J-
<3V.
AN INTRODUCTIOxNf
OSTEOLOGY OF THE MAMMALIA.
AN INTRODUCTION
OSTEOLOGY OF THE MAMMALIA
•BEING THE SUBSTANCE OF
THE COURSE OF LECTURES DELIVERED
AT
THE ROYAL COLLEGE OF SURGEONS OF ENGLAND
IN 1870.
BY
WILLIAM HENRY FLOWER, F.B.S., F.R.C.S., SE
III
HUNTERIAN PROFESSOR OF COMPARATIVE ANATOMY AND PHYSIOLOGY,
AND
CONSERVATOR OF THE MUSEUM OF THE COLLEGE.
WITH NUMEROUS ILLUSTRATIONS.
SECOND EDITION, REVISED.
MACMILLAN AND CO.
1876.
[V/id Right of Translation ami Reproduction is Reserved.]
LONDON I
F. CLAY, SONS, AND TAYLOR,
BREAD STREET HILL, QUEEN VICTORIA STREET.
tt'lo
LIBRARY
741810
UNIVERSITY OF TORONTO
PREFACE.
The desire to acquire a knowledge of the structure of some
portion at least of the Animal Kingdom, now becoming so
general, is often checked by the difficulty of determining
where to make a beginning amid the vast extent and
variety of the materials at hand.
I have selected for my first course of lectures on Com-
parative Anatomy at the Royal College of Surgeons, the
structure and modifications of the Skeleton, because, as
the framework around which the rest of the body is built
up, it gives, more than any other system, an outline of the
general organization of the whole animal, and also because
it is the most convenient for study, on account of the
facility with which it can be preserved and examined.
Moreover, Osteology has special importance in com-
parison with the study of any other system, inasmuch as
large numbers of animals, all in fact of those not at
present existing on the earth, can be known to us by
little else than the form of their bones.
In endeavouring to gain anatomical knowledge, it sig-
nifies little with which group of animals a commencement
is made.
vi PREFACE.
The structure of Man has undoubtedly a more universal
interest than that of any other organized being, and
has, therefore, been more thoroughly worked out ; and as
the majority of terms used in describing the parts com-
posing the bodies of Vertebrate animals were originally
bestowed on account of their form, relation, or real or
fancied resemblance to some object, as they were met
with in Man, there are advantages in commencing with
members of the highest class, and mastering their essential
characters before proceeding to acquire knowledge of the
other groups.
But as human anatomy may be taken as a point of de-
parture from which to set out in the study of that of other
Vertebrates, so, on the other hand, those whose special
duty it is to become familiar with its details, will find
themselves greatly assisted by some knowledge of the
structure of lower forms. Thus the essential characters
of the human skull will be much better understood if the
student will also make himself acquainted with those of
some simpler condition of Mammalian cranium, as that of
the dog or sheep.
Although the present work contains the substance of a
course of lectures, the form has been changed, so as the
better to adapt it as a handbook for students. Theoretical
views have been almost entirely excluded ; and while it is
impossible in a scientific treatise to avoid the employment
of technical terms, it has been my endeavour to use no
more than are absolutely necessary, and to exercise due
care in selecting only those that seem most appropriate, or
which have received the sanction of general adoption.
PREFACE. vii
With very few exceptions, all the illustrations have been
drawn expressly for this work, with great care and fidelity,
by Mr. R. W. Sherwin, from specimens in the Museum of
the Royal College of Surgeons.
September 24.//1, 1 870.
NOTE TO SECOND EDITION.
This edition has been revised throughout, and a new
diagram of the arrangement of the principal bones of the
skull introduced in place of the table at p. 104 of the
former edition.
I have to thank many friends for pointing out errors
and omissions, most of which, it is hoped, have now been
corrected.
May 22nd, 1876.
CONTENTS.
CHAPTER I.
PAGE
:lassification of the mammalia
CHAPTER II.
THE SKELETON 7
CHAPTER III.
THE VERTEBRAL COLUMN IO
CHAPTER IV.
SPECIAL CHARACTERS OF THE CERVICAL VERTEBRA IN THE
MAMMALIA 26
CHAPTER V.
SPECIAL CHARACTERS OF THE THORACIC AND LUMBAR VER-
TEBRA 45
CHAPTER VI.
SPECIAL CHARACTERS OF THE SACRAL AND CAUDAL VER-
TEBRA 60
b
x CONTENTS.
CHAPTER VII.
PAGE
THE STERNUM ' 72
CHAPTER VIII.
THE RIBS . 87
CHAPTER IX.
THE SKULL OF THE DOG 96
CHAPTER X.
THE SKULL IN THE ORDERS PRIMATES, CARNIVORA, INSECTI-
VORA, CHIROPTERA, AND RODENTIA 128
CHAPTER XI.
THE SKULL IN THE UNGULATA, HYRACOIDEA, AND PRO-
BOSCIDIA l62
CHAPTER XII.
THE SKULL IN THE CETACEA AND THE SIRENIA . . . . 185
CHAPTER XIII.
THE SKULL IN THE EDENTATA, MARSUPIALIA, AND MONO-
TREMATA 2C5
CHAPTER XIV.
THE SHOULDER GIRDLE 221
CONTENTS. xi
CHAPTER XV.
PAGE
THE ARM AND FORE-ARM ....... 24I
CHAPTER XVI.
THE HAND OR MANUS 254
CHAPTER XVII.
THE PELVIC GIRDLE 283
CHAPTER XVIII.
THE THIGH AND LEG 297
CHAPTER XIX.
THE HIND FOOT OR PES . 308
CHAPTER XX.
THE CORRESPONDENCE BETWEEN THE BONES OF THE ANTE-
RIOR AND POSTERIOR EXTREMITY AND THE MODIFICA-
TIONS OF THE POSITIONS OF THE LIMBS 328
INDEX m 34
AN INTRODUCTION
OSTEOLOGY OF THE MAMMALIA
CHAPTER I.
CLASSIFICATION OF THE MAMMALIA.
[t is not the object of the present work to enter in
letail into the subject of the Classification of the Mam-
lalia ; but, as it will be necessary to refer frequently to the
>rincipal subdivisions in which the various animals treated
►f are arranged, a brief outline of the system adopted will be
tecessary.
A perfect arrangement ot any group of animals can only
>e attained simultaneously with a perfect knowledge of their
structure and life history. We are still so far from this
that any classification now advanced must be regarded as
irovisional, and merely representing our present state of
mowledge. Moreover, as naturalists will estimate differ-
ently the importance to be attached to different structural
modifications as indicative of affinity, it must be long before
there will be any general agreement upon this subject.
2 CLASSIFICATION OF THE MAMMALIA. [chap.
The classification and the names of the subdivisions
used throughout this work correspond, in the main, with
those given by Professor Huxley in his " Introduction to
the Classification of Animals," 1869.
The whole of the animals composing the class are arranged
primarily in three natural divisions, which, presenting very
marked differentiating characters, and having no existing
intermediate or transitional forms, may be considered as
sub-classes of equivalent value, taxonomically speaking, though
very different in the numbers and importance of the animals
composing them.
These three groups, to adopt the names originally pro-
posed for them by De Blainville, are: — 1. Monodelphia;
2. Didelphia ; and 3. Ornithodelphia.
I. The Monodelphia, sometimes called Placentalia,
comprise the great bulk of the class. The main characteristic
of the animals composing it is, that their young are nourished
for a considerable period within the uterus of the mother
by means of an organ called the placenta, a villous and
vascular development from the outer surface of the foetal
envelopes, which, being in contact with corresponding
vascular developments from the inner wall of the uterus,
permits an interchange of materials between the circu-
lating fluids of mother and young, thus brought into the
closest proximity. This organ varies much in shape and
structure in the different minor divisions of the sub-
class.
It is very difficult to subdivide the Monodelphia into any
groups larger than orders, or to arrange these orders in
anything like a linear series, as most of them have affinities
in many directions.
One group may be placed apart as having no distinct
I.] MONODELPHIA. 3
relationship with any of the others, being chiefly distinguished
by negative characters. This is the order Edentata, com-
prising the Sloths, the Armadillos and Ant-eaters of America,
and the Pangolins and Orycteropus or Cape Ant-eater, of the
Old World. These are animals of generally low organiza-
|»n for the division to which they belong.
The remaining Monodelphian Mammals are : — 1.
umates, the highest order, culminating in the genus
01110 of Linnaeus, and comprising also all the animals
commonly known as Monkeys. With these are generally
united a group of very inferior structure (Lemurina), con-
taining the various species of Lemurs and allied animals,
which, without question, connect the Primates on the one
hand with the Insectivora, Carnivora, and Chiroptera on
the other ; though it is doubtful, at present, whether they
should be associated with the Monkeys, or -should con-
stitute a distinct order by themselves. 2. Chiroptera, or
Bats. 3. Insectivora, or Hedgehogs, Shrews, Moles, &c.
4. Carnivora, divided into the Terrestrial Carnivora, or
Fissipedia, Cats, Dogs, and Bears, and the various modifi-
cations of these types ; and the Aquatic Carnivora, or
Pimiipedia, Seals, Walrus, and Eared Seals, or Sea Lions.
5. Cetacea, containing two sub-orders, the Mystacoceti,
or Whalebone Whales, and the Odontcceti, Cachalots,
Narwhals, Dolphins, and Porpoises. 6. Sikenia, a small
order of aquatic vegetable-feeding animals, of which the
Manati (Manatus) and Dugong (Halicore) are the sole
living representatives. 7. Ungulata, the very large order
of hoofed quadrupeds, divided into the Perissodactyla, or
" odd-toed " Ungulates, containing the Horse, Tapir, and
Rhinoceros; and the Artiodactyla, or " even- toed," again
subdivided into four sections, a. The non-ruminating, or
Suiiia, consisting of the Pigs, Peccaris, and Hippopotamus.
4 CLASSIFICATION OF THE MAMMALIA. [chap.
b. The cushion-footed, or Tylopoda, the Camels and Llamas.
c. The Tragulina, or Chevrotains, a group of little deer-like
animals formerly associated with the Musk-deer. d. The
Pecora, or true Ruminants, comprising the Deer, Giraffes,
Antelopes, Sheep, Goats, and Oxen. The last three divisions
constitute the order Ruminantia of Cuvier. 8. Hyra-
coidea, an order consisting of a single genus, Hyrax, a small
animal having many affinities with the Perissodactyle Un-
gulata, with which it is often associated. 9. Probosctdea,
represented at present only by the two species of Elephant ;
and 10. Rodentia, a well-marked group, but with varied
affinities, both to the Insectivora and Primates on the one
hand, and to the Ungulata and Proboscidea on the other, and
also to the Didelphia. This order contains the Hares, Rats,
Guinea-pigs, Porcupines, Beavers, Squirrels, &c.
II. The sub-class Didelphia contains only one order,
Marsupialia, consisting of animals presenting great diver-
sity of superficial appearance and habits of life, although
all united by many essential anatomical and physiological
characters. The young are born in an exceedingly rudi-
mentary condition before the formation of a placenta, and
are transferred to the nipple of the mother, to which they
remain firmly attached for a considerable time, nourished
by the milk injected into the mouth by compression of the
muscle covering the mammary gland. The nipples are
nearly always concealed in a fold of the abdominal integu-
ment, or " pouch " {inarsufiium), which serves to support
and protect the young in their early helpless condition.
The existing species are entirely confined to Australia, its
neighbouring islands, and the American continent ; though,
in former times, they had a more extensive geographical
range. The Wombats, Kangaroos, Phalangers, Koalas,
I.] ORNITHODELPHIA. 5
Bandicoots, Dasyures, Thylacines, and Opossums, are the
best known representatives of this group.
III. The Ornithodelphia, equivalent to the order
Monotremata, consist of only two existing genera; and
hitherto, no extinct animals which can be referred to other
genera of this remarkable and well-characterized group have
been discovered. These two isolated forms, in many re-
spects widely dissimilar, yet having numerous common
characters which unite them together and distinguish them
from the rest of the Mammalia, are the Ornithoi'hynchus
and the Echidna, both restricted in their geographical range
to the Australian continent and the island of Tasmania,
[any of the characters in which they differ from the two
>ther sub-classes tend to connect them with the inferior
group of Vertebrates, the Sauropsida, especially the Lacer-
tians ; for though the name Ornithodelphia owes its origin
to the resemblance of the structure of the female repro-
luctive organs to those of birds, there is nothing specially
>ird-like about them ; all the Sauropsida (Birds and Reptiles)
agreeing in these respects.
The accompanying diagram (page 6) is intended to ex-
hibit the relationships which appear to exist between the
different groups of the Mammalia. If all known extinct
forms were inserted, many of the intervals between the
boundary lines of the groups would be filled up ; other-
wise no great modification would be required in their
I relative position. But our knowledge of the systematic
position and relations of the past forms of Mammalian life
is in general so imperfect and fragmentary, that it seemed
better to confine the diagram to a representation of the
present condition of Mammalian life upon the earth.
CHAPTER I L
THE SKELETON.
The term Skeleton, in its widest sense, is used to denote a
system of hard parts forming a framework which supports
or protects the softer organs and tissues of the body," and
which may be either entirely external or superficial as re-
gards those organs and tissues, or may be more or less .
embedded in enveloping softer structures. In the former
case it is called an Exoskeleton, in the latter an Endoskeleton.
It is of the Endoskeleton alone that this work proposes
to treat, as in the class Mammalia the external skeleton,
when it exists, performs a relatively subordinate part in the
economy.1
The branch of anatomy called Osteology is commonly
restricted to a study of such parts of the endoskeleton as
are composed of bony or osseous tissue, a tissue charac-
terized by a peculiar histological structure and chemical
composition, being formed mainly of a gelatinous basis,
strongly impregnated with phosphate and carbonate of
lime, and disposed in a definite manner, containing nume-
rous minute nucleated spaces or cavities called lacimce,
Pjnnected together by delicate channels called canaliculi,
The» Armadillos and their extinct allies are the only known mam-
uils which have an ossified exoskeleton.
8 THE SKELETON. [CHAP.
which radiate in all directions from the sides of the lacunas.
This structure is readily recognized when a thin section of
bone is examined under a moderately high magnifying power.
Parts composed of bone are, of all the tissues of the body
(with the exception of the teeth), the most imperishable,
often retaining their exact form and intimate structure ages
after every trace of all other portions of the organization has
completely disappeared; and thus in the .case of extinct
animals affording the only means of attaining a knowledge
of their characters and affinities.
It must, however, be remembered that, at one period of
life, the parts composing the skeleton exist in a fibrous or
a cartilaginous form, that their transformation into bone is
a subsequent and gradual process, and that even in the
Mammalia, though in a less degree than in some of the
other Vertebrata, the whole of the internal skeletal system
is never entirely osseous, but that portions may remain
permanently in a cartilaginous or fibrous condition.
The different bones composing the skeleton are con-
nected together either by sutures, or by moveable joints
or articulations.
In the first, the edges of the bones are in close contact,
often interlocking by means of projections of one bone
fitting into corresponding depressions of the other, and are
held together by the periosteum, or fibrous membrane invest-
ing the bones, passing directly from one to the other, per-
mitting no motion, beyond, perhaps, a slight yielding to
external pressure. The bones of the cranium are connected
together in this manner. In old animals there is a great
tendency for such bones to become joined together by
the extension of ossification from one to the other and
consequent obliteration of the suture. This process is
called synostosis.
ii.] . THE SKELETON. 9
The various forms of joints may be arranged under two
principal heads. In one, the contiguous surfaces of the
bones are connected by interposed fibrous tissue, passing
directly from one to the other, filling up the space between
them, and allowing of only a limited amount of motion, as
the case with the bodies of the vertebrae.
The other and more frequent and more perfect form of
)int is that in which the contiguous extremities of the bones
re covered by a thin layer of very smooth cartilage, and
irrounded by a capsular ligament, attached only round the
Iges of the articular surfaces, and which is lined by a
wvial membrane, so called from its secreting a viscid
jricating fluid termed synovia. The amount of motion
jrmitted in these " synovial joints " varies according to the
of the opposed articular surfaces and the arrangement
the ligaments which hold them together. When the two
irfaces are nearly flat, and the bones firmly bound by strong
lort ligaments, as in those which compose the carpus and
irsus, the motion is reduced to an extremely slight gliding
)f one on the other. Joints in the form of a hinge, as at
the elbow, allow of a free motion in one plane only. Ball
and socket joints, as at the shoulder and hip, allow of the
greatest variety of movements.
The Endoskeleton is divided into an axial portion, be-
longing to the head and trunk, and an appendicular portion,
belonging to the limbs. There are also certain bones called
splanchnic, being developed within the substance of some of
the viscera. Such are the os cordis and os penis found in
some Mammals. These, however, are more appropriately
treated of with the anatomy of the organ of which they form
a part.
The Axial Skeleton consists of the vertebral column, the
skull, the sternum, and the ribs.
CHAPTER III.
THE VERTEBRAL COLUMN.
General Characters. — The Vertebral Column consists of a
series of distinct bones called Vertebrcz, arranged in close
connection with each other along the dorsal side of the neck
and trunk, and in the median line. It is generally prolonged
posteriorly beyond the trunk to form the axial support of the
appendage called the tail. Anteriorly it is articulated with
the occipital region of the skull.1
The number of distinct bones of which the vertebral
column is composed varies greatly among the Mammalia,
the main variation being due to the elongation or otherwise
of the tail. Apart from this, in most Mammals, the number
is not far from thirty, though it may fall as low as twenty-six
(as in some Bats) or rise as high as forty (Hyrax and
Choloepus)!1
The different vertebras, with some excep'ions, remain
through life quite distinct from each other, though closely
connected by means of fibrous structures which allow of a
certain, but limited, amount of motion between them.
1 For the sake of uniformity, in all the following descriptions of the
vertebral column, the long axis of the body is supposed to be in the
horizontal position.
'2 These numbers are not exact, owing to the uncertainty in the mode
of reckoning the sacral vertebra;.
CHAP, in.] GENERAL CHARACTERS. u
The exceptions are, — near the posterior part of the trunk,
in nearly all Mammals which possess completely developed
hinder limbs, two or more vertebrae become ankylosed
together to form the " sacrum" the portion of the vertebral
column to which the pelvic girdle is attached. As a rule,
none of the other vertebrae are normally united by bone,
but in some species there are constant ossiflc unions of
certain vertebrae, more particularly in the region of the
neck. These will be specially noticed presently.
Although the vertebrae of different regions of the column
of the same animal, or of different animals, present great
diversities of form, there is a certain general resemblance
among them, or a common plan on which they are con-
structed, which is more or less modified by alteration of
form or proportions, or by the superaddition or suppression
of parts to fit them to fulfil their special purpose in the
economy.
An ordinary vertebra (see Fig. 2) consists in the first place
of a solid piece of bone, the body or centrum (c), of the
form of a disk or short cylinder. The bodies of contiguous
vertebrae are connected together by a very dense, tough, and
elastic fibrous material, called the intervertebral substance, of
peculiar and complex arrangement. This substance forms
the main, and in some cases the only, union between the
vertebrae. Its elasticity provides for the vertebrae always
returning to their normal relation to each other and to the.
column generally, when they have been disturbed therefrom
by muscular action.
A process (/) rises on each side from the dorsal surface
of the body. These meeting in the middle line above form
together an arch, surrounding a space or short canal (nc).
As in this space lies the posterior prolongation of the great
cerebro-spinal nervous axis, or spinal cord, it is called the
12 THE VERTEBRAL COLUMN. [chap.
neural canal, and the arch is called the neural arch, in con-
tradistinction to another arch on the ventral surface of the
body of the vertebra, called the hamal arch} The last is,
however, never formed in mammals by any part of the
vertebra itself, but only by certain bones, placed more or
less in apposition with it, and which will not here be con-
sidered as parts of the vertebral column, strictly speaking.
Fig. 2. — Anterior surface of human thoracic vertebra (fourth), §. c body or centrum ;
nc neural canal ; / pedicle and / lamina of the arch ; t transverse process ; az
anterior zygapophysis.
The lower portions of each side of the arch (/), usually
thick and more or less vertical in direction, constitute its
pedicles. The upper more compressed and more horizontal
portions (/) are the lamince. The pedicles are usually
notched in front and behind, but most deeply behind, to
form the sides of the intervertebral foramina for the trans-
mission of the nerves issuing from the spinal cord. Occa-
sionally the foramina for these nerves perforate the pedicles,
instead of being truly intervertebral.
The laminae meet in the median line above, at a more or
less open angle. At the point of their junction there is
1 So called because it encloses the heart and the great central blood-
vessels.
GENERAL CHARACTERS. 13
usually a single median process projecting dorsally, called
the spinous process or neural spine.
In most cases upon the anterior and posterior edges of the
laminae of the arch are flattened, slightly projecting, more or
less oval, smooth surfaces or facets, which in the natural state
are covered with a thin layer of cartilage, and come into
contact and articulate (by synovial joints) with the corre-
sponding surfaces of the immediately antecedent and suc-
ceeding vertebrae. These have been called by Professor ■
Owen zygapophyses ; that placed on the front edge of the
arch being the anterior zygapophysis, that on the hinder edge
the posterior zygapophysis. As a general rule the latter have
their faces directed downwards, overlying the upward
directed anterior zygapophyses of the vertebra next behind.
This is a useful rule to remember in ascertaining which is
the front and which the posterior surface of a vertebra.
Sometimes, especially in the lumbar region, the posterior
zygapophyses have their faces directed outwards, in which
case the corresponding anterior zygapophyses look inwards
ig. 3, az).
These articular surfaces on the arch constitute a second
mode by which the vertebrae are united, and their size and
conformation aid to regulate the amount of motion allowed
between the component parts of the column. They are often
entirely wanting when flexibility is more needed than
strength, as in the greater part of the caudal region of
long-tailed animals.
In addition to the body and the arch, there are certain
projecting parts called processes, more or less developed in
different vertebrae. Many difficulties exist about the signi-
fication, homologies, and terminology of these processes.
Probably, when more is known of the development of the
vertebrae in a large series of animals, some further light will
"
H THE VERTEBRAL COLUMN. [chap.
be thrown on the subject ; but at present it does not appear
that there is that uniformity in the plan of construction of
all vertebrae which has often been supposed, and definitions
of the different parts applicable in every case have not yet
been arrived at, and it may even be doubted whether this
will ever be possible.
The principal processes commonly met with are as follow:—
i. From the middle of the upper part of the arch a
process generally single, but sometimes bifid at the end,
grows out vertically. This is the spinous process, or neural
spine already mentioned ; about its homology in different
vertebrae there never can be any question. It may however
be completely absent, when the arch is round or smooth
above, as in the cervical region in some animals ; on the
other hand, it may grow out into a very long conspicuous
rod of bone, as in the anterior dorsal region of others.
2. Occasionally a process grows in the median line from
the under-surface of the body. This maybe single and long
Fig. 3.— Anterior surface of the lumbar vertebra of Hare (Lepus timidus). s spinous
process ; m metapophysis ; az anterior zygapophysis ; / transverse process ; h
hypapophysis.
iand slender, as in the anterior lumbar vertebrae of the Hare
(Fig. 3, h), or a sharp median ridge, as in the cervical verte-
brae of many Ungulata and the cervical and caudal vertebrae
of the Ornithorhynchus, or double, as in the atlas vertebra of
m.] GENERAL CHARACTERS. 15
the last-named animal and the caudal vertebrae of many
others. This is termed a hypapophysis. Most commonly
there is not even a trace of any such process.
3. From the sides of the lower part of the arch, or from
the body, lateral processes project more or less directly out-
wards. These are called transverse processes. There may be
but one, or there may be two, superior and inferior, on each
side of a vertebra. In the latter case the superior is some-
times called a diapophysis, and the inferior a parapophysis ;
though it is questionable whether the processes to which
these terms have been applied can always be regarded as
strictly homologous.
4. Besides these principal laterally projecting processes,
there are often others arising from the side of the arch, more
FlG. 4. — Side view of first lumbar vertebra of Dog {Cards familiar is), f. J spinous
process ; az anterior zygapophysis ; pz posterior zygapophysis ; m metapophysis ;
a anapophysis ; t transverse process.
especially developed in the lumbar region, though by no
means constant even there. Of these there may be one or
two on each side. They have often been called accessory
processes ; but in the more precise system of nomenclature
introduced by Professor Owen, the one which is situated
highest on the arch (see Fig. 4, ;;/), projects more or less
1 6 THE VERTEBRAL COLUMN. [chap.
forwards as well as outwards, is usually thick and rounded,
and is nearly always in relation with the anterior, zygapo-
physis, is termed metapophysis ;l the one placed rather lower
(Fig. 4, a), and which projects more or less backwards, and
is generally rather slender or styhform, is called anapophysisi
These, with the zygapophyses before mentioned, sometimes
called oblique processes, but which are rather articular surfaces
than true processes, are all the processes commonly met with
on any Mammalian vertebra.
Development of the Vertebra. — The first indication of thq
formation of a vertebral column in the embryo is the
appearance of a longitudinal primitive dorsal groove in the
germinal membrane, the edges of which {lamince dorsales)
rise up and meet above, so as to convert the groove into a
canal. From the tissue lining this canal (uppermost layer
of the germinal membrane) the brain and spinal cord are
developed, and in its walls are formed anteriorly the cranium,
and posteriorly the vertebral column ; the canal itself be-
coming the cerebral cavity and the neural canal of the spine.
In the floor of this canal, formed by a horizontal lamina
which separates it from another and larger, ventral or haemal
canal (formed by the approximation in the middle line below
of the lamince ventrales), a slender rod of peculiar structure
is developed. This is the notochord or chorda dorsalist
around which the bodies of the future vertebrae are deve-:
loped. In the Mammalia it almost completely disappears at
a very early period, traces only remaining in the axis of the
intervertebral substance, though in many of the inferior
Vertebrata it is persistent as a continuous rod for a longer
period, and sometimes permanently.
1 It is also called "mammillary process" in some works on Human
Anatomy.
in.] DE VEL OPMENT. 1 7
The formation of the arches of the vertebrae in the
lamina dorsales is preceded by the appearance of dark-
looking cellular masses called proto-vertebrcz or somatomes,
corresponding in number, though not exactly in situation, to
the future vertebrae, and which undergo a series of changes
(for a description of which the student is referred to special
treatises on embryology) out of which ultimately results a
vertebra, similar in shape to that which it presents in adult
life, but formed of a continuous piece of hyaline cartilage.
The mode of ossification of this cartilaginous vertebra in
the different groups of Mammals still offers an interesting
field for investigation, but the following is a summary of the
most important facts ascertained regarding it.
Leaving out for the present the greatly modified two
anterior vertebrae, the atlas and the axis, which must be
specially considered afterwards, and also the comparatively
rudimentary vertebrae of the caudal region, each vertebra
consists at one period of three pieces of bone, as distinct
from each other, and remaining so for as long a period, as
many of the separate elements of the skull.
One constitutes the greater part, but usually not the whole,
of the body or centrum. Each of the others forms one side
of the arch, and usually more or less of the upper lateral
part of the body. These last ultimately unite to each other
in the middle line above, and to the central piece on each
side below. The line of union between them and the central
piece is readily distinguishable in all vertebrae up to the time
the animal is about half-grown, and is named by Professor
Huxley the neuro-central suture. (See Fig. 8, p. 27, ncs.)
As a general rule all the processes (except the hypapo-
physes) arise from the part of the vertebra situated above
the neuro-central suture, but there are notable exceptions.
