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1897

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4

PRACTICAL ANATOMY
OF THE RABBIT

AN ELEMENTARY
LABORATORY TEXTBOOK IN
MAMMALIAN ANATOMY

By
_B. A. BENSLEY, Ph.D.

Associate Professor of Zoology in the
University of Toronto

TORONTO:
THE UNIVERSITY PRESS io |

PHILADELPHIA:
P. BLAKISTON’S SON & CO. —_
1910 /

EN,

Noyes |

Copyricut, CanapA, 1910, By
Tue UNiversiry Press

PREFACE.

The object of the present book is to set forth the chief facts of
mammalian structure in an elementary, practical form; further, to use
the anatomy of a typical mammal as a means of applying the more
useful definitions of human anatomy and, so far as the limitations of a
single type permit, also the broader conceptions of morphological zoology.
On the practical side, its chief aim is to place before the student the
materials necessary for a practical study of the type, rather than a
descriptive account of its organization, though in some cases, notably
in the treatment of the skeleton, it has been possible to follow a descrip-
tive method without departing from the original plan.

The inclusion of a section devoted to certain general aspects of the
structure of the rabbit will, it is hoped, encourage the student to prose-
cute his practical study with a more liberal point of view. As to the
subject-matter of this section, its selection has been a matter of no little
difficulty, and, doubtless, in many respects it might have been improved
upon. One must feel, however, that the first question is not one of
detail, but of general principle. Progress depends to a considerable
extent on the ability to attack small problems with a large spirit. At
the present time a vast amount of effort is being devoted to the planning
of laboratory courses, and with increasing specialization it becomes more
than ever the duty of the instructor to see that the student does not
leave the laboratory, provided with a mass of detailed information, but
-with general conceptions as crude as when he entered it.

As a laboratory type the rabbit has been made familiar to students
through various zoological textbooks and especially through the
“ Zootomy’’ of Parker. The use of the animal, however, so far as one
may judge, has not been as extensive as its general convenience would
seem to warrant. It may, therefore, be of some value to direct atten-
tion to this form by providing more facilities for its study. It is un-
fortunate, in many respects, that no recent and adequate account of
the anatomy of the rabbit is available, as is the case with other mammals
used for laboratory study, the classic ‘Anatomie des Kaninchens’’ of
Krause, published in 1884, being still the common source of information.

Mammalian dissection is probably of most value to two classes of
students, namely, medical or premedical students using it as an intro-
duction to human anatomy, histology, or physiology, and zoological
students using it as an introduction, or as part of the laboratory prac-
tice of vertebrate zoology. For the latter class two aspects of the
subject are especially worthy of consideration. One is the more or less
detailed study devoted to a single type; the other, the study of a
specialized type, the latter point being of more importance if the sub-

iv PREFACE.

ject is being used as an introductory one. In many respects the con-
tinuous study of a single animal is a good corrective for the rough
general kind of dissection as suggested by the zoological textbooks, and
may be made to share the well-known merit of human anatomy as a
laboratory discipline. Again, for the student who afterwards is con-
cerned with vertebrate evolution, the study of a specialized type, such
as a mammal, gives him, at the outset, something definite and concrete
on which to base his conceptions of sequence. Primitive structure is of
great value as a means of explanation, but the question, now as hereto-
fore, is whether or not the study of primitive animals as a preliminary
step represents the correct procedure from a laboratory standpoint.
The more the student becomes interested in tracing sequence, the more
he will be convinced of the necessity of stating his problem before he
begins to solve it.

The practical outlines on which the present book is based have been
used for several years and in different forms in the laboratories of the
University of Toronto. It would be difficult to make due acknowledg-
ments to those colleagues and students who at one time or another have
assisted in its preparation. Indeed, our chief obligation is to Professor
Ramsay Wright, who, in establishing laboratory courses of this kind,
has laid the foundation on which we have tried to build.

B, A. BENSLEY.
University of Toronto,

January 3rd, 1910.

CONTENTS

INTRODUCTION... 1... ... .. 0... 1

Part I. A GENERAL CONSIDERATION OF THE
STRUCTURE OF THE RABBIT.

DIVISIONS AND METHODS....

oP Rtencat ny din hm Tawke He, iene. eb hoaid 3
INTERPRETATION OF STRUCTURE.......005.0 fee cee eee ee 4
ZOOLOGICAL POSITION....... 0 ...... AS Hse Ok eh | ame 6
GENERAL ANATOMY......... Be Bee ereeen ee “At, eee cee tues .. 8

Epithelial Tissues... .. 2... 0.07. 00. wee se law ae 29
Connective Tissues.. ... ..0.. 0 0. 00. we ee ee we 1B

Muscular Tissues........ Boe Wh oa. BOR Aoi ieee ee. UD
Nervous Tissues .... 26.0 6. 0k cee es tag. “21
‘TERMINOLOGY 24.4625 Ge e08a Bie Ge wenden 23
THE GENERAL FEATURES AND Geounn Bian OF THE m ORIAN Sysumue 25
The Skeletal System...... ... ....... fe we rhe wes ae 530
The Nervous System......... Mo BR Ee ek TRUE ASG COS
The Digestive System......... ...... 40

The Respiratory System.. .. ... .... cee ee ee 48
The Vascular System.... .. ©... 0 7. wee ee ee ee 48
The Urinogenital System.......... ee, betase. be ee ae 6346
The Serous Cavities.......... a re eee tee eee ae 49
REGIONAL SECTIONS....

Part II. OSTEOLOGY OF THE RABBIT.

GENERAL DIVISIONS OF THE SKELETON....... .. ... .. 0. 4! 68

THE VERTEBRAL COLUMN ......-..000. cece e eee ia ee. wa b8
THE (RIBS +4) 2c! aiiche GerSh. we bh <eeo ds cher sige ae ona 73
THE STERNUM. ar Zenitss’, dae Tetcue fie Sane ... 74
THE SKELETON OF THE Beas, elena ie. Gat. ee “aoe ower udhs deed rte. MO
The Skull as a Whole.... i Mess Camas, Clk wm, “ee Ta a” stele 75
The Bones of the Skull........ ..... icin ees tae Sow ae, 85
The Hyoid Apparatus........ oe as tau «BME Acts 97
THE SKELETON OF THE ANTERIOR Tae ee ae: owe 98
THE SKELETON OF THE POSTERIOR LIMB........ .. 0 6.00. ee eee 103

vi ContTENTS.

Part III. DISSECTION OF THE RABBIT.

]. EXTERNAL FEATURES. .. ... ...... BS ade fa eae end Pa BAR ese .. 110
2. THE ABDOMINAL WALL.......0 02.0.0. 0 202 ce tee ne eee 113
3. THE STOMACH AND SPLEEN......... Bade 5708, - a eae ini Sate can 116
4. THE LIVER........ Sania fierhe- toticebbo eee Sabeade we vs a0)
5. THE INTESTINES. . ee en aiahsener se ates Bradys saves Sods 122
6. THE Tiemoeenres: Svar eee ne 127
7. THE ABDOMINAL AORTA, INFERIOR noe Gave, AND Scuparauiie
TRUNKS........ EM ee. chains IS we ae - cares SS
@ Tue Anrerion Limn:. bakin fin, cates onde cots eBe nhab~ Beane VO:
9. THE POSTERIOR Tsuki... ns eae cee Sante Sais dee: Saree igs Ave. Saree an 144
10. THE HEAD AND NECK..... ...0..00 0. 6s eee Hse Sse, DE
11. THE THORAX...... eed. Uitecer See ke amneks ve ane 72
12. THE VERTEBRAL AND Gece NUSeRUMDURD eee ate . 180
13. THE CENTRAL NERVOUS SYSTEM. . Ain nan Gekes, shales .. 184

APPENDIX. DIRECTIONS FOR THE PRESERV ALON OF Mangas. 194

INTRODUCTION.

$ alaboratory exercise, the anatomical study of an animal is largely a
matter of applying a certain practical method of exposition, the
student’s attention being concentrated on those facts which may

be made out by direct observation. For this reason, and also because
continuity is a prime consideration, various important aspects of
structure are of necessity left in the background. It is to be con-
sidered, namely, that in studying the structure of any organism, the
final object is not simply to determine in what its structure consists,
that is, its anatomy in a restricted sense, but also to understand what
the latter signifies when considered either as functional mechanism or, in
general, asa product of the various factors underlving it. Every organism
reflects in its structure the operation of a variety of influences, and
consequently one cannot form an adequate conception of animal or-
ganization without considering it from various points of view. In
many respects, as indicated below, the interpretation of structure is
not simply a matter of what is to be found in a given form, but also of
what the latter represents in comparison with others. Assuming, as
in the present case, that the student is principally occupied with the
routine of a type dissection, the question of how far he may go afield
in the consideration of accessory facts is one which must be determined
by his own inclinations. His first need, one which the present book
endeavours to fill, is to understand the sources of information. Part
I, therefore, the subject matter of which has been selected especially
with reference to the student who has had no previous experience in
the biological sciences, is designed to indicate some of the possibilities
in this connection, and also to serve in other ways as an adjunct to the
practical account of the structure of the rabbit as outlined in Parts II
and III. With the introduction obtained in this way by using the
rabbit as an object lesson the student should be able to extend his informa-
tion independently, using for this purpose special textbooks in the
_ respective subjects.

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, the chief of which are Anatomy, the study of organized
structure; Physiology, the study of function; and Embryology, the study
of development. Anatomy, or Comparative Anatomy, the latter referring
to the comparative study of organisms, and Embryology are also
considered as divisions, or as practical methods, of Morphology, the
general science of the evolution of form.

The term “Anatomy” was originally applied to the dissection or
study of the human body, and is still considered as referring more
especially to the latter. Even in the early stages of biological science,
however, the use of the term was extended to organisms generally; and
afterwards, chiefly as a result of the introduction of the microscope as a
new method of examining structure, it attained its present compre-
hensiveness as a term applying 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 ap-
plication of the microscope; or, again, to distinguish as Special or Des-
criptive 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 considering 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 to be recognized as 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 relations to surrounding parts. The plan is essentially
one of analysis, since conceptions of structure are based on the recogni-
tion of differences, the latter being estimated by various features, such
as form, color, texture, or position. On the other hand, because of the
class of structure with which it deals, dissection is also to be recognized
as a preliminary method in comparison with various others involving
the use of the microscope.

4 ANATOMY OF THE RABBI‘.

THE INTERPRETATION OF STRUCTURE.

Gross structure is, in a sense, only the outward expression of the
finer microscopic structure underlying it, the latter being the true basis
of the body. This refers not so much to the individual features of
organs as to the relation existing between their appearance as gross
objects and their tissue composition. 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 structure, however, may be con-
sidered from two points of view—physiological, and morphological. The
former is more easily understood. All parts of the body are constructed on
a basis of use or function; and although the various processes and activi-
ties of the body are more properly considered under the head of physio-
logy, a thorough conception of the anatomy of an organ is usually to be
gained only by a consideration of its particular réle in the general
economy.

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 directly 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 consists in explaining its adult
structure by reference either to its embryonic development, or to the
equivalent conditions in lower existing, or perhaps fossil, forms. The
recognized principle of embryology is that known as the Law of Re-
capitulation. 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 conditicn, but also reflects in passing the features of lower, and
presumably its own ancestral, forms. That of comparative anatomy
depends on the comparison of higher, specialized animals with lower, or
generalized ones, the latter being assumed, in one feature or ancther, to
have remained in a backward or primitive state of specialization, and
therefore to reflect in such features a low grade of structure of a kind
possessed by the ancestors of existing higher forms. These relations
form a basis for the comparison of the embryonic development of or-
ganisms 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 is a matter of
distinguishing its more general features from its more special ones, the
former being in all cases those to which the ontogenetic and phylogenetic
principles are especially applicable.

All characters of animals have an evolutionary basis, the general

INTERPRETATION OF STRUCTURE. 5

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 resemblances 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.
Asa 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 com-
mon origin. On the other hand, their differences are chiefly marks of diver-
gence in evolution. Although it is conceivable that many of the internal
features of animals are the result of a general progressive development,
more conspicuous in comparison with those of primitive types,
the majority of their differences are such as have resulted from
adaptive modifications of structure, by which they have become differ-
ently adjusted to the particular conditions of their accepted habitats.
Adaptation is one great factor in modifying animal form, producing first
divergences, as between one type and its contemporaries; although such
features may afterwards become settled in particular groups, and thus
appear for these as primitive, general, or group-characters. Adaptation,
in other words, is not a matter of present conditions only, of fixed
environment, or an environment of a general or special kind. The
rabbit as a gnawing animal or rodent, for example, is also an air-
breathing, walking vertebrate, and shares these larger and also more
ancient features with many other vertebrates of otherwise 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, ora
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 neces-
sary by the opposing effects of heredity and specialization is not 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, except where the inter-
mediate member of a known series is being considered, that there are also
organs which are sub-functional or progressive.

6 ANATOMY OF THE RasBit.

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 pcssible 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 study of an animal as a type or representative of a group,
however, concerns only in a general way the features common to its
various members, 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 it. The question of what
an animal is actually representative is a matter of comparison with other
forms, in other words, of 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 statement of the zoological position of the
rabbit may be found useful; and it may also be considered as illustrating,
through the comparison 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-colored forms, long-haired Angoras, Lop-Ear
Rabbits, and Belgian “Hares” are more familiar. They are all descen-
dents 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 family Leporidae contains a large number of closely related
species formerly. included in the single genus Lepus. They are variously
known as hares and rabbits, but the latter designation is considered to
apply more exactly to the European rabbit and its domesticated races,
the others, with one or two exceptions, being more properly described as
hares. The more familiar species include the North American Cotton-
Tail (Sylvilagus floridanus, Lepus sylvaticus), and the Prairie Hare or
Jack-Rabbit (Lepus campesiris); the European Common Rabbit
(Oryctolagus cuniculus), and Hare (Lepus europeus). The two European
species differ in several well marked features, which form the basis of the
accepted distinctions between hares and rabbits. The rabbit is dis-
tinguished by its shorter ears and less elongated hind limbs; also by its
burrowing habits, and by the circumstance that the young are born in
a blind and naked ‘condition. The hare is more nearly a running or
cursorial type, and is distinguished by its longer ears—which, moreover,
are tipped with black—longer hind limbs and prominent eyes. Unlike
the rabbit it does not burrow, but inhabits only an open “form,” and the
young when born are clothed with hair and able to see.

ZooLocicaL Position. 7

The various species constituting this family are distinguished by.
several features, including the imperfect development of the clavicle, longer
ears and limbs, and the presence of a distinct although greatly reduced
tail, from the Picas or Tailless Hares (Ochodontide) of the mountain-
ous districts of Central Asia and of North America (Rocky Mountains).
The two families are allied, however, 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 sub-order 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, con-
tains 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, the 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 obliteration of intermediate teeth, com-
prising posterior incisors, canines, and anterior premolars; also with
elaboration and often great complexity of the remaining premolar and
molar teeth, the lower jaw, and, indeed, the parts of the skull
generally. Characteristic of these animals is the extension, both for-
ward and backward, of the jaw-musculature. The articulation of the lower
jaw exhibits an elongated articular process fitting 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. The teeth are
further arcuate in shape, and are provided with open roots, so that their
growth is not limited, as it is in the majority of mammals. The rodents
are in many particulars primitive types. For example, they tend to
retain the five-toed (pentadactyl), plantigrade foot, characteristic of
ptimitive mammalia and, indeed, of terrestrial vertebrates, and exhibit
also unelaborated cerebral hemispheres in the brain. In other respects,
however, as in the rodent characters above-mentioned and in the
elaboration of the intestine, especially the caecum, they exhibit the
characters of highly specialized herbivores.

Like all higher or placental mammalia (Placentalia), the rabbit is
viviparous, the young being retained through a period of gestation in the
maternal uterus, to the wall of which they are attached by a vascular con-
nection, the placenta. In this feature the placental mammalia differ
from the marsupial mammalia (Marsupialia) of Australia and South
America, the latter being viviparous, but, with one exception, without
placenta; also from the egg-laying mammalia (Monotremata) of Aus-
tralia, the latter being oviparous, like the majority of the lower, reptilian
forms. These three sub-classes of mammals are united, however, by the
common features of the class Mammalia. They are warm-blooded
animals, provided with a complete double circulation, and with a hairy
investment for the surface of the body. In all, the young are nourished
for a time after birth through the secretion of modified cutaneous, milk-

producing, or mammary glands.

8 ANATOMY OF THE Rassi'.

Many of the more general features of the rabbit are such as are
not recognized by group designation, but yet are shared with other
terrestrial vertebrates, including mammals, reptiles, birds, and, in part,
amphibians. This refers to the development of the lungs and associated
respiratory tracts, both the true respiratory tracts and 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 associa-
ted with the elaboration of the pelvic girdle, are all features of general
significance in the terrestrial vertebrates.

Finally, the rabbit agrees with other members of the phylum Chordata
in the possession of a ground-plan underlying the most general features of
its organs, and the position, arrangement, and plan of development of its
organ-systems. All Vertebrata or back-boned animals possess an axial
skeleton formed by the segmented vertebral column. In a very com-
prehensive way they possess as chordates a still more fundamental
axial support, the notochord, the latter being an embryonic structure
except in the lowest chordates. In a more restricted sense, as Craniota,
they possess an organized head region with differentiated brain,
special sense organs, and enclosing primary skull. They possess a series
of branchial (branchiomeric) structures, appearing either in the adult
condition, asin fishes, or as part of the underlying plan in the embryonic
condition; and they add to their general features in the arrangement of
the organ-systems the further feature of transverse segmentation
(metamerism) of a considerable portion of the body.

GENERAL ANATOMY.

Although in every respect a continuous structure, the body is differ-
entiated into a large number of parts, or organs, the latter being
more or less individual in form, composition, or function. Organs
are arranged for the most part in systems, each of which is concerned
with some general or fundamental function, to which several organs
may contribute.

In a more general way the body may be considered as an assemblage
of tissues. The latter are layers or aggregations of similarly differen-
tiated ‘cells. They are of several different kinds, and are variously
' associated in the formation of organs. Being structures of an inter-
mediate position they may be considered either as organ components
or as products of specialized cells.

As a body-unit a cell consists of a small mass of living protoplasm,
containing a central body, the nucleus, and 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

EPITHELIAL STRUCTURES. 9

also in its general activity or metabolism. 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
accompanying 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 surrounding
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 func-
tions 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 b
another to stimuli arising outside of
the body. Moreover, the protozoan
cell is capable of giving rise to new
cells by division of its substance into
two parts, which process originates in
the nucleus, and is associated at some
stage, usually at least, with union or
conjugation of parent cells.

All the cells of the body of a multi-
cellular 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 ,,P0,1, Develoning ovum of the rabbit
of the female. The fertilized egg n.m., nuclear membrane; p.f., cells of the
does not exhibit the functions of a pr yotoplasm, sail ack ae
one-celled body, but possesses the
potential of these functions, and the latter appear, to a large extent
individually, in the differentiation of its division products into special-
ized tissue-elements.

The primary tissues of the body are of four kinds—epithelial, con-
nective, 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.

]. EpmITHELIAL TISSUES.

Epithelial tissues are distinguished chiefly as surface investments,
such as those of the exterior of the body, the interior of the alimentary
canal, the lungs, the respiratory and accessory respiratory tracts, and the

10 ANATOMY OF THE Rappit.

ducts of the urinogenital organs. In all epithelia the cellular feature is a
prominent one, and it is largely for this reason that as lining membranes
they are not conspicuous in gross structure. They are noteworthy,
however, for their products, the hairs and the various kinds of secreting
organs or glands. )

The epithelium of the skin (Fig. 2, ep.) is known as the epidermis or
scarf-skin. Although composed of several layers of cells, it forms
an exceedingly thin membrane, extending over the surface of the body
and connecting at certain points with the epithelia of the internal
surfaces. It is supported by a 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, and in the greater portion of the alimen-
tary tract the epithelial layer is asso-
ciated with a thin layer of smooth
muscle to form a mucous tunic
(Fig. 15, t.ms.).

The coating of hairs on the surface
of the body, the presence of which is
a notable mammalian feature, is a
protective investment arising from
the epidermis. A hair is produced by
the modification of the central por-
tion 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
papilla, through which the structure
is nourished. On the general surface
of the body the hair follicles are
arranged in groups (Fig. 4), 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,
Fic. 2. From a section of the upper lip of a a.p.). They are placed in the broad

four-day-old rabbit: a.p., erector muscle of 2 é
the hair (a.p.l', is that of the adjacent fol angles formed by the inclined follicles

licle); ¢.t., connective tissue of the corium; i a

ep., epithelium; f. hair follicle; s. hair With the corium, and their contrac-

shaft; s.g., sebaceous gland. tion throws the hair into a more
nearly erect position.

Epithelial glands are ingrowths of the general layer, the cells of which
become greatly modified as secreting structures. The lumen or cavity
of the gland, in most cases greatly complicated through the division of
the gland substance, is connected with the general surface by a duct
which thus serves to carry away its secretion. In some cases the con-
nection of a gland with the epithelial surface is embryonic, and in the

EPITHELIAL STRUCTURES. 11

adult condition the gland is found separated 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. In
other cases the secreting element is a single cell, the latter thus repre-
senting a unicellular gland lying directly in the general layer. The
mucus-secreting goblet cells of the intestinal wall are structures of this
nature.

The majority of 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.

Cutaneous glands of two types are commonly present in mammals in
association with the hairs, namely, sudoriparous or sweat-glands, which
are glands of the tubular type, and seba-
ceous 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 con-
nection 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 an acinous type.

Apart from the mucus-secreting cells of
the general epithelium, the glands of the
alimentary canal comprise the important
but less elaborated glands of the wall, such
as the gastric glands cf the wall of the
stomach, and the greatly elaborated, out-
standing glands which lie beyond the wall
and are connected 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 Fic. 3. A, Diagram of a multi-
infraorbital glands—conspicuous structures ¢ellular gland: al. alveolar type: d.,

= : : ‘ duct; ep., general epithelium;
in the dissection of the surrounding por- tubular type. B, The pancreatic duct

tions of the head and neck. Their ducts 324, 2:scctated portion of the duo-
communicate with the cavity of the mouth.

There is a close association between the epithelia of the surface of the
body and the nervous tissues, arising from the circumstance that they are
derivatives of a common embryonic layer, the ectoderm. In the adult
we may distinguish as sensory epithelia special aggregations of cells lying
either in a deep or 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

Ui

12 ANATOMY OF THE RABBI’.

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 latter consist microscopically of thin pavement-like
cells. They differ from epithelia in origin, being formed, not in con-
nection with originally free surfaces, but in relation to spaces of the
mesoderm or intermediate layer of the body. Endothelia form the
linings of blocdvessels 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 together, 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 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 condition. All
connective tissues are products of an em-
bryonic tissue, the mesenchyme (Fig. 20,
ms.), which consists of branched cells con-
nected together by their outstanding pro-
cesses. Through the activity of the cells
there is formed an intercellular material
consisting either of a homogeneous matrix,
or more frequently a matrix containing
formed elements of a supportive nature.

Fic. 4. From a section of the skin

of the side of the body of an adult

rabbit. x about 10; showing the

grouping of the hair-follicles: co., A. ORDINARY CONNECTIVE TISSUES.

corium; ep., epithelium ; _m.¢.m.,
cee pee eerie, tan 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. 5). White fibres are elements of great strength.
They are fine, unbranched fibres which do not occur independently,
but are joined in a parallel fashion with one another, forming
in this way fibre bundles of larger or smaller size. The yellow fibres are
of greater diameter. They branch and anastomose, but are not asso-
ciated 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

Connective. TissuE STRUCTURES. 13

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 sub-
cutaneous tissue (Fig. 4) which connects
the skin with the body; but areolar tissue

- 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. 5). When stretched
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.

Fic. 5. Areolar connective tissue Fibrous connective

(subcutaneous tissue) of the rabbit;

tissue may be

from an embalmed specimen: cc. greatly modified through the concentration
connective tissue cell; wf, bundle of of either one of the fibrous elements. Con-

centration of white fibres is most common.
This condition is illustrated in the thick connective tissue layer forming
the true skin or corium (Fig. 4), but is more conspicuous in the glisten-

white fibres; y.f., yellow elastic fibre.

ing white tendons (Fig. 6) 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 attachment.
The structures known anatomically as fasciae are
special sheets of connective tissue covering chiefly
individual muscles or muscle groups.

Fat or adipose tissue is a soft form. of con-
nective tissue in which the cells are greatly
enlarged and contain fatty material in the form of
globules. It tends to occur in certain situations and
in particular association with the bloodvessels,
but otherwise is found in situations where areolar
connective tissue might be expected to occur.
Special fat masses, sometimes distinguishable by
their darker coloration, occur at the side of the
neck in the rabbit. In the foetus (cf. Plate VI) large
masses of vascular connective tissue are found in
this situation, and are probably similar in origin
to the 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, ciliary body, and iris of the eye, is due
partly to the presence of special connective tissue

Fic. 6. From a section

of the tendon of origin of .~

the biceps muscle: m_f.,
muscle fibres ending on the
tendon; t., fibrous con-
nective tissue of the ten-
don.

14 ANATOMY OF THE RABBIT.

cells, chromatophores, and partly to the presence of pigment granules in
epithelium. The absence of pigmentation in animals belonging to species
normally colored—albinism—is indicated by the white coloration of the
hair and by the pink coloration of the eyes, the latter being due to the
circumstance that the bloodvessels of the vascular tunic are not concealed
by pigment.

B. SKELETAL TISSUES.

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

ka’ ner . of two kinds—cartilage and bone.
; Z Simple or hyaline cartilage
(Fig. 7) 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
y often in groups of two to four,
Fic. 7. Hyaline cartilage: c.c., cartilage each group being contained in a
cell; 1, lacuna; m., matrix. small oval space, the cartilage
lacuna. The size of the spaces, and also their distance apart, is subject
to great variation. The addition of fibrous elements, usually of white
fibres, produces a modification known as fibrocartilage. White fibro-
cartilage occurs in certain situations, as in the symphysis of the pelvis,
or in connection with the interarticular 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 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, how-
ever, it forms the entire skeleton,
with the exception of a small por-
tion which, as described below, is
formed of membrane bone. In the Fic. 8. Intramembranous bone; from a

: ground section of the rabbit's femur: c.l.,
course of development, except in circumferential lamellae; h.c., Haversian
the sitiiations indievted, the earti- met, bia Maverten Jemelines “aly. inter:
lage is replaced by bone. atk

Bone is a compact, resistant, but yet somewhat elastic tissue, possess-
ing 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 (intramembranous bone) is illustrated in the accompanying
figure (8) of a ground transverse section of the dried shaft of the femur.

SKELETAL STRUCTURES. 15.

The bone materials are deposited in layers or lamellae, which are com-
parable to highly modified white fibres of fibrous connective tissue. -The
lamellae enclose between them greatly branched spaces, the lacunae, in
which in the natural condition the bone-cells are accommodated. On
account of certain differences in development, the lamellae are disposed in
different ways. Some are disposed concentrically around longitudinal
spaces, the Haversian canals, forming in this way the so-called Haversian
systems. . The canals are occupied in the natural condition by bloodvessels.
Others of them, the interstitial lamellae, are disposed in a somewhat
parallel fashion between the Haversian systems; while a third series, the
circumferential lamellae, are disposed in a parallel fashion with respect to
the periphery or the internal surface of the bone.
In the natural condition the bone is enclosed
except on its articular surfaces by a layer of con-
nective 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.

It is only in a few cases that the bones of the
skeleton may be looked upon as solid structures—
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 bloodvessels and
marrow spaces. Thus in a long bone (Fig. 9) the
central portion or shaft consists of a cylinder of com-
pact 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 can-
cellous tissue. In the short, flat, or irregular bones
of the skeleton no continuous marrow cavity is
formed.

In point of origin bones are of two chief kinds Fic. 9. Divided femur
—membrane or derm bones, and cartilage or Se eo eal
replacing bones, but a third group is represented ¢piphysis; ¢1., epiphysial
by the tendon or sesamoid bones which are s.. shaft.” i
developed in the tendons of muscles. The mem-
brane bones are few in number. They comprise the roofing and
facial bones of the skull, most of which are distinguished by their
flattened, tabulate character. They are formed in connective
tissue membranes, and although they sometimes contain cartilage they
are not formed on a cartilage basis. Moreover, they are elements lying
in a superficial position with respect to the skeleton proper. They owe
this condition, and also their designation as derm bones, to the circum-
stance that they represent surface plates which in lower vertebrates are
associated with the skin.

16 ANATOMY OF THE RABBIT.

Cartilage bones, on the other hand, are the characteristic elements of
the skeleton. They are known as replacing bones because they are
formed on a cartilage basis, the latter, as indicated above, representing
the primary cartilage skeleton of the embryo. In the course of develop-
ment, except in certain regions where the cartilage persists throughout
life, the cartilage material is replaced by bone, which tends to surround
and also invade it. :

The way in which bones are formed on a cartilage basis serves to
explain many peculiarities of the adult skeleton. In the embryonic
condition the cartilage rudiments are associated to form a complete but
primitive skeleton. In many cases the replacement of these elements by
bone is not direct, certain readjustments being necessary, both for -pur-
poses of growth and on account of the much more special functional
requirements 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, but
described as the perichondrium. The osteoblasts of this layer are
concerned with the formation of bone material, both in the interior

(endochondral bone) and on the surface

tr. ma. (intramembranous bone). The forma-
tion of endochondral bone is preceded
ef. by certain changes which take place in

the interior of the cartilage. In the
: latter, in certain areas, known as the
tr mu. centres of ossification, the matrix
becomes partly dissolved, the cells en-
larged and ultimately broken down.
These changes are associated with a

Fic, 10. Outline sketch of the proximal deposition of calcareous material, or
end of the femur of a young animal: cf. calcification, by which the portion of the

principal epiphysis for the head of the : : 2
femur. The accessory epiphyses are for . cartilage undergoing transformation is

diird (ee) woouamters: ales pig rc temporarily strengthened. Into this

, area the active cells of the perichondrium
are carried through the agency of vascular ingrowths, the periosteal buds,
and the result of their presence is the deposition of bone material in
association with the remaining portions of the matrix. This condition
is partly illustrated in the distal epiphysis of the humerus shown in
Fig. 12, the figure being that of a vertical section of the elbow-joint of a
four-day-old rabbit.

In the long bones the formation of the first or main centres of ossifica-
tion 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. 10), 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 endochondral bone is of short duration. Through
the activity of the osteoblasts lying directly in the perichondrium, or
later the periosteum, a process of formation of intramembranous bones
goes on during the whole period of growth, and the result of the peripheral

SKELETAL STRUCTURES. 17

deposition of bone lamellae is, as described above, that the transverse
diameter of the bone is greatly increased. The enlargement of the
marrow cavity, with which this is associated, is produced by the absorp-
tion of bone from the interior.

In young animals both the epiphysial centres and the masses of cartil-
age in which they are formed are sharply marked off from the body of the
bone (cf. Figs. 12-13). This is largely because the formation of the
epiphysial centres tends to lag behind that of the main centres, and thus
the cartilage extremities of the bones are evident long after the forma-
tion of the shaft is under way. In the epiphysial centres the bone
formation is endochondral. The bone masses which they form are distin-
guished 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 extends 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 growth, the duration of which differs in different
bones, the epiphyses become firmly coossified 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 of the lumbar
vertebrae, the epiphysial lines appear even
in old animals. In the foregoing figure
(9) 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 bones.

