally with the frontal 
process of the maxilla and with the lacrimal. The term nasion is applied to the 
middle of the frontonasal suture. From the centre of the notch the nasal process 
projects downward and forward beneath the nasal bones and frontal processes of 
the maxillae, and supports the bridge of the nose. The nasal process ends below 
in a sharp spine, and on either side of this is a small grooved surface which enters 
into the formation of the roof of the corresponding nasal cavity. The spine forms 
part of the septum of the nose, articulating in front with the crest of the nasal 
bones and behind with the perpendicular plate of the ethmoid. 
The internal surface (Fig. 279) of the squama is concave and presents in the 
upper part of the middle line a vertical groove, the sagittal sulcus, the edges of 
which unite below to form a ridge, the frontal crest; the sulcus lodges the superior 
sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. 
The crest ends below in a small notch which is converted into a foramen, the fora- 
men cecum, by articulation with the ethmoid. This foramen varies in size in 
different subjects, and is frequently impervious; when open, it transmits a vein 
from the nose to the superior sagittal sinus. On either side of the middle line the 
bone presents depressions for the convolutions of the brain, and numerous small 
furrows for the anterior branches of the middle meningeal vessels. Several small, 
irregular fossae may also be seen on either side of the sagittal sulcus, for the 
reception of the arachnoid granulations. 
Orbital or Horizontal Part {-pars orbitalis).-This portion consists of two thin 
triangular plates, the orbital plates, which form the vaults of the orbits, and are 
separated from one another by a median gap, the ethmoidal notch. 
Surfaces.-The inferior surface (Fig. 279) of each orbital plate is smooth and 
concave, and presents, laterally, under cover of the zygomatic process, a shallow 
depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depres- 
sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- 
ment of the cartilaginous pulley of the Obliquus oculi superior. The superior 
surface is convex, and marked by depressions for the convolutions of the frontal 
lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal 
vessels. 
The ethmoidal notch separates the two orbital plates; it is quadrilateral, and 
filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins 
of the notch present several half-cells which, when united with corresponding 
half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. 
Two grooves cross these edges transversely; they are converted into the anterior 
and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the 
orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal 
vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of the 
ethmoidal notch, on either side of the frontal spine, are the openings of the frontal 
air sinuses. These are two irregular cavities, which extend backward, upward, 236 
OSTEOLOGY 
and lateralward for a variable distance between the two tables of the skull; they 
are separated from one another by a thin bony septum, which often deviates to 
one or other side, with the result that the sinuses are rarely symmetrical. Absent 
at birth, they are usually fairly well-developed between the seventh and eighth 
years, but only reach their full size after puberty. They vary in size in different 
persons, and are larger in men than in women.1 They are lined by mucous mem- 
brane, and each communicates with the corresponding nasal cavity by means of a 
passage called the frontonasal duct. 
Supraorbital 
foramen 
With maxilla 
Frontal sinus 
With perpendicular plate of ethmoid 
With nasal 
Under surface of nasal process 
forming part of roof of nose 
Fig. 279.-Frontal bone. Inner surface. 
Borders.-The border of the squama is thick, strongly serrated, bevelled at the 
expense of the inner table above, where it rests upon the parietal bones, and at 
the expense of the outer table on either side, where it receives the lateral pressure 
of those bones; this border is continued below into a triangular, rough surface, 
which articulates with the great wing of the sphenoid. The posterior borders of 
the orbital plates are thin and serrated, and articulate with the small wings of the 
sphenoid. 
Structure.-The squama and the zygomatic processes are very thick, consisting of diploic 
tissue contained between two compact laminae; the diploic tissue is absent in the regions occupied 
by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of 
compact bone; hence the facility with which instruments can penetrate the cranium through 
this part of the orbit; when the frontal sinuses are exceptionally large they may extend backward 
for a considerable distance into the orbital portion, which in such cases also cqpsists of only two 
tables. 
1 Aldren Turner (The Accessory Sinuses of the Nose, 1901) gives the following measurements for a sinus of average 
size: height, 1J4 inches; breadth, 1 inch; depth from before backward, 1 inch. THE TEMPORAL BONE 
237 
Ossification (Fig. 280). - The frontal bone is ossified in membrane from two primary 
centres, one for each half, which appear toward the end of the second month of fetal life, one 
above each supraorbital margin. From each of these centres ossification extends upward to form 
the corresponding half of the squama, and backward to form the orbital plate. The spine is 
ossified from a pair of secondary centres, 
on either side of the middle line; similar 
centres appear in the nasal part and zygo- 
matic processes. At birth the bone consists 
of two pieces, separated by the frontal 
suture, which is usually obliterated, except 
at its lower part, by the eighth year, but 
occasionally persists throughout life. It is 
generally maintained that the development 
of the frontal sinuses begins at the end of 
the first or beginning of the second year, 
but Onodi's recent researches indicate that 
development begins at birth. The sinuses 
are of considerable size by the seventh or 
eighth year, but do not attain their full 
proportions until after puberty. 
Articulations. - The frontal articulates 
with twelve bones: the sphenoid, the eth- 
moid, the two parietals, the two nasals, the 
two maxill®, the two lacrimals, and the 
two zygomatics. 
Squama 
Spine 
Nasal part 
Zygomatic process 
Fig. 280.-Frontal bone at birth. 
The Temporal Bone (Os Temporale). 
The temporal bones are situated at the sides and base of the skull. Each consists 
of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the 
styloid process. 
The Squama {squama temporalis).-The squama forms the anterior and upper 
part of the bone, and is scale-like, thin, and translucent. 
Surfaces.-Its outer surface (Fig. 281) is smooth and convex; it affords attach- 
ment to the Temporalis muscle, and forms part of the temporal fossa; on its hinder 
part is a vertical groove for the middle temporal artery. A curved line, the tem- 
poral line, or supramastoid crest, runs backward and upward across its posterior 
part; it serves for the attachment of the temporal fascia, and limits the origin 
of the Temporalis muscle. The boundary between the squama and the mastoid 
portion of the bone, as indicated by traces of the original suture, lies about 1 cm. 
below this line. Projecting from the lower part of the squama is a long, arched 
process, the zygomatic process. This process is at first directed lateralward, its 
two surfaces looking upward and downward; it then appears as if twisted inward 
upon itself, and rtms forward, its surfaces now looking medial ward and lateralward. 
The superior border is long, thin, and sharp, and serves for the attachment of the 
temporal fascia; the inferior, short, thick, and arched, has attached to it some 
fibres of the Masseter. The lateral surface is convex and subcutaneous; the medial 
is concave, and affords attachment to the Masseter. The anterior end is deeply 
serrated and articulates with the zygomatic bone. The posterior end is connected 
to the squama by two roots, the anterior and posterior roots. The posterior root, a 
prolongation of the upper border, is strongly marked; it runs backward above the 
external acoustic meatus, and is continuous with the temporal line. The anterior 
root, continuous with the lower border, is short but broad and strong; it is directed 
medialward and ends in a rounded eminence, the articular tubercle (eminentia 
articularis). This tubercle forms the front boundary of the mandibular fossa, 
and in the recent state is covered with cartilage. In front of the articular tubercle 
is a small triangular area which' assists in forming the infratemporal fossa; this 
area is separated from the outer surface of the squama by a ridge which is continu- 
ous behind with the anterior root of the zygomatic process, and in front, in the 238 
OSTEOLOGY 
articulated skull, with the infratemporal crest on the great wing of the sphenoid. 
Between the posterior wall of the external acoustic meatus and the posterior root 
of the zygomatic process is the area called the suprameatal triangle (Macewen), 
or mastoid fossa, through which an instrument may be pushed into the tympanic 
antrum. At the junction of the anterior root with the zygomatic process is a pro- 
jection for the attachment of the temporomandibular ligament; and behind the 
anterior root is an oval depression, forming part of the mandibular fossa, for the 
reception of the condyle of the mandible. The mandibular fossa (glenoid fossa) 
is bounded, in front, by the articular tubercle; behind, by the tympanic part of 
the bone, which separates it from the external acoustic meatus; it is divided into 
two parts by a narrow slit, the petrotympanic fissure (Glaserian fissure). The 
Groove for middle 
temporal artery 
Parietal notch 
Suprameatal 
triangle 
Occipitalis 
Articular tubercle 
Post-glenoid process 
Mandibular fossa 
Petrotympanic fissure 
Vaginal process 
Styloglossus 
Occipital groove 
Tympanic part 
Styloid process 
Stylohyoideus 
Fig. 281.-Left temporal bone. Outer surface. 
anterior part, formed by the squama, is smooth, covered in the recent state with 
cartilage, and articulates with the condyle of the mandible. Behind this part 
of the fossa is a small conical eminence; this is the representative of a prominent 
tubercle which, in some mammals, descends behind the condyle of the mandible, 
and prevents its backward displacement. The posterior part of the mandibular 
fossa, formed by the tympanic part of the bone, is non-articular, and sometimes 
lodges a portion of the parotid gland. The petrotympanic fissure leads into the 
middle ear or tympanic cavity; it lodges the anterior process of the malleus, and 
transmits the tympanic branch of the internal maxillary artery. The chorda 
tympani nerve passes through a canal (canal of Huguier), separated from the an- 
terior edge of the petrotympanic fissure by a thin scale of bone and situated on 
the lateral side of the auditory tube, in the retiring angle between the squama 
and the petrous portion of the temporal. THE TEMPORAL BONE 
239 
The internal surface of the squama (Fig. 282) is concave; it presents depressions 
corresponding to the convolutions of the temporal lobe of the brain, and grooves 
for the branches of the middle meningeal vessels. 
Borders.-The superior border is thin, and bevelled at the expense of the internal 
table, so as to overlap the squamous border of the parietal bone, forming with 
it the squamosal suture. Posteriorly, the superior border forms an angle, the 
parietal notch, with the mastoid portion of the bone. The antero-inferior border 
is thick, serrated, and bevelled at the expense of the inner table above and of 
the outer below', for articulation with the great wing of the sphenoid. 
Mastoid Portion (para mastoidea).-The mastoid portion forms the posterior 
part of the bone. 
Pai ietal 
notch 
Eminentia 
arcuata 
Mastoid foramen 
Aquceductus vestibuli 
Aquceductus cochleae 
Internal acoustic meatus 
Fig. 282.-Left temporal bone. Inner surface. 
Surfaces.-Its outer surface (Fig. 281) is rough, and gives attachment to the 
Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one 
of these, of large size, situated near the posterior border, is termed the mastoid 
foramen; it transmits a vein to the transverse sinus and a small branch of the occipi- 
tal artery to the dura mater. The position and size of this foramen are very 
variable; it is not always present; sometimes it is situated in the occipital bone, 
or in the suture between the temporal and the occipital. The mastoid portion is 
continued below into a conical projection, the mastoid process, the size and form 
of which vary somewhat; it is larger in the male than in the female. This process 
serves for the attachment of the Sternocleidomastoideus, Splenius capitis, and 
Longissimus capitis. On the medial side of the process is a deep groove, the 
mastoid notch {digastric fossa), for the attachment of the Digastricus; medial to 
this is a shallow furrow', the occipital groove, which lodges the occipital artery. 240 
OSTEOLOGY 
The inner surface of the mastoid portion presents a deep, curved groove, the 
sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the 
opening of the mastoid foramen. The groove for the transverse sinus is separated 
from the innermost of the mastoid air cells by a very thin lamina of bone, and even 
this may be partly deficient. 
Borders.-The superior border of the mastoid portion is broad and serrated, for 
articulation with the mastoid angle of the parietal. The posterior border, also 
serrated, articulates with the inferior border of the occipital between the lateral 
angle and jugular process. Anteriorly the mastoid portion is fused with the 
descending process of the squama above; below it enters into the formation of 
the external acoustic meatus and the tympanic cavity. 
Tympanic antrum 
Tegmen tympani 
Prominence of lateral semicircular canal 
Prominence of facial canal 
Fenestra vestibuli 
Bristle in semicanal for Tensor tympani 
Septum canalis musculot ubarii 
Bristle in hiatus of facial canal 
Bony part of auditory tube. 
Carotid canal 
Promontory 
Bristle, in TM/rawwcZ 
Fenestra cochleae 
Sulcus tympanicus 
Mastoid cells 
Fig. 283.-Coronal section of right temporal bone. 
Bristle in stylomastoid foramen 
A section of the mastoid process (Fig. 283) shows it to be hollowed out into a 
number of spaces, the mastoid cells, which exhibit the greatest possible variety 
as to their size and number. At the upper and front part of the process they are 
large and irregular and contain air, but toward the lower part they diminish in 
size, while those at the apex of the process are frequently quite small and contain 
marrow; occasionally they are entirely absent, and the mastoid is then solid 
throughout. In addition to these a large irregular cavity is situated at the upper 
and front part of the bone. It is called the tympanic antrum, and must be distin- 
guished from the mastoid cells, though it communicates with them. Like the mas- 
toid cells it is filled with air and lined by a prolongation of the mucous membrane 
of the tympanic cavity, with which it communicates. The tympanic antrum is 
bounded above by a thin plate of bone, the tegmen tympani, which separates it 
from the middle fossa of the base of the skull; below by the mastoid process; later- 
ally by the squama just below the temporal line, and medially by the lateral semi- 
circular canal of the internal ear wdiich projects into its cavity. It opens in front 
into that portion of the tympanic cavity which is known as the attic or epitympanic THE' TEMPORAL BONE 
241 
recess. The tympanic antrum is a cavity of some considerable size at the time of 
birth; the mastoid air cells may be regarded as diverticula from the antrum, 
and begin to appear at or before birth; by the fifth year they are well-marked, 
but their development is not completed until toward puberty. 
Petrous Portion (pars petrosa [pyramis])The petrous portion or pyramid is 
pyramidal and is wedged in at the base of the skull between the sphenoid and 
occipital. Directed medialward, forward, and a little upward, it presents for 
examination a base, an apex, three surfaces, and three angles, and contains, in 
its interior, the essential parts of the organ of hearing. 
Base.-The base is fused with the internal surfaces of the squama and mastoid 
portion. 
Apex.-The apex, rough and uneven, is received into the angular interval between 
the posterior border of the great wing of the sphenoid and the basilar part of the 
occipital; it presents the anterior or internal 
orifice of the carotid canal, and forms the 
postero-lateral boundary of the foramen lac- 
erum. 
Surfaces.-The anterior surface forms the 
posterior part of the middle fossa of the 
base of the skull, and is continuous with the 
inner surface of the squamous portion, to which 
it is united by the petrosquamous suture, 
remains of which are distinct even at a late 
period of life. It is marked by depressions for 
the convolutions of the brain, and presents 
six points for examination: (1) near the 
centre, an eminence (eminentia arcuata') which 
indicates the situation of the superior semi- 
circular canal; (2) in front of and a little lateral 
to this eminence, a depression indicating the 
position of the tympanic cavity: here the 
layer of bone which separates the tympanic 
from the cranial cavity is extremely thin, 
and is known as the tegmen tympani; (3) a 
shallow groove, sometimes double, leading 
lateralward and backward to an oblique open- 
ing, the hiatus of the facial canal, for the passage of the greater superficial petrosal 
nerve and the petrosal branch of the middle meningeal artery; (4) lateral to the 
hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial 
petrosal nerve; (5) near the apex of the bone, the termination of the carotid canal, 
the wall of which in this situation is deficient in front; (6) above this canal the 
shallow trigeminal impression for the reception of the semilunar ganglion. 
The posterior surface (Fig. 282) forms the front part of the posterior fossa of 
the base of the skull, and is continuous with the inner surface of the mastoid 
portion. Near the centre is a large orifice, the internal acoustic meatus, the size of 
which varies considerably; its margins are smooth and rounded, and it leads into 
a short canal, about 1 cm. in length, which runs lateralward. It transmits the 
facial and acoustic nerves and the internal auditory branch of. the basilar artery. 
The lateral end of the canal is closed by a vertical plate, which is divided by a 
horizontal crest, the crista falciformis, into two unequal portions (Fig. 284). Each 
portion is further subdivided by a vertical ridge into an anterior and a posterior 
part. In the portion beneath the crista falciformis are three sets of foramina; 
one group, just below the posterior part of the crest, situated in the area cribrosa 
media, consists of several small ©Denina's for the nerves to the saccule: below and 
Fig. 284.-Diagrammatic view of the fundus 
of the right internal acoustic meatus. (Testut.) 
1. Crista falciformis. 2. Area facialis, with (2') 
internal opening of the facial canal. 3. Ridge 
separating the area facialis from the area crib- 
rosa superior. 4. Area cribrosa superior, with 
(4') openings for nerve filaments. 5. Anterior 
inferior cribriform area, with (5') the tractus 
spiralis foraminosus, and (5") the canalis cen- 
tralis of the cochlea. 6. Ridge separating the 
tractus spiralis foraminosus from the area crib- 
rosa media. 7. Area cribrosa media, with (7') 
orifices for nerves to saccule. 8. Foramen 
singulare. 242 
OSTEOLOGY - 
behind this area is the foramen singulare, or opening for the nerve to the posterior 
semicircular duct; in front of and below the first is the tractus spiralis foraminosus, 
consisting of a number of small spirally arranged openings, which encircle the canalis 
centralis cochleae; these openings together with this central canal transmit the 
nerves to tl\e cochlea. The portion above the crista falciformis presents behind, 
the area cribrosa superior, pierced by a series of small openings, for the passage of 
the nerves to the utricle and the superior and lateral semicircular ducts, and, in 
front, the area facialis, with one large opening, the commencement of the canal 
for the facial nerve (aquaeductus Fallopii). Behind the internal acoustic meatus 
is a small slit almost hidden by a thin plate of bone, leading to a canal, the aquae- 
ductus vestibuli, which transmits the ductus endolymphaticus together with a 
small artery and vein. Above and between these two openings is an irregular 
depression which lodges a process of the dura mater and transmits a small vein; 
in the infant this depression is represented by a large fossa, the subarcuate fossa, 
which extends backward as a blind tunnel under the superior semicircular canal. 
Semicanals for 
auditory 
tube and 
Tensor 
tympani 
Lev. veli palatini 
Rough quadrilateral surface 
Opening of carotid canal 
Inferior tympanic canaliculus 
Aquaeductus cochleae 
Mastoid canaliculus 
Stylopharyngeus 
Jugular fossa 
Vaginal process 
Stylomastoid foramen 
Styloid process 
Jugular surface 
Tympanomastoid fissure 
Fig. 285.-Left temporal bone. Inferior surface. 
The inferior surface (Fig. 285) is rough and irregular, and forms part of the 
exterior of the base of the skull. It presents eleven points for examination: (1) 
near the apex is a rough surface, quadrilateral in form, which serves partly for the 
attachment of the Levator veli palatini and the cartilaginous portion of the audi- 
tory tube, and partly for connection with the basilar part of the occipital bone 
through the intervention of some dense fibrous tissue; (2) behind this is the large 
circular aperture of the carotid canal, which ascends at first vertically, and then, 
making a bend, runs horizontally forward and medialward; it transmits into the 
cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial 
to the opening for the carotid canal and close to its posterior border, in front of THE TEMPORAL BONE 
243 
the jugular fossa, is a triangular depression; at the apex of this is a small opening, 
the aquaeductus cochleae, which lodges a tubular prolongation of the dura mater 
and transmits a vein from the cochlea to join the internal jugular; (4) behind these 
openings is a deep depression, the jugular fossa, of variable depth and size in different 
skulls; it lodges the bulb of the internal jugular vein; (5) in the bony ridge dividing 
the carotid canal from the jugular fossa is the small inferior tympanic canaliculus 
for the passage of the tympanic branch of the glossopharyngeal nerve; (6) in the 
lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the 
auricular branch of the vagus nerve; (7) behind the jugular fossa is a quadrilateral 
area, the jugular surface, covered with cartilage in the recent state, and articulating 
with the jugular process of the occipital bone; (8) extending backward from the 
carotid canal is the vaginal process, a sheath-like plate of bone, which divides 
behind into two laminae; the lateral lamina is continuous with the tympanic part 
of the bone, the medial with the lateral margin of the jugular surface; (9) between 
these laminae is the styloid process, a sharp spine, about 2.5 cm. in length; (10) 
between the styloid and mastoid processes is the stylomastoid foramen; it is the 
termination of the facial canal, and transmits the facial nerve and stylomastoid 
artery; (11) situated between the tympanic portion and the mastoid process is the 
tympanomastoid fissure, for the exit of the auricular branch of the vagus nerve. 
Angles.-The superior angle, the longest, is grooved for the superior petrosal 
sinus, and gives attachment to the tentorium cerebelli; at its medial extremity 
is a notch, in which the trigeminal nerve lies. The posterior angle is intermediate 
in length between the superior and the anterior. Its medial half is marked by 
a sulcus, which forms, with a corresponding sulcus on the occipital bone, the 
channel for the inferior petrosal sinus. Its lateral half presents an excavation 
-the jugular fossa-which, with the jugular notch on the occipital, forms the 
jugular foramen; an eminence occasionally projects from the centre of the fossa, 
and divides the foramen into two. The anterior angle is divided into two parts 
-a lateral joined to the squama by a suture {petrosquamous), the remains of which 
are more or less distinct; a medial, free, which articulates with the spinous process 
of the sphenoid. 
At the angle of junction of the petrous part and the squama are two canals, 
one above the other, and separated by a thin plate of bone, the septum canalis 
musculotubarii {processus cochleariformis); both canals lead into the tympanic 
cavity. The upper one {semicanalis m. tensoris tympani) transmits the Tensor 
tympani, the lower one {semicanalis tubae auditivae) forms the bony part of the 
auditory tube. 
The tympanic cavity, auditory ossicles, and internal ear, are described with 
the organ of hearing. 
Tympanic Part {pars tympanica).-The tympanic part is a curved plate of bone 
lying below the squama and in front of the mastoid process. 
Surfaces.-Its postero-superior surface is concave, and forms the anterior wall, 
the floor, and part of the posterior wall of the bony external acoustic meatus. 
Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment 
of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly 
concave; it constitutes the posterior boundary of the mandibular fossa, and is 
in contact with the retromandibular part of the parotid gland. 
Borders.-Its lateral border is free and rough, and gives attachment to the car- 
tilaginous part of the external acoustic meatus. Internally, the tympanic part 
is fused with the petrous portion, and appears in the retreating angle between 
it and the squama, where it lies below and lateral to the orifice of the auditory 
tube. Posteriorly, it blends with the squama and mastoid part, and forms the 
anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally 
with the back of the postglenoid process, while medially it bounds the petro- 244 
OSTEOLOGY 
tympanic fissure. The medial part of the lower border is thin and sharp; its lateral 
part splits to enclose the root of the styloid process, and is therefore named the 
vaginal process. The central portion of the tympanic part is thin, and in a consid- 
erable percentage of skulls is perforated by a hole, the foramen of Huschke. 
The external acoustic meatus is nearly 2 cm. long and is directed inward and 
slightly forward: at the same time it forms a slight curve, so that the floor of the 
canal is convex upward. In sagittal section it presents an oval or elliptical shape 
with the long axis directed downward and slightly backward. Its anterior wall 
and floor and the lower part of its posterior wall are formed by the tympanic 
part; the roof and Upper part of the posterior wall by the squama. Its inner 
end is closed, in the recent state, by the tympanic, membrane; the upper limit 
of its outer orifice is formed by the posterior root of the zygomatic process, imme- 
diately below which there is sometimes seen a small spine, the suprameatal spine, 
situated at the upper and posterior part of the orifice. 
Styloid Process (processus styloideus).-The styloid process is slender, pointed, 
and of varying length; it projects dowmward and forward, from the under surface 
of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the 
vaginal process of the tympanic portion, while its distal part (stylohyal) gives 
attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- 
glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament 
extends from the apex of the process to the lesser cornu of the hyoid bone, and 
in some instances is partially, in others completely, ossified. 
Septum canalis musculotubarii 
Fenestra vestibuli 
Sulcus tympanicus 
Tympanic antrum 
Bristle in facial 
canal 
Lateral wall of 
tympanic antrum 
Fig. 286.-The three principal parts of the temporal bone at birth. 1. Outer surface of petromastoid part. 
2. Outer surface of tympanic ring. 3. Inner surface of squama. 
Structure.-The structure of the squama is like that of the other cranial bones: the mastoid 
portion is spongy, and the petrous portion dense and hard. 
Ossification.-The temporal bone is ossified from eight centres, exclusive of those for the internal 
ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for 
the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just 
before the close of fetal life (Fig. 286) the temporal bone consists of three principal parts: 1. 
The squama is ossified in membrane from a single nucleus, which appears near the root of the 
zygomatic process about the second month. 2. The petromastoid part is developed from four 
centres, which make their appearance in the cartilaginous ear capsule about the fifth or sixth 
month. One {probtic) appears in the neighborhood of the eminentia arcuata, spreads in front 
and above the internal acoustic meatus and extends to the apex of the bone; it forms part of the 
cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second 
(ppisthotic) appears at the promontory on the medial wall of the tympanic cavity and surrounds 
the fenestra cochleae; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid 
canal, invests the lateral and lower part of the cochlea, and spreads medially below the internal 245 
THE SPHENOIDAL BONE 
acoustic meatus. A third (pterotic) roofs in the tympanic cavity and antrum; while the fourth 
(epiotic) appears near the posterior semicircular canal and extends to form the mastoid process 
(Vrolik). 3. The tympanic ring is an incomplete circle, in the concavity of which is a groove, 
the tympanic sulcus, for the attachment of the circumference of the tympanic membrane. This 
ring expands to form the tympanic part, and is ossified in membrane from a single centre which 
appears about the third month. The styloid process is developed from the proximal part of the 
cartilage of the second branchial or hyoid arch by two centres: one for the proximal part, the 
tympanohyal, appears before birth; the other, comprising the rest of the process, is named the 
stylohyal, and does not appear until after birth. The tympanic ring unites with the squama 
shortly before birth; the petromastoid part and squama join during the first year, and the tym- 
panohyal portion of the styloid process about the same time (Figs. 287, 288). The stylohyal 
does not unite with the rest of the bone until after puberty, and in some skulls never at all. 
Squama 
Squama 
Petrosquamous 
suture 
Petrosquamous suture 
Eminentia arcuata 
■Tympanic ring 
Fossa subarcuata 
Petromastoid portion 
Internal acoustic meatus 
Fig. 287.-Temporal bone at birth. 
Outer aspect. 
Fig. 288.-Temporal bone at birth. Inner 
aspect. 
The chief subsequent changes in the temporal bone apart from increase in size are: (1) The 
tympanic ring extends outward and backward to form the tympanic part. This extension does 
not, however, take place at an equal rate all around the circumference of the ring, but occurs most 
rapidly on its anterior and posterior portions, and these outgrowths meet and blend, and thus, 
for a time, there exists in the floor of the meatus a foramen, the foramen of Huschke; this foramen 
is usually closed about the fifth year, but may persist throughout life. (2) The mandibular fossa 
is at first extremely shallow, and looks lateralward as well as downward; it becomes deeper and 
is ultimately directed downward. Its change in direction is accounted for as follows. The part 
of the squama which forms the fossa lies at first below the level of the zygomatic process. As, 
however, the base of the skull increases in width, this lower part of the squama is directed hori- 
zontally inward to contribute to the middle fossa of the skull, and its surfaces therefore come 
to look upward and downward; the attached portion of the zygomatic process also becomes 
everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at 
first quite flat, and the stylomastoid foramen and rudimentary styloid process He immediately 
behind the tympanic ring. With the development of the air cells the outer part of the mastoid 
portion grows downward and forward to form the mastoid process, and the styloid process and 
stylomastoid foramen now come to he on the under surface. The descent of the foramen is 
necessarily accompanied by a corresponding lengthening of the facial canal. (4) The downward 
and forward growth of the mastoid process also pushes forward the tympanic part, so that the 
portion of it which formed the original floor of the meatus and contained the foramen of Huschke 
is ultimately found in the anterior wall. (5) The fossa subarcuata becomes filled up and almost 
obliterated. 
Articulations.-The temporal articulates with./we bones: occipital, parietal, sphenoid, mandible, 
and zygomatic. 
The Sphenoidal Bone (Os Sphenoidal; Sphenoid Bone). 
The sphenoidal bone is situated at the base of the skull in front of the temporals 
and basilar part of the occipital. It somewhat resembles a bat with its wings 246 
OSTEOLOGY 
extended, and is divided into a median portion or body, two great and two small 
wings extending outward from the sides of the body, and two pterygoid processes 
which project from it below. 
Body (corpus sphenoidalis).-The body, more or less cubical in shape, is hollowed 
out in its interior to form two large cavities, the sphenoidal air sinuses, which are 
separated from each other by a septum. 
Surfaces.-The superior surface of the body (Fig. 289) presents in front a promi- 
nent spine, the ethmoidal spine, for articulation with the cribriform plate of the 
ethmoid; behind this is a smooth surface slightly raised in the middle line, and 
grooved on either side for the olfactory lobes of the brain. This surface is bounded 
behind by a ridge, which forms the anterior border of a narrow, transverse groove, 
the chiasmatic groove (optic groove), above and behind which lies the optic chiasma; 
the groove ends on either side in the optic foramen, which transmits the optic 
nerve and opthalmic artery into the orbital cavity. Behind the chiasmatic groove 
is an olive-like elevation, the tuberculum sellae; and still more posteriorly, a deep 
depression, the sella turcica, the deepest part of which lodges the hypophysis 
Posterior Clinoid process 
Middle Clinoid process 
Groove for 
olfactory 
. lobe 
Ethmoidal 
spine 
With 
ethmoid 
With 
parietal 
'"'I 
Superior orbital 
fissure 
Optic foramen 
Foramen rotundum 
Foramen Vesalii 
Foramen ovale 
Foramen spinosum 
For abducent 
| nerve 
Spina angular is- 
Petrosal 
process 
With 
palatine 
Fig. 289.-Sphenoidal bone. Upper surface. 
cerebri and is known as the fossa hypophyseos. The anterior boundary of the 
sella turcica is completed by two small eminences, one on either side, called the 
middle clinoid processes, while the posterior boundary is formed by a square- 
shaped plate of bone, the dorsum sellae, ending at its superior angles in two tuber- 
cles, the posterior clinoid processes, the size and form of which vary considerably in 
different individuals. The posterior clinoid processes deepen the sella turcica, 
and give attachment to the tentorium cerebelli. On either side of the dorsum 
sellae is a notch for the passage of the abducent nerve, and below the notch a sharp 
process, the petrosal process, which articulates with the apex of the petrous portion 
of the temporal bone, and forms the medial boundary of the foramen lacerum. 
Behind the dorsum sellae is a shallow depression, the clivus, which slopes obliquely 
backward, and is continuous with the groove on the basilar portion of the occipital 
bone; it supports the upper part of the pons. 
The lateral surfaces of the body are united with the great wings and the medial 
pterygoid plates. Above the attachment of each great wing is a broad groove, 
curved something like the italic letter /; it lodges the internal carotid artery and THE SPHENOIDAL BONE 
247 
the cavernous sinus, and is named the carotid groove. Along the posterior part 
of the lateral margin of this groove, in the angle between the body and great wing, 
is a ridge of bone, called the lingula. 
The posterior surface, quadrilateral in form (Fig. 291), is joined, during infancy 
and adolescence, to the basilar part of the occipital bone by a plate of cartilage. 
Between the eighteenth and twenty-fifth years this becomes ossified, ossification 
commencing above and extending downward. 
The anterior surface of the body (Fig. 290) presents, in the middle line, a vertical 
crest, the sphenoidal crest, which articulates with the perpendicular plate of the 
ethmoid, and forms part of the septum of the nose. On either side of the crest 
is an irregular opening leading into the corresponding sphenoidal air sinus. These 
sinuses are two large, irregular cavities hollowed out of the interior of the body 
of the bone, and separated from one another by a bony septum, which is commonly 
bent to one or the other side. They vary considerably in form and size,1 are 
seldom symmetrical, and are often partially subdivided by irregular bony laminae. 
Sphenoidal crest 
Artic, with perpendicular 
plate of ethmoid 
Infratemporal 
crest 
Pharyngeal canal 
Groove for 
ala of vomer- 
nostrum 
Artic, with vomer 
Tensor vel 
palatini 
Medial pterygoid plate 
Hamulus. 
Fig. 290.-Sphenoidal bone. Anterior and inferior surfaces. 
Occasionally, they extend into the basilar part of the occipital nearly as far as the 
foramen magnum. They begin to be developed before birth, and are of a consid- 
erable size by the age of six. They are partially closed, in front and below, by two 
thin, curved plates of bone, the sphenoidal conchae (see page 250), leaving in the 
articulated skull a round opening at the upper part of each sinus by which it com- 
municates with the upper and back part of the nasal cavity and occasionally with 
the posterior ethmoidal air cells. The lateral margin of the anterior surface is 
serrated, and articulates with the lamina papyracea of the ethmoid, completing 
the posterior ethmoidal cells; the lower margin articulates with the orbital process 
of the palatine bone, and the upper with the orbital plate of the frontal bone. 
The inferior surface presents, in the middle line, a triangular spine, the sphenoidal 
rostrum, which is continuous with the sphenoidal crest on the anterior surface, 
and is received in a deep fissure between the alee of the vomer. On either side of 
the rostrum is a projecting lamina, the vaginal process, directed medialward from 
the base of the medial pterygoid plate, with which it will be described. 
1 Aldren Turner (op. cit.) gives the following as their average measurements: vertical height, '/« inch; antero-posterior 
depth, 7/s inch; transverse breadth, % inch. 248 
OSTEOLOGY 
The Great Wings (alae magnae).-The great wings, or ali-sphenoids, are two 
strong processes of bone, which arise from the sides of the body, and are curved 
upward, lateralward, and backward; the posterior part of each projects as a tri- 
angular process which fits into the angle between the squama and the petrous 
portion of the temporal and presents at its apex a downwardly directed process, 
the spina angularis (sphenoidal spine). 
Surfaces.-The superior or cerebral surface of each great wing (Fig. 289) forms 
part of the middle fossa of the skull; it is deeply concave, and presents depressions 
for the convolutions of the temporal lobe of the brain. At its anterior and medial 
part is a circular aperture, the foramen rotundum, for the transmission of the maxil- 
lary nerve. Behind and lateral to this is the foramen ovale, for the transmission 
of the mandibular nerve, the accessory meningeal artery, and sometimes the 
lesser superficial petrosal nerve.1 Medial to the foramen ovale, a small aperture, 
the foramen Vesalii, may occasionally be seen opposite the root of the pterygoid 
process; it opens below near the scaphoid fossa, and transmits a small vein from 
the cavernous sinus. Lastly, in the posterior angle, near to and in front of the spine, 
is a short canal, sometimes double, the foramen spinosum, which transmits the 
middle meningeal vessels and a recurrent branch from the mandibular nerve. 
Anterior clinoid process 
Posterior 
clinoid, 
process 
Notch for abducent 
nerve 
Superior 
orbital fissure 
Foramen rotundum 
Pterygoid canal 
Spina angularis 
■Lateral pterygoid plate 
-Medial pterygoid plate 
Vaginal process 
Hamulus 
Rostrum 
Fig. 291.-Sphenoidal bone. Upper and posterior surfaces. 
The lateral surface (Fig. 290) is convex, and divided by a transverse ridge, the 
infratemporal crest, into two portions. The superior or temporal portion, convex 
from above downward, concave from before backward, forms a part of the tem- 
poral fossa, and gives attachment to the Temporalis; the inferior or infratemporal, 
smaller in size and concave, enters into the formation of the infratemporal fossa, 
and, together with the infratemporal crest, affords attachment to the Pterygoideus 
externus. It is pierced by the foramen ovale and foramen spinosum, and at its 
posterior part is the spina angularis, which is frequently grooved on its medial 
surface for the chorda tympani nerve. To the spina angularis are attached the 
sphenomandibular ligament and the Tensor veli palatini. Medial to the anterior 
extremity of the infratemporal crest is a triangular process which serves to increase 
1 The lesser superficial petrosal nerve sometimes passes through a special canal {canaliculus innominatus of Arnold) 
situated medial to the foramen spinosum. THE SPHENOIDAL BONE 
249 
the attachment of the Pterygoideus externus; extending downward and medialward 
from this process on to the front part of the lateral pterygoid plate is a ridge which 
forms the anterior limit of the infratemporal surface, and, in the articulated skull, 
the posterior boundary of the pterygomaxillary fissure. 
The orbital surface of the great wing (Fig. 290), smooth, and quadrilateral in 
shape, is directed forward and medialward and forms the posterior part of the 
lateral wall of the orbit. Its upper serrated edge articulates with the orbital plate 
of the frontal. Its inferior rounded border forms the postero-lateral boundary of 
the inferior orbital fissure. Its medial sharp margin forms the lower boundary 
of the superior orbital fissure and has projecting from about its centre a little 
tubercle which gives attachment to the inferior head of the Rectus lateralis oculi; 
at the upper part of this margin is a notch for the transmission of a recurrent 
branch of the lacrimal artery. Its lateral margin is serrated and articulates with 
the zygomatic bone. Below the medial end of the superior orbital fissure is a 
grooved surface, which forms the posterior wall of the pterygopalatine fossa, 
and is pierced by the foramen rotundum. 
Margin (Fig. 289).-Commencing from behind, that portion of the circum- 
ference of the great wing which extends from the body to the spine is irregular. 
Its medial half forms the anterior boundary of the foramen lacerum, and presents 
the posterior aperture of the pterygoid canal for the passage of the correspond- 
ing nerve and artery. Its lateral half articulates, by means of a synchondrosis, 
with the petrous portion of the temporal, and between the two bones on the 
under surface of the skull, is a furrow, the sulcus tubae, for the lodgement of the 
cartilaginous part of the auditory tube. In front of the spine the circumference 
presents a concave, serrated edge, bevelled at the expense of the inner table below, 
and of the outer table above, for articulation with the temporal squama. At 
the tip of the great wing is a triangular portion, bevelled at the expense of the 
internal surface, for articulation with the sphenoidal angle of the parietal bone; 
this region is named the pterion. Medial to this is a triangular, serrated surface, 
for articulation with the frontal bone; this surface is continuous medially with 
the sharp edge, which forms the lower boundary of the superior orbital fissure, 
and laterally with the serrated margin for articulation with the zygomatic 
bone. 
The Small Wings (alae parvae).-The small wings or orbito-sphenoids are two 
thin triangular plates, which arise from the upper and anterior parts of the body, 
and, projecting lateralward, end in sharp points (Fig. 289). 
Surfaces.-The superior surface of each is flat, and supports part of the frontal 
lobe of the brain. The inferior surface forms the back part of the roof of the orbit, 
and the upper boundary of the superior orbital fissure. This fissure is of a triangular 
form, and leads from the cavity of the cranium into that of the orbit: it is bounded 
medially by the body; above, by the small wing; below, by the medial margin of 
the orbital surface of the great wing; and is completed laterally by the frontal 
bone. It transmits the oculomotor, trochlear, and abducent nerves, the three 
branches of the ophthalmic division of the trigeminal nerve, some filaments from 
the cavernous plexus of the sympathetic, the orbital branch of the middle menin- 
geal artery, a recurrent branch from the lacrimal artery to the dura mater, and the 
ophthalmic vein. 
Borders.-The anterior border is serrated for articulation with the frontal bone. 
The posterior border, smooth and rounded, is received into the lateral fissure of 
the brain; the medial end of this border forms the anterior clinoid process, which 
gives attachment to the tentorium cerebelli; it is sometimes joined to the middle 
clinoid process by a spicule of bone, and when this occurs the termination of the 
groove for the internal carotid artery is converted into a foramen (carotico-clinoid). 
The small wing is connected to the body by two roots, the upper thin and flat, 250 
OSTEOLOGY 
the lower thick and triangular; between the two roots is the optic foramen, for the 
transmission of the optic nerve and ophthalmic artery. 
Pterygoid Processes processus pterygoidei).-The pterygoid processes, one on 
either side, descend perpendicularly from the regions where the body and great 
wings unite. Each process consists of a medial and a lateral plate, the upper parts 
of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove, descends 
on the front of the line of fusion. The plates are separated below by an angular 
cleft, the pterygoid fissure, the margins of which are rough for articulation with 
the pyramidal process of the palatine bone. The two plates diverge behind and 
enclose between them a V-shaped fossa, the pterygoid fossa, which contains the 
Pterygoideus internus and Tensor veli palatini. Above this fossa is a small, oval, 
shallow depression, the scaphoid fossa, which gives origin to the Tensor veli palatini. 
The anterior surface of the pterygoid process is broad and triangular near its 
root, where it forms the posterior wall of the pterygopalatine fossa and presents 
the anterior orifice of the pterygoid canal. 
Lateral Pterygoid Plate.-The lateral pterygoid plate is broad, thin, and everted; 
its lateral surface forms part of the medial wall of the infratemporal fossa, and 
gives attachment to the Pterygoideus externus; its medial surface forms part of 
the pterygoid fossa, and gives attachment to the Pterygoideus internus. 
Medial Pterygoid Plate.--The medial pterygoid plate is narrower and longer 
than the lateral; it curves lateralward at its lower extremity into a hook-like pro- 
cess, the pterygoid hamulus, around which the tendon of the Tensor veli palatini 
glides. The lateral surface of this plate forms part of the pterygoid fossa, the 
medial surface constitutes the lateral boundary of the choana or posterior aperture 
of the corresponding nasal cavity. Superiorly the medial plate is prolonged on to 
the under surface of the body as a thin lamina, named the vaginal process, which 
articulates in front with the sphenoidal process of the palatine and behind this 
with the ala of the vomer. The angular prominence between the posterior margin 
of the vaginal process and the medial border of the scaphoid fossa is named the 
pterygoid tubercle, and immediately above this is the posterior opening of the 
pterygoid canal. On the under surface of the vaginal process is a furrow, which 
is converted into a canal by the sphenoidal process of the palatine bone, for the 
transmission of the pharyngeal branch of the internal maxillary artery and the 
pharyngeal nerve from the sphenopalatine ganglion. The pharyngeal aponeurosis 
is attached to the entire length of the posterior edge of the medial plate, and the 
Constrictor pharyngis superior takes origin from its lower third. Projecting 
backward from near the middle of the posterior edge of this plate is an angular 
process, the processus tubarius, which supports the pharyngeal end of the auditory 
tube. The anterior margin of the plate articulates with the posterior border of 
the vertical part of the palatine bone. 
The Sphenoidal Conchae {conchae sphenoidales; sphenoidal turbinated processes'). 
-The sphenoidal conchae are two thin, curved plates, situated at the anterior 
and lower part of the body of the sphenoid. An aperture of variable size exists 
in the anterior wall of each, and through this the sphenoidal sinus opens into the 
nasal cavity. Each is irregular in form, and tapers to a point behind, being broader 
and thinner in front. Its upper surface is concave, and looks toward the cavity 
of the sinus; its under surface is convex, and forms part of the roof of the corre- 
sponding nasal cavity. Each bone articulates in front with the ethmoid, laterally 
with the palatine; its pointed posterior extremity is placed above the vomer, 
and is received between the root of the pterygoid process laterally and the rostrum 
of the sphenoid medially. A small portion of the sphenoidal concha sometimes 
enters into the formation of the medial wall of the orbit, between the lamina 
papyracea of the ethmoid in front, the orbital plate of the palatine below, and the 
frontal bone above. THE ETHMOIDAL BONE 
251 
Ossification.-Until the seventh or eighth month of fetal life the body of the sphenoid consists 
of two parts, viz., one in front of the tuberculum sellae, the presphenoid, with which the small 
wings are continuous; the other, comprising the sella turcica and dorsum sellae, the postsphenoid, 
with which are associated the great wings, and pterygoid processes. The greater part of the bone 
is ossified in cartilage. There are fourteen centres in all, six for the presphenoid and eight for 
the postsphenoid. 
Presphenoid.-About the ninth week of fetal life an ossific centre appears for each of the small 
wings (orbitosphenoids) just lateral to the optic foramen; shortly afterward two nuclei appear 
in the presphenoid part of the body. The sphenoidal conchae are each developed from a centre 
which makes its appearance about the fifth month;1 at birth they consist of small triangular 
laminae, and it is not until the third year that they become hollowed out and cone-shaped; about 
the fourth year they fuse with the labyrinths of the ethmoid, and between the ninth and twelfth 
years they unite with the sphenoid. 
Postsphenoid,-The first ossific nuclei are those for the great wings (ali-sphenoids). One makes 
its appearance in each wing between the foramen rotundum and foramen ovale about the eighth 
week. The orbital plate and that part of the sphenoid which is found in the temporal fossa, as 
well as the lateral pterygoid plate, are ossified in membrane (Fawcett2). Soon after, the centres 
for the postsphenoid part of the body appear, one on either side of the sella turcica, and become 
blended together about the middle of fetal life. Each medial pterygoid plate (with the exception 
of its hamulus) is ossified in membrane, and its centre probably appears about the ninth or tenth 
week; the hamulus becomes chondrified during the third month, and almost at once undergoes 
ossification (Fawcett3). The medial joins the lateral pterygoid plate about the sixth month. 
About the fourth month a centre appears for each lingula and speedily joins the rest of the bone. 
The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone 
is in three pieces (Fig. 292): a central, consisting of the body and small wings, and two lateral, 
each comprising a great wing and ptery- 
goid process. In the first year after 
birth the great wings and body unite, 
and the small wings extend inward 
above the anterior part of the body, 
and, meeting with each other in the 
middle line, form an elevated smooth 
surface, termed the jugum sphenoidale. 
By the twenty-fifth year the sphenoid 
and occipital are completely fused. Be- 
tween the pre- and postsphenoid there 
are occasionally seen the remains of a 
canal, the canalis craniopharyngeus, 
through which, in early fetal fife, the 
hypophyseal diverticulum of the buccal 
ectoderm is transmitted (see page 166). 