The body of the vertebra is nearly always completed by
c
1 8 THE VERTEBRAL COLUMN. [chap. 1
the addition of a thin disk-like epiphysis at each end, which
for a considerable period after it is fully ossified remains
adhering by a rough surface to the central or main part
of the body, and is easily separated from it by maceration.
Its coalescence with the remainder of the body, especially in
the thoracic region, is one of the last acts in the completion
of the bony skeleton, and does not take place until after all
the epiphyses of the limb bones are firmly united. Hence
it may be taken as a safe indication that the animal is
thoroughly adult.
It must be noted that the epiphysis covers the whole
surface of the end of the body, whether ossified from the
centrum or the arch, and is therefore quite independent of
the position of the neuro-central suture.
These terminal epiphyses to the bodies of the vertebrae
are peculiar to the Mammalia, but not found universally
throughout the class, as they are wanting in the Ornitho-
delphia and the Sirenia. In man, the highest apes, and also
in some of the Didelphia, they have less solidity and import-
ance than in other Mammals, being often mere thin osseous
rings, representing the circumferential portion only of the
ordinary epiphysis.
The various processes of the vertebra have been divided
into those that are autogenous, or formed from separate
ossific centres, and exogenous., or outgrowths from either of
the just-mentioned primary vertebral constituents.
There can be no doubt but that an autogenous process
of one vertebra of an animal may be serially represented
by an exogenous process in another vertebra of the same
animal;1 and likewise that the corresponding processes of
1 Even the arches of some of the caudal vertebras appear to be
ossified directly from the body, and not independently, as is the rule
with the thoracic and lumbar vertebrae.
in. I DEVELOPMENT. 19
the same vertebra may be developed exogenously in one
animal and autogenously in another.
In nearly all the more prominent processes, moreover,
whether formed by exogenous or autogenous ossification,
the extreme tip remains cartilaginous for a considerable
time ; and at a comparatively late period in developmental
life (near the approach of maturity) a small ossific centre
forms in it. This spreads through the cartilage, and then
constitutes an epiphysis, which ultimately unites to, and
becomes indistinguishably incorporated with, the remainder
of the process.1
The spinous process is either formed by the coalescence
of outgrowths from the two pieces forming the neural arch,
or the greater part of it may be (as in the long spines of the
anterior thoracic vertebras of Ungulates) formed by a very
early autogenous ossification, which soon becomes united to
the upper part of the arch. In either case it is usually com
pleted by an epiphysis of comparatively late ossification.
There is one part connected with certain vertebrae which
requires some particular consideration, on account of the
great modifications it presents, being in some regions a
largely developed independent bone, articulated with the
vertebra by synovial joints, and in. other regions a small
rudiment, early and firmly united to, and incorporated with,
the vertebra itself.
The ribs in the thoracic region, though primarily formed
from a rod of cartilage continuous with that of the vertebra,
1 These epiphyses are sources of considerable difficulty in tracing
homologous parts, as it is questionable whether they should be treated
as separate elements of the skeleton, and, if not, where to draw the
line between an epiphysis and an element. They often appear mere
conveniences of growth, as it were, being developed upon the end of
a process when it is long, and being absent in a corresponding part of
stunted dimensions.
C 2
20 THE VERTEBRAL COLVMX. [chap.
always become distinct, independent, and moveably arti-
culated bones ; after their original segmentation they can
never be properly said to constitute part of the vertebra.
But it frequently happens that in certain of the vertebrae
anterior to the thoracic region, .and in certain of those
posterior to it, there are bony elements formed at an early
period, which, though very different from ribs in the ordinary
sense of the word, occupy a somewhat similar position
in relation to the vertebrae to that which the ribs do in the
thoracic region. These have hence been considered as
modified conditions of the same part, and have been called
pleur apophyses by Professor Owen.
Perhaps the clearest case of the presence of rib elements
in the vertebrae in any Mammal is afforded by the cervical
vertebrae of the Ornithodelphia, where the greater part of each
transverse process ossifies separately from the rest of the ver-
tebra, and remains for a long time only suturally connected
FlG. 5. — Third cervical vertebra of a nearly full-grown Echidna (E. hystri.x), the
• different pieces of which it is composed being slightly separated from one another.
>ia neural arch ; c centrum ; t transverse process ; v vcitebrarterial canal ; nc\
neuro-central suture.
with it (Fig. 5). They thus closely correspond to the cer-
vical ribs of reptiles, which are unquestionably homologous
serially with the thoracic ribs.
The anterior, or more properly inferior, bar of the trans
verse process of the seventh, and occasionally of some of the
other cervical vertebrae in Man, is autogenously developed,
in.] DIVISION INTO REGIONS. 21
and has some characters by which it may be placed in the
category of rudimentary ribs.
The transverse processes of the anterior lumbar vertebrae
of certain Mammals, as the Pig, are originally autogenous
elements, though coalescing very early with the rest of the
vertebrae.
In the sacral region, the separate lateral ossifications which
connect the vertebral column with the ilium present many,
characters allying them to ribs. . (See Fig. 6.)
j FlG. 6.— Anterior surface of first sacral vertebra (human), showing mode of develop-
ment, na neural arch ; c centrum ; p distinct (pleurapophysial) ossification for
attachment of ilium.
Finally, the transverse processes of the caudal vertebrae of
some animals (as the Manati and Beaver) are. separately
developed, though it is doubtful whether this circumstance
alone is sufficient to entitle them to be considered as costal
elements.
Division of Vertebral Column into Regions. — For con-
venience of description the whole vertebral column has
been divided into five regions, the cervical, thoracic,1 lumbar,
sacral, and caudal.
This division is useful, especially as it is not entirely
arbitrary, and in most cases is capable of ready definition,
1 Generally called dorsal, but it would be better to reserve this term
in morphology as relating to the upper surface of the body and opposed
to ventral.
22 THE VERTEBRAL COLUMN: [chap.
at least in the Mammalia; but at the contiguous extre-
mities of the regions, the characters of the vertebrae of one
are apt to blend into those of another region, either nor-
mally, or as peculiarities of individual skeletons.
i. The Cervical region constitutes the most anterior por-
tion of the column, or that which joins the cranium.
The vertebrae which belong to it are either entirely
destitute of moveable ribs, or, if they have any, these are
small, and do not join the sternum.
As a general rule they have a considerable perforation
through the base of the transverse process (the vcrte-
brarte7'ial canal, Owen), or, as it is sometimes described,
they have two transverse processes, superior and inferior,
which, meeting at their extremities, enclose a canal. (See
Fig. 7 ; Fig. 8, p. 27 ; and Figs. 17 and 18, p. 39.) This,
Fig. 7.— Anterior surface of sixth cervical vertebra of Dog, §. ^ spinous process
az anterior zygapophysis ; v vertebrarterial canal ; t transverse process ; t' its
inferior lamella.
however, rarely applies to the last vertebra of the region, in
which only the upper transverse process is usually developed.
The transverse process moreover very often sends down
near its extremity a more or less compressed plate {inferior
lamella, Fig. 7, /'), which being considered to be serially homo-
; III.] DIVISION INTO REGIONS. 23
I logous with the ribs of the thoracic vertebrae (though not
I developed autogenously) is often called " costal ;' or " pleura-
pophysial " plate. This is usually largest on the sixth, and
altogether wanting on the seventh vertebra.
The first and second cervical vertebrae, called respectively
I atlas and axis, are specially modified for the function of
supporting, and permitting the free movements of the head.
They are not united together by an " intervertebral sub-
I stance," but connected only by ordinary ligaments and
synovial joints.
The cervical region in Mammals presents the remarkable
peculiarity that, whatever the length or flexibility of the
neck, the number of vertebrae is the same, viz. seven, with
very few exceptions, which will be particularized fur-
ther on.
»2 . The Thoracic or Dorsal region consists of the vertebrae
hich succeed those of the neck, having ribs moveably
•ticulated to them. These ribs arch round the thorax, the
anterior one, and most usually some of the others, being
attached below to the sternum.
The characters of the ribs and their mode of articulation
with the vertebrae will be considered further on, but it may
now be stated that in the anterior part of the thorax the
vertebral extremity of each rib is divided into " head " and
" tubercle ; " that the former is attached to the side of the
body of the vertebra, the latter to its transverse process ;
and that the former (capitular) attachment corresponds to
the interspace between the vertebrae, the head of the rib
commonly articulating partly with the hinder edge of the
body of the vertebra antecedent to that which bears its
Ibercle. Hence the body of the last cervical vertebra
ually supports part of the head of the first rib. In the
24 THE VERTEBRAL COLUMN. [char
attachments commonly coalesce, and the rib is attached
solely to its corresponding vertebra.
3. The Lumbar region consists of those vertebrae of the
trunk in front of the sacrum (to be afterwards denned) which
bear no moveable ribs. It may happen that as the ribs
decrease in size posteriorly, the last being sometimes
more or less rudimentary, the step from the thoracic to the
lumbar region may be gradual and rather undetermined in
a given species. But most commonly this is not the case,
and the distinction is as well defined here as in any other
region.
As a general rule there is a certain relation between the
number of the thoracic and the lumbar vertebrae, the whole
number being tolerably constant in a given group of
animals, any increase of the one being at the expense of
the other. Thus in all known Artiodactyle Ungulata there
are 19 thoracico-lumbar vertebrae ; but these may consist of
12 thoracic and 7 lumbar, or 13 thoracic and 6 lumbar, or
14 thoracic and 5 lumbar.
The smallest number of thoracico-lumbar vertebrae in
Mammals occurs in some Armadillos, which have but 14.
The number found in Man, the higher Apes, and most Bats,
viz. 17, is exceptionally low ; 19 prevail? in the Artiodactyles,
nearly all Marsupials, and very many Rodents ; 20 or 21 in
i Carnivora and most Insectivora, 23 in Perissodactyla. The
highest and quite exceptional numbers are in the two-toed
sloth (Choltffius), 27, and Hyrax, 30.
The prevailing number of rib-bearing vertebrae is 12
or 13, any variation being generally in excess of these
numbers.
4. The Sacral region offers more difficulties of definition,
especially at its posterior portion.
Taking the human " os sacrum " as a guide for comparison,
in.] DIVISION INTO REGIONS. 25
it is generally defined as consisting of those vertebrae, between
the lumbar and caudal regions, which are ankylosed together
in the adult state to form a single bone. It happens, how-
ever, that the number of such vertebrae varies in different
individuals of the same or nearly allied species, especially as
age advances, when a certain number of the tail vertebrae
generally become incorporated with the true sacrum.
A more certain criterion is derived from the fact that some/
of the anterior vertebrae of the sacral region have distinct)
additional (pleurapophysial) centres of ossification, between!
the body and the ilium (see Fig. 6, p. 21). To these perhaps)
the term sacral ought properly to be restricted, the remaining^
ankylosed vertebrae being called pseudo-sacral, as suggested
by Gegenbaur. Our knowledge of the development of the
sacrum in different animals is not sufficient at present to
apply this test universally, but it appears probable that two
is the most usual number of true sacral vertebrae, as thus
defined in the Mammalia.
5. The Caudal Vertebrce are those placed behind the
sacrum, and terminating the vertebral column. They vary
in number greatly, being reduced to 5, 4, or even 3, in a
most rudimentary condition, in Man, some Apes and Bats,
and being numerous and powerfully developed, with strong
and complex processes in many Mammals, especially among
the Edentata, Cetacea, and Marsupialia. The highest
known number, 46, .is possessed by the African Long-tailed
Man is.
CHAPTER IV.
SPECIAL CHARACTERS OF THE CERVICAL VERTEBR/E IN THE
MAMMALIA.
Order Primates. — The human cervical vertebrae (ex-;
eluding for the present the first and second) have short,
wide, depressed bodies, hollowed in front from side to side,
and behind from above downwards,1 with wide neural canals,
and short, broad, and usually bifid spines (considerably
longer in the seventh vertebra than in the others), well
marked, broad, flat, anterior, and posterior zygapophyses,
and short, sub-bifid, widely perforated transverse pro-
cesses.
These vertebrae are, as usual, developed mainly from three
centres, one for each side of the arch, and one for the
centrum (see Fig. 8), but it will be observed that the whole
of the body is not formed from the latter, but that its lateral
parts, with the transverse processes, are ossified from the
arches.
Besides these main centres of ossification there are thin
and imperfect disk-like epiphyses on the ends of the body,
1 As before mentioned, the body is supposed to be placed horizontally,
so that the same terms of relative position may be used as when speak-
ing of the vertebral column of the ordinary less modified animals of the
class.
CHAP. IV.] CERVICAL VERTEBRAE. 27
very late in making their appearance, and not joined until
long after the rest of the vertebra is completed. A small
epiphysis is also formed on the end of the spinous
process.
Fig. 8. — Sixth cervical vertebra of a child, i. c centrum ; ncs neuro-central suture ;
v vertebrarterial canal ; az anterior zygapophysis.
Lastly, the inferior or ventral bar of the transverse process*
of the seventh vertebra is developed from a separate centre
of ossification, and occasionally the same part of the sixth
and fifth has its own separate nucleus. This bar of bone is
connected internally with a projection from the side of the
body, ossified from the arch; externally with the end of the
upper or true transverse process, which is an exogenous
growth from the arch, so that it is attached to the vertebra
entirely above the neuro-central suture. Occasionally it
acquires an abnormal development, and grows into a con-
siderable rib-like bone, in which case it is usually united at
its distal extremity with the first thoracic rib.
The first vertebra or atlas (Fig. 9) is little more than an
oval ring, thickened on each side into the so-called " lateral
mass," which bears an articular surface before and behind.
The anterior surfaces are very large, elongated from above
downwards, and hollowed for the reception of the condyles of
the occiput. The posterior articular surfaces are subcircular,
28 CERVICAL VERTEBRM. [chap.
flattened, or slightly-concave. The transverse processes are
short, stout, and perforated ; the arch presents scarcely a
rudiment of a spinous process. On its anterior edge im-
mediately above the articular surface is a deep notch or
groove (g) of some importance, as it corresponds with the
slight notch in front of the pedicle in other vertebrae, which
contributes with the deeper notch in the hinder border of
the pedicle of the preceding vertebra to form the " inter-
Fig. 9. — Human alias, young, showing development, f. ia inferior arch ; as articular
surface for occiput ; t transverse process ; g groove for first spinal nerve and
vertebral artery.
vertebral " foramen for the exit of a spinal nerve, and because
occasionally in man, and constantly in many animals, it is
converted by a bridge of bone into a canal, through which
the first cervical (or suboccipital) nerve passes out. The
inferior arch of the atlas (id) differs entirely from the bodies
of the other vertebrae, being a simple, depressed, slightly
curved bar of bone, with a smooth facet on its neural or
upper surface, for articulation with the odontoid process of
the axis.
The second cervical vertebra, axis, epistropheus, ox vertebra
de?itata (Fig. 10), has a body terminating anteriorly in
a large subconical median projection, the odontoid pro-
cess (0), which is received into, and articulates with, the con-
cavity of the inferior arch of the atlas. It is retained in its
v.]
MA AT.
2')
place by means of a strong transverse ligament passing
between the lateral masses of that bone, and separating its
canal into an upper or neural portion for the passage of the
spinal cord, and an inferior portion for the reception of the
odontoid process.
The axis has posterior zygapophyses placed on the arch,
serially continuous with those of the rest of the vertebrae, but
its anterior articular facets, like those of the atlas, do not
belong to the arch proper, but partly to the body and partly
to the arch, and are therefore not exactly serially homologous
with the zygapophyses of the other vertebrae. The trans-
verse processes are short, single, and perforated. The arch
is high, with a stout bifid spine.
The development of the atlas and axis offers some im-
portant points for consideration.
The arch of each is ossified from two centres, one on each
side, as in other vertebrae ; but if the axis is examined a year
Fig. io. — Diagram showing mode of ossification of human axis (haemal or ventral
surface), o odontoid process, or centrum of atlas ; c proper centrum of axis ; na
neural arch ; as anterior articular surface ; e e e epiphyses, completing the ends of
the centra.
or two after birth (Fig. io), its body appears to be composed
of two parts, one placed in front of the other, the first includ-
ing the odontoid process and the anterior part of the body,
the second all the remainder of the body. The arch is
3o CERVICAL VERTEBRA*:. [chap.
united to both. On the other hand, the atlas at the time
of birth has nothing corresponding to the centrum of other
vertebrae, its inferior arch being still cartilaginous.
It is therefore a generally received opinion among ana-
tomists that the anterior ossification of the axis is essentially
the body of the atlas, which unites with both arch and
centrum of the vertebra behind it. It must be observed,
however, that in its mode of ossification, at least in man, it
differs from the centra of all the other vertebrae, as at one
period it consists of two distinct lateral pieces, which after
a while coalesce in the middle line. The usual disk-like
epiphyses of the vertebral bodies are represented by one
at the posterior extremity of the body, by a small osseous
nodule which completes the odontoid process in front, and
by some irregular ossifications found between the two main
portions of which the body is composed.
The inferior arch of the atlas ossifies soon after birth
from one or more centres, and the resulting piece of bone
(Fig. 9, id) ultimately unites with the two pieces forming
the neural arch about the same time as that at which they
join together in the middle line above. This piece may^
probably be regarded as a detached "hypapophysial" seg-,
ment of the first vertebral centrum, the remainder of which
forms the odontoid portion of the body of the axis.
The cervical vertebrae of the other Primates resemble
those of man generally, the most noticeable deviations being
the following : —
In the atlas the groove for the first cervical nerve is usually
i converted into a foramen; and a median hypapophysial
tubercle or spine often projects backwards from its inferior
arch under the axis (especially in Mycetes and Lagothrix).
The spinous processes, especially of the third, fourth,!
fifth, and sixth cervical vertebrae, are immensely elongated
iv.] CARNIVORA. 31
in the Gorilla, and considerably so in the Chimpanzee and
Orang. These processes as a rule are not bifid, as in Man,^
but occasionally (as in Mycetes) they are trifid, having a pair'
of lateral backward-projecting processes developed near
their extremity.1
The inferior lamellae of the transverse processes are
generally larger proportionally than in man, especially in the
Lemarina. In the seventh vertebra, the transverse processes
vary much as to their perforate or imperforate condition.
In the Carnivora, the atlas (Fig. n) has very deep
anterior articular surfaces for the condyles of the skull. The
flG. 11. — Inferior surface of atlas of dog, \. sti foramen or first spinal nerve ;
v vertebrarterial canal.
first spinal nerve passes through a complete foramen. The
transverse processes are large, wing-like, flattened from above
downwards, and perforated by the vertebrarterial canal.
The axis (Fig. 12) has a long conical odontoid process,
and a large compressed neural spine, greatly extended from
before backwards, and especially produced forwards.
The remaining cervical vertebrae have small, narrow, com-
pressed, usually simple spines, gradually lengthening to the
seventh, and large transverse processes, with greatly developed
inferior lamellae (see Fig. 7, pp. 22) especially large in the
fifth and sixth. In the latter the lower edge of this lamella
1 These are named hyperapophyses by Mr. Mivart, who has called
particular attention to them: "On the Axial Skeleton in the Pri-
mates : " Proc. Zool. Soc. 1865, p. 545.
32 CERVICAL VERTEBRA. [chap.
is frequently hollowed in the middle, and produced at each
extremity, so that the transverse process has a trifid appear-
ance. This is especially marked in the Felidce. The trans-
verse process of the seventh vertebra has no inferior lamella,
and its base is imperforate.
t
Fig. 12. — Side view ot axis of Dog, 3. s spinous process; o odontoid process ; pz t
posterior zygapophysis ; t transverse process ; v vertebrarterial canal.
Metapophyses are generally more or less developed on the
cervical vertebrae of the Carnivora, and there are also in
some genera small backward projecting tubercles {hyper apo-
physes, Mivart) situated on the laminae of the arch, rather
internal to the posterior zygapophyses, not usually found in
other vertebrae.
In the Insectivora, the cervical vertebrae vary consider-
ably in their characters. The atlas has usually short trans-
verse processes. Generally the spinous process of the axis is
large and prominent, and that of the other vertebrae very
small, but in Centetes and Potamogale they are all more or less
elongated. The neural arches in some (as Myogale and
Sorex) are reduced to mere filaments. In the mole (Ta/pa)
the transverse processes of the fourth, fifth, and sixth
vertebrae are much expanded antero-posteriorly, and overlap
each other. Large single hypapophyses are developed from
the inferior surface of most of the cervical vertebrae in the
Shrews (Sorex) and some of their allies, and in GaleopitJiecus
R0DENT1A.
33
each vertebra bears at its hinder end a pair of hypapophysial
tubercles.
In the Chiroptera all the cervical vertebrae are broad, '
very short from before backwards, with slender neural arches
from which (except in the axis) no distinct spinous processes
are developed. In certain forms (as Vesperugp) some of the
vertebrae have distinct double hypapophysial spines project-
ing backwards.
In the Rodentia the atlas has usually broad, moderately
long, wing-like transverse processes. The odontoid process
is long and slender; the spinous process of the axis is much
developed, while as a rule that of the other cervical vertebrae
is exceedingly small. The transverse processes of the fifth
and sixth have large inferior lamellae ; that of the seventh
is sometimes perforated at the base (as in Lepiis), and
sometimes imperforate (as in Hydrocharits).
In the Capybara (Hydrochcerus) and some others, the side
of the arch of the atlas is perforated near its anterior border
for the exit of the first spinal (sub-occipital) nerve, and also
near its hinder border for the second cervical nerve.
In the Jerboas (Dipus) a very exceptional condition of i
the cervical vertebrae occurs. The atlas is free, but all the
others are ankylosed together by both bodies and arches,
and the bodies are very wide and depressed, as in the
Armadillos.
•Among the Ungulata, the atlas (Fig. 13) in the Pecora is
very long, with deep articular cavities for the occipital con-
dyles. The transverse processes are not wide, but much
extended from before backwards, and flattened from above
downwards. Each is perforated by a foramen (sri) which gives
exit to the inferior division of the first cervical nerve, but not
by the vertebral artery, which usually enters the neural canal
between the arches of the second and third vertebrae. The
D
34
CERVICAL VERTEBRAE.
[CHAW
I
j odontoid process ot the axis (Fig. 14) is of peculiar shape,
being like a spout, or hollow half-cylinder, with a prominent
sn
• Fig. 13. — Inferior surface of atlas of Red Deer {Cervus elaphus). sn foramen for
superior branch of first spinal nerve ; sn foramen for inferior branch of the same
nerve.
sharp semicircular rim. The canal for the second cervical
spinal nerve pierces the lamina of the axis near its anterior
border. The other vertebrae have more or less elongated
Fig.
-Anterior surface of axis of Red Deer, \. o odontoid process ; sn foramen
for second spinal nerve ; pz posterior zygapophysis.
bodies, which are opisthoccelous, i.e. concave behind and
convex in front. They are keeled below, the keel being often
developed into a hypapophysial spine posteriorly; the neural
spines are moderately long, and inclined forwards. The
transverse processes of the fifth, and especially of the sixth
iv.] UNGULATA. 35
have large inferior lamelke. That of the seventh is usually
imperforate.
In the Giraffe the bodies of the cervical vertebrae are very
long. The transverse processes are short, but so extended
from before backwards as to become divided into two, one
at the anterior and one at the posterior end of the vertebra.
That of the seventh is perforated.
In the Tylopoda (Camels and Llamas) the vertebrarterial
canal passes obliquely through the anterior part of the
pedicle of the arch, being in its posterior half confluent with
the neural canal. A similar condition occurs in Macrau-
c/iem'a, an extinct South American Perissodactyle Ungulate.
The Snina and Tragulina differ from the remaining exist-
ing Artiodactyles in the form of the odontoid process, which
is conical ; while on the other hand the Horse and Tapir
among the Perissodactyles have this process wide, flat, and
hollowed above, approaching the form it presents in the
Ruminants. In the Pig, the broad pedicles of all the cervical
vertebrae are perforated by canals for the passage of the
upper division of the spinal nerves.
The bodies of the cervical vertebrae in the Rhinoceros,
Tapir, and Horse are markedly opisthoccelous, but in the
Pig and Hippopotamus very slightly so.
In the Horse the bodies of the cervical vertebrae are
elongated, with a strong keel and hypapophysial spines.
The neural laminae are very broad, the spines almost obso-
lete, except in the seventh, and the transverse processes not
largely developed. The seventh is not perforated by the
vertebrarterial canal.
In the Rhinoceros, on the other hand, the bodies are
comparatively short, and not keeled, the laminae narrow, the
spines well marked, and the transverse processes greatly
developed, especially those of the atlas.
d 2
36 CERVICAL VERTEBRA?. [chap.
In the Elephant (order Proboscidea), the atlas mud
resembles the human atlas. The axis has a short conic
odontoid process, a very massive spine, broad above and bifu
posteriorly. The bodies of the other vertebrae are very shoi
flattened, sub-circular disks, very slightly opisthoccelous
Excepting the seventh they all have short spinous processes
and short, broad, and largely perforated transverse processc-
The seventh has a high spine, an imperforate transverse pn
cess, and on the hinder edge of its body a very distinct art
cular cavity for the head of the first rib. In the young animj
this is divided into two equal parts by the neurocentr
suture.
In the order Sirenta, the Dugong (Hali'core) has sever
cervical vertebrae, as in the Mammalia generally. The atlas
has short imperforate conical transverse processes. The axis
has a high arch and massive neural spine, a short rounded
odontoid process, and very rudimentary transverse processes.
The others have short and wide bodies, small spines, and
irregularly developed transverse processes, often not com-
pletely enclosing a vertebrarterial canal.
The Rhytina, a large animal of this order, which became
extinct towards the close of last century, had also seven
cervical vertebrae, and the Miocene Halitherium had the
same number.
The Manatis (genus Ma?ialus), of which there are two
well-marked species, one inhabiting the west coast of
Africa, and the other the east coast of Central and South
f America, never have more than six vertebrae in the cervical
region. These resemble generally those of the Dugong,
having short and wide bodies, and very irregular transverse
processes. In a specimen of M. senegalcnsis, in the
Museum of the College of Surgeons, the second and third
are ankylosed by their bodies, and the neural arches of most
iv.]
CETACEA.
37
of the others are widely open above. In the skeletons of M.
americanus, in the same museum, the vertebrae are all free,
and the arches, though slender, are complete, and with very
slightly developed spinous processes.
In the Cetacea the seven cervical vertebrae usually found1
in the Mammalia are always present, though often so short
and blended together, that it is not easy at first sight to re-
cognize their existence. In some genera of both sub-orders
all the vertebrae are free, though never allowing of much
motion between them ; but more commonly certain of them
re firmly united together by bone. Even where the atlas
sn
Fig. 15. — Section through middle line of united cervical vertebrae of Greenland Right
Whale (Balcena mysticetus), \. a articular surface for occipital condyle ; e epi-
physis on posterior end of body of seventh cervical vertebra ; sn foramen in arch
of atlas for first spinal nerve ; 1 arch of atlas 123456 conjoined arches of the
axis and four following vertebrae ; 7 arch of seventh vertebra.
and axis are separate the odontoid rarely forms a distinct
process (it is most distinct in Platanista), but still it is devel-
oped from an ossific centre of its own, as in other Mammals.
