^lakiston books are bound in high 
grade materials which are sturdy, ver- 
min-proof and water resisting 
they can be cleaned with soap and 
water. PRACTICAL ANATOMY 
OF THE RABBIT PRACTICAL ANATOMY 
OF THE RABBIT 
AN ELEMENTARY LABORATORY TEXT-BOOK 
IN MAMMALIAN ANATOMY 
By 
The Late B. A. BENSLEY, Ph.D. 
-tn 
Formerly Professor of Zoology in the University of Toronto 
Sixth Edition 
Revised and edited by 
E. HORNE CRAIGIE, Ph.D. 
Associate Professor of Comparative Anatomy and Neurology 
in the University of Toronto 
P. BLAKISTON'S SON & CO., INC. 
PHILADELPHIA Copyright, Canada, 1938 
BY THE 
University of Toronto Press 
Printed in Canada 
by The University of Toronto Press PREFACE TO THE FIFTH EDITION 
IN the preparation of the present edition of the "Anatomy of 
the Rabbit'', comparatively little alteration has been made in 
the body of the text. Many minor corrections and emendations 
have, however, been recorded. 
As explained in previous editions, the main purpose of the text 
is to set forth in some kind of practical sequence a plan for the 
orderly study of a typical mammal, supplemented by a brief 
exposition of the relation of this kind of study to the content and 
outlook of cognate biological sciences. 
The methods adopted by anatomical instructors are subject to 
wide variation, based no doubt upon personal preference and per- 
haps to some extent upon habit and upon laboratory facilities 
available. This is as it should be, though not capable of being 
covered by any system of texts. After all, a student must go 
through the process of acquiring a rather complex assortment of 
detached pieces of information before a comprehensive view of the 
ensemble of mammalian organization may be obtained. There is 
thus plenty of room for selection in the order of study, provided 
the requirement is met of avoiding the destruction of unidentified 
parts. One of the older difficulties of anatomical teaching, perhaps 
unintentionally fostered by all text-books, namely thorough, and 
often unstimulating, preliminary study of the skeleton before dis- 
section, is being overcome by judicious division of skeletal studies 
into an introductory survey followed at suitable intervals with 
special study during dissection. The method of using a region 
under dissection as a basis for topical teaching of related physio- 
logical and morphological associations has also much to recom- 
mend it. 
Teaching responsibility is ever an interesting issue but never- 
theless so often overlooked that it becomes an important question 
as to whether the opportunities and obligations of anatomical 
teaching are being met. For the non-professional student perhaps 
the chief consideration is the avoidance of half-assimilated, un- 
verified information. For the student looking forward to profes- 4 
Anatomy of the Rabbit 
sional courses, time as well as instructional sequence and useful 
selection is equally important. It would be unfortunate if the 
high reputation always enjoyed by the anatomical sciences, of 
moving safely forward point by point were not used to the extent 
possible to counterbalance the rather observable tendency towards 
pedagogical confusion. 
The writer appreciates the response of various instructors to 
his desire for information as to necessary and advisable emenda- 
tions of the text. He is under particular obligation to Dr. E. H. 
Craigie, University of Toronto, for a critical revision of the account 
of the central nervous system which should add materially to the 
value of this section from both structural and functional points of 
view. 
B. A. Bensley 
University of Toronto, 
October 1, 1931. PREFACE TO THE SIXTH EDITION 
IN the sixth edition, the essential features of the book, which 
have proved their value in over a quarter of a century of use 
of the preceding editions, remain unchanged. Nevertheless, rather 
extensive revisions have been carried out in an effort to make 
the text easier for the beginner to understand while, at the same 
time, making it more complete, more precise, and more up to 
date. 
The whole text has been carefully reviewed and changes in 
wording have been made where it was felt that simplification or 
greater accuracy of the statement would result therefrom. Certain 
sections have been rearranged with the aim of improving the 
sequence of the presentation, and some have been entirely re- 
written. The chapters on the nervous system and the endocrine 
organs, particularly, have been brought into line with recent 
advances in knowledge in these fields. Throughout the first part 
an attempt has been made to increase the emphasis upon the 
functional significance of structure, which is felt to be a funda- 
mental aspect of anatomical study. In addition there have been 
numerous changes and corrections in the details of description and 
the directions for dissection. 
Some of the illustrations, having been the objects of criticism, 
have been removed, replaced, or transferred to new locations. 
A few new ones have been introduced and these have been carefully 
chosen so as to elucidate relations which are not likely to be observed 
in class-room dissections. Finally, the index has been greatly 
extended. 
The new edition is offered in the hope that it will be found to 
be a real improvement in an already valuable work and with 
confident belief that the revisions would have met with the approval 
of the original author. 
The writer wishes to express his deep appreciation of the action 
of the heirs of the late Dr. Bensley in generously entrusting him 
with the preparation of this revised edition and also his gratitude 6 
Anatomy of the Rabbit 
to the various colleagues who have assisted with suggestions and 
criticisms. 
Grateful acknowledgements are due also to Dr. G. Winckler and 
to Dr. O. Zietzschmann for permission to copy the drawings upon 
which figures 40 and 44 are based. 
E. Horne Craigie 
Department of Biology, 
University of Toronto, 
November, 1937. PAGE 
Introduction 9 
PART I. A GENERAL CONSIDERATION OF THE 
STRUCTURE OF THE RABBIT 
Divisions and Methods 11 
The Interpretation of Structure 12 
Zoological Position 15 
General Anatomy 20 
The Tissues 22 
1. Epithelial Tissues 22 
2. Connective Tissues 26 
3. Muscular Tissues 32 
4. Nervous Tissues 34 
5. Blood and Lymph 36 
Special Anatomy 38 
Terminology 38 
The General Features and Ground Plan of the 
Organ-Systems 41 
Classification of the Organ-Systems 42 
General Organization 44 
Embryonic Plan of the Systems 46 
The Skeletal System 47 
The Muscular System 64 
The Nervous System 70 
The Digestive System 83 
The Respiratory System 91 
The Blood-Vascular System 94 
The Lymphatic System 98 
The Urinogenital System 100 
The Endocrine System 107 
The Serous Cavities 109 
Regional Sections 112 
PART II. OSTEOLOGY OF THE RABBIT 
Divisions of the Skeleton 130 
The Vertebral Column 130 
The Ribs 138 
CONTENTS PAGE 
The Sternum 139 
The Skeleton of the Head 140 
A. The Skull as a Whole 140 
B. The Bones of the Skull 153 
C. The Hyoid Apparatus 170 
The Skeleton of the Anterior Limb 171 
The Skeleton of the Posterior Limb 178 
PART III. DISSECTION OF THE RABBIT 
I. External Features 188 
II. The Abdominal Wall 191 
III. The Stomach and Spleen 194 
IV. The Liver 200 
V. The Intestines 202 
VI. The Urinogenital System 209 
VIL The Abdominal Aorta, Inferior Caval Vein, and 
Sympathetic Trunks 217 
VIII. The Anterior Limb 220 
IX. The Posterior Limb 233 
X. The Head and Neck 251 
XL The Thorax 273 
XII. The Vertebral and Occipital Musculature 284 
XIII. The Central Nervous System 289 
Appendix. The Preservation of Material 305 
Index 313 
Contents INTRODUCTION 
As a laboratory exercise the anatomical study of an animal is 
chiefly a matter of applying a certain practical method of exposition, 
the student's attention being concentrated on those facts which 
can be made out by direct observation. This method is educative 
in the technical sense because it involves accurate discernment of 
detail, and because, as a means of obtaining first-hand information, 
it is the foundation of laboratory practice. Within the range of 
natural science, which limits fact to what is reasonably demon- 
strable, laboratory practice takes its place as one of the principal 
methods by which first-hand knowledge of anything concrete is 
gained and it is important for the student as early as possible to 
form the habit of acquiring his knowledge in this way and of con- 
firming thus information obtained otherwise. 
In studying the structure of any organism, however, it is to be 
considered that the final object is not simply to determine in what 
its structure consists, i.e., its anatomy in a restricted sense, but 
also to understand what structure signifies, either as functional 
mechanism, or as the product of racial or evolutionary factors. 
While it is conceivable that a single organism, either as individual 
or as species, may be considered by itself, a very superficial study 
suffices to show that the structure and function of no living organism 
can be interpreted apart from the general arrangements of organized 
nature, and more especially from the corresponding features of 
those organisms most nearly allied in point of resemblance. 
This being the case, it is a very pertinent question what is the 
best procedure. So far as the present book is concerned, it is 
expected that the study of the type will begin with at least a 
preliminary survey of the prepared skeleton (part II). This will 
be followed by dissection (part HI), in which the order by sections 
will be found to be of less importance than that of details in any 
particular region and in which portions of the skeleton related to 
the part under examination may be included. The general matter 
of part I is purely accessory and, though necessarily incomplete in 
many ways, is designed to afford a comprehensive view of the 
various factors upon which mammalian structure depends. It will 10 
Anatomy of the Rabbit 
be found that only the first few chapters are introductory in most 
respects, the remainder being rather explanatory and hence most 
valuable if used to supplement the directions for dissection as 
this is carried out. 
Regional sections of the foetus as figured in part I, or frozen 
sections of the adult animal, are a useful adjunct, since they can 
be used either for points of general organization, or, being sub- 
stantially correct for two dimensions, can be used to remove some 
erroneous impressions of the position of organs incidental to their 
displacement in dissection. PART I 
A GENERAL CONSIDERATION OF THE 
STRUCTURE OF THE RABBIT 
DIVISIONS AND METHODS 
Biology, the science or study of living organisms, includes 
several related sciences, fundamental among which are: Anatomy, 
the study of organized structure; Physiology, the study of function; 
and Embryology, the study of development. Anatomy is an 
essential foundation for the other branches. Comparative 
Anatomy, the comparative study of different organisms, and 
Embryology are also considered either as divisions, or as practical 
methods, of Morphology, the general science of the evolution 
of form. 
The term "Anatomy", originally applied to the study of the 
structure of the human body, and still used as referring more 
especially to this, has come to be applied to the study of structure 
generally. 
It has been found convenient, especially in human anatomy, to 
distinguish as Gross Anatomy, the study of that kind of structure 
which is displayed by dissection, or is revealed by naked-eye 
appearances, and as Microscopic Anatomy, the study of finer 
structure through the application of the microscope; or, again, to 
distinguish as Special or Descriptive Anatomy, the study of the 
particular features of the organs of the body, and as General 
Anatomy, the study of its more fundamental composition. General 
Anatomy is practically equivalent to Histology, the latter con- 
sidering the body from the point of view of the structure and 
arrangement of its cells and tissues. 
These distinctions are of interest in the present case chiefly as 
defining more exactly the practical method and the kind of structure 
to be considered. Thus, dissection is a method of displaying 
structure of a gross and special kind. It consists in the orderly 
exposure and displacement of organs with the object of observing 
their features and their relations to surrounding parts. The plan 12 
Anatomy of the Rabbit 
is essentially one of analysis, since conceptions of structure are 
based on the recognition of differences, the latter being estimated 
by various features, such as form, colour, texture, or position. On 
the other hand, because of the class of structure with which it deals, 
dissection should also be recognized as a method preliminary to 
others involving the use of the microscope. Further, the analysis 
should be followed at each step by a synthesis in the mind of the 
student, who must keep before him the unity of the individual 
organism as a whole. 
THE INTERPRETATION OF STRUCTURE 
Gross structure is, in a sense, only an expression of the finer 
microscopic structure underlying it. Since this relation is more 
fully discussed below under the head of "General Anatomy", it 
need only be mentioned here as an element in the interpretation of 
structure as viewed from the gross standpoint. All animal struc- 
ture, however, may be considered from two points of view- 
physiological and morphological. 
The physiological aspect of structure concerns the functions 
or activities of the living organism and of its individual parts. The 
contraction of a skeletal muscle is a change in the axial relations of 
a mass of living protoplasm, but the form and connections of the 
muscle are such that the contraction results in movement of one 
bone upon another. The excretion of urine by the kidneys is the 
final stage of a process which rids the body of soluble waste nitro- 
genous materials by discharging them into a system of tubes con- 
nected with the outside of the body. It is essential to recognize 
that in these, as in the multitude of analogous cases, structure and 
function are intimately related and serve to explain each other. 
The morphological aspect of structure concerns various 
features of form and arrangement which, although they have been 
developed on a basis of utility, cannot be explained purely on that 
basis, because the factors controlling them lie outside of the body 
of the individual, and are such as have operated only through a long 
series of gradually changing conditions in the evolution of its type. 
As applied to a particular animal, the morphological method con- 
sists in explaining its adult structure by reference either to its Interpretation of Structure 
13 
embryonic development or to the equivalent conditions in lower 
forms, existing or fossil. A recognized principle of embryology is 
that known as the Law of Recapitulation. It is based on the 
general observation that the definitive structure of an organism 
is attained through a series of embryonic stages, in which it not 
only develops from a simple or ground type to a more complex 
condition but also reflects in passing the features of lower forms 
which presumably represent its ancestors. The application of 
comparative anatomy depends on the comparison of higher, special- 
ized animals with lower, or generalized ones, the latter being 
assumed, in one feature or another, to have remained in a backward 
or primitive state of specialization, and therefore to reflect in such 
features a grade of structure comparable with that possessed by 
the ancestors of existing higher forms. These relations form a 
basis for the comparison of the embryonic development of organisms 
with the evolution or history of the groups which they represent, the 
former being distinguished as ontogeny, the latter as phylogeny. 
The interpretation of the adult structure of an organism involves 
the distinction of its more general features from the more special 
ones and the application to them of ontogenetic and phylogenetic 
principles. 
The present form common to the individuals of one kind of 
animal may be explained only by reference to ancestry. Apart 
from influences of accident, the sum of characters of the individual 
is the result of development, under more or less fixed environmental 
conditions, of the primordial cell which constitutes the fertilized 
egg. Such features as are impressed upon the animal during 
growth or maturity are negligible in this connection, the develop- 
mental possibilities of the fertilized egg having been transmitted 
to it through the succession of generations. Through this the 
continuity of life, as the fossil remains of organisms of the past 
reveal, has carried onward the structure of the body for countless 
millions of years. 
With succession has come also modification, as is shown by the 
appearance on the earth at different geological times of progres- 
sively more specialized animals, which reveal in a large way the 
same kinds of differences observable among primitive and specialized 
animals living at the present day. That the entire skeleton of a 14 
Anatomy of the Rabbit 
mammal is patterned upon the primitive skeleton of the fossil 
amphibia of the Carboniferous and Permian is evident from a 
comparison of the components part for part, but it is equally 
evident from comparative anatomy that the viviparous condition 
of a higher mammal is founded upon an oviparous condition in 
lower forms even if no fossil evidence is forthcoming. That a 
mammal as an air-breathing vertebrate should develop gill struc- 
tures in the embryonic condition, though these are never used, is in 
itself an important fact bearing on adult structure, but such a 
condition also illustrates how extensively a living animal carries 
ancestral features, whether functionally modified or not. 
All characters of animals have thus an evolutionary basis, the 
general nature of which is easily understood although the process 
by which they have been developed is still a matter of uncertainty. 
In comparison with one another, animals present certain resem- 
blances and differences-diagnostic features, which are used as a 
basis for classifying them into major and minor groups. In many 
cases characters of resemblance have been shown to be secondary, 
and are hence described as convergent. In some of these the 
resemblances are of a gross type, and the structures are described 
as analogous; in other cases they are exact or homoplastic. 
As a rule, however, characters of resemblance are broad marks of 
affinity, comparable to those seen on a small scale in human 
families, or in human races, and determined as in the latter cases 
by heredity. The chief basis of comparison of animals with one 
another is the general assumption that structures which are similar 
or identical are homogenous-of common origin. On the other 
hand, their differences are chiefly marks of divergence in evolution. 
It is conceivable that many of the internal features of animals are 
the result of a general progressive development, more conspicuous 
in comparison of a series from primitive to specialized types. 
However, the majority of their differences are such as have resulted 
from adaptive modifications of structure, by which they have 
become differently adjusted to the particular conditions of their 
accepted habitats. Adaptation to environment is one great result 
of the modification of animal form, and is revealed in part by 
structural divergences, as between one type and its contemporaries; 
although such features may afterwards become settled in particular Zoological Position 
15 
groups, and thus appear for these as primitive, general, or group 
characters. Adaptation, in other words, is not a matter of present 
conditions only. The rabbit as a gnawing animal or rodent, for 
example, is also an air-breathing, walking vertebrate, and shares 
these relatively large and ancient features with many other verte- 
brates of different kinds. 
It is customary to include under the term specialization all 
those features in which an organism may be shown to be more 
highly modified in comparison with another type. If the latter is 
an ancestral type, or a lower form exhibiting ancestral features, 
its more primitive features are said to be prototypal, because they 
indicate the form from which the higher modification has been 
derived. Such comparisons not only reveal the fact that different 
animals are specialized in different degrees, but also show that a 
given form may be greatly specialized in some respects and primitive 
in others. 
Moreover, it is to be considered that animals are at the present 
time, as they have been in the past, more or less changeable, or 
plastic types. Some of the most interesting features which they 
exhibit depend on the circumstance that the adjustment of structure 
which is rendered necessary by the opposing effects of heredity and 
specialization is gradual rather than exact or immediate. Thus, it 
is not difficult to find in any specialized animal, in addition to those 
organs which are functional or in full development, others which 
are retrogressive in character and reduced in size. It is also to 
be assumed, although difficult of proof among living forms, that 
there are also organs which are sub-functional or progressive. 
ZOOLOGICAL POSITION 
It will be evident from the foregoing statement that every 
specialized animal possesses in its organization a vast assemblage of 
features which, if referred to their proper categories, are found to 
represent many grades of morphological value. In so far as the 
adult structure of a particular form is concerned, it is possible to 
consider them anatomically without discrimination; but, on the 
other hand, if they are to be explained, it is necessary to proceed 
on a basis of function, embryonic development, or evolution. The 16 
Anatomy of the Rabbit 
study of an animal as a type or representative of a group, however, 
concerns only in part the features common to the various members 
of the latter, since the majority of features present in any animal 
are of minor importance, and as such are significant chiefly as 
indicating the developments which may take place inside the group. 
\\ hat an animal actually represents is determined by comparison 
with other forms and is called its zoological position. This is 
expressed through the medium of classification, the latter being 
arranged to indicate, so far as is possible, the relationships of 
organisms to one another. In this connection the following state- 
ment of the zoological position of the rabbit may be found useful; 
and it may also be considered as illustrating, through the com- 
parison of this animal with allied forms, some of the more general 
characters of animals as outlined above. 
The domestic rabbit is represented by several races, of which 
the common variously-coloured forms, long-haired Angoras, Lop- 
ear Rabbits, and Belgian "Hares" are more familiar. They are 
all descendants of the wild rabbit {Oryctolagus cuniculus, Lepus 
cuniculus) of Europe. The latter is thought to have belonged 
originally to the countries bordering the western portion of the 
Mediterranean, but its distribution has been greatly extended 
northward and to other continents through human agency. 
The European common rabbit {Oryctolagus cuniculus) belongs 
to the family Leporidae, which contains a large number of closely 
related species formerly included under the single genus Lepus. 
In addition to Oryctolagus cuniculus and its derivatives, the more 
familiar species are the European Common Hare {Lepus europaeus) 
and in North America, the Cotton-tail Rabbit {Sylvilagus flori- 
danus), the Northern or Varying Hare {Lepus americanus), and 
the Prairie Hare or White-tailed Jack Rabbit {Lepus campestris). 
In recent decades, European hares have been several times intro- 
duced and liberated in North America, and are now established in 
certain parts of the Eastern United States and in Ontario, Canada. 
The two common European species differ in several well-marked 
features which form the basis of the recognized distinctions between 
"hares" and "rabbits". The rabbit is distinguished by its shorter 
ears and less elongated hind limbs; also by its burrowing habits, 
and by the circumstance that the young for a time after birth are Zoological Position 
17 
blind and naked. The hare is more nearly a running or coursing 
type, and is distinguished by longer ears, which are, moreover, 
tipped with black, longer hind limbs, and prominent eyes. It 
inhabits an open "form" and the young directly after birth are 
clothed with hair and able to see. Upwards of one hundred species 
of Leporidae have been described in North America. They are 
variously known as hares or rabbits. It is generally considered 
that the American forms, aside from two aberrant genera, are hares, 
but in form and habits the Varying and Prairie Hares of the genus 
Lepus conform more closely to the type of the European Hare, 
while the Cotton-tails, members of the genus Sylvilagus, make at 
least some approximation to the European Rabbit. 
The various species constituting this family are distinguished 
from the Picas or Tailless Hares (Ochodontidae) of the mountainous 
districts of Central Asia and of North America (Rocky Mountains), 
by several features, including the imperfect development of the 
clavicle, longer ears and limbs, and the presence of a distinct 
although greatly reduced tail. The two families are allied, how- 
ever, in the possession of a common feature, namely, the presence 
in the upper jaw of a second pair of incisor teeth. This feature 
distinguishes the suborder Duplicidentata from that of the 
Simplicidentata, the latter containing the majority of rodents 
and embracing all forms with a single pair of upper incisors. 
The mammalian order Rodentia, to which the family belongs, 
contains a very large assemblage of forms-the Squirrels, Marmots, 
Cavies, Beavers, Mice, and Porcupines being among the more 
familiar. This order is distinguished by the modification of the 
anterior incisors in both upper and lower jaws to form chisel-like 
cutting organs, these teeth having their enamel layer disposed 
chiefly if not wholly on their front surfaces, so that they remain in a 
permanently sharp condition. This modification is associated with 
an extensive loss of intermediate teeth, involving posterior incisors, 
canines, and anterior premolars. There is also elaboration, often 
very considerable, of the remaining premolar and molar teeth, of 
the lower jaw, and, indeed, of the parts of the skull generally. 
Characteristic of these animals is the extension, both forward and 
backward, of the jaw-musculature. The articulation of the lower 
jaw has an antero-posteriorly elongated articular process fitting 18 
Anatomy of the Rabbit 
into a corresponding longitudinal fossa on the skull, the jaw being 
able to move forward and backward in addition to vertically and 
from side to side. Further, the teeth are arcuate in shape, and are 
provided with open roots, so that their growth is not limited, as it 
is in the majority of mammals. In these respects and in the 
elaboration of the intestine, especially the caecum, the rodents 
exhibit the characters of highly specialized herbivores, but in many 
particulars they are primitive types. For example, they tend to 
retain the five-toed (pentadactyl), plantigrade foot, characteristic 
of primitive mammalia and, indeed, of terrestrial vertebrates, and 
exhibit also unelaborated cerebral hemispheres in the brain. 
The Duplicidentata present several structural features in which 
they differ from other rodents, and reference to an independent 
order Lagomorpha has been suggested. 
Like all higher or placental mammalia (Infraclass Eutheria), 
the rabbit is viviparous, that is, the young are born in a more or 
less advanced stage of development, after being retained through 
a period of gestation in the maternal uterus, to the wall of which 
they are attached by a vascular connection, the placenta. In this 
feature the placental mammalia differ from the marsupial mam- 
malia (Order Marsupialia of the Infraclass Metatheria) of Australia 
and South America, the latter being viviparous but, with one 
exception, lacking a placenta. The members of both these groups 
(which are associated in the subclass Theria) differ from those of 
the order Monotremata (subclass Prototheria) of Australia, which 
are not viviparous but oviparous, or egg-laying, like the majority 
of reptiles and other lower animals. These three divisions of 
mammals, however, are united by the common features of the 
class Mammalia. For example, they all are warm-blooded, are 
provided with a complete double circulation and a hairy investment 
for the surface of the body, and nourish the young for a time after 
birth by the secretion of cutaneous glands modified to produce 
milk, the mammary glands. 
Many of the more general features of the rabbit are not char- 
acteristic of any one group but are shared with other terrestrial 
vertebrates, including mammals, reptiles, birds, and, in part, 
amphibians. Such features are the development of the lungs and 
associated respiratory tracts, both the true respiratory tracts and Zoological Position 
19 
the accessory respiratory passages traversing the skull. Further, 
the loss of the branchial- or fish-type of respiration and the new 
disposition of the branchial structures; the development of a 
tri-segmented type of limb with a full complement of muscles, and 
originally a pentadactyl, plantigrade foot, for support of the body 
and for locomotion; the regional differentiation of the vertebral 
column, especially the mobility of the neck, the free occipital 
articulation, and the definition of the sacrum, the latter associated 
with the elaboration of the pelvic girdle, are all features of general 
significance in the terrestrial vertebrates. 
The rabbit is like all Vertebrata or Craniata in the possession 
of an axial skeleton formed by the segmented vertebral column and 
of an organized head region with differentiated brain, special sense 
organs, and enclosing primary skull. Also, the vertebrates exhibit 
a basic transverse segmentation (metamerism) of a considerable 
part of the body. 
Finally, the rabbit agrees with other members of the phylum 
Chordata in the ground plan underlying the most general features 
of its organs and the position, arrangement, and plan of development 
of its organ-systems. Particularly it possesses a dorsal, tubular 
central nervous system; a notochord, a fundamental axial support 
which is only embryonic except in the lowest chordates; and a 
series of gill clefts, such as occurs in every chordate either in the 
adult condition, or in the embryo alone. 
These facts may be set down in tabular form, as indicated below. 
A similar plan can be constructed for any group of organisms, but 
whether it constitutes a natural or an artificial classification depends 
on whether or not it is based upon an actual study of the affinities 
of the organisms concerned. A natural classification should show 
at a glance not only what the relative importance of any particular 
character may be, but also how it stands in the scale of specializa- 
tion. For example, the placental stage of vertebrate development, 
i.e., the development of the placenta itself in the highest stage of 
vertebrate evolution, is the culmination of a series of arrangements 
for the care of eggs and young, and the adherence of human struc- 
ture in the vast majority of features to the type of higher mammals 
is expressed by the fact that man is also a placental mammal. 20 
Anatomy of the Rabbit 
Phylum CHORDATA. Animals with notochord and gills. 
IProtozoa, Annulata, Mollusca, etc., invertebrate phyla. 
Sub Phylum CRANIATA. (VERTEBRATA) Chordates with organized head 
region. 
IAcrania. Lancelets. Also Ascidians and worm-like Chordates, some- 
times separately classified. 
Class MAMMALIA. Warm-blooded craniates, with hair coat. 
Young nourished from mammary glands. 
fCvCLOSTOMATA, PlSCES, AMPHIBIA, REPTILIA, AvES, 
lower vertebrate classes. 
Subclass THERIA. Viviparous mammals. 
IPrototheria. Oviparous mammals. 
Infraclass EUTHERIA. Placental mammals. 
IMetatheria. Viviparous mammals without placenta. 
Order RODENTIA. Gnawing placentals, with chisel-like incisors. 
ICarnivora, Ungulata, Primates, etc. Various placental orders 
otherwise adapted. 
Suborder DUPLICIDENTATA. Rodents with two pairs of upper incisors. 
fSiMPLiciDENTATA. One pair of upper incisors. 
Squirrels, Gophers, etc. 
Family LEPORIDAE. Hares and Rabbits. 
fOCHODONTIDAE. Picas. 
j Equivalent groups. 
GENERAL ANATOMY 
Although in every respect a continuous structure and forming 
a single organism, the body is differentiated into a large number of 
parts, or organs, which are more or less individual in form, com- 
position, or function. Organs are arranged for the most part in 
systems, each of which is concerned with some general or funda- 
mental function, to which several organs may contribute. 
In a more general way the body may be considered as an 
assemblage of tissues, since these are the materials of which the 
organs are composed. Tissues may be defined as layers or ag- 
gregations of similarly differentiated cells. They are of several 
different kinds and are variously associated in the formation of General Anatomy 
21 
organs. Being structures of intermediate rank, they may be con- 
sidered either as organ components or as combinations of specialized 
cells. 
As a body-unit a cell consists 
of a small mass of living proto- 
plasm, containing a central 
body, the nucleus imbedded in 
a mass of cytoplasm. The 
latter is surrounded or enclosed 
on its free border by a cell- 
membrane. The nucleus is a 
highly organized body, having 
an important function in the 
reproduction of the cell and also 
in its general activity or metabo- 
lism. It contains a characteristic 
formed material, chromatin, 
and frequently also a minute 
spherical body, the nucleolus. 
The chief features of a typical cell are illustrated in the accompany- 
ing figure (1) of the developing ovum, the latter being a single cell, 
noteworthy for its large size, and also one in which the external 
form is not greatly modified, as it is in the majority of the cells 
of the body. Its enclosing membrane, the zona pellucida, by which 
in its natural position in the ovary it is separated from the surround- 
ing follicular cells, is considered to belong in part to the latter. 
As fundamental living matter, protoplasm possesses certain 
properties on which the functions of the body ultimately depend. 
Considered collectively, these functions are not so well illustrated 
in the higher or multicellular organisms, in which particular 
functions are assigned to particular cells, as in the lower unicellular 
organisms, in which all functions are discharged by a single cell. 
In simple or protozoan animals the protoplasm is seen to be capable 
of ingesting food-materials, of discharging waste, of changing its 
form, and of reacting in one way or another to stimuli arising out- 
side of the body. Moreover, the protozoan cell is capable of giving 
rise to new cells by division of its substance into two parts, which 
Fig. 1. Developing ovum of the rabbit. 
From a section of the ovary: chr., chromatin; 
n.m , nuclear membrane; p.f., cells of the 
primary ovarian follicle; z.p., zona pellucida; 
pr., cytoplasm. 22 
Anatomy of the Rabbit 
process originates in the nucleus, and is usually associated at some 
stage with union or conjugation of parent cells. 
All the cells of the body of a multicellular organism are products 
of a single cell, the fertilized egg, but the latter is a product of 
fusion of two primary elements, the spermatozoon of the male 
parent and the ovum of the female. The fertilized egg does not 
exhibit the functions of a one-celled body, but possesses the poten- 
tial of these functions, and the latter appear, to a large extent 
individually, in the differentiation of its division-products into 
specialized tissue elements. 
In this way, the processes which go on within the body of a 
multicellular animal and the structure underlying these processes 
are all based upon the same elementary functions of life as those 
appearing in one-celled organisms. But the repeated division of 
the fertilized egg, in development toward the adult condition, gives 
rise by division of labour to a great variety of cells, each kind of 
which may be regarded as representing a minor aspect of some 
major function. 
The Tissues 
The primary tissues of the body are of four kinds-epithelial, 
connective, muscular, and nervous. To these-the fixed 
tissues-are to be added the fluid substances, blood and lymph, 
in which the cell elements, the red and white corpuscles, or in the 
latter case the white elements alone, are suspended in a fluid 
medium. The differences between these depend partly upon the 
characters of the cells composing them and partly upon the nature 
and quantity of the material between the latter, the intercellular 
matrix. 
The following survey of the principal features of the tissues will 
serve to make clear the extent to which the gross appearance of 
organs depends upon tissue composition, though the account is in 
no way intended as a guide to the microscopic structure of the rabbit 
which is more properly part of the subject-matter of histology. 
1. Epithelial Tissues 
Epithelial tissues are distinguished chiefly as surface invest- 
ments, such as those of the exterior of the body, and those of the Epithelial Tissues 
23 
interior of the alimentary canal, the lungs, the respiratory and 
accessory respiratory tracts, and the ducts of the urinogenital 
organs. In all epithelia the cellular feature is a prominent one, 
the amount of intercellular material being relatively small. With 
a few exceptions, they are not penetrated by blood-vessels. As 
constituents of lining membranes, they are not conspicuous in gross 
structure but they give rise to important 
derivatives, such as the hairs and the var- 
ious kinds of secreting organs or glands. 
Epithelium may be simple, i.e. one- 
layered, or it may be stratified, i.e. com- 
posed of several layers of cells. 
The epithelium of the skin (Fig. 2), 
which is known as the epidermis, or scarf- 
skin, is stratified, the deeper cells being 
formative, growing cells, while those at the 
surface are flattened squamous cells, and 
are successively discarded. The several 
layers combined produce but a thin mem- 
brane. It extends over the entire surface 
of the body and connects at certain points 
with the epithelia of the internal surfaces. 
It is supported by a thick resistant layer of 
connective tissue which forms the true skin 
or corium. 
The epithelium of the internal surfaces 
forms the chief portion of the mucous 
membranes. In the greater portion of the 
alimentary tract the epithelial layer is simple or one-layered and 
is associated with a thin layer of smooth muscle to form a mucous 
tunic (Fig. 13, t.ms.). 
Among secondary products of epithelial origin is the coating of 
hairs on the surface of the body, the presence of which is a strictly 
characteristic mammalian feature. It is a protective investment 
arising from the epidermis. Each hair is produced by the modifica- 
tion of the central portion of an ingrowth of the epidermis, termed 
the hair follicle (Fig. 2, f). The latter contains at its base a small 
elevation of the underlying vascular connective tissue, the hair 
Fig. 2. From a section of 
the upper lip of a four-day- 
old rabbit: a,a', erector mus- 
cles of the hair; c, connective 
tissue of corium; e, epidermis; 
f, hair follicle; g, sebaceous 
gland; p, papilla; s, hair shaft. 24 
Anatomy of the Rabbit 
papilla, through which the structure is nourished. On the general 
surface of the body of the rabbit the hair follicles are arranged in 
groups (Fig. 5), and on the lips certain large follicles are set apart 
for the production of the greatly enlarged sensory hairs or vibrissae. 
Connected with the hair follicles are thin strands of smooth muscle, 
the arrectores pilorum (Fig. 2, a,a')- They are placed in the 
broad angles formed by the inclined follicles with the corium and 
their contraction brings the hair into a more nearly erect position. 
Epithelial glands are composed of 
epithelial cells which have become greatly 
modified as secreting structures. In some 
cases the secreting element is a single cell, 
a unicellular gland lying directly in the 
general layer of epithelium. The mucus- 
secreting goblet cells of the intestinal wall 
are structures of this nature. In other 
cases groups of secreting cells form in- 
growths from the main layer, multi- 
cellular glands. The lumen or cavity 
of the gland, in most cases greatly com- 
plicated through the division of the gland 
substance, is connected with the general 
surface by a duct which serves to carry 
away its secretion. In some cases, how- 
ever, the connection of a gland with the 
epithelial surface is embryonic, and in the 
adult condition the gland is found sepa- 
rated from the epithelium from which it 
was originally formed. This condition is 
represented by the thyreoid and thymus 
glands of the neck and thorax respectively. 
Typical epithelial glands are accordingly external secreting, or 
exocrine glands, their secretions being discharged through ducts 
to free surfaces; while those which lose their ducts are internal 
secreting, or endocrine glands, their products being absorbed 
directly into the blood or lymph (cf. p. 107). There are many 
structures, such as the suprarenal gland and part of the pituitary 
body, commonly described as endocrine glands, which are not 
Fig. 3. A, Diagram of a 
multi-cellular gland: al., 
acinous type; d., duct; ep., 
general epithelium; t., tubu- 
lar type. B, The pancreatic 
duct and associated portion 
of the duodenum in the 
rabbit. Epithelial Tissues 
25 
necessarily epithelial in origin and of which the resemblance to 
ordinary glands is often only a matter of superficial appearance. 
Most multicellular glands conform to one of two types, 
namely, the tubular gland, in which the secreting portions are of 
uniform calibre, and the acinous or alveolar gland, in which the 
secreting portions are sacculated (Fig. 3, A). Both types occur in 
simple, little branched, and greatly branched conditions (Figs. 3, 
B;4). 
Cutaneous glands of two types are commonly present in 
mammals in association with the hairs, namely, sudoriferous or 
sweat-glands, which are of the tubular type, and sebaceous glands, 
which are of the acinous type. In the rabbit, glands are absent 
from the general surface, but are found in special situations, as, for 
example, in connection with the hair follicles of the lips, the internal 
surface of the ear, and the external genital 
organs. The inguinal glands comprise 
both tubular and acinous portions. The 
mammary glands of the female are 
greatly modified cutaneous glands of the 
sudoriferous type. 
Besides the mucus-secreting cells of the 
general epithelium, the glands of the ali- 
mentary canal comprise the important but 
less elaborated glands of the wall, such as 
the gastric glands of the stomach; and the 
greatly elaborated, outstanding glands 
which lie beyond the wall and are con- 
nected with the interior of the canal only through their ducts. 
The latter comprise the oral glands, the liver, and the pancreas. 
The oral glands include chiefly the submaxillary, parotid, 
sublingual, and infraorbital glands-conspicuous structures in 
the dissection of the surrounding portions of the head and neck. 
Their ducts communicate with the cavity of the mouth. 
The secretion of the oral glands has important mechanical 
functions in moistening the comminuted food in preparation for 
swallowing. In mammals it also contains ferments or enzymes, 
chiefly ptyalin, which is capable of transforming starch into soluble 
materials, though the digestive action is probably not exercised to 
Fig. 4. From a section of 
the parotid salivary gland of 
the rabbit. A, Duct system 
in relation to body of gland: 
g, acini of gland body; d, 
interlobular duct. B, Three 
individual acini, highly mag- 
nified. 26 
Anatomy of the Rabbit 
a great extent. Pancreatic secretion, on the other hand, has little 
or no mechanical action, but its enzymes are of the greatest im- 
portance in digestion. 
There is a close association between the epithelia of the surface 
of the body and the nervous tissues. In the adult we may dis- 
tinguish as sensory epithelia special aggregations of cells lying 
in either a deep or a superficial position, and associated more or 
less closely with the central nervous system. They comprise the 
olfactory epithelium of the nasal cavity, some of the cells of 
which are true nerve cells, the gustatory epithelium of the tongue, 
and the auditory epithelium of the 
membranous labyrinth of the ear. The 
retina-the nervous portion of the 
eye-is a modified portion of the central 
nervous system. 
As linings of surfaces, the ordinary 
epithelia may be distinguished from 
certain special coverings of internal 
spaces, the endothelia and mesothelia. 
The two latter consist microscopically 
of thin pavement-like cells. They differ 
from epithelia in origin, being formed, 
not in connection with originally free 
surfaces, but in relation to spaces of the 
mesoderm or intermediate layer of the 
body. Endothelia form the linings of 
blood-vessels and lymph canals, while 
mesothelia are the chief layers of the 
smooth, moist serous membranes 
which line the peritoneal, pleural, and 
pericardial cavities. 
2. Connective Tissues 
The connective tissues form the supporting elements of the 
body. As ordinary connective tissues they serve to connect 
organs or parts of organs, and as skeletal tissues they provide 
the rigid framework or skeleton from which all soft parts of the 
body are suspended. They are distinguished by the presence of 
Fig. 5. From a section of the 
skin of the side of the body of an 
adult rabbit. X about 10; show- 
ing the grouping of the hair 
follicles: co., corium; ep., epi- 
thelium; m.c.m., cutaneus max- 
imus muscle; t.s., subcutaneous 
tissue. Connective Tissues 
27 
two main components-the cell basis, and the intercellular 
substance or matrix. The cellular portion is formative, and is 
much more conspicuous in the embryonic than in the adult condi- 
tion. All connective tissues are products of an embryonic tissue, 
the mesenchyme (Fig. 20, ms.), which consists of branched cells 
connected by their outstanding processes. Through the activity 
of the cells there is formed an intercellular material consisting of 
either a homogeneous matrix, or more frequently a matrix con- 
taining formed elements of a supportive nature. 
A. Ordinary Connective Tissues 
In the adult condition the ordinary connective tissues, with 
few exceptions, consist of the cell basis with two kinds of fibrous 
elements, the white, and yellow 
fibres (Fig. 6). White fibres are fine, 
unbranched elements of great strength 
which do not occur independently 
but only in compact bundles of 
various sizes. The yellow fibres are 
of greater diameter. They branch 
and communicate, but are not as- 
sociated to form bundles. They also 
differ from white fibres in being 
highly elastic. The tissue produced 
in this way is known as fibrous 
connective tissue. It occurs in 
several forms according to the relative 
concentration of the two kinds of 
fibres or the admixture of other 
materials. 
The commonest kind of fibrous tissue in the adult is that 
described as areolar. It is characteristic of the subcutaneous 
tissue (Fig. 5) which connects the skin with the body; but occurs 
also in various positions where it has a similar function of joining 
structures loosely together. Subcutaneous connective tissue is a 
white material, the peculiar appearance and properties of which 
are due to the fact that the two kinds of fibrous elements are 
arranged in a loose felt-like network (Fig. 6). When stretched, 
Fig. 6. Areolar connective tissue 
(subcutaneous tissue) of the rabbit; 
from an embalmed specimen: c.c., 
connective tissue cell; w.f., bundle of 
white fibres; y.f., yellow elastic fibre. 28 
Anatomy of the Rabbit 
it is found to yield up to a certain point, beyond which it is tough 
and resistant. It tends to regain its original shape when the 
tension is removed. 
Fibrous connective tissue may be greatly modified through the 
concentration of either one of the fibrous elements. Concentration 
of white fibres is, however, the common 
modification. This condition is illustrated in 
the thick connective tissue layer forming the 
true skin or corium (Fig. 5), but is more con- 
spicuous in the glistening white tendons 
(Figs. 7, 34) by which muscles are attached to 
bone surfaces, in the ligaments uniting bones 
with one another, and in the thin, broad 
aponeuroses which serve for muscular at- 
tachment. The structures known anatomi- 
cally as fasciae are special sheets of con- 
nective tissue covering chiefly individual 
muscles or muscle groups. Concentration of 
yellow fibres occurs in the dorsal ligament of 
the neck (ligamentum nuchae) where greater 
elasticity is required. The ligament is not so 
conspicuous in the rabbit as in larger mammals 
where the yellow coloration is very noticeable. 
Fat or adipose tissue is a soft form of 
connective tissue in which the cells are greatly 
enlarged and contain fatty material in the 
form of globules. It tends to occur in certain 
definite situations, such as in association with the blood-vessels, 
but also is found in locations where areolar connective tissue might 
be expected to occur. Special fat masses, sometimes distinguished 
by unusually dark coloration, occur at the side of the neck and 
between the shoulder blades of the rabbit. In the foetus (cf. 
Plate VI) these are represented by large masses of vascular con- 
nective tissue. They correspond with the so-called storing or 
hibernating glands of certain other mammals. 
Coloration or pigmentation of certain portions of the body, 
especially of the skin and hairs and of the retina, the ciliary body, 
and the iris of the eye, is due to the presence of pigment granules, 
Fig. 7. From a section 
of the tendon of origin of 
the biceps muscle: m.f., 
muscle fibres ending on 
the tendon; t., fibrous 
connective tissue of the 
tendon. Connective Tissues 
29 
partly in special connective tissue cells, chromatophores, and partly 
in epithelium. The absence of such granules in animals belonging 
to species normally coloured constitutes albinism, a condition 
indicated by the whiteness of the hair and by the pink colour of 
the eyes, the latter being due to 
the circumstance that the blood- 
vessels of the vascular tunic are 
not concealed by pigment. 
B. Skeletal Tissties 
The skeletal tissues are solid 
forms of connective tissue which, 
on account of their more permanent 
shape, are better adapted to form 
a support for the body. They are 
of two kinds-cartilage and bone. 
Simple or hyaline cartilage 
(Fig. 8) is a semi-solid and some- 
what resilient material of a bluish 
or pearly coloration. It consists of a homogeneous matrix in 
which the cells are imbedded. The cells are distributed singly, 
or more often in groups of two 
to four, each cell, or occasionally 
two cells, being contained in a 
small oval space, the cartilage 
lacuna. The size of the spaces, 
and also their distance apart, are 
subject to great variation. The 
addition of fibrous elements, 
usually of white fibres, produces 
a modification known as fibro- 
cartilage. This occurs in 
certain definite situations, as in 
the symphysis of the pelvis, or 
in connection with the inter- 
articular menisci and at the capsular margins of the joints. 
In the adult skeleton cartilage is present only in small amount. It 
forms the articular surfaces of joints, the ventral portions or costal 
Fig. 8. Hyaline cartilage, from a 
fresh preparation of the costal 
cartilage of the rabbit: cc, cartilage 
cell; 1, lacuna; m, matrix; v, 
vacuole. 
Fig. 9. Intramembranous bone; from a 
ground section of the rabbit's femur: c.l., 
circumferential lamellae; h.c., Haversian 
canal; h.l., Haversian lamellae; i.l., inter- 
stitial lamellae; lac., lacuna. 30 
Anatomy of the Rabbit 
cartilages of the ribs, and a portion of the nasal septum; it is also 
found uniting the basal bones of the skull. In the embryo, however, 
it forms the entire skeleton, with the exception of a small portion 
which, as described below, is composed of membrane bone. In 
the course of development, except in the sit- 
uations indicated, the cartilage is replaced by 
bone. 
Bone is a compact, resistant, but yet 
somewhat elastic tissue, possessing much 
greater strength than cartilage, and therefore 
forming a more perfect skeletal support. As 
indicated below, its appearance as a tissue 
differs somewhat according to its mode of 
formation. The more typical structure (intra- 
membranous bone) is illustrated in the 
accompanying figure (9) of a ground trans- 
verse section of the dried shaft of the femur. 
Its dry weight consists of about one-third 
animal matter and two-thirds mineral matter, 
the latter being chiefly calcium phosphate. 
The bone materials are deposited in layers 
or lamellae, which are comparable to highly 
modified white fibres of fibrous connective 
tissue. The lamellae enclose between them 
greatly branched spaces, the lacunae, in 
which during life the bone cells are accom- 
modated. In the natural condition the bone 
is enclosed except on its articular surfaces by 
a layer of connective tissue, the periosteum. 
During the period of growth this membrane 
contains large numbers of bone-forming cells, the osteoblasts, 
through the activity of which the deposition of the bone lamellae 
is accomplished. 
Bone may be formed either with or without a cartilage basis, 
being known in the former case as cartilage or replacing bone, 
in the latter as membrane or derm bone. The former is the 
more usual, replacing units of the primary cartilage skeleton, which 
appears earlier in the embryo. This it does both by surrounding 
Fig. 10. Divided femur 
of the rabbit: c.t., can- 
cellous tissue; e., distal 
epiphysis; el., epiphysial 
line; m.c., marrow-cavity; 
s., shaft. Connective Tissues 
31 
and by invading the units referred to. In only a few regions, as 
already indicated, the cartilage persists throughout life. 
Membrane bone occurs less extensively. It is exemplified by 
the roofing and facial bones of the skull, most of which have a flat- 
tened tabulate form, and by the clavicle. It is formed in connective- 
tissue membranes and may contain cartilage, but does not develop 
on a cartilage basis. Skeletal units of this type lie superficial to 
the other skeletal elements, a feature which is due to the fact that 
they represent surface plates which in lower vertebrates are as- 
sociated with the skin. 
Only in a few cases are the bones of the skeleton solid-as a 
rule they consist of a fairly thin shell of hard or compact bone 
surrounding a central mass of spongy or cancellous bone. This 
arrangement is one of great mechanical strength, combined with 
lightness, and at the same time provision is made in the interior 
of the bone for blood-vessels and marrow-spaces. Thus in a long 
bone (Fig. 10) the central portion or shaft consists of a cylinder 
of compact bone surrounding an extensive space, the marrow- 
cavity. The ends or extremities consist each of a thin shell of 
compact bone continuing that of the shaft and surrounding a mass 
of cancellous tissue. In the short, flat, or irregular bones of the 
skeleton no continuous marrow-cavity is formed. 
The articulations of bones are of two types-immovable articula- 
tions or synarthroses, and movable articulations, diarthroses, 
or joints. In the former, motion is either absent or at least greatly 
restricted. In the latter, it is definitely provided for through 
the presence of joint-structures. Thus in a joint (Fig. 24, page 51) 
the apposed surfaces of the bones are accurately modelled in 
relation to one another, and are, moreover, covered by a layer 
of cartilage, the latter forming a joint cushion. Between the two 
surfaces is a space, the cavity of the joint, containing a viscid 
material, the synovia, which serves for lubrication. The space is 
enclosed by a connective tissue capsule. The strength of the joint 
depends largely on the enclosing capsule, but it is usually greatly 
increased by the presence of accessory ligaments. In the more 
complex joints, such as that of the knee (Fig. 24, B), interarticular 
cartilages (menisci) are enclosed between the bone surfaces, and 
the latter are connected directly by short ligamentous cords. The 32 
Anatomy of the Rabbit 
various ligaments of a joint permit free motion of the bones, 
but only up to a certain point. 
Several differences are observable in joints ac- 
cording to the forms of the apposed surfaces and 
the kind of motion provided for. Thus in the 
ball-and-socket joint, or enarthrosis, exemplified 
by those of the shoulder and hip, a bone is able to 
move in various directions about its base of attach- 
ment, although actually, in the limbs, this motion 
is almost restricted to an anteroposterior direction. 
In the ginglymus, or hinge-joint, as exemplified 
by the articulations at the elbow and at the knee, 
motion is restricted to a single plane. The gliding 
joint, or arthrodia, is one in which a slight degree 
of motion is made possible by one surface slipping 
over the other; it is exemplified in the accessory 
articulations of the vertebral arches. 
3. Muscular Tissues 
Muscular tissues are the active portions of the individual 
muscles which move the skeleton and of the muscle coats of visceral 
organs. Their chief feature consists in the elongation of the cells 
to form fibres. These fibres possess the contractile properties of 
simple protoplasm, but with the contraction limited to one direction. 
Except in a few cases the fibres are arranged in a parallel fashion, 
so that the line of contraction of the muscle or muscle layer is the 
same as that of each of its fibres. The result of contraction in 
both the muscle and its individual fibres is the shortening of the 
longitudinal axis and the increase of the transverse axis. Muscles 
are important in the production of heat. The latter is liberated 
not only when the muscle is in action but also in repose. 
Two chief types of muscle fibres occur in the body-the smooth 
or unstriated fibres, which are characteristic of the involuntary 
muscles or muscle coats of the visceral organs or of the skin, 
and the striated fibres which compose the individual or volun- 
tary muscles of the skeleton. Smooth fibres (Fig. 11) are elon- 
gated, spindle-like cells, the substance of which is longitudinally 
striated, but possesses no transverse markings. The single nucleus 
of the cell occupies a central position. The muscles which they form 
Fig. 11. Invo- 
luntary muscle, 
from a section of 
the muscular tunic 
of the intestine. Muscular Tissues 
33 
are distinguished as involuntary because their 
operation is not under the control of the will, their 
connections being with the autonomic nervous 
system. They respond slowly to stimulation but 
are capable of prolonged contraction. The striated 
fibres (Fig. 12) are very much larger, cylindrical 
structures, the substance of which possesses char- 
acteristic transverse striations in addition to the 
longitudinal ones. Each fibre is enclosed by a 
loosely attached membrane, the sarcolemma, and 
contains many nuclei.* The presence of the latter 
indicates that the fibre is not a single cell but a 
syncytium, i.e., an association of cells unseparated 
by cell boundaries. The muscles formed by such 
fibres are under the control of the will, their connections being 
directly with the central nervous system. They comprise not 
only the typical muscles of the skeleton, but also the special muscles 
connecting the skeleton with the skin. 
The muscular substance of the heart differs from both striated 
and smooth muscle in being composed of branched anastomosing 
fibres, which apparently form a 
continuous network. Like 
striated muscle, it possesses 
characteristic transverse mark- 
ings, but, like involuntary 
muscle, it is under the control 
of the autonomic nervous 
system. 
In the gross, voluntary 
muscles present a longitudinal 
striation which is roughly re- 
ferred to as the direction of 
the fibres, and which is of great 
value in identification. The 
*In the so-called white muscles the nuclei lie on the inner surface of the 
sarcolemma. In red muscles, such as the semitendinosus of the rabbit, many 
nuclei occur between the fibril bundles of the interior of the fibre. Red fibres 
contract more slowly than white but are more resistant to fatigue. The pro- 
portion of red and white fibres varies in different muscles. 
Fig. 12. Stri- 
ated (skeletal) 
muscle of the 
rabbit. 
Fig. 13. From a section of the pyloric 
end (antrum pyloricum) of the stomach of 
the rabbit: m.m., muscularis mucosae; 
t.m.c., circular layer of the muscular tunic; 
t.m.l., longitudinal layer of the muscular 
tunic; t.ms., mucous tunic; t.s., tela sub- 
mucosa; t.sr., serous tunic. 34 
Anatomy of the Rabbit 
striation is due to the circumstance that the fibres are ar- 
ranged in parallel groups or muscle bundles, each of which is 
surrounded and separated from the adjacent bundles by a con- 
nective tissue enclosure, the perimysium. 
Involuntary muscle is distinguished by its white or greyish 
coloration and by its smooth or homogeneous appearance. It forms 
characteristic layers in connection with visceral organs or with the 
skin, and is thus much less individual than the voluntary muscles 
in its relations to particular 
parts. It forms the muscular 
portion (muscularis mucosae) 
of the mucous tunic of the ali- 
mentary canal, and also a sepa- 
rate muscular tunic lying in 
the outer portion of its wall 
(Fig. 13). In the muscular tunic 
the fibres are arranged in both 
circular and longitudinal direc- 
tions. Involuntary muscle also 
forms a small constituent of 
many organs, such as certain 
glands, in which contractility is 
not a chief function. It is a large constituent of the wall of the 
urinogenital tubes, particularly the bladder and the uterus. In 
association with elastic connective tissue it is an important constit- 
uent of the walls of the blood-vessels. 
4. Nervous Tissues 
Nervous tissues are the essential components of the central 
nervous system and of the outlying nerves and ganglia. They 
comprise two kinds of elements--neurons or nerve cells and 
neuroglia cells. The former alone carry on the essential nervous 
functions, while the latter are supporting structures forming in the 
central nervous organs a mass of neutral tissue in which the neurons 
are imbedded. 
Nerve cells differ greatly in form, but typically each consists of 
a cell-body (Fig. 14) bearing two kinds of processes-a single 
axon, neurite, or neuraxis, and a series of branched protoplasmic 
Fig. 14. Nerve-cell from the anterior 
grey column of the spinal cord (cf. Fig. 16): 
d., dendrites; c.g.. chromatophile granules; 
nr., neurite. Nervous Tissues 
35 
processes, the dendrites. The nerve-cell body is characterized 
by the presence in its cytoplasm of granular masses, the chro- 
matophile or tigroid bodies, or Nissl granules. These extend 
into the dendrites but not into the axon. The dendrites, which 
may be greatly elaborated and may be few or 
many, conduct nerve impulses towards the cell 
body while the axon conducts them away from 
it. The latter may traverse a relatively enor- 
mous distance before it ends. A nerve fibre 
consists of an axon with, in some cases, certain 
enclosing sheaths. Two kinds of nerve fibres 
are distinguished-myelinated and unmyel- 
inated fibres. In the former, the axon is sur- 
rounded by a layer of fatty material, the med- 
ullary or myelin sheath. In peripheral nerves, 
a second sheath, the neurilemma, which is 
composed of independent cells, encloses the my- 
elin, and as the latter is interrupted at certain 
points, the nodes of Ranvier, the neurilemma 
there comes into contact with the axon itself. 
Unmyelinated fibres lack the myelin sheath. 
Both types of fibres are present, in varying 
proportions, in many peripheral nerves as well as in the central 
organs. 
A nerve is an association of nerve fibres, the latter being dis- 
posed in a parallel fashion and united together into bundles of 
larger or smaller size by connective tissue, which also forms a 
general peripheral investment, the epineurium. The dead-white 
coloration of most nerves is due to the fatty materials of the myelin 
sheaths, but nerves are commonly found imbedded in a fatty 
connective tissue which is associated with the epineurium and is 
also of white coloration. 
Nerve fibres, and hence nerves, are organs of conduction and as 
such are designated afferent if they conduct impulses towards the 
central nervous system or efferent if they conduct away from it. 
Sensory nerves are afferent, while motor nerves are efferent. 
Nerves, however, usually contain both afferent and efferent fibres 
and when the proportions of both are considerable, they are de- 
Fig. 15. Portions 
of two myelinated 
nerve fibres from the 
sciatic of the rabbit: 
a.c., axial cord; m.s.. 
myelin sheath, stained 
black with osmic acid; 
n., neurilemma; n.r., 
node of Ranvier. 36 
Anatomy of the Rabbit 
scribed as mixed. In the central connections as well as in the 
peripheral distribution of both afferent and efferent fibres, there is 
a marked difference between those associated with the external or 
somatic portions of the body and those connected with internal or 
visceral portions. Consequently somatic and visceral kinds of 
both afferent and efferent fibres are distinguished. 
While the nerve-cell 
bodies mostly lie within the 
central nervous organs, 
some are in the peripheral 
nerves. The majority of 
the latter are grouped in- 
to definite masses, each of 
which is called a ganglion. 
On account of the diff- 
erence in colour produced 
by the presence or absence 
of myelin, the cellular 
and the myelinated fibrous 
constituents of the central 
nervous organs produce 
characteristic patterns ac- 
cording to their varying 
concentration. Where cell 
bodies, dendrites, and unmyelinated fibres preponderate, the tissue 
has a greyish colour and is hence distinguished as grey matter; 
while the concentration of myelinated fibres produces an opaque 
white appearance similar to that seen in the larger peripheral 
nerves, whence the tissue is described as white matter. In the 
spinal cord (Fig. 16) the grey matter is disposed as a central core, 
the white substance as a peripheral investment. An essentially 
similar though much elaborated distribution is found in the basal 
portion of the brain, but the characteristic pattern in the cerebral 
hemispheres and in the cerebellum is one in which the grey substance 
forms a peripheral, investing, or cortical layer. 
5. Blood and Lymph 
Blood is fundamentally a cellular material, but owing to the 
fact that the intercellular matrix takes the form of a liquid medium, 
Fig. 16. Section of the spinal cord of the rabbit: 
c., central canal; f.m.a., anterior median fissure; 
s.m.p., posterior median sulcus; f.a., f.l., and f.p., 
anterior, lateral, and posterior funiculi of the cord; 
c.g.a. and c.g.p., anterior and posterior grey 
columns (horns of grey matter); r.a. and r.p., 
positions of anterior and posterior nerve roots; 
s.a., white substance. Blood and Lymph 
37 
the plasma, in which the cells, or corpuscles, are suspended, its 
features largely differ from those of the ordinary tissues of the body. 
On account of its liquid character, the appearances presented by 
blood in dissection, especially of preserved animals, are almost 
negligible, in spite of the importance of its functions. The cellular 
components comprise (a) erythrocytes, (ft) leucocytes, and (c) 
platelets. The erythrocytes or red blood cells are microscopic 
circular discs of fairly definite though not rigid contour, containing 
no nuclei in adult mammals. They have a yellow colour when 
seen singly, or deep red when observed in bulk, on account of the 
presence of haemoglobin. The latter material is 
the specific carrier of oxygen, with which it 
forms a readily dissociated chemical compound. 
Arterial, oxygenated blood is bright red, while 
venous blood is dark red. The number of red 
blood cells is relatively somewhat greater in the 
rabbit than in man, there being over six millions 
contained in each cubic millimetre. The cells 
are formed in the yolk-sac wall of the embryo, later in the spleen 
and liver, and in the marrow of bones. The leucocytes, also termed 
white or colourless blood cells, are amoeboid, nucleate cells, present 
in the blood in much smaller numbers than the erythrocytes, but 
occurring also in lymph. They are formed in the lymph glands, in 
the spleen, and elsewhere (cf. p. 100). Being capable of passing 
through the walls of the smaller vessels, they occur more or less 
throughout the tissues, where they have the function of carrying 
materials or of ridding the body of injurious substances and bac- 
teria. The platelets are minute, non-nucleate masses of cyto- 
plasm in the blood. 
In all multicellular animals, large proportions of the tissues are 
necessarily more or less distant from the surfaces of absorption and 
excretion. Blood and lymph, circulating through the vascular 
system, are the media by which communication with these is kept 
up, providing for the transportation of materials essential for the 
maintenance of life processes in the tissues. The composition of 
the blood varies from time to time according to the individual 
functions performed. Oxygen and food materials are carried to the 
tissues. Carbon dioxide and waste materials of other kinds are 
Fig. 17. Red blood 
corpuscles of the rabbit: 
f, face; p. profile. 38 
Anatomy of the Rabbit 
carried to organs from which they can be excreted. Blood, how- 
ever, has been shown to vary in composition in different species of 
animals, and to be chemically homologous in related ones; and it 
can develop substances conferring immunity to bacterial diseases, 
which substances also differ in different species and individuals. 
SPECIAL ANATOMY 
Terminology 
In special or descriptive anatomy it is necessary to employ an 
extensive system of terminology in order that the various structures 
of the body may be individually designated, classified, and referred 
to their respective positions. The terms used for this purpose may 
be classified into four groups, as follows: (1) general terms- 
those included in the names of parts, but applicable in themselves 
to similar structures (arteries, nerves, etc.) in various parts of the 
body; (2) specific terms or names of parts; (3) regional 
terms-those defining areas (topographic); and (4) terms of 
orientation. 
The terms of the first three groups will be defined so far as 
required wherever it seems necessary. The terms of orientation, 
however, being based on very general relations of the body, are of 
wider application and understanding of them is essential for any 
anatomical description to be intelligible. For these reasons they 
are selected for definition here to the exclusion of others of a more 
restricting or individualizing kind. 
In all vertebrates we may recognize a longitudinal axis, 
corresponding, in general, to the line formed by the vertebral 
column. In the usual or prone position of the body this axis is 
horizontal. The uppermost surface is then described as dorsal, 
the lowermost surface as ventral, the sides of the body as lateral. 
Any position forward, with respect to the long axis, is anterior 
in comparison with any position backward, which is posterior. 
In relation to the long axis it is convenient to recognize a 
median vertical plane, which is one dividing the body into right 
and left halves, and transverse, coronal, and sagittal planes. 
Transverse planes are situated at right angles to the longitudinal 
axis. Coronal planes are longitudinal and horizontal, at right Terminology 
39 
angles to the median vertical plane. Sagittal planes are longi- 
tudinal and vertical, parallel to and including (as midsagittal) the 
median vertical plane. 
The median vertical plane is the centre of bilateral symmetry, 
each half of the body, as divided by it, being in a general way the 
reverse counterpart of the other. Structures or situations partly 
in the median plane are unpaired, and are described as median, 
while positions situated wholly outside of the plane are paired, 
right and left, or dextral and sinistral. In relation to the median 
plane and to the sides of the body, structures are described as 
medial when nearer the former, and as lateral when nearer the 
sides of the body. The term intermediate is applied especially 
to a position between medial and lateral, but this restriction is 
perhaps not justifiable. 
In considering the extent of bilateral symmetry, it is necessary 
to bear in mind that, although a fundamental feature in verte- 
brates, it is not perfectly retained in the adult condition. Symmetry 
is destroyed by the migration of an unpaired structure from a 
median to a lateral position, as is seen, for example, in the case of 
the abdominal portion of the alimentary canal; or, again, by the 
reduction or disappearance of structures belonging to one side of the 
body, as, for example, in the case of the mammalian aortic arch. 
Referring to centre and circumference, either in the body as a 
whole, or in particular parts, the pairs of opposed terms deep and 
superficial, central and peripheral, or internal and external 
may be applied. It may be observed, however, that the terms 
internal and external are sometimes used in the sense of medial 
and lateral, both in descriptive language and in the names of parts. 
In distinction from the terms medial (medialis) and median 
(medianus) the term middle (medius) may be used to designate 
the position of a structure lying between two others, the latter being 
otherwise designated, for example, as anterior and posterior, lateral 
and medial, or right and left. 
The limbs being more or less independent structures, it is proper 
to apply to them certain terms not otherwise applicable to the main 
portion of the body. The chief terms which are used principally 
in this connection are proximal, meaning nearer the centre or base 
of attachment, and distal, toward the extremity. In the middle 40 
Anatomy of the Rabbit 
segment of the fore limb the respective positions of the bones 
(radius and ulna) are indicated as radial and ulnar. The terms 
tibial and fibular are also applicable, although with less reason, 
to the corresponding segment of the hind limb. The upper and 
lower surfaces of the fore foot are described respectively as dorsal 
and volar, those of the hind foot as dorsal and plantar. 
In determining the identity of structures in a quadrupedal 
mammal, considerable difficulty may at first arise from the fact 
that descriptive terms, such as those just defined, are frequently 
included in the names of parts, the latter being, at the same time, 
terms applied in the first instance to the human body, in which the 
recognized relations are somewhat different. In contrast with 
that of a quadrupedal vertebrate, the human body occupies a 
vertical or erect position, and is to be considered as having been 
rotated upward through ninety degrees on the posterior limbs. 
The latter accordingly occupy for the most part their original 
position, and the human arm largely reassumes this position when 
allowed to hang freely at the side of the body. In all, however, the 
face retains its forward direction. Thus the terms anterior and 
posterior as used in human anatomy mean ventral and dorsal, 
provided they refer to parts of the body, such as the entire trunk 
region, which have been affected by rotation. The terms superior 
and inferior as applied to man are similarly equivalent to anterior 
and posterior as applied to a lower form. Since it is unwise to 
change the form of the official terms of human anatomy, it becomes 
necessary to interpret all such terms when used for a quadrupedal 
mammal according to the relations exhibited by man. The human 
terms may in most cases be translated into terms acceptable for 
comparative anatomy by reading ventral for anterior, dorsal for 
posterior, cranial or oral for superior, and caudal or aboral for 
inferior. The exceptions then apply to those parts of the body 
unaffected by rotation. 
On the other hand, in ordinary description of organs and their 
position, where it is not a matter of the official names of parts, little 
advantage is to be gained from adherence to this principle. The 
terms anterior and posterior apply with much greater force to a 
lower vertebrate than to man, while the terms superior and inferior 
are only of interest in the latter. In this case the rule here followed Ground Plan of Organ-Systems 
41 
is to use the terms anterior and posterior for descriptive purposes 
without reference to the human relation. The same remark applies 
to the terms of direction, viz., upward, downward, forward, and 
backward. 
In this connection it may be pointed out that the custom has 
become more or less general in comparative anatomy of employing 
the termination ad with words otherwise signifying position alone, 
in order to indicate position or course toward, e.g., dorsad = 
dorsalward. In the present case this form is used only for course, 
position being indicated by the adverbial termination ly, e.g., 
dorsally. 
Reference may also be made here to the fact that the human 
structures to which identifying names are applied frequently fail in 
one way or another to correspond to structures in a lower form. 
Composite structures to which individualizing names are applied, 
for example, may be represented by independent parts. Also, 
structures which are similar in form or function may be convergent. 
Finally, although it is essential to endeavour to apply all terms as 
accurately as possible, it will be remembered that a terminology 
primarily arranged for one type cannot be exactly applied to 
another without considerable qualification. 
THE GENERAL FEATURES AND GROUND PLAN OF 
THE ORGAN-SYSTEMS 
It has already been stated as a general principle that the 
structure of an organism is the expression of an underlying plan 
and pattern, in the elaboration of which embryonic development 
and ancestry play a very large part. The manner in which the 
comparative method is applied in interpretation may be demon- 
strated by reference to any part of the body of an animal; and in the 
following pages will be found, under the head of the respective 
systems, a preliminary statement of how the origin of certain out- 
standing features of the rabbit may be explained and what grades 
of organization they may be presumed to illustrate. It will be 
recognized that the lower mammals are in most respects less 
specialized than man, and must accordingly show in their grades of 
organization various stages through which man must be assumed 
to have passed. 42 
Anatomy of the Rabbit 
Classification of the Organ-Systems 
The term organ-system is employed in descriptive anatomy 
to designate a group of organs which co-operate in a general function. 
In many respects the systems represent primitive functions, and 
it is therefore largely on account of the independent elaboration 
of these that the systems may be recognized also on a structural 
basis as groups of organs allied in origin and development. The 
exact number of systems recognized depends on certain arbitrary 
distinctions, the following being those usually distinguished. 
(1) The integumentary system comprises the skin, and its 
derivatives, such as the claws (or nails), hairs, and various glands 
of epidermal origin. 
(2) The skeletal system comprises the cartilage and bone 
elements of the skeleton, with their connections. 
(3) The muscular system comprises all contractile structures 
of the body. Since, however, the involuntary muscles are arranged 
as muscle layers in connection with visceral organs, the muscular 
system is usually considered as including only the individual or 
voluntary muscles of the skeleton and skin. 
(4) The nervous system comprises the central nervous 
system (the brain and spinal cord) and the peripheral nervous 
system, the latter consisting of the paired cranial and spinal 
nerves with their associated ganglia and the autonomic nervous 
system. The last is made up of a pair of ganglionated sympa- 
thetic trunks, with two series of ganglia, prevertebral and 
peripheral, interposed between these and the visceral organs, and 
of a set of visceral ganglia and nerves (parasympathetic system) 
connected with the cranial and sacral regions. Associated with the 
nervous system are the special sense organs of the head belonging 
fundamentally in part to the nervous system and in part to the 
surface layers of the body. 
(5) The digestive system comprises the digestive tube and 
its outstanding glandular appendages-the oral glands, the liver, 
and the pancreas. 
(6) The respiratory system comprises the lungs, and res- 
piratory passages, namely, the bronchi, the trachea, and the 
larynx. With this system may also be included the accessory 
respiratory passages formed by the nasal fossae. Classification of Organ-Systems 
43 
(7) The vascular system comprises the organs of circulation 
of the blood and the lymphatic system. The former are the heart, 
the arteries, the capillary vessels, and the veins; the latter the 
lymph-conducting canals, which are largely independent of the 
blood-vessels, and are therefore sometimes considered as forming 
with their associated lymph glands a separate lymphatic system. 
Fig. 18. Schematic representation of the chief organ-systems of a 
generalized vertebrate as seen in a transverse section of the abdominal region: 
Integument-int. 
Skeleton-v, vertebral body; av, vertebral arch; cv, vertebral canal. 
Muscular system-sm, skeletal muscle; vm, visceral muscle. 
Nervous system-ms, spinal cord, with the central canal, and the dorsal 
(posterior) and ventral (anterior) roots of the spinal nerves; grp, ganglion of 
the posterior root; rc, ramus communicans to sympathetic trunk; rma and 
rmp. anterior and posterior rami of a spinal nerve; ts, sympathetic trunk. 
Digestive system-i, intestine. 
Vascular system-ao, aorta. 
Urinogenital system-k, kidney; go, gonad (ovary or testis). 
Serous cavity-cp, general coelom, pleuroperitoneal, or peritoneal cavity; 
pv and pp, visceral and parietal parts of the serous tunic-visceral and parietal 
peritoneum; mes, mesentery. 
(8) The urinogenital system includes the reproductive and 
excretory organs, together with their common ducts-the urethra 
of the male and the vestibulum of the female-and the associated 
bulbourethral gland. The reproductive organs comprise, in the 
male, the central organs or testes, and the deferent ducts, both 
of which are paired, the unpaired seminal vesicle, and the paired 
prostatic and paraprostatic glands. In the female, the repro- 44 
Anatomy of the Rabbit 
ductive organs comprise the paired ovaries, uterine tubes, and 
uteri, together with the unpaired vagina. The excretory organs of 
both sexes comprise the paired 
kidneys and ureters and the un- 
paired urinary bladder. 
Only included in part, or 
omitted in this classification are 
certain organs which physiologi- 
cally at least may be grouped to- 
gether because they have general 
regulatory and growth-controlling 
functions. They constitute the 
internal secreting, hormone, or 
endocrine system, and include 
portions of the reproductive or- 
gans and pancreas, the hypophysis, 
pineal body, suprarenal, thyreoid, 
parathyreoid, and thymus glands. 
General Organization 
It has already been pointed out that all chordates have a 
structural ground plan involving the possession of an axial skeleton 
in the form of a notochord, a dorsal tubular central nervous system, 
and a series of gill clefts, and that all vertebrates are basically 
segmented. 
The rabbit being a vertebrate, its organ-systems are disposed 
in conformity with these fundamental principles. 
(1) Axial orientation. Associated with the elongated shape 
of the body in most animals there is a general lengthwise arrange- 
ment of the principal organ-systems, which thus lie more or less 
parallel to one another. This can be observed in invertebrates, 
such as the annulate worms, in respect of the more nearly original 
systems. In the vertebrates, the presence of the vertebral column 
establishes a structural axis, with reference to which the organ- 
systems are arranged (Figs. 18, 20). 
(2) Metamerism. A large portion of the body, mainly 
dorsolateral in position, is arranged on a segmented plan, in which 
Fig. 19. Rabbit-embryo of 101 days 
(4.8 mm.): m., mandibular; h., hyoid; 
1 and 2, first and second branchial 
arches; a.l., anterior limb-bud; me., 
metameres; p.l., posterior limb-bud. 
(After Minot and Taylor, in Keibels 
Normentafeln, V.; Fig. 12.) General Organization 
45 
parts are repeated serially and longitudinally around and to either 
side of the original axis. Metamerism does not appear to any 
extent on the surface of the adult body, but becomes evident 
internally in the subdivision of the vertebral column into vertebrae, 
and the paired, serial arrangement of the related spinal nerves, 
vessels, and musculature. Metamerism is externally evident in 
embryos (Fig. 19, me.) and is founded upon the serial arrangement 
of parts of the mesoderm (Fig. 20, my., d.m.). 
Fig. 20. Transverse section of a rabbit-embryo of about 10| days, show- 
ing the arrangement of the organ-systems: ao., aorta; ch., notochord; coe., 
coelomic cavity; d.m., dorsal mesoderm (myotomic and sclerotomic divisions); 
e., primitive alimentary canal (enteron); ect., ectoderm; l.b., limb-bud; ms., 
mesenchyme; my., external portion of a myotome; n., nephrotome of embry- 
onic kidney; intermediate mass of mesoderm; sp. and so., splanchnic (visceral) 
and somatic (parietal) portions of the ventral mesoderm. 
(3) Branchiomerism. This is a secondary segmentation, 
superposed upon the primary metamerism by the development of 
a series of gill clefts which do not always correspond precisely with 
the metameres. It is an adult feature of lower aquatic vertebrates, 
such as fishes (Fig. 30), where it is expressed in a series of true gill, 
or branchial structures, associated with gill filaments as functional 46 
Anatomy of the Rabbit 
respiratory organs. In higher terrestrial animals it appears as an 
embryonic feature (Fig. 19, m.,h., 1, 2) and is to be considered both 
as a determinant of adult form and as a mark of aquatic ancestry. 
It underlies the arrangement not only of structures which in the 
lower vertebrates belong to functional gills (branchial arches in the 
restricted sense) but also modified branchial structures such as the 
first visceral, or mandibular arch (m.) and the second visceral, or 
hyoid arch (h.). The modification of these structures in passing 
from the embryonic to the adult condition is very great, but their 
arrangement determines the position and relations of certain skeletal 
structures, including the auditory ossicles, the hyoid, and in part 
the laryngeal cartilages-a point of some value in the classification 
of the parts of the head skeleton. It also determines the succession 
of certain soft structures, including the fifth, seventh, ninth, and 
tenth cranial nerves; also the chief arterial vessels of the heart, 
which are more fully referred to below. 