In a comparison of the adult skeleton Fis: 11, “The sekinitelipestion ofthe
with the more primitive embryonic skull in a three-day-old rabbit: b.o.,
skeleton, several differences in the arrange- C2sigcciital pong on occinital
ment of the elements are evident. Thus occipital condyle; = fm. foramen

: i 7 magnum; ex.o., exoccipital; s.o.,
many bones, notwithstanding their pos- — supraoccipital.
session of several centres of ossification,
are to be looked upon as individual either in the cartilage or in the
bone condition. 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. 11), become fused together to form compound or
composite bones. In still other cases, as in the vertebrae, the apparently
single elements of the adult condition 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 another
by connective tissue in the form of ligaments, by cartilage, or in some
cases by both together, 2, by fibrocartilage. Ligamentous union,
distinguished as syndesmosis, is the most general type of articulation.

8.0.

3

18 ANATOMY OF THE RApBItT.

Cartilage union or synchondrosis occurs in certain situations, as in the
basal region of the skull. Union by fibrocartilage or symphysis is
characteristic of the articulation of the two sides of the pelvis (symphysis
pubis).

The articulations of bones are of two types—immovable articulations
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.12) 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

Fic 12. Section of the elbow-joint of a four-day-old
rabbit: c., capsule; e.b., endochondral bone in the
distal epiphysis of the humerus; e.a., extensor muscles
of the forearm; e.m., extensors of the hand; f.a., flexors
of the forearm; f.m., flexors of the hand; h., humerus;
ol., olecranon; r., radius; s.c., synovial cavity; u., ulna. Fic. 18. Section of the knee-joint of a

four-day-old rabbit: c., capsule; f., distal

epiphysis of femur; |.p., patellar ligament

7 * . is (insertion of quadriceps femoris); p.v.,
(Fig. 13), interarticular cartilages (men- popliteal vessels and nerves: t., proximal

isl} afte enclosed between the bone [REE cot eee oe
surfaces, and the latter are connected ligament; xx, anterior cruciate ligament.
directly by short ligamentous cords. The

various ligaments of a joint permit free motionof the bones, but only
up to a certain point.

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 direction. In the ginglymus or hinge-
joint, as exemplified by the distal articulations of the limb, motion is

Muscunar TIssuEs AND MuscLes. 19

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
of 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 may be considered to possess the contractile properties of proto-
plasm, but with the contraction limited to one direction. Exceptina 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 is the shortening of the
longitudinal axis and the increase of the transverse axis.

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 voluntary muscles of the skeleton
Smooth fibres (Fig. 14 B) are elongated, 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 are dis-
tinguished as involuntary because
their operation is not under the con-
trol of the will, their connections
being with the sympathetic nervous
system. The striated fibres (Fig. 14 A)
are very much larger, cylindrical
structures, the substance of which
possesses characteristic transverse
striations. Each fibre is enclosed by
a loosely attached membrane, the
sarcolemma, on the inner surface of
which many nuclei occur.* The
presence of these nuclei indicates
that the fibre is not a single cell but Fic. 14. A, Striated (skeletal) muscle of the
a syncytiem, 12, an asseciation of SPEi P_ Ouemietes cmece trom: te
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 both from striated and
smooth muscle in being composed of branched anastomosing fibres,

*The position of the nuclei is characteristic of the so-called white muscles.
In the semitendinosus of the rabbit, which is a red muscle, the nuclei occur
between the fibril bundles of the interior of the ‘fibre.

20 ANATOMY OF THE Raspi'.

.which apparently form a continuous network. Like striated muscle, it
possesses characteristic transverse markings, but, like involuntary
muscle, it is under the control of the sympathetic nervous system.

As gross structures the voluntary muscles are functional units, each.
of which has a particular action according to the movement per-
mitted by the parts of the skeleton to which it is attached. They
present a longitudinal striation which is roughly referred to as the direc-
tion of the fibres, and which is of great value in identification. The
striation is due to the circumstance that the fibres are arranged
in parallel groups or muscle bundles, each of which is surrounded and
separated from the adjacent bundles by a connective tissue enclosure,
the perimysium. ,

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 (Fig. 6). In
contraction it is usually seen that one end, thus designated as the
origin of the muscle, remains stationary, while the other, known as the
insertion, assumes a position nearer
the origin, carrying with it either the
structure which is to be moved, or
another portion determined by the
point of leverage or the position of
the joint. The action of the muscle
is estimated in a direct line between
origin and insertion, although the
effect of the contraction, on account
of the position of the joint, may be
otherwise. From these more typical ’
conditions, however, many modifica-
tions occur.

> _tms.

Fic. 15. 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 submucosa;
t.sr., serous tunic.

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. Furthermore, the recognition of origin and
insertion depends on usual but not invariable relations. The exact
effect of muscle contraction also depends as a rule on the synchronous
action of other muscles. A muscle like the diaphragm does not
possess an insertion after the fashion of ordinary muscles; and in some
cases, aSin the intrinsic muscle of the tongue or the so-called orbicular
or sphincter muscles, both origin and insertion may be absent.
Involuntary muscle is distinguished by its white or greyish coloration
and by its smooth or homogeneous appearance. It forms characteristic

Nervous Tissuzs. 21:

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 alimentary canal, and also a separate muscular
tunic lying in the outer portion of its wall (Fig. 15). In the muscular
tunic the fibres are arranged in both circular and longitudinal directions.
Involuntary muscle also forms a small constituent of many organs, such
as certain glands, in which contractility is not a chief function. It forms
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 constituent of the walls of the bloodvessels.

Although there is an underlying community of structure in the walls
of the bloodvessels, the two chief types of vessels, arteries and veins,
present conspicuous differences, both in functional behaviour, and in their
appearance in the dead animal. The differences are largely the result
of differences in the relative amounts
of the above-mentioned constituents.
The arteries are thick-walled, elastic
tubes, which, under the force of blood
from the heart, first become greatly
expanded, and then gradually con-
tract, so that the blood is forced into
the smaller capillary vessels. The
veins on the other hand are thinner-
walled, less elastic vessels, through
which the blood is fotced largely
through the pressure from behind.
In the dead animal the arteries
appear white, flat or collapsed, and ;
empty. The veins on the other hand 19.18, Newe-cil from the gnterign ergy
appear large and dark on account of dendrites; c.g, chromatophile granules ;
their distension with blood. ss a

4. NERvouS TISSUES.

Nervous tissues form the basis of the central nervous system and
of the outlying nerves and ganglia. They comprise two kinds of elements
—nerve cells and nerve fibres. In the central nervous system these
elements are imbedded in a mass of neutral tissue, the neuroglia.

Nerve cells are characteristic of the central nervous system and of
the spinal and sympathetic ganglia. They differ greatly in form, but
typically each consists of a cell-body (Fig. 16) bearing two kinds of
processes—a fibre-process, the neuraxis or neurite, and a series of branched
protoplasmic processes, the dendrites. The cell-body is distinguished by
the presence in its interior of granular masses, the chromatophile or
tigroid bodies. The latter extend into the dendrites, but not into the
neuraxis. The dendrites may be greatly elaborated, and may be present
to a considerable number. The nettraxis isa nerve.fibre process. Since
it continues as the central portion or axial cord of a nerve fibre, it may
traverse a relatively enormous distance on its way to a peripheral organ.

22

ANATOMY OF THE RABBIT.

A nerve fibre consists of a central core, the axial cord, enclosed, except

in the case of those of the olfactory nerve, by certain membranes.

Two

kinds of fibres are distinguished—medullated fibres, and non-medullated

fibres.

The former are characteristic of the peripheral nerves. In

these (Fig. 17) the axial cord is surrounded by a comparatively thick

Fig. 17. Portions of two
medullated 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.

membrane of fatty material, the medullary or
myelin sheath. The latter is continuous except
at certain points, the nodes of Ranvier, where the
axial cord appears free except for an external
investment of the whole fibre, the neurilemma.

In the non-medullated nerve fibres the myelin
sheath is lacking. This type of fibre is chiefly
distributed in connection with the sympathetic:
system.

A nerve is an association of nerve fibres, the
latter being disposed 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 a nerve is due to the
fatty materials of the myelin sheaths, but nerves
are commonly found imbedded in a fatty con-
nective tissue which is associated with the
epineurium and is also of white coloration.

Nervé fibres, and also nerves, are distinguished
functionally as afferent and efferent. They are

organs of conduction, which carry impulses either from the peripheral
parts of the body to the central nervous system, or in the opposite

direction. Sensory nerves are
afferent, while motor nerves
are efferent. Nerves, however,
usually contain both afferent
and efferent fibres and are
hence described as mixed. In
the distribution of afferent
and efferent fibres there is a
marked difference between
the external or somatic por-
tions of the body and the
internal or visceral portions.
Consequently, both somatic
and visceral kinds of afferent
and efferent fibres are con-
veniently distinguished. (

On account of certain diff-
erences in coloration, the
cellular and white fibrous’
constituents of the ~ central

smp.

~ fp.
LES ae ce

f.m.a

Fic. 18. 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., anterior and posterior nerve
roots; s.a., white substance.

nervous system produce characteristic patterns where either. one is

TERMINOLOGY. 23

concentrated. Thus the cellular material is greyish, and is hence
distinguished as the grey substance, while white fibrous material pro-.
duces when concentrated an opaque white appearance similar to that
seen in the peripheral nerves, and is hence described as white substance.
In the spinal cord (Fig. 18) the grey substance is disposed as a central
core, the white substance asa peripheral investment. A similar relation
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.

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.

Although few in number, the terms of orientation may be regarded as
the most generally useful terms of descriptive anatomy. This is because
they are based on very general relations of the body, and are therefore of
wide application. For this reason they are here selected for definition
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 forwards, with respect to the
long axis, is anterior in comparison with any position backwards, which is
posterior.

In relation to the long axis it is convenient to recognize a median
vertical plane of section, which is one dividing the body into right and
left halves; also transversal planes, which are planes situated at right
angles to the median plane and to the long axis, and sagittal planes.
The latter are vertical planes parallel to, and also including (as mid-
sagittal), the median vertical plane.

The median vertical plane is the plane of bilateral symmetry, each
half of the body as thus defined being in a general way the reverse
counterpart of the other. Structures situated in part in the median
plane are unpaired, and are described as median, while structures 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

24 ANATOMY OF THE RABBIT.

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 vertebrates, 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 ali-
mentary 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
mamualian aortic arch.

Referring to centre and circumference, either in the body as a whole,
or in particular parts, the terms deep and superficial, central and periph-
eral, 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 comparison with the terms medial (medialis) and median (medi-
anus) the term middle (medius) may be used to designate the position of
a structure lying between two others, the latter being otherwise desig-
nated, for example, as anterior and posterior, or one in the median plane.

The limbs being more or less independent structures, it is proper to
apply to them certain terms otherwise applicable to the main portion of
the body. The chief terms not properly applied elsewhere are proximal,
meaning nearer the centre or base of attachment, and distal, toward the
extremity. In the middle 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 dorsal and ventral
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 some-
what different. In comparison with that of a quadrupedal vertebrate
the human body occupies a vertical or erect position, and is to be con-
sidered 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 indeed largely reassumes this
position when allowed to hang freely at the side of the body. As in all
cases, the face retains its forward direction. Thus the terms anterior
and posterior as used in human anatomy mean dorsal and ventral,
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 anterior and posteriot 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

GENERAL PLAN OF ORGANIZATION. 25

man. On the other hand, in ordinary description little advantage is
to be gained from adherence to this principle. The terms anterior
and posterior apply with 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 is to use the terms anterior and pos-
terior for descriptive purposes without reference to the human relation.
The same applies to the terms of direction—upward, downward, forward,
and backward. It may be pointed out, however, that it has become
the practice with some to employ in place of anterior and posterior, such
terms as cephalic and caudal, thereby eliminating one of the difficulties;
or similarly to use the termination—ad, in connection with words sig-
nifying position, for the purpose of indicating direction (¢.g., dorsad,
cephalad, laterad, for dorsalward, etc.).

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 essen-
tial to endeavor 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.

In ‘order to arrive at a proper understanding of the special features
of organs, or of the relations to one another of organ groups, it will be
found useful in many cases to consider them in the light of their deriva-
tion from a general or ground form. A brief statement of what may
be accomplished in this way and of the methods involved has already
been given above (p. 4) in discussing the general interpretation of
structure and the zoological position of the type, so that in the following
pages only the actual facts of organization will be considered. In this
connection it will be remembered that the subject is a very broad one,
and in the present case it will not be possible to do more than select
in the various organ systems the more important features, the con-
sideration of which will be of direct assistance in the practical study of
the type. Before taking up the individual organ systems, however,
it will be advisable to refer in the first place to the plan of classification,
and secondly to explain the more fundamental features of vertebrate
organization as something underlying the disposition of the systems
themselves. It will also be convenient to summarize the chief features
of the embryonic organ systems, since it is by reference to embryonic
conditions that the general features of the body are most readily recog-
nized.

26. ANATOMY OF: THE RABBIT.

F'” Classification of the Organ Systems.—The term organ system is
employed in descriptive anatomy to designate a group of organs which
cooperate in a general function. In many respects the systems repre-
sent 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 de-
velopment. The exact number of systems recognized depends on certain
arbitrary distinctions, the following being those usually distinguished :

‘(1)-The integumentary system, comprising the skin, and its ap-
pendages, namely, the hairs and the general cutaneous, mammary, and
inguinal glands.

(2) The skeletal system, comprising the cartilage and bone elements
of the skeleton, with their connections.

(3) The muscular system, comprising 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, comprising 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. A special portion of the peripheral nervous system is set apart
as the sympathetic nervous system. The latter consists of a pair of
ganglionated sympathetic trunks lying along the ventral surface of the
vertebral column, and of two series of ganglia, prevertebral and peripheral,
connecting the trunks with the visceral organs.

(5) The digestive system, comprising the digestive tube and its out-
standing glandular appendages—the oral glands, the liver, and the
pancreas.

(6) The respiratory system, comprising the lungs, and respiratory
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.

(7) The vascular system, comprising the organs of circulation,
namely, the heart, arteries, capillary vessels,and veins. The lymph-
conducting canals are also portions of the circulatory system, but since
they are largely independent of the bloodvessels, they are usually con-
sidered as forming with their associated lymph glands a separate
lymphatic system. :

(8) The urinogenital system, comprising 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 reproductive organs comprise the paired ovaries, uterine
tubes and uteri, together with the unpaired vagina. The excretory

GENERAL PLAN OF ORGANIZATION. 27

organs of both sexes comprise the paired kidneys and ureters and the
unpaired urinary bladder.

Certain organs of the body are not included in this classification:
(1) The thymus and thyreoid glands are connected with the digestive tube
in the embryonic condition, and for this reason are sometimes included
with the digestive system, although in the adult they occur as in-
dependent structures. (2) The suprarenal body is situated close to the
kidney of either side, but is independent of the latter, both in the adult
condition and in point of development. (3) The special (olfactory, optic
and auditory) sense-organs of the head are highly elaborated structures,
the relations of which are partly with the central nervous system.

General Organization—In the rabbit, as in all vertebrates, .the
general plan of organization involves three chief features, as follows:
(1) axial orientation—the arrangement of the chief organ-systems
longitudinally about a more or less central, axial support; (2) meta-
merism—the arrangement of a con-
siderable portion of the body on a
segmented or metameric plan,
according to. which structures are
repeated in a serial fashion along
the axis; (3) branchiomerism — the
arrangement of a small anterior
portion of the body on a serial but
branchial plan, the latter depending
not on the. succession of true
metameres but of visceral arches.

The extent to which the general
disposition of the organ-systems is
dependent on a fundamental plan will
be evident from a comparison of the
accompanying figure (20) of a trans-

Fic. 19. Rabbit-embryo of 103 days (4.8 Verse section of the rabbit-embryo, or
mm.):m., mandibular; h.. hyoid; land 2, first of the schematic section of a general-

and second branchial arches; a.l., anterior : : >
limb-bud ; me., metameres; p.l., posterior ized vertebrate (Fig. 21), with the

elbels Normentafeln, Vii Fey” ™ actual sections of the rabbit-foetus

as given in the plates, more especially
the abdominal section of Plate VIII and the thoracic section of Plate
VII. It will be considered more fully below in connection with the
general features of the organs.

Metamerism (Fig. 19, me.) is characteristic of a dorsolateral portion
of the body, identifiable in the embryo as that including the dorsal and
intermediate portions of the middle layer or mesoderm (Fig. 20, d.m.
and n.). In the adult it determines a number of features of serial
arrangement, including the succession of the vertebrae and ribs, the
divisions of the related dorsal musculature and its extensions to the ribs
and abdominal wall, and indirectly the succession of the spinal nerves
and their branches, of the parietal branches of the aorta, and the parietal
roots of the inferior caval vein, as well as of the tributaries of the azygos
vein.

28 ANATOMY OF THE RABBIT.

Branchiomerism is an adult feature of lower aquatic vertebrates, such
as fishes, where it appears as a succession of true, gill (or branchial)
structures, which support gill filaments as functional 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. As in lower vertebrates, it underlies not
only structures of branchial significance (branchial arches in the restricted
sense) (Fig. 19, 1, 2), but also modified branchial structures, including
the first or mandibular arch (m.), and the second or hyoidarch (n.). So
great is the modification of these structures in passing from the embryonic

Fic. 20. Transverse section of a rabbit-embryo of about 104 days,
showing the arrangement of the organ-systems: ao., aorta; ch., not-
ochord; coe., coelomic cavity; d.m., dorsal mesoderm (myotomic
and scierotomic divisions); e., primitive alimentary canal (enteron);
ect., ectoderm; 1.b., limb-bud; ms., mesenchyme; my., external
portion of a myotome; n., nephrotome of embryonic kidney; inter-
mediate mass of mesoderm; sp. and so., splanchnic (visceral) and
somatic (parietal) portions of the ventral mesoderm.

to the adult condition that the recognition of the ground-plan is perhaps
here of less general importance. It, however, 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.

GENERAL PLAN OF ORGANIZATION. 29

Embryonic Plan of the Organ Systems.—In the individual organ-
systems the main features of the general plan, as estimated on 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 secondarily of a seg-
mented cartilaginous, afterwards bony, vertebral column.

2. The formation of (a) a primary cartilage skull (chondrocranium)
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).

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 ventral
wall of the digestive tube, afterwards connected with the outside 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 ventral position
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, combining the aortic
arches, and passing 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.

9. 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.

10. The formation of the kidneys, either as embryonic or 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, n.).

11. The formation, in the ventral portion of the body, of an extensive
space, the coelomic cavity or coelom, afterwards differentiated into
pericardial, pleural and peritoneal portions.

30 ANATOMY OF THE Rassir.

THE SKELETAL SYSTEM*.

- That portion of the skeleton which in the adult is designated as axial
includes the vertebral column, together with the associated ribs and
sternum, and the skeleton of the head. The axial relation belongs in the
first instance to the bodies of the vertebrae and to a small portion of the
base¥of the skull. A line drawn through the centres of the vertebral

a

bodies indicates the position of the primary axial support, the notochord.

Fic. 21. 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; a.v., vertebral arch; c.v., vertebral canal.

Muscular system—s.m., skeletal muscle;' v.m., visceral muscle.» . . . o

Nervous system—m.s., spinal cord, with the central canal, and the dorsal (pos-
terior) and ventral (anterior) roots of the spinal nerves; g.r.p., ganglion of the
posterior root; rf.c., ramus communicans to sympathetic trunk; r.m.a. and
r.m.p., anterior and posterior rami of a spinal nerve; t.s., sympathetic trunk.

Digestive system—i., intestine.

Wascular system—ao., aorta.

Urinogenital system—k., kidney; go., gonad (ovary or testis).

Serous cavity—c.p., general coelom, pleuroperitoneal, or peritoneal cavity;
p.v. and p.p., visceral and parietal parts of the serous tunic—visceral and parietal
peritoneum; mes., mesentery.

The arches of the vertebrae are identified with the general functions of
support of the related musculature and enclosure of the spinal cord. In
lower vertebrates the line formed by the vertebral column and the base
of the skull is for the most part straight. In a mammal the vertebral

*The majority of the features mentioned below are illustrated in the plate
figures of regional sections of the rabbit-foetus which tollow, and for this reason the
references are not indicated except in special cases.

THE SKELETAL SysTEM. 31

column presents marked dorsolumbar and cervical flexures. The axis
of the skull proper, the basicranial axis, identifiable as a line passing
‘through the centres of the basioccipital, basisphenoid and presphenoid
bones, may differ by a considerable angle from that of the related cervical
vertebrae. Further, the basicranial line, if continued forward in the
rabbit, would pass through the dorsal wall of the skull immediately in
front of the orbits (See Plate II, or Fig. 33 of the divided skull). It
accordingly differs by a considerable angle from the basal line of the face,
or basifacial axis.

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
(cf. Plates III-V). Asa 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 proper. Thus, 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 includes
the series of visceral arches suspended from the ventral surface of the
neurocranium. The addition to the primary head skeleton of a large
number of membrane bones results in more or less confusion of the
original divisions, since the membrane portions of the visceral cranium
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 larynx
(in part) (Plate II), although highly modified, remain in a more or less
independent relation.

The skull, or cranium—using that term in a general sense—may be
described as consisting of a cranial portion (the cranium proper) and of
a facial portion, the latter including as visceral structures the upper Jaw
and the mandible, and as cerebral structures the parts of the turbinated
bones and the associated secondary respiratory tract formed by the
nasal fossae. In a mammal the investing membrane bones of the face
are largely associated with a great extension of the nasal capsules, or that
portion of the primary skull from which the turbinated cartilages are
formed. Thus, as illustrated in the transverse section of Plate III, the
nasoturbinals and maxilloturbinals are formed on lateral extensions of
the primary septum (mesethmoid cartilage), but are supported more
directly, and in the adult wholly, by the investing membrane bones
(nasals, maxillae and premaxillae).

The elements of ‘the head skeleton may be classified as follows:

1. The CEREBRAL CRANIUM (cranium cerebrale or neurocranium),
including:
(a) The primary cartilage skull (chondrocranium), enclosing
the brain, and containing in its wall the olfactory and
auditory capsules (embryonic) ;

32 ANATOMY OF THE RABBIT.

(b) The secondary bone skull (osteocranium), replacing (a) and
comprising the occipital, sphenoid, ethmoid, inferior turbinal,
and periotic bones;

(c) The associated derm elements, comprising the interparietal,
parietal, frontal, nasal, vomerine, lacrimal, tympanic,* and
squamosal bones.

2. The VISCERAL CRANIUM (cranium viscerale or splanchno-
cranium), including;
(a) The primary mandibular and hyoidt visceral arches (embry-
onic) ;
(b) The secondary elements, replacing (a)—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, com-
prising the premaxillary, maxillary, zygomatic, mandibular,
palatine and vestigial pterygoid bones.

The anterior and posterior portions of the appendicular skeleton
include each a proximal or girdle portion and a distal portion, the free
extremity. In each the free extremity is divisible into proximal, middle
and distal segments. The proximal joint of the limb, either of the
shoulder or hip, is an enarthrosis, although it will be seen by examination
of the rabbit that the glenoid cavity of the shoulder is not greatly
elaborated asa concave surface. The distal joints of the limbs conform to
the type of the ginglymus, and with minor exceptions the movements are
restricted to one, namely, the sagittal, plane. In each limb they are
described as movements of flexion and extension, since the general effect
of movement is to bend of straighten particular parts on one another.
Similar motions are observable in the limb as a whole, but are not spoken of
as of flexion and extension, since the shoulder and hip joints are of a totally
different type. In the limb as a whole, the chief motions are of pre- and
post-traction, but it is convenient to recognize also movements of ad-
duction (toward the body) and of abduction (away from the body). In
both cases the axis of the upper arm, or of the thigh, is assumed to be
parallel to the median vertical plane.

In mammals, as in other terrestrial vertebrates, the anterior and
posterior limbs are equivalent part for part. Thev are said to be
serially homologous or homoplastic. There is, however, particularly in
the mammalia, a pronounced difference between the anterior and
posterior limbs in the respective positions of the different segments.
Consequently, in studying the related musculature, it is advisable to
consider not only the functional relations of muscles, but also the equival-

*The identification of the tympanic as a derm element has been questioned.
+The 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. 33.

ence of the bone surfaces. This may be estimated either from the
rotations of the limbs in embryonic development, or by reference to an
ideal or neutral condition as indicated in the accompanying diagram
(Fig. 22). The neutral type (A) may be defined as one in which the
proximal segment (humerus or femur) is situated at right angles to the
median vertical plane, the middle segment directed downward parallel.
to the median plane, and the distal segment again at right angles to it.
In this condition the bones of the middle segment are parallel, with the
radius, or the tibia, according to the particular limb, anterior in position.
The first digit is also anterior. The entire anterior surface is indicated
in the accompanying diagram by shaded lines. The angles b. and c.
are ‘“‘extension”’ angles; e. and f. “flexion” angles; a. is an ‘‘abduction”’
angle, while d. is an ‘‘adduction”’ angle.

In both limbs of a mammal, the entire appendage is rotated downward
to a position more or less underneath the body. In the anterior limb
(B) the proximal segment is rotated backward, the middle and distal
segments forward. The two divisions thus come to differ from one

A B Cc
tr

e
ca j
Fic. 22. Schematic representation of the respective positions of the segments

in the mammalian limbs: A, neutral; B, anterior limb; C, posterior limb. Ex-
planation in text: tr.p., transverse plane

another to the extent of two right angles. Also, in the front limb, the in-
teresting condition is observable that the radius and ulna are crossed on
one another, the position of the former being chiefly anterior, although
its proximal end is lateral, and its distal end, like the first digit, medial.
In the rabbit, as in most mammals, the hand is thus fixed in a prone
position, while in man the hand may be rotated to a supine position in
which the radius is wholly lateral, or in which the two bones are parallel.

In the posterior limb (C) all three segments are rotated forward. Con-
sequently the bones of the middle segment retain their original parallel
position with reference to one another. The extension angles of the
knee and ankle are anterior, the flexion angles posterior. They differ
from the corresponding angles of the anterior limb only at the middle
joint, but here the difference amounts to two right angles. It will be
observed also that the distal or ankle joint of the posterior limb retains
a primitive condition, in which the foot is placed approximately at right
angles to the leg; in other words, it is of a plantigrade type, one in which

4

34 ANATOMY OF THE RABBIT.

the sole of the foot rests on the ground. Thus the muscles described as
flexors in the foot pass over the heel. They are functionally flexors of
the toes, but extensors of the foot as a whole. Those described as
extensors, lie for the most part on the anterior surface of the tibia, and
are turned from their original course to the dorsal surface of the foot.
They are functionally extensors of the toes, but flexors of the foot as a
whole.

THE NERVOUS SYSTEM.

In the central nervous system, the more general features relate to the
form of the whole structure as a neural tube, containing a central cavity,
the neurocoele. This is differentiated into two portions, namely, a less
modified portion, the spinal cord,or spinal medulla, containing as its
cavity the central canal, and a greatly expanded portion, the brain, or
encephalon, which is divided into a series of paired and unpaired seg-
ments, and contains in its interior a corresponding series of idivisions of
the original cavity, known as its ventricles.

Although the internal structure of the brain is a matter of the dis-
position of its nerve-centres and fibre-tracts, it is customary to estimate
its primary divisions by reference to a general plan, the latter being in
most respects one that is common to vertebrates generally and thus
appears in a less elaborated condition in the embryo, or in the adults of
lower forms. The main features of this plan are indicated in the ac-
companying diagram (Fig. 23).

The brain as first formed in the embryo appears as an anterior ex-
panded portion of the neural tube, or rather 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.

1

The first of the primary divisions, the prosencephalon, or primary
fore-brain, becomes divided during development into two portions,
namely, an anterior portion, the end-brain or telencephalon, which is
largely a paired structure, and a second portion, unpaired, the dience-
phalon, orinter-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. The anterior
portion of the telencephalon, moreover, becomes differentiated, so that a
small terminal olfactory segment, the rhinencephalon, is more or less
perfectly marked off from the rest. In the mammalian brain this part
is chiefly identifiable as the paired olfactory bulb, the latter being the
anterior portion of the olfactory lobe or olfactory brain, and containing
in its interior an extension of the lateral ventricle.

The unpaired portion of the prosencephalon is considered as belonging
in part to the telencephalon and in part to the diencephalon. Its
cavity, the third ventricle, is connected with the lateral ventricles through
the interventricular foramen. Its anterior wall is formed by a transverse
connection of the cerebral hemispheres, the lamina terminalis. ' In all

THE Nervous System. 35

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

B _— bo

A

-

oa

Fic. 23. Plan of the divisions of the vertebrate brain: A, embryonic; B, adult,
projection from dorsal surface; C, adult, sagittal section.

Primary divisions—PR, prosencephalon; T, telencephalon; DI, diencephalon;

S, mesencephalon; RH, rhombencephalon; MT, metencephalon; MY, myelence-
phalon; S, spinal cord.

a.c., cerebral aqueduct; b.o., olfactory bulb; cb., cerebellum; c.m., mummillary
body; c.0., optic chiasma; c.p., pineal body; c.q., corpora quadrigemina; ep., epitha-
lamus; f.i., interventricular foramen; h., hypophysis; h.c., cerebral hemisphere;
hyp., hypothalamus; inf., infundibulum; 1.t., lamina terminalis; p., pons; p.c.,
chorioid plexus of third ventricle: p.cr., cerebral peduncle; t+, thalamus, also in-
dicates position of massa intermedia; v.l., lateral ventricle; v.m.p., posterior

medullary velum; v.q., fourth ventricle.

being in contact with the pituitary body or hypophysis and its base
connected with a small grey elevation, the tuber cinereum. Its cavity is
the recessus infundibuli. Immediately in front of the infundibulum the

36 ANATOMY OF THE RABBIT.

ventral portions of the optic tracts join to form the optic chiasma, and
immediately behind it the floor is thickened, forming .externally a pair
of rounded protuberances, the mammillary bodies. In the brain of the
rabbit this structure consists superficially of a larger median portion with
faint lateral elevations appended to it. Collectively, these structures are
considered to form a major division, the hypothalamus, the latter con-
sisting of two portions, namely, an optic portion, comprising the in-
fundibulum, tuber cinereum, and the optic chiasma, and a mammillary
portion, including the mammillary bodies.

The more dorsal portion of the diencephalon, containing the major
part of the third ventricle, is known as the thalamencephalon. Its
lateral walls are greatly thickened, while its roof is extremely thin,
especially in its anterior part. Here the actual roof of the ventricle is
formed only of a thin layer of tissue, 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 downward into the third ventricle,
reaching out also into the lateral ventricles.

The dorsal portion of the thalamencephalon bears posteriorly the pineal
body, the latter together with certain related structures, the habenulae
and habenular commissure, forming the epithalamus. The general
portion of the thalamencephalon bordering the third ventricle, and
broadly connected across the latter by the massa intermedia, is the
thalamus. In the brain of the rabbit it will be seen that the thalamus is
chiefly indicated externally by a rounded protuberance, the pulvinar.
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. To the medial side of this is a third protuberance, the
medial geniculate body. The medial and lateral geniculate bodies as thus
defined constitute the metathalamus (Fig. 53).

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. Its floor is chiefly formed by a pair of divergent
cords, the cerebral peduncles.

The parts of the mesencephalon and prosencephalon together con-
stitute 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 conjunctiva (Fig.55). The rhombencephalon
itself is divisible into two portions, especially well defined in the
mammalia, namely, the metencephalon, or hind-brain, and the myelence-
phalon, or after-brain. The former includes the small brain, or cerebellum,

37

Tur Nervous SYSTEM.

Cerebrum

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38 ANATOMY OF THE RABBIT.

and a ventral structure of a commissural nature, the pons. The my-
elencephalon 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 membranes underlying the latter. One of these,
the anterior medullary velum, is connected forwards with the mesence-
phalon, 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 dependent 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
af the skull. Of these the spinal nerves are less modified, both in
structure and distribution.