38 CERVICAL VERTEBRAL. [chap.
Among the Mystacoceti, in the Right Whales (genus Balcena)
khe whole of the seven cervical vertebrae are usually united
into one mass by their bodies, though sometimes the seventh
is free. The arches are also more or less united above,
though generally not in a continuous mass. Small slit-like
openings between the narrow pedicles of the arches permit
the exit of the cervical spinal nerves, and in the adult condi-
tion afford the only indication by which the number of the
united vertebrae can be ascertained. Already before birth
most of the bodies have coalesced, and it is even doubtful
whether they ever exist in a separate condition.
The Fin Whales or Rorquals (genus Balccnoptei'd) present
a totally different condition of cervical vertebrae, as these are,
as a rule, all distinct and free, though occasionally, as an
individual peculiarity, an irregular ankylosis may take place
between two or more of them.1
Fig. 16. — Anterior surface of atlas of common Fin Whale (Bahvnofitera tftusculus), -,1..
su foramen for first spinal nerve.
In the common large Fin Whale of our coasts (B.
musculus) the atlas (Fig. 16) has short, stout, conical, imper-
forate transverse processes. The axis (Fig. 17) has a broad
oval body, high massive arch, very short odontoid process,
1 See Professor Struthers "On the Cervical Vertebras and their
Articulations in Fin Whales." {Jownal of Anatomy and Physiology,
November 1872.)
iv. 1
CETACEA.
:>o
and very wide, oblong wing-like transverse processes directed
somewhat backwards, and with an oval perforation near the
[7. — Anterior surface of axis of common Fin Whale {Balcenoptera musculus),
o odontoid process.
,se. The other cervical vertebra? (Fig. 18) have similar
broad, very short bodies, small arches, without spines, and
very long transverse processes, composed of a slender upper
Fig. 18. — Anterior surface of fourth cervical vertebra of the same animal, ^5. az ante-
rior of zygapophysis ; t upper transverse process ; f lower transverse process.
and lower bar, widely separated at their bases, but united at
their extremities so as to enclose a very large space between
them. In the seventh the upper process only exists, and the
lower one is occasionally imperfect in the sixth.1 In very
young animals these processes are formed only of cartilage •
Professor Turner has shown that, in a fatal Balcenoptera sibbaldii,
the inferior transverse process of the seventh is present in a cartilagi-
nous condition. {Journal of Anatomy and Physiology, May 1871 .)
^hJL
40 CERVICAL VERTEBRA, [chap.
and as ossification takes place gradually from within out-
wards, and does not reach the outer extremity until the
animal approaches maturity, specimens are frequently met
with in museums, which, instead of completely annular
transverse processes, show only truncated upper and lower
bars. In some species, however (as in Megaptera longimana),
most of the cervical vertebrae remain permanently in this
condition.
Among the Odontoceti, all the cervical vertebrae are free in
the Gangetic Dolphin (P/afaw'sfa), and in the allied South
American genera Inia and Pontoporia, also in the Nar-
iwhal (Monodon) and the Beluga, or the White Whale. In
most of these genera the atlas has a large hypapophysial
process, projecting under and articulating with the body of
the axis, which develops no distinct odontoid. In the
Narwhal irregular ankyloses between the bodies of the cervical
, vertebrae are very frequent. In all the other Delphinidce
(including Delphinus, Orca, Pseudorca, Globicephalus, P/io-
) ccena, &c), at least the first and second cervical vertebrae
| are united by both body and spine, and most commonly
some of the succeeding vertebrae are joined to them. If
any are free, it is always those situated most posteriorly,
and they have extremely thin, sub-circular disk-like bodies,
and irregular and comparatively rudimentary transverse
processes.
< In Hyperoodon, the whole of the cervical vertebrae are
jankylosed together. In the other Ziphioids several of the
/posterior vertebrae are free, and the allied Cachalot or Sperm
(Whale (P/iyseter), presents a condition not met with in any
pother known Cetacean : the atlas is free, and all the other
[neck vertebrae are completely united.
Among the various members of the order Edentata, the
cervical vertebrae present very different conditions.
IV.] MARSUPIALIA. 41
In the Armadillos {Dasypodidce) the bodies are extremely
short, broad, and depressed, and several are commonly anky-
losed together ; the corresponding neural arches being also
united, the neural and vertebrarterial canals form continuous
tubes. The orifices for the spinal nerves perforate the united
pedicles. The atlas is always free. The vertebrae that are
united are the second and third, or the second, third, and
fourth, and in some species the fifth also. The spinous
process of the axis is very large, but the neural arches of the
hinder free vertebrae are extremely narrow, and the spinous
processes rudimentary. The transverse process of the
seventh has an inferior lamella, nearly as large as that of
the sixth, but it is usually not perforated.
In Orycterofius, the Pangolins (Mams), and the Anteaters
(Myrmecophaga), the neck vertebrae are more normal in form,
and are not ankylosed. In the last-named genus, the verte-
brarterial canal of several of the vertebrae perforates the
pedicle obliquely, and enters the neural canal posteriorly,
much as in the Camels.
Among the leaf-eating Edentates, or Sloths, the neck
vertebrae present some remarkable peculiarities, especially
as to number.
All the known species of three-toed Sloths (genus Brady- 1
pus) have nine cervical vertebrae, i.e. nine vertebrae in front of (
the one which bears the first thoracic rib (or first rib con-
nected with the sternum, and corresponding in its general
relations with the first rib of other Mammals), but the ninth,
and sometimes the eighth, bears a pair of short moveable
ribs. The eighth is perforated by the vertebrarterial canal,
but not the ninth.
The common species of two-toed Sloth ( Cholozpus didac-
tylus) has seven cervical vertebrae, but a closely allied
species (C. hoffmamiii) has but six.
42 CERVICAL VERTEBRAL. [chap.
In the very heterogeneous order Marsupialia (sub-class
Didelphia) the cervical vertebrae vary much in their characters,
though the number is always seven, as in the great majority
of the Mammalia.
One of the most important variations is in the mode of
ossification of the atlas. In the Wombat (P/iasco/omys),
Y^.Od\&{Phascolarctos),Phalangista, and Kangaroo (Macropus),
there is no distinct ossific nucleus in the inferior arch of the
bone, which remains either permanently open in the middle
line below, or (as in some of the smaller Kangaroos) is com-
pleted by the union of prolongations ot the arches inwards.
This, however, is not the case with the carnivorous Mar-
supials. In the Thylacine (see Fig. 19) there is a distinct
heart-shaped piece of bone in the centre of the inferior arch
of the atlas, which appears never to become united to the
remainder, as it is still attached by ligament in skeletons
otherwise perfectly mature, and is commonly lost in mace-
Fig. 19 — Inferior surface of atlas of Thylacine ( Tkylacinus cynocefihalus), §. h dis-
tinct ossification in centre of inferior arch, with pointed hypapophysial pro-
jection.
ration. In Perameles and Diddphys the atlas is completely
ossified below by a wide intermediate piece, quite as in
ordinary Mammals.
As to the other vertebrae, in the Kangaroos the transverse
processes are long and slender, and (including the seventh)
have a very small perforation close to the base. The inferior
lamella arises near the base of the process, and is very
I v. ] MONO TREMA TA. 43
large in the sixth, but generally absent in the seventh
vertebra.
In the Wombat, the bodies are wide and depressed. The
transverse processes are perforated in all ; the inferior lamella
of the sixth is much developed antero-posteriorly. The
spines of all are rather short.
In Perameles lagotis the greater part ot the transverse pro-
cess of the axis is ossified separately from the rest of the
vertebra, and remains sometime distinct, as in the Mono-
tremata. In this genus, as in the other carnivorous Marsu-
pials, the inferior lamellae of the transverse processes of the
fourth, fifth, and sixth vertebrae, but especially of the latter,
are particularly large.
Some species of American Opossums (as Didelphys
virgifiiana and its nearest allies) have the spinous processes
of the second, third, fourth, and fifth cervical vertebrae, very
high, square, and massive, and being closely applied to each
other by flattened surfaces, form a solid wall of bone along
the top of the neck.
In both genera of Monotremata (sub-class Ornitho-
delphia) the cervical vertebrae are seven in number, and in
both the inferior arch of the atlas is completely ossified,
apparently from a separate centre ; but in Ornithorhynchus
a large bifurcated hypapophysis is developed, which is quite
wanting in Echidna.
In Ornithorhynchus also all the other cervical vertebrae
have a single median hypapophysial spine, equally wanting
in Echidna.
In both, the axis has a high compressed spine, and the
odontoid portion remains long distinct from the true centrum
of the bone. In both, the transverse processes are of auto-
genous formation, and remain suturally connected with the
remainder of the vertebra until the animal is nearly full-
44 CERVICAL VERTEBRAE. [chap. i\\
grown (see Fig. 5, p. 20) ; that of the axis is still distinct
in an adult Omithorhynchas. Though in this respect they
present an approximation to the Sauropsida (Reptiles and
Birds), they differ from that group, inasmuch as there is not
a gradual transition from these autogenous transverse pro-
cesses of the neck (or cervical ribs, as they may be con-
sidered) into the thoracic ribs, for in the seventh vertebra
the costal element is much smaller than in the others,
indicative of a very marked separation of neck from thorax,
not seen in the Sauropsida
CHAPTER V.
ECIAL CHARACTERS OF THE THORACIC AND LUMBAR
VERTEBRAE.
It will be most convenient to consider the vertebrae of
these two regions together.
In Man, there are seventeen trunk vertebrae, twelve
thoracic or rib-bearing, and five lumbar.
The bodies increase in size from before backwards, and
also change their form. The first is like a cervical ver-
tebra, broad and depressed. They soon become more
compressed, especially at the lower part, so as to be subtri-
angular when seen from one end (Fig. 2, p. 1%) ; after the
middle of the thoracic region they become more circular in
outline, and in the lumbar region they are wide transversely.
The ends of the bodies are flat or slightly concave.
The neural canal does not alter greatly in size throughout
this region, though it does somewhat in form. In the first
vertebra it is wider in proportion to its height than in any
of the others.
The arches have comparatively narrow pedicles, arising
from the anterior half of the body, deeply notched behind,
for the canal for the exit of the spinal nerves. The laminae
are broad. The spines are moderately long, subequal
throughout the series, rather slender, and sloping backwards
46 TRUNK VERTEBRA. [chap.
in the thoracic region ; broader (in the antero-posterior
direction) and more upright in the lumbar region, and pre-
senting but scarcely any indication of that convergence
towards a point in the posterior thoracic region so fre-
quently seen in other Mammals. They are generally simple
and slightly dilated at their ends ; but in the lumbar region,
the posterior edge is often more or less bifid.
The zygapophyses are well developed throughout. In
the thoracic region they are oval, flat facets, looking pretty
nearly directly upwards (the anterior) and downwards (the
posterior) : the anterior, developed on the top of the pedicle
and projecting forwards, being supported by the "oblique
process ; " the posterior is placed on the under-surface of the
hinder part of the lamina. In the lumbar region, their form
and position change, the anterior having their outer edges
turned upwards, and supported by a short rounded meta-
pophysis {mamillary process). The posterior ones have
undergone a corresponding change, so that their faces, instead
of looking downwards, are directed obliquely outwards ; they
are also much curved.
The transverse processes project throughout the series
from the arch, near the junction of the pedicle with the
lamina. In the greater part of the thoracic region they are
tolerably long, project somewhat upwards, and slightly for-
wards, and are dilated and tuberous at the extremities, on
the under surface of which (except in the two last) they show
a smooth concave facet for the attachment of the tubercle of
the rib. In the posterior part of the thoracic region they
are shorter, and begin to resolve themselves into three dis-
tinct processes, generally conspicuous in the first lumbar.
One of these projects outwards, and, elongating in the second
and third lumbar, it forms its principal transverse process.
One projects upwards and forwards, by the side of the an-
v.J ' PRIMATES. 47
terior zygapophysis ; this is the metapophysis, or mammillary j
process. The other projects backwards, and represents in ;
a rudimentary condition the process so largely developed in |
many animals called anapophysis. It gradually becomes
smaller in the second and third lumbar vertebrae, and gene- ]
rally disappears in the fourth.
The lumbar transverse processes are thus not serially
homologous with the thoracic ribs, but with the part of the
transverse process of the thoracic vertebrae to which the
tubercle of the rib is attached, and are complementary to
the ribs, becoming greatly augmented in size directly these
cease. Neither are they normally developed autogenously.1
The sides of the bodies of the thoracic vertebrae bear
facets for the articulations of the heads of the ribs. Except
the last three or four, each vertebra supports a portion of the
heads of two ribs, having a large facet near its anterior edge
(placed partly on the body and partly on the side of the
pedicle) for the head of its own rib (i.e. the rib which arti-
culates also with the transverse process), and on the hinder
border of the upper angle of the body a small facet to re-
ceive the anterior edge of the succeeding rib. In the hinder
part of the thoracic region the rib is connected only with
its corresponding vertebra, and not with the one in
front.
Among the remaining Primates, 19 is the prevailing
number of trunk vertebrae, of which usually 12 to 14 bear
ribs. The Gorilla and Chimpanzee (genus Troglodytes),
agree with Man in having 17. The Orang (Simia) has
usually but 16. The Gibbons (Hylobates) and Spider
1 There are several specimens in the College Museum which show
the co-existence, on the first lumbar vertebra, of a rudimentary (supple-
mental) rib, with a transverse process serially homologous with the
transverse processes of the other lumbar vertebrae.
48 TRUNK VERTEBRA. [chap.
S Monkeys (A teles) have mostly 18. Among the Lemurina,
\ Loris and Nycticebus have as many as 23 or 24.
Of thoracic vertebrae, the Gorilla and Chimpanzee have
13, the Orang 12, the Gibbons usually 13 ; other Old World
Monkeys mostly 12 ; the American Monkeys from 12 to 15 ;
the Lemurs from 12 to 16.
As a general rule the vertebral column, taken as a whole,
is straighter than it is in Man, showing a much less marked
sigmoid curve.
Except in the most anthropoid Apes, and a few others, the
spinous processes of the anterior thoracic vertebrae lean
backwards, and those of the lumbar and some of the poste-
rior dorsal vertebrae forwards, so that they converge to a
point near the hinder part of the thoracic region, sometimes
called " the centre of motion " of the vertebral column.1
This may be between two vertebrae, but more often there is
one, which has an upright spine, towards which the others
are directed ; this is the " anticlinal vertebra." It is at this
point that the thoracic vertebrae begin to change their
characters, and assume those of the lumbar vertebrae ; and
the simple elongated transverse processes break up as it
were into the metapophyses, anapophyses, and lumbar
transverse processes, all of which are conspicuous in these
animals.
The transverse processes of the lumbar vertebrae are
usually placed lower on the sides of the vertebrae than
in Man.
In Galago the hinder edges of the neural spines of the
lumbar vertebrae bear a pair of backward-projecting pro-
cesses, which clasp the anterior edge of the succeeding
1 This disposition of the spines of the trunk vertebrn? is still more
marked in many of the inferior mammals, especially the terrestrial
Carnivora.
v.] INSECTIVORA. 49
spine. Similar processes are developed, but to a less ex-
tent, in the Howling Monkeys (Mycetes) and in Lagothrix.
The foramina for the exit of the spinal nerves, instead of
being " intervertebral," perforate the pedicles of the arches
in the Potto (Perodidicus). In the same genus, two or three
of the anterior thoracic vertebrae have very long slender
spinous processes, which in the living animal project beyond
the general level of the skin, forming distinct conical
prominences, covered only by an exceedingly thin and
naked integument
In the Carnivora, the trunk vertebrae are nearly always \\
20 or 21 in number. The genera Felts, Cant's, and Viverra\\
have 13 thoracic and 7 lumbar, Hyatt a 15 and 5, Mustela,
Nasua, Procyon, and Ursus 14 and 6, Meles 15 and 5 ;
Mephitis has the exceptionally high number of 16 and 6,1
and Mellivora but 14 and 4. Among the Seals, Cystophoral
and Otaria have 15 and 5, Trichecus 14 and 6, and Phoca
14 and 5.
The spines of the anterior thoracic vertebrae are long and
slender, and slope back to about the eleventh (the anticlinal),
after which they are shorter, thicker (from before backwards),
and lean forwards. From this point also metapophyses and
anapophyses become distinctly developed; the latter are
especially large in the Felidce. The lumbar vertebrae have
long transverse processes directed forwards and rather
downwards, and short, stout, compressed spinous pro-
concesses.
In the Seals, the trunk vertebrae present much the same
characters, but the anapophyses are usually but slightly
developed, or may be altogether absent, and the spinous
processes show no convergence to a " centre of motion."
Among the Insectivora, the number of the trunk vertebrae I
varies much in the different genera, from 18 (13 thoracic and f
50 TRUNK VERTEBRA. [chap. '
5 lumbar) in Tupaia, 19 (13 and 6) in Talpa and most
Soriddce, 19 (14 and 5) in Galeopithecus, 21 (15 and 6) in
Erinaceus, 22 (19 and 3) in Chrysochloris, to 24 (19 and 5)
in Centetes.
There are also great differences in the development of the
processes of the vertebrae, which appear to accord with the
diversities in the habits and movements of the animal. The
transverse processes of the lumbar vertebrae are very short
in the comparatively slow moving, running, or burrowing
Hedgehogs (Erinaceus), Shrews (Sorex) and Moles (Talpa),
but they are very long, broad, and inclined downwards in the
jumping Macroscelides and Rhynchocyon, where the lumbar
muscles are greatly developed and the hinder extremities
disproportionately large.
In the Mole, there are distinct, small, oval, flat ossicles on
the under-surfaces of the interspaces between the lumbar
vertebrae. Similar ossicles, but in a more rudimentary con-
dition, are occasionally found in the same situation in some
other Insectivora, as the Hedgehog, but not in any other
Mammals.
. The usual number of thoracic and lumbar vertebrae in the
Chiroptera is 17, being either 12 and 5, or less commonly
' 1 1 and 6. The transverse processes of the lumbar vertebrae
are almost obsolete, as are also the spinous processes through-
out the series.
I Among the Rodentia, the most prevalent number is 19 ;
but it falls as low as 16 (13 thoracic and 3 lumbar) in Fiber
zibeticus, and rises as high as 23 (17 and 6) in Capromys, and
even as 25 (17 and 8) in Loncheres.
The characters of the vertebrae vary much in the different
genera, as among the Insectivora. In the Hares (genus
Lepus) the anterior thoracic vertebrae have long slender
spinous processes; the lumbar vertebrae (see Fig. 3, p. 14)
v.] SIRENIA. 51
have very long and slender transverse processes directed
downwards and forwards and widening at their extremities ;
long metapophyses projecting upwards and forwards, small
anapophyses, and remarkably long, single, compressed
median hypapophyses. These latter are not found in the
Rodentia generally.
In the Ungulata, the bodies of the trunk vertebrae are
generally slightly opisthoccelous. The spinous processes in
the anterior thoracic region are exceedingly high and com-
pressed. The transverse processes of the lumbar vertebras
are long, flattened, and project horizontally outwards or
slightly forwards from the arch. The metapophyses are
moderately developed, and there are no anapophyses. The)
canals for the exit of the spinal nerves frequently pierce the^
pedicle of the neural arch.
In the Artiodactyle sub-order the number of thoracic and
lumbar vertebrae together is always 19, though the former
may vary from 12 to 15. Among the Perissodactyles the
number 23 is equally constant, the Horse and Tapir having
18, and the Rhinoceros 19 thoracic vertebrae.
Some species of Hyrax have as many as 22 thoracic andV
8 lumbar vertebrae, making altogether 30, the highest num-'i
ber in any terrestrial Mammal
The Elephants have 23 in all, 19 or 20 of which bear ribs^i
In the order Sirenia, the thoracic vertebrae are numerous
and the lumbar very few ; thus the Dugong (Halicore) has
19 thoracic and 4 lumbar, and the Manati {Manatus) 17 and
2. The bodies are rather triangular, being compressed and
keeled below, and in the young state have no distinctly
ossified terminal epiphyses. The bodies of all the thoracic
vertebrae bear articular facets for the heads of the ribs.
The spinous processes are not very high, but the zyga-
pophyses are well developed throughout the series. The
e 2
52 TRUNK VERTEBRA. [chap.
metapophyses are rudimentary, and there are no distinct
anapophyses.
As there is no sacrum in the Cetacea the lumbar region
passes directly into the caudal, and they can only be dis-
tinguished by the presence of " chevron bones " in the
latter.
The thoracic vertebrae vary in number from 9 in Hyper-
oodon, to 15 and occasionally 16 in some Fin- Whales
{Balamopterd), and the lumbar vertebrae from 3 in Inia (the
Amazonian fresh-water Dolphin) to 24 or even more in some
of the true Dolphins (Delphinus).
The bodies are short in the anterior part of the thoracic
region, but posteriorly become more or less elongated and
cylindrical. Their terminal epiphyses are strongly ossified
disks, very distinct in young animals, but coalescing com-
pletely with the rest of the body in adult age. The spinous
processes are high and compressed. The zygapophyses are
very little developed, and only found in the anterior thoracic
region. The metapophyses are distinct (see Fig. 20, m\
placed at first near the ends of the transverse processes,
but gradually rising on the arch, are ultimately transferred
to the sides of the anterior edge of the neural spine, from
which they project forwards, clasping between them the
hinder edge of the spine of the vertebra in front.
In most Cetacea the transverse processes in the anterior
thoracic region arise rather high on the side of the neural
arch of the vertebra, but in the hinder part of the same
region become gradually placed lower, until finally they are
transferred to near the middle of the side of the body,
which position they occupy in the lumbar region (see Fig.
20). The transverse processes of the lumbar vertebrae are
thus evidently serially homologous with the transverse pro-
cesses of the anterior dorsal vertebrae, which, in their turn,
v.]
CETACEA.
53
continue backwards the upper series of cervical transverse
processes.
In the Physetcridcz (comprising Physeter, Hyperoodon,
Ziphius, and the allied forms) a very different and peculiar
arrangement occurs (Fig. 21). The transverse processes in the
anterior thoracic region (t) are placed quite similarly to those
of the ordinary Dolphins ; but passing backwards, instead
Fig. 20. — Anterior surface of vertebrae of Dolphin {Globicephalus melas), \. a fifth
thoracic ; b seventh thoracic ; c eighth thoracic ; d first lumbar; r rib ; m meta-
pophysis ; t transverse process. The dotted lines indicate the position of the
neuro-central suture.
of changing their position on the vertebrae, they gradually
become smaller, and finally disappear ; while, simultaneously
with their diminution in size, other processes (f) rise from
the body of the vertebra, in the situation of the capitular
attachment of the rib, which, rapidly increasing in length,
become continuous serially with the lumbar transverse pro-
cesses. In two or three vertebrae the two co-exist (Fig. 21,
54
TRUNK VERTEBRA.
[chap.
b and c), resembling the upper and lower transverse pro-
cesses of the neck, and sometimes even meeting at their
extremities so as to enclose a canal. The lumbar transverse
processes in this case therefore are not serially homologous
with the transverse processes of the anterior thoracic region,
and of the upper transverse processes of the neck, as in the
former case, but rather with the lower transverse processes
Fro 21.— Anterior surface of vertebrae of Sperm Whale (Fhyseter nmcrocephalus). M
A eighth thoracic; b ninth thoracic; c tenth thoracic; d fifth lumbar; r rib ;
m mctapophysis ; t upper transverse process ; t' lower transverse process.
of that region ; and yet tried by every other test, the special
homology of the transverse processes of the lumbar vertebrae
of a Dolphin (Fig 20, d t) and a Sperm Whale (Fig. 21, d ()
is perfectly evident.
The mode of ossification of the thoracic and lumbar
vertebrae of the Cetacea appears, so far as it has been
v.] EDENTATA. 55
ascertained, to differ from that of all other Mammals, inas-
much as the neuro-central suture (see Fig. 20) is always
placed a little above the junction of the arch and the body,
the whole of the latter, with any process which may arise
from it, being ossified from the central nucleus. Conse-
quently, in the thoracic vertebrae of the Dolphins, the trans-
verse process is anteriorly an outgrowth from the arch, then
partly from the arch and partly from the body, and finally
from the body alone — a condition quite unknown in other
Mammals.
It would appear, from the conflicting statements on the
subject, that the transverse processes of the lumbar region
are sometimes ossified autogenously, and sometimes exo-
genously from the centrum.
The members of the order Edentata present some great
peculiarities in the condition of the trunk vertebrae, especially
those of the lumbar region.
As to numbers, the Three-toed Sloths (Bradypus) have
20 altogether (either 17 and 3, or 15 and 5) ; and the Two-
toed Sloths (Cholcspus) have sometimes as many as 24 tho-
racic and 3 lumbar, making altogether 27 trunk vertebrae.
The Great Anteater (Myrmecop/iaga) has 18 (15 and 3); the
little Two-toed Anteater (Cyclothurus), 17(15 and 2). The
Armadillos have 15 to 19, the Pangolins {Mants) commonly
18 (13 and 5), and the Cape Anteater (Oiycteropus) 21 (13
and 8).
The vertebral column of the Sloths is remarkable for the
extremely broad, flat laminae and short neural spines, lying
backwards on the next succeeding vertebrae, throughout the
whole column down to the sacrum. All the processes are
very short, and the spines are bifid in the lumbar region.
In Bradypus a small (anapophysial) process projects
backwards from the hinder edge of the transverse process
56 TRUNK VERTEBRAE. [chap.
of each lumbar vertebra, having on its inner surface a facet,
which articulates with a corresponding facet on the anterior
edge of the arch of the succeeding vertebra, below the
ordinary zygapophysis.
In Megatherium, Myrmecophaga, Cydothurus, and Dasypus
(in fact, all the remaining American Edentates), a disposition
thus slightly indicated in the Sloths, is carried out to a great
extent, and results in a very complex and altogether peculiar
method of articulation between the vertebrae.
It will be most convenienrto describe it from one species,
the Great AxiteaXer (Myrmecophaga jubata), but it is the same
in principle in all the above-named genera.
Fig. 22.— Side view of twelfth and thirteenth thoracic vertebrae of Great Anteater
(Myrinecnphaga jubata), g. ;// metapophysis ; tc facet for articulation of tubercle
of rib; cc ditto for capitulum of rib; az anterior zygapophysis; az1 additional
anterior articular facet; pz posterior zygapophysis; pz1 and pz2 additional pos-
terior articular facets.
The anterior thoracic vertebrae articulate in a perfectly
normal manner by large anterior and posterior zygapophyses.
These retain the horizontal position of their facets through-
out. On the eleventh dorsal vertebra, the upper surface of
the backward projecting process which bears the posterior
zygapophysis {pz) below, develops an articular surface
v.]
EDENTATA.
57
(pzx) which looks upwards and articulates with a corre-
sponding downward directed process (az[) developed on the
upper part of the arch of the following vertebra, rather
below the metapophysis (;//). Thus the vertebra has a
process projecting backwards, with flattened articular facets
I on its upper and under surface, fitting into a deep recess
on the anterior edge of .the arch of the vertebra behind,
and the articulation is now by two zygapophysial surfaces
on each side of the arch instead of one.
In the thirteenth thoracic vertebra a third articular facet
(fz2) is developed on the hinder margin of the lamina of
the arch, still higher than the last additional one (pzl),
and separated from it by a deep notch. This looks mainly
Fig. 23. — "Posterior surface of second
lumbar vertebra of Great Anteater, §.
t transverse process; pz posterior zyga-
pophysis; pz1, pz'2, and pz3, additional
posterior articular facets.
Fig. 24. — Anterior surface of third lum-
bar vertebra of Great Anteater, 3.