The fundamental significance of branchiomerism lies in the fact 
that respiration by means of gill perforations of the pharynx is 
characteristic of that branch of the animal kingdom designated 
Chordata. In the various invertebrate phyla are found respiratory 
surfaces of many kinds, such as thin surface membranes, external 
tufted, or invaginated tubes, and analogous structures, but these 
provide for diffusion without perforation of the body tube. 
Embryonic Plan of the Systems 
In the individual organ-systems the main features of the general 
plan, as estimated from a study of embryonic development, may 
be outlined as follows: 
1. The formation of an axial skeletal support, consisting 
primarily of a strand of cellular tissue, the notochord, and second- 
arily of a segmented cartilaginous, afterwards bony, vertebral 
column. 
2. The formation of (a) a primary cartilage skull (chondro- 
cranium) as a support for the brain and capsules of the special 
sense organs (neurocranium or cerebral cranium); and (b) a series 
of cartilaginous visceral arches (splanchnocranium or visceral 
cranium). The Skeletal System 
47 
3. The formation of the chief skeletal muscle in a dorsolateral 
position along the axis. 
4. The formation of the central nervous system as a tube of 
nervous matter (neural tube), lying on the dorsal side of the axial 
support, and differentiated into a general posterior portion, the 
spinal cord, and an anterior expanded portion, the brain. 
5. The formation of the digestive tube as a median structure, 
lying directly beneath the axial support, and of special glandular 
appendages arising from the epithelium of its wall. 
6. The formation of the lungs as paired outgrowths of the ven- 
tral wall of the digestive tube, afterwards connected with the out- 
side of the body by accessory respiratory tracts traversing the head. 
7. The formation of the circulatory system primarily on an 
aquatic plan. This involves the formation of (a) the heart in a 
position ventral to the digestive tube and immediately behind the 
gills; (b) a ventral aorta, passing forward to the gills, and dividing 
into a paired series of branchial aortic arches; (c) a dorsal aorta, 
in which the upper ends of the aortic arches unite, and which passes 
backward along the ventral surface of the axial support; and (d) a 
series of paired veins returning the blood from various parts of the 
body to the heart. 
8. The formation of the reproductive organs or gonads in 
association with the dorsal lining of the coelomic cavity, and their 
connection with the outside of the body by modified kidney ducts. 
9. The formation of the kidneys, either as embryonic or as 
permanent structures, from an intermediate mass of tissue, lying 
in general between the dorsal musculature and the lining of the 
coelomic cavity (cf. position of embryonic kidney in Fig. 20). 
10. The formation, in the ventral portion of the body, of an 
extensive space, the coelomic cavity or coelom, afterwards differen- 
tiated into pericardial, pleural, and peritoneal portions. 
The Skeletal System 
The designation "vertebrate" has reference to a common feature 
of fishes, amphibians, reptiles, birds, and mammals-the possession 
of a backbone or vertebral column, composed of individual Fig. 21. The skeleton: a, atlas; c, carpus; c7, seventh cervical vertebra; 
cl, clavicle; cr, cranial portion of skull; e, epistropheus; f, fibula; fa, facial 
portion of skull; fm, femur; h, hyoid; hm, humerus; 17, seventh lumbar ver- 
tebra; m, mandible; pl, pelvis (coxal bone); r, fifth rib; rd, radius; t, tibia; 
tl2, twelfth thoracic vertebra; tr, tarsus. The position of the clavicle is shown 
above its designation. The Skeletal System 
49 
segments, the vertebrae. Vertebrates are, however, more properly 
described as animals having an internal skeleton. 
Vertebrate The skeleton being composed of nearly rigid 
Animals materials, it is necessary, in order that movement 
may be possible, that these should form many 
separate pieces, designated cartilages or bones according to the 
material composing them. In the embryonic condition, cartilage 
rudiments form a complete but primitive skeleton and in some 
lower vertebrates the skeleton remains entirely cartilaginous 
throughout life. In most cases, however, the cartilage rudiments 
later are largely replaced by bone and membrane bones are added. 
In many cases the replacement of these elements by bone is not 
direct, certain readjustments being necessary both for purposes of 
growth and to meet the much more special functional requirements 
of the adult skeleton. 
The way in which replacing bones are formed on the cartilage 
basis explains many peculiarities of the adult skeleton. In the 
embryonic condition the cartilage rudiments are enclosed by a 
connective tissue sheath, equivalent to the periosteum of a bone 
(p. 30), but described as the perichondrium. Like the periosteum, 
this sheath contains many osteoblasts, which form bone material 
both in the interior of the cartilage (endochondral bone) and on 
its surface (intramembranous bone). The formation of endo- 
chondral bone proceeds from certain localized areas, known as 
centres of ossification, into which active cells of the perichondrium 
are carried by vascular ingrowths. From these centres the de- 
position of bone material to replace the cartilage gradually extends 
through the remainder of the latter. This condition is partly 
illustrated in the distal epiphysis of the humerus shown in figure 
24 A, where the area of endochondral bone (eb) appears in the 
centre of the mass of cartilage. 
In long bones the formation of the first or main centres of 
ossification takes place in the shaft, and there are formed afterwards 
accessory or epiphysial centres for the extremities. A divided 
extremity, such as the proximal end of the femur (Fig. 22), may 
possess several such centres-a principal one for the chief epiphysis 
or actual extremity of the bone and several subsidiary centres for 
its outstanding processes. In the shaft the formation of endochon- 50 
Anatomy of the Rabbit 
dral bone is of short duration. Through the activity of the osteo- 
blasts lying directly in the perichondrium, or later the periosteum, 
a process of formation of intramem- 
branous bone goes on, continuing to 
the end of the period of growth, and 
the result of this peripheral deposition 
of bone lamellae is, that the trans- 
verse diameter of the bone is greatly 
increased. The enlargement of the 
marrow-cavity, with which this is 
associated, is produced by the ab- 
sorption of bone from the interior. 
In young animals both the 
epiphysial centres and the masses of 
cartilage in which they are formed are sharply marked off from 
the body of the bone (cf. Fig. 24). This is largely because the 
formation of the epiphysial centres tends to lag behind that of the 
main centres, and thus the cartilage ex- 
tremities of the bones are evident long 
after the formation of the shaft is under 
way. In the epiphysial centres the bone 
formation is endochondral. The bone 
masses which they form are distinguished 
as epiphyses. During the period of growth 
they are connected with the body of the 
bone by plates of epiphysial cartilage, into 
which the surrounding perichondrium ex- 
tends as an ossification ridge. In this 
region bone formation takes place, with 
the result that the whole structure is greatly 
increased in length. 
After the period of growffh, the duration of which differs in 
different bones, the epiphyses become firmly co-ossified with the 
body of the bone, although the lines of junction or epiphysial lines 
may still be visible. Thus in the distal extremities of the radius 
and ulna, in the proximal extremities of the fibula, or in the bodies 
Fig. 22. Outline sketch of the 
proximal end of the femur of a 
young animal: c.f., principal epi- 
physis for the head of the femur. 
The accessory epiphyses are for 
the great (tr.ma.), lesser (tr.mi.), 
and third (tr.t.) trochanters. 
Fig. 23. The occipital por- 
tion of the skull in a three- 
day-old rabbit: bo, basi- 
occipital bone; ch, occipital 
portion of chondrocranium; 
co, occipital condyle; eo, 
exoccipital; fm, foramen mag- 
num; so, supraoccipital. The Skeletal System 
51 
of the lumbar vertebrae, the epiphysial lines appear even in old 
animals. In the foregoing figure (10) of the divided femur it will 
be seen that the position of the epiphysial lines is indicated by bands 
of compact tissue. Finally, in thoroughly macerated bones of 
young animals, the epiphyses are usually found to be readily 
separable from the main parts of the bones. 
In a comparison of the adult skeleton with the more primitive 
embryonic skeleton, several differences in the arrangement of the 
elements are evident. Thus many bones, notwithstanding their 
possession of several centres of ossification, are to be looked upon 
Fig. 24. Vertical sections of elbow and knee of four-day-old rabbit. 
A, elbow: c, capsule; eb, endochondral bone in the distal epiphysis of the 
humerus; ea, extensor muscles of the forearm; em, extensors of the hand; 
fa, flexors of the forearm; fm, flexors of the hand; h, humerus; ol, olecranon; 
r, radius; sc, synovial cavity; u, ulna. B, knee: a, anterior cruciate ligament; 
c, capsule; f, femur; Ip, patellar ligament; p, posterior cruciate ligament; pv, 
popliteal vessels; t, tibia; x,x, anterior and posterior ligaments of the lateral 
meniscus; x'x', anterior and posterior ligaments of the medial meniscus. 
as individual, while in other cases, as in the basal portion of the 
skull, separate bone elements are produced in a mass of cartilage 
primarily continuous. These either remain distinct throughout 
life, or, as in the occipital region (Fig. 23), become fused together 
to form compound or composite bones. In still other cases, as 
in the vertebrae, the apparently single elements of the adult condi- 
tion are the products not only of originally distinct bones, but also 
of primarily separate cartilage masses. 
The bones of the skeleton are united or articulated with one 52 
Anatomy of the Rabbit 
another by connective tissue in the form of ligaments, by cartilage, 
or in some cases by both together, i.e., by fibrocartilage. Liga- 
mentous union, distinguished as syndesmosis, is the most general 
type of articulation. Cartilage union or synchondrosis occurs 
in certain situations, as in the basal region of the skull. Union by 
fibrocartilage or symphysis is found in the articulation of the two 
sides of the pelvis (symphysis pubis), and in that of the two halves 
of the mandible. 
The articulations of bones are of two types-immovable articu- 
lations or synarthroses, and movable articulations, diarthroses, 
or joints. In the former, motion is either absent or, at least, greatly 
restricted. In the latter, it is definitely provided for through the 
presence of joint-structures. Thus in a joint (Fig. 24) the apposed 
surfaces of the bones are accurately modelled in relation to one 
another, and are, moreover, covered by a layer of cartilage, the 
latter forming a joint cushion. Between the two surfaces is a space, 
the cavity of the joint, containing a viscid material, the synovia, 
which serves for lubrication. The space is enclosed by a connective 
tissue capsule. The strength of the joint depends largely on the 
enclosing capsule, but it is usually greatly increased by the presence 
of accessory ligaments. In the more complex joints, such as that 
of the knee (Fig. 24, B), interarticular cartilages (menisci) are 
enclosed between the bone surfaces, and the latter are connected 
directly by short ligamentous cords. The various ligaments of a 
joint permit free motion of the bones, but only up to a certain 
point, which varies according to. the functional needs of each 
particular joint. 
Several differences are observable in joints according to the 
form of the apposed surface and the kind of motion provided for. 
Thus in the ball-and-socket joint or enarthrosis, exemplified by 
those of the shoulder and hip, a bone is able to move in various 
directions about its base of attachment, although actually, in the 
limbs, this motion is almost restricted to an anteroposterior direc- 
tion. In the ginglymus or hinge-joint, as exemplified by the 
distal articulations of the limb, motion is restricted to a single plane. 
The gliding joint or arthrodia is one in which a slight degree of 
motion is made possible by one surface slipping over the other; The Skeletal System 
53 
it is exemplified in the accessory articulations of the vertebral 
arches. 
The internal skeleton of a vertebrate nearly always consists of 
a principal or axial portion and an appendicular portion. The 
axial skeleton is formed by the vertebral column, the ribs, the 
sternum, and the skeleton of the head; the appendicular skeleton 
by the parts devoted to the support of the limbs, though in the 
case of terrestrial vertebrates it would be more precise to say that 
these are devoted to the support of the body on the limbs and to 
locomotion. In both fore and hind limbs, the skeletal support 
consists of a proximal portion lying within the contour of the body 
and forming the pectoral and pelvic girdles, and of a distal 
portion, lying beyond the general contour of the body and compris- 
ing the skeleton of the free extremities. The limbs of verte- 
brates present an extraordinary range of adaptations, being modified 
in the various groups into fins, paddles, wings, and walking or 
running limbs. In the majority of cases their adherence to a 
common ground plan is evident from their composition. 
The vertebral column of the rabbit consists of 7 cervical, 12 
thoracic, 7 lumbar, 4 sacral, and 14-16 caudal vertebrae. The 
vertebrae are found to be gradually modified from any intermediate 
part of the column forward or backward, but a characteristic type 
of vertebra can be identified for each region. In 
fishes which live in a medium of about the same weight 
as their bodies, the line of the vertebral column is 
straight, and there is little indication of regional diff- 
erentiation. In terrestrial vertebrates, on the other hand, especially 
in mammals, the vertebrae are not arranged in a straight line but 
form a curve dorsad in the trunk or thoraco-lumbar region. This 
constitutes an arch between the attachments to the fore and hind 
limbs for the support of the body in a light medium 
when the limbs raise it from the ground. The 
anterior and posterior ends of the body, which 
project beyond the supporting limbs, are sustained by the column 
curving ventrad in the cervical and caudal regions (with, of course, 
stout ligaments dorsally). In man, the curvatures are modified in 
relation to the assumption of an erect attitude, a lumbar curve 
ventrad developing to counteract the dorsal curve of the thoracic 
Vertebral 
Regions 
Curvatures 54 
Anatomy of the Rabbit 
region, and the caudal region is reduced to a vestige, the coccyx, 
consisting of coalesced vertebrae. 
The individual vertebra is made up of a massive ventral body, 
or centrum, and a dorsal arch, both composed of replacing bone 
(Fig. 26). Both body and arch bear processes which extend into 
the surrounding muscles and serve for their attachment. The 
Fig. 25. Mid-lumbar vertebrae of bear (A, fifth), rabbit (B, fifth), and 
man (C, third): a, inferior articular process; c, body; m, mamillary and superior 
articular process; s, spinous process; t, transverse process. 
principal processes are dorsomedian or spinous, lateral or trans- 
verse, and in the lumbar region, dorsolateral or mamillary. Less 
prominent processes bearing surfaces for mutual articulation are 
also present. 
Generally speaking every vertebra 
has three principal functions-to support 
the body, to protect the spinal cord, and 
to offer support for muscles. 
Any vertebra of the rabbit may be com- 
pared with the corresponding vertebra of 
any mammal or in a gen- 
eral way with those of any 
vertebrate, and will be 
found to show resemb- 
lances and differences corresponding 
with those of the precise functions per- 
formed by the bones compared. The fifth lumbar vertebra of the 
rabbit, for example, would be found distinguished by the great 
The Forms 
of Vertebrae 
Fig. 26. Lumbar vertebra 
of four-day-old rabbit. Cartilage 
dotted, bone shaded. X 5. The Skeletal System 
55 
development of its processes, since the latter support powerful 
muscles used in leaping. The corresponding human vertebra, or 
the third as functionally more nearly equivalent, is weak in mus- 
cular expansion, but its body is massive for purposes of axial support. 
A corresponding vertebra of the bear will be found more or less 
intermediate between the two types (Fig. 25). 
The axial line of the vertebrae passes through the centres of 
the bodies, the position occupied in the embryo by the notochord 
(Fig. 20). Some of the lower aquatic 
chordates, such as lampreys, exhibit the 
notochord in both young and adult con- 
ditions, and show little indi- 
cation of the development of 
the elements of vertebrae. 
Others, of slightly more ad- 
vanced grade, such as sharks (Fig. 27), 
show the notochord surviving more or less 
to the adult condition with the vertebral 
elements developed round about it. 
The head skeleton of a mammal, usually 
but inaptly called the skull, is a complex 
of individual bones and cartilage, the 
arrangement and functions of which may 
be determined with a little effort. The 
general disposition of the bone elements, demonstrable in the 
rabbit or any mammal is as indicated in figure 28. Briefly, there 
is a linear series of basal segments, comprising from behind forward 
basioccipital, basisphenoid, presphenoid, and 
mesethmoid. The three first-named form the 
floor of the brain-case, while the mesethmoid forms 
the nasal septum. Associated with the basioccipital 
are paired, lateral exoccipital bones, and a supraoccipital ele- 
ment, together forming an occipital ring enclosing the aperture for 
transmission of the spinal cord from the cranial cavity (Fig. 23). 
The basisphenoid and presphenoid bear lateral expansions, respec- 
tively the greater and lesser wings, or alisphenoids and orbito- 
sphenoids, which assist in the formation of the side walls of the 
brain-case. The bone capsule (periotic) lodging the internal ear 
The 
Notochord 
Fig. 27. Transverse sec- 
tion of shark vertebra (carti- 
lage stage), from young speci- 
men of Atlantic dogfish, 
Acanthias: i, intercalary car- 
tilage, completing arch; n, 
notochord; v, body of ver- 
tebra. 
Composition 
of the Skull 56 
Anatomy of the Rabbit 
on either side is solidly built into the lateral cranial wall between 
the exoccipital and alisphenoid, while further forward the light 
scroll-like surfaces of the ethmoid bone, or ethmoturbinal, 
representing the chief portions of the nasal capsule, are attached 
on each side of the base of the mesethmoid. The original pro- 
portions of the nasal capsule are, however, more nearly commen- 
surate with the general cavity of the nose; and additional turbinal 
surfaces, comprising the nasoturbinals and maxilloturbinals, 
are attached secondarily to the nasal and maxillary bones. 
Fig. 28. Composition of the mammalian skull. Cartilage dotted, 
cartilage bone shaded, derm bones plain: I-XII, cranial nerves; as, alisphenoid; 
bh, body of hyoid; bo, basioccipital; bs, basisphenoid; c, canine teeth; cm, 
Meckel's (mandibular) cartilage (I); e, mesethmoid; et, ethmoturbinal; ex, 
exoccipital; f, frontal; hy, hyoid (II); i, incisors; 1, lacrimal; m, molar teeth; 
mn, mandible; mx, maxilla; mt, maxilloturbinal; n, nasal; nt, nasoturbinal; 
os, orbitosphenoid; p, premaxilla; pa, parietal; pl, palatine; pm, premolar 
teeth; pt, pterygoid; sq, squamosal; so, supraoccipital; th, thyreohyal (III); 
v, vomer; z, zygomatic. 
To this foundation of cartilage bones there is added a series of 
enclosing membrane bones, for the most part thin and superficial, 
but nevertheless making up the greater part of the facial portion 
of the head skeleton as opposed to the cranial or brain-containing 
portion. The series comprises the interparietal (absent in the 
hare and many other mammals), paired parietals, squamosals, 
frontals, and nasals as roofing bones, and paired premaxillary, 
maxillary, palatine, pterygoid, and mandibular bones forming 
the solid supports of the mouth. Several lateral elements also take 
part, including the lacrimal, at the anterior border of the orbit, 
the zygomatic, forming the central portion of the corresponding 
arch, for protection of the orbit and muscular support, and finally The Skeletal System 
57 
the bladder-like tympanic bone, which forms the enclosure of the 
middle ear and protects the delicate bones of the auditory chain. 
An important though inconspicuous portion of the head skeleton 
is formed by the hyoid apparatus supporting the tongue, and 
certain cartilages of the larynx, with which the hyoid is intimately 
associated. The relation of this complex to the skull is indicated 
in a mammal by the suspension of the hyoid apparatus from its 
base. The three bones of the auditory chain (the series of small 
bones in the middle ear-malleus, incus, and stapes) and the 
elements just referred to, together with certain replacing or derm 
Fig. 29. Lateral view of skull of rabbit foetus, 45 mm: cb, co, cn, cranial, 
orbital, and nasal portions of primary chondrocranium; fr, frontal; i, incus; 
ip, interparietal; m, malleus; mn, mandible; mx, maxilla; na, nasal; pa, parietal; 
pl, palatine; pmx, premaxilla; sq, squamosal; st, styloid process; t, tympanic; 
zy, zygomatic. Born plate model, after Voit. 
elements, constitute the modified remnant in the mammal of what 
is often regarded as a third main division of the internal skeleton, 
namely, the visceral skeleton. 
The skull consists primarily in the embryo of a cartilage trough, 
the extent of which is roughly definable as the area occupied by the 
occipital, anterior and posterior sphenoidal, and ethmoidal portions 
(Fig. 29). As a cartilage skull it is designated as the chondro- 
cranium, and after its conversion into bone 
as the osteocranium. It is no more than 
an enclosure for the brain, except that it 
has associated with it the cartilage capsules 
of the nasal, visual, and auditory organs, and, in the case of the 
first and last of these, the capsules are incorporated with the skull 
Chondrocranium 
AND OsTEOCRANIUM 58 
Anatomy of the Rabbit 
proper. This, the primary skull, is designated as the neuro- 
cranium or cerebral cranium, to distinguish it from a second 
portion of the head skeleton, 
the splanchnocranium or 
visceral cranium, which in- 
cludes the series of visceral 
arches suspended from the 
ventral surface of the neuro- 
cranium. The addition to 
the primary head skeleton of 
a large number of membrane 
bones results in more or less 
obscuring of the original divi- 
sions, since the membrane 
portions of the visceral cran- 
ium are, with the exception of the mandible, united by suture with 
those of the cerebral cranium, while the true cartilage or cartilage 
bone portions of the former, occurring as the auditory ossicles, 
the hyoid, and the larynx (in part), although highly modified, 
remain in a more or less independent relation. 
The components are strikingly distinct in the mammalian skull 
during the later stages of foetal development, the cartilage of the 
chondrocranium and the bones ossifying in its interior forming a 
foundation basal mass, from which are suspended elements of the 
same nature, principally auditory and hyoid, in a somewhat arch- 
or rod-like form. The auditory arch is formed by the two more 
lateral bones of the auditory chain, incus and malleus, of which the 
incus is attached to the skull, while the malleus is extended as the 
cartilage of Meckel almost the whole length of the inner surface 
of the mandible. The bulk of the skull is formed already by the 
surface elements distributed in the characteristic fashion, but as 
yet only loosely associated (cf. Fig. 29). 
This condition of the developing skull in a mammal finds its 
explanation far back in the history of the vertebrates and is only 
made clear by the study of some one of the lower fishes such as 
shark or sturgeon. In a shark (Fig. 30) 
the entire internal skeleton is formed in 
cartilage which persists throughout life. 
The principal part of the head skeleton is 
Fig. 30. The chondrocranium and visceral 
arches of the Atlantic dogfish, Acanthias: ca, 
auditory capsule; ch, chondrocranium; cn, nasal 
capsule; h,h', dorsal and ventral segments of 
hyoid arch (II); i, intercalary cartilage of 
vertebral column; m,m', dorsal and ventral 
portions of mandibular arch (I), functional 
upper and lower jaws; malleus and incus of 
mammalian ear; or, orbit, depression for optic 
capsule; v, vertebra; 1-5, branchial arches. 
Head Skeleton of 
Lower Vertebrates The Skeletal System 
59 
a massive cartilaginous box (chondrocranium), enclosing the brain, 
and including, as a result of growth and fusion, the nasal and auditory 
capsules. The eye capsules are free, and are accommodated at 
the side of the cranium in an orbital depression, 
to be seen on the skull of all vertebrates. This 
type of structure is obviously the basis of the 
mammalian skull, except that in the latter the 
cartilage mass is at once more restricted to its basal 
portion and more specialized in its replacement by 
definite bone centres. 
It is, however, in respect of the visceral arches 
suspended from the chondrocranium that the 
structure of the shark skull is most illuminating. The first or 
mandibular arch forms the upper and lower jaws. Its composition 
reflects that of the external part of the auditory chain in the 
mammalian embryo, these bones corresponding with the posterior 
ends of the two cartilaginous jaws of the sharks, a relation which 
establishes the fact, for a long time scarcely believed by zoologists, 
that in the history of mammals this arch has undergone a profound 
change of function. The second or hyoid arch, though developed 
to an extent out of keeping with the degree of development of the 
primitive tongue, is nevertheless obviously homologous with the 
hyoid arch of a mammal. In most sharks its upper portion has 
an important accessory function in the support of the jaws and 
this part probably becomes the third bone (stapes) of the auditory 
chain in the mammal. Following the hyoid arch are five ordinary 
or branchial arches supporting the filaments of the gills and 
serving as pillars of the gill apertures. These arches are the parts 
of an extensive system out of which have been formed by special- 
ization part of the hyoid apparatus and those portions of the 
laryngeal cartilages of mammals which are of visceral rather than 
tracheal origin. 
So far as the surface or roofing portion of the skull is concerned, 
it is represented in a shark only by dermal teeth or shagreen denticles 
(Fig. 31), uniformly distributed in the skin of the body, and slightly 
modified in shape and size at the aperture of the mouth to constitute 
Fig. 31. Sha- 
green denticles of 
the smooth dog- 
fish, Mustelus; en- 
larged. 60 
Anatomy of the Rabbit 
definite teeth lining the jaws. In sturgeons and related fishes, 
however, these structures are already concentrated into a 
Derm definite pattern of surface plates, having in general the 
Bones same disposition as derm elements in the skull of all higher 
vertebrates, and distributed in such a way that they form 
an almost complete enclosure for those parts of the chondrocranium 
which they invest. The pattern of the dorsal elements is best 
indicated in fossil amphibia and early reptilia, in which the plan 
is almost diagrammatic. 
The elements of the head skeleton may be classified as follows: 
1. The CEREBRAL CRANIUM (cranium cerebrale or neuro- 
cranium), including: 
(a) The primary cartilage skull (chondrocranium), enclosing 
the brain, and containing in its wall the olfactory and 
auditory capsules (embryonic); 
(&) The secondary bone skull (osteocranium), replacing (fl) 
and comprising the occipital, sphenoid, ethmoid, 
inferior turbinal, and periotic bones; 
(c) The associated derm elements, comprising the inter- 
parietal, parietal, frontal, nasal, vomerine, lacri- 
mal, tympanic,* and squamosal bones. 
2. The VISCERAL CRANIUM (cranium viscerale or splanch- 
nocranium), including: 
(a) The primary mandibular and hyoidf visceral arches 
(embryonic); 
(b) The secondary elements, replacing (fl)-the malleus, 
incus, and stapes of the auditory chain; the hyoid 
bone and its connections with the skull; 
(c) The associated derm elements of the face and palate, 
comprising the premaxillary, maxillary, zygomatic, 
mandibular, palatine, and vestigial pterygoid bones. 
Accessory structures intimately associated with the visceral 
skeleton, though related functionally to the digestive system, are 
*The identification of the tympanic as a derm element has been questioned. 
jThe thyreoid cartilage of the larynx and its connection with the hyoid 
(greater cornu) are modified branchial arches, but the structure as a whole is not 
included with the head skeleton. The Skeletal System 
61 
the teeth. Those of the rabbit present two characteristically 
mammalian features; they are heterodont, or differentiated in 
different regions of the jaw; and they are diphyodont, that is to 
say, the adult series are permanent teeth, which, excepting those 
designated as molars, replace deciduous, or milk teeth of the 
young animal. In lower vertebrates, in contrast with this condi- 
tion, there is usually a multiple tooth change, new teeth being 
developed as required (polyphyodont type). More- 
over, in the rabbit, as in all mammalia, the number is 
restricted, so that, considering the differentiation of 
the teeth, it is possible to express their relations by a dental 
formula. In the mammalia generally the teeth are differentiated 
into incisors, canines, premolars, and molars, and in placental 
mammals the full dental formula is indicated as i. f, c. t, pm. f, m. 3. 
In the rabbit as in other rodents, however, the dentition is greatly 
modified by the elaboration of two pairs of incisors for gnawing and 
the corresponding obliteration of intermediate teeth, the place of 
the latter being occupied by an extensive gap, or diastema, in which 
no teeth occur. The dental formula of the rabbit is i. f, c. §, pm. f, 
m. f. It will also be observed in this animal that the absence of 
the intermediate teeth allows the lips to be approximated behind the 
incisors, and since in this region the lips are also provided with 
hairs on their internal surfaces, the main part of the oral cavity is 
separated almost completely from a small space enclosing the 
incisor teeth. This adaptation, however, is not so perfectly de- 
veloped in the rabbit as in certain other members of the rodent order. 
If the human skull be compared with that of the rabbit or other 
mammal, it is seen to differ most markedly in the enormous develop- 
ment of the cranial region, and in the anteroposterior compression 
of the face, with which is associated, shortening of 
the jaw region reduction of the nasal cavities, and 
rotation of the orbits to a forward position. A most 
instructive feature is the readjustment of the axes 
of the skull, coincident with the assumption of the erect position. 
In both quadrupedal and bipedal positions the face naturally retains 
its forward direction. In most mammals, as in vertebrates gen- 
erally, the axial line of the cranium, known as the basicranial axis, 
and that of the face, the basifacial axis, tend to be nearly in a 
Dentition 
The Human 
Skull 62 
Anatomy of the Rabbit 
straight line or at least parallel; while in man, or in related primates, 
they tend to form an obtuse angle which is progressively reduced 
from lower to higher types. 
It will be evident from a study of the limb skeleton of the rabbit 
that there is a general correspondence in structure between its 
anterior and posterior divisions. This not only app- 
lies to the distinction of girdle portions and the 
divisibility of the free extremity into proximal, middle, 
and distal portions, but extends to very many 
smaller details of composition. The relation in structure between 
anterior and posterior limbs is described as serial homology, 
since two structures in the same 
animal cannot be homologous in 
the usual meaning of the term. 
The pelvic girdle is more uni- 
formly and solidly developed than 
the pectoral girdle, as shown by its 
strength in the three principal 
directions about the point of 
attachment of the limb, the great 
development of the ventral union, 
and the strong attachment to the 
sacrum. On the other hand, the 
pectoral girdle is notable chiefly 
for the strong development of the 
scapula as opposed to the weakness 
of the ventral, pectoral portion. 
In the rabbit the clavicle is vesti- 
gial, and in many mammals, such 
as the ungulates, it is entirely 
absent. In man, however, as well 
as in other mammals in which the 
fore limb is capable of much move- 
ment transversely instead of only 
anteroposteriorly, the clavicle is well developed and is articulated 
at its ends with the scapula and sternum. In this condition it 
acts as a prop upon which the well-developed pectoral muscles 
of adduction move the limb. 
The Limb 
Skeleton 
Fig. 32. Plan of the anterior limb 
skeleton in walking vertebrates, the 
equivalent elements of the posterior limb 
indicated in brackets: si, scapula (ilium), 
pp, procoracoid (pubis); ci, coracoid 
(ischium); hf, humerus (femur); rt', 
radius (tibia); uf', ulna (fibula); rt, 
radial carpal (tibial tarsal); i, inter- 
medium; uf, ulnar carpal (fibular tarsal); 
c,c, centrals; 1-5, distal carpals (tarsals); 
m, metacarpals (meta-tarsajs); ph, 
phalanges of the^digits. The Skeletal System 
63 
Both pectoral and pelvic girdles in terrestrial vertebrates con- 
form more or less closely to a tri-radiate shape if the two halves 
are considered individually. The corresponding portions may be 
identified (Fig. 32), though in mammals the ventral portion in the 
case of the pectoral girdle is greatly reduced. Of the ventral 
elements, those commonly present in vertebrates are the coracoid, 
which forms the posterior ray, and the pro- 
coracoid, the anterior ray, the latter being 
partly covered in front by a derm splint, the 
clavicle. This condition though not character- 
istic of mammals generally is still found in 
monotremes, and rudiments of the coracoid extension ventrally are 
Ground Pattern 
in Terrestrial 
Vertebrates 
Fig. 33. Homologies of the mammalian limb. A, forefoot, rabbit. 
B, forefoot, horse. C, human hand, r, radius; u, ulna; I-V, metacarpa bones. 
identifiable in embryonic marsupials. Adult marsupials and 
placentals show only a small hook-like coracoid process, and the 
clavicle in either perfect or less perfect development. 
There is no more striking feature of homology than that shown 
by the free extremities in the different forms of vertebrates. This 
is true homology because it concerns the resemblances, part for 
part, in the anterior or in the posterior limb of any one vertebrate 
as compared with the corresponding elements in the same position 
in other forms. The front limb of the rabbit (Fig. 33) is slightly 64 
Anatomy of the Rabbit 
elongated and semi-digitigrade, the weight being supported on the 
tips of the bones of the palm (metacarpals), as shown in figure 21. 
These modifications make it more efficient for running than a more 
primitive limb, which is shorter and plantigrade (having the palm 
or sole applied to the ground), though it is less specialized and less 
efficient as a running organ than the limb of the horse (Fig. 33, B). 
The human hand retains a fairly primitive form as to its general 
proportions, but is modified into a seizing or grasping type, the 
thumb being opposable to the remaining digits. The limbs of the 
rabbit, of the horse, and of man, however, are all modifications of a 
primitive, five-toed limb, sometimes termed the ideal pentadactyl 
plantigrade type, in which the palm of the hand or sole of the 
foot is placed flat on the ground. The composition of this primitive 
limb, traceable in one form or another throughout the higher 
vertebrates, and also the serial homologies of the parts are indicated 
in figure 32. 
The Muscular System 
The contractile tissues are not arranged in a definite continuous 
system as is the case with most other organ complexes of the body. 
Smooth or involuntary muscle fibres, modified mesenchyme cells 
of the embryo, which are under the control of the sympathetic 
nervous system, form, the muscle coats of the 
digestive tube, and are important not only for 
its repeated, peristaltic movements, but also for 
its elasticity and expansive power. Smooth muscle 
is also a constituent of many other visceral organs, especially glands, 
in the active secretion of which it appears to play a mechanical 
part. It is further distributed through the walls of the blood- 
vessels, especially the arteries, where it forms the mechanical organ 
of the vasomotor function. This consists in the control of the 
diameter of the vessels by vasodilator and vasoconstrictor nerves 
connected with the vagus nerve and the sympathetic nervous 
system. The constrictive action is stimulated by secretion of the 
suprarenal glands. Vessel regulation of this kind is important, 
first, in maintaining tone of the vessel walls and therefore blood- 
pressure, and, second, in controlling heat loss from the surface of 
the body. Action of the vasomotor nerves may be demonstrated 
Involuntary 
Muscle The Muscular System 
65 
physiologically in a variety of ways. Transection of the cervical 
sympathetic nerve of one side in the living rabbit is followed by 
vasodilatation of the ear, the congestion of which can be seen, and 
the heat loss is demonstrable by feeling with the hand. Stimulation 
of the cut end which is attached to the brain is followed by vaso- 
constriction. 
Cardiac muscle, most nearly allied in action to smooth muscle, 
is the mechanical organ of the rhythmical contraction or beat of the 
heart. The contraction takes place according to the succession 
of the chambers or the course of the blood, and the rate and strength 
of the beat is under the control of the vagus and 
sympathetic nerves, the action of which can be 
experimentally demonstrated. The excised heart in 
the case of lower vertebrates continues to beat for some time 
automatically or under stimulation. This behaviour has been 
interpreted as purely automatic action of the heart muscle, but 
may depend upon intracardiac nerve connections. 
The voluntary muscles of the body form the nearest approach 
to a continuous system of all contractile tissues. They consist 
for the most part of parallel fibres, the association 
of which into fasciculi is responsible for the appear- 
ance of longitudinal striping when the gross muscle 
is viewed from the side, and more or less for the 
grained appearance of the cut surface. The control of action is 
exercised directly from the spinal cord or from the brain. 
A muscle is typically spindle shaped, consisting of a middle 
fleshy portion, termed the belly of the muscle, and of tapering ends 
which provide for attachment. The attachment is effected by a 
strong band of fibrous connective tissue, the muscle tendon 
(Figs. 7, 34). Some muscles, such as those of the abdominal wall, 
are disposed in the form of flattened sheets, the ends of which are 
attached by broad, thin sheets of connective tissue, the apon- 
euroses. In unipennate muscles the fibres are attached obliquely 
to the side of the tendon, or in bipennate muscles to both sides, 
like the vane of a feather. In the so-called biceps, triceps, and 
quadriceps muscles of the limbs, the origin is divided into two, 
three, or four portions. 
A typical muscle of the skeleton has the disposition of parts 
The Heart 
Voluntary 
Muscle 66 
Anatomy of the Rabbit 
illustrated in figure 34 by the biceps (a flexor of the forearm) and 
the long head of the triceps (an extensor of the forearm). The fixed 
tendon, or tendon of origin, of the biceps is in relation to the 
glenoid border of the scapula, the movable tendon, 
or tendon of insertion, with the lower border of 
the ulna. Noting the position of the muscle in front 
of the elbow-joint, it will be seen that its contraction 
results in flexion, i.e., in bringing the forearm into a position nearer 
the arm, or of raising the forearm and hand from the ground. The 
analogous action of the triceps in producing an exactly opposite 
movement (flexion) of the forearm is similarly demonstrated. It 
will be evident that the immediate result of contraction upon the 
bones is limited by the form of the joint. In this case a hinge-joint 
confines motion to one plane, while in the case of the shoulder and 
hip, a joint of the ball-and-socket type allows motion on points at 
various angles to a plane according to which muscle or group of 
muscles may be brought into action. 
The recognition of origin and insertion depends on usual but 
not invariable relations. The exact effect of muscle contraction 
depends as a rule on the relative positions of the parts and on the 
synchronous action of other muscles. A muscle like that forming 
the diaphragm does not possess an insertion after the fashion of 
ordinary muscles; and in some cases, as in the intrinsic muscle of 
the tongue or the so-called orbicular or sphincter muscles, both 
origin and insertion may be absent. 
In the study of the skeletal muscles, moreover, it should be 
borne in mind that the identification of "origin" and "insertion" is 
largely a matter of convention. Actually "fixed" and "movable" 
points depend upon the movement being effected at the moment. 
An excellent example of the necessity of convention in this respect 
is afforded by the human arm in which, as opposed to the ordinary 
use of the muscles, most of the relation would be reversed if the 
body is considered suspended by the hands, that is in the "brachiate' ' 
position commonly assumed by arboreal primates. Also the action 
commonly attributed to any muscle is usually an artificial abstrac- 
tion, for in life muscles act in groups, not singly, and the precise 
effect of any given contraction will be modified by the other muscles 
acting at the same time. Finally, it should be noted that a muscle 
A Typical 
Muscle The Muscular System 
67 
does not always act as a unit, but sometimes one part may contract 
independently of the remainder. 
Voluntary muscle arises chiefly from the segmented areas or 
myotomes of the embryo. The extent to which segmentation is 
shown in the adult, however, depends for the most part on how far 
the definitive muscle is removed from the vertebral 
Origin column or segmented portions of the skeleton. The 
vertebral muscles themselves show throughout their 
attachments to successive vertebrae the marks of segmental origin, 
but many others, such as those of the abdomen, to a certain extent 
those of the limbs, and those of the eye show practically no indica- 
tions thereof. 
While the bulk of voluntary muscle is 
skeletal, part at least is related to the skin. 
This forms a cutaneous sheet, divisible 
into the cutaneus max- 
imus and platysma, and 
the facial, palpebral, and 
auricular muscles of the head. The first 
two and the last of these are commonly 
developed to a considerable extent in 
mammals, though reduced in man. The 
trunk musculature comprises a special 
group of cervical and occipital muscles in 
relation to the neck and head, and the 
general series which are more nearly 
vertebral. The appendicular muscles 
are distributed in special groups connecting 
the limb as a whole with the trunk and the 
various segments of the limb with one 
another. 
As already indicated the skeletons of anterior and posterior 
limbs are serially equivalent part for part. This is also true of the 
related muscles and their actions upon the parts 
of the limb. The respective actual positions 
of the proximal, middle, and distal segments, 
however, are rather different in the front as 
compared with the hind limb of a mammal, a condition easily 
Distribution 
Fig. 34. Arm muscles of 
rabbit from the medial sur- 
face, illustrating muscle 
action, flexion, and extension: 
b, biceps (flexor); tr, long 
head of triceps (extensor); 
i, insertion; o, origin; sc, 
scapula; h, humerus; r, 
radius; u, ulna. 
Equivalence of 
Limb Muscles 68 
Anatomy of the Rabbit 
discernible from the fact that the elbow is directed backward, the 
knee forward. Similarly there are peculiarities of the muscles and 
muscle surfaces, owing to this difference in position and to a twisting 
which has occurred in the anterior limb but not in the posterior 
one, as explained below. There are also conventional ideas prevail- 
ing in anatomy as to flexion and extension, that is bending or 
straightening parts of the limb, and as to flexor and extensor 
muscles and surfaces. For example, ventral bending of the hand 
is called flexion but dorsal bending is called extension, and the 
corresponding movements of the foot are similarly named, although 
flexion at the ankle results in straightening the foot while extension 
does the reverse. 
Fig. 35. Schematic representation of the respective positions of the 
segments in the mammalian limbs. A, neutral; B, anterior limb; C, posterior 
limb. Explanation in text: tr.p., transverse plane. Radial or tibial side of 
limb shaded, ulnar or fibular unshaded. 
The corresponding surfaces and muscles, and in general the 
differences presented by fore and hind limbs may be determined 
by a study of their embryonic relations, but it is simpler, even if 
less accurate, to refer the differences to the common basis of a 
more or less primitive or neutral type as illustrated in figure 35. 
In lower vertebrates, such as reptiles and amphibians, it is easily 
observable that the front and hind limbs are more nearly similar 
to one another than in mammals, especially in respect of the setting 
out from the body of the elbow and knee, so that the limbs are held 
nearly at right angles to the body axis. This common tendency 
is further expressed by the existence of a plantigrade condition of 
the hand and foot, and by a parallel arrangement of the bones of The Muscular System 
69 
the forearm and leg. There is thus an approximation to a neutral 
plan as indicated in (A), where the animal is considered to be facing 
the observer or the limb viewed from in front. This neutral plan 
is, however, never quite realized, because, even in primitive verte- 
brates, where the limbs can scarcely be said to support the body, 
the adjustments for forward progression have already altered the 
respective positions of the segments. 
It will be noted that as regards surfaces and angles in the 
neutral type, the radial side of the fore limb and the tibial side of 
the hind limb, shaded in the diagram, are anterior in position. 
Apart from the possible movements of the limb as a whole or of 
the segments upon one another, it will be seen that there are 
certain angle surfaces, a, b, c, dorsal and lateral in position, which 
may be identified as extension angles and certain others, d, e, f, 
ventral and medial, or flexion angles. In the relation of the limb 
respectively to dorsal and ventral surfaces of the body, a is like- 
wise an "abduction" angle while d is an "adduction" angle. 
In mammals the limbs are set in rather close to and more nearly 
underneath the body, a position better fitted for complete and 
permanent support. As compared with the neutral type, the elbow, 
as indicated in profile in (B), is rotated backward through ninety 
degrees, the hand forward through ninety degrees. The radius 
and ulna are crossed upon one another, the radial side of the limb 
being lateral at the elbow and medial at the hand. The extension 
angle b, at the elbow, is now posterior, that of the wrist, c, anterior. 
Many interesting observations may be made by placing the human 
arm in the corresponding positions. In most mammals, for 
example, the hand is fixed in a prone position with the radius and 
ulna crossed. In man and to a certain extent in some mammals 
the hand may be placed in a supine position or the limb held as 
in the neutral type. In either case the bones of the forearm are 
parallel. The human condition in respect to this character there- 
fore appears to be rather primitive, and is in great contrast to 
that shown in specialized running animals such as the horse, where 
the radius takes over almost the entire support of the forearm and 
the ulna becomes simply an accessory of the elbow-joint. 
The hind limb of a mammal (C) is rotated in its entirety forward 
through ninety degrees. The tibia and fibula retain their parallel 70 
Anatomy of the Rabbit 
position. The extension and flexion angles retain their mutual 
positions but the former become anterior and the latter posterior. 
The foot, in its more usual plantigrade condition, presents one of 
the striking cases of muscle arrangements in the limbs, in that, 
for example, an extensor muscle, originating on the front of the 
leg, and terminating on the dorsum of the toes, will extend the 
toes and will bend the foot on the leg at the ankle joint. In an 
anatomical sense the foot is not thereby flexed. 
The Nervous System 
There is probably no system of organs in which external form is 
so little suggestive of actual function as is the case with the nervous 
system. This is perhaps less true of its peripheral portion, con- 
sisting of nerves which can be seen ramifying through all parts of 
the body, than of the central portion comprising the brain and 
spinal cord. In examining the external form as a preliminary 
step to the study of the functional arrangements, it is advisable 
to bear in mind that the nervous system is a great correlating 
mechanism, consisting of centres where exceedingly complex inter- 
Fig. 36. Plan of the central and peripheral connections of a spinal nerve: 
an, afferent (sensory) neurone; asn, afferent visceral neurone; ca, cp, anterior 
(ventral) and posterior (dorsal) columns of grey matter; en, efferent (motor) 
neurone; esn, efferent sympathetic neurone; grp, dorsal root ganglion; i, 
intestine (visceral organs); m, skeletal muscle; na, np, anterior (ventral) and 
posterior (dorsal) rami of spinal nerve; ra, rp, anterior and posterior roots of 
spinal nerve; rc, ramus communicans (sympathetic); sk, skin; sp, white matter 
of cord; ts, ganglion of sympathetic trunk. Slightly modified, from Herrick. The Nervous System 
71 
connections are made between the nerve elements, and of con- 
ducting paths to and from these centres connecting them with 
outlying parts of the body. 
In accordance with its prime importance and at the same time 
the non-resistant character of the tissue of which it is composed, 
the central nervous system is protected within the canal of the 
vertebral column and cavity of the brain-case. It is furthermore 
surrounded by connective tissue membranes, meninges. In 
higher vertebrates, three of these are differentiated, the dura 
mater, which forms a tough external investment; the arachnoidea, 
which is a very delicate, somewhat spongy web lying internal to 
this; and the pia mater, a thin membrane lying next the nervous 
matter and richly supplied with blood-vessels for the nourishment 
of the latter. Still further protection is afforded by the cere- 
brospinal fluid, which fills the spaces between these membranes as 
well as the cavities within the brain. The nerves, on the other 
hand, are distributed freely throughout the body, and though not 
so adequately protected are more capable of withstanding or repair- 
ing mechanical injury. Also they are commonly found surrounded 
by connective tissue where mechanical injury is relatively little 
likely to occur. 
The most typical of the structural arrangements of the nervous 
system may be made out from a study of the connections of any 
one of the paired nerves of the spinal series (Fig. 36). In the 
spinal cord the difference in appearance as between the white and 
the grey matter has already been described (p. 36). A spinal nerve 
arises by two roots, one of which is dorsal and bears a small 
ganglion containing nerve-cell bodies, the other ventral and 
without a ganglion. Impulses passing through the dorsal root are 
centripetal or afferent in that they pass only in the direction of 
the central nervous system, but they are also in many cases sensory 
in that their effects may be consciously experienced. The most 
characteristic sensory impulses are those which come from the skin. 
Many afferent impulses do not enter consciousness and a majority 
of these come from deeper parts. In a similar 
fashion the impulses of the ventral root are 
centrifugal or efferent, in that they pass only 
in a direction away from the central nervous 
system, and are in most cases motor in that their effects are 
Composition of 
a Spinal Nerve 72 
Anatomy of the Rabbit 
commonly observed as muscular contraction. The two roots, 
however, unite immediately outside the spinal cord, and sub- 
sequently re-divide in such a way that three nerves are formed, 
each containing a proportion of both kinds of fibres. Two of these 
nerves, known as the dorsal and ventral rami, are then dis- 
tributed as somatic nerves to the body wall, while a third is dis- 
tributed as a visceral nerve, or ramus communicans, having 
important secondary connections in the sympathetic nervous 
system. 
Unlike the somatic nerves, which take a direct course to their 
terminations, the communicating rami of each side unite in a 
position ventral to the vertebral column to form a longitudinal 
sympathetic trunk consisting of a connected series of ganglia. 
This trunk is similarly connected with a prevertebral series of 
ganglia, and through them with certain peripheral ganglia on the 
surface of the visceral organs. The longitudinal trunks and their 
connections with the thoracic and lumbar nerves form the sym- 
pathetic portion of the autonomic division of the peripheral nervous 
system. The corresponding connections of the sacral and certain 
cranial nerves (the third, seventh, ninth, tenth, and eleventh) 
constitute the parasympathetic portion of this division. The 
latter does not join the sympathetic trunk, and its fibres end only 
in the peripheral ganglia. The two divisions differ also in their 
responses to certain drugs. Most organs controlled by the auton- 
omic system receive fibres from both, which usually produce 
opposite effects upon stimulation. It is usual to consider that 
only the visceral efferent elements constitute the autonomic division, 
though visceral afferent fibres run through the trunks and ganglia 
along with the efferent components and are thus included in the 
gross anatomical structures. The cell bodies of the afferent 
neurons, however, lie in the dorsal root ganglia of the spinal .nerves 
as indicated in figure 36. 
From the foregoing, it is apparent that the visceral efferent 
peripheral pathway, unlike the somatic one, always involves two 
successive neurons. One fibre springs from a cell body in the 
central nervous system and ends in an autonomic ganglion-the 
preganglionic fibre-while the other arises from a cell body in 
the ganglion and ends in the organ to be controlled-the post- 
ganglionic fibre. The Nervous System 
73 
It is difficult to determine what portion of a muscular con- 
traction, even of one which is considered to be purely voluntary, 
results from an impulse actually originating in the central nervous 
system. The living body, however, affords many 
examples of muscular actions as direct responses 
to immediately previous incoming stimuli, 
without conscious experience being a necessary factor in producing 
the result. In vertebrates in which the spinal cord is divided, the 
lower part thus being separated from the brain, stimulation of the 
skin below the level of the section is followed by co-ordinated 
movements. These are evidently brought about through direct 
Reflex Action 
Fig. 37. The brain from the left side: bo, olfactory bulb; c, cerebellum; 
fc, paraflocculus cerebelli; h, cerebral hemisphere; ip, piriform lobe; m, medulla 
oblongata; s, spinal cord. Numerals indicate the corresponding cranial 
nerves: 2, optic; 4, trochlear; 5, trigeminal; 6, abducens; 7, facial; 8, acoustic; 
9, glossopharyngeal; 10, vagus; 11, spinal accessory; 12, hypoglossal. 
connections within the spinal cord between the dorsal and ventral 
roots either of one spinal nerve or of neighbouring nerves. This 
is known as reflex action. Such responses, of which the well- 
known scratch reaction of the dog is an example, occur in all 
animals. 
The spinal cord reflects in its form the basic architectural 
pattern of the central nervous system, being developed in the 
embryo as a tube and retaining this condition throughout life. 
The cavity, however, is reduced to a very slender 
central canal while the walls become enormously 
thickened by proliferation of the cells and their fibre 
extensions, through which are established the nervous functions 
of the system, as a connected conducting mechanism. The cord 
traverses the vertebral canal, showing slight enlargements in the 
cervical and lumbar regions in relation to the nerve supply of the 
The Spinal 
Cord 74 
Anatomy of the Rabbit 
limbs, and at about the level of the second sacral vertebra narrows 
into the slender, thread-like filum terminale, by which it is 
continued almost to the middle of the length of the tail. 
Superficial examination of the brain of the rabbit (Fig. 37) 
shows that its larger part is formed by the paired cerebral hemi- 
spheres. They are closely pressed together on the dorsal side 
but separated posteriorly on the ventral side. The external layer, 
the grey cortex is important as the principal part of the physical 
substratum of intelligence. In the rabbit, as in all animals which 
have not large cerebral hemispheres, the cortex is smooth, con- 
trasting with its condition in mammals with larger hemispheres, 
where it is corrugated. The amount of this corruga- 
tion is roughly related to the absolute size of the 
brain. Thus it is considerable in the cat and dog 
but reaches a high degree of elaboration in man and in the whale. 
At the anterior tips of the cerebral hemispheres in the rabbit are 
the slightly expanded olfactory bulbs which can be seen to be 
connected backwards with the posteroventral portion of the hemi- 
sphere, known as the pyriform lobe. These parts of the brain 
being directly related to the sense of smell, their size in different 
mammals corresponds with the degree of development of that sense 
and is markedly reduced in man. The development of the cerebral 
hemispheres even in lower mammals is such that important parts 
of the brain, notably the diencephalon and mesencephalon (p. 75), 
are concealed dorsally and laterally. However, the chiasma or 
crossing of the optic nerves on the ventral aspect of the diencephalon 
is evident, while more posteriorly the convergent cords of the 
cerebral peduncles may be seen passing backwards on that of the 
mesencephalon. The posterior part of the brain is formed largely 
by the cerebellum above, the corrugation of which is one of its 
outstanding features, and below by the somewhat tapering medulla 
oblongata, by which the brain is connected with the spinal cord. 
On the ventral side, the medulla oblongata is crossed in front by a 
bridge of fibres, not so conspicuous in the rabbit as in many mam- 
mals and in man, which is known as the pons and which appears 
to connect the two sides of the cerebellum. (Actually it is part 
of the path to the latter from the cerebral hemisphere.) These, 
the outstanding surface features of the brain, afford but a moderate 
conception of its details, the nature of which can be made out only 
The Brain The Nervous System 
75 
by more thorough examination and by reference to the plan of 
development of the organ as a whole. 
Like the spinal cord, with which it is continuous, the brain forms 
primarily a portion of the neural tube, containing a central cavity 
or neurocoele, but, unlike the spinal cord, it is greatly enlarged and 
elaborated to include both the highest controlling centres of the 
whole nervous mechanism and the special centres of the nervous 
mechanism for a variety of functions connected with the head. It 
accordingly not only forms a more or less distinct division, known 
as the brain or encephalon, as opposed to the less elaborated 
spinal cord or spinal medulla, but also develops a series of paired 
and unpaired subdivisions containing portions of the original cavity, 
distended to form ventricles. 
The primary divisions of the brain are more or 
less similar and homologous in all vertebrates. The 
more elaborate condition of the organ in a mammal 
may be explained by reference to the general plan 
as indicated in figure 39, which is based upon 
general features of form in vertebrates and upon 
embryonic development. For comparison in the 
gross the brain of the frog (Fig. 38) offers one of 
the best examples. 
The brain as first formed in the embryo appears 
as an anterior expanded portion of the neural tube, 
or rather as three expansions arranged in a linear 
series. They are described as the primary 
cerebral vesicles; or, as primary divisions of the 
future brain, they are designated in anteroposterior 
order as the prosencephalon, mesencephalon, 
and rhombencephalon. 
The first of the primary divisions, the prosencephalon, or 
primary fore-brain, gives rise during development to a pair of 
hollow outgrowths and thus becomes divisible into an anterior 
portion, the end-brain or telencephalon, which is largely a 
paired structure, and a second portion, unpaired, the diencephalon 
or inter-brain. The larger, paired portion of the telencephalon 
is the basis of the cerebral hemispheres. It contains, as divisions 
of the primary cavity, a pair of cavities, the lateral ventricles. 
Originally, the whole of the telencephalon was concerned with 
Fig. 38. The 
brain of the frog 
from the dorsal 
surface: c, cerebel- 
lum; d, dience- 
phalon; fv, fourth 
ventricle; h, cere- 
bral hemisphere; 
o, olfactory lobe; 
ol, optic lobe. 76 
Anatomy of the Rabbit 
olfactory functions, but it has been invaded by an increasing 
number of fibres from more posterior parts bearing non-olfactory 
nerve impulses. In the frog, a small part of it has already become 
free from olfactory connections and in the higher vertebrates the 
non-olfactory part becomes increasingly preponderant. In the 
mammalian brain, the olfactory portion, or rhinencephalon, is 
more or less perfectly marked off from the rest. This portion, 
sometimes termed olfactory lobe or olfactory brain, includes the 
Fig. 39. Plan of the divisions of the vertebrate brain: A, embryonic; 
B, adult, projection from dorsal surface; C, adult, sagittal section. The con- 
tour of the mammal an brain is indicated by broken lines. 
Primary divisio -PR, prosencephalon; T, telencephalon; DI, dience- 
phalon; MS, mesencephalon; RH, rhombencephalon; MT, metencephalon; 
MY, myelencephalon; S, spinal cord. 
a.c., cerebral aqueduct; b.o., olfactory bulb; c., corpora quadrigemina; 
c.a., anterior commissure; cb., cerebellum; c.m., mamillary body; c.o., optic 
chiasma; c.p., pineal body; f.i., interventricular foramen; h., hypophysis; 
h.c., cerebral hemisphere; in., infundibulum; l.t., lamina terminalis; p., pons; 
pl., chorioid plexus of third ventricle; p.c., cerebral peduncle; t., thalamus, 
also indicates position of massa intermedia; v.l., lateral ventricle; v.m.p., 
posterior medullary velum; v.q., fourth ventricle. The Nervous System 
77 
olfactory bulb and the pyriform lobe, already mentioned, with a 
number of related parts. 
The unpaired portion of the prosencephalon is considered as 
belonging in part to the telencephalon and in part to the dience- 
phalon. Its cavity, the third ventricle, is connected with each 
lateral ventricle through an interventricular foramen. Its 
anterior wall is formed by a transverse connection of the cerebral 
hemispheres, the lamina terminalis. In all vertebrates this 
portion of the brain is remarkable for the manner in which its wall 
is differentiated. The ventral portion extends downward as a 
slender funnel-like structure, the infundibulum, the tip of the 
latter being attached to the pituitary body or hypophysis and 
its base being connected with a small grey elevation, the tuber 
cinereum. Its cavity is the recessus infundibuli. Immediately 
in front of the infundibulum the optic tracts cross each other on 
the ventral surface of the brain, forming the optic chiasma, and 
immediately behind it the floor is thickened, forming externally a 
pair of rounded protuberances, the mamillary bodies. In the 
brain of the rabbit, the latter bodies are fused so that superficially 
they consist of a larger median portion with faint lateral elevations 
appended to it. Collectively, these ventral structures are con- 
sidered to form a major division of the fore-brain, the hypo- 
thalamus, the latter consisting of two portions, namely, an optic 
portion, comprising the optic chiasma and some adjacent tissue, 
and a mamillary portion, including the mamillary bodies, the tuber 
cinereum, the infundibulum, and the hypophysis. The optic 
portion belongs to the telencephalon and is better termed telence- 
phalon medium, while the mamillary portion belongs to the 
diencephalon. 
The more dorsal portion of the diencephalon, containing the 
major part of the third ventricle, is sometimes known as the 
thalamencephalon, a term now falling into disuse. Its lateral 
walls are greatly thickened, while its roof is extremely thin, espe- 
cially in its anterior part. Here the actual roof of the ventricle is 
formed of a layer of tissue only one cell in thickness, the epithelial 
chorioid lamina, but the latter has associated with it a series of 
vascular ingrowths of the investing pia mater, the latter being 
described in this relation as the chorioid web (tela chorioidea). 
The two structures together form a chorioid plexus. This extends 78 
Anatomy of the Rabbit 
downward into the third ventricle, reaching out also into the lateral 
ventricles. 
The dorsal portion of the diencephalon bears posteriorly the 
pineal body, an endocrine gland borne upon a stalk which is 
attached to certain other small dorsal parts of the brain, the 
habenulae and habenular commissure. These all together 
form the epithalamus. The lateral wall of the third ventricle 
is formed by the thalamus, which has become so massive in the 
mammal that it bulges medially to fuse with that of the other side 
and thus to produce a broad bridge across the middle of the ventricle, 
the massa intermedia. In the brain of the rabbit it will be seen 
that the thalamus is chiefly indicated externally by a rounded 
protuberance, the lateral thalamic tubercle. The latter is 
dorsal in position and is imperfectly marked off from a second 
protuberance, the lateral geniculate body, lying on its postero- 
lateral side. Postero-medial to this is a third protuberance, the 
medial geniculate body. The medial and lateral geniculate 
bodies as thus defined constitute the metathalamus (Fig. 86). 
The second of the primary divisions, the mesencephalon, or 
mid-brain, is noteworthy in a mammal as lacking a ventricle. 
Its cavity is a narrow canal, the cerebral aqueduct, leading from 
the third ventricle backward to the fourth ventricle, or cavity of the 
rhombencephalon. Externally, its roof is differentiated into four 
rounded elevations, the corpora quadrigemina, of which the 
anterior pair are much larger than the posterior ones and correspond 
with the optic lobes of the frog. Its floor is formed by the cerebral 
peduncles, the ventral surface of which is formed by a pair of 
cords converging from in front. 
The parts of the mesencephalon and prosencephalon together 
constitute the large brain, or cerebrum. 
The third primary division, the rhombencephalon, or primary 
hind-brain, is a greatly elaborated portion from which arise the 
majority of the cranial nerves. The constricted area joining it with 
the mesencephalon is known as the isthmus rhombencephali. 
It includes the anterior medullary velum and brachia con- 
junctiva (Fig. 89). The rhombencephalon itself is divisible into 
two portions, especially well defined in the mammalia, namely, the 
metencephalon and the myelencephalon. The former includes The Nervous System 
79 
the small brain, or cerebellum, and a ventral region, the pons, 
which is marked by a thick transverse band of fibres on the surface. 
The myelencephalon is a transitional portion connecting the brain 
with the spinal cord. The cavity of the rhombencephalon is the 
fourth ventricle. It is a peculiarly shaped space, the floor and 
lateral walls of which are very greatly thickened, while the roof is 
for the most part thin. The roof appears at first sight to be formed 
largely by the cerebellum, but is in reality formed by two mem- 
branes underlying the latter. One of these, the anterior medul- 
lary velum, is connected forwards with the mesencephalon, while 
the other, the posterior medullary velum, covers a triangular 
space over which the posterior margin of the cerebellum does not 
extend. The posterior medullary velum has the same structure 
as the chorioid plexus of the third ventricle, but is much more 
poorly developed. 
Apart from its principal divisions, which, as indicated above, 
are more or less common to all vertebrates, the brain depends for 
its external form on the elaboration of certain parts in comparison 
with others. In the mammalia the cerebral hemispheres and the 
cerebellum are the chief form-determinants, although the pons and 
the corpora quadrigemina may also be considered in this connection. 
It will be seen also that the form of the brain is more or less depen- 
dent on the existence at certain places of well-marked flexures 
(cf. Plate II). The first of these, the cephalic flexure, is in the 
region of the mesencephalon, the anterior portion of the brain being 
bent downward; the second, or pontine flexure, is at the fourth 
ventricle; while the third, or cervical flexure, is at the point where 
the myelencephalon passes over into the spinal cord. 
The peripheral nervous system embraces two groups of paired 
and, for the most part, metamerically arranged nerves, namely, the 
spinal nerves-those arising from the spinal cord and leaving the 
vertebral column through the intervertebral foramina-and the 
cranial or cerebral nerves-those arising from the brain and 
passing through the foramina of the skull. Of these the spinal 
nerves (p. 71) are less modified, in both structure and distribution. 
The cranial nerves, those arising from the brain and making 
their exit through the walls of the skull, are comparable in some Cerebrum 
Olfactory lobe 
(rhinencephalon) 
Corpus striatum, pallium, 
and minor divisions 
Corpora quadrigemina 
Cerebral peduncles 
Hypothalamus 
Thalamus 
Metathalamus 
Epithalamus 
PLAN OF THE DIVISIONS OF THE BRAIN 
(Encephalon) 
Cerebral hemisphere 
Telencephalon medium 
{Optic portion 
of hypothalamus) 
Mamillary portion 
of hypothalamus 
Thalamencephalon 
Cerebellum 
Pons 
Metencephalon 
Myelencephalon 
Medulla oblongata 
Telencephalon 
(End-brain) 
Diencephalon 
(Inter-brain) 
III, Rhombencephalon 
(Posterior cerebral vesicle) " 
(Primary hind-brain) 
I. Prosencephalon 
(Anterior cerebral vesicle) 
(Primary fore-brain) 
II. Mesencephalon 
(Middle cerebral vesicle) 
(Primary mid-brain) The Nervous System 
81 
respects to the spinal nerves, but in many ways are different in 
nature in addition to being in some cases highly 
specialized. Three pairs, respectively, olfactory, 
optic, and acoustic, or first, second, and eighth 
of the series are afferent nerves from the special 
sense organs of smell, sight, and hearing, the function of the acoustic 
nerve including also transmission of afferent impulses of equilibrium. 
The optic nerve differs from all others both structurally and 
developmentally, being really an outlying part of the brain itself. 
The third, fourth, and sixth nerves, respectively, oculomotor, 
trochlear, and abducent, are distributed as somatic motor nerves 
to the muscles of the eyeball, but also contain fibres of muscle sense. 
The Cranial 
Nerves 
Fig. 40. Branches of the left ophthalmic nerve in the region of the orbit, 
dorsal view, after Winckler: f, frontal nerve; 1, lacrimal nerve; mx, maxillary 
nerve; n, nasociliary nerve; o, orbital nerve. 
Of the remaining cranial nerves the fifth, seventh, ninth, and 
tenth are branchiomeric. Although the connections of these nerves 
are not fully considered in the dissection as here outlined, their 
chief characteristics as branchiomeric structures may be indicated. 
The fifth, or trigeminal nerve is the nerve of the mandibular 
arch. It arises in two parts, one of which, the portio major, is 
sensory, the other, the portio minor, motor. The portio major 
splits into three main branches, the ophthalmic (Fig. 40), maxillary, 
and mandibular nerves, and the portio minor unites with the last 
of these. Thus, while the terminal branches of all three divisions 
are distributed as somatic sensory nerves to the skin of the head, 
the mandibular nerve carries in addition visceral motor fibres for 
certain muscles (masticatory group, mylohyoid, and digastric) 82 
Anatomy of the Rabbit 
regarded as belonging to this, the first visceral arch. Visceral 
sensory fibres are carried from the anterior part of the mouth by 
the lingual branch of the mandibular nerve and by the palatine 
branches of the spheno-palatine ganglion, but both of these, despite 
Fig. 41. Dissection from the ventral surface of the neck. On the right 
side the platysma and depressor conchae posterior are reflected with the skin. 
The vagus nerve is in proper relation to the external jugular vein and the 
common carotid artery. On the left side the external jugular vein, parotid 
and submaxillary glands, and the sternohyoid, sternomastoid, and cleido- 
mastoid muscles are removed, the common carotid displaced medially and the 
nerves laterally, but otherwise in proper relation. 
be, basioclavicularis; cc, common carotid artery; cm, cleidomastoideus; 
c3, c4, c5, cervical spinal nerves; d, digastricus; fa, anterior facial vein; fp, 
posterior facial vein; ges, superior cervical ganglion; gn, ganglion nodosum; 
gp, parotid gland; gs, submaxillary gland; gt, thyreoid gland; lep, deep cervical 
lymph gland; m, masseter; my, mylohyoideus; pi, pterygoideus internus; 
pl, platysma; rev, cardiac branch of vagus nerve (n. depressor); rdh, descending 
branch of hypoglossal nerve; s, stylohyoideus major; sh, sternohyoideus; 
sm, sternomastoideus; st, sternothyreoideus; t, thyreohyoideus; ts, sym- 
pathetic trunk; vje, external jugular vein; vji, internal jugular vein; X, vagus 
nerve; XII, hypoglossal nerve. From dissection by W. H. T. Baillie, drawing 
by E. B. Logier. The Digestive System 
83 
their close peripheral association with the trigeminal, really belong 
to the seventh nerve, the connection of the former being through 
the chorda tympani, that of the latter through the great superficial 
petrosal. 
The seventh, or facial nerve is the nerve of the second, or 
hyoid arch. It is distributed chiefly as a motor nerve to the 
cutaneous muscles of the head, which are modified visceral muscles 
from the region of the hyoid arch, but contains also taste fibres 
from the front part of the tongue. The ninth, or glossopharyn- 
geal nerve, belonging to the third visceral (first branchial) arch, 
and the tenth, or vagus, belonging to the fourth and succeeding 
visceral arches in lower forms, are distributed as visceral efferent 
nerves to the pharyngeal and laryngeal musculature, and as visceral 
afferent nerves to various visceral organs, the ninth nerve supplying 
the gustatory organs of the back part of the tongue. The vagus 
contains a variety of fibres, both afferent and efferent, the former 
from the larynx and respiratory organs, the latter distributed to 
the organs of circulation and digestion. 
The eleventh, or spinal accessory nerve has apparently been 
formed by an association of certain motor components separated 
off from the vagus with others derived from the anterior spinal 
nerves. The spinal elements have a characteristic distribution to 
the cleidomastoid, sternomastoid, and trapezius muscles of the 
side of the neck and shoulder while the other components join the 
vagus and are distributed with it. 
The twelfth, or hypoglossal nerve has the relation of the 
ventral or motor portion of a spinal nerve, and is distributed as a 
motor nerve to the muscles of the tongue. 
The Digestive System 
The digestive system comprises as its chief portions the 
digestive tube or alimentary canal and the digestive glands. 
The digestive tube is divisible into several parts, which, with the 
exception of the caecum and its vermiform process, are arranged in 
a linear series. The digestive glands comprise the oral glands, 
the liver, and the pancreas. They are parts of an extensive series 
of epithelial glands, otherwise contained within the wall of the tube, 
and for this reason not appearing as gross structures. 84 
Anatomy of the Rabbit 
The parts of the digestive tube may be classified as follows: 
1. Oral Cavity 
Vestibulum oris 
Oral cavity proper 
2. Pharynx 
Nasal portion 
Oral portion 
Laryngeal portion 
3. Oesophagus 
4. Stomach 
5. Small Intestine 
Duodenum 
Mesenterial intestine 
Jejunum 
Ileum 
6. Large Intestine 
Caecum 
Vermiform process 
Colon 
Rectum 
The digestive system performs a variety of functions, both 
mechanical and chemical, all connected directly or indirectly with 
the digestion of food. In the oral cavity solid food is divided into 
small parts by the action of the teeth, and is mixed with salivary 
secretion, so that it is more easily swallowed and 
passed along the oesophagus to the stomach. The 
secretion of the oral glands is thus important 
chiefly for the lubricating properties of its mucous 
element, but that of the parotid especially contains an enzyme, 
ptyalin, which is capable of converting starch into soluble material. 
Food is further reduced to a pulp-like mass in the stomach, while 
the gastric secretion, containing pepsin and rennin, exercises a 
dissolving action upon protein, and a coagulating action upon 
milk. The liver secretion, known as bile, contains salts which co- 
operate with the pancreatic secretion in its action upon fats and 
which neutralize the acidity of the gastric secretion, thereby prepar- 
ing the contents of the intestine for the action of the pancreatic 
juice and intestinal enzymes. The pancreatic secretion contains a 
variety of enzymes, degrading proteins and starches, and breaking 
fats into fatty acids and glycerin. The actions of the dissolving 
enzymes are successive, secretion being dependent to some extent 
on antecedent bodies by which the stimulus for secretion is deter- 
mined. The preliminary processes of digestion refer in this way 
Digestion as 
a Process The Digestive System 
85 
to the mechanical action of food passage along the canal, and to 
the provision of converting enzymes. Absorption, which is the 
final object of the digestive process, is accomplished in the lower 
part of the small intestine and in the large intestine through the 
blood-vessels and lymphatics of the wall. The relatively great 
extent of the wall, including the enormous development of the 
caecum in the rabbit and other rodents, is related to the com- 
paratively great bulk and low nutritive quality of the ingested food. 
The caecum also provides room for retention of materials long 
enough for bacterial action upon cellulose, which is not otherwise 
digested, to make resulting products available for assimilation. 
Fig. 42. Plan of successive embryonic stages in displacement of the 
digestive tube and common mesentery from the mid-line position (man): 
a, tr, d, ascending, transverse, and descending colons; r, rectum; si, small 
intestine; st, stomach. Modified from figures by Toldt and Hertwig. 
The liver has a variety of other functions besides those men- 
tioned above. It stores nutritive material in the form of glycogen 
("animal starch'') and fat, and perhaps also protein. It removes 
various waste substances from the blood, eliminating some (bile 
pigments) in the bile and preparing others, the nitrogen-containing 
substances, to be returned to the circulation for final excretion by 
the kidneys. It is one of the minor situations where red blood 
corpuscles are developed. From it, as well as from various other 
tissues, is obtained a substance (heparin) which prevents clotting 
of the blood. In the liver also there is stored an antianaemic 
substance, formed by the action of a specialized digestive enzyme 
on food protein, which stimulates the production of red corpuscles 
in bone marrow. 86 
Anatomy of the Rabbit 
In its most general features the digestive system is significant 
as an epithelial tube, in which the food is modified, by solution or 
otherwise, so that it is capable of being absorbed through the 
epithelial surface. In the form of the digestive tube as seen in a 
vertebrate, however, a number of gross mechanical features are 
evident, such as, for example, the increase in capacity, or in absorp- 
tive area, through the folding of the mucous membrane, or the 
expansion of the wall; or again, the presence of a special muscular 
tunic, and its modification at certain places, as in the oesophagus, 
the pyloric limb of the stomach, and the first portion of the colon. 
Moreover, many features of the abdominal portion of the tube, 
and, indeed, certain of its recognized divisions, depend on its relation 
to an extensive serous sac-in a mammal the peritoneal 
cavity. In this connection it is to be considered that 
the digestive tube is primarily a median structure. It 
has this relation in the earlier stages of embryonic 
development (Figs. 20, 42), and in many of the lower vertebrates 
it does not deviate to a great extent from a median position. In 
all higher vertebrates, however, the tube becomes greatly elongated 
in comparison with the cavity in which it lies, and thus becomes 
extensively displaced to one side or other of the median plane. 
This development, while advanced in all mammals, may be said 
to reach an extreme in the herbivorous mammalia; and in many 
cases it is further increased by the independent elaboration of the 
blind intestine or caecum. In the rabbit the combined length of 
the small and large intestines is approximately eleven times that 
of the body. 
In considering the divisions of the digestive tube in the rabbit, 
the posterior, or post-cephalic portion, comprising the oesophagus 
and succeeding parts, may be distinguished from the anterior, or 
cephalic portion, the latter comprising the oral cavity and pharynx. 
The former is a free portion embracing the digestive tube proper, 
while the latter is a fixed portion exhibiting a variety of general 
mammalian features connected with the organization of the head. 
The form of the anterior, or cephalic portion of the digestive 
tube (Plate II) depends on its fixed relation with respect to the 
enclosing parts of the head-skeleton. In the rabbit, as in mam- 
mals generally, the oral cavity is divisible into two portions, of 
Form and 
Symmetry The Digestive System 
87 
which one is the oral cavity proper, while the other, the vestibu- 
lum oris, is a space enclosed between the alveolar process of the 
jaws and the teeth on the one hand, and the cheeks and lips on the 
other. As in other vertebrates, the tongue is a muscular 
structure projecting upward and forward into the oral 
cavity from its base of attachment on the hyoid ap- 
paratus, but its greater elaboration and the differen- 
tiation of special processes, the circumvallate and foliate papillae, 
for the accommodation of the gustatory organs, are features char- 
acteristic of mammals. The 
roof of the oral cavity is 
formed by an extensive pala- 
tal surface, comprising the 
hard palate, and the 
membranous, or soft 
palate. These structures 
also form the floor of the 
accessory respiratory tracts 
of the nose, the posterior 
aperture being thus carried 
backward to a point almost 
directly above the aperture of 
the larynx. 