The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not 
attain their full size until after puberty. 
Certain intrinsic ligaments are attached to the sphenoid. The more important of these are: 
the pterygospinous, stretching between the spina angularis and the lateral pterygoid plate (see 
cervical fascia); the interclinoid, a fibrous process joining the anterior to the posterior clinoid 
process; and the caroticoclinoid, connecting the anterior to the middle clinoid process. These 
ligaments occasionally ossify. 
Articulations.-The sphenoid articulates with twelve bones: four single, the vomer, ethmoid, 
frontal, and occipital; and four paired, the parietal, temporal, zygomatic, and palatine.4 
Fig. 292.-Sphenoidal bone at birth. Posterior aspect. 
The Ethmoidal Bone (Os Ethmoidale; Ethmoid Bone). 
The ethmoidal bone is exceedingly light and spongy, and cubical in shape; it 
is situated at the anterior part of the base of the cranium, between the two orbits, 
at the roof of the nose, and contributes to each of these cavities. It consists of 
four parts: a horizontal or cribriform plate, forming part of the base of the cranium; 
a perpendicular plate, constituting part of the nasal septum; and two lateral masses 
or labyrinths. 
1 According to Cleland, each sphenoidal concha is ossified from four centres. 
2 Journal of Anatomy and Physiology, 1910, vol. xliv. 
3 Anatomischer Anzeiger, March, 1905. 
4 It also sometimes articulates with the tuberosity of the maxilla (see page 257). 252 
OSTEOLOGY 
Cribiform Plate (lamina cribrosa; horizontal lamina).- Ine cribriform plate 
(Fig. 293) is received into the ethmoidal notch of the frontal bone and.joofs in 
the nasal cavities. Projecting upward from the middle line of this plate is a thick, 
smooth, triangular process, the crista galli, so called from its resemblance to a 
cock's comb. Its posterior border, long, thin, and slightly curved, serves for the 
attachment of the falx cerebri. 
Its anterior border, short and 
thick, articulates with the frontal 
bone, and presents two small pro- 
jecting alee, which are received 
into corresponding depressions in 
the frontal bone and complete 
the foramen cecum. Its sides are 
smooth, and sometimes bulging 
from the presence of a small air 
sinus in the interior. On either 
side of the crista galli, the cribri- 
form plate is narrow and deeply 
grooved; it supports the olfactory 
bulb and is perforated by fora- 
mina for the passage of the olfac- 
tory nerves. The foramina in the 
middle of the groove are small 
and transmit the nerves to the 
roof of the nasal cavity; those at the medial and lateral parts of the groove are 
larger-the former transmit the nerves to the upper part of the nasal septum, 
the latter those to the superior nasal concha. At the front part of the cribriform 
plate, on either side of the crista galli, is a small fissure which is occupied by a 
process of dura mater. Lateral to this fissure is a notch or foramen which trans- 
mits the nasociliary nerve; from this notch a groove extends backward to the 
anterior ethmoidal foramen. 
Perpendicular plate 
Ala 
Crista galli 
Cribriform plate 
Anterior ethmoidal 
T00™ 
Posterior ethmoidal 
groove 
Fig. 293.-Ethmoidal bone from above. 
Fig. 294.-Perpendicular plate of ethmoid. Shown by removing the right labyrinth. 
Perpendicular Plate (lamina perpendicularis; vertical plate).-The perpendicular 
plate (Figs. 294, 295) is a thin, flattened lamina, polygonal in form, which descends 
from the under surface of the cribriform plate, and assists in forming the septum 
of the nose; it is generally deflected a little to one or other side. The anterior border THE ETHMOIDAL BONE 
253 
articulates with the spine of the frontal bone and the crest of the nasal bones. 
The posterior border articulates by its upper half with the sphenoidal crest, by its 
lower with the vomer. The inferior border is thicker than the posterior, and serves 
for the attachment of the septal cartilage of the nose. The surfaces of the plate 
are smooth, except above, where numerous grooves and canals are seen; these 
lead from the medial foramina on the cribriform plate and lodge filaments of the 
olfactory nerves. 
The Labyrinth or Lateral Mass (labyrinthus ethmoidalis) consists of a number 
of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, 
anterior, middle, and posterior, and inter- 
posed between two vertical plates of bone; 
the lateral plate forms part of the orbit, 
the medial, part of the corresponding 
nasal cavity. In the disarticulated bone 
many of these cells are opened into, but 
when the bones are articulated, they are 
closed in at every part, except where 
they open into the nasal cavity. 
Surfaces.-The upper surface of the laby- 
rinth (Fig. 293) presents a number of 
half-broken cells, the walls of which are 
completed, in the articulated skull, by 
the edges of the ethmoidal notch of the 
frontal bone. Crossing this surface are 
two grooves, converted into canals by articulation with the frontal; they are the 
anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. 
The posterior surface presents large irregular cellular cavities, which are closed in 
by articulation with the sphenoidal concha and orbital process of the palatine. 
The lateral surface (Fig. 296) is formed of a thin, smooth, oblong plate, the lamina 
papyracea (os planum), which covers in the middle and posterior ethmoidal cells 
Crista galli 
Labyrinth 
Superior nasal 
concha 
Superior meatus 
Uncinate, process 
Perpendicular plate 
Middle nasal concha 
Fig. 295.-Ethmoidal bone from behind. 
. Ala 
Ethmoidal 
cells 
Perpendicular 
plate 
Uncinate process 
Fig. 296.-Ethmoidal bone from the right side. 
and forms a large part of the medial wall of the orbit; it articulates above with 
the orbital plate of the frontal bone, below with the maxilla and orbital process 
of the palatine, in front with the lacrimal, and behind with the sphenoid. 
In front of the lamina papyracea are some broken air cells which are overlapped 
and completed by the lacrimal bone and the frontal process of the maxilla. A 
curved lamina, the uncinate process, projects downward and backward from this 
part of the labyrinth; it forms a small part of the medial wall of the maxillary 
sinus, and articulates with the ethmoidal process of the inferior nasal concha. 254 
OSTEOLOGY 
The medial surface of the labyrinth (Fig. 297) forms part of the lateral wall 
of the corresponding nasal cavity. It consists of a thin lamella, which descends 
from the under surface of the cribriform plate, and ends below in a free, convoluted 
margin, the middle nasal concha. It is rough, and marked above by numerous 
grooves, directed nearly vertically downward from the cribriform plate; they 
lodge branches of the olfactory nerves, which are distributed to the mucous mem- 
brane covering the superior nasal concha. The back part of the surface is sub- 
divided by a narrow oblique fissure, the superior meatus of the nose, bounded above 
by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells 
open into this meatus. Below, and in front of the superior meatus, is the convex 
Frontal sinus 
Crista galli 
Sella turcica 
U ncinate 
process of 
ethmoid 
Openings into 
maxillary sinus 
Hamulus 
Medial pterygoid plate 
Fig. 297.-Lateral wall of nasal cavity, showing ethmoidal bone in position. 
surface of the middle nasal concha; it extends along the whole length of the medial 
surface of the labyrinth, and its lower margin is free and thick. The lateral surface 
of the middle concha is concave, and assists in forming the middle meatus of the 
nose. The middle ethmoidal cells open into the central part of this meatus, and a 
sinuous passage, termed the infundibulum, extends upward and forward through 
the labyrinth and communicates with the anterior ethmoidal cells, and in about 
50 per cent, of skulls is continued upward as the frontonasal duct into the frontal 
sinus. 
Ossification.-The ethmoid is ossified in the cartilage of the nasal capsule by three centres: 
one for the perpendicular plate, and one for each labyrinth. 
The labyrinths are first developed, ossific granules making their appearance in the region of 
the lamina papyracea between the fourth and fifth months of fetal life, and extending into the 
conchae. At birth, the bone consists of the two labyrinths, which are small and ill-developed. 
During the first year after birth, the perpendicular plate and crista galli begin to ossify from a 
single centre, and are joined to the labyrinths about the beginning of the second year. The 
cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. 
The development of the ethmoidal cells begins during fetal life. THE NASAL BONES 
255 
Articulations.-The ethmoid articulates with fifteen bones: four of the cranium-the frontal, 
the sphenoid, and the two sphenoidal conchae; and eleven of the face-the two nasals, two maxillae, 
two lacrimals, two palatines, two inferior nasal conchae, and the vomer. 
Sutural or Wormian1 Bones.-In addition to the usual centres of ossification of the cranium, 
others may occur in the course of the sutures, giving rise to irregular, isolated bones, termed 
sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, 
but are occasionally seen at the fontanelles, especially the posterior. One, the pterion ossicle, 
sometimes exists between the sphenoidal angle of the parietal and the great wing of the sphenoid. 
They have a tendency to be more or less symmetrical on the two sides of the skull, and vary 
much in size. Their number is generally limited to two or three; but more than a hundred have 
been found in the skull of an adult hydrocephalic subject. 
Applied Anatomy.-An arrest in the ossifying process may give rise to deficiencies, gaps, or 
fissures in the cranium, which are of importance from a medicolegal point of view, as they are 
liable to be mistaken for fractures. The fissures generally extend from the margins toward the 
centre of a bone, but the gaps may be found in the middle as well as at the edges. In course of 
time they may become filled with thin laminae of bone. In many of these cases, however, the 
gaps must be regarded as due to absorption of bone already formed rather than as congenital 
deficiencies; this is especially the case when they appear in the centre of a bone such as the parietal, 
the ossification of which has already been described as occurring in a regular manner radiating 
from one centre. The condition is most commonly seen in very badly nourished children affected 
with congenital syphilis, and is called craniotabes. 
THE FACIAL BONES (OSSA FACIEI). 
The Nasal Bones (Ossa Nasalia). 
The nasal bones are two small oblong bones, varying in size and form in different 
individuals; they are placed side by side at the middle and upper part of the face, 
Fossa for lacrimal sac 
Infraorbital 
foramen • 
Fig. 298.-Articulation of -nasal and lacrimal bones with maxilla. 
and form, by their junction, "the bridge" of the nose (Fig. 334). Each has two 
surfaces and four borders. 
1 Ole Worm, Professor of Anatomy at Copenhagen, 1624-1639, was erroneously supposed to have given the first 
detailed description of these bones. 256 
OSTEOLOGY 
Surfaces.-The outer surface (Fig. 299) is concavoconvex from above downward, 
convex from side to side; it is covered by the Procerus and Compressor naris, and 
perforated about its centre by a foramen, for the transmission of a small vein. 
The inner surface (Fig. 300) is concave from side to side, and is traversed from above 
downward, by a groove for the passage of a branch of the nasociliary nerve. 
Borders.-The superior border is narrow, thick, and serrated for articulation with 
the nasal notch of the frontal bone. The inferior border is thin, and gives attach- 
ment to the lateral cartilage of the nose; near its middle is a notch which marks 
the end of the groove just referred to. The lateral border is serrated, bevelled 
at the expense of the inner surface above, and of the outer below, to articulate 
with the frontal process of the maxilla. The medial border, thicker above than 
below, articulates with its fellow of the opposite side, and is prolonged behind into 
a vertical crest, which forms part of the nasal septum: this crest articulates, from 
above downward, with the spine of the frontal, the perpendicular plate of the 
ethmoid, and the septal cartilage of the nose. 
Foramen 
for vein 
Crest 
Groove 
for nerve 
Fig. 299.-Right nasal bone. Outer surface. 
Fig. 300.-Right nasal bone. Inner surface. 
Ossification.-Each bone is ossified from one centre, which appears at the beginning of the 
third month of fetal life in the membrane overlying the front part of the cartilaginous nasal 
capsule. 
Articulations.-The nasal articulates with four bones: two of the cranium, the frontal and 
ethmoid, and two of the face, the opposite nasal and the maxilla. 
The Maxillae (Upper Jaw). 
The maxillae are the largest bones of the face, excepting the mandible, and 
form, by their union, the whole of the upper jaw. Each assists in forming the 
boundaries of three cavities, viz., the roof of the mouth, the floor and lateral 
wall of the nose and the floor of the orbit; it also enters into the formation of two 
fossae, the infratemporal and pterygopalatine, and two fissures, the inferior orbital 
and pterygomaxillary. 
Each bone consists of a body and four processes-zygomatic, frontal, alveolar, 
and palatine. 
The Body (corpus maxillae).-The body is somewhat pyramidal in shape, and 
contains a large cavity, the maxillary sinus (antrum of Highmore). It has four 
surfaces-an anterior, a posterior or infratemporal, a superior or orbital, and a 
medial or nasal. 
Surfaces.-The anterior surface (Fig. 301) is directed forward and lateralward. 
It presents at its lower part a series of eminences corresponding to the positions 
of the roots of the teeth. Just above those of the incisor teeth is a depression, 
the incisive fossa, which gives origin to the Depressor alae nasi; to the alveolar 
border below the fossa is attached a slip of the Orbicularis oris; above and a little 
lateral to it, the Nasalis arises. Lateral to the incisive fossa is another depression, THE MAXILLAE 
257 
the canine fossa; it is larger and deeper than the incisive fossa, and is separated 
from it by a vertical ridge; the canine eminence, corresponding to the socket of 
the canine tooth; the canine fossa gives origin to the Caninus. Above the fossa 
is the infraorbital foramen, the end of the infraorbital canal; it transmits the infra- 
orbital vessels and nerve. Above the foramen is the margin of the orbit, which 
affords attachment to part of the Quadratus labii superioris. Medially, the anterior 
surface is limited by a deep concavity, the nasal notch, the margin of which gives 
attachment to the Dilatator naris posterior and ends below in a pointed process, 
which with its fellow of the opposite side forms the anterior nasal spine. 
Med. palp. lig. 
Lacrimal tubercle 
Dilatator naris posterior 
'Alveolar canals 
Incisive fossa 
Maxillary tuberosity 
Fig. 301.-Left maxilla. Outer surface. 
The infratemporal surface (Fig. 301) is convex, directed backward and lateral- 
ward, and forms part of the infratemporal fossa. It is separated from the anterior 
surface by the zygomatic process and by a strong ridge, extending upward from 
the socket of the first molar tooth. It is pierced about its centre by the apertures 
of the alveolar canals, which transmit the posterior superior alveolar vessels and 
nerves. At the lower part of this surface is a rounded eminence, the maxillary 
tuberosity, especially prominent after the growth of the wisdom tooth; it is rough 
on its lateral side for articulation with the pyramidal process of the palatine bone 
and in some cases articulates with the lateral pterygoid plate of the sphenoid. 
It gives origin to a few fibres of the Pterygoideus internus. Immediately above 
this is a smooth surface, which forms the anterior boundary of the pterygopalatine 
fossa, and presents a groove, for the maxillary nerve; this groove is directed lateral- 
ward and slightly upward, and is continuous with the infraorbital groove on the 
orbital surface. 
The orbital surface (Fig. 301) is smooth and triangular, and forms the greater 
part of the floor of the orbit. It is bounded medially by an irregular margin which 
in front presents a notch, the lacrimal notch; behind this notch the margin articu- 
lates with the lacrimal, the lamina papyracea of the ethmoid and the orbital process 
of the palatine. It is bounded behind by a smooth rounded edge which forms 
the anterior margin of the inferior orbital fissure, and sometimes articulates at 
its lateral extremity with the orbital surface of the great wing of the sphenoid. 258 
OSTEOLOGY 
It is limited in front by part of the circumference of the orbit, which is continuous 
medially with the frontal process, and laterally with the zyogmatic process. Near 
the middle of the posterior part of the orbital surface is the infraorbital groove, 
for the passage of the infraorbital vessels and nerve. The groove begins at the 
middle of the posterior border, where it is continuous with that near the upper 
edge of the infratemporal surface, and, passing forward, ends in a canal, which 
subdivides into two branches. One of the canals, the infraorbital canal, opens 
just below the margin of the orbit; the other, which is smaller, runs downward in 
the substance of the anterior wall of the maxillary sinus, and transmits the anterior 
superior alveolar vessels and nerve to the front teeth of the maxilla. From the 
back part of the infraorbital canal, a second small canal is sometimes given off; it 
runs downward in the lateral wall of the sinus, and conveys the middle alveolar 
nerve to the premolar teeth. At the medial and forepart of the orbital surface, 
just lateral to the lacrimal groove, is a depression, which gives origin to the Obliquus 
oculi inferior. 
With frontal 
Bones partially closing orifice of sinus 
marked in red 
With nasal bone 
Ethmoid- 
Inferior nasal concha- 
Palatine 
■Ant. nasal spine 
Bristle passed 
dhrough incisive 
canal 
Fig. 302.-Left maxilla. Nasal surface. 
The nasal surface (Fig. 302) presents a large, irregular opening leading into the 
maxillary sinus. At the upper border of this aperture are some broken air cells, 
which, in the articulated skull, are closed in by the ethmoid and lacrimal bones. 
Below the aperture is a smooth concavity which forms part of the inferior meatus 
of the nasal cavity, and behind it is a rough surface for articulation with the per- 
pendicular part of the palatine bone; this surface is traversed by a groove, com- 
mencing near the middle of the posterior border and running obliquely downward 
and forward; the groove is converted into a canal, the pterygopalatine canal, by the 
palatine bone. In front of the opening of the sinus is a deep groove, the lacrimal 
groove, which is converted into the nasolacrimal canal, by the lacrimal bone and 
inferior nasal concha; this canal opens into the inferior meatus of the nose and 
transmits the nasolacrimal duct. More anteriorly is an oblique ridge, the conchal 
crest, for articulation with the inferior nasal concha. -The shallow concavity above 
this ridge forms part of the atrium of the middle meatus of the nose, and that 
below it, part of the inferior meatus. THE MAXILLAE 
259 
The Maxillary Sinus or Antrum of Highmore (sinus maxiliar is).-The maxillary 
sinus is a large pyramidal cavity, within the body of the maxilla: its apex, directed 
lateralward, is formed by the zygomatic process; its base, directed medialward, 
by the lateral wall of the nose. Its walls are everywhere exceedingly thin, and 
correspond to the nasal orbital, anterior, and infratemporal surfaces of the body 
of the bone. Its nasal wall, or base, presents, in the disarticulated bone, a large, 
irregular aperture, communicating with the nasal cavity. In the articulated 
skull this aperture is much reduced in size by the following bones: the uncinate 
process of the ethmoid above, the ethmoidal process of the inferior nasal concha 
below, the vertical part of the palatine behind, and a small part of the lacrimal 
above and in front (Figs. 302, 303); the sinus communicates with the middle meatus 
of the nose, generally by two small apertures left between the above-mentioned 
bones. In the recent state, usually only one small opening exists, near the upper 
Frontal sinus 
.Posterior ethmoidal foramen 
Orbital process of palatine 
Anterior 
ethmoidal foramen 
Optic foramen 
Sphenopalatine foramen 
Sella turcica 
Probe in foramen rotundum 
Fossa for 
lacrimal sac 
Uncinate process _ 
of ethmoid 
Openings of 
maxillary sinus 
Inferior nasal 
concha 
Probe in pterygopalatine canal 
Probe in pterygoid canal 
Palatine bone 
■Lateral pterygoid plate 
Pyramidal process of palatine 
Fig. 303.-Left maxillary sinus opened from the exterior. 
part of the cavity; the other is closed by mucous membrane. On the posterior 
wall are the alveolar canals, transmitting the posterior superior alveolar vessels 
and nerves to the molar teeth. The floor is formed by the alveolar process of the 
maxilla, and, if the sinus be of an average size, is on a level with the floor of 
the nose; if the sinus be large it reaches below this level. 
Projecting into the floor of the antrum are several conical processes, correspond- 
ing to the roots of the first and second molar teeth;1 in some cases the floor is 
perforated by the fangs of the teeth. The infraorbital canal usually projects into 
the cavity as a well-marked ridge extending from the roof to the anterior wall; 
additional ridges are sometimes seen in the posterior wall of the cavity, and 
1 The number of teeth whose roots are in relation with the floor of the antrum is variable. The sinus "may extend 
so as to be in relation to all the teeth of the true maxilla, from the canine to the dens sapientiae." (Salter.) 260 
OSTEOLOGY 
are caused by the alveolar canals. The size of the cavity varies in different skulls, 
and even on the two sides of the same skull.1 
Applied Anatomy.-The extreme thinness of the walls of this cavity affords an explanation 
of the fact that a tumor growing from the maxillary sinus and encroaching upon the adjacent 
parts may push up the floor of the orbit, and displace the eyeball; may project into the nose; 
may protrude forward on to the cheek; or may make its way backward into the infratemporal 
fossa, or downward into the mouth. 
The Zygomatic Process {processus zygomaticus; malar process').-The zygomatic 
process is a rough triangular eminence, situated at the angle of separation of the 
anterior, zygomatic, and orbital surfaces. In front it forms part of the anterior 
surface; behind, it is concave, and forms part of the infratemporal fossa; above, 
it is rough and serrated for articulation with the zygomatic bone; while below, 
it presents the prominent arched border which marks the division between the 
anterior and infratemporal surfaces. 
The Frontal Process {processus frontalis; nasal process').-The frontal process 
is a strong plate, which projects upward, medialward, and backward, by the side 
of the nose, forming part of its lateral boundary. Its lateral surface is smooth, 
continuous with the anterior surface of the body, and gives attachment to the 
Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament. 
Its medial surface forms part of the lateral wall of the nasal cavity; at its upper 
part is a rough, uneven area, which articulates with the ethmoid, closing in the 
anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the 
posterior end of which articulates with the middle nasal concha, while the anterior 
part is termed the agger nasi; the crest forms the upper limit of the atrium of the 
middle meatus. The upper border articulates with the frontal bone and the anterior 
with the nasal; the posterior border is thick, and hollowed into a groove, which is 
continuous below with the lacrimal groove; on the nasal surface of the body: by 
the articulation of the medial margin of the groove with the anterior border of 
the lacrimal a corresponding groove on the lacrimal is brought into continuity, 
and together they form the lacrimal fossa for the lodgement of the lacrimal sac. 
The lateral margin of the groove is named the anterior lacrimal crest, and is con- 
tinuous below with the orbital margin; at its junction with the orbital surface is 
a small tubercle, the lacrimal tubercle, which serves as a guide to the position of 
the lacrimal sac. 
The Alveolar Process {processus alveolaris).-The alveolar process is the thickest 
and most spongy part of the bone. It is broader behind than in front, and exca- 
vated into deep cavities for the reception of the teeth. These cavities are eight 
in number, and vary in size and depth according to the teeth they contain. That 
for the canine tooth is the deepest; those for the molars are the widest, and are 
subdivided into minor cavities by septa; those for the incisors are single, but 
deep and narrow. The Buccinator arises from the outer surface of this process, 
as far forward as the first molar tooth. When the maxillae are articulated with each 
other, their alveolar processes together form the alveolar arch; the centre of the 
anterior margin of this arch is named the alveolar point. 
The Palatine Process {processus palatinus; palatal process').-The palative 
process, thick and strong, is horizontal and projects medialward from the nasal 
surface of the bone. It forms a considerable part of the floor of the nose and the 
roof of the mouth and is much thicker in front than behind. Its inferior surface 
(Fig. 304) is concave, rough and uneven, and forms, with the palatine process of 
the opposite bone, the anterior three-fourths of the hard plate. It is perforated 
by numerous foramina for the passage of the nutrient vessels; is channelled at the 
1 Aldren Turner (op. cit.) gives the following measurements as those of an average sized sinus: vertical height 
opposite first molar tooth, IM inch; transverse breadth, 1 inch; and antero-posterior depth, IM inch. THE MAXILLA 
261 
back part of its lateral border by a groove, sometimes a canal, for the transmission 
of the descending palatine vessels and the anterior palatine nerve from the spheno- 
palatine ganglion; and presents little depressions for the lodgement of the palatine 
glands. When the two maxillae are articulated, a funnel-shaped opening, the 
incisive foramen, is seen in the middle line, immediately behind the incisor teeth. 
In this opening the orifices of two lateral canals are visible; they are named the 
incisive canals or foramina of Stensen; through each of them passes the terminal 
branch of the descending palatine artery and the nasopalatine nerve. Occasionally 
two additional canals are present in the middle line; they are termed the foramina 
of Scarpa, and when present transmit the nasopalatine nerves, the left passing 
through the anterior, and the right through the posterior canal. On the under 
surface of the palatine process, a delicate linear suture, well seen in young skulls, 
may sometimes be noticed extending lateralward and forward on either side from 
Incisive canals 
Incisive foramen 
Foramina of Scarpa 
Palatine process of maxilla 
Horizontal plate of palatine bone 
Lesser palatine foramina 
Greater palatine foramen 
Fig. 304.-The bony palate and alveolar arch. 
the incisive foramen to the interval between the lateral incisor and the canine tooth. 
The small part in front of this suture constitutes the premaxilla {os incisivumf 
which in most vertebrates forms an independent bone; it includes the whole thick- 
ness of the alveolus, the corresponding part of the floor of the nose and the anterior 
nasal spine, and contains the sockets of the incisor teeth. The upper surface of 
the palatine process is concave from side to side, smooth, and forms the greater 
part of the floor of the nasal cavity. It presents, close to its medial margin, the 
upper orifice of the incisive canal. The lateral border of the process is incorporated 
with the rest of the bone. The medial border is thicker in front than behind, and 
is raised above into a ridge, the nasal crest, which, with the corresponding ridge 
of the opposite bone, forms a groove for the reception of the vomer. The front 
part of this ridge rises to a considerable height, and is named the incisor crest; 
it is prolonged forward into a sharp process, which forms, together with a similar 262 
OSTEOLOGY 
process of the opposite bone, the anterior nasal spine. The posterior border is ser- 
rated for articulation with the horizontal part of the palatine bone. 
Ossification.-The maxilla is ossified in membrane. Mall1 and Fawcett2 maintain that it is 
ossified from two centres only, one for the maxilla proper and one for the premaxilla. These 
centres appear during the sixth week of fetal life and unite in the beginning of the third month, 
but the suture between the two portions persists on the palate until nearly middle life. Mall 
states that the frontal process is developed from both centres. The maxillary sinus appears as 
a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does 
not reach its full size until after the second dentition. The maxilla was formerly described as 
ossifying from six centres, viz., one, the orbitonasal, forms that portion of the body of the bone 
which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and 
the lateral wall of the nasal cavity; a second, the zygomatic, gives origin to the portion which lies 
lateral to the infraorbital canal, including the zygomatic process; from a third, the palatine, is 
developed the palatine process posterior to the incisive canal together with the adjoining part 
of the nasal wall; a fourth, the premaxillary, forms the incisive bone which carries the incisor 
Fig. 305.-Anterior surface of maxilla at birth. 
Fig. 306.-Inferior surface of maxilla at birth. 
Maxillary sinus 
Fig. 307.-Nasal surface of maxilla at birth. 
Palatine process 
teeth and corresponds to the premaxilla of the lower vertebrates;3 a fifth, the nasal, gives rise to 
the frontal process and the portion above the canine tooth; and a sixth, the infravomerine, lies 
between the palatine and premaxillary centres and beneath the vomer; this centre, together with 
the corresponding centre of the opposite bone, separates the incisive canals from each other.. 
Articulations.-The maxilla articulates with nine bones: two of the cranium, the frontal and 
ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, 
vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital surface, 
and sometimes with the lateral pterygoid plate of the sphenoid. 
CHANGES PRODUCED IN THE MAXILLA BY AGE. 
At birth the transverse and antero-posterior diameters of the bone are each greater than the 
vertical. The frontal process is well-marked and the body of the bone consists of little more than 
the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary 
sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical 
diameter is the greatest, owing to the development of the alveolar process and the increase in 
size of the sinus. In old age the bone reverts in some measure to the infantile condition; its 
height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the 
lower part of the bone contracted and reduced in thickness. 
1 American Journal of Anatomy, 1906, vol. v. 
2 Journal of Anatomy and Physiology, 1911, vol. xlv. 
3 Some anatomists believe that the premaxillary bone is ossified by two centres (see page 299). THE ZYGOMATIC BONE 
263 
The Lacrimal Bone (Os Lacrimale) 
The lacrimal bone, the smallest and most fragile bone of the face, is situated 
at the front part of the medial wall of the orbit (Fig. 309). It has two surfaces 
and four borders. 
Surfaces.-The lateral or orbital surface (Fig. 308) is divided by a vertical ridge, 
the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal 
groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites 
with the frontal process of the maxilla, and the lacrimal fossa is thus completed. 
The upper part of this fossa lodges the lacrimal sac, the lower part, the naso- 
lacrimal duct. The portion behind the crest is smooth, and forms part of the 
medial wall of the orbit. The crest, with a part of the orbital surface imme- 
diately behind it, gives origin to the lacrimal part of the Orbicularis oculi and 
ends below in a small, hook-like projection, the lacrimal hamulus, which articu- 
lates with the lacrimal tubercle of the maxilla, and completes 
the upper orifice of the lacrimal canal; it sometimes exists as 
a separate piece, and is then called the lesser lacrimal bone. 
The medial or nasal surface presents a longitudinal furrow, 
corresponding to the crest on the lateral surface. The area in 
front of this furrow forms part of the middle meatus of the 
nose; that behind it articulates with the ethmoid, and completes 
some of the anterior ethmoidal cells. 
Borders.-Of the four borders the anterior articulates with 
the frontal process of the maxilla; the posterior with the lamina 
papyracea of the ethmoid; the superior with the frontal bone. 
The inferior is divided by the lower edge of the posterior lacri- 
mal crest into two parts: the posterior part articulates with 
the orbital plate of the maxilla; the anterior is prolonged 
downward as the descending process, which articulates with the lacrimal process 
of the inferior nasal concha, and assists in forming the canal for the nasolacrimal 
duct. 
Articulates with Maxilla 
with frontal 
aiA Ethmoid 
With 
Infer, nasal concha 
Fig. 308.-Left lacri- 
mal bone. Orbital sur- 
face. Enlarged. 
Ossification.-The lacrimal is ossified from a single centre, which appears about the twelfth 
week in the membrane covering the cartilaginous nasal capsule. 
Articulations.-The lacrimal articulates with four bones: two of the cranium, the frontal 
and ethmoid, and two of the face, the maxilla and the inferior nasal concha. 
The Zygomatic Bone (Os Zygomaticum; Malar Bone). 
The zygomatic bone is small and quadrangular, and is situated at the upper 
and lateral part of the face: it forms the prominence of the cheek, part of the 
lateral wall and floor of the orbit, and parts of the temporal and infratemporal 
fossae (Fig. 309). It presents a malar and a temporal surface; four processes, the 
frontosphenoidal, orbital, maxillary, and temporal; and four borders. 
Surfaces.-The malar surface (Fig. 310) is convex and perforated near its centre 
by a small aperture, the zygomaticofacial foramen, for the passage of the zygomatico- 
facial nerve and vessels; below this foramen is a slight elevation, which gives 
origin to the Zygomaticus. 
The temporal surface (Fig. 311), directed backward and medialward, is concave, 
presenting medially a rough, triangular area, for articulation with the maxilla, 
and laterally a smooth, concave surface, the upper part of which forms the anterior 
boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near 
the centre of this surface is the zygomaticotemporal foramen for the transmission 
of the zygomaticotemporal nerve. 264 
OSTEOLOGY 
Processes.-The frontosphenoidal process is thick and serrated, and articulates 
with the zygomatic process of the frontal bone. On its orbital surface, just within 
the orbital margin and about 11 mm. below the zygomaticofrontal suture is a 
tubercle of varying size and form, but present in 95 per cent, of skulls (Whitnail1). 
Fig. 309.-Left zygomatic bone in situ. 
The orbital process is a thick, strong plate, projecting backward and medialward 
from the orbital margin. Its antero-medial surface forms, by its junction with 
the orbital surface of the maxilla and with the great wing of the sphenoid, part 
of the floor and lateral wall of the orbit. On it are seen the orifices of two canals, 
With Frontal 
Bristles passed 
through 
zygomatico- 
orbital foramina 
Fig. 310.-Left zygomatic bone. Malar surface. 
Fig. 311.-Left zygomatic bone. Temporal surface. 
the zygomaticoorbital foramina; one of these canals opens into the temporal fossa, 
the other on the malar surface of the bone; the former transmits the zygomatico- 
temporal, the latter the zygomaticofacial nerve. Its postero-lateral surface, smooth 
1 Journal of Anatomy and Physiology, vol. xlv. The structures attached to this tubercle are: (1) the check 
ligament of the Rectus lateralis; (2) the lateral end of the aponeurosis of the Levator palpebrae superioris; (3) the 
suspensory ligament of the eye (Lockwood); and (4) the lateral extremities of the superior and inferior tarsi. THE PALATINE BONE 
265 
and convex, forms parts of the temporal and infratemporal fossae. Its anterior 
margin, smooth and rounded, is part of the circumference of the orbit. Its superior 
margin, rough, and directed horizontally, articulates with the frontal bone behind 
the zygomatic process. Its posterior margin is serrated for articulation, with the 
great wing of the sphenoid and the orbital surface of the maxilla. At the angle 
of junction of the sphenoidal and maxillary portions, a short, concave, non-articular 
part is generally seen; this forms the anterior boundary of the inferior orbital fissure: 
occasionally, this non-articular part is absent, the fissure then being completed by 
the junction of the maxilla and sphenoid, or by the interposition of a small sutural 
bone in the angular interval between them. The maxillary process presents a rough, 
triangular surface which articulates with the maxilla. The temporal process, 
long, narrow, and serrated, articulates with the zygomatic process of the temporal. 
Borders.-The antero-superior or orbital border is smooth, concave, and forms 
a considerable part of the circumference of the orbit. The antero-inferior or maxil- 
lary border is rough, and bevelled at the expense of its inner table, to articulate 
with the maxilla; near the orbital margin it gives origin to the Quadratus labii 
superioris. The postero-superior or temporal border, curved like an italic letter f, 
is continuous above with the commencement of the temporal line, and below with 
the upper border of the zygomatic arch; the temporal fascia is attached to it. 
The postero-inferior or zygomatic border affords attachment by its rough edge to 
the Masseter. 
Ossification.-The zygomatic bone is generally described as ossifying from three centres- 
one for the malar and two for the orbital portion; these appear about the eighth week and fuse 
about the fifth month of fetal life. Mall describes it as being ossified from one centre which 
appears just beneath and to the lateral side of the orbit. After birth, the bone is sometimes 
divided by a horizontal suture into an upper larger, and a lower smaller division. In some quad- 
rumana the zygomatic bone consists of two parts, an orbital and a malar. 
Articulations.-The zygomatic articulates with four bones: the frontal, sphenoidal, temporal, 
and maxilla. 
Groove for 
nasolacrimal duct 
Frontal process 
Orbital process 
Maxillary_ sinus 
Sphenopalatine 
notch 
Sphenoidal 
process 
■Conchal crest 
Conchal crest - 
Fig. 312.-Articulation of left palatine bone with maxilla. 
The palatine bone is situated at the back part of the nasal cavity between the 
maxilla and the pterygoid process of the sphenoid (Fig. 312). It contributes 
to the walls of three cavities: the floor and lateral wall of the nasal cavity, the 
The Palatine Bone (Os Palatinum; Palate Bone). 266 
OSTEOLOGY 
roof of the mouth, and the floor of the orbit; it enters into the formation of two 
fossse, the pterygopalatine and pterygoid fossae; and one fissure, the inferior orbital 
fissure. The palatine bone somewhat resembles the letter L, and consists of a 
horizontal and a vertical part and three outstanding processes-viz., the pyramidal 
process, which is directed backward and lateralward from the junction of the two 
parts, and the orbital and sphenoidal porcesses, which surmount the vertical 
part, and are separated by a deep notch, the sphenopalatine notch. * 
The Horizontal Part (pars horizontalis; horizontal plate) (Figs. 313, 314.).-The 
horizontal part is quadrilateral, and has two surfaces and four borders. 
Surfaces.-The superior surface, concave from side to side, forms the back part 
of the floor of the nasal cavity. The inferior surface, slightly concave and rough, 
forms, with the corresponding surface of the opposite bone, the posterior fourth 
of the hard palate. Near its posterior margin may be seen a more or less marked 
transverse ridge for the attachment of part of the aponeurosis of the Tensor veli 
palatini. 
Maxillary surface 
Superior meatus. 
Sphenopalatine foramen- 
Sphenopalatine 
foramen 
Sphenoidal process 
Articular portion 
VERTICAL PART 
VERTICAL PART 
Pterygo- 
palatine 
canal 
Non-articular 
portion 
Maxillary 
process 
Posterior 
nasal 
spine 
Pyramidal 
process 
Musculus uvulce 
HORIZONTAL 
PART 
Fig. 313.-Left palatine bone. Nasal aspect. 
Enlarged. 
HORIZONTAL PART 
Fig. 314.-Left palatine bone. Posterior aspect. 
Enlarged. 
Borders.-The anterior border is serrated, and articulates with the palatine process 
of the maxilla. The posterior border is concave, free, and serves for the attachment 
of the soft palate. Its medial end is sharp and pointed, and, when united with 
that of the opposite bone, forms a projecting process, the posterior nasal spine 
for the attachment of the Musculus uvulae. The lateral border is united with 
the lower margin of the perpendicular part, and is grooved by the lower end of 
the pterygopalatine canal. The medial border, the thickest, is serrated for articu- 
lation with its fellow of the opposite side; its superior edge is raised into a ridge, 
which, united with the ridge of the opposite bone, forms the nasal crest for articu- 
lation with the posterior part of the lower edge of the vomer. 
The Vertical Part (pars perpendicularis; perpendicular plate) (Figs. 313, 314).- 
The vertical part is thin, of an oblong form, and presents two surfaces and four 
borders. 
Surfaces.-The nasal surface exhibits at its lower part a broad, shallow depres- 
sion, which forms part of the inferior meatus of the nose. Immediately above this 
is a well-marked horizontal ridge, the conchal crest, for articulation with the 
inferior nasal concha; still higher is a second broad, shallow depression, which THE PALATINE BONE 
267 
forms part of the middle meatus, and is limited above by a horizontal crest less 
prominent than the inferior, the ethmoidal crest, for articulation with the middle 
nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which 
forms part of the superior meatus. 
The maxillary surface is rough and irregular throughout the greater part of its 
extent, for articulation with the nasal surface of the maxilla; its upper and back 
part is smooth where it enters into the formation of the pterygopalatine fossa; 
it is also smooth in front, where it forms the posterior part of the medial wall of 
the maxillary sinus. On the posterior part of this surface is a deep vertical groove, 
converted into the pterygopalatine canal, by articulation with the maxilla; this 
canal transmits the descending palatine vessels, and the anterior palatine nerve. 
Borders.-The anterior border is thin and irregular; opposite the conchal crest is a 
pointed, projecting lamina, the maxillary process, which is directed forward, and 
closes in the lower and back part of the opening of the maxillary sinus. The 
posterior border (Fig. 314) presents a deep groove, the edges of which are serrated 
for articulation with the medial pterygoid plate of the sphenoid. This border 
is continuous above with the sphenoidal process; below it expands into the 
pyramidal process. The superior border supports the orbital process in front and the 
sphenoidal process behind. These processes are separated by the sphenopalatine 
notch, which is converted into the sphenopalatine foramen by the under surface of 
the body of the sphenoid. In the articulated skull this foramen leads from the 
pterygopalatine fossa into the posterior part of the superior meatus of the nose, 
and transmits the sphenopalatine vessels and the superior nasal and nasopalatine 
nerves. The inferior border is fused with the lateral edge of the horizontal part, 
and immediately in front of the pyramidal process is grooved by the lower end 
of the pterygopalatine canal. 
The Pyramidal Process or Tuberosity {processus pyramidalis}.-The pyramidal 
process projects backward and lateralward from the junction of the horizontal 
and vertical parts, and is received into the angular interval between the lower 
extremities of the pterygoid plates. On its posterior surface is a smooth, grooved, 
triangular area, limited on either side by a rough articular furrow. The furrows 
articulate with the pterygoid plates, while the grooved intermediate area completes 
the lower part of the pterygoid fossa and gives origin to a few fibres of the Ptery- 
goideus internus. The anterior part of the lateral surface is rough, for articulation 
with the tuberosity of the maxilla; its posterior part consists of a smooth triangular 
area which appears, in the articulated skull, between the tuberosity of the maxilla 
and the lower part of the lateral pterygoid plate, and completes the lower part 
of the infratemporal fossa. On the base of the pyramidal process, close to its 
union with the horizontal part, are the lesser palatine foramina for the transmis- 
sion of the posterior and middle palatine nerves. 
The Orbital Process {processus orbitalis').-The orbital process is placed on a 
higher level than the sphenoidal, and is directed upward and lateralward from 
the front of the vertical part, to which it is connected by a constricted neck. It 
presents five surfaces, which enclose an air cell. Of these surfaces, three are articu- 
lar and two non-articular. The articular surfaces are: (1) the anterior or maxillary, 
directed forward, lateralward, and downward, of an oblong form, and rough for 
articulation with the maxilla; (2) the posterior or sphenoidal, directed backward, 
upward, and medialward; it presents the opening of the air cell, which usually 
communicates with the sphenoidal sinus; the margins of the opening are serrated 
for articulation with the sphenoidal concha; (3) the medial or ethmoidal, directed 
forward, articulates with the labyrinth of the ethmoid. In some cases the air 
cell opens on this surface of the bone and then communicates with the posterior 
ethmoidal cells. More rarely it opens on both surfaces, and then communicates 
with the posterior ethmoidal cells and the sphenoidal sinus. The non-articular 268 
OSTEOLOGY 
surfaces are: (1) the superior or orbital, directed upward and lateralward; it is 
triangular in shape, and forms the back part of the floor of the orbit; and (2) the 
lateral, of an oblong form, directed toward the pterygopalatine fossa; it is separated 
from the orbital surface by a rounded border, which enters into the formation of 
the inferior orbital fissure. 
The Sphenoidal Process {processus sphenoidalis).-The sphenoidal process is 
a thin, compressed plate, much smaller than the orbital, and directed upward 
and medialward. It presents three surfaces and two borders. The superior surface 
articulates with the root of the pterygoid process and the under surface of the 
sphenoidal concha, its medial border reaching as far as the ala of the vomer; it 
presents a groove which contributes to the formation of the pharyngeal canal. 
The medial surface is concave, and forms part of the lateral wall of the nasal cavity. 
The lateral surface is divided into an articular and a non-articular portion: the 
former is rough, for articulation with the medial pterygoid plate; the latter is 
smooth, and forms part of the pterygopalatine fossa. The anterior border forms 
the posterior boundary of the sphenopalatine notch. The posterior border, serrated 
at the expense of the outer table, articulates with the medial pterygoid plate. 
The orbital and sphenoidal processes are separated from one another by the 
sphenopalatine notch. Sometimes the two processes are united above, and form 
between them a complete foramen (Fig. 313), or the notch may be crossed by one 
or more spicules of bone, giving rise to two or more foramina. 
Ossification.-The palatine bone is ossified in membrane from a single centre, which makes 
its appearance about the sixth or eighth week of fetal fife at the angle of junction of the two parts 
of the bone. From this point ossification spreads medialward to the horizontal part, downward 
into the pyramidal process, and upward into the vertical part. Some authorities describe the 
bone as ossifying from four centres: one for the pyramidal process and portion of the vertical 
part behind the pterygopalatine groove; a second for the rest of the vertical and the horizontal 
parts; a third for the orbital, and a fourth for the sphenoidal process. At the time of birth the 
height of the vertical part is about equal to the transverse width of the horizontal part, whereas 
in the adult the former measures about twice as much as the latter. 
Articulations.-The palatine articulates with six bones: the sphenoid, ethmoid, maxilla, 
inferior nasal concha, vomer, and opposite palatine. 
The Inferior Nasal Concha (Concha Nasalis Inferior; Inferior Turbinated Bone). 
The inferior nasal concha extends horizontally along the lateral wall of the 
nasal cavity (Fig. 315) and consists of a lamina of spongy bone, curled upon itself 
like a scroll. It has two surfaces, two borders, and two extremities. 
The medial surface (Fig. 316) is convex, perforated by numerous apertures, 
and traversed by longitudinal grooves for the lodgement of vessels. The lateral 
surface is concave (Fig. 317), and forms part of the inferior meatus. Its upper 
border is thin, irregular, and connected to various bones along the lateral wall 
of the nasal cavity. It may be divided into three portions: of these, the anterior 
articulates with the conchal crest of the maxilla; the posterior with the conchal 
crest of the palatine; the middle portion presents three well-marked processes, 
which vary much in their size and form. Of these, the anterior or lacrimal process 
is small and pointed and is situated at the junction of the anterior fourth with 
the posterior three-fourths of the bone: it articulates, by its apex, with the descend- 
ing process of the lacrimal bone, and, by its margins, with the groove on the back 
of the frontal process of the maxilla, and thus assists in forming the canal for the 
nasolacrimal duct. Behind this process a broad, thin plate, the ethmoidal process, 
ascends to join the uncinate process of the ethmoid; from -its lower border a thin 
lamina, the maxillary process, curves downward and lateralward; it articulates 
with the maxilla and forms a part of the medial wall of the maxillary sinus. The 
inferior border is free, thick, and cellular in structure, more especially in the middle THE VOMER 
269 
of the bone. Both extremities are more or less pointed, the posterior being the 
more tapering. 
Frontal sinus 
Crista galli 
Sella turcica 
Uncinate 
process 
oj ethmoid 
Openings into 
maxillary sinus 
Medial pterygoid plate 
'Pterygoid hamulus 
Ossification.-The inferior nasal concha is ossified from a single centre, which appears about 
the fifth month of fetal life in the lateral wall of the cartilaginous nasal capsule. 
Articulations.-The inferior nasal concha articulates with four bones: the ethmoid, maxilla, 
lacrimal, and palatine. 
Fig. 315.-Lateral wall of right nasal cavity showing inferior concha in situ. 
Fig. 316.-Right inferior nasal concha. 
Medial surface. 