£ transverse process ; ;« metapophysis ;
az ant-rior zygapophysis ; azl,az*, and
az3, additional anterior articular facets.
outwards, and articulates with a corresponding facet (az2,
Fig. 24) on the anterior edge of the arch of the fourteenth
vertebra, placed to the inner side of the metapophysis, which
is now situated on a process projecting forwards into the
notch between the two upper articular facets of the ante-
58 TRUNK VERTEBRAE. [chap.
cedent vertebra. So that there are now three distinct arti-
culations connecting the arches of the vertebrae on each
side, the processes of the vertebras which bear them inter-
locking in a " tenon and mortise " fashion.
This condition continues as far as the second lumbar, in
which, in addition to these three facets, a fourth (/3) is
developed on the under surface of the hinder edge of the
transverse process near its outer extremity, which articulates
with a similar facet (az3) on the upper surface of the
transverse process of the third lumbar, so that there are now
four pairs of articular facets, or zygapophyses, on each arch.
The same occurs also between the third lumbar and the
first sacral vertebra.
In the Armadillos the lumbar metapophyses are very long,
and project upwards, outwards, and forwards, supporting
the bony carapace, while the broad transverse processes
are exceedingly reduced.
An allied extinct genus, Glyptodon, had the greater
number of the trunk vertebrae completely ankylosed, a con-
dition altogether unique in the Mammalia.
In neither of the Old World Edentates, Mams and
Orycteropus, is there any development of the articular facets
other than the ordinary zygapophyses. In the former genus,
the metapophyses (contrary to the usual rule) project rather
backwards than forwards. The anterior zygapophyses of the
lumbar and posterior thoracic region are largely developed,
and very concave, completely embracing the semicylindrical
surfaces of the posterior zygapophyses. There are no
distinct anapophyses. In Orycteropus the lumbar vertebrae
are numerous (8), with carinated bodies, long and slender
spines inclined forwards, long, broad, and flat transverse pro-
cesses pointing forwards and downwards, well developed
metapophyses and rudimentary anapophyses.
v.] EDENTATA.. 59
In the Marsupialia, the number of thoracico-lumbar
vertebrae is invariably 19, although there are some apparent
exceptions, in which the last lumbar assumes the form of a
sacral vertebra. The rib-bearing vertebrae are always 13,
except in the Koala (Phascolarcios), which has but 11,
and one species of Wombat {Phascolomys vombatus), which
has 15. The Hairy-nosed Wombat (P. latifrons) has the
ordinary number.
n the Kangaroos, the lumbar vertebrae have largely
eloped metapophyses and anapophyses, and moderate-
sized transverse processes much curved forwards.
In the running and jumping Bandicoots (Perame/es) the
lumbar vertebrae have very slender, long, forward-directed
spines, and long transverse processes. In the climbing
Opossums (Didelphys), on the other hand, the spines are
very short and broad from before backwards.
The Monotremata agree with the Marsupials in the total
number of trunk vertebrae, but those that bear ribs are more
numerous, viz. 16 in Echidna, and 17 in Omithoi'hynchus.
The spinous and transverse processes are very short, and
the ribs have no articulation with the latter, but are
attached to the bodies only, the greater part of the articular
surface being below the neuro-central suture, the reverse of
what occurs in the higher Mammals. In the thoracic ver-
tebrae the canals for the exit of the spinal nerves perforate
the neural arch.
CHAPTER VI.
SPECIAL. CHARACTERS OF THE SACRAL AND CAUDAL
VERTEBRAE.
Sacral Vertebra. — The difficulties in denning the sacral ver-
tebrae have been noticed at p. 24. Their essential character
is best illustrated by tracing it up from the simple condition
it presents in the tailed Amphibians (as Menopoma). In these
animals a series of similar small straight ribs are moveably
articulated to the ends of the transverse processes of all
the trunk vertebrae, which are not distinctly divisible into
separate regions. To the distal extremity of one of these
the ilium is attached. This vertebra with its rib thus
constitutes the " sacrum," and the ilium is clearly seen not
to be a " pleurapophysis," as it is sometimes called, or any
part of a vertebra, but a something distinct and superadded.
In the Crocodiles there are two vertebras with strongly
developed rib-like bones connecting them to the ilium, and
remaining long only suturally united to their vertebrae.
The inferior ossification of the transverse processes of the
true sacral vertebrae in Mammals (see Fig. 6, p. 21) is clearly
of the same nature, though more rudimentary in character,
and coalescing at an earlier period with the remainder of the
vertebra. It is not yet known that it exists in all Mammals,
but this may be considered probable, as it is certainly found,
at least in the first sacral vertebra, in such different forms as
h
chap, vi.] CAUDAL VERTEBRA. 61
Man, the Chimpanzee, Orang, Cat, Sheep, Elephant, Sloth,
and Wombat.
The ankylosis of additional vertebrae in the Mammalia is
probably related to the greater fixity and more complete
attachment of the pelvis to the vertebral column in this
class;1 for the innominate bone is not only articulated
by its iliac portion to the true sacral vertebrae, but it has
also a posterior connection with the vertebral column by
its ischial portion, by means either of very strong ligaments,
or in some cases by bony union.2
In Man there are usually five ankylosed vertebrae, con-
stituting the " os sacrum " of anthropotomy, but only two, or
sometimes three, have distinct costal elements. The re-
mainder may be called pseudo-sacral, and belong more pro-
perly to the caudal series. The sacrum as a whole is broad,
strongly curved in the longitudinal direction, with the con-
cavity downwards, and its anterior extremity forms with the
body of the last lumbar vertebra a more prominent " sacro-
vertebral angle" than in other Mammals.
In the Gorilla, Chimpanzee, and Orang, there are
generally five ankylosed vertebrae, to which the last lumbar
not unfrequentiy becomes united in old animals. The
whole sacrum thus formed is long and narrow, gradually
tapering posteriorly, and much less curved than in Man.
In the other Monkeys, there are usually two or three,
rarely four, ankylosed vertebrae ; the first two, or true sacrals,
are broad, and behind these the sacrum suddenly contracts.
1 This is carried to a still greater extent in birds.
2 Hence the following definition of the sacrum : " The posterior
limit of the sacral region is characterized, not by the union of the
different osseous pieces, which varies according to age, but by the place
of insertion of the ischio-sacral ligaments." (A. Milne Edwards,
Famille ties Chevrotains, p. 52. )'
62 CAUDAL VERTEBRA. [chap.
In the Lemur ina the number of united vertebrae varies
from 2 to 5.
In the Carnivora, as a general rule, there appears to be
but one true sacral vertebra, though one or more are ankylosed
to it behind, especially in the Bears and Seals, where as
many as 4 or 5 may be united by bone in old animals. In
the Dog there are usually 3 ankylosed vertebrae.
In most Ungulata and Rodentia the sacrum consists of
one broad vertebra joining the ilia, and a series of narrow
ones, varying in number with age, gradually diminishing in
width, ankylosed to it behind.
In the Beaver among Rodents, the Cape Anteater (Oryc-
teropus) among Edentates, and the Wombat among Marsu-
pials, the sacrum consists of numerous anky)csed vertebrae,
with widely- expanded transverse processes, which are longer
in the hindermost vertebrae, and nearly meet the ischia.
In most other Edentata, as the Sloths, Anteaters, and
Armadillos, this modification is carried further, and the
transverse processes of the hinder pseudo-sacral vertebrae
form a complete bony union with the ischia, converting
into a foramen what is usually the sacro-sciatic notch.
In some of the Armadillos as many as 10 vertebrae are
thus most firmly fused together, and with the innominate
bones.
In Marsupialia usually but one vertebra supports the iliac
bones, though another is commonly ankylosed with it.
In the Monotremata, the Echidna has 3, and the Orni-
thorhynchus 2 ankylosed vertebrae.
The Cetacea having no iliac bones, have no part of
the vertebral column specially modified into a sacrum ; but
in the Sirenia, the rudimentary ilia are attached by liga-
ment to the end of the transverse processes of one vertebra,
which may hence be regarded as sacral.
GENERA L CHAR A CTERS.
^
Caudal Vertebra?. — The vertebrae of the tail vary greatly
in number and in characters in different animals. When
it is well developed, as, for example, in the long-tailed
Carnivora, from one of which the accompanying figures
5. — .Anterior surface of third caurial vertebra of Leopard {Felts leopardus), 5.
az anterior zygapophysis ; pz posterior zygapophysis ; m metapophysis ; / trans-
verse process.
are taken, the anterior vertebrae (Figs. 25 and 26) are
comparatively short and broad, with complete neural
arches, though without distinct spines, prominent metapo-
physes, and anterior and posterior zygapophyses (the latter
Fig. 26— Upper surface of the t>ird caudal vertebra of leopard, §. az anterior
zygapophysis ; pz posterior zygapophysis ; m metapophysis ; t transverse procei-s.
especially being raised on pedicles), and well-developed
>ingle transverse processes. But a gradual change takes
place in these characters (see Figs. 27 and 28), the body
lengthens out and becomes more and more cylindrical ; the
64
CAUDAL VERTEBRM.
[CHAM
neural arch diminishes and finally disappears, leaving for a
while a pair of processes at each extremity of the vertebra,
the remains of the parts of the arch which bore the zygapo-
physes ; the transverse process is much reduced, and con-
fined to the posterior extremity of the body, a second one
appearing at the anterior extremity. Even these rudiments
of processes gradually cease to be perceptible, and nothing
is left but a cylindrical rod of bone, representing the centrum
alone of the vertebra. These diminish in size towards the
apex of the tail, the last being usually a mere rounded nodule.
Fig. 27. — Anterior surface of twelfth
caudal vertebra of Leopard, £. in
metapophysis : / processes serially
continuous with those which support
the posterior zygapophyses in the an-
terior vertebrae ; k hypapophyses The
process on the side of the body be-
tween m and h is the anterior trans-
verse process.
Fig. 28.— Upper surface of twelfth caudal
vertebra of" Leopard, {J. m metapo-
physes ; / processes serially continuous
with those which support the posterior
zygapophyses in the anterior vertebra:.
/ transverse process ; t' anterior traus-
verse process.
Connected with the under-surface of the caudal vertebrae
of many animals which have the tail well developed, are
certain bones, formed more or less in the form of an in-
verted arch (Fig. 29), called chevron bones (French, Os en V;
German, Unterbogen; hcem apophyses, Owen). These are
always situated nearly opposite to an intervertebral space, and
are generally articulated both to the vertebra in front and the
vi.] GENERAL CHARACTERS. 65
vertebra behind ; but sometimes chiefly or entirely either
to one or the other. They are usually articulated movably
to prominences (hypapophyses) on the lower surface of the
body of the vertebra, but occasionally become ankylosed to
it. They ossify from two centres, one on each side, which |
usually coalesce in the median line below, though not unfre-
quently, especially at the beginning and end of the series,
where they are less developed, the two lateral portions remain
>rmanently separate. They serve to give a larger surface of
FlG. 29. — Anterior surface of fourth caudal vertebra of Porpoise {Phcaena com-
munis), i. s spinous process; m metapophysis ; / transverse process ; h chevron
bone.
attachment for the inferior muscles of the tail, and also to
protect the caudal vessels, which run within the canal formed
by the series of these bony arches. They are always best
developed near the anterior extremity of the tail, and are
never found under the posterior rudimentary vertebrae.
In Man the caudal vertebrae are quite rudimentary ;
usually 4 in number, all ankylosed together, and constituting
F
66 CAUDAL VERTEBRAE. [chap.
the coccyx, or os coccygis, of anthropotomy. The first is some-
times ankylosed to the sacrum.
Among the Simiina there are but 4 to 5 caudal vertebn
in the Anthropoid Apes and in the Barbary and Blacl
Macaques, no more than 10 in some Baboons, and as man)
as 32 in Semnopithecus, and 2>Z m some of the Spider M01
keys (A teles).
In the latter the tail is prehensile, and the vertebras are
broader and altogether more strongly developed than in the
weak, pendant, though almost equally long tails of the Old
World monkeys.
Chevron bones are found in all except those species that
have the tails quite rudimentary. They are most fully de-
veloped in Ateles, where the extremities are often bifurcated.
They are attached to a pair of projections on the anterior
end of the lower surface of the vertebra.
In the Lemurina, the number of the caudal vertebras
varies from 5 to 29.
Among the Carnivora, the Bears have very short tails,
with from 8 to 1 o vertebras, the Seals from 9 to 14; some
of the Lynxes have but 13, but most of the animals of the
order have tails of moderate or great length ; the greatest
number of vertebras being found in Paradoxurus, which
may have as many as ^6.
Chevron bones are usually not much developed; they
are articulated (sometimes ankylosed) to the front ends of
the vertebras, as in the Primates.
In the Insectivora, the tail is very variable. It is short
and simple in Erinaceus and Centetes, long in Soletwdon,
Gymmira, Potamogale, Tupaia and Phynchocyon ; in the
last-named genus the chevron bones are well developed and
bifid.
In the Chiroptera, the tail is sometimes exceedingly
vi.] RODENTIA. 67
rudimentary, as in Desmodus ; sometimes elongated, but
composed of long, simple, slender, cylindrical vertebral
bodies; and generally enclosed in the interfemoral cuta-
neous expansion.
Among the different members of the order Rodentia,
there are great differences in the condition of the caudal
vertebrae.
In the Hares, Guinea Pigs, Capybara, &c, the tail is
almost rudimentary. In the Cape Jumping Hare (Pedetes)
it is nearly as long and powerful as that of a Kangaroo,
with well-developed chevron bones.
In the true Porcupines the tail is generally short j but in
some allied genera (Tree Porcupines) it is much elongated
and prehensile.
In the Beaver {Castor) there are 25 caudal vertebrae, all
short, broad, and depressed, and with wide transverse pro-
cesses, becoming double (anterior and posterior) about the
middle of the tail, not by development of a new process,
but by gradual division of the one existing in the anterior
region.
In the Ungulata, the tail is variable in length, but of
simple character and function ; it is never prehensile,
nor has it ever chevron bones, although occasionally, as
in the Ox, a pair of well-developed hypapophyses may be
produced so as to meet in the median line, enclosing a
small canal.1 The vertebrae are most numerous in the
Oxen, and least so in some Deer, especially Moschus, in
which animal the tail is quite rudimentary.
The Elephant has a long tail, composed of 31 vertebrae
of simple character, without chevron bones.
In the Hyrax the tail is almost rudimentary.
1 The Eocene Anoplotherium appears to have had chevron bones,
beneath the vertebras of its long tail.
F 2
68 CAUDAL VERTEBRAE. [chap.
As the tail is the principal organ of locomotion in the
Cetacea, it is always very well developed, and consists of
numerous (from 18 to 30) vertebrae.
Chevron bones are always present, and of simple character,
though with long compressed median spines (see Fig. 29,
p. 65). They are mainly attached to the posterior extremity
of the vertebra immediately in front of them.
The characters of the caudal vertebrae in the various
animals of the order are tolerably uniform, the tail having
the same function in all. In the anterior part of the region
the bodies are very massive and cylindrical ; the arches have
high spines, with metapophyses on their anterior edges, and
the transverse processes are tolerably long, and directed
straight outwards. In passing backwards the arches and all
the processes gradually disappear, and the bodies become
much compressed, and elevated vertically. Suddenly a
change takes place (at the spot where the end of the
vertebral column becomes enclosed in the horizontal,
laterally extended cutaneous expansions, constituting the
"flukes" of the- tail), and the vertebrae altogether alter
their characters, becoming much smaller, wide transversely
and depressed. There is always one vertebra which is
transitional in its character between these two forms. Most
of the caudal vertebrae are perforated by a vertical canal on
each side, at first passing through the base of the transverse
process, but posteriorly through the body of the vertebra
itself. This transmits an ascending branch of the caudal
artery.
The Sirenia have numerous, much depressed caudal
vertebrae, with wide transverse processes, gradually dimin-
ishing in length from the commencement towards the
apex. They are thus very different from those of the
Cetacea.
VI]
E DENT A TA.
69
Among the Edentata, the Sloths have a quite rudi-
mentary tail, consisting of from 6 to 10 depressed vertebrae
without chevron bones.
In the allied Megatherium the tail was greatly developed,
with long processes and large chevron bones, as is the
case with nearly all the Entomophagous Edentates, but
mostly so in the Pangolins {Mams), one species of which
(M. longicauda) has 46 tail vertebras, the highest number
known in any Mammal. Cyclothurus has a prehensile tail of
40 vertebrae. The little Chlamydophorus has a rather short
tail of 15 vertebrae, remarkable for being expanded, de-
pressed and spatulate towards the end, the transverse pro-
cesses actually increasing in size instead of gradually
diminishing, as is almost universally the case.
The chevron bones are usually much developed. They
are Y-shaped, having long, simple, compressed spines in
Orycteropus ; V-shaped in Manis and most Armadillos ; but
FlG. 30. —Anterior surface of third caudal vertebra of Great Armadillo (Priodotites
gigas), h. s spinous process ; m mctapophysis ; az anterior zygapophysis ; t trans-
verse process ; h chevron bone with diverging processes.
in Prwdontes, they have wide, diverging, lateral processes,
instead of a median spine. They are attached rather to
the vertebra in front than to that behind them.
70 CAUDAL VERTEBRA. [chap.
In the Marsupialia, as might be supposed in so hetero-
geneous a group, there is great diversity in the condition of
the caudal vertebrae.
In the Wombat (Phascolomys) and Koala (Phascolardos)
"the tail is comparatively rudimentary.
In the Kangaroo, on the other hand, it is very large, and
serves as an organ of support when standing upright. It is
composed of from 21 to 25 vertebrae, the first few with short
bodies and large processes ; afterwards the bodies lengthen
out, becoming cylinders contracted in the middle. The
zygapophyses soon cease, but the metapophyses continue
longer. The neural arch is not continued longer than about
the middle of the tail ; the transverse processes are gradually
placed further and further back on the vertebra, and then a
new one arises near the anterior end, so that they become
double.
The chevron bones are placed quite between the verte-
brae, so that it is difficult to say to which they most
properly belong. In the proximal part of the tail their
free edge is compressed and develops a process forwards
and backwards, giving a hatchet shape when seen side-
ways. Further back they also send out broad processes
laterally, so as to be cruciform, with a flat inferior
surface.
In some Marsupials the tail is prehensile, as in the
Opossums (Didelfthys), with from 19 to 35 vertebrae, and the
Phalangers (Phalangista), with from 21 to 31.
Chevron bones are generally present in the tails of all
the Marsupials, except the Wombat and Koala. In the
Thylacine they are few, and comparatively rudimentary.
The tails of the two animals composing the order
Monotremata differ considerably.
The Echidna has 12 caudal vertebrae. These have no
vi. ] MONO TREMA TA. 71
hypapophyses, but there are two single median chevron
bones near the middle of the tail, more like the lumbar
subvertebral ossicles of the Mole than ordinary chevron
bones. The Ornithorhynchus has 20 or 21 caudal vertebrae,
with wide transverse processes, a single median hypapo-
physis, and no chevron bones.
CHAPTER VII.
THE STERNUM.
The Sternum of Mammals is a bone, or generally a series
of bones, placed longitudinally in the mesial line, on the
inferior or ventral aspect of the thorax, and connected on
each side with the vertebral column by a series of more or
less ossified bars called ribs.1
It is present in all Mammals, but varies much in cha-
racter in the different groups.
When in its usual and most complete form (see Fig. 31),
it may be divided into three parts, called respectively, —
1. Presternuvi, or "manubrium sterni " of human ana-
tomy.
2. Mesostemum, body of the sternum or gladiolus.
3. Xiphistermnn, xiphoid or ensiform process of the ster-
num.
The mesostemum is usually composed of several distinct
segments, which may become ankylosed together, but more
often permanently retain their individuality, being con-
nected either by fibrous tissue or by synovial joints.
1 For much valuable information upon the structure and development
of the sternum, see W. K. Parker's " Monograph on the Shoulder-girdle
and Sternum of the Vertebrata," published by the Ray Society, 1868.
WAP. VII.
GENERA L CHAR A CTERS.
The ribs are attached to the sides of the sternum : the
first pair to the presternum ; the second to the presternum
and the mesosternum at their point of junction ; the
remainder to the mesosternum, opposite the interspaces
between each segment, though two or more pairs are often
clustered round the last segment. The xiphisternum bears
no ribs.
Developme?it. — The osseous sternum is preceded by a
continuous or non-segmented piece of cartilage ; and as the
ins
Fig. 31. — Human sternum and sternal ribs, \. ps presternum; ms mesosternum;
xs xiphisternum ; c point of attachment of clavicle ; 1 to 10 the cartilaginous
sterna! ribs.
portion of the body in which this is developed is formed
by the union in the middle line of the two " ventral
laminae " of the embryo, traces of this original median
division are generally seen in very young sterna, and are
74
THE STERNUM.
[chap.
often persistent through life in the form of fissures or
fenestras in the middle line of the sternum. Each segment
ossifies from a single nucleus, or from two nuclei placed
one on each side of the middle line, and which usually
become blended together in the course of growth. Some-
times epiphyses are added to the ends of the segments.
The terminal portion of the xiphisternum generally remains
cartilaginous through life.
Special Characters of the Sternum in the various Orders. \
Order Primates.- — In Man (see Fig. 31, p. 73) the presternum
is broad and flat, hollowed in the middle line in front, and
expanded laterally to give large surfaces for the attachment
of the clavicles and the first pair of
ribs. The mesostemum is elongated,
but is also comparatively broad and
flattened. It consists of four distinct
segments. The xiphisternum is a
more or less elongated posterior ap-
pendage, varying somewhat in form
and size in different individuals.
The ossification of the human
sternum is endosteal, or commencing
within the substance of the primitive
hyaline cartilage. The presternum
Fig 32.— sternum of young ossifies from one, or sometimes two,
mesosterl centres, which may be placed side by
side, or one in front of the other.
Each of the segments of the mesostemum has a distinct
centre, though these may be double in their earliest con-
dition, and sometimes remain so for a long period.
The segments of the mesostemum usually unite together
SO as to form one continuous bony piece, to which the pre- J
sternum often remains throughout life connected only by
xs
Orang [Stoma satyrus).
presternum ; ms
num ; -cs xiphisternum.
VII. J
PRIMA TES.
75
fibrous tissue, although it is not unfrequently ankylosed in
old age.
The xiphisternum ossifies irregularly and imperfectly.
The Gorilla, Chimpanzee, Orang, and Gibbons, resemble
Man, and differ from the other monkeys in the breadth and
flatness of the sternum. It is broadest in proportion to its
length in the Siamang (Hylobates syndactylies). In the Orang
(Fig. 32), each segment of the mesosternum is developed
from a pair of lateral ossifications,
which commonly remain separate until
the animal is about half-grown.1
In the lower Monkeys the pre-
sternum is somewhat broad, but the
bones constituting the mesosternum
are elongated and compressed, and are
not ankylosed together as in Man and
the highest Apes. Their number varies
from three to five. In the Howling
Monkey (Mycetes) the presternum has
in front of it two large diverging horns
(pro-ostea, Parker), which ossify sepa-
rately and support the clavicles and
either the whole or part of the first
pair of ribs.
In the Carnivora, the sternum
(Fig. 33) is generally composed of
eight or nine pieces altogether, in-
cluding the presternum and the xiphi-
sternum.
The presternum, or manubrium, is long and narrow,
somewhat expanded near the front for the attachment of
1 The sternum of a young Gorilla in the Museum of the College of
Surgeons presents the same condition.
Fig. 33 — Sternum-and sternal
ribs of Dog (Cams fami-
liaris), \. ps presternum ;
ms mesosternum ; xs xiphi-
sternum.
Surge<
I!
76 THE STERNUM. [chap.
the first pair of sternal ribs, and terminating anteriorly in a
conical rounded projection.
The segments of the mesosternum are elongated, and
more or less four-sided, contracted at the middle, and
widening at each extremity. They ossify, according to
Parker, edosteally, or from without inwards, the bony
deposit commencing in the inner layer of the perichon-
drium, as in the shafts of long bones; and they remain
permanently distinct from each other.
The xiphisternum is long, narrow, and flat, and .generally
ends in an expanded flattened cartilage.1
In the Pinnipedia, the presternum is produced considerably
in front of the attachment of the first pair of ribs.
In the Insectivora, the sternum is variable in form, but
always more or less elongated and segmented. The pre-
sternum is always more or less expanded laterally in this
claviculated group of animals. It is bilobate in front id
the Hedgehog (Erinaceus), trilobate in the Shrews (Sorex).
In Rhyjichocyon it is broad in front, narrow posteriorly,
strongly keeled below, and with two horn-like processes
projecting outwards and forwards between the attachment
of the clavicles and the first pair of ribs.
The mesosternum is usually narrow, as in the Carnivora,
but in the Hedgehog, where it consists of three segments,
it is broad and flat posteriorly. In this genus the xiphi-
sternum is rudimentary, whereas in the Shrews it is long
and ends in a flat expanded cartilage.
The Mole {Talpa) and its nearest allies have a remarkably
developed presternum, which is longer than the whole of the
mesosternum (Fig. 34). It is strongly keeled below, except
at the front part, which is much thickened. On its superior
or inner surface it is grooved in the middle line. Laterally it
1 This is not preserved in the specimen figured.
INSECT1V0RA.
77
gives off a pair of wing-like processes, behind which the first
pair of ribs are attached. It is distinctly separated from the
mesosternum, which consists of five segments of nearly equal
width. The xiphisternum has a broad oval cartilaginous ex-
pansion posteriorly, not shown in the figure,
which is taken from a dried specimen.
As the clavicle is supported at the
anterior extremity of the elongated pre-
sternum, it is widely separated from the
first rib, and the anterior extremities are
brought into such close juxtaposition with
the head, that the animal appears to have
no neck.
In the Chiroptera, the sternum pre-
sents a considerable general resemblance
to that of Man. The presternum is large,
trilobate in front, and strongly keeled.
In many of the Insectivorous Bats the seg-
ments of the mesosternum are (at least in
adults) firmly ankylosed together, but in the frugivorous
Bats (Pleropus, &c.) they continue separated.
In the Rodentia, the sternum is long and narrow, consist-
ing of a presternum (which is generally broad in the forms
which have the clavicle well developed, as the Rats, Beavers,
&c), a mesosternum of three, or more usually four, seg-
ments, and a long xiphisternum, with a broad cartilaginous
terminal expansion. The segments of the mesosternum
often have epiphyses at each end.
The presternum is compressed and produced forwards in
those species in which the clavicle is absent or rudimentary,
as the Aguti, the Hares, and the Capybara. In the latter
it much resembles that of the Horse or Tapir.
Order Ungulata. — In the Ruminantia there are usually
Fig. 34. — Sternum of
Common Mole ( Tal-
pa europcea). ps pre-
sternum ; ms meso-
sternum ; xs xiphi-
sternum ; c point of
attachment of cla-
vicle.
7*
THE STERNUM.
[CHAl
seven segments altogether in the sternum (Fig. 35). The
presternum is narrow, rounded in front, and bearing the
first pair of sternal ribs close to its apex. The succeeding
pieces gradually widen, the posterior segments of the meso-
sternum being square, flat, and rather massive (especially in
FlG. 35. — Sternum and sterna) ribs of
the Red Deer (Cermts elaphus), \. ps
presternum ; vis mesosternum ; xs
xiphisternum.
Fig. 36. — Sternum of the Pig (Sus
scrofa), \. ps presternum ; tns meso-
sternum ; jrs xiphisternum.
the Giraffe) ; they are hollowed at the middle of their
lateral borders. The xiphisternum is thin and flat.