The chief features of the 
pharynx depend on the fact 
that it is not merely a simple portion of the digestive tube but is also 
related structurally and functionally with the tubes of the respira- 
tory system. It is divisible into an oral portion, representing the 
direct connection of the oral cavity with the oesophagus, a dorsal 
or nasal portion, connected with the nasal fossae, and also with 
the middle ear through the internal auditory tube, and a ventral 
or laryngeal portion, containing the aperture of the larynx 
(Fig. 43). 
The oesophagus is a slender but greatly expansible tube leading 
from the pharynx to the stomach. In its passage backward it 
traverses the neck and the thorax, and in both regions occupies a 
median position. In the thorax (Plate VII) it will be observed 
to lie between the heart and the dorsal aorta, thus exhibiting the 
Principal 
Divisions 
Fig. 43. The nasopharynx and related parts 
of the head as seen in median section (anterior 
end to the left): 1, tongue; 2, hyoid; 3, tonsil; 
4, epiglottis; 5, entrance to trachea; 6, entrance 
to oesophagus; 7, basioccipital bone; 8. soft 
palate; 9, pharyngeal aperture of auditory 
(Eustachian) tube; 10, cranial cavity; 11, 
ethmoturbinal scrolls; 12, nasal cavity; 13, nasal 
septum; 14, hard palate; 15, oral cavity. 88 
Anatomy of the Rabbit 
original relation of the digestive tube to the aortic portion of the 
vascular system. The function of the oesophagus is that of a 
simple conveyer to the stomach. The succeeding portions of the 
digestive tube are those associated with the peritoneal cavity, and 
Fig. 44. Developmental stages in the coiling of the intestine. Redrawn 
with modifications after Zietzschmann. A. Primary intestinal loop. B. The 
loop twisted through 180°. C. The loop twisted through 360°, intestine 
differentiated as in rabbit, ac, ascending colon; c, caecum; d, duodenum; 
de, descending colon; i, ileum; j, jejunum; 1, liver; s, stomach; tc, transverse 
colon. 
with the exception of the terminal portion, the rectum, are dis- 
placed from a median position. Consequently, the divisions which 
are recognized are based partly on the differential characters of the 
wall and partly on the position of structures, more especially in The Digestive System 
89 
relation to the supporting peritoneum. Thus, the chief features 
of the stomach depend on the expansion of the organ and the 
rotation of its pyloric end forward and to the right. In the intestinal 
tract as a whole the chief, although by no means most conspicuous 
feature of position depends on the looping of the entire structure 
on itself, so that the terminal portion, chiefly the transverse colon, 
crosses the ventral surface of the duodenum and then turns back- 
ward as the descending colon on the dorsal surface of the mesenterial 
small intestine (Fig. 42). In .the development of this twisted 
arrangement and its many variants in different mammals the 
superior mesenteric artery has acted more or less as an axis of 
rotation (Fig. 44). The duodenum is marked off from the 
mesenterial intestine as an extensive loop, containing the major 
part of the pancreas and its duct, and lying on the right side of the 
dorsal wall of the abdomen. The common bile duct enters its 
first portion immediately beyond the pylorus, so that in it materials 
received from the stomach are mixed successively with bile and 
with pancreatic juice. The mesenterial intestine is a greatly 
convoluted portion, lying chiefly on the left side of the abdominal 
cavity, and loosely supported by the broad, frill-like mesentery. 
Here the digestive processes are advanced greatly and a good deal 
of absorption takes place. From the pylorus to the sacculus 
rotundus there is no abrupt change in the character of the wall, 
although the first portion of the mesenterial intestine, that desig- 
nated as the jejunum, and the duodenum may be considered 
together as a more vascular portion with thicker walls in com- 
parison with the second portion, the ileum, in which the wall is 
less vascular and more transparent. 
The main portion of the large intestine, the colon, although 
greatly specialized, may be considered to consist, as in man, of 
ascending, transverse, and descending parts, that is to say, the 
ascending colon lies on the right side of the body and passes in a 
general way from its point of origin on the caecum forward to a 
point where it becomes flexed to the left as the transverse colon; 
the latter crosses the body and is flexed backward as the descend- 
ing colon. In the rabbit, however, that portion definable as the 
ascending colon is greatly elongated, and is composed of five 
principal limbs, united by flexures. The last two of these are 90 
Anatomy of the Rabbit 
concealed in dissection from the ventral surface by the base of the 
superior mesenteric artery, since they lie on its right side. The 
descending colon is also only nominally related to the left side of 
the body-wall in the rabbit, its supporting peritoneum, the descend- 
ing mesocolon, being fused with that of the ascending limb of the 
duodenal loop so that it is restored to an approximately median 
position. The caecum, like the colon, is much enlarged and 
particularly elongated, its course as it lies in the body being com- 
Fig. 45. The caecum and vermiform process: c', c", c'", first, second, 
and third limbs of the caecum; ca, beginning of the ascending colon; il, ileum; 
pv, vermiform process (appendix); sr, sacculus rotundus. 
parable to two turns of a left-hand spiral (Fig. 45). Its blind ter- 
minal portion, the thick-walled vermiform process, is also relatively 
large and its internal surface area is further increased by the 
presence of a long spiral fold or spiral valve (Fig. 46) comparable 
with that present in the intestines of sharks and skates. It may 
be observed at this point that in their vascular supply the more 
typical divisions, namely, the transverse and descending colons, The Respiratory System 
91 
have arterial branches, respectively, the middle and left colic 
arteries, comparable to those of man; while on the other hand the 
right colic relation, on account of the great complexity of its parts, 
is represented by a large number of vessels, branches of a common 
ileocaecocolic trunk. 
Fig. 46. The caecum with its ventral wall removed to show the lumen 
and the contained spiral valve: a, ileocaecal aperture. 
The Respiratory System 
In all air-breathing vertebrates the lungs (Fig. 47) are paired 
sacs which arise embryonically as ventral outgrowths of the digestive 
tube, and are secondarily connected with the outside of the body 
through special perforations of the anterior portion of the head 
and through the oral cavity. The principal connection in a 
mammal is represented by an extensive nasal cavity bearing on its 
lateral walls the olfactory sense-organs. It is distinguished as an 
accessory respiratory tract from the true respiratory tract 
formed by the trachea and its terminal divisions, the bronchi. 
The respiratory system, as represented by the lungs and related 
tubes, is nominally ventral to the oesophagus, but this relation 92 
Anatomy of the Rabbit 
is chiefly true of the trachea. In the thorax (Plate VII) the 
bronchi are, in general, interposed between the oesophagus and 
the heart, the lungs being expanded laterally into the paired 
pleural cavities. 
In addition to the carrying of air over the sensory, olfactory 
surfaces, other accessory functions more closely related to respira- 
Fig. 47. The heart and lungs from the ventral surface: ad, right atrium; 
ao, aorta; ap, pulmonary artery; as, left atrium; d, right superior caval vein; 
i', i", left and right inferior lobes of lung; 1, aortic ligament; m', m", middle 
lobes; ml, medial lobule of right inferior lobe; s, left superior caval vein; 
s', s", superior lobes; tr, trachea; vd, right ventricle; vi, inferior caval vein; 
vp, pulmonary veins; vs, left ventricle. 
tion are the warming of the air and removal therefrom of particles 
of foreign material, both of which are performed by the mucous 
membrane of the nose, including that of the turbinated surfaces. 
The sole functions of the true respiratory tract and lungs are 
respiratory. 
In a mammal, respiration is both a physicochemical and a 
mechanical process. The former is fundamental, and consists in The Respiratory System 
93 
the supply of oxygen to the blood, and in this way to the tissues, 
for the oxidative phases of metabolism; also in the discharge of 
waste gases, principally carbon dioxide, from the 
blood to the air. The absorption and transport 
of oxygen is a specific function of the red blood 
cells. Though the oxygen, of which a certain 
amount always remains in the lungs during the process of breathing, 
must pass through the thin epithelial covering of the terminal air 
sacs into the capillaries before it can be taken into the blood cells, 
the latter from their flattened shape and very great numbers 
present a relatively enormous surface for absorption, the process 
being thereby facilitated. The lungs themselves are highly elastic, 
expansible sacs. They have the structure of greatly ramified 
saccular glands, except that the free internal surfaces are every- 
where in contact with air. The division of the trachea into its 
bronchi, together with the bronchial ramifications, forms the trunk 
and main branch portions of a rather complex system of tubes 
(Fig. 48), of which the terminal air-spaces are the final and func- 
tional parts. 
What is commonly described as respiration, or the act of 
breathing, is a mechanical, muscular process accessory to the 
fundamental exchange which really constitutes respiration. It 
consists in the expansion of the thorax, so that a partial vacuum 
is created and the lungs fill with air, the expansion being followed 
by relaxation, in which the air is expelled. The first 
portion of this action, known as inspiration, is 
brought about by the contraction of the intercostal 
and related muscles, by which the ribs are raised, and by the 
contraction of the dome-shaped diaphragm, by which the posterior 
wall of the thorax is flattened, and incidentally the abdominal 
viscera are displaced backward. Both actions tend to enlarge the 
thoracic space, in consequence of which air passes in from the 
pharynx and distends the lungs. The action of the diaphragm is 
controlled directly by the phrenic nerves, but all respiratory 
movements are dependent upon the cervical and thoracic spinal 
nerves. The excitation of these nerves is regulated through a 
respiratory centre in the medulla oblongata which is stimulated 
both by afferent fibres in the vagus nerve and by carbon dioxide in 
the blood. 
Respiration as 
a Process 
Breathing 94 
Anatomy of the Rabbit 
The expulsion of air, or expiration, is accomplished by relaxation 
of the muscles mentioned above, assisted by contraction of the 
transverse thoracic muscles (p. 274) and the muscles of the ventral 
abdominal wall. 
Respiration as a general func- 
tion is common to all organisms. 
Though always con- 
structed for easy 
diffusion, theorgans 
by which the func- 
tion is discharged differ pro- 
foundly in the various groups. 
This is true even within the limits 
of the vertebrates, where lower 
forms are characterized by gills 
for aquatic respiration, and the 
higher forms by lungs for air 
respiration. The occurrence of a 
great variety of intermediate and 
transitional growth stages, in 
which gills are replaced by lungs, with no modification from one to the 
other, introduces a peculiar condition into the history of verte- 
brates. This condition is characterized by the appearance of gill 
structures in the embryos of all higher forms (Fig. 19), by the 
somewhat later development of air sacs in addition to these, and 
by the gradual elaboration of the latter in the vertebrate series 
from a simple type, as illustrated in the frog or better in lower- 
tailed amphibians, to the greatly branched lung tubes of mammals 
and the highly complex and special arrangements in birds. 
The Blood-Vascular System 
In the rabbit, as in all vertebrates, the blood-vascular system 
(Fig. 49) embraces a central, muscular organ of propulsion, the 
heart, and a series of branched tubes, the blood- 
vessels, the latter being of three different kinds: 
(a) thick-walled, elastic, distributing vessels- 
arteries; (6) microscopic terminal canals in the 
peripheral organs-capillaries; and (c) thin-walled collecting 
vessels-veins. 
Lungs and 
Gills 
Fig. 48. The larger terminal rami- 
fications of the left inferior bronchial 
ramus, from the dorsal surface; metallic 
cast of the interior. Cf. Figs. 47 and 
86, i. 
Plan of the 
Circulation The Blood-Vascular System 
95 
The chief mammalian feature in this system consists in the 
division of the heart into two portions, 
each consisting of a receiving chamber, or 
atrium, and a driving chamber, or 
ventricle, and the arrangement of their 
vascular connections in such a way that 
two complete circulations are established. 
One of these is the long, or systemic 
circulation. It is concerned with the 
distribution of blood to the various parts 
of the body, with the exception of the lungs. 
It is established by the left ventricle, the 
aorta, the carotid and subclavian branches 
of its arch, and the parietal and visceral 
branches of its thoracic and abdominal 
portions. The blood is collected from the 
anterior portions of the body through 
paired internal and external jugular and 
subclavian veins, communicating with the 
right atrium of the heart through paired 
superior cavals; from the posterior portions 
of the body through the unpaired and asymmetrical inferior caval 
vein, the latter passing forward on the right of the median plane 
and entering the posterior end of the right atrium. The second, 
short, or pulmonary circulation, is concerned with the distribu- 
tion of the blood to the lungs for purposes of aeration. It is 
established by the right ventricle, the pulmonary artery and its 
paired branches, and the capillaries of the lungs. The blood is 
delivered to the left atrium through several pulmonary veins. 
A similar division of the circulatory organs occurs as a homoplastic 
modification in birds, which, it will be observed, are also warm- 
blooded vertebrates. 
In general, the blood which is distributed to the various parts 
of the body passes through but one set of capillary vessels, and is 
then returned through the systemic veins to the heart. In all 
vertebrates, however, a special portion of the systemic venous 
circulation is set aside as the hepatic portal system distinguished 
by the possession of a second series of capillary vessels rami- 
fying in the liver. Thus, in the rabbit, the blood distrib- 
Fig. 49. The mammalian 
circulation: rv, Iv, right and 
left ventricles; ra, la, right 
and left atria; sc, sp, semi- 
lunar valves of aorta and 
pulmonary artery; vt, vm, 
right and left atrioventricular 
valves. 96 
Anatomy of the Rabbit 
uted to the stomach, spleen, and intestine through the coeliac 
and the superior and inferior mesenteric arteries, is collected into a 
main intestinal vessel, the portal vein, and the latter passes to the 
liver and divides in that organ into a series of portal capillaries. 
The liver receives also oxygenated blood, though in much smaller 
quantity, through the hepatic artery, and both the systemic 
capillaries proceeding from this and the portal capillaries unite in 
the tributaries of the hepatic veins. In lower vertebrates and in 
the embryos of the higher forms, where the kidney is a mesonephros 
(p. 103), a second system of venous capillaries occurs in that organ 
and is known as the renal portal system. 
The ultimate function of the vascular system is connected with 
interchange of materials in the tissues. This is brought about 
through the medium of microscopic capillaries, the gross parts 
of the system being concerned with transportation of materials 
from one part of the body to another. The 
propulsive action of the heart is muscular 
and rhythmic, contraction, or systolic 
phases, alternating with expansion, or 
diastolic phases (c/. p. 65). The flow is maintained in one 
direction principally by the atrioventricular valves of the heart and 
by the semilunar valves of the aorta and pulmonary arteries, though 
there are also valves in the course of some of the veins. The arteries 
are tubes with thickened elastic walls. They are expanded by the 
impulse of blood from the heart, contraction of which is followed 
by a pulse wave in the arteries. The passage of blood into the 
capillaries takes place more slowly and uniformly, while the arteries 
contract to their previous diameter. In the return of the blood 
the veins are largely passive, acting merely as closed channels 
connecting the capillaries with the heart. The control of the 
muscular action of the heart and arteries through the vagus and 
sympathetic nerves is an important element in maintaining tone 
in the walls of the vessels and thereby the pressure of the blood 
(cf. p. 64). 
Many of the peculiar features of the mammalian circulation 
which at first sight do not appear to be general, but are so in reality, 
depend on the circumstance that the complete partition of the 
organs is a final stage of a general progressive development, observ- 
Functions of 
Circulatory System The Blood-Vascular System 
97 
able in air-breathing vertebrates, in which the lungs and their 
vascular connections become per- 
fected for pulmonary respiration. 
On the other hand, the vascular 
system as it appears in the embryo, 
more especially its aortic portion, 
is arranged according to the type 
of branchial respiration as found 
in fishes. In this condition the blood 
is sent forward from the heart through 
a ventral aorta. The latter is con- 
nected with a series of paired bran- 
chial aortic arches, traversing the 
rudimentary gill 
structures, and thus 
passing upward 
around the sides of 
the primitive pharynx. The dorsal 
aorta is formed by the junction of the 
branchial aortic arches, and passes 
backward as a main distributing 
vessel on the ventral side of the axial 
support. The heart itself is formed primarily on a two-chambered 
plan, similar to that in fishes, where all the blood is received by 
a single atrium and is delivered forward to the gills by a single 
ventricle. 
The definitive condition of the chief arterial vessels is arrived 
at by an extensive modification of the branchial plan. As indicated 
in the accompanying diagram (Fig. 50), the arch condition is 
retained by the aorta and by the pulmonary artery. It is interest- 
ing to note also that the primary connection of these vessels is repre- 
sented in the foetus by an open canal, the ductus arteriosus (Botalli), 
which closes shortly after birth but is indicated in the adult by 
a short fibrous cord between the left pulmonary artery and the 
aorta, the arterial ligament (Fig. 47, 1). The adult aortic arch 
represents only the left one of a pair (the fourth) while that of the 
right side is represented only imperfectly by the base of the right 
subclavian artery (the innominate artery and the common carotids 
Primitive 
Aortic Arches 
Fig. 50. Plan of the branchial 
aortic arches. The adult mammalian 
vessels are indicated in black (sys- 
temic) or shaded (pulmonary): 1-6, 
primary arches; ao., aorta; a.p., 
pulmonary artery; c.e., external 
carotid; c.i., internal carotid; d.a., 
ductus arteriosus (Botalli); i., in- 
nominate artery; s.d., right sub- 
clavian; s.s., left subclavian. (From 
Weber, after Boas.) 98 
Anatomy of the Rabbit 
being derived from parts of the ventral aorta, as is apparent in 
figure 50). Hence a condition of asymmetry results, which is 
expressed mainly in the sinistral position of the aortic arch with 
reference to the oesophagus (Plate VII). By comparison with the 
embryonic plan, it is seen that the primitive features of the heart 
and the arterial vessels include the ventral position of the heart 
itself, the equivalence of the two atria and of the two ventricles- 
these structures being partitioned internally but imperfectly 
divided externally-the forward position of the first portion of the 
aorta, and the position of the aorta as a median vertebral trunk. 
The vascular system is noteworthy for several departures from 
the condition of symmetry, one of which has already been men- 
tioned. In addition, it is seen that in a mammal, as in terrestrial 
vertebrates generally, the base of the pulmonary artery (Fig. 47) 
is rotated in a spiral fashion about the base of the aorta, so that 
from its beginning on the right ventricle it passes across the ventral 
surface of the base of the aorta, and divides on the dorsal side 
of the latter into its two main branches. Moreover, the separation 
of the ventricular portion of the heart into two chambers is as- 
sociated with an enormous increase in the muscularity of the wall 
in the left ventricle, or, in other words, in that portion which is 
concerned with the larger, systemic circulation. The inferior caval 
vein (Plate VIII), a highly specialized vessel, is asymmetrical, 
since from its beginning in the pelvic cavity to its termination on 
the right atrium it lies wholly to the right of the median plane. 
The azygos vein of the thorax (Plate VII), a vessel uniting the 
majority of the paired intercostal veins, and interesting as a remnant 
of the primitive circulation, is also asymmetrical, since the trunk 
lies to the right of the bodies of the vertebrae, and is connected at 
its base with the right superior caval vein. 
The Lymphatic System 
The lymphatic system, both in its functional relation and in 
origin, is an appendage of the venous portion of the vascular system. 
The system is an important one, of which, unfortunately, little 
may be seen by ordinary dissection, the structures which are re- 
vealed in this way being mainly the lymph glands, or lymph nodes. 
These, when they occur as superficial structures, are found either 
singly, as in the head and neck, or more or less grouped, as in the The Lymphatic System 
99 
axillary and inguinal spaces. As deep structures they are con- 
spicuous in the intestinal mesenteries, and in the walls of the 
digestive tube, occurring in the latter chiefly as continuous masses 
of lymph follicles, as, for example, in the walls of the sacculus 
rotundus, the vermiform process, or the tonsil; or, again, as ag- 
gregated lymph follicles (Peyer's patches) at various points in 
the wall of the small intestine. 
The conducting portion of the system comprises an extensive 
series of canals, beginning as lymphatic capillaries in peripheral 
organs, and ending as lymphatic trunks which empty into the great 
veins. The lymphatic trunks of the anterior portion of the body are 
designated from their association with the corresponding veins as 
jugular and subclavian. They enter the venous system on either 
side at the point of junction of the internal and external jugular 
veins or of the common jugular and subclavian (Fig. 82). 
The lymphatic vessels of the posterior portion of the body, in- 
cluding the intestine, unite to form a common canal, the thoracic 
duct. The latter lies for the most part between the aorta and the 
vertebral column, and traverses the thorax in this position to enter 
the venous system at the same point as the jugular and subclavian 
trunks of the left side. All these trunks are so thin-walled that 
it is not usually possible to see them in ordinary dissection. 
The lymphatic capillaries are terminal vessels, differing from 
blood capillaries both in the character of their walls and in their 
relations to other portions of the system, since they are not inter- 
posed, as in the blood-vascular system, between vessels of a larger 
order. The lymphatic vessels connecting the capillaries with the 
lymphatic trunks form extensive plexuses, in connection with which 
the lymph nodes are distributed. 
The lymph or fluid present in lymph vessels, in the spaces of 
lymph nodes, and elsewhere in the tissues of the body is comparable 
to the fluid part or plasma of the blood. While blood is a carrier 
for both in-going and out-going materials of metabolism, on account 
of being confined to the capillaries it is not brought into direct 
contact with the tissue-cells of the body. The cells are, however, 
bathed in lymph, which can permeate the tissues by diffusion, and 
lymph contains cells of a type that can migrate through the walls 
of vessels. The lymph is thus a general medium of transmission 100 
Anatomy of the Rabbit 
with special cell functions. The fat-carrying function of the 
intestinal lymphatics, in which the delivery of food materials 
directly to the blood is the principal consideration, is doubtless a 
very special phase of the transfer mechanism. 
The cell contents of lymph vessels and spaces are amoeboid 
cells or leucocytes (of. p. 37). Leucocytes of several kinds are 
found in various situations in the body. Since they 
are wandering cells, their situation at any one time 
reveals little of their points of origin. They are 
formed originally in lymph nodes, in the spleen, in 
the bone marrow, in endothelial linings, and by local proliferation 
of connective tissue cells. They serve a variety of purposes of 
which the phagocytic action, chiefly 
ingestion and destruction of 
bacteria, and disintegration of ery- 
throcytes and other cell debris, is 
one of the chief. 
Lymph nodes are centres for 
the proliferation of certain types 
of leucocytes. They are also 
concentration points for such cells 
and local centres of phagocytic 
action. They appear to be situated 
strategically with reference to parts 
of the body served. In local 
infection, the activity of leuco- 
cytes of various kinds at the point 
of injury can be correlated with 
that of leucocytes in the nearest 
lymph nodes and the general 
relation can be observed in the appearance and behaviour of 
the two regions themselves. The spleen is a lymphatic organ, 
the largest in the body, with functions comparable to those of 
lymph nodes. It contains large vessels which act as reservoirs 
for blood and it also stores iron. 
The Urinogenital System 
The urinogenital system comprises two primary systems- 
reproductive and urinary-differing widely in their central organs, 
Lymphatic 
Functions 
Fig. 51. Homologies of male (A) and 
female (B) urinogenital systems: b, 
urinary bladder; cc, crura clitoridis; cp, 
crura penis; dd, ductus deferens; ep, 
epididymis; k, kidney; ov, ovary; r, 
rectum; t, testis; tu, uterine tube; u, 
urethra; ut, uterus; ur, ureter; va, 
vagina; vs, seminal vesicle; vs', vesti- 
bulum, urethra. The Urinogenital System 
101 
but associated to a certain extent by having common ducts. In 
the rabbit, as indicated in the accompanying diagram (Fig. 51), 
this association extends only to the presence in the two sexes of a 
urinogenital canal, or urinogenital sinus connecting both urinary 
and genital structures with the outside of the body. This canal is 
designated in the male as the urethra, but in the female as the 
Fig. 52. The principal stages in specialization of the female urinogenital 
ducts in vertebrates. A, frog; B, monotreme; C, marsupial, bl, bladder; 
cl, cloaca; k, kidney; od, oviduct; ov, ovary; r, rectum; u, ureter; us, urinogeni- 
tal sinus (vestibulum); ut, uterine tube; v, vagina. Chiefly from figures of 
Gegenbaur and Wiedersheim. 
vestibulum, since the structure known from the human relation 
as the female urethra is only a urinary canal leading from the 
bladder, and in man is not directly connected with the reproductive 
ducts. 
In primitive vertebrates (Fig. 52), the urinary and genital ducts 
open into the posterior end of the digestive tube, the latter forming 
in this relation a common canal, the 
cloaca. In terrestrial vertebrates, the 
urinary bladder is developed as a ventral 
outgrowth of the digestive tube, and, 
except in amphibians, both sets of ducts undergo a migration from 
their original position on to the wall of its canal, the latter being 
thus transformed into a urinogenital sinus. This development 
reaches its extreme in the placental mammals, where the urinogenital 
sinus is completely separated from the digestive tube, and where 
the urinary ducts are also transferred from a posterior or hypocystic 
position on the wall of the urinogenital sinus to an anterior or 
epicystic position on the dorsal wall of the bladder. 
Urinogenital Ducts 
in Vertebrates 102 
Anatomy of the Rabbit 
The chief organs of the urinary system are the kidneys. They 
are paired organs, lying against the dorsal abdominal wall, approxi- 
mately in the position of the embryonic inter- 
mediate cell mass (Fig. 20, n.) from which they are 
formed. During development, the left kidney is 
displaced backward, out of the position of symmetry, by the 
posterior expansion of the greater curva- 
ture of the stomach. The kidneys 
appear as solid organs, brownish in 
colour and bean-like in general shape, 
enclosed by a fibrous coat, and connected 
medially with the expanded end of the 
ureter. In the rabbit the kidney appears 
as an almost continuous mass, in which, 
however, slight traces of lobulation 
can be distinguished. In many mam- 
mals, such as sheep and bear, the organ 
is composed of distinct and separable 
lobules. This condition is clearly shown 
in the human kidney during foetal life, 
and though the organ is much more 
concentrated in the adult, the lobulated condition there appears 
internally in the division of the ureter into several 
renal calyces, each of them connected with a cor- 
responding renal papilla. 
When horizontally divided (Fig. 53), the kidney is 
seen to be made up of a more vascular and granular external layer, 
termed the cortex, and of a somewhat radially striated, central 
mass, termed the medulla. In the rabbit, there is a single renal 
papilla, and the expanded end or pelvis of the ureter is undivided. 
Notwithstanding the solid appearance of cortex and medulla, the 
kidney is made up of a system of tubules, the relation of which 
to the vascular system is such that water and certain soluble 
substances to be excreted are passed into them from the blood 
stream. The primary tubule (Fig. 54, A) begins in each case in 
the cortical substance with a cup-like structure, known as a renal 
or Malpighian corpuscle. This consists of a double capsule con- 
taining a glomerulus or knot of capillaries from the renal artery. 
The Kidneys 
Fig. 53. The left kidney, 
divided horizontally lengthwise, 
cut surface of dorsal half: c, 
cortical substance; m, medullary 
substance; p, renal papilla; u, 
ureter. 
Form in 
Mammals The Urinogenital System 
103 
The cavity between the two layers of the capsule, represented 
in solid black in figure 54, is continuous 
with that of the tubule. The blood in 
the glomerulus is separated from this cavity 
only by a very thin membrane composed of 
the lining of the capillary and that of the tubule, both of which linings 
are uninterrupted, and through this mem- 
brane fluid passes into the tubule. The 
succeeding parts of the tube system have 
a characteristic course in the kidney sub- 
stance, which accounts for the difference in 
appearance between the cortex and me- 
dulla, and are ultimately connected with 
common collecting tubules opening on 
the surface of the papilla. Blood capillaries 
again come into contact with each tubule 
at certain points in its course, where further 
excretion and selective reabsorption occur. 
The excreted fluid, urine, contains char- 
acteristic nitrogenous waste materials, usu- 
ally urea, but in some cases uric acid or 
hippuric acid. These are formed in the liver 
and perhaps elsewhere in the body. 
Like all other parts of the urinogenital 
system, the mammalian kidney affords in its 
structure and embryonic development a re- 
markable illustration of the extent to which 
the adult form and relations of an organ 
may depend upon ancestry, and of the greatness of the changes 
which may occur before these adult condi- 
tions are attained. In the vertebrate 
subphylum, three successive pairs of 
kidneys have been recognized. They 
occur in antero-posterior order in the body, they are of increasing 
specialization, and their order of appearance and functional value 
are directly associated with the degree of general specialization 
of the groups in which they occur. These organs have been 
designated as pronephros, mesonephros, and metanephros. 
Internal Structure 
and Function 
Fig. 54. Kidney tubules. 
A, plan of arrangement in 
adult mammal: c, cortex; m, 
medulla; gl, vascular glome- 
rulus; tc, proximal convoluted 
portion of tubule; tr, proxi- 
mal straight portion of tubule 
(Henle's loop); tp, collecting 
tubule to renal papilla. From 
Weber, after v. Ebner. B, 
plan of a single primitive 
kidney tubule in lower verte- 
brates: gl, glomerulus; np, 
nephrostome; cl, coelomic 
epithelium; t, body of tubule; 
d, longitudinal duct. 
Homologies of 
Vertebrate Kidneys 104 
Anatomy of the Rabbit 
The metanephros is the adult kidney in mammals, while the other 
two are embryonic in that class. The mesonephros is, however, 
the adult kidney in fishes and amphibians, where its duct serves 
in the male as both reproductive duct and ureter. The presence 
of this kidney and of its duct in embryonic mammals determines 
the form of the ductus deferens and its connections with the 
terminal portions of the urinary system. The pronephros, on the 
other hand, is in all vertebrates a vestigial kidney present only in 
embryos. Its duct system, however, which opens proximally to 
Fig. 55. The male urinogenital ducts and related structures, viewed from 
the lateral surface. After Rauther: a, anal aperture; bu, bulbourethral gland; 
cc, proximal end of corpus cavernosum; dd, ductus deferens; ga, anal (rectal) 
gland; gi, inguinal gland; g, glans penis: par, paraprostatic glands; pr, 
prostate; r, rectum; ur, ureter; uv, urethra (membranous portion); vs, seminal 
vesicle; vu, urinary bladder. 
the body cavity, plays an important part in the formation of the 
oviduct in the female of all classes. The tubules of the pronephros 
and often those of the mesonephros connect with the coelome by 
ciliated openings, the nephrostomes, which do not occur in more 
specialized kidneys. Thus the development and structure of the 
pronephros and, in a less perfect way, those of the mesonephros 
show that the primary connections of the kidney tubules are with 
the coelomic cavity (Fig. 54, B). 
In the rabbit, as in all mammals, the male gonad or testis 
(Fig. 58), in which the male germ cells, spermatozoa, are matured, The Urinogenital System 
105 
is connected with the peripheral duct system (Fig. 55) by means 
of the epididymis and the ductus deferens, which are parts 
of the mesonephric connections of the embryo. While the ductus 
deferens is a single tube, the epididymis consists 
of an aggregation of small tubules, lying chiefly 
toward the anterior end of the testis, but with 
the tubules not individually discernible. In the 
embryo of every vertebrate, the testis is formed in association 
with the dorsal abdominal 
wall, but in many mammals 
it moves backward to a 
scrotal position, either perio- 
dically, or permanently in 
the course of development. 
This change, known as the 
descent of the testis, is 
brought about through the 
agency of a muscular cord, 
the gubernaculum, the con- 
nections of which in the 
rabbit, are retained in the 
adult condition. The migra- 
tion of the organ determines 
a number of peculiarities in 
the relations of its blood- 
vessels and peritoneal con- 
nections. 
The female gonad or 
ovary (Fig. 56) lies on the 
dorsal wall of the abdominal 
cavity, thus retaining to a 
large extent the primitive 
position. It has, however, 
gubernacular connections corresponding with those of the testis and 
these are plainly discernible in the adult animal as the ovarian 
and round ligaments, of which the latter is inserted into a small 
pocket of the abdominal wall simulating the testis sac. 
The Testis and 
its Duct 
Fig. 56. The female urinogenital system: 
a, aorta; as. internal spermatic artery; an, 
umbilical artery; c, clitoris; gp, inguinal gland; 
gr, rectal gland; h, hydatid of uterine tube; hr, 
middle haemorrhoidal artery; i, inferior caval 
vein; lo, ovarian ligament; It, round ligament; 
lu, umbilical ligament; ms, mesosalpinx; mt, 
mesometrium; o, ovary; ot, ostium tubae; r, 
rectum; rp, peritoneal recess (rudimentary 
vaginal process); tu, uterine tube; u, ureter; 
ut, uterus; vg, vagina; vs, vestibulum; vu, 
urinary bladder. 106 
Anatomy of the Rabbit 
Though inconspicuous in gross size as compared with the testis, 
the ovary is concerned with the formation of cells of relatively large 
dimensions, the female germ cells or ova, which, however, are 
produced in much smaller numbers than the spermatozoa. The 
ova undergo their primary development as single cells in the tissue 
of the organ, but at times, through rupture of the enclosing follicles, 
they are released at the surface, and thence pass 
directly into the open mouth of the uterine tube, 
the narrow first part of the oviduct. In this tube 
the ova may come into contact with spermatozoa, 
fusion with one of which constitutes fertilization of the ovum. 
If fertilized, they begin their 
segmentation and further de- 
velopment into an embryo, 
the latter becoming attached 
to the wall of the more 
posterior part of the oviduct, 
which is enlarged to form the 
uterus. A placental con- 
nection is formed by which 
nourishment is carried to the embryo during the period of intra- 
uterine life, in the rabbit about thirty days. The rabbit has two 
complete uteri, the cavities of which are connected distally with 
the unpaired vagina, and through this with the urinogenital sinus 
or vestibulum. The size and appearance of the uteri depend upon 
the age of the animals examined, and upon whether or not they 
are pregnant or have borne young. The uteri of pregnant females 
are greatly enlarged and vascular. They contain from five to 
eight young, the position of which may be easily seen from the 
expansion of those parts of the tubes in which they lie. 
The paired condition of the uteri in the rabbit is especially 
instructive because of its primitive nature as compared with the 
arrangement in many other mammals. Paired oviducts (Fig. 
52, A) are the rule in lower vertebrates, where the function is 
simply to carry the eggs to the outside of the body. This condition 
is retained with minor modifications to the monotreme stage of 
mammals, but in higher forms of the latter the ducts are successively 
coalesced. In marsupials there are still paired vaginae, while in 
The Ovary 
and Oviducts 
Fig. 57. Three stages of specialization of the 
uterus. A, uterus duplex; B, uterus bicornis; 
C, uterus simplex, t, uterine tube; u, uterus; 
v, vagina. The Endocrine System 
107 
placentals the vagina is unpaired. In the rabbit, as in many lower 
placentals, there are two complete uteri, and as an organ the whole 
structure represents the stage of uterus duplex (Fig. 57, A). 
A partly fused condition existing in some mammals, for example 
sheep, is known as uterus bicornis (Fig. 57, B), while the com- 
pletely fused condition in man is known as uterus simplex (Fig. 
57, C). It is characterized by the independent opening of the two 
uterine tubes into a single uterine cavity. The successive stages 
of coalescence are doubtless associated with progressive reduction 
of the number of young, the success of the species being determined 
by greater perfection of the placental apparatus. 
The Endocrine System 
In contrast to the organ-systems usually recognized, which have 
a structural continuity and are associated with contributory but 
more or less separate functions, digestive, nervous, and the like, 
there are certain organs which have a detached distribution, belong 
structurally and embryonically to different systems and body- 
layers, and yet have common general functions in chemical and 
physical regulation, including growth. They are described as 
internal secreting, ductless, or endocrine glands. Their effects 
are exerted through relatively small quantities of very active 
substances, hormones, thrown into the circulation. In a physio- 
logical sense, they constitute an internal secreting or endocrine 
system. They include the suprarenal bodies, the thyreoid, 
the parathyreoids, the thymus, the hypophysis, the pineal 
body, and portions of the male and female gonads and of the 
pancreas. 
Both the testis and the ovary produce substances which have a 
pronounced effect upon metabolism and growth, especially the 
development of secondary sex characters in the young, and, in the 
adult female, changes connected with pregnancy. A more specific 
action is shown by the pancreas, imbedded in which are small 
groups or islands of cells that produce insulin, a regulator of 
oxidation for starches, sugars, and fats, and by the suprarenal bodies, 
which produce the blood pressure increasing or vaso-constricting 
substance, adrenaline or epinephrine. 
The suprarenal bodies are double, each being composed, in 108 
Anatomy of the Rabbit 
mammals, of an inner medulla and an outer cortex which differ 
in origin, in structure, and in function. The medulla is an aggrega- 
tion of cells which have a common origin with those of the sym- 
pathetic nerve ganglia, and the adrenalin which it secretes has an 
effect somewhat similar to that of stimulating these nerve cells. 
The cortex is derived from the lining of the body cavity and forms 
a mass (interrenal gland) associated with the mesonephros in lower 
vertebrates. Its secretion is necessary for the maintenance of life. 
It appears to be concerned in maintenance of normal functioning 
of the kidneys and in the regulation of inorganic substances in the 
body, especially sodium and potassium. 
Like the pancreas, the thyreoid gland develops as an outgrowth 
of the lining of the digestive tube. It becomes detached therefrom, 
however, and gives directly into the blood a secretion which takes 
part in the regulation of growth. This has a high content of iodine 
in combination with colloid material. Thyreoid deficiency in man 
is associated with the conditions known as cretinism and myx- 
oedema, and hyperactivity with exophthalmic goitre. 
The parathyreoid bodies are minute cell-masses lying in, or 
immediately outside of, the thyreoid. They are produced em- 
bryonically from the dorsal part of the epithelial lining of certain 
gill clefts. They have been shown to have essential functions in 
connection with calcium-phosphorus metabolism. 
The thymus is developed from the ventral part of the epithelial 
lining of the embryonic gill clefts. It is thus paired in origin, but 
in mammals the masses of the two sides fuse ventrally and migrate 
backwards to a position near the heart. The functions of the 
thymus are still problematical, but an extract has been shown to 
increase fertility and when administered through successive genera- 
tions to produce accruing precocity in development. The gland 
becomes lymphoid in character at some time after birth and is 
more or less reduced after the animal reaches maturity. 
The hypophysis is embryonically of double origin, while struc- 
turally four divisions are recognized. The anterior portion and the 
smaller intermediate and tuberal portions are formed from the 
epithelium of the roof of the mouth, while the posterior portion is 
an outgrowth from the brain. Experimental removal of the anterior 
lobe retards growth in young animals the body retaining an The Serous Cavities 
109 
infantile condition. Hyperactivity of this part in human adults 
is associated with the condition known as acromegaly, abnormal 
enlargement of the hands, feet, or parts of the head. The posterior 
lobe produces a substance similar in some respects in its action to 
adrenaline and, like the latter, related functionally with the activity 
of the sympathetic system. It restricts cardiac output and oxygen 
consumption. Possibly, one component regulates passage of sub- 
stances through the walls of capillaries, and another may stimulate 
uterine contractions in parturition. 
The pineal body is also an outgrowth of the brain. Its functions 
are not yet well understood but it has been reported to produce 
a growth-regulating substance. 
The Serous Cavities 
The organs collectively described as visceral are those associated 
with the serous cavities. They belong to several systems, but 
present the common feature of being projected into the-membranous 
linings of these cavities so that they are more or less completely 
invested by them without interrupting them at any point. 
The serous sacs are extensive body-spaces, derivatives of a 
primary body cavity or coelom. They are usually considered 
loosely as containing the visceral organs, but the condition is more 
accurately described as one in which the visceral organs encroach, 
chiefly from a dorsal position, on the enclosing membranes. The 
latter are thus divided into two portions, one of which is distributed 
as a parietal or peripheral layer, forming the enclosure of the sac, 
while the other is disposed as a visceral layer on the surface of the 
visceral organs (Fig. 21). The serous sacs are enclosed by thin, 
moist, serous membranes, consisting chiefly of mesothelium, 
which give to the visceral organs their characteristic appearance. 
In lower vertebrates, where the diaphragm is absent or imper- 
fectly developed, the coelom is divided into two chief portions-the 
pericardial cavity, enclosing the heart, and the pleuroperitoneal 
cavity, lodging the remaining visceral organs, including the lungs 
in terrestrial vertebrates. In the mammalia the pleuroperitoneal 
cavity is completely divided into two portions by the diaphragm, 
the smaller pleural portion being again divided into right and left 
pleural cavities through the presence of certain structures filling 110 
Anatomy of the Rabbit 
the median portion of the thorax. There are thus recognizable in 
a mammal four large serous spaces, namely, the pericardial, peri- 
toneal, and paired pleural cavities. 
The pericardial cavity, the smallest of these spaces, is situated 
between the paired pleural cavities. Its enclosing membrane, the 
pericardium, forms a capacious sac for the heart, and is reflected 
directly over the surface of the latter as a thin membrane, the 
epicardium. 
The pleural cavities are those lodging the lungs, the latter 
being projected into them from a medial position. The lining 
membrane or pleura is divided into three chief portions-the 
pulmonary pleura, investing the greater part of each organ, the 
costal pleura, lining the internal surface of the thorax, and the 
diaphragmatic pleura, covering the anterior surface of the 
diaphragm. The latter is broadly connected with the pulmonary 
pleura through the pulmonary ligament. 
The peritoneal cavity, the largest of the serous spaces, com- 
prises in a mammal a general portion, the abdominal cavity, and 
its posterior extension into the pelvis-in the male also into the 
sac of the testis. The general relation of the cavity to the 
abdominal organs is indicated diagrammatically in figure 18. Its 
lining membrane, the peritoneum, is divisible into two principal 
portions, the parietal peritoneum, lining the abdominal wall, 
and the visceral peritoneum, investing the visceral organs. Of 
the latter the kidneys encroach only to a minor extent on the serous 
lining, so that they are covered by peritoneum only on their ventral 
surfaces. The digestive tube, on the other hand, is removed to such 
an extent from the abdominal wall that the peritoneum forms a 
complete serous coat, and is connected with the parietal peritoneum 
of the wall through a thin transparent membrane, the mesentery. 
The latter consists of two plates of peritoneum, enclosing between 
them a thin layer of connective tissue, the lamina mesenterii 
propria, for the transmission of nerves, blood-vessels, and lymph 
canals. 
As indicated in an earlier chapter, the relations of the abdominal 
portion of the digestive tube are greatly modified by its elongation 
and displacement from a median position. Thus, while in the 
embryo the common mesentery (Fig. 42) is recognizable as a The Serous Cavities 
111 
continuous median vertical fold, in the adult it follows the con- 
volutions of the digestive tube, and is therefore considered as 
divided into corresponding parts. In many cases the relations of 
these are greatly complicated by secondary adhesions. In the 
rabbit the mesoduodenum, mesentery of the jejunum, and 
descending mesocolon will be recognized as parts in which a more 
typical arrangement is retained. Moreover, in the anterior portion 
of the abdominal cavity the peri- 
toneum is concerned not only with 
the investment of two large visceral 
structures, the stomach and the liver, 
but also with the formation of a lining 
for the posterior surface of the dia- 
phragm. Thus the general condition 
is less simple than in the region of the 
small and large intestines. The peri- 
toneum, passing from the dorsal wall, 
successively invests the spleen, the 
stomach, and the liver, and passes 
over from the last-named structure 
to the diaphragm and the ventral 
body-wall through the coronary, 
triangular, and falciform liga- 
ments. A portion of the peritoneum 
passing between two organs, such as 
the stomach and the liver, rather than 
connecting either to the body-wall, 
is termed an omentum or sometimes 
a ligament. Thus the peritoneal 
attachments of the stomach are 
differentiated into the mesogastrium (connecting the stomach with 
the diaphragm and dorsal body-wall and divisible into gastrosplenic 
and phrenicospenic ligaments), the greater omentum (a broad fold 
connected to the greater curvature and to the transverse meso- 
colon), and the lesser omentum (passing between the lesser curva- 
ture and the liver). Similarly, in the posterior part of the body 
the peritoneum passes from the rectum to the urinary bladder, 
Fig. 58. Diagram showing the 
relation of the testis to its invest- 
ments: ai, inguinal ring; ce, caput 
epididymidis; cr, cremaster muscle; 
dd, ductus deferens; g, guber- 
naculum; mes, mesorchium; ptv and 
vtv, parietal and visceral layers of 
the tunica vaginalis propria; pv, 
cavity of the vaginal process; s, 
integument of the scrotum; sv, 
spermatic vessels; t, testis. 112 
Anatomy of the Rabbit 
enclosing also in the female the vagina. It is then continued to the 
ventral body-wall as the middle umbilical fold. 
In the male, as indicated in the accompanying diagram (Fig. 58), 
the peritoneal relations of the testis are greatly modified by the 
migration of the organ from an abdominal to a scrotal position. 
The entire sac lodging the testis is an evaginated portion of the 
abdominal wall, and since in the rabbit the cavity is widely open 
throughout life to the abdominal cavity, the lining membrane-that 
designated as the parietal layer of the tunica vaginalis propria- 
is continuous with the parietal peritoneum of the abdomen. It 
thus represents a permanent vaginal process, an outpouching of 
the peritoneum which in man becomes closed off. Like other 
structures of the abdominal cavity, the testis itself is covered by 
peritoneum, the latter being designated as the visceral layer of the 
tunica vaginalis propria. This investment is connected with 
the parietal layer by the mesorchium, and in the rabbit it will 
be observed that the latter is chiefly attached forwards on the 
dorsal wall of the abdomen, i.e., in a position indicating the original 
situation of the testis itself. 
In the female the ovary is situated close to the dorsal wall 
of the abdomen, and its supporting peritoneum, the mesovarium, 
is insignificant. Its duct in passing backward, however, becomes 
greatly displaced from a dorsal position, and thus comes to be 
supported by a broad fold of peritoneum. The latter is considered 
to consist of two portions, one, the mesosalpinx, being the support 
of the uterine tube, the other, the mesometrium, that of the 
uterus. The entire fold, however, forms a continuous structure, 
and is known in this relation as the broad ligament. 
REGIONAL SECTIONS 
The following plate-figures (I-VIII) are from characteristic 
sections of a rabbit-foetus of 56 mm., and may be used either in 
connection with the general features of topography as outlined 
above, or for the identification of various minor structures appear- 
ing in the dissection. 
Certain points regarding the sections are perhaps worthy of 
notice. First, in the longitudinal section illustrated in Plates I and 
II it will be noticed that paired structures frequently appear; this Regional Sections 
113 
being because of the fact that the section is not exactly median, at 
least in certain places. Second, in using sections of the foetus for 
gross anatomical features it is necessary to make allowance in some 
cases for the different proportions of organs, and consequent slight 
differences in position, in the foetal as compared with the adult 
condition. Finally, many of the features appearing in the original 
sections are such as could not be reproduced in the plates, although 
they are indicated in the accompanying skeleton figures, and may 
be referred to in this way. 28. Thymus gland. 
29. Oesophagus. 
30. Trachea. 
31. Tongue. 
32. Oral cavity. 
33. Basicranium. 
34. Nasal septum. 
III-VIII indicate levels of corres- 
ponding transverse sections. 
IQ' Abdominal cavity. 
20. Stomach (pyloric portion). 
21. Liver. 
22. Umbilicus (base of cord and 
vessels). 
23. Lung. 
24. Pleural cavity. 
25. Heart and aorta. 
26. Pericardial cavity. 
27. Sternum. 
DESIGNATIONS FOR PLATE I 
11. Telencephalon. 
12. Lumbar vertebrae. 
13. Thoracic vertebrae. 
14. Cervical vertebrae. 
15. Pelvis. 
16. Ganglia of sympathetic trunk. 
16A. Superior mesenteric ganglion 
(prevertebral). 
17. Diaphragm. 
18. Intestines. 
i. Cutaneus maximus muscle. 
2. Fat-masses of neck. 
3. Spinal musculature. 
4. Vertebral canal. 
5. Cranial cavity. 
6. Spinal cord. 
7. Myelencephalon. 
8. Metencephalon. 
9. Mesencephalon. 
10. Diencephalon. 
114 I 
A MEDIAN VERTICAL SECTION OF THE ENTIRE BODY 
115 1. Transverse sinus of dura 
mater. 
2. Dura mater. 
3. Pallium of cerebral hemis- 
phere. 
4. Lateral ventricle. 
5. Olfactory bulb. 
6. Olfactory tract. 
6a. Divided olfactory nerve in 
the cribriform plate. 
7. Chorioid plexus of third 
ventricle. 
8. Anterior commissure. 
DESIGNATIONS FOR PLATE II 
21. Posterior medullary velum. 
22. Cervical flexure. 
23. Central canal of spinal cord. 
24. Hypophysis. 
25. Frontal bone. 
26. Nasal bone. 
27. Nasal fossa. 
28. Mesethmoid cartilage. 
29. Cartilage of vomeronasal 
organ. 
30. Premaxilla. 
31. Nasopalatine duct and car- 
tilage. 
41. Oral portion of pharynx. 
42. Epiglottis and epiglottic 
cartilage. 
43. Thyreoid cartilage of 
larynx. 
44. Laryngeal cavity. 
45. 45a. Cricoid cartilage. 
46. Oesophagus. 
47. Cricothyreoideus muscle. 
48. Thyreoid gland. 
49. Sternohyoideus muscle. 
50. Genioglossus muscle. 
51. Geniohyoideus muscle. 
9. Thalamus. 
10. Optic chiasma. 
11. Tuber cinereum. 
12. Mamillary body. 
13. Superior colliculus. 
14. Inferior colliculus. 
15. Anterior medullary velum. 
16. Cerebral peduncle; cephalic 
flexure. 
17. Isthmus rhombencephali. 
18. Fourth ventricle. 
19. Pons; pontine flexure. 
20. Cerebellum. 
32. Maxilla. 
33. Hard palate (palatine and 
maxilla). 
34. Presphenoid. 
35. Intersphenoidal synchon- 
drosis. 
36. Basisphenoid; hypophyseal 
fossa. 
37. Sphenooccipital synchon- 
drosis. 
38. Basioccipital. 
38a. Supraoccipital. 
39. Nasal portion of pharynx. 
40. Soft palate. 
52. Mylohyoideus muscle. 
53. Mandible. 
54. Occipital musculature. 
55. Semispinalis capitis. 
56. Rhomboideus minor. 
57. Superior portion of trape- 
zius. 
58. Atlas. 
59. Epistropheus. 
59a. Odontoid process. 
60. Third cervical vertebra. 
61. Median vertebral vein. 
62. Body of hyoid bone. 
116 II 
A MEDIAN VERTICAL SECTION OF THE HEAD 
117 DESIGNATIONS FOR PLATE III 
1. Nasal bone. 
2. Levator alae nasi muscle. 
3. Nasal septum. 
4. Nasoturbinal cartilage. 
5. Maxilloturbinal (concha inferior). 
6. Nasal fossa. 
7. Nasolacrimal duct. 
8. Vomeronasal organ and cartilage. 
9. Pre maxilla. 
10. Small upper incisor. 
11. Large upper incisor. 
12. Nasopalatine ducts. 
13. Oral cavity. 
14. Tongue. 
15. Vibrissae. 
16. Caninus muscle. 
17. Terminals of superior maxillary nerve. 
18. Buccal glands. 
19. Buccinator muscle. 
20. Terminals of inferior alveolar nerve. 
21. Quadratus labii inferioris muscle. 
22. Mandible. 
23. Lower incisor. 
24. Meckel's cartilage (primary mandibular 
arch). 
25. Mentalis muscle. 
118 HI 
A TRANSVERSE SECTION OF THE ANTERIOR NASAL REGION 
119 DESIGNATIONS FOR PLATE IV 
i. Superior sagittal sinus of dura mater. 
2. Lateral ventricle. 
3. Cerebral hemisphere. 
4. Pia mater. 
5. Frontal bone. 
6. Cartilage of orbital wing. 
7. Mesethmoid cartilage. 
8. Cupula posterior cartilage. 
9. Obliquus superior muscle. 
10. Ophthalmic vessels and nerves. 
11. Levator palpebrae superioris muscle. 
12. Rectus medialis muscle. 
25. Nasal tract; choana. 
26. Palatine bone. 
27. Oral cavity. 
28. Palatine nerve. 
29. Sphenopalatine ganglion. 
30. Infraorbital vein. 
31. Internal maxillary artery. 
32. Maxillary nerve. 
33. Maxilla. 
34. Zygomatic bone. 
35. Submaxillary duct. 
36. Buccinator muscle. 
13. Retractor oculi muscle. 
14. Rectus inferior muscle. 
15. Sclera. 
16. Retina and chorioidea. 
17. Vitreous body. 
18. Lens. 
19. Posterior chamber of eye. 
20. Anterior chamber. 
21. Cornea. 
22. Ciliary body and iris. 
23. Upper eyelid. 
24. Lower eyelid. 
37. Masseter muscle. 
38. Parotid duct. 
39. Facial nerve. 
40. External maxillary artery and vein 
(anterior facial vein). 
41. Platysma muscle. 
42. Inferior labial artery and vein. 
43. Mandible. 
44. Genioglossus muscle. 
45. Digastricus muscle. 
46. Quadratus labiiinferioris muscle. 
47. Geniohyoideus muscle. 
120 IV 
A TRANSVERSE SECTION OF THE ORBITAL REGION 
121 I. Parietal bone. 
2. Transverse sinus of dura mater. 
3. Superior colliculus. 
4. Cerebral aqueduct. 
5. Isthmus rhombencephali. 
6. Pons. 
7. Trigeminal nerve. 
8. Basilar artery. 
9. Facial nerve. 
10. Cartilaginous auditory capsule. 
11. Cochlea. 
DESIGNATIONS FOR PLATE V 
21. Longus capitis. 
22. Rectus capitis anterior. 
23. Oral portion of pharynx. 
24. Thyreohyoideus muscle. 
25. Sternohyoideus muscle. 
26. Greater cornu of hyoid. 
27. Stylohyoideus major muscle. 
28. Lingual artery. 
29. Hypoglossal nerve. 
30. Tendon of digastricus muscle. 
31. External maxillary artery. 
12. Basioccipital bone. 
13. Tensor tympani muscle. 
14. Tympanic cavity. 
15. Malleus. 
16. Tributaries of posterior facial vein. 
17. Squamosal bone. 
18. Cephalic portion of median vertebral vein. 
19. Nasal portion of pharynx. 
20. Origin of basioclavicularis and levator 
scapulae major muscles. 
32. Stylohyoideus minor. 
33. Styloglossus. 
34. Internal maxillary artery. 
35. Tympanic bone. 
36. Mandible. 
37. Submaxillary gland. 
38. Anterior facial vein. 
39. Internal carotid artery. 
122 V 
A TRANSVERSE SECTION OF THE AUDITORY REGION 
123 DESIGNATIONS FOR PLATE VI 
i. Rhomboideus minor. 
2. Superior portion of trapezius. 
2a. Levator scapulae minor. 
3. Splenius. 
4. Semispinalis capitis. _ 
5. Rectus capitis posterior superficialis. 
6. Obliquus capitis major. 
7. Arch of epistropheus. 
8. Ganglion of posterior root. 
9. Longissimus cervicis. 
19. Oesophagus. 
20. Recurrent nerve. 
21. Inferior thyreoid vein. 
22. Trachea. 
23. Thyreoid gland. 
24. Cardiac branch of vagus (n. depressor). 
25. Sympathetic trunk. 
26. Vagus nerve. 
27. Common carotid artery. 
28. Internal jugular vein. 
10. Longissimus capitis. 
11. Vertebral artery and vein. 
12. Longus atlantis. 
13. Vertebral body. 
14. Transverse process (anterior root). 
15. Median vertebral vein. 
16. Longus colli. 
17. Longus capitis. 
18. Fat-body. 
29. Sternohyoideus muscle. 
30. Sternothyreoideus muscle. 
31. Sternomastoideus muscle. 
32. Descending ramus of hypoglossal nerve. 
33. External jugular vein. 
34. Basioclavicularis muscle. 
35. Levator scapulae major muscle. 
36. Cleidomastoideus. 
37. Platysma. 
124 VI 
A TRANSVERSE SECTION OF THE ANTERIOR CERVICAL REGION 
125 i. Semispinalisdorsi. 
2. Longissimus dorsi. 
3. Iliocostalis. 
4. Spinal cord. 
5. Ganglion of posterior root and intercostal 
nerve. 
6. Tubercle of rib. 
7. Head of rib. 
8. Sympathetic trunks. 
9. Azygos vein. 
10. Thoracic aorta. 
11. Oesophagus. 
DESIGNATIONS FOR PLATE VII 
24. Costal pleura. 
25. Bone ribs. 
26. Costal cartilage. 
27. Sternum. 
28. Cutaneus maximus muscle. 
29. Inferior portion of trapezius. 
30. Rhomboideus major. 
31. Inferior angle of scapula. 
32. Latissimus dorsi. 
33. Serratus posterior. 
34. Intercostales externi and interni. 
34a. Intercostalis internus. 
35. Thoracic portion of serratus anterior. 
36. Obliquus externus abdominis. 
37. Transversus thoracis. 
38. Pectoralis major. 
39. Rectus abdominis. 
40. Long head of triceps. 
41. Extensor antibrachii parvus. 
42. Medial head of triceps. 
43. Lateral head of triceps. 
44. Distal extremity of humerus. 
45. Proximal portion of radius. 
12, 12a. Right and left vagi. 
13. Lung. 
14. Bronchi. 
15. Branches of pulmonary artery. 
16. Pulmonary veins. 
17. Right atrium. 
18. Tricuspid valve. 
19. Right ventricle. 
20. Left atrium. 
21. Left ventricle. 
22. Pericardial cavity. 
23. Pulmonary pleura. 
126 VII 
A TRANSVERSE SECTION OF THE THORAX 
127 DESIGNATIONS FOR PLATE VIII 
1. Spinal cord. 
2. Vertebral canal. 
3. Vertebral body. 
4. Sacrospinalis muscle. 
5. Quadratus lumborum. 
6. Psoas major. 
7. Psoas minor. 
8. Sympathetic trunk. 
18, 18a. Posterior and anterior lobules of left 
lobe of liver. 
19, 19a. Right lobe of liver. 
20. Obliquus internus abdominis and trans- 
versus abdominis. 
21. Obliquus externus abdominis. 
22. Rectus abdominis. 
22a. Cutaneus maximus. 
9. Abdominal aorta. 
10. Inferior caval vein. 
11. Descending mesocolon. 
12. Ureter. 
13. Renal pelvis. 
14. Renal papilla. 
15. Left kidney. 
16. Parietal peritoneum. 
17. Visceral peritoneum. 
23. Middle umbilical fold. 
24. Urinary bladder (canal of foetal allantois). 
25. Umbilical arteries. 
26. Duodenum. 
27. Pancreas and mesoduodenum. 
28. Descending colon. 
29. Parts of mesenterial small intestine. 
30. Caecum. 
128 VIII 
A TRANSVERSE SECTION OF THE ABDOMEN 
129 PART II 
OSTEOLOGY OF THE RABBIT 
For a practical study of the rabbit's skeleton, a thoroughly 
cleaned, but otherwise rough, unmounted skeleton will be found 
most convenient. The skull should be divided with a fine saw at 
a little to one side of the median plane, or a second skull may be 
provided for this purpose (cf. Fig. 65). The most useful specimens 
for reference are: (1) a well-mounted skeleton of the adult animal, 
showing the natural relations of the bones; and (2) a rough skeleton 
of a young animal of from one to five weeks, showing the primary 
composition of cartilage bones. For the special study of the skull 
(pp. 153-71) a disarticulated specimen may be employed, but the 
majority of the features may be made out in the intact or divided 
skulls. The general account of the skull as given below will be 
found to cover most of the osteological points noted in the dissection. 
DIVISIONS OF THE SKELETON 
The skeleton is divisible into two main portions, namely, the 
axial skeleton and the appendicular skeleton. The former 
comprises the vertebral column, the ribs, the sternum, and the 
skeleton of the head; the latter, the supports of the anterior and 
posterior limbs, and the associated pectoral and pelvic girdles. 
THE VERTEBRAL COLUMN 
The vertebral column (columna vertebralis) is formed of a 
linear series of segments, the vertebrae. In accordance with its 
function as a general support of the body, and also its relations with 
the nervous system and the spinal musculature, the vertebrae, with 
minor exceptions, are constructed on the same plan. Those of 
particular regions, moreover, resemble each other specially closely 
in function and form, so that it is possible to classify them into 
cervical (neck), thoracic (chest), lumbar (abdominal), sacral (hip), 
and caudal (tail) groups. 
A typical vertebra-for the characters of which any one of the 
thoracic or lumbar series may be taken (Fig. 59, D-F)-consists of The Vertebral Column 
131 
a basal portion, the vertebral body (corpus vertebrae), and of 
a dorsal, vertebral arch (arcus vertebrae). The two portions 
enclose a large aperture, the vertebral foramen (foramen verte- 
Fig. 59. Representative vertebrae: A. atlas, anterior surface; B, epistro- 
pheus, lateral surface; C, fifth cervical vertebra, anterior surface; D, fourth 
thoracic, lateral surface; E, F, second lumbar vertebra, anterior and lateral 
surfaces. 
a.a., anterior arch of atlas; a.p., posterior arch of atlas; a.v., vertebral arch; 
c.v., vertebral body; d., dens epistrophei; f.a.a., anterior articular facet of 
epistropheus; f.a.s., superior articular pit of atlas; f.a.s.', superior articular 
facet of epistropheus; f.c.i., inferior costal demifacet for head of rib; f.c.s., 
superior costal demifacet; f.c.t., costal facet of transverse process; f.d., fovea 
dentis; f.i., intervertebral foramen; f.tr., foramen transversarium; f.v., foramen 
vertebrale; 1., lamina of vertebral arch; m.l., lateral mass of atlas; p.a., 
accessory process of lumbar vertebra; p.a.i., inferior articular process; p.a.s., 
superior articular process; p.m., mamillary process; p.s., spinous process; 
p.s.a., anterior spinous process; p.t., transverse process; p.tn., triangular 
process; r., radix of vertebral arch; r.a., r.p., anterior and posterior radices of 
transverse process of cervical vertebra; t.a., t.p., anterior and posterior 
tubercles of atlas. 
brale). The successive foramina form an almost complete tube, 
the vertebral canal (canalis vertebralis), for the accommodation 
of the spinal cord. 132 
Anatomy of the Rabbit 
The body of a vertebra is a cylindrical, or somewhat dorso- 
ventrally compressed, mass of bone, which bears at either end an 
articular surface for attachment to the adjacent vertebra. The 
articular surfaces are borne on thin plate-like epiphyses, the epiphy- 
sial lines being evident even in older animals, especially in the 
lumbar region. Dorsally, the body bears on either side the pedicle 
or root of the vertebral arch (radix arcus vertebrae), so that the 
dorsal surface of the body forms the floor of the vertebral foramen. 
The dorsal portion of the arch, borne on the pedicles, is distinguished 
as the lamina. The anterior and posterior margins of the pedicle 
are notched, each notch or incisure being opposite that of the 
adjacent vertebra, so that together they form a rounded aperture, 
the intervertebral foramen (foramen intervertebrale), for the 
passage outward of a spinal nerve. 
The arch of the vertebra bears various projections or processes. 
On either side is a horizontal plate of bone, the transverse process 
(processus transversus), and, dorsally, there is a median projection, 
the spinous process (processus spinosus), all three serving for the 
attachment of ligaments which hold the vertebrae together and 
for the attachment of the spinal musculature. Special surfaces 
for articulation with the adjacent vertebrae are borne on low 
articular processes (processus articulares) on the anterior and 
posterior margins of the arch. The anterior or superior articular 
surfaces are directed for the most part toward the dorsal surface, 
and are overlapped in the natural condition by the inferior 
articular surfaces of the next vertebra, which are directed 
ventrad. A certain amount of movement is permitted by one 
surface slipping across the other, the mechanism illustrating the 
arthrodia, or gliding-joint. 
Cervical Region 
The cervical vertebrae (vertebrae cervicales) are seven in 
number and serve mainly for the support of the head. As the 
latter has to be freely movable in a variety of directions, the 
articulations are such as to permit considerable flexibility in this 
region and the first two cervical vertebrae (the atlas and the 
epistropheus) are specially modified to provide for movements of The Vertebral Column 
133 
the skull. The posterior vertebrae (Fig. 59, C) are dorsoventrally 
compressed, with low arches and short spinous processes. In the 
seventh vertebra, however, the spinous process begins to be elon- 
gated as in the succeeding thoracic vertebrae. In each vertebra 
the transverse process is perforated by a costo-transverse fora- 
men (foramen transversarium), which serves for the passage of the 
vertebral artery forward to the head. This aperture divides the 
base of the transverse process into a dorsal, or posterior root 
(radix posterior) and a ventral, or anterior root (radix anterior). 
The development of these parts shows that the anterior root is 
really a reduced rib which has become fused to the body and to 
the transverse process and is comparable in its general relations 
to the normal ribs of the thoracic vertebrae. 
The first vertebra is the atlas (Fig. 59, A). It is 
peculiar in lacking the vertebral body, the latter being 
represented by the odontoid process of the epistropheus 
(cf. Plate II); also in possessing special articular surfaces, and in 
having its transverse process greatly flattened dorsoventrally. It 
consists of a ventral half-ring, the anterior arch (arcus anterior), 
a dorsal half-ring, the posterior arch (arcus posterior), and paired 
lateral masses (massae laterales) uniting them and forming the 
bases of the transverse processes. The anterior arch bears on its 
ventral side a small backwardly-directed process, the anterior 
tubercle (tuberculum anterius). A similar posterior tubercle 
(tuberculum posterius) projects forward on the dorsal surface of 
the posterior arch and is comparable to the spinous process of an 
ordinary vertebra. The anterior surface of the atlas bears on either 
side an extensive concave smooth surface, the superior articular 
pit (fovea articularis superior), for articulation with one of the 
convex occipital condyles of the skull. Its posterior surface bears 
on either side a smaller, somewhat triangular, inferior articular 
facet (facies articularis inferior) for articulation with the epis- 
tropheus. These surfaces take the place of the arch articulations 
of ordinary vertebrae. As a result of the flattening of the transverse 
process, the costo-transverse foramen is extended into a tubular 
canal. The anterior aperture of this is connected by a shallow 
groove, the sulcus arteriae vertebralis, with a foramen perforat- 
ing the posterior arch. Through this latter foramen, represented 
Atlas 134 
Anatomy of the Rabbit 
in some mammals by separate alar and intervertebral foramina, 
the vertebral artery and the first cervical nerve enter the vertebral 
canal. 
The space enclosed by the atlas is divided into a dorsal portion, 
corresponding to the vertebral foramen of other vertebrae, and a 
ventral portion which in the natural condition lodges the odontoid 
process of the epistropheus. The division is effected partly by a 
small tubercle on the inner side of each lateral mass, and partly 
by a transverse ligament which is stretched between these tubercles 
and over the dorsal surface of the odontoid process. On the floor 
of the ventral portion, a rounded articular surface, the fovea 
dentis, marks the point of articulation of the anterior articular facet 
of the odontoid process with the inner surface of the anterior arch. 
The second vertebra is the epistropheus or 
axis (Fig. 59, B). It resembles the succeeding 
cervical vertebrae more closely than does the atlas. 
It is noteworthy for its great size, for the lateral compression of its 
arch and spinous process, and for the possession of a stout forwardly- 
directed odontoid process, or tooth (dens epistrophei). It is 
articulated with the atlas through an anterior articular facet, 
borne on the ventral surface of the odontoid process, and by large 
paired superior articular facets borne on its base. The spinous 
process of this vertebra and the transverse processes of the atlas 
are three main points of attachment for the occipital musculature, 
which passes between the head and neck. 
Thoracic Region 
The thoracic vertebrae (vertebrae thoracales) are twelve in 
number. They form the backbone of the chest region and provide 
attachment for certain muscles of the shoulder and muscles and 
ligaments of the neck, but are distinguished chiefly by the possession 
of articular pits for the attachment of ribs (Fig. 59, D). A 
typical rib is articulated at two points, namely, one on the body 
of the vertebra, the other on the transverse process. The former 
is marked by a small round depression, the costal pit (fovea 
costalis), or costal facet. In the last two vertebrae the facet is 
borne wholly on the vertebral body to which the rib belongs, but 
in the remaining vertebrae a complete articulating surface is formed 
Epistropheus The Vertebral Column 
135 
by two demifacets, one on the vertebra to which the rib belongs, 
the other on the vertebra immediately in front. The point of 
articulation of a rib with a transverse process is marked on the 
latter by an oval facet, the costal pit of the transverse process 
(fovea costalis transversalis). It is present only in the first ten 
of the thoracic vertebrae, the other two having the costal articula- 
tions on their bodies only. 
In all vertebrae of the thoracic series the spinous processes are 
well developed, mainly for attachment of the dorsal ligament of the 
neck, which supports much of the weight of the head. They 
increase in length to the third, and then become gradually shorter 
but wider, so that their surfaces are, on the whole, slightly increased 
in extent. The anterior ten are directed backward, the eleventh 
is almost vertical (anticlinal vertebra), while the twelfth is directed 
forward, like those of the succeeding lumbar vertebrae. The 
anticlinal vertebra is a centre about which the body bends in such 
movements as galloping. 
Dorsolaterally, the more posterior vertebrae of the region have 
small mamillary processes corresponding with the more conspicuous 
ones of the lumbar region. 
Lumbar Region 
The lumbar vertebrae (vertebrae lumbales) are seven in 
number. As they not only support the longer part of the trunk 
but also provide the origins for some of the proximal muscles of the 
hind limb, they are large vertebrae, conspicuous for their extensive 
surfaces and processes for muscular attachment (Fig. 59, E, F). 
The transverse processes continue the general line of the ribs of the 
thoracic region, being directed forward and downward, as well 
as outward. The tip of each is formed by a thin triangular plate 
(processus triangularis), which represents a vestigial rib fused with 
the original process. At the posterior side of the base of each is a 
short, flattened projection, the accessory process (processus 
accessorius). The spinous process is notably broad, and is directed 
forward. The articular processes are rotated upward, so that their 
surfaces are directed more nearly toward, or away from, the median 
plane, instead of to the dorsal or ventral surface. The anterior 
articular surfaces are borne on the bases of stout, upwardly-directed 136 
Anatomy of the Rabbit 
mamillary processes (processus mamillares). The latter are 
most characteristic of the lumbar vertebrae, but, as mentioned 
above, appear in the posterior thoracic region as small elevations 
of the transverse processes. Each of the first three of the lumbar 
Fig. 60. The os sacrum: A, ventral (pelvic) surface; B, dorsal surface, 
c.v., bodies of coalesced vertebrae; f.a., auricular surface; f.s.a., anterior 
sacral foramina; f.s.m., median sacral foramina; f.s.p., posterior sacral 
foramina; p.a.s., superior articular process of first vertebra; p.m., mamillary 
process of first vertebra; pr., promontory; p.s., spinous processes. 
vertebrae bears a median ventral projection, the anterior spinous 
process (processus spinosus anterior), for the attachment of the 
lumbar portion of the diaphragm. 
Sacral Region 
The sacral vertebrae (vertebrae sacrales) are four in number 
and are modified for the attachment of the pelvic girdle. In con- 
trast to the true vertebrae-those united by ligament and articular 
surfaces-of the remaining portions of the vertebral column, they 
are false vertebrae, being united in the young by synchondroses, 
and in the adult coalesced to form a composite structure, the os The Vertebral Column 
137 
sacrum (Fig. 60). The axis of the sacrum forms an obtuse angle 
with that of the lumbar vertebrae, the angle being indicated by a 
ventral projection, the promontory (promontorium), formed by 
the last lumbar and first sacral vertebrae. The sacrum is the 
medium through which the vertebral column-in other words, the 
posterior portion of the trunk-is supported on the posterior limbs. 
Its anterior dorsal portion bears on either side a roughened area, 
the auricular surface (facies auricularis), for articulation with 
the pelvic girdle. This surface is borne for the most part on the 
transverse process of the first sacral vertebra. 
The sacrum exhibits many features resulting from its formation 
through the fusion of originally distinct vertebrae. On the ventral 
or pelvic surface (facies pelvina), the lines of junction may be 
traced either between the bodies, or between the transverse pro- 
cesses. Four pairs of apertures on this surface, the anterior sacral 
foramina (foramina sacralia anteriora), lead into the intervertebral 
foramina, and give passage to the sacral spinal nerves. On the 
dorsal surface (facies dorsalis) a pair of posterior sacral fora- 
mina lie in the line of junction of the first and second vertebrae. 
The spinous processes are evident in all four vertebrae. The 
combined articular and mamillary processes are conspicuous only 
in the first two, but are represented in the succeeding two by low, 
roughened tubercles. In the middle line dorsally the vertebral 
arches are separated by conspicuous apertures, the median sacral 
foramina. 
Caudal Region 
The caudal or coccygeal vertebrae (vertebrae caudales, 
s. coccygeae) are sixteen in number. They are segments of small 
size, increasing slightly to the third, and then gradually decreasing 
to the end of the column. As only the small tail muscles are 
attached to them, they lack any marked projections. The arches 
are complete in the first seven. The transverse processes are 
vestigial in all except the third. At the end of the column the 
segments are reduced to slender cylinders of bone representing the 
vertebral bodies. 138 
Anatomy of the Rabbit 
THE RIBS 
The ribs (costae) are twelve in number on either side. Each 
is composed of a dorsal portion, the costal bone (os costale), or 
bone-rib, and a ventral portion, the costal cartilage (cartilago 
costalis) (Fig. 61). From their attachment on the vertebral column 
the bone-ribs are directed outward, downward, and backward. 
The costal cartilages are directed for the most part inward, down- 
ward, and forward. The first costal cartilage forms a pronounced 
angle with the corresponding bone-rib. In the succeeding ribs the 
angle is gradually replaced by a broad curve. 
Ribs are classified as true or sternal ribs (costae verae), and 
false or asternal ribs (costae spuriae). The former-comprising 
the anterior seven-are those directly attached to the sternum. 
The latter-comprising the posterior five-are either indirectly 
attached, or unattached. Those unattached are designated as 
floating ribs. 
Generally speaking, the bone-ribs are cylindrical; but the 
anterior five or six are more or less flattened, with their main sur- 
faces respectively medial and lateral. The compression is most 
marked in old animals. The first rib is extremely short. The 
succeeding ribs increase in length to the sixth, and then decrease 
to the twelfth. The arch formed by each rib has its greatest con- 
vexity, or angle, at some point toward the dorsal surface. Passing 
backward, the point of greatest convexity changes from a medio- 
dorsal to a laterodorsal position. This, together with the elonga- 
tion of the more posterior ribs, results in an enormous increase in 
the posterior extent of the thoracic cavity. 