A spinal nerve (Fig. 21) is a product’of two roots, one of which, the
radix posterior, is sensory and arises from the dorsal side of the cord,
while the other, the radix anterior, is motor and arises from its ventral
side. The posterior root bears a root-ganglion. The combined nerve is
distributed in three chief parts, of which two, the anterior and posterior
rami, are distributed as mixed nerves to the skeletal muscle and the skin,
—the anterior ramus being in practically all cases the prominent nerve—
while the third, the ramus communicans, is connected with the sym-
pathetic trunk.

The sympathetic trunk is formed on either side by a series of ganglia
joined together by connecting cords. It is connected not only with the
spinal nerves through the rami communicantes, but also with a series of
prevertebral (coeliac, superior mesenteric, etc.) ganglia and plexuses
from which nerves pass, chiefly in association with the bloodvessels, to
the peripheral ganglia and plexuses of various organs.

The anterior and posterior rami of the spinal nerves contain both
sensory and motor components, and are typical somatic nerves. The
ramus communicans is a visceral connection containing similar com-

Tue Nervous System. 39

ponents, here better described as afferent and efferent. It connects the
central nervous system either with the actual viscera, or with visceral
structures in a general sense, the chief relations of the sympathetic
system being with the smooth muscle of visceral organs, or with that of
the bloodvessels in various parts of the body.

The cranial nerves are comparable in some respects to the spinal
nerves, but in various ways are highly modified structures. The third,
fourth and sixth, respectively oculomotor, trochlear and abducent nerves,
which are distributed to the muscles of the eye, are considered as belong-
ing to the somatic motor division. The second, or optic nerve, and the
nervous portion, or retina of the eye, are specialized parts of the
central nervous system, arising embryonically as an outgrowth of the
latter. The nerves of the remaining special sense-organs, including the
first, or olfactory nerve and the eighth, or acoustic nerve, have been con-
sidered as parts of an extensive system of nerves, which, in lower aquatic
vertebrates, also contains representatives of the branchiomeric series, and
is distributed widely to sense-organs lying in the skin.

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 characteristic as
branchiomeric structures may be indicated. The fifth, or trigeminal nerve,
the nerve of the mandibular arch, arises in two parts, one of which, the
portio major, is sensory, the other, the portio minor, motor. The portio
minor unites with the third or mandibular division of the portio major.
Thus, the terminal branches of all three divisions, ophthalmic, maxillary,
mandibular, are distributed as somatic sensory nerves to the skin of the
head, and, in addition, the mandibular nerve distributes visceral motor
branches to certain muscles (masticatory group, mylohyoid and digastric)
regarded as belonging to this, the first arch. A visceral sensory con-
nection with the mouth is considered to be formed by the lingual branch
of the mandibular nerve and by the palatine branches of the spheno-
palatine ganglion. Both are, however, connected with the central
nervous system through the seventh nerve, the former by the chorda
tympani, and the latter by the great superficial petrosal.

The seventh, or facial nerve is the nerve of the second, or hyoid arch.
It is chiefly distributed as a visceral motor nerve to the cutaneous
muscles of the head. The ninth, or glossopharyngeal nerve, belonging to
the third arch, the tenth, or vagus, belonging to the fourth and succeeding
arches in lower forms, and the eleventh, or spinal accessory nerves, the
latter apparently related to the vagus as a motor portion, are distributed
as visceral motor nerves to the pharyngeal and laryngeal musculature,
and as visceral sensory nerves to various visceral organs, the ninth nerve
supplying the gustatory organs of the tongue. The spinal accessory,
moreover, has a characteristic distribution to the cleidomastoid, sterno-
mastoid and trapezius muscles of the side of the neck and shoulder. 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.

40 ANATOMY OF THE RABBIT.

THE DIGESTIVE SYSTEM.

The digestive system comprises as its chief portions the digestive tube
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.

The parts of the digestive tube may be classified as follows:

1. Oral Cavity. 5. Small Intestine.
Oral cavity proper. Duodenum.
Vestibulum oris. Mesenterial intestine.
Jejunum.
2. Pharynx. Tleum.
Nasal portion.
Oral portion. 6. Large Intestine.
Laryngeal portion. Caecum.
Vermiform process.
3. Oesophagus. Colon.
Rectum.
4. Stomach.

In its most general features the digestive system is significant as an
epithelial tube, in which the food during its passage is subjected to the
action of digestive juices provided by the epithelial glands, and 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 absorptive
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 modifica-
tion 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 (Fig. 20), 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.

Tur DicEstive SYSTEM. 41

In considering the divisions of the digestive tube in the rabbit, the
posterior, or post-cephalic portion, comprising the oesophagus and suc-
ceeding 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 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 that it lies between the heart
and the dorsal aorta, thus exhibiting the original relation of the digestive
tube to the aortic portion of the vascular system. The succeeding
portions of the digestive tube are those associated with the peritoneal
cavity, and with the exception of the terminal portion, the rectum, are
displaced 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 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 backward on the dorsal surface of the mesenterial small
intestine. The duodenum is sharply 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 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. 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 designated as the jejunum, and
the duodenum may be considered together as a more vascular portion
with thicker walls in comparison 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, trans-
verse, 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 descending 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. Two of these, in dissection from the
ventral surface, are concealed by the base of the superior mesenteric artery,
since they lie on its right side. The descending colon is also only nom-
inally related to the left'side of the body wall, its supporting peritoneum,
the descending mesocolon, being closely connected with the mesoduodenum

42 ANATOMY OF THE RABBIT.

of the ascending limb of the duodenal loop. The course of the caecum as
it lies in the body is comparable to two turns of a left-hand spiral, its blind
termination, the vermiform process, being dorsal in position and directed
for the most part backward. It may be observed at this point that in
their vascular supply the more typical divisions, namely, the transverse
and descending colons, 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 ileo-
caecocolic trunk.

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 mammals generally, the
oral cavity is divisible into two portions, of which one is the oral cavity
proper, while the other, the vestibulum 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. Asin other vertebrates, the tongue is a muscular
structure projecting upward and forward into the oral cavity from its
base of attachment on the hyoid apparatus, but its greater elaboration,
as well as the differentiation of special processes, the circumvallate
and foliate papillae, for the accommodation of the gustatory organs, are
features of mammalian significance. The roof of the oral cavity is
formed by an extensive palatal 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 more directly above the aper-
ture of the larynx.

As accessory structures the teeth present two mammalian features;
they are heterodont, or differentiated according to particular regions, and
the adult series, excepting those designated as molars, are permanent
teeth, replacing deciduous, or milk teeth of the young animal. The
condition is thus described as diphyodont in comparison with that in
lower vertebrates, where there is usually a multiple tooth change, new
teeth being developed as required (polyphyodont type). Moreover, 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
bya dental formula. In the mammalia generally the teeth are differen-
tiated into incisors, canines, premolars and molars, and in placental
mammals the full dental formula is indicated as i. 3, c. +, pm. 7, m. 3.
In the rabbit as in other rodents, however, the dentition is greatly
modified by the elaboration of two pairs of incisors 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. 2, c. §, pm. 3,m.3. 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 the lips are in this region
also provided with hairs on their internal surfaces, the oral cavity is
separated almost completely from a small space enclosing the incisor
teeth. This adaptation, however, is not so perfectly developed in the
rabbit as in certain others of the rodent order.

THE RESPIRATORY AND VASCULAR SYSTEMS. 43

The chief features of the pharynx depend on its relation as a common
or general portion of the digestive tube with the tubes of the respiratory
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 a ventral or laryngeal
portion, containing the aperture of the larynx.

THE RESPIRATORY SYSTEM.

In all air-breathing vertebrates the lungs arise embryonically as
ventral outgrowths of the digestive tube, and are secondarily con-
nected with the outside of the body through special perforations of
the anterior portion of the head and through the oral cavity. As
indicated above, this 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
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.

THE VASCULAR SYSTEM.

In the rabbit, as in all vertebrates, the vascular system embraces a
central, muscular organ of propulsion, the heart, and a series of branched
tubes, the bloodvessels, the latter being of three different kinds: (a) thick-
walled, elastic, distributing vessels—arteries; (b) microscopic terminal
canals in the peripheral organs—capillaries ; and (c) thin-walled collecting
vessels—veins.

The chief mammalian feature in this system consists in the division
of the heart into two portions (Plate VII), each consisting of a receiving
chamber, or atrium, and a driving chamber, or ventricle, and the arrange-
ment of their vascular connections in such a way that two complete.
circulations are established. One of these is the long, or systemic circula-
tion. 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, com-
municating with the right atrium of the heart through paired superior
cavals; from the posterior portions of the body through the unpaired
and also 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

44 ANATOMY OF THE Raspit.

the distribution 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 by 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.

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, observable in air-breathing verte-
brates, in which the lungs and their vascular connections become perfected
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 connected with a series of paired
branchial 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 two-chambered plan,
similar to that in fishes, where all the
blood is received by single atrium and is
delivered forward to the gills by a single
ventricle.

; ; The definitive condition of the chief
are aa rental aces arterial vessels is arrived at by an extensive
are indicated in black (systemic) or modification of the branchial plan. As
shaded (pulmonary). 1-6, primary : ° 7 7 i
arches; ao., aorta; a.p., pulmonary indicated in the accompanying diagram
artery; ce, external carotid; ci. in (Fig. 24) the arch condition is retained by

ternal carotid; d.a., ductus arteriosus
(Botalli); i., innominate artery: sd the aorta and by the pulmonary artery,

rere. aud itis interesting to note also that the

primary connections of these vessels, repre-
sented in the embryo by an open canal, the ductus arteriosus
(Botalli), is indicated in the adult condition by a short fibrous
cord, the arterial ligament. The adult aortic arch represents only the
left one of a pair, and since that of the right is only represented
imperfectly by the innominate artery and the base of the subclavian of
that side, a condition of asymmetry results, which is mainly expressed
by the sinistral position of the 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

Tur VascuLar System. , 45

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 these having already been mentioned. In
addition, it is seen that in a mammal,as in terrestrial vertebrates generally,
the base of the pulmonary artery 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
associated 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 asvmmetrical, since from its begin-
ning 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.

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 ramifying in the liver. Thus, in the rabbit, the blood
distributed to the stomach, spleen, and intestine through the coeliac,
superior and inferior mesenteric arteries, is collected into a main
intestinal vessel, the portal vein, and the latter, approaching the liver
through the lesser omentum, divides in that organ into a series of portal
capillaries. The portal capillaries, like the systemic capillaries proceed-
ing from the hepatic artery, unite in the tributaries of the hepatic veins.
In lower vertebrates, although not in the mammalia, a second system of
venous capillaries occurs in connection with the kidneys, and is known as
the renal portal 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 appear in this way being
the lymph glands, or lymph nodes, centres of cell formation, occurring
in the course of the conducting vessels. These as superficial structures
are found either singly, as in the head and neck, or more or less grouped,
as in the axillary and inguinal spaces. As deep structures they are
conspicuous 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 aggregated lymph follicles
(Peyer’s patches) at various points in the intestinal wall.

The conducting portion of the system comprises an extensive series

46 ANATOMY OF THE RABBIT.

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. 52).

The lymphatic vessels of the posterior portion of the body,
including the intestine, unite to form a common canal, the thoracic
duct. The latter lies for the most part between the aorta and the verte-
bral 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.

The lymphatic capillaries are terminal, absorptive vessels, differing
from blood capillaries both in the charactér of their walls and in their
relations to other portions of the system, since they are not interposed
as in the vascular system between vessels’of a larger order. The lym-
phatic vessels connecting the capillaries with the lymphatic trunks form
extensive plexuses, in connection with which the lymph nodes are dis-
tributed.

THE URINOGENITAL SYSTEM.

The urinogenital system comprises two primary systems—reproductive
and urinary—differing widely in their central organs, but associated to a
certain extent by having common ducts. In the rabbit, as indicated in
the accompanying diagram (Fig. 25), 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 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 associated with the reproductive ducts.

In general, however, the relations of the urinary and reproductive
organs involves two chief features. First, in primitive vertebrates, 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 higher mammalia, where
the urinogenital sinus is completely separated from the digestive tube, and
where the urinary ducts are also transferred from a posterior or hypo-
cystic position on the wall of the urinogenital sinus to an anterior or
epicystic position on the dorsal wall of the bladder.

Secondly, there is a more fundamental association between the
reproductive and excretory organs, depending on the circumstance that
the former are primarily in the vertebrates organs connected with the

THE URINOGENITAL SYSTEM. 47

lining of the coelom and discharging their products into the cavity, while
the kidneys are primarily tubular structures communicating also with
this cavity, so that they become modified in part as reproductive ducts.
The coelomic connections of the kidney tubules are with few exceptions
only seen in the embryonic condition, since the definitive kidneys in all
vertebrates are structures in which the tubules are connected with the
vascular system, and have either lost, or, as in the specialized permanent
kidneys of the mammalia, have not developed, the coelomic apertures.

The embryonic development of a mammal includes the formation
not only of a final kidney or metanephros, but also of two embryonic
structures, one of which, the first kidney or pronephros, is embryonic in
all vertebrates, while the second, designated as the mesonephros, or
embryonic kidney, is one occurring in the adult condition of intermediate

Fic. 25, Diagrams of the male (A) and female (B) urinogenital
systems of the rabbit: b., urinary bladder; k., kidney; ur.,
ureter; r, rectum.

(A)—c.p., crus penis; d.d., ductus deferens; ep., epididymis;
g., gubernaculum; t., testis; v.s., seminal vesicle; u.v., male urethra,

(B)—c.c., crus clitoridis; 0., ovary; t.u., uterine tube; u.m.,
female urethra; ut., uterus; va., vagina; vs., vestibulum.

forms. It is from the ducts of the primary kidneys that the reproductive
ducts arise. Thus, in the female of most vertebrates the oviduct opens
by an expanded funnel into the coelomic cavity, usually at some distance
from the ovary; and, although in the rabbit the structure is said to arise
as a secondary development, it exhibits here as in other mammals the
feature of a coelomic opening, coupled with that of close association with

48 ANATOMY OF THE RABBIT.

the ovary, so that the products of the latter, while nominally discharged
into the coelom, are actually received directly into the uterine tube.
The oviduct itself is phylogenetically the oldest of the urinogenital ducts,
since it is identifiable in the embryo as the duct of the pronephros.

In the rabbit, as in all mammals, the testis is connected with the
urethra through the canal formed by the epididymis and ductus
deferens, these structures comprising in a modified form a portion of the
mesonephros and its duct. Since the excretory functions are fully
provided for by the development of a permanent kidney and its duct,
the ureter, the ducts of the embryonic kidney have in the adult no urinary
connections; but in intermediate vertebrates, in which the mesonephros
occurs as an adult kidney, the interesting condition is observable in the
male that the duct of this structure serves both urinary and reproductive.
functions. :

It will be seen in the rabbit that the female genital ducts, apart
from the common urinogenital sinus, include an unpaired portion, the
vagina, and a paired portion, comprising the uteri and uterine tubes.
In all vertebrates up to and including the monotrematous mammalia
the oviducts open separately either into the cloaca, or into the urino-
genital sinus. In the higher mammalia, however, a process of fusion is
observable, extending from the partial coalescence of the vaginae, as
in marsupial mammals, to the complete coalescence of both vaginae
and uteri, as in man. Thus, there are recognized in the mammalia
the types of (a) unpaired uterus—uterus simplex; (b) semi-divided
uterus—uterus bicornis; and (c) completely divided uterus, such as that
of the rabbit—uterus duplex.

In the respective positions of the central organs, as exemplified by the
rabbit, there are several features of general significance. Thus, the
kidneys (Plate VIII) are paired structures lying on the dorsal wall of
the abdominal cavity, where they are interposed between the peritoneum
and the dorsal musculature. They are covered by peritoneum only on
their ventral surfaces. As indicated above, the permanent kidneys of
a-mammal are highly specialized structures, but they show in these rela-
tions features common to lower forms and dependent in both cases on
the primary position of the intermediate mass, from which in the em-
bryo the kidneys are formed.

The gonads are primarily associated with the dorsal lining of the
coelomic cavity, although certain observations on the development of
these structures in the lower vertebrates appear to indicate that their
elements are assembled from other parts of the embryo. In some of the
mammalia, as in all lower vertebrates, the testis occupies an abdominal
position in the adult condition; but usually it undergoes an extensive mi-
gration, passing from the abdominal cavity into a special sac of peritoneum
enclosed by the scrotum. This change—described as the descent of
the testis—is effected through the agency of a muscular cord, -he guber-
naculum. In many cases, as in man, the cavity enclosing the testis is
completely separated from the abdominal cavity, but in the rabbit a
more primitive condition is retained in which the sac of the testis is
widely open to the abdominal cavity, and the organ thus passes freely

THE SERous Cavities. 49

from one cavity to the other. It is also observable in this animal that
the gubernaculum is represented in the adult as a short thick cord
connecting the end of the testis with the wall of the enclosing sac (Fig. 26).
_ In the female the round ligament of the uterus is a structure similar
in a general way to the gubernaculum, and in the rabbit will be seen to
be inserted in a depression of the body-wall resembling both in form and
position a rudimentary vaginal process. The ligament is continued,
however, beyond this point, ending in the wall of the urinogenital aper-
ture. The presence of this structure is an indication that the ovary,
as well as testis, is subject to change in position. In the adult condition,
however, the ovary occupies approximately an original position on the
dorsal wall of the abdominal cavity ; and it will be observed in the rabbit
that the position of the structure is one also defined by the points of
origin of the spermatic arteries and veins of both sexes, with the ex-
ception, however, of the left spermatic vein in the male.

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 completely invested by them.

The serous sacs are extensive body-spaces, derivatives of a primary
body cavity or coelom. They are usually considered 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. 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 imperfectly
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 in terrestrial vertebrates
the lungs. 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 the median portion of the thorax.
There are thus recognizable in a mammal four large serous spaces,
namely, the pericardial, peritoneal, and paired pleural cavities.

The pericardial cavity, the smallest of these spaces, is situated
between the paired pleural cavities. Its enclosing membrane, the peri-
cardium, 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 pro-
jected into them froma medial position. The lining membrane or pleura

5

50 ANATOMY OF THE RABBIT.

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, comprises in a
mammal a general portion, the abdominal cavity, and its posterior ex-
tension into the pelvis—in the male also into the sac of the testis. The
general relations of the cavity to the abdominal organs is indicated dia-
grammatically in Fig. 21. Its lining membrane, the peritoneum, is
divisible into two 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 sur-
faces. The digestive tube, on the
other hand, is removed to such an
extent from the abdominal wall that
the peritonetm forms a complete
serous coat, and is connected with
the parietal peritoneum of the wall
through a thin transparent mem-
brane, 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 trans-
mission of nerves, bloodvessels and
lymph canals. ; :
As indicated above, the relations
of the abdominal portion of the diges-
tive tube are greatly modified by its
elongation and displacement from a
median position. Thus, while in the
embryo the common mesentery is
recognizable as a continuous median

Fic. 26. Diagram showing [the relation of
the testis to its investments: a.i., inguinal

ting; c.e., caput epididymidis; cr., cremaster
muscle; d.d., ductus deferens; g., guber-
naculum; mes., mesorchium; p.t.v. and
v.t.v., parietal and visceral layers of the tunica
vaginalis propria; p.v., cavity of the vaginal
process; s., integument of the scrotum;
S.v., Spermatic vessels; t., testis.

vertical fold, in the adult it follows
the convolutions 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, 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
peritoneum 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 diaphragm. ‘Thus the general condition
is less simple than in the small and large intestines. The peritoneum,

Tue SERovus Cavirizs. 51

passing from the dorsal wall, successively invests the spleen, the
stomach, and the liver, and is reflected from the last-named structure
to the diaphragm and the ventral body-wall through the coronary,
triangular, and falciform ligaments. Its gastric portion is differentiated
into the mesogastrium (phrenicosplenic and gastrolienal ligaments), the
greater omentum, and the lesser omentum. Similarly, in the posterior
part of the body the peritoneum passes from the rectum to the urinary
bladder, enclosing also in the female the vagina. It is then reflected to
the ventral body-wall as the middle umbilical fold.

In the male, as indicated in the accompanying diagram (Fig. 26), 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, and thus represents a permanent vaginal
process. 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 ccnnected 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, 7.e., in a position indicating the original situation of
the testis itself.

In the female the ovary is closely associated with the -dorsal wall
of the abdomen, and its supporting peritoneum, the mesovarium, is in-
significant. 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, how-
ever, 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 56mm., and may be used either in connection with
the general features of topography as outlined above, or for the identi-
fication of various minor structures appearing 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 being because of
the fact that the section is not exactly median, at least in certain places.
Secondly, in using sections of the foetus for gross anatomical features
it is necessary to make allowance in some cases for the different propor-
tions 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 repro-
duced in the plates, although they are indicated in the accompanying
skeleton figures, and may be referred to in this way.

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53

A MEDIAN VERTICAL SECTION OF THE ENTIRE Bopy.

DESIGNATIONS FOR PLATE II.

1. Transverse sinus of dura mater.

2. Dura mater.

3. Pallium of cerebral hemisphere.

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.

9. Thalamus.

10. Optic chiasma.

11. Tuber cinereum.

12. Mammillary 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.

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 cartilage.

32. Maxilla.

33. Hard palate (palatine and maxilla).
34, Presphenoid.

35. Intersphenoidal synchondrosis.
36. Basisphenoid; hypophysial fossa.
37. Sphenooccipital synchondrosis.
38. Basioccipital.

38a. Supraoccipital.

39. Nasal portion of pharynx.

40. Soft palate.

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.
52. Mylohyoideus muscle.
53. Mandible.

54. Occipital musculature.
55. Semispinalis capitis.
56, Rhomboideus minor.
57. Superior portion of trapezius.
58. Atlas. .

59. Epistropheus.

59a. Odontoid process.

60. Third cervical vertebra.
61, Median vertebral vein.
62. Body of hyoid bone.

54

II.

A MEDIAN VERTICAL SECTION OF THE HEAD.

a
or

DESIGNATIONS FOR PLATE III.

. Nasal bone.
. Levator alae nasi muscle.

3. Nasal septum.

. Nasoturbinal cartilage.

5, Maxilloturbinal (concha inferior).
3. Nasal fossa.

. Nasolacrimal duct.

8. Vomeronasal organ and cartilage.

. Premaxilla.

. Small upper incisor,
. Large upper incisor,
. Nasopalatine ducts.

3. Oral cavity.

. Tongue.

. Vibrissae.

3. Caninus muscle.

. Terminals of superior maxillary nerve.
. Buccal glands.

. Buccinator muscle.

. Terminals of inferior alveolar nerve.

. Quadratus labii inferioris muscle.

. Mandible.

3. Lower incisor.

. Meckel’s cartilage (primary mandibular

arch),

. Mentalis muscle.

II.

A TRANSVERSE SECTION OF THE ANTERIOR NASAL REGION.

57

DESIGNATIONS FOR PLATE IV.

1. Superior sagittal sinus of dura mater. 25. Nasal tract; choana.
2. Lateral ventricle. 26. Palatine bone.
3. Cerebral hemisphere. 27. Oral cavity.
4. Pia mater. 28. Palatine nerve.
, 5. Frontal bone. 29. Sphenopalatine ganglion.
6. Cartilage of orbital wing. 30. Infraorbital vein.
7. Mesethmoid cartilage. 31. Internal maxillary artery.
8. Cupula posterior cartilage. 32. Maxillary nerve.
i 9. Obliquus superior muscle. 33. Maxilla.
10. Ophthalmic vessels and nerves. 34. Zygomatic bone.
11. Levator palpebrae superioris muscle. 35. Submaxillary duct.
12. Rectus medialis muscle. 36. Buccinator muscle.

13. Retractor bulbi muscle. 37. Masseter muscle.

14, Rectus inferior muscle. 38. Parotid duct.

15. Sclera. 2. 39. Facial nerve.

16. Retina and chorioidea. 40. External maxillary artery and vein
17. Vitreous body. (anterior facial vein).

18. Lens. | 41. Platysma muscle.

19. Posterior chamber of eye. 42. Inferior labial artery and vein.’
20. Anterior chamber. 43. Mandible.

21. Cornea. fa 44, Genioglossus muscle.

22. Ciliary body and iris. 45. Digastricus muscle.

23. Upper eyelid. 46. Quadratus labii inferioris muscle.
24. Lower eyelid. 47. Geniohyoideus muscle.

IV.

A TRANSVERSE SECTION OF THE ORBITAL REGION.

59

A 09 WD ee

=

=
a

DESIGNATIONS FOR PLATE V.

. Parietal bone.
. Transverse sinus of dura mater.

Superior colliculus.
Cerebral aqueduct.
Isthmus rhombencephali.
Pons.

. Trigeminal nerve.

. Basilar artery.

. Facial nerve.

. Cartilaginous auditory capsule.
. Cochlea.

2. Basioccipiial bone.

3. Tcnsor tympani muscle.

. Tympanic cavity.

. Malicus.

. Tributari.s of posterior facial vein.

. Squamosal bone.

. Cephalic portion of median vertebral vcin.
. Nasal poriion of pharynx.

. Origin of basioclavicularis and levator

scapulae major muscles.

60

. Longus capitis.

. Rectus capitis anterior.

. Oral portion of pharynx.

. Thyreohyoideus muscle.

. Sternohyoideus muscle.

. Greater cornu of hyoid.

. Stylohyoideus major muscle.
. Lingual artery.

. Hypoglossal nerve.

. Tendon of digastricus muscle,
. External maxillary artery.

. Stylohyoideus minor.

. Styloglossus.

. Internal maxillary artery,
. Tympanic bone.

3. Mandible.

. Submaxillary gland.

. Anterior facial vein.

. Internal carotid artery,

A TRANSVERSE SECTION OF THE AUDITORY REGION.

61

DESIGNATIONS FOR PLATE VI.

1. 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.

Qs

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.

Shope

62

. Oesophagus.
. Inferior thyreoid nerve.
. Inferior thyreoid vein.

Trachea.

. Thyreoid gland.
. Cardiac branch of vagus (n. depressor).
. Sympathetic trunk.

Vagus nerve.

. Common carotid artery
. Internal jugular vein.

. Sternohyoideus muscle.

. Sternothyreoideus muscle.

. Sternomastoideus muscle.

. Descending ramus of hypoglossal nerve.
2 External jugular vein.

. Basioclavicularis muscle.

. Levator scapulae major muscle.

. Cleidomastoideus.

. Platysma.

VI.

A TRANSVERSE SECTION OF THE ANTERIOR CERVICAL REGION.

Re

FR SSONS obwNW

DESIGNATIONS FOR PLATE VII.

Semispinalis dorsi. 24. Costal pleura.
Longissimus dorsi. 25. Bone ribs. —
. Tliocostalis. 26. Costal cartilage.
Spinal cord. : .27. Sternum. ‘
Ganglion of posterior root and intercostal 28. Cutaneus maximus muscle.
nerve. 29, Inferior portion of trapezius
Tubercle of rib. 30. Rhomboideus major.
Head of rib. 31. Inferior angle of scapula.
. Sympathetic trunks. 32, Latissimus dorsi.
Azygos vein. 33. Serratus posterior. _ .
Thoracic aorta. 34. Intercostales externi and intcrni
. Oesophagus. 34a. Intercostalis internus.

12a. Right and left vagi. 35. Thoracic portion of serratus antcrior.
Lung. 36. Obliquus externus abdominis. Gy
. Bronchi. 37. Transversus thoracis.
. Branches of pulmonary artery. 38. Pectoralis major.
. Pulmonary veins. 39. Rectus abdominis.
. Right atrium. 40. Anconaeus longus (caput longum of
. Tricuspid valve. triceps). ‘
. Right ventricle. 41. Extensor antibrachii parvus.
. Left atrium. 42. Anconaeus medialis.
. Left ventricle. 43, Anconaeus lateralis.
. Pericardial cavity. 44, Distal extremity of humerus.
. Pulmonary pleura. 45. Proximal portion of radius.

64

Vil.

A TRANSVERSE SECTION OF THE THORAX.

65

WOON DOR who

. Spinal cord.

Vertebral canal.
Vertebral body. $
Sacrospinalis muscle.

Quadratus lumborum.-

Psoas major.
Psoas minor.

. Sympathetic trunk.
. Abdominal aorta.

DESIGNATIONS FOR PLATE VIII.

18, 18a. Posterior and anterior lobules of left
lobe of liver.

19,19a. Right lobe of liver. _ a 2

20. Obliqaus internus abdominis and trans-
versus abdominis.

21. Obliquus externus abdominis.

22. Rectus abdominis.

22a. Cutaneus maximus.

. Inferior caval vein.

. Descending mesocolon.
. Ureter.

. Renal pelvis.

. Renal papilla.

. Left kidney.

. Parietal peritoneum.

. Visceral peritoneum.

66

. Middle umbilical fold.

. Urinary bladder (canal of foetal allantois).
. Umbilical arteries. ,

. Duodenum.

. Pancreas and mesoduodenum.

. Descending colon.

. Parts of mesenterial small intestine.

20. Caecum.

VIII.

A TRANSVERSE SECTION OF THE ABDOMEN.

67

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. 33). 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. 85-97) 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 asa
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 also
present certain features in common, so that it is possible to classify
them into cervical, thoracic, lumbar, sacral, and caudal groups.

A typical vertebra—for the characters of which any one of the
thoracic or lumbar series may be taken (Fig. 27, D-F)—consists of 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 vertebrale). The successive
foramina form an almost complete tube, the vertebral canal (canalis
vertebralis), for the accommodation of the spinal cord.

The body of a vertebra is a cylindrical, or somewhat dorsoventrally
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 epiphysial lines being evident
even in older animals, especially in the lumbar region. The dorsal por-

68

THE VERTEBRAL COLUMN. 69

tion of ‘the body bears on either side the pedicle, or root of the vertebral
arch (radix arcus vertebrae), the dorsal surface of the body forming
in this‘Way the floor of the vertebral foramen. The dorsal portion of
the arch, borne on the pedicle, is distinguished as the lamina. The
anterior and posterior margins of the pedicle are notched, each notch

Fic, 27. Representative vertebrae: A, atlas, anterior surface; B, epistropheus,
lateral surface; C, fifth cervical vertebra, anterior surface; D, fourth dorsal, 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.1., 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 vertebralé; 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. supefior articular process; p.m., mammillary process; p.s.,
spinous process; p.s.a., anterior spinous process; p.t., transverse process; p.tn., trian-
gular 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. :

or incisure being converted, through its association with that of the
adjacent vertebra, into a rounded aperture, the intervertebral foramen
(foramen intervertebrale), for the passage outward of a spinal nerve.

7

70 ‘ANATOMY OF THE RABBIT.

The arch of the vertebra is noteworthy for its projections or processes.
On either side is a horizontal plate of bone, the transverse process (pro-
cessus transversus), and, dorsally, a median projection, the spinous
process (processus spinosus), all three serving for the attachment of the
vertebrae to one another by ligaments, and for the attachment of the spinal
musculature. Special articular surfaces, borne on low articular pro-
cesses (processus articulares), are found 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, which are
directed toward the ventral surface. A certain amount of movement
is permitted by one surface slipping across the other, the mechanism
illustrating the arthrodia, or gliding-joint.

The cervical vertebrae (vertebrae cervicales) are seven in number.
The posterior five are similar, while the anterior two are specially modified
in relation to the skull. The posterior vertebrae (Fig. 27, C) are dorso-
ventrally compressed, their arches low, and the spinous process short.
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 bv a costo-transverse foramen (foramen
transversarium), the latter serving for the passage of the vertebral artery
forward to the head: Through the presence of this aperture, the base
of the transverse process is divided into two parts, namely, a dorsal,
or posterior root (radix posterior), and a ventral, or anterior root (radix
anterior). The anterior root is a coalesced rib, and is comparable in its
general relations to the normal ribs of the thoracic vertebrae.