In the Pig (Fig. $6) and Hippopotamus the presternum
is compressed and keeled ; the articular facets for the first
vn.] UNGULATA. 79
pair of ribs are close together on its upper surface ; but
the mesosternum is broad and flat, the first segment being
transitional, compressed in front, and broad posteriorly. The
xiphisternum is narrow and pointed. The sternum of the
Pig very often retains indications of the primordial median
fissure through life.
The Horse and the Tapir have a very peculiar sternum.
The presternum is extremely compressed and projects forward
like the prow of a boat. In the Tapir, its anterior portion
is originally, and commonly remains, a distinct ossification
(pro-osteon, Parker). The segments which follow gradually
widen, and the hinder part of the sternum is broad and flat.
The last mesosternal segment in the Tapir is generally
divided in the middle line, and is not followed by a
xiphisternal element.
The sternum of the Rhinoceros, on the other hand, is
very narrow throughout, with a long, rather spatulate xiphi-
sternum.
Order Cetacea. — Each of the two primary divisions of
this order has a distinct form of sternum.
Among the Odo7itoceti, the typical Dolphins have a very
broad presternum of peculiar form, emarginate in the
middle line in front, and with a pair of lateral processes
behind the attachment of the first pair of ribs. This is
followed by two or three mesosternal segments, but no
xiphisternum. An indication of the primordial median
fissure can generally be traced, except in very old animals,
either as a hole in the presternum, or as a division of the
posterior mesosternal segment.
In the Porpoise (Phoccena) the sternum is shorter and
broader than in most Dolphins, and its various elements
early coalesce into a single bone.
In the Cachalot (Physeter macrocephalus) the sternum
8o
THE STERNUM.
[chap.
ossifies from three distinct pairs of nuclei, and a large
median fontinelle remains between the first and second
Fig. 37. — Sternum of Cachalot or Sperm Whale (Physctcr macrocephalus), J4.
pair.1 In the specimen in the Museum of the Royal College
of Surgeons, which is very nearly adult, each half of the
Fig. 38.— Sternum of Greenland Right Whale [Batoua mysticetus), ,',,.
presternum (ps) has coalesced with the corresponding
half of the first segment of the mesosternum (ms1), but the
1 I have observed this in animals evidently of great age.
1. 1
CETACEA.
8l
resulting pieces are not united by bone across the middle
line, while the second or last pair of mesosternal segments
(ms2) are ankylosed together mesially, but not with the
portion of the sternum in front of them.
In the Whalebone Whales (Mystacoceti) the sternum is
comparatively rudimentary, consisting only of a broad,
flattened presternum, produced posteriorly into a xiphoid
process in some species. There are never any mesosternal
segments, and consequently no ribs, other than the first
pair, are attached to it.
). — Sternum of Common Rorqual or Fi
Whale {Balcenoptera musculus), fa.
Fig. 40. — Sternum of Pike Whale
{Balcenoptera rostrata), J0.
The presternum is ossified from one, or perhaps a pair of
symmetrical nuclei. In the Right Whales (Balcena, Fig. 38)
it is heart-shaped, or longitudinally oval. In the Fin Whales
[Balcenoptera) it is transversely oval or trilobate, with a
backward projecting xiphoid process.1 In young animals
1 In the cartilaginous sternum of a young Balanoptera sibbaldii
Professor Turner found the xiphisternum to be quite distinct from the
presternum, and connected with it by fibrous tissue. {Journal of
Anatomy, May 1870.) In most Whales the sternum shows no such
evidence of segmentation.
82 THE STERNUM. [chap.
ossification of the cartilaginous sternum advances forwards
on each side of the middle line, so that the ossified portion
at one period appears deeply notched in front ; as the bone
meets across the middle line anteriorly, this notch usually
becomes converted into a hole (see Fig. 39), which finally
closes with complete maturity.
In the Pike Whale (B. rostraia) the sternum is cross
shaped (Fig. 40), the first ribs being attached behind the
lateral arms of the cross.
In the Sirenia the sternum is a simple, flattened, some-
what elongated bone, which in the adult shows no trace of
segmentation.
iy
*
!:
Fig. 41. — Sternum of a young Dugong (Halicore indicus), \. From a specimen
the Leyden Museum.
In a young Dugong (Halicore), Fig. 41, there are two
distinct ossifications, — a presternum (ps), to which the first
pair of ribs are attached, and a xiphisternum (xs). The
second, third, and fourth pairs of sternal ribs are attached
to the intermediate unossified portion, representing a rudi-
mentary mesosternum.
VII.] EDENTATA. 83
In the Manati (Manatus) the sternum is of somewhat
similar form, and has three pairs of ribs attached to its
lateral margins near the middle.
Among the Edentata there is considerable variation in
the characters of the sternum.
In the Cape Anteater (Orycteropus) the sternum is of
quite a normal form. The presternum is trefoil-shaped,
expanding laterally near the front to meet the largely de-
veloped clavicles, then contracting to the width of the
mesosternal segments, which are four in number, simple,
flattened, oblong, with lateral margins nearly parallel,
rather broader above than below, united together by fibrous
tissue, and succeeded posteriorly by a moderately deve_
loped xiphisternum.
fin Mam's dalmannii the sternum is flat, consisting of
i'en segments, several of which are sometimes divided
the middle line by synovial cavities. The xiphisternum
very long, partially cleft in the middle line, and ending
in a large, flattened, cartilaginous expansion. In the Long-
tailed Pangolin (Mam's longicanda) the xiphisternum is of a
remarkable form, being prolonged into a pair of cartila-
ginous processes, each about nine inches long, and con-
nected posteriorly with some rudimentary abdominal ribs.1
In the Anteaters (Myrmecophagd) the presternum is broad,
flat, and oval. The segments of the mesosternum (Fig. 42)
are eight in number, short, deep, broad above, and sending
a club-shaped process downwards ; each is ossified from a
principal endosteal centre and eight epiphyses, is connected
by synovial articulations with the segment before and behind,
and has at either end an upper and lower hollowed surface,
which, with the corresponding surfaces on the contiguous
segment, form articulating facets for the double- headed I
I1 Parker, op. cit.
G 2
84
THE STERNUM.
[CHAP,
sternal ribs. This mode of articulation curiously resembles
that at the vertebral end of the rib. The xiphisternum is
rather long and simple.
In the small Tree Anteater (Cyclothurus didactylus) the
presternum is very broad and trilobate, sending out lateral
expansions behind the attachment of the clavicles to meet
the first pair of ribs. The hinder, narrow part of the manu-
brium is segmented off from the larger anterior part, and
mst
FlG. 42 — Side view of three mesosternal segments from a young Anteater (Myrmc-
copliaga tatnandua), showing the mode of articulation of the sternal ril
copied from Parker's figure, mst the upper or inner surface of the mesosternal
segment ; sy the synovial articulation between the .segments.
resembles a mesosternal segment ; but it is in front of the
attachment of the second pair of ribs. The true mesosternal
segments are six in number, of nearly equal width, high,
rounded above, and compressed below, with a synovial
cavity between each. The sternal ribs are articulated by a
single oval condyle. The xiphisternum is long, stout, and
styliform.
In the Armadillos' (Dasypodida) the presternum is broad,
and in Priodontes gigas (Fig. 44, p. 95) strongly keeled. The
mesosternal segments, four to six in number, are broad above,
VII.]
EDENTATA.
85
but very narrow below ; and, according to Prof. Parker, each
ossifies from eleven centres. They are connected by syn-
ovial joints to each other, and to the strongly ossified sternal
ribs, which have broad, sub-bifid heads. The xiphisternum
expands posteriorly into a wide cartilaginous flap.
In the Sloths the sternum is long and narrow. The Three-
id species (Bradypus) have a rather broad presternum, but
rith no prolongation in front of the attachment of the first
FlG. 43. — Sternum and adjacent parts of the skeleton of a young Ornithorhynchus
(O. paradoxus), c clavicle ; ic interclavicle , po pro-osteon (a part of the true
sternum) ; ps presternum ; ms mesoaternum ; sr sternal ribs ; ir intermediate ribs ;
vr vertebral ribs.
rib. This is followed by eight small mesosternal segments,
and a very small rounded xiphisternum. In the Two-toed
Sloths (Choiapus), the presternum is narrow, slightly keeled,
and forms a considerable projection in front of the attach-
ment of the first rib. The mesosternum has twelve seg-
ments, and the xiphisternum is rudimentary or absent.
86 THE STERNUM. [chap. vii.
In the Marsupialia the sternum presents no especial
aberrant characteristics. The presternum is rather broad at
the point of attachment of the first pair of ribs. Its anterior
extremity often does not ossify. There are usually four
quite distinct, elongated segments to the mesosternum,
connected to one another by fibrous tissue, and sometimes
completed at each end by epiphyses. The xiphisternum
has an elongated, narrow, ossified portion, and terminates
in a laterally expanded cartilage, which may contain one
or two endosteal bony patches.
In the Monotremata the Ornithorhynchus (Fig. 43) has
a broad presternum (ps), with a small partially ossified
pro-osteon (po) in front of it ; three keeled mesosternal
segments (ms), which commence to ossify in pairs, and
no xiphisternum. The Echidna agrees in all important
respects, but it has an ossified xiphisternum.
The T-shaped bone, interclavicle or episternum {ic) in front
of the presternum, which connects it with the clavicle, and
which appears to have no homologue among the other
Mammalia, belongs more properly to the shoulder-girdle
than to the sternal apparatus.
CHAPTER VIII.
THE RIBS.
The ribs form a series of long, narrow, and more or less
flattened bones, extending laterally from the sides of the
vertebral column, curving downwards towards the median
line of the body below, and mostly joining the sides of the
sternum.
Free ribs are normally only attached to the thoracic ver-
tebras, although, as before shown, certain parts, which may
be serially homologous with ribs, are found in other regions
of the vertebral column ; but in such cases they become
ankylosed with their corresponding vertebrae. In the
thoracic region, the ribs are never normally ankylosed
with the vertebrae, but are articulated to them by synovial
joints, which permit a certain, though limited, amount of
motion.
As a general rule, the first thoracic rib joins the pre-
sternum or manubrium ; sometimes, as in the Whalebone
Whales, this is the only rib united below to the sternum, but
usually a larger number are so connected, while the more
posterior are either attached by their extremities to the
edges of the ribs in front of them, and thus indirectly join
the sternum, or else they are quite free below, meeting no
part of the skeleton. These differences have given rise to
88 THE RIBS. [chap.
the division into true ribs and false ribs (by no means good
expressions), signifying those that join the sternum directly
and those that do not; and of the latter, those that are
free below are called floating ribs.
Each primary piece of cartilage, out of which one of the
half hoops or ribs is developed, is, moreover, divided trans-
versely into two portions, which assume different characters,
as they usually undergo a different mode of ossification, and
remain more or less distinguishable from each other during
life. The portion nearest the vertebral column is called
the vertebral rib. This is the larger segment, and becomes
firmly ossified at an early period by ectostosis;1 it is the
bone commonly spoken of as a " rib."
The portion towards the sternal extremity or sternal rib
is usually imperfectly ossified, and always at first (except
in Monotremes) by endostosis.2 Sometimes it remains per-
manently in a cartilaginous state ; but, on the other hand, in
some cases it becomes as firmly ossified as the vertebral
ribs.
The vertebral ribs are variously connected with the
sternal ; by continuous cartilage ; by intercalation of fibrous
tracts ; or by synovial joints.
Occasionally, in the Mammalia, an " intermediate "
portion of the rib is segmented off, as in Reptiles ; this is
best developed in the Monotremata (Fig. 43, ir), where,
however, it is only partially ossified by endostosis. In all
other instances in which it occurs it is quite rudimentary.
The vertebral ribs, when in their most typical condition,
have two points of attachment to the vertebra ; the tubercle
1 The bony deposit commencing at the surface, and advancing in-
wards, as in ordinary long bones.
2 The bony deposit being irregularly scattered throughout the carti-
lage, often beginning near its central part.
viii] GENERAL CHARACTERS. • 89
{tuberculuni) and the head {capitulum). The ' former is
superior and posterior, and attached to the transverse pro-
cess of the vertebra ; the latter, inferior and anterior, and
attached to the body of the vertebra, or the inferior part of
the arch near the body, and always very near the neuro-
central suture. Commonly, in fact, the articular surface is
cut by this suture. Sometimes, as in Man, the greater part
of the articulation is above the suture ; or, on the other
hand, it may be, as in the Monotremes, below the suture.
The distinction between the two points of attachment is
most marked in the anterior ribs; in passing backwards
they approach nearer to each other, sometimes becoming
blended, or sometimes either one or the other (generally
the tubercular) attachment is lost in the hindermost ribs.
The tubercle articulates, by a nearly flat or slightly con-
vex surface, to a facet on the under-surface of the extremity
of the transverse process of the corresponding vertebra, but
the more rounded capitulum (at least in the anterior ribs) is
placed opposite to the intervertebral space in front of this
vertebra, and portions of two vertebras commonly contribute
to form the articular cavity for its reception. Thus the first
rib is articulated by its tubercle to the transverse process of
the first thoracic vertebra, and by its head to the hinder
part of the seventh cervical, and front part of the first
thoracic vertebra, and so on. The posterior ribs, as a rule,
are connected solely with their own corresponding ver-
tebrae.
The amount of motion permitted by these articulations
is sufficient to allow the thorax to expand and contract in
respiration. In inspiration the ribs are drawn forwards, and
approach nearer to a right angle with the vertebral column ;
while in expiration they fall back, and occupy a more
oblique position to the axis of the column.
9o THE RIBS. [chap.
The sternal ribs are connected with the sternum either by
interposed fibrous tissue, or by distinct synovial joints. The
first is attached to the side of the presternum, the second
opposite to the junction of the presternum and the first
mesosternal segment, and the succeeding ones opposite to
the interspaces between the other mesosternal segments j
though two or more may be attached to the hinder end of
the last of these segments. The inferior ends of the so-
called "false ribs" are attached by fibrous tissue, or by
synovial joints, to the hinder borders of the sternal ribs in
front ; though, as before said, the most posterior are free or
"floating."
The ribs of Mammals never have " uncinate processes,"
like those found in Birds and Reptiles.
The most prevalent number is thirteen pairs ; the lowest
is nine (in Hyperoodon\ the highest twenty-four (in the Two
toed Sloth, Cholcepus.
Special Characters of the Ribs in the various Group.
Mammalia. Order Primates. — In Man there are nor-
mally twelve pairs of ribs, of which the first seven are
reckoned as true ribs, and the last two as floating ribs.
The last pair may be rudimentary or absent ; or, on
the other hand, the seventh cervical or the first lumbar
vertebra may have an additional movable rib articulated
with it.
The first vertebral rib is much shorter, broader, flatter,
and more curved than the others. These gradually increase
in length until the seventh, after which they again diminish
to the twelfth. In breadth they gradually decrease from
the first to the last.
The portion of the rib between the head and the tubercle
is called the neck ; it is wanting in the last two ribs, in
which the two attachments are blended. The greatest point
s of
viii.] PRIMATES. 91
of curvature on the external surface of the rib is called the
angle.
Each vertebral rib has a main centre of ossification and
two epiphyses, one for the head, and (except in the last
two), one for the tubercle.
The sternal ribs generally remain cartilaginous throughout
life, being only partially ossified by endostosis in old age
or under abnormal conditions. They are not distinctly
separated from the vertebral ribs except by their difference
of structure; but synovial joints are (except in the first)
interposed between their inferior extremities and the
sternum.
Among the higher Simiina the ribs do not differ very
notably from those of Man, except in number ; but in the
1 lower forms, and especially in the Lemurina, they more
resemble those of the Carnivora. Among the Old World
Monkeys, the number varies from 11 to 13 pairs. The
; Gorilla and Chimpanzee {Troglodytes) have 13, and the
Orang (Simla) 12. In the American Monkeys there are
from i2 to 15 pairs; in the Lemurs from 12 to 16 pairs.
In the most typical forms of Carnivora, the vertebral
ribs are comparatively slender, subcylindrical, and little
curved. The most anterior especially are short and straight,
the thorax being thus more compressed in front than it is in
Man and the -higher Primates. The sternal ribs (see Fig.
33? P- 75), are long, slender, have a feeble granular ossifica-
tion, and are not otherwise segmented off from the vertebral
ribs. In all the Felidce and Canidce there are 13 pairs, in
the Vlverrldce 13 or 14, in the Jlycenida 14 or 15, in the
Mustelidce 14 to 16, in the Procyonldce 14, in the Ursldce 14
or 15, in the Pinnipedla 14 or 15.
In the Ungulata, the ribs are generally more or less
flattened and broad, notably so in the Ox and Camel, and
92 THE RIBS. [chap.
least so in the Pcrissodactyla. The anterior ribs have
scarcely any curve, the thorax being very narrow in this
region. The sternal ribs (see Fig. 35, p. 78), especially
those near the front of the series, are short, stout, rather
flattened or prismatic, tolerably well ossified, and articulated
with the vertebral ribs by a cup-and-ball synovial joint.
The Artiodactyles have from 12 to 15 pairs of ribs, the
Horse and Tapir 18, the Rhinoceros 19, the Elephant 19
or 20, and the Hyrax 20 to 22.
In the Sirenia, the total number of ribs is very great,
though but few are attached to the sternum. In the
Manati they acquire an extraordinary thickness and so-
lidity of texture. This animal has seventeen pairs, of
which but three are attached by flexible cartilages to the
sternum.
Order Cetacea. — In the Whalebone Whales the ribs differ
greatly from those of the rest of the Mammalia in their ex-
tremely loose connection, both with the vertebral column
above and with the sternum below, probably to allow of
greater alteration in the capacity of the thorax in respiration,
necessitated by the prolonged immersion beneath the sur-
face of the water which these animals undergo.
At their vertebral extremities they are attached only by
their tubercle to near the end of the transverse process, but
apparently not by synovial articulation. The heads of only
a few of the anterior ribs are developed, and are rarely suf-
ficiently long to reach the bodies of the vertebras, their
place being supplied by a ligamentous band. The first rib
is the only one connected with the sternum, either directly
or indirectly, the whole of the remainder being free or
floating ribs. The sternal ribs are mere cartilaginous rudi-
ments, connected by an intermediate layer of fibrous tissue
to the inferior extremity of the vertebral rib ; at least such
viii. 1 CETACEA. 93
is their condition in the fcetus of Balcena mysticetus, as
described by Eschricht and Reinhardt.
BalcEiioptera rostrata, the smallest of the Whalebone
Whales, has but n pairs of ribs, Megaptera longimana 14
pairs, the Greenland Right Whale {Balcena mysticetus)
usually 13, and the larger Fin Whales (Balcenoptera musculus
and sibbaldii) 15, and occasionally 16, the highest number
known in any Cetacean. In these last, it not unfrequently
happens that the hindermost rib, having only the middle
or lower portion developed, is separated by a wide interval
from the vertebral column, a very rare condition, as in most
other cases where the hinder ribs are rudimentary the part
in immediate connection with the vertebra remains.
The first rib presents a very anomalous condition in some
Whalebone Whales, being apparently double, probably owing
to the coalescence of a supplemental cervical rib with the
ordinary first thoracic rib. In some species (as Balcenoptera
laticcps) this appears to be of constant occurrence ; in others,
it is occasional.1
In the Odontoceti or Toothed-whales, as the common Dol-
phin and Porpoise, the ribs (usually T2 or 13 pairs) are long
and slender. The first four or five have tubercles, by which
they articulate with the transverse process of the thoracic
vertebrae, and long necks and heads, reaching to the side of
the antecedent vertebra, near the junction of the body and
the arch (see Fig. 20, p. 53). The posterior ribs, however,
lose the neck, and are solely articulated by the tubercle to
the transverse process. There are usually 7 pairs of rather
short, straight, but strongly ossified sternal ribs, and often
small intermediate ribs, sometimes distinctly ossified.
In the aberrant Physeteridce, including the Sperm Whale,
1 See Professor Turner " On the so-called Two-headed Ribs in Whales
and in_Man." {Journal of Anatomy and Physiology, May 1871.)
94 THE RIBS. [chap.
Hyperoodon and various forms of Ziphioids, the ribs are
connected to the vertebrae throughout the greater part of the
series by both head and tubercle ; but a few of the most
posterior have only a single point of attachment in con-
sequence of the changes which take place in the condition
of the transverse processes of the vertebrae, described at
p. 53. In this family the sternal ribs are either permanently
cartilaginous, or very imperfectly ossified. The Hyperoodon
has but 9 pairs of vertebral ribs, the smallest number
known in any Mammal, the Sperm Whale (Physeter) 11,
of which the last is quite rudimentary; Ziphius 10, and
Kogia 14.
Among the Edentata, the Sloths have very numerous
ribs (from 15 to 24 pairs). In the anterior part of the thorax
the sternal ribs are firmly ossified, and indistinguishable
from the vertebral ribs (at least in adult age), but posteriorly
they are separated from the latter by a less perfectly ossified
intermediate rib.
In the Armadillos the ribs are comparatively few (10 to
12 pairs), and are broad and flat, the first extremely so. The
first sternal rib is very short and incorporated with the ver-
tebral rib, but the others are very strongly ossified, and
articulated by synovial joints with the sternum, with each
other, and with the vertebral ribs.
The peculiar double articulation of the sternal ribs with
the sternum in the Anteater {Myrmecophagd) has been already
described (see p. 83). The ribs of the small climbing Two-
toed Anteater {Cydothurus didactylus) are remarkable for a
thin lamelliform expansion of their hinder border, over-
lapping the succeeding rib. This animal has 15 pairs, the
great Anteater 16, the Cape Anteater (Orycteropus) 13.
The Marsupialia have nearly always 13 pairs of ribs;
the Koala (Phascolarctos) with but 11, and the common
v i n. I MARSUPIAL TA. 95
Wombat (Phascolomys vombatus) with 15, beir.g the only
known exceptions. The sternal ribs are articulated by
synovial joints with the sternum, but are not distinctly
segmented from the vertebral ribs, and are but feebly
ossified by endostosis. There are no intermediate ribs.
Fk;. 44 — Sternum and Tibs of the Great Armadillo {Priodontes gigas), \.
J>s presternum ; .xs xiphisternum.
In the Monotremata the intermediate ribs are well
marked (see Fig. 43, p. 85), and only partly ossified by
endostosis, while the sternal ribs (except the first) are,
according to Parker, strongly ossified ectosteally, as in Birds.
The hinder sternal ribs are very broad and flat. The
Echidna has 16, and the Ornithorhynchus 17 pairs of
vertebral ribs; they do not divide above into head and
tubercle, but are attached only to the sides of the bodies
of the vertebrae.
CHAPTER IX.
THE SKULL.
The skull is the term commonly applied to the expanded an-
terior portion of the axial skeleton situated within the head.
It consists mainly of the cranium, a strong bony case or
frame, enclosing the brain, and affording support and pro-
tection to the organs of smell, sight, hearing, and taste,
and formed by the close union, either by sutures or by
synostosis, of numerous bones.
To the inferior surface of the cranium are suspended
(i) the Mandible, or lower jaw, movably articulated by a
synovial joint; and (2) a group of skeletal structures called
the hyoidean apparatus.
The diagram at p. 106 is intended to show, at a single
view, the names applied to the various bones of which the
skull is composed, and to give some idea of their relative
position.
It will be well to commence the study of the skull by
describing that of a Dog, as a good average specimen of the
class, and one which is easily procurable at various ages ;
and I would strongly advise the student to follow the
description with a skull in his hand, or two would be better.
in one of which a longitudinal median section has been:
made. In the other, the various bones should be separatee
chap. ix. J THE SKULL OF TL1E DOG. 97
from each other. For this purpose a young animal, still
retaining the milk teeth, will be best.1
The skull has a longitudinal central axis {the cranio-facial
j-r F>a IP
CE \
45. — Longitudinal and vertical section of the skull of a Dog {Cants familiaris ,
with mandible and hyoid arch. £. an anterior narial aperture; MP maxillo-
turbinal bone; ET ethmo-turbinal; Na nasal; ME ossified portion of the
mesethmoid ; CE cribriform plafe of the ethmo-turbinal ; Fr frontal ; Pa parietal ;
IP interparietal: SO suprnoccipital ; ExO exoccipital ; BO basioccipital " Per
periotic ; BS basisphenoid ; Pt pteryg id ; AS alisphenoid ; OS orbitosphenoid ;
PS presphenoid ; PI palaiine ; Vo vomer ; Mx maxilla ; PMx premaxilla ;
s!i stylohval ; eh epihyal ; ch ceratohyal ; bk basihyal ; th thyrohval ; j symphysis
of mandible ; cp coronoid process ; cd condyle ; a angle ; id inferior dental canal ;
the mandible is displaced downwards to show its entire form ; the * indicates the
part of the cranium to which the condyle is articulated.
I axis, Huxley) around which all its parts are arranged, and
I its structure will be best understood by commencing with
i the description of the bones forming this axis.
1 When the zoologist wishes to throw into the strongest relief the
distinctive characters of different species, he selects for comparison fully
adult examples ; when the anatomist wishes to trace their community of
structure and their resemblances, younger specimens are better adapted
tor his purpose.
9§ THE SKULL [chap.
When the skull remains in connection with the vertebral
column, it will be seen that its axis is a continuation for-
wards of the axis of that column, consisting of the bodies of
the vertebrae ; and that its hinder termination is placed in
the same line with the odontoid process of the second cer-
vical vertebra, the anterior termination of the axis of the
spinal column.
The large cavity above the axis of the skull (cerebral
cavity) is in direct continuity with the spinal canal above
the axis of the vertebral column.
Beginning at the posterior end of the axis, the section
will be seen to have passed through a flat, elongated bone
(Fig. 45, BO), terminating freely behind at the inferior
margin of the great opening (foramen magnum) at the hinder
end of the cerebral cavity, by which this cavity is continued
into the vertebral canal, and through which the backward
prolongation of the brain (the medulla spinalis) passes. This
bone is the basioccipital.
Immediately in front of this is a bone (the basisphenoid.
BS) not quite so elongated from before backwards, but of
greater vertical depth ; the interior being more or less
cellular in structure. The under surface is flat, but the,
upper surface is hollowed in the middle, and raised at each
extremity. This hollow corresponds to the part called
"sella turcica" in the human skull, and lodges the pituitary
body of the brain.
Further forwards, and likewise separated by a vertical
fissure, is a bone (PS) of about the same length as the last,
but still more elevated, and very cellular within. Its in-
ferior contour is perfectly straight, but above it is somewhat
irregular. This is the presphenoid.
So far the cranio-facial axis consists of bones placed in
a continuous line, more or less depressed, and broad from
IX.] OP THE DOG. 99
side to side, and forming the floor of the cranial cavity;
but the continuation of the axis forward is of a different
character. The anterior end of the presphenoid narrows
considerably, and the segment in front of it, in very young
skulls, is a much compressed vertical plate of cartilage, of
very considerable size, both from before backwards and
from above downwards. Ossification of this cartilage com-
mences in the posterior end and upper part, and spreads
forwards and downwards, but it never or very rarely reaches
its anterior extremity ; and in the animal now described a
narrow inferior margin remains permanently cartilaginous.
The ossified portion of this cartilage {ME) constitutes the
lamina perpefidicularis of the ethmoid bone, the anterior
unossified portion the septal cartilage of the nose, which is
the anterior termination of the cranio-facial axis. The
term mesethmoid may be applied to the whole of this element
of the skull, whether ossified or not.