The vertebral end, or head of the rib (capitulum costae), is 
articulated with the body of the vertebra to which it belongs, and 
also, in the case of the first ten, with the vertebra immediately in 
front. The articulation with a transverse process is marked by a 
small smooth elevation, the costal tubercle (tuberculum costae). 
It is present only in the first nine ribs. Except in the first rib, and 
in the last four, the tubercle bears a sharp, dorsally-directed process 
for muscular attachment. The slender portion of the rib inter- 
vening between the head and tubercle is the neck (collum costae), 
the remaining larger portion being distinguished as the body of the 
rib (corpus costae). The Sternum 
139 
The bony thorax is formed by the ribs and the sternum with the 
assistance of the thoracic vertebra. It encloses a large space, the 
thoracic cavity (cavum thoracis). The latter is conical in shape, 
with the apex directed forward. The 
dorsoventral diameter of the cavity 
is considerably greater than the 
transverse diameter. Apart from 
the intercostal spaces, the cavity 
is open at two points: anteriorly, 
the first thoracic vertebra, the first 
rib, and the manubrium sterni 
together enclose a small opening, 
the superior thoracic aperture 
(apertura thoracis superior); pos- 
teriorly, the seventh and succeed- 
ing ribs, together with the posterior 
thoracic vertebrae and the xiphoid 
process of the sternum, enclose a 
much larger opening, the inferior 
thoracic aperture (apertura thor- 
acis inferior). In the natural con- 
dition it is largely closed by the 
diaphragm. The curved boundary 
formed by the ribs in this region is 
the costal arch (arcus costarum), 
the angle formed at the point of 
attachment of the xiphoid process 
being the infrasternal angle 
(angulus infrasternalis). 
Through their articulations with the vertebral column, and the 
nature of the costal cartilages, the ribs are capable of being moved, 
or rotated, forward. The movement results in an increase of the 
extent of the thoracic cavity, and is of importance in respiration. 
THE STERNUM 
The sternum (Fig. 61) consists of a linear series of six segments, 
the sternebrae. The first segment is the manubrium sterni. 
Fig. 61. The sternum and first rib, 
ventral view: 1-7, the true ribs; 8, first 
false rib; c.c., head of rib; cl.c., neck of 
rib; cr., costal cartilage; cr.c., body of rib; 
c.s., body of sternum; m.s., manubrium 
sterni; o.c., bone-rib; p.x., xiphoid pro- 
cess; t.c., costal tubercle. 140 
Anatomy of the Rabbit 
It is about twice the length of the middle segments. It is some- 
what triangular in section, two of its surfaces being ventrolateral, 
the third dorsal and directed toward the thoracic cavity. To its 
anterior tip is attached the sternoclavicular ligament, by which 
the greatly reduced clavicle is united with the sternum. 
The four middle segments are similar in appearance, and form 
the body (corpus sterni). The sixth segment, described as the 
xiphoid process (processus xiphoideus), is an elongated strip of 
bone with a broad, thin plate of cartilage attached to its posterior 
end. 
The first costal articulation is situated at about the middle of 
the manubrium, the remaining six at the points of junction of the 
segments. Five of them occur singly, while the sixth and seventh 
costal cartilages are attached together at the point of junction of 
the last segment of the corpus sterni with the xiphoid process. 
THE SKELETON OF THE HEAD 
The head-skeleton comprises: (1) the series of elements con- 
stituting the skull; and (2) the hyoid bone, with its connections. 
The skull, or cranium-using that term in a general sense-includes 
the cranium proper, that portion enclosing the brain and contain- 
ing in its wall the auditory capsules, and the bones of the face 
(ossa faciei), the latter including the series of elements related for 
the most part to the jaws and palate. The primary relations of the 
constituents of the head-skeleton have already been indicated 
above (p. 55). 
A. The Skull as a Whole 
The skull (Figs. 62-6) is a composite structure, consisting of a 
large number of elements, which, with the exception of the man- 
dible, are united by immovable articulations, so that they produce 
the effect of a continuous mass. In this the sutures between 
component bones appear as fine lines of varying distinctness. The 
mandible is a more or less independent structure, articulated with 
the main body of the skull by a typical joint. 
The posterior, cranial portion of the skull has a somewhat 
conical shape, its apex being directed forward. It is separated from 
the anterior, facial portion by a depression on either side of the The Skull as a Whole 
141 
skull, the orbital cavity (orbita), which serves for the accommoda- 
tion of the optic bulb. Unlike the remaining special sense-organs, 
the eye is not included within the skull-wall. The two portions 
are united both medially and laterally, the lateral connection being 
established by the zygomatic arch (arcus zygomaticus), which 
bridges the lateral portion of the orbit. The facial portion has 
also a somewhat conical shape, its apex being formed by the anterior 
extremity of the upper jaw and the incisor teeth. Its base is 
formed in part by the connection with the cranial portion, as 
already described, and also by the anterior walls of the orbits. 
The cranial portion exhibits an extensive posterior surface, 
the nuchal surface (planum nuchale), situated in general at right 
angles to the cervical portion of the vertebral column and also to 
the dorsal, lateral, and ventral walls of the skull. This surface 
includes the external aspect of the occipital bone, with the 
exception, chiefly, of the basilar part of the latter. Its dorsal 
portion forms an area of attachment for the spinal and special 
occipital musculature. Its ventral portion is perforated by a large 
aperture, the foramen magnum occipitale, for the passage of 
the central nervous system from the cranial cavity into the vertebral 
canal. On either side of this is a smooth, ridge-like projection, the 
occipital condyle (condylus occipitalis), for articulation with the 
superior articular pits of the atlas. At a little distance lateral to 
the occipital condyle, the nuchal surface is continued downward 
through the medium of a somewhat triangular, pointed jugular or 
paramastoid process (processus jugularis). This structure is 
separated from the occipital condyle by a pronounced notch, the 
posterior boundary of a deep narrow excavation, the jugular fossa 
(fossa jugularis), which lies between the condyle and the tympanic 
bulla. The jugular process serves for the attachment of muscles 
belonging to the tongue, hyoid, and mandible, namely, the stylo- 
glossus, stylohyoidei major and minor, and the digastricus, the 
suspensory ligament of the lesser cornu of the hyoid also being 
included in the ligament of the stylohyoideus minor. The nuchal 
surface is separated from the dorsal surface of the skull by a shield- 
shaped promontory and crest (crista nuchae). The lateral con- 
tinuation of this crest is the superior nuchal line (linea nuchae 
superior). It forms a curved ridge, the position of which indicates 142 
Anatomy of the Rabbit 
the dorsal limit of the occipital musculature. The posterior, some- 
what tri-radiate tip of the projection, together with a thin ridge 
extending ventrad from it, is the external occipital protuberance 
(protuberantia occipitalis externa), an important median point of 
attachment for the occipital muscles and the dorsal ligament of the 
neck. 
Fig. 62. Lateral surface of the skull: AS, alisphenoid (ala magna); BO, 
basioccipital (basilar portion of occipital); BS, basisphenoid (body of posterior 
sphenoid); F, frontal; I, interparietal; L, lacrimal; M, maxilla; MS, mastoid 
portion of petrosal (petromastoid); N, nasal; OS, orbitosphenoid (ala parva); 
P, parietal; PL, palatine; PM, premaxilla; SO, supraoccipital (squamous 
portion of occipital); SQ, squamosal; T, tympanic; ZY, zygomatic. 
a.p., piriform aperture of nose; d.i., incisor teeth; d.m., molars; d.pm., 
premolars; f.i., infraorbital foramen; f.mx., maxillary fossa; f.o., optic foramen; 
f.s., stylomastoid foramen; f.t., temporal fossa; 1.1., lateral lamina of pterygoid 
process; l.m., medial lamina; m.a.e., osseous portion of external acoustic 
meatus; p.a., alveolar process of maxilla; p.e., ethmoidal portion of orbitos- 
phenoid; p.f., frontal process of premaxilla; p.j., jugular process of occipital; 
p.m., mastoid process of mastoid; p.mx., maxillary process of frontal; p.o., 
orbital process of maxilla; p.o.e., external occipital protuberance; p.s., squa- 
mosal process of parietal; p.s.a. and p.s.p., anterior and posterior supraorbital 
processes of frontal; p.z., zygomatic process of squamosal; p.z.m., zygomatic 
process of maxilla; s, sphenoorbital process of maxilla; s.m., spina masseterica; 
sq., squamosal process of squamosal. 
The ventral wall of the cranial portion is the basal part (basi- 
cranium) of the entire skull. Its axial line, the basicranial axis, 
continues, in general, that of the bodies of the vertebrae, and its 
posterior portion is equivalent, morphologically, to vertebral seg- 
ments. It is formed by a linear series of three bones, namely, 
from back to front, the basilar portion of the occipital, the body 
of the posterior sphenoid, and that of the anterior sphenoid 
(respectively basioccipital, basisphenoid, and presphenoid 
bones). Its extremely narrow, anterior portion forms the roof of 
a deep groove which encloses the nasal portion of the pharynx. The Skull as a Whole 
143 
As viewed from the ventral surface, it is seen to disappear in the 
facial complex at some distance dorsal to the posterior margin of 
the bony palatine bridge. Laterally, it is separated from the orbit 
on either side by a vertical plate formed by the palatine bone, and 
also by two downward projections of the posterior sphenoid, the 
medial and lateral laminae of the pterygoid process (processus 
pterygoideus). These structures enclose between them the 
pterygoid fossa (fossa pterygoidea), the walls of which serve for 
the attachment of the external and internal pterygoid muscles 
of the mandible. 
The lateral wall of the cranial portion of the skull forms anteri- 
orly a large part of the boundary of the orbit. The components 
which do this are two upward projections of the basicranium, 
namely, the lesser or orbital wing of the anterior sphenoid, or 
orbitosphenoid and the greater or temporal wing of the pos- 
terior sphenoid, or alisphenoid, and two membrane elements, 
the frontal bone of the roof of the skull and the squamosal bone. 
The latter is distinguishable as the support of the posterior root 
of the zygomatic arch, which projects outward and then downward 
immediately behind the orbit. This root is formed by a zygomatic 
process (processus zygomaticus) of the squamosal bone, the tip 
of which process forms a vertical plate, united by a horizontal 
suture with the zygomatic bone. On the ventral side of the 
process, close to the cranial wall, is the glenoid cavity or man- 
dibular fossa (fossa mandibularis), for articulation with the 
mandible. On its dorsal side, but more especially on the adjacent 
portion of the cranial wall, there is a shallow, horizontal groove, 
lodging in the natural condition the temporalis muscle of the 
mandible, and therefore representing a greatly reduced temporal 
fossa (fossa temporalis). In the natural condition the anterior 
portion of the groove is converted into a foramen through the 
presence of a stout ligament extending from the posterior supra- 
orbital process to the base of the zygomatic arch. The dorsal 
boundary of the fossa is formed by a pronounced ridge, the tem- 
poral line (linea temporalis), the latter forming also the lateral 
margin of the roof of the skull in this region. 
Behind the posterior root of the zygomatic arch, the external 
surface of the lateral wall is largely occupied by the swollen tym- 144 
Anatomy of the Rabbit 
panic bulla (bulla tympani), formed by the tympanic bone. It con- 
tains the capacious tympanic cavity (cavum tympani) and encloses 
the three small bones of the 
middle ear, the auditory 
ossicles (ossicula auditus), 
the relations of which are 
more fully dealt with below 
(p. 161). The dorsal portion 
of the tympanic bulla is con- 
tinuous with a short bony 
tube which opens at a short 
distance dorsally by a large 
oval aperture. This tube is 
part of a more extensive 
canal, the external acoustic 
meatus (meatus acusticus 
externus) which, in the nat- 
ural condition, leads down- 
ward through the base of the 
external ear to the tympanic 
membrane. The tympanic 
bulla is not exposed to the 
cranial cavity. It is applied 
closely to the external surface 
of the periotic or petro- 
mastoid bone (ospetrosum), 
which forms the lateral 
boundary of the cranial cavity, 
and contains the structures of 
the internal ear. The external 
or mastoid portion of this 
bone appears in the space en- 
closed between the tympanic bulla and the jugular process of the 
occipital bone, where it is readily distinguishable by its pitted ap- 
pearance. Its ventral portion bears a slender projection, lying 
parallel to the jugular process, the mastoid process (processus 
mastoideus) which is the point of insertion of one of the neck 
muscles (sternomastoid). 
Fig. 63. Dorsal surface of the skull: F, 
frontal; I, interparietal; L, lacrimal; M, maxilla; 
MS, mastoid portion of petrosal (petromastoid); 
N, nasal; P, parietal; SO, supraoccipital (squa- 
mous portion of occipital); SQ, squamosal; ZY, 
zygomatic. 
f.mx., maxillary fossa; f.t., temporal fossa; 
l.n.s., superior nuchal line; l.t., temporal line; 
p.f., frontal process of premaxilla; p.mx., 
maxillary process of frontal; p.o.e., external 
occipital protuberance; p.s.a. and p.s.p., an- 
terior and posterior supraorbital processes of 
frontal; p.sc., subcutaneous process of lacrimal; 
p.z., zygomatic process of squamosal; p.z.m., 
zygomatic process of maxilla; s.f., frontal spine; 
s.m., spina masseterica. The Skull as a Whole 
145 
A series of foramina, lying partly within the orbit, and extending 
thence posteriorly along the boundary between the lateral and 
ventral walls to the occiput, put the cranial cavity in communica- 
tion with the outside, and serve for the passage of nerves and vessels. 
The first and largest of these, the optic foramen (foramen opti- 
cum), occupies the middle portion of the orbit, and, in the natural 
condition, transmits the optic nerve. Following this is a vertical 
slit-like aperture-not to be confused with the perforations of the 
external lamina of the pterygoid process-the superior orbital 
fissure (fissura orbitalis superior). It represents both the superior 
orbital fissure of the normal mammalian skull and the foramen 
rotundum, and provides for the passage outward of the third, 
fourth, and sixth cranial nerves, together with the first and second 
divisions of the fifth. The lateral lamina of the pterygoid process 
presents three foramina, of which the largest, anterior, and medial 
one, the anterior sphenoidal foramen (alar canal), serves for the 
transmission of the internal maxillary artery, while the remaining 
two, the middle and posterior sphenoidal foramina, transmit 
muscular branches (masseterico temporal and pterygobuccinator) 
of the mandibular nerve. On the medial side of the base of the 
medial lamina of the pterygoid process there is a shallow longitu- 
dinal groove, representing the pterygoid canal (canalis ptery- 
goideus) of the human skull. This accommodates a nerve (the 
Vidian, from the facial and the sympathetic). Immediately in 
front of the tympanic bulla, on the ventral surface of the skull, an 
irregular aperture, the foramen lacerum, leads directly into the 
cranial cavity. It is incompletely divided into two parts by a 
slender bony splint. It contains, in addition to the foramen 
lacerum, which is ventral and transmits the internal carotid artery, 
the foramen ovale of the typical mammalian skull, which is the 
antero-dorsal part and serves to transmit the mandibular portion 
of the fifth nerve. Looking into the aperture from the front, it is 
seen to communicate not only with the cranial cavity, but also with 
two apertures in the anterior portion of the auditory complex. 
One of these-that toward the middle line-is the internal carotid 
foramen (foramen caroticum internum). It is the anterior end 
of a canal transmitting the internal carotid artery; the posterior 
end of this canal, the point at which the internal carotid artery 146 
Anatomy of the Rabbit 
enters the tympanic bone, or the external carotid foramen 
(foramen caroticum externum), being visible as a rounded aperture 
lying on the posteromedial surface of the tympanic bulla. The 
second, lateral aperture communicating with the foramen lacerum 
is that of the auditory (Eustachian) tube (tuba auditiva). It 
leads into the tympanic cavity, and in the natural condition the 
tube places this cavity in communication with the nasal portion 
of the pharynx. Associated with the mastoid process is a small 
aperture, the stylomastoid foramen (foramen stylomastoideum), 
the external opening of the facial canal, which serves for the passage 
of the facial nerve. A slit-like aperture, the jugular foramen 
(foramen jugulare), lies in the jugular fossa, between the posterior 
ventral margin of the tympanic bulla and the occipital condyle. 
It transmits the first portion of the internal jugular vein from the 
transverse sinus of the dura mater, and also the ninth, tenth, and 
eleventh cranial nerves. Finally, immediately in front of the dorsal 
portion of the condyle, the occipital segment is perforated by 
several small apertures together representing the hypoglossal 
canal (canalis hypoglossi), and serving for the transmission of the 
hypoglossal nerve. 
The roof of the cranial portion is largely formed by two pairs of 
thin membrane elements, the frontal and parietal bones. The 
former occupy a general position between the orbits, while the 
latter are interposed between the frontal bones and the occipital 
segment. A small portion of the roof is formed posteriorly, how- 
ever, by a small lozenge-shaped element, the interparietal bone, 
and by the shield-shaped projection, described above, which is part 
of the occipital bone. 
The facial portion of the skull is largely formed by the invest- 
ing bones of the upper jaw, palate, and mandible, but it encloses 
also the entire olfactory region of the primary skull, including the 
nasal fossae and associated turbinal bones. The upper jaw-the 
maxilla of the human skull-is formed of two primary, and, in the 
rabbit, separate, elements, the maxilla and premaxilla. They 
together form the greater portion of the facial region--in the adult 
condition also a large portion of the lateral walls of the nasal fossae 
-and bear in a ventrolateral position low alveolar processes 
(processus alveolares) for the sockets or alveoli of the incisor and The Skull as a Whole 
147 
cheek-teeth. The maxilla bears the anterior root of the zygomatic 
arch, the latter being formed partly by a short zygomatic process 
arising from its lateral surface, by the zygomatic or malar bone, 
which is fused with it, and by the corresponding zygomatic process 
of the squamosal bone, constituting the posterior root. The 
anterior root of the zygomatic arch is perforated by a deep narrow 
infraorbital canal (canalis infraorbitalis), which opens on the 
facial surface by a vertical slit-like aperture, the infraorbital 
foramen. It serves for the transmission of the infraorbital vessels 
and nerves from the orbit to the face. 
The ventral portion of the maxilla is associated with the pala- 
tine bone to form the hard palate (palatum durum). This 
structure is represented chiefly by a bony palatine bridge con- 
necting the two sides of the skull between the more anterior cheek- 
teeth. It forms a portion of the roof of the oral cavity and a por- 
tion of the floor of the nasal cavity. Immediately in front of it, 
the palatal surface is perforated by a pair of large incisive foramina 
(foramina incisiva), which are broadly open to the nasal fossae. 
A considerable portion of the anterior and dorsal wall of the 
orbit is formed by the facial complex. Dorsally, the roofing 
element of this region, the frontal bone, bears a curved lateral 
projection, the supraorbital process (processus supraorbitalis), 
which overhangs the orbit. Its narrower base expands into anterior 
and posterior tips, which lie parallel to the adjacent portion of the 
skull, and enclose with the latter corresponding anterior and 
posterior supraorbital incisures. Ligaments convert these 
incisures into foramina. The anterior wall of the orbit is formed 
in part by a loosely articulated element, the lacrimal bone, the 
lateral margin of which projects from the orbital rim as a blunt 
subcutaneous process (processus subcutaneus). This bone is 
frequently missing from the dried skull unless care has been taken 
to keep it in place. On the ventral side of its base is the orbital 
opening of the nasolacrimal canal (canalis nasolacrimalis), the 
bony enclosure of the nasolacrimal duct, which in the natural 
condition leads from the corneal surface of the eye to the anterior 
portion of the nasal fossa. A smaller projection forming the ventral 
boundary of the nasolacrimal aperture is the hamulus lacrimalis. 
Finally, in the ventral anterior angle of the orbit, the bases of the 148 
Anatomy of the Rabbit 
three posterior cheek-teeth encroach to a considerable extent on 
the orbital space. They are separated from the orbital wall by a 
deep infraorbital groove (sulcus infraorbitalis), which leads for- 
ward into the canal of the same name. They partly conceal two 
important apertures of this region, the orbital opening of the 
pterygopalatine canal (canalis pterygopalatinus), leading to the 
palatal surface, and the sphenopalatine foramen (foramen 
sphenopalatinum), leading to the nasal fossa. The pterygopalatine 
canal opens ventrally in the palato-maxillary suture of the hard 
palate by a rounded aperture, the greater palatine foramen 
(foramen palatinum majus). 
The nasal cavity (cavum nasi) is enclosed by the maxilla and 
premaxilla, with the assistance of paired roofing elements, the 
nasal bones. Apart from the incisive foramina, which are closed 
in the natural condition, the cavity is open at two points. Poste- 
riorly it communicates with the ventral surface of the skull by the 
choanae, which, in the rabbit, are incompletely divided. An- 
teriorly it opens to the outside by the piriform aperture (apertura 
piriformis). The cavity is divided into right and left portions, 
the nasal fossae. 
In a divided skull may be examined the space enclosed by the 
cranial portion, the cranial cavity (cavum cranii). Its form 
depends on that of the brain. It is divisible into three portions, 
known as the cranial fossae. The anterior cranial fossa (fossa 
cranii anterior) is a small division lodging in the natural condition 
the olfactory bulbs of the brain. The middle cranial fossa, 
the largest division of the cavity, accommodates the enlarged 
cerebral hemispheres. The posterior cranial fossa is a small 
division extending backward to the foramen magnum and contain- 
ing in the natural condition the cerebellum and related posterior 
portions of the brain. It is partly set off from the middle cranial 
fossa by a fold of the dura mater, the tentorium cerebelli, which 
projects inward from the dorsal and lateral walls of the skull. 
This fold is usually found adhering to the internal surface of the 
skull, unless the latter has been very thoroughly cleared, and in 
all cases its position is indicated by a low ridge of bone. The 
marked difference in diameter between the middle and posterior cra- 
nial fossae is accounted for by the great thickness of the auditory por- The Skull as a Whole 
149 
tion of the skull. The anterior surface of the periotic bone will be 
observed to form an extensive posterior wall for the middle 
cranial fossa. 
The floor of the middle and posterior cranial fossae is not 
smooth, like the external base of the skull, but presents 
in its anterior portion a pro- 
minent elevation, the sella 
turcica, which is borne on 
the body of the posterior 
sphenoid. The sella turcica 
contains a large central de- 
pression, the hypophyseal 
fossa (fossa hypophyseos), 
which in the natural condition 
lodges the hypophysis or 
pituitary body. The aper- 
ture of the fossa is partly 
enclosed laterally by a pair 
of pointed posterior clinoid 
processes (processus clinoidei 
posteriores), the tips of which 
are directed forward; and a 
corresponding pair of ante- 
rior clinoid processes lie at 
the anterior end of the fossa, 
with the tips directed back- 
ward. The posterior, and also 
dorsal wall of the fossa, de- 
scribed as the dorsum sellae, 
leads by an abrupt curve back- 
ward on to the floor of the 
posterior cranial fossa, the 
sloping portion of the floor, 
or clivus, supporting in the 
natural condition the pons and 
medulla oblongata. Toward 
the anterior end of the middle 
Fig. 64. Ventral surface of the skull: AS, alis- 
phenoid (ala magna); B, basioccipital (basilar 
portion of occipital); BS, basisphenoid (body of 
posterior sphenoid); EXO, exoccipital; M, 
maxilla; PL, palatine; PMX, premaxilla; PR, 
presphenoid (body of anterior sphenoid); SO, 
supraoccipital (squamous portion of occipital); 
SQ, squamosal; T, tympanic; ZY, zygomatic. 
ch, choana; c.hy., hypoglossal canal; c.o., 
occipital condyle; f.c.e., external carotid fora- 
men; f.in., incisive foramen; f.j., jugular fora- 
men; f.l., foramen lacerum; f.m., mandibular 
fossa; f.m.o., foramen magnum; f.p.m., greater 
palatine foramen; f.s.a., anterior sphenoidal 
foramen; m.a.e., osseous portion of external 
acoustic meatus; p.j., jugular process; p.o.e., 
external occipital protuberance; p.pl., palatine 
process of maxilla; p.pra., palatine process of 
premaxilla; p.pt., medial and lateral laminae of 
pterygoid process of posterior sphenoid; s.m., 
spina masseterica. 150 
Anatomy of the Rabbit 
cranial fossa, the lateral walls of the skull are greatly compressed, 
so that the anterior portion of the basicranium, especially the 
body of the anterior sphenoid, is largely excluded from the cranial 
cavity. The usually paired optic foramina are here confluent, 
there being a single aperture for the transmission of the optic 
nerves. The posterior ventral boundary of this aperture contains 
a broad groove, the sulcus chiasmatis, which in the intact 
animal lodges the optic chiasma. 
In the anterior cranial fossa the floor is largely formed by a 
perforated area, borne on the cribriform plate (lamina cribrosa) 
of the ethmoid bone, and serving for the transmission of the 
divided olfactory nerves. Its median portion projects slightly into 
the cranial fossa as a low ridge, the crista galli, which is interposed 
between the tips of the olfactory bulbs. 
In the ventrolateral portion of the cranial cavity may be found 
the internal openings of the foramina described above, namely, the 
superior orbital fissure, the foramen lacerum, the jugular foramen, 
and the hypoglossal canal. The superior orbital fissure is almost 
ventral in position to the foramen opticum, and is connected back- 
ward with the foramen lacerum by a broad groove, the sulcus 
sphenoidalis, which, in the natural condition, lodges the roots of 
the fifth nerve. This groove continues to the medial surface of the 
periotic bone, where it is bridged over by the tentorium cerebelli. 
On the lateral wall of the posterior cranial fossa, and enclosed 
by the compact, white, petrous portion of the periotic bone, 
is a series of three apertures leading into its substance. One of 
these, much larger than the remaining two, is the parafloccular 
fossa (fossa parafloccularis). It provides accommodation for the 
flocculus, a small stalked appendage of the cerebellum. Ventral 
to this fossa, and also somewhat in front of it, a thin ledge of bone 
extends over an oval opening, the internal aperture of the facial 
canal (canalis facialis), which serves for the transmission of the 
seventh cranial (facial) nerve. Immediately behind and below this 
aperture is the opening of the internal acoustic meatus (meatus 
acusticus internus) for the transmission of the eighth cranial 
(acoustic) nerve. The two apertures tend to be enclosed by a 
shallow bony ridge, largely formed by the projecting ledge described The Skull as a Whole 
151 
above, and resembling superficially the complete common tube 
represented by the internal acoustic meatus of the human skull. 
In the divided skull it is seen that the division of the nasal 
cavity into right and left fossae is effected chiefly through a median 
vertical, cartilaginous plate, the nasal septum (septum nasi), or 
cartilaginous portion of the mesethmoid. This is continuous 
posteriorly with a small crescentic vertical plate of bone, the 
perpendicular plate (lamina perpendicularis) of the ethmoid 
bone-the bony portion of the mesethmoid-and the latter is also 
Fig. 65. The skull in vertical section: BO, basioccipital (basilar portion of 
occipital); BS, basisphenoid (body of posterior sphenoid); ET, ethmoturbinal; 
F, frontal; I, interparietal; M, maxilla; MT, maxilloturbinal; N, nasal; NT, 
nasoturbin.J; P, parietal; PL, palatine; PMX, premaxilla; PR, presphenoid 
(body of anterior sphenoid); PT, petrous portion of petromastoid; SO, supra- 
occipital (squamous portion of occipital); T, tympanic; V, vomer. 
a.p., piriform aperture of nose; c.f., internal aperture of facial canal; c.o., 
occipital condyle; f.c.a., f.c.m., and f.c.p., anterior, middle, and posterior 
cranial fossae; f.f., parafloccular fossa; f.h., hypophyseal fossa; f.in., incisive 
foramen; f.s., sphenopalatine foramen; 1., perpendicular plate of the ethmoid; 
m.a.i., internal acoustic meatus; o., optic foramen; p.a., alveolar process of 
maxilla; p.d., hard palate; p.o.e., external occipital protuberance; p.pt., 
pterygoid process of posterior sphenoid; s.n., nasal septum; t.c., tentorium 
cerebelli. 
the terminal element of the series of median bones constituting the 
basicranium. Posteriorly, the ventral portion of the cartilaginous 
nasal septum is supported by a vertical bony plate, the vomer, 
the dorsal margin of which is grooved to receive it. Anteriorly, the 
nasal septum bears on its ventral margin the paired enclosures of 
the vomeronasal organ, which are also supported by the grooved 
surface formed in the middle line by the adjacent dorsal surfaces 
of the palatine processes of the premaxilla. The relations of these 
structures, as well as of the cartilage supporting the nasopalatine 
duct, are best seen in very young animals (cf. Plate III). 152 
Anatomy of the Rabbit 
The delicate, folded, or scroll-like turbinated bones, charac- 
teristic of the nasal cavity, are borne on its posterior and lateral 
walls. Occupying the anterior portion of the lateral wall of the 
nasal fossa is a finely-ridged mass of bone, the concha inferior, or 
maxilloturbinal. It is easily distinguishable from a more dorsal 
and posterior series of broader folds, which together constitute the 
ethmoturbinal. In the rabbit, as in mammals generally, the 
latter is divisible into a more dorsal elongated portion attached 
to the nasal bone, the nasoturbinal, and a more ventral portion, 
Fig. 66. Lateral surface of the left half of the mandible: a.m., angle; c.m., 
body of mandible; cp.m., articular portion (head) of mandible; d.i., d.m., and 
d.pm., incisor, molar, and premolar teeth; f.m., mental foramen; i.m.a. and 
i.m.p., anterior and posterior mandibular incisures; p.c., coronoid process; 
p.cd., ondyloid process; t.m. and t.pt., masseteric and pterygoid tuberosities. 
also posterior portion, the ethmoturbinal proper, composed of 
several shorter folds decreasing in length from above downward. 
In the natural condition the turbinated bones bear a considerable 
portion of the nasal epithelium, the surface of which is greatly 
increased by the folding of the underlying bone. That covering 
the ethmoturbinal contains the olfactory sense organs, while that 
covering the maxilloturbinal is non-sensory and possesses the 
mechanical function of freeing the air of the respiratory tracts from 
foreign materials, as well as of warming it slightly in its passage. 
On this account the respective structures are conveniently distin- 
guished as sensory (olfactory) turbinals and respiratory 
turbinals. 
The mandible (mandibula) is composed of two portions, 
united anteriorly by the symphysis mandibulae. Each half The Bones of the Skull 
153 
comprises a horizontal portion, forming in conjunction with that 
of the opposite side the body of the mandible (corpus mandibulae), 
and a posterior, vertical portion, the ramus mandibulae, the 
latter serving for the insertion of the muscles of mastication and for 
articulation with the skull. The body of the mandible bears on its 
dorsal margin the alveoli of the lower teeth. The mandibular 
ramus forms a broad plate, the lateral surface of which is occupied 
in the intact animal by the masseter muscle, while the medial 
surface forms an area of insertion for the external and internal 
pterygoids. The surface of the ramus is greatly increased in its 
posteroventral portion through the expansion of the bone to form 
the angle (angulus mandibulae), or angular apophysis. The 
elongated articular surface is borne at the end of a vertical, or 
slightly oblique, condyloid process (processus condyloideus). 
The nerve and vessels of the mandible enter at the mandibular 
foramen (foramen mandibulare), the latter being situated on the 
medial surface of the bone immediately behind the last cheek-tooth. 
B. The Bones of the Skull 
1. The Occipital Bone 
The occipital bone (os occipitale) is the first of the basicranial 
segments as numbered from the occipital articulation forward. 
It forms the posterior boundary of the skull, and establishes the 
connection of the latter with the vertebral column. Its external 
surface is identifiable for the most part with the nuchal surface, 
but a portion of it falls in the horizontal plane of the basis cranii. 
The internal surface is partly exposed to the cranial cavity, and 
forms the posterior, dorsal, and ventral boundaries of the posterior 
cranial fossa. The remaining portion is excluded from the cranial 
cavity, being applied instead to the broad posterior surfaces of the 
petrotympanic bones. 
The occipital bone is divisible into four portions, namely, the 
basilar portion (pars basilaris) or basioccipital, the paired 
lateral portions (partes laterales), or exoccipitals, and the 
squamous portion (squama occipitalis), or supraoccipital. 
All four portions take part in the formation of the foramen magnum. 
In the young animal (Fig. 23) they are represented by separate 154 
Anatomy of the Rabbit 
elements, formed in a continuous mass of cartilage, and united 
for a time by synchondroses, but in the course of growth they 
become fused to form a single occipital bone. 
The basioccipital is that portion lying below and in front of 
the foramen magnum. Its main surfaces are respectively dorsal 
and ventral. Its anterior margin is united with the posterior 
margin of the basisphenoid by a thin, transverse cartilage union, 
the sphenooccipital synchondrosis (synchondrosis spheno- 
occipitalis). Posteriorly its dorsal and ventral surfaces come 
together in a thin concave edge which forms the ventral boundary 
of the foramen magnum. Laterally it is bounded by the petro- 
tympanic bone and by the lateral portion of the occipital. The 
dorsal surface bears a median groove, deeper in its middle portion, 
where the lateral margins of the bone are raised to form a pair 
of rounded bosses for articulation with the petrotympanic. The 
groove represents the sloping portion or clivus of the occipital, and 
lodges in the natural condition, as described above, the ventral 
portion of the medulla oblongata. The ventral surface presents 
a similar groove, in the posterior portion of which there is a small 
ridge-like elevation, the pharyngeal tubercle (tuberculum 
pharyngeum). 
The exoccipital is directed dorsad from the basioccipital in 
such a way that it falls in the plane of the nuchal surface. It is 
applied to the posterior surface of the petrotympanic bone, and 
also extends downward beyond the latter as the jugular process. 
The occipital condyle is borne on the exoccipital, with the exception, 
however, of its ventral tip, which belongs to the basioccipital. 
The portion of the occipital bone connecting the basioccipital and 
exoccipital contains the jugular fossa and the apertures repre- 
senting the hypoglossal canal. Its anterior margin bears a 
jugular incisure (incisura jugularis), forming the occipital 
boundary of the jugular foramen, the remaining portion of the 
latter being formed by the petrotympanic. 
The supraoccipital is the dorsal portion of the bone. Its 
dorsal margin is bent sharply forward, so that it tends to fall, like 
the basioccipital, in a horizontal plane. Its external surface bears 
the nuchal crest and the external occipital protuberance. 
A pair of lateral wing-like expansions rest upon, and partly over- The Bones of the Skull 
155 
lap, the dorsal margins of the petrotympanic bones. The anterior 
boundary is formed by the interparietal, parietal, and squamosal 
bones, but in young skulls the squamosal connection is represented 
by a vacuity. The internal surface bears a median longitudinal 
groove, lodging in the natural condition the vermis of the cerebellum. 
It is crossed at its anterior end by a shallow transverse groove 
(sulcus transversus), which marks the position of the transverse 
sinus of the dura mater. 
2. The Posterior Sphenoid 
The sphenoid bone, as identified from the human condition, 
is a complex of elements belonging to two segments, namely, the 
posterior sphenoid (os sphenoidale posterius) and the anterior 
sphenoid (os sphenoidale anterius). In the rabbit, as in mammals 
generally, these segments are separate throughout life. 
The posterior sphenoid comprises: (1) a median portion, the 
body, or basisphenoid; (2) paired dorsolateral expansions, the 
greater wings (alae magnae), or alisphenoids; and (3) paired 
ventral projections, the pterygoid processes. 
The basisphenoid continues the basis cranii forward from the 
basioccipital to the body of the anterior sphenoid. It is united 
with the latter by the intersphenoidal synchondrosis. Its 
surfaces correspond for the most part to those of the basioccipital. 
The ventral surface forms the chief part of the bony roof of the 
nasopharynx. It is perforated in its middle by a round aperture, 
the foramen cavernosum, which leads into the interior of the 
bone. The dorsal surface is occupied by the hypophyseal fossa 
and related structures, namely, the dorsum sellae and the pos- 
terior clinoid processes. On the lateral surface of the base of 
the posterior clinoid process a faint groove, the sulcus caroticus, 
marks the course of the internal carotid artery. The interior of the 
bone contains a cavity of considerable size, the sphenoidal sinus 
(sinus sphenoidalis), which communicates with both the foramen 
cavernosum and the hypophyseal fossa. 
The alisphenoid extends laterad at first, but soon changes its 
direction so that its axis becomes dorsoventral. At the same time 
the bone is rotated in such a way that its surfaces tend to fall in a 
transverse plane. It is bounded anteriorly by the orbitosphenoid, 156 
Anatomy of the Rabbit 
dorsally by the squamosal, and posteriorly by the petrotympanic. 
The anterior margin of its root along with the basisphenoid, and 
to a certain extent with the orbitosphenoid, encloses the superior 
orbital fissure. The foramen lacerum is formed by the pos- 
terior margin of its root in association with the petrotympanic. 
The external surface of the alisphenoid is convex, both toward 
the orbit and toward the ventral surface of the skull. In the 
posterior portion of the orbit this surface bears a jagged elevation, 
the crista alae magnae. The internal surface forms a portion 
of the floor and anteroventral wall of the middle cranial fossa. 
At its base a broad groove, the sulcus sphenoidalis, indicates 
the position of the root of the fifth nerve and the related semilunar 
(Gasserian) ganglion. 
The pterygoid process comprises the two plates described 
above as the medial and lateral laminae. The former is vertical, 
and its medial surface is directed toward the nasopharynx. The 
latter is almost horizontal. The medial lamina ends ventrally in a 
hooked projection, the hamular process (hamulus pterygoideus). 
In the young animal this portion is formed of an elevation of 
cartilage tipped by a separate membrane element, the pterygoid 
bone. The pterygoid fossa is formed in part by the medial and 
lateral laminae and in part by the divided posterior end of the 
palatine bone. The posterior basal portion of the lateral lamina is 
extensively excavated, like the adjacent portions of the alisphenoid. 
It bears a shallow groove, representing a pterygoid canal (canalis 
pterygoideus), and is perforated by the three apertures described 
above as the anterior, middle, and posterior sphenoidal 
foramina. 
3. The Anterior Sphenoid 
The anterior sphenoid (os sphenoidale anterius) consists of 
two portions, namely, a median portion, the body, or presphenoid, 
and a pair of lateral expansions, the lesser wings (alae parvae), or 
orbitosphenoids. 
The presphenoid is a constricted bony splint which continues 
the basis cranii forward from the basisphenoid. It is joined 
anteriorly with the perpendicular plate of the ethmoid and with the 
cartilaginous nasal septum. In the divided skull, or better in one 
from which the roof has been removed, the actual dorsal surface The Bones of the Skull 
157 
of the bone is seen to be exposed to the cranial cavity only in its 
posterior portion, where it is occupied by the sulcus chiasmatis 
and the optic foramina. That part of the floor immediately in 
front of the optic foramina is formed by the coalesced roots of the 
orbitosphenoids, the dorsal surface of the presphenoid being thus 
excluded. 
The orbitosphenoid forms a long, low plate, lying in the 
ventral portion of the orbit, and divided by a shallow notch at the 
level of the optic foramen into a posterior portion, the orbito- 
sphenoid proper, and an anterior portion, the ethmoidal process 
(processus ethmoidalis). The orbitosphenoid proper lies behind 
the optic foramen. It is in contact dorsally with the orbital portion 
of the frontal, and ventrally with the alisphenoid; it assists the 
latter in the formation of the superior orbital fissure. Its posterior 
tip is in contact with the squamosal. Its internal surface forms a 
considerable portion of the anteroventral wall of the middle cranial 
fossa. 
The ethmoidal process extends forward from the optic fora- 
men. Its dorsal margin is articulated with the orbital portion of 
the frontal, and its ventral margin with the orbital portion of the 
palatine. Anteriorly it projects toward the lacrimal bone, thus 
occupying, in part, a space which, in the typical mammalian skull, 
is filled by the lamina papyracea of the ethmoid. Its internal 
surface is associated with the ethmoid bone and with the nasal 
cavity. It falls for the most part below the level of the cranial 
cavity. 
4. The Squamosal Bone 
The temporal bone, or temporal complex, as recognized 
from the human condition, is an association of three elements- 
squamosal, tympanic, and periotic-which in the human skull 
are coalesced to form a single bone. It is usually described as 
consisting of four portions, of which the squamosal and tympanic 
portions are two, while the periotic bone is considered to consist 
of two others, one of which, the petrous portion, is a solid white 
portion lodging the internal ear, while the second, or mastoid 
portion, is a mass of less compact character appearing externally 
in the wall of the skull. In the rabbit the original elements are not 
coalesced, but the periotic and tympanic bones are so closely 158 
Anatomy of the Rabbit 
associated that it is proper to describe them as forming a petro- 
tympanic bone. 
The squamosal bone (os squamosum) is a rectangular plate, 
forming part of the lateral wall of the cranium, and bearing the 
posterior root of the zygomatic arch. It is articulated anteriorly 
with the orbitosphenoid and with the orbital portion of the frontal, 
dorsally with the frontal and parietal, posteriorly with the supra- 
occipital and petrotympanic, and ventrally with the alisphenoid. 
Its posterior margin bears a prominent, slightly decurved squa- 
mosal process (processus squamosus). It lies on the lateral 
surface of the petrotympanic immediately above the opening of the 
bony external acoustic meatus. The posterior root of the zygo- 
matic arch is formed by a lateral and afterwards ventral projection, 
the zygomatic process of the squamosal. The base of this 
process bears ventrally the mandibular fossa, and dorsally, in 
association with the body of the squamosal, the temporal fossa. 
The internal surface of the squamosal forms a considerable portion 
of the wall of the cranial cavity, the middle cranial cavity being, 
in fact, broadest in this region. 
5. The Petrotympanic Bone 
The petrotympanic bone (os petrotympanicum) is a some- 
what oblong bone lying in the lateral wall of the cranium between 
the posterior sphenoid and occipital bones. It is chiefly indicated 
externally by the tympanic bulla and the bony external acoustic 
meatus. It is articulated anteriorly with the alisphenoid and 
squamosal, dorsally with the supraoccipital, and posteriorly with 
the exoccipital. Except for the presence of the squamosal process 
of the squamosal bone, the lateral and ventral surfaces are exposed 
to the outside of the skull. The internal surface is exposed to the 
posterior cranial fossa, with the exception, however, of a small 
ventral portion which is articulated with the basioccipital bone. 
Only a small portion of the anterior surface is in contact with the 
squamosal bone, the larger part being applied to the tentorium 
cerebelli and forming with the latter a posterior wall for the middle 
cranial fossa. The dorsal portion of the bone corresponds in thick- 
ness with the wing of the supraoccipital with which it is articulated. 
The posterior surface is applied to the anterior surface of the The Bones of the Skull 
159 
exoccipital, and is thus excluded both from the cranial cavity and 
from the external surface of the skull. Viewing the skull from 
behind, however, it is seen that a small dorsal portion protrudes 
in a triangular space formed by the dorsolateral margin of the 
exoccipital and the ventrolateral margin of the supraoccipital wing. 
This portion is distinguishable by its pitted character. It forms 
the mastoid portion (pars mastoidea) as distinguished from the 
solid white petrous portion (pars petrosa), which is exposed to 
the cranial cavity, and which contains the structures of the internal 
ear. The mastoid portion lies for the most part above the tympanic 
cavity, but it is also continued ventrad between the external 
acoustic meatus and the exoccipital as the mastoid process. 
The stylomastoid foramen lies between the latter and the ex- 
ternal acoustic meatus. 
The petrous portion, as viewed from its medial surface, is 
roughly oblong; it is placed obliquely with reference to the basi- 
occipital and basisphenoid. The parafloccular fossa occupies its 
posterodorsal portion, and extends into the substance of the bone, 
forming a much larger depression than is indicated by the diameter 
of its rim. The related dorsal margin of the bone is occupied by a 
groove which leads into a canal at its posterior margin. It indicates 
the position of the lateral portion of the transverse sinus of the dura 
mater. The ventral, thicker portion of the bone, enclosing the 
apertures of the internal acoustic meatus and the facial canal, 
is also that lodging the vestibulum and cochlea of the internal ear. 
A small aperture at its anteroventral angle, only visible when the 
petrotympanic is freed from its connections, represents the hiatus 
canalis facialis of the human skull. It transmits the great super- 
ficial petrosal nerve, a branch of the facial nerve passing to the 
sphenopalatine ganglion. 
The tympanic surface of the petrous portion is described below 
in connection with the structures of the tympanic cavity. 
The tympanic portion forms the spherical, expanded, shell- 
like, tympanic bulla, which contains in its interior the tympanic 
cavity, and is continuous dorsally with the bony enclosure of the 
external acoustic meatus. The boundary between the two is 
indicated externally by a shallow oblique groove, the position of 
which indicates roughly that of the tympanic membrane within. 160 
Anatomy of the Rabbit 
The medioventral margin of the bone is articulated with the basi- 
occipital, but the swollen portion is separated from the latter by a 
broad groove terminating posteriorly in the jugular fossa and the 
jugular foramen. Immediately in front of the jugular fossa, the 
rounded aperture of the external carotid foramen, transmitting 
in the natural condition the internal carotid artery, leads into the 
carotid canal of the interior 
of tympanic portion. At the 
anterior end of the groove, 
communicating with the fora- 
men lacerum, is the anterior 
opening of the carotid canal, 
the internal carotid foramen, 
and on its lateral side the much 
larger aperture of the auditory 
(Eustachian) tube. The rela- 
tions of these apertures are seen 
to best advantage when the 
petrotympanic is disarticulated 
from the associated posterior 
sphenoid bone. The auditory 
tube is then seen to lead directly 
into the tympanic cavity. A 
fine bristle may be passed 
through the carotid canal from 
one foramen to the other. 
6. The Structures of the Tympanic Cavity 
The relations of the tympanic cavity and associated structures 
may be studied with advantage in a skull from which the lateral 
wall of the tympanic bulla and external acoustic meatus has been 
removed, the surface displayed being as indicated in Fig. 67. 
The tympanum or middle ear is enclosed by the tympanic and 
petromastoid portions of the temporal complex. The attached 
margin of the tympanic bulla encloses a roughly triangular area, 
into the ventral part of which the petrous portion of the petro- 
mastoid projects as a smooth, white, convex ridge, the promontory 
Fig. 67. Petrotympanic portion of the 
auditory complex of the left side X 3. The 
lateral portions of the tympanic bulla and 
external acoustic meatus have been removed, 
exposing the structures of the tympanic 
cavity. MS, mastoid portion; P, petrous 
portion; T, tympanic portion (bulla tym- 
pani). c.m., mastoid cells; c.t., tympanic 
cavity; f.c., cochlear fenestra; in., incus; 
m.a.e., external acoustic meatus; m.m., 
manubrium of the malleus; m.so., supra- 
occipital margin of petromastoid; p.m., 
mastoid process; st., stapes; t.a., aperture of 
auditory tube. The Bones of the Skull 
161 
(promontorium). Above and behind the promontory the tympanic 
cavity is extended toward the mastoid portion of the bone as the 
tympanic or mastoid antrum (antrum tympanicum), and the 
interior of the mastoid portion is partly occupied by small extensions 
of the tympanic antrum, termed the mastoid cells (cellulae 
mastoideae). At the anteroventral angle of the area already 
described, a deep notch indicates the point of entrance of the 
auditory tube. The exposed surface of the petromastoid presents 
two apertures, one of which, situated posteroventrally, is open in 
the dried skull, and is the cochlear fenestra (fenestra cochleae). 
In the natural condition it is closed by a thin membrane which 
separates the tympanic cavity from the perilymphatic space con- 
taining the membranous labyrinth. The second aperture, the 
vestibular fenestra (fenestra vestibuli), lies above and in front 
of that just described. It is closed by the base of the stapes. 
The auditory ossicles (ossicula auditus) comprise three ele- 
ments, namely, the malleus, incus, and stapes, which bridge the 
space intervening between the tympanic membrane and the opening 
to the internal ear as represented by the vestibular fenestra. They 
occupy the dorsal angle of the triangular area already described, 
and lie immediately above the promontory. The malleus is the 
lateral element. The main portion, termed the head, is concealed 
by the projecting edge of the external acoustic meatus. It bears 
a stout vertical process, the manubrium mallei, which in the 
natural condition lies in contact with the tympanic membrane. 
The incus is the intermediate element; it is directly articulated 
with the malleus, and bears a downwardly-directed long limb 
(crus longum), for articulation with the minute head of the stapes. 
The latter element is a small stirrup-shaped bone, occupying an 
almost transverse position, and articulated at its base with the 
margin of the vestibular fenestra. 
7. The Interparietal Bone 
The interparietal (os interparietale) is a small, lozenge-shaped 
element, surrounded by the two parietal bones and the supra- 
occipital. It is the first of the membrane roofing elements of the 
cranium proceeding forward from the supraoccipital, and in the 
rabbit's skull is not fused with the occipital segment as it is in man. 162 
Anatomy of the Rabbit 
8. The Parietal Bone 
The parietal bone (os parietale) is a characteristic roofing bone 
covering a large portion of the middle cranial fossa. It is somewhat 
rectangular in shape, and is connected by serrate sutures with the 
surrounding elements and with its fellow of the opposite side, the 
sutures producing a characteristic pattern on the external surface 
of the skull. The sutures are medial, anterior, lateral, and posterior 
in position, and are designated respectively as sagittal, coronal, 
squamosal, and lambdoidal. The posterolateral angle of the 
bone is produced ventrally into a long, curved squamous process 
(processus squamosus), which lies in the angle formed by the ten- 
torium cerebelli and the lateral wall of the middle cranial fossa. 
It is not exposed to the external surface of the skull. 
9. The Frontal Bone 
The frontal bone (os frontale) is a paired element, lying 
directly in front of the parietal, and forming with its fellow of the 
opposite side the anterior portion of the roof of the cranial cavity 
and also a considerable portion of its lateral, orbital wall. Unlike 
the condition in the human skull, the two bones are separate 
throughout life, so that there is a permanent frontal suture. 
Each consists of a frontal portion (pars frontalis), the external or 
dorsal surface of which continues that of the parietal, and of an 
orbital portion (pars orbitalis), enclosing the dorsal part of the 
orbit. The two parts are connected at the supraorbital border, 
with which is also connected the base of the divided supraorbital 
process. The anterior end of the frontal portion is deeply notched 
where it comes in contact with the nasal and premaxillary bones. 
Two processes are thus formed, one medial, the other lateral to the 
nasal. The medial process is associated with that of the opposite 
side to form a triangular frontal spine, while the lateral or max- 
illary process (processus maxillaris) projects forward between the 
nasal and premaxillary bones, on the one hand, and the subcutaneous 
process of the lacrimal, the orbital process of the maxilla, and the 
body of the latter, on the other. 
The orbital portion of the frontal forms a considerable portion 
of the orbital wall. Its anterior margin is in contact with the 
lacrimal bone, its ventral margin with the slender sphenoorbital The Bones of the Skull 
163 
process of the maxilla, the ethmoid process of the orbitosphenoid, 
and the orbitosphenoid proper. Its internal surface is divided by a 
vertical ridge into anterior and posterior portions, in relation 
respectively to the anterior and middle cranial fossae. The anterior 
cranial fossa is enclosed by the frontal bones, with the exception, 
however, of a small portion of the floor which is formed by the 
cribriform plate of the ethmoid. 
10. The Ethmoid Bone 
The ethmoid bone (os ethmoidale), the chief representative of 
the embryonic cartilaginous nasal capsule, is a delicate, greatly 
sculptured structure, almost completely enclosed by the membrane 
bones of the face. Its features may be studied either in the divided 
skull, or in one from which the roof of the nasal and cranial cavities 
has been removed. It consists of three main portions, namely, the 
cribriform plate, the perpendicular plate, and the paired 
lateral masses or ethmoidal labyrinths. 
The cribriform plate (lamina cribrosa) is exposed to the 
anterior cranial fossa. It is somewhat heart-shaped, with its apex 
in contact with the ethmoidal processes of the orbitosphenoids. 
Its lateral portions are perforated by numerous foramina, giving 
passage in the natural condition to the branches of the olfactory 
nerves. Its median portion forms a low vertical ridge, the crista 
galli, continuous in front with the perpendicular plate. 
The perpendicular plate (lamina perpendicularis) is the bony, 
posterior portion of the nasal septum, and as such is exposed to the 
nasal cavity. It is united with the cartilaginous nasal septum and 
also with the presphenoid. It forms the terminal member of the 
chain of bones lying in the basicranial axis. 
The ethmoidal labyrinth (labyrinthus ethmoidalis) occupies 
for the most part the posterior portion of the nasal fossa, but the 
nasoturbinal extends forward to its anterior end, and is attached 
for the greater part of its length to the internal surface of the nasal 
bone. It is broadest in its middle portion, where it projects into 
the space left between the ethmoturbinal proper and the maxillo- 
turbinal, and contains at this point a pouch-like cavity, termed the 
marsupium nasale. The whole structure is comparable to one 
of the folds of the ethmoturbinal proper; but it is frequently seen 164 
Anatomy of the Rabbit 
to be divided into anterior and posterior parts by a thin vertical 
line of cartilage, the anterior division being probably allied to the 
maxilloturbinal. Its middle, ventral portion bears a stout, back- 
wardly-directed uncinate process (processus uncinatus), which 
is applied to the medial surface of the maxilla. 
The ethmoturbinal proper consists, as described above, of 
several shorter scrolls, decreasing in length from above downward. 
Like the posterior part of the nasoturbinal, they are attached 
directly to the cribriform plate, the perforations of which may be 
seen in the divided skull opening into the ethmoidal scrolls 
or spaces contained by them. They are roughly comparable to the 
superior and middle turbinated bones of the human skull, but in 
the rabbit, as in most mammals, the ethmoturbinal surfaces are 
relatively much more extensive than in man. 
In the typical mammalian skull the ethmoid bone is exposed 
to the orbit, where it forms a thin plate of bone, the lamina 
papyracea. In the rabbit, however, the space usually occupied 
by the lamina papyracea is partly filled by the lacrimal bone, the 
ethmoidal process of the orbitosphenoid, and the sphenoorbital 
process of the maxilla. 
11. The Inferior Turbinated Bone 
The inferior turbinated bone (concha nasalis inferior), or 
maxilloturbinal, is a finely ridged structure, situated anteriorly 
in the nasal fossa, and supported by the maxilla and premaxilla. 
It represents the similarly-named structure of the human skull, the 
lowermost of three scroll-like bones, of which the remaining two, 
the superior and middle turbinated bones, belong to the ethmo- 
turbinal. In the natural condition it is covered by a non-olfactory 
epithelium, and is thus distinguishable in function as well as in 
position from the latter. 
12. The Maxilla 
The maxilla, the largest element of the facial region, is asso- 
ciated with its fellow of the opposite side to form the main portion 
of the upper jaw. It consists of a central portion, the body (corpus 
maxillae), and of five processes, namely, alveolar, palatine, 
orbital, zygomatic, and sphenoorbital. In the adult condition The Bones of the Skull 
165 
the zygomatic bone is fused with the maxilla, so that the extent of 
the zygomatic process appears to be greatly increased. 
The body of the maxilla is greatly fenestrated on its external 
surface, the perforated area extending backward to the anterior 
rim of the orbit, and thus including the maxillary fossa and the 
infraorbital foramen. The dorsal boundary of the bone is 
formed by the frontal process of the premaxilla and by the maxillary 
process of the frontal. Anteriorly, it is united with the premaxilla, 
the ventral part of the suture appearing in the diastema separating 
the incisors from the cheek-teeth. The ventral portion of the bone 
forms part of the lateral boundary of the incisive foramen. 
Behind the palatine bridge it is applied to the lateral surface of the 
palatine bone, and is projected into the orbit as a broad ridge en- 
closing the alveoli of the four posterior cheek-teeth. 
In the divided skull the medial surface of the body of the maxilla 
is found to be concealed by the ethmoturbinal. It contains a deep 
longitudinal excavation, the maxillary sinus (sinus maxillaris), 
widely open to the nasal fossa, but only seen to advantage when the 
ethmoturbinal is removed. The lateral wall of the sinus corres- 
ponds in position to the fenestrated area of the external surface. 
It bears the chief part of the nasolacrimal canal. 
The alveolar process (processus alveolaris) is that portion of 
the maxilla lodging the sockets of the cheek-teeth. In the rabbit 
it is separated by the diastema, in which no teeth occur, from a 
corresponding but imperfectly differentiated process of the pre- 
maxilla. 
The palatine process (processus palatinus) extends toward 
the median plane. It forms with its fellow of the opposite side 
about two-thirds of the palatine bridge. 
The orbital process (processus orbitalis) is directed obliquely 
toward the dorsal surface of the skull. In conjunction with the 
lacrimal bone and the maxillary process of the frontal, it forms the 
anterior orbital rim. It is continuous with the fenestrated portion 
of the body, and its appearance as a process is largely due to its 
solid character as compared with the perforated surface lying in 
front of it. 
The zygomatic process (processus zygomaticus) forms the 
anterior root of the zygomatic arch, and in the adult condition 166 
Anatomy of the Rabbit 
is fused with the anterior end of the zygomatic bone. Its ventral 
angle bears a prominent masseteric spine for the attachment 
of the ligament of the masseter muscle. 
The sphenoorbital process (processus sphenoorbitalis) lies 
on the medial wall of the orbit, in a position opposite to the middle 
portion of the ridge lodging the posterior cheek-teeth. It forms a 
stout buttress, the tip of which is applied to the anteroventral 
angle of the frontal bone. In this position it is visible from the 
orbit, lying between the lacrimal bone and the ethmoidal process 
of the orbitosphenoid. 
13. The Premaxilla 
The premaxilla or incisive bone (os incisivum) forms the 
anterior portion of the upper jaw. It comprises a central portion, 
the body-including with the latter the scarcely differentiated 
alveolar portion containing the large and small incisors-a 
frontal process, and a palatine process. The body forms a 
portion of the palatal surface of the skull and of the lateral bound- 
ary of the incisive foramen. Its dorsal surface forms part of the 
boundary of the piriform aperture, the remaining portion of this 
being formed by the nasal bone. The palatine process extends 
backward on the medial side of the bone, closely applied on the 
palatal surface to its fellow of the opposite side, and forms in this 
way a medial boundary for the incisive foramen. Its dorsal surface, 
in conjunction with that of the corresponding process of the other 
side, bears a broad palatine groove (sulcus palatinus), lodging a 
portion of the cartilage of the vomeronasal organ and nasopalatine 
duct. The frontal process (processus frontalis) is a thin bony 
splint, extending backward between the nasal and maxillary bones, 
and terminating between the former and the maxillary process of 
the frontal. 
14. The Zygomatic Bone 
The zygomatic bone (os zygomaticum) is a separate element 
only in very young animals. In the adult it is fused anteriorly 
with the zygomatic process of the maxilla, the position of the 
original suture being roughly identifiable as the point where the free 
horizontal portion of the zygomatic arch arises from the transverse 
zygomatic process. It forms an almost sagittal plate of bone The Bones of the Skull 
167 
bridging the orbit and serving for the attachment of the masseter 
muscle of the mandible. Its dorsal margin forms posteriorly 
a smooth, horizontal articulation with the zygomatic process of the 
squamosal, the end of the bone projecting considerably behind 
the articulation. 
15. The Nasal Bone 
The nasal bone (os nasale) is a thin, elongated bone forming 
the roof of the nasal fossa, and, in conjunction with its fellow of the 
opposite side, the dorsal boundary of the piriform aperture. It is 
loosely articulated with the maxilla and with the bone of the 
opposite side by smooth (harmonic) sutures. The medial margin 
is supported by the dorsal edge of the nasal septum. The internal 
surface bears the nasoturbinal scroll. 
16. The Vomer 
The vomer is the median, somewhat sickle-shaped, vertical 
plate of bone separating the ventral portions of the nasal fossae. 
It is visible from the palatal surface through the incisive foramina, 
but its extent is best shown in the divided skull. It forms a 
support for the ventral border of the nasal septum, and its pos- 
terior portion bears a shelf-like projection, the ala vomeris, which 
assists in the support of the ethmoturbinal. 
17. The Lacrimal Bone 
The lacrimal bone (os lacrimale) is a small element lying in the 
anterior wall of the orbit. It is loosely articulated with the sur- 
rounding bones. It consists of a basal portion, somewhat rectan- 
gular on its orbital surface, and of two processes, namely, the 
subcutaneous process and the hamulus lacrimalis. The sub- 
cutaneous process is the prominent hook-like projection extending 
laterad beyond the orbital rim. The hamulus lacrimalis is a small 
process, directed toward the nasal cavity. It bears a groove which, 
in association with a corresponding groove of the maxillary bone, 
forms the first portion of the nasolacrimal canal. 
18. The Palatine Bone 
The palatine bone (os palatinum) forms the posterior portion 
of the palatine bridge and the major portion of the lateral wall of the 168 
Anatomy of the Rabbit 
nasopharynx. It consists of two portions-horizontal and 
perpendicular. The horizontal portion (pars horizontalis) is 
that lying in the plane of the palatal surface. It is articulated 
in front with the palatine process of the maxilla, the suture be- 
tween the two bones enclosing the greater palatine foramen, the 
ventral termination of the pterygopalatine canal. The perpen- 
dicular portion (pars perpendicularis) is the vertical plate ex- 
tending backward from the palatine bridge. Its medial surface is 
divided by a low ridge into a dorsal portion, in particular relation 
to the nasopharynx, and a ventral portion, in relation to the oral 
cavity, the ridge indicating the position of the soft palate. Its 
lateral surface is partly applied to the maxilla and partly exposed 
to the orbit. Its dorsal margin is articulated with the presphenoid 
and with the ethmoidal process of the orbitosphenoid, but a small 
posterior portion is free, so that the anterior portion of the basi- 
sphenoid is visible from the orbit. The free ventral margin forms 
posteriorly a thick projecting angle, the pyramidal process 
(processus pyramidalis), the base of which is cleft where it articulates 
with the medial and lateral laminae of the pterygoid process. 
Between the pyramidal process and the alveolus of the last cheek- 
tooth there is a conspicuous palatine notch (incisura palatina), 
connecting the orbit with the palatal surface. In the entire skull 
only the posterior portion of the lateral surface is visible from the 
orbit, the anterior portion being concealed by the projecting bases 
of the posterior cheek-teeth. The ridge of bone on which the 
alveoli of these teeth are borne is separated from the palatine bone 
by the infraorbital groove. The medial wall of the latter, 
formed by the palatine bone, contains the orbital opening of the 
pterygopalatine canal and the sphenopalatine foramen. 
19. The Mandible 
The mandible (mandibula) or lower jaw comprises the two 
dentary bones (ossa dentalia), which, in the rabbit, as in mammals 
generally, are united by a fibrous or fibrocartilaginous connection 
(symphysis mandibulae); not coalesced, as in the human skull, to 
form a continuous structure. As indicated above, each of the 
dentary bones comprises: (1) a horizontal, tooth-bearing portion 
which, in conjunction with that of the opposite side, forms the The Bones of the Skull 
169 
body of the mandible (corpus mandibulae); and (2) a posterior, 
vertical plate, the mandibular ramus (ramus mandibulae), for 
muscle attachment and articulation. The horizontal portion 
is deep posteriorly, where it lodges the alveoli of the cheek-teeth. 
Anteriorly, in the diastema separating the latter from the incisors, 
its dorsal surface is rounded and depressed, the space thus formed 
corresponding to a similar space in the upper jaw and serving 
chiefly for the accommodation of the lips, which in this region en- 
croach medially on the oral cavity. The medial surface of the 
horizontal portion forms an acute angle with that of the bone of the 
opposite side, except anteriorly, where it bears a roughened area 
for articulation with the latter. Running backward from the 
symphysis there is a broad horizontal ridge, representing the 
mylohyoid line (linea mylohyoidea), the line of attachment of the 
mylohyoid muscle. The mandibular foramen, through which, 
in the natural condition, the inferior alveolar nerve and artery 
gain access to the interior of the bone, lies on this surface at the 
junction of the horizontal portion with the ramus. The corres- 
ponding mental foramen (foramen mentale), through which 
branches of these structures leave the mandible, is situated on the 
lateral surface in front of the first premolar. The mandibular 
foramen is closely connected with a second aperture lying at the 
ventral end of the sulcus ascendens, directly behind the last molar, 
and serving for the transmission of a vein connecting the inferior 
alveolar and inferior orbital veins. 
The mandibular ramus forms in general an obtuse angle 
with the horizontal portion. As in other herbivores, the ventral 
part, distinguished as the angle, is greatly increased in size at the 
expense of the condyloid process and to a still greater extent of the 
coronoid process, the latter being vestigial. In addition to a low 
pterygoid tuberosity (tuberositas pterygoidea), situated at the 
posterior projecting point of the angle, the posterior and ventral 
margins of the angle are excavated on the medial side of the bone, 
so that they form the boundary of a pronounced, though shallow, 
inferior pterygoid depression for the insertion of the ptery- 
goideus internus muscle. The area occupied by the pterygoideus 
internus is separated by a low ridge from a more dorsally placed 
superior depression for the pterygoideus externus muscle. A some- 170 
Anatomy of the Rabbit 
what similar depression, termed the masseteric fossa, occupies 
the lateral surface of the angle, its raised ventral margin terminating 
posteriorly in the masseteric tuberosity (tuberositas masseterica). 
The articular portion or head of the mandible is greatly elongated 
in the anteroposterior direction in accordance with the antero- 
posterior action of the lower jaw, this feature being one which is 
of general occurrence in the rodent order, and more fully expressed 
in the great extension forward and backward of the attachment 
areas of the muscles of mastication. The connection of the articu- 
lating portion with the condyloid process, the so-called neck 
of the mandible (collum mandibulae), is a thin plate of bone, the 
anterior and posterior margins of which are barely notched by the 
anterior and posterior mandibular incisures. Connecting 
the anterior incisure with the rim of the alveolus of the last cheek- 
tooth there is a deep groove, the sulcus ascendens, the lateral 
margin of which is formed by the reduced coronoid process 
(processus coronoideus). Its low medial margin is formed by a 
bony stay which extends to the 
medial surface of the horizontal 
portion opposite the last cheek- 
tooth, and is continued forward 
into the mylohyoid line. The sulcus 
ascendens lodges in the natural 
condition the insertion portion of 
the greatly reduced temporalis 
muscle. 
C. The Hyoid Apparatus 
The hyoid bone (os hyoideum) 
(Fig. 68) is a stout, somewhat 
wedge-shaped bone lying in front 
of the larynx and between the 
angles of the mandible. Its ven- 
tral portion is connected with the 
thyreoid cartilage of the larynx by 
the median hyothyreoid liga- 
Fig. 68. Lateral surface of the 
hyoid and larynx: c.a., arytenoid car- 
tilage; c.c., cricoid cartilage; c.i., in- 
ferior cornu of thyreoid cartilage; c.m., 
lesser cornu of hyoid; c.mj., greater 
cornu of hyoid; c.s., superior cornu of 
thyreoid cartilage; c.t., left plate of the 
thyreoid cartilage; e., epiglottic cartilage; 
f.t.s., thyreoid foramen; l.h., lateral 
hyothyreoid ligament; l.h.m., median 
hyothyreoid ligament; m.ct., cricothy- 
reoideus muscle; o.h., hyoid bone; s.m., 
stylohyoideus minor muscle; s.mj., stylo- 
hyoideus major muscle; tr., cartilaginous 
tracheal rings. Skeleton of the Anterior Limb 
171 
ment. With its lateral portion are articulated two independent 
elements, termed the lesser and greater cornua. The lesser cornu 
(cornu minus) is a small, partly cartilaginous structure, attached 
to the anterodorsal angle of the hyoid, and connected through the 
stylohyoideus minor muscle with the jugular process of the skull. 
The muscle tendon contains near the jugular process a small 
ossification representing a detached styloid process. The greater 
cornu (cornu majus) is a larger element extending obliquely 
dorsad, and similarly suspended from the jugular process by the 
stylohyoideus major muscle. The connection of the lesser cornu 
with the styloid process through the stylohyoideus minor replaces 
the stylohyoid ligament of the human skull and the chain of ele- 
ments commonly occurring in mammals and other vertebrates in 
this region. In most mammals the term "lesser", as applied to it, 
is inappropriate. The lesser cornu, the styloid process, and their 
connections, together with the hyoid bone itself, indicate the relation 
of the embryonic hyoid arch, from which the skeletal structures in 
question are derived. The greater cornu belongs to the succeeding 
visceral arch, and is connected with the superior cornu of the 
thyreoid cartilage of the larynx by the lateral hyothyreoid 
ligament. This cornu is commonly represented in mammals by 
a small thyreohyal process. 
THE SKELETON OF THE ANTERIOR LIMB 
The skeleton of the anterior limb is divisible into two portions, 
namely, a proximal portion, comprising the scapula and the 
clavicle, and a distal portion, comprising the supports of the 
free extremity. The scapulae and clavicles of the two sides 
together form the pectoral girdle. The pectoral girdle is lightly 
constructed, and, apart from its muscular connections, which 
constitute its main support, is directly attached to the axial skeleton 
only through the sternoclavicular ligament. 
The skeleton of the free extremity is divisible into proximal, 
middle, and distal segments. The proximal segment contains a 
single bone, the humerus; the middle segment two elements, the 
radius and ulna; while the distal segment comprises, in addition 
to the accessory sesamoid bones, twenty-eight elements of the 172 
Anatomy of the Rabbit 
regular series, of which nine form the carpus, five the metacarpus, 
and fourteen the phalanges of the digits. 
The positions occupied by the principal parts in the natural 
state are shown in figure 24. 
The Scapula 
I he scapula (Fig. 69) is a somewhat triangular plate of bone 
lying in the natural position on the lateral surface of the anterior 
part of the thorax, with its apex directed downward and forward. 
In the rabbit, as in quadrupedal mammals generally, the main 
surfaces are respectively medial and lateral, and differ in this respect 
Fig. 69. Lateral surface of the left scapula: a., acromion; a.i., a.l., and 
a.m., inferior, lateral, and medial angles; c.g., glenoid cavity; c.s., neck of the 
scapula; f.s. and f.i., supraspinous and infraspinous fossae; m., metracromion; 
m.a., m.s., and m.v., axillary, superior, and vertebral borders; p.c., coracoid 
process; s.s., scapular spine. 
from the human condition, in which, from the transverse widening 
of the thorax, the corresponding surfaces are more nearly ventral 
and dorsal. Of its three borders, one, the superior border (margo 
superior), is directed toward the occiput; another, the vertebral 
border (margo vertebralis), toward the vertebral column; and the 
third or axillary border (margo axillaris), toward the arm-pit. 
The corresponding angles are called medial (superior-between 
the superior and vertebral borders), inferior, and lateral (glenoid- 
between the superior and axillary borders). The lateral surface 
bears a stout bony plate, the scapular spine (spina scapulae), 
which arises from the body of the bone through about two-thirds Skeleton of the Anterior Limb 
173 
of its extent, and ends ventrally in a free projection, the acromion. 
The posterior margin of the acromion bears a backwardly-directed 
process, the metacromion (processus hamatus). Through the 
presence of the scapular spine, the lateral surface of the bone is 
divided into two areas for muscular attachment. One of these, 
the supraspinous fossa (fossa supraspinata), lies in front of the 
spine, the other, the infraspinous fossa (fossa infraspinata), 
behind it. The infraspinous fossa 
is the more extensive one. The 
medial surface, on the other hand, 
presents a single large shallow de- 
pression, the subscapular fossa 
(fossa subscapularis), which is trian- 
gular in shape and occupies practic- 
ally the entire surface. The apex or 
lateral angle of the scapula, some- 
times termed the head of the bone, 
is expanded to a considerable extent 
in comparison with the slender por- 
tion-the so-called neck of the scapula 
(collum scapulae)-connecting it with 
the body of the bone. It bears a con- 
cave depression, the glenoid cavity 
(cavitas glenoidalis), for articulation 
with the humerus. The articulating 
surface is borne chiefly on that part 
of the bone corresponding to the axil- 
lary border, but it also extends in an 
anterior direction to the base of an 
overhanging projection, the coracoid 
process (processus coracoideus). The 
free portion of the latter forms a 
blunt, hook-like projection toward 
the medial surface of the bone. 
The Clavicle 
The clavicle (clavicula) is imperfectly developed in the rabbit, 
consisting of a slender, curved rod of bone, tipped by cartilage, 
Fig. 70. Anterior surface of the 
left humerus: c., capitulum; c.h., 
head of humerus; e.l. and e.m., 
lateral and medial epicondyles; f.r., 
radial fossa; s.h., deltoid tuberosity; 
s.i., intertubercular groove; t.h., 
trochlea humeri; t.mi. and t.mj., 
lesser and greater tubercles. 174 
Anatomy of the Rabbit 
which lies in the interspace between the manubrium sterni and 
the head of the humerus. It occupies only a portion of this inter- 
space, being attached medially by the sternoclavicular ligament 
and laterally by the cleidohumeral ligament. 
The Humerus 
The humerus (Fig. 70) is typical of the long bones of the proxi- 
mal and middle segments of the fore and hind limbs in consisting of a 
central portion, the body or shaft of the bone, and of proximal and 
distal extremities for muscle attachment and articulation. The 
proximal extremity bears on its medial side a smooth, convex 
projection, the head of the humerus (caput humeri), for articulation 
with the scapula. The articulation is nominally a ball-and-socket 
joint, or enarthrosis, but the articulating surfaces are somewhat 
restricted, and the muscular arrangements of the limb are such 
that the range of lateral motion (abduction and adduction) is small. 
Immediately in front of the head of the bone there is a small eleva- 
tion, the medial tuberosity or lesser tubercle (tuberculum 
minus). It is separated by a longitudinal furrow of the anterior 
surface, the intertubercular groove (sulcus intertubercularis), 
from a much larger lateral elevation, the lateral tuberosity or 
greater tubercle (tuberculum majus). Extending distad from 
the latter is a triangular area, the deltoid tuberosity (tuberositas 
deltoidea), the tip of which reaches almost to the middle of the bone 
and forms a pronounced angle on its anterior surface. These 
tuberosities are for muscle attachment, mainly for the insertion of 
muscles moving the shoulder-joint. 