Fig. 317.-Right inferior nasal concha. 
Lateral surface. 
The Vomer. 
The vomer is situated in the median plane, but its anterior portion is frequently 
bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms 
the hinder and lower part of the nasal septum (Fig. 318); it has two surfaces and 
four borders. The surfaces (Fig. 319) are marked by small furrows for blood- 
vessels, and on each is the nasopalatine groove, which runs obliquely downward 
and forward, and lodges the nasopalatine nerve and vessels. The superior border, 
the thickest, presents a deep furrow, bounded on either side by a horizontal pro- 
jecting ala of bone; the furrow receives the rostrum of the sphenoid, while the 270 
OSTEOLOGY 
margins of the alee articulate with the vaginal processes of the medial pterygoid 
plates of the sphenoid behind, and with the sphenoidal processes of the palatine 
bones in front. The inferior border articulates with the crest formed by the maxillae 
and palatine bones. The anterior border is the longest and slopes downward and 
Rostrum of sphenoid 
Crest of nasal bones 
Frontal spine 
Space for triangular! 
cartilage of septum 
Crest of palatines 
'Crest of maxiUce 
Fig. 318.-Median wall of left nasal cavity showing vomer in situ. 
forward. Its upper half is fused with the perpendicular plate of the ethmoid; 
its lower half is grooved for the inferior margin of the septal cartilage of the nose. 
The posterior border is free, concave, and separates the choanee. It is thick and 
bifid above, thin below. 
Ossification.-At an early period 
the septum of the nose consists of a 
plate of cartilage, the ethmovomerine 
cartilage. The postero-superior part 
of this cartilage is ossified to form 
the perpendicular plate of the eth- 
moid; its antero-inferior portion per- 
sists as the septal cartilage, while the 
vomer is ossified in the membrane 
covering its postero-inferior part. 
Two ossific centres, one on either 
side of the middle line, appear about 
the eighth week of fetal life in this 
part of the membrane, and hence the 
vomer consists primarily of two lam- 
ellae. About the third month these 
unite below, and thus a deep groove 
is formed in which the cartilage is lodged. As growth proceeds, the union of the lamellae 
extends upward and forward, and at the same time the intervening plate of cartilage undergoes 
absorption. By the age of puberty the lamellae are almost completely united to form a median 
plate, but evidence of the bilaminar origin of the bone is seen in the everted alae of its upper 
border and the groove on its anterior margin. 
Aloe. 
Fig. 319.-The vomer. THE MANDIBLE 
271 
Articulations.-The vomer articulates with six bones: two of the cranium, the sphenoid and 
ethmoid; and four of the face, the two maxillae and the two palatine bones; it also articulates 
with the septal cartilage of the nose. 
Applied Anatomy.-The surfaces of the vomer are covered by mucous membrane, which is 
intimately connected with the periosteum, little, if any, submucous connective tissue intervening. 
Hence polypi are rarely found growing from this surface, though they frequently grow from the 
lateral walls of the nasal cavities, where the submucous tissue is abundant. 
The Mandible (Mandibula; Inferior Maxillary Bone; Lower Jaw). 
The mandible, the largest and strongest bone of the face, serves for the reception 
of the lower teeth. It consists of a curved, horizontal portion, the body, and two 
perpendicular portions, the rami, which unite with the ends of the body nearly 
at right angles. 
The Body (corpw mandibulae).--The body is curved somewhat like a horseshoe, 
and has two surfaces and two borders. 
Coronoid process 
Condyle 
TEMPORALIS" 
Mental 
protuberance' 
-Arntfle 
Groove for external 
maxillary artery 
Fig. 320.-Mandible. Outer surface. Side view. 
Surfaces.-The external surface (Fig. 320) is marked in the median line by a 
faint ridge, indicating the symphysis or line of junction of the two pieces of which 
the bone is composed at an early period of life. This ridge divides below and 
encloses a triangular eminence, the mental protuberance, the base of which is de- 
pressed in the centre but raised on either side to form the mental tubercle. On either 
side of the symphysis, just below the incisor teeth, is a depression, the incisive 
fossa, which gives origin to the Mentalis and a small portion of the Orbicularis 
oris. Below the second premolar tooth, on either side, midway between the upper 
and lower borders of the body, is the mental foramen, for the passage of the mental 
vessels and nerve. Running backward and upward from each mental tubercle 
is a faint ridge, the oblique line, which is continuous with the anterior border of the 
ramus; it affords attachment to the Quadratus labii inferioris and Triangularis; 
the Platysma is attached below it. 
The internal surface (Fig. 321) is concave from side to side. Near the lower 
part of the symphysis is a pair of laterally placed spines, termed the mental spines, 
which give origin to the Genioglossi. Immediately below these is a second pair 
of spines, or more frequently a median ridge or impression, for the origin of the 272 
OSTEOLOGY 
Geniohyoidei. In some cases the mental spines are fused to form a single eminence, 
in others they are absent and their position is indicated merely by an irregularity 
of the surface. Above the mental spines a median foramen and furrow are some- 
times seen; they mark the line of union of the halves of the bone. Below the mental 
spines, on either side of the middle line, is an oval depression for the attachment 
of the anterior belly of the Digastricus. Extending upward and backward on either 
side from the lower part of the symphysis is the mylohyoid line, which gives origin 
to the Mylohyoideus; the posterior part of this line, near the alveolar margin, 
gives attachment to a small part of the Constrictor pharyngis superior, and to 
the pterygomandibular raphe. Above the anterior part of this line is a smooth 
triangular area against which the sublingual gland rests, and below the hinder 
part, an oval fossa for the submaxillary gland. 
Genio- 
glossus 
Genio- 
hyoideus 
Mylohyoid line 
Fig. 321.-Mandible. Inner surface. Side view. 
BODY 
Borders.-The superior or alveolar border, wider behind than in front, is hollowed 
into cavities, for the reception of the teeth; these cavities are sixteen in number, 
and vary in depth and size according to the teeth which they contain. To the 
outer lip of the superior border, on either side, the Buccinator is attached as 
far forward as the first molar tooth. The inferior border is rounded, longer than 
the superior, and thicker in front than behind; at the point where it joins the 
lower border of the ramus a shallow groove; for the external maxillary artery, 
may be present. 
The Ramus (ramus mandibulae; perpendicular portions).-The ramus is quadri- 
lateral in shape, and has two surfaces, four borders, and two processes. 
Surfaces.-The lateral surface (Fig. 320) is flat and marked by oblique ridges 
at its lower part; it gives attachment throughout nearly the whole of its extent 
to the Masseter. The medial surface (Fig. 321) presents about its centre the oblique 
mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. 
The margin of this opening is irregular; it presents in front a prominent ridge, 
surmounted by a sharp spine, the lingula mandibulae, which gives attachment to 
the sphenomandibular ligament; at its lower and back part is a notch from which 
the mylohyoid groove runs obliquely downward and forward, and lodges the mylo- 
hyoid vessels and nerve. Behind this groove is a rough surface, for the insertion THE MANDIBLE 
273 
of the Pterygoideus internus. The mandibular canal runs obliquely downward 
and forward in the ramus, and then horizontally forward in the body, where it 
is placed under the alveoli and communicates with them by small openings. On 
arriving at the incisor teeth, it turns back to communicate with the mental foramen, 
giving off two small canals which run to the cavities containing the incisor teeth. 
In the posterior two-thirds of the bone the canal is situated nearer the internal 
surface of the mandible; and in the anterior third, nearer its external surface. It 
contains the inferior alveolar vessels and nerve, from which branches are dis- 
tributed to the teeth. The lower border of the ramus is thick, straight, and con- 
tinuous with the inferior border of the body of the bone. At its junction with the 
posterior border is the angle of the mandible, which may be either inverted or everted 
and is marked by rough, oblique ridges on each side, for the attachment of the 
Masseter laterally, and the Pterygoideus internus medially; the stylomandibular 
ligament is attached to the angle between these muscles. The anterior border is 
thin above, thicker below, and continuous with the oblique line. The posterior 
border is thick, smooth, rounded, and covered by the parotid gland. The upper 
border is thin, and is surmounted by two processes, the coronoid in front and the 
condyloid behind, separated by a deep concavity, the mandibular notch. 
The Coronoid Process {processus coronoideus) is a thin, triangular eminence, 
which is flattened from side to side and varies in shape and size. Its anterior 
border is convex and is continuous below with the anterior border of the ramus; 
its posterior border is concave and forms the anterior boundary of the mandibular 
notch. Its lateral surface is smooth, and affords insertion to the Temporalis and 
Masseter. Its medial surface gives insertion to the Temporalis, and presents 
a ridge which begins near the apex of the process and runs downward and forward 
to the inner side of the last molar tooth. Between this ridge and the anterior 
border is a grooved triangular area, the upper part of which gives attachment 
to the Temporalis, the lower part to some fibres of the Buccinator. 
The Condyloid Process (processus condyloideus) is thicker than the coronoid, 
and consists of two portions: the condyle, and the constricted portion which sup- 
ports it, the neck. The condyle presents an articular surface for articulation with 
the articular disk of the temporomandibular joint; it is convex from before back- 
ward and from side to side, and extends farther on the posterior than on the ante- 
rior surface. Its long axis is directed medialward and slightly backward, and if 
prolonged to the middle line will meet that of the opposite condyle near the ante- 
rior margin of the foramen magnum. At the lateral extremity of the condyle 
is a small tubercle for the attachment of the temporomandibular ligament. The 
neck is flattened from before backward, and strengthened by ridges which descend 
from the forepart and sides of the condyle. Its posterior surface is convex; its 
anterior presents a depression for the attachment of the Pterygoideus externus. 
The mandibular notch, separating the two processes, is a deep semilunar depres- 
sion, and is crossed by the masseteric vessels and nerve. 
Ossification.-The mandible is ossified in the fibrous membrane covering the outer surfaces 
of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see 
p. 109), and are two in number, a right and a left. Their proximal or cranial ends are connected 
with the ear capsules, and their distal extremities are joined to one another at the symphysis 
by mesodermal tissue. They run forward immediately below the condyles and then, bending 
downward, lie in a groove near the lower border of the bone; in front of the canine tooth they 
incline upward to the symphysis. From the proximal end of each cartilage the malleus and 
incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as 
the lingula, is replaced by fibrous tissue, which persists to form the sphenomandibular ligament. 
Between the lingula and the canine tooth the cartilage disappears, while the portion of it below 
and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. 
Ossification takes place in the membrane covering the outer surface of the ventral end of 
Meckel's cartilage (Figs. 322 to 325), and each half of the bone is formed from a single centre 
18 274 
OSTEOLOGY 
which appears, near the mental foramen, about the sixth week of fetal life. By the tenth week 
the portion of Meckel's cartilage which lies below and behind the incisor teeth is surrounded and 
invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- 
, Lingual nerve 
Mental nerve 
Inf. alveolar n. 
Lingual nerve 
Inf. alveolar n. 
Auriculo- 
'temporal n. 
Stapes 
Chorda tympani 
Facial nerve 
■Facial nerve. 
Mylohyoid nerve 
Mylohyoid nerve 
Chorda tympani 
Reichert's cartilage 
Fig. 322.-Mandible of human embryo of 24 mm. 
long. Outer aspect. (From model by Low.) 
Fig. 323.-Mandible of human embryo of 24 mm. long. 
Inner aspect. (From model by Low.) 
ance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through 
the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei 
in the front part of both alveolar walls and along the front of the lower border of the bone. These 
accessory nuclei possess no separate ossific centres, but are invaded by the surrounding membrane 
Meckel's cartilage 
Mandibular nerve 
Mental, nerve 
Anterior process of malleus 
Fig. 324.-Mandible of human embryo of 95 mm. long. Outer aspect. Nuclei of cartilage stippled. 
(From model by Low.) 
bone and undergo absorption. The inner alveolar border, usually described as arising from a 
separate ossific centre (splenial centre}, is formed in the human mandible by an ingrowth from 
the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, 
in which ossification takes place during the first year. 
Auriculotemporal nerve 
Lingual nerve 
Meckel's 
cartilage 
Inf. alveolar 
nerve 
Ant. process of malleus 
Chorda tympani 
Fig. 325.-Mandible of human embryo of 95 mm. long. Inner aspect. Nuclei of cartilage stippled. 
(From model by Low.) 
Symphysis 
Mylohyoid nerve. 
The foregoing description of the ossification of the mandible is based on the researches of 
Low1 and Fawcett,2 and differs somewhat from that usually given. 
Articulations.-The mandible articulates with the two temporal bones. 
1 Proceedings of the Anatomical and Anthropological Society of the University of Aberdeen, 1905, and Journal of 
Anatomy and Physiology, vol. xliv. 
2 Journal of the American Medical Association, September 2, 1905. THE HYOID BONE 
275 
CHANGES PRODUCED IN THE MANDIBLE BY AGE. 
At birth (Fig. 326), the body of the bone is a mere shell, containing the sockets of the two 
incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one 
another. The mandibular canal is of large size, and runs near the lower border of the bone; the 
mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse 
(175°), and the condyloid portion is nearly in line with the body. The coronoid process is of 
comparatively large size, and projects above the level of the condyle. ■ 
After birth (Fig. 327), the two segments of the bone become joined at the symphysis, from 
below upward, in the first year; but a trace of separation may be visible in the beginning of the 
second year, near the alveolar margin. The body becomes elongated in its whole length, but 
more especially behind the mental foramen, to provide space for the three additional teeth devel- 
oped in this part. The depth of the body increases owing to increased growth of the alveolar 
part, to afford room for the roots of the teeth, and by thickening of the subdental portion which 
enables the jaw to withstand the powerful action of the masticatory muscles; but the alveolar 
portion is the deeper of the two, and, consequently, the chief part of the body lies above the 
oblique line. The mandibular canal, after the second dentition, is situated just above the level 
of the mylohyoid line; and the mental foramen occupies the position usual to it in the adult. 
The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth 
year it is 140°. 
In the adult (Fig. 328), the alveolar and subdental portions of the body are usually of equa 
depth. The mental foramen opens midway between the upper and lower borders of the bone, 
and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost 
vertical in direction, the angle measuring from 110° to 120°. 
In old age (Fig. 329), the bone becomes greatly reduced in size, for with the loss of the teeth 
the alveolar process is absorbed, and, consequently, the chief part of the bone is below the oblique 
line. The mandibular canal, with the mental foramen opening from it, is close to the alveolar 
border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the 
condyle is more or less bent backward. 
The Hyoid Bone (Os Hyoideum; Lingual Bone). 
The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the 
styloid processes of the temporal bones by the stylohyoid ligaments. It consists 
of five segments, viz., a body, two greater cornua, and two lesser cornua. 
The Body or Basihyal (corpus oss. hyoidd}.-The body or central part is 
of a quadrilateral form. Its anterior surface (Fig. 330) is convex and directed 
forward and upward. It is crossed in its upper half by a well-marked transverse 
ridge with a slight downward convexity, and in many cases a vertical median 
ridge divides it into two lateral halves. The portion of the vertical ridge above 
the transverse line is present in a majority of specimens, but the lower portion is 
evident only in rare cases. The anterior surface gives insertion to the Geniohyoid- 
eus in the greater part of its extent both above and below the transverse ridge; 
a portion of the origin of the Hyoglossus notches the lateral margin of the Genio- 
hyoideus attachment. Below the transverse ridge the Mylohyoideus, Sterno- 
hyoideus, and Omohyoideus are inserted. The posterior surface is smooth, 
concave, directed backward and downward, and separated from the epiglottis by 
the hyothyroid membrane and a quantity of loose areolar tissue; a bursa intervenes 
between it and the hyothyroid membrane. The superior border is rounded, and 
gives attachment to the hyothyroid membrane and some aponeurotic fibres of the 
Genioglossus. The inferior border affords insertion medially to the Sternohyoideus 
and laterally to the Omohyoideus and occasionally a portion of the Thyreohyoideus. 
It also gives attachment to the Levator glandulae thyreoideae, when this muscle 
is present. In early life the lateral borders are connected to the greater cornua 
by synchondroses; after middle life usually by bony union. 
The Greater Cornua or Thyrohyals (cornua majord).--The greater cornua 
project backward from the lateral borders of the body; they are flattened from 
above downward and diminish in size from before backward; each ends in a tubercle 
to which is fixed the lateral hyothyroid ligament. The upper surface is rough 276 
OSTEOLOGY 
Fig. 326.-At birth. 
Fig. 327.-In childhood. 
Fig. 328.-In the adult. 
Fig. 329.-In old age. 
Side view of the mandible at different periods of life. THE EXTERTOR OF THE SKULL 
277 
close to its lateral border, for muscular attachments: the largest of these are the 
origins of the Hyoglossus and Constrictor pharyngis medius which extend along 
the whole length of the cornu; the Digastricus and Stylohyoideus have small 
insertions in front of these 
near the junction of the body 
with the cornu. To the medial 
border the hyothyroid mem- 
brane is attached, while the 
anterior half of the lateral 
border gives insertion to the 
Thyreohyoideus. 
The Lesser Cornua or Cera- 
tohyals {cornua minord).-The 
lesser cornu are two small, 
conical eminences, attached 
by their bases to the angles of 
junction between the body and 
greater cornua. They are con- 
nected to the body of the bone 
by fibrous tissue, and occasionally to the greater cornua by distinct diarthrodial 
joints, which usually persist throughout life, but occasionally become ankylosed. 
The lesser cornua are situated in the line of the transverse ridge on the body 
and appear to be morphological continuations of it (Parsons1). The apex of each 
cornu gives attachment to the stylohyoid ligament;2 the Chondroglossus rises 
from the medial side of the base. 
■Greater cornu 
Constrictor Pharyngis Mediuss 
Hyoglossus. 
Lesser cornu 
Chondroglossus 
Genioglossus 
Dtgastricus & 
Stylohyoideus 
Body 
Thyreohyoideis 
Omohyoideus 
Mylohyoideos 
Sternohyoideus 
Geniohyoideus 
Fig. 330.-Hyoid bone. Anterior surface. Enlarged. 
Ossification.-The hyoid is ossified from six centres: two for the body, and one for each cornu. 
Ossification commences in the greater cornua toward the end of fetal life, in the body shortly 
afterward, and in the lesser cornua during the first or second year after birth. 
Applied Anatomy.-The hyoid bone is occasionally fractured, generally from direct violence, 
as in hanging, forcible grasping of the throat in garroting or throttling, or by a blow. The frac- 
ture generally occurs about the junction of the greater cornu with the body of the bone, but 
sometimes takes place through the latter; since the muscles of the tongue have important con- 
nections with this bone, there is great pain upon any attempt being made to move the tongue, 
as in speaking or swallowing. 
THE EXTERIOR OF THE SKULL. 
The skull as a whole may be viewed from different points, and the views so 
obtained are termed the normte of the skull; thus, it may be examined from above 
(norma verticalis), from below (norma basalis), from the side (norma lateralis), 
from behind (norma occipitalis), or from the front (norma frontalis). 
Norma Verticalis.-When viewed from above the outline presented varies 
greatly in different skulls; in some it is more or less oval, in others more nearly 
circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, 
nearly transverse in direction, between the frontal and parietals; (2) the sagittal 
sutures, medially placed, between the parietal bones, and deeply serrated in its 
anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the 
parietals and the occipital. The point of junction of the sagittal and coronal suture 
is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they 
indicate respectively the positions of the anterior and posterior fontanelles in the 
fetal skull. On either side of the sagittal suture are the parietal eminence and parietal 
1 See article on "The Topography and Morphology of the Human Hyoid Bone," by F. G. Parsons, Journal of 
Anatomy and Physiology, vol. xliii. 
2 These ligaments in many animals are distinct bones, and in man may undergo partial ossification. 278 
OSTEOLOGY 
foramen-the latter, however, is frequently absent on one or both sides. The 
skull is often somewhat flattened in the neighborhood of the parietal foramina, 
and the term obelion is applied to that point of the sagittal suture which is on 
a level with the foramina. In front is the glabella, and on its lateral aspects are 
the superciliary arches, and above these the frontal eminences. Immediately above 
the glabella may be seen the remains of the frontal suture; in a small percentage 
of skulls this suture persists and extends along the middle line to the bregma. 
Passing backward and upward from the zygomatic processes of the frontal bone 
are the temporal lines, which mark the upper limits of the temporal fossae. The 
zygomatic arches may or may not be seen projecting beyond the anterior portions 
of these lines. 
Norma Basalis (Fig. 331).-The inferior surface of the base of the skull, exclu- 
sive of the mandible, is bounded in front by the incisor teeth in the maxillae; behind, 
by the superior nuchal lines of the occipital; and laterally by the alveolar arch, 
the lower border of the zygomatic bone, the zygomatic arch and an imaginary 
line extending from it to the mastoid process and extremity of the superior nuchal 
line of the occipital. It is formed by the palatine processes of the maxillae and 
palatine bones, the vomer, the pterygoid processes, the under surfaces of the 
great wings, spinous processes, and part of the body of the sphenoid, the under 
surfaces of the squamae and mastoid and petrous portions of the temporals, and 
the under surface of the occipital bone. The anterior part or hard palate projects 
below the level of the rest of the surface, and is bounded in front and laterally 
by the alveolar arch containing the sixteen teeth of the maxillae. Immediately 
behind the incisor teeth is the incisive foramen. In this foramen are two lateral 
apertures, the openings of the incisive canals (foramina of Stensen) which transmit 
the anterior branches of the descending palatine vessels, and the nasopalatine 
nerves. Occasionally two additional canals are present in the incisive foramen; 
they are termed the foramina of Scarpa and are situated in the middle line; when 
present they transmit the nasopalatine nerves. The vault of the hard palate 
is concave, uneven, perforated by numerous foramina, marked by depressions for 
the palatine glands, and traversed by a crucial suture formed by the junction of the 
four bones of which it is composed. In the young skull a suture may be seen ex- 
tending on either side from the incisive foramen to the interval between the lateral 
incisor and canine teeth, and marking off the os incisivum or premaxillary bone. 
At either posterior angle of the hard palate is the greater palatine foramen, for the 
transmission of the descending palatine vessels and anterior palatine nerve; and 
running forward and medialward from it a groove, for the same vessels and nerve. 
Behind the posterior palatine foramen is the pyramidal process of the palatine bone, 
perforated by one or more lesser palatine foramina, and marked by the commence- 
ment of a transverse ridge, for the attachment of the tendinous expansion of the 
Tensor veli palatini. Projecting backward from the centre of the posterior border 
of the hard palate is the posterior nasal spine, for the attachment of the Musculus 
uvulae. Behind and above the hard palate are the choanae, measuring about 
2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are 
separated from one another by the vomer, and each is bounded above by the body 
of the sphenoid, below by the horizontal part of the palatine bone, and laterally 
by the medial pterygoid plate of the sphenoid. At the superior border of the 
vomer may be seen the expanded alae of this bone, receiving between them the ros- 
trum of the sphenoid. Near the lateral margins of the alae of the vomer, at the 
roots of the pterygoid processes, are the pharyngeal canals. The pterygoid process 
presents near its base the pterygoid canal, for the transmission of a nerve and artery. 
The medial pterygoid plate is long and narrow; on the lateral side of its base is the 
scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity 
the hamulus, around which the tendon of this muscle turns. The lateral pterygoid THE EXTERIOR OF THE SKULL 
279 
plate is broad; its lateral surface forms the medial boundary of the infratemporal 
fossa, and affords attachment to the Pterygoideus externus. 
Incisors 
Canine 
Incisive canal 
Pramolars. 
Transmits left nasopalatine nerve 
Transmits descending palatine vessels 
Transmits right nasopalatine nerve 
Lesser palatine foramina 
Posterior nasal spine 
Musculus uvulae 
Pterygoid hamulus 
Sphenoidal process of palatine 
Pharyngeal canal 
Tensor tympani 
Pharyngeal tubercle 
Situation of auditory tube and 
semicanal for Tensor tympani 
. Tensor veli palatini 
Inferior tympanic canaliculus 
Aquaeductus cochleae 
Jugular foramen 
Mastoid canaliculus 
Tympanomastoid fissure. 
Fara/men 
Magmam. 
Median nuchal line 
Fig. 331.-Base of skull. Inferior surface. 280 
OSTEOLOGY 
Behind the nasal cavities is the basilar portion of the occipital bone, presenting 
near its centre the pharyngeal tubercle for the attachment of the fibrous raphe 
of the pharynx, with depressions on either side for the insertions of the Rectus 
capitis anterior and Longus capitis. At the base of the lateral pterygoid plate 
is the foramen ovale, for the transmission of the mandibular nerve, the accessory 
meningeal artery, and sometimes the lesser superficial petrosal nerve; behind this are 
the foramen spinosum which transmits the middle meningeal vessels, and the promi- 
nent spina angularis (sphenoidal spine), which gives attachment to the spheno- 
mandibular ligament and the Tensor veli palatini. Lateral to the spina angularis 
is the mandibular fossa, divided into two parts by the petrotympanic fissure; the 
anterior portion, concave, smooth, bounded in front by the articular tubercle, 
serves for the articulation of the condyle of the mandible; the posterior portion, 
rough and bounded behind by the tympanic part of the temporal, is sometimes 
occupied by a part of the parotid gland. Emerging from between the laminae 
of the vaginal process of the tympanic part is the styloid process; and at the base 
of this process is the stylomastoid foramen, for the exit of the facial nerve, and 
entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between 
the tympanic part and the mastoid process, is the tympanomastoid fissure, for the 
auricular branch of the vagus. Upon the medial side of the mastoid propess is 
the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, 
the occipital groove for the occipital artery. At the base of the medial pterygoid 
plate is a large and somewhat triangular aperture, the foramen lacerum, bounded 
in front by the great wing of the sphenoid, behind by the apex of the petrous 
portion of the temporal bone, and medially by the body of the sphenoid and basilar 
portion of the occipital bone; it presents in front the posterior orifice of the ptery- 
goid canal; behind, the aperture of the carotid canal. The lower part of this opening 
is filled up in the recent state by a fibrocartilaginous plate, across the upper or 
cerebral surface of which the internal carotid artery passes. Lateral to this aperture 
is a groove, the sulcus tubae auditivae, between the petrous part of the temporal and 
the great wing of the sphenoid. This sulcus is directed lateralward and backward 
from the root of the medial pterygoid plate and lodges the cartilaginous part of the 
auditory tube; it is continuous behind with the canal in the temporal bone which 
forms the bony part of the same tube. At the bottom of this sulcus is a narrow 
cleft, the petrosphenoidal fissure, which is occupied, in the recent condition, by a 
plate of cartilage. Behind this fissure is the under surface of the petrous portion 
of the temporal bone, presenting, near its apex, the cpiadrilateral rought surface, 
part of which affords attachment to the Levator veli palatini; lateral to this surface 
is the orifice of the carotid canal, and medial to it, the depression leading to the 
aquaeductus cochleae, the former transmitting the internal carotid artery and the 
carotid plexus of the sympathetic, the latter serving for the passage of a vein from 
the cochlea. Behind the carotid canal is the jugular foramen, a large aperture, 
formed in front by the petrous portion of the temporal, and behind by the occipital; 
it is generally larger on the right than on the left side, and may be subdivided 
into three compartments. The anterior compartment transmits the inferior 
petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory 
nerves; the posterior, the transverse sinus and some meningeal branches from the 
occipital and ascending pharyngeal arteries. On the ridge of bone dividing the 
carotid canal from the jugular foramen is the inferior tympanic canaliculus for 
the transmission of the tympanic branch of the glossopharyngeal nerve; and on the 
wall of the jugular foramen, near the root of the styloid process, is the mastoid 
canaliculus for the passage of the auricular branch of the vagus nerve. Extending 
forward from the jugular foramen to the foramen lacerum is the petrooccipital fissure 
occupied, in the recent state, by a plate of cartilage. Behind the basilar portion 
of the occipital bone is the foramen magnum, bounded laterally by the occipital THE EXTERIOR OF THE SKULL 
281 
condyles, the medial sides of which are rough for the attachment of the alar 
ligaments. Lateral to each condyle is the jugular process which gives attachment 
to the Rectus capitis lateralis muscle and the lateral atlantobccipital ligament. 
The foramen magnum transmits the medulla oblongata and its membranes, the 
accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, 
and the ligaments connecting the occipital bone with the axis. The mid-points 
on the anterior and posterior margins of the foramen magnum are respectively 
termed the basion and the opisthion. In front of each condyle is the canal for the 
passage of the hypoglossal nerve and a meningeal artery. Behind each condyle 
is the condyloid fossa, perforated on one or both sides by the condyloid canal, for 
the transmission of a vein from the transverse sinus. Behind the foramen magnum 
is the median nuchal line ending above at the external occipital protuberance, while 
on either side are the superior and inferior nuchal lines; these, as well as the surfaces 
of bone between them, are rough for the attachment of the muscles which are 
enumerated on pages 227 and 228. 
Parietal 
Frontal 
Occipital 
Fig. 332.-Side view of the skull. 
Norma Lateralis (Fig. 332).-When viewed from the side the skull is seen to 
consist of the cranium above and behind, and of the face below and in front. The 
cranium is somewhat ovoid in shape, but its contour varies in different cases and 
depends largely on the length and height of the skull and on the degree of promi- 
nence of the superciliary arches and frontal eminences. Entering into its formation 
are the frontal, the parietal, the occipital, the temporal, and the great wing of the 
sphenoid. These bones are joined to one another and to the zygomatic by the follow- 282 
OSTEOLOGY 
ing sutures: the zygomaticotemporal between the zygomatic process of the temporal 
and the temporal process of the zygomatic; the zygomaticofrontal uniting the zygo- 
matic bone with the zygomatic process of the frontal; the sutures surrounding the 
great wing of the sphenoid, viz., the sphenozygomatic in front, the sphenofrontal 
and sphenoparietal above, and the sphenosquamosal behind. The sphenoparietal 
suture varies in length in different skulls, and is absent in those cases where the 
frontal articulates with the temporal squama. The point corresponding with the 
posterior end of the sphenoparietal suture is named the pterion; it is situated about 
3 cm. behind, and a little above the level of the zygomatic process of the frontal 
bone. 
The squamosal suture arches backward from the pterion and connects the tem- 
poral squama with the lower border of the parietal: this suture is continuous 
behind with the short, nearly horizontal parietomastoid suture, which unites the 
mastoid process of the temporal with the region of the mastoid angle of the parietal. 
Extending from above downward and forward across the cranium are the coronal 
and lambdoidal sutures; the former connects the parietals with the frontal, the latter, 
the parietals with the occipital. The lambdoidal suture is continuous below with 
the occipitomastoid suture between the occipital and the mastoid portion of the 
temporal. In or near the last suture is the mastoid foramen, for the transmission 
of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, 
and lambdoidal sutures is known as the asterion. Immediately above the orbital 
margin is the.superciliary arch, and, at a higher level, the frontal eminence. Near 
the centre of the parietal bone is the parietal eminence. Posteriorly is the ex- 
ternal occipital protuberance, from which the superior nuchal line may be followed 
forward to the mastoid process. Arching across the side of the cranium are the 
temporal lines, which mark the upper limit of the temporal fossa. 
The Temporal Fossa (fossa temporalis).-The temporal fossa is bounded above 
and behind by the temporal lines, which extend from the zygomatic process of the 
frontal bone upward and backward across the frontal and parietal bones, and then 
curve downward and forward to become continuous with the supramastoid crest 
and the posterior root of the zygomatic arch. The point where the upper temporal 
line cuts the coronal suture is named the stephanion. The temporal fossa is bounded 
in front by the frontal and zygomatic bones, and opening on the back of the latter 
is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic 
arch, formed by the zygomatic and temporal bones; below, it is separated from the 
infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, 
and by a ridge, continuous with this crest, which is carried backward across the 
temporal squama to the anterior root of the zygomatic process. In front and 
below, the fossa communicates with the orbital cavity through the inferior orbital 
or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and 
convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and 
temporal bones. It is traversed by vascular furrows; one, usually well-marked, runs 
upward above and in front of the external acoustic meatus, and lodges the middle 
temporal artery. Two others, frequently indistinct, may be observed on the 
anterior part of the floor, and are for the anterior and posterior deep temporal 
arteries. The temporal fossa contains the Temporalis muscle and its vessels and 
nerves, together with the zygomaticotemporal nerve. 
The zygomatic arch is formed by the zygomatic- process of the temporal and 
the temporal process of the zygomatic, the two being united by an oblique suture; 
the tendon of the Temporalis passes medial to the arch to gain insertion into the 
coronoid process of the mandible. The zygomatic process of the temporal arises 
by two roots, an anterior, directed inward in front of the mandibular fossa, where 
it expands to form the articular tubercle, and a posterior, which runs backward 
above the external acoustic meatus and is continuous with the supramastoid THE EXTERIOR OF THE SKULL 
283 
crest. The upper border of the arch gives attachment to the temporal fascia; 
the lower border and medial surface give origin to the Masseter. 
Below the posterior root of the zygomatic arch is the elliptical orifice of the 
external acoustic meatus, bounded in front, below, and behind by the tympanic 
part of the temporal bone; to its outer margin the cartilaginous segment of the 
external acoustic meatus is attached. The small triangular area between the 
posterior root of the zygomatic arch and the postero-superior part of the orifice is 
termed the suprameatal triangle, on the anterior border of which a small spinous 
process, the suprameatal spine, is sometimes seen. Between the tympanic part 
and the articular tubercle is the mandibular fossa, divided into two parts by the 
petrotympanic fissure. The anterior and larger part of the fossa articulates with 
the condyle of the mandible and is limited behind by the external acoustic meatus: 
the posterior part sometimes lodges a portion of the parotid gland. The styloid 
process extends downward and forward for a variable distance from the lower 
part of the tympanic part, and gives attachment to the Styloglossus, Styiohy- 
oideus, and Stylopharyngeus, and to the stylohyoid and stylomandibular ligaments. 
Projecting downward behind the external acoustic meatus is the mastoid process, 
to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and 
Longissimus capitis are attached. 
External acoustic meatus 
Tympanic part of temporal 
Mandibular cavity 
Styloid process 
Inferior orbital fissure 
Infratemporal crest 
Zygomatic process (cut) 
Pterygomaxillary fissure 
Lateral pterygoid plate 
Pterygoid hamulus 
Fig. 333.-Left infratemporal fossa. 
The Infratemporal Fossa (fossa infratemporalis; zygomatic fossa) (Fig. 333).-The 
infratemporal fossa is an irregularly shaped cavity, situated below and medial to the 
zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla 
and the ridge which descends from its zygomatic process; behind, by the articular 
tubercle of the temporal and the spina angularis of the sphenoid; above, by the great 
wing of the sphenoid below the infratemporal crest, and by the under surface of 284 
OSTEOLOGY 
the temporal squama; below, by the alveolar border of the maxilla; medially, by 
the lateral pterygoid plate. It contains the lower part of the Temporalis, the 
Pterygoidei interims and externus, the internal maxillary vessels, and the man- 
dibular and maxillary nerves. The foramen ovale and foramen spinosum open on 
its roof, and the alveolar canals on its anterior wall. At its upper and medial 
part are two fissures, which together form a T-shaped fissure, the horizontal limb 
being named the inferior orbital, and the vertical one the pterygomaxillary. 
The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), 
horizontal in direction, opens into the lateral and back part of the orbit. It is. 
bounded above by the lower border of the orbital surface of the great wing of the 
sphenoid; below, by the lateral border of the orbital surface of the maxilla and the 
orbital process of the palatine bone; laterally, by a small part of the zygomatic 
bone d medially, it joins at right angles with the pterygomaxillary fissure. Through 
the inferior orbital fissure the orbit communicates with the temporal, infratem- 
poral, and pterygopalatine fossse; the fissure transmits the maxillary nerve and 
its zygomatic branch, the infraorbital vessels, the ascending branches from the 
sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein 
with the pterygoid venous plexus. 
The pterygomaxillary fissure is vertical, and descends at right angles from the 
medial end of the preceding; it is a triangular interval, formed by the diver- 
gence of the maxilla from the pterygoid process of the sphenoid.. It connects 
the infratemporal with the pterygopalatine fossa, and transmits the terminal part 
of the internal maxillary artery. 
The Pterygopalatine Fossa (fossa pterygopalatina; sphenomaxillary fossa).-The 
pterygopalatine fossa is a small, triangular space at the angle of junction of the 
inferior orbital and pterygomaxillary fissures, and placed beneath the apex of 
the orbit. It is bounded above by the under surface of the body of the sphenoid 
and by the orbital process of the palatine bone; in front, by the infratemporal 
surface of the maxilla; behind, by the base of the pterygoid process and lower part 
of the anterior surface of the great wing of the sphenoid; medially, by the vertical 
part of the palatine bone with its orbital and sphenoidal processes. This fossa 
communicates with the orbit by the inferior orbital fissure, with the nasal cavity 
by the sphenopalatine foramen, and with the infratemporal fossa by the pterygo- 
maxillary fissure. Five foramina open into it. Of these, three are on the posterior 
wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, 
in this order downward and medial ward. On the medial wall is the sphenopalatine 
foramen, and below is the superior orifice of the pterygopalatine canal. The fossa 
contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part 
of the internal maxillary artery. 
Norma Occipitalis.-When viewed from behind the cranium presents a more 
or less circular outline. In the middle line is the posterior part of the sagittal 
suture connecting the parietal bones; extending downward and lateralward from 
the hinder end of the sagittal suture is the deeply serrated lambdoidal suture join- 
ing the parietals to the occipital and continuous below with the parietomastoid and 
occipitomastoid sutures; it frequently contains one or more sutural bones. Near 
the middle of the occipital squama is the external occipital protuberance or inion, 
and extending lateralward from it on either side is the superior nuchal line, and 
above this the faintly marked highest nuchal line. The part of the squama above 
the inion and highest lines is named the planum occipitale, and is covered by the 
Occipitalis muscle; the part below is termed the planum nuchale, and is divided 
by the median nuchal line which runs downward and forward from the inion to the 
foramen magnum; this ridge gives attachment to the ligamentum nuchae. The 
1 Occasionally the maxilla and the sphenoid articulate with each other at the anterior extremity of this fissure; the 
zygomatic is then excluded from it. THE EXTERIOR OF THE SKULL 
285 
muscles attached to the planum nuchale are enumerated on p. 227. Below and in 
front are the mastoid processes, convex laterally and grooved medially by the 
mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for 
the passage of the mastoid emissary vein. 
Supraorbital foramen 
Superior orbital fissure 
Lamina papyracea of ethmoid 
Lacrimal 
Inferior orbital fissure 
Zygomaticofacial foramen 
Infraorbital foramen 
Nasal cavity 
Inferior nasal concha 
Mental foramen 
Fig. 334.-The skull from the front. 
Norina Frontalis (Fig. 334).-When viewed from the front the skull exhibits a 
somewhat oval outline, limited above by the frontal bone, below by the body of the 
mandible, and later ally by the zygomatic bones and the mandibular rami. The 
upper part, formed by the frontal squama, is smooth and convex. The lower part, 
made up of the bones of the face, is irregular; it is excavated laterally by the orbital 
cavities, and presents in the middle line the anterior nasal aperture leading to the 
nasal cavities, and below this the transverse slit between the upper and lower 
dental arcades. Above, the frontal eminences stand out more or less prominently, 
and beneath these are the superciliary arches, joined to one another in the middle 
by the glabella. On and above the glabella a trace of the frontal suture sometimes 
persists; beneath it is the frontonasal suture, the mid-point of which is termed the 
nasion. Behind and below the frontonasal suture the frontal articulates with the 
frontal process of the maxilla and with the lacrimal. Arching transversely below 286 
OSTEOLOGY 
the superciliary arches is the upper part of the margin of the orbit, thin and promi- 
nent in its lateral two-thirds, rounded in its medial third, and presenting, at the 
junction of these two portions, the supraorbital notch or foramen for the supra- 
orbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic 
process which articulates with the zygomatic bone, and from it the temporal line 
extends upward and backward. Below the frontonasal suture is the bridge of the 
nose, convex from side to side, concavo-convex from above downward, and formed 
by the two nasal bones supported in the middle line by the perpendicular plate 
of the ethmoid, and laterally by the frontal processes of the maxillse which are 
prolonged upward between the nasal and lacrimal bones and form the lower and 
medial part of the circumference of each orbit. Below the nasal bones and between 
the maxillae is the anterior aperture of the nose, pyriform in shape, with the narrow 
end directed upward. Laterally this opening is bounded by sharp margins, to 
which the lateral and alar cartilages of the nose are attached; below, the margins 
are thicker and curve medialward and forward to end in the anterior nasal spine. 
On looking into the nasal cavity, the bony septum which separates the nasal 
cavities presents, in front, a large triangular deficiency; this, in the recent state, 
is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal 
cavity the anterior part of the inferior nasal concha is visible. Below and lateral 
to the anterior nasal aperture are the anterior surfaces of the maxillse, each 
perforated, near the lower margin of the orbit, by the infraorbital foramen for the 
passage of the infraorbital nerve and vessels. Below and medial to this foramen 
is the canine eminence separating the incisive from the canine fossa. Beneath 
these fossae are the alveolar processes of the maxillae containing the upper teeth, 
which overlap the teeth of the mandible in front. The zygomatic bone on either 
side forms the prominence of the cheek, the lower and lateral portion of the orbital 
cavity, and the anterior part of the zygomatic arch. It articulates medially with 
the maxilla, behind with the zygomatic process of the temporal, and above with 
the great wing of the sphenoid and the zygomatic process of the frontal; it is per- 
forated by the zygomaticofacial foramen for the passage of the zygomaticofacial 
nerve. On the body of the mandible is a median ridge, indicating the position 
of the symphysis; this ridge divides below to enclose the mental protuberance, the 
lateral angles of which constitute the mental tubercles. Below the incisor teeth 
is the incisive fossa, and beneath the second premolar tooth the mental foramen 
which transmits the mental nerve and vessels. The oblique line runs upward from 
the mental tubercle and is continuous behind with the anterior border of the ramus. 
The posterior border of the ramus runs downward and forward from the condyle 
to the angle, which is frequently more or less everted. 
The Orbits (^orbitae) (Fig. 334).-The orbits are two quadrilateral pyramidal cavi- 
ties, situated at the upper and anterior part of the face, their bases being directed 
forward and lateralward, and their apices backward and medialward, so that their 
long axes, if continued backward, would meet over the body of the sphenoid. 
Each presents for examination a roof, a floor, a medial and a lateral wall, a base, 
and an apex. 
The roof is concave, directed downward, and slightly forward, and formed in 
front by the orbital plate of the frontal; behind by the small wing of the sphenoid. 
It presents medially the trochlear fovea for the attachment of the cartilaginous 
pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal 
gland; and posteriorly, the suture between the frontal bone and the small wing 
of the sphenoid. 
The floor is directed upward and lateralward, and is of less extent than the 
roof; it is formed chiefly by the orbital surface of the maxilla; in front and laterally, 
by the orbital process of the zygomatic bone, and behind and medially, to a small 
extent, by the orbital process of the palatine. At its medial angle is the upper THE EXTERIOR OF THE SKULL 
287 
opening of the nasolacrimal canal, immediately to the lateral side of which is a 
depression for the origin of the Obliquus oculi inferior. On its lateral part is the 
suture between the maxilla and zygomatic bone, and at its posterior part that 
between the maxilla and the orbital process of the palatine. Running forward 
near the middle of the floor is the infraorbital groove, ending in front in the infra- 
orbital canal and transmitting the infraorbital nerve and vessels. 
The medial wall (Fig. 335) is nearly vertical, and is formed from before back- 
ward by the frontal process of the maxilla, the lacrimal, the lamina papyracea 
of the ethmoid, and a small part of the body of the sphenoid in front of the optic 
foramen. Sometimes the sphenoidal concha forms a small part of this wall (see 
page 250). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimo- 
ethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges 
the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which 
Frontal .sinus 
Posterior ethmoidal foramen 
Orbital process of palatine 
Optic foramen 
Anterior 
ethmoidal foramen 
Sphenopalatine foramen 
Sella turcica 
Probe in foramen rotundum 
Fossa for 
lacrimal sac 
Uncinate process _ 
of ethmoid 
Openings of 
maxillary sinus 
Probe in pterygoid canal 
Inferior nasal' 
concha 
Probe in pterygopalatine canal 
Palatine bone 
Lateral pterygoid plate 
Pyramidal process of palatine 
Fig. 335.-Medial wall of left orbit. 
the lacrimal part of the Orbicularis oculi arises. At the junction of the medial 
wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and 
sphenofrontal sutures. The point of junction of the anterior border of the lacrimal 
with the frontal is named the dacryon. In the frontoethmoidal suture are the 
anterior and posterior ethmoidal foramina, the former transmitting the nasociliary 
nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and 
vessels. 
The lateral wall, directed medialward and forward, is formed by the orbital 
process of the zygomatic and the orbital surface of the great wing of the sphenoid; 
these are united by the sphenozygomatic suture which terminates below at the 
front end of the inferior orbital fissure. On the orbital process of the zygomatic 
bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which 
transmit the branches of the zygomatic nerve. Between the roof and the lateral 288 
OSTEOLOGY 
wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure 
the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the 
abducent nerves enter the orbital cavity, also some filaments from the cavernous 
plexus of the sympathetic and the orbital branches of the middle meningeal artery. 
Passing backward through the fissure are the ophthalmic vein and the recurrent 
branch from the lacrimal artery to the dura mater. The lateral wall and the floor 
are separated posteriorly by the inferior orbital fissure which transmits the maxillary 
nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches 
from the sphenopalatine ganglion. 
The base of the orbit, quadrilateral in shape, is formed above by the supra- 
orbital arch of the frontal bone, in which is the supraorbital notch or foramen for 
the passage of the supraorbital vessels and nerve; below by the zygomatic bone and 
maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic 
bone and the zygomatic process of the frontal joined by the zygomaticofrontal 
suture; medially by the frontal bone and the frontal process of the maxilla united 
by the frontomaxillary suture. 