Above all the posterior, or basicranial, part of this axis,
constituted by the three first-mentioned bones, is the cere-
bral cavity, the walls of which constitute the " brain-case."
These walls are formed by several more or less expanded
and curved bones, which rise up from the sides of the axis
or floor of the cavity below, and, meeting in the middle line,
roof in the cavity above. These bones are arranged in
three sets from behind forwards, each corresponding with
one of the axial bones, and with the latter constituting one
of the three segments or bony rings into which the brain-
case may be divided.
The hindermost (or occipital) segment consists of the
basioccipital below; next on each side the exoccipitals(EO),
and a large, median, flat bone above, with its upper ex-
tremity prolonged forwards in the middle line between the
bones of the next segment, called the supraoccipital {$0)*
H 2
ioo THE SKULL [chap.
These four bones surround fat foramen magnum behind, and
all take share in its circumference, though the exoccipitals,
which bound it laterally, contribute most. On each side of
the foramen, and rather below than above, are the occipital
condyles, by which the skull articulates with the first cervical
vertebra; and externally to these, separated by a deep de-
pression, is a prominent process for muscular attachments,
called the parocripital (or paramasloid) process. The con-
dyles in the Dog are formed by the exoccipitals alone. The
part (IP) which appears to be an anterior prolongation of
the upper extremity of the supraoccipital, wedged in be-
tween the parietals, is ossified from a separate centre, and
in some animals remains permanently as a distinct bone. It
is then called interparietal.
The middle (or parietal) segment is formed by the
basisphenoid below. From the sides of this a pair of
wing-like bones (AS) extend outwards and upwards,
called alisphenoids ; and above these are large square-
shaped bones {Pa), meeting in the middle line above, the
parietals.
The occipital and the parietal segments are in contact
below and above, but there would be a considerable open
space between them laterally were it not for the inter-
position of a group of bones, which do not form part of the
segmented wall of the brain-case proper, but are more or
less connected with the organ of hearing, and will therefore
be described hereafter. These are the bones which, being
all united into one in Man, constitute the so-called temporal
bone of human anatomy.
The anterior (or frontal) segment is formed by the pre-
sphenoid below; then by the wing-like bones (OS) proj ecting*
from its sides, smaller than those of the second segment,
called orbitosphenoids ; and finally by two greatly expanded
IX.] OF THE DOG. roi
bones (/>), curving inwards above and in front, to close in
the cerebral cavity in. these directions, by meeting in the
middle line. These are the frontal bones.
Between the middle bones of the parietal and frontal
segments (alisphenoid and orbitosphenoid) is an irregular
vacuity, called the foramen lacerum anterius, or sphenoidal
fissure, through which several nerves pass to the orbit. This
is the second vacuity in the side wall of the skull, the first \
being the one between the occipital and parietal segment,
partially filled by the periotic bone.
As the occipital segment is not closed behind, so in the
ime way the frontal segment is open in front, the aperture
>eing bounded by all the bones which enter into its com-
>osition — presphenoid, orbitosphenoids, and frontals. The
linder edge of the mesethmoid rising up to meet the
rontals makes a median partition to this aperture (the crista
\alli of human anatomy), and it is further closed by a
special ossification (CE) connected with the organ of smell,
le cribriform plate.
Thus the brain-case may be described as a tube, dilated'
in the middle, composed of three bony rings or segments, ''
with an aperture at each end, and a fissure or space at the"'
sides between each of the segments.
The cranial cavity thus formed is of a general oval form,
but broader behind than in front. The floor is compara-
tively straight ; the upper surface arched. It is imperfectly
divided by bony ridges into three compartments. The
lost posterior^ of these, marked off in front by a sharp
-idge along the periotic bone (Per), extending from near the
junction of the basisphenoid and basioccipital, upwards,
mtwards, and backwards, along the line of junction of
the parietal and supraoccipital, and strongly marked by an
inward shelf-like projection from the former (the ossified
102 THE SKULL [chap.
tentorium cerebelli), is called the cerebellar fossa, as it
lodges that division of the brain. The most anterior and
smallest compartment is marked off by a vertical ridge on
the orbitosphenoid and the frontal. Its walls are chiefly
formed by the cribriform plate. This is the olfactory fossa
{rhitiencephalic fossa, Owen), for the lodgment of the olfac-
tory lobe. Between these two is the great cerebral fossa, in
which the hemisphere of the cerebrum lies. This is very
imperfectly divided below into two compartments, by a slight
ridge at the hinder edge of the orbitosphenoid and con-
tinued thence outwards at the junction of the frontal and
alisphenoid. This ridge corresponds with the Sylvian fissure
of the brain ; the part of the cerebral fossa in front of it
lodges the frontal lobe of the cerebrum, that behind it the
temporal lobe.
Through the lateral parts of the floor of the cranial cavity
are various perforations, or foramina, either holes passing
directly through the bones, or vacuities occasioned by want
of contact, for a limited space, of contiguous bones. These
are mainly for the purpose of allowing of the exit of the
various nerves which take origin from the brain ; and as
they are extremely constant in their position, and offer useful
landmarks for determining the homologies of the bones
throughout the vertebrate series, it is important that they
should be well known. (See Diagram at p. 106.)
i. The most anterior is the space, before spoken of, in
front of the anterior segment, occupied by the hinder part
of the ethmoturbinal, commonly called the " cribriform
plate." The numerous perforations in this plate transmit
the olfactory nerves arising from the olfactory lobes.
2. Near the hinder border of the orbitosphenoid is a con-
spicuous, nearly round, hole, through which the optic nerve
passes, and hence called optic* foramen.
ix. I OF THE DOG. i
3. At a very short distance behind this is a more irregular^
oval opening, between the orbitosphenoid and the ali-
sphenoid. This is the sphenoidal or orbital fissure, or(
foranwi lacerum antcriuj. It leads * into the orbit, and
allows the exit of the motor nerves of the eyeball, or third,
fourth, and sixth cranial nerves, and also the third division
f the trigeminal or fifth nerve.
4 and 5. The alisphenoid near its base is perforated by
o foramina ; the anterior small and somewhat round ; the
sterior larger and oval : these are the foramen rotundum
d the forameii ovale, and transmit respectively the second
d third divisions of the fifth nerve.
6. Between the alisphenoid and the exoccipital is a large
ace, almost entirely filled by the bony capsule of the organ
hearing, the periotic. In front of the inner end of this
ne is an opening {foramen lacerum medium basis cranii),
rough which the internal carotid artery sometimes enters
e cranial cavity.
7. Near the middle of the inner surface of the periotic (
the meatus auditorius interims, into which the seventh !
d eighth nerves enter : the former (the facial nerve)
sses through the bone and emerges on the other side
(by the stylo-mastoid foramen) ; the latter, the auditory, is
distributed to the internal organ of hearing within the/
periotic bone.
A deep depression seen above the internal auditory
meatus, and of nearly the same size, is not a foramen but a
fossa, lying within the concavity of the superior semicircular
canal. It lodges the flocculus, a small process of the cere-
bellum.
8. Between the periotic and the exoccipital an irregular^
space is left (the foramem lacerum posterius), through which j
the glossopharyngeal, pneumogastric, and spinal accessoryS
104 THE SKULL [chap.
nerves (the ninth, tenth, and eleventh) pass out of the
cranium.
/ 9. The exoccipital is perforated, a little in front of the
) condyle, by the condylar Joratnen^ which gives exit to the
/ twelfth, or hypoglossal, nerve.
iio. Lastly, the large median opening, behind the bones
of the posterior segment of the skull, is the foramen magnum,
through which the spinal cord passes out.
It will be seen from the foregoing description that the
three organs of special sense, situated in the walls of the
cranium, have definite relations with the three osseous
segments. The first, or organ of smell, is situated in front
of the frontal segment ; the second, or organ of sight,
receives its nerves by apertures situated between the frontal
and parietal segments or perforating the former ; the third,
or organ of hearing, is intercalated between the parietal
and occipital segment.
The portion of the skull anterior to the junction of the
presphenoid and the mesethmoid constitutes the face. This
differs entirely from the cranial cavity in having a complete
median partition, and consists mainly of two tubular cavities
placed one on each side of this partition. These are the
nasal cavities. They are open at each end, the orifices
being termed respectively anterior and posterior nares.
Each of these elongated cavities is deepest vertically in
its posterior part, where it is partially divided into an upper
and lower chamber : the upper one, the olfactory chamber,
being closed behind by the cribriform plate ; the lower, the
narial passage, terminating in the posterior nares.
Each nasal cavity may be described as having an inner
wall, an outer wall, a floor, and a roof.
The inner wall is formed mainly by the partially ossified
ix. I OF THE DOG. 105
mesethmoid cartilage {ME), but the lower part of the pos-
terior two-thirds also by the vomer { Vo). The greater part
of this bone has the form of a trough, hollow above, em-
bracing the inferior, thickened border of the mesethmoid
cartilage, and extending a little way behind this so as also
to underlie the anterior portion of the presphenoid ; but it
also develops from its under surface in the middle line a
thin plate, which passes vertically down to the centre of
the floor of the nasal passages, and completes the septum
inferiorly.
Above, rather behind the middle of the bone, the lateral
plates of the vomer, which embrace the mesethmoid carti-
lage, send out sideways a pair of wing-like processes, which
join the side walls of the nasal cavity, and form the partial
horizontal partition, dividing the narial passage from the
olfactory chamber.
The outer wall of the nasal cavity is formed mainly by
four bones : (1) a somewhat quadrate, thin, nearly vertical
plate of bone (/V), the pterygoid, attached above to the under
surface of the basisphenoid and presphenoid, supported
externally by a strong descending process of the alisphe-
noid, the external pterygoid plate, ending posteriorly and
inferiorly by a free border, and articulating in front with (2)
the palatine. This bone {PI) is of much greater extent ; for,
besides its vertical portion, forming the outer wall of the
nasal canal in front of the pterygoid, it sends from its upper
edge a lamina inwards to meet the horizontal plate of the
vomer, and aid in forming the roof of the hinder part of the
narial passage. It also sends a strong horizontal lamina
inwards from its lower edge, which, meeting its fellow in the
middle line, forms the posterior part of the floor of the narial
passage. In addition to these it sends a broad plate upwards
K forwards in the inner wall of the orbit.
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108 THE SKULL [chap.
3. In front of this is the maxilla (Mx), a still more con-
siderable bone. It not only forms the chief part of the outer
wall of the nasal cavity, but it also sends inwards a hori-
zontal plate, forming the middle part of its floor. At the
junction of its vertical and horizontal portions is the alveolar
border, in which the canine, premolar, and molar teeth are
lodged.
4. The most anterior bone of this series is the premaxilla
(PMx), which also has an ascending or vertical plate,
forming the outer wall of the nasal cavity, and a horizontal
plate forming the anterior part of its floor ; at their junc-
tion its alveolar border lodges the incisor teeth. The pre-
maxilla forms the outer and lower boundary of the anterior
nares. \
Besides these four, there is a small bone which enters into
the outer wall of the upper part of the nasal cavity, between
the ascending process of the palatine, the maxilla and the
frontal. This is perforated by the duct, which conveys the
tears from the orbit into the nasal cavity, and is hence
called lachrymal.
Above this a process from the frontal completes the
upper and posterior part of the outer wall of the olfactory
chamber.
The floor of the nasal cavity is formed, as above said, by
the horizontal plates of the palatine, maxilla, and premaxilla
meeting the corresponding bones of the opposite side in the
middle line. The inferior surface of this same horizontal
layer of bone is the roof of the mouth, or bony palate.
The roof of the nasal cavity is formed posteriorly by
the continuation of the frontal forwards beyond the cere
bral cavity, the " nasal process of the frontal" but mainl)
by a long narrow bone, the nasal bone (Na). The hinder
extremity of this lies upon the nasal process of the frontal
ix. I OF THE DOG. 109
its anterior end is free, and forms the upper boundary of
the anterior nares ; its outer side is in contact with the
ifrOntal, maxilla, and premaxilla; and its straight inner edge
lies 'against that of the corresponding bone of the opposite
side.
Within each nasal cavity are two very singular bones,
each being composed of a number of delicate lamellae
ifolded and arranged in an exceedingly complex manner,
forming a mass with so many passages and perforations that
the term " spongy bones " has been applied to them.
The most posterior is the larger, and placed rather higher
than the other ; its anterior extremity (ET) overlapping it.
It completely fills the proper olfactory chamber ; its hinder
extremity occupying the gap left in the cranial wall in front
of the anterior segment of the brain-case. The various
laminae are all connected together and to the hinder end of
the mesethmoid, by a plate of bone (CE) so full of perfora-
tions of varied form and size that it is called the cribriform
plate, and from it the name of ethmoid (or sieve-like) is
commonly applied to all the bony structures with which
lit is united. On their outer side these laminae are con-
nected to a thin flat plate of bone (the so-called os plcumm)
which lies against the inner wall of the maxillary, but does
inot ordinarily contract any.union with it.
This bone results from the ossification of the complexly
'folded cartilage, over the surface of which the olfactory
nerves are spread, the division into laminae permitting a
great increase of sensitive surface. As, although originally
distinct, it subsequently unites with the mesethmoid, by
Imeans of the cribriform plate, it is considered in human
lanatomy as part of the same bone, under the name of
"lateral mass of the ethmoid," and is described as con-
sting of the superior and middle " turbinated bones ;" but
no THE SKULL [chap.
the name ethmoturbinal, applied to it by Professor Owen, is
perhaps more appropriate.
The uppermost of the lamellae of the ethmoturbinal, lying
immediately under the nasal bones, is rather distinct from
the others, and extends much further forwards ; and as in
certain Mammals it becomes united by bone with the nasaj,
it is sometimes distinguished under the name of nasotur-
binal.
In front, and on a rather lower level, a similar, but smaller
and less complex bone (MT), consisting chiefly of horizontal
lamellae, is placed. This, though originally developed from
the same cartilage lining the outer wall of the nasal chamber
as the last, ossifies quite distinctly from it, and contracts a
bony union by a horizontal lamella on its outer side with
the maxilla. This is the maxilloturbinal, and corresponds
with the " inferior turbinated bone " of human anatomy.
It will be observed, that while the ethmoturbinal is placed
high in the nasal cavity, and above the direct channel by
which the air passes to the posterior nares, the maxillo-
turbinal, situated nearer the front of the chamber, before ijjl
has divided into an upper true olfactory chamber and J|
lower narial passage, nearly blocks up the whole cavity, so;
that air passing through in inspiration is filtered between its
meshes. The moist membrane which covers its bony plates
in life is supplied with nerves chiefly from the fifth pair,
and not from the olfactory ; so that it does not perform the
function of an organ of smell like the ethmoturbinal, but
rather serves to guard the entrance of the respiratory
passages from foreign substances, and perhaps to warm the
inspired air.
In describing the walls of the cranium, a large space was
mentioned on each side, between the posterior and middle
IX.] OF THE DOG. in
cranial segment, in which were inserted certain bones not
wt noticed. These bones form a definite group by them-
selves, at all events locally connected, though very different
in function and structure.
In a mass of cartilage, in the position just indicated,
ossification takes place from several centres (three, called
respectively pro-otic, epiotic, and opisthotic, according to
Professor Huxley and others, in the human skull;1 but the
process has not been accurately traced in other Mammals).
These very rapidly unite to form a single bone, which com-
pletely encloses the labyrinth or essential organ of hearing,
consisting of the vestibule, semicircular canals, and cochlea.
This bone is the periotic (Per). It is divided into two por-
.ions : an antero-internal, which forms a somewhat angular
>rojection within the cranial cavity, and is of remarkable
lensity — the petrous portion • and a postero-external, a sort
)f process from the former, smaller, less dense, and forming
i small portion of the wall of the cranium, appearing
jxternally just in front of the exoccipital — the mastoid
lortion.
The petrous is of course the more important, and has
Constant characters throughout the class, while the mastoid
s very variable, and sometimes can scarcely be said to exist,
t is in no case a separate bone ; and, although a portion of
may develop originally from a separate centre, it is always
before birth firmly united with the petrous, so that they
ill be spoken of here as one bone, under the name of
>tic.
j The essential characters of the petrous portion of the
eriotic are, that it contains within it the internal ear ;
it has on its inner or cranial side a foramen, through
hich the facial and the auditory nerves leave the cranial
1 Elements of Comparative Anatomy (1864), p. 148.
ii2 THE SKULL [< hai>.
cavity, the former to pass through the bone, escaping by the
stylomastoid foramen on the outer and under surface, the
latter to be distributed on the sensitive portions of the
organ of hearing ; and that it has on its outer side two
holes, one placed above the other, the fenestra oralis and
the fenestra rotunda, through which the internal ear com-
municates with the cavity of the tympanum, or middle-ear,
which is situated on the outer side of the petrous part of
the periotic bone.
Externally to the periotic bone are placed two bones
separately developed in fibrous tissue, which often acquire a
very close connection with the periotic, occasionally, as in
Man, becoming firmly ankylosed with it.
The upper one of these is the squamosal (Fig. 47, Sg),
which has a broad, scale-like, vertical portion spreading out
over the side of the cranial wall, uniting with the supra-
occipital behind, overlapping the lower edge of the parietal
and the hinder part of the alisphenoid, and also appearing
for a very small space in the inner side of the cranial wall.
From near its lower border it sends a strong process out-
wards, which soon curves forwards, called the zygomatic
process. This articulates with another bone (Ma), the malar
or jugal, which connects it with the maxilla, and so forms
the strong, lateral, nearly horizontal, or slightly arched
osseous bridge, which passes from the face to the hinder
part of the cranium, called the zygomatic arch. On the
under surface of the base of the zygomatic process of the
squamosal is a laterally extended, oblong surface, concave
from before backwards, for the articulation of the condyle
of the lower jaw, called the glenoid fossa (gf), the hinder
edge of which is projected into the postglenoid process (gj>).
The lower bone, on the outer side of the periotic, is
the tympanic (Ty). At birth this is a mere osseous ring,
rx.] OF THE DOG. 113
incomplete above, surrounding the inferior three-fourths of
the membrana tympani, but it undergoes a considerable
development in the course of the first few months. The
external edge of the ring is produced horizontally outwards
- to form the short, bony, external auditory meatus; while
the under and inner surface is greatly expanded, to form
the conspicuous rounded prominence, hollow within, called
the auditory bulla, which abuts against the outer edge of
the basioccipital below.1
The space that is left among this group of bones, — bounded 1
by the periotic (the part in which the before-mentioned
fenestrae are situated) within, the periotic and squamosal
above, the tympanic and its bullate expansion below, behind,
and in front, and by the meatus auditorius externus, closed
in the natural state by the membrana tympani, to the outer 1
side, — is called the tympanic cavity.
It contains within it the ossicula auditus, three small
bones called malleus, incus, and stapes, which, articulated
together, stretch across the cavity from the membrana
tympani to the fenestra ovalis."2 The cavity has an opening
at its antero-internal angle, through which the Eustachian
tube, connecting the tympanum with the pharynx, passes.
The inner side of the bulla is perforated lengthwise by a
canal, which commences posteriorly within the margin of
1 The whole of the bulla is generally considered as belonging to the
tympanic bone, but its inner part in many mammals is developed in a
distinct cartilaginous lamella, interposed between the lower edge of the
tympanic ring and the base of the skull. This may ossify from a sepa-
rate nucleus, or by extension of bony deposition inwards from the true
tympanic. The development of this region of the skull in the Mam-
malia still offers an interesting field for investigation.
2 As these bones are, in the Mammalia, completely subservient to
the organ of hearing, their modifications will not be described in the
present work.
I
ii4 THE SKULL [chap.
the foramen lacerum posterius (between the auditory bulla
and the exoccipital), and transmits the internal carotid artery.
This vessel appears again on the surface, at the anterior
extremity of the bulla, close to the Eustachian orifice ; then
runs upwards and inwards and enters the cranium through
the foramen lacerum medium.
This completes the enumeration of the bones of the
cranium. Before proceeding further, it will be desirable
to take a general survey of this part as a whole, pointing
out the most prominent features of its various surfaces.
The posterior surface is, in a general sense, a vertical
wall, somewhat triangular in form, broad below and pointed
above. In the middle line, at its lowest border, is the nearly
round forame?i magnum, bounded by the supraoccipital
above, the exoccipitals on each side, and the basioccipital
below. On the sides of the foramen magnum, and
approaching each other in the middle line below, but
diverging above, are smooth eminences, the occipital
condyles. Further outwards, and separated from these by
a deep valley, are the paroccipital processes, projecting
backwards and downwards. Outside of the upper part or
origin of these processes, the mastoid portion of the periotic
appears on the hinder wall of the skull. The remainder of
the region is formed by the supraoccipital, and it is dis-
tinctly marked off laterally by ridges, which, commencing
in the median line above, run downwards and outwards,
at the junction of the parietals and supraoccipital, and are
continued on the squamosal in front of the mastoid to the
upper edge of the external auditory meatus. The ridges
of each side taken together form the lambdoid or occipital
crest. They are far more conspicuous in old than in young
animals.
i x.J OF THE DOG. 115
The superior surface of the skull (Fig. 46) may be divided
into a cranial and a facial portion. The former is of a
somewhat oval form. On its upper surface posteriorly, in
full-grown dogs, is a median ridge joining behind with the
Fig. 46 - Upper surface of cranium of a Dogs \- SO supraoccipital ; JP inter-
parietal ; Pa parietal ; Sq squamosal : Fr frontal ; Ma malar ; L. lachrymal ;
Mx maxilla; Na nasal ; PM x premaxilla ; ap anterior palatine foramen ; io infra-
orbital foramen ; pof postorbital process of frontal boue.
superior angle of the occipital crest, and dividing anteriorly
into two less elevated ridges which curve outwards to the
superior posterior angle of the orbit. This ridge, as long
1 2
u6 THE SKULL [chap.
as it is single and median, is called the sagittal crest. It
bounds superiorly a large surface on the side of the skull,
limited behind by the occipital crest, and below by the
zygoma, called the " temporal fossa," from which the
temporal muscle takes its origin. In young dogs the upper
boundary of the surface for the origin of this muscle
is of less extent, not reaching so high as the middle
line of the cranium, and is but obscurely indicated on the
comparative smooth surface of the skull. As the muscle
increases in development its surface of origin gradually
ascends until it reaches the middle line, and with advancing
age a still larger space is afforded for it by the gradual
growth of the sagittal crest.
These changes in the upper part of the skull during
growth have been particularly noticed, because they take
place in very many animals, and, without altering in the
least the actual form of the brain-case, give rise to a very
different external appearance of the skull, either in mem-
bers of the same species, or in different but allied species.
The upper part of the skull, in front of tl^e diverging
boundary lines of the temporal fossa, is expanded and some-
what flattened, and has on each side a triangular process
(pof), which curves somewhat downwards, and indicates
the division of the temporal fossa behind from the orbit
in front. This is the postorbital process cf the frontal bone.
It is connected by a ligamentous band, in the living animal,
with a corresponding process arising from the zygoma ;
but when this is removed the orbit and temporal fossa are
widely continuous, their respective limits being only in
dicated by the above-mentioned processes.
The face is produced considerably in front of the orbits,
and not only becomes more depressed, but also more
compressed laterally, and is obliquely truncated anteriorly,
ix.] OF THE DOG. 117
terminating in the rounded incisor border of the premaxiila
(PMx) ; above which is placed the subcircular orifice of
the anterior nares.
The upper, and a considerable portion of the lateral,
surface of the cranium behind is formed by the parietal
bones (Pa), having the narrow interparietal (IP) ankylosed
with the supraoccipital (SO), extending between them for
about half their length. In front of this the parietals are
fmmonly united together by bone in old dogs.
Anteriorly to the parietals, the upper part of the temporal
>sa, the frontal plateau between the orbits, and the upper
If of the inner wall of the orbit, are formed by the frontal
ne. The remaining or lower portion of the temporal fossa
formed by the squamosal behind and by the alisphenoid
front. On the inner or cranial surface of the confluent
orbital and temporal fossae, a wide groove runs obliquely
downwards and backwards, which may be considered as the
boundary line of these two regions. In the lower part of this
groove are several large foramina placed in linear series.
The highest is the optic foramen, the next (of larger size)
the sphenoidal fissure, and the third the foramen rotundum
and anterior opening of the alisphenoid canal. The orbit
has no floor except for a very short space in front ; the
lower border of its inner wall passing directly into the outer
surface of the vertical ridge formed by the pterygoid, the
pterygoid process of the alisphenoid and the palatine bones,
and continuing the outer wall of the narial passage back
wards beyond the bony palate. The palatine bone forms a
considerable part of the inner wall of the orbit, joining the
frontal anteriorly, though separated from it for a considerable
space posteriorly by the orbitosphenoid. The lachrymal (Z)
appears in the anterior boundary of the orbit, the malar (Ma)
oins its outer boundary, and the upper surface of the hinder
join
u8
THE SKULL
[chap
end of the alveolar" border of the maxilla projects back-
wards, so as to form a partial floor to its anterior extremity.
EarO
BO,
PMx
Fig. 47.— Under surface of the cranium of a Dog, \. SO supraoccipital : ExO
exoccipital ; BO basioccipital ; Per mastoid portion of periotic ; Ty tympanic
bulla; BS basisphenoid ; Sq zygomatic process of squamosal; Ma malar; AS
alisphenoid ; Ft pten goid ; PS presohenoid ; Fr frontal ; Vo vomer ; PI palatine ;
Mx maxilla ; PMx premaxilla ; fin foramen magnum ; oc occipital condyje ;
ftp paroccipital process ; cf condylar foramen ; flp foramen lacerum posterius : svi
stylo-mastoid foramen ; earn external auditory meatus ; pgf postglenoiri foramen :
gp postglenoid process ; gf glenoid fossa ; flm foramen lncerum medium;^
foramen ovale ; as posterior opening of alisphenoid cand ; fr foramen rotundum
and anterior opening of alisphenoid canal : sf sphenoidal fis-ure or foramen
lacerum anterius ; op optic foramen ; /^/posterior palatine foramen ; apf 'anterior
palatine foramen.
In front of the orbits the face is formed above by the
ix.] OF THE DOG. 119
long narrow nasals (Na) pointed behind, and widening and
obliquely truncated in front to form the upper border of
the narial aperture; on each side by the maxillae (Mx),
having near the middle of their surface the large infraorbital
foramen (io), through which the terminal branches of the
second division of the fifth or sensory nerve of the face pass
to be distributed to the upper lip and whiskers ; and quite
anteriorly by the premaxillae (PMx), which complete the
boundaries of the nares, and send up narrow processes
between the nasals and maxillae, towards, though not meet-
ing with, similar processes which run from the frontals.
The inferior surface of the skull (Fig. 47) is formed
anteriorly by the nearly flat, elongated surface of the palate,
narrower in front than behind, composed anteriorly of the
premaxillae (PMx) ; then of the maxillae (Mx), which diverge
posteriorly and allow the palatines (PI) which form the
hinder border to reach in the middle line almost to the centre
of the palatal surface. In front and at the sides this surface
is bounded by the alveolar borders of the premaxillae and
maxillae, in which the teeth are set. Anteriorly are two con-
siderable oval foramina (ap/)t placed longitudinally very near
the middle line, formed mainly in the premaxillae, though
their boundary is completed posteriorly by the maxillae ;
these are the anterior palatine foramina. The naso-palatine
nerve descends through them to spread over the anterior
surface of the soft palate. Not far from the hinder border of
the palate, and more distant from the middle line, near the
suture between the maxilla and palatine, are several much
smaller foramina (posterior palatine), also for the transmission
of branches of the fifth nerve and blood vessels.