The distal extremity of the humerus bears a grooved articular 
surface, the trochlea humeri, for articulation with the radius 
and ulna. On its lateral side is a smaller surface, the capitulum 
humeri, for articulation with the radius alone. Immediately 
above the trochlea the medial and lateral portions of the bone are 
thickened to form two areas for muscular attachment. One of 
these, the lateral epicondyle (epicondylus lateralis), is a general 
point of origin for the extensor muscles of the dorsal surface of the 
hand, while the other, the medial epicondyle (epicondylus 
medialis), is a similar point of origin for the flexor muscles of the 
ventral or volar surface. Between the epicondyles the extremity Skeleton of the Anterior Limb 
175 
of the bone is greatly excavated, so that the projecting portions 
of the radius in front and of the ulna behind are received into 
depressions of the surface when the forearm is respectively flexed 
or extended. On the anterior side is the radial fossa (fossa 
radialis); on the posterior side the olecranon fossa (fossa olecrani), 
so-called because it accommodates the olecranon process of the 
ulna. 
Between the radial and olecranon fossae the bone is reduced to 
a very thin lamina, which is sometimes pierced by an opening of 
very variable size, the supratrochlear foramen.* 
The Radius and Ulna 
The radius (Fig. 71) is the shorter of the two bones of the 
forearm, since its proximal extremity does not extend backward 
beyond the front of the elbow-joint. It is anterodorsal in its general 
position, but crosses the ulna in such a way that its proximal 
extremity tends to be lateral, while its distal extremity is medial. 
The proximal extremity, termed the head of the radius (capitulum 
radii) is immovably articulated with the ulna. It bears an ex- 
tensive articular surface, meeting both trochlea and capitulum of 
the humerus, and thus forming a considerable portion of the elbow- 
joint. The body of the bone is solidly united with the ulna by 
the interosseous ligament of the forearm. The distal extremity 
is largely formed by an epiphysis, which is well marked even in 
older animals. It bears a grooved, carpal articular surface 
(facies articularis carpea), for articulation with the navicular and 
lunate bones. 
The ulna (Fig. 71) is a somewhat S-shaped bone, the shaft of 
which is vertically flattened, so that it possesses two main surfaces, 
respectively anterodorsal and posteroventral. The former, in con- 
junction with the related surface of the radius, continues the area 
of origin of the extensor muscles of the hand from the lateral 
epicondyle of the humerus distad on to the forearm, while the latter 
has a similar function with respect to the flexor muscles. The 
proximal portion of the bone is laterally compressed. It bears a 
crescentic depression, the semilunar notch (incisura semi-lunaris), 
the articulating surface of which continues that of the medial 
*In an examination of 255 specimens, this was found in 173, or 68 per cent. 176 
Anatomy of the Rabbit 
portion of the head of the radius, and is received into the trochlea 
humeri. Behind the elbow-joint the bone forms the large projecting 
portion of the elbow, the olecranon, which is a strong process for 
the insertion of the extensor muscles (anconaei) acting on the 
forearm and provides leverage for their action. The distal ex- 
tremity of the bone is formed by an epiphysis, similar to, but much 
longer than, that of the radius. It is immovably articulated with 
the radius, and its tip is formed by a blunt styloid process (pro- 
cessus styloideus), which is articulated with the triquetral bone 
of the carpus. 
The elbow-joint is formed by the trochlea and capitulum of the 
humerus in conjunction with the semilunar notch of the ulna and 
the corresponding articular surface of the head of the radius. It is 
a hinge-joint, or ginglymus, permitting motion in one plane, i.e., 
extension and flexion of the forearm. The trochlear surface of the 
humerus, however, has a slight spiral trend, the anterior portion 
being medial in comparison with the posterior portion. 
Through the immovable articulation provided by the respective 
proximal and distal ends of the bones, and also through the inter- 
osseous ligament, the radius and ulna are prevented from changing 
their positions with respect to one another; in other words, the 
radius is unable to rotate on an axis formed by the ulna as it does 
in man, the forefoot being fixed in a position comparable to that 
of pronation in the human hand (c/. p. 68). 
The Carpus 
The carpus (Fig. 71) comprises nine small elements, the wrist 
or carpal bones (ossa carpi), which are interposed between the 
forearm and the digits. They are arranged in two main rows, 
namely, a proximal row, the elements of which are articulated 
with the radius and ulna; and a distal row, the elements of which 
are articulated with the five bones of the metacarpus. Enumerated 
from the medial side of the wrist laterad, the proximal row contains 
four elements, namely, the navicular, lunate, triquetral, and 
pisiform bones. The navicular and lunate are articulated with 
the distal extremity of the radius; the triquetral with the styloid 
process of the ulna. The pisiform bone lies on the ventral surface 
of the extremity of the ulna, and is therefore not exposed to the Skeleton of the Posterior Limb 
177 
Fig. 71. Skeleton of the forearm and hand from the dorsal surface: R, 
radius; U, ulna; C, carpus; M, metacarpus; P, phalanages; I-V, metacarpal 
bones, c., central bone; cp., capitate; c.r., head of radius; f.a.c., carpal artic- 
ular surface of radius; h., hamate bone; i.s., semilunar notch of the ulna; 1., 
lunate bone; mi., lesser multangular; mj., greater multangular; n., navicular; 
ol., olecranon; p.s., styloid process of the ulna; tr., triquetral bone; u., ungual 
phalanges. 178 
Anatomy of the Rabbit 
dorsal surface of the wrist. The distal row contains five elements, 
namely, the greater multangular, lesser multangular, central, 
capitate, and hamate bones. The first, second, and fourth are 
in association respectively with the first, second, and third meta- 
carpals. The central bone lies to the lateral side of the articulation 
at the base of the second metacarpal. As its name implies, it is 
originally an element interposed between the proximal and distal 
rows. The hamate is a comparatively large element associated 
with the fourth and fifth metacarpals, but extending also to the 
articulation of the third, where it tends to replace the greatly 
reduced capitate. It represents the two lateral members of the 
original distal row of carpals (Fig. 32) fused together. 
The AIetacarpus and Phalanges 
The metacarpus (Fig. 71) comprises five stout elements, the 
metacarpal bones (ossa metacarpalia), which form the basal 
supports of the digits. Each consists, in addition to a main portion 
or body, of a flattened proximal end, or base, and a rounded distal 
extremity, or head. The four lateral bones are normally developed, 
while the first, which belongs to a reduced digit, is of very small size. 
The phalanges or bones of the digits are distributed according 
to the formula 2, 3, 3, 3, 3. They are similar in form to the meta- 
carpals, with the exception, however, of the terminal, ungual 
phalanges, which are laterally compressed, pointed, and cleft at 
their tips for the attachment of the claws. 
Sesamoid Bones 
Accessory elements, sesamoid bones (ossa sesamuidea), de- 
veloped in the ligaments or tendons of muscles, are found on the 
volar surface of the foot in association with certain of the joints. 
They occur in transverse pairs at the metacarpophalangeal articu- 
lations and in linear pairs at the articulations of the second with 
the third phalanges. The pisiform bone of the carpus is also a 
sesamoid, being formed in the insertion tendon of the flexor carpi 
ulnaris muscle. 
THE SKELETON OF THE POSTERIOR LIMB 
In the posterior limb the proximal or girdle portion comprises 
the paired coxal bones, which are united ventrally at the pelvic Skeleton of the Posterior Limb 
179 
symphysis, thus forming the pelvic girdle. The distal portion, 
as in the anterior limb, comprises the supports of the free ex- 
tremity and is divisible into proximal, middle, and distal segments. 
The proximal segment contains a single element, the femur; the 
middle segment two elements, the 
tibia and fibula, which, however, 
are extensively coalesced; and the 
distal segment twenty-three ele- 
ments, of which six form the 
tarsus, five the metatarsus, and 
twelve the phalanges. 
The Coxal Bone 
The coxal bone (os coxae) 
(Fig. 72) is a somewhat triradiate 
structure, the posterior limbs of 
which are united, so that they 
enclose a large aperture, the 
obturator foramen (foramen 
obturatum). It is firmly articu- 
lated with the sacrum, and is 
united with its fellow of the oppo- 
site side by a thin strip of cartilage 
containing a small amount of 
fibrous material. The latter con- 
nection is the pubic symphysis 
(symphysis pubis), better termed 
in the rabbit the pelvic sym- 
physis, since it is somewhat more 
extensive than the corresponding 
articulation of the human pelvis. 
In the young animal each half 
of the pelvis consists of three ele- 
ments, namely, the ilium, is- 
chium, and pubis. They form 
the three rays of the coxal bone, 
and are united with one another in 
Fig. 72. Lateral surface of the left 
coxal bone: IL, ilium; IS, ischium; P, 
pubis, a., acetabulum; a.i., iliac wing; 
c.i., body of ilium; c.is., body of ischium; 
c.p., body of pubis; cr., iliac crest; e.i., 
iliopectineal eminence; f.a., acetabular 
fossa; f.o., obturator foramen; i.a., 
acetabular notch; i.mi., lesser sciatic 
notch; i.mj., greater sciatic notch; l.i., 
iliopectineal line; p.l., lateral process of 
ischial tuberosity; r.i.i., inferior ramus of 
ischium; r.i.p., inferior ramus of pubis; 
r.s.i., superior ramus of ischium; r.s.p., 
superior ramus of pubis; s.a.i., inferior 
anterior spine of the ilium; s.a.s., supe- 
rior anterior spine; s.i., ischial spine; 
s.p., symphysis pubis; s.p.i., inferior 
posterior spine; t.i., ischial tuberosity; 
t.p., pubic tubercle. 180 
Anatomy of the Rabbit 
the region of the acetabulum, which is the basin-like depression 
for the articulation of the pelvis with the femur. Only two of the 
original elements, however, actually take part in the formation 
of the acetabulum, the pubis being excluded through the develop- 
ment in the acetabular depression of a small triangular element, 
the os acetabuli. Although completely coalesced in the adult 
condition, and showing but few traces of their original separation, 
the three chief elements are nevertheless described as if distinct. 
The ilium (os ilium) is the anterior, also somewhat dorsal, 
portion of the bone; that part extending forward from the ace- 
tabulum. It comprises a basal portion, the body (corpus oss. 
ilium), which includes the anterior portion of the acetabulum and 
the cylindrical part of the bone in front of it, and an expanded 
portion, the iliac wing (ala oss. ilium), for muscle attachment and 
articulation with the sacrum. The body is somewhat triangular 
in section, its surface being divided into three areas, which are 
respectively medial, or sacral, ventrolateral, or iliac, and dorso- 
lateral, or gluteal. The corresponding borders are respectively 
ventral, or pubic, lateral, or acetabular, and dorsal, or ischial. 
The acetabular border terminates a short distance in front of the 
acetabulum in an abruptly truncated projection, the inferior 
anterior spine (spina anterior inferior), which is the origin of an 
extensor muscle of the leg. The ischial border forms the anterior 
half of a long depression of the dorsal surface of the coxal bone, 
the greater sciatic notch (incisura ischiadica major). The pubic 
border presents on its medial side a faint, ridge-like elevation, the 
iliopectineal line (linea iliopectinea), which connects the sharp 
anterior border of the pubis with the articular surface for the 
sacrum. 
The wing of the ilium forms a shovel-like expansion, the natural 
position of which is almost sagittal. Its lateral surface provides 
a fairly extensive area for the origin of the gluteal muscles. Its 
medial surface is a muscle surface only in its anterior portion, the 
posterior portion being occupied by the roughened auricular 
surface (facies auricularis), for connection with the sacrum. The 
dorsal margin is thin and straight. Posteriorly, where it is asso- 
ciated with the greater sciatic notch, there is a small projection, 
the inferior posterior spine (spina posterior inferior), also termed 
the tuber sacrale. Anteriorly it passes by a broad angle into the Skeleton of the Posterior Limb 
181 
anterodorsal margin of the bone, the latter forming the projecting 
end of the wing, which is distinguished as the iliac crest (crista 
iliaca). This portion is considerably thicker than the related dorsal 
and ventral margins, and also bears on its medial side a somewhat 
hook-shaped process. Its anteroventral angle is the superior 
anterior spine (spina anterior superior) or tuber coxae. The 
ventral margin is slightly longer than the dorsal margin, and is 
also concave. It is associated with the pubic border of the body 
of the ilium, and is not connected with the inferior anterior spine. 
The anterior elongation of the ilium is an adaptation to the powerful 
anterior thrust of the hind limb in progression. 
The ischium (os ischii) extends backward from the acetabulum, 
its axis continuing that of the ilium. It consists of a basal portion, 
or body (corpus oss. ischii), a superior ramus, and an inferior 
ramus. The body of the ischium is for the most part cylindrical. 
It forms the posterior part of the acetabulum, and presents in 
connection with the latter a deep acetabular notch (incisura 
acetabuli), which tends to interrupt the articular surface. The 
acetabular notch leads forward into a depression of the centre of the 
articular basin, the acetabular fossa (fossa acetabuli). In the 
natural condition the combined depressions serve for the attach- 
ment of the round ligament of the head of the femur. The dorsal 
margin of the bone, belonging in part to the body and in part to the 
superior ramus, bears a short hook-like projection, the ischial 
spine (spina ischiadica), a point of muscle origin (p. 236). The 
spine divides this margin into two parts, one of which forms the 
posterior half of the greater sciatic notch, already described, while 
the other forms a similar, and, in the rabbit, scarcely less extensive, 
posterior depression, the lesser sciatic notch (incisura ischiadica 
minor). Through both notches pass muscles which move the 
femur (p. 236). 
The superior or acetabular ramus of the ischium is the con- 
tinuation backward of the body of the bone. It is a somewhat 
flattened plate of bone, the thicker dorsal portion of which ter- 
minates in two blunt projections. One of these, the ischial 
tuberosity (tuber ischiadicum), forms the posterior end of the 
bone, while the other extends in a lateral direction and is described 
as the lateral process (processus lateralis). The inferior or 
symphyseal ramus is that part of the ischium which extends from 182 
Anatomy of the Rabbit 
the superior ramus downward and forward between the obturator 
foramen and the symphysis to meet the corresponding ramus of 
the pubis. 
The pubis (os pubis) consists of a basal portion or body lying 
immediately below the acetabulum, a superior or acetabular 
ramus extending from the body to the symphysis, and an inferior 
or symphyseal ramus extending backward along the symphysis 
to its junction with the ischium. The 
anterior margin of the bone, described 
as the pecten oss. pubis, is thin and 
sharp. Near the symphysis it bears 
a minute elevation, the pubic tuber- 
cle (tuberculum pubicum), and lat- 
erally a more extensive elevation, 
the iliopectineal eminence (emin- 
entia iliopectinea). The latter is more 
conspicuous in older specimens, where 
it is easily recognizable by its jagged 
outline. Its lateral margin is con- 
tinuous with the iliopectineal line. 
The Femur 
The femur (Fig. 73) is a some- 
what S-shaped bone, the body being 
very slightly curved, with the distal 
extremity bent downward, forming 
the articulation of the knee, while 
the proximal one, with its various 
processes, turns slightly upward in 
association with the pelvis. In con- 
sidering the general form, it will be 
remembered that in the natural 
sitting posture of the rabbit, the 
position of the femur is approximately 
horizontal, the convex surface of the 
shaft, which is equivalent to the ante- 
rior surface in man, being uppermost. 
The proximal extremity of the femur bears an extensive rounded 
portion or head (caput femoris), for articulation with the pelvic 
Fig. 73. Anterior surface of the 
left femur: c.l. and c.m., lateral and 
medial condyles; cl.f., neck of femur; 
cp.f., articular portion (head); e.l. 
and e.m.. lateral and medial epicon- 
dyles; f.p., patellar surface; t.mi., 
trochanter minor; t.mj., trochanter 
major, including t.p. and t.t., the 
first and third trochanters. Skeleton of the Posterior Limb 
183 
girdle. This portion is separated from the main part of the ex- 
tremity by a constricted area or neck (collum femoris), so that, 
unlike the case of the anterior limb, the points of muscle attach- 
ment fall a considerable distance from the point of articulation. 
The actual extremity of the bone is formed by a large process for 
muscular attachment, the great trochanter (trochanter major). 
It is divided into two portions, one of which, the first trochanter 
(trochanter primus), forms the large terminal, hook-like projection, 
while the other, the third trochanter (trochanter tertius), is 
the smaller lateral crest. On the medial side of the bone, imme- 
diately distal to the head, there is a triangular elevation, the 
lesser or second trochanter (trochanter minor s. secundus). 
Posteriorly, these projections form a smooth surface for muscle 
attachment, except, however, at the base of the trochanter major, 
where the surface of the bone presents a deep, though narrow, 
depression, the trochanteric fossa (fossa trochanterica). 
The distal extremity bears an extensive surface for articulation 
with the tibia. It is divided into two portions, known as the 
medial and lateral condyles, through the presence of a deep 
excavation, the intercondyloid fossa (fossa intercondyloidea). 
Immediately above the condyles, on the anterior surface of the 
bone, the intercondyloid fossa is replaced by a broad groove, the 
patellar surface (facies patellaris), which, in the natural condition, 
accommodates the convex internal surface of the patella. The 
medial and lateral portions of the bone, intervening between the 
distal portion of the patellar surface and the tips of the condyles, 
provide slightly elevated, roughened surfaces, the medial and 
lateral epicondyles, for muscular attachment. 
The Tibia and Fibula 
The tibia (Fig. 74) is the larger of the two bones of the leg, 
lying on the medial side of the fibula, and fused with the latter for 
more than one-half of its length. Its proximal extremity is trian- 
gular in section, the main surfaces being respectively anterolateral, 
anteromedial, and posterior. The anterior border is formed by a 
stout, ridge-like elevation, the tuberosity of the tibia (tuberositas 
tibiae), which in the natural condition serves for the insertion of 
the quadriceps femoris, the extensor tendon being carried over 184 
Anatomy of the Rabbit 
the knee by the patella and the patellar ligament. The articular 
portion is slightly differentiated into medial and lateral condyles 
corresponding to those of the distal end of the femur. On the 
articular surface the concave areas for the reception of the condyles 
of the femur are separated from one 
another by a small intervening, partly 
divided hillock, the intercondyloid 
eminence (eminentia intercondyloidea), 
and also posteriorly by a depression of 
the articular border, the posterior 
intercondyloid fossa. A correspond- 
ing anterior intercondyloid fossa lies 
in front of the intercondyloid eminence, 
but is poorly differentiated. 
The fibula (Fig. 74) is the smaller, 
lateral bone of the leg, and in the rabbit 
is so extensively fused with the tibia 
that scarcely more than a third of it 
is distinguishable. The free portion 
forms a flattened bony splint, the medial 
margin of which is firmly united with 
the tibia by the interosseous ligament 
of the leg. Its proximal extremity is 
connected with the lateral condyle of 
the tibia by an elongated epiphysis, the 
latter, like those of the distal ends of 
the radius and ulna, being distinguish- 
able even in older animals. 
The combined distal extremities of 
the tibia and fibula bear a roughly 
rectangular articular surface for the 
tarsus. The tibial portion of this sur- 
face presents two grooves, separated by 
a ridge, for articulation with the trochlea 
tali. On its medial side is a small 
projection, the medial malleolus (malleolus medialis) round 
which, in the intact animal, passes the insertion tendon of the 
extensor hallucis longus muscle. 
Fig. 74. Anterior surface of 
the left tibia (T) and fibula (F): 
c.l. and c.m., lateral and medial 
condyles; f.a.s., proximal artic- 
ular surface for the femur; m.l. 
and m.m., lateral and medial 
malleoli; t.t., tuberosity of tibia. Skeleton of the Posterior Limb 
185 
The fibular portion presents a transverse groove for the convex 
articular surface of the calcaneus. Immediately above it, on the 
lateral side of the bone, is a prominent projection, the lateral 
malleolus (malleolus lateralis). It forms the anterior boundary 
of a groove which in the natural con- 
dition lodges the insertion tendons of 
the peroneal muscles. 
The Tarsus 
The tarsus (Fig. 75) comprises six 
elements, the tarsal or ankle-bones 
(ossa tarsi), which, like the correspond- 
ing bones of the carpus, are arranged in 
proximal and distal rows. An exception 
is to be made, however, for one element, 
the navicular, which occupies an inter- 
mediate position. The proximal row 
contains two elements, the talus and 
calcaneus. The talus is medial and 
also slightly dorsal in position. Its 
proximal end, described as the body 
(corpus tali), bears an extensive pulley- 
like surface, the trochlea tali, for 
articulation with the tibia, and forming 
with the latter the chief portion of the 
ankle-joint. Its distal end, termed the 
head of the talus (caput tali), provides 
a convex articular surface for the navic- 
ular bone, and is separated from the 
larger trochlear portion by a slightly 
constricted intermediate portion or neck 
(collum tali). Its ventrolateral border 
is extensively articulated with the cal- 
caneus. The latter is a cylindrical 
element, fully twice as long as the talus, 
since it is extended backward behind the ankle-joint, as the tuber 
calcanei, or bone of the heel. Its dorsal surface bears a prominent 
Fig. 75. The bones of the left 
foot, viewed from the dorsal sur- 
face: T, tarsus; M, metatarsus; 
P, phalanges. II-V, the four 
metatarsal bones, cb., cuboid; 
cl., calcaneus; c.s., second cunei- 
form; c.t., third cuneiform; f.a., 
articular surface for fibular side 
of the tibiofibula; n, navicular; 
t, talus; t.c., tuber calcanei; t.t., 
trochlea tali. 186 
Anatomy of the Rabbit 
elevation for articulation with the fibular side of the tibiofibula. 
Its medial surface bears a flat, shelf-like process, the susten- 
taculum tali, which forms a ventral support for the talus. The 
distal extremity of the bone articulates with the cuboid and also 
with the navicular. 
The intermediate element, the navicular bone, is a somewhat 
cubical bone, lying on the medial side of the tarsus between the 
talus, on the one hand, and the proximal end of the second meta- 
tarsal bone and the second and third cuneiform bones, on the other. 
It represents the central bone of the primitive tarsus (Fig. 32) and 
its position is more nearly that of a central element than is the case 
with the bone called by this name in the rabbit's carpus. In this 
connection it will be remembered that the carpus and tarsus, like 
other parts of the limbs, are primarily constructed on the same plan. 
The distal row of the tarsus contains three elements, namely, the 
second and third cuneiform bones and the cuboid bone. The 
two former, and especially the first, are smaller than the cuboid and 
articulate respectively with the second (first developed) and third 
metatarsals. In the rabbit the first cuneiform bone-the first 
element of the distal row in the usual condition-is fused with the 
proximal end of the second metatarsal. The cuboid is a larger 
element articulating, like the hamate bone of the carpus, with two 
distal elements, the fourth and fifth metatarsals. Its ventral 
surface bears a transverse elevation, the tuberosity of the cuboid 
(tuberositas oss. cuboidei), in front of which is a groove for the 
accommodation of the peculiar insertion tendon of the peronaeus 
primus muscle. 
The Metatarsus and Phalanges 
The metatarsus (Fig. 75) comprises five elements, of which 
four are fully developed and greatly exceed in size the corresponding 
bones of the metacarpus, while one, the first metatarsal, is 
vestigial. The vestigial element lies on the plantar surface of the 
foot, for the most part ventral to the navicular and at the base 
of the second metatarsal. In each developed metatarsal there may 
be distinguished a main portion or body, a proximal extremity or 
base, and a distal extremity or head, the last-named portion 
articulating with the proximal phalanx of the digit. The base of Skeleton of the Posterior Limb 
187 
the fifth metatarsal bears a tuberosity for the insertion of the 
peronaeus secundus muscle. 
The phalanges are distributed according to the formula 
0, 3, 3, 3, 3, the terminal, ungual phalanges being modified like 
those of the anterior limb. 
Sesamoid Bones 
The sesamoid bones of the posterior limb occur at the knee- 
joint and on the plantar surface of the foot. On the anterior 
surface of the knee is the knee-pan or patella, through which, as 
indicated above, the tendon of the quadriceps femoris muscle is 
carried over the knee and continued as the patellar ligament to the 
tuberosity of the tibia. On the posterior surface there are three 
sesamoid bones, of which one (in the medial head of the gastroc- 
nemius) lies in association with the medial condyle of the femur, 
while the remaining two are associated respectively with the lateral 
condyle of the femur (imbedded in the lateral head of the gastroc- 
nemius and the plantaris) and that of the tibia (contained in the 
popliteus muscle). The sesamoids of the foot are situated at 
the metatarso-phalangeal joints and at those connecting the second 
and third phalanges. PART III 
DISSECTION OF THE RABBIT 
The plan of dissection as outlined in the following pages pre- 
supposes in the first place that the entire dissection is to be made 
on a single specimen, and, second, that the latter has been prepared 
for gross dissection according to the method given in the appendix. 
These points may be mentioned as explaining many details of 
procedure and also to a certain extent the selection in preference 
to others of those structures which are more readily made out by 
the method employed. 
Because of the convenience of dissecting in circumscribed 
regions, the plan has been divided, although of necessity very 
unequally, into several parts. The order of these is such that the 
visceral dissection is introduced at an early stage. The somewhat 
more logical plan of completing first the dissection of the anterior 
and posterior limbs may be followed, but on account of the fact 
that it involves a lengthy muscular dissection to begin with, it is 
perhaps not to be recommended. 
The account aims at a statement of the various structures as 
met with in order of dissection and the features by which they 
may be identified, rather than at a full description. The student 
should make his own observations and prove them by personal 
drawings and descriptions of selected parts. In this connection 
he will do well to bear in mind that while dissection is nominally a 
means of obtaining anatomical information, its chief value as a 
laboratory exercise consists in the training to be acquired from 
critical observation and analysis. It is therefore of quite as much 
practical importance that he should make his observations extensive 
and accurate as that he should employ only good instruments or 
maintain the proper sequence in dissection. 
I. EXTERNAL FEATURES 
The external structures, subdivisions of the body, and super- 
ficial skeletal points may be made out as follows: External Features 
189 
1. The division of the body into head (caput), neck (collum), 
trunk (truncus), tail (cauda), and anterior and posterior 
limbs or extremities (extremitates). 
2. In the head: 
(a) The division into a posterior, cranial portion (cranium), 
and an anterior, facial portion (facies). 
(b) The mouth (os), bounded by the cleft upper lip (labium 
superius) and the undivided lower lip (labium inferius). 
The large sensory hairs or vibrissae. 
(c) The nose (nasus) and its external apertures (nares an- 
teriores). 
(d) The eye (oculus) and its coverings, the eyelids, including 
the upper eyelid (palpebra superior), the lower eyelid 
(palpebra inferior), and the third eyelid (palpebra tertia). 
The third eyelid occupies the anterior angle of the eye, and 
is comparable to the conjunctival fold of the human eye. 
(e) The external ear (auricula) and its canal, the external 
acoustic meatus (meatus acusticus externus), leading to 
the tympanic membrane. 
(/) Points on the head skeleton, to be identified by feeling 
through the skin; zygomatic arch, supraorbital process, 
external occipital protuberance, angle of the mandible, 
symphysis of the mandible, and the hyoid bone. 
3. In the trunk: 
(a) The division into thorax, abdomen, and back or dorsum. 
(b) The inclusion with the trunk of the proximal portions of the 
limbs. The angle formed by the anterior limb with the 
trunk represents in part the axillary fossa (fossa axillaris). 
The depression is much less evident than in man on account 
of the different positions of its enclosing folds formed by the 
pectorales and latissimus dorsi muscles. A corresponding 
inguinal furrow separates the posterior limb from the 
abdomen and pelvis. 
(c) The anal aperture (anus), and on either side of it the 
inguinal spaces, hairless depressions on which the ducts 
of the inguinal glands open. 190 
Anatomy of the Rabbit 
(d) In the male: the urinogenital aperture at the extremity 
of the penis; the latter enclosed by a fold of integument, 
the prepuce (praeputium); the scrotal sacs (scrotum), 
lateral sacs of the integument lodging the testes. 
(e) In the female: the urinogenital aperture, enclosed by folds 
of the integument, forming the vulva. The clitoris, the 
homologue of the penis, is a small, rod-like structure con- 
tained in its ventral wall. The mammary nipples 
(papillae mammarum), eight (to ten) in number, on the 
ventral surface of the breast and abdomen. 
(/) The following skeletal points: on the axial skeleton, the 
manubrium sterni, xiphoid process, costal arch, spinous 
processes of thoracic and lumbar vertebrae; on the pectoral 
girdle, the acromion, clavicle, and respective borders and 
angles of the scapula; on the pelvic girdle, the iliac crest, 
pubic symphysis, and ischial tuberosity. 
4. In the anterior limb: 
(a) The division of the free portion into three segments, the 
arm (brachium), forearm (antibrachium), and hand 
(manus). 
(&) The position of the elbow (cubitus) in comparison with 
the knee. 
(c) The five digits, designated from the medial side as: first 
(d. primus), or pollex; second (d. secundus), or index; 
third, or middle (d. tertius s. medius); fourth (d. quartus); 
and fifth (d. quintus s. minimus). 
5. In the posterior limb: 
(a) The division into three segments, the thigh (femur), leg 
(crus), and foot (pes). 
(&) The knee (genu), and the popliteal fossa of its posterior 
surface, the latter not well defined. The projection of the 
heel (calx), and the angle formed by the foot with the leg. 
(c) The four digits (dd. secundus-quintus). The vestigial first 
digit, or hallux, is not distinguishable externally. The Abdominal Wall 
191 
IL THE ABDOMINAL WALL 
1. Place the animal on its back. Make a median incision of the 
skin of the ventral surface extending from the pubic symphysis 
to the manubrium sterni, being careful not to cut through more 
than the skin itself. Make two transverse incisions through the 
skin on the left side, the first passing just behind the arm, the 
second, just in front of the thigh, both extending round to the 
dorsal surface. Work the flaps loose from the surface, using 
the handle of the scalpel, until the side of the trunk is well 
exposed, but leave them attached to the body. On the right 
side of the body it is sufficient to clear the middle line. Identify 
the structures as follows: 
On the inner surface of the skin: 
(a) The thick compact connective tissue forming the corium. 
(&) The hair-follicles imbedded in it, appearing as dots. 
(c) The loose subcutaneous tissue (tela subcutanea) by 
which the skin is attached. 
(d) In the female: the mammary glands (mammae), forming 
a layer on the inner surface, and more or less closely aggre- 
gated about the mammary nipples. 
On the exposed surface: 
(e) The linea alba, a white aponeurotic line extending from 
the pubic symphysis to the xiphoid process of the sternum. 
(/) The cutaneus maximus muscle, a thin sheet of muscle 
fibres covering the entire lateral surface of the thorax and 
abdomen. Origin: the linea alba, the ventral surface of the 
sternum in its posterior portion, and the deltoid tuberosity. 
The portion originating on the last-named appears on the 
medial surface of the humerus. Insertion: the skin of the 
dorsolateral surface of the trunk. The fibres are directed 
upward (in the natural position of the animal) and back- 
ward. The muscle is continuous across the back with its 
fellow of the opposite side, and is extended backward to 
the dorsum of the tail. It is used in shaking the skin. 
The artery passing forward for a short distance in the inguinal 
region and lying in the subcutaneous tissue is the superficial epi- 192 
Anatomy of the Rabbit 
gastric, a branch of the femoral (p. 240). Passing into the ventral 
portion of the cutaneus maximus muscle, it anastomoses forward with 
the external thoracic artery, a branch of the lateral thoracic. The 
corresponding veins are usually conspicuous in the female, since the 
vessels supply the mammary glands. A second anastomosis in the 
cutaneus muscle is formed laterally by a branch of the subscapular 
artery which passes backward from the axillary border of the scapula, 
uniting with an anterior branch of the iliolumbar artery. 
The inguinal lymph nodes (lymphoglandulae inguinales) are 
small, oval, brownish bodies lying in the inguinal furrow. 
2. Separate the cutaneus maximus from the surface of the muscle 
beneath. Identify the following points of attachment of the 
abdominal muscles proper: 
(a) The linea alba. 
(b) The linea semilunaris, a slightly curved line situated 
laterally a short distance from the linea alba. 
(c) The ribs and the costal arch. 
(t/) The lumbodorsal fascia (fascia lumbodorsalis), a broad, 
white sheet of connective tissue extending over the back in 
the posterior thoracic and lumbar regions. 
(e) The inguinal ligament (ligamentum inguinale), a stout 
white cord, stretched between the symphysis pubis and the 
iliac crest. 
3. Identify on the surface the external oblique muscle (m. 
obliquus externus abdominis). Origin: the xiphoid process, the 
posterior ten ribs by separate slips, and the lumbodorsal fascia. 
Insertion: the linea alba and the inguinal ligament. The fleshy 
portion, or muscle proper, covers the abdomen lateral to the 
linea semilunaris, while between this line and the linea alba is 
the tendinous portion or aponeurosis. The fibres are directed 
from an anterior dorsal position downward and backward, the 
more dorsal ones almost directly backward. Some of the 
anterior slips of origin interdigitate with those of the thoracic 
portion of the serratus anterior muscle. Some are concealed by 
the pectoral muscles. 
The muscle crossing the breast from the sternum to the arm is the 
pectoralis major. That passing forward from the lumbodorsal fascia to the 
medial surface of the humerus is the latissimus dorsi. The margins of these 
muscles may be raised where they conceal the external oblique. The Abdominal Wall 
193 
4. Taking a line between the iliac crest and the xiphoid process, 
divide the muscle, and then separate it fully from the next, which 
may be distinguished by the cross direction of its fibres. Note 
the separate slips of origin and the difference in appearance 
between the fleshy portions of the muscle and its ventral 
tendinous expansion or aponeurosis; then remove it from the 
surface. 
Examine the following muscles, proceeding in a similar manner: 
(a) The internal oblique muscle (m. obliquus internus 
abdominis). Origin: the inguinal ligament, a second sheet 
of the lumbodorsal fascia, and the posterior four ribs. 
Insertion: the linea alba. The fibres pass downward and 
forward. The ventral aponeurosis is much broader than 
that of the external oblique. Near the mid-ventral line 
it is split into dorsal and ventral leaves, containing between 
them the thin rectus abdominis muscle. 
(&) The transverse muscle (m. transversus abdominis). 
Origin: seven posterior ribs, a third sheet of the lumbo- 
dorsal fascia, and the inguinal ligament. Insertion: the 
linea alba. The fibres are directed downward and slightly 
backward. 
(c) The rectus abdominis muscle. Origin: lateral border 
of the sternum, including the xiphoid process; also the 
ventral surfaces of the second to seventh costal cartilages. 
Insertion: at the anterior end of the pubic symphysis. It 
is a thin, strap-like muscle, enclosed by the aponeurosis 
of the internal oblique, and separated from its fellow of the 
opposite side by the linea alba. 
The artery passing forward, for the most part in this muscle, is the 
inferior epigastric, a branch of the external iliac (p. 218). It anas- 
tomoses with the internal mammary (p. 276). It gives off the exter- 
nal spermatic artery, a small vessel which perforates the abdominal 
wall and extends backward, supplying the sac of the testis in the male 
and ending in the female in the wall of the vulva. 
5. Divide the remaining portion of the wall on the left side, and 
its whole thickness on the right, by transverse and longitudinal 
incisions, so that the abdominal viscera are fully exposed. Note 
on the internal surface of the wall the smooth serous investment 
here forming the parietal peritoneum (peritonaeum parietale). 194 
Anatomy of the Rabbit 
III. THE STOMACH AND SPLEEN 
The cavity disclosed by the division of the abdominal wall is the 
peritoneal cavity (cavum peritonaei), the largest of the four 
great serous sacs representing the primary body-cavity or coelom 
(p. 109). The major portion of the cavity is abdominal, but it 
extends into the pelvis, and, in the male, also into the scrotal sacs. 
Its lining membrane is that appearing on the body-wall as the 
parietal peritoneum, noted above, and on the visceral structures 
as the visceral peritoneum (peritonaeum viscerale). The visceral 
structures here include the major portions of the digestive and 
urinogenital systems. 
The general relations of the visceral peritoneum should first be 
examined by raising a portion of the small intestine from the left 
side of the visceral mass. Note its enclosure by a complete serous 
coat, similar in appearance to the membrane covering the body- 
wall, and the extension of the latter into a mesentery for the 
attachment of the structure to the dorsal body-wall. Note the 
parallel arrangement of the arteries and veins, and also their 
frequent anastomoses. Lymphatic vessels (lacteal vessels) 
accompany the blood-vessels in the mesentery, but being trans- 
parent are not readily recognizable. Lymph nodes also occur, 
but in this portion of the mesentery they are aggregated near its 
dorsal attachment or root (radix mesenterii). 
For the general relations of the stomach see p. 89. 
1. Displace the posteroventral portion of the liver forward, expos- 
ing in this way the ventral surface of the stomach. Without 
injuring the enclosing peritoneum, examine the contour of the 
organ and its divisions, as follows: 
(a) The greater curvature (curvatura ventriculi major), its 
convex posterior surface. 
(b) The lesser curvature (curvatura ventriculi minor), the 
contracted, concave anterior surface. 
(c) The main portion or body of the stomach (corpus ven- 
triculi). It lies for the most part to the left of the median 
plane. The Stomach and Spleen 
195 
(J) The cardia or area of junction with the oesophagus, largely 
concealed by the lesser omentum (2c, p. 196). 
(e) The fundus, a small sac-like portion lying to the left of 
the cardia. 
(/) The pyloric limb (pars pylorica) forms the right portion 
of the organ. 
(g) The pylorus, the point of communication of the stomach 
with the intestine (duodenum). It is marked by an annular 
constriction, preceding which is a greatly thickened mus- 
cular portion of the pyloric limb, known as the pyloric 
antrum (antrum pyloricum). 
2. Raise the posterior portion of the stomach and turn it forward. 
Note on the dorsal surface of the greater curvature a flat elon- 
gated body, the spleen (lien). It has a pale coloration in the 
embalmed animal but is dark red in life. On the right side of its 
artery, enclosed in the peritoneum, will be seen a diffuse brownish 
glandular mass, a portion of the pancreas. Trace the course 
of the peritoneum from the dorsal abdominal wall to the liver, 
as follows: 
(a) A broad fold of peritoneum, the mesogastrium, connects 
the dorsal abdominal wall and the diaphragm with the left 
side and dorsal surface of the greater curvature. Its 
posterior portion is divided into two parts by the spleen. 
The dorsal part, the phrenicosplenic ligament (lig. 
phrenicolienale) connects the spleen with the dorsal body- 
wall. The ventral part, the gastrosplenic ligament (lig. 
gastrolienale) connects the spleen with the greater curvature 
(cf. Fig. 42). 
(b) The peritoneum is projected backward from the greater 
curvature as a free fold, the greater omentum (omentum 
majus, epiploon) (c/. p. Ill), which covers the surface of 
the intestines to a certain extent. It usually contains fat. 
It is composed of four layers, of which two, representing the 
ordinary layers of a mesentery, proceed backward from the 
surface of the stomach, and at the posterior free edge of the 
omentum turn forward as the other two in a more dorsal 
position to unite with the transverse mesocolon. Fig. 42 
shows how this arrangement develops. 196 
Anatomy of the Rabbit 
(c) The lesser omentum (omentum minus) passes from the 
lesser curvature and the duodenum to the posterior surface 
of the liver. Its thickened margin on the right side forms 
the hepatoduodenal ligament (lig. hepatoduodenale) 
which carries three important structures, namely, the 
common bile duct, the hepatic artery, and the portal vein. 
Its left portion forms a thin membrane, the hepatogastric 
omentum, connecting the caudate lobe of the liver with 
the lesser curvature. 
3. Working on the left side between the dorsal surface of the 
stomach and the body-wall, tear away sufficient of the peri- 
toneum to expose the first portion of the abdominal aorta as it 
emerges from the diaphragm. In doing so, try to avoid damag- 
ing the slender greater splanchnic nerve (g). Passing in the 
direction of the stomach is a median ventral branch of the 
aorta, the coeliac artery, the distribution of which may be 
traced. The following structures, however, should first be 
identified, especially the ganglia (d, e) which are likely to be 
damaged in disturbing the peritoneum, and may advantageously 
be examined first. 
(a) The superior mesenteric artery (a. mesenterica superior), 
a second, also much larger, median branch of the aorta, 
given off a little distance behind the coeliac artery and 
passing in the direction of the intestine. 
(&) The suprarenal gland (gl. suprarenalis) of the left side, a 
pale flattened body about a quarter of an inch or more in 
length, a short distance medial to the anterior part of the 
kidney. If the gland is halved, examination of the cut 
surfaces will show it to be composed of a relatively thick 
outer cortex and a central medulla. These two portions, 
despite their close association, are both developmentally 
and functionally distinct organs {cf. p. 108). 
(c) The inferior caval vein (v. cava inferior), a large thin- 
walled vessel lying to the right of the aorta. It is not 
conspicuous if empty. 
The following ganglia lie at the root of the mesentery and may be 
concealed by lymph nodes (p. 204, d) or by fat. The Stomach and Spleen 
197 
(d} The coeliac ganglion (g. coeliacum), a minute triangular 
ganglion of the sympathetic nervous system lies in front of 
the superior mesenteric artery. 
(e) The superior mesenteric ganglion (g. mesentericum 
superius) of the sympathetic system lies immediately behind 
the superior mesenteric artery, and also on its lateral walls. 
The two ganglia are connected by nerves which cross the 
superior mesenteric artery. 
(/) The nerves proceeding from the coeliac and superior mesen- 
teric ganglia accompany the corresponding arteries to the 
respective organs which they supply, forming the coeliac 
and superior mesenteric plexuses. 
(g) The (greater) splanchnic nerve (n. splanchnicus major) 
of the left side passes backward from its origin in the thorax 
(see p. 283), around the reduced left crus of the diaphragm, 
and, crossing the aorta obliquely, enters the coeliac and 
superior mesenteric ganglia as well as sending branches to 
the renal plexus. It is composed of preganglionic fibres 
(p. 72). 
Experimental section of the nerves in the living animal results in 
vaso-dilation, stimulation in vaso-constriction. 
(h) An outlying portion of the pancreas (cf. p. 203) is seen in 
the peritoneum after the branches of the splenic artery have 
been severed (4, a). 
4. Trace the plan of branching of the coeliac artery, beginning at 
the point of origin, and exposing the vessels in order. 
The coeliac artery (a. coeliaca) is a short trunk, its first main 
branch, the splenic artery, being given off near its origin from the 
aorta. The remaining portion of the vessel passes to the right in 
the direction of the lesser curvature, and divides into two parts, 
the left gastric and hepatic arteries. Small vessels, the inferior 
phrenic arteries (aa. phrenicae inferiores), are given off from the 
anterior wall of the coeliac and are distributed to the diaphragm. 
The distribution of the main branches is as follows: 
(a) The splenic artery (a. lienalis) passes in the direction of 
the spleen, giving off small branches (r.r. pancreatici) to 198 
Anatomy of the Rabbit 
the pancreas and one or more large vessels, the short 
gastric arteries (aa. gastricae breves), to the left portion 
of the greater curvature. Passing along the concave sur- 
face, or hilus, of the spleen it gives off several splenic 
branches (rr. lienales) to that organ, and also several 
more branches, comparable to the short gastric arteries, to 
the greater curvature. Toward the end of the spleen the 
artery passes into the free fold of the greater omentum, and 
at this point there is given off a large vessel, the left 
gastroepiploic artery (a. gastroepiploica sinistra), which 
passes to the right on the greater curvature and anastomoses 
with the right gastroepiploic artery. 
The gastrosplenic ligament, together with its vessels, may be 
divided, the spleen being allowed to fall backward toward the intestine. 
(&) The left gastric artery (a. gastrica sinistra) forms a short 
trunk, or more commonly a group of vessels, the branches 
of which pass in a somewhat radiate manner toward the 
lesser curvature of the stomach, reaching in this way both 
dorsal and ventral surfaces. Two larger vessels appear on 
the ventral surface respectively to the right and left of the 
cardia. That on the left distributes small branches (rr. 
oesophagei) to the oesophagus, while that on the right bears 
a small pyloric branch which anastomoses across the lesser 
curvature with the right gastric artery. 
The chief nerves of the coeliac plexus accompany the branches of 
the artery to the stomach where they are associated with the terminal 
ramifications of the vagus (p. 199). These two represent respectively 
the mutually antagonistic sympathetic and parasympathetic divisions 
of the nervous system. 
In dissecting the following arteries, care must be taken to avoid 
injuring the bile duct and the portal vein. 
(c) The hepatic artery (a. hepatica), the continuation of the 
coeliac, passes forward and to the right, giving off small 
branches to the pancreas. Its first main branch is the 
gastroduodenal artery (a. gastroduodenalis). The latter 
is distributed chiefly to the first portion of the intestine as 
the superior pancreaticoduodenal artery (a. pan- The Stomach and Spleen 
199 
creaticoduodenalis superior), but a recurrent branch, the 
right gastroepiploic artery (a. gastroepiploica dextra), 
traverses the greater omentum to the greater curvature 
where it anastomoses with the left gastroepiploic artery. 
After giving off the gastroduodenal artery, the hepatic 
enters the lesser omentum on its way to the liver. A small 
branch, the right gastric artery (a. gastrica dextra) passes 
to the pylorus and anastomoses across the lesser curvature 
with a branch of the left gastric artery. 
The veins of the stomach and spleen are tributaries of the portal 
vein. Accompanying the branches of the splenic artery are the 
tributaries of the splenic vein (v. lienalis), including the left gastro- 
epiploic vein. Accompanying the branches of the left gastric artery 
are the tributaries of the coronary vein (v. coronaria ventriculi). 
The splenic and coronary veins enter the left wall of the portal vein 
through a short common trunk. 
On the right side of the stomach the superior pancreaticoduo- 
denal vein is united with the right gastroepiploic vein to form a 
short trunk, the gastroduodenal vein (v. gastroduodenalis), which 
enters the right wall of the portal vein. The left gastroepiploic vein 
receives tributaries from the dorsal surface of the pyloric antrum. 
The abdominal portion of the tenth cranial, or vagus 
nerve (n. vagus) may be traced from the oesophagus to the 
surface of the stomach. The left cord appears on the left 
wall of the oesophagus; crossing the ventral surface of the 
latter obliquely to the right, it ramifies on the ventral 
portion of the lesser curvature. The right cord passes to 
the stomach in a similar manner from the dorsal surface 
of the oesophagus. These relations suggest the twisting 
which the stomach has undergone in developing its adult 
form and position. 
5. Cut across the stomach at the pyloric antrum. Divide the 
oesophagus, and remove the stomach from the body. Open the 
organ by means of an incision extending around the greater 
curvature to the oesophagus. 
On the cut end of the pyloric antrum the mucous and muscular 
tunics (c/. Fig. 13) may be distinguished and separated from one 
another by dividing the loose tissue of the tela submucosa. On the 200 
Anatomy of the Rabbit 
surface of the mucous tunic may be seen the gastric areas (areae 
gastricae), formed by the longitudinal folds and imperfect transverse 
ridges which tend to connect them. They are well marked only 
in the contracted condition of the stomach. The mucous tunic 
of the stomach is sharply differentiated from that of the oesophagus. 
IV. THE LIVER 
The liver (hepar) is noteworthy, first, as being the largest of the 
glandular structures of the body, and, secondly, as containing, in 
addition to the primary circulation formed by the hepatic artery 
and veins, the ramifications of the portal system. It is an appen- 
dage of the digestive tube, its connection with the latter being 
through the common bile duct. 
For the general relations of the liver, see p. 25. 
1. Examine the contour and plan of division as follows: 
(a) The convex anterior surface, applied to the diaphragm; 
the concave posterior surface fitting the convexity of the 
stomach; the thickened dorsal portion of the organ, and its 
thin posteroventral margin. 
(b) The division of the organ into right and left lobes, and of 
each lobe into anterior and posterior lobules. The 
posterior right lobule lies close to the dorsal body-wall and 
is separated from the anterior lobule by a rather wide space 
which accommodates the pyloric end of the stomach. 
(c) The gall bladder (vesica fellea), situated on the posterior 
surface of the right anterior lobule. 
(d) The quadrate lobe (lobus quadratus), represented by one 
or more small divisions of the medial margins of left and 
right anterior lobules-sometimes indicated only by small 
clefts in these margins. 
(e) The caudate lobe (lobus caudatus), a small independent 
lobe projecting backward from the base of the left posterior 
lobule, and accommodated in the natural condition in the 
space enclosed by the lesser curvature of the stomach. 
(/) The portal fissure (porta hepatis), a large depression 
accommodating the portal vein at its point of entrance. The Liver 
201 
2. Trace the peritoneal connections as follows: 
(a) The lesser omentum, represented by the hepatoduodenal 
ligament and the hepatogastric omentum, previously 
divided. 
(b) The falciform ligament (lig. falciforme hepatis), a broad 
median sheet connecting the anterior surface of the liver 
with the diaphragm and extending backward to the ventral 
abdominal wall. The position of this ligament indicates 
the line of division of the liver into right and left lobes. 
The free curved border of the ligament contains a thin cord, 
the round ligament (lig. teres hepatis), which marks the 
position of the umbilical vein in the foetus. The corres- 
ponding umbilical notch is less conspicuous than in man 
because of the highly lobulated condition of the whole organ 
in the rabbit. 
(c) The coronary ligament (lig. coronarium hepatis), a short 
circular fold, continuous with the dorsal extremity of the 
falciform, and connecting the anterior surface of the liver 
with the middle of the diaphragm. 
(d) The left triangular ligament (lig. triangulare sinistrum), 
a lateral continuation of the coronary connecting the left 
lobe with the diaphragm. 
3. Trace the branches of the common bile duct, the hepatic artery, 
and the portal vein. These structures traverse the lesser 
omentum side by side and their branches are similarly arranged. 
(a) The common bile duct (d. choledochus) is formed on the 
posterior surface of the liver by the union of a left hepatic 
duct (d. hepaticus) with a similar duct from the right 
anterior lobule. The latter receives the cystic duct (d. 
cysticus) from the gall bladder. Special ducts from the 
right posterior lobule and from the caudate lobe enter the 
common bile duct through a short common trunk. The 
common bile duct passes backward on the right side of the 
portal vein, and enters the digestive tube on the dorsal 
surface of the first (superior) portion of the duodenum 
immediately beyond the pylorus. 202 
Anatomy of the Rabbit 
(&) The hepatic artery (a. hepatica) approaches the liver by 
passing forward on the right side of the portal vein ventral 
to the bile duct. It distributes branches to the right 
posterior lobule and the caudate lobe, and at the base of the 
liver proper divides into right and left rami. The right 
ramus sends a branch, the cystic artery (a. cystica), to the 
gall bladder. 
(c) The portal vein (v. portae), a vessel of large calibre, but 
usually found in a collapsed condition, enters the lesser 
omentum from the dorsal surface of the pyloric antrum. It 
distributes branches to the right posterior lobule and the 
caudate lobe; then passing directly forward to the base of 
the left lobe is distributed to the latter, a right branch being 
given off to the right anterior lobule. 
4. Divide the lesser omentum with the structures described above. 
Divide the coronary and triangular ligaments, cutting near the 
liver so as not to injure the central tendon of the diaphragm, 
which resembles the coronary ligament. Remove the liver and 
examine its dorsal surface for the following: 
(a) The inferior vena cava, accommodated in a depression 
of the thickened dorsal portion of the organ. The vessel 
should be opened lengthwise. 
(&) The hepatic veins (vv. hepaticae) open almost directly 
from the substance of the liver into the inferior cava. They 
are typically four in number, there being separate vessels for 
the anterior and posterior parts of the right lobe and for the 
caudate lobe, in addition to a large vessel for the left lobe. 
(c) The renal impression (impressio renalis), an extensive 
excavation of the right posterior lobule for the accommoda- 
tion of the right kidney. 
V. THE INTESTINES 
The posterior portion of the digestive tube, or that portion 
extending from the pyloric aperture of the stomach to the anal 
aperture, is divisible into two main parts, not wholly distinguishable 
in calibre, namely, the small intestine (intestinum tenue), and the The Intestines 
203 
large intestine (intestinum crassum). Both are greatly elongated 
and convoluted. In examining them care must be taken to avoid 
injury to the blood-vessels and mesenteries, especially the dorsal 
attachments of the mesenteries, in which the chief plexuses and 
related ganglia of the sympathetic system will afterwards be traced. 
For the general relations of the intestines and mesenteries, see pp. 90, 109. 
For study of mucous surface, see note p. 305. 
1. Beginning at the pylorus, trace the course of the small intestine, 
as follows: Its first portion, the duodenum, forms a U-shaped 
loop lying on the dorsal wall of the abdominal cavity to the 
right of the vertebral column. The distal end of this loop, 
when traced from the right side, disappears in the peritoneum 
and may then be picked up in a forward position on the left side 
of the mass. This point marks the beginning of the second 
portion, the mesenterial small intestine (intestinum tenue 
mesenteriale), which may be traced to its termination on the 
greatly enlarged caecum. The connection with the caecum is 
through a rounded semi-expanded sac, the sacculus rotundus. 
The terminal portion of the small intestine is somewhat more 
difficult to follow on account of the adhesions of its peritoneum 
with that of the large intestine. 
2. Examine the divisions of the duodenal loop and related structures 
as follows: 
(a) The superior, descending, transverse (horizontal), and 
ascending portions of the duodenal loop. 
(&) The common bile duct, opening on the dorsal wall of the 
superior portion. 
(c) The mesoduodenum, a fold of peritoneum joining the 
various parts of the loop. 
(d) The pancreas (Fig. 3 B, p. 24). Its principal portion is 
here seen as a diffuse brownish mass lying in the mesoduo- 
denum (c/. pp. 84 and 107). Its duct (d. pancreatis) opens 
into the posterior portion of the ascending limb. 
(e) The superior pancreaticoduodenal artery, a branch of 
the gastroduodenal (see p. 198), passes backward on the 
first portion of the descending limb. 204 
Anatomy of the Rabbit 
(/) The inferior pancreaticoduodenal artery (a. pan- 
creaticoduodenalis inferior), a branch of the superior 
mesenteric (p. 207), enters the mesoduodenum from the left 
side and supplies the major portion of the loop. An 
anterior branch anastomoses with (e). 
3. In the mesenterial small intestine the following features may 
be identified: 
(a) The lighter coloration, due to the thicker wall and greater 
vascularity, of the first or duodenal portion, thus distin- 
guished as the jejunum (intestinum jejunum). 
(&) The darker coloration, due to the thinner wall, which allows 
the contents to show through, and diminished vascularity 
of the terminal or caecal portion, thus distinguished as the 
ileum (intestinum ileum). The two portions are not 
distinctly separable. The circular folds (plicae circulares), 
or valvulae conniventes, of the mucous tunic, which in 
many mammals contribute to the thickness of the wall in 
the duodenum and jejunum, are, in the rabbit, not definitely 
expressed. 
The colour differences are not usually well indicated in 
embalmed animals. 
(c) The mesentery, the peritoneal support of the mesenterial 
small intestine, is distinguished in its major portion by its 
broad frill-like character, which allows great freedom of 
movement to this portion of the digestive tube. Its terminal 
portion, however, beginning at a point where the intestine 
turns sharply forward on its way to the caecum, is adherent 
to the mesocolon. 
(<Z) The mesenteric lymph glands (lymphoglandulae mesen- 
tericae) are aggregated a short distance from the dorsal 
attachment of the mesentery, where they form a compact 
mass covering the left side of the superior mesenteric 
artery. 
(e) The wall of the sacculus rotundus shows externally a fine 
hexagonal pattern on account of the presence in it of a large 
number of lymph follicles. Similar structures, forming oval 
areas about 3 mm. in diameter and 5 mm. in length, may be The Intestines 
205 
found along the wall of the small intestine (aggregated 
lymph nodules of Peyer). 
(/) The finger-like processes, or villi, of the mucous tunic of the 
small intestine may be seen by making an incision of the 
wall and examining its internal surface. A small portion 
of the wall may be excised and examined under water. 
4. Trace the course of the large intestine, beginning at the sacculus 
rotundus, as follows: 
Its first portion, the blind intestine or caecum (intestinum 
caecum), distinguished by its great size, is connected with the 
large intestine proper only in the region of the sacculus rotundus. 
The organ consists of three limbs (Fig. 45), and terminates in the 
narrow but thick-walled vermiform process (processus vermi- 
formis) or appendix. The latter lies in a dorsal position, and is 
directed backward. 
The second portion, the colon, comprising the major portion 
of the large intestine proper, leaves the caecum in the region of the 
sacculus rotundus, in which position it is distinguished by its greatly 
sacculated walls. 
The third portion, the straight intestine or rectum (intes- 
tinum rectum), is a small terminal division situated in the middle 
line and enclosed for the most part by the pelvis. It is scarcely 
distinguishable from the related portion of the colon. 
5. In the caecum the following features may be distinguished: 
(a) The wall, which is otherwise smooth, is divided by a spirally 
arranged constriction, the latter denoting the position, 
internally, of a fold of the mucous tunic, the spiral valve. 
(5) The vermiform process is a narrow, light-coloured tube of 
about five inches in length, the wall patterned externally 
by lymph follicles, in the same way as that of the sacculus 
rotundus, and greatly thickened in comparison with that of 
the caecum proper. 
6. The colon is divisible into ascending, transverse, and descending 
portions, the relations of which may be traced as follows: 
(a) The ascending colon (colon ascendens) passes from its 
origin on the caecum to a point forward on the right side of 206 
Anatomy of the Rabbit 
the dorsal body-wall. This portion is greatly elongated in 
the rabbit, and instead of passing directly forward (i.e., 
upward in man-see Fig. 42), follows more or less closely 
the course of the caecum. It is composed of five principal 
limbs, each of these being a portion which runs either for- 
ward or backward and is united by a flexure to the next, 
which has the opposite direction. Three of the limbs are 
directed for the most part forward, the remaining two back- 
ward, and the third includes a pronounced secondary 
curvature in a lateral direction. 
The first limb of the colon bears three rows of small 
sacculations, the haustra, separated by three longitudinal 
muscle stripes, distinguished as the bands of the colon 
(taeniae coli). Two of these bands are free, while the third 
is enclosed by the supporting peritoneum, the mesocolon. 
The two free bands join toward the anterior end of the first 
limb, the second limb having two rows of haustra. 
(&) The transverse colon (colon transversum) is a short seg- 
ment, beginning forward on the right and crossing the 
middle line transversely to the left, where it bends sharply 
backward, and is replaced by the descending colon. 
(c) The descending colon (colon descendens) passes back- 
ward to a point in front of the pelvis, where it is replaced 
by the rectum. 
The descending mesocolon, which connects this por- 
tion with the dorsal body-wall, should be noted on account 
of its relation to the inferior mesenteric artery and sym- 
pathetic plexuses. It is connected for a considerable 
distance with the mesentery of the ascending limb of the 
duodenum. 
7. Displace the caecum, turning it over to the right side of the 
animal. Lay out the mesenterial small intestine, so that the 
mesentery and its blood-vessels are exposed. Remove the 
lymph glands from about the superior mesenteric artery, first 
noting their position a short distance from the root of the 
mesentery. They receive afferent lymphatic vessels from the 
wall of the intestine, and send off efferent vessels to one another 
and to the lymphatic trunks. The Intestines 
207 
Trace the branches of the superior mesenteric artery as follows: 
(a) The middle colic artery (a. colica media), a small vessel 
(frequently two) arising from the left wall and passing to 
the transverse colon. 
(&) The inferior pancreaticoduodenal artery (p. 204) arises at 
the same level, but from the right wall. 
(c) The ileocaecocolic artery (a. ileocaecocolica), a large 
branch, equalling in size the superior mesenteric trunk, is 
distributed to the terminal portion of the ileum, the caecum 
(including the vermiform process), and the ascending colon. 
Its branches are arranged in two series, a proximal group 
being given off near the point of origin of the main vessel, 
and a distal group, including the terminal portion of the 
vessel, at about two inches from the point of origin. 
The proximal branches include: 
(1) Small branches to the third, fourth, and fifth limbs of 
the ascending colon. 
(2) The appendicular artery (a. appendicularis) to the 
vermiform process. A branch of this vessel, given off 
near the point of origin, passes to the ileum, anasto- 
mosing with a branch of the superior mesenteric trunk. 
(3) An anterior ileocaecal artery to the terminal fourth 
(third limb) of the caecum proper and related portion 
of the ileum. 
(4) An anterior right colic artery to the flexure uniting 
the first and second limbs of the ascending colon. 
(5) A posterior right colic artery to the second limb of the 
ascending colon. This vessel anastomoses with (4) and 
with the special branch to the third limb (1). 
The distal branches include: 
(6) A posterior ileocaecal artery to the middle portion 
of the third limb of the caecum and the adjacent portion 
of the ileum; anastomosing with (3). 
(7) A caecal artery to the second limb and the posterior 
end of the third limb of the caecum. 
(8) Terminal branches to the parts about the sacculus 
rotundus; anastomosing with (4). 208 
Anatomy of the Rabbit 
(d) The intestinal arteries (aa. intestinales), about twenty in 
number, are given off from the superior mesenteric artery, 
and are distributed to the free portion of the mesenterial 
small intestine. The successive vessels are connected by 
anastomoses. All but two of the intestinal arteries arise 
from one side of the superior mesenteric artery, one forms 
the end of the latter, and one springs from its opposite side. 
The last anastomoses forward with a branch of the appen- 
dicular artery. 
8. Locate in the descending mesocolon the inferior mesenteric 
artery (a. mesenterica inferior), a small median vessel arising 
from the abdominal aorta. It has two main branches-the 
left colic artery (a. colica sinistra) to the anterior portion of 
the descending colon (anastomosing with the middle colic), and 
the superior haemorrhoidal artery (a. haemorrhoidalis 
superior) to the posterior portion of the colon and the rectum. 
9. The superior mesenteric vein (v. mesenterica superior), the 
chief tributary of the portal, collects the blood distributed by 
the superior mesenteric artery, its tributaries being similar in 
arrangement to the branches of the artery. The inferior 
mesenteric vein (v. mesenterica inferior) collects blood from 
the descending colon and rectum; it may be traced forward in 
the descending mesocolon. 
10. Sympathetic plexuses. In the descending mesocolon will be 
found the inferior mesenteric ganglion (g. mesentericum 
inferius), a narrow curved body situated in front of the inferior 
mesenteric artery. Surrounding the abdominal aorta and 
appearing in the mesocolon is the abdominal aortic plexus 
(plexus aorticus abdominalis). It is connected anteriorly with 
the coeliac and superior mesenteric plexuses (p. 197) accom- 
panying the corresponding vessels, and with the renal plexuses 
accompanying the renal vessels to the kidneys; posteriorly with 
the inferior mesenteric and spermatic plexuses about the 
inferior mesenteric and internal spermatic arteries, and with 
the hypogastric plexus about the pelvic vessels. 
11. By division of the rectum close in front of the pelvis and of 
the peritoneal attachments, the intestines may be separated The Urinogenital System 
209 
and laid out in an extended condition. The relations to one 
another of the ileum, caecum, and colon are studied thus to 
much better advantage than in the natural position. The 
caecum may be opened lengthwise and the spiral valve ex- 
amined. 
VI. THE URINOGENITAL SYSTEM 
For the general relations of the urinogenital organs, see p. 100. 
A. The Urinary Organs 
The central organs of excretion, the kidneys (renes), occupy an 
anterior position on the dorsal wall of the abdomen. The right 
kidney is placed a little farther forward than the left, and is largely 
covered by the right posterior lobule of the liver. In addition to a 
fibrous coat immediately surrounding the kidney substance, each 
organ is imbedded in a mass of fatty material, the adipose capsule 
(capsula adiposa), and is also held in position by the peritoneum, 
which is stretched across its ventral surface. 
1. If the peritoneum and adipose capsule are removed from the left 
kidney, the external features and vascular connections may be 
made out as follows: 
(a) The general convexity of contour. 
(b) The renal hilus (hilus renalis), a concavity of the medial 
surface of the organ. 
(c) The ureter, or duct of the kidney, a white tube passing 
backward from the hilus. 
(d) The renal artery (a. renalis), arising from the abdominal 
aorta and entering the kidney at the hilus. A branch of 
this vessel, the suprarenolumbar artery (a. suprarenolum- 
balis), passes to the body-wall in front of the kidney, giving 
off a small suprarenal artery to the suprarenal gland. 
(e) The renal vein (v. renalis), leaving the kidney at the hilus, 
and joining the inferior cava. 
The right renal artery leaves the aorta about one-half centimetre 
in front of the origin of the left vessel, than which it is considerably 
shorter. The two renal veins have similar relative positions, but the 
distance between their proximal ends is a little greater. 210 
Anatomy of the Rabbit 
2. Divide the kidney, beginning the incision at the hilus and 
removing the ventral half (Fig. 53). Examine the cut surface 
of the dorsal half for the following: 
(a) The renal pelvis (pelvis renalis), formed by the expanded 
funnel-like end of the ureter, which is fitted into the renal 
hilus. A central cone of kidney substance, the renal 
papilla (papilla renalis), projects into the pelvis. 
(b) The cortical substance (substantia corticalis); distinguish- 
able as a narrow peripheral zone of the kidney substance. 
(c) The medullary substance (substantia medullaris), form- 
ing the central and medial portion of the kidney, including 
the renal papilla. It is distinguished by its radial striations. 
(d) The fibrous coat (tunica fibrosa) of the kidney may be 
stripped from the surface. 
In the rabbit the kidney is not lobulated. Hence there is a single 
renal papilla, and the division of the kidney substance into renal 
pyramids is imperfectly expressed. The medullary substance, how- 
ever, possesses a slightly divided margin. 
The cortical substance is of darker coloration than the medullary 
in the natural condition, but in embalmed animals the colour relations 
are usually reversed. 
3. The urinary bladder (vesica urinaria) lies in the ventral 
posterior portion of the abdominal cavity. It is a muscular sac, 
capable of a considerable amount of distension, but usually 
found in preserved animals in a greatly contracted condition. 
Its rounded anterior end, the vertex, projects forward into the 
abdominal cavity, while its posterior portion or fundus, narrows 
to a canal, the urethra, which receives on its dorsal wall the 
apertures of the genital ducts and those of the related glands. 
The connections may be made out as follows: 
(a) The peritoneum is reflected from the dorsolateral surface of 
the rectum in the male and from the vagina in the female, 
to the bladder, and after investing the latter passes to the 
ventral abdominal wall. The peritoneum dorsal to the 
bladder forms in the male a double rectovesical fold (plica 
rectovesicalis), and in the female a similar vesicouterine 
fold, a recess of considerable extent (rectovesical or The Urinogenital System 
211 
vesicouterine pouch) being left between the adjacent 
structures. 
The ventral peritoneum forms a broad median vertical 
sheet, the middle umbilical fold (plica umbilicalis media). 
The free edge of this fold, extending from the vertex of the 
bladder to the umbilicus, contains a slender cord, the 
middle umbilical ligament (lig. umbilicale medium). 
The latter marks the position of the peripheral portions of 
the umbilical arteries in the foetus. 
(b) The umbilical artery (a. umbilicalis), a branch of the 
hypogastric, passes along the side of the bladder to the 
vertex. From the base of the artery branches are given off 
to the ureter (a. ureterica) and related portions of the 
genital ducts. 
B. The Male Genital Organs 
1. Continue the median ventral incision of the skin backward along 
the symphysis to the penis. Reflect the skin on both sides to 
clear the attachments of the penis to the ischium, and on the left 
to a point beyond the scrotum. Note the cremaster muscle 
(m. cremaster), a thin layer of muscle fibres forming the outer 
layer of the sac of the testis. It is continuous with the internal 
oblique muscle of the abdominal wall, and also contains fibres 
from the transverse muscle. It is supplied with blood from the 
external spermatic artery. Make a longitudinal incision through 
this muscle, cutting forward into the abdominal cavity. After 
the two flaps are spread apart, the following features may be 
made out: 
(a) The parietal layer (lamina parietalis) of the tunica 
vaginalis propria, a layer of peritoneum, continuous with 
that of the abdominal wall, forms the internal lining of the 
sac of the testis (cf. p. 112 and Fig. 58). The sac is widely 
open to the abdominal cavity, so that the testis passes 
freely from one cavity to the other. 
(5) The male reproductive gland, the testis, and its associated 
vessels and duct occupy the cavity of the sac, the testis 
being suspended from its dorsal wall. 212 
Anatomy of the Rabbit 
(c) The gubernaculum, a short thick cord containing smooth 
muscle hbres, joins the posterior end of the testis with the 
end of the sac. 
(d) The visceral layer (lamina visceralis) of the tunica 
vaginalis propria forms the peritoneal coat of the testis 
and is continuous with the mesorchium, a broad vertical 
fold of peritoneum connecting the testis dorsally and 
anteriorly with that of the body-wall. 
(e) The first portion of the duct of the testis, the epididymis, 
usually imbedded in fat, forms a thickened mass at the 
anterior end of the testis, and extends backward as a thinner 
cord along its side. The thickened anterior part is the 
caput epididymidis and the contracted posterior part 
the cauda epididymidis. The second portion of the duct, 
the ductus deferens, leaves the testis at its posterior end, 
where it is firmly attached to the gubernaculum. The 
connection with the epididymis may be shown by carefully 
separating the duct from the gubernaculum and the side of 
the testis. The ductus deferens receives its blood supply 
from the umbilical artery. 
(/) The internal spermatic artery (a. spermatica interna) 
arises from the abdominal aorta, in the neighbourhood of 
the inferior mesenteric artery, or opposite the sixth lumbar 
vertebra, the left artery usually behind the right. It sends 
branches to the epididymis and ductus deferens, and then 
follows a contorted course to enter the testis near its 
anterior end. 
The ductus deferens is supplied mainly by the arteria deferentialis 
which originates from the base of the umbilical artery or from the 
adjacent part of the common iliac. 
(g) The spermatic vein (v. spermatica) is formed by a net- 
work of vessels, the plexus pampiniformis, which sur- 
rounds the internal spermatic artery in its posterior portion. 
The left vein opens forwards into the inferior caval at the 
angle formed by the latter with the renal artery. That of 
the right side enters the inferior caval at about the level 
of the spermatic arteries. The Urinogenital System 
213 
Owing to the open communication of the testis sac with the 
abdominal cavity, the association of the ductus deferens with the 
spermatic vessels to form a spermatic cord (funiculus spermaticus) 
is very imperfectly expressed. 
2. The structure and attachments of the penis should be examined. 
Apart from its terminal portion, the glans penis, and the 
urethra, the body of the penis is formed chiefly by a pair of 
hollow fibrous structures, the cavernous bodies (corpora 
cavernosa penis). 
The cavernous bodies have thick white sheaths (tunicae albugineae) 
which fuse in a median septum. They are best seen by cutting the 
penis transversely after the study of the organs has been otherwise 
completed. 
Each cavernous body is firmly attached to the posterior margin 
of the ischium by a white fibrous cord, the crus penis. The 
latter is partly concealed by a short thick ischiocavernosus 
muscle, the origin of which occupies a similar position on the 
ischium. The penis is also attached to the symphysis by a short 
but stout unpaired suspensory ligament (lig. suspensorium) 
and by a thick spindle-shaped pubocavernosus muscle lying 
in a median position ventral to the ligament and between the 
two ischiocavernosi. 
Strictly speaking, a glans penis, which occurs in many mammals, 
is absent in the rabbit and the free extremity of the organ should 
be called simply pars libera. The glans, properly, is a swollen 
terminal portion of the erectile tissue (corpus spongiosum) in the 
wall of the urethra. 
When the study of these parts has been completed the attach- 
ments of the penis should be severed at the posterior border of the 
ischium and the symphysis should be divided. Pressing apart the 
two halves of the pelvis facilitates examination of the connections 
of the deferent ducts with the common urinogenital tube and 
related parts. Following this the urinogenital organs and pelvic 
portion of the rectum may be dissected out and removed from 
the body. 
The middle haemorrhoidal artery (a. haemorrhoidalis media), a branch 
of the hypogastric, passes to the side of the rectum, to the urethra, and to the 
seminal vesicle. The internal pudendal artery (a. pudenda interna), accom- 
panied by the corresponding nerve and vein, passes to the side of the penis, giving 
off the inferior haemorrhoidal artery to the terminal portion of the rectum 
and to the associated rectal or anal gland. The latter is an elongated, paired 
organ enveloping the rectum a short distance in front of the anus and pouring 214 
Anatomy of the Rabbit 
into it an oily secretion. The rectum is connected with the root of the tail by 
the rectocaudalis muscle, a somewhat spindle-shaped aggregation of smooth 
muscle fibres, arising from the body of the second caudal vertebra, and inserted a 
short distance forwards on the dorsal surface of the rectum. The sphincter ani 
externus and sphincter ani internus are two closely related muscles enclosing 
the rectum and urethra, the former arising from the dorsum of the tail. 
Immediately dorsolateral to the body of the penis and just under the skin 
lie the paired inguinal glands. At each side, a nearly spherical white inguinal 
gland and, closely associated, a brown inguinal gland pour their secretions 
into the hairless inguinal spaces. The former gland is sebaceous, the latter a 
modified sweat gland. 
The following parts of the urinogenital system may be made out: 
(a) The connection of the bladder with the outside of the body 
through the urethra. It comprises a short prostatic 
portion in relation to the genital ducts, a much longer 
membranous portion traversing the pelvis, and a terminal 
cavernous portion in the penis. 
(b) The seminal vesicle (vesicula seminalis) lies on the dorsal 
surface of the base of the bladder. It is a flattened median 
pouch, the anterior, slightly divided tip of which is directed 
forward. 
(c) The deferent ducts lie between the seminal vesicle and the 
dorsal wall of the bladder. They terminate in the ventral 
wall of the seminal vesicle. 
(J) The prostate (prostata), a white or yellowish mass of 
glandular tissue, lies in the posterior portion of the dorsal 
wall of the seminal vesicle. Its ducts, three or four in 
number on either side, open into the urethra. Accessory 
paraprostatic glands (gl. paraprostaticae), minute finger- 
like projections of the urethral wall, lie on either side of the 
base of the seminal vesicle. 
(e) The bulbourethral gland (gl. bulbourethralis); situated 
on the dorsal wall of the urethra behind the prostate. 
3. The internal surface of the dorsal wall of the urethra may be 
exposed by a longitudinal incision extending into the bladder. 
The crescentic aperture of the seminal vesicle lies immediately 
in front of an oval elevation, the colliculus seminalis, on 
either side of which some of the minute apertures of the prostate 
may sometimes be made out. The Urinogenital System 
215 
C. The Female Genital Organs 
1. The organs may be traced from the abdominal cavity backward, 
as follows: 
(a) The ovary (ovarium) is a small-in young animals minute- 
elongated structure of greyish or yellowish coloration lying 
on the dorsal body-wall some distance behind the kidney. 
It is readily distinguished by the circular translucent dots 
representing the larger vesicular ovarian follicles. In 
some cases the darker radiate impressions (corpora lutea) 
left by extruded eggs are discernible. 
(&) The mesovarium, a short fold of peritoneum suspending 
the ovary from the body-wall. 