The first vertebra is the atlas (Fig. 27, 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 in the
dorsoventral direction. It consists of a ventral half-ring, the anterior
arch (arcus anterior), a dorsal half-ring, the posterior arch (arcus pos-
terior), with paired lateral masses (massae laterales) uniting them.
The lateral masses also form 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) on the dorsal surface of the
posterior arch 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 the convex occipital condyles
of the skull. Its posterior surface bears on either side a somewhat
triangular inferior articular facet (facies articularis inferior) for articula-
tion with the epistropheus. These surfaces take the place of the arch-
articulations of ordinary vertebrae. Through the compression of the
transverse process, the costotransverse foramen is converted into a
canal. The anterior aperture of this leads by a shallow groove, the
sulcus arteriae vertebralis, into a second aperture perforating the
posterior arch.

THE VERTEBRAL COLUMN. 71

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 liga-
ment which is stretched. between them 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 (Fig. 27, 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 trans-
verse processes of the atlas form together three main points of attach-
ment for the occipital musculature.

The thoracic vertebrae (vertebrae thoracales) are twelve in number.
They are distinguished chiefly by the possession of articular pits for the
attachment of ribs (Fig. 27, D). A 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. In the
remaining vertebrae a complete articulating surface is formed by two
demifacets, one being on the vertebra to which the rib belongs, the other
on the vertebra immediately in front. The articulation of a rib with a
transverse process is marked 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.

In all vertebrae of the thoracic series the spinous processes are well-
developed. They increase in length to the third, and then become
gradually shorter, although their surfaces are, on the whole, slightly
increased in extent. The anterior ten are directed backward, ‘the elev-
enth is almost vertical, while the twelfth is directed forward, like those
of the succeeding lumbar vertebrae.

The lumbar vertebrae (vertebrae lumbales) are seven in number.
They are large vertebrae, conspicuous for their extensive surfaces and
processes for muscular attachment (Fig. 27, E, F). The transverse
processes continue the general line of the ribs of the thoracic region.
They are directed forward, as well as outward, and the tip of each is
formed by a thin triangular plate (processus triangularis), which represents
a fused rib. At the posterior side of the base of each is a short, flattened
projection, the accessory process (processus accessorius). The spinous
process is especially well-developed, and is directed forward. The
articular processes are rotated upward, so that their surfaces are directed

72 ‘ANATOMY OF THE RABBIT.

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 mammillary processes (processus
mammillares). The latter are most characteristic of the lumbar verte-
brae, but may be seen to arise in the posterior thoracic region as small
elevations of the transverse processes. Each of the first three of the
lumbar vertebrae bears a median ventral projection, the anterior spinous
process (processus spinosus anterior), for the attachment of the lumbar
portion of the diaphragm.

The sacral vertebrae (vertebrae sacrales) are four in number. In
contrast to the true vertebrae—those united by ligament and articular
surfaces—of the remaining portions of the vertebral column, they are
false vertebrae, united in the young by synchondroses, and in the adult
coalesced to form a composite structure, the os sacrum (Fig. 28). The

Fic. 28 The ossacrum: A, ventral (pelvic) surface; B, dorsal surface;
c.v., bodies of coalesced vertebrae; fa., 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., mam-
millary process of first vertebra; pr. promontory; p.s., spinous processes.

axis of the sacrum forms an obtuse angle with that of the lumbar ver-
tebrae, the angle being indicated by a ventral projection, the promon-.
tory (promontorium), formed by the last lumbar and first sacral ver-
tebrae. 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 Riss. 73:

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 processes. 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 foramina 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 mammillary 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 con-
spicuous apertures, the median sacral fora-
mina.

The caudal vertebrae (vertebrae caudales)
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. 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.

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. 29). 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 corres- His. 20.-The Sterium and first
pouding ‘bone-rib. In the succeeding ribs 9p. vette yews 4 7 the true
the angle is gradually replaced by a broad of rib;’ cl.c., neck of rib; er.,
curve. sie; ‘oe. Bade Sessa cue,

Ribs are classified as true ribs (costae m™anubrium sterni; o.c., bone-rib,

3 a p.x., xiphoid process; t.c., costal
verae), and false ribs (costae spuriae). The tubercle.
former—comprising the anterior seven—
are those directly attached to the sternum. The latter—comprising the
posterior five—are either indirectly attached, or unattached. The
unattached ribs are designated as floating ribs.

Generally speaking, the bone-ribs are cylindrical; but the anterior

74 ANATOMY OF THE RABBIT.

five or six are more or less flattened, with their main surfaces 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 convexity, or angle, at. some point toward the
dorsal surface. Passing backward, the point of greatest convexity
changes from a medial to a lateral position. This, together with the
elongation 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 intervening 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 bony thorax is formed by the ribs and the sternum with the
assistance of the thoracic vertebrae. 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); posteriorly, the seventh and succeeding ribs, together with
the posterior thoracic vertebrae and the xiphoid process of the sternum,
enclose a much larger opening, the inferior thoracic aperture (apertura
thoracis inferior). In the natural condition 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 consists of a linear series of six segments, the sternebrae.
The first segment is the manubrium sterni. It is about twice the length
of the middle segments. It is somewhat 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 SKELETON OF THE HEap. : 75

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, to the
posterior end of which is attached a broad, thin plate of cartilage.

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 constituting
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 containing in its wall the
auditory capsules, and the bones of the face (ossa faciei), the latter in-
cluding 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. 31).

A. THE SKULL AS A WHOLE.

The skull is a composite structure, consisting of a large number of
elements, which, with the exception of the mandible, are united by
synarthroses, so that they produce the effect of a continuous mass. The
mandible is a more or less independent structure, articulated with thé
main body of the skull by a typical joint.

The skull is roughly divisible into two portions, namely, an anterior,
facial portion, and a posterior, cranial portion. The cranial portion has
a somewhat conical shape, its apex being directed forward. It is sepa-
rated from the facial portion by a depression on either side of the skull,
the orbital cavity (orbita), which serves for the accommodation 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, 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 surface of the
occipital bone, with the exception, chiefly, of the basilar portion 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

76 ANATOMY OF THE RABBIT.

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 isa 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 some-
what triangular, pointed jugular 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 styloglossus, 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. Toward the dorsal margin of the nuchal surface,
the dorsal surface of the skull is projected backward as a shield-shaped

Fic. 30, 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;
FM, 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, premclars;
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; 1.m., medial
lamina; m.a.e., osseous portion of external acoustic meatus; p.a., alveolar process of
maxilla; p.e., ethmoidal portion of orbitosphenoid; 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 protuber-
ance; p.s., Squamosal 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., zygo-
matic process of maxilla; s, sphenoorbita]l process of maxilla; s.m., spina masseterica;
sq., Squamosal process of squamosal.

promontory. The lateral margin of this projection is the superior nuchal
line (linea nuchae superior). It forms a curved ridge, the position of
which indicates the dorsal limit of the occipital musculature. The
posterior, somewhat tri-radiate tip of the projection is the external
occipital protuberance (protuberantia occipitalis externa), an important

THE SKULL AS A WHOLE. 77

median point of attachment for the occipital muscles and the ligamentum
nuchae.

The ventral wall of the cranial portion is the basal portion (basi-
cranium) of the entire skull. As indicated above (p. 31), 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 segments. It is formed by a linear series of three bones,
namely, 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. As viewed from the ventral surface, it is seen to dis-
appear 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 forms anteriorly a large part of
the boundary of the orbit. The cranial wall of the orbit is partly formed
by two upward projections of the basicranium, namely, the lesser wing
of the anterior sphenoid, or orbitosphenoid, and the greater wing of the
posterior sphenoid, or alisphenoid. The remaining portion is formed by
membrane elements, including the frontal bone of the roof of the skull
and the squamosal bone, the latter distinguishable as the support of the
posterior root of the zygomatic arch. Immediately behind the orbit,
the root of the zygomatic arch projects outward and then downward.
It is formed by a zygomatic process (processus zygomaticus) of the
squamosal bone, and the tip of this forms a vertical plate, which is united
by a horizontal suture with the zygomatic bone. On the ventral side of
the process, close to the cranial wall, is the mandibular 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 supraorbital
process to the base of the zygomatic arch. The dorsal boundary of the
fossa is formed by a pronounced ridge, the temporal line (linea temporalis),
the latter forming also the lateral margin of the roof of the skull in this
region.

e Rehind the posterior root of. the zygomatic arch, the external surface
of the lateral wall is largely occupied by the swollen tympanic bulla
(bulla tympani), formed by the tympanic bone. It contains the capac-
ious tympanic cavity (cavum tympanicum) and certain skeletal structures
of the middle ear, namely, the auditory ossicles (ossicula auditus), the

78 ANATOMY OF THE RABBIT.

relations of which are more fully dealt with below (p. 90). The
dorsal portion of the tympanic bulla is continuous with a short bony
tube which opens at a short distance dorsad by a large oval aperture.
This tube is part of a more extensive canal, the external acoustic meatus
(meatus acusticus externus) which, in the natural condition, leads down-
ward through the base of the external ear to the tympanic membrane.
The tympanic bulla does nat form the lateral wall of the skull in this
region, and is not exposed to the cranial cavity. It is applied closely to
the external surface of the periotic or petromastoid bone, 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 enclosed
between the tympanic bulla and
the jugular process of the occi-
pital bone, where it is readily
distinguishable by its pitted
appearance. Its ventral portion
bears a slender projection, lying
parallel to the jugular process,
the mastoid process (processus
mastoideus).

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 communication with
the outside, and serve for the
passage of nerves and vessels.
The first and largest of these,
the optic foramen (foramen
opticum), occupies the middle

fn.s (0)

portion of the orbit, and trans-

mits, in the natural condition, pon

the optic nerve. Following this Fic. 31. Dorsal surface of the skull: F, frontal;
: 7 - 3 I, interparietal; L, lacrimal; M, maxilla; Ss,
isa vertical slit-like aperture— mastoid porlion of petrosal (petromastoid); N,

: nasal; P, parietal; SO, supraoccipital (squamous
not to be confused with the portion of occipital); SQ, squamosal; ;

perforations of the external *ygometic.
f.mx., maxillary fossa; f.t., temporal fossa;

lamina of the pterygoid process 1n.s.. superior nuchal line; ‘1t., temporal line;

ak : ey p.f., frontal process of premaxilla; .mxX.,

the superior orbital fissure maxillary process of frontal; p.o.e., external

(fissura orbitalis superior). It ee Eee tg ote
zs or and posterior supraorbital process:

represents both the superior frontal; p.sc., subcutaneous process at occa?

: p.z., zygomatic prosess of squamosal; .z.m,,

orbital fissure of. the normal zygomatic process of maxilla; s.f., froctal spine”

mammalian skull and_ the $.m., spina masseterica.

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

‘Tue SKULL AS A WHOLE. 79

process presents three foramina, of which the largest, anterior, and
medial one, the anterior sphenoidal foramen, 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 pterygobuccinnator) of the mandibular nerve. On the
medial side of the base of the medial lamina of the pterygoid process
there is a shallow longitudinal groove, representing the pterygoid canal
(canalis pterygoideus) of the human skull. 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, the foramen ovale of the
typical mammalian skull, and serves to transmit the mandibular portion
of the fifth nerve and the internal carotid artery. Looking into the aper-
ture 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 an-
terior end of a canal transmitting the internal carotid artery; the pos-
terior end of this canal, the point at which the internal carotid artery
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 com-
munication 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 trans-
verse 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, however, 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 space enclosed by the cranial portion of the skull is the cranial
cavity (cavum cranii). Its form depends on the external configura-
tion of the brain. It is divisible into three portions, known as the
cranial fossae. The anterior cranial fossa (fossa cranii anterior) is a

80 ANATOMY OF THE Rassit.

small division lodging in the natural condition the olfactory bulbs of
the brain. The middle cranial fossa, the largest division of the cavity,
lodges the enlarged cerebral hemispheres. The posterior cranial fossa is a
small division extending backward to the foramen magnum, and lodging
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 posi-
tion 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 portion 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 sphe-
noid. It contains a large
central depression, the hypo-
physial fossa (fossa hypophy-
seos), which in the natural Fic. 32. Ventral surface of the skull: AS, alisphenoid
condition lodges the hypo- {ola nasny):,b, tasceriita (asier portion of x
physis or pituitary body. The EXO, exoccipital; M, maxilla; PL, palatine; Pa
aperture of the fossa is partly Sas; "G0, sanheccen bus ce oe ee
enclosed laterally by a pair pital); SQ, squamosal; T, tympanic; 2¥, zygomatic.

$ “ é é i ; ¢c.hy., hypoglossal canal; c.o., occipital
of pointed posterior clinoid condyle; f.c.¢., external carotid foramen; f.in., incisive
processes (processus clinoidei h:,, 4, jugtlar foramen: fu, foramen lacerum;
posteriores), the tips of which EP Bicaiey pelatme foramen; f.s.a., anterior sphe-
. : .a.€., osseous portion of external
are directed forward; and a acoustic meatus; p.j., jugular process; p.o.e., external
corresponding pair of anterior cite! protuberance; ppl. palatine process of maxiliag
clinoid processes lie at the _ /ateral laminae of pterygoid process of posterior sphenoid;
; ¢ s.m., spina masseterica.
anterior end of the fossa, with
the tips directed backward. The posterior, and also dorsal wall of
the fossa, described as the dorsum sellae, leads by an abrupt curve

THe SKULL AS A WHOLE. 81

backward 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 cranial fossa, the lateral walls of the skull are greatly compressed,
so that the anterior portion of the bdsicranium, especially the body of the
antérior 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 lodges in the natural condition 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 hypo-
glossal canal. The superior orbital fissure is almost ventral in position
to the foramen opticum, and is connected backward with the foramen
lacerum by a broad groove, the sulcus sphenoidalis, which lodges in the
natural condition 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 subarcuate or floccular fossa (fossa subarcuata s.
floccularis). It lodges in the natural condition 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 open-
ing, the internal aperture of the facial canal (canalis facialis), which
serves for the transmission of the seventh cranial (facial) nerve. Imme-
diately 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
above, and resembling superficially the complete common tube repre-
sented by the internal acoustic meatus of the human skull.

The facial portion of the skull is largely formed by the investing
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 cheek-teeth. The maxilla bears the anterior

82 ANATOMY OF THE RABBIT.

root of the zygomatic arch, the latter being formed partly by a short
zygomatic process arising from its lateral surface, by the zygomatic 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 trans-
mission of the infraorbital vessels and nerves from the orbit to the face.

The ventral portion of the maxilla is associated with the palatine
bone to form the hard palate (palatum durum). This structure is repre-
sented chiefly by a bony palatine bridge connecting 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 portion 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 supra-
orbital 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. The latter
are ccnverted by ligament 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 sub-
cutaneous process (processus subcutaneus). On the ventral side of its
base is the orbital opening of the nasolacrimal canal (canalis nasola-
crimalis), 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 lacri-
malis. Finally, in the ventral anterior angle of the orbit, the bases of
the 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 forward 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 pre-
maxilla, with the assistance of paired roofing elements, the nasal bones.
Apart from the incisive foramina, which are closed in the natural con-
dition, the cavity is open at two points. Posteriorly it communicates
with the ventral surface of the skull by the choanae, which, in the rabbit,
are incompletely divided. Anteriorly it opens to the outside by the-

Tue SKULL AS A WHOLE. 83

piriform aperture (apertura piriformis). The cavity is divided into right
and left portions, the nasal fossae. In the divided skull it is seen that
the division 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 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 vomero-
nasal 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).

The delicate, foided, or scroll-like turbinated bones, characteristic of
the nasal cavity, are borne on its posterior and lateral walls. Occupying

Fic. 33. The skull in vertical section: BO, basioccipital (basilar portion of occipital);
BS, basisphenoid (body of posterior sphenoid); ET, ethmoturbinal; F, frontal; I, inter-
Sloe M, maxilla; MT, maxilloturbinal; N, nasal; NT, nasoturbinal; P, parietal:

L, palatine; PMX, premaxilla; PR, presphenoid (body of anterior sphenoid); PT, petrous
yan of petromastoid; SO, supraoccipital (squamous portion of occipital); T, tympanic;

, 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., foccular
fossa; f.h., hypophysial fossa; f.in., incisive foramen; f.s., sphenopalatine foramen; 1., per-
pendicular plate of the ethmoid; m.a.i., internal acoustic meatus; 0., 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 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 dis-
tinguishable from a more dorsal and posterior series of broader folds,
which together constitute the ethmoturbinal. In the rabbit,asin mammals
generally, the latter is divisible into a more dorsal elongated portion
attached to the nasal bone, the nasoturbinal, and a more ventral portion,
also posterior portion, the ethmoturbinal proper, composed of several

84 ANATOMY OF THE RABBIT.

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
distinguished as sensory (olfactory) turbinals and respiratory turbinals.

The mandible (mandibula) is composed of two portions, united
anteriorly by the symphysis mandibulae. Each half comprises a hori-
zontal 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 artticulation with the skull. The

Fic. 34. Lateral surface of the left ramus 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.,
condyloid process; t.m. and t.pt., masseteric and pterygoid
tuberosities.

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 natural condition 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 elon-
gated 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.

Tuer Bones oF THE SKULL. 85

B. THE BONES OF THE SKULL.
1. THE OCCIPITAL BONE.

The occipital bone (os occipitale) is the first of the basicranial seg-
ments 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 in this relation the posterior,
dorsal, and ventral boundaries of the posterior cranial fossa. The re-
maining 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 forma-
tion of the foramen magnum. In the young animal (Fig. 11) they are
represented by separate 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 ven-
tral. Its anterior margin is united with the posterior margin of the
basisphenoid by a thin, transverse cartilage union, the sphenooccipital
synchondrosis (synchondrosis sphenooccipitalis). 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 petrotympanic 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 pos-
terior 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 down-
ward 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 con-
necting the basioccipital and exoccipital contains the jugular fossa and
the apertures representing the hypoglossal canal. Its anterior margin+
bears a jugular incisure (incisura jugularis), forming the occipital

8

86 ANATOMY OF THE RaBBIt.

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 basi-
occipital, in a horizontal plane. Its external surface bears the superior
nuchal lines and the external occipital protuberance. A pair of lateral
wing-like expansions rest upon, and partly overlap, 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 sur-
face bears a longitudinal groove, lodging in the natural condition the
median 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 com-
plex 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,
ot 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 basi-
occipital 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, as described
above, by the hypophysial fossa and related structures, namely, the
dorsum sellae and the posterior 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 both with the foramen
cavernosum and the hypophysial fossa.

The alisphenoid extends at first laterad, 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, dorsally by the squamosal,
and posteriorly by the petrotympanic. The anterior margin of its root
encloses with the basisphenoid, and to a certain extent with the orbito-
sphenoid, the superior orbital fissure. The foramen lacerum is formed

* by the posterior margin of its root in association with the petrotympanic.

The external surface of the alisphenoid is convex, both toward the

THE BoNnEs OF THE SKULL. 87

orbit and toward the ventral surface of the skull. In the posterior por-
tion of the orbit this surface bears a jagged elevation, the crista alae
magnae. The internal surface forms a portion of the floor and antero-
ventral 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 hori-
zontal. The medial lamina ends ventrally in a hooked projection, the
hamular process (hamulus pterygoideus). In the young animal this por-
tion is formed of an elevation of cartilage tipped by a separate mem-
brane element, the pterygoid bone. The pterygoid fossa is formed in
part by the medial and lateral laminae and in part by the divided pos-
terior end of the palatine bone. The posterior base 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 por-
tions, 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 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 pre-
sphenoid being thus excluded.

The orbitosphenoid forms a long, low plate, lying in the ventral por-
tion of the orbit, and divided by a shallow notch at the level of the optic
foramen into a posterior portion, the orbitosphenoid 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 foramen. 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

88 ANATOMY OF THE Raspit.

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
asingle 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 appear-
ing 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 associated that it is proper to describe them as forming a
petrotympanic bone. '

The squamosal bone (cs 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 supraoccipital and petrotympanic, and
ventrally with the alisphenoid. Its posterior margin bears a prominent,
slightly decurved squamosal 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. Its base 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 petrotvmpanicum) is a somewhat 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 supra-
occipital, 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

Tuer Bones oF THE SKULL. 89

cranial fossa. The dorsal portion of the bone corresponds in thickness
with the wing of the supraoccipital with which it is articulated. The
posterior surface is applied to the anterior surface of the 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 distin-
guished 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 stylo-
mastoid foramen lies between the latter and the external acoustic
meatus.

The petrous portion, as viewed from its medial surface, is roughly
oblong; it is placed obliquely with reference to the basioccipital and
basisphenoid. The floccular 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, repre-
sents the hiatus canalis facialis of the human skull. It transmits the
great superficial 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, tym-
panic 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. The medioventral margin of the bone
is articulated with the basioccipital, 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 foramen 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 thé petro-

90 ANATOMY OF THE RABBIT.

tympanic 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 sur-
face displayed being as indicated in Fig. 35. 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 petromastoid projects as a smooth, white, convex ridge, the prom-
ontory (promontorium). Above and behind the promontory the
tympanic cavity is extended toward the mastoid portion of the bone

Fic. 35. Petrotympanic portion of the auditory complex of the left side x3.
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 tympani).

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; mso., ''"
supraoccipital margin of petromastoid; p.m., mastoid process; st., stapes; t.a.,

aperture of auditory tube. se

’ vibe
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 perilym-
phatic space containing 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 elements,
namely, the malleus, incus, and stapes, which bridge the space inter-

THE Bones oF THE SKULL. QI

vening 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 por-
tion. 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 supraoccipital. It is the
first of the membrane roofing elements of the cranium proceeding for-
ward from the supraoccipital, and in the rabbit’s skull is not fused with
the occipital segment.

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 sur-
rounding 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 lamb-
doidal. 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 tentorium 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 per-
manent 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 portion 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

92 ANATOMY OF THE RABBIT.

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 maxillary 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 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 re-
moved. 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 por-
tions 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, pos-
terior 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 maxilloturbinal, and contains at this point
a pouch-like cavity, termed the marsupium nasale. The whole struc-
ture is comparable to one of the folds of the ethmoturbinal proper;
but it is frequently seen 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.

THE Bones of THE SKULL. 93

stout, backwardly-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 cells (cellulae ethmoidales) 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 orbito-
sphenoid and the sphenoorbital process of the maxilla.

11. THE INFERIOR TURBINATED BONE.

The inferior turbinated bone (concha nasalis inferior), or maxillo-
turbinal, is a finely ridged structure, situated anteriorly in the nasal fossa,
and supported by the maxilla and premaxilla. It represents the simi-
larly-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 ethmoturbinal. In the natural con-
dition it is covered by a non-olfactory epithelium, and is thus distinguish-
able in function as well as in position from the latter.

12. THE MAXILLA.

The maxilla, the largest element of the facial region, is associated 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 spheno-
orbital. In the adult condition 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 sur-
face, 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 enclosing 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 longitu-

94 ANATOMY OF THE RABBIT.

dinal 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 corresponds in position with
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 premaxilla.

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 com-
pared 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 has fused with it
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 con-
taining 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 boundary of the incisive foramen. Its dorsal surface
forms part of the boundary of the piriform aperture, the remaining por-
tion 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 (pro-
cessus 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.

Tuer Bones oF. tHE SKULL. 95

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 zygo-
matic 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 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 con-
siderably 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 posterior portion bears a shelf-like
projection, the ala vomeris, which assists in the support of the ethmo-
turbinal.

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 surrounding bones,
and in the dried skull is frequently missing unless care has been taken
to keep it in place. It consists of a basal portion, somewhat rectangular
on its orbital surface, and of two processes, namely, the subcutaneous
process and the hamulus lacrimalis. The subcutaneous process is the
prominent hook-like projecting 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 naso-
pharynx. It consists of two portions—horizontal, and perpendicu-
lar. The horizontal portion (pars horizontalis) is that lying in the plane

96 ANATOMY OF THE RABBIT.

of the palatal surface. Itisarticulated in front with the palatine process
of the maxilla, the suture between the two bones enclosing the greater
palatine foramen, the ventral termination of the pterygopalatine canal.
The perpendicular portion (pars perpendicularis) is the vertical plate
extending 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 orbitosphenoid, but a small posterior portion is free, so that
the anterior portion of the basisphenoid 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 body of the mandible (corpus mandibulae) ;,
and (2) a posterior, vertical plate, the mandibular ramus (ramus mandi-
bulae), 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 corres-
ponding to a similar space in the upper jaw and serving chiefly for the
accommodation of the lips, which in this region encroach 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. Run-
ning backward from the symphysis there is a broad horizontal ridge,
representing the mylohyoid line (linea mylohyoidea), the line of attach-
ment 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

Tur Hyor. 97

of the horizontal portion with the ramus. The corresponding 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, distin-
guished 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 pro-
nounced, though shallow, pterygoid fossa for the insertion of the ptery-
goideus internus muscle. A somewhat similar, but less developed,
masseteric fossa occupies the corresponding 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 anteroposterior 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
articulating 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 re-
duced 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 for-
ward 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. 36) is a stout, somewhat wedge- -
shaped bone lying in front of the larynx and between the angles of the
mandible. Its ventral portion is connected with the thyreoid cartilage
of the larynx by the median hyothyreoid ligament. With its lateral
portion are articulated two independent elements, termed the lesser and
greater cornua. The lesser cornu (cornu minus) is a small, partly car-
tilaginous structure, attached to the anterodorsal angle of the hyoid,
and connected through the stylohyoideus minor muscle with the jugular
process of the skull. The greater cornu (cornu majus) is a larger element
extending obliquely dorsad, and similarly suspended from the jugular

98 ANATOMY OF THE RABBIT.

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
elements commonly occurring in mammals and other vertebrates in this
region. The muscle tendon contains near the jugular process a small
ossification representing a detached styloid process. This connection,
together with the hyoid bone itself, indicates the relation of the em-
bryonic 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 d
of the thyreoid cartilage of the larynx
by the lateral hyothyreoid ligament.

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 clavi-
cles of the two ‘sides together form the
pectoral girdle. The pectoral girdle is
lightly constructed, and, apart from its
muscular connections, which constitute

Fic. 36. Lateral surface of the
hyoid and larynx: c.a., arytenoid
cartilage; c.c., cricoid cartilage; c.i.,
inferior cornu of thyreoid cartilage;

¢.m., lesser cornu of hyoid; c.mj.,

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; ,

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; 1.h.m., median hyothyreoid
ligament; m.ct., cricothyreoideus
muscle; o.h., hyoid bone; s.m.,
stylohyoideus minor muscle; s.mj.,
stylohyoideus major muscle; try
cartilaginous tracheal rings.

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 regular series,
of which nine form the carpus, five the metacarpus, and fourteen the
phalanges of the digits.

THE SCAPULA.

The scapula (Fig. 37) 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 from the
human condition, in which, from the transverse widening of the thorax,
the corresponding surfaces are more nearly ventral and dorsal. Of its

Tus ANTERIOR LIMB SKELETON. 99

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 armpit. The corresponding angles are medial,
inferior, and lateral. 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 of its extent, and ends ventrally in a free pro-
jection, 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 depression, the sub-
scapular fossa (fossa subscapularis), which is triangular in shape and

Qa.-.L-

Fic. 37. Lateral surface of the left scapula: a., acromion,; a.i., a.l., and
a.m., inferior, lateral, and medial angles; c.g., glenoid cavity; cs., neck
of the scapula; fs. and f.i., supraspinous and infraspinous fossae: m.,
metacromion; m.a., m.s., and m.v., axillary, superior, and vertebral borders;
p.c., coracoid process; s.s., scapular spine.

occupies practically the entire surface. The apex or lateral angle of
the scapula, sometimes termed the head of the bone, is expanded to a
considerable extent in comparison with the slender portion—the so-
called neck of the scapula (collum scapulae)—connecting it with the
body of the bone. It bears a concave depression, the glenoid cavity
(cavitas glenoidalis), for articulation with the humerus. The articu-
lating surface is borne chiefly on that part of the bone corresponding to
the axillary 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 lying toward the medial surface of the bone.

100 ANATOMY OF THE Rapsit.

THE CLAVICLE.

The clavicle (clavicula) is imperfectly developed in the rabbit, con-
sisting of a slender, arcuate rod of bone, tipped by cartilage, which lies
‘in the interspace between the manubrium sterni and the head of the
humerus. It occupies only a portion of this interspace, being attached
medially by the sternoclavicular ligament and laterally by the cleido-
humeral ligament.

THE HUMERUS.

The humerus (Fig. 38) is typical of the long bones of the proximal
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 proxi-
mal 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 enar-
throsis, 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
elevation, the lesser tubercle (tuberculum
minus). It is separated by a longitudinal
furrow of the anterior surface, the inter-
tubercular groove (sulcus intertubercularis),
from a much larger lateral elevation, the
greater tubercle (tuberculum majus). Ex-
tending distad from the latter is a tri-
angular area, the humeral spine (spina
humeri), the tip of which reaches almost
to the middle of the bone and forms a
pronounced angle on its anterior surface.

The distal extremity of the humerus
bears a grooved articular surface, the
trochlea humeri, for articulation with the tk.
radius and ulna. -On ite lateral side is a [26.92 Untenot Suctacs of thelett

: A umerus: c., capitulum; c.h., head of
smaller surface, the capitulum humeri, for humerus; 1. and e.m., lateral and
articulation with the radius alone, Imm- 70s) pmegnevies: “2, redial tessa)
mediately above the trochlea the medial and cular groove; ey trochlea humeri;
lateral portions of the bone are thickened to tubercles. saad
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

Tue ANTERIOR LIMB SKELETON.

a similar point of origin for the flexor muscles
of the ventral or volar surface. Between the
epicondyles the extremity 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 greatly 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.

THE RADIUS AND ULNA.

The radius (Fig. 39) 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 antero-
dorsal in its general position, but is crossed
on 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 extensive articular surface, meet-
ing both the 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 articula-
tion with the navicular and lunate bones.

The ulna (Fig. 39) is a somewhat S-shaped
bone, the shaft of which is vertically flattened,
so that it possesses two main surfaces, respec-
tively anterodorsal and posteroventral. The
former, in conjunction with the related sur-
face 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 semilunaris),

3

Fic. 39. Skeleton of the fore-
arm and hand from the dorsal
surface: R, radius; U, ulna; C,
carpus; M, metacarpus; P,
phalanges; I-V, metacarpal
bones; c., central bone; cp.,
capitate; c.r., head of radius;
f.a.c., carpal articular surface of
radius; h., hamate bone; iss.,
semilunar notch of the ulna;
l., lunate bone; mi., lesser mul-
tangular; mj., greater mul-
tangular; n., navicular; ol.,
olecranon; p.s., styloid process ‘of
the ulna; tr., triquetral bone;
u., ungual phalanges.

102 ANATOMY OF THE RABBIT.

the articulating surface of which continues that of the medial
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. The
distal extremity 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 (processus
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 interosseous
ligament, the radius and ulna are unable to change their positions with
respect to one another; in other words, the radius is unable to rotate
on an axis formed by the ulna, the fore foot being fixed in a position
comparable to that of pronation in the human hand (cf. p. 33).

THE CARPUS.

The carpus (Fig. 39) 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 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 metacarpals. 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.