The truncated median part of the hinder edge of the palate
forms the lower margin of the posterior narial aperture.
.terally, the palate bones are continued backwards as
Lat
120 THE SKULL [chap.
vertical plates, thick and rounded below at first, but
gradually becoming more compressed. These are continued
still further backwards by the compressed pterygoid bones
(Ft), ending in the backward-projecting hamular processes,
and supported externally by the descending (pterygoid) plate
of the alisphenoid. The groove between these descending
lamellse of bone continues the narial passage backwards. It
has for its roof the vomer ( Vo) in front, then the presphenoid
(PS), and posteriorly a portion of the basisphenoid (£S) ;
but the palatines and pterygoids arch over so much towards
the middle line that they only leave a small strip of these
bones exposed. Inferiorly, this groove is not closed by
bone, but in the living animal the soft palate is stretched
across it.
The base of the skull, behind this " mesopterygoid "
fossa, presents in the middle a nearly flat elongated surface,
consisting of the basisphenoid (BS) and basioccipital (BO) ;
the latter, roughened for the attachment of muscles, and
terminating posteriorly at the inferior border of the foramen
magnum (/;;/), flanked on each side by the occipital condyles
(oc). The nearly straight lateral edges of the anterior half
of the basioccipital rise up to abut against the prominent
smooth rounded auditory bullae (Ty), which form so con-
spicuous a feature in this region of the skull, and which are
produced outwards into the lower wall of the external
auditory meatus (earn). In the antero-internal angle of the
bulla is seen the irregular orifice of the Eustachian canal.
Close to the inner side of this is an oval aperture, which is
at the same time the anterior extremity of the carotid canal
and the entrance to the foramen lacerum medium (flm)
through which the internal carotid artery enters the cranial
cavity. In front, and rather to the outer side of this, is the
foramen ovale (fo) piercing the alisphenoid, and imniedi-
IX.] OF THE DOG. 121
ately before this is a round aperture (as) leading to a short
canal running horizontally forwards through the same bone
at the root of its pterygoid process, and opening anteriorly
into the foramen rotundum (fr). Through this the external
carotid artery runs for part of its course, and it has been
called the alisphefioid canal}
In front of the outer side of the auditory bulla* is the
glenoid fossa for the articulation of the mandible, bordered
behind by the conspicuous curved postglenoid process (gp).
Immediately behind this the root of the zygoma is pierced
by a large hole, postglenmdjorameii (pgf), through which a
vein passes out from the lateral sinus within.
Behind the auditory bulla, to the inner side, is the large
foramen lacerum posterius (ftp), and, situated deeply within its
recesses, the posterior opening of the internal carotid canal.
On a ridge of the exoccipital, between this large foramen
and the depression immediately in front of the condyle, is
the small, nearly circular condylar foramen (cf), and at the
' outer termination of the same ridge rises the conical paroc-
cipital process (pp), abutting at its base against the hinder
end of the auditory bulla. Immediately behind the bulla,
and to the outer side of the abutment of the paroccipital
process against it, is an oval hole (sm), partially divided by
a constriction into an inner and an outer division. In
the inner division the end of a small cylindrical plug of
bone, the tympanohyal, can generally be seen. The outer
division is the stylomastoid foramen, through which the
seventh nerve, or portio dura, makes its exit. The bone
forming its outer boundary is the mastoid portion of the
iotic.
per
See H. N. Turner's " Observations relating to some of the Foramina
in the Base of the Skull in Mammalia,'' &c., Proc. Zool. Soc. 1848,
•63.
122 THE SKULL [chap.
Connected with the posterior lateral parts of the cranium
are two appended bony parts : the lower jaw or mandible,
and the hyoidean apparatus. The former forms the frame-
work for the floor of the mouth, and supports the lower
series of teeth ; the latter gives a firm yet movable point
of attachment to the root of the tongue and to the larynx,
or organ of voice.
The mandible consists of two symmetrical elongated rami
(see Fig. 45, p. 97), diverging behind, and coming in contact
in front at the middle line, by a roughened surface called the
symphysis (s) ; here they are firmly held together by inter-
posed fibrous tissue, or in old animals they may become
ankylosed.
Each ramus is compressed from side to side, has a
thickened rounded lower border, slightly curved in the
longitudinal direction, and a nearly straight upper alveolar
border, in which the teeth are implanted. The inferior
border inclines upward in front to meet the alveolar border
at the front of the symphysis. Near the posterior extremity
is the condyle (cd), a transversely-extended projection, with its
upper surface rounded in the antero-posterior direction, and
which, fitting into the glenoid cavity of the squamosal bone,
forms the hinge-like synovial articulation by which the lower
jaw moves on the skull. The upper border, between the
condyle and the hindermost tooth, rises into a high, com-
pressed, recurved process (the coronoid process, ep), to which
the temporal muscle is attached. The outer surface of this
process gradually subsides into a considerable hollow in the
side of the ramus, with prominent anterior, inferior, and
posterior edges, to which the masseter, another powerful
muscle for closing the jaw, is attached.
The point at which the vertical hinder edge of the ramus,
descending from the condyle, meets the horizontal inferior
ix. I OF THE DOG. 123
border, is called the angle, which in the Dog is prolonged
into a conspicuous compressed process, with an upturned and
slightly inverted pointed extremity, the angular process (a).
On the inner side of the ramus, a little way in front of and
below the condyle, is the inferior dental foramen {id), for the
admission of the inferior dental nerve (from the fifth pair)
and artery. On the outer side of the ramus, near its anterior
extremity, is the mental foramen, through which a branch of
the same nerve passes out to the lower lip and surrounding
structures.
Fig. 48. — Extracranial portion of hyoidean apparatus of Dog, front view, sh stylo-
hyal ; eh epihyal ; ch ceratohyal < these three constitute the "anterior cornu ") :
bh basihyal, or " body" of hyoid ; th thyrohyal, or "posterior cornu."
The hyoidean apparatus (Fig. 48) consists of a median 1
portion below, the basihyal (bh), from which two pairsj
of half arches, or " cornua," extend upwards and outwards./
The anterior (ch to sh) is the largest, and connects it withy
the cranium. The posterior (th) is united externally or
superiorly with the thyroid cartilage of the larynx. In the
Dog there are four distinct ossifications in the anterior arch.
I The first is a small cylindrical piece of bone lying in a
canal between the tympanic and periotic bones, immediately
to the inner and anterior side of the stylomastoid foramen,
124 THE SKULL [chap.
f and by its upper end firmly ankylosed with the surround-
ing bones. It can be seen much more distinctly in some
dogs' skulls than others, and is more conspicuously de-
veloped in some other Mammals. This I have calledj^-
paiwhyal, as it is always in relation with the hinder edge
of the tympanic bone, generally more or less surrounded by
it, and it extends upwards, embedded in, and afterwards
. ankylosed with, the periotic, to the hinder wall of the
tympanic cavity. Its lower end is truncated and con-
tinued into a band of cartilage, which connects it with
the proximal end of the bone which has been generally
j recognised as the uppermost of the series forming the
I anterior hyoidean arch, the stylohyal (s/i). The two suc-
1 ceeding bones {ep and ch) are named by Professor Owen
(respectively epihyal and ceratohyal. All three are elon-
gated, compressed, slightly curved or twisted on them-
selves, tipped at each end with cartilage, and connected
with each other by synovial joints. The stylohyal and
epihyal are nearly equal in length, the ceratohyal shorter
( and stouter.
The basihyal (bh) is a transversely-extended, flattened bar,
! with its extremities rather upturned and thickened. The
posterior cornu (t/i) consists of a single, nearly straight,
I compressed bone, the t/iyro/iyal, articulated inferiorly with
the outer end of the basihyal, just below the attach-
\ ment of the ceratohyal, and truncated at its superior ex-
, tremity, to which the thyroid cartilage of the larynx is
suspended.
Development of the Skull. — For a detailed and beautifully
illustrated account of the early development of the Mam-
malian skull, I must refer to Professor Parker's monograph
f* On the Structure and Development of the Skull in the
ix. j OF THE DOG. 125
Pig" {Philosophical Transactions, 1874), of which the fol-
lowing is a brief summary.
The notochord (see p. 16) extends into the basicranial
axis only as far as the hinder border of the pituitary body,
corresponding with the middle of the future basisphenoid
bone.
The skull is formed from —
• \ A cartilaginous basicranial plate, embracing the
irior extremity of the notochord.
b. A series of five paired descending cartilaginous arches,
developed in the visceral laminae, constituting the sides of
the face and neck ; of which two are in front of, and three
behind the mouth.
c. A pair of cartilaginous auditory capsules.
d. A pair of cartilaginous nasal capsules.
The basicranial plate grows up as an arch over the
occipital region of the skull, and coalescing with the auditory
capsules laterally gives rise to the primordial skeleton of
the occipital, periotic, and basisphenoidal regions, of the
skull : the parietal and frontal regions being afterwards
completed by ossification in membrane surrounding the
cranial cavity.
Of the arches, the first pair, constituting the trabecules
cranii, pass forward from below the front end of the basi-
cranial plate, enclosing the pituitary body, in front of which
they coalesce, and together with the olfactory capsules, give
rise to the presphenoidal, and ethmoidal regions of the
cranium (see Diagram on p. 106, I.).
The second arch (pterygopalatine)1 gives rise to the ptery-
goid, palatine, maxillary and malar regions, (IT.).
The cleft between this and the next arch is the mouth.
1 This is more properly an outgrowth from the third, than an inde-
ndent arch.
pendi
126 THE SKULL [chap.
The third, or first post-oral arch (III.), called the first,
in the older and more usual nomenclature, consist^ of
Meckel's cartilage, a slender rod, in relation above with the
periotic region of the skull. Of this, in the Mammalia, the
upper extremity becomes converted into the malleus, one
of the small bones in the tympanic cavity, while in con-
nection with the lower or distal part, the ramus of the man-
dible or lower jaw is developed partly by conversion of the
cartilage itself, but principally by the ossification of fibrous
or cartilaginous tissue deposited around it. The upper end
of the ramus afterwards acquires a secondary articular con-
nection with the squamosal bone, its primitive connection
with the malleus entirely disappearing.
The cleft which lies behind this arch becomes contracted
into the Eustachian tube, tympanic cavity, and meatus
auditorius externus, which would form a canal of commu-
nication between the pharynx and the external surface but
for the interposition of the delicate membrana tympani.
The .rod of cartilage forming the fourth visceral arch
(IV.), or second post-oral, becomes the anterior hyoid arch,
its proximal extremity being modified into the incus}
From the fifth arch (third post-oral), which corresponds
to the first branchial of branchiate vertebrates, is formed
the posterior hyoid arch, or thyrohyal. (V.)
Some of the changes which take place in the cranium while
advancing from youth to maturity have already been noticed ;
but it will be well, before proceeding to describe the modi-
fications of the mammalian skull, to mention certain others
which take place, to a greater or less degree, in all skulls.
1 The stapes, according to Parker, is formed independently of the
visceral arches, in a budding of the outer cartilaginous wall of the
auditory bulla.
ix.] OF THE DOG. 127
These depend mainly on the fact that the brain, and con-
sequently the cavity which contains it, and also the sense
capsules, increase in size in a much smaller ratio than the
external parts of the head, especially the jaws and pro-
minences for the attachment of muscles. The dispropor-
tionate growth and alteration of form of these parts,
concomitant with little or no change in the brain-case, is
effected partly by increase in thickness of the bones, but
mainly by the expansion of their walls and the develop-
ment of cells within, which greatly extend the outer surface
without adding to the weight of the bone.
In the Dog these cells are developed chiefly in the fore
part of the frontal bones, constituting the frontal sinuses,
and in the presphenoid, constituting the sphenoidal sinuses.
Air passes freely into them from the nasal passages. In
many animals they attain a much larger extent than in the
Dog, reaching their maximum in the Elephant (see Fig. 60,
p. 181), where the alteration of the external form of skull
during growth, without material change in the shape or size
of the cerebral cavity, is strikingly shown. At the same
time the alveolar borders of the jaws gradually enlarge to
adapt themselves to the increased size of the permanent
teeth which they have to support, and the various ridges and
tuberosities for the attachment of muscles become more
prominent.
During these changes a gradual consolidation takes place
in the structure of the skull generally, by the partial or com-
plete union of certain of the bones by synostosis. The
union of the different bones generally proceeds in a certain
definite order, which, however, varies much in different
species. Sometimes it extends so far as to lead to complete
obliteration of all the cranial sutures.
CHAPTER X.
THE SKULL IN THE ORDER PRIMATES, CARNIVORA,
INSECTIVORA, CHIROPTERA, AND RODENTIA.
Order Primates. Man. — On comparing a longitudinal
and vertical section of a young human skull, in which most
of the sutures are still distinctly seen (Fig. 49), with that of
the Dog, it will be seen to be composed of the same bones,
having very nearly the same connections, and yet the whole
form is greatly modified. This modification is mainly due
to the immense expansion of the upper part of the middle
or cerebral fossa of the brain cavity, which not only carries
the roof of the cavity a great distance from the basicranial
axis, but also forces, as it were, the anterior and posterior
walls from the vertical nearly to the horizontal position, so
that they are, roughly speaking, in the same line with the
short basicranial axis, instead of being perpendicular to it.
In addition to this great difference, the facial portion of the
skull is deeper from above downwards, and very much
shorter from before backwards.
Taking a survey of the human skull in the same order
as was done with that of the Dog, we find the craniofacial
axis, composed of the basioccipital bone (BO), terminating
at the anterior border of the foramen magnum (fm) behind.
and in this young skull still separated from the basisphenoiri
CHAP. X.]
THE SKULL OF MAX.
129
FlG. 49— Vertical, longitudinal, median section of a young human skull, with the first
dentition, \. As in the other sections of skulls figured, the mandible is displaced
downwards, so as to show its entire form PMx premaxilla ; MT maxillo-
turbinal ; ET ethmo-turbinal ; ME ossified portion of the mesethmoid ; Na nasal ;
eg crista galli of the me- ethmoid ; OS orbitosphenoid, or lesser wing of the
sphenoid ; AS alisphenoid, or greater wing of the sphenoid ; Fr frontal ; Pa
Iiriecal ; SO supraoccipital ; M mastoid portion of the periotic ; Sq squamosal ;
er petrous portion of the periotic ; the large foramen below the end of the line
the internal auditory meatus, the small depression above it is the nearly-
jliterated floccular fossa. ExO exoccipital, the line points to the condylar fora-
en;y>« foramen magnum ; BO basioccipital ; BS basisphenoid ; st sella turcica ;
6" presphenoid, ankylosed with the basisphenoid, forming the "body of the
>henoid ;" Pt pterygoid ; PI palatine ; Vo vomer ; Mx maxilla ; j symphysis of
mandible ; cp corohoid process ; cd articular condyle ; a angle ; sh stylohyal, or
" styloid process of temporal ; " ch ceratohyal, or lesser cornu of hyoid ; bh basi-
hyal, or body of hyoid ; th thyrohyal, or greater cornu of hyoid.
!
130 THE SKULL. [chap.
in front by a vertical fissure. The basisphenoid(BS) is short
and deep, and has a strongly marked pituitary fossa or "sella
turcica " (st) above. It has completely united with the pre-
sphenoid (PS), though at birth the line of separation (below
the spot called the olivary process or tuber culum sellce) is still
visible. In adult age large air-cells fill the interior of this con-
joined bone, which is the "body" of the so-called "sphenoid"
of human anatomy. Anteriorly the presphenoid narrows to
a sharp vertical edge, which is in contact with the mesethmoid
( ME) above and the vomer ( Vo) below. The whole of the
upper part of the mesethmoid is ossified in the specimen
described, constituting the " lamina perpendicularis," but the
anterior and lower part forms the septal cartilage of the nose.
Its upper border forms a strong compressed triangular pro-
jection into the cranial cavity, called the "crista galli" (eg).
The posterior segment of the brain-case is completed, as
in the Dog, by the pair of exoccipitals (ExO), and a large
supraoccipital (SO).1 The triangular upper part of the latter
may be considered to represent the interparietal, though it
very soon becomes incorporated with the rest of the supra-
occipital. The middle segment is completed by large ali-
sphenoids (AS), the " greater wings of the sphenoid bone,"
and enormously extended, somewhat square-shaped parietals
(Pa) ; the frontal segment by narrow triangular orbito-
sphenoids (OS), the "lesser wings of the sphenoid bone,''2
and by large arched frontals (Fr).
Of the fossae into which the cranial cavity is divided, the
olfactory fossa is very small, rather narrow, elongated, and
1 The " occipital bone" of human anatomy is formed by the coales-
cence of the basioccipital, exoccipitals, and supraoccipital.
%1 The "sphenoid bone" of human anatomy is formed by the union
of the basisphenoid, presphenoid, alisphenoids, orbitosphenoids, and the
pterygoids. The basal portion ultimately ankyloses with the occipital.
x.| MAN. 131
shallow. The cribriform plate which closes it in front, in-
stead of being vertical, as in the Dog, is horizontal, and
almost in the same line with the basicranial axis. It is
bounded in the median line, and separated from the cor-
responding fossa of the other side by the prominent crista
galli of the mesethmoid. The middle fossa is, as before
said, of comparatively enormous extent ; it is bounded pos-
teriorly by the tentorial ridge, having the same relations to
bones as in the Dog, but lying more horizontally and being
far less prominent, having no osseous shelf-like inward exten-
sion. This fossa is distinctly divided into an anterior and
posterior portion, by the strongly projecting hinder ridge of
the orbitosphenoid. The floor of .the anterior portion is
arched in consequence of the inward projection of the roof
of the orbit, while the floor of the posterior, or " temporal
fossa," is deeply concave. The cerebellar fossa is of mode-
rate size, and lies entirely underneath the hinder part of
cerebral fossa.
"he " sella turcica," or depression in the basisphenoid for
the lodgment of the pituitary body of the brain, is bounded
posteriorly by an elevated transverse ridge, the corners of
which are called the " posterior clinoid processes." Cor-
responding processes projecting backwards from the orbito-
sphenoids are called " anterior clinoid processes."
The foramina in the base of the skull scarcely differ from
those of the Dog. 1. The olfactory has been already
described. 2. The optic is a large round hole close to the
inner and posterior part of the orbitosphenoid. 3. The
sphenoidal fissure is larger than in the Dog, and produced
externally into a long narrow slit. 4 and 5. The foramen
rotundum and the foramen ovale pierce the alisphenoid, one
near its anterior, the other near its posterior border. Close
behind the last-named is a small hole (" foramen spinosum "),
k 2
132 THE SKULL. [chap
through which a branch of the external carotid artery
(middle meningeal) enters the brain-cavity. 6 and 8. Th<
foramen lacerum medium basis cranii and the foramei
lacerum posterius have the same functions and relation as
in the Dog. 7. Between these two the periotic has th<
conspicuous meatus auditorius internus on its inner sid<
The depression above this, for the lodgment of the floe
cuius, is distinctly seen in fcetal human skulls up to the
time of birth, but it afterwards becomes gradually oblit<
rated. 9. The condylar foramen perforates the exoccipital
as in the Dog ; and lastly (10), the foramen magnum hi
the same general subcircular form, and is bounded by th<
same bones, but differs greatly in direction, its plane looking
mainly downwards instead of backwards.
The nasal cavities differ chiefly from those of the Dog in
their shortness and greater vertical height. In their inner
wall, the descending median plate of the vomer (Vo) is
much more developed. The pterygoids (Pt) are extended
vertically, are narrow from before backwards, end below in
a marked " hamular " process, and soon ankylose with the
pterygoid plates of the alisphenoid anteriorly, but posteriorly
are separated from them by a well-marked "pterygoid
fossa." l The palatines (PI) and maxillae (Mx) are short
from before backwards. The premaxillae (PMx) are small
and early ankylosed with the maxillae.2 The nasals (Na)
1 The pterygoid, not being recognised as a distinct bone, is commonly
described \n works on human anatomy as " the internal pterygoid plate
of the sphenoid ; " the pterygoid process of the alisphenoid being the
'* external pterygoid plate."
2 The premaxilla is a distinct bone in the human foetus, but is covered
on its external or facial aspect by a process of the maxilla, which extends
over it towards the middle line, and becomes completely fused with it
before birth, so that no trace of the maxillo-premaxrlary suture is ever
seen on the outer side of the face. On the inner and palatal aspect of
x.] MAN. 133
are short, and nearly vertical, broad below and narrow
above. The anterior nares are also nearly vertical. The
turbinal bones are comparatively little developed, and of
simple structure, especially the lower or maxillo-turbinal
(MT). The flat bony-plate on the outer side of the ethmo-
turbinal or " os planum," instead of lying against the inner
side of the maxilla, forms part of the outer wall of the nasal
cavity and inner wall of the orbit, uniting with the frontal
above, the lachrymal in front, the maxilla below, and the
palatine behind.
The group of bones placed around the organ of hearing,
periotic, squamosal, and tympanic, though originally dis-
tinct, become united together soon after birth, to form the
so-called " temporal bone." They differ from the corre-
sponding bones in the Dog in the following particulars. The
periotic has a very much larger mastoid portion (M~), which
forms a considerable part of the wall of the cerebellar fossa.
In the new-born infant its outer surface is smooth
and flat, but as life advances, air-cells become developed
within it, communicating with the tympanic cavity, and
a strongly-marked descending projection, the " mastoid pro-
cess," appears on the lower and anterior part of its outer
surface. The squamosal {Sq) is a large flat vertical plate,
forming a considerable part of the wall of the posterior
cerebral fossa, behind the alisphenoid. Its zygomatic pro-
cess is comparatively slender and straight.* The tympanic
forms a long tubular external auditory meatus, but its inner
part joins the periotic, forming the floor of the tympanic
cavity without being inflated into an auditory bulla. Its
the bones the suture is always evident at birth, and can often be traced
even in adult skulls. See G. W. Callender " On the Formation and
Early Growth of the Bones of the Human Face." (Phil. Trans. 1869,
163.)
134 THE SKULL. [chap.
under surface is produced into a rough ridge, to the inner
side of which the large carotid canal perforates the base of
the periotic, being directed obliquely forwards and inwards.
In adult skulls the stylohyal becomes ankylosed with the
tympanic and periotic, constituting the " styloid process of
the temporal bone."
In examining the external aspect of the skull, the large
smooth subglobular or oval brain-case, constituting by far the
larger part of the whole cranium, is strikingly different from
that of the Dog. The occipital surface, instead of being ver-
tical, is nearly horizontal. The condyles, instead of being at
the hindermost part of the skull, are not far from the middle
of the base. The paroccipital process of the exoccipitals
are represented by mere rudiments, the so-called "jugular
eminences;" on the other hand, the mastoid processes,
almost obsolete in the Dog, are very greatly developed. The
occipital crest is represented by a slightly raised and rough-
ened line, the " superior curved line," and the sagittal crest
is absent.
The sutures connecting the bones of the upper surface
of the cranium are remarkable for their wavy or indented
character, processes from one bone interlocking with those
from the other in a most complex manner, at least on the
external surface, for seen from within they appear com-
paratively straight and simple. There are very often
irregular ossifications, separated from the contiguous bones,
lying among the indentations of the occipito-parietal suture,
called "Wormian bones."1 The' temporal fossae are but
indistinctly marked out by a curved line above, and are
separated from each other by a wide expanse formed
1 In works on human anatomy, the occipito-parietal suture is com-
monly cal'ed " lambdoid ; " the interparietal, "sagittal;" and the
fronto-parietal, ' ■ coron ll. "
x.] MAX 135
by the smooth rounded upper part of the parietal and
frontal bones. The orbit is completely encircled by bone,
the outer margin being formed by a process from the malar
ascending to join the post-orbital process of the frontal; and
it is, moreover, in great part separated from the temporal
fossa by an extension inwards of the ascending process of
the malar meeting the alisphenoid, although a communica-
tion is left between the two cavities below in the " spheno-
maxillary fissure." The axis of the orbital cavity is directed
more forwards than in the Dog. The face is altogether very
much shorter, broader, and flatter.
In the inferior surface of the skull, the palate is seen
to be much shorter and wider, than that of the Dog,
especially anteriorly, where its outline forms an almost
semicircular curve. The maxillo-palatine suture is nearly
straight transversely, and so is the hinder border of the palate,
though produced backwards into an obtuse spine at the
middle line. The distance between the hinder border of the
palate and the foramen magnum is much shorter relatively,
the space between the pterygoids being particularly short
and wide. The true pterygoids and pterygoid plates of the
alisphenoid are widely separated posteriorly, leaving a con-
siderable fossa between them ; and the latter are larger
and project further backwards than the former. The under
surface of the tympano-periotic region is rough and irregular,
instead of being smooth and bullate, and the perforation for
the internal carotid artery is very conspicuous. There is
no alisphenoid canal, scarcely any postglenoid process, no
distinct glenoid venous foramen, a very small paroccipital,
and a very large mastoid process. By the inclination of the
occipital surface downwards, instead of backwards, an
inferior view of the skull includes nearly all this surface,
with the large foramen magnum and the condyles.
136 THE SKULL. [chap.
In accordance with the general form of the face the
mandible is short. The two rami of which it is originally
formed unite together at the symphysis within a year after
birth. They are widely divergent behind, and approach
in front at a much more obtuse angle than in the Dog. The
horizontal portion of each ramus is deep and compressed,
the lower margin straight or slightly concave, and produced
anteriorly rather in front of the alveolar margin, so as to
occasion the mental prominence, characteristic of the human
lower jaw. The anterior symphysial margin (Fig. 49, s),
therefore, instead of sloping upwards, from behind forwards,
is vertical, or rather inclined in the other direction. Pos-
teriorly, the condyle (cd) is more elevated than in the Dog,
and is less transversely extended. The coronoid process
(cp) is smaller and less recurved. The posterior border,
between the condyle and the angle (a), is nearly straight
and vertical, and the angle is rounded, compressed, slightly
everted, and not produced into any hook-like process, as in
the Dog. The depression for the masseter muscle is very
faintly marked.
The hyoidean apparatus differs in several particulars from
that of the Dog. The tympanohyai can generally be
recognised in the skull of an infant at birth, and for a few
years after, as a cylindrical piece of bone, with a truncated
lower extremity, about one-twentieth of an inch in diameter,
seated in a depression in the hinder border of the tympanic,
immediately to the anterior and inner side of the stylo-
mastoid foramen. Its upper end becomes soon ankylosed
with the periotic. The tympanic is produced around it an-
teriorly, constituting the " vaginal process." The stylohyal
(s/i), at first a long styliform piece of cartilage, continuous
with the tympanohyai, commences to ossify by a separate
centre before birth, and, at a very variable period after-
\ I MAN. 13.7
wards, is usually ankylosed with the tympanohyal and sur-
rounding cranial bones, constituting the so-called " styloid
process." This is a condition not met with in any other
Mammal. Below the stylohyal the greater part of the an-
terior hyoid arch is represented by a slender ligament (the
u stylohyoid " ligament), there being no ossification corre-
sponding to the Dog's epihyal ; but the ceratohyal (c/i) to
which the ligament is attached below, is a small bony
nodule, the " lesser cornu of the hyoid " of human anatomy,
which is articulated synovially to the upper corner of the
outer extremity of the basihyal, though sometimes in old
age becoming ankylosed. The basihyal (bti), or " body of
the hyoid," is transversely oblong, hollowed posteriorly, and
deeper from above downwards than in the Dog. The thy-
rohyals (///) or "greater cornuaof the hyoid," are elongated,
nearly straight and somewhat compressed. They usually
become ankylosed before middle life with the outer extre-
mities of the basihyal.