(c) The internal spermatic artery (a. spermatica interna) 
arises from the abdominal aorta, immediately behind the 
origin of the inferior mesenteric artery, and crosses the 
body-wall transversely to the ovary. 
(d) The spermatic vein (v. spermatica) leaves the medial side 
of the ovary, and crossing the body-wall enters the inferior 
caval vein. 
(e) The uterine tube (tuba uterina), the first portion of the 
oviduct, distinguishable by its narrow calibre, opens into 
the abdominal cavity through a broad funnel-like expansion, 
the ostium abdominale tubae uterinae. The margin 
bears a large number of short folds and processes, the 
fimbriae tubae, which tend to enclose the margin of the 
ovary. A single cyst-like hydatid may be seen in the 
funnel-like expansion of the tube, but in embalmed animals 
is usually found collapsed. 
(/) The mesosalpinx is the peritoneum supporting the uterine 
tube. It is continuous with the mesovarium. 
(g) The uterus, the second portion of the oviduct; distin- 
guished by its greater diameter and muscular walls. The 
size of this portion is enormously increased in animals 
which contain or have borne young. 
(A) The mesometrium is the supporting peritoneum of the 
uterus, and is a continuation of the mesosalpinx. The 
mesometrium, mesosalpinx, and mesovarium together con- 
stitute the broad ligament (lig. latum uteri). 216 
Anatomy of the Rabbit 
(i) The ovarian ligament (lig. ovarii proprium) crosses the 
mesosalpinx, connecting the ovary with the anterolateral 
end of the uterus. It is continued by: 
(j) The round ligament (lig. teres uteri), which may be traced 
from the anterior end of the uterus to the body-wall below 
the posterior portion of the inguinal ligament, where it is 
inserted into a small peritoneal recess, the homologue of the 
testis sac of the male. 
(&) The uterine artery (a. uterina) runs through the meso- 
metrium after originating from the umbilical artery. 
(Z) The vagina is a flattened median tube with muscular walls; 
it receives anteriorly the apertures of the right and left uteri. 
2. Preparatory to dissecting the urinogenital structures of the 
pelvis, the median incision of skin of the ventral surface should 
be continued backward to the base of the clitoris, which organ 
appears as a flexible median rod imbedded in the ventral wall 
of the vestibulum. Corresponding with the glans penis of the 
male, there is a short terminal portion, the glans clitoridis, 
covered by a fold of skin. The structure and attachments of 
the clitoris should now be examined. 
(a) The cavernous bodies (corpora cavernosa clitoridis) form 
the body of the structure, as in the penis of the male, and 
are attached to the posterior border of the ischium through 
short fibrous cords, the crura clitoridis. 
(b) The suspensory ligament (lig. suspensorium clitoridis) is 
a short median cord joining the base of the clitoris with the 
posterior end of the symphysis. 
(c) The pubocavernosus and ischiocavernosus muscles 
pass from the posterior border of the ischium to the base 
of the clitoris, the former being median in position, the 
latter situated at either side. 
The attachments of the clitoris should be severed and the sym- 
physis divided. By pressing apart the two sides of the pelvis the 
urinogenital tube may be dissected out and removed, together with 
the terminal portion of the rectum. 
The related structures, the middle haemorrhoidal artery, etc., appearing in 
this dissection are as in the male (see small print, pp. 213-4). 
In the urinogenital ducts, examine the extent of the vagina 
backward and its connection with the canal of the bladder (female The Abdominal Aorta 
217 
urethra) to form the common vestibulum. The canal and the 
vestibulum together correspond with the male urethra {cf. Fig. 51, 
p. 99). The bulbourethral gland (gl. bulbourethralis) (c/. 
p. 214) lies on the dorsal wall of the vestibulum. 
If the vestibulum be slit open and the incision be extended into 
the bladder and also forward into the left uterus the apertures of 
these structures may be examined from the interior. There is an 
external uterine aperture (orificium externum uteri) for each 
division of the uterus. 
VIL THE ABDOMINAL AORTA, INFERIOR CAVAL VEIN, 
AND SYMPATHETIC TRUNKS 
The dissection and removal of the intestines and urinogenital 
organs clears the dorsal body-wall for an examination of the 
abdominal portion of the aorta, the inferior caval vein, and the 
sympathetic trunks. If the inferior cava does not contain blood its 
tributaries should be cleared first, in order to keep them from being 
damaged; otherwise the branches of the aorta should first be traced. 
The anterior portion of the inferior cava has been removed with 
the liver. 
1. The abdominal portion of the 
aorta, described as the ab- 
dominal aorta (aorta ab- 
dominalis) extends from the 
hiatus aorticus of the dia- 
phragm to the seventh lum- 
bar vertebra, where it is 
replaced by the paired com- 
mon iliac arteries. It passes 
backward in a median posi- 
tion along the ventral sur- 
faces of the bodies of the 
vertebrae. Its natural con- 
tinuation backwards on the 
sacrum and the caudal verte- 
brae is represented by the 
greatly reduced median 
sacral artery. 
Fig. 76. Plan of the pelvic blood-vessels. 
Arteries: a, aorta; aei, inferior epigastric; 
af, femoral; ah, hypogastric; ahm, middle 
haemorrhoidal; ai, sciatic; aic, common iliac; 
aie, external iliac; ail, iliolumbar; ao, 
obturator; as, sacral; au, umbilical. Veins: 
vci, inferior cava; vf, femoral; vh, hypo- 
gastric; vh', common hypogastric; vie, 
external iliac; vil; iliolumbar. 218 
Anatomy of the Rabbit 
The branches of the vessel are distributed in two series: (1) 
visceral branches (rami viscerales) to the parts of the 
digestive tube and the urinogenital organs; and (2) parietal 
branches (rami parietales) to the body-wall. 
The visceral branches comprise the paired renal and 
spermatic arteries, and the unpaired coeliac, superior 
mesenteric, and inferior mesenteric arteries, which have 
already been traced. 
The parietal branches comprise: 
(a) The superior phrenic arteries (aa. phrenicae superiores), 
very small vessels arising by a common trunk in the hiatus 
aorticus and passing to the diaphragm (usually seen better 
on the right side). 
(&) The suprarenolumbar artery (a. suprarenolumbalis), 
arising on either side from the renal artery, and passing 
anterolaterad to the body-wall, supplying also the supra- 
renal body. 
Occasionally the suprarenal artery originates separately. 
(c) The lumbar arteries (aa. lumbales), seven pairs of vessels 
distributed metamerically to the lumbar portion of the 
body-wall. Six pairs arise from the dorsal wall of the aorta, 
the seventh from the median sacral artery. They arise as 
single trunks, branching into right and left. 
(J) The median sacral artery (a. sacralis media) arises from 
the dorsal wall of the aorta near its posterior end, and passes 
backward on the ventral surface of the sacrum in the middle 
line. Its first portion is concealed from the ventral surface 
by the common hypogastric vein. 
2. The common iliac artery (a. iliaca communis) is a short 
paired trunk, the branches of which pass to the posterior limb, 
the wall of the pelvis, and the pelvic viscera. After giving off 
the iliolumbar artery (a. iliolumbalis), the point of origin of 
which varies considerably and which passes laterad to the body- 
wall, the common iliac divides into two branches the connections 
of which may be traced as follows: 
(a) The external iliac artery (a. iliaca externa) is the larger, 
lateral branch, directed toward the inguinal ligament, over 
which it passes to the medial surface of the limb, becoming The Abdominal Aorta 
219 
the femoral artery. Near its crossing with the ligament it 
gives off the inferior epigastric artery (a. epigastrica 
inferior), the main portion of which passes forward in the 
medial portion of the abdominal wall. 
(b) The hypogastric artery (a. hypogastrica) is the smaller, 
medial branch, directed backward on the dorsal wall of the 
pelvis. Its course may be traced without injury to the 
nerves of the lumbosacral plexus. At its junction with the 
external iliac the vessel gives off the umbilical artery 
(a. umbilicalis) to the bladder, or in the female first to the 
vagina and uterus (a. uterina). The obturator artery 
(a. obturatoria) passes laterad to the pelvic wall and the 
middle haemorrhoidal to the side of the rectum and 
urethra. The main vessel leaves the pelvic cavity as the 
sciatic artery (a. ischiadica), passing to the lateral side 
of the abductor caudae anterior, and reappears posteriorly, 
dividing into the internal pudendal and lateral caudal 
arteries. 
3. The inferior caval vein (v. cava inferior) is formed on the 
dorsal surface of the posterior end of the aorta by the union of 
the paired external iliac veins with the common hypogastric, 
the latter a short median trunk receiving the paired hypogastric 
veins. From this position it passes to the right side of the aorta 
(rarely to the left) almost to its ventral surface, and then runs 
forward on the right side to the diaphragm. Its visceral roots 
or tributaries (radices viscerales) comprise the paired renal 
and spermatic veins, and the hepatic veins from the liver 
(p. 202). Its parietal tributaries (radices parietales) include 
the inferior phrenic veins (vv. phrenicae inferiores), which 
enter the inferior cava from either side of the diaphragm, the 
lumbar veins (vv. lumbales), a series of vessels corresponding 
to the lumbar arteries, and the paired iliolumbar vein (v. 
iliolumbalis). 
4. The external iliac vein (v. iliaca externa), the continuation 
of the femoral vein of the thigh, approaches the inferior cava 
from the dorsal side of the inguinal ligament. It receives the 
inferior epigastric vein from the abdominal wall and the 220 
Anatomy of the Rabbit 
vesical vein from the bladder, the latter including in the female 
also the veins of the uterus. 
5. The sympathetic trunk (truncus sympathicus). Its lumbar 
and sacral portions, and, with due care, its caudal portions may 
be traced on either side by working between the abdominal aorta 
(or its continuation, the median sacral artery) and the bcdy- 
wall. Except on the ventral surface of the sacrum, the ganglia 
of opposite sides lie close together. The lumbar portion of 
each trunk comprises seven ganglia with their connections. 
The ganglia lie on the lateral surfaces of the lumbar arteries near 
the points where the latter disappear dorsally in the body-wall. 
The rami communicantes may be found passing from the 
ganglia toward the spinal nerve-roots. The sacral portion 
comprises four ganglia of which the first is much larger than the 
others. The caudal portion comprises two minute ganglia 
and an unpaired terminal ganglion uniting the two trunks. 
VIII. THE ANTERIOR LIMB 
For this dissection the skin must first be reflected from the 
lateral surface of the limb and the side of the neck to the dorsal 
median line. It is advisable at first to divide the skin at the elbow, 
leaving the forearm and hand covered, so that the tendons of the 
muscles do not become dried out before they can be examined. 
Covering the side and ventral surface of the neck is a broad thin 
sheet of muscle, the platysma, replacing the cutaneus maximus 
of the trunk. It forms a continuous layer over the dorsal surface 
of the neck, at which place it is also continuous with the cutaneus 
maximus. Passing forward from the manubrium sterni is a narrow 
band of fibres, closely associated with the platysma but lying 
beneath it, the depressor conchae (parotideoauricularis) pos- 
terior, which is inserted into the external base of the ear. The 
entire sheet of muscle is so closely attached to the skin that it is 
sometimes removed with the latter. If in place, it should be raised 
from the surface, separated posteriorly from its attachment, and 
turned forward on the head. 
The dissection is mainly muscular, but the arteries and nerves 
should be kept intact for later examination. The Anterior Limb 
221 
Identify the manubrium sterni. The muscle directed forward 
from it toward the angle of the mandible is the sternomastoideus, 
one of the muscles of the head. The external jugular vein lies on 
its lateral side. Identify the clavicle rudiment and the cleido- 
humeral ligament, attaching it to the humerus. Find the mid- 
dorsal line of the neck, indicating the position of the neck ligament 
(ligamentum nuchae). Then proceed to uncover the muscles, 
beginning with those on the ventral side and working around to 
the shoulder. 
For the general muscle relations of the limbs, see p. 67. 
1. Muscles arising from the axial skeleton and inserted on the 
scapula and clavicle.* 
(a) The cleidomastoideus. Origin: Mastoid portion of the 
skull. Insertion: Middle portion of the clavicle. 
The muscle lying on its medial side and arising from the manubrium 
sterni is the sternomastoideus, one of the muscles of the head. 
(b) The basioclavicularis (basiohumeralis). Origin: Basiocci- 
pital bone. Insertion: Lateral third of the clavicle and the 
cleidohumeral ligament. 
(c) The levator scapulae major. Origin: Cartilage union of 
basioccipital and basisphenoid (sphenooccipital synchon- 
drosis). Insertion: Metacromion. 
The superficial cervical artery (p. 275) passes obliquely forward 
and outward under cover of these muscles, ramifying beneath the 
superior portion of the trapezius in the fat-mass of the side of the neck. 
Its ascending cervical branch passes forward on the lateral surface 
of the external jugular vein. 
(d) The trapezius. Origin in two portions. Superior (cer- 
vical) portion. External occipital protuberance and dorsal 
ligament of the neck (ligamentum nuchae). Insertion: 
Metacromion and supraspinous fascia. Inferior (thoracic) 
portion. Origin: Spinous processes of the thoracic verte- 
brae and the lumbodorsal fascia. Insertion: Dorsal half 
*The structures of Group 2 may be dissected first if preferred, the serratus 
anterior muscle being exposed from the lateral surface and divided together with 
the latissimus dorsi. 222 
Anatomy of the Rabbit 
of the scapular spine. The muscle forms a broad triangular 
sheet on the dorsolateral surface of the shoulder. 
The levator scapulae major, basioclavicularis, and trapezius should 
be divided. On the ventrolateral surface of the superior portion of the 
trapezius and levator scapulae major may be found nerves from the 
ventral rami of the third, fourth, and fifth cervical spinal nerves. The 
great auricular nerve (n. auricularis magnus) passes from the third 
to the ear. 
(e) The rhomboideus minor. Origin: Ligamentum nuchae. 
Insertion: Anterior two-thirds of the vertebral border of 
the scapula. 
(/) The levator scapulae minor. Origin: Mastoid and supra- 
occipital portions of the skull. Insertion: Medial surface 
of the inferior angle of the scapula. 
(g) The rhomboideus major. Origin: Spinous processes of 
the first seven thoracic vertebrae. Insertion: Posterior 
third of vertebral border. The rhomboidei are almost 
continuous. 
By dividing the rhomboidei the scapula may be displaced laterad. 
The operation is facilitated by dividing the latissimus dorsi, the re- 
lations of which should, however, first be noted (2, a). 
(Ji) The serratus anterior. Origin in two portions. Cervical 
portion: Transverse processes of the posterior five cervical 
vertebrae and the anterior two ribs. Thoracic portion: 
Third to ninth ribs by separate slips alternating with those 
of the external oblique. Common insertion: Medial surface 
of the vertebral border of the scapula. 
The transverse artery of the neck (a. transversa colli) lies on the 
medial side of the cervical portion. 
2. Muscles arising from the axial skeleton and the pectoral girdle 
and inserted on the humerus, for the most part at its proximal 
extremity. 
Note the axillary lymph glands lying in the fat of the axillary fossa, 
(a) The latissimus dorsi. Origin: Lumbodorsal fascia and 
four posterior ribs. Insertion: Deltoid tuberosity. Along 
flat triangular muscle, covering a considerable portion of 
the lateral surface of the thorax; having its dorsal angle The Anterior Limb 
223 
covered by the thoracic portion of the trapezius. Its 
insertion end passes to the medial side of the humerus. 
(b) The pectoralis primus (p. tenuis). Origin: Manubrium 
sterni. Insertion: Deltoid tuberosity. 
A branch of the thoracoacromial artery appears between this 
muscle and the cleidohumeralis (3, a). 
The muscle should be raised from the surface and divided. 
(c) The pectoralis secundus (p. major). Origin: Entire 
lateral portion of the sternum. Insertion: Anteromedial 
surface of the humerus, beginning below the head, and 
extending to the boundary between the middle and distal 
thirds. The anterior fibres are covered by those of (&). 
Some of the posterior fibres are inserted highest on the 
humerus. 
By working backward from the clavicle the muscle can be detached 
from those underneath and divided. 
(d) The pectoralis tertius (p. minor). Origin consisting of 
two portions. First portion: The sternum from its anterior 
end to the attachment of the fourth rib. Second portion: 
The whole length of the manubrium sterni and costal 
cartilage of the first rib, lying dorsal to the first portion. 
Insertion: The superficial fibres of the first portion are 
attached to the clavicle. The remaining fibres, combined 
with those of the second portion and those of the pecto- 
scapularis, pass to the dorsal side of the clavicle and over 
the shoulder to be inserted on the scapular spine. The 
muscle forms a broad fleshy mass covering the antercdorsal 
portion of the shoulder. 
(e) The pectoralis quartus. Origin: The sternum, from the 
attachment of the fourth to seventh costal cartilages. 
Insertion: Anterior surface of the head of the humerus, 
passing thence to its medial side. The muscle overlaps the 
more posterior fibres of the first portion of (d). 
(/) The pectoscapularis. Origin: The manubrium sterni at 
the point of attachment of the first costal cartilage. In- 
sertion as indicated above. A slender muscle dorsal to the 
second portion of the p. tertius, which should be divided. 224 
Anatomy of the Rabbit 
Blood-vessels and Nerves of the Axillary Fossa 
After division of the pectorals and the clavicle, the blood-vessels 
and nerves of the axillary fossa will be fully exposed. 
The axillary artery (a. axillaris), the continuation of the sub- 
clavian, crosses from the first rib to the medial surface of the 
humerus, after reaching which it is called the brachial artery. 
Its branches are: 
(a) The transverse scapular (suprascapular) artery (a. trans- 
versa scapulae). It arises from the anterior wall and, 
taking a position dorsal to the clavicle, accompanies the 
p. tertius and pectoscapularis to the front of the shoulder, 
where, under cover of these muscles, it passes into the 
supraspinatus muscle (3, e). 
(b) The thoracoacromial artery (a. thoracoacromialis). It 
arises from the ventral wall or in common with (c), passes 
between the pectorales tertius and quartus, then between 
the p. primus and the cleidohumeralis. It distributes 
branches to these muscles and, taking a position ventral to 
the clavicle, passes to the platysma and the skin. 
(c) The lateral (long) thoracic artery (a. thoracalis lateralis) 
arises from the posterior wall or in common with (b), 
distributes branches chiefly to the p. secundus, and sends 
a long superficial branch, the external thoracic artery, 
backward through the cutaneus maximus muscle. This 
vessel is usually conspicuous in the female, where it distri- 
butes external mammary branches to the mammary 
glands. It anastomoses posteriorly with the superficial 
epigastric branch of the femoral. 
(d) The subscapular artery (a. subscapularis) is a large 
branch given off from the distal portion of the axillary 
artery. It distributes branches to the subscapularis muscle, 
and sends a thoracodorsal branch into the latissimus 
dorsi. Perforating the teres major muscle near the axilla, 
it appears on the lateral surface of the shoulder, where it 
sends a large branch into the inferior portion of the tra- 
pezius, and a second into the cutaneus maximus. The 
latter vessel supplies the proximal end of the long head of The Anterior Limb 
225 
the triceps, but its chief portion passes backward uniting 
with an anterior superficial branch of the iliolumbar, and 
thus forming one of three anastomoses covering the ab- 
dominal region and in the female the mammary glands. 
(e) The circumflex arteries of the head of the humerus. 
See p. 231. 
(/) The deep artery (a. profunda brachii). See p. 231. 
The axillary vein (v. axillaris) begins at the medial side of the 
humerus and crosses the axillary fossa to the first rib whence it is 
continued as the subclavian. It receives the lateral thoracic 
and subscapular veins, which accompany the corresponding 
arteries, and also the cephalic vein (p. 232), which reaches the 
medial side of the shoulder from the anterior surface of the arm by 
passing between the teres major and subscapular muscles near the 
neck of the scapula. 
The brachial plexus (plexus brachialis) is the network of 
nerves formed from the ventral rami of the posterior five cervical 
and first thoracic spinal nerves. The cervical nerves also take part 
in the formation of the more general cervical plexus embracing all 
nerves of the cervical series. The strands of the brachial plexus 
cross the axillary fossa and at the medial surface of the humerus 
are largely replaced by the three chief trunks of the free extremity, 
the radial, median, and ulnar nerves (p. 233). These nerves are 
formed principally from the eighth cervical, with which is combined 
the first thoracic, but adjacent nerves also contribute. Especially, 
the seventh cervical gives a branch running mainly to the median 
and also connecting with the common trunk of the median and 
ulnar just before it divides into these nerves, and from the same 
source a slightly larger branch passes to the radial nerve. From 
the last-mentioned branch a subscapular nerve runs to the teres 
major, accompanied by a nerve to the latissimus dorsi, which latter 
frequently receives also a fascicle from the radial nerve. Another 
subscapular nerve to the muscle of that name arises mainly from 
the sixth cervical, these two being connected by a loop. A supra- 
scapular nerve, formed chiefly from the sixth cervical, passes to 
the anterior border of the scapula, entering the supraspinatus muscle. 
By dividing the axillary nerves and vessels and the two parts of the serratus 
anterior muscle, the limb may be removed from the body. 226 
Anatomy of the Rabbit 
3. Muscles arising from the pectoral girdle and inserted on the 
humerus. These muscles act on the humerus through the 
shoulder-joint, and except for the unimportant difference in 
origin are similar to those of Group 2. 
The course of the cephalic vein (p. 232) should be traced 
before separating the muscles of the front of the forearm. 
Note the supraspinous and infraspinous fasciae covering 
the corresponding portions of the lateral surface of the shoulder, 
(a) The cleidohumeralis. Origin: Lateral portion of the 
clavicle and the cleidohumeral ligament. Insertion: Ante- 
rior surface of the humerus in its distal third. The muscle 
is a continuation of the basioclavicularis, but represents the 
brachial part of the brachiocephalic muscle, which, in 
many mammals with reduced 
clavicle, extends from the mas- 
toid portion of the skull to the 
front of the arm. The cervical 
part is the cleidomastoideus. 
(&) The deltoideus. Ac- 
romial portion. Origin: 
The acromion. Inser- 
tion : Distal portion of 
the deltoid tuberosity. 
Scapular portion. 
Origin : Infraspinous 
fascia. The end of the 
muscle forms a curved 
line over the dorsal por- 
tion of the infraspinatus, 
leaving only a small 
triangular portion of the 
latter exposed. In- 
sertion : The distal por- 
tion of the muscle passes 
beneath the metacrom- 
ion, which also serves as 
a point of attachment, 
and is replaced on the 
Fig. 77. Transverse section through the 
distal portion of the arm; semidiagrammatic; 
a.b., brachial artery; a.c.r., radial collateral 
artery; b., biceps; br.l. and br.m., lateral and 
medial heads of the brachialis; d., deltoideus 
(insertion); e.a.p., extensor antibrachii 
parvus; f., brachial fascia; h., humerus; 
n.m., median nerve; n.r., radial nerve; n.u., 
ulnar nerve; tr.l-tr.3, long, lateral, and 
medial heads of the triceps; v.b., brachial 
vein; v.c., cephalic vein. The Anterior Limb 
227 
lateral surface of the humerus, beneath the acromial por- 
tion, by a thin tendon, through which it is inserted beside 
the acromial portion. 
The scapular portion of the deltoideus should be separated from the 
infraspinatus and divided, the distal end being reflected together with 
the metacromion. 
(c) The infraspinatus. Origin: Posterior portion of the lateral 
surface of the scapula, including the spine. Insertion: 
Greater tubercle of the humerus. The muscle fills the 
infraspinous fossa. 
(d) The supraspinatus. Origin: Anterior portion of the 
lateral surface of the scapula (supraspinous fossa), supras- 
pinous fascia, and, to a certain extent, the subscapular 
fascia. Insertion: Greater tubercle of the humerus. 
The extent of this muscle is evident only after removal of the loosely 
attached fleshy parts of the pectorals from its surface. 
(e) The subscapularis. Origin: Entire medial surface of the 
scapula. Insertion: Lesser tubercle of the humerus. 
(/) The teres major. Origin: Dorsal portion of the axillary 
border of the scapula. Insertion: In common with the 
latissimus dorsi on the anterior surface of the humerus. 
(g) The teres minor. Origin: Ventral portion of the axillary 
border of the scapula. Insertion: Greater tubercle. 
The muscle is closely associated with the infraspinatus but is 
separated from the teres major by the tendon of origin of the long- 
head of the triceps. 
(/;) The coracobrachialis. Origin: Coracoid process. In- 
sertion : Distal portion of the upper third of the humerus 
on its medial surface. 
4. Muscles arising from the scapula and humerus and inserted 
on the proximal ends of the radius and ulna (extensors and 
flexors of the forearm) (Figs. 34, 35, 77). 
A. Extensor (anconaeus) group. The muscles arise for the 
most part behind the axis of the humerus, and are inserted on the 
olecranon. 228 
Anatomy of the Rabbit 
(a) The extensor antibrachii parvus (anconaeus quartus). 
Origin: Fascia of the medial surface of the humerus. In- 
sertion: Medial surface of the olecranon. 
The muscle should be divided, or detached from its origin, and 
reflected. 
(b) The anconaeus minimus (epitrochleonanconaeus). Or- 
igin : Medial epicondyle of the humerus. Insertion: Medial 
surface of the olecranon. 
(c) The triceps brachii. Origin in three portions. Caput 
longum (anconaeus longus): Ventral portion of the 
axillary border of the scapula. Caput laterale (anconaeus 
lateralis): Greater tubercle and related portion of the 
lateral surface of the humerus. Caput mediate (ancon- 
aeus medialis): Posterior surface of the humerus. 
The three portions are almost separate muscles. Insertion on 
the olecranon. 
B. Flexor group. The muscles arise in front of the axis of 
the humerus and are inserted on the radius and ulna in front of 
the elbow-joint. 
(a) The biceps brachii. Origin: Anterior border of glenoid 
cavity. Insertion: Ventromedial surface of the ulna and 
medial surface of the radius. The muscle possesses only 
one head in the rabbit. 
(&) The brachialis. Origin: Anterior and lateral surfaces of 
the humerus, divided unequally into a larger lateral and a 
smaller medial portion by the insertion tendons of the 
deltoideus and cleidohumeralis muscles. Insertion: In 
common with the biceps. 
5. Muscles arising from the distal end of the humerus and the 
radius and ulna and inserted on the hand (extensors and flexors 
of the hand and of the individual digits). The long insertion 
tendons pass through perforations of the dorsal carpal and 
transverse (ventral) carpal ligaments (Fig. 78). 
A. Extensor group. The muscles have a general area of 
origin from the lateral epicondyle of the humerus and the antero- 
dorsal or anterolateral surface of the radius and ulna. Insertion 
dorsal. The Anterior Limb 
229 
(a) The extensor carpi radialis longus. Origin: Lateral 
epicondyle. Insertion: Base of the second metacarpal. 
(&) The extensor carpi radialis brevis. Origin: Lateral 
epicondyle. Insertion: Base of the third metacarpal. 
The muscle is partly fused with the foregoing one, and the 
tendons are closely associated on the wrist. 
(c) The abductor pollicis. Origin: Anterolateral surface of 
the radius and ulna. Insertion: Base of the first meta- 
carpal. The muscle is partly concealed by (e). Its tendon 
forms a conspicuous cross with those of (a) and (&). 
(d) The extensor pollicis et indicis. Origin: Anterolateral 
surface of the radius and ulna. Insertion: Ungual phalanx 
of the pollex and the head of the second metacarpal. Its 
tendon is the first of five in the centre of the carpus. 
(e) The extensor digitorum communis. Origin: Lateral 
epicondyle and proximal end of the ulna. Insertion: By 
four tendons on all phalanges of the four lateral digits. 
(/) The extensor digiti quarti proprius. Origin: Lateral 
epicondyle. Insertion: Ungual phalanx of the fourth digit. 
(g) The extensor digiti quinti proprius. Origin: Lateral 
epicondyle and lateral surface of the ulna. Insertion: 
Head of the fifth metacarpal and base of the first phalanx 
of this digit. 
(A) The extensor carpi ulnaris. Origin: Lateral epicondyle 
and proximal portion of the lateral surface of the ulna. 
Insertion: Base of the fifth metacarpal. 
B. Flexor group. The muscles have a general area of origin 
from the medial epicondyle of the humerus and the posteroventral 
or posteromedial surface of the radius and ulna. Insertion volar, 
the tendons (except that of a) passing under a very strong trans- 
verse carpal ligament, which stretches from the navicular and 
greater multangular to the pisiform and hamate bones. 
(a) The pronator teres. Origin: Medial epicondyle. Inser- 
tion : Ventral surface of the radius. 
(&) The flexor carpi radialis. Origin: Medial epicondyle. 
Insertion: Base of the second metacarpal. 230 
Anatomy of the Rabbit 
(c) The flexor digitorum sublimis. Origin: In common with 
the ulnar portion of the profundus from the medial epicon- 
dyle; proximal portion of the ulna. Insertion: Bases of the 
second phalanges of the four lateral digits. 
(d) The palmaris. Origin: 
Medial epicondyle. In- 
sertion: Superficially on 
the volar fascia. This 
extremely slender muscle 
lies between the super- 
ficial portion of the pro- 
fundus and the flexor 
carpi ulnaris. 
(e) The flexor digitorum 
profundus. Origin in 
four portions. Super- 
ficial portion: Medial 
epicondyle. Radial por- 
tion: Ventral surface of 
the radius. Middle por- 
tion: Ventral surface of 
the ulna. Ulnar por- 
tion: Medial epicondyle in common with (c). Insertion: 
By five tendons on the bases of the ungual phalanges. In 
exposing these, care should be taken not to destroy the 
flexor digiti quinti (6, a). 
(f) The flexor carpi ulnaris. Origin: Medial epicondyle and 
medial surface of the olecranon, forming two short but 
separate heads. Insertion: Pisiform bone. 
6. Muscles arising from the bones of the hand and inserted on the 
individual digits. 
(a) The flexor digiti quinti. Origin: Pisiform bone and ten- 
don sheath of the flexor digitorum profundus. Insertion: 
Sesamoid bones of the metacarpophalangeal joint of the 
fifth digit, extending to the ungual phalanx. This is a small 
muscle superficial to the most lateral division of the tendon 
of the flexor digitorum profundus. It represents both the 
Fig. 78. Transverse section of the distal end 
of the forearm. Showing the relative positions 
of the muscle tendons: ap, abductor pollicis; ar, 
radial artery; au, ulnar artery; ecu, extensor 
carpi ulnaris; edc, extensor digitorum communis; 
emp, extensor digiti quinti proprius; epi, 
extensor pollicis et indicis; eqp, extensor digiti 
quarti proprius; erb, extensor carpi radialis 
brevis; erl, extensor carpi radialis longus; fcr, 
flexor carpi radialis; feu, flexor carpi ulnaris; 
fdp, flexor digitorum profundus; fds, flexor 
digitorum sublimis; led, dorsal carpal ligament; 
let, transverse carpal ligament; nm, median 
nerve; nu, ulnar nerve; p, palmaris; r, radius; 
u, ulna; vc, cephalic vein; vr, radial vein; vu, 
ulnar vein. The Anterior Limb 
231 
flexor digiti quinti brevis and the abductor digiti quinti of 
some species. 
(&) The lumbricales. Origin: From the point of division of 
the tendon of the flexor digitorum profundus. Insertion: 
First phalanges of the second to fifth digits. 
(c) The adductor digiti quinti, adductor digiti quarti, and 
adductor indicis. Three slender muscles. Origin: Close 
together on the dorsal part of the tendon sheath of the 
flexor digitorum profundus. Insertion: By long thin ten- 
dons, respectively, to the radial sides of the fifth and fourth 
digits and the ulnar side of the second digit, just dorsal 
to the interossei. 
(d) The flexor pollicis brevis. A minute muscle. Origin: 
The lateral part of the transverse carpal ligament. In- 
sertion: The outer side of the base of the first phalanx of 
the pollex. 
(e) The interossei. Origin: In pairs from the bases of the 
second to fifth metacarpals and related portions of the 
carpal bones. Insertion: Sesamoid bones of the meta- 
carpophalangeal joints. The fibres of each pair interlace 
so that the members cannot be smoothly separated. 
Differentiation into volar and dorsal interossei is suggested, 
but they cannot be dissected apart. 
Blood-vessels and Nerves of the Arm and Forearm 
The axillary artery gives rise to posterior and often anterior 
branches; the circumflex arteries to the head of the humerus and 
the deep artery which latter, arising in one or two branches and 
passing between the coraco-brachialis and teres muscles to the 
lateral surface of the shoulder, gives branches to the deltoideus 
and to the proximal ends of the lateral and long heads of the triceps. 
The deep artery continues on the lateral side of the medial head 
of the triceps and passes to the lateral head of the brachialis, near 
the elbow, as the radial collateral artery. 
The brachial artery (a. brachialis), the continuation of the 
axillary, passes distad on the medial surface of the arm between the 232 
Anatomy of the Rabbit 
biceps and the medial head of the triceps. Crossing to the anterior 
surface of its distal extremity, it passes beneath the head of the 
pronator teres to the medial surface of the radius, dividing at this 
point-a short distance in front of the elbow-into the radial and 
ulnar arteries. Its chief branches on the arm are the ulnar 
collateral arteries (superior, middle, and inferior) to the muscles 
and the elbow-joint. 
The radial artery (a. radialis) passes distad on the ventro- 
medial border of the radius, in company with the median nerve, 
lying at first between the flexor carpi radialis and the radial portion 
of the flexor digitorum profundus. Toward the distal end of the 
radius it crosses the ventral surface of the tendon of the flexor carpi 
radialis, and appears in a superficial position on the medial border 
of the carpus. It reaches the volar surface of the hand after passing 
obliquely across the tendon of the flexor digitorum sublimis. 
The ulnar artery (a. ulnaris) crosses the ulna obliquely from its 
origin, reaching in this way the lateral border of the flexor carpi 
ulnaris, along which it passes to the end of the forearm and to the 
ulnar side of the pisiform bone. It passes to the ventral surface 
of the fifth digit, and then turns across the hand, forming the volar 
arch. 
The single brachial vein (v. brachialis) accompanies the 
brachial artery and lies behind it. It is formed in front of the elbow 
by the union of two vessels, the radial and ulnar veins, which 
accompany the corresponding arteries and join one another at the 
point of separation of the latter. The radial vein anastomoses 
with the radial portion of the cephalic at a point distal to the middle 
of the forearm. 
The cephalic vein (v. cephalica) is a large superficial vessel 
appearing on the dorsal surface of the forearm. From the radial 
side of the latter it receives a large tributary which anastomoses 
with the radial vein. It is accompanied by branches of the super- 
ficial ramus of the radial nerve. It passes to the front of the arm 
across the angle of the elbow, lying at first on the anterior margin 
of the lateral head of the brachialis, and afterwards on the lateral 
surface of the arm between the acromial portion of the deltoideus 
and the lateral head of the triceps. It disappears from this surface 
in the triangular space enclosed by these muscles and the insertion The Posterior Limb 
233 
of the levator scapulae major, receiving at this point a large tribu- 
tary from the shoulder. It appears on the medial surface of the 
shoulder at the distal end of the axillary border of the scapula, 
between the teres major and the subscapularis, entering the axillary 
vein at about the same place as the subscapular vein, or in common 
with the latter. 
The radial nerve (n. radialis) passes behind the brachial artery 
to the posterior surface of the humerus. It perforates the medial 
head of the triceps, appearing afterwards on the lateral side of the 
brachialis in company with the collateral radial artery. A super- 
ficial ramus, given off on the distal portion of the arm, accom- 
panies the cephalic vein: it passes along the surface of the extensor 
carpi radialis, dividing into branches for the dorsum of the hand. 
The remaining portion is chiefly distributed as the ramus pro- 
fundus to the extensor muscles of the forearm. 
The median nerve (n. medianus) passes distad along the 
medial surface of the arm, lying at first in front of the brachial 
artery and then on its medial side. It accompanies the brachial 
artery, passing beneath the head of the pronator teres, and then 
traverses the forearm, in company with the radial artery, to the 
volar surface of the hand. 
The ulnar nerve (n. ulnaris) lies behind the brachial artery. 
Toward the distal extremity of the humerus it accompanies the 
inferior ulnar collateral artery. It passes from the medial surface 
of the elbow, between the anconaeus minimus and the base of the 
olecranon, to the dorsal surface of the olecranon head of the flexor 
carpi ulnaris, and then crosses the ulna obliquely, in company with 
the ulnar artery, to the lateral border of the muscle and along it to 
the insertion tendon. At the wrist it crosses the dorsal surface of 
the tendon, and passing between the tendon of the sublimis and 
the pisiform bone, reaches the volar surface of the hand. 
IX. THE POSTERIOR LIMB 
Dissect on the side opposite to that of injection. The dis- 
section is largely a muscular one; to be conducted in the same 
way as in the anterior limb. The corresponding muscle groups 
should be compared with respect to the difference in orientation 
of the equivalent segments. 234 
Anatomy of the Rabbit 
1. Muscles arising from the ventral surface of the posterior thoracic 
and lumbar vertebrae and inserted on the pelvic girdle, or on 
the lesser trochanter of the femur. These muscles are chiefly 
distinguished by their vertebral position, on account of which, 
and on account of the fixed condition of the pelvic girdle, they 
combine the characters of vertebral and appendicular muscles, 
(a) The psoas minor. Origin: Bodies of the four posterior 
lumbar vertebrae. Insertion: Pecten of the pubis. The flat, 
pointed tendon forms a square cross with a dorsal (sacral) 
continuation of the inguinal ligament, which is stretched 
transversely from the middle of the inguinal ligament to the 
centre of the body of the first sacral vertebra, and on which 
the tendon is also inserted. 
It is necessary to divide the inguinal ligament and reflect its sacral 
continuation, together with the tendon of the psoas minor. 
(&) The psoas major. Origin: Internal surfaces of the bases 
of the last three ribs and bodies of the corresponding 
thoracic vertebrae; also the lumbar vertebrae. Insertion: 
Lesser trochanter. 
(c) The iliacus. Origin: Bodies of the last lumbar and first 
sacral vertebrae, extending to the sacroiliac union. In- 
sertion: With the psoas major on the lesser trochanter. 
The two muscles together form the iliopsoas. 
The lumbar portion of the lumbosacral plexus, beginning with 
the fourth lumbar nerve, lies on the ventral surface of the psoas major 
and between the latter and the iliacus. The fifth and sixth lumbar 
nerves together give rise to the greater part of the femoral nerve 
(p. 241), the trunk of which may be traced from a position between the 
two muscles distad over the dorsal surface of the inguinal ligament to 
the medial surface of the thigh. The remaining four nerves crossing 
the dorsal body-wall obliquely are the twelfth thoracic and first three 
lumbar. 
The psoas major should be freed at its lateral margin and turned 
toward the middle line, the fourth lumbar nerve being divided. 
(d) The quadratus lumborum. Origin: Bodies of the 
posterior five thoracic vertebrae and the bases of the corres- 
ponding five ribs; bodies and transverse processes of the 
lumbar vertebrae. Insertion: Triangular processes of six 
lumbar vertebrae and the posterior ventral angle of the iliac 
wing, together with the adjacent portion of its medial surface. The Posterior Limb 
235 
2. Muscles arising from the pelvic girdle and sacrum and inserted 
on the femur, for the most part at its proximal extremity. 
The muscles of this group enclose the proximal portion of the 
femur on its lateral, posterior, and medial sides. They are partly 
covered by the flexors of Group 3, namely, the biceps, sartorius, and 
gracilis (pp. 238, 239), which must be examined and divided. To 
begin the dissection, identify the sciatic vein (p. 241) and cut along 
its first portion, thereby freeing the first portion of the biceps in 
front from the superficial head of the semimembranosus behind. 
A continuation of this incision distad and towards the front of the 
thigh will separate the two portions of the biceps. Now cut along 
the aponeurotic line joining the tip of the great trochanter with the 
sacrum and carry the incision distad along the intermuscular 
septum of the lateral surface of the thigh to the knee. Raise the 
first head of the biceps slightly by working the handle of the scalpel 
under its distal portion. Divide the muscle from its posterior 
margin, being careful not to injure the slender tensor fasciae cruris 
muscle and the branches of the sciatic nerve which lie beneath it. 
Reflecting the proximal end will expose the short muscles of the 
thigh. 
Dissect on the lateral surface posteriorly. 
(a) The glutaeus maximus. Origin in two fleshy portions, 
joined by an aponeurosis. First portion: Fascia covering 
the sacrum in its entire length. This portion is triangular 
in shape, and is covered posteriorly by the first head of the 
biceps. Second portion: Anteroventral border of the iliac 
wing, fused with the tensor fasciae latae and the first head 
of the rectus femoris; also from the dorsal border and 
lumbar fascia through the aponeurosis mentioned above. 
Insertion: Third trochanter. The axis of the first portion 
is transverse, that of the second horizontal. 
Both portions of the muscle should be divided. The sciatic nerve 
and artery are then exposed. 
(&) The glutaeus medius. Anterior border of the wing of the 
ilium and the iliac crest and fascia of the first two sacral 
vertebrae. Insertion: Greater trochanter. Some of the 
fibres pass around the medial surface of the tip of the greater 236 
Anatomy of the Rabbit 
trochanter and are inserted in the lateral wall of the 
trochanteric fossa. 
The muscle should be divided. 
(c) The glutaeus minimus. Origin: Entire lateral surface 
of the body and wing of the ilium. Insertion: Greater 
trochanter. 
Remove the entire muscle. The piriformis is in contact with its 
dorsal margin posteriorly. 
(d) The tensor fasciae latae. Origin: Anterior portion of 
the ventral border of the wing of the ilium. Insertion: 
Broad fascia of the lateral surface of the thigh. The muscle 
is fused with the first head of the rectus femoris in front, 
and with the second portion of the glutaeus maximus behind. 
(e) The piriformis. Origin: Lateral portions of the second 
and third sacral vertebrae. Insertion: Tip of the great 
trochanter. The muscle passes through the greater sciatic 
notch. 
The muscle should be divided, care being taken to avoid injury to 
the nerves and blood-vessels beneath it. 
(/) The gemellus superior. Origin: Tendinous from the 
ischial spine and fleshy from the body of the ischium 
immediately in front of it. Insertion: Lateral wall of the 
trochanteric fossa. 
The muscle extending from the ischial spine to the sacrum is the 
abductor caudae anterior (p. 289). 
(g) The obturator interims. Origin: Internal extent of the 
obturator foramen. Insertion: Trochanteric fossa. The 
muscle passes over the ischium in the lesser sciatic notch, 
only its insertion portion appearing from the lateral surface. 
To see its origin, reflect the tendon through the lesser sciatic 
notch and examine the muscle from the internal surface 
of the pelvis. 
(A) The gemellus inferior. Origin: Posterior portion of the 
superior ramus of the ischium and the ischial tuberosity. 
Insertion: Trochanteric fossa. 
(*) The quadratus femoris. Origin: Ventral surface of the 
ischial tuberosity and the superior ramus of the ischium 
immediately in front of it. Insertion: The superficial fibres The Posterior Limb 
237 
are inserted on and below the third trochanter, the remain- 
ing ones below the trochanteric fossa. 
(j) The obturator externus. Origin: External extent of the 
obturator foramen. Insertion: Trochanteric fossa. The 
muscle is largely concealed from this surface, but may be 
fully displayed by the division of the pectineus and adduc- 
tores brevis and longus. 
Dissect on the medial surface posteriorly, after examination 
and division of the sartorius and the gracilis (p. 238). 
(k) The pectineus. Origin: Pecten of the pubis. Insertion: 
Immediately below the lesser trochanter. 
(Z) The adductor brevis. Origin: Anterior portion of the 
symphysis pubis. Insertion: Below the pectineus. 
(m) The adductor longus. Origin: Posterior portion of the 
symphysis and inferior ramus of the ischium. Insertion: 
Posterior surface of the shaft of the femur to its distal third. 
(n) The adductor magnus. Origin: Ventral surface of the 
ischial tuberosity. Insertion: Medial surface of the distal 
end of the femur, extending to the medial condyle of the 
tibia. 
3. Muscles arising from the pelvic girdle and the femur and inserted 
on the proximal portions of the tibia and fibula (extensors and 
flexors of the leg) (Fig. 79). 
A. Extensor group (quadriceps femoris). The muscles lie 
for the most part in front of the axis of the femur. They have a 
common insertion on the tibial tuberosity through the patella and 
the patellar ligament. 
(a) The rectus femoris. Origin in two portions. First 
portion: Superior anterior spine, fused with the tensor 
fasciae latae, and ventral border of the iliac wing. Second 
portion: By a stout round tendon from the inferior 
anterior spine, immediately in front of the acetabulum. 
This part is cylindrical in shape and is almost a separate 
muscle. 
The two portions of the muscle should be divided. 
(&) The vastus lateralis. Origin: Anterior surface of the 
great trochanter and the lateral intermuscular ligament. 
The muscle should be divided. 238 
Anatomy of the Rabbit 
(c) The vastus intermedius. Origin in two portions. First 
portion: Great trochanter, below the origin of the vastus 
lateralis. Second portion: Anterior surface of the femur. 
(</) The vastus medialis. Origin: Medially, at the base of 
the collum femoris and adjacent portion of the shaft. 
Common insertion (a-d): Tibial tuberosity. 
B. Flexor group (hamstring muscles). With the exception of 
the sartorius, the muscles lie behind the axis of the femur, 
and are inserted on the 
medial and lateral surfaces 
of the knee-joint and the 
corresponding proximal 
portions of the leg. They 
form the boundaries of the 
popliteal fossa. 
(a) The sartorius. Or- 
igin : Posterior portion 
of the inguinal liga- 
ment, especially its 
sacral extension. In- 
sertion: Medial con- 
dyle of the tibia. This 
muscle is an extremely 
thin and narrow band 
of fibres, lying on the 
more anterior portion 
of the medial surface 
of the thigh. It is 
fused distally with the 
gracilis, and is a flexor 
only through its con- 
nection with the latter, 
since its position is 
that of a rotator. 
(6) The gracilis. Origin: 
The entire extent of 
the pubic symphysis. 
Fig. 79. Transverse section through the middle 
of the thigh: a.l., adductor longus; a.m., adductor 
magnus; b.f. 1 and b.f. 2, first and second heads 
of the oiceps femoris; f., femur; gr., gracilis; n.p., 
peroneal nerve; n.s.m., greater saphenous nerve: 
n.t., tibial nerve; r.f. 1 and r.f. 2, first and second 
heads of the rectus femoris; s, sartorius; sm., 
semimembranosus; st., semitendinosus; t.f.c., tensor 
fasciae cruris; t.f.l., tensor fasciae latae; v.i. 1 and 
v.i. 2, first and second heads of the vastus inter- 
medius; v.is., sciatic vein; v.i., vastus lateralis; 
v.m., vastus medialis; v.s.m., great saphenous vein. The Posterior Limb 
239 
Insertion: Through a broad tendinous expansion ending 
in the fascia of the proximal portion of the medial surface 
of the leg. The muscle forms a broad, comparatively thin 
sheet, covering the posterior portion of the medial surface 
of the thigh. Its insertion tendon is perforated by the 
great saphenous artery and vein and the greater saphenous 
nerve. 
The sartorius and gracilis should be raised from the surface and 
divided. 
(c) The biceps femoris. Origin in two portions. First 
portion (caput breve): Spinous processes of three posterior 
sacral and three anterior caudal vertebrae. This portion 
is triangular in shape, the distal end, or apex of the triangle, 
passing into a thin flat tendon which is inserted on the 
lateral margin of the patella. Second portion (caput 
longum): Dorsal surface of the ischial tuberosity, fused 
with the adductor magnus, and the lateral process, fused 
with the second, or deep portion of the semimembranosus 
(see below). This portion is also triangular, the base being 
distal and providing a broad insertion on the fascia of the 
proximal third of the lateral surface of the leg. The first, 
or superficial head of the semimembranosus, covers this 
portion at its origin, which is also crossed by the sciatic vein. 
Directions for freeing the biceps and dividing its first portion 
have been given on page 235, this procedure being necessary to 
expose the short thigh muscles. The freeing of the second portion 
should now be completed, an incision first following the sciatic vein 
to the posterior margin of the muscle, and the muscle should be 
divided. 
(d) The tensor fasciae cruris. Origin: By a long slender 
tendon, from the transverse process of the fourth sacral 
vertebra. Insertion: Lateral fascia of the leg. This 
slender muscular slip underlies the biceps femoris. 
(e) The semimembranosus. Origin in two portions. First 
(superficial) portion: Fascia covering the first head of the 
biceps. Second (deep) portion: Lateral process of the 
ischial tuberosity. Insertion: In common with the gracilis 
on the fascia of the proximal portion of the medial surface 240 
Anatomy of the Rabbit 
of the leg. This fascia is contracted into two ligaments, 
one of which carries the insertion of the muscle to the distal 
end of the tibial tuberosity, the other to the distal end of the 
leg, where it joins the tendon of the heel (tendo calcaneus). 
(/) The semitendinosus. Origin: Ischial tuberosity. In- 
sertion: Medial condyle of the tibia. The muscle is com- 
pletely enclosed by the adductor magnus, which must be 
split to expose it. 
Blood-vessels and Nerves of the Thigh 
The femoral artery (a. femoralis) traverses the medial surface 
of the thigh, beginning at the dorsal side of the inguinal ligament, 
where it continues the external iliac artery. Immediately distal 
to the inguinal ligament it gives off the deep artery of the thigh 
(a. profunda femoris). The latter passes to the dorsal side of the 
pectineus and adductor brevis muscles and is distributed to the 
posterior proximal portion of the limb, chiefly to the adductores 
longus and magnus. A second branch, the lateral circumflex 
artery (a. circumflexa femoris lateralis), is given off from the 
anterior wall. It passes between the second head of the rectus 
femoris and vastus lateralis, on the one hand, and the two portions 
of the vastus intermedius, on the other. It supplies various parts 
of the quadriceps femoris group. A third branch of the femoral, 
the superficial epigastric artery (a. epigastrica superficialis), 
given off medially, and passing to the abdominal wall, has been 
divided (p. 191). At the beginning of the distal third of the thigh, 
a small branch, the a. genu suprema, passes over the medial 
condyle of the femur to the knee-joint, and at about the point 
of origin of this vessel a large branch, the great saphenous artery 
(a. saphena magna), arises from the posterior wall. It passes across 
the medial surface of the distal end of the adductor longus, and 
through the tendon of the gracilis, to the medial surface of the leg. 
The femoral artery passes between the adductores longus and 
magnus, continuing as the popliteal artery (a. poplitea). 
The hypogastric artery (p. 219) appears in the greater sciatic 
notch, continuing thence as the sciatic artery (a. ischiadica). 
The vessel passes backward to the dorsal surface of the superior 
ramus of the ischium, where it divides into lateral caudal and The Posterior Limb 
241 
internal pudendal branches. Its smaller branches are distributed 
to the glutaei and biceps femoris muscles. 
The femoral vein (v. femoralis) traverses the medial surface 
of the thigh in company with the femoral artery. It begins at the 
proximal end of the lower third of the thigh as a continuation of the 
popliteal vein (v. poplitea), which accompanies the corresponding 
artery. Its tributaries comprise the great saphenous, super- 
ficial epigastric, lateral circumflex, and profunda femoris 
veins. 
The sciatic vein (v. ischiadica) traverses the lateral surface of 
the thigh near its posterior margin, lying at first between the biceps 
and semimembranosus and afterwards on the posterior margin of 
the former. At the dorsal border of the ischium, in front of the 
ischial tuberosity, it receives the lateral caudal and internal 
pudendal veins. 
The femoral nerve (n. femoralis) arises from the lumbo-sacral 
plexus, chiefly from the fifth lumbar. Its position between the 
psoas major and iliacus muscles has already been noted (p. 234). 
Immediately beyond the inguinal ligament it divides into two 
portions, one of which is distributed to the muscles of the anterior 
side of the thigh, while the other, the great saphenous nerve 
(n. saphenus major), passes to the medial surface of the thigh and 
leg in company first with the femoral artery and afterwards with 
the great saphenous artery. 
The sciatic nerve (n. ischiadicus), formed chiefly from the 
seventh lumbar and first sacral nerves, appears laterally in the 
greater sciatic notch. It passes backward beneath the piriformis 
muscle, and then turns distad to the thigh, where it lies on the 
lateral surfaces of the adductores magnus and longus. It dis- 
tributes branches to the posterior musculature of the thigh. In 
the proximal portion of the thigh it divides into two chief branches, 
which are closely associated as far as the knee. The anterior 
branch is the peroneal nerve (n. peronaeus), the posterior branch 
the tibial nerve (n. tibialis). The lesser saphenous nerve (p. 248) 
is a small branch given off from the tibial above the knee-joint. 
For the origin of this and related nerves see p. 249. 
The superior gluteal nerve (n. glutaeus superior) appears in 
the greater sciatic notch, leaving the sciatic close to the inferior 242 
Anatomy of the Rabbit 
posterior spine of the ilium. It passes between the glutaeus mini- 
mus and the lateral surface of the ilium, ending in the tensor fasciae 
latae. Its branches are distributed to the glutaei medius and 
minimus and the piriformis muscles. 
The inferior gluteal nerve (n. glutaeus inferior) perforates the 
posterior portion of the piriformis, and is distributed to the glutaeus 
maximus. 
The posterior cutaneous nerve (n. cutaneus femoris posterior) 
accompanies the hypogastric artery backward to the ischial tuber- 
osity, where it turns to the posterior margin of the thigh and the 
medial surface of the sciatic vein, ending in branches to the skin. 
The pudendal nerve (n. pudendus) accompanies the sciatic 
artery and afterwards the internal pudendal to the penis or clitoris. 
In preparation for the muscular dissection of the leg, the insertion 
tendons of the biceps femoris, tensor fasciae cruris, gracilis, and 
semimembranosus muscles should be removed from about the knee- 
joint. The adductor magnus may be detached from the medial 
condyle of the femur, but the popliteal vessels must be kept intact. 
The superficial blood-vessels of the leg should be noted, since it is 
necessary to clear them away in separating the muscles. They 
include, medially, the great saphenous artery and vein and, laterally, 
the branches of the small saphenous artery to the insertion portions 
of the muscles of the thigh and its continuation on the postero- 
lateral border of the leg; also the sciatic vein, together with its 
continuation, the anterior tibial vein, and the accessory small 
saphenous vein (p. 247). The tibial and peroneal nerves may be 
cut, after first noting their position. 
4. Muscles arising from the medial and lateral condyles of the 
femur and from the proximal portions of the tibia and fibula, 
including the tibial condyles; inserted on the foot. The group 
includes the typical extensors and flexors of the foot, together 
with the peronaei muscles, which individually are extensors and 
flexors, but collectively have the relation of lateral tractors 
(Fig. 80). 
A. Extensor group. Muscles occupying an anterior position 
on the leg and inserted on the dorsum of the foot. The Posterior Limb 
243 
(a) The extensor hallucis longus. Origin: Middle portion 
of the anteromedial surface of the tibia and from the medial 
condyle behind the 
tibial collateral lig- 
ament. Insertion: 
The tendon passes 
around the medial 
malleolus of the 
tibia and beneath 
the base of the sec- 
ond (first function- 
al) metatarsal, con- 
tinuing to its dorsal 
surface and uniting 
with the first ten- 
don of the extensor 
digitorum longus. 
This muscle is 
also identified as 
a tibialis posterior 
with displaced in- 
sertion tendon and 
is grouped with 
the flexors. 
The posterior tibial 
artery, the continua- 
tion of the great saphenous, and the tibial nerve accompany the 
tendon in the malleolar groove. 
(ft) The tibialis anterior. Origin: Lateral condyle of the 
tibia and corresponding surface of the tibial tuberosity. 
Insertion: Base of the second metatarsal. The tendon 
passes beneath the obliquely placed crural ligament of 
the lower portion of the leg. 
The muscle should be divided and its head reflected. 
The anterior tibial artery and vein, and the peroneal nerve, appear 
on the anterior surface of the tibia at the lateral side of the crural 
ligament. 
(c) The extensor digitorum longus. Origin: By a flattened 
tendon from the lateral portion of the patellar surface of the 
Fig. 80. Transverse section of the proximal 
portion of the leg: a.s.m., great saphenous artery; 
a.s.p., small saphenous artery; a.p., a.t.a., anterior 
tibial artery; b.f., biceps femoris (insertion); e.d.l., 
extensor digitorum longus; e.h.l., extensor hallucis 
longus; f., fibula; f.d.l., flexor digitorum longus; 
g.l. and g.m., lateral and medial heads of the 
gastrocnemius; gr., gracilis (insertion tendon); n.s., 
greater saphenous nerve; n.s.m., lesser saphenous 
nerve; n.t., tibial nerve; pl., plantaris; s., soleus; 
t., tibia; t.a., tibialis anterior; t.f.c., tensor fasciae 
cruris (insertion); v.is., sciatic vein; v.s.m., great 
saphenous vein; v.s.p., small saphenous vein; 1-4, 
the peronaei (primus-quartus). 244 
Anatomy of the Rabbit 
femur. This tendon passes through the capsule of the knee- 
joint, and the fleshy portion of the muscle lies on the antero- 
lateral surface of the tibia. Insertion: The distal tendon 
passes beneath the crural ligament, then beneath the 
cruciate ligament of the dorsum of the foot, dividing 
into four portions for insertion on all the phalanges of the 
digits. 
The muscle may be displaced by dividing the crural ligament. 
The branches of the anterior tibial artery lie behind this muscle, 
one in a medial position, in contact with the tibia, the other on the 
peronaei muscles in company with the peroneal nerve. 
B. Peronaeus group. These muscles arise from the lateral 
surface of the leg, and are inserted on all surfaces at the lateral side 
of the foot. The insertion tendons reach the foot from beneath the 
lateral malleolus. The muscles can be separated after the tendons 
are released from this position. 
(a) The peronaeus longus (p. primus). Origin: Lateral con- 
dyle of the tibia and head of the fibula. Insertion: End 
of the reduced first metatarsal. The tendon crosses the 
plantar surface of the foot, passing around the distal end 
of the cuboid bone. 
The muscle should be divided. 
(&) The peronaeus* brevis (p. secundus). Origin: Lateral 
condyle of the tibia and corresponding surface of the shaft; 
also the crural interosseous ligament joining the tibia and 
fibula. Insertion: Tuberosity of the base of the fifth 
metatarsal. 
(c) The peronaeus tertius. Origin: The head of the fibula 
and the crural interosseous ligament, fused with the flexor 
digitorum longus. Insertion: Head of the fifth metatarsal, 
and distally, united with the tendon of the extensor digi- 
torum longus, on the phalanges of this digit. 
(d) The peronaeus quartus. Origin: The fibula and the 
interosseous ligament, fused with the peronaeus brevis and 
with the flexor digitorum longus. Insertion: Head of the 
fourth metatarsal. The Posterior Limb 
245 
C. Flexor group. The muscles arise from the medial and 
lateral condyles of tibia and femur (the flexor digitorum sublimis 
from the posterior surface of the tibia). They lie behind the axis 
of the tibia, and are inserted both on the heel and on the plantar 
surface of the foot. 
(a) The triceps surae comprises: 
(1) The gastrocnemius. Origin in two portions. Caput 
laterale: Lateral condyles of tibia and femur and related 
femoral sesamoid. Caput mediate: The main origin is 
on the medial condyle of the femur and its sesamoid, but a 
smaller portion of the muscle originates in part with 
(immediately dorsal to) the caput laterale and in part by 
a flat tendon from the lateral edge of the patella. 
(2) The soleus: Origin: By a strong tendon from the 
head of the fibula. 
Insertion: Through the Achilles' tendon (tendo cal- 
caneus). The latter passes over the posterior end of the 
tuber calcanei, and is attached to its ventral surface. The 
tendon is covered by that of the plantaris muscle. 
The small saphenous artery and vein lie at the posterior margin of 
the lateral head of the gastrocnemius in company with the lesser 
saphenous nerve. 
(b) The plantaris. Origin: Lateral condyle of the femur and 
associated sesamoid. Insertion: The tendon passes over 
the heel to the plantar surface of the foot, and divides into 
four parts for insertion on the second phalanges of the four 
developed digits. 
The two muscles should be divided. 
(c) The popliteus. Origin: Lateral condyle of the femur. 
The tendon passes through the capsule of the knee-joint. 
The muscle contains the tibial sesamoid. It crosses the 
posterior surface of the tibia obliquely, and is inserted on 
the proximal portion of its posteromedial angle. 
(d) The flexor digitorum longus. Origin: Lateral condyle 
of the tibia and head of the fibula, extending to the posterior 
surface of the interosseous ligament and associated portions 
of the tibia and fibula. Insertion: The tendon passes 246 
Anatomy of the Rabbit 
beneath the sustentaculum tali, reaching the plantar surface 
of the foot, where it is partly covered by the plantaris ten- 
don. It divides into four parts for insertion on the ungual 
phalanges of the four developed digits. 
The tibial nerve lies on the medial surface of the head of the plan- 
taris and afterwards on the medial surfaces of the popliteus and flexor 
digitorum longus. 
5. Muscles arising from the foot and inserted on the individual 
digits. 
(a) The lumbricales. Origin: Tendon of the flexor digitorum 
longus. Insertion: Medial surfaces of the first phalanges 
of the three lateral digits. 
(ft) The adductor indicis and the adductor minimi digiti. 
Two extremely slender slips of muscle. Origin: Near the 
middle of the dorsal wall of the tendon-sheath of the flexor 
digitorum longus. Insertion: By long, thin tendons re- 
spectively to the lateral side of the first phalanx of digit 
two and the medial side of that of digit five. 
(c) The interossei (metatarsi). Origin: From the dorsal por- 
tion of the tendon-sheath of the flexor digitorum longus, 
external and distal to the origin of the adductors. Insertion: 
Heads of the four metatarsals. 
Vessels and Nerves of the Leg and Foot 
The great saphenous artery passes distad on the medial 
surface of the leg, and is continued as the posterior tibial artery 
(a. tibialis posterior) around the medial malleolus to the plantar 
surface of the foot. Above the ankle-joint it gives off the malleolar 
artery (a. malleolaris) to the posterior surface of the distal end 
of the tibiofibula. 
The popliteal artery, the continuation of the femoral, passes 
between the medial head of the gastrocnemius on the one hand and 
the lateral head and the plantaris on the other, reaching the anterior 
surface of the popliteus, and afterwards the anterior surfaces of the 
tibia and fibula by passing between their proximal ends. It dis- 
tributes branches to the muscles about the knee-joint, including a 
branch to the distal portion of the vastus lateralis, which is given The Posterior Limb 
247 
off at about the point of origin of the small saphenous artery. It 
then continues as the anterior tibial artery. The vessel appears 
in front of the interosseous ligament of the leg and of the peronaeus 
brevis, and continues to the dorsum of the foot after passing 
beneath the crural ligament. A large branch, given off in the 
upper part of the leg also reaches the dorsum of the foot from a 
more lateral position. 
The small saphenous artery (a. saphena parva) appears on 
the proximal portion of the posterolateral margin of the leg, running 
along the border of the lateral head of the gastrocnemius in company 
with the corresponding vein and the lesser saphenous nerve. 
The great saphenous vein (v. saphena magna), a large 
tributary of the femoral, accompanies the corresponding artery 
and the greater saphenous nerve, and is continued as the posterior 
tibial vein (v. tibialis posterior), to the plantar surface of the foot. 
The popliteal vein, the root of the femoral, accompanies the 
corresponding artery in the popliteal fossa. It receives the small 
saphenous vein (v. saphena parva) from the posterior margin 
of the lateral head of the gastrocnemius. 
The sciatic vein is continued on the lateral surface of the leg as 
the anterior tibial vein (v. tibialis anterior). It receives the 
accessory small saphenous vein (v. saphena parva accessoria) 
from the posterior surface, and is continued to the dorsum of the 
foot passing to the fibular side of the crural ligament. 
The greater saphenous nerve, the posterior branch of the 
femoral nerve, accompanies first the femoral artery and afterwards 
the great saphenous artery, passing distad to the medial surface 
of the leg. 
The tibial nerve, the posterior division of the sciatic, passes 
between the medial and lateral heads of the gastrocnemius to the 
medial surface of the head of the plantaris. It traverses the leg, 
lying on the medial surface first of the popliteus and afterwards 
of the flexor digitorum longus, and passing beneath the medial 
malleolus reaches the plantar surface of the foot. In the proximal 
portion of the leg it distributes muscular branches to the flexor 
group. 248 
Anatomy of the Rabbit 
The lesser saphenous nerve (n. saphenus minor) accompanies 
the small saphenous artery and vein on the posterior margin of the 
lateral head of the gastrocnemius. 
The peroneal nerve, the anterior division of the sciatic, passes 
distad, lying at first between the insertion of the biceps and the 
lateral head of the gastrocnemius, and thus appearing on the surface 
after the removal of the former. It perforates the anterior portion 
of the lateral head of the gastrocnemius and afterwards the fused 
heads of the peronaeus tertius and flexor digitorum longus, travers- 
ing the leg at first behind the peronaeus longus and then around its 
medial margin to the front of its tendon. It passes to the fibular 
side of the crural ligament and thence to the dorsum of the foot. 
The nerve distributes branches to the tibialis anterior and extensor 
digitorum longus. 
The Lumbosacral Plexus 
The structure of the lumbosacral plexus may be examined by 
breaking away the ventral portion of the pelvis, or by dividing the 
sacroiliac articulation in such a way that the two sides of the pelvis 
may be pressed apart, the ventral or pelvic face of the sacrum being 
thus exposed. The posterior portions of the psoas and iliacus mus- 
cles may be picked away with the forceps, and 
the abductor caudae anterior muscle (p. 289) 
may be detached from its origin on the ischial 
spine. 
The lumbosacral plexus (plexus lumbo- 
sacralis) is formed by the ventral roots of the 
four posterior lumbar and four sacral spinal 
nerves (Fig. 81). It is divisible into a lum- 
bar plexus (plexus lumbalis), from which 
arises the femoral nerve, and a sacral plexus 
(plexus sacralis), from which arises the sciatic 
nerve. It is subject to certain variation. 
The femoral nerve is formed usually 
from the fifth, sixth, and seventh lumbar, 
especially from the loop connecting the fifth 
and sixth (ansa lumbalis n). The obturator 
nerve (n. obturatorius), which accompanies 
the obturator artery, is formed from the fifth, 
Fig. 81. Plan of the 
lumbosacral plexus: L,S,C, 
lumbar, sacral, and caudal 
vertebrae; nl, ns, corres- 
ponding spinal nerves; nf, 
femoral nerve; no, obtur- 
ator nerve; nis, sciatic 
nerve; np, pudendal nerve. The Posterior Limb 
249 
sixth, and seventh lumbars but chiefly from the sixth, and is dis- 
tributed to the obturatores, adductores, and gracilis muscles. 
The sciatic nerve, together with the superior and inferior 
gluteal nerves, arises chiefly from the loop connecting the last 
lumbar and first sacral nerves (ansa lumbalis in). 
The internal pudendal nerve is formed from the loop connecting 
the second and third sacral nerves (ansa sacralis n), but chiefly 
from the second. 
The Articulations of the Posterior Limb 
The more perfect development and larger size of the joints of the 
posterior limb make them much more favourable for examination 
than the corresponding parts of the anterior limb. 
The muscular attachments should be removed from about the 
articular capsules and the structures examined as follows: 
A. The hip-joint (articulatio coxae) is an enarthrosis, formed 
by the head of the femur with the parts of the ischium, ilium, and 
the os acetabuli enclosing the acetabulum, together with the 
articular capsule (capsula articularis) and accessory ligaments. 
The articular capsule extends from the acetabular margin to the 
proximal end of the neck of the femur. It is strongest on its dorsal 
side, but is especially thickened at three points, forming the ischio- 
capsular (dorsal), iliofemoral (anterior), and pubocapsular 
(ventral) ligaments. 
By dividing the capsule, the contents of the joint and the smooth 
articular surfaces may be examined; also the attachment of the head 
of the femur to the wall of the acetabular fossa through the round 
ligament (lig. teres femoris). The glenoid lip (labrum glenoi- 
dale) is the ring of fibrocartilage surrounding the margin of the 
acetabulum and connecting with the articular capsule. 
B. The knee-joint (articulatio genu) is a hinge-joint or 
ginglymus with a slight spiral trend. It is formed by the articular 
surfaces of the medial and lateral condyles of the femur and tibia, 
with the associated articular capsule, ligaments, and interarticular 
fibrocartilages (see section, Fig. 24). 
The tibial collateral ligament (lig. collaterale tibiale) is a 
stout band of connective tissue stretching from the medial condyle 250 
Anatomy of the Rabbit 
of the femur to the posteromedial angle of the medial condyle of 
the tibia. 
The fibular collateral ligament is a similar structure con- 
necting the lateral condyle of the femur with the anterior surface 
of the head of the fibula. 
The sesamoid bones of the popliteal region have articular sur- 
faces taking part in the formation of the joint. That on the medial 
condyle of the femur is contained in the medial head of the gastro- 
cnemius, that on the lateral condyle of this bone in the lateral head 
of the gastrocnemius and the plantaris, and that on the lateral 
tibial condyle in the popliteus. 
The common tendon of the quadriceps femoris, the patella, and 
the patellar ligament are associated with the capsule, forming the 
anterior wall of the joint. 
Between the apposed surfaces of the condyles, in the interior of 
the joint, there are two short, cruciate ligaments and two thin 
plates of fibrocartilage, the medial and lateral menisci. The 
anterior cruciate ligament (lig. cruciatum anterius) passes from 
the lateral wall of the intercondyloid fossa of the femur to the 
anterior end of the intercondyloid eminence of the tibia. The 
posterior cruciate ligament passes from the medial wall of the 
intercondyloid fossa of the femur to the posterior intercondyloid 
fossa of the tibia. The medial meniscus (meniscus medialis), 
a thin crescentic plate of fibro-cartilage, lies on the articular surface 
of the medial condyle of the tibia, and is connected by ligament with 
the anterior and posterior intercondyloid fossae of the bone. The 
larger, lateral meniscus lies on the lateral condyle of the tibia, 
and is attached by ligament anteriorly to the medial portion of the 
articular surface, and posteriorly, to the medial wall of the inter- 
condyloid fossa of the femur. The tendon of origin of the extensor 
digitorum longus traverses the anterior part of the joint on its 
way from the patellar surface of the femur to the front of the leg. 
The interosseous ligament of the leg (lig. interosseum cruris) forms an 
almost complete sheet connecting the uncoalesced portions of tibia and fibula. 
C. The ankle-joint (articulatio talocruralis) is a ginglymus 
with a considerable amount of spiral torsion. The articulating 
surfaces are formed chiefly by the tibia and talus, but also by the 
fibular side of the tibiofibula and the calcaneus. On the tibial side The Head and Neck 
251 
the calcaneotibial ligament (lig. calcaneotibiale) connects the 
medial malleolus with the sustentaculum tali. On the fibular side 
the calcaneofibular ligament (lig. calcaneofibulare) connects the 
posterior portion of the groove for the peronaei muscles forwards 
with the lateral surface of the calcaneus, and a second ligament 
extends from the anterior margin of the groove backward to the 
lateral surface of the calcaneus. The tibionavicular ligament 
(lig. tibionaviculare) connects the anterior surface of the distal 
end of the tibia with the dorsal surface of the navicular bone. The 
joint contains in its interior a short strong ligament connecting the 
medial side of the lateral malleolus with the lateral and ventral 
surfaces of the trochlea tali. 
X. THE HEAD AND NECK 
This dissection includes the various structures of the region, with the excep- 
tion of the cervical and occipital musculature and the central nervous system, 
which are treated in the succeeding parts, and the special musculature of the ear, 
which has been omitted. 
To begin the dissection, the median ventral incision of the skin 
should be extended forward to the mandibular symphysis and the 
skin should be separated from the underlying platysma along the 
side of the head, and reflected until the surface is clear to a point 
near the dorsal median line of the skull. The insertion of the 
platysma on the cheek, and that of its special portion, the depressor 
conchae posterior, on the base of the ear, should be noted. A second 
band of muscle, similar in its relation to the platysma, arises from 
the lateral border of the mandible, immediately in front of the 
masseter muscle, and is inserted into the base of the ear. This is 
the depressor conchae (parotideoauricularis) anterior. 
In removing the skin of the upper and lower eyelids, two 
muscles, the orbicularis oculi and the depressor palpebrae 
inferioris, may be observed. The former is a somewhat circular 
band of fibres enclosing both eyelids, the fibres lying directly on 
the skin, and being concentrated at the anterior and posterior 
angles. The latter is a very slender muscle arising from the 
zygomatic arch and inserted into the skin of the lower eyelid. The 
corresponding levator palpebrae superioris arises from the orbital 
wall, and is here concealed by the projecting supraorbital process. 252 
Anatomy of the Rabbit 
1. On the lateral surface of the head the following structures may 
be made out without further dissection: 
(a) The parotid gland (gl. parotis), a diffuse, white or brownish 
gland lying immediately behind the angle of the mandible. 
Its duct (d. parotideus) crosses the masseter (c) in close 
association with the branches of the facial nerve and, 
perforating the mucous membrane of the cheek, opens into 
the oral cavity. 
(&) The chief part of the seventh cranial or facial nerve 
(n. facialis) appears in the anterior portion of the parotid 
gland, its branches crossing the masseter. They are dis- 
tributed as motor nerves to the cutaneous muscles of the 
face, including the platysma. 
(c) The masseter muscle. Origin: The zygomatic arch; 
tendinous from its anterior angle and fleshy behind. In- 
sertion : Lateral surface of the angle of the mandible. 
(d) The external maxillary artery (a. maxillaris externa) 
appears at the ventral border of the mandible immediately 
in front of the masseter. It passes upward to the anterior 
margin of the eye, ending in the angular artery (a. angul- 
aris). Its chief branches to the anterior portion of the face 
are: (1) the submental artery (a. submentalis) to the 
chin, a small branch rising near where the external maxillary 
crosses the ventral margin of the mandible; (2) the inferior 
labial artery (a. labialis inferior) to the lower lip; and 
(3) the superior labial artery to the upper lip. 
A small vessel, the transverse facial artery, crosses the cheek, 
running along the ventral border of the zygomatic arch. It is a branch 
of the superficial temporal (p. 260). 
(e) The anterior facial vein (v. facialis anterior) accompanies 
the external maxillary artery. It begins in front of the eye 
as the angular vein, and receives as tributaries the 
superior and inferior labial veins. 
2. Dissection of the facial muscles. These muscles arise from the 
facial portion of the skull, and are inserted into the skin about 
the upper and lower lips. The Head and Neck 
253 
(a) The quadratus labii superioris. Origin: Dorsal portion 
of the maxillary fossa. Insertion: Skin of the upper lip.* 
(&) The subcutaneus faciei. Origin: Lateral border of the 
premaxilla, its frontal process, and the supraorbital process 
of the frontal. Insertion: Skin of the dorsal surface of the 
nose. 