The apex, situated at the back of the orbit, corresponds to the optic foramen1 
a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. 
It will thus be seen that there are nine openings communicating with each 
orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital 
foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic 
foramen, and the canal for the nasolacrimal duct. 
THE INTERIOR OF THE SKULL. 
In order to study the interior of the skull the skull-cap should be removed by 
a saw-cut carried around the cranium about the level of the frontal eminences 
and the upper limits of the squamosal sutures, cutting the occipital bone about 
2.5 cm. above the external protuberance. 
Inner Surface of the Skull-cap.-The inner surface of the skull-cap is concave 
and presents depressions for the convolutions of the cerebrum, together with 
numerous furrows for the lodgement of branches of the meningeal vessels. Along 
the middle line is a longitudinal groove, narrow in front, where it commences at 
the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its 
margins afford attachment to the falx cerebri. On either side of it are several 
depressions for the arachnoid granulations, and at its back part, the openings of 
the parietal foramina when these are present. It is crossed, in front, by the coronal 
suture, and behind by the lambdoidal, while the sagittal lies in the medial plane 
between the parietal bones. 
Upper Surface of the Base of the Skull (Fig. 336).-The upper surface of the 
base of the skull or floor of the cranial cavity presents three fossae, called the anterior, 
middle, and posterior cranial fossae. 
Anterior Fossa (fossa cranii anterior).-The floor of the anterior fossa is formed 
by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the 
small wings and front part of the body of the sphenoid; it is limited behind by the 
posterior borders of the small wings of the sphenoid and by the anterior margin 
of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, 
and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and sup- 
port the frontal lobes of the cerebrum; they are convex and marked by depressions 
for the brain convolutions, and grooves for branches of the meningeal vessels. 
1 Some anatomists describe the apex of the orbit as corresponding with the medial end of the superior orbital fissure. 
It seems better, however, to adopt the statement in the text, since the ocular muscles take origin around the optic 
foramen, and diverge from it to the bulb of the eye. THE INTERIOR OF THE SKULL 
289 
The central portion corresponds with the roof of the nasal cavity, and is markedly 
depressed on either side of the crista galli. It presents, in and near the median 
Groove for super, sagittal sinus 
Grooves for anter. meningeal vessels 
Foramen caecum 
Slit for nasociliary nerve 
Crista galli 
Groove for nasociliary nerve 
Anterior ethmoidal foramen 
Orifices for olfactory nerves 
Posterior ethmoidal foramen 
Ethmoidal spine 
Olfactory grooves- 
Chiasmatic groove 
Optic foramen 
Anterior clinoid process 
Middle clinoid process 
Tuberculum sellae 
Posterior clinoid process 
Groove for abducent nerve 
Orifice of carotid canal 
Foramen lacerum 
Depression for semilunar ganglion 
Internal acoustic meatus 
Slit for dura mater 
Groove for superior petrosal sinus 
J ugular foramen 
Hypoglossal canal 
Aquceductus vestibuli 
Condyloid foramen 
Mastoid foramen 
Posterior meningeal grooves 
Fig. 336.-Base of the skull. Upper surface. 
line, from before backward, the commencement of the frontal crest for the attach- 
ment of the falx cerebri; the foramen cecum, between the frontal bone and the crista 
galli of the ethmoid, which usually transmits a small vein from the nasal cavity 290 
OSTEOLOGY 
to the superior sagittal sinus; behind the foramen cecum, the crista galli, the 
free margin of which affords attachment to the falx cerebri; on either side of the 
crista galli, the olfactory groove formed by the cribriform plate, which supports 
the olfactory bulb and presents foramina for the transmission of the olfactory 
nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either 
olfactory groove are the internal openings of the anterior and posterior ethmoidal 
foramina; the anterior, situated about the middle of the lateral margin of the olfac- 
tory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the 
nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like 
opening above mentioned; the posterior ethmoidal foramen opens at the back part 
of this margin under cover of the projecting lamina of the sphenoid, and transmits 
the posterior ethmoidal vessels and nerve. Farther back in the middle line is the 
ethmoidal spine, bounded behind by a slight elevation separating two shallow lon- 
gitudinal grooves which support the olfactory lobes. Behind this is the anterior 
margin of the chiasmatic groove, running lateralward on either side to the upper 
margin of the optic foramen. 
The Middle Fossa (fossa cranii media).-The middle fossa, deeper than the pre- 
ceding, is narrow in the middle, and wide at the sides of the skull. It is bounded 
in front by the posterior margins of the small wings of the sphenoid, the anterior 
clinoid processes, and the ridge forming the anterior margin of the chiasmatic 
groove; behind, by the superior angles of the petrous portions of the temporals 
and the dorsum sellae; laterally by the temporal squamae, sphenoidal angles of the 
parietals, and great wings of the sphenoid. It is traversed by the squamosal, 
sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. 
The middle part of the fossa presents, in front, the chiasmatic groove and tuber- 
culum sellae; the chiasmatic groove ends on either side at the optic foramen, which 
transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind 
the optic foramen the anterior clinoid process is directed backward and medialward 
and gives attachment to the tentorium cerebelli. Behind the tuberculum sellae 
is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges 
the hypophysis, and presents on its anterior wall the middle clinoid processes. 
The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum 
sellae, the upper angles of which are surmounted by the posterior clinoid processes: 
these afford attachment to the tentorium cerebelli, and below each is a notch for 
the abducent nerve. On either side of the sella turcica is the carotid groove, which 
is broad, shallow, and curved somewhat like the italic letter f. It begins behind 
at the foramen lacerum, and ends on the medial side of the anterior clinoid process, 
where it is sometimes converted into a foramen (carotico-clinoid) by the union of 
the anterior with the middle clinoid process; posteriorly, it is bounded laterally 
by the lingula. This groove lodges the cavernous sinus and the internal carotid 
artery, the latter being surrounded by a plexus of sympathetic nerves. 
The lateral parts of the middle fossa are of considerable depth, and support 
the temporal lobes of the brain. They are marked by depressions for the brain 
convolutions and traversed by furrows for the anterior and posterior branches 
of the middle meningeal vessels. These furrows begin near the foramen spinosum, 
and the anterior runs forward and upward to the sphenoidal angle of the parietal, 
where it is sometimes converted into a bony canal; the posterior runs lateralward 
and backward across the temporal squama and passes on to the parietal near 
the middle of its lower border. The following apertures are also to be seen. In 
front is the superior orbital fissure, bounded above by the small wing, below, by the 
great wing, and medially, by the body of the sphenoid; it is usually completed 
laterally by the orbital plate of the frontal bone. It transmits to the orbital 
cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, 
and the abducent nerves, some filaments from the cavernous plexus of the THE INTERIOR OF THE SKULL 
291 
sympathetic, and the orbital branch of the middle meningeal artery; and from the 
orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and 
the ophthalmic veins. Behind the medial end of the superior orbital fissure is 
the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral 
to the foramen rotundum is the foramen ovale, which transmits the mandibular 
nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve.1 
Medial to the foramen ovale is the foramen Vesalii, which varies in size in different 
individuals, and is often absent; when present, it opens below at the lateral side 
of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale 
is the foramen spinosum, for the passage of the middle meningeal vessels, and a 
recurrent branch from the mandibular nerve. Medial to the foramen ovale is 
the foramen lacerum; in the recent state the lower part of this aperture is filled up 
by a layer of fibrocartilage, while its upper and inner parts transmit the internal 
carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the 
pterygoid canal and a meningeal branch from the ascending pharyngeal artery 
pierce the layer of fibrocartilage. On the anterior surface of the petrous portion 
of the temporal bone are seen the eminence caused by the projection of the superior 
semicircular canal; in front of and a little lateral to this a depression corresponding 
to the roof of the tympanic cavity; the groove leading to the hiatus of the facial 
canal, for the transmission of the greater superficial petrosal nerve and the petrosal 
branch of the middle meningeal artery; beneath it, the smaller groove, for the pas- 
sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the 
depression for the semilunar ganglion and the orifice of the carotid canal. 
The Posterior Fossa (fossa cranii posterior).-The posterior fossa is the largest 
and deepest of the three. It is formed by the dorsum sellae and clivus of the 
sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the 
mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the 
parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. 
It is separated from the middle fossa in and near the median line by the dorsum 
sellae of the sphenoid and on either side by the superior angle of the petrous por- 
tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, 
is grooved for the superior petrosal sinus, and presents at its medial end a notch 
upon which the trigeminal nerve rests. The fossa is limited behind by the grooves 
for the transverse sinuses. In its centre is the foramen magnum, on either side of 
which is a rough tubercle for the attachment of the alar ligaments; a little above 
this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal 
branch from the ascending pharyngeal artery. In front of the foramen magnum 
the basilar portion of the occipital and the posterior part of the body of the sphenoid 
form a grooved surface which supports the medulla oblongata and pons; in the 
young skull these bones are joined by a synchondrosis. This grooved surface is 
separated on either side from the petrous portion of the temporal by the petro- 
occipital fissure, which is occupied in the recent state by a plate of cartilage; the 
fissure is continuous behind with the jugular foramen, and its margins are grooved 
for the inferior petrosal sinus. The jugular foramen is situated between the lateral 
part of the occipital and the petrous part of the temporal. The anterior portion 
of this foramen transmits the inferior petrosal sinus; the posterior portion, the 
transverse sinus and some meningeal branches from the occipital and ascending 
pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, 
and accessory nerves. Above the jugular foramen is the internal acoustic meatus, 
for the facial and acoustic nerves and internal auditory artery; behind and lateral 
to this is the slit-like opening leading into the aquaeductus vestibuli, which lodges 
the ductus endolymphaticus; while between these, and near the superior angle of 
1 See footnote, page 248. 292 
OSTEOLOGY 
the petrous portion, is a small triangular depression, the remains of the fossa sub- 
arcuata, which lodges a process of the dura mater and occasionally transmits a small 
vein. Behind the foramen magnum are the inferior occipital fossae, which support 
the hemispheres of the cerebellum, separated from one another by the internal 
occipital crest, which serves for the attachment of the falx cerebelli, and lodges 
the occipital sinus. The posterior fossae are surmounted by the deep grooves for 
the transverse sinuses. Each of these channels, in its passage to the jugular foramen, 
grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the 
temporal, and the jugular process of the occipital, and ends at the back part of 
the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, 
the orifice of the mastoid foramen may be seen; and, just previous to its termina- 
tion, the condyloid canal opens into it; neither opening is constant. 
Rostrum of sphenoid 
Crest of nasal bones 
Frontal spine- 
Space for triangular, 
cartilage of septum 
Crest of palatines 
'Crest of maxillce 
Fig. 337.-Medial wall of left nasal fossa. 
The Nasal Cavity (cavum nasi; nasal fossa) -The nasal cavities are two irregular 
spaces, situated one on either side of the middle line of the face, extending from the 
base of the cranium to the roof of the mouth, and separated from each other by a 
thin vertical septum. They open on the face through the pear-shaped anterior nasal 
aperture, and their posterior openings or choanae communicate, in the recent 
state, with the nasal part of the pharynx. They are much narrower above than 
below, and in the middle than at their anterior or posterior openings: their depth, 
which is considerable, is greatest in the middle. They communicate with the 
frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded 
by a roof, a floor, a medial and a lateral wall. 
The roof (Figs. 337, 338) is horizontal in its central part, but slopes down- 
ward in front and behind; it is formed in front by the nasal bone and the spine 
of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, 
by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the 
sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid THE INTERIOR OF THE SKULL 
293 
are the foramina for the olfactory nerves, and on the posterior part of the roof 
is the opening into the sphenoidal sinus. 
The floor is flattened from before backward and concave from side to side. 
It is formed by the palatine process of the maxilla and the horizontal part of 
the palatine bone; near its anterior end is the opening of the incisive canal. 
The medial wall (septum nasi) (Fig. 337), is frequently deflected to one or other 
side, more often to the left than to the right. It is formed, in front, by the crest 
of the nasal bones and frontal spine; in the middle, by the perpendicular plate 
of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; beloiv, 
by the crest of the maxillae and palatine bones. It presents, in front, a large, 
triangular notch, which receives the cartilage of the septum; and behind, the 
free edge of the vomer. Its surface is marked by numerous furrows for vessels 
and nerves and by the grooves for the nasopalatine nerve, and is traversed by 
sutures connecting the bones of which it is formed. 
Frontal spine 
Nasal bone 
Probe passed through 
nasolacrimal canal 
Cribriform plate of ethmoid. 
Bristle passed through 
infundibulum 
Sphenoid 
Frontal proc, of maxilla 
Lacrimal 
Ethmoid 
Uncinate proc, of ethmoid 
Inferior nasal concha 
Palatine 
Superior meatus 
Middle meatus 
■Inferior meatus 
Palatine proc, of maxilla- 
Anterior nasal spine- 
Horizontal part of palatine- 
Posterior nasal spine- 
Incisive canal- 
Fig. 338.-Roof, floor, and lateral wall of left nasal cavity. 
The lateral wall (Fig. 338) is formed, in front, by the frontal process of the 
maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and 
inferior nasal concha; behind, by the vertical plate of the palatine bone, and the 
medial pterygoid plate of the sphenoid. On this wall are three irregular antero- 
posterior passages, termed the superior, middle, and inferior meatuses of the nose. 
The superior meatus, the smallest of the three, occupies the middle third of the 
lateral wall. It lies between the superior and middle nasal conchae; the spheno- 
palatine foramen opens into it behind, and the posterior ethmoidal cells in front. 
The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed 
above and behind the superior concha. The middle meatus is situated between the 
middle and inferior conchae, and extends from the anterior to the posterior end of 
the latter. The lateral wall of this meatus can be satisfactorily studied only after 
the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, 294 
OSTEOLOGY 
limited below by the edge of the uncinate process of the ethmoid and above by 
an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained 
within this bulla and open on or near to it. Through the hiatus semilunaris 
the meatus communicates with a curved passage termed the infundibulum, which 
communicates in front with the anterior ethmoidal cells and in rather more than 
fifty per cent, of skulls is continued upward as the frontonasal duct into the frontal 
air-sinus; when this continuity fails, the frontonasal duct opens directly into the 
anterior part of the meatus. Below the bulla ethmoidalis and hidden by the unci- 
nate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare); 
an accessory opening is frequently present above the posterior part of the inferior 
nasal concha. The inferior meatus, the largest of the three, is the space between 
the inferior concha and the floor of the nasal cavity. It extends almost the entire 
length of the lateral wall of the nose, is broader in front than behind, and presents 
anteriorly the lower orifice of the nasolacrimal canal. 
The Anterior Nasal Aperture (Fig. 334) is a heart-shaped or pyriform opening, 
whose long axis is vertical, and narrow end upward; in the recent state it is much 
contracted by the lateral and alar cartilages of the nose. It is bounded above by 
the inferior borders of the nasal bones; laterally by the thin, sharp margins which 
separate the anterior from the nasal surfaces of the maxillae; and below by the same 
borders, where they curve medialward to join each other at the anterior nasal 
spine. 
The choanae are each bounded above by the under surface of the body of the 
sphenoid and ala of the vomer; below, by the posterior border of the horizontal 
part of the palatine bone; laterally, by the medial pterygoid plate; they are 
separated from each other by the posterior border of the vomer. 
DIFFERENCES IN THE SKULL DUE TO AGE. 
At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion 
is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half 
in the adult. The frontal and parietal eminences are prominent, and the greatest width of the 
skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid 
processes are not developed. Ossification of the skull bones is not completed, and many of them, 
e. g., the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. 
Unossified membranous intervals, termed fontanelles, are seen at the angles of the parietal bones; 
these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle 
line, and two, an antero-lateral and a postero-lateral, on either side. 
Fig. 339.-Skull at birth showing anterior and 
posterior fontanelles. 
Fig. 340.--The lateral fontanelles. 
The anterior or bregmatic fontanelle (Fig. 339) is the largest, and is placed at the junction of 
the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measures about 4 cm. in its 
antero-posterior and 2.5 cm. in its transverse diameter. The posterior fontanelle is triangular CRANIOLOGY 
295 
in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fonta- 
nelles (Fig. 340) are small, irregular in shape, and correspond respectively with the sphenoidal 
and mastoid angles of the parietal bones. An additional fontanelle is sometimes seen in the 
sagittal suture at the region of the obelion. The fontanelles are usually closed by the growth 
and extension of the bones which surround them, but sometimes they are the sites of separate 
ossific centres which develop into sutural bones. The posterior and lateral fontanelles are obliter- 
ated within a month or two after birth, but the anterior is not completely closed until about the 
middle of the second year. 
The smallness of the face at birth is mainly accounted for by the rudimentary condition of 
the maxillae and mandible, the non-eruption of the teeth, and the small size of the maxillary air 
sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and 
the lower border of the anterior nasal aperture is only a little below the level of the orbital floor. 
With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these 
changes are still more marked after the second dentition. 
The skull grows rapidly from birth to the seventh year, by which time the foramen magnum 
and petrous parts of the temporals have reached their full size and the orbital cavities are only 
a little smaller than those of the adult. Growth is slow from the seventh year until the approach 
of puberty, when a second period of activity occurs: this results in an increase in all directions, 
but it is especially marked in the frontal and facial regions, where it is associated with the develop- 
ment of the air sinuses. 
Obliteration of the sutures of the vault of the skull takes place as age advances. This process 
may commence between the ages of thirty and forty, and is first seen on the inner surface, and 
some ten years later on the outer surface of the skull. The dates given are, however, only approxi- 
mate, as it is impossible to state with anything like accuracy the time at which the sutures are 
closed. Obliteration usually occurs first in the posterior part of the sagittal suture, next in the 
coronal, and then in the lambdoidal. 
In old age the skull generally becomes thinner and lighter, but in a small proportion of cases 
it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- 
ing feature of the old skull is the diminution in the size of the maxillae and mandible consequent 
on the loss of the teeth and the absorption of the alveolar processes. This is associated with a 
marked reduction in the vertical measurement of the face and with an alteration in the angles 
of the mandible. 
SEXUAL DIFFERENCES IN THE SKULL. 
Until the age of puberty there is little difference between the skull of the female and that of 
the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity 
about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less 
strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, 
and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is 
sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- 
what flattened. The contour of the face is more rounded, the facial bones are smoother, and the 
maxillae and mandible and their contained teeth smaller. From what has been said it will be seen 
that more of the infantile characteristics are retained in the skull of the adult female than in that 
of the adult male. A well-marked male or female skull can easily be recognized as such, but in 
some cases the respective characteristics are so indistinct that the determination of the sex may 
be difficult or impossible. 
CRANIOLOGY. 
Skulls vary in size and shape, and the term craniology is applied to the study of these varia- 
tions. The capacity of the cranial cavity constitutes a good index of the size of the brain which 
it contained, and is most conveniently arrived at by filling the cavity with shot and measuring 
the contents in a graduated vessel. Skulls may be classified according to their capacities as 
follows: 
1. Microcephalic, with a capacity of less than 1350 c.cm.-e. g., those of native Australians 
and Andaman Islanders. 
2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm.-e. g., those of African 
negroes and Chinese. 
3 Megacephalic, with a capacity of over 1450 c.cm.-e. g., those of Europeans, Japanese, and 
Eskimos. 
In comparing the shape of one skull with that of another it is necessary to adopt some definite 
position in which the skulls should be placed during the process of examination. They should 
be so placed that a line carried through the lower margin of the orbit and upper margin of the 
external acoustic meatus is in the horizontal plane. The normae of one skull can then be com- 
pared with those of another, and the differences in contour and surface form noted. Further, 296 
OSTEOLOGY 
it is necessary that the various linear measurements used to determine the shape of the skull 
should be made between definite and easily localized points on its surface. The principal points 
may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. 
The Points in the Median Plane are the: 
Mental Point. The most prominent point of the chin. 
Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar 
arch. 
Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base 
of the anterior nasal spine. 
Nasion. The central point of the frontonasal suture. 
Glabella. The point in the middle line at the level of the superciliary arches. 
Ophryon. The point in the middle line of the forehead at the level where the temporal lines 
most nearly approach each other. 
Bregma. The meeting point of the coronal and sagittal sutures. 
Obelion. A point in the sagittal suture on a level with the parietal foramina. 
Lambda. The point of junction of the sagittal and lambdoidal sutures. 
Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. 
Inion. The external occipital protuberance. 
Opisthion. The mid-point of the posterior margin of the foramen magnum. 
Basion. The mid-point of the anterior margin of the foramen magnum. 
The Points on Either Side of the Median Plane are the: 
Gonion. The outer margin of the angle of the mandible. 
Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal 
bone and the frontal process of the maxilla. 
Stephanion. The point where the temporal line intersects the coronal suture. 
Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the 
parietal. 
Auricular Point. The centre of the orifice of the external acoustic meatus. 
Asterion. The point of meeting of the lambdoidal, mastobccipital, and mastoparietal sutures. 
The horizontal circumference of the cranium is measured in a plane passing through the glabella 
(Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 
50 cm. in the female and 52.5 cm. in the male. 
The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the 
vertex to the opisthion: while the basinasal length is the distance between the basion and the 
nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, 
represent the vertical circumference of the cranium. 
The length is measured from the glabella to the occipital point, while the breadth or greatest 
transverse diameter is usually found near the external acoustic meatus. The proportion of 
, , . . , (breadth X 100) . 7 , 7 , , 7 
breadth to length jeDgth 1S ^erme(^ ^ ie index or index of breadth. 
The height is usually measured from the basion to the bregma, and the proportion of height 
, (height X 100) . , . , 7 . , . , 
to length ; n constitutes the vertical or height index. 
length 
In studying the face the principal points to be noticed are the proportion of its length and 
breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection 
of the jaws. 
The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible 
be wanting, to the alveolar point; while its width is represented by the distance between the 
zygomatic arches. By comparing the length with the width of the face, skulls may be divided 
into two groups; dolichofacial or leptoprosope (long faced) and brachyfacial or chemoprosope (short 
faced). 
The orbital index signifies the proportion which the orbital height bears to the orbital width, 
thus: 
orbital height X 100 
orbital width 
The nasal index expresses the proportion which the width of the anterior nasal aperture bears 
to the height of the nose, the latter being measured from the nasion to the lower margin of the 
nasal aperture, thus: 
nasal width X 100 
nasal height 
The degree of projection of the jaws is determined by the gnathic or alveolar index, which repre- 
sents the proportion between the basialveolar and basinasal lengths, thus: 
basialveolar length X 100 
basinasal length CRANIOLOGY 
297 
The following table, modified from that given by Duckworth,1 illustrates how these different 
indices may be utilized in the classification of skulls: 
Index. 
Classification. 
Nomenclature. 
Examples. 
1. 
Cephalic 
Below 75 
Between 75 and 80 
Above 80 
Dolichocephalic 
Mesaticephalic 
Brachycephalic 
Kaffirs and Native Australians. 
Europeans and Chinese. 
Mongolians and Andamans. 
2. 
Orbital 
Below 84 
Between 84 and 89 
Above 89 
Microseme 
Mesoseme 
Megaseme 
Tasmanians and Native Austra- 
lians. 
Europeans. 
Chinese and Polynesians. 
3. 
Nasal 
Below 48 
Between 48 and 53 
Above 53. 
Leptorhine 
Mesorhine 
Platyrhine 
Europeans. 
Japanese and Chinese. 
Negroes and Native Australians. 
4. 
Gnathic 
Below 98 
Between 98 and 103 
Above 103 
Orthognathous 
Mesognathous 
Prognathous 
Europeans. 
Chinese and Japanese. 
Native Australians. 
Applied Anatomy.-Occasionally a protrusion of the brain or its membranes may take place 
through one of the sutures, owing to non-closure. When the protrusion consists of membranes 
only, and is filled with cerebrospinal fluid, it is called a meningocele; when it consists of brain as 
well as membranes, it is termed an encephalocele. These malformations are usually found in the 
middle line, and most frequently at the back of the head, the protrusion taking place between 
the centres of ossification of the occipital squama (see p. 231). They generally occur through the 
upper part of the vertical fissure, which is the last to close, but not uncommonly through 
the lower part, when the foramen magnum may be incomplete. More rarely these protrusions 
are met with in other situations, as in the sagittal, lambdoidal, and other sutures, or through 
abnormal gaps at the sides or base of the skull. 
The chief function of the skull is to protect the brain, and therefore those portions of the skull 
which are most exposed to external violence are thicker than those which are shielded from injury 
by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamse, 
being protected by the temporales muscles, and the inferior occipital fossae, being shielded by the 
muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented 
by its elasticity, its rounded shape, and its construction of a number of secondary elastic arches, 
each made up of a single bone. The manner in which vibrations are transmitted through the 
bones of the skull is also of importance as regards its protective mechanism, at all events as far 
as the base is concerned. In the vault, the bones being of a fairly equal thickness and density, 
vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the 
varying thickness and density of the bones, this is not so; and therefore in this situation there 
are special buttresses which serve to carry the vibrations in certain definite directions. At the 
front of the skull, on either side, is the ridge which separates the anterior from the middle fossa 
of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; 
and if any violence is applied to the vault, the vibrations would be carried along these buttresses 
to the sella turcica, where they meet. This part has been termed the "centre of resistance," 
and here there is a special protective mechanism to guard the brain. The subarachnoid cavity 
at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion 
to shield the brain from injury. In like manner, when violence is applied to the base of the skull, 
as in falls upon the feet, the vibrations are carried backward through the occipital crest, and 
forward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. 
Fractures of the skull are best considered as affecting either the vault or the base. Fractures 
of the vault generally involve the whole thickness of the bone; but sometimes the inner table 
alone is fractured, and portions of it driven inward. As a rule, in fractures of the skull, the inner 
table is more splintered and comminuted than the outer, and this is due to several causes. It 
is thinner and more brittle; the force of the violence as it passes inward becomes broken up, and 
is more diffused by the time it reaches the inner table; the bone being in the form of an arch bends 
as a whole and spreads out, and thus presses the particles together on the convex surface of the 
arch, i. e., the outer table, and forces them asunder on the concave surface or inner table; and, 
lastly, there is nothing firm under the inner table to support it and oppose the force. Fractures 
of the vault may be either simple, or starred and comminuted, and the fragments may be de- 
pressed or elevated. Cases of fracture with elevation of the fractured portion are uncommon, 
and can only be produced by direct wound. In comminuted fracture, a portion of the skull is 
1 Morphology and Anthropology, by W. L. H. Duckworth, M.A., Cambridge University Press. 298 
OSTEOLOGY 
broken into several pieces, the lines of fracture radiating from a centre where the chief impact 
of the blow was felt; if the fracture is also depressed, a fissure circumscribes the radiating lines, 
enclosing a portion of the skull. If this area is circular it is termed a "pond" fracture, and has 
probably been caused by a round instrument, as a life preserver or hammer; if elliptical in shape 
it is termed a "gutter" fracture, and owes its shape to the instrument which has produced it, 
as a poker. Fracture of the outer table alone only occurs in the region of the frontal sinuses where 
the two tables are completely separated. 
Fractures of the base of the skull may be produced by indirect or direct violence. I. In cases 
of the former class the violence is applied to the vertex or some part of the cranial convexity, 
as when a person falls from a height on to his head and a fracture of the base results. The mechan- 
ism of this form of fracture was formerly explained by the doctrine of contre-coup, i. e., that the 
force was transmitted from one side of the skull to the other; but this view is no longer held, 
and there are at the present day two theories as to the mode of causation of these fractures, 
(a) According to Aran's theory of irradiation all fractures of the base are produced by a fissure, 
which starts from the point of injury and radiates to the base. There can be little doubt that 
many cases of fracture of the base, especially of the middle fossae, are caused in this way, but it 
is insufficient to explain all, since instances have been met with of fracture of the base of the skull 
in which there has been no fracture of the vault. (6) To explain these cases, another theory, 
known as the compression or bursting theory, has been suggested. If a hollow, elastic sphere 
is compressed from above downward, it will bulge laterally, and, if the compression is sufficient, 
it will eventually burst in the situation where it bulges. Now, the skull is an elastic sphere, and 
when compression is applied to it, its diameter will be reduced along the line of greatest pressure 
and will therefore be increased in other directions, and may increase to such an extent that burst- 
ing occurs. In a hollow elastic sphere of uniform thickness, the bulging and subsequent bursting 
take place at the equatorial line midway between the two points of compression; but the skull 
is not of uniform thickness, and therefore the bulging and subsequent bursting take place at the 
weakest part. 
II. Direct violence may be applied to the base of the skull in several different ways: by the 
impact of the vertebral column against the condyles of the occipital bone, in falls on the buttocks 
or feet; by the condyle of the mandible being driven against the mandibular fossa, in blows or falls 
on the chin; by the thrusting of a pointed instrument through the orbit or nose; by gunshot 
wounds through the mouth; and by a fall or a stab on the back of the head. 
In the majority of cases the fracture is compound. The most common place for fracture of 
the base to occur is through the middle fossa, and here the fissure usually takes a fairly definite 
course. Starting from the point struck, which is generally somewhere in the neighborhood of 
the parietal eminence, it runs downward through the parietal and the temporal squama and 
across the petrous portion, frequently traversing and implicating the internal acoustic meatus, 
to the foramen lacerum. From this it may pass across the body of the sphenoid, through the 
sella turcica, to the foramen lacerum of the other side, and may indeed travel around the whole 
cranium, so as to completely separate the anterior from the posterior part. The course of the 
fracture explains the symptoms to which fracture in this region may give rise: thus, if the fissure 
pass across the internal acoustic meatus, injury to the facial and acoustic nerves may result, 
with consequent facial paralysis and deafness; or the tubular prolongation of the arachnoid 
around these nerves in the meatus may be torn and thus permit of the escape of the cerebro- 
spinal fluid should there be a communication between the internal ear and the tympanic cavity 
together with rupture of the tympanic membrane, as is frequently the case: again, if the fissure 
pass across the sella turcica and the mucoperiosteum covering the under surface of the body of 
the sphenoid is torn, blood will find its way into the pharynx and be swallowed, and after a time 
vomiting of blood will result. Fractures of the anterior fossa, involving the bones forming the 
roof of the orbit and nasal cavity, are generally the result of blows on the forehead; but fracture 
of the cribriform plate of the ethmoid may be a complication of fracture of the nasal bone. When 
the fracture implicates the roof of the orbit, the blood finds its way into this cavity, and, travelling 
forward, appears as a subconjunctival ecchymosis. If the roof of the nasal cavity be fractured, 
the blood escapes from the nose. In rare cases there may be also escape of cerebrospinal fluid 
from the nose, should the dura mater and arachnoid have been torn. In fractures of the posterior 
fossa, extravasation of blood may appear at the nape of the neck, beneath the muscles attached 
to the superior nuchal line of the occipital bone. 
Diseases of the Skull.-An inflammatory condition affecting the bones and the pericranium 
together is generally caused by septic infection either of a scalp wound exposing and bruising 
the bone, or of a compound fracture, and is termed septic osteomyelitis. Occasionally it may 
occur independently of injury, and then follows the same course, and is due to the same causes 
as acute infective osteomyelitis in the long bones. 
The most common chronic disease of the skull is due to syphilis. In acquired syphilis the 
disease usually occurs as nodes, which arise most commonly in the pericranium, but may also 
arise in the diploe, or more rarely on the inner surface of the skull. The formation of gummata 
under the periosteum generally leads to caries, which may be either limited, if the gumma is CRAN10L0GY 
299 
localized, or widespread if the gumma is diffuse. The caries is often complicated by necroszs, 
for a condition of sclerosis is frequently set up in the surrounding bone, and the vessels in the 
Haversian canals become compressed and the vitality of the bone is interfered with; hence we 
often find a central necrosing area surrounded by a zone of caries. Large carious sequestra may 
be thrown off after prolonged suppuration, leaving considerable areas of the dura mater exposed. 
A common result of syphilitic disease of the skull is the production of large hard masses of bone 
on its surface, which give it a tuberculated appearance; in other cases, the skull presents a curious 
worm-eaten appearance; this is due to the fact that the osteogenetic powers of the pericranium 
are small and the formation of bone on the surface slight. In hereditary syphilis, in addition 
to the formation of gummata, which are usually of the subperiosteal variety, atrophic or hyper- 
trophic changes may take place. In the atrophic cases the bone becomes abnormally thin, or 
even perforated. In the hypertrophic cases, a deposit of porous bone takes place around the 
anterior fontanelle; these deposits are separated by the coronal and sagittal sutures and are 
known as Parrot's nodes; such a skull has received the name of natiform, from its fancied resem- 
blance to the buttocks. 
Hypertrophic changes also occur in the skull in ostitis deformans, acromegaly, leontiasis ossea, 
and in rickets. In rickety cases the skull becomes enlarged from the formation of periosteal 
outgrowths of soft tissue on the outer side of the skull. These deposits are very rich in blood- 
vessels, and occur between the ridges of the cranial bones and their centres of ossification, and 
are symmetrically arranged-often about the anterior fontanelle. The anterior fontanelle itself, 
instead of closing between the eighteenth and twenty-fourth months, as it normally does, remains 
patent in rickets until the third or even the sixth year. The general shape of the skull alters. 
The forehead is high and square, with prominent frontal eminences, and the head tends to be 
cubical or box-shaped; the enlargement of the head in rickets appears to be greater than it really 
is because the development of the facial bones is retarded. The base of the nose may appear 
sunken, from retarded development of the basis cranii. In marked cases of rickets these changes 
in the shape of the skull are permanent. In congenital hydrocephalus, or enlargement of the 
head due to the presence of excess of fluid in the ventricles of the brain, the cranium becomes 
globular, and its bones are thin and atrophic. They are often widely separated, the intervening 
fontanelles being much enlarged and partially filled in by numerous sutural bones; the atrophy 
of the cranium and brain may be so extreme that the light of a candle may be plainly visible 
through the whole thickness of the enlarged head. 
The tympanic antrum, situated in the mastoid portion of the temporal bone, is often the seat 
of suppuration as a result of infection extending backward from the tympanic cavity. In such 
cases, the surgeon has to open the antrum in order to give exit to the pus; this he does by intro- 
ducing his gouge in the suprameatal triangle (see p. 238). A line is drawn horizontally through 
the upper border of the bony external acoustic meatus, and a second vertically through the 
posterior wall of the meatus, and the gouge is applied in the angle where these two lines intersect; 
if the instrument be introduced at a higher level it will open the middle fossa of the skull. It 
is to be carried in the direction of the external acoustic meatus-inward, forward, and a little 
upward-for the distance of from 1 to 1.5 cm., when the antrum will be reached. In some cases 
of middle-ear trouble, septic thrombosis of the transverse sinus takes place, and it becomes neces- 
sary to work backward and explore the sinus. 
In connection with the bones of the face a common malformation is cleft palate. The cleft 
usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend 
through the soft palate; or the posterior part of the whole 
of the hard palate may be involved, the cleft extending as 
far forward as the incisive foramen. In the severest forms, 
the cleft extends through the alveolus and passes between 
the incisive or premaxillary bone and the rest of the max- 
illa; that is to say, between the lateral incisor and canine 
teeth. In some instances, the cleft runs between the central 
and lateral incisor teeth; and this has induced some 
anatomists to believe that the premaxillary bone is devel- 
oped from two centres (Fig. 341) and not from one, as was 
stated on p. 262. The medial segment, bearing a central 
incisor, is called an endognathion; the lateral segment, bear- 
ing the lateral incisor, is called a mesognathion. The cleft 
may affect one or both sides; if the latter, the central part is frequently displaced forward and re- 
mains united to the septum of the nose, the deficiency in the alveolus being complicated with a cleft 
in the lip (hare-lip). On examining a cleft palate in which the alveolus is not implicated, the cleft 
will generally appear to be in the median line, but occasionally is unilateral and in some cases bilat- 
eral. To understand this it must be bornein mind that three processes are concerned in the formation 
of the palate-the palatine processes of the two maxillae, which grow in horizontally and unite 
in the middle line, and the ethmovomerine process, which grows downward from the base of 
the skull and frontonasal process to unite with the palatine processes in the middle line. In 
Endognaihion 
M esognathion 
Exognathion 
Fig. 341.--The premaxilla and its sutures. 
(After Albrecht.) 300 
OSTEOLOGY 
those cases where the palatine processes fail to unite with each other and with the medial process, 
the cleft of the palate is median; where one palatine process unites with the medial septum, the 
other failing to do so, the cleft in the palate is unilateral. In some cases where the palatine pro- 
cesses fail to meet in the middle, the ethmovomerine process grows downward between them and 
thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard 
palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as 
a rule, the union of the various processes progresses from before backward, and therefore the 
posterior part of the palate is more frequently defective than the anterior. 
The bones of the face are sometimes fractured as the result of direct violence. Those most 
commonly broken are the nasal bones and the mandible; the latter is by far the most frequently 
fractured of all the facial bones. Fracture of the nasal bone is for the most part transverse, and 
takes place about 1.25 cm. from the free margin. The broken portion may be displaced back- 
ward or more generally to one side by the force which produced the lesion. The zygomatic bone 
is probably never broken alone--that is to say, without fracture of some of the other bones of 
the face. The zygomatic arch is occasionally fractured, and when this occurs as a result of direct 
violence the fragments may be displaced inward. Fractures of the maxilla may vary much in 
degree, from the chipping off of a portion of the alveolar arch, to an extensive comminution of 
the whole bone from severe violence, as the kick of a horse. The most common situation for a 
fracture of the mandible is in the neighborhood of the canine tooth, as at this spot the bone is 
weakened by the deep socket for the root of this tooth; it is next most frequently fractured at 
the angle; then at the symphysis; and finally the neck of the condyle or the coronoid process 
may be broken. Occasionally a double fracture may occur, one in either half of the bone. The 
fractures are usually compound, from laceration of the mucous membrane covering the gums. 
Displacement readily occurs and is difficult to rectify; it results in inequality in the line of the 
teeth and is commonly due to the muscles attached in the region of the symphysis dragging this 
portion downward. 
The maxilla and the mandible are frequently the seat of necrosis; but the disease more often 
affects the lower than the upper jaw. It may be the result of periostitis from tooth irritation, 
injury, or the action of some specific poison, as syphilis, or from salivation by mercury; it some- 
times occurs in children after attacks of the exanthematous fevers, and a special form occurs 
from the action of the fumes of phosphorus in persons engaged in the manufacture of matches. 
In the vast majority of cases, however, it is of dental origin. 
Tumors originate in the jaw bones not infrequently, and may be either innocent or malignant. 
In the maxilla, cysts may occur in the antrum; or in either jaw in connection with the teeth; 
those connected with the roots of fully developed teeth are known as dental cysts; those con- 
nected with unerupted teeth, dentigerous cysts. Malignant tumors show a marked degree of 
malignancy when occurring in the maxilla. The results of distention of the walls of the maxillary 
antrum are given on page 260. 
The maxilla sometimes requires removal for tumors or other conditions. In order to remove 
it, the patient should be placed in the recumbent position, in a good light, with the head and 
shoulders just raised. The central incisor tooth on the affected side is then extracted. One 
incision is begun just below the medial canthus of the eye and passes along the side of the nose, 
around the ala, and down the middle line of the upper lip into the paouth. A second incision is 
made from the commencement of the first, along the lower border of the orbit as far as the promi- 
nence of the zygomatic bone. The flap thus formed is reflected, so as to expose the bone. The 
periosteum attached along the lower margin of the orbit is now to be incised, and with the handle 
of the scalpel the periosteum covering the floor of the orbit is raised from the bone; for in all 
cases it is essential that this fibrous layer should not be removed. The mouth is now widely 
opened with a gag, and the mucous membrane covering the hard palate incised down to the 
bone in the middle line, and the soft palate separated from the hard. The surgeon having first 
separated the ala of the nose from its bony attachment, proceeds to divide the connections of 
the bone with the other bones of the face. They are (1) the junction with the zygomatic bone, 
the line of section being carried into the inferior orbital fissure; (2) the frontal process of the 
maxilla; a small portion of its upper extremity, connected with the nasal bone in front, the lacrimal 
bone behind, and the frontal bone above, being left; (3) the connection with the opposite maxilla 
and with the palatine bone in the roof of the mouth. The bone is now firmly grasped with lion- 
forceps; and by means of a rocking movement upward and downward, the remaining attach- 
ments of the orbital plate with the ethmoid, and of the back of the bone with the palatine, are 
broken through. Occasionally, in removing the maxilla, it will be found that the orbital plate 
can be saved, and this should always be done if possible. A horizontal saw-cut should then be 
made just below the infraorbital foramen. 
THE EXTREMITIES. 
The extremities, or limbs, are long, jointed appendages, each of which is con- 
nected to the trunk by one end, and is free in the rest of its extent. They are THE CLAVICLE 
301 
four in number: an upper pair, connected with the thorax and subservient mainly 
to prehension; and a lower pair, connected with the vetrebral column and intended 
for support and locomotion. Both pairs are constructed after one common type, 
but certain differences are observed between the upper and lower, dependent 
on the peculiar offices they have to perform. 
The bones by which the upper and lower limbs are attached to the trunk con- 
stitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle 
of the superior extremity is formed by the scapulae and clavicles, and is imperfect 
in front and behind. In front, however, it is completed by the upper end of the 
sternum, with which the medial ends of the clavicles articulate. Behind, it is 
widely imperfect, the scapulae being connected to the trunk by muscles only. 
The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, 
which articulate with each other in front, at the symphysis pubis. It is imperfect 
behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, 
with the sacrum, is a complete ring, massive and comparatively rigid, in marked 
contrast to the lightness and mobility of the shoulder girdle. 
THE BONES OF THE UPPER EXTREMITY (OSSA EXTREMITATIS SUPERIORIS). 
The Clavicle (Clavicula; Collar Bone). 
The clavicle (Figs. 342, 343) forms the anterior portion of the shoulder girdle. 
It is a long bone, curved somewhat like the italic letter/, and placed nearly horizon- 
tally at the upper and anterior part of the thorax, immediately above the first 
rib. It articulates medially with the manubrium sterni, and laterally with the 
acromion of the scapula.1 It presents a double curvature, the convexity being 
directed forward at the sternal end, and the concavity at the scapular end. Its 
lateral third is flattened from above downward, while its medial two-thirds is of 
a rounded or prismatic form. 
Sternal extremity 
Acromial extremity 
Fig. 342.-Left clavicle. Superior surface. 
Lateral Third.-The lateral third has two surfaces, an upper and a lower; and 
two borders, an anterior and a posterior. 
Surface.-The upper surface is flat, rough, and marked by impressions for the 
attachments of the Deltoideus in front, and the Trapezius behind; between these 
impressions a small portion of the bone is subcutaneous. The under surface is 
flat. At its posterior border, near the point where the prismatic joins with the 
flattened portion, is a rough eminence, the coracoid tuberosity (conoid tubercle); 
this, in the natural position of the bone, surmounts the coracoid process of the 
1 The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly 
absent in those animals whose fore-limbs are used only for progression, but is present for the most part in animals 
whose anterior extremities are clawed and used for prehension, though in some of them-as, for instance, in a large 
number of the carnivora-it is merely a rudimentary bone suspended among the muscles, and not articulating with 
either the scapula or sternum. 302 
OSTEOLOGY 
scapula, and gives attachment to the conoid ligament. From this tuberosity an 
oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and 
afford attachment to the trapezoid ligament. 
Borders.-The anterior border is concave, thin, and rough, and gives attachment 
to the Deltoideus; at its medial part there is frequently a tubercle, the deltoid 
tubercle. The posterior border is convex, rough, thicker than the anterior, and gives 
attachment to the Trapezius. 
Medial Two-thirds.-The medial two-thirds constitute the prismatic portion 
of the bone, which is curved so as to be convex in front, concave behind, and is 
marked by three borders, separating three surfaces. 
Borders.-The anterior border is continuous with the anterior margin of the flat 
portion. Its lateral part is smooth, and corresponds to the interval between the 
attachments of the Pectoralis major and Deltoideus; its medial part forms the 
lower boundary of an elliptical surface for the attachment of the clavicular portion 
of the Pectoralis major, and approaches the posterior border of the bone. The 
superior border is continuous with the posterior margin of the flat portion, and 
separates the anterior from the posterior surface. Smooth and rounded laterally, 
it becomes rough toward the medial third for the attachment of the Sternocleido- 
mastoideus, and ends at the upper angle of the sternal extremity. The posterior 
or subclavian border separates the posterior from the inferior surface, and extends 
from the coracoid tuberosity to the costal tuberosity; it forms the posterior boun- 
dary of the groove for the Subclavius, and gives attachment to a layer of cervical 
fascia which envelops the Omohyoideus. 
Articular capsule 
Articular capsule 
Fig. 343.-Left clavicle. Inferior surface. 
Surfaces.-The anterior surface is included between the superior and anterior 
borders. Its lateral part looks upward, and is continuous with the superior sur- 
face of the flattened portion; it is smooth, convex, and nearly subcutaneous, being 
covered only by the Platysma. Medially it is divided by a narrow subcutaneous 
area into two parts: a lower, elliptical in form, and directed forward, for the 
attachment of the Pectoralis major; and an upper for the attachment of the 
Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks 
backward toward the root of the neck. It is limited, above, by the superior 
border; belowq by the subclavian border; medially, by the margin of the sternal 
extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, 
and is in relation, by its lower part, with the transverse scapular vessels. This 
surface, at the junction of the curves of the bone, is also in relation with the brachial 
plexus of nerves and the subclavian vessels. It gives attachment, near the sternal 
extremity, to part of the Sternohyoideus; and presents, near the middle, an oblique 
foramen directed lateralward, which transmits the chief nutrient artery of the 
bone. Sometimes there are two foramina on the posterior surface, or one on the 
posterior and another on the inferior surface. The inferior or subclavian surface is THE CLAVICLE 
303 
bounded, in front, by the anterior border; behind, by the subclavian border. 