Tue Posterior Limp SKELETON. 103

THE METACARPUS AND PHALANGES. :

The metacarpus (Fig. 39) comprises five stout elements, the meta-
carpal.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 metacarpals, 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 sesamoidea), developed in
connection with the ligaments of muscles, are found on the volar surface
of the foot in association with certain of the joints. They occur in trans-
verse pairs at the metacarpophalangeal articulations and in linear pairs
at the articulations of the second with the third phalanges. The pisi-
form 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 symphysis,
thus forming the pelvic girdle. The distal portion—comprising, as in
the anterior limb, the supports of the free extremity—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 elements, of which six form the tarsus, five
the metatarsus, and twelve the phalanges.

THE COXAL BONE.

The coxal bone (os coxae) (Fig. 40) is a somewhat triradiate struc-
ture, the posterior limbs of which are united, so that they enclose a large
aperture, the obturator foramen (foramen obturatum). It is firmly
articulated with the sacrum, and is united with its fellow of the opposite
side by a thin strip of cartilage containing a small amount of fibrous
material. The latter connection is the pubic symphysis (symphysis pubis),
better termed in the rabbit the pelvic symphysis, 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 elements,
namely, the ilium, ischium, and pubis. They form the three rays
of the coxal boné, and are united with one another in 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

104

ANATOMY OF THE RABBIT.

excluded through the development 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 describedas if distinct.

The ilium (os ilium) is the anterior,
also somewhat dorsal, portion of the
bone; that part extending forward from
the acetabulum. 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 ex-
panded 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). 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 eleva-
tion, the iliopectineal line (linea iliopect-
inea), 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),

Fic. 40. 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;
ec p., body of pubis; cr., iliac crest; e.i.,
iliopectineal eminence; f.a., acetabular

fossa; f.0., obturator foramen; das
acetabular notch; imi., lesser’ sciatic
notch; i.mj., greater sciatic notch; li.,

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., superior
anterior spine; s.i., ischial spine; s.p.,
symphysis pubis; s.p.i., inferior posterior
spine; t.i., ischial tuberosity; t.p., pubic
tubercle.

for connection with the sacrum. The dorsal margin is thin and straight.
Posteriorly, where it is associated with the greater sciatic notch, there
is a small projection, the inferior posterior spine (spina posterior inferior)
Anteriorly it passes by a broad angle into: the anterodorsal margin of

Tus Posterior Limp SKELETON. 105

the bone, the latter forming the projecting end of the wing, which is dis-
tinguished 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). The ven-
tral 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 ischium (os ischii) extends backward from the acetabulum, its
axis continuing thatof the ilium. It consists of a basal portion, or body
(corpus oss. ischii), asuperior ramus, and aninferiorramus. 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). 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).

The superior ramus of the ischium is the continuation backward of
the body of the bone. It is a somewhat flattened plate of bone, the
thicker dorsal portion of which terminates in two blunt projections.
One of these, the ischial tuberosity (tuber ischiadicum), forms the pos-.
terior end of the bone, while the other extends in a lateral direction and
is described as the lateral process (processus lateralis). The inferior
ramus is that part of the ischium which extends from 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 imme-
diately below the acetabulum, a superior ramus extending from the body
to the symphysis, and an inferior 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 tubercle (tuberculum
pubicum), and laterally a more extensive elevation, the iliopectineal
eminence (eminentia iliopectinea). The latter is more conspicuous in
older specimens, where it is easily recognizable by its jagged outline.
Its lateral margin is continuous with the iliopectineal line.

THE FEMUR.

The femur (Fig. 41) is a somewhat S-shaped bone, the body being
very slightly arcuate, while of the two extremities, the distal one is
bent downward, forming the articulation of the knee, the proximal one,

106.. ANATOMY. OF THE Rapsit.

with its various processes, slightly upward in association with the pelvis.
In considering the general form, it will be remembered that in the natural
sitting posture of the rabbit, the position of the femur is approxi-
mately horizontal, the convex surface of the shaft, which is equivalent
to the anterior 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 girdle.
This portion is separated from the main part of the extremity by a con-
stricted area or neck (collum femoris), so that, unlike the case of the
anterior limb, the points of muscle attachment: 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 termi-
nal, hook-like projection, while the other,
the third trochanter (trochanter tertius), is
the smaller lateral crest. On the medial
side of the bone, immediately distal to the
head, there is a triangular elevation, the
lesser, or second trochanter (trochanter
minor s. secundus). Posteriorly, these pro-
jections 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 inter-
condyloid fossa (fossa intercondyloidea).
Immediately above the condyles, on the
anterior surface of the bone, the inter-
condyloid. fossa is replaced by a broad
groove, the patellar ;surface (facies patel-
laris), which, in the natural condition,
accommodates the convex internal surface
of the patella. The medial and lateral Fic, 41. Anterior surface of the left
portions of the bone, intervening between femur: el. and cm. lateral and
the distal portion of the patellar surface eb wits ie ee ee

< ; and e.m., lateral and medial epicon-
and the tips of the condyles, provide dyles; f.p., patellar surface; t.mi.,

slightly elevated, roughened surfaces, the trochanter minor; t.mj., trochanter
major, including t.p. and t.t., the first

medial and lateral epicondyles, for muscular and third trochanters.
attachment.

Tue Posterior Limp SKELETON. 107

THE TIBIA-AND FIBULA.

The tibia (Fig. 42) 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 triangular in section, the
main surfaces being respectively anterolateral, anteromedial, and pos-
terior. The anterior border is formed by a stout ridge-like elevation,
the tuberosity of the tibia (tuberositas tibiae), which in the natural con-
dition serves for the insertion of the quadriceps femoris, the extensor
tendon being carried over the knee by the
patella and the patellar ligament. The arti- tt.
cular portion is slightly differentiated into J a
medial and lateral condyles corresponding to ey | OMT
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 inter-
condyloid eminence (eminentia intercondy-
loidea), and also posteriorly by a depression
of the articular border, the posterior inter-
condyloid fossa. A corresponding anterior
intercondyloid fossa lies in front of the inter-
condyloid eminence, but is poorly differ-
entiated.

The fibula (Fig. 42) 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 bv 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
distinguishable even in older animals.

The combined distal extremities of the tibia __ mé.
and fibula bear a roughly rectangular articular 7 ™%-~~*"~—
surface for the tarsus. The tibial portion of
this surface presents two grooves, separated ine oe ee
by a ridge, for articulation with the trochlea ci. and cm. lateral and medial
tali. On its medial sideis a small projection, Se gg Rae Toe ag a ara
the medial malleolus (malleolus medialis). oe mallecli;

The fibular portion presents a_ trans-
verse groove for the convex articular surface of the calcaneus. Imme-
diately above it, on the lateral side of the bone, is a prominent projec-
tion, the lateral malleolus (malleolus lateralis). It forms the anterior
boundary of a groove which in the natural condition lodges the inser-
tion tendons of the peroneal muscles.

108 ANATOMY OF THE RABBIT.

THE TARSUS.

The tarsus (Fig. 43) comprises six elements, the tarsal, or ankle-bones
(ossa tarsi), which, like the corresponding bones of the carpus, are
arranged in proximal and distal rows. An exception is to be made, how-
ever, for one element, the navicular, which occupies an intermediate
position. The proximal row contains two elements, the talus and cal-
caneus. 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,
these two surfaces together forming the chief
portion of the ankle-joint. Its distal end,
termed the head of the talus (caput tali), pro-
vides a convex articular surface for the navi-
cular bone, and is separated from the larger
trochlear portion by a slightly constricted
intermediate portion or neck (collum tali).
Its ventrolateral border is extensively arti-
culated with the calcaneus. 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 prom-
inent elevation for articulation with the
fibular side of the tibiofibula. Its medial
surface bears a flat, shelf-like process, the
sustentaculum 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 metatarsal bone and the second
and third cuneiform bones, on the other.
Its position is more nearly that of a central Fic. 43. The bones of the left foot,
element than is the case with the bone called P°ygd from the dorsal surface:

» metatarsus;

by this name in the rabbit’s carpus. In this phalanges. II-V, the four me-
tatarsal bones: cb., cuboid; cl.,

connection it will be remembered that the calcaneus; c.s., second cuneiform:

: s c.t., third cuneiform: f.a.,
carpus and tarsus, like other parts of the limbs, articular surface for fibular side of
are primarily constructed on the same plan. the tibofibula: n navicular; t,

talus; t.c., tuber calcanei; t.t.,

The distal row of the tarsus contains ¢rochiea tall.
three elements, namely, the second and
third cuneiform ‘bones and the cuboid bone. The two former and
especially the first, are smaller bones, articulated 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 con-

THE Postertor LIMB SKELETON. , 109

dition—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 accom-
modation of the peculiar insertion tendon of the peronaeus primus
muscle. ;

THE METATARSUS AND PHALANGES.

The metatarsus (Fig. 48) comprises five elements, of which four are
fully developed and greatly exceed in size the corresponding bones of
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 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 lies in association
with the medial condyle of the femur, while the remaining two are asso-
ciated respectively with the lateral condyle of the femur and that of the
tibia. The sesamoids of the foot are situated at the metatarsophalangeal
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 presupposes
in the first place that the entire dissection is to be’ made on a single
specimen, and secondly 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 itself 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 atid prove them by personal drawings and de-
scriptions of selected parts. In this connection he will do well to bear
in mind that while dissection is nominally a means of obtaining anatom-
ical 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 superficial
skeletal points may be made out as follows:

1. The division of the body into the head (caput), neck (collum),
trunk (truncus), tail (cauda), and the 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.

EXTERNAL FEATURES. “111

(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 compar-
able to the conjunctival fold of the human eye.:

(e) The external ear (auricula), and its canal, the external
acoustic meatus (meatus acusticus externts), leading to the
tympanic membrane.

(f) 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 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.

(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 contained in its ventral wall: The
mammary nipples (papillae mammarum), eight (to ten) in
number on the ventral surface of the breast and abdomen.

(f) 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).

(b) The position of the elbow (cubitus) in comparison with the
knee.

112 ANATOMY OF THE RABBIT.

(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). ;

(b) 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 hailux, does not appear above the integument.

Tue ABDOMINAL WALL, 113

Il. THE ABDOMINAL WALL.

1. Place the animal in the supine position. Make a median in-
cision of the skin of the ventral surface extending from the pubic
symphysis to the tip of the mandible, being careful not to cut through
more than the skin itself. Make three transverse incisions on the left
side, the first on the medial surface of the arm and extending to the
elbow, the second midway between the anterior and posterior limbs, the
third on the medial surface of the thigh and extending to the knee.
Work the flaps loose from the surface, using the handle of the scalpel,
until the side of the trunk is well exposed. On the right side of the
body it is sufficient to clear the middle line. Identify the structures
as follows:

On the skin:
(a) The thick compact connective tissue forming the corium.
(b) The imbedded hair-follicles.

(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 aggregated
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.

(f) 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 humeral spine. The last-
named portion appears on the medial surface of the humerus.
Insertion: The skin of the dorsolateral surface of the trunk.
The fibres are directed upward and backward. 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 epigastric, a
branch of the femoral (p. 149).

The abdominal vein, a conspicuous vessel‘in the female, traverses the
lateral portion of the abdominal wall from the inguinal furrow to the
axillary fossa, lying on the external surface of the cutaneus maximus. It
is a tributary of the inferior epigastric (p. 134), and anastomoses forwards
with the external mammary vein of the axilla. The corresponding
arteries are the external mammary branch of the long: thoracic (p. 137),
and the abdominal branch of the inferior epigastric, the latter arising
directly from an external spermatic trunk.

The inguinal lymph nodes (lymphoglandulae inguinales) are small,
oval, brownish bodies lying in the inguinal furrow.

114 ANATOMY OF THE RABBIT.

2. Remove the cutaneus maximus from the surface. 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.

(d) The lumbodorsal fascia (fascia lumbodorsalis), a broad, white
sheet of connective tissue extending over 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 posterior ten ribs by separate slips,
the xiphoid process, and the lumbodorsal fascia. Insertion: The linea
alba and the inguinal ligament. 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.

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 and
aponeurotic portions of the muscle; 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 lumbo-
dorsal 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. It contains the rectus abdominis.

(b) The transverse muscle (m. transversus abdominis). Origin:
Seven posterior ribs, a third sheet of the lumbodorsal fascia,
and the inguinal ligament. Insertion: The lineaalba. 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. Insert-
jon: At the anterior end of the pubic symphysis. Itis a thin,
strap-like muscle, enclosed by the aponeurosis of the internal

Tue ABDOMINAL WALL, 115

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. 134). It anastomoses
with the internal mammary (p. 174). It gives off the external 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. An abdominal branch of this vessel
passes forward on the abdominal wall as described above.

5. Divide the remaining portion of the wall on the left side, and its
whole thickness on the right, by a transverse incision, so that the viscera
are fully exposed. Note on the internal surface of the wall the smooth
serous investment here forming the parietal peritoneum (peritonaeum
parietale).

116 ANATOMY OF THE Razsir.

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. 49). 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 peritonaeum 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 ex-
tension of the latter into a mesentery for the support of the structure
from the dorsal body-wall. Note the parallel arrangement of the
arteries and veins, and also their frequent anastomoses. Lymphatic
vessels (lacteal vessels) accompany the bloodvessels in the mesentery,
but being transparent are not readily recognizable. Lymph nodes also
occur, but in this portion of the mesentery they are aggregated at its
dorsal attachment, or root (radix mesenterii).

1. Displace the posteroventral portion of the liver forward, exposing
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 ventriculi).
It lies for the most part to the left of the median plane.

(d) The cardia, or area of junction with the oesophagus.

(e) The fundus, a small sac-like portion lying to the left of the
cardia.

(f) The pyloric limb (pars pylorica), lying to the right of the
body 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 muscular
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 dark red, elongated

THE STOMACH AND SPLEEN. 117

body, the spleen (lien). 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.

(b) The peritoneum is projected backward from the greater

(c)

curvature as a free fold, the greater omentum (omentum
majus), which covers the intestines to a certain extent. It
usually contains fat. It is composed of four leaves, of which
two come from the surface of the stomach and two others
pass forward in a dorsal position from the free posterior
border to unite with the transverse mesocolon.

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 vessels of this relation, 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 with the lesser
curvature.

3. Working on the left side between the dorsal surface of the stomach
and the body-wall, remove sufficient of the peritoneum to expose the
first portion of the abdominal aorta as it emerges from the diaphragm.
Passing in the direction of the stomach is a median ventral branch, the
coeliac artery, the distribution of which may be traced. The following
structures, however, should first be identified.

10

(a)

(b)

(c)

(d)
(e)

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
yellowish disc-shaped body lying some distance from the
anteromedial margin of the left kidney.

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 coeliac ganglion (g. coeliacum) of the sympathetic nervous
system lies in front of the superior mesenteric artery.

The superior mesenteric ganglion (g. mesentericum superius)
of the sympathetic system lies immediately behind the su-
perior mesenteric artery, and also on its lateral walls.

")

118 ANATOMY OF THE RABBIT.

(f) The nerves proceeding from the coeliac and superior me-.
senteric ganglia accompany the corresponding arteries,
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. 178), around the reduced left crus of the diaphragm
and crossing the aorta obliquely enters the superior mesen-
teric ganglion.

(h) A portion of the pancreas (cf. p. 122) is seen in the peritoneum
after the branches of the splenic artery have been severed
(4, a).

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 (rr. pancreatici) to the pan-
creas 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 surface, 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 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.

(b) 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 curva-
ture 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
cesphagus, 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 connect with the terminal
ramifications of the vagus (p. 119).

THE STOMACH AND SPLEEN. 119.

(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. pancreaticoduoden-
alis superior), but a small recurrent branch, the right gas-
troepiploic artery (a. gastroepiploica dextra), traverses the
greater omentum to the greater curvature where it ana-
astomoses 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
gastroepiploic 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 backward in a

similar manner on the dorsal surface of the oesophagus.

4. 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 (cf. Fig. 15) may be distinguished and separated from one another
by dividing the loose tissue of the tela submucosa. On the 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 differen-
tiated from that of the oesophagus.

120

ANATOMY OF THE RABBIT.

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 ad-
dition to the primary circulation formed by the hepatic artery and
veins, the ramifications of the portal system. It is an appendage of the
digestive tube, its connection with the latter being through the common

bile duct.

1. Examine the general 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.

(c) The gall bladder (vesica fellea), situated on the posterior

surface of the right anterior lobule.

(d) The quadrate lobe (lobus quadratus), an imperfectly de-

(e)

veloped lobe lying to the medial side of the gall bladder.
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.

2. Trace the peritoneal connections as follows:

(a)

The lesser omentum, represented by the hepatoduodenal
ligament.

(b) The falciform ligament (lig. falciforme hepatis), a broad

(c)

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 arcuate 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 coronary ligament (lig. coronarium hepatis), a short
circular fold, continuous with 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)

(b)

(c)

(a)

(b)

(c)

THE Liver. 121

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.

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.

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, being careful not to injure
the central tendon of the diaphragm, which resembles the coronary
ligament.
following:

Remove the liver and examine its dorsal surface for the

The inferior vena cava; it is 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.
The renal impression (impressio renalis), an extensive
excavation of the right posterior lobule for the accommoda-
tion of the right kidney.

122 ANATOMY OF THE RABBIT.

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 large intestine (intestinum
crassum). Both are greatly elongated and convoluted. In examining
them care must be taken to avoid injury to the bloodvessels and me-
senteries, 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.
41, 50.

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 end of this loop, when traced from the right side,
disappears in the peritoneum and may then be picked up ina 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 is
somewhat more difficult to follow on account of the adhesions of its
peritoneum with that.of the large intestine.

2. Examine the aivieians of the duodenal loop and related structures,
as follows:

(a) The superior, descending, transverse (horizontal), and as-
cending portions of the duodenal loop.

(b) 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. 3B, p. 11). Its principal portion is here
seen as a diffuse brownish mass lying in the mesoduodenum.
Its duct (d. pancreatis) opens into the posterior portion of
the ascending limb.

(©) The superior pancreaticoduodenal artery, a branch of the

™ gastroduodenal (see p. 119), passes backward on the first
portion of the descending limb. :

(f) The inferior pancreaticoduodenal artery (a. pancreaticoduo-
denalis inferior), a branch of the superior mesenteric (p.125),
enters the mesoduodenum from the left side and supplies the
major portion of the loop. An anterior branch an-
astomoses with (e).

Tur INTESTINES. . 123

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).

(b) The darker coloration, due to the thinner walls, which allow
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. Also 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.

(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.

(d) The mesenteric lymph glands (lymphoglandulae mesentericae)
are aggregated at the dorsal root of the mesentery, where
they form a compact mass surrounding the base of the
superior mesenteric artery.

(e) The wall of the sacculus rotundus shows externally a hexagonal
pattern on account of the presence init of a large number
of lymph follicles. Similar structures, forming oval areas
about 3mm. in diameter and 5mm. in length, may be found
along the intestinal wall (aggregated lymph nodules of Peyer).

(f) 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.
Its course is comparable to two turns of a spiral. Its closed end, formed
by the vermiform process (processus vermiformis), 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, (intestinum 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. ,

124 ANATOMY OF THE RABBIT.

5. In the caecum the following features may be distinguished:

(a) The wall, which is otherwise smooth, is divided by a spirally
atranged constriction, the ‘latter denoting the position, °
internally, of a fold of the mucous tunic, the spiral valve.

(b) The vermiform procéss is a narrow, light-colored 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.

Fic. 44. Plan of the connections of the large and small
intestines: c., ascending colon; cae., caecum; h., haustra;
i., ileum; s.r., sacculus rotundus; t.c., band of the colon;
v.s., Spiral valve.

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 forwards on the right side of the
dorsal body-wall. This portion is greatly elongated in the
rabbit, and instead of passing directly forward follows:a
tortuous course. It is composed of five principal limbs,
united by flexures. Three of the limbs are directed for the
most part forward, the remaining two backward.

The first limb of the colon bears three rows of small.saccu-
lations, 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 run together toward the anterior end of the first limb.

(b) The transverse colon (colon transversum)' is a short segment,
beginning forwards 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 INTESTINES. 125

The descending colon (colon descendens) passes backward to
a point in front of the pelvis, where it is replaced by the
rectum.

The descending mesocolon, which connects this portion
with the dorsal body-wall, should be noted on account of
its relation to the inferior mesenteric artery and sympathetic
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. Lay out the
mesenterial small intestine, so that the mesentery and its bloodvessels
are exposed. Remove the lymph glands from about the base of the
mesenteric artery, and trace its branches as follows:

(a) The middle colic artery (a. colica media), a small vessel arising

from the left wall and passing to the transverse colon.

(b) The inferior pancreaticoduodenal artery (p. 122) arises at

(c)

the same level, but from the right wall.

-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,
anastomosing with a branch of the superior mesen-
teric trunk.

(3) An anterior ileocaecal artery to the terminal fourth
(third limb) of the caecum proper and related por-
tion 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 posterior portion of the third
limb of the caecum.

126 ANATOMY OF THE RABBIT.

(8) Terminal branches to the parts, about the sacculus
rotundus; anastomosing with (4).

(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. The end of the superior mesenteric artery has
the relation of one of the intestinal arteries. It anastomoses
forwards witha single branch given off from the side of the
vessel opposite to the intestinal arteries, and the latter in
turn anastomoses forwards with a branch of the appendicular
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 supérior), 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. 118)
accompanying 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 dividing the rectum close in front of the pelvis, and severing
the peritoneal attachments, the intestines may be separated and laid out
in an extended condition. The relations to one another of the ileum,
caecum, and colon are studied to much better advantage than in the
natural position.

Tur URINOGENITAL SYSTEM. 127

VI. THE URINOGENITAL SYSTEM.
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. By removing the peritoneum and adipose capsule 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 sur-
face of the organ.

(c) The ureter, or duct of the kidney, a white tube passing back-
ward 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 twelfth intercostal artery (a. intercostalis xII),
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.

2. Divide the kidney, beginning the incision at the hilus and re-
moving the ventral half. 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. The enclosed space is largely occupied by a conical
projection of the kidney substance, the renal papilla (papilla
renalis). |

(b) The cortical substance (substantia corticalis); distinguish-
able as a narrow peripheral zone of the kidney substance.

(c) The medullary substance (substantia medullaris), forming
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, however, possesses
a slightly divided margin.

128 ANATOMY OF THE RABBIT.

The distinction of medullary and cortical portions depends on differ-
ences in the arrangement of the minute tubules which compose the kidney.
The medullary substance is largely composed of straight collecting tubules
converging on the renal papilla, while the cortical substance is occupied
by convoluted portions of the tubules and their vascular connections, the
glomeruli. In the natural condition the two parts are also distinguishable
in coloration, the cortical substance being darker. In embalmed animals,
however, the color features 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 ventral surface of the
rectum in the male and from the uterus in the female, to the
bladder, and after investing the latter passes to the ventral
abdominal wall. The dorsal peritoneum 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 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 hypo-
gastric, 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. - Make a longi-
tudinal incision through this muscle, cutting forward into the abdominal
cavity. On spreading apart the two flaps 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

THE URINOGENITAL SystTEM. 129

abdominal wall, forms the internal lining of the sac of the
testis (cf. p. 51). The sac is widely open to the abdominal
cavity, so that the testis passes freely from one cavity to the
other.

(b) The male reproductive gland, the testis, with its associated
vessels and duct, occupy the cavity of the sac, the testis
being suspended from its dorsal wall.

(c) The gubernaculum, a short thick cord containing smooth
muscle fibres, 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 con-
tinuous with the mesorchium, a broad vertical fold of peri-
toneum connecting the testis forwards with the dorsal body-
wall.

(e) The first portion of the duct of the testis, the epididymis,
forms a thickened mass at the anterior end of the testis, and
extends backward as a thinner cord along its side. The
thickened anterior portion is the caput epididymidis and
the contracted posterior portion the cauda epididymidis.
The second portion, the ductus deferens, leaves the testis at
its posterior end, where it is firmly attached to the guberna-
culum. The connection with the epididymis may be shown
by carefully separating the duct from the gubernaculum
and the side of the testis.

(f) The internal spermatic artery (a. spermatica interna) arises
from the abdominal aorta, that of the left side immediately
behind the origin of the inferior mesenteric. It enters the
anterior end of the testis.

(g) The spermatic vein (v. spermatica) is formed by a network of
vessels, the plexus pampiniformis, which surrounds the
internal spermatic artery in its posterior portion. It 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.)
Owing to the open communication of the testis sac with the abdominal

the association of the ductus deferens with the spermatic vessels to form
a spermatic cord (funiculus spermaticus) is very imperfectly expressed.

2. The connections of the deferent ducts with the common urino-
genital tube and related parts may be displayed by dividing the sym-
physis and dissecting in the interior of the pelvis. The structure and
attachments of the penis should first be examined.

Apart from its terminal portion, the glans penis, and the urethra, the
body of the penis is chiefly formed of a pair of hollow fibrous structures,
the cavernous bodies (corpora cavernosa penis). Each of these is firmly
attached to the posterior margin of the ischium by a fibrous cord, the
crus penis. The latter is largely concealed by a short thick ischiocaver-

130 ANATOMY OF THE RABBIT. :
nosus muscle, the origin of which occupies a similar position on the
ischium. The penis is also attached to the symphysis hy a short but
stout suspensory ligament (lig. suspensorium) and by a small pubo-
cavernosus muscle lying between the latter and the ischiocavernosus.
The attachments of the penis should be severed and the symphysis
divided. By pressing apart the two sides.of the pelvis the urinogenital
tubes, with the penis and the 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 and to
the seminal vesicle. The internal
pudendal .artery (a. pudenda inter-
na), accompanied by the corres-
ponding 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 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 ver-
tebra, 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.

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
Urptiiga, It com Fic. 45, The male urinogenital ducts and related

* Ic. . e male urinogenita: ucts and relate
prises a short pros- srchures. viewed from the Jateral sania, ee

1 1 7 - auther: a., anal aperture; ay ourethra:
tatic portion an rela gland; c.c., corees paverncenas mad. ducts de-
tion to the genital ferens; g.a., anal (rectal) gland; g,i., inguinal gland;

g.p., glans penis; par., paraprostatic glands; pr.,
ducts, a much prostate; r., rectum; ur., ureter; u.v., urethra

longer membranous ae v.s., seminal vesicle; v.u.,

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.

. THE URINOGENITAL SYSTEM. 131

(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.

(d) 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 urethal 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 be made out.

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 thekidney. 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.

(b) 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 ovi-
duct, 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.

(f) The mesosalpinx is the peritonéum supporting the uterine
tube. It is continuous with the mesovarium.

(g) The uterus, the second portion of the oviduct; distinguished

132 ANATOMY OF. THE RABBIT. .

by its greater diameter and muscular walls. The size of this
portion is enormously increased in animals which contain or
have borne young.

(h) The mesometrium is the supporting peritoneum of the uterus,
and is a continuation of the mesosalpinx. The mesometrium,
mesosalpinx and mesovarium together constitute the broad
ligament (lig. latum uteri).

(i) The round ligament of the uterus (lig. teres uteri) crosses the
broad ligament, and 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 (cf. p. 49).

(j) 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, the structure and attachments of
the latter being then examined as follows:

(a) The cavernous bodies (corpora cavernosa clitoridis) form the
body of the structure, as in 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
on either side, the former being medial in position.

The attachments of the clitoris should be severed and the symphysis
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 note p. 130).

In the urinogenital ducts examine the extent of the vagina back-
wards and its connection with the canal of the bladder to form the
common vestibulum. The latter is comparable to the male urethra
(ef. p. 47, Fig. 25). The bulbourethral gland (gl. bulbourethralis) (cf.
p. 131) lies on the dorsal wall.

By slitting open the vestibulum and extending the incision 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.

THE ABDOMINAL AorTA, ETC. _ 133

VII. 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 abdominal
aorta (aorta abdominalis), extends from the hiatus aorticus of the
diaphragm to the seventh lumbar vertebra, where it is replaced by the
paired common iliac arteries. It passes backward in a median position
along the ventral surfaces of the bodies of the vertebrae. Its natural
continuation backwards on the sacrum and the caudal vertebrae is
represented by the greatly reduced median sacral artery.

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), small
vessels arising in the hiatus aorticus and passing to the
diaphragm.

(b) The twelfth intercostal artery (a. intercostalis x1), arising
on either side from the renal artery, and passing laterad to
the body-wall.

(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 (d), each through
a common trunk.

(d) 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. 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 trunk, the
branches of which pass to the posterior limb, the wall of the pelvis, and
the pelvic viscera. It gives off the iliolumbar artery (a. iliolumbalis),
which passes laterad to the body-wall, and then divides into two branches
the connections of which may be traced as follows: |

11

134 ANATOMY OF THE RABBIT.

(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 as the
femoral artery. It gives off the inferior epigastric artery
(a. epigastrica inferior), which passes forward on the medial
portion of the abdominal wall (see note p. 115).

(b) The hypogastric artery (a. hypogastrica) is the smaller medial
branch, directed backward on the dorsal wall of the pelvis.
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 (see note p. 130) to the
side of the rectum. The main vessel leaves the pelvic cavity,
passing to the lateral side of the abductor caudae anterior,
and reappears posteriorly as the internal pudendal (note
p. 180). The intermediate branches pass to the posterior
limb and the side of the tail (p. 149).

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. 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. 121).
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 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,
sacral, and caudal portions may be traced on either side by working
between the abdominal aorta (or its continuation, the median sacral
artery) and the body-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 two are much
larger than the others. The caudal portion comprises two minute
ganglia and an unpaired terminal ganglion uniting the two trunks.

THE ANvERIOR Lime. 135

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.
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, in-
separable from the platysma but lying beneath it, the depressor conchae
(parotideoauricularis) posterior, which is inserted into the external base
of the ear. The entire sheet of muscle 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.

For the general muscular relations of anterior and posterior limbs see p. 33.

*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: Sphenooccipital syn-
chondrosis. Insertion: Metacromion. :

The superficial cervical artery (p. 173) 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 (cervical) portion: External occipital protuberance and
the ligamentum nuchae. Insertion: Metacromion and
stpraspinous fascia. ;

Inferior (thoracic) portion. Origin: Spinous processes of the
thoracic vertebrae and the lumbodorsal fascia. Insertion:
Dorsal two-thirds of the scapular spine. The muscle forms
a broad triangular sheet on the lateral surface of the shoulder.

The levator scapulae major, basioclavicularis, and trapezius should
be divided. On the ventral surface of the origin of the superior
portion of the trapezius and levator scapulae- major may be found
the ventral rami of the third and fourth cervical spinal nerves. The
great auricular nerve (n. auricularis magnus) passes from the third to
the ear.

*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.

i . oh ant if ye 5 a wie
136 ANATOMY OF THE RABBIT.

(e) The rhomboideus minor. Origin: Ligamentum nuchae.
Insertion: Anterior two-thirds of the vertebral border of the
scapula. ,

(f) The rhomboideus major. Origin: Spinous processes of the
first seven thoracic vertebrae. Insertion: Posterior third of
vertebral border.

. 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.).

(g) The levator scapulae minor. Origin: Mastoid and supra-
occipital portions of the skull. Insertion: Medial surface of
the inferior angle of the scapula.

(h) 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 alter-
nating 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.

(a) The latissimus dorsi. Origin: Lumbodorsal fascia and four
posterior ribs. Insertion: Humeral spine. A long flat
triangular muscle, covering a considerable portion of the
lateral surface of the thorax; having its dorsal angle 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: Humeral spine.

A branch of the thoracoacromial artery appears between this muscle
and the deltoidens.

(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 (b). Some of the posterior
fibres are inserted highest on the humerus.

The two muscles should be separated and cut across.

(d) The pectoralis tertius (p. minor). Origin consisting of two
portions;

First portion: Middle line of the sternum between the attach-
ments of the second to fourth ribs.

second portion: Manubrium sterni, extending to the level of
the first rib.