The muscle is closely associated in front of the eye with a conspicuous 
band of fibres arising from the anterodorsal margin of the zygomatic 
arch. The latter muscle is probably a corrugator supercilii, operating 
in conjunction with the orbicularis in firmly closing the eye. 
(c) The zygomaticus minor. Origin: Anterior end of the 
zygomatic arch. Insertion: Skin of the angle of the mouth. 
(d) The levator alae nasi. Origin: Maxillary fossa. Insertion: 
Lateral cartilage of the nose. The muscle is very slender, 
and is inserted by a long tendon which underlies the in- 
sertion portion of the quadratus labii superioris. 
(e) The buccinator is a broad stout band of fibres enclosing 
the cheek and attached to the alveolar borders of the upper 
jaw and mandible. 
(/) The caninus. Origin: Lateral border of the upper jaw. 
Insertion: Hairy portion of the mucous membrane of the 
mouth. The muscle is very broad, but short and extremely 
thin. 
(g) The quadratus labii inferioris. Origin: Ventral border 
of the mandible. Insertion: Skin of the lower lip. 
(/z) The mentalis. The muscle surrounds the anterior portion 
of the mandible behind the incisor teeth. It is attached 
externally to the skin of the lower lip through the insertion 
portion of the quadratus labii inferioris, which largely 
overlies it. 
Because of the great size and mobility of the ears, the cutaneous 
auricular muscles, comprising some twenty different members, are 
especially well developed. These muscles are not individually described, 
but their extent should be noted in contrast to the vestigial character 
of the ear muscles in man. 
*The levator alae nasi, and zygomaticus minor muscles may be considered to 
be subdivisions of this muscle. 254 
Anatomy of the Rabbit 
3. Dissection on the ventral surface of the neck to free the external 
jugular vein and its tributaries. The cervical fascia and a 
portion of the parotid gland must be removed. 
The external jugular vein (v. jugularis externa) is formed 
behind the angle of the mandible by the union of the anterior and 
posterior facial veins. It passes backward in a superficial position 
to the superior thoracic aperture. Its connections in the lower part 
of the neck comprise the transverse scapular vein (v. transversa 
scapulae) of the shoulder and its union with the vein of the other 
side by the transverse jugular vein (v. jugularis transversa) 
(Fig. 85). 
The posterior facial vein is formed in front of the base of the 
ear by the union of the superficial temporal vein, which runs 
forward immediately dorsal to the external auditory meatus after 
emerging from the cranial cavity, and the inferior ophthalmic 
vein, which passes back from the orbit. 
As the superficial temporal runs along the lower margin of the temporal 
muscle, it is joined by one or more small deep temporal veins from the substance 
thereof. The posterior facial is joined by the anterior auricular vein from 
the ear and then passes downward through the parotid gland, receiving the small 
transverse facial vein and being crossed by the facial nerve. Immediately below 
the latter it receives the posterior auricular vein from the ear and the back of 
the head. At about the same level it is joined by a deep vessel, the posterior 
internal maxillary, emerging from behind the mandible. 
In addition to the tributaries described above, the anterior 
facial vein receives from beneath the anterior margin of the 
masseter the deep facial vein (v. facialis profunda). The latter 
arises in the lower anterior portion of the orbit, and passes down- 
ward beneath the masseter muscle. The anterior facial vein 
receives at the ventral border of the mandible the internal max- 
illary vein (v. maxillaris interna). The latter also begins in the 
orbit, where it is connected with the deep facial. It is also identified 
as the sublingual vein. At the medial surface of the mandible it 
receives the inferior alveolar vein-to be seen at a later stage- 
from the interior of the mandible. 
A small, unpaired median submental vein enters the anterior facial of 
one side. 
The external jugular vein may be divided and turned forward together with 
the parotid gland. The Head and Neck 
255 
4. Examination of the more superficial structures of the ventral 
surface of the head and neck. 
(a) The submaxillary gland (gl. submaxillaris), one of the 
salivary series, is a somewhat compact rounded or oval gland 
lying at the medial side of the extreme ventral portion of the 
angle of the mandible. Its whitish-coloured duct (d. sub- 
maxillaris) may be seen running upward and slightly for- 
ward to enter the mouth (cf. p. 260). It crosses the lateral 
surface of the digastric muscle but is medial to the external 
maxillary artery. 
(&) The angle of the mandible is covered by two muscles of 
mastication, the masseter lying on the lateral surface, and 
the pterygoideus internus on the medial surface, the 
latter being overlapped ventrally by a part of the former. 
(c) The digastricus. Only its insertion portion is visible (the 
origin being through the stylohyoid ligament from the 
jugular process of the occipital bone). It passes forward 
along the medial surface of the mandible, to the anterior 
portion of which it is attached. 
(d) The mylohyoideus is a transverse sheet of muscle arising 
from the medial surface of the mandible on either side and 
inserted on the hyoid bone. 
(e) The sternomastoideus. Origin: In common with that 
of the opposite side, from the manubrium sterni. Insertion : 
Mastoid process of the skull. 
(/) The sternohyoideus. Origin: In common with that of the 
opposite side, from the dorsal surface of the manubrium and 
anterior portion of the body of the sternum, extending to 
the third costal articulation. Insertion: Greater cornu of 
the hyoid. 
The two muscles are closely associated in the middle line. They 
should be separated from each other and divided. 
(g) The sternothyreoideus. Origin: In common with the 
sternohyoideus. Insertion: Lateral plate of the thyreoid 
cartilage of the larynx. The muscle forms a thin band 
lying on the side of the trachea. It is continued from the 
thyreoid cartilage to the greater cornu of the hyoid as the 
thyreohyoideus. 256 
Anatomy of the Rabbit 
(h) The trachea occupies a median position, and is supported 
by cartilaginous tracheal rings. 
(i) The thyreoid cartilage of the larynx; a saddle-shaped 
cartilage, composed of right and left thyreoid plates 
(Fig. 68). 
(j) The cricoid cartilage, a thick annular cartilage situated 
between the thyreoid cartilage and the first tracheal ring. 
It is connected ventrally with the thyreoid cartilage by the 
cricothyreoideus muscle. 
(&) The deep cervical lymph gland (lymphoglandula cervi- 
calis profunda) is a large elongated reddish-coloured gland 
in the upper portion of the neck, opposite the thyreoid 
cartilage. 
(Z) The thyreoid gland (gl. thyreoidea) lies on the ventral 
surface of the trachea behind the cricoid cartilage. It is 
composed of right and left portions connected across the 
middle line by a thin median portion, the isthmus {cf. 
p. 108). 
(w) The common carotid artery (a. carotis communis) passes 
forward from the superior thoracic aperture along the side 
of the trachea. Its branches on the neck include the 
superior thyreoid artery (a. thyreoidea superior), to the 
thyreoid gland, and the (superior) laryngeal artery 
(a. laryngea). The latter arises at the level of the thyreoid 
plate, passing to the larynx and to the sternohyoid and 
sternothyreoid muscles. 
(n) The internal jugular vein (v. jugularis interna) lies to the 
lateral side of the common carotid artery, traversing the 
neck from the jugular foramen of the skull to the superior 
thoracic aperture. 
(o) The tenth cranial or vagus nerve (n. vagus) is the largest 
of four nerves accompanying the carotid artery. It lies to 
the lateral side of the common carotid, between the latter 
and the internal jugular vein. It gives off the n. laryngeus 
superior to the larynx, the latter passing to the dorsal side 
of the common carotid artery. 
The action of the vagus on the heart is inhibitory, that on the 
stomach is excitatory. Section of the nerves increases heart beat. The Head and Neck 
257 
{p) The ramus descendens of the twelfth cranial or hypo- 
glossal nerve crosses the root of the vagus from a lateral 
to a medial position. It passes backward on the ventral 
surface of the artery, and is chiefly distinguishable by its 
branches to the sternohyoideus and related muscles. 
(g) The cervical portion of the sympathetic trunk lies on 
the dorsal surface of the common carotid, and is slightly 
medial in relation to the vagus. 
Section and stimulation of the sympathetic in the neck is one of the 
classic demonstrations of vaso-motor action. The result of section can 
be seen in reddening and loss of heat in the ear (vaso-dilation), and con- 
traction of the pupil of the eye. Stimulation has the opposite effect 
(vaso-constrict ion). 
(r) The ramus cardiacus of the vagus (n. depressor) lies on 
the dorsal surface of the common carotid on the medial side 
of the sympathetic trunk, arising at the level of the posterior 
margin of the thyreoid cartilage. It is an afferent nerve. 
Its fibres are said to originate from cells in the upper pole 
of the jugular ganglion. Those of the left terminate 
peripherally in the arch of the aorta, those of the right 
in the subclavian. 
Occurring in the rabbit as a separate nerve, the depressor is impor- 
tant experimentally. Stimulation of the proximal end in the living 
animal produces fall of blood pressure and retardation of the heart beat. 
The former is due to reflex action on the blood-vessels (c/. p. 64), while 
the latter depends upon reflex stimulation of the vagus, since slowing 
of the heart does not take place if the vagi are also divided. 
(s) The third and fourth cervical nerves may be traced 
from their origin in the intervertebral foramina to the 
musculature of the neck. They encircle the basioclavicularis 
muscle, under cover of the sternomastoideus and cleido- 
mastoideus. 
5. Dissection of the muscles of mastication and related structures 
of the mandible. 
(a) The masseter muscle. Origin: The zygomatic arch. 
Insertion: Lateral surface of the angle of the mandible 
(1, a). Some of the most anterior fibres curve round the 
ventral edge of the mandible and pass back medial to it, 
covering the ventral part of the internal pterygoid (c). 258 
Anatomy of the Rabbit 
They are inserted along the ventral edge almost to its 
posterior extremity. 
The masseter muscle consists of external and internal divisions 
which are readily separable posteriorly but not anteriorly. The external 
originates from the lateral surface of the zygomatic arch along slightly 
less than the anterior half of its length, tendinous from its anterior angle 
and fleshy behind that. Its insertion is near the ventral edge of the 
mandible. The main part of the internal division takes origin from the 
internal surface of the same part of the arch and is inserted dorsal to the 
external division. In the rabbit a readily separable portion, probably 
to be included with the internal division, originates from the remainder 
of the inner surface of the arch and is inserted on the lateral surface 
of the ramus of the mandible. 
The orbital structures should be freed from the zygomatic arch by 
passing a knife along its dorsal margin. The zygomatic arch may then 
be divided anteriorly and posteriorly and removed, together with the 
whole insertion of the masseter muscle. 
(&) The temporalis is a slender, somewhat triangular muscle 
arising from the reduced temporal fossa (sulcus temporalis) 
of the skull and inserted by a long stout tendon on the 
edge and adjacent part of the lateral surface of the reduced 
coronoid process. Fibres from the masseter and the superior 
portion of the external pterygoid muscles are attached along 
the side of the tendon. The muscle may be exposed by 
dividing the temporal portion of the posterior supraorbital 
ligament which holds its tendon in place; then divided. 
On account of the narrowmess of the space lying between the two 
limbs of the mandible, and the great depth of its angle, it is necessary, 
in order to expose the surface for the deep dissection of the ventral 
portion of the head and neck, to remove one-half of the mandible entirely. 
Hence the following order: Divide the mandibular symphysis, and pass 
a knife along the medial surface of the bone to be removed. The tip 
of the knife must be kept close to the bone, so that the underlying soft 
parts, except for being divided, will be kept uninjured. The medial 
surface of the mandible should be clean when removed. The bone may 
be turned laterad and detached from the skull at the articulation. 
The structures appearing on the cut surface include the insertion 
of the digastricus and the margin of the mylohyoideus; also: 
(c) The pterygoideus internus muscle. Origin: Pterygoid 
process of the skull. Insertion: Ventral portion of the 
medial surface of the angle. The Head and Neck 
259 
(d) The pterygoideus externus. The muscle comprises two 
portions. Superior head. Origin: Infratemporal surface 
of the alisphenoid. Insertion: Medial surface of the ramus 
of the mandible and sulcus ascendens. 
This portion has also been described as a division of the temporalis. 
Inferior head. Origin: Posterior edge and both surfaces 
of the lateral plate of the pterygoid process. Insertion: 
The depression in front of the neck of the mandible, the 
interarticular cartilage of the temporo-mandibular joint, 
and the whole medial edge of the head of the mandible. 
(e) The inferior alveolar artery (a. alveolaris inferior) lies 
between the two pterygoidei. Its cut end marks the point 
of entrance into the mandible through the mandibular 
foramen. The corresponding inferior alveolar vein 
leaves the mandible at this point. 
(/) The inferior alveolar nerve (n. alveolaris inferior) accom- 
panies the inferior alveolar artery to the mandible. The 
continuation of the nerve is the mental nerve. It appears 
at the mental foramen, and passes to the lower lip. 
The origin of the inferior alveolar nerve may be traced. It 
arises from the mandibular nerve (n. mandibularis), the third 
division of the fifth cranial or trigeminal nerve (n. trigeminus). 
The mandibular nerve also gives off anteriorly the stout lingual 
nerve to the tongue and posteriorly the slender mylohyoid nerve 
to the digastric and mylohyoid muscles. These structures, together 
with the inferior alveolar artery, may be freed from their loose 
connections with the pterygoidei, so that they may be left in place 
for further study. The two pterygoidei may then be detached at 
their point of origin from the skull and removed. 
6. The branches of the common carotid may be traced in the 
anterior portion of the ventral surface of the neck as follows: 
(a) The internal carotid (a. carotis interna) is a small vessel 
given off from the dorsal wall (pp. 145, 300). The trunk 
then passes forward as the external carotid (a. carotis 
externa). 
(5) The occipital artery (a. occipitalis) passes from the dorsal 
wall to the posterior portion of the head. 260 
Anatomy of the Rabbit 
The stylohyoideus major, a slender muscle arising with the 
digastricus from the stylohyoid ligament and inserted on the greater 
cornu of the hyoid, should be divided. The tendon of the digastricus 
may be reflected. 
(c) The lingual artery (a. lingualis) arises from the ventral 
wall and passes forward into the tongue. 
The hypoglossal nerve crosses the ventral surface of the artery and 
should be kept intact. 
(J) The external maxillary artery (a. maxillaris externa) is 
given off immediately in front of the lingual artery, some- 
times in common with it. It passes forward on the medial 
surface of the ventral border of the mandible (medial to the 
digastricus), giving branches to the submaxillary gland and 
to the muscles of mastication. The vessel has been divided 
at the point where it passes around the ventral border of the 
mandible to the lateral surface of the face. 
(e) The internal maxillary artery (a. maxillaris interna), one 
of the two terminal branches of the external carotid, passes 
in the direction of the orbit (p. 269), giving off the inferior 
alveolar artery to the mandible. 
(/) The superficial temporal artery (a. temporalis super- 
ficialis), the second terminal branch, passes dorsad to the 
temporal region, supplying the latter and the base of the 
ear. The transverse facial artery, which crosses the 
cheek, is an anterior branch of this vessel. 
7. Dissection of the tongue and hyoid. 
The mylohyoideus should be reflected. Note the position of the lingual 
nerve. 
Dorsal to the anterior part of the mylohyoideus lies the sublingual gland, 
from which several small ducts run dorsad between the geniohyoid and the 
hyoglossus muscles to the floor of the mouth. The submaxillary duct turns 
forward behind the sublingual gland and runs along its dorsal surface to open 
on the floor of the mouth near the mandibular symphysis. 
(a) The stylohyoideus major muscle. Origin: Jugular pro- 
cess of the occipital bone. Insertion: Tip of the greater 
cornu of the hyoid. The muscle has been divided. 
The superficial temporal and internal maxillary arteries should be 
divided. The Head and Neck 
261 
(b~) The styloglossus. Origin: Jugular process. Insertion: 
The muscle passes downward and forward, expanding at 
the base of the tongue into a broad sheet, the fibres of which 
extend to its anterior tip. 
The muscle should be carefully separated from two others on its 
dorsomedial side and divided. 
(c) The stylohyoideus minor. Origin: Jugular process. In- 
sertion: Lesser cornu of the hyoid. A slender muscle 
having about the same direction, but ending on the more 
dorsal part of the hyoid apparatus. 
The remaining muscle is the stylopharyngeus, a thin delicate 
muscle, the insertion of which is on the lateral wall of the pharynx. 
(d) The geniohyoideus. Unpaired. Origin: Mandibular 
symphysis. Insertion: Ventral surface of the body of the 
hyoid. 
(e) The genioglossus. Origin: Medial surface of the man- 
dible immediately behind the symphysis. The fibres pass 
upward and slightly backward into the substance of the 
tongue. 
(/) The hyoglossus. Origin: The body of the hyoid and the 
greater and lesser cornua by more or less separate heads. 
The muscle passes into the base of the tongue, enclosed on 
either side by the styloglossi. 
(g) The lingualis, or intrinsic muscle of the tongue, consists 
of a mass of fibres with no skeletal attachments. 
(h) The lingual nerve (n. lingualis), one of the chief branches 
of the mandibular, passes forward and downward to the 
side of the tongue and enters its substance immediately 
below the ventral border of the styloglossus. 
The lingual is the sensory nerve of the tongue. It contains fibres 
for general sensibility and near its point of origin is joined by the chorda 
tympani (p. 272), the latter containing gustatory fibres. 
(i) The twelfth cranial or hypoglossal nerve (n. hypoglos- 
sus) enters the base of the tongue. It lies on the lateral 
side of the external carotid artery and on the medial side 
of the stylohyoideus major. It is distributed as a motor 
nerve to the lingual muscles. 
(j) The ramus lingualis of the ninth cranial, or glosso- 262 
Anatomy of the Rabbit 
pharyngeal nerve (n. glossopharyngeus), enters the base 
of the tongue at a point dorsal to the hypoglossus and be- 
tween the stylohyoideus minor and the stylopharyngeus. 
It is a gustatory nerve of the tongue. 
8. Dissection of the extra-cranial roots of the ninth to twelfth 
nerves (Fig. 82). 
These nerves, which for the most part have 
already been exposed, may be traced to their 
origin in the jugular and hypoglossal foramina. 
The tympanic bulla should be cleared and the 
tendons of origin of tongue muscles removed 
from the jugular process. 
(a) The ninth (glossopharyngeal) nerve 
is farthest forward. Its two main 
branches are the ramus lingualis 
to the posterior part of the tongue, 
for taste, and the ramus pharyn- 
geus, the latter entering the lateral 
wall of the pharynx. 
(b) The tenth (vagus) nerve bears an 
elongated ganglionic enlargement, the 
plexus ganglioformis (ganglion 
nodosum). It lies immediately below 
the jugular foramen. The superior 
laryngeal nerve and the ramus car- 
diacus (depressor nerve) are given 
off at the level of the origin of the in- 
ternal carotid artery. 
(c) The eleventh cranial, or spinal accessory nerve (n. 
accessorius), is dorsal to the vagus. The nerve passes 
dorsad to the medial side of the mastoid attachments of 
the sternomastoideus and cleidomastoideus muscles, giving 
branches to the latter, and then passes backward to the 
ventral surface of the trapezius to which it is distributed. 
(d) The twelfth (hypoglossal) nerve arises behind the foregoing 
nerves, since it comes from the hypoglossal foramina of the 
occipital. It crosses their roots, forming a broad curve 
on the lateral surface of the root of the external carotid 
Fig. 82. Plan of the 
extra-cranial roots of the 
IX-XII cranial nerves and 
sympathetic trunk; ven- 
tral surface, right side, the 
sympathetic and depres- 
sor nerve shown as dis- 
placed from the dorsal 
surface of the artery. 9, 
10, 11, 12, glossopharyn- 
geal, vagus, spinal acces- 
sory, and hypoglossal 
nerves; ac, carotid artery; 
c, cervical root of ramus 
descendens XII; gn, gan- 
glion nodosum vagi; Is, 
superior laryngeal; nd, 
depressor nerve; rd, ramus 
descendens hypoglossi; s, 
sympathetic. The Head and Neck 
263 
artery, and enters the base of the tongue. The ramus 
descendens is given off at about the point where it crosses 
the artery. It has a slender root from the third cervical 
nerve. 
(e) The cervical portion of the sympathetic trunk begins 
in the superior cervical ganglion (g. cervicale superius). 
It lies to the medial side of the vagus ganglion and of the 
internal carotid artery. The nerves proceeding from the 
ganglion accompany the branches of the external and 
internal carotid arteries to the head. 
9. The oral cavity and pharynx. 
The glossopharyngeal nerve and the superior laryngeal nerve 
and artery may be divided, and the external carotid artery with 
the associated nerves separated from the oesophagus and trachea. 
The latter may be displaced downward to a slight extent by dividing 
the loose connective tissue along the ventral surface of the vertebral 
column. An incision extending from the oral cavity backward 
into the oesophagus will expose the internal surface of this portion 
of the digestive tube sufficiently to make out its features. The 
incision divides the constrictor pharyngis muscle, a broad band 
of muscle fibres enclosing the posterior portion of the pharynx. 
For the general relations of the oral cavity see p. 87 and Fig. 43. 
The divisions are: 
(a) The oral cavity (cavum oris), divisible into the oral 
cavity proper, and the vestibulum oris, the latter lying 
between the alveolar processes and teeth on the one hand 
and the lips on the other. 
(b) The pharynx. Its oral portion (pars oralis) continues the 
oral cavity, and connects it with the oesophagus. Its 
dorsal, also anterior, nasal portion (pars nasalis), or 
nasopharynx, lies above the soft palate, and receives the 
posterior aperture of the nose. Its ventral and posterior 
laryngeal portion (pars laryngea), not well-defined, con- 
tains the aperture of the larynx, the aditus laryngis. 
In the oral cavity: 
(a) The hard palate (palatum durum) forms the anterior 
portion of the roof; its mucous membrane is thrown into a 
series of transverse ridges. 264 
Anatomy of the Rabbit 
(b) The soft palate (palatum molle) is the thin, narrow, 
posterior, membranous portion of the roof. It is very long 
in the rabbit, extending from the bony palatine bridge 
backward to a point above the laryngeal aperture, where 
it ends with a concave free margin. 
(c) The nasopalatine or incisive ducts (dd. nasopalatini) 
open by small slits about a millimetre behind the secondary 
incisors, each opening being covered by a slight projection 
from its medial margin. The ducts connect the anterior 
portion of the nasal cavity with the mouth, and a probe 
may readily be passed backward along them from their 
oral apertures. 
(d) The tongue (lingua) projects upward and forward from its 
basal attachments on the hyoid into the floor of the mouth. 
Its connection with the latter is extended forward in the 
middle line by a vertical membranous fold, the frenulum 
linguae. Its dorsal surface is divided into a posterior 
smooth and hard portion, and an anterior softer and rougher 
portion, occupied by fine low elevations, the fungiform 
papillae (papillae fungiformes). At the posterior end of 
the smooth portion there is on either side a minute spherical 
elevation, set low into the mucous membrane, the vallate 
papilla (papilla vallata), and in a more lateral and anterior 
position an oval area, the papilla foliata, the surface of 
which is marked by fine parallel ridges. Both vallate and 
foliate papillae are occupied by microscopic taste-buds. 
In the pharynx: 
(a) The tonsil (tonsilla) appears as a rounded mass of lymph 
follicles lying on the anterior wall of a deep lateral de- 
pression, the tonsillar sinus (sinus tonsillaris). The 
vertical slit-like aperture of the sinus is bounded by low 
anterior and posterior folds. 
(&) The epiglottis, a valve-like fold guarding the entrance 
to the larynx, projects upward from the floor into the 
pharyngeal cavity. 
(c) By removing the posterior portion of the soft palate, the 
connection of the nasopharynx with the nasal fossae will be 
exposed; also on the lateral wall the pharyngeal aperture 
of the auditory tube (ostium pharyngeum tubae). The Head and Neck 
265 
10. Examination of the larynx. 
By cutting around the base of the tongue on the opposite side 
of the body, the whole structure, together with the hyoid, larynx, 
and a portion of the trachea back to about the end of the thyreoid 
gland may be removed. This affords a good opportunity of re- 
dissecting on the opposite side from the medial surface of the man- 
dible outward, also of clearing and examining the hyoid apparatus, 
which is not usually available with the prepared skeleton (Fig. 68). 
The laryngeal cartilages should be cleared externally and the parts 
made out as follows: 
(a) The thyreoid cartilage (cartilago thyreoidea) forms the 
largest portion of the structure. It is an unpaired saddle- 
shaped cartilage, described as consisting of right and left 
laminae. Its anterodorsal angle at each side projects 
forward as the cornu superior, connected by ligament with 
the greater cornu of the hyoid. The corresponding postero- 
dorsal angle, the cornu inferior, overlies the dorsolateral 
portion of the cricoid cartilage. The anterior dorsal portion 
of each plate bears a small thyreoid foramen (foramen 
thyreoideum) for the entrance of the superior laryngeal 
nerve. 
(b) The cricoid cartilage (cartilago cricoidea) is an annular 
cartilage, partly enclosed by the posterior portions of the 
thyreoid laminae and surrounding the first tracheal ring. 
Its ventral portion, the arch of the cricoid cartilage, falls 
some distance behind the thyreoid cartilage, the intervening 
space being largely occupied by the cricothyreoidei 
muscles. Its dorsal portion, the lamina of the cricoid, 
forms a greatly expanded plate serving for the support of 
the arytenoid cartilages. 
(c) The paired arytenoid cartilages (cartilagines arytenoi- 
deae) lie one on either side of the anterior tip of the cricoid 
plate. 
(d) The corniculate cartilages (cartilagines corniculatae) are 
minute slender, curved cartilages situated at the apices of 
the arytenoids. 
(e) The epiglottic cartilage (cartilago epiglottica) is a trian- 
gular plate supporting the epiglottis. 266 
Anatomy of the Rabbit 
(J) The rudimentary vocal folds (plicae vocales) may be seen 
as vertical folds of the internal surface of the larynx, 
especially prominent when the thyreoid cartilage is bent 
downward on the cricoid. Each fold is attached at one 
end to the thyreoid, at the other end to an arytenoid 
cartilage, and forms the posterior boundary of a shallow 
pouch, the laryngeal ventricle (ventriculus laryngis). 
In addition to the cricothyreoidei, the laryngeal cartilages are 
connected by several small muscles, including the cricoarytenoidei 
posterior and lateralis, the thyreoarytenoideus and the arytenoideus 
transversus, the last named being an unpaired muscle connecting the 
arytenoid cartilages. 
11. The eye and related structures of the orbital cavity. 
The eyeball should be carefully separated from the bony orbital 
rim. The first portion of the nasolacrimal duct (d. nasolacrimalis), 
passing from its aperture on the medial surface of the lower eyelid 
to the lacrimal bone, will be divided. The muscles and glands of 
the orbit may be made out as follows: 
(a) The levator palpebrae superioris. Origin: Wall of the 
orbit above the optic foramen. Insertion: Upper eyelid. 
This thin sheet of muscle should be separated from the underlying 
rectus superior of the eyeball. 
(b) The obliquus superior. Origin: Anterior margin of the 
optic foramen. The muscle passes upward on the wall of 
the orbit, then beneath a fibrous cord, the trochlea, which 
bridges a small portion of the orbital wall and changes the 
course of the tendon by a considerable angle. Insertion: 
Anterodorsal portion of the eyeball. 
(c) The obliquus inferior. Origin: Lacrimal bone. In- 
sertion: Posteroventral portion of the eyeball. 
The oblique muscles are relatively large in the rabbit, a feature 
correlated with the lateral direction of the eyes. 
(J) The four recti muscles, superior, inferior, medialis, 
and lateralis, arise from the boundary of the optic foramen, 
and are inserted respectively on the dorsal, ventral, anterior, 
and posterior portions of the periphery of the eyeball. The Head and Neck 
267 
(e) The retractor oculi (best seen after the removal of the 
eye) arises in common with the foregoing recti muscles 
and is inserted on the 
medial portion of the 
eyeball around the 
optic nerve. It con- 
sists of four distinct 
parts. 
(J) The Harderian 
gland (gl. Harderi- 
ana) is a large com- 
pact gland lying in 
the anterior portion 
of the orbit. It is 
composed of two por- 
tions, one of which 
is greyish red, the 
other white. The 
duct opens on the inner surface of the third eyelid. 
(g) The lacrimal gland (gl. lacrimalis) is a much smaller, also 
darker, structure lying close to the skull in the temporal 
angle of the orbit. It communicates by several fine ducts 
with the inner surface of the upper eyelid. 
The infraorbital gland (gl. infraorbitalis) is a diffuse white or 
yellow gland lying in the anteroventral angle of the orbit immediately 
medial to the zygomatic arch. The gland is one of the salivary series, 
its duct passing downward and opening through the mucous membrane 
of the cheek into the cavity of the mouth. 
To examine the structure of the eye, the muscles of the eyeball 
should be divided at their insertions, and the whole structure 
removed. The second cranial or optic nerve (n. opticus) is 
divided; also the ophthalmic artery, a small branch of the 
internal carotid which accompanies the nerve outward from the 
optic foramen to the eyeball. 
The eye may be divided by a circular incision into medial and 
lateral hemispheres, the lateral hemisphere, containing the lens, 
being again divided vertically. The parts should be examined 
under water. The chief structures (Fig. 83) comprise: 
Fig. 83. Diagram of the parts of the eye in 
vertical section: c.a., anterior chamber; c.c., 
ciliary body; ch., chorioidea; co., cornea; c.p., 
posterior chamber; c.r., ciliary portion of the 
retina; c.v., vitreous body; d.h., Harderian duct; 
d.l'., position of the lacrimal ducts; d.n., nasola- 
crimal duct; i., iris; 1., lens; n.o., optic nerve; 
o.r., optic portion of the retina; p.i., lower eye- 
lid; p.s., upper eyelid; p.t., third eyelid; r.b., 
retractor oculi; r.i., rectus inferior; r.s., rectus 
superior; sc., sclera; z.,_ suspensory zonular 
fibres of the lens. 268 
Anatomy of the Rabbit 
(a) The fibrous tunic (tunica fibrosa oculi), the strong peri- 
pheral coat enclosing the whole structure. It is divisible 
into a medial portion, the sclera, or sclerotic coat, a thick 
white investment of fibrous connective tissue enclosing the 
greater part.of the eyeball, and a smaller transparent lateral 
portion, the cornea, covering the exposed surface. 
(&) The vascular tunic (tunica vasculosa oculi), the thin 
middle coat of the eye; pigmented, except in albino animals. 
It is divisible into: (1) a general portion, the chorioidea, 
lying on the inner surface of the sclera; (2) a muscular 
portion, the ciliary body (corpus ciliare), composed of 
numerous, radially arranged ciliary folds (plicae ciliares) 
and forming an annular ridge about the periphery of the 
lens; and (3) the iris, the latter forming a circular fold 
suspended about the periphery of the lens and on its outer 
surface. 
(c) The retina, the innermost layer of the eye, forms a thin 
soft membrane covering the inner surface of the chorioidea. 
It is divisible into a larger optic portion, the sensory part 
of the eye, and a smaller ciliary portion, lying about the 
periphery of the lens and distinguishable by the radiate 
markings of its surface, the latter formed by the projecting 
ridges of the ciliary body. 
(d) The transparent lens of the eye is suspended by fine fila- 
ments, the zonular fibres, reflected from the margin of the 
ciliary body. 
(e) The vitreous body (corpus vitreum), a transparent mass, 
of gelatinous consistence, occupies the large space enclosed 
by the lens and the retina. 
(/) The space enclosed between the surface of the lens and the 
cornea is divisible into a larger portion, the anterior 
chamber (camera oculi anterior), lying outside of the iris, 
and a smaller portion, the posterior chamber (camera 
oculi posterior), lying between the iris and the lens. These 
two chambers communicate through the central aperture 
enclosed by the free margin of the iris, the pupil (pupilia). The Head and Neck 
269 
12. Following the removal of the eye, the blood-vessels and nerves 
of the orbit may be freed from the remaining portions of the 
eye muscles and examined. In order to see their connections 
in the anterior angle of the orbit, it is necessary to break away 
the anterior root of the zygomatic arch, and also the bony ridge 
which lodges the alveoli of the posterior cheek-teeth. 
(a) The internal maxillary artery enters the orbit through 
the anterior sphenoidal foramen in the root of the lateral 
lamina of the pterygoid process. At the posterior ventral 
angle of the orbit it gives off the inferior ophthalmic 
artery (a. ophthalmica inferior). This vessel passes 
upward and forward on the medial wall of the orbit, giving 
branches to the eye muscles. It divides into two branches, 
the frontal artery, which leaves the orbit through the 
anterior foramen of the supraorbital process, and the 
lacrimal artery, which passes through the corresponding 
posterior foramen. The ethmoidal artery, a small branch 
of the frontal, passes through the minute ethmoidal foramen 
of the orbital portion of the frontal into the nasal cavity. 
The internal maxillary artery passes forward along the 
ventral boundary of the orbit, and at the opening of the 
infraorbital canal gives off a branch, the pterygopalatine 
artery, continuing as the infraorbital artery. A small 
branch, the superior dental artery (a. dentalis superior) 
is given off laterally to the alveoli of the upper teeth. 
The infraorbital artery (a. infraorbitalis) passes 
through the infraorbital canal to the face. 
The pterygopalatine artery (a. pterygopalatina) 
divides almost immediately into the anterior palatine 
artery, which traverses the pterygopalatine canal to the 
mucous membrane of the hard palate, and the spheno- 
palatine artery, which enters the nasal cavity by the 
sphenopalatine foramen. 
(&) The divisions of the third cranial, or oculomotor nerve, 
supply the eye muscles, with the exception of the obliquus 
superior, rectus lateralis, and retractor oculi. 270 
Anatomy of the Rabbit 
This nerve enters the orbit from the superior orbital fissure in com- 
pany with certain parts of the trigeminal (e,/). The small nerves 
passing through the middle and posterior sphenoidal foramina of the 
pterygoid process are the pterygobuccinator and masseterico- 
temporal nerves, branches of the mandibular, passing to the muscles 
of mastication. 
(c) The fourth cranial, or trochlear nerve (n. trochlearis), 
is distributed to the obliquus superior muscle. 
(d) The sixth cranial, or abducent nerve (n. abducens), is 
distributed to the rectus lateralis, and to the retractor oculi. 
(e) The ophthalmic nerve (n. ophthalmicus), the first division 
of the fifth cranial, or trigeminal nerve (n. trigeminus), 
accompanies the inferior ophthalmic artery on the medial 
wall of the orbit. It is entirely sensory. It gives off a 
lacrimal nerve, which passes upward through the posterior 
foramen of the supraorbital process, after giving off small 
branches to the lacrimal gland, and is distributed to the 
skin of the upper eyelid. The ophthalmic then passes 
forward a short distance and divides into two parts. One 
of these, the frontal nerve, leaves the orbit through the 
anterior supraorbital foramen and branches in the skin. 
The other, the nasociliary nerve, is distributed partly to 
the anterior portion of the orbit, while its main division 
leaves the orbit as the ethmoidal nerve, which passes 
through the small ethmoidal foramen of the orbital part 
of the frontal bone to supply the interior of the nose. The 
nasociliary nerve is also connected with the minute ciliary 
ganglion lying on the optic nerve by a very delicate long 
root of the ciliary ganglion. 
The lacrimal, frontal, and nasociliary nerves appear as 
separate structures in the orbit, their origin being deep. 
(/) The branches of the maxillary nerve (n. maxillaris), the 
second division of the trigeminus, traverse the ventral por- 
tion of the orbit passing forward in company with the 
internal maxillary artery. They include the spheno- 
palatine nerve (n. sphenopalatinus) and the infraorbital 
nerve (n. infraorbitalis). The latter gives off superior 
alveolar branches to the upper teeth, passing forward 
through the infraorbital groove and foramen to the face. The Head and Neck 
271 
The connections of the sphenopalatine nerve may be examined 
by first dividing both nerves at the posterior angle of the orbit; then 
separating the slender sphenopalatine nerve from the ventral sur- 
face of the cord and turning the principal, infraorbital portion 
forward. A third nerve, the nerve of the pterygoid canal, should 
remain intact on the orbital wall. If the infraorbital nerve alone 
is divided, the sphenopalatine nerve will be found on the surface 
of the bone below the nerve of the pterygoid canal, from which 
it may be distinguished by its lighter coloration. 
The sphenopalatine nerve is continued forward as the anterior 
(major) palatine nerve, which passes through the pterygopalatine 
canal to the posterior portion of 
the hard palate, but the spheno- 
palatine nerve is also connected 
with the sphenopalatine gang- 
lion. Nasal rami pass to the 
mucous membrane of the nose, 
and the nasopalatine nerve en- 
ters the nasal region, traversing 
the surface of the septum and 
reaching the anterior portion of 
the palate through the incisive 
foramina. 
The nerve of the pterygoid 
canal (n. canalis pterygoidei), or 
Vidian nerve, is a slender cord 
which passes backward along the 
orbital wall from the posterodorsal 
angle of the sphenopalatine gang- 
lion. It lies on the medial side of 
the sphenopalatine and infraorbital 
nerves and on the lateral surface of 
the palatine bone. Posteriorly, it 
enters the groove representing the 
pterygoid canal. 
This nerve is composed of two parts, separated posteriorly. 
One of them, the deep petrosal nerve (n. petrosus profundus), 
is connected with the sympathetic plexus of the internal carotid 
Fig. 84. Diagram of the parts of the 
ear in vertical projection. To show the 
general relations of the structures 
covered by the dissection. 
p, petrous portion of the petrotym- 
panic bone; t., tympanic portion (bulla 
ty mpani). 
c., cochlea; c.s., bony semicircular 
canals; c.t., tympanic cavity; d.c., 
cochlear duct; d.e., endolymphatic duct; 
d.m., dura mater; d.s., semicircular 
ducts; f.c., cochlear fenestra; f.v., vesti- 
bular fenestra; i., incus; m, malleus; 
m.a.e., external acoustic meatus, termin- 
ating at the tympanic membrane; m.a.i., 
internal acoustic meatus; s., sacculus; 
s.e., endolymphatic sac; st., stapes; t.a., 
auditory tube; u., utriculus; v, vesti- 
bulum; VIII, acoustic nerve. 272 
Anatomy of the Rabbit 
artery, its fibres corning from the superior cervical ganglion. The 
other, the great superficial petrosal nerve (n. petrosus super- 
ficialis major), enters the skull at the foramen lacerum, passing 
into the petrosal bone, in the interior of which it is connected with 
the trunk of the facial. The nerve constitutes the motor root of 
the sphenopalatine ganglion, the sensory root being that provided 
by the sphenopalatine nerve. 
The sphenopalatine ganglion is one of several representing the 
parasympathetic division of the autonomic system in the head, and 
having motor and sensory roots from the cerebral nerves in addition 
to autonomic connections. The series includes the ciliary 
ganglion, which lies on the optic nerve, the sphenopalatine 
ganglion, the otic ganglia, associated with the mandibular nerve, 
and the submaxillary ganglion, associated with the lingual nerve. 
13. Examination of the middle ear. 
By breaking away the ventrolateral portion of the tympanic 
bulla and clearing the surface, the structures of the tympanic cavity 
may be studied. They are chiefly those already described in 
connection with the skeleton (p. 160), but the following soft parts 
may be identified. 
(a) The tympanic membrane (membrana tympani) is 
stretched almost vertically across the lower end of the 
external acoustic meatus. 
(b) The tensor tympani is a slender muscle, the origin of 
which forwards from the alisphenoid is concealed. It is 
inserted on the manubrium mallei. 
(c) The stapedius is a minute muscle arising from the periotic 
bone above the cochlear fenestra and inserted on the stapes. 
(d) The chorda tympani is a delicate nerve which crosses the 
tympanic cavity, lying between the long crus of the incus 
and the manubrium mallei. 
The nerve is a continuation of the intermediate nerve, a sensory 
root of the facial, which arises independently of the chief or motor root 
and joins the facial in the facial canal of the periotic bone. Its peri- 
pheral connections are with the lingual nerve and the submaxillary 
ganglion. 
(e) The internal carotid artery traverses the carotid canal 
of the tympanic bone. By breaking away the posterior The Thorax 
273 
portion of the bulla, the entrance of the vessel into the 
external carotid foramen may be seen. 
The dissection of the parts of the ear as here outlined includes only the 
external and middle portions together with the associated acoustic nerve and its 
entrance to the periotic bone. The parts of the internal ear (Fig. 84) are not 
readily made out without the use of special methods, though their position may 
be estimated by carefully breaking away the surface of the ventral portion of the 
periotic. They include (1) the bony labyrinth, consisting of a series of con- 
nected spaces lodged in the interior of the petrous bone, and comprising the 
cochlea, vestibulum, and the bony semicircular canals; and (2) the mem- 
branous labyrinth, consisting of a second series of spaces contained within the 
first, and comprising the duct of the cochlea, the sacculus, the utriculus, 
and the semicircular ducts, together with their connections and the endolym- 
phatic duct and sac. The membranous labyrinth contains the sensory portion 
of the ear and its cavity is occupied by a fluid material, the endolymph. The 
wall is separated from that of the bony labyrinth by an extensive perilymphatic 
space also occupied by a fluid material termed the perilymph. 
XL THE THORAX 
1. Examination of the thoracic wall. For this purpose the lateral 
surface of the thorax may be conveniently cleared, on the side 
from which the anterior limb has been removed, by dissecting 
away the attachments of the muscles already examined in the 
previous dissections. These include the origins of the pectorales, 
pectoscapularis, serratus anterior (thoracic portion), obliquus 
externus, and rectus abdominis. 
The dorsal portion of the exposed surface is occupied by the 
spinal musculature, to be examined at a later stage. On the ventral 
portion appear the ribs, and between them, filling the intercostal 
spaces, the intercostal muscles. The external intercostals (mm. 
intercostales externi) arise from the posterior margins of the bone 
ribs, the fibres passing obliquely downward and backward to be 
inserted on the anterior margins of the next succeeding ribs. The 
internal intercostals (mm. intercostales interni), the fibres of 
which are disposed in the opposite direction, are concealed for the 
most part from this surface, but appear ventrally between the 
costal cartilages, where they are not covered by the external inter- 
costals. They are best examined at a later stage from the interior 
of the thorax. 274 
Anatomy of the Rabbit 
In preparation for the removal of a section of the thoracic wall, 
the pectorales should be divided on the opposite side of the thorax, 
close to the sternum, so that the limb may be displaced. 
The nerves and vessels of the neck must be kept intact until the following 
dissection accounts for their thoracic connections. 
The scaleni muscles (p. 288) should be examined, since it is necessary to 
destroy their costal insertions. 
A triangular section of the wall, including the sternum and the 
costal cartilages, may be removed by making three incisions, one 
on either side of the sternum, extending from the middle of the first 
rib backward to the end of the ninth bone rib, and the third across 
the ventral surface close in front of the diaphragm. Do not cut 
into the diaphragm. 
The transversus thoracis muscle appears on the inner surface 
of the section removed. It is a thin sheet of fibres arising from the 
body and xiphoid process of the sternum and inserted on the ribs, 
from the second to the sixth, at the junctions of the bone ribs with 
the costal cartilages. 
A very thin layer of muscle fibres passing in the same direction as those of 
the internal intercostal muscles lies immediately internal to them in the lateral 
wall of the thorax and is named intracostal and subcostal muscles. These and 
the transversus thoracis muscle together represent a thoracic continuation of the 
transversus abdominis. 
The artery passing along the ventral wall between the transverse thoracic 
muscle and the internal intercostals is the internal mammary (p. 276). 
For the general relations of heart and lungs, see pp. 92 and 95. 
2. Dissection of structures in the superior thoracic aperture. 
The nerves and blood-vessels of this region are concealed by the 
thymus gland, a large triangular flattened structure of fatty 
consistence, lying partly ventral to the heart and extending forward 
from its base to the anterior end of the thorax (c/. p. 108). The 
thymus should be carefully raised from behind and dissected away, 
all vessels except those of the gland itself being kept intact. 
The following structures, including the aortic arch and the 
arteries arising from it, the superior caval veins, and the vagus, 
phrenic, and sympathetic nerves, cannot be dissected exactly in the 
order given below, but must be separated from one another and 
identified as they appear. The left superior caval vein is superficial, 
crossing the ventral surface of the aortic arch. Care should be The Thorax 
275 
taken not to injure the nerves {c-f) in exposing the branches of the 
subclavian artery. 
(a) The arch of the aorta (arcus aortae). Beginning at the 
base of the heart, the aorta at first passes forward, and then 
describing a curve, in the course of which it lies slightly to 
left of the median plane, turns backward along the ventral 
surfaces of the bodies of the thoracic vertebrae. With the 
exception of the coronary arteries (p. 279) the first branches 
are the large vessels arising from the convex surface of the 
arch. They comprise the common carotid and sub- 
clavian arteries. On the right side the carotid and sub- 
clavian arise from a short common trunk, the innominate 
artery (a. anonyma). The left common carotid arises 
immediately to the left of this vessel or from its base. The 
left subclavian arises some distance farther out along the 
arch. The subclavian artery (a. subclavia) is the first 
portion of the artery of the anterior limb. It passes from 
its point of origin laterad to the anterior margin of the first 
rib, where it becomes the axillary artery. Near its point 
of origin it gives off several branches, the relations of which 
are subject to considerable variation. They include: 
(1) The vertebral artery (a. vertebralis). This vessel 
passes into the costotransverse foramen of the sixth 
cervical vertebra, and, traversing the canal formed by 
this and the corresponding foramina of the remaining 
cervical vertebrae, reaches the interior of the cranial 
cavity. Its union on the ventral surface of the medulla 
oblongata with its fellow of the opposite side to form 
the basilar artery will be seen at a later stage (p. 299). 
(2) The superficial cervical artery (a. cervicalis super- 
ficialis)-divided in a previous dissection (p. 221)-is a 
small vessel which passes forward and outward beneath 
the insertions of the cleidomastoideus, basioclavicularis, 
and levator scapulae major muscles, ramifying ex- 
tensively in the fat mass of the side of the neck under 
cover of the superior portion of the trapezius. Its 
ascending cervical branch lies on the lateral side of 
the external jugular vein. 276 
Anatomy of the Rabbit 
(3) The transverse artery of the neck (a. transversa 
colli), also divided in a previous dissection (p. 222), 
passes laterad around the neck of the first rib to the 
wall of the thorax. It passes through the loop formed 
by the eighth cervical and first thoracic spinal nerves. 
It runs dorsad, first on the medial side of the scalenus 
anterior, then on the medial side of the cervical portion 
of the serratus anterior. A strong branch passes to the 
inferior angle of the scapula. The artery supplies the 
serratus anterior and the rhomboidei. 
(4) The a. intercostalis suprema passes backward to the 
internal surface of the thoracic wall, giving off the first 
three (or four) intercostal arteries in the intercostal 
spaces, and also small branches to the oesophagus and 
trachea. 
(5) The internal mammary artery (a. mammaria 
interna), the first portion of which has been removed 
with the ventral wall of the thorax, passes backward 
to the ventral abdominal wall as the superior epi- 
gastric artery (a. epigastrica superior) anastomosing 
with the inferior epigastric (p. 219). 
(b) The superior caval vein (v. cava superior) is formed at the 
base of the neck by the union of the internal and external 
jugular veins, the latter vessel receiving at this point the 
subclavian vein (v. subclavia). The right superior caval 
passes almost directly backward, crossing the ventral surface 
of the right subclavian artery, and enters the anterior por- 
tion of the right atrium. The left vessel crosses both the 
left subclavian artery and the arch of the aorta, reaching 
the right atrium from the dorsal surface of the heart. 
(c) The vagus nerve. On the right side the nerve crosses the 
ventral surface of the subclavian artery, passing dorsad to 
the wall of the oesophagus. It gives off the recurrent 
nerve (n. recurrens), the latter curving around the sub- 
clavian artery and passing forward along the side of the 
trachea to the larynx. On the left side the vagus passes 
between the arch of the aorta and the base of the heart The Thorax 
277 
to the ventrolateral wall of the oesophagus. The recurrent 
nerve passes forward on the dorsal side of the arch. 
(t/) The ramus cardiacus of the vagus. In front of the sub- 
clavian artery the nerve is at first closely associated with 
the vagus trunk, lying on its medial side. On the right 
side it passes to the dorsal surface of the subclavian, and 
on the left to the dorsal surface of the aortic arch. It 
ends in the cardiac plexus (plexus cardiacus), a network 
of sympathetic nerves 
lying between the aor- 
tic arch and the pul- 
monary artery. 
(e) The phrenic nerve (n. 
phrenicus) is a stout 
cord arising chiefly from 
the fourth cervical 
spinal nerve. That of 
the left side crosses the 
ventral surface of the 
subclavian artery and 
the aortic arch, passing 
then along the pericar- 
dium to the diaphragm. 
That of the right side 
accompanies the thor- 
acic portion of the in- 
ferior caval vein. The 
nerve controls the res- 
piratory movements of 
the diaphragm. 
(/) The sympathetic 
trunk. At the base of 
the neck the cervical 
portion of the sympathetic trunk enters the inferior 
cervical ganglion (g. cervicale inferius). The latter lies 
in front of, and somewhat dorsal to, the subclavian artery. 
The first thoracic ganglion lies behind the artery and is 
connected with the inferior cervical by the ansa subclavia, 
Fig. 85. Plan of the venous and lym- 
phatic trunks of the anterior portion of 
the body. After McClure and Silvester. 
a., azygos vein; ao., aorta; c.s., left supe- 
rior caval vein; d.th., thoracic duct; j.e., 
j.i., and j.tr., external, internal, and trans- 
verse jugular veins; s., left subclavian vein; 
tr.s., transverse scapular vein. 278 
Anatomy of the Rabbit 
a loop formed by two cords, one of which passes to the 
dorsal, the other to the ventral side of the subclavian artery. 
The nerves proceeding from the inferior cervical ganglion 
enter the cardiac plexus and the sympathetic plexuses of 
the subclavian and its branches. 
3. Dissection of the heart. 
The character and relations of the enclosing serous sac, the 
pericardium, should first be noted. Its relation to the heart is 
similar to that of the peritoneum and pleura investing other visceral 
organs (p. 109). It comprises a parietal layer, that portion com- 
monly known as the pericardium, and a visceral layer, the epi- 
cardium, which forms an immediate investment for the heart 
substance. The parietal layer forms a loose, capacious sac, the 
serous membrane being greatly strengthened by the presence of a 
thin layer of connective tissue which forms an external investment 
and is usually considered as part of the pericardium. 
The paired pleural cavities containing the lungs are broadly separated by a 
longitudinal vertical partition, the mediastinum or mediastinal septum, the 
space enclosed by the latter being largely occupied by the heart and by the cavity 
of the pericardium. For a considerable area ventrally the pericardium is loosely 
applied to the thoracic wall, the intervening space, which is bounded laterally 
by the membrane lining the pleural cavities (pleura, p. 281), being known as the 
anterior mediastinum. A corresponding dorsal space lying between the heart 
and the bodies of the thoracic vertebrae, and also bounded laterally by the pleura, 
is the posterior mediastinum. It is occupied by several structures, namely, 
the oesophagus, the thoracic aorta, the bronchi, and the pulmonary blood-vessels, 
and caudally forms a thin septum similar to mesentery. 
The pericardium should be removed, and the external features 
of the heart and its great vessels examined. These are as follows: 
(a) The posterior, somewhat conical, ventricular portion of 
the heart. The left ventricle (ventriculus sinister) may 
be distinguished both by its position and by the more solid 
character of its wall. The right ventricle (ventriculus 
dexter) is less muscular, and the wall is readily pressed 
inward. The line of division is indicated on the ventral 
surface by a faint depression, the anterior longitudinal 
sulcus. 
(&) The pulmonary artery (a. pulmonalis) leaves the base of 
the right ventricle, passing forward and to the left in a The Thorax 
279 
somewhat spiral fashion around the aorta. On the dorsal 
surface of the latter it divides into the right and left 
pulmonary arteries, one for each lung. At the point of 
division the pulmonary artery is connected with the aorta 
by a short fibrous cord, the arterial ligament (lig. arte- 
riosum), representing the foetal connection of the two 
vessels through the ductus arteriosus (p. 97). 
(c) The left coronary artery (a. coronaria sinistra) passes 
backward on the ventral surface of the heart, lying in 
the anterior longitudinal sulcus. A corresponding right 
coronary artery (a. coronaria dextra) passes to the right 
side of the heart, lying between the right ventricle and the 
right atrium. 
The two vessels supply the substance of the heart. They are the 
first branches of the aorta, arising from the aortic sinuses at its base, 
(d) The left atrium (atrium sinistrum) is the thin-walled 
chamber lying to the left at the base of the heart. The 
pulmonary veins (venae pulmonales), several on either 
side, enter the left atrium, passing from the medial portions 
of the lungs. 
(e) The right atrium (atrium dextrum) resembles the left in 
the character of its wall. It receives the right and left 
superior caval veins and the unpaired inferior caval vein. 
The heart may be removed by dividing the great blood-vessels. 
The arch of the aorta should be removed with the heart by dividing 
the vessel at a point beyond the origin of the left subclavian, and 
then severing the carotids and subclavians at their bases. This 
exposes the surface for the subsequent examination of the posterior 
end of the trachea and its connections with the lungs. 
Open the right ventricle by a longitudinal incision of the ventral 
wall, extending the incision forward into the pulmonary artery. 
Open both atria by transverse incisions. By washing out the 
cavities, the internal features of the wall, including the arrangement 
of the valvular structures, may be examined as follows: 
In the right ventricle: 
(a) The trabeculae carneae; muscular ridges of the internal 
surface of the wall. 280 
Anatomy of the Rabbit 
(&) The tricuspid valve (valvula tricuspidalis). The thin 
membranous flaps composing the valve enclose the atrio- 
ventricular aperture, and project into the cavity of the 
ventricle. Their margins, which are otherwise free, are 
connected by slender fibrous cords, the chordae tendineae, 
with the papillary muscles (mm. papillares), the latter 
being thick muscular projections, of somewhat conical 
shape, arising from the opposite walls. 
In the rabbit the valve is composed of only two flaps, of which the 
ventral one is very free, and has large papillary muscles, while the dorsal 
one is closely attached to the wall, with the papillary muscle reduced or 
absent. For this reason the term right atrioventricular valve is more 
appropriate than "tricuspid". 
(c) The semilunar valves (valvulae semilunares) of the pul- 
monary artery are three extremely thin folds guarding the 
entrance to the vessel from the right ventricle. Each fold 
forms a pocket opening towards the artery and the cavity 
of the pocket is a pulmonary sinus. Two of the valves are 
usually found intact, the third being destroyed on opening 
the vessel. 
In the atria: 
(a) The respective positions of the pulmonary and systemic 
veins at their points of entrance. 
(b) The complete separation of the two chambers. In the 
partition separating them may be seen a thin fibrous portion 
denoting the position of the embryonic foramen ovale. 
Open the left ventricle by a ventral longitudinal incision, cutting 
well through the tip of the ventricle and extending the incision 
across the pulmonary artery and into the aorta. On account of 
the great thickness of the wall the internal structure is not so easily 
examined as in the right ventricle. 
(a) The bicuspid or left atrioventricular valve (valvula 
bicuspidalis) is similar in general structure to the tricuspid 
valve of the right ventricle, but is more nearly circular in 
form, with stout, closely grouped papillary muscles. The Thorax 
281 
(&) The semilunar valves of the aorta are three in number, 
and are similar to those of the pulmonary artery. Each 
encloses an aortic sinus. 
4. Examination of the lungs and their connections (Figs. 47, 86). 
The removal of the ventral wall of the thorax opens the pleural 
cavities by taking away a considerable portion of the costal pleura, 
which is adherent to the internal surfaces of the ribs. The chief 
features may be made out as follows: 
(a) Each pleural cavity (cavum 
pleurae) is a closed serous sac, the 
lining membrane, or pleura, 
being distributed over the costal 
surface as the costal pleura, 
partly over the anterior surface 
of the diaphragm as the dia- 
phragmatic pleura, and over 
the surface of the lung as the 
pulmonary pleura, and enter- 
ing into the formation of the 
mediastinum as the mediastinal 
pleura. 
A secondary fold on the right side of the mediastinal septum contains 
the inferior vena cava and forms a pocket in which lies the medial lobule 
of the inferior lobe of the right lung. Posteriorly, the pulmonary 
pleura passes from the medial margin of the left lung and from the 
medial margins of both inferior lobules of the right lung to the medias- 
tinal septum and backward to the diaphragm, forming the pulmonary 
ligament (lig. pulmonale). 
(b) The lungs (pulmones) are paired expansible structures, the 
surfaces of which are free, except posteriorly, where they 
are attached to the diaphragm through the pulmonary liga- 
ment, and medially where they are connected with the 
pulmonary blood-vessels and the respiratory tubes. 
(c) Each lung is divided into three portions, the superior, 
middle, and inferior lobes. On account of the smaller 
size of the left lung, the superior lobe is imperfectly de- 
veloped. On the right side the inferior lobe is divided into 
Fig. 86. Plan of the respiratory 
tubes as seen from the ventral sur- 
face. tr, trachea; br, br', left and 
right bronchi; ep, eparterial bron- 
chus; s, m, m', i, i', bronchial rami to 
superior, middle, and inferior lobes; 
11, Im, bronchial rami to lateral and 
medial lobules. 282 
Anatomy of the Rabbit 
two portions, the medial and lateral lobules, the inferior 
caval vein passing between them. 
(d) The trachea divides at its posterior end into two portions, 
the right and left bronchi, one for each lung. Each 
bronchus is again divided into smaller portions, the bron- 
chial rami, which penetrate the substance of the organ 
and redivide into smaller tubes. On the right side a small 
eparterial bronchus is given off from the right bronchus. 
It passes to the superior lobe of this side, and lies in front 
of the right pulmonary artery. 
(e) The branches of the pulmonary artery and the pulmonary 
veins may be traced for a short distance on the medial 
portion, or hilus, of each organ. 
(/) The vagus nerve passes to the dorsal side of the bronchus, 
giving oft a number of branches, which accompany the 
bronchus to the lung. 
The lungs may be removed, together with a portion of the 
trachea, care being taken to leave the vagus nerves in place. The 
lungs may then be examined to better advantage, and the surface 
also may be prepared for the next dissection. 
5. The following structures may now be traced on the dorsal wall 
of the thorax: 
(a) The oesophagus. It traverses the thorax in a median 
position, entering the diaphragm at the hiatus oesophageus. 
(&) The vagus nerves. The right and left nerves pass backward 
along the lateral walls of the oesophagus, and are connected 
with one another through nerve plexuses lying on its dorsal 
and ventral surfaces. The left cord is that appearing at the 
posterior end of the oesophagus in a ventral position and 
passing to the ventral surface of the stomach. The right 
cord occupies a corresponding dorsal position and passes to 
the dorsal surface of the stomach (p. 199). 
(c) The thoracic aorta (aorta thoracalis) passes backward on 
the ventral surface of the vertebral column, leaving the 
thorax through the hiatus aorticus, the latter being the 
aperture enclosed by the crura of the diaphragm. Its The Thorax 
283 
branches in the thorax are the intercostal arteries (aa. 
intercostales), beginning with the fourth, which are given 
off metamerically in the intercostal spaces, and pass laterad 
to the thoracic wall. 
(d) The thoracic portions of the sympathetic trunks lie on 
the lateral surfaces of the bodies of the thoracic vertebrae. 
The posterior ganglia give origin to the splanchnic nerve, 
the latter passing backward into the abdominal cavitv 
(p. 197). 
(e) The levatores costarum; a series of small muscles arising 
from the transverse processes of the vertebrae and the heads 
of the ribs and inserted on the anterior margins of the next 
succeeding ribs. They assist the intercostals in respiration. 
(/) The intercostal nerves (nn. intercostales) accompany the 
intercostal arteries to the lateral wall of the thorax. 
(g) The azygos vein (v. azygos) is a small, asymmetrical, 
venous trunk lying to the right of the dorsal surface of the 
aorta. It receives the majority of the intercostal veins, 
which accompany the corresponding arteries and nerves, the 
tributaries extending backward to the first lumbar veins. 
It opens forward into the right superior caval. The more 
anterior intercostal veins are tributaries of the right and 
left supreme intercostal veins which open into the 
corresponding superior cavals. 
6. The diaphragm (diaphragma) is a muscular and tendinous 
sheet forming the posterior wall of the thorax and separating 
the pleural cavities from the peritoneal cavity. It is somewhat 
dome-shaped in the relaxed condition, but in contraction it 
becomes flattened in such a way that the space occupied by the 
lungs is considerably increased, while the liver and related 
structures of the abdominal cavity are displaced backward. 
As a muscle the diaphragm arises in three portions. The first, 
or lumbar portion, consists of two muscular and fibrous cords, 
the crura, the right much larger and stronger than the left, arising 
from the anterior spinous processes of the first three lumbar verte- 
brae. The second, or costal portion, arises from the internal 
surfaces of the posterior ribs. The third, or sternal portion, 284 
Anatomy of the Rabbit 
arises from the xiphoid process of the sternum. Its insertion is 
represented by its own tendinous central portion, or centrum 
tendineum, although the latter is virtually attached forward 
to the lungs and pericardium through the broad pulmonary liga- 
ment. The centrum tendineum is shaped somewhat like a trefoil, 
the fibres of the costal and sternal portions radiating outward 
from its margin. 
The following may be made out on the posterior surface: 
(a) The cut margins of the falciform, coronary, and left trian- 
gular ligaments. 
(&) The hiatus aorticus, an aperture enclosed by the two 
crura and serving for the transmission of the aorta. 
(c) The hiatus oesophageus, ventral to the foregoing, and 
serving for the passage of the oesophagus. 
(d) The foramen venae cavae, situated slightly to the right 
and serving for the transmission of the vena cava inferior. 
(e) The superior phrenic arteries (aa. phrenicae superiores) 
arise from the aorta at about the point of origin of the 
eleventh intercostals or from one of the latter, and enter the 
crura. 
The inferior phrenic arteries are minute branches arising at the base 
of the coeliac. 
(/) The inferior phrenic veins (vv. phrenicae inferiores), one 
on either side of the foramen venae cavae, at which point 
they enter the inferior cava. 
The superior phrenic veins pass forward from the diaphragm, 
opening into the superior cavals. 
XII. THE VERTEBRAL AND OCCIPITAL MUSCULATURE 
Dissect on the dorsal surface of the body from the occiput 
backward; also on the lateral and ventral surfaces of the neck. 
The serratus posterior muscle lies on the dorsolateral surface 
of the thorax. It arises from the dorsal spinous ligament of the 
neck (ligamentum nuchae) and from the lumbodorsal fascia back to 
the last rib, and is inserted on the lateral surfaces of the eight 
posterior ribs. Vertebral and Occipital Musculature 
285 
The splenius muscle is a somewhat triangular sheet arising 
from the ligamentum nuchae and inserted on the supraoccipital and 
mastoid portions of the skull, extending also to the transverse 
process of the atlas. 
These two muscles should be divided, the serratus posterior being removed 
from the surface. 
1. The long muscles of the vertebral column. 
Apart from the iliopsoas, psoas minor, and quadratus lum- 
borum-muscles of appendicular insertion lying on the ventral 
surface of the vertebral column-the vertebral musculature com- 
prises chiefly modified segmental muscles lying on the dorsal sur- 
face, for the most part in the area enclosed by the spinous and 
transverse processes of the vertebrae. They include the sacro- 
spinalis, semispinalis, and intertransversarii. Their insertions are 
extended in part laterad to the ribs. In the cervical region they 
are represented by short muscles, separated for the most part from 
the thoracic and lumbar portions, and arising by accessory bundles 
from the anterior ribs, the corresponding thoracic, and the posterior 
cervical vertebrae. In the cervical region the muscles are easily 
separated from one another, but in the posterior part of the body 
it is necessary to dissect away the tough investment of lumbodorsal 
fascia which covers them. 
(a) The sacrospinalis. Origin: Crest of the ilium and dorsal 
surface of the sacrum; mamillary processes of the six pos- 
terior lumbar vertebrae; investing lumbodorsal fascia. 
This muscle is the largest and strongest muscle of the 
body. It extends forward over the surface of the ribs. Its 
medial border is separated from the middle line by a space 
of considerable width, in which the semispinalis and multi- 
fidus muscles are accommodated. In the lumbar region it 
is inserted in a continuous mass on the long transverse 
processes of the vertebrae and in the interspaces. In the 
thoracic region the muscle divides into two portions, namely, 
a thin lateral portion, the iliocostalis or longissimus 
costarum, and a thick medial portion, the longissimus. 
The latter receives in the posterior portion of the thorax 
strong accessory bundles from the semispinalis muscle on 286 
Anatomy of the Rabbit 
its medial side, the two muscles being inseparable at this 
point. 
The iliocostalis is inserted laterally on the ribs as the 
iliocostalis dorsi. It receives medially from the ribs a 
number of accessory bundles, which are inserted forwards 
to the seventh cervical vertebra as the iliocostalis cervicis. 
The longissimus is inserted by broad fleshy bands on the 
posterior margins of the ribs, medial to the accessory origins 
of the iliocostalis, this portion of the muscle forming the 
longissimus dorsi. Continuing to the neck it is inserted 
on the transverse processes of the three posterior cervical 
vertebrae, medial to the origin of the cervical portion of the 
serratus anterior, but a number of accessory slips carry the 
insertion forward to the transverse process of the atlas. 
This portion is the longissimus cervicis. A separate band 
of fibres arising chiefly from the transverse processes of 
the second to fourth thoracic vertebrae joins the lateral, 
ventral portion of the splenius, and forms the longissimus 
capitis. It is inserted with the splenius on the mastoid 
portion of the skull. 
(b) The semispinalis and multifidus. The band of muscle 
lying between the longissimus and the middle line, is com- 
posed of partly fused slips, arising for the most part by very 
long tendons from the mamillary and transverse processes, 
and inserted forwards on the spinous processes. It is 
divisible into two portions, which are superficially separated 
by a constricted area lying at the level of the last thoracic 
vertebra, this being also the point where the muscle is fused 
with the longissimus. The anterior portion, the semispin- 
alis dorsi, is inserted by a series of fleshy slips on the 
spinous processes of more anterior thoracic vertebrae, but 
extends to the spinous process of the third or fourth cervical 
vertebra. The posterior portion, the multifidus, increases 
in size backward to the sacrum, where it is continuous with 
the abductor caudae posterior. 
An almost separate muscle, covering the neck as a broad 
sheet immediately beneath the splenius and longissimus 
capitis, is the semispinalis capitis. It arises from the Vertebral and Occipital Musculature 
287 
transverse processes of the five posterior cervical and the 
transverse processes of the first four thoracic vertebrae. It 
is lightly attached on a line from the transverse process 
of the atlas to the external occipital protuberance, but is 
inserted on the lateral surface of the latter. The more 
posterior and medial portion of the muscle is composed of 
separate slips arising in common with the longissimus 
capitis, two closely applied slips, however, at the free margin 
of the muscle, arising from the semispinalis dorsi and the 
longissimus. The principal, lateral portion is crossed by a 
tendinous inscription. 
A second muscle, the semispinalis cervicis, is covered 
by the foregoing one. It arises from the articular processes 
of the posterior cervical and first thoracic vertebrae, and is 
inserted on the spinous processes of the cervical vertebrae, 
chiefly on that of the epistropheus. 
(c) The intertransversarii are short muscles connecting the 
lateral portions of the vertebrae. They are distinguishable 
in part by their darker coloration. They increase in size 
backwards, being most conspicuous in the lumbar region, 
where they form thick muscular pads interposed between 
the mamillary and accessory processes. The last slip is 
attached to the crest of the ilium. 
2. The following muscles constitute an occipital group, composed 
of short muscles arising from the atlas and axis and inserted on 
the atlas and the occipital portion of the skull. 
(a) The rectus capitis posterior superficialis. Origin: 
Spinous process of the epistropheus. Insertion: External 
occipital protuberance. 
(6) The obliquus capitis superior. Origin: Transverse pro- 
cess of the atlas. Insertion: Lateral surface of the occipital 
protuberance. 
The foregoing muscles should be divided. 
(c) The rectus capitis posterior minor. Origin: Posterior 
tubercle of the atlas. Insertion: External occipital pro- 
tuberance. 288 
Anatomy of the Rabbit 
(d) The rectus capitis posterior major. Origin: Spinous 
process of the epistropheus. Insertion: Laterally on the 
supraoccipital bone. 
(e) The obliquus capitis inferior. Origin: Spinous process 
of the epistropheus. Insertion: Dorsal surface of the 
transverse process of the atlas. 
(/) The rectus capitis lateralis. Origin: In common with 
the obliquus capitis superior, which covers it. Insertion: 
Base of the jugular process of the occipital. 
3. Muscles of the lateral and ventral surfaces of the neck: 
(a) The scalenus anterior. Origin: Transverse processes of 
the four posterior cervical vertebrae. Insertion: First rib. 
(6) The scalenus medius. Origin: Transverse process of the 
fifth cervical vertebra. Insertion: Lateral surfaces of the 
third to fifth ribs. 
(c) The scalenus posterior. Origin: Transverse processes of 
the fourth to sixth cervical vertebrae. Insertion: First rib. 
The medius is superficial; the anterior more or less separated from 
the posterior by the origin of the cervical portion of the serratus anterior. 
(d) The scalenus medialis. Origin: The sternum at the 
point of attachment of the first rib. Insertion: Middle of 
the ventral portion of the first rib. 
The foregoing muscles comprising the scalenus group, are destroyed 
by the removal of the ventral thoracic wall (p. 274). 
(e) The longus colli. Origin: Bodies of the first six thoracic 
vertebrae. Insertion: The muscle passes forward on the 
ventral surface of the bodies of the vertebrae, giving off 
insertion fibres, and also receiving strands of origin. It 
terminates on the anterior tubercle of the atlas. 
(/) The longus capitis is partly fused with the foregoing 
muscle, but its origin is in a more lateral position from the 
transverse processes of the first six cervical vertebrae. 
Insertion: Sphenooccipital synchondrosis. 
(g) The longus atlantis. Origin: Lateral to the longus 
capitis, from the transverse processes of the third to sixth 
cervical vertebrae. Insertion: Transverse process of the 
atlas. 
The longus capitis should be divided near its insertion. The Central Nervous System 
289 
(7?) The rectus capitis anterior. Medial portion of the 
ventral surface of the transverse process of the atlas. 
Insertion: Basioccipital bone. 
The caudal musculature in the rabbit comprises, in addition to 
the posterior extension of the cutaneus maximus, the following axial 
muscles: 
(a) The extensor caudae medialis. It lies in the furrow between 
the spinous and articular processes of the posterior sacral and 
anterior caudal vertebrae, and is inserted on the transverse pro- 
cesses and dorsal surfaces of the caudal vertebrae. 
(b) The abductor caudae posterior lies in the groove between the 
articular and transverse processes and is inserted on succeeding 
vertebrae. It appears to continue the multifidus, but corresponds 
to the more medial portion of the longissimus. 
(c) The abductor caudae anterior. Origin: Ischial spine. In- 
sertion: Lateral surface of the sacrum and the transverse processes 
of the caudal vertebrae. 
(d) The flexor caudae. Origin: Ventral surface of the sacrum and 
anterior caudal vertebrae. Insertion: Ventral surfaces of succeed- 
ing vertebrae. 
These muscles are also known as sacro-coccygei, dorsalis, lateralis, 
and ventralis (a, b, d), and coccygeus (c). 
XIII. THE CENTRAL NERVOUS SYSTEM 
1. The spinal cord and nerve roots. 
To expose the whole cord or a portion of it from the dorsal 
surface, the muscles should be removed on both sides of the verte- 
bral arches and the latter broken away with bone forceps. The 
following features may be made out when the extent of exposure 
is sufficient: 
(u) The spinal cord (medulla spinalis) is a thick, subcylin- 
drical white cord traversing the vertebral column in the 
vertebral canal. Its diameter is not uniform, as it exhibits 
two slight enlargements, one in the cervical, the other in the 
lumbar region. These enlargements are the regions from 
which the nerves to the limbs arise and are due to the 
increased number of nerve elements present on that account. 
At about the middle of the sacrum the cord contracts to a 
slender filament, the filum terminale, which may be 290 
Anatomy of the Rabbit 
traced backward to the middle of the tail, and which is 
produced in development by the more rapid growth of the 
bony canal than of the spinal cord within it. 
(b) The enclosing membranes or meninges of the cord are three 
in number, of which two are readily identified. Lining the 
internal surface of the bone is a thick fibrous investment, 
the dura mater; on the surface of the nervous matter a 
thin vascular membrane, the pia mater. The dura and 
pia are connected by a loose web of connective tissue, the 
arachnoidea. 
(c) The nerve roots have a regional distribution-eight cervical, 
twelve dorsal, seven lumbar, four sacral, and six caudal. 
The cervical nerves are numbered from the vertebrae lying behind 
the intervertebral foramina from which they proceed, the remaining 
nerves from the vertebrae lying in front of the intervertebral foramina. 
The nerve transmitted by the intervertebral foramen between the 
seventh cervical and first thoracic vertebrae is described as the eighth 
cervical. 
(d) The origin and primary divisions of the nerve roots may be 
worked out by removing carefully the lateral portions of the 
arches of one or two vertebrae. The posterior, or sensory 
root (radix posterior), arises from the dorsolateral surface 
of cord, and expands immediately into a spinal ganglion 
(g. spinale). The more slender anterior, or motor root 
(radix anterior), arises by a number of filaments from the 
ventrolateral surface. The combined roots give origin to 
the posterior, anterior, and communicating rami. The 
posterior ramus is an inconspicuous branch (except in the 
first two cervicals) passing to the dorsal musculature and 
skin. The anterior ramus is the chief portion of the 
spinal nerve, the successive rami appearing as the com- 
ponents of the cervical and lumbosacral plexuses or as 
individual spinal nerves. The ramus communicans is a 
slender filament which passes ventrad to join the sym- 
pathetic trunk. 
2. A small portion of the spinal cord may be excised and examined 
(preferably under water) for the following (see Fig. 16, p. 36). The Central Nervous System 
291 
(a) The division of the cord into lateral halves by two median 
depressions, the anterior median fissure (fissura mediana 
anterior) and the posterior median sulcus (sulcus me- 
dianus posterior). 
(&) The division of each half into three columns by shallow 
grooves, the anterior and posterior lateral sulci. The 
grooves are marked by the attachments of the anterior and 
posterior nerve roots. The three columns of each half of 
the cord are the anterior, lateral, and posterior funiculi. 