It is narrowed medially, but gradually increases in width laterally, and is contin- 
uous with the under surface of the flat portion. On its medial part is a broad 
rough surface, the costal tuberosity (rhomboid impression), rather more than 2 cm. 
in length, for the attachment of the costoclavicular ligament. The rest of this 
surface is occupied by a groove, which gives attachment to the Subclavius; the 
coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins 
of the groove. Not infrequently this groove is subdivided longitudinally by a 
line which gives attachment to the intermuscular septum of the Subclavius. 
The Sternal Extremity (extremitas sternalis; internal extremity).--The sternal 
extremity of the clavicle is triangular in form, directed medialward, and a little 
downward and forward; it presents an articular facet, concave from before back- 
ward, convex from above downward, which articulates with the manubrium sterni 
through the intervention of an articular disk. The lower part of the facet is con- 
tinued on to the inferior surface of the bone as a small semi-oval area for articula- 
tion with the cartilage of the first rib. The circumference of the articular surface 
is rough, for the attachment of numerous ligaments; the upper angle gives attach- 
ment to the articular disk. 
The Acromial Extremity (extremitas acromialis; outer extremity).-The acromial 
extremity presents a small, flattened, oval surface directed obliquely downward, 
for articulation with the acromion of the scapula. The circumference of the 
articular facet is rough, especially above, for the attachment of the acromio- 
clavicular ligaments. 
In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the 
male. In those persons who perform considerable manual labor it becomes thicker and more 
curved, and its ridges for muscular attachment are prominently marked. 
Structure.-The clavicle consists of cancellous tissue, enveloped by a compact layer, which 
is much thicker in the intermediate part than at the extremities of the bone. 
Ossification.-The clavicle begins to ossify before any other bone in the body; it is ossified 
from three centres-viz., two primary centres, a medial and a lateral, for the body,1 which appear 
during the fifth or sixth week of fetal life; and a secondary centre for the sternal end, which 
appears about the eighteenth or twentieth year, and unites with the rest of the bone about the 
twenty-fifth year. 
Applied Anatomy.-The clavicle is very frequently fractured, since it is much exposed to vio- 
lence, and is the only bony connection between the upper limb and the trunk, acting as a buttress 
to keep the point of the shoulder away from the thorax. It is, moreover, slender, and is very 
superficial. It may be broken by direct or indirect violence. The most common cause is, however, 
indirect violence, as the result of force applied to the hand or shoulder, and the bone then gives 
way at the junction of its lateral with its intermediate third, that is to say, at the junction of 
the two curves, for this is its weakest part. The fracture is generally oblique, and the displace- 
ment of the lateral fragment is downward, forward, and medialward. The deformity is mainly 
due to the weight of the arm acting upon the fragment when the buttress-like action of the bone 
is gone, assisted by the muscles which pass from the thorax to the upper extremity. The medial 
fragment, as a rule, is little displaced. Beneath the bone the main vessels of the upper limb and 
the great nerve cords of the brachial plexus lie on the first rib and are liable to be wounded, espe- 
cially in fracture from direct violence, when the force of the blow drives the broken ends inward. 
Fortunately the subclavius intervenes between these structures and the clavicle, and often protects 
them from injury. 
The clavicle is occasionally the seat of sarcomatous tumors, rendering the operation of excision 
of the entire bone necessary. This is an operation of considerable difficulty and danger. It is 
best performed by exposing the bone freely, disarticulating at the acromial end, and turning it 
forward. The removal of the lateral part is comparatively easy, but resection of the medial part 
is fraught with difficulty, the main danger being the risk of wounding the great veins which are 
in relation with its deep surface. 
Great deformity of the clavicle may be met with in rickets, the natural curvatures of the bone 
being exaggerated until it takes on an S-shape, and "green-stick" fracture is not uncommonly 
seen associated therewith. 
1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. 304 
OSTEOLOGY 
The Scapula (Shoulder Blade). 
The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- 
gular bone, with two surfaces, three borders, and three angles. 
Surfaces.-The costal or ventral surface (Fig. 344) presents a broad concavity, 
the subscapular fossa. The medial two-thirds of the fossa are marked by several 
oblique ridges, which run lateralward and upward. The ridges give attachment 
Coracoacromial 
ligament 
Articular capsule 
Articular 
capsule. 
Fig. 344.-Left scapula. Costal surface. 
to the tendinous intersections, and the surfaces between them to the fleshy fibres, 
of the Subscapularis. The lateral third of the fossa is smooth and covered by the 
fibres of this muscle. The fossa is separated from the vertebral border by smooth 
triangular areas at the medial and inferior angles, and in the interval between 
these by a narrow ridge which is often deficient. These triangular areas and the THE SCAPULA 
305 
intervening ridge afford attachment to the Serratus anterior. At the upper part 
of the fossa is a transverse depression, where the bone appears to be bent on itself 
along a line at right angles to and passing through the centre of the glenoid cavity, 
forming a considerable angle, called the subscapular angle; this gives greater 
strength to the body of the bone by its arched form, while the summit of the 
arch serves to support the spine and acromion. 
Coracoliumeral 
ligament 
Coraco-acromial ligament 
Trapezoid ligament 
Conoid ligament 
Articular 
capsule 
Fig. 345.-Left scapula. Dorsal surface. 
The dorsal surface (Fig. 345) is arched from above downward, and is subdivided 
into two unequal parts by the spine; the portion above the spine is called the 
supraspinatous fossa, and that below it the infraspinatous fossa. 306 
OSTEOLOGY 
The supraspina tons fossa, the smaller of the two, is concave, smooth, and broader 
at its vertebral than at its humeral end; its medial two-thirds give origin to the 
Supraspinatus. 
The infraspinatous fossa is much larger than the preceding; toward its vertebral 
margin a shallow concavity is seen at its upper part; its centre presents a promi- 
nent convexity, while near the axillary border is a deep groove which runs from 
the upper toward the lower part. The medial two-thirds of the fossa give origin 
to the Infraspinatus; the lateral third is covered by this muscle. 
The dorsal surface is marked near the axillary border by an elevated ridge, 
which runs from the lower part of the glenoid cavity, downward and backward 
to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves 
for the attachment of a fibrous septum, which separates the Infraspinatus from 
the Teres major and Teres minor. The surface between the ridge and the axillary 
border is narrow in the upper two-thirds of its extent, and is crossed near its 
centre by a groove for the passage of the scapular circumflex vessels; it affords 
attachment to the Teres minor. Its lower third presents a broader, somewhat 
triangular surface, which gives origin to the Teres major, and over which the Latis- 
simus dorsi glides; frequently the latter muscle takes origin by a few fibres from 
this part. The broad and narrow portions above alluded to are separated by an 
oblique line, which runs from the axillary border, downward and backward, to 
meet the elevated ridge: to it is attached a fibrous septum which separates the 
Teres muscles from each other. 
The Spine (spina scapulae).--The spine is a prominent plate of bone, which 
crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its 
upper part, and separates the supra- from the infraspinatous fossa. It begins 
at the vertical border by a smooth, triangular area over which the tendon of inser- 
tion of the lower part of the Trapezius glides, and, gradually becoming more ele- 
vated, ends in the acromion, which overhangs the shoulder-joint. The spine is 
triangular, and flattened from above downward, its apex being directed toward 
the vertebral border. It presents two surfaces and three borders. Its superior 
surface is concave; it assists in forming the supraspinatous fossa, and gives origin 
to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous 
fossa, gives origin to a portion of the Infraspinatus, and presents near its centre 
the orifice of a nutrient canal. Of the three borders, the anterior is attached to the 
dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents 
two lips and an intervening rough interval. The Trapezius is attached to the supe- 
rior lip, and a rough tubercle is generally seen on that portion of the spine which 
receives the tendon of insertion of the lower part of this muscle. The Deltoideus 
is attached to the whole length of the inferior lip. The interval between the lips 
is subcutaneous and partly covered by the tendinous fibres of these muscles. The 
lateral border, or base, the shortest of the three, is slightly concave; its edge, thick 
and round, is continuous above with the under surface of the acromion, below 
with the neck of the scapula. It forms the medial boundary of the great scapular 
notch, which serves to connect the supra- and infraspinatous fossae. 
The Acromion.-The acromion forms the summit of the shoulder, and is a large, 
somewhat triangular or oblong process, flattened from behind forward, projecting 
at first lateralward, and then curving forward and upward, so as to overhang the 
glenoid cavity. Its superior surface, directed upward, backward, and lateralward, 
is convex, rough, and gives attachment to some fibres of the Deltoideus, and in the 
rest of its extent is subcutaneous. Its inferior surface is smooth and concave. 
Its lateral border is thick and irregular, and presents three or four tubercles for the 
tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, 
is concave, gives attachment to a portion of the Trapezius, and presents about 
its centre a small, oval surface for articulation with the acromial end of the clavicle. THE SCAPULA 
307 
Its apex, which corresponds to the point of meeting of these two borders in front, 
is thin, and has attached to it the coracoacromial ligament. 
Borders.-Of the three borders of the scapnla, the superior is the shortest and 
thinnest; it is concave, and extends from the medial angle to the base of the cora- 
coid process. At its lateral part is a deep, semicircular notch, the scapular notch, 
formed partly by the base of the coracoid process. This notch is converted into 
a foramen by the superior transverse ligament, and serves for the passage of the 
suprascapular nerve; sometimes the ligament is ossified. The adjacent part of 
the superior border affords attachment to the Omohyoideus. The axillary border 
is the thickest of the three. It begins above at the lower margin of the glenoid 
cavity, and inclines obliquely downward and backward to the inferior angle. 
Immediately below the glenoid cavity is a rough impression, the infraglenoid 
tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Tri- 
ceps brachii; in front of this is a longitudinal groove, which extends as far as the 
lower third of this border, and affords origin to part of the Subscapularis. The 
inferior third is thin and sharp, and serves for the attachment of a few fibres of 
the Teres major behind, and of the Subscapularis in front. The vertebral border 
is the longest of the three, and extends from the medial to the inferior angle. It 
is arched, intermediate in thickness between the superior and the axillary borders, 
and the portion of it above the spine forms an obtuse angle with the part below. 
This border presents an anterior and a posterior lip, and an intermediate narrow 
area. The anterior lip affords attachment to the Serratus anterior; the posterior 
lip, to the Supraspinatus above the spine, the Infraspinatus below; the area 
between the two lips, to the Levator scapulae above the triangular surface at the 
commencement of the spine, to the Rhomboideus minor on the edge of that surface, 
and to the Rhomboideus major below it; this last is attached by means of a fibrous 
arch, connected above to the lower part of the triangular surface at the base of 
the spine, and below to the lower part of the border. 
Angles.-Of the three angles, the medial, formed by the junction of the superior 
and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, 
and gives attachment to a few fibres of the Levator scapulae. The inferior angle, 
thick and rough, is formed by the union of the vertebral and axillary borders; 
its dorsal surface affords attachment to the Teres major and frequently to a fewT 
fibres of the Latissimus dorsi. The lateral angle is the thickest part of the bone, 
and is sometimes called the head of the scapula. On it is a shallow pyriform, 
articular surface, the glenoid cavity, which is directed lateralward and forward 
and articulates with the head of the humerus; it is broader below than above 
and its vertical diameter is the longest. The surface is covered with cartilage 
in the recent state; and its margins, slightly raised, give attachment to a fibro- 
cartilaginous structure, the glenoidal labrum, which deepens the cavity. At its 
apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the 
Biceps brachii is attached. The neck of the scapula is the slightly constricted por- 
tion which surrounds the head; it is more distinct below and behind than above 
and in front. 
The Coracoid Process (processus coracoideus).-The coracoid process is a thick 
curved process attached by a broad base to the upper part of the neck of the scapula; 
it runs at first upwrard and medialward; then, becoming smaller, it changes its 
direction, and projects forward and lateralward. The ascending portion, flattened 
from before backward, presents in front a smooth concave surface, across which 
the Subscapularis passes. The horizontal portion is flattened from above (Town- 
ward; its upper surface is convex and irregular, and gives attachment to the Pec- 
toralis minor; its under surface is smooth; its medial and lateral borders are rough; 
the former gives attachment to the Pectoralis minor and the latter to the coraco- 
acromial ligament; the apex is embraced by the conjoined tendon of origin of the 308 
OSTEOLOGY 
Coracobrachialis and short head of the Biceps brachii and gives attachment to 
the coracoclavicular fascia. On the medial part of the root of the coracoid process 
is a rough impression for the attachment of the conoid ligament; and running 
from it obliquely forward and lateralward, on to the upper surface of the horizontal 
portion, is an elevated ridge for the attachment of the trapezoid ligament. 
Structure.-The head, processes, and the thickened parts of the bone, contain cancellous 
tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous 
fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin 
as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent 
muscles are separated only by fibrous tissue. 
Ossification (Fig. 346).--The scapula is ossified from seven or more centres: one for the body, 
two for the coracoid process, two for the acromion, one for the vertebral border, and one for the 
inferior angle. 
Fig. 346.-Plan of ossification of the scapula. From seven centres. 
Ossification of the body begins about the second month of fetal life, by the formation of an 
irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends 
so as to form the chief part of the bone, the spine growing up from its dorsal surface about the 
third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid 
process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the 
fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid 
process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between 
the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succes- 
sion, and usually in the following order; first, in the root of the coracoid process, in the form of a 
broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous 
part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral 
border. The base of the acromion is formed by an extension from the spine; the two separate 
nuclei of the acromion unite, and then join with the extension from the spine. The upper third 
of^the glenoid cavity is ossified from a separate centre (subcoracoid), which makes its appear- 
ance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. 
Further, an epiphysial plate appears for the lower part of the glenoid cavity, while the tip of the THE HUMERUS 
309 
coracoid process frequently presents a separate nucleus. These various epiphyses are joined 
to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine 
sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; 
in some cases of supposed fracture of the acromion with ligamentous union, it is probable that 
the detached segment was never united to the rest of the bone. 
Articulations.-The scapula articulates with the humerus and clavicle. 
Applied Anatomy.-Fractures of the body of the scapula are rare, owing to the mobility of the 
bone, the thick layers of muscles by which it is encased, and the elasticity of the ribs on which 
it rests. Fracture of the neck is also uncommon. The most frequent course of a fracture is from 
the scapular notch to the infraglenoid tuberosity, and it derives its principal interest from its 
simulation of a subglenoid dislocation of the humerus. The diagnosis can be made by noting 
the alteration in the position of the coracoid process. The acromion is more frequently broken 
than any other part of the bone, and fibrous union is very liable to follow. 
The presence of "winged scapulae" (scapulae alatae) described in thin persons of feeble muscular 
development in whom the lower angles of the blade bones project unduly, is due partly to abnormal 
roundness of the thoracic wall ("barrel-shaped chest," p. 226), and partly to weakness and 
flaccidity of the Latissimus dorsi and Serratus anterior. The shoulders are held low in these 
subjects, and the clavicles slope downward and forward, carrying with them the scapulse, which 
fit ill to the posterior wall of the chest and so tend to project from it. 
Tumors of various kinds grow from the scapula. Of the innocent form probably the osteomata 
are the most common. When an osteoma grows from the venter of the scapula, as it sometimes 
does, it is of the compact variety, such as usually grows from membrane-formed bones, as the 
bones of the skull. Sarcomatous tumors sometimes grow from the scapula, and may necessitate 
removal of the bone, with or without amputation of the upper limb. The bone may be excised 
by a T-shaped incision, and the flaps being reflected, the removal is commenced from the vertebral 
border, so that the subscapular vessels which he along the axillary border are among the last 
structures divided, and can be readily secured. 
The Humerus (Arm Bone). 
The humerus (Figs. 347, 348) is the longest and largest bone of the upper 
extremity; it is divisible into a body and two extremities. 
Upper Extremity.-The upper extremity consists of a large rounded head joined 
to the body by a constricted portion called the neck, and two eminences, the greater 
and lesser tubercles. 
The Head (caput humeri').-The head, nearly hemispherical in form,1 is directed 
upward, medialward, and a little backward, and articulates with the glenoid cavity 
of the scapula. The circumference of its articular surface is slightly constricted, 
and is termed the anatomical neck, in contradistinction to a constriction below the 
tubercles called the surgical neck which is frequently the seat of fracture. Fracture 
of the anatomical neck rarely occurs. 
The Anatomical Neck (collum anatomicum) is obliquely directed, forming an 
obtuse angle with the body. It is best marked in the lower half of its circum- 
ference; in the upper half it is represented by a narrow groove separating the head 
from the tubercles. It affords attachment to the articular capsule of the shoulder- 
joint, and is perforated by numerous vascular foramina. 
The Greater Tubercle (tuberculum majus; greater tuberosity).-The greater 
tubercle is situated lateral to the head and lesser tubercle. Its upper surface is 
rounded and marked by three flat impressions: the highest of these gives insertion 
to the Supraspinatus; the middle to the Infraspinatus; the lowest one, and the 
body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral 
surface of the greater tubercle is convex, rough, and continuous with the lateral 
surface of the body. 
The Lesser Tubercle (tuberculum minus; lesser tuberosity).-The lesser tubercle, 
although smaller, is more prominent than the greater: it is situated in front, and 
1 Though the head is nearly hemispherical in form, its margin, as Humphry has shown, is by no means a true circle. 
Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and back- 
ward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface in this 
direction-that is to say, obliquely upward, lateralward, and forward. 310 
OSTEOLOGY 
Articular capsule 
Surgical Neck 
Bra ch ioradialis 
Extensor carpi radialis 
long us 
Articular capsule 
Common origin of 
Extensor carpi rad. brev. 
,, digitorum communis 
,, digiti quinti prop. 
,, carpi ulnaris 
Supinator 
Common origin of 
Flexor carpi radialis 
Palmar is longus 
Flexor digitonim sublimis 
Flexor carpi ulnaris 
Fig. 347.-Left huinerus. Anterior view. THE HUMERUS 
311 
is directed medialward and forward. Above 
and in front it presents an impression for the 
insertion of the tendon of the Subscapularis. 
The tubercles are separated from each other 
by a deep groove, the intertubercular groove 
(bicipital groove), which lodges the long tendon 
of the Biceps brachii and transmits a branch 
of the anterior humeral circumflex artery to 
the shoulder-joint. It runs obliquely down- 
ward, and ends near the junction of the upper 
with the middle third of the bone. In the 
recent state its upper part is covered with a 
thin layer of cartilage, lined by a prolongation 
of the synovial membrane of the shoulder- 
joint; its lower portion gives insertion to the 
tendon of the Latissimus dorsi. It is deep 
and narrow above, and becomes shallow and 
a little broader as it descends. Its lips are 
called, respectively, the crests of the greater 
and lesser tubercles (bicipital ridges'), and form 
the upper parts of the anterior and medial 
borders of the body of the bone. 
The Body or Shaft (corpus humeri). - The 
body is almost cylindrical in the upper half of 
its extent, prismatic and flattened below, and 
has three borders and three surfaces. 
Borders.-The anterior border runs from the 
front of the greater tubercle above to the coro- 
noid fossa below, separating the antero-medial 
from the antero-lateral surface. Its upper part 
is a prominent ridge, the crest of the greater 
tubercle; it serves for the insertion of the tendon 
of the Pectoralis major. About its centre it 
forms the anterior boundary of the deltoid 
tuberosity; below, it is smooth and rounded, 
affording attachment to the Brachialis. 
The lateral border runs from the back part of 
the greater tubercle to the lateral epicondyle, 
and separates the antero-lateral from the pos- 
terior surface. Its upper half is rounded and 
indistinctly marked, serving for the attachment 
of the lower part of the insertion of the Teres 
minor, and below this giving origin to the lateral 
head of the Triceps brachii; its centre is tra- 
versed by a broad but shallow oblique depres- 
sion, the radial sulcus (musculospiral groove). 
Its lower part forms a prominent, rough margin, 
a little curved from behind forward, the lateral 
supracondylar ridge, which presents an anterior 
lip for the origin of the Brachioradialis above, 
and Extensor carpi radialis longus below, a 
posterior lip for the Triceps brachii, and an 
intermediate ridge for the attachment of the 
lateral intermuscular septum. 
Articular 
capsule 
Articular 
capsule 
Fig. 348.-Left humerus. Posterior view. 312 
OSTEOLOGY 
The medial border extends from the lesser tubercle to the medial epicondyle. 
Its upper third consists of a prominent ridge, the crest of the lesser tubercle, which 
gives insertion to the tendon of the Teres major. About its centre is a slight 
impression for the insertion of the Coracobrachialis, and just below this is the 
entrance of the nutrient canal, directed downward; sometimes there is a second 
nutrient canal at the commencement of the radial sulcus. The inferior third 
of this border is raised into a slight ridge, the medial supracondylar ridge, which 
becomes very prominent below; it presents an anterior lip for the origins of the 
Brachialis and Pronator teres, a posterior lip for the medial head of the Triceps 
brachii, and an intermediate ridge for the attachment of the medial intermuscular 
septum. 
Surfaces.-The antero-lateral surface is directed lateralward above, where it is 
smooth, rounded, and covered by the Deltoideus; forward and lateralward below, 
where it is slightly concave from above downward, and gives origin to part of 
the Brachialis. About the middle of this surface is a rough, triangular elevation, 
the deltoid tuberosity for the insertion of the Deltoideus; below this is the radial 
sulcus, directed obliquely from behind, forward, and downward, and transmitting 
the radial nerve and profunda artery. 
The antero-medial surface, less extensive than the antero-lateral, is directed 
medialward above, forward and medialward below; its upper part is narrow, and 
forms the floor of the intertubercular groove which gives insertion to the tendon of 
the Latissimus dorsi; its middle part is slightly rough for the attachment of some 
of the fibres of the tendon of insertion of the Coracobrachialis; its lower part 
is smooth, concave from above downward, and gives origin to the Brachialis.1 
The posterior surface appears somewhat twisted, so that its upper part is directed 
a little medialward, its lower part backward and a little lateral ward. Nearly 
the whole of this surface is covered by the lateral and medial heads of the Triceps 
brachii, the former arising above, the latter below the radial sulcus. 
The Lower Extremity.-The lower extremity is flattened from before backward, 
and curved slightly forward; it ends below in a broad, articular surface, which is 
divided into two parts by a slight ridge. Projecting on either side are the lateral 
and medial epicondyles. The articular surface extends a little lower than the 
epicondyles, and is curved slightly forward; its medial extremity occupies a lower 
level than the lateral. The lateral portion of this surface consists of a smooth, 
rounded eminence, named the capitulum of the humerus; it articulates with the cup- 
shaped depression on the head of the radius, and is limited to the front and lower 
part of the bone. On the medial side of this eminence is a shallow groove, in which 
is received the medial margin of the head of the radius. Above the front part 
of the capitulum is a slight depression, the radial fossa, which receives the anterior 
border of the head of the radius, when the forearm is flexed. The medial portion 
of the articular surface is named the trochlea, and presents a deep depression be- 
tween two well-marked borders; it is convex from before backward, concave from 
side to side, and occupies the anterior, lower, and posterior parts of the extremity. 
The lateral border separates it from the groove which articulates with the margin 
of the head of the radius. The medial border is thicker, of greater length, and 
consequently more prominent, than the lateral. The grooved portion of the artic- 
ular surface fits accurately within the semilunar notch of the ulna; it is broader and 
deeper on the posterior than on the anterior aspect of the bone, and is inclined 
1 A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infre- 
quently found projecting from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondyle. 
It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial 
epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by 
this fibrous band the median nerve and brachial artery pass, when these structures deviate from their usual course. 
Sometimes the nerve alone is transmitted through it, or the nerve may be accompanied by the ulnar artery, in cases 
of high division of the brachial. A well-marked groove is usually found behind the process, in which the nerve and 
artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably 
serves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. THE HUMERUS 
313 
obliquely downward and forward toward the medial side. Above the front part 
of the trochlea is a small depression, the coronoid fossa, which receives the coronoid 
process of the ulna during flexion of the forearm. Above the back part of the troch- 
lea is a deep triangular depression, the olecranon fossa, in which the summit of the 
olecranon is received in extension of the forearm. These fossae are separated from 
one another by a thin, transparent lamina of bone, which is sometimes perforated 
by a supratrochlear foramen; they are lined in the recent state by the synovial 
membrane of the elbow-joint, and their margins afford attachment to the anterior 
and posterior ligaments of this articulation. The lateral epicondyle is a small, 
tuberculated eminence, curved a little forward, and giving attachment to the radial 
collateral ligament of the elbow-joint, and to a tendon common to the origin of 
the Supinator and some of the Extensor muscles. The medial epicondyle, larger 
and more prominent than the lateral, is directed a little backward; it gives attach- 
ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, 
and to a common tendon of origin of some of the Flexor muscles of the forearm; 
the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles 
are continuous above with the supracondylar ridges. 
Structure.-The extremities consist of cancellous tissue, covered with a thin, compact layer 
(Fig. 349); the body is composed of a cylinder of compact tissue, thicker at the centre than toward 
the extremities, and contains a large medullary canal which extends along its whole length. 
Ossification (Figs. 350, 351).-The humerus is ossi- 
fied from eight centres, one for each of the following 
parts: the body, the head, the greater tubercle, the 
lesser tubercle, the capitulum, the trochlea, and one 
for each epicondyle. The centre for the body appears 
near the middle of the bone in the eighth week of fetal 
life, and soon extends toward the extremities. At birth 
the humerus is ossified in nearly its whole length, only 
the extremities remaining cartilaginous. During the 
first year, sometimes before birth, ossification commences 
in the head of the bone, and during the third year the 
centre for the greater tubercle, and during the fifth that 
for the lesser tubercle, make their appearance. By the 
sixth year the centres for the head and tubercles have 
joined, so as to form a single large epiphysis, which fuses 
with the body about the twentieth year. The lower end 
of the humerus is ossified as follows. At the end of 
the second year ossification begins in the capitulum, 
and extends medialward, to form the chief part of the 
articular end of the bone; the centre for the medial part 
of the trochlea appears about the age of twelve. Ossifi- 
cation begins in the medial epicondyle about the fifth 
year, and in the lateral about the thirteenth or four- 
teenth year. About the sixteenth or seventeenth year, 
the lateral epicondyle and both portions of the articu- 
lating surface, having already joined, unite with the 
body, and at the eighteenth year the medial epicon- 
dyle becomes joined to it. 
Articulations.-The humerus articulates with the scapula, ulna, and radius. 
Applied Anatomy.-There are several points of surgical interest connected with the ossification 
of the humerus. The upper end, though the first to ossify, is the last to join the body, and the 
length of the bone is mainly due to growth from the upper epiphysial plate. Hence, in cases of 
amputation of the arm in young subjects, the humerus continues to grow considerably, and the 
end of the bone which immediately after the operation was covered with a thick cushion of soft 
tissue begins to project, thinning the soft parts and rendering the stump conical. This may 
necessitate the removal of about 5 pm. of the bone, and even after this operation a recurrence 
of the conical stump may take place. The region of the upper epiphysis, moreover, is the common 
site for the growth of tumors, both innocent and malignant 
Fractures of the humerus present several points of surgical interest. The bone may be broken 
by direct or indirect violence, like the other long bones, but, in addition to this, it is probably 
more frequently fractured by muscular action than any other bone of this class. It is usually 
Epiphysial line 
Fig. 349.-Longitudinal section of head of 
left humerus. 314 
OSTEOLOGY 
the body, just below the insertion of the Deltoideus, which is thus broken, and the accident has 
been known to happen from throwing a stone. Fractures of the upper end may take place either 
through the anatomical or surgical neck, or a separation of the greater tubercle may occur. Frac- 
ture of the anatomical neck is a very rare accident; in fact, it is doubted by some whether it ever 
occurs. Fracture of the surgical neck of the bone is not uncommon, and impaction may occur; 
on the other hand, the upper end of the lower fragment may be displaced into the axilla and may 
damage the vessels or nerves. The fracture somewhat closely simulates dislocation of the shoulder- 
joint, but can be distinguished by the fact that the head of the bone remains in its normal posi- 
tion and the great tubercle still forms the most prominent point of the shoulder. Separation 
of the upper epiphysis sometimes occurs in the young subject, and is marked by a characteristic 
deformity, consisting in the presence of an abrupt projection at the front of the joint some short 
distance below the coracoid process, caused by the upper end of the diaphysis. In fractures of 
Epiphyses of head and 
tubercles blend at fifth 
year, and unite with 
body at twentieth 
year 
Unites with body' 
at eighteenth year 
Fig. 350.-Plan of ossification of the humerus. 
Fig. 351.-Epiphysial lines of humerus in a young 
adult. Anterior aspect. The lines of attachment of 
the articular capsules are in blue. 
the body of the humerus the lesion may take place at any point, but appears to be more common 
in the lower thap the upper part of the bone. The points of interest in connection with these 
fractures are: (1) that the radial nerve may be injured as it lies in the groove on the bone, or 
may become involved in the callus which is subsequently thrown out; and (2) the frequency 
of non-union, which is believed to be more common in the humerus than in any other bone. 
An important distinction to make in fractures of the lower end is between those that involve the 
elbow-joint and those which do not; the former are always serious, as they may lead to impair- 
ment of the utility of the limb; they include the T-shaped fracture and oblique fractures which 
involve the articular surface. Those which do not involve the joint are the transverse fracture 
above the epicondyles, and the so-called epitrochlear fracture, where the tip of the medial epi- 
condyle is broken off, generally from direct violence. 
The Ulna (Elbow Bone). 
The ulna (Figs. 353, 354) is a long bone, prismatic in form, placed at the medial 
side of the forearm, parallel with the radius. It is divisible into a body and 
two extremities. Its upper extremity, of great thickness and strength, forms THE ULNA 
315 
a large part of the elbow-joint; the bone diminishes in size from above downward, 
its lower extremity being very small, and excluded from the wrist-joint by the 
interposition of an articular disk. 
The Upper Extremity (proximal extremity} (Fig. 352).-The upper extremity 
presents two curved processes, the olecranon and the coronoid process; and two 
concave, articular cavities, the semilunar and radial notches. 
The Olecranon (olecranon process}.-The olecranon is a large, thick, curved 
eminence, situated at the upper and back part of the ulna. It is bent forward at the 
summit so as to present a prominent lip which is received into the olecranon fossa 
of the humerus in extension of the forearm. Its base is contracted where it joins the 
body and the narrowest part of the upper end of the ulna. Its posterior surface, 
directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. 
Its superior surface is of quadrilateral form, marked behind by a rough impression for 
the insertion of the Triceps brachii; and in front, near the margin, by a slight trans- 
verse groove for the attachment of part of the posterior ligament of the elbow-joint. 
Its anterior surface is smooth, concave, and 
forms the upper part of the semilunar notch. 
Its borders present continuations of the groove 
on the margin of the superior surface; they 
serve for the attachment of ligaments, viz., 
the back part of the ulnar collateral liga- 
ment medially, and the posterior ligament 
laterally. From the medial border a part 
of the Flexor carpi ulnaris arises; while to 
the lateral border the Anconaeus is attached. 
The Coronoid Process (processus coronoideus}. 
--The coronoid process is a triangular emi- 
nence projecting forward from the upper and 
front part of the ulna. Its base is continuous 
with the body of the bone, and of consider- 
able strength. Its apex is pointed, slightly 
curved upward, and inflexion of the forearm 
is received into the coronoid fossa of the 
humerus. Its upper surface is smooth, con- 
cave, and forms the lower part of the semi- 
lunar notch. Its antero-inferior surface is 
concave, and marked by a rough impression 
for the insertion of the Brachialis. At the 
junction of this surface with the front of the 
body is a rough eminence, the tuberosity of the ulna, which gives insertion to a 
part of the Brachialis; to the lateral border of this tuberosity the oblique cord is 
attached. Its lateral surface presents a narrow, oblong, articular depression, the 
radial notch. Its medial surface, by its prominent, free margin, serves for the 
attachment of part of the ulnar collateral ligament. At the front part of this 
Surface is a small rounded eminence for the origin of one head of the Flexor 
digitorum sublimis; behind the eminence is a depression for part of the origin 
of the Flexor digitorum profundus; descending from the eminence is a ridge which 
gives origin to one head of the Pronator teres. Frequently, the Flexor pollicis 
longus arises from the lower part of the coronoid process by a rounded bundle of 
muscular fibres. 
The Semilunar Notch (incisura semilimaris; greater sigmoid cavity}.-The semi- 
lunar notch is a large depression, formed by the olecranon and the coronoid process, 
and serving for articulation with the trochlea of the humerus. About the middle 
of either side of this notch is an indentation, which contracts it somewhat, and 
Olecranon 
Coronoid 
process 
Fig. 352.-Upper extremity of left ulna. 
Lateral aspect. 316 
OSTEOLOGY 
ULNA 
Articular capsule 
RADIUS 
Flexor digitorum 
sublimis 
Pronator 
teres 
Occasional origin 
of Flexor pollicis longus 
Radial origin of 
Flexor digitorum 
sublimis 
flexor pollicis longus 
Articular 
capsule 
Brachioradialis 
Groove for Abductor 
pollicis longus and 
Extensor pollicis brevis 
Styloid process 
Styloid process 
Fig. 353.-Bones of left forearm. Anterior aspect. THE ULNA 
317 
ULNA 
Articular capsule 
RADIUS 
Flexor digitorum sublimis 
Dorsal border of ulna giving attachment to an aponeurosis common to- 
Flexor digitorum pro- 
fundus 
Flexor carpi ulnaris 
Extensor carpi ulnaris 
Articular capsule 
For- 
Abductor pollicis 
longus 
Extensor pollicis 
brevis 
For Extensor digiti quinti proprius 
For Extensor carpi ulnaris 
For Ext. carpi radialis longus 
For Extensor carpi radialis brevis 
For- 
Extensor indicis proprius 
For Extensor pollicis longus 
Fig. 354.-Bones of left forearm. Posterior aspect. 
Extensor digitorum communis 318 
OSTEOLOGY 
indicates the junction of the olecranon and the coronoid process. The notch is 
concave from above downward, and divided into a medial and a lateral portion by 
a smooth ridge running from the summit of the olecranon to the tip of the coronoid 
process. The medial portion is the larger, and is slightly concave transversely; 
the lateral is convex above, slightly concave below. 
The Radial Notch (incisura radialis; lesser sigmoid cavity).-The radial notch 
is a narrow, oblong, articular depression on the lateral side of the coronoid process; 
it receives the circumferential articular surface of the head of the radius. It is 
concave from before backward, and its prominent extremities serve for the attach- 
ment of the annular ligament. 
The Body or Shaft (corpus ulnae).-The body at its upper part is prismatic 
in form, and curved so as to be convex behind and lateralward; its central part 
is straight; its lower part is rounded, smooth, and bent a little lateralward. It 
tapers gradually from above downward, and has three borders and three surfaces. 
Borders.--The volar border (margo volaris; anterior border) begins above at the 
prominent medial angle of the coronoid process, and ends below in front of the 
styloid process. Its upper part, well-defined, and its middle portion, smooth and 
rounded, give origin to the Flexor digitorum profundus; its lower fourth serves 
for the origin of the Pronator quadratus. This border separates the volar from 
the medial surface. 
The dorsal border (margo dorsalis; posterior border) begins above at the apex of 
the triangular subcutaneous surface at the back part of the olecranon, and ends 
below at the back of the styloid process; it is well-marked in the upper three- 
fourths, and gives attachment to an aponeurosis which affords a common origin to 
the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- 
fundus; its lower fourth is smooth and rounded. This border separates the medial 
from the dorsal surface. 
The interosseous crest (crista interossea; external or interosseous border) begins 
above by the union of two lines, which converge from the extremities of the radial 
notch and enclose between them a triangular space for the origin of part of the 
Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower 
fourth smooth and rounded. This crest gives attachment to the interosseous mem- 
brane, and separates the volar from the dorsal surface. 
Surfaces.-The volar surface (facies volaris; anterior surface), much broader 
above than below, is concave in its upper three-fourths, and gives origin to the 
Flexor digitorum profundus; its lower fourth, also concave, is covered by the 
Pronator quadratus. The lower fourth is separated from the remaining portion 
by a ridge, directed obliquely downward and medialward, which marks the extent 
of origin of the Pronator quadratus. At the junction of the upper with the 
middle third of the bone is the nutrient canal, directed obliquely upward. 
The dorsal surface (facies dorsalis; posterior surface) directed backward and 
lateralward, is broad and concave above; convex and somewhat narrower in the 
middle; narrow, smooth, and rounded below. On its upper part is an oblique 
ridge, which runs from the dorsal end of the radial notch, downward to the dorsal 
border; the triangular surface above this ridge receives the insertion of the 
Anconaeus, while the upper part of the ridge affords attachment to the Supinator. 
Below this the surface is subdivided by a longitudinal ridge, sometimes called the 
perpendicular line, into two parts: the medial part is smooth, and covered by the 
Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from 
above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis 
longus, and the Extensor indicis proprius. 
The medial surface (facies medialis; internal surface) is broad and concave 
above, narrow and convex below. Its upper three-fourths give origin to the 
Flexor digitorum profundus; its lower fourth is subcutaneous. 319 
THE RADIUS 
The Lower Extremity (distal extremity).-The lower extremity of the ulna is 
small, and presents two eminences; the lateral and larger is a rounded, articular 
eminence, termed the head of the ulna; the medial, narrower and more projecting, 
is a non-articular eminence, the styloid process. The head presents an articular 
surface, part of which, of an oval or semilunar form, is directed downward, and 
articulates with the upper surface of the triangular articular disk which separates it 
from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, 
and received into the ulnar notch of the radius. The styloid process projects from 
the medial and back part of the bone; it descends a little lower than the head, 
and its rounded end affords attachment to the ulnar collateral ligament of the 
wrist-joint. The head is separated from the styloid process by a depression for 
the attachment of the apex of the triangular articular disk, and behind, by a shallow 
groove for the tendon of the Extensor carpi ulnaris. 
Appears at 
tenth year 
Olecranon 
Joins body at 
sixteenth year 
Appears at 
fourth year 
Joins body at 
twentieth year 
Inferior extremity 
Fig. 355.-Plan of ossification of the ulna. 
From three centres. 
Fig. 356.-Epiphysial lines of ulna in a young adult. 
Lateral aspect. The lines of attachment of the articular 
capsules are in blue. 
Structure.-The structure of the ulna is similar to that of the other long bones. 
Ossification (Figs. 355, 356).-The ulna is ossified from three centres: one each for the body, the 
inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, 
about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth 
the ends are cartilaginous. About the fourth year, a centre appears in the middle of the head, 
and soon extends into the styloid process. About the tenth year, a centre appears in the olecranon 
near its extremity, the chief part of this process being formed by an upward extension of the body. 
The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. 
Articulations.-The ulna articulates with the humerus and radius 
The Radius. 
The radius (Figs. 353, 354) is situated on the lateral side of the ulna, which 
exceeds it in length and size. Its upper end is small, and forms only a small part 
of the elbow-joint; but its lower end is large, and forms the chief part of the wrist- 320 
OSTEOLOGY 
joint. It is a long bone, prismatic in form and slightly curved longitudinally. It 
has a body and two extremities. 
The Upper Extremity {proximal extremity).-The upper extremity presents a 
head, neck, and tuberosity. The head is of a cylindrical form, and on its upper 
surface is a shallow cup or fovea for articulation with the capitulum of the humerus. 
The circumference of the head is smooth; it is broad medially where it articulates 
with the radial notch of the ulna, narrow in the rest of its extent, which is embraced 
by the annular ligament. The head is supported on a round, smooth, and con- 
stricted portion called the neck, on the back of which is a slight ridge for the inser- 
tion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, 
the radial tuberosity; its surface is divided into a posterior, rough portion, for the 
insertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on 
which a bursa is interposed between the tendon and the bone. 
The Body or Shaft {corpus radii).-The body is prismoid in form, narrower 
above than below, and slightly curved, so as to be convex lateralward. It presents 
three borders and three surfaces. 
Borders.-The volar border {margo volaris; anterior border) extends from the lower 
part of the tuberosity above to the anterior part of the base of the styloid process 
below, and separates the volar from the lateral surface. Its upper third is promi- 
nent, and from its oblique direction has received the name of the oblique line of the 
radius; it gives origin to the Flexor digitorum sublimis and Flexor pollicis longus; the 
surface above the line gives insertion to part of the Supinator.. The middle third of 
the volar border is indistinct and rounded. The lower fourth is prominent, and gives 
insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; 
it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted. 
The dorsal border {margo dorsalis; posterior border) begins above at the back of 
the neck, and ends below at the posterior part of the base of the styloid process; 
it separates the posterior from the lateral surface. It is indistinct above and below, 
but well-marked in the middle third of the bone. 
The interosseous crest {crista interossea; internal or interosseous border) begins 
above, at the back part of the tuberosity, and its upper part is rounded and indis- 
tinct; it becomes sharp and prominent as it descends, and at its lower part divides 
into two ridges which are continued to the anterior and posterior margins of the 
ulnar notch. To the posterior of the two ridges the lower part of the interosseous 
membrane is attached, while the triangular surface between the ridges gives inser- 
tion to part of the Pronator quadratus. This crest separates the volar from the 
dorsal surface, and gives attachment to the interosseous membrane. 
Surface.-The volar surface {facies volaris; anterior surface) is concave in its 
upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and flat 
in its lower fourth, and affords insertion to the Pronator quadratus. A prominent 
ridge limits the insertion of the Pronator quadratus below, and between this and 
the inferior border is a triangular rough surface for the attachment of the volar 
radiocarpal ligament. At the junction of the upper and middle thirds of the 
volar surface is the nutrient foramen, which is directed obliquely upward. 
The dorsal surface {facies dorsalis; posterior surface) is convex, and smooth in 
the upper third of its extent, and covered by the Supinator. Its middle third is 
broad, slightly concave, and gives origin to the Abductor pollicis longus above, 
and the Extensor pollicis brevis below. Its lower third is broad, convex, and 
covered by the tendons of the muscles which subsequently run in the grooves on 
the lower end of the bone. 
The lateral surface {facies lateralis; external surface) is convex throughout its 
entire extent. Its upper third gives insertion to the Supinator. About its centre is 
a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow, and 
covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis. THE RADIUS 
321 
The Lower Extremity.-The lower extremity is large, of quadrilateral form, 
and provided with two articular surfaces-one below, for the carpus, and another 
at the medial side, for the ulna. The carpal articular surface is triangular, concave, 
smooth, and divided by a slight antero-posterior ridge into two parts. Of these, 
the lateral, triangular, articulates with the navicular bone; the medial, quadri- 
lateral, with the lunate bone. The articular surface for the ulna is called the ulnar 
notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates 
with the head of the ulna. These two articular surfaces are separated by a promi- 
nent ridge, to which the base of the triangular articular disk is attached; this disk 
separates the wrist-joint from the distal radioulnar articulation. This end of the 
bone has three non-articular surfaces-volar, dorsal, and lateral. The volar surface, 
rough and irregular, affords attachment to the volar radiocarpal ligament. The 
dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, 
and is marked by three grooves. Enumerated from the lateral side, the first 
groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral 
of these two transmits the tendon of the Extensor carpi radialis longus, the medial 
the tendon of the Extensor carpi radialis brevis. The second is deep but narrow, 
and bounded laterally by a sharply defined ridge; it is directed obliquely from above 
downward and lateralward, and transmits the tendon of the Extensor pollicis 
longus. The third is broad, for the passage of the tendons of the Extensor indicis 
proprius and Extensor digitorum communis. The lateral surface is prolonged 
obliquely downward into a strong, conical, projection, the styloid process, which 
gives attachment by its base to the tendon of the Brachioradialis, and by its apex 
to the radial collateral ligament of the wrist-joint. The lateral surface of this 
process is marked by a flat groove, for the tendons of the Abductor pollicis longus 
and Extensor pollicis brevis. 
Structure.-The structure of the radius is like that of the other long bones. 
Ossification (Figs. 357, 358).-The radius is ossified from three centres: one for the body, 
and one for either extremity. That for the body makes its appearance near the centre of the bone, 
during the eighth week of fetal life. About the end of the second year, ossification commences 
in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the 
body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional 
centre sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. 
Articulations.-The radius articulates with four bones: the humerus, ulna, navicular, and 
lunate. 
Applied Anatomy of the Ulna and Radius.-The two bones of the forearm are more often 
broken together, than is either the radius or ulna separately. It is therefore convenient to con- 
sider in the first instance the fractures of both bones and subsequently the principal fractures 
which take place in either bone. Fractures of both bones may be produced by either direct or 
indirect violence, though more commonly by direct violence. When indirect force is applied to 
the forearm the radius as a rule gives way, though both bones may suffer. Fracture from indirect 
force generally takes place somewhere about the middle of the bones, while that from direct 
violence may occur at any part, but is most frequent in the lower half of the bones. The fracture 
is usually transverse, but may be more or less oblique. A point of interest in connection with 
these fractures is the tendency for the two bones to unite across the interosseous membrane; 
the limb should therefore be put up in a position midway between supination and pronation, 
which is not only the most comfortable position, but also separates the bones most widely from 
each other. Anterior and posterior splints are applied in these cases, and should be rather wider 
than the limb, so as to prevent any side pressure on the bones. 
The special fractures of the ulna are: (1) Fracture of the olecranon, which is usually caused 
by direct violence, by falls on the elbow with the forearm flexed, but occasionally by muscular 
action in sudden contraction of the Triceps brachii; the most common site of this fracture is at 
the constricted portion where the olecranon joins the body of the bone, and the fracture is usually 
transverse; but any part may be broken, and even a thin shell may be torn off. Fractures from 
direct violence are occasionally comminuted. If the fibrous structures around the process are 
not torn the displacement is slight, otherwise the olecranon may be drawn up for a very consider- 
able distance. (2) Fracture of the coronoid process may occur as a complication of dislocation 
backward of the bones of the forearm, but it is doubtful if it ever takes place as an uncomplicated 
injury. (3) Fractures of the body of the ulna may occur at any part, but usually take place at 
21 322 
OSTEOLOGY 
or a little below the middle of the bone. They are generally the result of direct violence, but may 
occur as a complication of dislocation of the radius. (4) The styloid process may be knocked 
off by direct violence. 