Insertion: The superficial fibres of the first portion are attached
to the clavicle. The remaining fibres, combined with those

(e)

f)

Tue ANTERIOR Limp. 137

of the second portion and those of the pectoscapularis, pass
to the dorsal side of the clavicle and over the shoulder to be
inserted on the scapular spine.

The pectoralis quartus. Origin: The sternum, from the
attachment of the fourth to seventh costal cartilages. In-
sertion: 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 sternum at the point of
attachment of the first costal cartilage. Insertion as indi-
cated above. A slender muscle lying behind and lateral to
the second portion of (d). In order to make out its extent
the first portion of (d) should be divided.

BLOODVESSELS AND NERVES OF THE AXILLARY Fossa.

By dividing the remaining pectorals and the clavicle, the blood-
vessels and nerves of the axillary fossa will be exposed.
*The axillary artery (a. axillaris), the continuation of the subclavian,
crosses from the first rib to the medial surface of the humerus, where it
is replaced by the brachial artery. Its branches include:

(a) The thoracoacromial artery (a. thoracoacromialis); it arises

from the anterior wall and passes laterad to the shoulder, reach-
ing the latter at a point directly above and in front of the head
of the humerus. A superficial branch of this artery passes
between the pectoralis primus and the deltoideus, giving
twigs on either side.

(b) The lateral (long) thoracic artery (a. thoracalis lateralis) is a

(c)

(d

war

larger branch given off from the posterior wall. Its branches
include short anterior vessels to the pectoral muscles and
long (external mammary) branches, especially developed in
the female, to the side of the thorax. —

The subscapular artery (a. subscapularis) is a large branch
which passes around the axillary border of the scapula, per-
forating the teres major muscle, and is distributed to the
muscles of this region, including the cutaneus maximus. A
branch of this vessel, the thoracodorsal artery (a. thoraco-
dorsalis), passes backward to the latissimus dorsi.

The superficial cervical artery (p. 173) crosses the ventral surface

of ue brachial plexus, passing obliquely laterad to the side of the
neck.
The deep artery of the arm (a. profunda brachii) is given off
at about the point of origin of the subscapular. It passes
to the posterior surface of the humerus giving branches to
the shoulder, and is continued distad on the lateral surface
of the anconaeus medialis and afterwards of the lateral head
of the brachialis as the radial collateral artery. This artery
accompanies the branches of the radial nerve.

138 ANATOMY OF THE RABBIT.

**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 con-
tinued as the subclavian. It receives the lateral thoracic and sub-
scapular veins, which accompany the corresponding arteries, and also
the cephalic vein (p. 143), 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 ansae of the ventral rami of the posterior five cervical
and first thoracic spinal nerves. The cervical ansae 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 re-
placed by the three chief trunks of the free extremity, the radial, median,
and ulnar nerves (p. 143). The suprascapular nerve (n. suprascapularis)
is a large nerve formed from the fifth cervical ansa; it enters the muscle
in the region of the neck of the scapula and passing around the
superior border of the bone is distributed to the supraspinatus and
infraspinatus muscles. The subscapular nerves (nn. subscapulares),
arising from the sixth and seventh ansae, are distributed to the subsca-
pular, teres major, and latissimus dorsi muscles.

The axillary lymph glands (lymphoglandulae axillares) are pink or
brownish bodies lying in the fat of the axillary fossa.

4. 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. 143) should be traced before
separating the muscles of the front of the forearm.

Note the supraspinous and infraspinous fasciae covering the corres-
ponding portions of the lateral surface of the shoulder.

(a) The deltoideus. Origin: Lateral portion of the clavicle and
the cleidohumeral ligament. Insertion: Anterior surface of
the humerus in its distal third. The muscle is a continuation
of the basioclavicularis.

‘(b) The abductor brachii superior. Origin: The acromion. In-
sertion: Distal portion of the humeral spine.

(c) The abductor brachii inferior. Origin: Infraspinous fascia.
The end of the muscle forms a curved line over the dorsal
portion of the infraspinatus, leaving only a small triangular
portion of the latter exposed. Insertion: The distal portion
of the muscle passes beneath the metacromion, which also
serves as a point of attachment, and is replaced on the lateral
surface of the humerus, beneath the abductor brachii superior,
by the long thin tendon, through which it is inserted.

The abductores are also considered as second and third portions of
the deltoideus.

THE ANTERIOR Limes.

139

The abductor brachii inferior should be separated from the in-
fraspinatus and divided, the distal end being reflected together with

the metacromion.

(d) The infraspinatus. Origin: Posterior portion of the lateral

surface of the scapula, including the spine.
Greater tubercle of the humerus.

infraspinous fossa.

Insertion:
The muscle fills the

(e) The supraspinatus. Origin: Anterior portion of the lateral
surface of the scapula (supraspinous fossa), supraspinous
fascia, and, to a certain extent, the subscapular fascia.
Insertion: Greater tubercle of the humerus.

(f) The subscapularis. Origin:

Entire medial surface of the

scapula. Insertion: Lesser tubercle of the humerus.

(g) The teres major. Origin:
Dorsal portion of the
axillary border of the
scapula. Insertion : In
common with the latis-
simus dorsi on the ante-
rior surface of the
humerus.

(h) The teres minor. Origin:
Ventral portion of the
axillary border of the
scapula. Insertion:
Greater tubercle.

(i) The coracobrachialis.
Origin: Coracoid process.
Insertion: Distal portion
of the upper third of the
humerus on its medial
surface.

5. Muscles arising from _ the
scapula and humerus and inserted on
the proximal ends of the radius and
ulna (extensors and flexors of the
forearm), (Fig. 46).

A. Extensor (anconaeus) group.
The muscles arise for the most part
behind the axis of the humerus, and
are inserted on the olecranon.

(a) The extensor antibrachii
parvus (anconaeus quar-

Anterior

Lateral

Posterior

Fic. 46. 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.

tus). Origin: Fascia of the medial surface of the humerus,
Insertion: Medial surface of the olecranon.

The muscle should be divided, or detached from its origin, and re-

flected’

!

140 ANATOMY OF THE RABBIT.

(b) The anconaeus minimus (epitrochleoanconaeus). Origin:
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 mediale (anconaeus medialis): Posterior surface of the
humerus.
The three portions are practically 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.

(b) 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 abductores muscles. Insertion: In common
with the biceps.

6. 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 the individual digits). The long insertion tendons pass through
perforations of the dorsal carpal and transverse (ventral) carpal liga-
ments (Fig. 47).

A. Extensor group. The muscles have a general area of origin from
the lateral epicondyle of the humerus and the anterodorsal, or antero-
lateral surface of the radius and ulna. Insertion dorsal.

(a) The extensor carpi radialis longus. Origin: Lateral epi-
condyle. Insertion: Base of the second metacarpal.

(b) The extensor carpi radialis brevis. Origin: Lateral epi-
condyle. 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 metacarpal.
The muscle is partly concealed by (e). Its tendon forms a
conspicuous cross with those of (a) and (b).

(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 epi-

THE ANTERIOR Lims. 141

condyle and proximal end of the ulna. Insertion: By four
tendons on all phalanges of the four lateral digits.

(f) The extensor digiti quarti proprius. Origin: Lateral epi-
condyle. 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.

(h) The extensor carpi ulnaris. Origin: Lateral epicondyle and
proximal portion of the lateral surface of the ulna. Insertion:
Base of the fifth metacarpal.

Dorsat

em,
Lateral

Volar:

Fic. 47. Transverse section of the distal end of the
forearm.’ Showing the relative positions of the muscle-
tendons: a.p., abductor pollicis; a.r., radial artery;
a.u., ulnar artery; e.c.u., extensor carpi ulnaris; e.d.c.,

. extensor digitorum communis; e.m.p., extensor digiti
quinti proprius; e.p.i., extensor pollicis et indicis;
e.q.p., extensor digiti quarti proprius; e.r.b., extensor
carpi radialis brevis; e.r.]., extensor carpi radialis longus;
f.c.r., flexor carpi radialis; f.c.u., flexor carpi ulnaris;
f.d.p., flexor digitorum profundus; f.d.s., flexor digitorum
sublimis; 1.c.d., dorsal carpal ligament; 1.c.t., transverse
carpal ligament; n.m., median nerve; n.u., ulnar nerve;
p., palmaris; r., radius; u., ulna; v.c., cephalic vein;
v.r., radial vein; v.u., ulnar vein.

B. Flexor group. The muscles have a general area of origin from the
medial epicondyle of the humerus and the posteroventral or postero-
medial surface of the radius and'ulna. Insertion volar.

(a) The pronator teres. Origin: Medial epicondyle. Insertion: —
Ventral surface of the radius.

(b) The flexor carpi radialis. Origin: Medial epicondyle. In-
sertion: Base of the second metacarpal.

(c) The flexor digitorum sublimis. Origin: In common with the
ulnar portion of the profundus from the medial epicondyle;
proximal portion of the ulna. Insertion: Bases of the second
phalanges of the four lateral digits.

142 ANATOMY OF THE RABBIT.

(d) The palmaris. Origin: Medial epicondyle. Insertion: Super-
ficially on the volar fascia. This extremely slender muscle
lies between the superficial portion of the profundus and
the flexor carpi ulnaris. ;

(e) The flexor digitorum profundus. Origin in four portions:
Superficial portion: Medial epicondyle.
Radial portion: Ventral surface of the radius.
Middle portion: Ventral surface of the ulna.
Ulnar portion: Medial epicondyle in common with (c)
Insertion: By five tendons on the bases of the ungual
phalanges.

(f) The flexor carpi ulnaris. Origin: Medial epicondyle and
medial surface of the olecranon, forming two short but
separate heads. Insertion: Pisiform bone.

7. Muscles arising from the bones of the hand and inserted on the
individual digits:.
(a) The flexor digiti quinti. Origin: Pisiform bone and tendon
sheath of the flexor digitorum profundus. Insertion:
Sesamoid bones of the metacarpophalangeal joint of the
fifth digit, extending to the ungual phalanx.

(b) 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 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 metacarpophalangeal
joints.

BLOODVESSELS AND NERVES OF THE ARM AND FOREARM.

*The brachial artery (a. brachialis), the continuation of the axillary,
passes distad on the medial surface of the arm between the biceps and
the anconaeus medialis. 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 ventromedial
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,

Tur AnTERIOR Limes. 143

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. Itis formed in front of the elbow by the union
of two vessels, the radial and ulnar veins, which accompany the corres-
sponding 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 superficial 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 abductor
brachii superior and the anconaeus lateralis. It disappears from this
surface in the triangular space enclosed by these muscles and the inser-
tion of the levator scapulae major, receiving at this point a large tributary
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 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 anconaeus
medialis, appearing afterwards on the lateral side of the brachialis in
company with the collateral radial artery. A superficial ramus, given off
on the distal portion of the arm, accompanies 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 profundus to the extensor muscles of the fore-
arm.

The median nerve (n. medianus) passes distad along the medial sur-
face 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 cf the pronator teres, and then traverses the forearm, in com-
pany 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, be-
tween 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. '

144 ANATOMY OF THE Rassit.

IX. THE POSTERIOR LIMB.

Dissection on the side opposite to that of injection. The dissection
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.

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 the fixed condition of
the pelvic girdle they combine the characters of vertebral and appen-
dicular 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 liga-
ment to the centre of the body of the first sacral vertebra,
and on which it is also inserted.

It is necessary to divide the inguinal ligdment and reflect its sacral
continuation, together with the tendon of the psoas minor.

(b) 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. Inser-
tion: 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 lumbar is the chief
root of the femoral nerve, (p. 149), 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 corresponding
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.

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

Tues Posterior Lime. 145

on its lateral, posterior, and medial sides. They are partly covered by
the flexors of Group 3, namely, the biceps, sartorius, and gracilis, which
must be divided. To begin the dissection, see directions for removing
the a (p. 148). The position of the sciatic vein (p. 149) should be
noted.

Dissection 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 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.

(b) The glutaeus medius. Ventral border of.the wing of the
ilium and the iliac crest. Insertion: Greater trochanter.
Some of the fibres pass around the medial surface of the tip
of the greater 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 should be divided, care being taken to avoid injury to
the nerves and bloodvessels beneath it.

(f) 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. 183).

(g) The obturator internus. 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

146 ANATOMY OF THE RABBIT.

surface. To see its origin reflect the tendon through the
lesser sciatic notch and examine the muscle from the internal
surface of the pelvis.

(h) The gemellus inferior. Origin: Posterior portion of the
superior ramus of the ischium and the ischial tuberosity.
Insertion: Trochanteric fossa.

(i) The quadratus femoris. Origin: Ventral surface of the
ischial tuberosity and the superior ramus of the ischium
immediately in front of it. Insertion: With (j) in the
trochanteric fossa.

(j) The obturator externus: Origin: External extent of the obtur-
ator foramen. Insertion: Trochanteric fossa. The muscle is
largely concealed from this surface, but may be fully dis-
played by the division of the pectineus and adductores
brevis and longus. ;

Dissection on the medial surface posteriorly, after division of
thegracilis.

(k) The pectineus. Origin: Pecten of the pubis. Insertion:
Immediately below the lesser trochanter. :

(1) 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. 48.) es

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 practically a separate
muscle.
The two portions of the muscle should be divided.

(b) The vastus lateralis. Origin: Anterior surface of the great
trochanter and the lateral intermuscular ligament.
The muscle should be divided.

Tus Posterior Limes.

(c) The vastus intermedius.
First portion:
vastus lateralis.

147

‘

Origin in two portions:

Great trochanter, below the origin of the

Second portion: Anterior surface of the femur.

(d) The vastus medialis.

Origin:

Medially, at the base of the

collum femoris and adjacent portion of the shaft.

Common insertion (a-d):

B. Flexor group (hamstring
muscles). With the exception of
the sartorius, the muscles lie behind
the axis of the femur, and are in-
_serted on the medial and lateral
surfaces of the knee-joint and the
corresponding proximal portions of
the leg. They form the bound-
aries of the popliteal fossa.

(a) The sartorius. Origin:
Posterior portion of the
inguinal ligament, eSpe-
cially its sacral extén-
sion. Insertion: Medial
condyle of the tibia.
This is an extremely
thin and narrow band
of fibres, lying on the
more anterior portion
of the medial surface of
the thigh. The muscle
is fused distally with
the gracilis. It has the
position of a rotator
muscle, and is only a
flexor through its con-
nection with the latter.

(b) The gracilis. Origin :
The entire extent of
the pubic symphysis.
Insertion: Through a
broad tendinous expan-
sion ending in the fascia
of the proximal portion
of the medial surface of
the thigh. The muscle

Tibial tuberosity.

Anterior

Lateral

Posterior

Fic. 48. Transverse section through the middle
of the thigh: a.J., adductor longus; a.m., ad-
ductor magnus; b.f.1 and b.f. 2, first and second

heads of the biceps 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., semi-
tendinosus; 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 intermedius; v.is.,
sciatic vein; v.l., vastus lateralis; v.m., vastus
medialis; v.s.m., great saphenous vein.

forms a broad, comparatively thin sheet, covering the pos-

terior portion of the medial surface of the thigh.

Its inser-

tion 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.

148 ANATOMY OF THE RABBIT.

(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. 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.

To free the biceps and divide it: Incision along the aponeurotic
line joining the tip of the great trochanter with the sacrum;
also distad along the intermuscular septum of the lateral
‘surface of the thigh from the great trochanter to the knee.
The sciatic vein lies on the lateral surface towards the ischial
tuberosity. An incision along it will free the superficial
head of the semimembranosus from the biceps. Raise 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. The first head of the biceps may be separated
and reflected in order to expose the short muscles of the thigh.

(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. 1

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 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).

(f) The semitendinosus. Origin: Ischial tuberosity. Insertion:
Medial condyle of the tibia. The muscle is completely en-
closed by the adductor magnus, which must be split to
expose it.

Tux Posterior Lime. 149

BLOODVESSELS AND NERVES OF THE THIGH.

*The femoral artery (a. femoralis) traverses the medial surface of the
thigh, beginnimg 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 muscle, and is dis-
tributed to the posterior proximal portion of the limb. A second branch
the lateral circumflex artery (a. circumflexa femoris lateralis), passes
forward from the anterior wall between the insertion of the psoas major
and the origin of the vastus medialis. Its first branches are distributed
medially to the vastus medialis and rectus femoris. The trunk passes
to the lateral side of the head of the second portion of the rectus femoris,
and is distributed chiefly to the first head of the rectus femeris and to the
tensor fasciae latae. 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. 113). 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. 134) 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 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 tribu-
taries comprise the great saphenous, superficial epigastric, lateral circum-
flex, 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.

*kThe femoral nerve (n. femoralis) arises from the lumbosacral
plexus, chiefly from the fifth lumbar. Its position between the psoas
major and iliacus muscles has already been noted (p. 144).. 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 greater saphenous nerve (n. saphenus major), passes to the

12

150 ANATOMY OF THE RABBIT.

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) 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 distributes branches to the
posterior musculature of the thigh. In the proximal portion of the
thigh it divides into two chief branches, which are closely connected as
farasthe knee. The anterior branch is the peroneal nerve (n. peronaeus),
the posterior branch the tibial nerve (n. tibialis). The lesser.saphenous
nerve (p. 154) is a small branch given off from the tibial above the knee-
joint.

: For the origin of this and related nerves see p. 155.

The superior gluteal nerve (n. glutaeus superior) appears in the
greater sciatic notch, leaving the sciatic close to the inferior posterior
spine of the ilium. It passes between the glutaeus minimus 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 pos-
terior portion of the piriformis, and is distributed to the glutaeus maxi-
mus.

The posterior cutaneous nerve (n. cutaneus femoris posterior) accom-
panies the hypogastric artery backward to the ischial tuberosity, 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 semi-
membranosus 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
bloodvessels 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 sciatic vein, together -with
its continuation, the anterior tibial vein, and the accessory small saphe-
nous vein (p. 153).

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. 49).

A. Extensor group. Muscles occupying an anterior position on the
leg and inserted on the dorsum of the foot.

(a) The extensor hallucis longus. Origin: Middle portion of the

anteromedial surface of the tibia and from the medial con-

THE Posterior Lime. 151

dyle ‘behind the tibial collateral ligament. Insertion: The
tendon passes around the medial malleolus of the tibia and
beneath the base of the second metatarsal, uniting with the
- first tendon of the extensor digitorum longus.

The posterior tibial artery, the continuation of the great saphenous,
and the tibial nerve accompany the tendon in the malleolar groove.

(b) 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: Bya
flattened tendon from
the lateral margin of
the facies patellaris of
the femur. This ten-
don passes through
the capsule of the
knee - joint, and the
fleshy portion of the tote:
muscle lies on the
anterolateral surface
of the tibia. Inser-
tion: The distal ten-
don passes beneath
the crural ligament,
then beneath the cru-
ciate ligament of the Peceiss
dorsum of the foot, ; ;
dividing into four por- Fic. 49. Transverse section of ‘the proximal

portion or ois leg: jer beroneel artes ire

i i great saphenous artery; ‘ a.s.p., small saphenous
Hons for mset tion ell SRSLY: a.t.a., anterior tibial artery; b-f., biceps
all the phalanges of femoris (insertion); e.d.l., extensor digitorum
th di it Jongus; e.h.l., extensor hallucis longus; f., fibula;

ee EO Eee gee eid

ic. and medial heads of the gastrocnemius; gr.,

The muscle mee be dis (insertion tendon); n.s., greater saphenous nerve;
placed iby dividing the n.s.m., lesser saphenous nerve; n.t., tibial nerve;
crural ligament. pl., plenary ae SOleUe t., tibia; oe ee sean

_ anterior; t.f.c., tensor fasciae cruris (insertion);

DE peroneal and ante v.is., sciatic vein; v.s.m., great saphenous vein;
TOF tibial arteries lie v.s.p., small saphenous vein; 1-4, the peronaei (pri-
behind this muscle. the mus-quartus).
former in a medial posi- , ;
tion. in contact with the tibia, the latter 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.

Anterior

Medal

152 ANATOMY OF THE RABBIT.

(a) The peronaeus longus (p. primus). Origin: Lateral condyle
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.

(b) The peronaeus brevis (p. sectindus). 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 meta-
tarsal.

(c) The peronaeus tertius. Origin: The head of the fibula and
the crural interosseous ligament, fused with the extensor
digitorum longus. Insertion: Head of the fifth metatarsal,
and distally, united with the tendon of the extensor digitorum
longus, on the phalanges of this digit.

(d) The peronaeus quartus. Origin: The fibula and the inter-
osseous ligament, fused with the peronaeus brevis and with the
extensor digitorum longus. Insertion: Head of the fourth
metatarsal.

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 mediale: Medial condyle of the femur and its sesamoid.
(2) The soleus: Origin: Head of the fibula.

Insertion: Through the Achilles’ tendon (tendo calcaneus). 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 in 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 pos-
terior surface of the tibia obliquely, and is inserted on the
proximal portion of its posteromedial angle.

Tue Posterior Limes. 153

(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 beneath the
sustentaculum tali, reaching the plantar surface of the foot,
where it is partly covered by the plantaris tendon. 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 plantaris
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.

(b) The interossei (metatarsi). Origin: From the dorsal portion
of the tendon-sheath of the flexor digitorum longus. In-
sertion: 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 divides into two branches,
the anterior tibial and peroneal arteries. It distributes branches to the
muscles about the knee-joint, including a branch to the distal portion of
the vastus lateralis, which is given off at about the point of origin of
the small saphenous artery.

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 anterior tibial artery (a. tibialis anterior) lies on the medial
margin of the peronaeus longus, and passes to the fibular side of the
crural ligament in company with the anterior tibial vein and the peroneal
nerve to the dorsum of the foot.

The peroneal artery occupies a more medial position, traversing the
leg close to the tibia and the interosseous ligament. It reaches the
dorsum of the foot after passing beneath the crural ligament.

**The great saphenous vein (v. saphena magna), a large tributary
of the femoral, accompanies the corresponding artery, and the greater

154 ANATOMY OF THE Rassi'.
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 corre-
sponding 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.

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, traversing 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 structure of the lumbosacral plexus may be examined by break-
ing 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 muscles may be picked
away with the forceps, and the abductor caudae anterior muscle (p. 183)
may be detached from its origin on the ischial spine. :

The lumbosacral plexus (plexus lumbosacralis) is formed by the
ventral roots of the four posterior lumbar and four sacral spinal nerves.
It is divisible into a lumbar plexus (plexus lumbalis), from which arises
the femoral nerve, and a sacral plexus (plexus sacralis), from which
arises the sciatic nerve.

The femoral nerve is formed from the fifth, sixth, and seventh lumbar,
especially from the loop connecting the fifth and sixth (ansa lumbalis 11).
From the same loop arises a smaller, obturator nerve (n. obturatorius),

Tur Posterior Limp. 155

which accompanies the obturator artery, and is distributed to the
obturatores, adductores, and gracilis muscles.

The sciatic nerve, together with the superior and inferior gluteal
nerves, arise from the loop connecting the last lumbar and first sacral
nerves (ansa lumbalis 111).

The internal pudendal nerve is formed from the loop connecting the
second and third sacral nerves (ansa sacralis 11), but chiefly from the
second. :

THE ARTICULATIONS OF THE POSTERIOR Limp.

The more perfect development and larger size of the joints of the
posterior limb make them much more favorable 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 aceta-
buli 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.
The external supports of the joint comprise the iliofemoral, ischiocapsular,
and pubocapsular 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 liga-
ment (lig. teres femoris). The glenoid lip (labrum glenoidale) 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 inarticular fibrocartilages (see section,
Fig. 13).

The tibial collateral ligament (lig. collaterale tibiale) is a stout band
of connective tissue stretching from the medial condyle of the femur to
the posteromedial angle of the medial condyle of the tibia.

The fibular collateral ligament is a similar structure connecting the
lateral condyle of the femur with the lateral surface of the tibia imme-
diately in front of the head of the fibula.

The sesamoid bones of the popliteal region have articular surfaces
taking part in the formation of the joint. That on the medial condyle
of the femur is contained in the medial head of the gastrocnemius, that
on the lateral condyle of this bone in the lateral head of the gastroc-
nemius and the plantaris, and that on the lateral tibial condyle in the
popliteus.

The common tendon of the quadriceps femoris, the patella, and the

156 ANATOMY OF THE RABBIT.

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 intercon-
dyloid 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) 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 intercondyloid fossa of the femur.

C. The ankle-joint (articulatio talocruralis) is a ginglymus with a
considerable amount of spiral torsion. The articulating surfaces are
chiefly formed by the tibia and talus, but also by the fibular side of the
tibiofibula and the calcaneus. On the tibial side the calcaneotibial liga-
ment (lig. calcaneotibiale) connects the medial malleolus with the sus-
tentaculum 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 back-
ward to the lateral surface of the calcaneus. The tibionavicular liga-
ment (lig. tibionaviculare) connects the anterior surface of the distal
end of the tibia with the dorsal surface of the navicular bone.

Tur Heap anp NEcK. 157

X. THE HEAD AND NECK.

This dissection includes the various structures of the region, with the exception
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 skin, which has already been divided to
the mandibular symphysis and partly reflected, 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 concen-
trated 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.

1. On the lateral surface of the head the following structures may
be made out without further dissection:

(a) The masseter muscle. Origin: The zygomatic arch;
tendinous from its anterior angle. Insertion: Lateral sur-
face of the angle of the mandible,

(b) 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 and perforating
the mucous membrane of the cheek opens into the oral
cavity.

(c) 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 distributed as
motor nerves to the cutaneous muscles of the face, including
the platysma.

(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. angularis). Its
chief branches to the anterior portion of the face are: (1)
the submental artery (a. submentalis) to the chin; (2) the

158 ANATOMY OF THE Raspit.

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 branch of
the superficial temporal (p. 162).

(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.

(a) The quadratus labii superioris. Origin: Dorsal portion of the |
maxillary fossa. Insertion: Skin of the upper lip.*

(b) 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.

(c) The zygomaticus minor. Origin: Anterior end of the zygo-
matic 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.

(f) 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.

(h) 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.

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 levator alae nasi, and zygomaticus minor muscles may be considered to
be subdivisions of this muscle.

Tur Heap AND NECK. 159

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. 52).

The posterior facial vein (v. facialis posterior) is formed below the
base of the ear by the union of the superficial and deep temporal veins
of the temporal region, the inferior ophthalmic vein, from the posterior
portion of the orbit, and the anterior auricular vein from the ear. It
passes downward in the substance of the parotid gland, and in its first
portion is covered by the root of the facial nerve. Immediately below
the latter it receives the posterior auricular vein from the ear and back
of the head.

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 downward beneath the masseter muscle.
The anterior facial vein receives at the ventral border of the mandible
the internal maxillary vein (v. maxillaris interna). The latter also
begins in the orbit, where it is connected with the deep facial. 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.

The external jugular vein may be divided and turned forward together with the
parotid gland. ‘

4, Examination of the more superficial structures of the ventral
surface of the head and neck.

(a) The submaxillary gland (gl. submaxillaris), a somewhat
compact rounded or oval gland lies at the medial side of the
extreme ventral portion of the angle of the mandible. Its
duct (d. submaxillaris) may be seen running forward toward
the mouth.

(b) 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.

(c) The digastricus. Only its insertion portion is visible. 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.

(f) 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 one another and divided.

160

(g)

(h)
(i)
(3)

(k)

(1)

(m)

(n)

(0)

(p)

(q)

(r)

ANATOMY OF THE RABBIT.

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.

The trachea occupies a median position, and is supported by
cartilaginous tracheal rings.

The thyreoid cartilage of the larynx; a saddle-shaped carti-
lage, composed of right and left thyreoid plates (Fig. 36).

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 cervicalis
profunda) is a large elongated reddish-colored gland in the
upper portion of the neck, opposite the thyreoid cartilage.
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 narrower median portion, the isthmus.

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 sternothryeoid muscles.

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.

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 ramus descendens of the twelfth cranial or hypoglossal
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.

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.

The ramus cardiacus of the vagus (n. depressor) lies on the

Tus Heap anp NEcK. 161

dorsal surface of the common carotid on the medial side of
the sympathetic trunk. It arises at the level of the posterior
margin of the thyreoid cartilage.

(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 cleidomastoideus.

5. Dissection of the muscles of mastication and related structures of
the mandible.

On account of the narrowness 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:

(a) The masseter muscle. Origin: The entire surface of the

-

zygomatic arch; tendinous from its anterior angle (spina
masseterica). Insertion: Lateral surface of the angle of the
mandible (1, a).

-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.

(b) 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
medial side of the reduced coronoid process. The muscle
may be exposed by dividing the temporal portion of the
posterior supraorbital ligament which holds its tendon in
place; then divided.

To remove one-half of the mandible:

Divide the mandibular symphysis, and pass a knife along the
medial surface of the side 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 pro-

cess of the skull. Insertion: Ventral portion of the medial
surface of the angle.

(d) The pterygoideus externus. Origin: Lateral plate of the

pterygoid process. Insertion: Dorsal portion of the medial
surface of the angle. Both muscles are strongly de-
veloped.

(e) The inferior alveolar artery (a. alveolaris inferior) lies be-

‘tween. the two pterygoidei. Its cut end marks the point of
entrance into the mandible through the mandibular foramen.

162 ANATOMY OF THE RABBIT.

The corresponding inferior alveolar vein leaves the mandible
at this point.

(f) The inferior alveolar nerve (n. alveolaris inferior) accom-
panies the inferior alveolar artery to the mandible. The con-
tinuation 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. trige-
minus), which also gives off anteriorly the stout lingual nerve
to the tongue and posteriorly the slender mylohyoid nerve.
These structures, together with the inferior alveolar artery,
may be freed from their loose connections with the ptery-
goidei, 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 neck as follows:

(a) The internal carotid (a. carotis interna) is a small vessel given
off from the dorsal wall (pp. 171, 190). The trunk then
passes forward as the external carotid (a. carotis externa).

(b) The occipital artery (a. occipitalis) passes from the dorsal wall
to the posterior portion of the head.

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.

(c) The lingual artery (a. lingualis) arises from the ventral wall
and passes forward into the tongue.

(d) The external maxillary artery (a. maxillaris externa) is given
off immediately in front of the lingual artery, sometimes in
common with it. It passes forward on the medial surface
of the ventral border of the mandible (medial to the digas-
tricus), 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. 168), giving off the inferior
alveolar artery to the mandible.

(f) The superficial temporal artery (a. temporalis superficialis),
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:
(a) The stylohyoideus major muscle. Origin: Jugular process

THE Heap anp NEcK. 163

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.

(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
medial side and divided.

(c) The stylohyoideus minor. Origin: Jugular process. In-
sertion: Lesser cornu of the hyoid. A slender muscle lying
to the medial side of the styloglossus.

_ The remaining muscle is the stylopharyngeus, the insertion of which
is on the lateral wall of the pharynx.

(d) The geniohyoideus. Origin: Mandibular symphysis. In-
sertion: Anterior surface of the body of the hyoid: unpaired.

(e) The genioglossus. Origin: Medial surface of the mandible
immediately behind the symphysis. The fibres pass upward
and slightly backward into the substance of the tongue.

(f) 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. Near its point of origin the
lingual nerve receives the chorda tympani (p. 171).

(i) The twelfth cranial or hypoglossal nerve (n. hypoglossus)
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 glossopharyngeal
nerve (n. glossopharyngeus) enters the base of the tongue
at a point dorsal to the hypoglossus and between the stylo-
hyoideus 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.
These nerves, which for the most part have already been exposed,
may be traced to their origin in the jugular foramen. The tympanic
bulla should be exposed by removing whatever portions of the parotid
gland are still in place. The lingual and hypoglossal nerves may be

164 ANATOMY OF THE Rassi’.

divided—the latter at the base of the tongue—so.that the external
carotid artery may be displaced backward.