(c) On the cut surface the white substance (substantia alba) 
is seen to form a peripheral investment enclosing the grey 
substance (substantia grisea) of the centre of the cord. 
The grey portion is somewhat H-shaped in section, each 
half being composed of anterior larger and posterior smaller 
masses, known in section as the horns of the grey matter, 
or as complete structures, the anterior and posterior grey 
columns. In the median plane, but nearer the dorsal than 
the ventral surface, is the minute central canal (canalis 
centralis), the cavity of the spinal cord. 
3. The brain may be exposed by breaking away the supraorbital 
processes of the frontal bone and then removing the roof of the 
skull with bone forceps. In order to clear the brain and the 
roots of the cerebral nerves, it is necessary to remove the entire 
lateral wall of the skull on both sides. The chief part of the 
operation consists in removing the temporal portion of the skull 
by successive steps, exposing first the paraflocculus of the 
cerebellum, a small stalked body which is almost completely 
enclosed by the dorsal portion of the petrosal. The entire 
petrotympanic bone is easily detached, and if removed en masse 
the paraflocculus and probably also the roots of the facial and 
acoustic nerves will be destroyed. 
The arches of the first three or four cervical vertebrae should be 
removed, unless the anterior portion of the cord has been exposed 
in the previous dissection. 
The spinal cord may be divided at about the level of the third 
vertebra. The brain should then be raised very gently from the 
ventral wall of the skull and the nerve roots divided with a small 292 
Anatomy of the Rabbit 
sharp knife or with fine scissors. This operation requires con- 
siderable care, since the nerves are strongly attached at their points 
of exit from the cranial wall, but very lightly attached to the brain, 
so that they are in danger of being torn away. 
The anterior end of the brain may be freed by cutting close to 
the bone under and in front of the small anterior expansions formed 
by the olfactory bulbs. 
Portions of the dura mater removed with the brain may be cut 
away with scissors. It is adherent chiefly along two lines: one 
representing the longitudinal fissure between the cerebral hemi- 
spheres, the other the tentorium cerebelli. These parts contain the 
superior sagittal and transverse venous sinuses. 
On the ventral surface of the brain as removed appear the 
basilar and internal carotid arteries and their branches. These 
vessels should be kept intact for examination at a later stage. 
For the primary divisions of the brain see p. 75. 
4. The superficial features may be identified as follows: 
IN THE PROSENCEPHALON: 
(a) The greatly enlarged cerebral hemisphere (hemisphaer- 
ium cerebri), the dominant portion which correlates and 
co-ordinates the activities of all the rest of the nervous 
system, forms with its fellow of the opposite side the largest 
portion of the brain. The two structures are separated by 
the longitudinal cerebral fissure, but are connected with 
each other by the commissures indicated below. 
(&) The olfactory bulb (bulbus olfactorius) is a small ex- 
pansion lying at the anterior end of each hemisphere. Its 
anterior and ventral surfaces receive the fascicles of the 
first cranial or olfactory nerve, the various divisions of 
which may be found on the skull, where they may be traced 
into the perforations of the cribriform plate. 
(c) The olfactory bulb is the anterior portion of the olfactory 
brain. When traced backward on the ventral surface of 
the brain it is seen to be replaced by a white band of fibres, 
the olfactory tract (tractus olfactorius), lying on the 
surface of a somewhat wider strip of grey matter. This 
strip expands into a portion of the brain which, from its The Central Nervous System 
293 
shape, is known as the lobus piriformis, and in which 
the olfactory tract has its termination. The olfac- 
tory brain as thus defined is sepa- 
rated superficially from the re- 
maining portions of the cerebral 
hemisphere by a longitudinal fur- 
row, the limbic fissure (fissura 
limbica), which passes along its 
lateral margin. The anterior por- 
tion of the furrow, known as the 
anterior rhinal fissure, separates 
the olfactory tract laterally from 
the narrow anterior portion of the 
cerebral hemisphere. The corres- 
ponding posterior portion of the 
furrow, the posterior rhinal fis- 
sure, separates the lobus pirifor- 
mis from the posterior enlarged 
portion of the hemisphere. The 
slight angle formed at the junction 
of the anterior and posterior rhinal 
fissures is the point of origin of a 
faint depression extending upward 
on the cerebral hemisphere. It 
represents a rudimentary, lateral 
cerebral (Sylvian) fissure, which 
is an important feature in the brain of man and other mam- 
mals with convoluted hemispheres. 
(</) The corpus callosum is a broad, white commissural band 
passing transversely between the hemispheres and thus 
providing for the co-ordination of their action. Its median 
portion may be exposed dorsally by pressing apart the 
medial margins of the hemispheres at the longitudinal 
cerebral fissure. 
(e) The pineal body (corpus pineale) is a small, somewhat 
conical structure lying between the dorsal posterior tips of 
the cerebral hemispheres, and connected by a hollow stalk 
with the unpaired portion of the brain (the diencephalon) 
Fig. 87. Dissection to 
show the radiation of the 
corpus callosum from a dorsal 
viewpoint. The longitudinal 
white line close to the median 
plane is the position of a 
delicate band of hippocampal 
fibres, the medial longitudinal 
stria, while the broader pale 
band a little farther laterally 
is the intersection of the 
corpus callosum with fibres 
connecting the cerebral cortex 
with lower parts (corona 
radiata). Just behind the 
latter appears the cut stump 
of a longitudinal band of 
cortical association fibres, the 
cingulum. 294 
Anatomy of the Rabbit 
lying below it (cf. p. 109). The connection is concealed by 
a mass of pigmented vascular tissue, the beginning of the 
chorioid plexus of the third ventricle, and usually also by 
a small portion of the dura mater containing part of the 
sagittal venous sinus. The latter may be carefully de- 
tached. By pressing apart the tips of the hemispheres and 
pulling away the pineal body with the tissue to which it is 
attached, the dorsal surface of the diencephalon will be 
sufficiently exposed to make out the following features: 
(/) The slit-like aperture appearing in 
the middle line after the removal 
of the pineal body represents the 
dorsal portion of the third ven- 
tricle (ventriculus tertius) (Fig. 88), 
the roof of which is formed ante- 
riorly by the superficial portion of 
the chorioid plexus (plexus chor- 
ioideus), the latter dipping down 
into the ventricle at this point. 
(g) The lateral margins of the aperture 
are largely formed by two minute 
spindle-shaped masses, one on either 
side, the habenulae. Their pos- 
terior ends are united by a slender 
transverse band, the habenular 
commissure (commissura habenu- 
larum). The fibres of the commissure are faintly trace- 
able forward, where they form a pair of thin whitish fila- 
ments (medullary striae). The habenulae receive impulses 
from various olfactory regions of the cerebral hemisphere 
and tactile and other related sensory impulses which they 
correlate with them, sending resultant excitation impulses 
to motor centres, especially those concerned with feeding. 
(A) The posterior commissure (commissura posterior) crosses 
the posterior portion of the roof immediately behind and 
below the habenular commissure. It is a composite struc- 
ture which, like other commissures, connects parts on the 
two sides of the brain. 
Fig. 88. Diagram, showing 
the arrangement of the parts of 
the thalamencephalon as viewed 
from the dorsal surface, after re- 
moval of the pineal body: a., 
anterior thalamic tubercle; c.h., 
habenular commissure; c.p., pos- 
terior commissure; c.s., superior 
colliculus (of mesencephalon); 
g.l. and g.m., lateral and medial 
geniculate bodies; h., habenula; 
m.i., massa intermedia; p., lateral 
thalamic tubercle; v.t., third 
ventricle. The Central Nervous System 
295 
(i) The walls of the third ventricle are formed by the thalami. 
They are broadly connected by the intermediate mass 
(massa intermedia) or middle commissure, which may be 
seen from the dorsal surface crossing the cavity. This is 
not a true commissure (a band of nerve fibres connecting 
corresponding structures bilaterally), but is simply a fusion 
of the grey matter lining the ventricle, brought about by 
the increased thickness of the thalami. The latter contain 
various reflex centres and serve especially as a vestibule 
through which pass all impulses proceeding to the cerebral 
hemisphere, except the olfactory ones. 
(j) On either side of the middle line, or of the habenulae, the 
dorsal portion of the thalamus forms a low, somewhat oval 
projection, the lateral thalamic tubercle. This swelling 
represents superficially a mass of grey matter through 
which pass most of the sensory impulses to the hemispheres 
from lower parts of the nervous system other than visual 
and auditory. 
The anterior tubercle of the thalamus is a faint elevation of very 
small dimensions lying in the angle enclosed between the lateral tubercle 
and the anterior portion of the aperture of the third ventricle. 
(&) The parts of the metathalamus are distinguishable exter- 
nally as two rounded projections of the lateral surfaces of 
the thalamencephalon. One of them, the lateral genicu- 
late body (corpus geniculatum laterale), lies to the lateral 
side of the lateral thalamic tubercle, and is only separated 
from it by a faint depression of the surface. It contains the 
vestibule of the hemisphere for visual impulses. The 
medial geniculate body occupies a more posterior and 
medial position and is the vestibule of the hemisphere for 
auditory stimuli. 
(Z) The optic tract (tractus opticus) comes to the lateral 
geniculate body from the optic chiasma on the ventral 
surface of the brain. 
(m) On the ventral surface, the optic chiasma (chiasma 
opticum), forms a conspicuous cross-like elevation, the 
posterior portion of which is traceable into the optic tracts, 
the anterior portion into the bases of the second cranial, 296 
Anatomy of the Rabbit 
or optic nerves. Thus the optic tracts are simply the 
direct continuation of the optic nerves after they have 
crossed in the chiasma. 
(n) The hypophysis, or pituitary body, lies immediately 
behind the optic chiasma (of. p. 108). It is a somewhat 
elongate, rounded, glandular organ attached to the base of 
the brain by a slender stalk. 
On account of its enclosure by the walls of the hypophyseal fossa, 
and also its slight attachment to the brain, the hypophysis is commonly 
detached in removing the brain from the skull, in which case a slit-like 
aperture, representing the ventral portion of the third, ventricle is 
exposed. 
(o) The tuber cinereum is a small elevation of grey matter 
appearing on the ventral surface after the removal of the 
hypophysis. It is the base of attachment of the infundi- 
bulum, the latter being the slender extension of the brain 
downward to the hypophysis. When the hypophysis is 
removed the infundibulum which attaches it to the brain 
is, naturally, broken, exposing the cavity in its base as the 
slit mentioned above. The region of the tuber cinereum 
contains centres concerned chiefly with the correlation of 
olfactory with visceral sensory impulses. 
{p} The mamillary body (corpus mamillare) forms a con- 
spicuous rounded elevation, lying at the posterior end of the 
tuber cinereum. The structure is externally single, but 
there is an indication of lateral lobes. It also receives 
impulses from the olfactory correlation regions of the 
cerebral hemisphere and combines them with others, chiefly 
visceral. 
IN THE MESENCEPHALON: 
(a) The dorsal surface is marked by four elevations, the corpora 
quadrigemina. The anterior pair, distinguished as the 
colliculi superiores, is much larger than the posterior 
pair, the colliculi inferiores. The superior colliculi cor- 
respond to the optic lobes of submammalian vertebrates 
and receive many of the fibres of the optic tracts. The 
inferior colliculi are important reflex centres belonging to 
the auditory system. The Central Nervous System 
297 
(b') The ventral surface is occupied by a pair of broad white 
bands converging from in front, the cerebral peduncles, 
separated by a faint median depression, the interpedun- 
cular fossa (fossa interpeduncularis). These bands con- 
tain the main descending pathways carrying the impulses 
from the cerebral hemispheres to the motor centres of the 
brain and spinal cord. 
(c) The third cranial, or oculo- 
motor nerve (n. oculomo- 
torius), which controls the 
majority of the eye-muscles, 
arises from the ventral surface 
of the cerebral peduncle. 
IN THE RHOMBENCEPHALON: 
(a) The cerebellum forms an 
arch over the posterior por- 
tion of the brain, and is sup- 
ported by stout pillars from 
its sides. In addition to the 
ridges of its surface the whole 
structure is divided into sev- 
eral lobes, including the me- 
dian portion or vermis, the 
lateral hemispheres, and the 
stalked bodies, or parafloc- 
culi, arising from the hemis- 
pheres. 
The flocculus is a small fold ventral to the stalk of each para- 
flocculus. 
The cerebellum is concerned chiefly with the co-ordina- 
tion of muscular action, the regulation of the "tone" of 
the muscles, and the preservation of the equilibrium of the 
body. The cerebellar hemispheres are specially related to 
the cerebral hemispheres, so as to co-ordinate the con- 
tractions of muscles activated by impulses from the latter. 
(&) The anterior medullary velum (velum medullare 
anterius) is the thin membrane underlying the anterior 
portion of the cerebellum and connecting the latter with the 
Fig. 89. The rhombencephalon. 
Ventral view (the cerebellum not 
figured). 
ct, trapezoid body; fc, foramen 
caecum; flc, cervical flexure; fma, 
anterior median fissure; p, pons; pc, 
cerebral peduncle (mesencephalon); 
py, pyramid. 
Ill, oculomotor nerve; IV, troch- 
lear; V>, portio major of the trige- 
minus; V2, portio minor; VI, ab- 
ducens; VII, facial; VIII, acoustic; 
IX-XI, glossopharyngeal, vagus, and 
spinal accessory group; XII, hypo- 
glossal; ci, first cervical spinal. 298 
Anatomy of the Rabbit 
inferior colliculi. It forms a small anterior portion of the 
roof of the fourth ventricle. 
(c) The fourth cranial, or trochlear nerve (n. trochlearis), 
which supplies the superior oblique muscle of the eye, arises 
from the anterior medullary velum. The first portion of 
the nerve is usually to be found on the lateral surface of the 
cerebral peduncle. 
(d) The posterior medullary velum (velum medullare pos- 
terius) underlies the posterior margin of the cerebellum, and 
extends backward over the triangular space enclosed by the 
walls of the fourth ventricle. The structure forms a 
chorioid plexus, similar in character to that of the third 
ventricle but much less extensive. It is commonly torn 
away in the preparation of the brain, in which case the 
interior of the fourth ventricle is exposed. 
(e) On the ventral surface (Fig. 89), the pons forms a broad 
band extending transversely across the brain and upward 
into the supports of the cerebellum. Its surface is divided 
into two parts by a median depression, the sulcus basilaris, 
occupied by the basilar artery. It is not really a commissure 
but is part of the pathway connecting the cerebral hemi- 
spheres with those of the cerebellum. 
(/) The anterior median fissure of the spinal cord ends at the 
posterior margin of the pons in a faint depression, the 
foramen caecum. 
(g) The anterior funiculus of the cord is largely replaced for- 
wards by the pyramid (pyramis), a narrow band extending 
forward on either side of the middle line to the posterior 
margin of the pons. The pyramid is really the reduced 
continuation backwards of the cerebral peduncles after they 
have passed through the pons, where many of their fibres 
end. 
(h) The trapezoid body (corpus trapezoideum) is another, 
smaller transverse band just behind the pons, and is part 
of the auditory pathway. It lies in the angle formed by 
the lateral margin of the pyramid with the posterior border 
of the pons. The Central Nervous System 
299 
(i) The fifth cranial, or trigeminal nerve (n. trigeminus), 
arises by two roots, a larger sensory root, the portio major, 
and a smaller motor root, the portio minor. The two 
parts appear at the lateral border of the pons. 
The portio major is the common trunk of the ophthalmic, maxillary, 
and mandibular nerves, providing for the cutaneous sensibility of most 
of the head. The portio minor (motor, to muscles of mastication) joins 
the mandibular, so that the latter becomes a mixed nerve. The cut end 
of the portio major may be identified on the cranial wall and traced 
forward into the semilunar ganglion, the latter lying in a depression 
at the anterior ventral end of the petrosal bone. 
(j) The sixth cranial, or abducent nerve (n. abducens), 
which controls the lateral rectus muscle of the eye, is a 
slender cord arising at the anterior end of the pyramid. 
(&) The seventh cranial, or facial nerve (n. facialis), and the 
eighth, or acoustic nerve (n. acusticus), arise from the 
lateral margin of the trapezoid body. 
The two nerves are closely associated, the former being slightly 
anterior in position. Its chief portion is the motor root which controls 
the facial muscles. In addition the nerve receives a sensory filament, 
the portio intermedia or intermediate nerve, bearing gustatory and 
related impulses. 
(Z) The glossopharyngeus, vagus, and accessorius arise 
by several roots arranged in a linear series along the lateral 
margin of the medulla. The trunk of the accessorius 
extends backward on the spinal cord, its roots, about ten 
in number, arising as far back as the fifth cervical spinal 
nerve. It is an efferent nerve, while the two former are 
mixed nerves to various visceral organs. 
(m) The twelfth cranial, or hypoglossal nerve (n. hypo- 
glossus), which moves the tongue, arises by several roots 
from the ventral surface of the medulla and at the lateral 
margin of the pyramid, its point of origin corresponding to 
that of the ventral root of a spinal nerve. 
5. The arteries of the brain may be traced on its ventral surface 
as follows: 
(a) The basilar artery (a. basilaris) is a median trunk formed 
on the ventral surface of the medulla oblongata by the 300 
Anatomy of the Rabbit 
union of the vertebral arteries, the latter here represented 
by their cut ends. 
(&) The inferior cerebellar artery (a. cerebelli inferior) is the 
largest of several transverse vessels arising from the basilar 
and passing laterad to the cerebellum. 
(c) The posterior cerebral artery (a. cej-ebri posterior) is 
formed on either side at the level of the anterior margin of 
the pons by the division of the basilar. It passes to the 
posterior portion of the cerebral hemisphere. 
(d) The superior cerebellar artery (a. cerebelli superior) is a 
branch of the posterior cerebral, passing to the anterior 
portion of the cerebellum. 
(e) The cut end of the internal carotid artery lies on either 
side of the tuber cinereum. It is connected backwards with 
the posterior cerebral by a posterior communicating artery. 
(/) The middle cerebral artery (a. cerebri media) is given off 
from the internal carotid, passing to the middle portion 
of the hemispheres. 
(g) The anterior cerebral artery (a. cerebri anterior), the 
continuation of the carotid, passes to the anterior portion 
of the ventral surface and the olfactory bulb. The anterior 
cerebral unites with that of the other side to form a short 
common trunk between the hemispheres which redivides 
into paired vessels supplying the medial surfaces. A com- 
plete anastomotic loop is thus formed round the hypo- 
thalamus by the internal carotid, anterior cerebral, posterior 
communicating, and posterior cerebral arteries. This is 
the circle of Willis. 
The fusion of the anterior cerebral arteries replaces an inter- 
connection by an anterior communicating artery, which occurs in man 
and many other mammals. 
6. By dividing the supports of the cerebellum on either side, 
the entire structure may be removed and the surface exposed, 
as in Fig. 90, for an examination of the structures of the dorsal 
surface of the rhombencephalon. The posterior medullary 
velum is removed with the cerebellum, but a small portion of 
the anterior medullary velum should remain in place. The Central Nervous System 
301 
{a} The fourth ventricle (ventriculus quartus) is the extensive 
space enclosed by the rhombencephalon. It is connected 
forwards with the cerebral aqueduct and backwards with 
the central canal of the spinal cord. Its roof is formed 
principally by the anterior and posterior medullary vela, 
the latter being attached to the cerebellum close to one 
another, so that they underlie it. 
(&) The rhomboid fossa (fossa rhomboidea) is the shallow 
depression enclosed by the thick lateral and anterior walls 
and floor of the ventricle. The middle line shows a narrow 
depression, the posterior median fissure (fissura mediana 
posterior), on either side of which the floor is raised into 
a low ridge, described as the medial eminence (eminentia 
medialis). The posterior end of the fossa forms with the 
enclosing wall the somewhat triangular figure described as 
the calamus scriptorius. 
(c) The lateral supports of the 
cerebellum, now represent- 
ed by their cut ends, are 
formed by fibre-bands con- 
necting the cerebellum with 
adjacent portions of the 
brain. In each a middle 
band, the brachium pon- 
tis, represents the direct 
continuation of the pons 
into the cerebellum, bring- 
ing impulses to the latter 
from the cerebral cortex. 
An anterior band, the 
brachium conjunctivum, 
contains chiefly fibres lead- 
ing out of the cerebellum. 
(d) A third band, the inferior 
cerebellar peduncle or 
restiform body (corpus 
restiforme), comes from behind as a thick ridge, convex 
medially, forming the lateral wall of the rhomboid fossa. 
Fig. 90. The rhombencephalon. 
Dorsal view, after removal of the cere- 
bellum; be, brachium conj unctivum; 
bp, brachium pontis; cl, clava; cli, 
inferior colliculus (mesencephalon); cr, 
restiform body; em, medial eminence; 
fc, fasciculus cuneatus; fg, fasciculus 
gracilis; fmp, posterior median fissure of 
the rhomboid fossa; fr, rhomboid fossa; 
smp, posterior median sulcus of the 
medulla; sip, posterior lateral sulcus; 
vma, anterior medullary velum. 302 
Anatomy of the Rabbit 
Before turning dorsad into the cerebellum it passes under 
a rounded elevation, the acoustic tubercle, where part of 
the auditory nerve ends. The restiform body conveys 
impulses from various centres in the spinal cord and medulla 
oblongata. 
(e) The posterior funiculus, in passing forward from the cord, 
is divided into medial and lateral portions. The medial 
portion, the fasciculus gracilis, forms a narrow band 
terminating forwards in a club-shaped expansion, the clava. 
The lateral portion, the fasciculus cuneatus, appears to 
pass into the restiform body but does not actually do so. 
Its fibres and those of the fasciculus gracilis convey im- 
pulses of muscle and joint sensibility from the trunk to 
the brain. 
7. The brain may be divided by a median vertical section, and 
one-half examined from the medial surface (Fig. 91). In 
addition to many of the features already made out on the surface, 
the following may be noted: 
Fig. 91. The brain in median section: a, anterior commissure; ac, 
cerebral aqueduct; bo, olfactory bulb; cb, cerebellum; cc, central canal of 
spinal cord; ccl, corpus callosum; cf, body of the fornix; cl.i, inferior colliculus; 
cl.s, superior colliculus; cm, mamillary body; co, optic chiasma; cp, pineal 
body; fl.c, cervical flexure; h, habenular commissure; he, cerebral hemisphere; 
hp, hippocampus; inf, infundibulum; It, laminal terminalis; mo, medulla 
oblongata; p, posterior commissure; pc, chorioid plexus of the third ventricle; 
pd.c, cerebral peduncle; pn, pons; sp, splenium; spl, septum pellucidum; tc, 
tuber cinereum; th, thalamus, massa intermedia; vma, anterior medullary 
velum; vmp, posterior medullary velum; vq, fourth ventricle; vt, third 
ventricle. I, olfactory nerve (origin); II, optic nerve. 
(a) The deep but extremely narrow cavity formed by the third 
ventricle is the first space appearing in the brain from the The Central Nervous System 
303 
anterior end, the first two (paired) ventricles lying laterally 
in the hemispheres. Each is connected with the third 
ventricle by a narrow transverse canal, the interventric- 
ular foramen (foramen interventriculare). 
(&) The anterior boundary of the third ventricle is formed 
ventrally by the narrow transverse wall connecting the two 
hemispheres, the lamina terminalis, in the dorsal portion of 
which is the small anterior commissure (commissura 
anterior). The ventral portion of the ventricle is projected 
above the optic chiasma forming the recessus opticus, 
and into the infundibulum, forming the recessus in- 
fundibuli. 
(c) The mesencephalon contains no ventricular expansion, its 
substance being perforated only by a narrow tube, the 
cerebral aqueduct (aquaeductus cerebri), which connects 
the third with the fourth ventricle. 
(d) The corpus callosum is shown in section. Anteriorly it 
appears to end in a somewhat club-shaped expansion, but 
in reality is extended as a thin sheet of fibres downward 
toward the lamina terminalis. Posteriorly it bends down- 
ward, forming the splenium, the latter being attached to 
the body of the fornix, which lies below it. 
The fornix consists of a pair of longitudinal fibre-bands, fused for a 
short distance in the middle line to form the unpaired body of the 
fornix (corpus fornicis). They begin in the hippocampus and end in 
the mamillary body, conveying to the latter impulses resulting from 
the correlation of olfactory with other stimuli. 
(e) Between the body of the fornix and the anterior portion of 
the corpus callosum is a thin area of the wall, the septum 
pellucidum, the lateral ventricles lying close together in 
this region. 
8. The nervous matter covering the corpus callosum may be re- 
moved from one hemisphere by first marking out a triangular 
area on the dorsolateral surface; then scraping the material 
carefully away until the white surface of the corpus callosum 
is well exposed. By removing the corpus callosum the interior 
of the hemisphere may be examined. 304 
Anatomy of the Rabbit 
(a) The lateral ventricle (ventriculus lateralis) is the ex- 
tensive space enclosed by the hemisphere. It extends 
forward into the olfactory bulb and backward into the 
posterior free end of the hemisphere, passing a considerable 
distance behind the opening of the interventricular foramen. 
(&) The excised portion of the hemisphere, forming the mod- 
erately thick roof and dorsolateral wall, consists largely of 
the peripheral grey cortex described as the pallium. 
(c) The floor is formed by a greatly thickened mass of nervous 
matter, appearing from the interior of the ventricle in the 
form of two convex ridges. One of these, posterior and 
medial in position, is the hippocampus. The other is 
smaller, anterior and lateral in position, and is the corpus 
striatum. Between the two bodies the pigmented vascular 
tissue of the chorioid plexus of the lateral ventricle may 
be made out. The hippocampus is a region where olfactory 
stimuli are correlated with others, chiefly of visceral origin. 
The corpus striatum is related to the control of bodily 
movements. 
(d) On the medial wall, the thickened posterior portion forms 
the body of the fornix, immediately in front of which is the 
thinner portion of the wall, described above as the septum 
pellucidum. 
9. The passage of the olfactory nerves to the ethmoturbinal sur- 
faces may be traced by removing the nasal bones and working 
downward toward the cribriform plate, or the remaining portion 
of the skull containing the nasal region still intact may be 
divided vertically for a more extended examination of the nasal 
fossae. The features to be observed are largely those described 
in connection with the skeleton (pp. 152, 163). APPENDIX 
THE PRESERVATION OF MATERIAL1 
The method commonly used in the preparation of material for 
dissecting purposes consists in first embalming the body with suit- 
able preserving fluids; afterwards filling the arteries with a coloured 
injection mass, so that they are more easily traced. The objects 
served by embalming are: (1) preserving the body from decomposi- 
tion for a sufficient length of time to complete the dissection; 
(2) keeping the body as nearly intact as possible; and (3) having 
the organs in good condition for study. The point last mentioned 
is an important one, since much depends on having the parts of the 
animal in such condition that they are easily and comfortably 
handled, and also easily observed. The desired results are accom- 
plished, first, by introducing the preserving fluid through the blood- 
vessels, instead of by immersing the animal, as was formerly the 
practice;2 secondly, by using in the preserving fluid such materials 
'The methods here given apply only to the preservation of specimens for 
ordinary dissection, either singly, or in numbers for a laboratory course; with a 
few observations on the difficulties which are likely to be experienced. Especially 
in the matter of injections, the student who has acquired some knowledge of the 
vascular system will be able to make complete injections of the portal system and 
also satisfactory injections of the systemic veins, though the latter are somewhat 
more difficult on account of the presence of valves in the vessels. Finer vascular 
injections and injections of the lymphatic system according to the directions given 
in the anatomical text-books may also be suggested. 
Owing to imperfect preservation of the contents of the digestive tube, 
examination of the inner wall in embalmed animals does not usually reveal its 
essential features. It is well to have at hand a demonstration specimen prepared 
as follows: Remove stomach and intestines from a freshly killed animal. Wash 
out the parts with weak salt solution. Fill, without distending, with 3 per cent 
bichromate of potash, formalin-bichromate, or any of the standard fixing agents, 
and tie the ends. Immerse the parts in the solution, and after a time examine 
by slitting them lengthwise. 
2For sometimes convenient but less uniform preservation of small mammals 
ordinary immersion methods may be employed, the animal being placed in a 
preserving solution after making small incisions in the thoracic and abdominal 
walls. Formaldehyde solutions of 2 per cent or better, and grade alcohols 306 
Anatomy of the Rabbit 
as will leave the organs in a condition as near the natural one as 
possible and at the same time keep them moist and flexible through- 
out dissection. 
A suitable fluid for the purpose is that recommended by Keiller3 
for the preservation of human subjects. The formula is as follows: 
Formalin 1.5 parts 
Carbolic acid 2.5 " 
Glycerin 10.0 " 
Water 86.0 " 
100.0 
A convenient method of making up the fluid, especially when 
embalming the animals in numbers, is to prepare the mixture of 
formalin, carbolic acid, and glycerin as a stock-solution, to be 
diluted for use by adding to each part of stock six parts of water. 
The amount required varies according to the size of the animal, the 
flow of the fluid in the vessels, the length of time during which the 
animal is left under the action of the fluid, and the height of the 
pressure column. Not less than 1500 c.c. should be allowed for 
each specimen. 
The apparatus needed for embalming includes a reservoir for the 
fluid, provided with an exit pipe to which a rubber tube may be 
attached; about six feet of rubber tubing to connect with the operat- 
ing table; several three-way pieces to divide the stream in case 
several specimens are to be handled at the same time; selected 
rubber tubing of the size indicated below to attach the cannulae; 
clamps for the tubing; and, finally, glass or metal cannulae for 
insertion into the femoral artery. 
Glass cannulae suitable for the purpose are readily made by 
heating ordinary glass tubing over the Bunsen flame and drawing 
it out to the desired thinness. The tubing used for the purpose 
should be of about 6 mm. outside diameter. The cannula when 
beginning with 30 per cent and changing to 60 or 70 per cent are useful for this 
purpose. The addition of small quantities of glycerine or carbolic acid or both 
improves the brightness and flexibility of the tissues. 
3Keiller, W. "On the Preservation of Subjects, etc." (American Journal of 
Anatomy, vol. II, 1902-3). Several modifications, apparently successful, have 
been employed. The Preservation of Material 
307 
completed should be about 7 cm. long; and its narrow end should 
have a uniform diameter of 1.5-2 mm. for about 2 cm. at the tip. 
A slanting tip, produced by careful grinding on an emery stone 
aids insertion into the vessel. The tip should be touched lightly 
in the flame in order to round the margin by fusion, otherwise it 
might damage the wall of the vessel. 
The rubber tubing used to connect the cannula with the main 
tube should be of the best quality of soft rubber, and should have 
an inside diameter of 4 mm., i.e., of proper size to slip on and off 
the cannula easily, but yet to retain its hold on the latter under 
moderate pressure. 
The reservoir for holding the embalming fluid may be an 
aspirator or irrigator bottle, an enamel fountain, percolator, or 
ordinary funnel. It may have a capacity of one or two quarts. 
The capacity, however, is immaterial, so long as the operator keeps 
the fluid replaced. The reservoir is suspended in such a way that 
it may be moved up and down within a distance of four feet above 
the top of the operating table. 
When large numbers of animals have to be prepared, it is useful 
to connect the reservoir by wide rubber tubing to a horizontal brass 
pipe six feet long, which is provided with five jets with taps. A 
short length of quarter-inch rubber tubing connects each jet to a 
Y-tube of glass or brass, which is in turn connected by slightly 
smaller tubing to two cannulae. Thus ten animals may be em- 
balmed simultaneously. 
At the time of beginning the embalming process the operator 
should have before him the reservoir, suspended at a height of 
about three feet, and a column of fluid, free from air-bubbles or 
foreign material to the tip of the cannula. This condition must 
be maintained throughout the operation. If at any time the 
pressure falls in the apparatus sufficiently to admit air, or allow 
coagulated blood to run back through the cannula, there is almost 
certain to be trouble, not only with the specimen under treatment, 
but also others which come after. The column of fluid is held back 
until the proper time by a clamp placed on the rubber tubing. 
The animal is killed by administering ether or illuminating gas. 
It is placed on its back on the table, with the head away from the 
operator. The skin is first divided by a small incision on the inner 308 
Anatomy of the Rabbit 
side of the right thigh.4 By inserting the fingers well down into 
the incision, the skin may be torn backward and toward the ventral 
middle line, and at the same time the superficial epigastric vessels 
will be carried with the subcutaneous tissue well out of the oper- 
ator's way. Small portions of the inner surface of the thigh and 
of the abdominal wall will be exposed. The white cord represent- 
ing the inguinal ligament lies in the bottom of the inguinal furrow. 
Appearing from beneath the ligament in this position, and passing 
to the surface of the thigh, are the femoral nerve, artery, and vein, 
covered by an exceedingly thin layer of muscle belonging to the 
sartorius. The three structures may be separated from one 
another, and the muscle pulled away at the same time, by working 
lengthwise along the structures with fine forceps. The artery 
must be thoroughly cleared for about 3 cm. from the inguinal 
ligament. Care must be exercised in this operation to avoid 
breaking its branches or the tributaries of the vein. The artery 
lies in front of the vein and is distinguishable by its smaller size, 
its flattened or collapsed condition, and its white coloration. 
The vein will be found greatly distended with blood. The nerve 
lies in front and partly on the lateral side of the artery. 
When the femoral artery has been fully exposed, a ligature of 
coarse thread, previously moistened, may be passed around its base, 
close to the inguinal ligament. An ordinary single knot may be 
placed on the ligature, but must be left loose until the cannula is 
inserted. By grasping the bare edge of the artery at about 2 cm. 
from the ligament, the operator may make a V-shaped incision in 
the vessel with fine scissors. The tips of the scissors are directed 
toward the ligament. The incision must be clean-cut, and care 
must be taken not to cut more than half-way through the vessel. 
By taking up the little angular flap with fine forceps, the cannula 
may be worked into the vessel and pushed well down into it beyond 
the inguinal ligament. The knot is then tightened by a gentle 
even pull on the ends of the thread. The knot should never be 
pulled very tight or doubled. 
4The embalming may be done from the common carotid artery of the neck, a 
vessel much larger than the femoral artery and therefore easier of manipulation. 
This is not recommended, however, because of the damage done to various 
important structures of the cervical region. The Preservation of Material 
309 
At the moment when the cannula is securely fastened into the 
vessel, the clamp is to be removed from the connecting tube and 
the fluid allowed to run in. At the beginning of the process a little 
care in arranging the animal will be amply rewarded by conven- 
ience in dissection. The hind limb on the side opposite the incision 
should be drawn backward. The front limbs should be drawn 
apart, so that the breast is well exposed, and held in this position 
by a thick cord, or, better, a stout flexible wire, passing around the 
back of the animal. The body should be turned slightly to the 
operator's left. 
The animal is sufficiently embalmed in two hours. About eight 
animals may easily be kept on the table by one operator, provided 
he has at his disposal a sufficient number of cannulae, one for each 
specimen, since the first may be taken off the apparatus after the 
eighth has been put on. After some practice the number can be 
greatly increased. 
Since small difficulties frequently occur in the process, especially 
in placing the cannulae and in keeping them clear of obstruction, 
a number of points may be mentioned which indicate to the oper- 
ator just how the operation is succeeding. The entrance of the 
cannula into the artery, in the first place, is usually accompanied 
by a slight rise of blood into its tip. General muscle contractions 
in the recently killed animal are a safe indication of uniform flow 
of the fluid to these and also other parts of the body, and no clogging 
of the vessels need be feared. The fluid may usually be observed 
running in the cannula, and, of course, falling in the reservoir. 
Finally, there are characteristic changes in the body. The abdo- 
men becomes greatly distended, the subcutaneous tissue swollen, 
the eyes protrude, and there is usually more or less frothing at 
the nose. Leakage, either in the area of the incision or at the nose, 
is sometimes a sign of too much pressure. In the former case the 
leakage is frequently behind the cannula, and may be stopped by 
artery forceps. In the latter case there is no recourse but to confine 
the fluid to the nasal cavity by tying the nostrils. 
After the embalming process the rubber tube is disconnected 
from the cannula, the latter being left carefully in place and closed 
by a stopper made by tying a short piece of rubber tubing in a knot. 
The animal is then set aside, preferably for twenty-four hours to 310 
Anatomy of the Rabbit 
several days, but if wanted for use immediately the injection may 
be made after several minutes, usually with satisfactory results. 
The injection mass may be made by mixing ordinary starch and 
water to the consistence of thin cream; then adding a finely-ground 
colouring material, such as vermilion or a very small quantity of 
carmine. There is some advantage in using a 5 per cent or even 
stronger formalin and about one part in seven of glycerin instead 
of water alone in making up this mass, the arteries having after- 
wards a brighter appearance, which is doubtless due partly to 
better preservation and partly to the fixing of the starch in the 
vessels. The glycerin keeps the starch suspended better. The 
mass must be thoroughly strained before use, in order to avoid 
the presence in it of particles which are too large to go through the 
cannula. The injection is made with a syringe, the latter being 
provided with a rubber tube of the same kind as that used in the 
embalming process. The mass is sent in by applying a gentle, 
even pressure, and it is sometimes advantageous to allow the in- 
jection to run backward and forward in the tube, each time applying 
a little more pressure. When the vessels have been filled in this 
way, the tube is clamped. By drawing on one cord of the ligature 
the knot is loosened sufficiently to withdraw the cannula, and by 
keeping a finger pressed on the end of the vessel, the knot may 
then be drawn tight without loss of injection. 
It sometimes happens, despite ordinary precautions, that the 
cannula becomes clogged either with settled starch or with coagu- 
lated blood. In this case it may easily be removed, cleaned, and 
replaced. The same cannula should always be used. 
Material prepared according to the directions given above will 
keep indefinitely, provided, however, that precautions are taken 
to avoid contamination from the surface. These are especially 
necessary in view of the thick coating of hairs. It is a good plan, 
therefore, to sponge the animal with a preserving fluid which will 
penetrate the coat immediately, or if many specimens are being 
prepared, to immerse the whole animal for a moment. A suitable 
fluid for this purpose is formalin-alcohol, made by adding 2 per cent 
of formalin to a mixture of equal parts of ordinary spirit and water. 
The alcohol ensures immediate penetration and assists the formalin 
in preservation. The fluid should be squeezed out of the coat so The Preservation of Material 
311 
far as practicable. An excess is undesirable because the alcohol 
tends to withdraw fluid from the body if the animals are kept for 
some time before dissection, but more especially because the fluid 
is likely to get into the material during dissection where it has the 
effect of removing glycerin, so that the tissues become brittle and 
dry rapidly on exposure. 
For the storage of material, either before or during dissection, 
no precaution is necessary except that of protecting the body from 
undue exposure to evaporation. The animals may be stored in a 
spirit tank if raised above the level of the fluid, or may be kept 
individually in special prepared boxes for convenience in the 
laboratory. A zinc-lined copper box with sliding top, or a paraffin- 
wax-lined galvanized box with slip over cover, of dimensions 
7 x 7 x 24 inches, will be found to be adequate and of proper 
proportions for animals of average size. If less costly individual 
containers are required, ordinary water-proofed paper sheets or 
bags may be employed, the latter being now obtainable through 
regular trade channels. INDEX 
Acetabulum, 180, 249 
Acromion, 173 
Adaptation, 14 
Ansa subclavia, 277 
Antrum, pyloric, 195, 199 
tympanic (mastoid), 161 
Aorta, 47, 95, 97, 98, 114, 126, 128, 217, 275, 
282 
Aperture, piriform, 148, 166, 167 
Aponeurosis, 27, 65, 192 
Aqueduct, cerebral (Sylvian), 78, 122, 303 
Arachnoidea, 290 
Arch, costal, 139 
volar, 232 
■ -zygomatic, 141, 147, 158 
Arches, aortic, 97, 98 
visceral, 59, 60, 81, 82, 83 
Arteries, 94, 96, 97 
Artery, alveolar inferior, 169, 259, 260 
angular, 252 
appendicular, 207 
- axillary, 224, 231, 275 
----- basilar, 122, 275, 299 
brachial, 231 
caecal, 207 
Artery, carotid, 97, 124 
common, 256, 275 
■ external, 259 
• internal, 122, 145, 155, 259, 
272, 300 
caudal, lateral, 219, 240 
cerebellar, inferior, 300 
■-■- superior, 300 
cerebral, anterior, 300 
middle, 300 
posterior, 300 
cervical, ascending, 221, 275 
superficial, 221, 275 
circumflex, 225, 231 
lateral of femur, 240 
coeliac, 196, 197, 218 
colic, left, 91, 208 
middle, 91, 207 
right, 91, 207 
collateral, radial, 231 
ulnar, 232 
communicating, anterior, 300 
posterior, 300 
coronary, 279 
cystic, 202 
deep of arm, 225, 231 
thigh, 240 
deferential, 212 
dental, superior, 269 
epigastric inferior, 193, 219, 276 
superficial, 191, 224, 240 
superior, 276 
ethmoidal, 269 
facial, transverse, 260 
femoral, 219, 240, 246 
frontal, 269 
gastric, left, 197, 198 
right, 198 
short, 198 
gastroduodenal, 198, 199 
gastroepiploic, left, 198, 199 
right, 199 
genu suprema, 240 
haemorrhoidal, inferior, 213 
• - middle, 213, 216, 
219 
superior, 208 
Artery, hepatic, 196, 197, 198, 202 
hypogastric, 219, 240 
ileocaecal, 207 
ileocaecocolic, 207 
iliac, common, 217, 218 
• external, 218 
■ iliolumbar, 192, 218 
infraorbital, 269 
innominate, 97, 275 
intercostal, 276, 283 
supreme, 276 
intestinal, 208 
■ labial inferior, 120, 252 
superior, 252 
lacrimal, 269 
laryngeal, 256 
lingual, 122, 260 
lumbar, 218 
malleolar, 246 
mammary, external, 224 
internal, 193, 274 
maxillary external, 120, 122, 252, 
260 
internal, 120, 122, 260, 
269 
mesenteric, inferior, 208, 218 
superior, 196, 218 
obturator, 219 
occipital, 259 
ophthalmic, 267 
inferior, 269 
palatine, anterior, 269 
pancreaticoduodenal, inferior, 204 
superior, 198, 
203 
phrenic, inferior, 197, 284 
superior, 218, 284 
popliteal, 240, 246 
pterygopalatine, 269 
pudendal, internal, 213, 219, 241 
pulmonary, 96, 97, 98, 126, 278 
radial, 232 
renal, 102, 209, 218 
sacral, median, 217, 218 
saphenous, great, 239, 240, 243, 246 
small, 245, 247 
sciatic, 219, 240 
spermatic, external, 193, 211 
internal, 212, 215, 218 
sphenopalatine, 269 
splenic, 197 
subclavian, 97, 275 
submental, 252 
subscapular, 192, 224 
suprarenal, 209, 218 
suprarenolumbar, 209, 218 
temporal, superficial, 252, 260 
thoracic, external, 192, 224 
lateral, 224 
thoracoacromial, 223, 224 
thoracodorsal, 224 
• thyreoid, superior, 256 
tibial, anterior, 243, 247 
posterior, 243, 246 
transverse facial, 252 
of neck, 222, 276 
--■-■- scapular, 224 
ulnar, 232 
umbilical, 128, 211, 219 
uterine, 216 
vertebral, 124, 275, 300 
Articulations, 31, 51 314 
Index 
Articulations, of posterior limb, 249 
Atrium, 279, 280 
Axes of skull, 61 
Bladder, gall, 200, 201 
urinary, 44, 101, 111, 128, 210, 219 
Blood, 36, 100 
Body, cavernous, 213, 216 
lateral geniculate, 78, 295 
mamillary, 77, 116, 296, 303 
medial geniculate, 78, 295 
pineal. See gland, pineal 
pituitary. See hypophysis 
restiform, 301 
spongy of urethra, 213 
■ - trapezoid, 298 
Bone, 30, 49 
acetabular, 180 
alisphenoid, 55, 143, 155 
atlas, 116, 133 
basioccipital, 55, 116, 122, 142, 153, 
154 
basisphenoid, 55, 116, 142, 155 
clavicle, 62, 63, 173 
coracoid, 62, 63 
costal, 138 
coxal, 178, 179 
dentary, 168 
epistropheus, 116, 124, 134 
ethmoid, 56, 60, 150, 151, 163 
ethmoturbinal, 152, 163, 164 
■ exoccipital, 55, 153, 154 
femur, 50, 51, 62, 182 
fibula, 62, 184 
frontal, 56, 60, 116, 120, 143, 146, 147, 
162 
humerus, 51, 62, 126, 174 
hyoid, 57, 58, 60, 116, 122, 140, 170 
ilium, 62, 179, 180 
incisive, 166 
inferior turbinal, 60 
interparietal, 56, 60, 146, 161 
ischium, 62, 179, 181 
lacrimal, 56, 60, 147, 167 
malar, 147 
malleus, 122. (See also ossicles, 
auditory) 
maxilla, 56, 60, 116, 120, 146, 164 
maxilloturbinal, 118, 152, 164 
mesethmoid, 55, 151 
nasal, 56, 60, 116, 118, 148, 167 
nasoturbinal, 152, 163, 167 
occipital, 50, 60, 141, 153 
orbitosphenoid, 55, 143, 156, 157 
palatine, 56, 60, 116, 120, 147, 167 
parietal, 56, 60, 122, 146, 162 
patella, 183, 184, 187, 237, 250 
periotic, 55, 60, 144, 149, 150, 157 
petromastoid, 144 
petrotympanic, 154, 158 
pisiform, 176, 178 
premaxilla, 56, 60, 116, 118, 146, 151, 
166 
presphenoid, 55, 142, 156 
procoracoid, 63 
- pterygoid, 56, 60 
pubis, 62, 179, 182 
radius, 62, 126, 175 
sacral, 136 
scapula, 62, 126, 172 
sesamoid, 178, 187 
of popliteal region, 250 
sphenoid, 60, 155 
squamosal, 56, 60, 122, 143, 157, 158 
sternum, 62 
Bone, supraoccipital, 55, 116, 153, 154 
temporal, 157 
tibia, 62, 183 
turbinated, 152, 164 
tympanic, 57, 60, 122, 157 
ulna, 62, 175 
vomer, 60, 151, 167 
zygomatic, 56, 60, 120, 147, 166 
Bones, of auditory chain, 57, 60, 161 
carpal, 62, 176 
limb, 53, 62 
metacarpal, 62, 178 
metatarsal, 62, 186 
phalanges, 178, 187 
sesamoid, 178, 187 
tarsal, 62, 185 
Brachium conjunctivum, 78, 301 
pontis, 301 
Branchiomerism, 45 
Breathing, 93 
Bronchus, 42, 91, 126, 282 
Bulb, olfactory, 74, 116, 292, 304 
Bulla, tympanic, 144, 158, 159 
Caecum, 18, 83, 84, 85, 86, 90, 128, 203, 205 
Calamus scriptorius, 300 
Canal, facial, 150, 159 
•--- hypoglossal, 146, 150, 154 
infraorbital, 147 
nasolacrimal, 147, 165, 167 
pterygoid, 145, 156 
pterygopalatine, 148, 168 
Capillaries, 94, 95, 96, 99, 102, 103 
Cartilage, 29 
arytenoid, 265 
corniculate, 265 
costal, 126, 138 
cricoid, 116, 256, 265 
cupula posterior, 120 
epiglottic, 116, 265 
• • of Meckel, 58, 118 
mesethmoid, 116, 120 
- 7 nasopalatine, 116 
nasoturbinal, 116 
thyreoid, 116, 256, 265 
- vomeronasal, 116, 118 
Cavity, cranial, 148, 158 
glenoid of scapula, 173 
skull, 143 
oral. See oral cavity. 
■ tympanic, 122, 144, 146, 159, 160, 
161 
Cell, 21 
Centre, respiratory, 93 
Cerebellum, 74, 79, 80, 116, 297, 298, 301 
Cerebral hemisphere, 74, 75, 79, 80, 116, 118, 
292, 297, 298, 304 
Chiasma, optic, 74, 77, 116, 295 
Choana, 148 
Chondrocranium, 46, 57, 60 
Chordata, 20 
Circle of Willis, 300 
Clava, 302 
Clitoris, 190, 216, 242 
Clivus, 149, 154 
Cloaca, 101 
Cochlea, 122 
Coelome, 47, 104, 109, 194 
Colliculus, inferior, 116, 296 
seminalis, 214 
superior, 116, 122, 296 
Colon, 84, 89, 90, 128, 205 
Column, vertebral, 46, 47, 53 
Commissure, anterior, 116, 302, 303 
habenular, 294, 302 Index 
315 
Commissure, middle, 295 
■ - posterior, 302 
Condyle, occipital, 141, 154 
Convergence, 14 
Cord, spermatic, 213 
Cords, vocal. See vocal folds. 
Corium, 27, 191 
Corpora lutea, 215 
quadrigemina, 78, 79, 80, 296 
Corpus callosum, 293, 303 
striatum, 80, 304 
Cortex, cerebral, 74, 304 
Craniata, 20 
Cranium, 140 
::- cerebral, 46, 58, 60 
visceral, 46, 58, 60 
Crest, nuchal, 142, 154 
Crista galli, 150, 163 
Crus clitoridis, 216 
penis, 213 
Denticles, shagreen, 59 
Diaphragm, 109, 110, 114, 217, 277, 283 
Diastema, 61, 165, 169 
Diencephalon, 74, 75, 80, 114 
Digestion, 84 
Digits, 190 
Divergence, 14 
Duct, bile, 89, 196, 201 
cystic, 201 
-- deferent, 43, 104, 105, 212 
hepatic, 201 
~ incisive. See duct, nasopalatine 
nasolacrimal, 118, 147 
nasopalatine, 116, 118, 264 
parotid, 120, 252 
submaxillary, 120, 255, 260 
thoracic, 99 
Ductus arteriosus (Botalli), 97 
Duodenum, 84, 89, 128, 203 
Duplicidentata, 20 
Dura mater, 71, 116, 118, 290 
Ear, 122, 159, 160, 273 
Epicardium, 278 
Epididymis, 105, 212 
Epiglottis, 116, 264 
Epiphysis, 49, 50 
Epithalamus, 78, 80 
Evolution, 14 
Extension, 68 
Eye, 120, 267 
Eyelids, 189 
Fascia, 27 
■ infraspinous, 226 
lumbodorsal, 192 
supraspinous, 226 
Fasciculus cuneatus, 302 
gracilis, 302 
Fat masses of neck, 114, 124 
Fenestra, cochlear, 161 
vestibular, 161 
Fertilization, 22 
Filum terminale, 74, 289 
Fissure, cerebral, lateral, 293 
cerebral, longitudinal, 292 
limbic, 293 
orbital, superior, 145, 150, 156, 157 
portal, 200 
rhinal, anterior, 293 
• posterior, 293 
Flexion, 68 
Flexures of embryonic brain, 116 
Flocculus, 297 
Fold, middle umbilical, 112, 128, 211 
rectovesical, 210 
vesicouterine, 210 
Follicle, hair, 23, 24, 191 
Follicles, lymph, 204 
■ vesicular ovarian, 215 
Foot, 18, 19 
Foramen caecum, 298 
carotid external, 146, 160 
internal, 145, 160 
cavernosum, 155 
greater palatine, 148, 168 
incisive, 147, 165 
infraorbital, 147, 165 
interventricular, 303 
jugular, 146, 150, 154 
lacerum, 145, 146, 150, 156 
magnum occipitale, 141 
mandibular, 153, 169 
mental, 169 
obturator, 179 
-- optic, 145, 150, 157 
ovale, 145, 280 
rotundum, 145 
sphenoidal, 145, 156 
sphenopalatine, 148, 168 
stylomastoid, 146, 159 
Fornix, 303, 304 
Fossa, acetabular, 181 
axillary, 189, 222 
cranial, 148, 149, 150 
hypophyseal, 149, 155 
infraspinous, 173 
interpeduncular, 297 
jugular, 141, 146, 154 
mandibular, 143, 158 
maxillary, 165 
nasal, 147, 148 
parafloccular, 150, 159 
popliteal, 190 
pterygoid, 143, 156 
rhomboid, 301 
subscapular, 173 
supraspinous, 173 
temporal, 158 
Funiculi, 291, 302 
Furrow, inguinal, 189 
Ganglia of sympathetic trunk, 220, 263, 277 
Ganglion, cervical, inferior, 277, 278 
superior, 263 
ciliary, 270, 272 
coeliac, 197 
mesenteric, inferior, 208 
superior, 114, 197 
nodosum, 262 
otic, 272 
semilunar, 299 
sphenopalatine, 120, 159, 271, 272 
submaxillary, 272 
Gill clefts, 14, 19 
Girdle, pectoral, 53, 62, 63, 171 
pelvic, 53, 62, 63, 179 
Gland, anal, 213 
buccal, 118 
bulbourethral, 43, 214, 216 
endocrine, 24, 107 
Harderian, 267 
infraorbital, 25, 267 
•-- inguinal, 25, 189, 214 
lacrimal, 267 
lymph, 98, 99, 100, 194, 204 
axillary, 222 
deep cervical, 256 
mammary, 25, 191, 224 316 
Index 
Gland, oral, 25, 42 
paraprostate, 43, 214 
-- parathyreoid, 107, 108 
parotid, 25, 252 
pineal, 107, 109, 293 
pituitary. See hypophysis 
prostate, 43, 214 
rectal, 213 
sublingual, 25, 260 
submaxillary, 25, 122, 255 
suprarenal, 107, 108, 196 
thymus, 107, 108, 114, 274 
thyreoid, 107, 108, 116, 124, 256 
- - types, 24, 25 
Glands, lymph, inguinal, 192 
mesenteric, 204, 206 
Glans clitoridis, 216 
• penis, 213 
Gubernaculum, 105, 212 
Habenula, 78, 294 
Hallux, 190 
Heart, 43, 47, 65, 94, 95, 96, 98, 114, 126, 278 
Hippocampus, 303, 304 
Homology, serial, 62 
-- true, 63 
Hydatid, 215 
Hypophysis, 77, 107, 108, 116, 149, 296 
Ileum, 89, 204 
Impression, renal, 202 
Incisure, supraorbital, 147 
Infundibulum, 77, 296 
Inguinal space, 189 
Intestine, 18, 84, 86, 89, 90, 114, 128, 202 
blind. See caecum 
large, 203 
small, 202, 203 
straight. See rectum 
Isthmus (rhombencephali), 116, 122 
Jejunum, 89, 204 
Joint, ankle, 250 
hip, 249 
knee, 249 
Kidney, 44, 47, 102, 103, 104, 128, 209 
Labyrinth, ethmoidal, 163 
Labyrinth of ear, 273 
Lamina papyracea, 164 
Larynx, 58, 60, 116, 256, 263, 265 
Leporidae, 20 
Ligament, arterial, 97, 279 
broad, 112, 215 
calcaneofibular, 251 
-calcaneotibial, 251 
■ carpal, 228, 229 
cleidohumeral, 174 
coronary, 111, 201 
■ cruciate of foot, 244 
■ of knee, 250 
crural, 243 
falciform, 111, 201 
fibular collateral, 250 
-gastrosplenic, 111, 195 
hepatoduodenal, 196 
hyothyreoid, lateral, 171 
median, 170 
iliofemoral, 249 
inguinal, 192, 234 
interosseous of forearm, 175 
-leg, 184, 250 
ischiocapsular, 249 
ovarian, 105, 216 
Ligament, patellar, 184, 237, 250 
phrenicosplenic, 111, 195 
pubocapsular, 249 
pulmonary, 281 
round, of hip, 249 
liver, 201 
uterus, 105, 216 
sternoclavicular, 140, 174 
stylohyoid, 260 
suspensory, 213, 216 
tibial collateral, 249 
■ tibionavicular, 251 
triangular, 111, 201 
umbilical, middle, 211 
Ligamentum nuchae (dorsal ligament of the 
neck), 135, 221 
Line, epiphysial, 50 
superior nuchal, 141 
temporal, 143 
Linea alba, 191 
semilunaris, 192 
Liver, 25, 42, 83, 84, 85, 95, 96, 103, 114, 
128, 200 
Lobe, piriform, 293 
Lung, 42, 47, 91, 94, 114, 126, 281 
Lymph, 37, 99, 100 
nodes. See gland, lymph 
Lymphatic vessels, 99, 100, 194 
Malleolus, lateral, 185 
■ medial, 184 
Mammalia, 18, 20 
Mandible, 17, 18, 56, 58, 118, 120, 122, 146, 
152, 153, 168 
Marsupium nasale, 163 
Mass, intermediate, 295 
Mastoid portion of petrotympanic bone, 157, 
159, 161 
Meatus, acoustic, external, 144, 158, 159, 
189 
internal, 150, 159 
Mediastinum, 278 
Medulla oblongata, 74 
Membrane, tympanic, 159, 161, 272 
Meninges, 71, 290 
Meniscus, 52 
of knee joint, 250 
Mesencephalon, 74, 75, 78, 79, 80, 114 
Mesentery, 110, 128, 194, 204 
Mesocolon, 90, 206 
Mesoduodenum, 203 
Mesogastrium, 195 
Mesometrium, 112, 215 
Mesorchium, 112 
Mesosalpinx, 112, 215 
Mesovarium, 112, 215 
Metacromion, 173 
Metamerism, 19, 44 
Metathalamus, 78, 80, 295 
Mucous membranes, 23 
Muscle, abductor caudae anterior, 289 
posterior, 286, 289 
digiti quinti, 231 
pollicis, 229 
adductor brevis, 237 
digiti, 231 
indicis, 246 
longus, 237, 240 
magnus, 237, 240 
minimi digiti, 246 
anconaeus, 227, 228 
arrectores pilorum, 24 
arytenoideus transversus, 266 
auricular, cutaneous, 253 
basioclavicularis, 122, 124, 221 Index 
317 
Muscle, biceps brachii, 66, 228 
femoris, 235, 239 
brachialis, 228, 231 
brachiocephalic, 226 
buccinator, 118, 120, 253 
caninus, 118, 253 
cardiac, 37, 65 
cleidohumeralis, 224, 226 
cleidomastoideus, 124, 221 
coccygeal, 289 
constrictor pharyngis, 263 
coracobrachialis, 227 
cremaster, 211 
cricoarytenoideus, 266 
cricothyreoideus, 116, 256, 265 
cutaneus maximus, 114, 126, 128, 
191, 220, 224, 226 
deltoideus, 226, 231 
depressor conchae anterior, 251 
■ posterior, 220, 
251 
palpebrae inferioris, 251 
digastricus, 120, 122, 255, 259 
extensor antibrachii parvus, 126, 
228 
carpi radialis brevis, 229 
- longus, 229 
ulnaris, 229 
caudae medialis, 289 
digiti quarti proprius, 229 
- quinti proprius, 229 
digitorum communis, 229 
• -- longus, 243, 248 
hallucis longus, 184, 243 
facial, 252 
flexor carpi radialis, 229 
carpi ulnaris, 230 
caudae, 289 
digiti quinti, 230 
digitorum longus, 245 
profundus, 230 
sublimis, 230 
pollicis brevis, 231 
gastrocnemius, 187, 245 
gemellus inferior, 236 
• superior, 236 
genioglossus, 116, 120, 261 
geniohyoideus, 116, 120, 261 
glutaeus maximus, 235 
medius, 235 
minimus, 236 
gracilis, 238, 239 
hamstring, 238 
hyoglossus, 261 
iliacus, 234 
iliocostalis, 126, 285, 286 
iliopsoas, 234 
infraspinatus, 227 
• intercostal, 126, 273 
interosseiis, 231, 246 
intertransversarius, 287 
intracostal, 274 
involuntary, 32, 64 
ischiocavernosus, 213, 216 
of jaw, 17 
-latissimus dorsi, 126, 189, 192, 222, 
224, 225 
levator alae nasi, 118, 253 
costarum, 283 
palpebrae superioris, 120, 
251, 266 
scapulae major, 122, 124, 
221 
minor, 124, 222 
lingualis, 261 
Muscle, longissimus, 285 
' capitis, 124, 286 
cervicis, 124, 286 
costarum, 285 
dorsi, 126, 286 
longus atlantis, 124, 288 
capitis, 122, 124, 288 
colli, 124, 288 
lumbrical, 231, 246 
masseter, 120, 167, 252, 255, 257 
mentalis, 118, 253 
multifidus, 286 
mylohyoideus, 116, 169, 255, 259 
obliquus capitis inferior, 288 
major, 124 
superior, 287 
externus, 126, 128, 192 
• inferior, 266 
internus, 128, 193, 211 
superior, 120, 266 
obturator externus, 237 
internus, 236 
orbicularis oculi, 251 
palmaris, 230 
papillary, 280 
pectineus, 237 
pectoralis major (secundus), 126, 
189, 192 
pectoralis (primus-quartus), 223, 
224 
pectoscapularis, 223 
peroneus, 185, 242, 244 
brevis, 244 
longus, 244 
quartus, 244 
tertius, 244 
piriformis, 236 
plantaris, 187, 245 
platysma, 120, 124, 220, 224, 251, 
252 
popliteus, 187, 245 
pronator teres, 229 
psoas major, 128, 234 
minor, 128, 234 
pterygoid, external, 169, 259 
-internal, 169, 255, 258 
pubocavernosus, 213, 216 
quadratus femoris, 236, 240 
labii inferioris, 118, 120, 
253 
superioris, 253 
lumborum, 128, 234 
quadriceps femoris, 183, 237 
rectocaudalis, 214 
rectus abdominis, 126, 128, 193 
capitis anterior, 122, 289 
lateralis, 288 
posterior major, 288 
minor, 287 
- superficia- 
lis, 124 
femoris, 237 
inferior, 120, 266 
lateralis, 266 
medialis, 120, 266 
superior, 266 
retractor oculi, 120, 267 
rhomboideus major, 126, 222, 276 
minor, 116, 124, 222, 
276 
sacrococcygeal, 289 
sacrospinalis, 128, 285 
sartorius, 238 
scalenus anterior, 288 
medialis, 288 318 
Index 
Muscle, scalenus medius, 288 
■- posterior, 288 
semimembranosus, 235, 239 
semispinalis capitis, 116, 124, 286 
cervicis, 287 
dorsi, 126, 286 
semitendinosus, 240 
serratus anterior, 126, 192, 222, 276 
posterior, 126, 284 
soleus, 245 
sphincter ani, 214 
splenius, 124, 285 
stapedius, 272 
sternohyoideus, 116, 122, 124, 255, 
256, 257 
sternomastoideus, 124, 144, 221, 255 
sternothyreoideus, 124, 255, 256 
styloglossus, 122, 261 
stylohyoideus major, 122, 171, 260 
minor, 122, 171, 261 
stylopharyngeus, 261 
subcostal, 274 
subcutaneus faciei, 253 
subscapularis, 224, 225, 227 
supraspinatus, 224, 225, 227 
• temporal, 170, 258 
■ tensor fasciae cruris, 239 
fasciae latae, 236 
tympani, 122, 272 
teres major, 225, 227 
minor, 227 
thyreoarytenoideus, 266 
thyreohyoideus, 122, 255 
tibialis anterior, 243, 248 
posterior, 243 
transversus abdominis, 128, 193, 
211, 274 
• thoracis, 126, 274 
trapezius, 116, 124, 126, 221 
triceps brachii, 66, 126, 225, 228, 
231 
surae, 245 
vastus intermedius, 238 
lateralis, 237, 246 
medialis, 238 
voluntary, 32, 65, 66, 67 
zygomaticus minor, 253 
Nasal epithelium, 152 
Nerve, 35, 71 
abducent, 81, 270, 299 
accessorius. See nerve, spinal 
accessory 
acoustic, 81, 150, 299, 302 
alveolar inferior, 118, 169, 259 
superior, 270 
auricular, 222 
• chorda tympani, 272 
cranial, 79, 81 
cutaneous, posterior, 242 
depressor. See nerve, vagus, cardiac 
branch 
ethmoidal, 270 
facial, 83, 120, 122, 145, 
146, 252, 272, 299 
femoral, 234, 241, 248 
frontal, 270 
glossopharyngeal, 83, 146, 261, 262, 
299 
gluteal, inferior, 242, 249 
superior, 241, 249 
■ hypoglossal, 83, 122, 124, 257, 261, 
262, 299 
infraorbital, 270 
• intercostal, 126, 283 
Nerve, intermediate, 272, 299 
lacrimal, 270 
• laryngeal, superior, 256, 262 
lingual, 259, 261, 272 
lumbar, 234 
mandibular, 81, 82, 145, 259, 261, 270 
maxillary, 81, 118, 120, 270 
median, 225, 233 
■ mental, 259 
:- mylohyoid, 259 
nasociliary, 270 
nasopalatine, 271 
obturator, 248 
oculomotor, 81, 269, 297 
olfactory, 81, 116, 150, 292, 304 
ophthalmic, 81, 120, 270 
optic, 81, 267, 296 
■ palatine, 120 
anterior, 271 
peroneal, 241, 243, 248 
petrosal, deep, 271 
great superficial, 159, 272 
phrenic, 277 
of the pterygoid canal. See nerve, 
Vidian 
pudendal, 242, 249 
radial, 225, 232, 233 
recurrent, 124, 276 
saphenous, greater, 239, 241, 247 
lesser, 245, 248 
sciatic, 241, 249 
sphenopalatine, 270, 271, 272 
spinal, 71, 79, 222, 290 
accessory, 83, 146, 262, 299 
■ splanchnic, 197, 283 
subscapular, 225 
suprascapular, 225 
tenth. See nerve, vagus 
tibial, 24, 243, 246, 247 
trigeminal, 81, 122, 156, 259, 270, 299 
trochlear, 81, 270, 298 
ulnar, 225, 233 
-vagus, 83, 124, 126, 146, 198, 199, 
256, 262, 276, 282, 299 
cardiac branch, 124, 257, 262, 
277 
recurrent branch, 124 
;- Vidian, 145, 271 
Nervous system, autonomic, 42, 72 
central, 42, 47 
Nipples, 190, 191 
Nodes, lymph. See gland, lymph 
Notch, acetabular, 181 
sciatic, greater, 180 
lesser, 181 
Notochord, 19, 46, 55 
Oesophagus, 84, 86, 87, 114, 116, 124, 126, 
276, 282 
Olecranon, 176 
Omentum, 111 
greater, 195 
hepatogastric, 196 
lesser, 195, 196, 201 
Ontogeny, 13 
Oral cavity, 84, 86, 87, 114, 118, 120, 263 
Orbit, 141 
Ossicles, auditory, 57, 58, 59, 60, 144, 161 
Ovary, 44, 105, 106, 107, 215 
Oviduct, 104, 106 
Palate, 87, 116, 147, 263, 264 
Pallium, 304 
Pancreas, 25, 26, 42, 83, 84, 107, 128, 197, 
203 Index 
319 
Paraflocculus, 291, 297 
Peduncle, cerebellar, 301 
■ cerebral, 74, 78, 80, 116, 297, 298 
Pelvis, renal, 128, 210 
Penis, 190, 213, 242 
Pericardium, 109, 110, 114, 126, 278 
Peritoneum, 110, 111, 128, 193, 194 
Petrous portion of petrotympanic bone, 157, 
159, 160 
Peyer, aggregated lymph nodules of, 205 
Pharynx, 84, 86, 87, 97, 116, 122, 146, 263, 
264 
Phylogeny, 13 
Pia mater, 71, 120, 290 
Placenta, 18, 19 
Plate, cribriform, 150, 163 
Pleura, 110, 114, 126, 278, 281 
Plexus, aortic, 208 
brachial, 225 
cardiac, 277, 278 
cervical, 225 
chorioid, 77, 116, 294, 298, 304 
coeliac, 197, 198 
• ganglioformis, 262 
hypogastric, 208 
lumbosacral, 234, 248 
mesenteric, inferior, 208 
superior, 197 
pampiniformis, 212 
renal, 208 
spermatic, 208 
Pollex, 190 
Pons, 74, 79, 80, 116, 122, 298 
Portal system, 95, 96 
Pouch, rectovesical, 210 
vesicouterine, 211 
Prepuce, 190 
Process, alveolar, 146, 164, 165 
■ - clinoid, 149, 155 
coracoid, 63, 173 
coronoid, 170 
jugular, 141, 144, 154 
mastoid, 144, 159 
odontoid, 116, 134 
orbital, of maxilla, 164, 165 
palatine, of maxilla, 164, 165 
paramastoid, 141 
pterygoid, 143, 145, 155, 156, 168 
pyramidal, 168 
sphenoorbital, 164, 166 
supraorbital, 147, 162 
thyreohyal, 171 
vermiform, 83, 84, 90, 205 
xiphoid, 140 
zygomatic, 147, 158, 164, 165 
Prosencephalon, 75, 77, 80 
Protuberance, external occipital, 142, 154 
Pylorus, 195 
Pyramid, 298 
Recapitulation, 13 
Rectum, 84, 88, 111, 205, 213, 219 
Reproduction, 18 
Respiration, 93, 97 
Retina, 26 
Rhinencephalon, 76 
Rhombencephalon, 75, 78, 80 
Rib, 126, 138 
Rodentia, 17, 20 
Rotation of forearm, 176 
Sac, scrotal (sac of testis), 105, 110, 190, 193, 
211, 216 
Sacculus rotundus, 203, 204 
Sacrum, 53, 62 
Scroll. See bone, turbinated 
Sella turcica, 149 
Septum pellucidum, 303, 304 
Sinus, aortic, 279, 281 
maxillary, 165 
pulmonary, 280 
sphenoidal, 155 
superior sagittal of dura mater, 120, 
292 
transverse of dura mater, 116, 122, 
146, 155, 159, 292 
Skull, 18, 19, 55-60, 139 
human, 61 
Specialization, 15 
Spinal cord, 36, 42, 73, 114, 116, 126, 128, 
289, 291 
Spleen, 100, 195, 198 
Sternum, 114, 126, 139 
Stomach, 84, 89, 111, 114, 194, 199 
Sulcus ascendens of mandible, 170 
basilaris, 298 
Sustentaculum tali, 186 
Suture, coronal, 162 
frontal, 162 
harmonic, 167 
lambdoidal, 162 
sagittal, 162 
Sympathetic trunk, 72, 114, 126, 128, 220, 
257, 263, 277, 283 
Symphysis, 52 
Teeth, 17, 18, 59, 60, 61 
Telencephalon, 75, 77, 80, 114 
Tendon of Achilles, 245 
Tentorium cerebelli, 148 
Testis, 104, 105, 106, 107, 112, 211 
Thalamencephalon, 77 
Thalamus, 78, 80, 116, 295 
Thorax, 139 
Tissues, 20, 22 
-connective, 26 
epithelial, 22 
muscular, 32 
nervous, 34 
Tongue, 87, 114, 118, 264 
Tonsil, 264 
Trachea, 42, 91, 114, 124, 256, 276 
Tract, olfactory, 116, 292 
• optic, 295 
Trochanters (of femur), 183 
Trochlea humeri, 174 
tali, 184, 185 
Tube, auditory, 146, 160, 161, 264 
Eustachian, 146, 160, 161, 264 
uterine, 106, 215 
Tuber cinereum, 77, 116, 296 
Tubercle, acoustic, 302 
pharyngeal, 154 
Tuberosity, deltoid, 174 
Tubules, renal, 102, 103 
Tunica vaginalis propria, 112, 211, 212 
Tympanum, 160 
Umbilicus, 114 
Ureter, 43, 44, 101, 104, 128, 209 
Urethra, 43, 101, 210, 213, 214, 217, 219 
Uterus, 44, 106, 107, 215, 216, 219 
Vagina, 44, 106, 107, 112, 216, 219 
Valve, spiral, 90, 205 
Valves, atrioventricular, 96, 280 
semilunar, 96, 280, 281 
Vas deferens. See duct, deferent 
Vein, alveolar, inferior, 169, 254, 259 
■ angular, 252 320 
Index 
Vein, auricular, anterior, 254 
posterior, 254 
axillary, 225 
azygos, 98, 126, 283 
brachial, 232 
caudal, lateral, 241 
caval, inferior, 98, 128, 196, 202, 217, 
219, 279 
superior, 98, 274, 276, 279 
cephalic, 225, 232 
circumflex, lateral, 241 
coronary, 199 
- deep, of femur, 241 
epigastric, inferior, 219 
superficial, 241 
facial, anterior, 120, 122, 252, 254 
deep, 254 
posterior, 122, 254 
transverse, 254 
femoral, 241 
gastroduodenal, 199 
gastroepiploic, 199 
hepatic, 202, 219 
hypogastric, common, 218, 219 
iliac, external, 219 
iliolumbar, 219 
infraorbital, 120 
intercostal, 98, 283 
jugular, external, 124, 221, 254 
internal, 124, 146, 254 
transverse, 254 
labial, inferior, 120, 252 
superior, 252 
lumbar, 219 
• maxillary, external, 120 
internal, 254 
posterior internal, 254 
mesenteric, 208 
ophthalmic, inferior, 254 
orbital, inferior, 169 
pancreaticoduodenal, 199 
phrenic, inferior, 219, 284 
superior, 284 
popliteal, 241, 247 
portal, 96, 196, 199, 202 
pudendal, internal, 241 
pulmonary, 126, 279 
radial, 232 
Vein, renal, 209, 219 
saphenous, great, 239, 240, 247 
small, 245, 247 
scapular, transverse, 254 
sciatic, 241, 247 
spermatic, 212, 215, 219 
splenic, 199 
subclavian, 276 
sublingual, 254 
submental, 254 
subscapular, 225 
temporal, deep, 254 
--- superficial, 254 
thoracic, lateral, 225 
thyreoid, inferior, 124 
tibial, anterior, 247 
- posterior, 247 
ulnar, 232 
vertebral, median, 122, 124 
vesical, 220 
Veins, 94, 95, 96 
Velum, anterior medullary, 78, 79, 116, 297, 
298 
■ -- posterior medullary, 79, 116, 298 
Ventricle, of brain, 75, 78 
fourth, 78, 79, 116, 298, 301 
of heart, 95, 98, 126, 278, 279 
laryngeal, 266 
lateral, 75, 76, 78, 116, 118, 303, 
304 
third, 77, 78, 294, 295, 302, 303 
Vertebrae, 53, 54, 114, 126, 128, 130, 131, 
132 
caudal, 53, 130, 137 
cervical, 53, 114, 130, 131, 132, 
134 
coccygeal, 137 
lumbar, 53, 114, 130, 131, 135 
sacral, 53, 130, 136 
thoracic, 53, 114, 130, 131, 134 
Vertebral column, 19, 53, 130 
Vertebrates, 20, 49 
Vesicle, seminal, 43, 213, 214 
Vestibulum, 43. 101, 106, 217 
Vibrissae, 118, 189 
Vocal folds, 266 
Vomeronasal organ, 116, 118, 151 
Vulva, 190