Fractures of the radius may consist of: (1) Fracture of the head of the bone; this for the most 
part takes place in conjunction with some other lesion, but may occur as an uncomplicated injury. 
(2) Fracture of the neck also may occur, but is usually complicated with other injury. (3) Frac- 
tures of the body of the radius are very common, and may take place at any part of the bone. 
They may be caused by direct or indirect violence. In fracture of the upper third of the body- 
that is to say, above the insertion of the Pronator teres-the displacement is very great. The 
upper fragment is strongly supinated by the biceps and supinator and flexed by the biceps; 
while the lower fragment is pronated and drawn toward the ulna by the two pronators. If such 
a fracture be put up in the ordinary position, midway between supination and pronation, the 
bone will unite with the upper fragment in a position of supination, and the lower one in the mid- 
position, and thus considerable impairment of the movement of supination will result; the limb 
should therefore be put up with the forearm supinated. (4) The most important fracture of the 
Head 
Appears at 
fifth year 
Unites with body 
about puberty 
Appears at 
second year 
Unites with body 
about twentieth 
year 
Lower extremity 
Fig. 357.-Plan of ossification of the radius. 
From three centres. 
Fig. 358.-Epiphysial lines of radius in a young 
adult. Anterior aspect. The line of attachment of the 
articular capsule of the wrist-joint is in blue. 
radius is that of the lower end (Colles' fracture'). The fracture is transverse, and generally takes 
place about 2.5 cm. from the lower extremity. It is caused by falls on the palm of the hand, and 
is an injury of advanced life, occurring more frequently in the female than in the male. In conse- 
quence of the manner in which the fracture is caused, the upper fragment is driven into the lower, 
and impaction commonly is the result; excess of violence may, however, disimpact, the lower 
fragment being split into two or more pieces, so that no fixation occurs. Separation of the lower 
epiphysis of the radius may take place in the young. This injury and Colles' fracture may be 
distinguished from other injuries in this neighborhood-especially dislocation of the wrist, with 
which they are liable to be confounded-by observing the relative positions of the styloid processes 
of the ulna and radius. In the natural conditions of parts, with the arm hanging by the side, 
the styloid process of the radius is on a lower level than that of the ulna. After fracture or separa- 
tion of the epiphysis the styloid process of the radius is on the same level as, or on a higher level 
than, that of the ulna, whereas it would be unaltered in position in dislocation. Reduction in the 
case of Colles' fracture is usually easily effected by traction on the hand, the limb being subse- 
quently splinted with the hand deflected toward the ulnar side. THE CARPUS 
323 
THE HAND. 
The skeleton of the hand (Figs. 359, 360) is subdivided into three segments: the 
carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or 
bones of the digits. 
The Carpus (Ossa Carpi). 
The carpal bones, eight in number, are arranged in two rows. Those of the 
proximal row, from the radial to the ulnar side, are named the navicular, lunate, 
triangular, and pisiform; those of the distal row, in the same order, are named the 
greater multangular, lesser multangular, capitate, and hamate. 
Common Characteristics of the Carpal Bones.-Each bone (excepting the pisi- 
form) presents six surfaces. Of these the volar or anterior and the dorsal or posterior 
surfaces are rough, for ligamentous attachment; the dorsal surfaces being the 
broader, except in the navicular and lunate. The superior or proximal, and inferior 
or distal surfaces are articular, the superior generally convex, the inferior concave; 
the medial and lateral surfaces are also articular where they are in contact with 
contiguous bones, otherwise they are rough and tuberculated. The structure in 
all is similar, viz., cancellous tissue enclosed in a layer of compact bone.. 
Bones of the Proximal Row (upper row).-The Navicular Bone (os naviculare manus; 
scaphoid bone) (Fig. 361).-The navicular bone is the largest bone of the proximal 
row, and has received its name from its fancied resemblance to a boat. It is situated 
at the radial side of the carpus, its long axis being from above downward, lateralward, 
and forward. The superior surface is convex, smooth, of triangular shape, and artic- 
ulates with the lower end of the radius. The inferior surface, directed downward, 
lateralward, and backward, is also smooth, convex, and triangular, and is divided 
by a slight ridge into two parts, the lateral articulating with the greater multangu- 
lar, the medial'with the lesser multangular. On the dorsal surface is a narrow, 
rough groove, which runs the entire length of the bone, and serves for the attach- 
ment of ligaments. The volar surface is concave above, and elevated at its lower 
and lateral part into a rounded projection, the tubercle, which is directed forward 
and gives attachment to the transverse carpal ligament and sometimes origin to 
a few fibres of the Abductor pollicis brevis. The lateral surface is rough and narrow, 
and gives attachment to the radial collateral ligament of the wrist. The medial 
surface presents two articular facets; of these, the superior or smaller is flattened 
of semilunar form, and articulates with the lunate bone; the inferior or larger is 
concave, forming with the lunate a concavity for the head of the capitate bone. 
Articulations.-The navicular articulates with five bones: the radius proximally, greater and 
lesser multangulars distally, and capitate and lunate medially. 
The Lunate Bone (os lunatum; semilunar bone) (Fig. 362).-The lunate bone may 
be distinguished by its deep concavity and crescentic outline. It is situated in 
the centre of the proximal row of the carpus, between the navicular and triangular. 
The superior surface, convex and smooth, articulates with the radius. The inferior 
surface is deeply concave, and of greater extent from before backward than trans- 
versely: it articulates with the head of the capitate, and, by a long, narrow facet 
(separated by a ridge from the general surface), with the hamate. The dorsal 
and volar surfaces are rough, for the attachment of ligaments, the former being 
the broader, and of a somewhat rounded form. The lateral surface presents a 
narrow, flattened, semilunar facet for articulation with the navicular. The medial 
surface is marked by a smooth, quadrilateral facet, for articulation with the 
triangular. 
Articulations.-The lunate articulates with five bones: the radius proximally, capitate and 
hamate distally, navicular laterally, and triangular medially. 324 
OSTEOLOGY 
The Triangular Bone {os triquetum; cuneiform bone) (Fig. 363).-The triangular 
bone may be distinguished by its pyramidal shape, and by an oval isolated facet 
for articulation with the pisiform bone. It is situated at the upper and ulnar side 
of the carpus. The superior surface presents a medial, rough, non-articular portion, 
and a lateral convex articular portion which articulates with the triangular articular 
disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously 
curved, and smooth for articulation with the hamate. The dorsal surface is rough 
Groove for tendon of 
Flexor carpi radialis 
Carpus 
Opponens pollicis 
Flexor carpi ulnaris 
Flexor pollicis brevis 
Abductor pollicis 
longus 
Flexor digiti quinti brevis 
OPPONENS DIGITI QUINTI 
Metacarpus 
Sesamoid 
bones 
Adductor 
pollicis 
Flexor brevis 
and 
Abductor 
DIGITI QUINTI. 
Abductor 
pollicis 
BREVIS 
Flexor 
POLLIOIS HRKVTS 
Phalanges 
Flexor 
pollicis ' 
LONGUS 
Flexor 
DIGITORUM 
SUBLIMIS 
<Flexor 
DIGITORUM 
PROFUNDUS 
. Flexor 
DIGIT. 
SUBLIMIS 
Flexor 
DIGITORUM 
SUBLIMIS 
Flexor digitorum sublimis 
Flexor 
DIGITORUM 
PROFUNDUS 
Flexor digitorum profundus 
Flexor 
■ DIGITORUM 
PROFUNDUS 
Fig. 359.-Bones of the left hand. Volar surface. THE CARPUS 
325 
for the attachment of ligaments. The volar surface presents, on its medial part, 
an oval facet, for articulation with the pisiform; its lateral part is rough for liga- 
mentous attachment. The lateral surface, the base of the pyramid, is marked by a 
flat, quadrilateral facet, for articulation with the lunate. The medial surface, 
the summit of the pyramid, is pointed and roughened, for the attachment of the 
ulnar collateral ligament of the wrist. 
Carvus 
Ext. carpi radialis 
LONGUS 
Ext. carpi radialis 
brevis 
Ext. carpi ulnaris 
Meta c a rjous 
Ext. 
pouliots. 
BREVIS 
Ext. 
pol licis ■ 
longus 
rialanges 
f ¥ Row 
Ext. digit. 
COJIMUN. & 
Ext. digiti 
QUINTI 
I??Row 
Ext. digitorum 
COMMUNIS AND 
Ext. indicis 
PROPRIUS. 
'ext. oicit. 
COMMON. ' 
e*T- O,CIT 
c°MMuty. 
Fig. 360.-Bones of the left hand. Dorsal surface. 326 
OSTEOLOGY 
Articulations.-The triangular articulates with three bones: the lunate laterally, the pisiform 
in front, the hamate distally; and with the triangular articular disk which separates it from the 
lower end of the ulna. 
For radius 
For unate 
Tubercle 
For capitate 
For greater 
multangular 
For lesser multangular 
Fig. 361.-The left navicular bone 
The Pisiform Bone (os pisiforme) (Fig. 364).-The pisiform bone may be known 
by its small size, and by its presenting a single articular facet. It is situated on a 
plane anterior to the other carpal bones and is spheroidal in form. Its dorsal 
For triangular 
For radius 
For hamate 
For capitate 
For navicular 
Fig. 362.-The left lunate bone. 
surface presents a smooth, oval facet, for articulation with the triangular: this facet 
approaches the superior, but not the inferior border of the bone. The volar surface 
is rounded and rough, and gives attachment to the transverse carpal ligament, 
For pisiform 
For lunate 
For triangular 
For hamate 
Fig. 363.-The left triangular bone. 
Fig. 364.-The left pisiform bone. 
and to the Flexor carpi ulnaris and Abductor digiti quinti. The lateral and medial 
surfaces are also rough, the former being concave, the latter usually convex. 
Articulation.-The pisiform articulates with one bone, the triangular. 
For lesser 
multangular 
Groove 
For navicidar 
For lesser 
Ridge 
multangular 
For 2nd 
metacarpal 
For 1st metacarpal 
For 2nd metacarpal 
Fig. 365.-The left greater multangular bone. 
Bones of the Distal Row (lower row).-The Greater Multangular Bone (os mul- 
tangulum majus; trapezium) (Fig. 365).--The greater multangular bone may be 
distinguished by a deep groove on its volar surface. It is situated at the radial THE CARPUS 
327 
side of the carpus, between the navicular and the first metacarpal bone. The 
superior surface is directed upward and medialward; medially it is smooth, and 
articulates with the navicular; laterally it is rough and continuous with the lateral 
surface. The inferior surface is oval, concave from side to side, convex from before 
backward, so as to form a saddle-shaped surface for articulation with the base 
of the first metacarpal bone. The dorsal surface is rough. The volar surface is 
narrow and rough. At its upper part is a deep groove, running from above obliquely 
downward and medialward; it transmits the tendon of the Flexor carpi radialis, 
and is bounded laterally by an oblique ridge. This surface gives origin to the 
Opponens pollicis and to the Abductor and Flexor pollicis brevis; it also affords 
attachment to the transverse carpal ligament. The lateral surface is broad and 
rough, for the attachment of ligaments. The medial surface presents two facets; 
the upper, large and concave, articulates with the lesser multangular; the lower, 
small and oval, with the base of the second metacarpal. 
Articulations.-The greater multangular articulates with four bones: the navicular proximally, 
the first metacarpal distally, and the lesser multangular and second metacarpal medially. 
The Lesser Multangular Bone (os multangulum minus; trapezoid bone) (rig. 366). 
■-The lesser multangular is the smallest bone in the distal row. It may be known 
by its wedge-shaped form, the broad end 
of the wedge constituting the dorsal, the 
narrow end the volar surface; and by its 
having four articular facets touching each 
other, and separated by sharp edges. 
The superior surface, quadrilateral, smooth, 
and slightly concave, articulates with the 
navicular. The inferior surface articulates 
with the proximal end of the second 
metacarpal bone; it is convex from side 
to side, concave from before backward 
and subdivided by an elevated ridge into two unequal facets. The dorsal and 
volar surfaces are rough for the attachment of ligaments, the former being the 
larger of the two. The lateral surface, convex and smooth, articulates with the 
greater multangular. The medial surface is concave and smooth in front, for 
articulation with the capitate; rough behind, for the attachment of an inter- 
osseous ligament. 
For navicular 
Volar 
surface 
For greater 
multangular 
Dorsal 
surface 
For 
capitate 
For 2nd 
metacarpal 
Fig. 366.-The left lesser multangular bone. 
Articulations.-The lesser multangular articulates with four bones: the navicular proximally, 
second metacarpal distally, greater multangular laterally, and capitate medially. 
For lunate 
For 
navicular 
For 
hamate^ 
For lesser 
multangular 
For 2nd 
metacarpal 
For 3rd 
metacarpal 
For 4th metacarpal 
Volar surface 
The Capitate Bone {os capitatum; os magnum) (Fig- 367).--The capitate bone 
is the largest of the carpal bones, and occupies the centre of the wrist. It presents, 
above, a rounded portion or head, which is received into the concavity formed by 
Fig. 367.-The left capitate bone. 328 
OSTEOLOGY 
the navicular and lunate; a constricted portion or neck; and below this, the body. 
The superior surface is round, smooth, and articulates with the lunate. The inferior 
surface is divided by two ridges into three facets, for articulation with the second, 
third, and fourth metacarpal bones, that for the third being the largest. The 
dorsal surface is broad and rough. The volar surface is narrow, rounded, and rough, 
for the attachment of ligaments and a part of the Adductor pollicis obliquus. 
The lateral surface articulates with the lesser multangular by a small facet at 
its anterior inferior angle, behind which is a rough depression for the attach- 
ment of an interosseous ligament. Above this is a deep, rough groove, forming 
part of the neck, and serving for the attachment of ligaments; it is bounded supe- 
riorly by a smooth, convex surface, for articulation with the navicular. The medial 
surface articulates with the hamate by a smooth, concave, oblong facet, which 
occupies its posterior and superior parts; it is rough in front, for the attachment 
of an interosseous ligament. 
Articulations.-The capitate articulates with seven bones: the navicular and lunate proximally, 
the second, third, and fourth metacarpals distally, the lesser multangular on the radial side, and 
the hamate on the ulnar side. 
For lunate 
For triangular 
For capitate. 
For 4:th metacarpal. 
For 5th metacarpal 
Hamulus 
For 5th metacarpal 
Fig. 368.-The left hamate bone. 
The Hamate Bone (os hamatum; unciform bone) (Fig. 368).-The hamate bone 
may be readily distinguished by its wedge-shaped form, and the hook-like process 
which projects from its volar surface. It is situated at the medial and lower angle 
of the carpus, with its base downward, resting on the fourth and fifth metacarpal 
bones, and its apex directed upward and lateralward. The superior surface, the 
apex of the wedge, is narrow, convex, smooth, and articulates with the lunate. 
The inferior surface articulates with the fourth and fifth metacarpal bones, by 
concave facets which are separated by a ridge. The dorsal surface is triangular 
and rough for ligamentous attachment. The volar surface presents, at its lower 
and ulnar side, a curved, hook-like process, the hamulus, directed forward and 
lateralward. This process gives attachment, by its apex, to the transverse carpal 
ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis 
and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor 
tendons into the palm of the hand. It is one of the four eminences on the front 
of the carpus to which the transverse carpal ligament of the wrist is attached; 
the others being the pisiform medially, the oblique ridge of the greater multangular, 
and the tubercle of the navicular laterally. The medial surface articulates with 
the triangular bone by an oblong facet, cut obliquely from above, downward 
and medial ward. The lateral surface articulates with the capitate by its upper 
and posterior part, the remaining portion being rough, for the attachment of 
ligaments. 
Articulations.-The hamate articulates with five bones: the lunate proximally, the fourth 
and fifth metacarpals distally, the triangular medially, the capitate laterally. THE METACARPUS 
329 
The Metacarpus. 
The metacarpus consists of five cylindrical bones which are numbered from the 
lateral side (ossa metacarpalia I-V); each consists of a body and two extremities. 
Common Characteristics of the Metacarpal Bones.-The Body (corpus; shaft).- 
The body is prismoid in form, and curved, so as to be convex in the longitudinal 
direction behind, concave in front. It presents three surfaces: medial, lateral, 
and dorsal. The medial and lateral surfaces are concave, for the attachment of 
the Interossei, and separated from one another by a prominent anterior ridge. 
The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened 
area which is covered in the recent state, by the tendons of the Extensor muscles. 
This surface is bounded by two lines, which commence in small tubercles situated 
on either side of the digital extremity, and, passing upward, converge and meet 
some distance above the centre of the bone and form a ridge which runs along the 
rest of the dorsal surface to the carpal extremity. This ridge separates two 
sloping surfaces for the attachment of the Interossei dorsales. To the tubercles 
on the digital extremities are attached the collateral ligaments of the metacarpo- 
phalangeal joints. 
The Base or Carpal Extremity (basis') is of a cuboidal form, and broader behind 
than in front: it articulates with the carpus, and with the adjoining metacarpal 
bones; its dorsal and volar surfaces are rough, for the attachment of ligaments. 
The Head or Digital Extremity (capitulum) presents an oblong surface markedly 
convex from before backward, less so transversely, and flattened from side to side; 
it articulates with the proximal phalanx. It is broader, and extends farther up- 
ward, on the volar than on the dorsal aspect, and is longer in the antero-posterior 
than in the transverse diameter. On either side of the head is a tubercle for the 
attachment of the collateral ligament of the metacarpophalangeal joint. The 
dorsal surface, broad and flat, supports the Extensor tendons; the volar surface 
is grooved in the middle line for the passage of the Flexor tendons, and marked 
on either side by an articular eminence continuous with the terminal articular 
surface. 
Characteristics of the Individual Metacarpal Bones.--The First Metacarpal 
Bone (os metacarpale I; metacarpal bone of the thumb) (Fig. 369) is shorter and 
stouter than the others, diverges to a greater degree 
from the carpus, and its volar surface is directed 
toward the palm. The body is flattened and broad 
on its dorsal surface, and does not present the ridge 
which is found on the other metacarpal bones; its 
volar surface is concave from above downward. On 
its radial border is inserted the Opponens pollicis; 
its ulnar border gives origin to the lateral head of 
the first Interosseus dorsalis. The base presents a 
concavo-convex surface, for articulation with the 
greater multangular; it has no facets on its sides, but 
on its radial side is a tubercle for the insertion of the 
Abductor pollicis longus. The head is less convex 
than those of the other metacarpal bones, and is 
broader from side to side than from before backward. 
On its volar surface are two articular eminences, of 
which the lateral is the larger, for the two sesamoid 
bones in the tendons of the Flexor pollicis brevis. 
The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index 
finger) (Fig. 370) is the longest, and its base the largest, of the four remaining 
bones. Its base is prolonged upward and medialward, forming a prominent ridge. 
For greater 
multangular 
For greater 
multangular 
Fig. 369.-The first metacarpal. 
(Left.) 330 
OSTEOLOGY 
It presents four articular facets: three on the upper surface and one on the ulnar 
side. Of the facets on the upper surface the intermediate is the largest and is 
concave from side to side, convex from before backward for articulation with the 
lesser multangular; the lateral is small, flat and oval for articulation with the greater 
multangular; the medial, on the summit of the ridge, is long and narrow for articu- 
lation with the capitate. The facet on the ulnar side articulates with the third 
metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface 
and the Flexor carpi radialis on the volar surface of the base. 
For greater 
multangular 
For Ard 
metacarpal 
Styloid, 
process 
For 
capitate 
For leaser 
multangular 
For 
capitate 
For lesser 
mult- 
angular 
For 2nd 
meta- 
carpal 
For 4ih 
metacarpal 
Fig. 370.-The second metacarpal. (Left.) 
Fig. 371.-The third metacarpal. (Left.) 
The Third Metacarpal Bone {os metacarpale III; metacarpal bone of the middle 
finger) (Fig. 371) is a little smaller than the second. The dorsal aspect of its 
base presents on its radial side a pyramidal eminence, the styloid process, which 
extends upward behind the capitate; immediately distal to this is a rough surface 
for the attachment of the Extensor carpi radialis brevis. The carpal articular 
facet is concave behind, flat in front, and articulates with the capitate. On the 
radial side is a smooth, concave facet for articulation with the second metacarpal, 
and on the ulnar side two small oval facets for the fourth metacarpal. 
The Fourth Metacarpal Bone {os metacarpale IV; metacarpal bone of the ring 
finger) (Fig. 372) is shorter and smaller than the third. The base is small and 
quadrilateral; its superior surface presents two facets, a large one medially for 
articulation with the hamate, and a small one laterally for the capitate. On the 
radial side are two oval facets, for articulation with the third metacarpal; and on 
the ulnar side a single concave facet, for the fifth metacarpal. 
The Fifth Metacarpal Bone {os metacarpale V; metacarpal bone of the little finger) 
(Fig. 373) presents on its base one facet on its superior surface, which is concavo- 
convex and articulates with the hamate, and one on its radial side, which articulates 
with the fourth metacarpal. On its ulnar side is a prominent tubercle for the inser- 
tion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body 
is divided by an oblique ridge, which extends from near the ulnar side of the base 
to the radial side of the head. The lateral part of this surface serves for the attach- THE PHALANGES OF THE HAND 
331 
ment of the fourth Interosseus dorsalis; the medial part is smooth, triangular, and 
covered by the Extensor tendons of the little finger. 
For 
capitate 
For 3rd 
metacarpal 
For 
hamate 
For 5th 
meta- 
carpal 
For 4th 
metacarpal 
For hamate 
Fig. 372.-The fourth metacarpal. (Left.) 
Fig. 373.-The fifth metacarpal. (Left.) 
Articulations.-Besides their phalangeal articulations, the metacarpal bones articulate as 
follows: the first with the greater multangular; the second with the greater multangular, lesser 
multangular, capitate and third metacarpal; the third with the capitate and second and fourth 
metacarpals; the fourth with the capitate, hamate, and third and fifth metacarpals; and the 
fifth with the hamate and fourth metacarpal. 
The phalanges are fourteen in number, three for each finger, and two for the 
thumb. Each consists of a body and two extremities. The body tapers from above 
downward, is convex posteriorly, concave in front from above downward, flat 
from side to side; its sides are marked by rough ridges which give attachment 
to the fibrous sheaths of the Flexor tendons. The proximal extremities of the bones 
of the first row present oval, concave articular surfaces, broader from side to side 
than from before*backward. The proximal extremity of each of the bones of the 
second and third rows presents a double concavity separated by a median ridge. 
The distal extremities are smaller than the proximal, and each ends in two condyles 
separated by a shallow groove; the articular surface extends farther on the volar 
than on the dorsal surface, a condition best marked in the bones of the first row. 
The ungual phalanges are convex on their dorsal and flat on their volar surfaces; 
they are recognized by their small size, and by a roughened, elevated surface of 
a horseshoe form on the volar surface of the distal extremity of each which serves 
to support the sensitive pulp of the finger. 
The Phalanges of the Hand (Phalanges Digitorum Manus). 
Articulations.-In the four fingers the phalanges of the first row articulate with those of the 
second row and with the metacarpals; the phalanges of the second row with those of the first 
and third rows, and the ungual phalanges with those of the second row. In the thumb, which 
has only two phalanges, the first phalanx articulates by its proximal extremity with the meta- 
carpal bone and by its distal with the ungual phalanx. 
Ossification of the Bones of the Hand.-The carpal bones are each ossified from a single centre, 
and ossification proceeds in the following order (Fig. 374): in the capitate and hamate, during 
the first year, the former preceding the latter; in the triangular, during the third year; in the 
lunate and greater multangular, during the fifth year, the former preceding the latter; in the 
navicular, during the sixth year; in the lesser multangular, during the eighth year; and in the 
pisiform, about the twelfth year. 332 
OSTEOLOGY 
Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying 
between the navicular, lesser multangular, and capitate. During the second month of fetal life 
it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navic- 
ular. Sometimes the styloid process of the third metacarpal is detached and forms an additional 
ossicle. 
The metacarpal bones are each ossified from two centres: one for the body and one for the 
distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one 
for the base of the first metacarpal bone.1 The first metacarpal bone is therefore ossified in the 
same manner as the phalanges, and this has led some anatomists to regard the thumb as being 
made up of three phalanges, and not of a metacarpal bone and two phalanges. Ossification com- 
mences in the middle of the body about the eighth or ninth week of fetal life, the centres for the 
second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; 
about the third year the distal extremities of the metacarpals of the fingers, and the base of the 
metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year. 
CARPUS 
One centre for each bone : 
All cartilaginous at birth 
METACARPALS OF FINGERS 
Two centres for each bone : 
One for body 
One for head 
PHALANGES 
Two centres for each bone : 
One for body 
One for 'proximal 
extremity 
Fig. 374.-Plan of ossification of the hand. 
The phalanges are each ossified from two centres: one for the body, and one for the proximal 
extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of 
the proximal extremity commences in the bones of the first row between the third and fourth 
years, and a year later in those of the second and third rows. The two centres become united 
in each row between the eighteenth and twentieth years. 
In the ungual phalanges the centres for the bodies appear at the distal extremities of the 
phalanges, instead of at t|ie middle of the bodies, as in the other phalanges. Moreover, of all 
the bones of the hand, the ungual phalanges are the first to ossify. 
Applied Anatomy.-The carpal bones are little liable to fracture, except from extreme violence, 
when the parts are so comminuted as to necessitate amputation. Occasionally they are the 
1 Allen Thomson demonstrated the fact that the first metacarpal bone is often developed from three centres: that is 
to say, there is a separate nucleus for the distal end, forming a distinct epiphysis visible at the age of seven or eight 
years. He also stated that there are traces of a proximal epiphysis in the second metacarpal bone, Journal of Anatomy 
and Physiology, 1869. THE HIP BONE 
333 
seat of tuberculous disease. The metacarpal bones and the phalanges are sometimes broken 
from direct violence. There are two diseases of the metacarpal bones and phalanges which require 
special mention on account of their frequent occurrence. One is tuberculous dactylitis, con- 
sisting in a deposit of tuberculous material in the medullary canal, expansion of the bone, with 
subsequent caseation and necrosis. The other is chondroma, which is perhaps more commonly 
found in connection with the metacarpal bones and phalanges than with any other bones. The 
tumors are usually multiple, and spring from beneath the periosteum about the epiphysial plate. 
THE BONES OF THE LOWER EXTREMITY (OSSA EXTREMITATIS INFERIORIS). 
The Hip Bone (Os Coxae; Innominate Bone). 
The hip bone is a large, flattened, irregularly shaped bone, constricted in the 
centre and expanded above and below. It meets its fellow on the opposite side 
in the middle line in front, and together they form the sides and anterior wall of 
the pelvic cavity. It consists of three parts, the ilium, ischium, and pubis, which 
are distinct from each other in the young subject, but are fused in the adult; 
the union of the three parts takes place in and around a large cup-shaped articular 
cavity, the acetabulum, which is situated near the middle of the outer surface of the 
bone. The ilium, so-called because it supports the flank, is the superior broad and 
expanded portion which extends upward from the acetabulum. The ischium is the 
lowest and strongest portion of the bone; it proceeds downward from the acetab- 
ulum, expands into a large tuberosity, and then, curving forward, forms, with 
the pubis, a large aperture, the obturator foramen. The pubis extends medialward 
and downward from the acetabulum and articulates in the middle line with the 
bone of the opposite side: it forms the front of the pelvis and supports the external 
organs of generation. 
The Ilium (os ilii).-The ilium is divisible into two parts, the body and the 
ala; the separation is indicated on the internal surface by a curved line, the arcuate 
line, and on the external surface by the margin of the acetabulum. 
The Body (corpus oss. ilii).-The body enters into the formation of the acetab- 
ulum, of which it forms rather less than two-fifths. Its external surface is partly 
articular, partly non-articular; the articular segment forms part of the lunate 
surface of the acetabulum, the non-articular portion contributes to the acetabular 
fossa, The internal surface of the body is part of the wall of the lesser pelvis and 
gives origin to some fibres of the Obturator interims. Below, it is continuous with 
the pelvic surfaces of the ischium and pubis, only a faint line indicating the place 
of union. 
The Ala (ala oss. ilii).-The ala is the large expanded portion which bounds 
the greater pelvis laterally. It presents for examination two surfaces--an external 
and an internal-a crest, and two borders--an anterior and a posterior. The 
external surface (Fig. 375), known as the dorsum ilii, is directed backward and lateral- 
ward behind, and downward and lateralward in front. It is smooth, convex in front, 
deeply concave behind; bounded above by the crest, below by the upper border 
of the acetabulum, in front and behind by the anterior and posterior borders. 
This surface is crossed in an arched direction by three lines-the posterior, anterior, 
and inferior gluteal lines. The posterior gluteal line (superior curved line), the short- 
est of the three, begins at the crest, about 5 cm. in front of its posterior extremity; 
it is at first distinctly marked, but as it passes downward to the upper part of the 
greater sciatic notch, where it ends, it becomes less distinct, and is often altogether 
lost. Behind this line is a narrow semilunar surface, the upper part of which 
is rough and gives origin to a portion of the Glutaeus maximus; the lower part is 
smooth and has no muscular fibres attached to it. The anterior gluteal line (middle 
curved line), the longest of the three, begins at the crest, about 4 cm. behind its 334 
OSTEOLOGY 
anterior extremity, and, taking a curved direction downward and backward, ends 
at the upper part of the greater sciatic notch. The space between the anterior 
and posterior gluteal lines and the crest is concave, and gives origin to the Glutaeus 
medius. Near the middle of this line a nutrient foramen is often seen. The 
inferior gluteal line (inferior curved line), the least distinct of the three, begins in 
Ant. superior 
spine 
Posterior 
superior' 
spine 
■Anterior inferior spine 
Posterior- 
inferior 
spine 
Articular capsule 
Ligamentum teres 
Pectineus 
Gemellus superior 
Spine of ischium 
Rectus 
abdominis 
Pyramidalis 
Gemellus inferior 
Adductor 
longus 
Fig. 375.-Right hip bone. External surface. 
front at the notch on the anterior border, and, curving backward and downward, 
ends near the middle of the greater sciatic notch. The surface of bone included 
between the anterior and inferior gluteal lines is concave from above downward, 
convex from before backward, and gives origin to the Glutaeus minimus. Between 
the inferior gluteal line and the upper part of the acetabulum is a rough, shallow 
groove, from which the reflected tendon of the Rectus femoris arises. THE HIP BONE 
335 
The internal surface (Fig. 376) of the ala is bounded above by the crest, below, 
by the arcuate line; in front and behind, by the anterior and posterior borders. 
It presents a large, smooth, concave surface, called the iliac fossa, which gives 
origin to the Iliacus and is perforated at its inner part by a nutrient canal; and 
below this a smooth, rounded border, the arcuate line, which runs downward, for- 
ward, and medialward. Behind the iliac fossa is a rough surface, divided into two 
Levator ani 
Constrictor urethrae 
Transversus perinaei superfic. 
Fig. 376.-Right hip bone. Internal surface. 
Cms penis 
Ischiocavernosus 
portions, an anterior and a posterior. The anterior surface {auricular surface), 
so called from its resemblance in shape to the ear, is coated with cartilage in the 
recent state, and articulates with a similar surface on the side of the sacrum. 
The posterior portion, known as the iliac tuberosity, is elevated and rough, for 
the attachment of the posterior sacroiliac ligaments and for the origins of the 
Sacrospinalis and Multifidus. Below and in front of the auricular surface is the 336 
OSTEOLOGY 
preauricular sulcus, more commonly present and better marked in the female 
than in the male; to it is attached the pelvic portion of the anterior sacroiliac 
ligament. 
The crest of the ilium is convex in its general outline but is sinuously curved, 
being concave inward in front, concave outward behind. It is thinner at the centre 
than at the extremities, and ends in the anterior and posterior superior iliac spines. 
The surface of the crest is broad, and divided into external and internal lips, 
and an intermediate line. About 5 cm. behind the anterior superior iliac spine 
there is a prominent tubercle on the outer lip. To the external lip are attached 
the Tensor fasciae latae, Obliquus externus abdominis, and Latissimus dorsi, and 
along its whole length the fascia lata; to the intermediate line the Obliquus internus 
abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, 
Quadratus lumborum, Sacrospinalis, and Iliacus. 
The anterior border of the ala is concave. It presents two projections, separated 
by a notch. Of these, the uppermost, situated at the junction of the crest and 
anterior border, is called the anterior superior iliac spine; its outer border gives 
attachment to the fascia lata, and the Tensor fasciae latae, its inner border, to the 
Iliacus; while its extremity affords attachment to the inguinal ligament and gives 
origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius 
takes origin and across which the lateral femoral cutaneous nerve passes. Below 
the notch is the anterior inferior iliac spine, which ends in the upper lip of the 
acetabulum; it gives attachment to the straight tendon of the Rectus femoris and 
to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine 
is a broad, shallow groove, over which the Iliacus and Psoas major pass. This 
groove is bounded medially by an eminence, the iliopectineal eminence, which 
marks the point of union of the ilium and pubis. 
The posterior border of the ala, shorter than the anterior, also presents two 
projections separated by a notch, the posterior superior iliac spine and the posterior 
inferior iliac spine. The former serves for the attachment of the oblique portion 
of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds 
with the posterior extremity of the auricular surface. Below the posterior inferior 
spine is a deep notch, the greater sciatic notch. 
The Ischium (os ischii).--The ischium forms the lower and back part of the 
hip bone. It is divisible into three portions-a body and two rami. 
The Body (corpus oss. ischii).--The body enters into and constitutes a little 
more than two-fifths of the acetabulum. Its external surface forms part of the 
lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal 
surface is part of the wall of the lesser pelvis; it gives origin to some fibres of the 
Obturator internus. Its anterior border projects as the posterior obturator tubercle; 
from its posterior border there extends backward a thin and pointed triangular 
eminence, the ischial spine, more or less elongated in different subjects. The 
external surface of the spine gives attachment to the Gemellus superior, its internal 
surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed 
extremity the sacrospinous ligament is attached. Above the spine is a large notch, 
the greater sciatic notch, converted into a foramen by the sacrospinous ligament; 
it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, 
the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, 
and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of 
these, the superior gluteal vessels and nerve pass out above the Piriformis, the 
other structures below it. Below the spine is a smaller notch, the lesser sciatic 
notch; it is smooth, coated in the recent state with cartilage, the surface of which 
presents two or three ridges corresponding to the subdivisions of the tendon of 
the Obturator internus, which winds over it. It is converted into a foramen by 
the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the THE HIP BONE 
337 
Obturator internus, the nerve which supplies that muscle, and the internal 
pudendal vessels and nerve. 
The Superior Ramus (ramus superior oss. ischii; descending ramus).-The 
superior ramus projects downward and backward from the body and presents 
for examination three surfaces: external, internal, and posterior. The external 
surface is quadrilateral in shape. It is bounded above by a groove which lodges 
the tendon of the Obturator externus; below, it is continuous with the inferior 
ramus; in front it is limited by the posterior margin of the obturator foramen; 
behind, a prominent margin separates it from the posterior surface. In front of 
this margin the surface gives origin to the Quadratus femoris, and anterior to this 
to some of the fibres of origin of the Obturator externus; the lower part of the sur- 
face gives origin to part of the Adductor magnus. The internal surface forms part 
of the bony wall of the lesser pelvis. In front it is limited by the posterior margin 
of the obturator foramen. Below, it is bounded by a sharp ridge which gives 
attachment to a falciform prolongation of the sacrotuberous ligament, and, more 
anteriorly, gives origin to the Transversus perinaei and Ischiocavernosus. Poste- 
riorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided 
into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, 
quadrilateral portion. The lower portion is subdivided by a prominent longitudinal 
ridge, passing from base to apex, into two parts; the outer gives attachment to 
the Adductor magnus, the inner to the sacrotuberous ligament. The upper portion 
is subdivided into two areas by an oblique ridge, which runs downward and out- 
ward ; from the upper and outer area the Semimembranosus arises; from the lower 
and inner, the long head of the Biceps femoris and the Semitendinosus. 
The Inferior Ramus (ramus inferior oss. ischii; ascending ramus).-The inferior 
ramus is the thin, flattened part of the ischium, which ascends from the superior 
ramus, and joins the inferior ramus of the pubis-the junction being indicated in 
the adult by a raised line. The outer surface is uneven for the origin of the Obturator 
externus and some of the fibres of the Adductor magnus; its inner surface forms 
part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly 
everted, forms part of the outlet of the pelvis, and presents two ridges and an 
intervening space. The ridges are continuous with similar ones on the inferior 
ramus of the pubis: to the outer is attached the deep layer of the superficial peri- 
neal fascia (fascia of Colles), and to the inner the inferior fascia of the urogenital 
diaphragm. If these two ridges be traced downward, they will be found to join 
with each other just behind the point of origin of the Transversus perinaei; here 
the two layers of fascia are continuous behind the posterior border of the muscle. 
To the intervening space, just in front of the point of junction of the ridges, the 
Transversus perinaei is attached, and in front of this a portion of the crus penis 
vel clitoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and 
forms part of the medial margin of the obturator foramen. 
The Pubis (os pubis).-The pubis, the anterior part of the hip bone, is divisible 
into a body, a superior and an inferior ramus. 
The Body (corpus oss. pubis).-The body forms one-fifth of the acetabulum, 
contributing by its external surface both to the lunate surface and the acetabular 
fossa. Its internal surface enters into the formation of the wall of the lesser pelvis 
and gives origin to a portion of the Obturator internus. 
The Superior Ramus (ramus superior oss. pubis; ascending ramus)-1The superior 
ramus extends from the body to the median plane where it articulates with its 
fellow of the opposite side. It is conveniently described in two portions, viz., a 
medial flattened part and a narrow lateral prismoid portion. 
The Medial Portion of the superior ramus, formerly described as the body of 
the pubis, is somewhat quadrilateral in shape, and presents for examination two 
surfaces and three borders. The anterior surface is rough, directed downward and 338 
OSTEOLOGY 
outward, and serves for the origin of various muscles. The Adductor longus arises 
from the upper and medial angle, immediately below the crest; lower down, the 
Obturator externus, the Adductor brevis, and the upper part of the Gracilis take 
origin. The posterior surface, convex from above downward, concave from side 
to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin 
to the Levator ani and Obturator internus, and attachment to the puboprostatic 
ligaments and to a few muscular fibres prolonged from the bladder. The upper 
border presents a prominent tubercle, the pubic tubercle (pubic spine), which pro- 
jects forward; the inferior crus of the subcutaneous inguinal ring (external abdominal 
ring), and the inguinal ligament (Poupart's ligament) are attached to it. Passing 
upward and lateralward from the pubic tubercle is a well-defined ridge, forming 
a part of the pectineal line which marks the brim of the lesser pelvis: to it are 
attached a portion of the inguinal falx (conjoined tendon of Obliquus internus 
and Transversus), the lacunar ligament (Gimbernat's ligament), and the reflected 
inguinal ligament (triangular fascia). Aledial to the pubic tubercle is the crest, 
which extends from this process to the medial end of the bone. It affords attach- 
ment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The 
point of junction of the crest with the medial border of the bone is called the angle; 
to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal 
ring is attached. The medial border is articular; it is oval, and is marked by eight 
or nine transverse ridges, or a series of nipple-like processes arranged in rows, 
separated by grooves; they serve for the attachment of a thin layer of cartilage, 
which intervenes between it and the interpubic fibrocartilaginous lamina. The 
lateral border presents a sharp margin, the obturator crest, which forms part of the 
circumference of the obturator foramen and affords attachment to the obturator 
membrane. 
The Lateral Portion of the ascending ramus has three surfaces: superior, inferior, 
and posterior. The superior surface presents a continuation of the pectineal line, 
already mentioned as commencing at the pubic tubercle. In front of this line, the 
surface of bone is triangular in form, wider laterally than medially, and is covered 
by the Pectineus. The surface is bounded, laterally, by a rough eminence, the 
iliopectineal eminence, which serves to indicate the point of junction of the ilium 
and pubis, and below by a prominent ridge which extends from the acetabular 
notch to the pubic tubercle. The inferior surface forms the upper boundary of 
the obturator foramen, and presents, laterally, a broad and deep, oblique groove, 
for the passage of the obturator vessels and nerve; and medially, a sharp margin, 
the obturator crest, forming part of the circumference of the obturator foramen, 
and giving attachment to the obturator membrane. The posterior surface consti- 
tutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from 
above downward, and affords origin to some fibres of the Obturator internus. 
The Inferior Ramus (ramus inferior oss. pubis; descending ramus).-The inferior 
ramus is thin and flattened. It passes lateralward and downward from the medial 
end of the superior ramus; it becomes narrower as it descends and joins with the 
inferior ramus of the ischium below the obturator foramen. Its anterior surface 
is rough, for the origin of muscles-the Gracilis along its medial border, a portion 
of the Obturator externus • where it enters into the formation of the obturator 
foramen, and between these two, the Adductores brevis and magnus, the former 
being the more medial. The posterior surface is smooth, and gives origin to the 
Obturator internus, and, close to the medial margin, to the Constrictor urethrae. 
The medial border is thick, rough, and everted, especially in females. It presents 
two ridges, separated by an intervening space. The ridges extend downward, and 
are continuous with similar ridges on the inferior ramus of the ischium; to the 
external is attached the fascia of Colles, and to the internal the inferior fascia ol 
the urogenital diaphragm. The lateral border is thin and sharp, forms part of the THE HIP BONE 
339 
circumference of the obturator foramen, and gives attachment to the obturator 
membrane. 
The Acetabulum (cotyloid cavity).-The acetabulum is a deep, cup-shaped, hemi- 
spherical depression, directed downward, lateralward, and forward. It is formed 
medially by the pubis, above by the ilium, laterally and below by the ischium; 
a little less than two-fifths is contributed by the ilium, a little more than two- 
fifths by the ischium, and the remaining fifth by the pubis. It is bounded by a 
prominent uneven rim, which is thick and strong above, and serves for the attach- 
ment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and 
deepens the surface for articulation. It presents below a deep notch, the acetabular 
notch, which is continuous with a circular non-articular depression, the acetabular 
fossa, at the bottom of the cavity: this depression is perforated by numerous 
apertures, and lodges a mass of fat. The notch is converted into a foramen by 
the transverse ligament; through the foramen nutrient vessels and nerves enter 
the joint; the margins of the notch serve for the attachment of the ligamentum 
teres. The rest of the acetabulum is formed by a curved articular surface, the 
lunate surface, for articulation with the head of the femur. 
Three primary (Ilium, Ischium, and Pubis) 
Five secondary 
By eight centres 
Fig. 377.-Plan of ossification of the hip bone. The three primary centres unite through a Y-shaped piece about 
puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. 
The Obturator Foramen (foramen obturatum; thyroid foramen).-The obturator 
foramen is a large aperture, situated between the ischium and pubis. In the male 
it is large and of an oval form, its longest diameter slanting obliquely from before 
backward; in the female it is smaller, and more triangular. It is bounded by a 
thin, uneven margin, to which a strong membrane is attached, and presents, 
superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely 
medialward and downward. This groove is converted into a canal by a ligamentous 
band, a specialized part of the obturator membrane, attached to two tubercles: 
one, the posterior obturator tubercle, on the medial border of the ischium, just in 
front of the acetabular notch; the other, the anterior obturator tubercle, on the 340 
OSTEOLOGY 
obturator crest of the superior ramus of the pubis. Through the canal the 
obturator vessels and nerve pass out of the pelvis. 
Structure.-The thicker parts of the bone consist of cancellous tissue, enclosed between two 
layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and centre of 
the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. 
Ossification (Fig. 377).-The hip bone is ossified from eight centres: three primary-one each 
for the ilium, ischium, and pubis; and five secondary-one each for the crest of the ilium, the 
anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity 
of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or 
more for the Y-shaped piece at the bottom of the acetabulum. The centres appear in the follow- 
ing order: in the lower part of the ilium, immediately above the greater sciatic notch, about 
the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; 
in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three 
primary centres are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, 
and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth 
year, the inferior rami of the pubis and ischium are almost completely united by bone. About 
the thirteenth or fourteenth year, the three primary centres have extended their growth into the 
bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of 
cartilage, which now presents traces of ossification, often by two or more centres. One of these, 
the os acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them 
about the age of eighteen; it forms the pubic part of the acetabulum. The ilium and ischium 
then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped 
portion. At about the age of puberty, ossification takes place in each of the remaining portions, 
and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate 
centres are frequently found for the pubic tubercle and the ischial spine, and for the crest and 
angle of'the pubis. 
Articulations.-The hip bone articulates with its fellow of the opposite side, and with the 
sacrum and femur. 
The Pelvis. 
The pelvis, so called from its resemblance to a basin, is a bony ring, interposed 
between the movable vertebrae of the vertebral column which it supports, and the 
lower limbs upon which it rests; it is stronger and more massively constructed 
than the wall of the cranial or thoracic cavities, and is composed of four bones: 
the two hip bones laterally and in front and the sacrum and coccyx behind. 
The pelvis is divided by an oblique plane passing through the prominence of 
the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis 
pubis, into the greater and the lesser pelvis. The circumference of this plane is 
termed the line a terminalis or pelvic brim. 
The Greater or False Pelvis {pelvis major).-The greater pelvis is the expanded 
portion of the cavity situated above and in front of the pelvic brim. It is bounded 
on either side by the ilium; in front it is incomplete, presenting a wide interval 
between the anterior borders of the ilia, which is filled up in the recent state by 
the parietes of the abdomen; behind is a deep notch on either side between the ilium 
and the base of the sacrum. It supports the intestines, and transmits part of their 
weight to the anterior wall of the abdomen. 