(a) The ninth (glossopharyngeal) nerve is farthest forward. Its
two main branches are the ramus lingualis to the tongue,
and the ramus pharyngeus, the latter entering the lateral
wall of the pharynx. :

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 cardiacus are given off
at the level of the origin of the internal carotid artery.

The eleventh cranial, or. spinal accessory nerve (n. accessorius) is
dorsal to the vagus, with which it is united above the plexus ganglio-
formis by a ramus internus. The nerve passes dorsad to the medial
side of the mastoid attachments of the sternohyoideus and cleidomas-
toideus muscles, giving branches to the latter, and then passes backward
to the ventral surface of the trapezius to which it is distributed.

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 artery and enters the base of the tongue.
The ramus descendens is given off at about the point where it crosses the
artery.

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 associ-
ated nerves separated from the oesophagus and trachea. The latter may
be displaced downward to a slight extent by dividing the loose con-
nective tissue along the ventral surface of the vertebral column. An
incision extending from the anterior end of the oral cavity backward into
the oesophagus will expose the internal surface of the digestive tube
sufficiently to make out its features. The incision divides the con-
strictor pharyngis muscle, a broad band of muscle fibres enclosing the
posterior portion of the pharynx.

The general 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,

Tue Heap anp NEcK. 165

lies above the soft palate, and receives the posterior aperture
of the nose. Its ventral and posterior laryngeal portion
(pars laryngea), not well-defined, contains 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.

(b) The soft palate (palatum molle) is the thin, narrow, posterior,
membranous portion of the roof. Itis 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 ducts (dd. nasopalatini) open by minute
apertures immediately behind the small incisors. They
connect the anterior portion of the nasal cavity with the
mouth.

(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 are two small spherical elevations, the
vallate papillae (papillae vallatae), partly sunk in the mucous
membrane, and on either side 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 depres-
sion, the tonsillar sinus (sinus tonsillaris). The vertical slit-
like aperture of the sinus is bounded by low anterior and
posterior folds, the glossopalatine and pharyngopalatine
arches.

(b) The epiglottis, a triangular 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 con-
nection of the nasopharynx with the nasal fossae will be
exposed; also on the lateral wall the small pharyngeal
aperture of the auditory tube (ostium pharyngeum tubae).

10. Examination of the larynx. And
By cutting around the base of the tongue on the opposite side of the

13

166 ANATOMY OF THE RABBIT.

body, the whole structure, together with the hyoid, larynx, and a por-
tion 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 oppo-
site side from the medial surface of the mandible outward, also of clearing
and examining the hyoid apparatus, which is not usually available with
the prepared skeleton (p. 97). The laryngeal cartilages should be
cleared externally and the parts made out as follows:

(a) The thyreoid cartilage (cartilago thyreoidea) (Fig. 36) forms
the largest portion of the structure. It is a unpaired saddle-
shaped cartilage, described as consisting of right and left
laminae. Its anterodorsal angle projects forward as the
cornu superior; connected by ligament with the greater
cornu of the hyoid. The corresponding posterodorsal 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 carti-
lage, 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 arytenoideae) lie
one on either side of the anterior tip of the cricoid plate.

(d) The corniculate cartilages (cartilagines corniculatae) are
slender curved terminal cartilages supported by the ary-
tenoids.

(e) The epiglottic cartilage (cartilago epiglottica) is a triangular
plate supporting the epiglottis. ?

(f{) 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 forms the posterior boundary of a
shallow pouch, the laryngeal ventricle (ventriculus laryngis).

In addition to the criothryreoidei the laryngeal cartilages are
connected by several small muscles, including the cricoarytenoidei
posterior and lateralis, the thryreoarytenoideus 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:

THE HEAD AND NEcK. 167

(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: Antero-
dorsal portion of the eyeball.

(c) The obliquus inferior. Origin: Lacrimal bone. Insertion:
Posteroventral portion of the eyeball.

(d) 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.

(e) The retractor bulbi (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 consists of four distinct parts.

(f) The Harderian gland (gl. Harderiana) is a large compact gland
lying in the anterior portion of the orbit. It is composed of
two portions, 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
yellowish gland lying in the anteroventral angle of the orbit immedi-
ately 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. 50) comprise:

(a) The fibrous tunic (tunica fibrosa oculi), the strong peripheral
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.

168

ANATOMY OF THE RABBIT.

(b) 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), 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 in 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 filaments,
the zonular fibres, reflected from the margin of the ciliary

body.
The vitreous body (cor-
pus vitreum), a trans-
parent mass, of gela-
tinous consistence,
occupies the large space
enclosed by the lens
and the retina.

(f) 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 be-

(e)

tween the iris and the lens.

Fic. 50. 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
tetina; c.y., 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
eyelid; p.s., upper eyelid; p.t., third eyelid;
r.b., retractor bulbi; 1.i., rectus inferior; rs.,
rectus superior; sc., sclera; z., suspensory
zonular fibres of the lens.

The central space enclosed

by the free margin of the iris is the pupil (pupilla).
12. Following the removal of the eye, the bloodvessels 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 zygo-
matic arch, and also the bony ridge which lodges the alveoli of the pos-

terior 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

Tue Heap anv NEcK. 169

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, con-
tinuing 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 sphenopalatine artery, which enters the
nasal cavity by the sphenopalatine foramen.

(b) The divisions of the third cranial, or oculomotor nerve, supply
the eye muscles, with the exceptiom of the obliquus superior
and the rectus lateralis.

This nerve enters the orbit from the superior orbital fissure in
company with certain parts of the trigeminal (e, f). The small
nerves passing through the middle and posterior sphenoidal formina
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 dis-

tributed to the obliquus superior muscle.

(d) The sixth cranial, or abducent nerve (n. abducens), is dis-
tributed to the rectus lateralis.

(e) The ophthalmic nerve (n. ophthalmicus), the first division of
the fifth cranial, or trigeminal nerve (n. trigeminus), accom-
panies the inferior ophthalmic artery on the medial wall of
the orbit. It gives off a lacrimal nerve, which passes upward
through the posterior foramen of the supraorbital process,
and then passing forward a short distance divides in two parts.
One of these, the frontal nerve, leaves the orbit through the
anterior supraorbital foramen, while the other, the naso-
ciliary nerve, is partly distributed to the anterior portion of
the orbit, and is connected with the minute ciliary ganglion
lying on the optic nerve, forming its sensory root. Its chief
portion leaves the orbit through the ethmoidal foramen of
the orbital portion of the frontal bone as the ethmoidal nerve

170 ANATOMY OF, THE RABBIT.

(f) 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 sphenopalatine nerve (n.
sphenopalatinus) and the infraorbital nerve (n. infraorbitalis).
The latter passes forward through the infraorbital groove and
foramen to the face.

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 surface 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.

The sphenopalatine nerve ends in the sphenopalatine ganglion (g.
sphenopalatinum). This is a small, somewhat radiate structure lying
immediately behind the sphenopalatine foramen. The nerves proceed-
ing from the ganglion include: (1) nasal rami, to the mucous membrane
of the nasal cavity; (2) the nasopalatine nerve, which enters the nasal
region through the sphenopalatine foramen in company with the nasal
rami, and, traversing the nasal septum, passes through the incisive
foramen to the anterior portion of the hard palate; and (38) the anterior
palatine nerve, which passes through the pterygopalatine canal to the
posterior portion of the hard palate.

The nerve of the pterygoid canal (n. canalis pterygoidei) is a slender
cord which passes backward along the orbital wall from the posterodorsal
angle of the ganglion. 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 artery. The other, the
great superficial petrosal nerve (n. petrosus superficialis 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 con-
stitutes 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 sym-
pathetic system in the head, and having motor and sensory roots from
the cerebral nerves in addition to their sympathetic 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. 90); but the following soft parts may be identified.

(a)

(b)

(c)
(d)

(e)

THe Heap anp NEck. 171
The tympanic membrane (membrana tympani) is stretched
almost vertically across the lower end of the external acoustic
meatus. .

The tensor tympani is a slender muscle, the origin of which
forwards from the alisphenoid is concealed. It is inserted
on the manubrium mallei.

The stapedius is a minute muscle arising from the periotic
bone above the cochlear fenestra and inserted on the stapes,

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
peripheral, connections are with the lingual nerve and the submax-
illary ganglion.
The internal carotid artery
traverses the carotid canal
of the tympanic bone. By
breaking away the posterior
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 asso-
ciated acoustic nerve and its
entrance to the periotic bone.
The parts of the internal ear
(Fig. 51) 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 laby-
rinth, consisting of a series of con-
nected spaces lodged in the in-
terior of the petrous bone, and
comprising the cochlea, vestibu-
lum, 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

Fic. 51. 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 petrotympanic

bone; t., tympanic portion (bulla tym-
pani).

c., cochlea; c.s. bony semicircular
canals; c.t., tympanic cavity; d.c.,

cochlear duct; d.e., endolymphatic duct;

.m., dura mater; ds., semicircular
ducts; f.c., cochlear fenestra; f.v., vesti-
bular fenestra; i., incus;, m, malleus;
m.a.e., external acoustic meatus, ter-
minating at the tympanic membrane;
m.a.i., internal acoustic meatus; Si,
sacculus; s.e., endolymphatic sac; st.,
stapes; t.a., auditory tube; u., utriculus;
v, vestibulum; VIII, acoustic nerve.

sacculus, the utriculus, and the semicircular ducts, together with their

connections and the endolymphatic duct and sac.

The membran-

ous 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 perilym-
phatic space also occupied by a fluid material termed the perilymph.

1

172 ANATOMY OF THE RABBIT.

XI. 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 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 intercostals. They are best examined at a later stage from
the interior of the thorax.

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. 182) 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.

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.

The artery passing along the ventral wall between the foregoing muscle and
the internal intercostals is the internal mammary (p. 174).

2. Dissection of structures in the superior thoracic aperture.

The nerves and bloodvessels of this region are concealed by the
thymus gland, a large triangular flattened structure of fatty consis-
tence, extending forward from the base of the heart to the anterior end
of the thorax. The thymus should be carefully scraped away, all vessels
except those of the structure 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

Tun THORAX. 173

sympathetic nerves, cannot be dissected in the order given below, but
must be separated from one another and identified as they appear.

(a) The arch of the aorta (arcus aortae). Beginning at the base
of the heart, the aorta passes at first 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. 176), the first branches
are the large paired vessels arising from the anterior wall.
They comprise the common carotid and subclavian arteries.
On the right side the carotid and subclavian 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 branches of the common carotid artery have already been
traced, with the exception of the intra-cranial portion of the
internal carotid (p. 190).

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
is replaced by 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 seventh cervical vertebra,
and traversing the canal formed by this and the correspond-
ing 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. 190).

(2) The superficial cervical artery (a. cervicalis superficialis)—
divided in a previous dissection (p. 135)—is a small vessel
which passes forward and outward beneath the insertions
of the cleidomastoideus, basioclavicularis and levator
scapulae major muscles, ramifying extensively 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.

(3) The transverse artery of the neck (a. transversa colli), also
divided in a previous dissection (p. 136), 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. T he artery sup-
plies the serratus anterior and the rhomboidei.

174

(c) The vagus nerve. On

ANATOMY OF THE RABBIT.

(4) Thea. intercostalis suprema passes backward to the internal
surface of the thoracic wall, giving off the first three inter-
costal 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 epigastric artery (a. epigastrica superior)
anastomosing with the inferior epigastric (p. 115).

(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
portion of the right
atrium. The left vessel
crosses both the left
subclavian artery and
the arch of the aorta,
reaching the right at-
rium from the dorsal
surface of the heart.

the right side the nerve
crosses the ventral sur-
face of the subclavian
artery, passing dorsad
to the wall of the oeso-
phagus. It gives off
the recurrent nerve
(n. recurrens), the latter
curving around the sub- ___Fic. 52, Plan of the venous and lymphatic

trunks of the anterior portion of the body.

clavian artery and After McClure and Silvester.

: a., azygos vein; ao., aorta; c.s., left s i
passing forward along caval vein; d.th., thoracic duct; j.e., aoa

the side of the trachea i-tr., external, internal, and transverse’ jugular
to the larynx. On the DS eas vein; tr.s., transverse
left side the vagus

passes between the archof the aorta and the base of the
heart to the ventrolateral wall of the oesophagus. The recur-

rent nerve passes forward on the dorsal side of the arch.

(d) The ramus cardiacus of the vagus. In front of the subclavian

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

Tus THoRAX. 175

dorsal surface of the aortic arch. It ends in the cardiac
plexus (plexus cardiacus), a network of sympathetic nerves
lying between the aortic arch and the pulmonary 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 pericardium to the
diaphragm. That of the right side accompanies the thoracic
portion of the inferior caval vein.

(f) 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, 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 sub-
clavian and its branches.

3. Dissection of the heart.

The character and relations of the enclosing serous sac, the peri-
cardium, should first be noted. Its relation to the heart is similar to
that of the peritoneum and pleura investing other visceral organs (p. 49).
It comprises a parietal layer, that portion commonly known as the peri-
cardium, and a visceral layer, the epicardium, 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, 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 bloodvessels.

The pericardium should be removed, and the external features of the
heart and its great vessels examined as follows:

(a) The posterior, somewhat conical, ventricular portion of the
heart. The left ventricle (ventriculus sinister) may be dis-
tinguished both by its position and by the more solid charac-
ter 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 de-
pression, the anterior longitudinal sulcus.

176 ANATOMY OF THE Rassit.

(b) The pulmonary artery (a. pulmonalis) leaves the base of the
right ventricle, passing forward and to the left in a some-
what spiral fashion around the aorta. On the dorsal sur-
face 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. arteriosum), repre-
senting the foetal connection of the two vessels through the
ductus arteriosus (p. 44).

(c) The left coronary artery (a. coronaria sinistra) passes back-
ward 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 and the unpaired inferior caval veins.

The heart may be removed by dividing the great bloodvessels. The
arch of the aorta should be removed with the heart by dividing the
vessel at a point beyond the crigin 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; also
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 sur-.
face of the wall.

(b) 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 con-
nected 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.

(c) The semilunar valves (valvulae semilunares) of the pulmonary
artery are three extremely thin folds guarding the entrance
to the vessel from the right ventricle. Two of the valves

THE THorRAx. 177

are usually to be found, 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 par-

' tition 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 thick-
ness of the wall the internal structure is not so easily examined as in the
right ventricle.

(a) The bicuspid valve (valvula bicuspidalis) is similar in general
structure to the tricuspid valve of the right ventricle.

(b) The semilunar valves of the aorta are three in number, and
are similar to those of the pulmonary artery.

4. Examination of the lungs and their connections. ;

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:

5 (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 diaphragmatic pleura, and
over the surface of the lung as the pulmonary pleura. Pos-
teriorly the pulmonary pleura passes from the medial margin
of the left lung to the medial lobule of the right and thence
backward to the diaphragm, forming a broad sheet of attach-
ment, 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 bloodvessels 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 developed. On
the right side the inferior lobe is divided into 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 bronchial rami, which
penetrate the substance of the organ and redivide into smaller
tubes.

178
(e)

(f)

ANATOMY OF THE Rassit.

The branches of the pulmonary artery and the pulmonary
veins may be traced for a short distance on the medial por-
tion, or hilus, of each organ.

The vagus nerve passes to the dorsal side of the bronchus,
giving off 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 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 posi-
tion, entering the diaphragm at the hiatus oesophageus.

(b) The vagus nerves. The right and left nerves pass backward

(c)

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. 119).

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 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

(e)

(f)
(g)

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 cavity (p. 118).
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.

The intercostal nerves (nn. intercostales) accompany the
intercostal arteries to the lateral wall of the thorax.

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.

Tue THorax. 179

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 dis-
placed 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 vertebrae. The second, or
costal portion, arises from the internal surfaces of the posterior ribs.
The third, or sternal portion, 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
forwards to the lungs and pericardium through the broad pulmonary

ligament. 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 triangular
ligaments.

(b) 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.

(f) 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.

180 ANATOMY OF THE RABBIT.

XII. THE VERTEBRAL AND OCCIPITAL MUSCULATURE.

Dissection on the dorsal surface of the body from the occiput back-
ward; 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 ligamentum nuchae and from the lumbo-
dorsal fascia back to the last rib, and is inserted on the lateral surfaces
of the eight posterior ribs.

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 lumborum—
muscles of appendicular insertion lying on the ventral surface of the
vertebral column—the vertebral musculature comprises chiefly modified
segmental muscles lying on the dorsal surface, for the most part in the
area enclosed by the spinous and transverse processes of the vertebrae.
They include the sacrospinalis, 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 medial
surface of the iliac wing; mammillary processes of the six
posterior lumbar vertebrae; investing lumbodorsal fascia.

This muscle is the largest and strongest muscle of the body. It
extends forward over the surfaces of the ribs. Its medial
border is separated from the middle line by a space of con-
siderable width, in which the semispinalis and multifidus
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 slender
lateral portion, the iliocostalis, and a thick medial portion,
the longissimus. The latter receives in the posterior portion
of the thorax strong accessory bundles from the semi-
spinalis muscle on its medial side, the two muscles being
inseparable at this point.

THE VERTEBRAL MuscuLature. 181

The iliocostalis is inserted laterally on the ribs. It receives
medially from the ribs a number of accessory bundles, which
are inserted forwards to the seventh cervical vertebra.

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 trans-
verse processes of the four 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 first three thoracic
vertebrae joins the medial, ventral portion of the splenius,
and forms the longissimus capitis.

(b) The semispinalis and multifidus. The band of muscle lying
between the longissimus and the middle line, is composed of
partly fused slips, arising for the most part by very long
tendons from the mammillary 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 semispinalis dorsi,
is inserted by a series of fleshy slips on the spinous process of
more anterior thoracic vertebra, 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, the semispinalis capitis, arises from
the articular processes of the five posterior cervical and the
transverse processes of the first four thoracic vertebrae. It
is inserted on the lateral surface of the external occipital
protuberance. 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, how-
ever, at the free margin of the muscle, arising from the
semispinalis dorsi and the longissimus.

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,

182

ANATOMY OF THE RABBIT.

where they form thick muscular pads interposed between
the mammillary and accessory process. 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)

(b)

(c)

(d)

(e)

(f)

The rectus capitis posterior superficialis. Origin: Spinous
process of the atlas. Insertion: External occipital pro-
tuberance.
The obliquus capitis superior. Origin: Transverse process of
the atlas. Insertion: Lateral surface of the occipital pro-
tuberance.

The foregoing muscles should be divided.
The rectus capitis posterior minor. Origin: Posterior tubercle
of the atlas. Insertion: External occipital protuberance.
The rectus capitis posterior major. Origin: Spinous process
of the epistropheus. Insertion: Laterally on the supra-
occipital bone.
The obliquus capitis inferior. Origin: Spinous proeess 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)
(b)

(c)
(d)

(e)

The scalenus anterior. Origin: Transverse processes of the
four posterior cervical vertebrae. Insertion: First rib.
The scalenus medius. Origin: Transverse process of the
fifth cervical vertebra. Insertion: Lateral surfaces of the
third to fifth ribs.
The scalenus posterior. Origin: Transverse processes of
the fourth to.sixth cervical vertebrae. Insertion: First rib.
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. 172).
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.

(f) The longus capitis is partly fused with the foregoing muscle,

but its origin is in a more lateral position from the trans-
verse processes of the first six cervical vertebrae. Insertion:
Sphencoccipital synchondrosis.

(g)

(h)

THE VERTEBRAL MUSCULATURE. 183

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 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 inthe furrow between the
spinous and articular processes of the sacral and caudal vertebrae,
and is inserted on the transverse processes and dorsal surfaces of
the caudal vertebrae.

(b) The abductor caudae posterior arises as a continuation of the
multifidus in the groove between the articular and transverse process
and is inserted on succeeding vertebrae.

(c) The abductor caudae anterior. Origin: Ischial spine. Insertion:
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 succeeding
vertebrae.

184

1. The

ANATOMY OF THE RABBIT.

XIII. THE CENTRAL NERVOUS SYSTEM.

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 vertebral arches and

the latter broken away with the bone forceps. The following features
may be made out according to the extent of exposure:

(a)

(b)

The spinal cord (medulla spinalis) is a thick cylindrical white
cord traversing the vertebral column in the vertebral canal.
It is of almost uniform diameter, but exhibits two slight
enlargements, one in the cervical, the other in the lumbar
region. At about the middle of the sacrum it contracts to
a slender filament, the filum terminale, which may be traced
backward to the middle of the tail.

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

(c)

(d)

tissue, the arachnoidea.

The regional distribution of the nerve roots—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,
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 ventro-
lateral 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 components of the cervical
and lumbosacral plexuses or as individual spinal nerves.
The ramus communicans is a slender filament which passes
ventrad to join the sympathetic trunk.

THE Crentray Nervous System. 185

2. A small portion of the spinal cord may be excised and examined
(preferably under water) for the following: (see p. 22, fig. 18).

(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 medianus
posterior).

(b) 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 sub-
stance (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
flocculus of the cerebellum, a small stalked body which is almost com-
pletely enclosed by the dorsal portion of the petrosal. The entire petro-
tympanic bone is easily detached, and if removed en masse the flocculus
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 ver-
tebra. The brain should then be raised very gently from the ventral
wall of the skull and the nerve roots divided with a small sharp knife or
with fine scissors. This operation requires considerable 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 across 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 hemispheres, the other the

186 ANATOMY: OF THE RABBIT.

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. 34.

4. The superficial features may be identified as follows:

IN THE PROSENCEPHALON:

(a) The greatly enlarged cerebral hemisphere (hemisphaerium
cerebri) 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 one
another by the commissures indicated below.

(b) The olfactory bulb (bulbus olfactorius) is a small expansion
lying at the anterior end of each hemisphere. Its cut end
represents the point of origin 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
lobe, or 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 latter forming the olfactory tract
(tractus olfactorius). The tract ends posteriorly in an
expanded portion of the brain, which, from its shape, i
described as the lobus piriformis. The olfactory brain as
thus defined is separated superficially from the remaining
portions of the cerebral hemisphere by a longitudinal furrow,
the limbic fissure (fissura limbica), which passes along its
lateral margin. The anterior portion of the furrow, known
as the anterior rhinal fissure, separates the olfactory tract
laterally from the narrow anterior portion of the cerebral
hemisphere. The corresponding posterior portion of the fur-
row, the posterior rhinal fissure, separates the lobus piriformis
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.

(d) The corpus callosum is a broad white commissural band
passing transversely from one hemisphere to the other. Its
median portion may be exposed 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

(f)

(g)

(h)

(i)

(j)

(k)

THE CentRAL Nervous System. 187

with the unpaired portion of the brain (the thalamencephalon)
lying below it. 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 detached. By

pressing apart the tips of the hemispheres and removing the

pineal body the dorsal surface of the thalamencephalon 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 ventricle (ventriculus tertius) (Fig. 53), the roof of
which is formed anteriorly by the superficial portion of the
chorioid plexus (plexus chorioideus), the latter entering the
ventricle at this point.

The lateral margins of the aperture are largely formed by two
mjnute spindle-shaped masses,one on either side, the habenulae.
Their posterior ends are united by a slender transverse band,
the habenular commissure (com-

missura habenularum). The fibres mi.

of the commissure are faintly trace-
able forward, where they form a pair
of thin whitish filaments (medullary
striae). —

The posterior commissure (commis-
sura posterior) crosses the posterior
portion of the roof immediately
behind and below the habenular
commissure.

H . Fic. 53. Diagram, showing
The walls of the third ventricle are che aaancomens of Hie Sere

formed by the thalami. They are of the thalamencephalon as
: : ViCWwe rom € orsal sur-
broadly connected by the. inter- face, jafter, removal of the
. 4 5 pinea ody: a., anterior
mediate mass (massa intermedia), OF Fislemic Aaticnie? a
middle commissure, which may be habenular commissure; c.p.,

: osterior commissure; Gs.,

seen from the dorsal surface crossing Superior colliculus (of mesence:
phalon); g.l. and g.m., lateral

the cavity. and medial geniculate bodies;

On either side of the middle line, or a ee

of the habenulae, the dorsal portion ventricle. e

of the thalamus forms a low, some-

what oval projection, the pulvinar or posterior tubercle.
The anterior tubercle of the thalamus is a faint elevation of very

small dimensions lying in the angle enclosed between the pulvinar and

the anterior portion of the aperture of the third ventricle.

The parts of the metathalamus are distinguishable externally

as two rounded projections of the lateral surfaces of the

thalamencephalon. One of them, the lateral geniculate

body (corpus geniculatum laterale), lies to the lateral side of

the pulvinar, and is only separated from it by a faint depres-

188

ANATOMY OF THE RABBIT.

sion of the surface. The medial geniculate body occupies a
more posterior and medial position.

(1). The optic tract (tractus opticus) connects the geniculate
bodies, especially the lateral one, with the ventral surface of
the brain, ending in the optic chiasma.

(m) On the ventral surface, the optic chiasma (chiasma opticum),
forms a conspicuous elevation, the posterior portion of which
is traceable into the optic tracts, the anterior portion into
the bases of the second cranial, or optic nerves.

(n) The hypophysis, or pituitary body, lies immediately behind
the optic chiasma.

On account of its enclosure by the walls of the hypophysial 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 toward the hypophysis.

(p) The mammillary body (corpus mammillare) forms a con-
spicuous rounded elevation, lying at the posterior end of the
tuber cinereum. The structure is single, but there is an
indication of lateral lobes.

IN THE MESENCEPHALON:

(a) The dorsal surface is marked by four elevations, the corpora
quadrigemina. The anterior pair, distinguished as the
colliculi superiores, are much larger than the posterior pair,
the colliculi inferiores.

(b) The ventral surface is occupied by a pair of divergent cords,
the cerebral peduncles (pedunculi cerebri), separated by a
faint median depression, the interpeduncular fossa (fossa
interpeduncularis).

(c) The third cranial, or oculomotor nerve (n. oculomotorius),
arises from the ventral surface of the cerebral peduncle.

IN THE RHOMBENCEPHALON:

(a) The cerebellum forms an arch over the posterior portion of
the brain, and is supported by stout pillars from its sides.
In addition to the ridges of its surface the whole structure is
divided into several lobes, including the median portion or
vermis, the lateral hemispheres, and the stalked bodies, or
flocculi, arising from the hemispheres.

(b) The anterior medullary velum (velum medullare anterius) is
the thin membrane underlying the anterior portion of the
cerebellum and connecting the latter with the inferior
colliculi. It forms a small anterior portion of the roof of the
fourth ventricle.

Tue CentraL Nervous System.

189

(c) The fourth cranial, or trochlear nerve (n. trochlearis), 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 posterius)
underlies the posterior margin of the cerebellum, and extends
.s 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. 54),
the pons forms a broad com-
missural band extending trans-
versely across the brain ‘and
upward into the supports of the
cerebellum. Its surface is
divided into two parts by a
median ‘depression, the sulcus
hasilaris, occupied by the
basilar artery. '

(f) The anterior median fissure of
the spinal cord ends at the
posterior margin of the pons
in a faint depression, the fora-
men caecum.

(g) The anterior funiculus of the
cord is largely replaced forwards
by the pyramid (pyramis), a

narrow band extending forward:

on either side of the middle
line to the posterior margin of
the pons.

(bh) The trapezoid body (corpus
trapezoideum) lies in the angle
formed by the lateral margin
of the pyramid with the pos-
terior border of the pons.

(i) The fifth cranial, or trigeminal
nerve (n. trigeminus), arises by
two roots, a larger sensory

Fic. 54. The rhombencephalon.
Ventral view (the cerebellum not
figured).

c.t., trapezoid body;
caecum; fl.c., cervical flexure; f.m.a.,

f.c., foramen

anterior median fissure; p., “pons;

p.c., cerebral peduncle (mesencep-
halon); py., pyramid.
III, oculomotor nerve; IV, troch-

lear; V1, portio major of the trige-
minus; , portio minor; VI,
abducens; VII, facial; VIII, acoustic:
IX-XI, glossopharyngeal, vagus, and
spinal accessory group; XII, hypo-
glossal; CI, first cervical spinal.

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, the portio minor joining 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
in the semilunar ganglion, the latter lying in a depression at the
anterior ventral end of the petrosal bone.

190
(3)
(k)

()

(m)

ANATOMY OF THE Rassrr.

The sixth cranial, or abducent nerve (n. abducens), 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 Atom 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. In addition
the nerve receives a sensory filament, the portio intermedia or
intermediate nerve.

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 back-
ward on the spinal cord, its roots, about ten in number,
arising as far back as the fifth cervical spinal nerve.

The twelfth cranial, or hypoglossal nerve (n. hypoglossus),
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.

4. The arteries of the brain may be traced on its ventral surface as

follows:

(a)

(b)

(c)

(d)

(e)

(f)

(g)

The basilar artery (a. basilaris) is a median trunk formed on
the ventral surface of the medulla oblongata by the 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..

The posterior cerebral artery (a. cerebri 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.

The superior cerebellar artery (a. cerebelli superior) is a
branch of the posterior cerebral, passing to the anterior
portion of the cerebellum.

The cut end of the internal carotid artery lies on either side
of the tuber cenereum. It is connected backwards with the
posterior cerebral.

The middle cerebral artery (a. cerebri media) is given off
from the internal carotid, passing to the middle portion of
the hemispheres.

The anterior cerebral artery (a. cerebri anterior), the con-
tinuation of the carotid, passes to the anterior portion of
the ventral surface and the olfactory bulb. The anterior
cerebral is connected with that of the other side, a complete
anastomotic loop being formed around the hypothalamus by
combined branches of the vertebral and carotid arteries.
This is the circle of Willis.

THE Centra, Nervous System. 191

5. By dividing the supports of the cerebellum on either side, the
ntire structure may be removed and the surface exposed, as in Fig
5, for an examination of the structures of the dorsal surface of the
hombencephalon. The posterior medullary velum is removed with the
erebellum, but a small.portion of the anterior medullary velum should
emain in place. ;

(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.

(b) The rhomboid fossa (fossa
rhomboidea) is the shallow de-
pression enclosed by the thick
lateral and anterior walls and
floor of the ventricle. The
middle line shows a shallow
depression, the posterior me-
dian 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 represented by
their cut ends, are formed by
fibre-bands passing into the

- j = Fic. 55. The rhombencephalon.
cerebellum from adjacent ven Dorsal view, after removal of the

tral portions of the brain. In cerebellum: "b.c., brachium conjune-
5 D tivum; .p., brachium pontis; cl.,
each a middle band, the clava; he inferior colliculus (me-

brachium pontis, enters the sencephalon); c.r., restiform body;

z e.m., medial eminence, f.c., tasciculus
pons; an anterior band, the cuneatus; f.g., fasciculus gracilis;
br hi C ti t f.m.p., posterior median fissure of

achium conjunctivum, enters the rhomboid fossa; f.r., gore

1 fossa; s.m.p., posterior median sulcus

the mesencephalon, while a of the medulla; s.l.p., posterior

posterior connection 1s estab- rae in Spee! v.m.a., anterior
lished with the medulla through ™°C™*"Y YOu™

the restiform body.

(d) The lateral wall of the fossa is formed by a thick ridge of
nervous matter, convex on its medial side, the restiform
body (corpus restiforme). Its anterior portion bears a large
spherical elevation overlying the origin of the acoustic nerve.

192
(e)

ANATOMY OF THE RABBIT.

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 ter-
minating forwards in a club-shaped expansion, the clava.
The lateral portion, the fasciculus cuneatus, passes into the
restiform body.