The Lesser or True Pelvis {pelvis minor).-The lesser pelvis is that part of the 
pelvic cavity which is situated below and behind the pelvic brim. Its bony walls 
are more complete than those of the greater pelvis. For convenience of descrip- 
tion, it is divided into an inlet bounded by the superior circumference, and outlet 
bounded by the inferior circumference, and a cavity. 
The Superior Circumference.-The superior circumference forms the brim of the 
pelvis, the included space being called the superior aperture or inlet {apertura pelvis 
[minoris] superior) (Fig. 378). It is formed laterally by the pectineal and arcuate 
lines, in front by the crests of the pubes, and behind by the anterior margin of the 
base of the sacrum and sacrovertebral angle. The superior aperture is somewhat 
heart-shaped, obtusely pointed in front, diverging on either side, and encroached 
upon behind by the projection forward of the promontory of the sacrum. It has THE PELVIS 
341 
three principal diameters: antero-posterior, transverse, and oblique. The antero- 
posterior or conjugate diameter extends from the sacrovertebral angle to the sym- 
physis pubis; its average measurement is about 110 mm. in the female. The 
transverse diameter extends across the greatest width of the superior aperture, 
from the middle of the brim on one side to the same point on the opposite; its aver- 
age measurement is about 135 mm. in the female. The oblique diameter extends 
from the iliopectineal eminence of one side to the sacroiliac articulation of the 
opposite side; its average measurement is about 125 mm. in the female 
Fig. 378.-Diameters of superior aperture of lesser pelvis (female). 
The cavity of the lesser pelvis is bounded in front and below by the pubic sym- 
physis and the superior rami of the pubes; above and behind, by the pelvic surfaces 
of the sacrum and coccyx, which, curving forward above and below, contract 
the superior and inferior apertures of the cavity; laterally, by a broad, smooth, 
quadrangular area of bone, corresponding to the inner surfaces of the body and 
superior ramus of the ischium and that part of the ilium which is below the arcuate 
line. From this description it will be seen that the cavity of the lesser pelvis 
is a short, curved canal, considerably deeper on its posterior than on its anterior 
wall. It contains, in the recent subject, the pelvic colon, rectum, bladder, and some 
of the organs of generation. The rectum is placed at the back of the pelvis, in 
the curve of the sacrum and coccyx; the bladder is in front, behind the pubic sym- 
physis. In the female, the uterus and vagina occupy the interval between these 
viscera. 
The Lower Circumference.-The lower circumference of the pelvis is very irregular; 
the space enclosed- by it is named the inferior aperture or outlet (apertura pelvis 
[minoris] inferior) (Fig. 379), and is bounded behind by the point of the coccyx, 
and laterally by the ischial tuberosities. These eminences are separated by three 
notches: one in front, the pubic arch, formed by the convergence of the inferior 
rami of the ischium and pubis on either side. The other notches, one on either 
side, are formed by the sacrum and coccyx behind, the ischium in front, and 
the ilium above; they are called the sciatic notches; in the natural state they are 
converted into foramina by the sacrotuberous and sacrospinous ligaments. When 
the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, 
bounded, in front, by the pubic arcuate ligament and the inferior rami of the 
pubes and ischia; laterally, by the ischial tuberosities; and behind, by the sacro- 
tuberous ligaments and the tip of the coccyx. 342 
OSTEOLOGY 
The diameters of the outlet of the pelvis are two, antero-posterior and trans- 
verse. The antero-posterior diameter extends from the tip of the coccyx to the 
lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the 
female. It varies with the length of the coccyx, and is capable of increase or 
diminution, on account of the mobility of that bone. The transverse diameter, 
measured between the posterior parts of the ischial tuberosities, is about 115 mm. 
in the female.1 
Fig. 379.-Diameters of inferior aperture of lesser pelyis (female). 
Axes (rig. 380).-A line at right angles to the plane of the superior aperture 
at its centre would, if prolonged, pass through the umbilicus above and the middle 
of the coccyx below; the axis of the superior aperture 
is therefore directed downward and backward. The 
axis of the inferior aperture, produced upward, would 
touch the base of the sacrum, and is also directed 
downward, and slightly backward. The axis of the' 
cavity-i. e., an axis at right angles to a series of 
planes between those of the superior and inferior 
apertures-is curved like the cavity itself: this curve 
corresponds to the concavity of the sacrum and 
coccyx, the extremities being indicated by the central 
points of the superior and inferior apertures. A 
knowledge of the direction of these axes serves to 
explain the course of the fetus in its passage through 
the pelvis during parturition. 
Position of the Pelvis (Fig. 380).-In the erect 
posture, the pelvis is placed obliquely with regard 
to the trunk: the plane of the superior aperture 
forms an angle of from 50° to 60°, and that of the 
inferior aperture one of about 15° with the horizontal 
plane. The pelvic surface of the symphysis pubis 
looks upward and backward, the concavity of the 
sacrum and coccyx downward and forward. The position of the pelvis in the erect 
posture may be indicated by holding it so that the anterior superior iliac spines 
and the front of the top of the symphysis pubis are in the same vertical plane. 
Fig. 380.-Median sagittal section of 
pelvis. 
1 The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors 
no doubt due mainly to differences in the physique and stature of the population from whom the measurements have 
been taken. THE PELVIS 
343 
Differences between the Male and Female Pelves.-The female pelvis (Fig. 
382) is distinguished from that of the male (Fig. 381) by its bones being more 
delicate and its depth less. The whole pelvis is less massive, and its muscular 
Fig. 381.-Male pelvis. 
impressions are slightly marked. The ilia are less sloped, and the anterior iliac 
spines more widely separated; hence the greater lateral prominence of the hips. 
The preauricular sulcus is more commonly present and better marked. The supe- 
Fig. 382.-Female pelvis. 
rior aperture of the lesser pelvis is larger in the female than in the male; it is more 
nearly circular, and its obliquity is greater. The cavity is shallower and wider; 
the sacrum is shorter, wider, and its upper part is less curved; the obturator 344 
OSTEOLOGY 
foramina are triangular in shape and smaller in size than in the male. The inferior 
aperture is larger and the coccyx more movable. The sciatic notches are wider 
and shallower, and the spines of the ischia project less inward. The acetabula 
are smaller and look more distinctly forward (Derry1). The ischial tuberosities 
and the acetabula are wider apart, and the former are more everted. The pubic 
symphysis is less deep, and the pubic arch is wider and more rounded than in the 
male, where it is an angle rather than an arch. • 
The size of the pelvis varies not only in the two sexes, but also in different 
members of the same sex, and does not appear to be influenced in any way by the 
height of the individual. Women of short stature, as a rule, have broad pelves. 
Occasionally the pelvis is equally contracted in all its dimensions, so much so 
that all its diameters measure 12.5 mm. less than the average, and this even in 
well-formed women of average height. The principal divergences, however, are 
found at the superior aperture, and affect the relation of the antero-posterior 
to the transverse diameter. Thus the superior aperture may be elliptical either 
in a transverse or an antero-posterior direction, the transverse diameter in the 
former, and the antero-posterior in the latter, greatly exceeding the other diameters; 
in other instances it is almost circular. 
In the foetus, and for several years after birth, the pelvis is small in proportion 
to that of the adult, and the projection of the sacrovertebral angle less marked. 
The characteristic differences between the male and female pelvis are distinctly 
indicated as early as the fourth month of fetal life. 
Applied Anatomy.-There is arrest of development in the bones of the pelvis in cases of extro- 
version of the bladder; the anterior part of the pelvic girdle is deficient, the superior rami of 
the pubes are iinperfectly developed, and the symphysis is absent.- "The pubic bones are sepa- 
rated to the extent of from two to four inches, the superior rami shortened and directed forward, 
and the obturator foramen diminished in size, narrowed, and turned outward. The iliac bones 
are straightened out more than normal. The sacrum is very peculiar. The lateral curve, instead 
of being concave, is flattened out or even convex, with the iliosacral facets turned more outward 
than normal, while the vertical curve is straightened."2 
Fractures of the pelvis are divided into those of the greater and those of the lesser pelvis. 
Fractures of the greater pelvis vary in extent; a small portion of the crest may be broken, or one 
of the spinous processes may be torn off, or the bone may be extensively comminuted. This 
latter accident is the result of some crushing violence, and may be complicated with fracture 
of the lesser pelvis. These cases may be accompanied by injury to the intestine as it lies in the 
hollow of the bone, or to the iliac vessels as they course along the margin of the lesser pelvis. 
A fracture of the lesser pelvis generally occurs through the superior ramus of the pubis and the 
inferior ramus of the ischium, as these are the weakest parts of the bony ring, and may be caused 
either by crushing violence applied in an antero-posterior direction, when the fracture occurs 
from direct force, or by compression laterally, when the acetabula are pressed together and the 
bone gives way in the same place from indirect violence. Sometimes both sides of the pelvis 
are fractured, and it is in these cases that the contained viscera are likely to be injured: the 
urethra, the bladder, the rectum, the small intestines, the vagina, and even the uterus, have all 
been lacerated by displaced fragments. Fractures of the acetabulum are occasionally met with; 
either a portion of the rim may be broken off, or a fracture may take place through the bottom 
of the cavity, and the head of the femur be driven into the pelvic cavity. Separation of the 
Y-shaped cartilage at the bottom of the acetabulum may also occur in the young subject, splitting 
the bone into its three portions. 
The coccyx is not infrequently displaced forward to nearly a right angle with the sacrum by 
a kick or by a fall backward. The condition is attended with great pain in walking and on mak- 
ing any expiratory effort, such as coughing, defecation, etc., because the Coccygei and Levatores 
ani which form the pelvic diaphragm are attached to this bone. Such injuries often give rise to 
severe persistent pain, which is exceedingly intractable and difficult of cure. The condition is 
known as coccygodynia and for its relief removal of the coccyx has been practised. 
The pelvic bones often undergo important deformity in rickets, the effects of which in the 
adult woman may interfere seriously with child-bearing. The deformity is due mainly to the 
weight of the trunk, which presses on the sacrovertebral angle and greatly increases it, so that 
the antero-posterior diameter of the pelvis is diminished, and may measure as little as 40 mm., 
1 Journal of Anatomy and Physiology, vol. xliii. 
2 Wood, Heath's Dictionary of Practical Surgery, i, 426. THE FEMUR 
345 
the entrance into the pelvis becoming reniform. In other cases all the pelvic bones give way, 
so that a general diminution in all the diameters of the pelvis results, the pelvic entrance becom- 
ing triangular or asymmetrical. If the pubic symphysis be forced forward, the rickety pelvis 
may even come to resemble closely the deformed pelvis of osteomalacia; in this disease the weight 
of the trunk causes an increase in the sacrovertebral angle, and a lessening of the antero-posterior 
diameter of the superior aperture, and at the same time the pressure of the heads of the femora 
on the acetabula causes these cavities, with the adjacent bone, to be pushed upward and back- 
ward, so that the oblique diameters of the pelvis are also diminished, and the cavity of the pelvis 
assumes a triradiate shape, with the symphysis pubis pushed forward. 
The Femur (Thigh Bone). 
The femur (Figs. 384, 385), the longest and strongest bone in the skeleton, is 
almost perfectly cylindrical in the greater part of its extent. In the erect posture 
it is not vertical, being separated above from its fellow' by a considerable interval, 
which corresponds to the breadth of the pelvis, but inclining gradually downward 
and medialward, so as to approach its fellow toward its lower part, for the purpose 
of bringing the knee-joint near the line of gravity of the body. The degree of this 
inclination varies in different persons, and is greater in the female than in the male, 
on account of the greater breadth of the pelvis. The femur, like other long bones, 
is divisible into a body and two extremities. 
Obturator internus and Gemelli 
Piriformis 
Insertion of Obturator 
/ externus 
Fovea capitis, 
for lig. teres 
Greater trochanter 
Lesser trochanter 
Fig. 383.-Upper extremity of right femur viewed from behind and above 
The Upper Extremity {proxivtal extremity, Fig. 383).--The upper extremity 
presents for examination a head, a neck, a greater and a lesser trochanter. 
The Head {caput femoris).-The head which is globular and forms rather more 
than a hemisphere, is directed upward, medialward, and a little forward, the greater 
part of its convexity being above and in front. Its surface is smooth, coated with 
cartilage in the recent state, except over an ovoid depression, the fovea capitis 
femoris, which is situated a little below and behind the centre of the head, and gives 
attachment to the ligamentuni teres. 
The Neck (collum femoris').-The neck is a flattened pyramidal process of bone, 
connecting the head with the body, and forming with the latter a wide angle open- 
ing medialward. The angle is widest in infancy, and becomes lessened during 
growth, so that at puberty it forms a gentle curve from the axis of the body of the 
bone. In the adult, the neck forms an angle of about 125° with the body, but this 
varies in inverse proportion to the development of the pelvis and the stature. In 346 
OSTEOLOGY 
Obturator internus 
and Gemelli 
the female, in consequence of the 
increased width of the pelvis, the 
neck of the femur forms more 
nearly a right angle with the body 
than it does in the male. The 
angle decreases during the period 
of growth, but after full growth has 
been attained it does not usually 
undergo any change, even in old 
age; it varies considerably in differ- 
ent persons of the same age. It is 
smaller in short than in long bones, 
and when the pelvis is wide. In 
addition to projecting upward and 
medialward from the body of the 
femur, the neck also projects some- 
what forward; the amount of this 
forward projection is extremely 
variable, but on an average is from 
12° to 14°. 
The neck is flattened from before 
backward, contracted in the middle, 
and broader laterally than medially. 
The vertical diameter of the lateral 
half is increased by the obliquity of 
the lower edge, which slopes down- 
ward to join the body at the level 
of the lesser trochanter, so that it 
measures one-third more than the 
antero-posterior diameter. The 
medial half is smaller and of a 
more circular shape. The anterior 
surface of the neck is perforated by 
numerous vascular foramina. Along 
the upper part of the line of junc- 
tion of the anterior surface with 
the head is a shallow groove, best 
marked in elderly subjects; this 
groove lodges the orbicular fibres 
of the capsule of the hip-joint. 
The posterior surface is smooth, and 
is broader and more concave than 
the anterior: the posterior part of 
the capsule of the hip-joint is 
attached to it about 1 cm. above 
the intertrochanteric crest. The 
superior border is short and thick, 
and ends laterally at the greater 
trochanter; its surface is perforated 
by large foramina. The inferior 
border, long and narrow, curves a 
little backward, to end at the lesser 
trochanter. 
The Trochanters.-The trochan- 
ters are prominent processes which 
Piriformis 
Fovea capitis 
Tubercle 
Articular capside 
Lateral epicondyle 
Articular capsule 
Adductor 
tubercle 
Medial 
epicondyle 
Fig. 384.-Right femur. Anterior surface. THE FEMUR 
347 
afford leverage to the muscles 
that rotate the thigh on its axis. 
They are two in number, the 
greater and the lesser. 
The Greater Trochanter (tro- 
chanter major; great trochanter) is 
a large, irregular, quadrilateral 
eminence, situated at the junc- 
tion of the neck with the upper 
part of the body. It is directed a 
little lateral ward and backward, 
and, in the adult, is about 1 cm. 
lower than the head. It has 
two surfaces and four borders. 
The lateral surface, quadrilateral 
in form, is broad, rough, convex, 
and marked by a diagonal im- 
pression, which extends from 
the postero-superior to the 
antero-inferior angle, and serves 
for the insertion of the tendon 
of the Glutaeus medius. Above 
the impression is a triangular 
surface, sometimes rough for 
part of the tendon of the same 
muscle, sometimes smooth for 
the interposition of a bursa be- 
tween the tendon and the bone. 
Below and behind the diagonal 
impression is a smooth, trian- 
gular surface, over which the 
tendon of the Glutaeus maxi- 
mus plays, a bursa being inter- 
posed. The medial surface, of 
much less extent than the 
lateral, presents at its base a 
deep depression, the trochanteric 
fossa (digital fossa), for the in- 
sertion of the tendon of the Ob- 
turator externus, and above and 
in front of this an impression 
for the insertion of the Obtura- 
tor internus and Gemelli. The 
superior border is free; it is thick 
and irregular, and marked near 
the centre by an impression for 
the insertion of the Piriformis. 
The inferior border corresponds 
to the line of junction of the 
base of the trochanter with the 
lateral surface of the body; it is 
marked by a rough, prominent, 
slightly curved ridge, which gives 
origin to the upper part of the 
Vastus lateralis. The anterior 
border is prominent and some- 
Articular 
capsule 
Adductor 
tubercle 
Medial 
epicondyle 
Lateral 
epicondyle 
Groove for 
tendon of 
Popliteus 
Articular 
capsule. 
.Fig. 385.-Right femur. Posterior surface. 348 
OSTEOLOGY 
what irregular; it affords insertion at its lateral part to the Glutaeus minimus. 
The posterior border is very prominent and appears as a free, rounded edge, which 
bounds the back part of the trochanteric fossa. 
The Lesser Trochanter (trochanter minor; small trochanter) is a conical eminence, 
which varies in size in different subjects; it projects from the lower and back part 
of the base of the neck. From its apex three well-marked borders extend; two of 
these are above-a medial continuous with the lower border of the neck, a lateral 
with the intertrochanteric crest; the inferior border is continuous with the middle 
division of the linea aspera. The summit of the trochanter is rough, and gives 
insertion to the tendon of the Psoas major. 
A prominence, of variable size, occurs at the junction of the upper part of the 
neck with the greater trochanter, and is called the tubercle of the femur; it is the 
point of meeting of five muscles: the Glutaeus minimus laterally, the Vastus 
lateralis below, and the tendon of the Obturator internus and twTo Gemelli above. 
Running obliquely downward and medialward from the tubercle is the intertro- 
chanteric line (spiral line of the femur); it winds around the medial side of the body 
of the bone, below the lesser trochanter, and ends about 5 cm. below this eminence 
in the linea aspera. Its upper half is rough, and affords attachment to the ilio- 
femoral ligament of the hip-joint; its lower half is less prominent, and gives origin 
to the upper part of the Vastus medialis. Running obliquely downward and medial- 
ward from the summit of the greater trochanter on the posterior surface of the 
neck is a prominent ridge, the intertrochanteric crest. Its upper half forms the pos- 
terior border of the greater trochanter, and its lower half runs downward and 
medialw'ard to the lesser trochanter. A slight ridge is sometimes seen commencing 
about the middle of the intertrochanteric crest, and reaching vertically downward 
for about 5 cm. along the back part of the body: it is called the linea quadrata, 
and gives attachment to the Quadratus femoris and a few fibres of the Adductor 
magnus. Generally there is merely a slight thickening about the middle of 
the intertrochanteric crest, marking the attachment of the upper part of the 
Quadratus femoris. 
The Body or Shaft (corpus femoris).-The body, almost cylindrical in form, is 
a little broader above than in the centre, broadest and somewhat flattened from 
before backward below. It is slightly arched, so as to be convex in front, and con- 
cave behind, where it is strengthened by a prominent longitudinal ridge, the linea 
aspera. It presents for examination three borders, separating three surfaces. 
Of the three borders, one, the linea aspera, is posterior, one is medial, and the 
other, lateral. 
The linea aspera (Fig. 385) is a prominent longitudinal ridge or crest, on the 
middle third of the bone, presenting a medial and a lateral lip, and a narrow 
rough, intermediate line. Above, the linea aspera is prolonged by three ridges. 
The lateral ridge is very rough, and runs almost vertically upward to the base of 
the greater trochanter. It is termed the gluteal tuberosity, and gives attachment 
to part of the Glutaeus maximus: its upper part is often elongated into a roughened 
crest, on which a more or less well-marked, rounded tubercle, the third trochanter, 
is occasionally developed. The intermediate ridge or pectineal line is continued 
to the base of the lesser trochanter and gives attachment to the Pectineus; the 
medial ridge is lost in the intertrochanteric line; between these two a portion of the 
Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing 
between them a triangular area, the popliteal surface, upon which the popliteal 
artery rests. Of these two ridges, the lateral is the more prominent, and descends 
to the summit of the lateral condyle. The medial is less marked, especially at its 
upper part, where it is crossed by the femoral artery. It ends below at the summit 
of the medial condyle, in a small tubercle, the adductor tubercle, which affords 
insertion to the tendon of the Adductor magnus. THE FEMUR 
349 
From the medial lip of the linea aspera and its prolongations above and below, 
the Vastus medialis arises; and from the lateral lip and its upward prolongation, 
the Vastus lateralis takes origin. The Adductor magnus is inserted into the linea 
aspera, and to its lateral prolongation above, and its medial prolongation below. 
Between the Vastus lateralis and the Adductor magnus two muscles are attached 
-viz., the Glutaeus maximus inserted above, and the short head of the Biceps 
femoris arising below. Betweeen the Adductor magnus and the Vastus medialis 
four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis 
and Adductor longus below. The linea aspera is perforated a little below its centre 
by the nutrient canal, which is directed obliquely upward. 
The other two borders of the femur are only slightly marked: the lateral border 
extends from the antero-inferior angle of the greater trochanter to the anterior 
extremity of the lateral condyle; the medial border from the intertrochanteric line, 
at a point opposite the lesser trochanter, to the anterior extremity of the medial 
condyle. 
The anterior surface includes that portion of the shaft which is situated between 
the lateral and medial borders. It is smooth, convex, broader above and below 
than in the centre. From the upper three-fourths of this surface the Vastus inter- 
medius arises; the lower fourth is separated from the muscle by the intervention 
of the synovial membrane of the knee-joint and a bursa; from the upper part of it 
the Articularis genu takes origin. The lateral surface includes the portion between 
the lateral border and the linea aspera; it is continuous above with the correspond- 
ing surface of the greater trochanter, below with that of the lateral condyle: from 
its upper three-fourths the Vastus intermedius takes origin. The medial surface 
includes the portion between the medial border and the linea aspera; it is continu- 
ous above with the lower border of the neck, below with the medial side of the 
medial condyle: it is covered by the Vastus medialis. 
■ Medial groove 
Lateral groove 
Medial epicondyle 
Semilunar area 
Lateral epicondyle 
Fig. 386.-Lower extremity of right femur viewed from below. 
The Lower Extremity {distal extremity, Fig. 386).-The lower extremity, larger 
than the upper, is somewhat cuboid in form, but its transverse diameter is greater 
than its antero-posterior; it consists of two oblong eminences known as the condyles. 
In front, the condyles are but slightly prominent, and are separated from one another 
by a smooth shallow articular depression called the patellar surface; behind, they 
project considerably, and the interval between them forms a deep notch, the 
intercondyloid fossa. The lateral condyle is the more prominent and is the broader 
both in its antero-posterior and transverse diameters, the medial condyle is the 
longer and, when the femur is held with its body perpendicular, projects to a lower 
level. When, however, the femur is in its natural oblique position the lower sur- 
faces of the two condyles lie practically in the same horizontal plane. The condyles 
are not quite parallel with one another; the long axis of the lateral is almost 350 
OSTEOLOGY 
directly anteroposterior, but that of the medial runs backward and medialward. 
Their opposed surfaces are small, rough, and concave, and form the walls of the 
intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid 
line, and below by the central part of the posterior margin of the patellar surface. 
The posterior cruciate ligament of the knee-joint is attached to the lower and front 
part of the medial wall of the fossa and the anterior cruciate ligament to an impres- 
sion on the upper and back part of its lateral wall. Each condyle is surmounted 
by an elevation, the epicondyle. The medial epicondyle is a large convex eminence 
to which the tibial collateral ligament of the knee-joint is attached. At its upper 
part is the adductor tubercle, already referred to, and behind it is a rough impres- 
sion which gives origin to the medial head of the Gastrocnemius. The lateral 
epicondyle, smaller and less prominent than the medial, gives attachment to the 
fibular collateral ligament of the knee-joint. Directly below it is a small depression 
from which a smooth well-marked groove curves obliquely upward and backward 
to the posterior extremity of the condyle. This groove is separated from the 
articular surface of the condyle by a prominent lip across which a second, shallower 
groove runs vertically downward from the depression. In the recent state these 
grooves are covered with cartilage. The Popliteus arises from the depression; 
its tendon lies in-the oblique groove when the knee is flexed and in the vertical 
groove when the knee is extended. Above and behind the lateral epicondyle is 
an area for the origin of the lateral head of the Gastrocnemius, above and to the 
medial side of which the Plantaris arises. 
The articular surface of the lower end of the femur occupies the anterior, inferior, 
and posterior surfaces of the condyles. Its front part is named the patellar surface 
and articulates with the patella; it presents a median groove which extends down- 
ward to the intercondyloid fossa and two convexities, the lateral of which is broader, 
more prominent, and extends farther upward than the medial. The lower and 
posterior parts of the articular surface constitute the tibial surfaces for articulation 
with the corresponding condyles of the tibia and menisci. These surfaces are 
separated from one another by the intercondyloid fossa and from the patellar 
surface by faint grooves which extend obliquely across the condyles. The lateral 
groove is the better marked; it runs lateralward and forward from the front part 
of the intercondyloid fossa, and expands to form a triangular depression. When 
the knee-joint is fully extended, the triangular depression rests upon the anterior 
portion of the lateral meniscus, and the medial part of the groove comes into con- 
tact with the medial margin of the lateral articular surface of the tibia in front 
of the lateral tubercle of the tibial intercondyloid eminence. The medial groove 
is less distinct than the lateral. It does not reach as far as the intercondyloid 
fossa and therefore exists only on the medial part of the condyle; it receives the 
anterior edge of the medial meniscus when the knee-joint is extended. Where the 
groove ceases laterally the patellar surface is seen to be continued backward as 
a semilunar area close to the anterior part of the intercondyloid fossa; this semi- 
lunar area articulates with the medial vertical facet of the patella in forced flexion 
of the knee-joint. The tibial surfaces of the condyles are convex from side to side 
and from before backward. Each presents a double curve, its posterior segment 
being an arc of a circle, its anterior, part of a cycloid.1 
Structure.-The body of the femur is a cylinder of compact tissue, hollowed by a large medullary 
canal. The wall of the cylinder is of great thickness and density in the middle third of the body, 
where the bone is narrowest and the medullary canal best formed; but above and below this the 
wall becomes thinner, while the medullary canal is gradually filled up by cancellous tissue, so 
that the upper (Fig. 387) and lower ends of the body, and the articular extremities more especially, 
consist of cancellous tissue, invested by a thin compact layer. 
1 A cycloid is a curve traced by a point in the circumference of a wheel when the wheel is rolled along in a straight 
line. THE FEMUR 
351 
The cancelli in the ends of the femur are disposed along the lines of greatest pressure and 
tension. In the upper end (Fig. 388) the chief lamellae are arranged in the following manner. 
A series of bony planes at right angles to the articular surface of the head converge to a central 
Epiphyseal line 
Fig. 387.-Longitudinal section of head and neck of femur. 
dense wedge, which presents few and dense cancelli. The wedge is supported by strong lamellae, 
which extend to the sides of the neck and are especially marked along its upper and lower borders. 
Any force therefore applied to the head of the femur is transmitted directly to the central wedge 
and thence to the junction of the neck with the body. This 
junction is especially strengthened by a series of dense lamellae 
which extend from the lesser trochanter to the lateral end of 
the superior border of the neck; this arrangement will ob- 
viously oppose considerable resistance to either tensile or 
shearing force. A smaller bar stretching across the junction 
of the greater trochanter with the neck and body resists the 
shearing force of the muscles attached to this prominence. 
These two bars, one at the junction of body and neck, the 
other at the junction of body and greater trochanter, form the 
upper layers of a series of arches which extend across between 
the sides of the body and transmit to the body forces applied 
to the upper end of the bone. In the cancellous tissue of the 
neck is a thin vertical plate of bone, the calcar femorale, which 
springs from the compact wall of the body in the region of 
the linea aspera. Medially it is attached to the interior sur- 
face of the posterior wall of the neck of the bone; laterally it 
continues the plane of the posterior wall of the neck into the 
greater trochanter where it shades off into the general cancel- 
lous tissue. It is thus situated in a plane anterior to the inter- 
trochanteric crest and to the base of the lesser trochanter 
(Fig. 389). 
In the lower end, the cancelli spring on all sides from the ironer surface of the cylinder, and 
descend in a perpendicular direction to the articular surface, the cancelli being strongest and 
having a more accurately perpendicular course above the condyles. In addition to this, there 
Fig. 388.-Scheme showing disposi- 
tion of principal cancellous lamellae 
in upper extremity of femur. 352 
OSTEOLOGY 
are horizontal planes of cancellous tissue, so that the spongy tissue in this situation presents 
an appearance of being mapped out into a series of cubical areas. 
Articulations.-The femur articulates with three bones: the hip bone, tibia, and patella. 
Ossification (Figs. 390, 391, 392).-The femur is ossified from five centres: one for the body, 
one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, 
except the clavicle, it is the first to show traces of ossification; this commences in the middle of 
the body, at about the seventh week of fetal life, and rapidly extends upward and downward. 
The centres in the epiphyses appear in the following order: in the lower end of the bone, at the 
ninth month of fetal life (from this centre the condyles and epicondyles are formed); in the head, 
at the end of the first year after birth; in the greater trochanter, during the fourth year; and 
in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the 
epiphyses are joined to the body is the reverse of that of their appearance; they are not united 
until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, 
lastly, the inferior extremity, which is not united until the twentieth year. 
Appears at 
4-th year ; 
joins body 
about 18th yr. 
Appears al 
end of Isi yr. ; 
joins body 
about \8th yr. 
Appears 13th-\Ath 
year ; joins body 
about ISlh year 
Calcar 
jemorale 
Appears at 
9th month of 
foetal life 
J bins body at 
20th year 
Lower extremity 
Fig. 389.-Oblique section of upper extremity of 
femur showing calcar femorale. 
Fig. 390.-Plan of ossification of the femur. From 
five centres. 
Applied Anatomy.-The lower end of the femur is the only epiphysis in which ossification has 
commenced at the time of birth. The presence of this ossific centre is, therefore, a proof, in a 
newly born child found dead, that the child has arrived at the full period of uterogestation, and 
is always relied upon in medicolegal investigations. The position of the epiphysial plate should 
be carefully noted. It is on a level with the adductor tubercle, and the epiphysis does not, there- 
fore, form the whole of the cartilage-clad portion of the lower end of the bone. It is essential to 
bear this point in mind in performing excision of the knee, since growth in length of the femur 
takes place chiefly from the lower epiphysis, and any interference with the epiphysial cartilage 
in a young child would involve such ultimate shortening of the limb, from want of growth, as to 
render the limb almost useless. Separation of the lower epiphysis may take place up to the age THE FEMUR 
353 
of twenty, at which time it becomes completely joined to the body of the bone; but, as a matter 
of fact, few cases occur after the age of sixteen or seventeen. The epiphysis of the head of the 
femur is the seat of origin, in a large number of cases, of tuberculous disease of the hip-joint. 
In the majority of cases the disease begins in the highly vascular and growing tissue at the 
end of the body in the neighborhood of the epiphysial cartilage, and extends into the joint. The 
epiphysis for the head is entirely intracapsular. 
Fractures of the femur are divided, like those of the other long bones, into fractures of the 
upper end; of the body; and of the lower end. The fractures of the upper end may be classified 
into (1) fracture of the neck; (2) fracture at the junction of the neck with the greater trochanter: 
(3) fracture of the greater trochanter; and (4) separation of the epiphysis, either of the head or 
of the greater trochanter. The first of these, fracture of the neck, is usually termed intracapsular 
fracture, but this is scarcely a correct designation, as, owing to the attachment of the articular 
capsule, the fracture is partly within and partly without the capsule when the fracture occurs 
at the lower part of the neck. It generally takes place in old people, principally women, and 
Fig. 391.-Epiphysial lines of femur in a young 
adult. Anterior aspect. The lines of attachment of 
the articular capsules are in blue. 
Fig. 392.-Epiphysial lines of femur in a young adult. 
Posterior aspect. The lines of attachment of the articular 
capsules are in blue. 
usually from a very slight degree of indirect violence. Probably the main cause of its occurrence 
in old people is the senile degenerative change which takes place in the bone. Merkel believes 
that it is mainly due to the absorption of the calcar femorale. As a rule the fragments become 
united by fibrous tissue, but frequently no union takes place, and the opposed surfaces become 
smooth and eburnated. 
Fractures at the junction of the neck with the greater trochanter are usually termed extra- 
capsular, but this designation is also incorrect, as the fracture is partly within the capsule, owing 
to its attachment in front to the intertrochanteric line, which is situated below the line of fracture. 
These fractures are produced by direct violence to the greater trochanter, as from a fall laterally 
on the hip. From the manner in which the accident is caused the neck of the bone is driven into 
the trochanter, where it may remain impacted, or the trochanter may be split into two or more 
fragments, disimpaction resulting. 
Fractures of the body may occur at any part, but the most usual situation is at or near the 
centre of the bone. They may be caused by direct or indirect violence. Fractures of the upper 
third of the body are almost always the result of indirect violence, while those of the lower third 354 
OSTEOLOGY 
are the result, for the most part, of direct violence. Fractures of the body are generally oblique, 
but they may be transverse, longitudinal, or spiral. The transverse fracture occurs most fre- 
quently in children. The fractures of the lower end of the femur include transverse fracture 
above the condyles, the most common; and this may be complicated by a vertical fracture be- 
tween the condyles, constituting the T-shaped fracture. In these cases the popliteal artery is in 
danger of being wounded. Oblique fracture separating either the medial or lateral condyle, and 
a longitudinal incomplete fracture between the condyles, may also take place. 
The femur as well as the other bones of the leg is frequently the seat of acute osteomyelitis 
in children. This is no doubt due to their greater exposure to injury, which is often the exciting 
cause of this disease. Necrosis of portions of the diaphysis frequently ensues, especially in the 
region of the popliteal surface of the femur, and the disease may continue for years, great trouble 
being experienced with discharging sinuses which periodically close and reopen to allow of the 
exit of a piece of dead bone. 
Tumors are not infrequently found growing from the femur: the most common forms being 
sarcoma which may grow either from the periosteum or from the medullary tissue within the 
interior of the bone, and exostosis which commonly originates in the neighborhood of the epiphysial 
cartilage of the lower end. The periosteal sarcomata of the femur and most of the central growths 
are usually of a very high degree of malignancy, although the "myeloid" growth, which is of but 
low malignancy, may also be found. The region of the lower epiphysial line is by far the com- 
moner seat for all these tumors, and it should be noted that the lower epiphysis has the longest 
period of active growth, and that these tumors usually appear toward the end of the period of 
active growth of the bone. 
Sarcomata about the upper end of the femur are seen occasionally, but very rarely in comparison 
with those at the lower end. Secondary carcinoma also occurs in this bone, most commonly due 
to a primary focus in the breast, and spontaneous fracture of the bone may take place in these 
cases. 
The Patella (Knee Cap). 
The patella (Figs. 393, 394) is a flat, triangular bone; situated on the front of 
the knee-joint. It is usually regarded as a sesamoid bone, developed in the 
tendon of the Quadriceps femoris, 
and resembles these bones (1) in 
being developed in a tendon; (2) in 
its centre of ossification presenting 
a knotty or tuberculated outline; 
(3) in being composed mainly of 
dense cancellous tissue. It serves 
to protect the front of the joint, 
and increases the leverage of the 
Quadriceps femoris by making it 
act at a greater angle. It has an 
anterior and a posterior surface 
three borders, and an apex. 
Surfaces.-The anterior surface is convex, perforated by small apertures for the 
passage of nutrient vessels, and marked by numerous rough, longitudinal striae. 
This surface is covered, in the recent state, by an expansion from the tendon of 
the Quadriceps femoris, which is continuous below with the superficial fibres of 
the ligamentum patellae. It is separated from the integument by a bursa. The 
posterior surface presents above a smooth, oval, articular area, divided into two 
facets by a vertical ridge; the ridge corresponds to the groove on the patellar 
surface of the femur, and the facets to the medial and lateral parts of the same 
surface; the lateral facet is the broader and deeper. Below the articular surface 
is a rough, convex, non-articular area, the lower half of which gives attachment 
to the ligamentum patellae; the upper half is separated from the head of the tibia 
by adipose tissue. 
Borders.--The base or superior border is thick, and sloped from behind, down- 
ward, and forward: it gives attachment to that portion of the Quadriceps femoris 
which is derived from the Rectus femoris and Vastus intermedins. The medial and 
lateral borders are thinner and converge below: they give attachment to those 
Fig. 393.-Right patella. 
Anterior surface. 
Fig. 394.-Right patella. 
Posterior surface. THE TIBIA 
355 
portions of the Quadriceps femoris which are derived from the Vasti lateralis and 
medialis. 
Apex.-The apex is pointed, and gives attachment to the ligamentuni patellae. 
Structure.--The patella consists of a nearly uniform dense cancellous tissue, covered by a 
thin compact lamina. The cancelli immediately beneath the anterior surface are arranged 
parallel with it. In the rest of the bone they radiate from the articular surface toward the other 
parts of the bone. 
Ossification.-The patella is ossified from a single centre, which usually makes its appearance 
in the second or third year, but may be delayed until the sixth year. More rarely, the bone is 
developed by two centres, placed side by side. Ossification is completed about the age of puberty. 
Articulation.--The patella articulates with the femur. 
Applied Anatomy.--The main surgical interest about the patella is in connection with fractures, 
which are of frequent occurrence. They are most often produced by musculai' action-that is 
to say, by violent contraction of the quadriceps femoris while the limb is in a position of semi- 
flexion, so that the bone is snapped across the condyles of the femur and the fracture is transverse. 
Fracture of the patella is also produced by direct violence, such as falls on the knee, and here 
the fracture is usually stellate and the bone comminuted. Owing to the displacement of the 
fragments, and the difficulty there is in maintaining them in apposition, rmion takes place by 
fibrous tissue which may subsequently stretch, producing wide separation of the fragments and 
permanent lameness. Truly satisfactory results after this fracture are generally only to be 
obtained by opening the joint and wiring the fragments together, and this is especially so when 
there is marked separation of the fragments owing to laceration of the retinacula. 
It is an anatomical possibility, if the fracture involve only the lower and non-articular part 
of the bone, for this to take place without injury to the synovial membrane and without involving 
the cavity of the knee-joint. 
The Tibia (Shin Bone). 
The tibia (Figs. 396, 397) is situated at the medial side of the leg, and, 
excepting the femur, is the longest bone of the skeleton. It is prismoid in form, 
expanded above, where it enters into the 
knee-joint, contracted in the lower third, 
and again enlarged but to a lesser extent 
below. In the male, its direction is vertical, 
and parallel with the bone of the opposite 
side; but in the female it has a slightly 
oblique direction downward and lateralward, 
to compensate for the greater obliquity of 
the femur. It has a body and two extremities. 
The Upper Extremity (prozimaZ extremity). 
-The upper extremity is large, and expanded 
into two eminences, the medial and lateral 
condyles. The superior articular surface pre- 
sents two smooth articular facets (Fig. 395). 
The medial facet, oval in shape, is slightly 
concave from side to side, and from before 
backward. The lateral, nearly circular, is 
concave from side to side, but slightly convex from before backward, especially 
at its posterior part, where it is prolonged on to the posterior surface for a 
short distance. The central portions of these facets articulate with the con- 
dyles of the femur, while their peripheral portions support the menisci of the 
knee-joint, which here intervene between the two bones. Between the artic- 
ular facets, but nearer the posterior than the anterior aspect of the bone, is the 
intercondyloid eminence (spine of tibia), surmounted on either side by a prominent 
tubercle, on to the sides of which the articular facets are prolonged; in front of 
and behind the intercondyloid eminence are rough depressions for the attachment 
of the anterior and posterior cruciate ligaments and the menisci. The anterior 
surfaces of the condyles are continuous with one another, forming a large somewhat 
Tuberosity 
Intercondyloid eminence 
Fig. 395.-Upper surface of right tibia. 356 
OSTEOLOGY 
Articular capsule 
flattened area; this area is trian- 
gular, broad above, and perforated 
by large vascular foramina; narrow 
below where it ends in a large ob- 
long elevation, the tuberosity of 
the tibia, which gives attachment 
to the ligamentum patellae; a 
bursa intervenes between the deep 
surface of the ligament and the 
part of the bone immediately 
above the tuberosity. Posteriorly, 
the condyles are separated from 
each other by a shallow depres- 
sion, the posterior intercondyloid 
fossa, which gives attachment to 
part of the posterior cruciate liga- 
ment of the knee-joint. The 
medial condyle presents posteriorly 
a deep transverse groove, for the 
insertion of the tendon of the 
Semimembranosus. Its medial 
surface is convex, rough, and 
prominent; it gives attachment 
to the tibial collateral ligament. 
The lateral condyle presents pos- 
teriorly a flat articular facet, nearly 
circular in form, directed down- 
ward, backward, and lateralward, 
for articulation with the head of 
the fibula. Its lateral surface is 
convex, rough, and prominent in 
front: on it is an eminence, situated 
on a level with the upper border 
of the tuberosity and at the junc- 
tion of its anterior and lateral 
surfaces, for the attachment of 
the iliotibial band. Just below 
this a part of the Extensor digi- 
torum longus takes origin and a 
slip from the tendon of the Biceps 
femoris is inserted. 
The Body or Shaft {corpus tibiae). 
-The body has three borders and 
three surfaces. 
Borders.-The anterior crest or 
border, the most prominent of the 
three, commences above at the 
tuberosity, and ends below at the 
anterior margin of the - medial 
malleolus. It is sinuous and 
prominent in the upper two-thirds 
of its extent, but smooth and 
rounded below; it gives attach- 
ment to the deep fascia of the 
leg. 
Styloid process 
Fibular 
collateral 
ligament 
Articular 
capsule 
Medial malleolus 
Fig. 396.-Bones of the right leg. Anterior surface. 
Lateral malleolus THE TIBIA 
357 
The medial border is smooth and rounded above and below, but more prominent 
in the centre; it begins at the back part of the medial condyle, and ends at the 
posterior border of the medial 
malleolus; its upper part gives 
attachment to the tibial collat- 
eral ligament of the knee-joint 
to the extent of about 5 cm., 
and insertion to some fibres of 
the Popliteus; from its middle 
third some fibres of the Soleus 
and Flexor digitorum longus 
take origin. 
The interosseous crest or lat- 
eral border is thin and promi- 
nent, especially its central part, 
and gives attachment to the 
interosseous membrane; it com- 
mences above in front of the 
fibular articular facet, and 
bifurcates below, to form the 
boundaries of a triangular rough 
surface, for the attachment of 
the interosseous ligament con- 
necting the tibia and fibula. 
Surfaces.-The medial surface 
is smooth, convex, and broader 
above than below; its upper 
third, directed forward and 
medialward, is covered by the 
aponeurosis derived from the 
tendon of the Sartorius, and by 
the tendons of the Gracilis and 
Semitendinosus, all of which 
are inserted nearly as far for- 
ward as the anterior crest; in 
the rest of its extent it is sub- 
cutaneous. 
The lateral surface is narrower 
than the medial; its upper two- 
thirds present a shallow groove 
for the origin of the Tibialis 
anterior; its lower third is 
smooth, convex, curves grad- 
ually forward to the anterior 
aspect of the bone, and is 
covered by the tendons of the 
Tibialis anterior, Extensor hal- 
lucis longus, and Extensor digi- 
torum longus, arranged in this 
order from the medial side. 
The posterior surface (Fig. 397) 
presents, at its upper part, a 
prominent ridge, the popliteal 
line, which extends obliquely 
downward from the back part of 
Articular 
capsule 
Articular 
capsule 
- Styloid 
process 
FIBULA 
Articulates with talus 
Fig. 397.-Bones of the right leg. Posterior surface. 
Articular capsule. 358 
OSTEOLOGY 
the articular facet for the fibula to the medial border, at the junction of its upper 
and middle thirds; it marks the lower limit of the insertion of the Popliteus, serves 
for the attachment of the fascia covering this muscle, and gives origin to part of 
the Soleus, Flexor digitorum longus, and Tibialis posterior. The triangular area, 
above this line, gives insertion to the Popliteus. The middle third of the posterior 
surface is divided by a vertical ridge into two parts; the ridge begins at the popliteal 
line and is well-marked above, but indistinct below; the medial and broader por- 
tion gives origin to the Flexor digitorum longus, the lateral and narrower to part 
of the Tibialis posterior. The remaining part of the posterior surface is smooth 
and covered by the Tibialis posterior, Flexor digitorum longus, and Flexor hallucis 
longus. Immediately below the popliteal line is the nutrient foramen, which is 
large and directed obliquely downward. 
The Lower Extremity (distal extremity').-The lower extremity, much smaller 
than the upper, presents five surfaces; it is prolonged downward on its medial 
side as a strong process, the medial malleolus. 
Surfaces.-The inferior articular surface is quadrilateral, and smooth for articu- 
lation with the talus. It is concave from before backward, broader in front than 
behind, and traversed from before backward by a slight elevation, separating 
two depressions. It is continuous with that on the medial malleolus. 
Upper extremity 
Appears before or 
shortly after birth 
Joins body 
about 20th year 
Appeals at 2nd. 
year 
Joins body about 
\8th year 
Lower extremity 
Fig. 398.-Plan of ossification of the tibia. From three 
centres. 
Fig. 399.-Epiphysial lines of tibia and fibula 
in a young adult. Anterior aspect. 
The anterior surface of the lower extremity is smooth and rounded above, and 
covered by the tendons of the Extensor muscles; its lower margin presents a rough 
transverse depression for the attachment of the articular capsule of the ankle- 
joint. 
The posterior surface is traversed by a shallow groove directed obliquely down- 
ward and medialward, continuous with a similar groove on the posterior surface 
of the talus and serving for the passage of the tendon of the Flexor hallucis longus. 
The lateral surface presents a triangular rough depression for the attachment 
of the inferior interosseous ligament connecting it with the fibula; the lower part THE FIBULA 
359 
of this depression is smooth, covered with cartilage in the recent state, and articu- 
lates with the fibula. The surface is bounded by two prominent borders, con- 
tinuous above with the interosseous crest; they afford attachment to the anterior 
and posterior ligaments of the lateral malleolus. 
The medial surface is prolonged downward to form a strong pyramidal process, 
flattened from without inward-the medial malleolus. The medial surface of this 
process is convex and subcutaneous; its lateral or articular surface is smooth and 
slightly concave, and articulates with the talus; its anterior border is rough, for 
the attachment of the anterior fibres of the deltoid ligament of the ankle-joint; 
its posterior border presents a broad groove, the malleolar sulcus, directed obliquely 
downward and medialward, and occasionally double; this sulcus lodges the tendons 
of the Tibialis posterior and Flexor digitorum longus. The summit of the medial 
malleolus is marked by a rough depression behind, for the attachment of the 
deltoid ligament. 
Structure.-The structure of the tibia is like that of the other long bones. The compact wall 
of the body is thickest at the junction of the middle and lower thirds of the bone. 
Ossification.-The tibia is ossified from three centres (Figs. 398, 399): one for the body and 
one for either extremity. Ossification begins in the centre of the body, about the seventh week 
of fetal life, and gradually extends toward the extremities. The centre for the upper epiphysis 
appears before or shortly after birth; it is flattened in form, and has a thin tongue-shaped process 
in front, which forms the tuberosity (Fig. 399); that for the lower epiphysis appears in the second 
year. The lower epiphysis joins the body at about the eighteenth, and the upper one joins about 
the twentieth year. Two additional centres occasionally exist, one for the tongue-shaped process 
of the upper epiphysis, which forms the tuberosity, and one for the medial malleolus. 
Articulations.-The tibia articulates with three bones: the femur, fibula, and talus. 
The Fibula (Calf Bone). 
The fibula (Figs. 396, 397) is placed on the lateral side of the tibia, with which 
it is connected above and below. It is the smaller of the two bones, and, in 
proportion to its length, the most slender of all the long bones. Its upper 
extremity is small, placed toward the back of the head of the tibia, below the level 
of the knee-joint, and excluded from the formation of this joint. Its lower extremity 
inclines a little forward, so as to be on a plane anterior to that of the upper end; 
it projects below the tibia, and forms the lateral part of the ankle-joint. The 
bone has a body and two extremities. 
The Upper Extremity or Head (capitulum fibulae; proximal extremity).-The 
upper extremity is of an irregular quadrate form, presenting above a flattened 
articular surface, directed upward, forward, and medialward, for articulation with 
a corresponding surface on the lateral condyle of the tibia. On the lateral side 
is a thick and rough prominence continued behind into a pointed eminence, the 
apex (styloid process'), which projects upward from the posterior part of the head. 
The prominence, at its upper and lateral part, gives attachment to the tendon of 
the Biceps femoris and to the fibular collateral ligament of the knee-joint, the liga- 
ment dividing the tendon into two parts. The remaining part of the circumference 
of the head is rough, for the attachment of muscles and ligaments. It presents in 
front a tubercle for the origin of the upper and anterior fibres of the Peronaeus 
longus, and a surface for the attachment of the anterior ligament of the head; 
and behind, another tubercle, for the attachment of the posterior ligament of the 
head and the origin of the upper fibres of the Soleus. 
The Body or Shaft (corpus fibulae).--The body presents four borders-the 
antero-lateral, the antero-medial, the postero-lateral, and the postero-medial; and 
four surfaces-anterior, posterior, medial, and lateral. 
Borders.-The antero-lateral border begins above in front of the head, runs ver- 
tically downward to a little below the middle of the bone, and then curving some- 
what lateralward, bifurcates so as to embrace a triangular subcutaneous surface 360 
OSTEOLOGY 
immediately above the lateral malleolus. This border gives attachment to an 
intermuscular septum, which separates the Extensor muscles on the anterior 
surface of the leg from the Peronaei longus and brevis on the lateral surface. 
The antero-medial border, or interosseous crest, is situated close to the medial 
side of the preceding, and runs nearly parallel with it in the upper third of its 
extent, but diverges from it in the lower two-thirds. It begins above just beneath 
the head of the bone (sometimes it is quite indistinct for about 2.5 cm: below the 
head), and ends at the apex of a rough triangular surface immediately above the 
articular facet of the lateral malleolus. It serves for the attachment of the inter- 
osseous membrane, which separates the Extensor muscles in front from the Flexor 
muscles behind. 
The postero-lateral border is prominent; it begins above at the apex, and ends 
below in the posterior border of the lateral malleolus. It is directed lateralward 
above, backward in the middle of its course, backward, and a little medial ward 
below, and gives attachment to an aponeurosis which separates the Peronaei on 
the lateral surface from the Flexor muscles on the posterior surface. 
The postero-medial border, sometimes called the oblique line, begins above at the 
medial side of the head, and ends by becoming continuous with the interosseous 
crest at the lower fourth of the bone. It is well-marked and prominent at the upper 
and middle parts of the bone. It gives attachment to an aponeurosis which sep- 
arates the Tibialis posterior from the Soleus and Flexor hallucis longus. 
Surfaces.-The anterior surface is the interval between the antero-lateral and 
antero-medial borders. It is extremely narrow and flat in the upper third of its 
extent; broader and grooved longitudinally in its lower third; it serves for the 
origin of three muscles; the Extensor digitorum longus, Extensor hallucis longus, 
and Peronaeus ter tins. 
The posterior surface is the space included between the postero-lateral and the 
postero-medial borders; it is continuous below with the triangular area above 
the articular surface of the lateral malleolus; it is directed backward above, back- 
ward and medialward at its middle, directly medialward below. Its upper third 
is rough, for the origin of the Soleus; its lower part presents a triangular surface, 
connected to the tibia by a strong interosseous ligament; the intervening part of 
the surface is covered by the fibres of origin of the Flexor hallucis longus. Near 
the middle of this surface is the nutrient foramen, which is directed downward. 
The medial surface is the interval included between the antero-medial and the 
postero-medial borders. It is grooved for the origin of the Tibialis posterior. 
The lateral surface is the space between the antero-lateral and postero-lateral 
borders. It is broad, and often deeply grooved; it is directed lateralward in the 
upper two-thirds of its course, backward in the lower third, where it is continuous 
with the posterior border of the lateral malleolus. This surface gives origin to 
the Peronaei longus and brevis. 
The Lower Extremity or Lateral Malleolus (malleolus lateralis; distal extremity; 
external malleolus).-The lower extremity is of a pyramidal form, and somewhat 
flattened from side to side; it descends to a lower level than the medial malleolus. 
The lateral surface is convex, subcutaneous, and continuous with the triangular, 
subcutaneous surface on the lateral side of the body. The medial surface (Fig. 
400) presents in front a smooth triangular surface, convex from above downward, 
which articulates with a corresponding surface on the lateral side of the talus. 
Behind and beneath the articular surface is a rough depression, which gives attach- 
ment to the posterior talofibular ligament. The anterior border is thick and rough, 
and marked below by a depression for the attachment of the anterior talofibular 
ligament. The posterior border is broad and presents the shallow malleolar sulcus, 
for the passage of the tendons of the Peronaei longus and brevis. The summit 
is rounded, and give attachment to the calcaneofibular ligament. THE FIBULA 
361 
Articulations.-The fibula articulates with two bones: the tibia and talus. 
Ossification.-The fibula is ossified from three centres (Fig. 401): one for the body, and one 
for either end. Ossification begins in the body about the eighth week of fetal fife, and extends 
toward the extremities. At birth the ends are cartilaginous. Ossification commences in the 
lower end in the second year, and in the upper about the fourth year. The lower epiphysis, 
the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins 
about the twenty-fifth year. 
Applied Anatomy of the Tibia and Fibula.-In fractures of the bones of the leg, both bones 
are generally involved, but either bone may be broken separately, the fibula more frequently 
than the tibia. Fracture of both bones may be caused by either direct or indirect violence. When 
it occurs from indirect force, the fracture in the tibia is at the junction of the middle and lower 
thirds of the bone. Many causes conduce to render this the weakest part of the bone. The 
fracture of the fibula is usually at a rather higher level. These fractures present great variety, 
both as regards their direction and condition. They may be oblique, transverse, longitudinal,* 
or spiral. When oblique, they are for the most part the result of indirect violence, and the direc- 
tion of the fracture is downward, forward, and medialward in many cases, but may be down- 
ward and lateralward, or downward and backward. When transverse, the fracture is often at- 
the upper part of the bone, and is the result of direct violence. The spiral fracture of the tibia 
generally starts as a vertical fissure, involving the ankle-joint, and is associated with fracture of 
the fibula higher up. It is the result of torsion, from twisting of the body while the foot is fixed. 
Upper extremity 
Interosseous 
crest 
Appears about 
kth year 
Unites about 
25th year 
For talus- 
For posterior 
talofibular ligt. 
Appears at 
2nd year 
Unites about 
20th year 
Lower extremity 
Fig. 400.-Lower extremity of right fibula. 
Medial aspect. 
Fig. 401.-Plan of ossification of the 
fibula. From three centres. 
Fractures of the tibia alone are almost always the result of direct violence, except where the 
malleolus is broken off by twists of the foot. Fractures of the fibula alone may arise from indirect 
or direct force, those of the lower end being usually the result of the former, and those higher 
up being caused by a direct blow on the part. 
The tibia is the bone which is most commonly and most extensively distorted in rickets. It 
bends at the junction of the middle and lower third, its weakest part, and presents a curve forward 
with generally some lateral displacement. 
The tibia is more often the seat of acute infective necrosis than any other bone in the body, 
and with the formation of the sequestrum, a large amount of new bony material is thrown out 
by the periosteum. The sequence of events in this disease can be very closely followed in the 
case of the tibia, and it is not uncommon to find a patient from whom the whole diaphysis of the 
tibia has been removed, going about with a new bone entirely of periosteal formation. Chronic 
bone abscess is more frequently met with in the cancellous tissue of the head or lower end of the 
tibia than in any other bone in the body. These abscesses are very chronic, and in most cases 
the result of tuberculous osteitis, although they are sometimes due to the organisms of suppura- 
tion or even the Bacillus typhoszis. 362 
OSTEOLOGY 
THE FOOT. 
The skeleton of the foot (Figs. 403 and 404) consists of three parts: the tarsus, 
metatarsus, and phalanges. 
The Tarsus (Ossa Tarsi). 
The tarsal bones are seven in number, viz., the calcaneus, talus, cuboid, navicular, 
and the first, second, and third cuneiforms. 
Groove for Peronceus brevis 
Trochlear process 
Groove for Peronceus longus 
For tendo calcaneus 
Lateral process of tuberosity 
For posterior facet of talus 
For middle facet of talus 
For anterior facet of talus 
For cuboid 
Medial process of tuberosity 
Groove for Flexor hallucis longus 
Sustentaculum tali 
Groove Jor inter osseus ligament 
Fig. 402.-The left calcaneus. A. Postero-lateral view. B. Antero-medial view. 
The Calcaneus {os colds') (Fig. 402).-The calcaneus is the largest of the tarsal 
bones. It is situated at the lower and back part of the foot, serving to transmit 
the weight of the body to the ground, and forming a strong lever for the muscles 
of the calf. It is irregularly cuboidal in form, having its long axis directed forward 
and lateralward; it presents for examination six surfaces. 
Surfaces.-The superior surface extends behind on to that part of the bone which 
projects backward to form the heel. This varies in length in different individuals, THE TARSUS 
363 
Groove for tendon of 
Flexor hallucis longus 
Groove for tendon of 
Peronaeus longus 
Groove, for tendon of 
Peronaeus brevis 
Tarsus 
Peronaeus tertius 
Peronaeus brevis 
Metatarsus 
Ext. digitorum brevis 
Phalanges 
% 
X? 
X 
x 
% 
Ext. hallucis longus 
Fig. 403.-Bones of the right foot. Dorsal surface. 364 
OSTEOLOGY 
Abductor hallucis 
Medial head of 
Lateral head of quadrates 
PLANTS 
.Flexor hallucis brevis 
Tubercle of 
navicular 
Tibialis anterior 
Plexor brevis 
and Abductor 
DIGITI QUINTI 
Two sesamoid- 
bones 
Flexor digitorum 
brevis 
Flexor pigitorum 
LONGUS 
Fig. 404.-Bones of the right foot. Plantar surface. THE TARSUS 
365 
is convex from side to side, concave from before backward, and supports a mass of 
fat placed in front of the tendo calcaneus. In front of this area is a large usually 
somewhat oval-shaped facet, the posterior articular surface, which looks upward 
and forward; it is convex from behind forward, and articulates with the posterior 
calcaneal facet on the under surface of the talus. It is bounded anteriorly by a 
deep depression which is continued backward and medialward in the form of a 
groove, the calcaneal sulcus. In the articulated foot this sulcus lies below a similar 
one on the under surface of the talus, and the two form a canal (sinus tarsi) for the 
lodgement of the interosseous talocalcaneal ligament. In front and to the medial 
side of this groove is an elongated facet, concave from behind forward, and with its 
long axis directed forward and lateralward. This facet is frequently divided into 
two by a notch: of the two, the posterior, and larger is termed the middle articular 
surface; it is supported on a projecting process of bone, the sustentaculum tali, 
and articulates with the middle calcaneal facet on the under surface of the talus; 
the anterior articular surface is placed on the anterior part of the body, and articu- 
lates with the anterior calcaneal facet on the talus. The upper surface, anterior 
and lateral to the facets, is rough for the attachment of ligaments and for the origin 
of the Extensor digitorum brevis. 
The inferior or plantar surface is uneven, wider behind than in front, and convex 
from side to side; it is bounded posteriorly by a transverse elevation, the calcaneal 
tuberosity, which is depressed in the middle and prolonged at either end into a 
process; the lateral process, small, prominent, and rounded, gives origin to part 
of the Abductor digiti quinti; the medial process, broader and larger, gives attach- 
ment, by its prominent medial margin, to the Abductor hallucis, and in front 
to the Flexor digitorum brevis and the plantar aponeurosis; the depression between 
the processes gives origin to the Abductor digiti quinti. The rough surface in 
front of the processes gives attachment to the long plantar ligament, and to the 
lateral head of the Quadratus plantae; while to a prominent tubercle nearer the 
anterior part of this surface, as well as to a transverse groove in front of the tubercle, 
is attached the plantar calcaneocuboid ligament. 
The lateral surface is broad behind and narrow in front, flat and almost sub- 
cutaneous; near its centre is a tubercle, for the attachment of the calcaneofibular 
ligament. At its upper and anterior part, this surface gives attachment to the 
lateral talocalcaneal ligament; and in front of the tubercle it presents a narrow 
surface marked by two oblique grooves. The grooves are separated by an elevated 
ridge, or tubercle, the trochlear process (peroneal tubercle), which varies much in 
size in different bones. The superior groove transmits the tendon of the Peronaeus 
brevis; the inferior groove, that of the Peronaeus longus. 
The medial surface is deeply concave; it is directed obliquely downward and 
forward, and serves for the transmission of the plantar vessels and nerves into the 
sole of the foot; it affords origin to part of the Quadratus plantae. At its upper 
and forepart is a horizontal eminence, the sustentaculum tali, which gives attach- 
ment to a slip of the tendon of the Tibialis posterior. This eminence is concave 
above, and articulates with the middle calcaneal articular surface of the talus; 
below, it is grooved for the tendon of the Flexor hallucis longus; its anterior margin 
gives attachment to the plantar calcaneonavicular ligament, and its medial, 
to a part of the deltoid ligament of the ankle-joint. 
The anterior or cuboid articular surface is of a somewhat triangular form. It is 
concave from above downward and lateralward, and convex in a direction at right 
angles to this. Its medial border gives attachment to the plantar calcaneonavicular 
ligament. 
The posterior surface is prominent, convex, wider below than above, and divisible 
into three areas. The lowest of these is rough, and covered by the fatty and fibrous 
tissue of the heel; the middle, also rough, gives insertion to the tendo calcaneus 366 
OSTEOLOGY 
and Plantaris; while the highest is smooth, and is covered by a bursa which inter- 
venes between it and the tendo calcaneus. ■ 
Articulations.-The calcaneus articulates with two bones: the talus and cuboid. 
For navicular 
Neck 
Trochlea for tibia 
tor transverse inferior tibio- 
fibular ligament 
Posterior process 
For lat. malleolus 
For med malleolus 
Trochlea for tibia 
For navicular 
Groove for Flexor 
hallucis longus 
For calcaneus 
For plantar calcaneo- 
navicular ligament 
For navicular 
Anterior calcaneal 
articular surface 
Middle calcaneal 
articular surface 
Groove for interosseous 
talocalcaneal ligament 
Posterior calcaneal 
articular surface 
Groove for Flex, 
hallucis longus 
Fig. 405.-The left talus. A. Supero-lateral view. B. Infero-medial view. C. Inferior view. 
The Talus (astragalus; ankle bone) (Fig. 405).-The talus is the second largest 
of the tarsal bones. It occupies the middle and upper part of the tarsus, support- 
ing the tibia above, resting upon the calcaneus below, articulating on either side 
with the malleoli, and in front with the navicular. It consists of a body, a neck, 
and a head. THE TARSUS 
367 
The Body (corpus tali).-The superior surface of the body presents, behind, a 
smooth trochlear surface, the trochlea, for articulation with the tibia. The trochlea 
is broader in front than behind, convex from before backward, slightly concave 
from side to side: in front it is continuous with the upper surface of the neck of 
the bone. 
The inferior surface presents two articular areas, the posterior and middle cal- 
caneal surfaces, separated from one another by a deep groove, the sulcus tali. 
The groove runs obliquely forward and lateralward, becoming gradually broader 
and deeper in front: in the articulated foot it lies above a similar groove upon 
the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled 
up in the recent state by the interosseous talocalcaneal ligament. The posterior 
calcaneal articular surface is large and of an oval or oblong form. It articulates 
with the corresponding facet on the upper surface of the calcaneus,1 and is deeply 
concave in the direction of its long axis which runs forward and lateralward at 
an angle of about 45° with the median plane of the body. The middle calcaneal 
articular surface is small, oval in form and slightly convex; it articulates with the 
upper surface of the sustentaculum tali of the calcaneus. 
The medial surface presents at its upper part a pear-shaped articular facet for 
the medial malleolus, continuous above with the trochlea; below the articular 
surface is a rough depression for the attachment of the deep portion of the deltoid 
ligament of the ankle-joint. 
The lateral surface carries a large triangular facet, concave from above downward, 
for articulation with the lateral malleolus; its anterior half is continuous above with 
the trochlea; and in front of it is a rough depression for the attachment of the ante- 
rior talofibular ligament. Between the posterior half of the lateral border of the 
trochlea and the posterior part of the base of the fibular articular surface is a tri- 
angular facet (Fawcett2) which comes into contact with the transverse inferior 
tibiofibular ligament during flexion of the ankle-joint; below the base of this facet 
is a groove which affords attachment to the posterior talofibular ligament. 
The posterior surface is narrow, and traversed by a groove running obliquely 
downward and medialward, and transmitting the tendon of the Flexor hallucis 
longus. Lateral to the groove is a prominent tubercle, the posterior process, to 
which the posterior talofibular ligament is attached; this process is sometimes 
separated from the rest of the talus, and is then known as the os trigonum. Medial 
to the groove is a second smaller tubercle. 
The Neck (collum tali).-The neck is directed forward and medialward, and 
comprises the constricted portion of the bone between the body and the oval head. 
Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral 
surface is concave and is continuous below with the deep groove for the inter- 
osseous talocalcaneal ligament. 
The Head (caput tali).-The head looks forward and medialward; its anterior 
articular or navicular surface is large, oval, and convex. Its inferior surface has two 
facets, which are best seen in the recent condition. The medial, situated in front 
of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and 
rests on the plantar calcaneonavicular ligament; the lateral, named the anterior 
calcaneal articular surface, is somewhat flattened, and articulates with the facet on 
the upper surface of the anterior part of the calcaneus. 
Articulations.-The talus articulates with four bones: tibia, fibula, calcaneus, and navicular. 
The Cuboid Bone (os cuboideum) (Fig. 406).-The cuboid bone is placed on the 
lateral side of the foot, in front of the calcaneus, and behind the fourth and fifth 
metatarsal bones. It is of a pyramidal shape, its base being directed medialward. 
1 Sewell (Journal of Anatomy and Physiology, vol. xxxviii) pointed out that in about 10 per cent, of bones a small 
triangular facet, continuous with the posterior calcaneal facet, is present at the junction of the lateral surface of the 
body with the posterior wall of the sulcus tali. 
2 Edinburgh Medical Journal, 1895. 368 
OSTEOLOGY 
Surfaces.-The dorsal surface, directed upward and lateralward, is rough, for the 
attachment of ligaments. The plantar surface presents in front a deep groove, 
the peroneal sulcus, which runs obliquely forward and medialward; it lodges the 
tendon of the Peronaeus longus, and is bounded behind by a prominent ridge, 
to which the long plantar ligament is attached. The ridge ends laterally in an 
eminence, the tuberosity, the surface of which presents an oval facet; on this facet 
glides the sesamoid bone or cartilage frequently found in the tendon of the Pero- 
naeus longus. The surface of bone behind the groove is rough, for the attachment 
of the plantar calcaneocuboid ligament, a few fibres of the Flexor hallucis brevis, 
and a fasciculus from the tendon of the Tibialis posterior. The lateral surface 
presents a deep notch formed by the commencement of the peroneal sulcus. The 
For 3rd cuneiform 
For ^th metatarsal 
Occasional facet 
for navicular 
For 5th 
metatarsal 
Peronceal 
sulcus 
Tuberosity For calcaneus 
Fig. 406.-The left cuboid. A. Antero-medial view. B. Postero-lateral view. 
posterior surface is smooth, triangular, and concavo-convex, for articulation with 
the anterior surface of the calcaneus; its infero-medial angle projects backward 
as a process which underlies and supports the anterior end of the calcaneus. The 
anterior surface, of smaller size, but also irregularly triangular, is divided by a 
vertical ridge into two facets: the medial, quadrilateral in form, articulates with 
the fourth metatarsal; the lateral, larger and more triangular, articulates with the 
fifth. The medial surface is broad, irregularly quadrilateral, and presents at 
its middle and upper part a smooth oval facet, for articulation with the third 
cuneiform; and behind this (occasionally) a smaller facet, for articulation with 
the navicular; it is rough in the rest of its extent, for the attachment of strong 
interosseous ligaments. 
Articulations.--The cuboid articulates with four bones: the calcaneus, third cuneiform, and 
fourth and fifth metatarsals; occasionally with a fifth, the navicular. 
For lsi cuneiform 
For 2nd cuneiform 
For 3rd 
cuneiform 
Occasional 
s facet for 
cuboid 
For talus 
Tuberosity 
Fig. 407.-The left navicular. A. Antero-lateral view. B. Postero-medial view. 
The Navicular Bone (os naviculare pedis; scaphoid bone) (Fig. 407).-The 
navicular bone is situated at the medial side of the tarsus, between the talus 
behind and the cuneiform bones in front. THE TARSUS 
369 
Surfaces.-The anterior surface is convex from side to side, and subdivided by two 
ridges into three facets, for articulation with the three cuneiform bones. The 
posterior surface is oval, concave, broader laterally than medially, and articulates 
with the rounded head of the talus. The dorsal surface is convex from side to side, 
and rough for the attachment of ligaments. The plantar surface is irregular, and 
also rough for the attachment of ligaments. The medial surface presents a rounded 
tuberosity, the lower part of which gives attachment to part of the tendon of the 
Tibialis posterior. The lateral surface is rough and irregular for the attachment of 
ligaments, and occasionally presents a small facet for articulation with the cuboid 
bone. 
Articulations.-The navicular articulates with/ozzr bones: the talus and the three cuneiforms; 
occasionally with a fifth, the cuboid. 
The First Cuneiform Bone {os cuneiform, primum; internal cuneiform) (Fig. 408).- 
The first cuneiform bone is the largest of the three cuneiforms. It is situated at the 
medial side of the foot, between 
the navicular behind and the base 
of the first metatarsal in front. 
Surfaces.-The medial surface 
is subcutaneous, broad, and 
quadrilateral; at its anterior 
plantar angle is a smooth oval 
impression, into which part of 
the tendon of the Tibialis ante- 
rior is inserted; in the rest of its 
extent it is rough for the attach- 
ment of ligaments. The lateral 
surface is concave, presenting, 
along its superior and posterior 
borders a narrow L-shaped sur- 
face, the vertical limb and pos- 
terior part of the horizontal limb 
of which articulate with the second cuneiform, while the anterior part of the 
horizontal limb articulates with the second metatarsal bone: the rest of this 
surface is rough for the attachment of ligaments and part of the tendon of the 
Peronaeus longus. The anterior surface, kidney-shaped and much larger than 
the posterior, articulates with the first metatarsal bone. The posterior surface 
is triangular, concave, and articulates with the most medial and largest of the 
three facets on the anterior surface of the navicular. The plantar surface is 
rough, and forms the base of the wedge; at its back part is a tuberosity for the 
insertion of part of the tendon of the Tibialis posterior. It also gives insertion 
in front to part of the tendon of the Tibialis anterior. The dorsal surface is the 
narrow end of the wedge, and is directed upward and lateralward; it is rough for 
the attachment of ligaments. 
For 1st metatarsal 
For 2nd 
metatarsal 
For 
2nd cuneiform 
For tendon of 
Tibialis anterior 
For navicular 
Fig. 408.-The left first cuneiform. A. Antero-medial view. 
B. Postero-lateral view. 
Articulations.-The first cuneiform articulates with four bones: the navicular, second cunei- 
form, and first and second metatarsals. 
The Second Cuneiform Bone (os cuneiforms secundum; middle cuneiform) (Fig. 
409).-The second cuneiform bone, the smallest of the three, is of very regular 
wedge-like form, the thin end being directed downward. It is situated between 
the other two cuneiforms, and articulates with the navicular behind, and the 
second metatarsal in front. 
Surfaces.-The anterior surface, triangular in form, and narrower than the pos- 
terior, articulates with the base of the second metatarsal bone. The posterior sur- 
face, also triangular, articulates with the intermediate facet on the anterior surface 370 
OSTEOLOGY 
of the navicular. The medial surface carries an L-shaped articular facet, running 
along the superior and posterior borders, for articulation with the first cuneiform, 
and is rough in the rest of its extent for the attachment of ligaments. The lateral 
surface presents posteriorly a smooth 
facet for articulation with the third 
cuneiform bone. The dorsal surface 
forms the base of the wedge; it is 
quadrilateral and rough for the at- 
tachment of ligaments. The plantar 
surface, sharp and tuberculated, is 
also rough for the attachment of 
ligaments, and for the insertion of a 
slip from the tendon of the Tibialis 
posterior. 
For lfii cuneiform 
For navicular 
Fig. 409.-The left second cuneiform. A. Antero-medial 
view. B. Postero-lateral view. 
For 2nd metatarsal 
For 3rd cuneiform 
Articulations.-The second cuneiform articulates with four bones: the navicular, first and 
third cuneiforms, and second metatarsal. 
The Third Cuneiform Bone (os cuneiforms tertium; external cuneiform) (Fig. 410). 
-The third cuneiform bone, intermediate in size between the two preceding, is 
wedge-shaped, the base being uppermost. It occupies the centre of the front row 
of the tarsal bones, between the second cuneiform medially, the cuboid laterally, 
the navicular behind, and the third metatarsal in front. 
Surfaces.-The anterior surface, triangular in form, articulates with the third 
metatarsal bone. The posterior surface articulates with the lateral facet on the 
anterior surface of the navicular, and is rough below for the attachment of liga- 
mentous fibres. The medial surface presents an anterior and a posterior articular 
facet, separated by a rough depression: the anterior, sometimes divided, articulates 
with the lateral side of the base of the second metatarsal bone; the posterior skirts 
For navicular 
For 2nd cuneiform 
For 4th 
metatarsal 
For cuboid 
For 2nd 
metatarsal 
For 3rd 
metatarsal 
Fig. 410.-The left third cuneiform. A. Postero-medial view. B. Antero-lateral view. 
the posterior border, and articulates with the second cuneiform; the rough depres- 
sion gives attachment to an interosseous ligament. The lateral surface also pre- 
sents two articular facets, separated by a rough non-articular area; the anterior 
facet, situated at the superior angle of the bone, is small and semi-oval in shape, 
and' articulates with the medial side of the base of the fourth metatarsal bone; 
the posterior and larger one is triangular or oval, and articulates with the cuboid; 
the rough, non-articular area serves for the attachment of an interosseous ligament. 
The three facets for articulation with the three metatarsal bones are continuous 
with one another; those for articulation with the second cuneiform and navicular 
are also continuous, but that for articulation with the cuboid is usually separate. 
The dorsal surface is of an oblong form, its postero-lateral angle being prolonged 
backward. The plantar surface is a rounded margin, and serves for the attachment THE METATARSUS 
371 
of part of the tendon of the Tibialis posterior, part of the Flexor hallucis brevis, 
and ligaments. 
Articulations.-The third cuneiform articulates with six bones: the navicular, second cunei- 
form, cuboid, and second, third, and fourth metatarsals. 
The Metatarsus. 
The metatarsus consists of five bones which are numbered from the medial 
side (ossa metatarsalia I.-V.); each presents for examination a body and two 
extremities. 
Common Characteristics of the Metatarsal Bones.-The body is prismoid in 
form, tapers gradually from the tarsal to the phalangeal extremity, and is curved 
longitudinally, so as to be concave below, slightly convex above. The base or 
posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, 
and by its sides with the contiguous metatarsal bones: its dorsal and plantar 
surfaces are rough for the attachment of ligaments. The head or anterior extremity 
presents a convex articular surface, oblong from above downward, and extend- 
ing farther backward below than above. Its sides are flattened, and on each is a 
depression, surmounted by a tubercle, for ligamentous attachment. Its plantar 
surface is grooved antero-posteriorly for the passage of the Flexor tendons, and 
marked on either side by an articular eminence continuous with the terminal 
articular surface. 
For sesamoid bones 
For 3rd 
metatarsal 
For 1st 
cuneiform 
For 1st 
cuneiform 
Far Peronceus 
longus 
For 2nd 
cuneiform 
For 3rd 
cuneiform 
Fig. 411.-The first metatarsal. (Left.) 
Fig. 412.-The second metatarsal. (Left.) 
Characteristics of the Individual Metatarsal Bones. - The First Metatarsal 
Bone (os metatarsale I; metatarsal bone of the great toe) (Fig. 411).--The first 
metatarsal bone is remarkable for its great thickness, and is the shortest of 
the metatarsal bones. The body is strong, and of well-marked prismoid form. 
The base presents, as a rule, no articular facets on its sides, but occasionally 
on the lateral side there is an oval facet, by which it articulates with the second 
metatarsal. Its proximal articular surface is of large size and kidney-shaped; its 372 
OSTEOLOGY 
circumference is grooved, for the tarsometatarsal ligaments, and medially gives 
insertion to part of the tendon of the Tibialis anterior; its plantar angle presents 
a rough oval prominence for the insertion of the tendon of the Peronaeus longus. 
The head is large; on its plantar surface are two grooved facets, on which glide 
sesamoid bones; the facets are separated by a smooth elevation. 
The Second Metatarsal Bone (os metatarsale II) (Fig. 412).-The second meta- 
tarsal bone is the longest of the metatarsal bones, being prolonged backward 
into the recess formed by the three cuneiform bones. Its base is broad above, 
narrow and rough below. It presents four articular surfaces: one behind, of a 
triangular form, for articulation with the second cuneiform; one at the upper part 
of its medial surface, for articulation with the first cuneiform; and two on its lateral 
surface, an upper and lower, separated by a rough non-articular interval. Each 
of these lateral articular surfaces is divided into two by a vertical ridge; the two 
anterior facets articulate with the third metatarsal; the two posterior (sometimes 
continuous) with the third cuneiform. A fifth facet is occasionally present for 
articulation with the first metatarsal'; it is oval in shape, and is situated on the 
medial side of the body near the base. 
For 3rd 
metatarsal 
For 2nd ( 
metatarsal 
For 2nd 
meta- 
tarsal 
For 
3rd 
cuneiform 
For Mh 
metatarsal 
For cuboid 
Fig. 413.-The third metatarsal. (Left.) 
For 3rd cuneiform 
Fig. 414.-The fourth metatarsal. (Left.) 
For 5th metatarsal 
The Third Metatarsal Bone (os metatarsale 111) (Fig. 413).-The third meta- 
tarsal bone articulates proximally, by means of a triangular smooth surface, 
with the third cuneiform; medially, by two facets, with the second metatarsal; 
and laterally, by a single facet, with the fourth metatarsal. This last facet is 
situated at the dorsal angle of the base. 
The Fourth Metatarsal Bone (os metatarsale IV) (Fig. 414).-The fourth meta- 
tarsal bone is smaller in size than the preceding; its base presents an oblique 
quadrilateral surface for articulation with the cuboid; a smooth facet on the medial 
side, divided by a ridge into an anterior portion for articulation with the third 
metatarsal, and a posterior portion for articulation with the third cuneiform; on 
the lateral side a single facet, for articulation with the fifth metatarsal. 
The Fifth Metatarsal Bone (os metatarsale F) (Fig. 415).-The fifth metatarsal 
bone is recognized by a rough eminence, the tuberosity, on the lateral side of its THE PHALANGES OF THE FOOT 
373 
base. The base articulates behind, by a triangular surface cut obliquely in a trans- 
verse direction, with the cuboid; and medially, v'ith the fourth metatarsal. On 
the medial part of its dorsal surface is inserted the tendon of the Peronaeus tertius 
and on the dorsal surface of the tuberosity that of the Peronaeus brevis. A strong 
band of the plantar aponeurosis connects the projecting part of the tuberosity 
with the lateral process of the tuberosity of the calcaneus. The plantar surface 
of the base is grooved for the tendon of the Abductor digiti quinti, and gives origin 
to the Flexor digiti quinti brevis. 
For Uh 
metatarsal 
For cuboid 
Tuberosity 
Fig. 415.-The fifth metatarsal. (Left.) 
Articulations.-The base of each metatarsal bone articulates with one or more of the tarsal 
bones, and the head with one of the first row of phalanges. The first metatarsal articulates with 
the first cuneiform, the second with all three cuneiforms, the third with the third cuneiform, the 
fourth with the third cuneiform and the cuboid, and the fifth with the cuboid. 
The Phalanges of the Foot (Phalanges Digitorum Pedis). 
The phalanges of the foot correspond, in number and general arrangement, 
with those of the hand; there are two in the great toe, and three in each of the 
other toes. They differ from them, however, in their size, the bodies being much 
reduced in length, and, especially in the first row, laterally compressed. 
First Row.-The phalanges of the first row closely resemble those of the hand. 
The body of each is compressed from side to side, convex above, concave below. 
The base is concave; and the head presents a trochlear surface for articulation 
with the second phalanx. 
Second Row.-The phalanges of the second row are remarkably small and short, 
but rather broader than those of the first row. 
The ungual phalanges, in form, resemble those of the fingers; but they are smaller 
and are flattened from above downward; each presents a broad base for articula- 
tion with the corresponding bone of the second row, and an expanded distal 
extremity for the support of the nail and end of the toe. 
Articulations.-In the second, third, fourth, and fifth toes the phalanges of the first row articu- 
late behind with the metatarsal bones, and in front with the second phalanges, which in their 
turn articulate with the first and third: the ungual phalanges articulate with the second. In 374 
OSTEOLOGY 
the great toe the first phalanx articulates proximally with the metatarsal bone and distally with 
the ungual phalanx. 
Ossification of the Bones of the Foot (Fig. 416).-The tarsal bones are each ossified from a 
single centre, excepting the calcaneus, which has an epiphysis for its posterior extremity. The 
centres make their appearance in the following order: calcaneus at the sixth month of fetal life; 
talus, about the seventh month; cuboid, at the ninth month; third cuneiform, during the first 
year; first cuneiform, in the third year; second cuneiform and navicular, in the fourth year. 
The epiphysis for the posterior extremity of the calcaneus appears at the tenth year, and unites 
with the rest of the bone soon after puberty. The posterior process of the talus is sometimes 
ossified from a separate centre, and may remain distinct from the main mass of the bone, when 
it is named the os trigonum. 
Appears 10th year ; 
unites after puberty 
TARSUS. 
One centre for each bone, 
except calcaneus 
OUTER FOUR METATARSALS. 
Two centres for each bone * 
One for body 
One for head 
Appears 3rd year 
Unite 18th-20th year 
Appears 1th week 
Apps. 1th wk. 
Unite 18-20 yr. 
Apps. 3rd yr. 
Unite 17-18 yr. 
App. 4th yr. 
PHALANGES. 
Two centres for each bone : 
One for body 
One for metatarsal 
extremity 
App. 2 4 mo. 
App. 6-7th yr. 
Unite 17-18 yr. 
Unite 17 18 yr. 
App. H-imo. 
App. 6th yr. 
App. 7th ivk. 
Fig. 416.-Plan of ossification of the foot. 
The metatarsal bones are each ossified from two centres: one for the body, and one for the 
head, of the second, third, fourth, and fifth metatarsals; one for the body, and one for the base, 
of the first metatarsal.1 Ossification commences in the centre of the body about the ninth week, 
and extends toward either extremity. The centre for the base of the first metatarsal appears 
about the third year; the centres for the heads of the other bones between the fifth and eighth 
years; they join the bodies between the eighteenth and twentieth years. 
The phalanges are each ossified from two centres: one for the body, and one for the base. 
The centre for the body appears about the tenth week, that for the base between the fourth and 
tenth years; it joins the body about the eighteenth year. 
1 As was noted in the first metacarpal (see footnote, page 332), so in the first metatarsal, there is often a second 
epiphysis for its head. COMPARISON OF THE BONES OF THE HAND AND FOOT 
375 
Comparison of the Bones of the Hand and Foot. 
The hand and foot are constructed on somewhat similar principles, each con- 
sisting of a proximal part, the carpus or the tarsus, a middle portion, the meta- 
carpus, or the metatarsus, and a terminal portion, the phalanges. The proximal 
part consists of a series of more or less cubical bones which allow a slight amount 
of gliding on one another and are chiefly concerned in distributing forces transmitted 
to or from the bones of the arm or leg. The middle part is made up of slightly 
movable long bones which assist the carpus or tarsus in distributing forces and 
also give greater breadth for the reception of such forces. The separation of the 
individual bones from one another allows of the attachments of the Interossei and 
protects the dorsi-palmar and dorsi-plantar vascular anastomoses. The terminal 
portion is the most movable, and its separate elements enjoy a varied range of 
movements, the chief of which are flexion and extension. 
The function of the hand and foot are, however, very different, and the general 
similarity between them is greatly modified to meet these requirements. Thus the 
foot forms a firm basis of support for the body in the erect posture, and is there- 
fore more solidly built up and its component parts are less movable on each other 
than those of the hand. In the case of the phalanges the difference is readily 
noticeable; those of the foot are smaller and their movements are more limited 
than those of the hand. Very much more marked is the difference between the 
metacarpal bone of the thumb and the metatarsal bone of the great toe. The meta- 
carpal bone of the thumb is constructed to permit of great mobility, is directed at 
an acute angle from that of the index finger, and is capable of a considerable range 
of movements at its articulation with the carpus. The metatarsal bone of the 
great toe assists in supporting the weight of the body, is constructed with great 
solidity, lies parallel with the other metatarsals, and has a very limited degree of 
mobility. The carpus is small in proportion to the rest of the hand, is placed 
in line with the forearm, and forms a transverse arch, the concavity of which 
constitutes a bed for the Flexor tendons and the palmar vessels and nerves. The 
tarsus forms a considerable part of the foot, and is placed at right angles to the 
leg, a position which is almost peculiar to man, and has relation to his erect pos- 
ture. In order to allow of their supporting the weight of the body with the least 
expenditure of material the tarsus and a part of the metatarsus are constructed 
in a series of arches (Figs. 417, 418), the disposition of which will be considered 
after the articulations of the foot have been described. 
Applied Anatomy.-Considering the injuries to which the foot is subjected, it is surprising 
how seldom the tarsal bones are fractured. This is no doubt due to the fact that the tarsus is 
composed of a number of bones, articulated by a considerable extent of surface, and joined 
together by very strong ligaments which serve to break the force of violence applied to this part 
of the body. When fracture does occur, these bones being composed for the most part of a soft 
cancellous structure, covered only by a thin shell of compact tissue, are often extensively com- 
minuted, especially as most of the fractures are produced by direct violence; and, as there is 
only a very scanty amount of soft parts over the bones, the fractures are very often compound, 
and amputation is often necessary. 
When fracture occurs in the anterior group of tarsal bones, it is almost invariably the result 
of direct violence; but fractures of the posterior group-that is, of the calcaneus and talus-are 
usually produced by falls from a height on to the feet. 
In club-foot (talipes'), especially in congenital cases, the bones of the tarsus become altered in 
shape and size, and displaced from their proper positions. This is principally the case in con- 
genital talipes equinovarus, in which the head of the talus becomes twisted and atrophied, and 
a similar condition may be present in the other bones, more especially the navicular. The tarsal 
bones are peculiarly liable to become the seat of tuberculous caries following comparatively trivial 
injuries, especially as they are not maintained in a condition of rest to the same extent as some 
other parts of the body after similar injuries. Caries of the calcaneus or talus may remain limited 
to the one bone for a long period, but when one of the other bones is affected, the remainder 376 
OSTEOLOGY 
frequently become involved, since the disease spreads through the large and complicated synovial 
membrane which is more or less common to these bones. 
Amputation of the foot is often required either for injury or disease. The principal amputa- 
tions are as follows: (1) Syme's: amputation at the ankle-joint by a heel flap, with removal of 
Fig. 417.-Skeleton of foot. Medial aspect. 
the malleoli and sometimes a thin slice from the lower end of the tibia. (2) Pirogoff's: amputa- 
tion of the whole of the tarsal bones (except the posterior part of the calcaneus), and a thin slice 
from the tibia and fibula, including the two malleoli. The sawn surface of the calcaneus is then 
turned up and united to the cut surface of the tibia. (3) Subastragalar: amputation of the^foot 
below the talus through the joint between it and the calcaneus. 
Fig. 418.-Skeleton of foot. Lateral aspect. 
The bones of the tarsus occasionally require removal individually: This is especially the case 
with the talus for tuberculous disease limited to that bone; or the talus may require excision in 
cases of subastragalar dislocation, or in cases of inveterate talipes. The cuboid has been removed 
for the same reason. 
Fractures of the metatarsal bones and phalanges are nearly always the result of direct violence, 
and in the majority of cases the injury is caused by severe crushing accidents, necessitating 
amputation. The metatarsal bones, and especially that of the great toe, are frequently diseased, 
either in tuberculous subjects or in patients with perforating ulcer of the foot. 
The Sesamoid Bones (Ossa Sesamoidea). 
Sesamoid bones are small more or less rounded masses embedded in certain 
tendons and usually related to joint surfaces. Their functions probably are to 
modify pressure, to diminish friction, and occasionally to alter the direction of a 
muscle pull. That-they are not developed to meet certain physical requirements 
in the adult is evidenced by the fact that they are present as cartilagionus nodules 
in the fetus, and in greater numbers than in the adult. They must be regarded, 
according to Thilenius, as integral parts of the skeleton phylogenetically inherited.1 
1 Morpholog. Arbeiten, 1906, v, 309. THE SESAMOID BONES 
377 
Physical necessities probably come into play in selecting and in regulating the 
degree of development of the original cartilaginous nodules. Nevertheless, irreg- 
ular nodules of bone may appear as the result of intermittent pressure in certain 
regions, e. g., the "rider's bone," which is occasionally developed in the Adductor 
muscles of the thigh. 
Sesamoid bones are invested by the fibrous tissue of the tendons, except on the 
surfaces in contact with the parts over which they glide, where they present 
smooth articular facets. 
In the upper extremity the sesamoid bones of the joints are found only on the 
palmar surface of the hand. Two, of which the medial is the the larger, are constant 
at the metacarpophalangeal joint of the thumb; one is frequently present in the 
corresponding joint of the little finger, and one (or two) in the same joint of the 
index finger. Sesamoid bones are also found occasionally at the metacarpophal- 
angeal joints of the middle and ring fingers, at the interphalangeal joint of the 
thumb and at the distal interphalangeal joint of the index finger. 
In the lower extremity the largest sesamoid bone of the joints is the patella, 
developed in the tendon of the Quadriceps femoris. On the plantar aspect of the 
foot, two, of which the medial is the larger, are always present at the metatar- 
sophalangeal joint of the great toe; one sometimes at the metatarsophalangeal 
joints of the second and fifth toes, one occasionally at the corresponding joint of 
the third and fourth toes, and one at the interphalangeal joint of the great toe. 
Sesamoid bones apart from joints are seldom found in the tendons of the upper 
limb; one is sometimes seen in the tendon of the Biceps brachii opposite the radial 
tuberosity. They are, however, present in several of the tendons of the lower 
limb, viz., one in the tendon of the Peronaeus longus, where it glides on the cuboid; 
one, appearing late in life, in the tendon of the Tibialis anterior, opposite the smooth 
facet of the first cuneiform bone; one in the tendon of the Tibialis posterior, oppo- 
site the medial side of the head of the talus; one in the lateral head of the Gastroc- 
nemius, behind the lateral condyle of the femur; and one in the tendon of the Psoas 
major, where it glides over the pubis. Sesamoid bones are found occasionally 
in the tendon of the Glutaeus maximus, as it passes over the greater trochanter, 
and in the tendons which wind around the medial and lateral malleolj.