6. The brain may be divided by a median vertical section, and one-
half examined from the medial surface (Fig. 56). In addition to many
of the features already made out on the surface the following may be

noted:

(a) The deep but extremely narrow cavity formed by the third
ventricle is the first space appearing in the brain from the
anterior end, the first two (paired) ventricles lying laterally
in the hemispheres. They are connected with the third
ventricle by a narrow transverse canal, the interventricular
foramen (foramen interventriculare).

Fic. 56. The brain in median section: a., anterior commissure; a.c., cerebral aque-

duct; b.o., olfactory bulb; cb., cerebellum; c.cl., corpus callosum; c.f., body of the
fornix; cli i., inferior colliculus; cl.s., superior celliculus; c. m., "mammil ary body;
c.0., optic chiasma; c.p., pineal body; fA. c., cervical flexure; h., habenular cOmmissure;
h.c., cerebral hemisphere: hp. hippocampus; inf., infundibulum; 1.t., laminal terminalis;
m. of, medulla oblongata; p., posterior commissure; p.c., chorioid ‘plexus of the third
ventricle; pd.c., cerebral peduncle; pn., pons; sp., splenium; s.pl., septum pellucidum;

t.c.,

tuber cinereum; th., thalamus, massa intermedia; v.m.a., anterior medullary

velum; v.m.p., posterior medullary velum; v.q., fourth ventricle: v.t., third ventricle.
I, olfactory nerve (origin); II, optic nerve.

(b) The anterior boundary of the third ventricle is formed

(c)

ventrally by the narrow partition separating the two hemi-
spheres, in the dorsal portion of which is the small anterior
commissure (commissura anterior). The ventral portion of
the ventricle is projected toward the optic chiasma forming
the recessus opticus, and into the infundibulum, forming the
recessus infundibuli.

The mesencephalon contains no ventricular expansion, its
substance being perforated only by a narrow tube, the cere-

(d)

(e)

Tue Centra, Nervous System. 193

bral aqueduct (aquaeductus cerebri), which connects the third
with the fourth ventricle.

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 downward,
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 mammillary body, and
passing upward as the columns of the fornix (columnae fornicis), meet
in the body of the fornix, and afterwards diverge laterad as the pillars
of the fornix (crura fornicis), ending in the hippocampus.
Between the body of the fornix and the anterior portion of the
corpus callosum is a thin area of the wall, the septum pelluci-
dum, the lateral ventricles lying close together in this region.

7. The nervous matter covering the corpus callosum may be removed
‘om one hemisphere by first marking out a triangular area on the
orsolateral surface; then scraping the material carefully away until the
thite surface of the corpus callosum is well exposed. By removing the
orpus callosum the interior of the hemisphere may be examined.

(a)

(b)

(c)

(d)

The lateral ventricle (ventriculus lateralis) is the extensive
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 moder-
ately thick roof and dorsolateral wall, consists largely of the
peripheral grey cortex described as the pallium.

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. ;

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.

8. The passage of the olfactory nerves to the ethmoturbinal surfaces
1ay be traced by removing the nasal bones and working downward
yward the cribriform plate, or the remaining portion of the skull con-
aining the nasal region still intact may be divided vertically for a more
xtended examination of the nasal fossae. The features to be observed
re largely those described in connection with the skeleton (pp. 83, 92).

APPENDIX.
THE PRESERVATION OF MATERIAL.*

The method commonly used in the preparation of material for
dissecting purposes consists in first embalming the body with suitable
preserving fluids; afterwards filling the arteries with a colored injection
mass, so that they are more easily traced. The ‘objects served by
embalming are: (1) preserving the body from decomposition 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 accomplished, first, by introducing the preserving
fluid through the bloodvessels, instead of by immersing the animal, as
was formerly the practice; secondly, by using in the preserving fluid
such materials 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
throughout dissection. .

A suitable fluid for the purpose is that recommended by Keiller} for
the preservation of human subjects. The formula is as follows:

Formalin............ Jae Ga ek a aes: ae Lead parts
Carbolic Acid........ 2.2... be cme He cee eee
GIVGEri:, as. Aedes FOG. AE SS! Eee Gees een BLOODS
Waters cei dy shee: Rar eteg ne Ne ai Mele. ah Ou Os
100.0

A convenient method of making up the fluid, especially when em-
balming 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 6 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

*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 textbooks may also be suggested.

+Keiller, W. ‘‘On the Preservation of Subjects. etc.’’ (American Journal of
Anatomy), Vol. II., 1902-3. : :

THE PRESERVATION OF MA‘TERIAL. 195

af the fluid; and the height of the pressure column. Not less than
1500 ce. should be allowed for each specimen.

The apparatus needed for. embalming includes a reservoir for the
Juid, provided with an exit pipe to which a rubber tube may be at-
tached; about 6 feet of rubber tubing to connect with the operating
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
lesired thinness. The tubing used for the purpose should be of about
3 mm. outside diameter. The cannula when completed should be about
7 cm. long; and its narrow end should have a uniform diameter of
|.5-2 mm. for about 2 cm. at the tip. The tip should be touched lightly
n the flame in order to round the margin by fusion, otherwise it might
lamage 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
liameter of 4mm., i.e., of proper size to slip on and off the cannula easily,
sut yet to retain its hold on the latter under moderate pressure.

The reservoir for holding the embalming fluid may be an aspirator or
rrigator bottle, an enamel fountain, percolator or ordinary funnel. It
nay have a capacity of one or two quarts. The capacity, however, is
mmaterial, so long as the operator keeps the fluid replaced. The
‘eservoir is suspended in such a way that it may be moved up and down
vithin a distance of four feet above the top of the operating table.

At the time of beginning the embalming process the operator should
1ave before him the reservoir, suspended at a height of about three
eet, and a column of fluid, free from air-bubbles or foreign material to
he tip of the cannula. This condition must be maintained throughout
he operation. If at any time the pressure falls in the apparatus
ufficiently to admit air, or allow coagulated blood to run back through
he cannula, there is almost certain to be trouble, not only with the
pecimen under treatment, but also others which come after. The
column of fluid is held back until the proper time by a clamp placed on
he rubber tubing.

The animal is killed by administering ether or illuminating gas. It
s placed on its back on the table, with the head away from the operator.
“he skin is first divided by a small incision on the inner side of the right
high.* By inserting the fingers well down into the incision, the skin
aay be torn backward and toward the ventral middle line, and at the
ame time the superficial epigastric vessels will be carried with the
ubcutaneous tissue well out of the operator’s way. Small portions of

* The embalming may be done from the common carotid artery of the neck, a
essel much larger than the femoral artery and therefore easier of manipulation.
‘his is not recommended, however, becauise of the damage done'to various important
sructures of the cervical region.

196 ANATOMY OF THE RABBIT.

the inner surface of the thigh and of the abdominal wall will be exposed.
The white cord representing 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 be-
longing 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 the 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, flattened or collapsed condition,
and by 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 isinserted. 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 the
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.

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
atranging the animal will be amply rewarded by convenience in dis-
section. 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 backofthe animal. The body
should be turned slightly to the operator’s left.

The animal is sufficiently embalmed in two hours. About eight
animals may 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.

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 operator 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

THE PRESERVATION OF MATERIAL. 197

the body, and no clogging of the vessels need be feared. The fluid
ay usually be observed running in the cannula, and, of course, falling

the reservoir. Finally, there are characteristic changes in the body.
ae abdomen becomes greatly distended, the subcutaneous tissue
rollen, the eyes protrude, and there is usually more or less frothing at
e nose. Leakage, either in the area of the incision or at the nose, is
metimes a sign of too much pressure. In the former case the leakage
frequently behind the cannula, and may be stopped by artery forceps.
_ the latter case there is no recourse but to confine the fluid to the
sal cavity by tying the nostrils.

After the embalming process the rubber tube is disconnected from
e cannula, the latter being left carefully in place. The animal is then
t aside for twenty-four hours in an upright position. After this it is
ady for injection.

The injection mass may be made by mixing ordinary starch and
iter to the consistence of thin cream; then adding a finely-ground
loring material, such as vermilion or a very small quantity of carmine.
lere is some advantage in using a 5% formalin instead of water alone
making up this mass, the arteries having afterwards a brighter appear-
ce, which is doubtless due partly to better preservation and partly to
2 fixing of the starch in the vessels. The mass must be thoroughly
ined before use, in order to avoid the presence in it of particles which
» too large to go through the cannula. The injection is made with
iyringe, the latter being provided with a rubber tube of the same kind
that used in the embalming process. The mass is sent in by applying
rentle, even pressure, and it is sometimes advantageous to allow the
ection to run backward and forward in the tube, each time applying
ittle more pressure. When the vessels have been filled in this way,
> tube is clamped. By drawing on one cord of the ligature the knot
loosened sufficiently to withdraw the cannula, and by keeping a
yer pressed on the end of the vessel, the knot may then be drawn
ht without loss of injection.

It sometimes happens, despite ordinary precautions, that the cannula
somes clogged either with settled starch or with coagulated blood.
this case it may be easily removed, cleaned, and replaced. The same
inula should always be used.

Material prepared according to the directions given above will keep
efinitely, provided, however, that precautions are taken to avoid con-
uination from the surface. These are especially necessary in view of

thick coating of hairs. It is a good plan, therefore, to sponge the
mal with a preserving fluid which will penetrate the coat imme-
tely, or if many specimens are being prepared, to immerse the whole
mal for a moment. A suitable fluid for this purpose is formalin-
yhol, made by adding 2% of formalin to a mixture of equal parts of
inary spirit and water. The alcohol ensures immediate penetration

assists the formalin in preservation. The fluid should be squeezed
of the coat as much as possible. The presence of a considerable
ntity is not harmful, unless, after the dissection has begun, the fluid
ald gain access to the tissues and destroy the effect of the glycerin
he embalming fluid.

15

198 ANATOMY OF THE RABBIT.

For the storage of material either before or during dissection no pre-
caution is necessary except that of protecting the body from undue
exposure to evaporation. A convenient plan for handling the material,
however—one that is in use at the present time in the laboratories of the
University of Toronto—is that of providing for each specimen a zinc-
lined copper box, with sliding top, and of dimensions ample for the
largest specimens—namely, 6x 6x 20inches. This type of storage box
was designed several years ago by Professor Ramsay Wright for the
purpose, but is one which has proved useful for storing purposes in many
other ways.

INDEX

«Abdomen, 111
Abdominal aorta, 133
cavity; 50, 116
wall, muscles of, 113
Abduction in limbs, 32
Accessory respiratory. tracts, 43
See Nose.
Acinous glands, 11
Acoustic meatus, external, 77, 88, 89, 111
internal, 81, 89
Adaptation, 5
Adduction in limbs, 32
Adipose tissue, 13
Afferent nerves, 22
Albinism, 14
Alveolar glands, 11
Anal aperture, 111
glands, 11, 130
Analogy, 5
Anastomoses of intestinal vessels, 116
Anatomy defined, 3
Ankle, bones of, 108
joint, 156
Aorta, see Arteries.
Aortic arches, branchial, 44
Aperture, anal, 111
ot auditory tube, 165_
of larynx, 165
of mouth, 110
of nose, external, 111
internal, rig 165
piriform, 83,
of thorax, inferior, superior, 74
urinogenital,
of uterine Hee snteeals 131
of uterus, external,
Aponeuroses, 13
Appendicular skeleton, 32, 98
Arachnoidea, 184
Arch of aorta, 173
Arches, branchial aortic, 44
visceral, 28, 31
Arrectores pilorum, 10
Arterial ligament, 44, 176
Arteries, chief
aorta, abdominal, 133
arch of, 173
thoracic, 178
development of, dorsal, ventral, 29, 44
carotid, 160,
coeliac, 117, 118_
iliac, 133
intercostal, 133, 178
lumbar, 133
mesenteric, inferior, 126
superior, 117,
pulmonary, 44, 176
renal, 127
spermatic, internal, 129, 131
subclavian, 173
See Bloodvessels,
\rthrodia, 19
\rticulations, nature of, 17
of ankle, 156
of hip, knee, 155
\symmetry, 24
in digestive tube, 40
in vascular system, 24, 45
itria of heart, 43, 17
1uditory epithelium, 12
ossicles, 77, 90
tube, 79, 89, 165
xial skeleton, 30, 68
in chordates, 8
xis, basicranial, 31, 77
basifacial,

Axis—continued.
longitudinal, of body, 23, 30
Dogiyon of organ systems with respect to,

Axillary fossa, 111
lymph nodes of, 188
vessels and nerves of, 137

Ball and socket joints, 18
Basicranium, 31,
Biceps muscles, 20
Bilateral symmetry, 23
Bile duct,
Biology, 3
Bipennate muscles, 20°
Bladder, urinary, 128
Bloodvessels, general structure of, 21
lining membranes of, 12
of abdomen, 133; wali, 113, 115, 174
of brain, 190
of limbs, anterior, 137, 142
posterior, 149, 153
of neck, 160, 162
of orbit, 168
of pelvis, 133
See Arteries, Veins.
Body, divisions of, 110
posture of, 23, 24
pituitary, 35, 188
Bones, structure, development, types of, 14
articulations of, 17
Brain, general divisions, 34
dissection, 186
flexures of, 38
olfactory, 34, 186
Branchiomerism, ne 28
Bronchi, 177
Bulb, olfactory, 34, 186
Bulbourethral gland, 131, 132

Caecum, 42, 12
Capillary ee blood, 43
lymphatic, 46
Capsules of joints, 18
of sense organs, 31
Carpus, bones of, 102
Cartilage, structure of, 14
bones, 15; of skull, 31
Caudal vertebra,
Caval veins, inferior, 117, 134, 176
superior, 174, 176
Cavity, abdominal, 50, 116
of central nervous system, 34
of larynx, 166
of mouth, 42, 164
of nose, 48, 82, 92, 193
orbital,
pericardial, 49, 175
peritoneal, 50, 116
pleural, 49, 177
serous, 49
of skull, 79
of thorax, 74
tympanic, 89, 90, 171
Cell, structure of, 8 ;
Central nervous system, general divisions, 34
brain, 186
spinal cord, 184
Cerebral cranium, 31
hemispheres, 34, 186
nerves, see Nervous System.
Cerebellum, 36, 188 :
Cerebrum, 36 '
Cervical vertebrae, 70
Characters of animals, 5
Chondrocranium, 31

200

Chordates, characters of, 8
Chorioid plexus, structure of, 36
of lateral ventricles, 193°
of third ventricle, 187

Circulation, organs of, 26
See Vascular and Lymphatic Systems.
pulmonary, 43
portal, 45
systemic, 43
Classification, purpose of, 6
of organ systems, 26
Clavicle, 100
Clitoris, 111,
structure of, 132
Cloaca in lower vertebrates, 46
Cochlea, 171
Celom, 49, 116
Colon, 41, 124
Coloration of skin, etc., 13
Column, vertebral, 68
Comparative anatomy defined, 3
method of,
Conjugation in Protozoa, 9
Connective tissues, 12
Convergence, 5
Condyles of femur, 106
occipital, 76, 85
of tibia, 107
Cord, spermatic, 129°
spinal, 34, 184
vocal, 166
Corpora quadrigemina, 188
Corpus callosum, 186, 193
Coxal bone, 103
Cranial cavity, 79
nerves, see Nervous System.
Craniota, characters of,
Cranium, cerebral, visceral, 31
See Skeleton.

Deferent ducts, 129
Dental formula, 42
Dentition, in rabbit, 42
in rodents, 7
Descent of testis, 48
Descriptive anatomy, 3
terms, 23
Diaphragm, 179
Diarthrosis, 18
Digestive tube, wall of, 10, 21, 119
Digestive system, 40
glands of, 11; anal, 130; oral, irifraorbi-
tal. 167; parotid, 157; submaxillary,

liver, 120: pancreas, 118, 122
intestines, small, 122; large, 123
mouth, 42, 164
pharynx, 48, 164
oesophagus, 41, 164, 178; connection with

stomach,
stomach, 41, nC
Digits, anterior limb, 108, 112
posterior limb, 109, 112
Dissection, method’ of, 3
of rabbit, 110
Ducts, of liver, 121
nasopalatine, 165
of oral glands, infraorbital, 167
parotid, 157; submaxillary, 159
of pancreas, 122
of prostate, 159
thoracic, 46
urinogenital, 46, 127, 129, 131
Ductus arteriosus, 4
deferens, 129
Duodenum, 41, 122
Duplicidentata, 7
Dura mater, 184

‘Ear, external, 111
middle, 89, 90, 171
internal, 171; capsule of, 31

INDEX.

Efferent nerves, 22
Egg, fertilized, 9
Egg-laying mammals, i
Elastic fibres of eprinesiiye tissue, 12
Elbow, position of, 33,
Embryo, organ systems os 29
Embryonic kidney, 4
Embryology, 3
method of, 4
Enarthrosis, 18
Encephalon, see Brain.
Endothelia, 12 .
Environment, relations of animals to, 5
Epicardium, 175
Epicondyles, of femur, 106
of humerus, 100
Epidermis, 10
Iypididymis, 129
Epiglottis, 165
Epiphyses of bones, 17
Epistropheus, 70
Epithelial, tissues, 9
Erect posture in man, 24
Eustachian, tube, see Auditory Tube.
Extension in limbs, 3
Fye, 111; dissection, M66
Eyelids, 111

Facets, articular, of vertebr, 70, 71
Fascia, 13
Fat, 13
Femur, 105
Fertilized egg, 9
Fibres, of connective tissue, 12
muscle, 19
nerve,
Fibrocartilage, 14
Fibrous connective tissue, 12
Fibula, 107
Flexion in limbs, 32
Flexures of brain, 38
Flocculus of cerebellum, ge
Follicles, of hairs, 10, 11
lymphatic, 45; of eae. 123; of tonsil,
165

ovarian, 131
Foot, 112
skeleton of, 108
See Hand.
Foramina of skull,
Forearm, 111
muscles of, 140
nerves and vessels of, 142
skeleton of, 101
Fore brain, 34,
Formula, dental, 42
Function, relation of structure to, 4
Functional organs, 5

4
a pees 120
anglia
spinal, 38, 184
sympathetic, of head, 170
prevertebral; celiac, 117
inferior mesenteric, 126; superior
mesenteric, 117
of trunks, cervical, 164, 175
thoracic, 178; lumbar,
caudal, 134
Gastric glands, 11
General. anatomy, 3
Genital organs, external, 111
female, 131
male, 128
Ginglymus, 18
Girdle, pectoral, 98

chief, 78

sacral,

of digestive system, 11
anal, 180; gastric 11; oral, 157, Pan
167; liver, 120, pancreas, 118, 12

Glands—continued.
epithelial, 10
of lymphatic system, 45
axillary, 138; inguinal, 113
mesenteric, 116
of orbit, Harderian, lacrimal, 167
of skin, 11
inguinal, 11, mammary, 7, 11, 113
suprarenal, 117
thymus, 172
thyreoid, 160
of urinogenital system,
: bulbourethral, prostate, 131
Gliding joint, 19
Gonads, 48
Grey substance of nervous system, 23
Gross anatomy, 3
Gubernaculum, 48, 129
Gustatory epithelium, 12; organs, 165

Hairs, structure of, 10

Hand, 111
skeleton of, 102

Hard palate, 42, 165

Hares and rabbits, distinction of, 6

Head, dissection of, 157
skeleton of, 75

Heart, 48, 175

Hemispheres of brain, 34, 186
of cerebellum, 18

Hepatic portal system, 45
See Portal Vein.

Heredity, 5

Hind brain, 36

dinge joints, 18

Hip joint, 155

distology, 3

Tomogeny, 5

Tomoplasy, 5

Tumerus, 100

Tyoid apparatus, 97°
arch, 28

Typophysis, 35, 188

leum, 123
lium, 104
ncisors in rodents, 7 :
nguinal furrow, 111; lymph nodes of, 113
glands, 11
nsertion of muscles, 20
ntegument, see Skin.
nterarticular cartilages, 14
ntercellular substance, 12
nterpretation of structure, 4
ntestines, 40, 41
divisions of, 122
large, 123
lymphatics of, 116, 123
muscle layers of, 21
serous coat of, 116
small, 122
avoluntary muscles, 19, 20
schium, 105

2junum, 123 ~
vints, structure of, 1
ankle, 156; hip, knee, 155
igular veins, external, 158; internal, 160

idney, 127
embryonic, 47
position of, 48

nee joint, 18, 155
position of, 33

abyrinth of ear, 171
ethmoidal, 92
icrimal apparatus,
Harderian and lacrimal glands, 167
nasolacrimal canal, 82, 94; duct, 166
icteal vessels, 116
irynx, 165

INDEX.

; 201

Leg, 112
muscles of, 150
nerves and vessels of, 153
skeleton of, 107
Leporide, characters of, 6
Lepus, genus defined, 6
Ligaments, 13
Limbs, general position of, 32
anterior, divisions, 111
dissection of, 1385
skeleton, 98
posterior, divisions, 112
dissection of, 144
‘ skeleton, 103
Lips, 110
Tjiver, 11, 120
Long axis of body, 23, 30
Lumbar vertebra, 71
Lumbosacral plextis, 144, 154
Lungs, 43, 177
Lymph, 9
Lymphatic system, 45
follicles of sacculus rotundus, 123
vermiform process, 124; tonsil, 165
glands, axillary, 138; cervical,
inguinal, 113; intestinal, 123; mesen-
teric, 116,
vessels of mesentery, 116
thoracic duct,

Mammalia, characters of, 7

Mammary glands, 7, 11, 113
nipples of, 1

Mandible, 84, 96

Mandibular arch, 28

Marsupial mammalia, 7

Meatus, acoustic, external, 77, 88, 89, 111
internal, 81, 89

Medulla oblongata, 37

Membrane bone, 15; of skull, 31
mucous, 10
tympanic, 171

Meninges of central nervous system, 184

Mesencephalon, 36, 188

Mesenchyme, 12 :

Mesenterial small intestine, 41, 123

Mesentery, 116, 123
structure of, 50

Mesoderm, 27

Metacarpus, 103

Metatarsus, 109

Microscopic anatomy, 3

Mid-brain, 36, 188

Middle ear, see Ear.

Mixed nerves, 22

Monotremata, 7

Morphology, 3

. Morphological aspect of structure, 4

Motor nerves, 22
Mouth, cavity of, 42, 164

glands of, see Digestive System.
Mucous membrane, .

tunic of stomach, 119; of intestine, 10
Multicellular organisms, 9 -
Muscles, structure and types of, 19

of abdominal wall, 113

of face. 158 f

of limbs, anterior, 135; posterior, 144

‘of mastication, 161

of neck, 159, see vertebral

occipital, 182

of skin, 118, 135, 157

of tongue, 162

vertebral, 180

Nasal cavity, 43, 83, 92, 193

Nasopalatine ducts, 165

Nasopharynx, 164

Neck, dissection of, 158

Nerves, structure and types of, 22

Nervous system, general divisions, 34
central, brain, 186; spinal cord, 184

'

202 ‘

Nervous system—continued.
peripheral,
cranial nerves, 39
I. olfactory, 186
II. optic, 167, 188
* oculomotor, 169, 188
. trochlear, 169, is9
Vv. hergemanal, “162, 169, 170,
1

- abducent, 169, 190
. facial, 157, 170, 190
. acoustic, 190
IX. gichopiarynece!, 163, 164,
9
X. vagus, 119, 160, 164, 174,
178, 190

XI. accessory, 164, 190
XII. byperiossal, 160, 163, 164,

spinal nerves, composition of, 38

cervical, 1385, 1
lumbar, sacral, 144, 154
thoracic, 178

plexuses of, brachial, cervical,

138; lumbosacral, 144, 154
sympathetic system, 38
ganglia, celiac, 117; mesenteric,
inferior, 126; superior, 117; of
head, 170, see trunks.
plexuses, abdominal, 118, 126
cardiac, 175 .
trunks, cervical, 160, 164; lumbar,
sacral, 134; thoracic, 178
Nervous tissues, 21
Nose, apertures of, external,

internal, 83, 164
cavity of, 43, 83, 92, 193
Notochord, in chordates, 8; in rabbit, 29, 30

Ochodontide, 7

Oesophagus, "41, 164, 178

Olfactory brain, 34, 186
epithelium, 11

Omenta, greater, lesser, 117

Ontogeny, 4

Orbicular muscles, 20

Orbit, 75; structures of, 166

Organs, definition of, 8
relative development of, 5
visceral, 49

Organ systems, see Systems.

Origin of muscles,

Ossicles of ear, 77, 90

Osteocranium, 31

Osteology of rabbit, 68

Ovary, 131; Position of, 49

Oviduct, 47, 131

Ovum, 9

Palate, 42, 165
Pancreas, 11, 118, 122
Parotid gland, 11, 157
Pectoral girdle, 98
Pelvic girdle, 103
Penis, 111; structure of, 129
Pericardium, 49, 175
Perichondrium, 16
Periosteum, 15
Peritoneal cavity, 50, 116
Peritoneum, general ‘relations of, 50; parietal,
115; visceral, 116
of bladder, 128
of intestines, 116, 122, 128, 124, 125
of kidney, 127
of liver, 120
of ovary, 131
of stomach, 117
of testis, 129
Phalanges, teas of hand, 103, 112; of foot,
109, 112

111; piriform,

INDEX.

Pharynx, 43, 164
Phylogeny, 4
Physiological aspect: of structure, 4
Physiology, 3
Pia mater, 184
Pigmentation of an. etc., 13
Pineal body, 36,
Pituitary body, 35, 88
Placenta, 7
Placental mammals, 7
Planes of body, 23
Plantigrade foot, 7, 33
Pleura, pleural cavity, 49,-177
Plexuses, of spinal nerves, brachial, 138
cervical 188; lumbosacral, 144, 154
of sympathetic nerves, abdominal aortic,
126; cardiac, 175; celiac, 118, hypogas-
tric, 126; mesenteric, ‘inferior, 126;
superior, 118; renal, spermatic, 126-
Pons, 38, 189
Popliteal fossa, 112
Portal Eyetets hepatic, 45, see Portal Vein.
renal,
Portal vein, 119, 121
Posture of body, in ae 24
in quadrupeds, 23,
Prevertebral ganglia, ca
Pronation, 33
Prone position of body, 23
Prosencephalon, 34, 186
Prostate, 131
Protozoa, cells of, 9
Pubis, 105
Pulmonary artery, 176; circulation, 43

Quadriceps muscles, 20

Rabbit, races of, 6
Radius, 10L
Rami.communicantes, 38, 184

~ Recapitulation, law of,

Rectum, 123
Reduced organs, 5
Regional sections, 51
Renal portal system, 45
Replacing bones, 15
Reproduction in Protozoa, 9
Reproductive organs, 46
female, 131
male, 128
Respiration, branchial, pulmonary, 44
relation of ribs to, 74; diaphragm, 179
Respiratory system, 43
accessory respiratory tracts, see Nose.
lungs, 177
respiratory tracts, eo 177
Retrogressive organs,
Rhombencephalon, 34, O96, 188
Ribs, 73
Rodents, characters of, 7
Roots of spinal nerves, 38, 184

Sacculus rotundus, 122
Sacral vertebra,
Sacrum, 72
Scapula, 98
Scrotum, 111, 128
Sebaceous glands, 11
Sections, regional, 51
Segmentation of body, 27
Seminal vesicle, 130
Sense organs, special, capsules of, 31 .
epithelium of,
See Ear, Eye, Nose.
Sensory spitbella, 11
hairs, 10, 110
nerves, 22
Septum of nose, 83
of thorax, 175

INDEX.

Serous cavities, 49
membranes, 12, 49
tunic of intestine, 116
Sesamoid bones,
of limbs, anterior, 103; posterior: 109
Simplicidentata, 7
Skeletal system, 30
tissues, 12, 14
Skeleton, appendicular, 32, 68
of anterior limb, 98
of posterior limb, 103
axial, 30,
skull, 75; Pemery composition of, 31;
bones of,
vertebral ae 68
Skin, structure of, 10, 13, 113
glands of, 11
muscles of, 113, 135, 157
Skull, see Skeleton.
Smooth muscle, 19, 21
Soft palate, 165
Somatic nerves, 22
Special anatomy, 3
Spermatic cord, 129
Sphincter muscles, 20
Spinal column, 30, 68
cord, 34, 184
nerves, see Nervous System.
Spleen, 117
Sternum, 74
Stomach, 41, 116; structure of wall, 119
Subcutaneous tissue, 13,
Subfunctional orsane, 5
Sublingual gland, 1
Submaxillary aa. 11, 159
Sudoriparous glands, 11
Supination, 33
Suprarenal gland, 117
Sweat glands, 11
Symmetry, bilateral, 23
Sympathetic nervous system, see Nervous
System.
Symphysis, 18; of mandible, 84
of pelvis, 103
Synarthrosis, 18
Synchondrosis, 18
Systems, organ, defined, 8, 26
classification of,
general arrangement, 27
in embryo, 29
digestive, 40
lymphatic, 45
nervous, 34
respiratory, 43
skeletal, 30
urinogenital, 46
vascular, 43
Systemic circulation, 43

Tarsus, bones of, 108
Taste buds of tongue, 165
Teeth of rabbit, 42; of rodents, 7
Tendon, 13, 20
Tentorium cerebelli, 80
Terminology, 23
Terrestrial vertebrates, 8
Testis, 48, 129; descent of, 48
Thalamus, 36, 187
Thigh, 112; muscles of, 144
nerves and vessels of, 149
[Thoracic aorta, 178
cavity, 74
duct, 46
vertebre, 71
Thorax, bony, 74
dissection of, 172
[Thymus gland, 172
Thyreoid gland, 160
Tibia, 107

203

Tissues, defined, 8
classification of, 9
connective, 12
epithelial, 9
muscular, 19
nervous, 21

skeletal, 12, 14
Poneue, 162, 165
Tonsil, 165

Trachea, 43, 160, 177
Tracts, respiratory, see Respiratory System.
Triceps muscles, 20
Trunk, divisions of, 111
skeleton, 68
Trunks, lymphatic, 46
sympathetic, 38, 134, 160, 164, 178
Tube, auditory, 79, 89, 1
digestive, wall of, 10, 21, 119, see Diges-
tive System.
neural, 34
uterine, 131
Tunics of digestive tube, mucous, 10
muscular, 2
serous, 116
of stomach, 119
Turbinated bones, 83, 9
‘Tympanic cavity, 89, 90, 171
membrane, 171

Ulna, 101
Unicellular glands, 11
-organisms, 9
Unipennate muscles, 20
Ureter, 127; epicystic position of, 46
Urethra, 46, 130
Urinary organs, 46, 127
Urinogenital aperture, 111
sinus,
system, 46, 127
Uterine tube, 131
Uterus, 181; types of, 48

. Vagina, 132

Vascular system, 43
asymmetry in, 24, 45
See Arteries, Bloodvessels, \Veins.
Veins, trunk, caval, inferior, 117, 134, 176
superior, 174, 176
hypogastric, iliac, 134
jugular, external, 158; internal, 160
portal, 119, 121 *
renal, 127
spermatic, 129, 181
Ventricles of brain, 34, 187, 191, 193
of heart, 43, 175
Vermiform process, 123
Vertebral column, 68
Vertebrates, characters of, 8
terrestrial,
organ systems in, 27
Vesicle, seminal, 130
Vestibulum 46, 132
Visceral arches, 28, 81
nerves, 22
cranium, 31
organs, 49
peritoneum, 116
Vocal folds, 166
Voluntary muscles, 19
Vulva, 1

White fibres of connective tissue, 12
White substance of nervous system, 23
Wild rabbits, species of, 6

Wrist, bones of, 102

Yellow fibres of connective tissue, 12

Zoological position of rabbit, 6

ekesiaees