The Simiina have the skull formed generally on the same
plan as that of Man, with certain modifications in detail.
The facial portion is enlarged and elongated as compared
with the cerebral portion, though to a very variable extent
in different members of the sub-order.
In nearly all, the brain-cavity maintains the same general
form as in Man, though it is usually of less comparative
vertical extent. With few exceptions, the middle compart-
ment for the lodgment of the cerebrum retains its
relative situation and superiority in size to the cerebellar
and the olfactory fossae, completely overlying them both ;
and consequently the occipital region of the skull with the
foramen magnum behind, and the cribriform plate of the
ethmoid in front, are in the same general horizontal line
138 THE SKULL. [chap.
with the basicranial axis as in Man, and not perpendicular
to them as in the Dog.
It is remarkable that the deviations from this general rule,
especially as regards the plane of the occipital surface, are
not in relation to the general position of the animals in a
descending series, from Man to the lowest Monkeys; for the
occipital surface is nearly vertical in the anthropoid Gibbons
(Hylobates), especially H. syndactylies (the Siamang). and
completely so in the American Howling Monkeys (Mycetes),
where the cerebral fossa does not project in the least degree
behind the cerebellar fossa; while in the Baboons (Cynoce-
phalus\ among the Old World Monkeys, and still more in
some of the smaller and lower forms of American Monkeys
(as Saimiris), the posterior development of the cerebral
fossa is so great as to throw the supraoccipital bone con-
siderably more into the posteriorly prolonged base of the
skull even than in man.
The olfactory fossa is always small. It is not only very ;
short, but, in consequence of the considerable projection
inwards of the portion of the frontal forming the roof of the
orbit on each side of it, is both narrow from side to side, |
and deep from above downwards.
In most of the Simiina, including the Gorilla and Chim-
panzee, the frontals meet along the middle line over the
presphenoid, between the mesethmoid in front and the
orbitosphenoids behind ; but the Orang agrees with Man in
wanting this postethmoid union of the frontals, and so also
do some of the Cebidce.
The fossa on the inner surface of the periotic for the
floccular process of the cerebellum is almost obliterated in
the adult Gorilla, Chimpanzee, Orang, and Gibbons, but is
persistent, and often very large, in all other Monkeys.
A partial ossification of the tentorium from the inner
x.] PRIMATES. 139
edge of the periotic takes place in some of the American
Monkeys, as Mycetes and Cebus.
The suture between the basisphenoid and the pre-
sphenoid remains distinct in the Baboons and all the lower
Monkeys, until the animal has nearly attained its full size
and acquired its permanent teeth ; but it is completely
obliterated, and the cancellous structure of the two bones is
continuous, in the Gorilla, Chimpanzee, and Orang, while
the animal still retains all its milk-teeth.
The nasal cavities, with their surrounding bones, are
generally longer and of less vertical extent than in Man,
but, as in the case of the inclination of the occipital plane,
not following any regular serial descent. Thus the propor-
tions of these parts are more like those of Man in many
of the smaller American Cebidce than in the long-faced or
"Dog-headed" Baboons (Cynocephali) of the Old World.
The vomer is generally longer, and of less vertical extent,
than in Man. The turbinals have much the same general
characters, their relative situation of course varying with
the elongation, or otherwise, of the nasal passages. The os
planum of the ethmoturbinals always forms part of the inner
wall of the orbit, having the same relations as in Man.
The pterygoid plate of the alisphenoid is usually largely
developed, and generally projects considerably backwards
beyond the pterygoid bone (which is narrow, and has a very
distinct hamular process), and there is always a wide and
deep fossa between them.
The premaxilla is always distinct on the facial surface,
and the suture between it and the maxilla is only obliterated
in aged specimens. It generally extends upwards on the
side of the anterior nares, so far as to meet the nasal and
completely exclude the maxilla from taking any part in the
boundary of this opening.
140 THE SKULL. [chap.
The lachrymal foramen is never situated externally, to the
orbit, although, in the lower forms, it may be close upon
the margin.
As in Man the postorbital process of the frontal meets
the orbital process of the malar so as completely to encircle
the outer side of the orbit ; and an extension backwards and
inwards of these bones joining the alisphenoid divides the
orbit from the temporal fossa.
The nasal bones vary much in length and breadth, but
they present the peculiarity throughout the order of a great
tendency to ankylose together in the middle line, even at a
comparatively early age.
In all the smaller and middle-sized Monkeys the general
surface of the calvaria is oval and smooth, but in the larger
Baboons and Orangs there are well-marked supraorbital,
sagittal, and occipital ridges. These attain their greatest
development in the adult male Gorilla, where they com-
pletely mask the original form of the cranium. Their size,
in this sex, appears to increase with age; while in the oldest
females, on the other hand, they are but slightly apparent.
The paroccipital process is always rudimentary, as in
Man.
The squamosal in the higher forms is developed much as in
Man; but in the lower forms it is more reduced, and takes a
smaller share in the formation of the side wall of the cranium.
It generally comes in contact, at its upper anterior angle,
with the frontal, but not in the Orang or in the Cebidtr., in
which animals the union of the parietal and the alisphenoid
separates the frontal from the squamosal, as is usually the
case with Man. The glenoid surface is natter than in Man,
and there is a well-marked postglenoid process.
The zygoma is usually narrow, horizontal, and slightly
arched outwards.
x.J PRIMATES. 141
The periotic generally resembles that of Man, and the
mastoid portion is- conspicuous on the outer side of the
skull between the squamosal and the exoccipital ; but its
surface is smooth and rounded, without any distinct mas-
toid process.
In all the Old World species, the tympanic forms an elon-
gated inferior wall to the external auditory meatus, which
has consequently a considerable bony tube ; but in all the
American Monkeys this bone retains more or less its primi-
tive annular condition, and the cavity of the tympanum is
close to the external wall of the cranium. This character
alone will readily serve to determine to which of the two
great divisions of Monkeys a skull may belong.
No auditory bulla is developed in any of the Old World
Monkeys, but in all the Cebidce and Hapalidce the inferior
surface of the ankylosed periotic and tympanic is much
swollen.
The carotid canal is always very conspicuous, entering the
under surface of the periotic near its hinder border. There
is often a glenoid foramen, but never an alisphenoid canal.
The foramen rotundum perforates the alisphenoid, but
the foramen ovale is usually a notch on its posterior border,
completed by the periotic behind.
The mandible presents the same general characters as
that of Man, but the horizontal portion of the ramus
is usually more elongated, and the anterior border slopes
upwards and forwards, there being a complete absence of
mental protuberance. The condyle is extended trans-
versely, the coronoid process well developed and recurved.
The posterior or ascending portion of the ramus is broad
and flat ; the angle well developed, square, or more or
less rounded, but without any special pointed process as in
the Dog.
1 42
THE SKULL.
[chat
In the Howling Monkeys (Mycetcs) the hinder or ascend-
ing portion of the ramus is remarkable for its extent, both
vertically and antero-posteriorly, corresponding to a certain
extent with the extraordinary development of the vocal
organs, which it partially covers and protects.
The Simiina are remarkable in never, or very rarely,
having an ossified stylohyal ; but on looking closely at the
base of the periotic, immediately to the anterior and inner
side of the stylomastoid foramen, a very small depression,
in which there is sometimes a minute ossified tympano-hyal,
can generally be seen. To this the ligament representing
the stylohyal is attached.
In very few of the Old World Monkeys is there any
ossification in the anterior hyoid arch (see Fig. 50) ; but in
some Cercopitheci a short, bony, ceratohyal is found. This
occurs also in the American Monkeys (Fig. 51), with occa-
sionally'the addition of a second piece (epihyal).
The thyrohyals are always well-developed, long, narrow,
nearly straight, and somewhat flattened.
Fig. 50. — Inferior surface of hyoid bones
of Baboon {Cynocephahis porcarins,.
bh basihyal ; tk thyrohyal.
Fig. 51. — Inferior sui face of hyoid bones
of an American Monkey (Laqothrix
humboldtii). th thyrohyal ; ch cerato-
hyal ; eh epihyal.
The basihyal varies much in form. In the anthropoid Apes
it is broad transversely; but in nearly all the other Monkeys j
its anteroposterior extent exceeds its breadth, owing to a
x] PRIMATES. 143
great development from the posterior border. It is generally
convex below, and concave above and behind, forming a
considerable cavity, in which the median laryngeal air-sac
is lodged. This condition is enormously exaggerated in
the American Howling Monkey (Mycetes), where the basi-
hyal is transformed into an immense subglobular, thin-
walled, bony capsule, with a large orifice posteriorly,
by which the laryngeal air-sac enters, and having the
straight narrow thyrohyals attached on each side. In this
genus there are no ossifications in the anterior arch.
While, in nearly all the characters in which the skull
of Man differs from that of the Dog,, the Simiina agree
with the former ; the Leniurina, on the other hand, more
resemble the lower type.
In the Common Lemur the general proportions of face
to cerebral cavity, and the inclination of the occipital and
olfactory planes of the cranium, are quite dog-like. The
orbits, although completely surrounded behind by the
junction of the postorbital processes of the frontal and the
malar, are yet perfectly continuous with the temporal fossa
beneath this bony bar ; that extension inwards of the
frontal and malar to meet the alisphenoid, and thus form a
posterior external wall of the orbit, so characteristic of
Man and all Monkeys, being absent. The lachrymal fora-
men, situated on the facial part of the bone, is altogether
external to the margin of the orbit. The os planum of
the ethmo-turbinal does not enter into the inner wall of
the orbit, but is shut out from it by the maxilla, as in
most inferior mammals'. The inferior surface of the tym-
panic is developed into a large rounded bulla. The hyoid
apparatus much resembles that of the Dog, having the
stylohyal, epihyal, and ceratohyal all distinctly ossified in
144 THE SKULL. [chap.
the anterior arch, and the basihyal in the form of a narrow
transverse bar.
Some of the Lemurina have much shorter faces than the
common species, though still possessing all the essential
characters of the group. Among these, Tarsius is remark-
able for the extraordinary size of the orbits, which are so
expanded that their margins form prominent, thin, bony
rings, and the interorbital part of the skull is reduced to
an exceedingly delicate septum. The orbit is also partially
separated from the temporal fossa as in the Sim una.
The general characteristics of the skull of the Carnivora
have been described, as seen in the Dog. The more obvious
modifications from this type relate to the comparative
length and compression or width of the facial portion, the
strength and curve of the zygomatic arch, and the extent to
which the various ridges and processes for the attachment
of muscles are developed. Thus the Cats have short and
round skulls, with wide zygomatic arches ; and in the Bears
(especially the Polar Bear, Ursus maritimus) the whole
skull is elongated, and the nasal cavities are greatly enlarged
as compared with the brain- case, and the maxillo-turbinal
bones are correspondingly developed.
But there are certain other modifications of the cranial
bones, which, being less obviously adaptive to functional
purposes, and being constantly associated with structural
modifications in other parts of the body, are of considerable
value in classifying the members of the group. Of these
the most important are related to the form and structure of
the auditory bulla, and the surrounding parts of the base of
the cranium.
In the Bears, the auditory bulla is comparatively little
inflated. It consists of a single bone (tympanic), readily
CARNIVORA.
M5
detached from the cranium in skulls of young animals. Its
form is more or less triangular, being broad and nearly
straight at the inner edge, and produced outwards into
a considerably elongated floor of the external auditory
meatus. Its greatest prominence is along the inner border;
from this it gradually slopes away towards the meatus. The
entrance of the carotid canal is a considerable circular
foramen, near the hinder part of the inner edge of the bulla.
In old animals it is partly concealed by the prominent lip of
the basioccipital, which abuts against the inner edge of the
Fig. 52. — Section of the left auditory bulla and surrounding bones of a Bear. {Ursus
ferox). Sq squamosal ; T tympanic ; BO basioccipital ; am external auditory
meatus ; t tympanic ring ; e Eustachian canal ; Car carotid canal. (From Proc.
Zool. Soc 1869.)
bulla ; and by the growth of this, and the paroccipital pro-
cess, it becomes almost included in the deep fossa leading
to the foramen lacerum posterius. When a section is made
through the auditory bulla (see Fig. 52) it is seen to be a
Kple thin-walled bony capsule, imperfect above, where it
146 THE SKULL. [chap.
fits on to the petrosal and squamosal bones, and prolonged
externally into the much thickened spout-like floor of the
meatus externus. At the inner extremity of this floor is a
freely projecting oval lip (/), which gives attachment to the
membrana tympani, and which is the original and first ossified
ring-like portion of the tympanic bone. In the front of the
floor of the bulla is the groove for the Eustachian canal (e) \
between this and the inferior part of the tympanic ring,
a low and thin ridge of bone with a concave free margin
rises from the floor of the cavity. This is the only
indication of any septum or division of the cavity of the
bulla.
Behind the bulla, the prominent and tuberous paroccipital
process projects downwards, outwards and backwards,
standing quite off* from the bulla, and only connected with
it by a low laterally compressed ridge. Between the
paroccipital process and the occipital condyle is a smooth
concave surface, the front of which is excavated into a deep
notch, the posterior boundary of the foramen lacerum
postenus, between which and the condyle is situated the
condylar foramen, which transmits the hypoglossal nerve.
At the outside of the bulla, just behind the external auditory
meatus, the mastoid process is distinct and prominent, and
widely separated from the paroccipital. There is a very
conspicuous glenoid foramen situated just behind the post-
glenoid process of the squamosal.
All the Ursidce, Procyofiidce, and Mustelidce agree with
the true Bears in the general characters of this region of
the skull; for even when (as in some of the smaller species)
the auditory bulla is considerably dilated, it always has its
greatest prominence near the middle of the inner border, and
gradually slopes away from this point to a prolonged floor of
the auditory meatus; and though there are often trabecular
X.]
CARNIVORA.
H7
or partial septa passing mostly transversely across the lower
part,1 there is no distinct and definite septum dividing it
into a separate outer and inner chamber. In all cases, on
looking into the external auditory meatus (in the dried
skull when the membrana tympani is removed) the oppo-
site wall of the bulla can be seen ; or if a probe is passed
into the meatus, no obstacle will prevent its touching the
inner wall.
Fig. 53. — Section of the left auditory bulla of the Tiger {Felis tigris). Sq squa-
mosal ; Ft periotic; BO basioccipital ; am external auditory meatus ; oc the outer
chamber ; ic the inner chamber : $ the septum ; * the aperture of communication
between the chambers. (From Proc. Zooi. Soc. 1869.)
In the Tiger, which may be taken as a type of the Fclidce,
the auditory bulla is very prominent, rounded and smooth
on the surface, rather longer from before backwards than
transversely, its greatest prominence being rather to the
inner side of the centre. The lower lip of the external
auditory meatus is extremely short; the meatus, in fact,
1 Especially developed in the Weasels {Mustela), in which also the
entire parietes of the bulla are thickened and cancellous.
L 2
148 THE SKULL. [chap.
looks like a large hole opening directly into the side of the
bulla. On looking into this hole, at a very short distance
(just beyond the tympanic ring), a wall of bone is seen quite
impeding the view, or the passage of any instrument, into
the greater part of the bulla. In the section (Fig. 53) it will
be seen that this wall is a septum (s), which rises from the
floor of the bulla, along its outer side, and divides it almost
completely into two distinct chambers ; one (oc), outer and
anterior, is the true tympanic chamber, and contains the
tympanic membrane and ossicula, and has at its anterior
extremity the opening of the Eustachian tube (e); while the
other (ic), internal and posterior, is a simple but much
larger cavity, having no aperture except a long but very
narrow fissure (*) left between the hinder part of the top
of the septum and the promontory of the periotic, which
fissure expands posteriorly, or rather at its outer end, into a
triangular space, placed just over the fenestra rotunda, so
that the opening of this fenestra is partly in the outer and
partly in the inner chamber of the bulla. . This chamber is
formed by a simple capsule of very thin but dense bone,
deficient only at a small oval space in the roof, where the
periotic projects into and fills up the gap, except such
portion of it as is left to form the aperture of communica-
tion with the outer chamber.
Not only are these two chambers thus distinct, but they
are originally developed in a totally different manner. At
birth the only ossification in the whole structure is the in-
complete ring of bone supporting the membrana tympani,
and developed originally in fibrous tissue. Ossification
extends from this, so as to complete the outer chamber,
and the very limited lip of the. meatus auditorius externus.
The inner chamber is formed from a distinct piece of hya-
line cartilage, which at birth is a narrow slip, pointed at
x.] CARN1V0RA. 149
each end, lying between the tympanic ring and the basi-
occipital, applied closely to the surface of the already
ossified periotic, and forming no distinct prominence on the
under surface of the skull. Soon after birth this increases
in size, and gradually assumes the bullate form of the wall
of the inner chamber. In young animals, even some time
after the ossification of the bulla is complete, the distinc-
tion between the two parts is clearly seen externally ; not
only are they marked off by a groove, but the tympanic
portion has a more opaque appearance than the other. The
septum is formed by an inversion of the walls of both,
applied together, and ultimately perfectly fused in Felt's,
although remaining permanently distinct in some of the
Viverridce.
The carotid foramen in the Tiger is only represented by
a minute groove deep in the recess of the foramen lacerum
posterius. In the smaller Cats, this groove is more super-
ficial, but always very minute, and apparently never converted
into an actual foramen, except by the contiguous wall of the
basioccipital.
The paroccipital process is flattened over the back of the
bulla, being applied closely to the whole of its prominent
rounded hinder end, and projecting, as a rough tubercle,
slightly beyond it. From the^ inner side of this process a
sharp ridge runs towards the occipital condyle. This forms
the posterior boundary of a deep fossa, at the bottom of
which is the foramen lacerum posterius, and in the hinder
part of which, under cover of the aforesaid ridge, the
condylar foramen opens. The mastoid process is a
moderately conspicuous rough projection, not very widely
separated from the paroccipital. There is no distinct
glenoid foramen.
The Viverridce agree with the Felidce in having the auditory
150 THE SKULL. [chap.
bulla divided into two cavities by a bony partition, in having
the paroccipital spread over the hinder surface of the bulla,
and in having no prolonged external auditory meatus ; but
the bulla is more elongated and compressed, and the inner
chamber is placed altogether behind the outer or true
tympanic chamber.
In the Hyaena this region of the skull much resembles the
same part in the Cats, but the bulla is simple and undivided.
In the Dogs there is a partial septum, and otherwise the
characters are intermediate between the two extremes of the
Bears on one side, and the Cats on the other.1
In nearly all the Carnivora the hyoidean apparatus is con-
structed on the same plan as described in the Dog, having a
narrow, transversely elongated, curved basihyal, either round,
or compressed from above downwards, a nearly straight
compressed thyrohyal, not ankylosed with the basihyal, and
a well-ossified anterior cornu, composed of three distinct
pieces of subequal length. In the Lion, Tiger, and Leopard,
however, the anterior arch is imperfectly ossified, the dif-
ferent bones being small, and connected together by long
ligamentous intervals ; but in the Puma, Cheetah, Lynx, and
Cat, the bones are large, and in close relation with each
other.
In the Seals the brain-cavity is very broad, round, and
rather depressed. The orbits are large, and the interorbital
portion of the skull greatly compressed. The olfactory
chambers of the nasal cavities are consequently very narrow,
and the ethmoturbinals little developed ; but in front of the
orbits the cavities widen, and the maxilloturbinals are very
1 For the various modifications of the structure of this part of the
skull in the different genera of the order, see "On the Value of the
Characters of the Base of the Cranium in the Classification of the Order
Carnivora." (Proc. Zool. Soc, 1869, p. 5.)
x.\ CARNIVORA. 151
large and complex. The mesethmoid is of considerable
vertical extent, and its ossified portion, which is extensive,
terminates anteriorly in a straight vertical line. In some
forms, as Cysfophora, this ossification extends in front of the
nasals. The hyoid resembles that of the typical Carnivora,
all the elements being well ossified and distinct. The
Otariidce, or Eared Seals, also called Sea Bears or Sea
Lions, are intermediate in most of their cranial characters
between the true Seals and the Bears.
The skulls of the animals composing the Order Insec-
tivora present great variations.
In some of the higher forms, as Galeopithecus, Tupaia,
Macroscelides, and Rhynchocyon, the cranium much resembles
that of the Lemurina, having a considerable and vaulted
cerebral cavity, large orbits, nearly vertical occipital plane,
large olfactory fossae, a well-developed zygomatic arch
sending up a postorbital process to meet a corresponding
one from the frontal so as either partially or completely to
encircle the orbit behind, and tympanies ankylosed with
the other cranial bones, dilated into a bulla, and pro-
duced externally into a tubular auditory meatus. The
face is generally elongated, and narrow anteriorly, but in
Galeopithecus it is broad and depressed.
In the M aero sceli dee, or Elephant Shrews, the auditory
meatus is very large, the tympanic bulla much inflated, and
there are sometimes also very large mastoid bullae.
In Tupaia, the malar has a large, oval, longitudinal per-
foration. There are also in this genus, as in some of the
other Insectivora, vacuities in the palate, arising from defects
If ossification, like those found in many Marsupials.
In the remaining Insectivora the cranial cavity is of small
Native size. The orbit and temporal fossa are completely
152 THE SKULL. [chap.
continuous, and there is often not even a trace of a post-
orbital process to the frontal or malar.
In the Eri?iaceidce (Hedgehogs) and the Centetidce the
tympanic is a mere ring unankylosed to the surrounding
bones, but a kind of bulla is formed by a lamella projecting
from the basisphenoid to join its inner and inferior edge.
In Erinaceus and Gymnura the zygomatic arch is com-
plete, but slender, and formed chiefly by the processes of the
maxilla and squamosal, which meet each other : the malar
being a small splint-like bone attached to the outer and
under side of the middle of the arch. In the Centetidce the
malar is entirely absent, and, as the zygomatic processes of
both maxilla and squamosal are very short, there is no bony
arch. Centetes (the Tenrec) has a remarkably elongated
and narrow skull (both cranium and face partaking of the
same character), with very prominent occipital and sagittal
crests. Both in this genus and in Erinaceus (the Hedge-
hog) the mesopterygoid fossa at the base of the skull is
very deep, and ends posteriorly in a hemispherical depression
in the basisphenoid, between the wing-like processes which
abut against the inner wall of the tympanic. Both parocci-
pital and mastoid processes are also well developed.
The Moles (Talpidce) have an elongated and depressed
cranium, broad posteriorly, and gradually narrowing to the
muzzle. The occiput slopes upwards and forwards, the
supraoccipital being greatly developed. The zygomatic
arches are complete, but very slender, and show no dis-
tinct malar bones. There are no postorbital or paroccipital
processes. A lamelliform expansion of the upper edge of
the periotic (pterotic, Parker) forms part of the lateral wall of
the cranium, as in the Echidna. The tympanic is united
with the other bones of the cranium to form a flattened
bulla, produced into a short meatus with a small external
x.] INSECTIVORA. 153
opening. There is a small " prenasal " ossicle in the anterior
extremity of the mesethmoid cartilage, as in the Pig.
In the Cape Golden Mole {Chrysochloris) the cranium is
conical, very broad and rounded behind, and pointed in
front. There are no postorbital processes. The zygoma is
complete, and tolerably strong. The tympanies ankylose
with the skull, and form a completely ossified bulla.
In the Shrews (Soricidce) the cranium is broad behind and
tapering forwards. The facial portion is long and narrow.
The occiput slopes much forwards. There is no zygoma
and no postorbital process. The postglenoid process of the
squamosal is remarkably large. The tympanic is ring-like,
and there is a large unossified space on each side of the
base of the skull.
The mandible in the Insectivora has generally an elon-
gated and rather narrow horizontal portion, above which
the transversely extended condyle is but slightly elevated,
and there are well developed coronoid and angular processes;
«latter is remarkably long and slender in the Shrews,
he hyoid is formed generally like that of the Carnivora,
three complete extracranial ossifications in the anterior
arch, a transversely extended basihyal, and tolerably long,
stout, flattened thyrohyals, sometimes ankylosed with the
basihyal.
Order Chiroptera. — In the large Frugivorous Bats
(Pterofius), the cranium is generally elongated, the cerebral
cavity large, oval, arched above, and contracted in front ;
its walls formed mainly by the greatly expanded parietals,
both supraoccipital and frontals being small. In old indi-
viduals of some species there are well-marked sagittal and
occipital crests. The base of the cranium is elongated, flat,
and thin. The facial part is long and rather compressed.
154 THE SKULL. [chap.
The postorbital processes of the frontals are long and
pointed, and partially define the orbits behind ; but there
is usually no corresponding ascending process from the
zygomatic arch, which is long and slender, and mainly
formed by the processes of the maxillary and squamosal,
the malar being a splint-like bone attached to their under
and outer surface. The lachrymal foramen is situated outside
the margin of the orbit. The nasals are long and narrow,
and often ankylose together in the middle line. The pre-
maxillse are small. The palate is elongated backwards ;
the horizontal plates of the palate bones being large and
early united in the middle line, without defects of ossifica-
tion. The pterygoids are small. . There is no alisphenoid
canal. The glenoid fossa is broad and shallow ; the post-
glenoid process very little developed, and with a venous
foramen behind it. The tympanies are very slightly con-
nected with the neighbouring bones, and are consequently
nearly always lost in macerated skulls. A wedge-shaped
portion of the mastoid appears on the outside of the skull
between the squamosal and the exoccipital. The par-
occipital process is long and rather slender, and directed
downwards and backwards. The periotic has a large and
deep fossa for the flocculus on its inner side.
sh
I'h^th
Fig. 54. — Hyoid bones of Frugivorous ¥>*t{Pteropus) from below, bh basihyal;
th thyrohyal ; sh stylohyal.
The mandible has a high, broad, recurved coronoid pro-
cess, a transversely extended condyle, and flattened rounded
angle, without a distinct process.
The hyoid (Fig. 54) has a narrow, transversely extended
x. ] CH1R0PTERA. 155
basibyal, with which the elongated, laterally compressed and
curved thyrohyals are commonly ankylosed. The anterior
cornu contains three slender ossifications of nearly equal
length.
The Insectivorous Bats generally have the skull shorter
and broader than the Pteropi. The cranial cavity in many
species is almost globular, with thin smooth walls, though
sometimes sagittal and occipital crests are developed. The
occipital foramen is very large. The zygoma is slender*.
Postorbital processes are sometimes well developed, but
more often small and rudimentary. The face is usually
short and broad, in some (as Mormops) bent upwards on the
cranium in a remarkable manner, so that the plane of the
palate is nearly perpendicular to the basicranial axis. The
premaxilla?. are generally small, sometimes not- meeting in
the middle line, and sometimes (as in Megaderma) altogether
wanting. The tympanies are annular, not ankylosed to the
surrounding bones, nor prolonged into a bony canal ex-
ternally, though often developing a partial bulla on their
inner side.
The mandible has a distinct angular process.
Order Rodentia. — In the Rodentia the cerebral cavity is
generally elongated, depressed, somewhat broad behind and
narrow anteriorly. The occipital plane is more or less
vertical; the cerebellar fossa altogether behind the cerebral,
and the tentorial plane, or division between these fossse,
approaching the vertical. The anterior part of the cerebral
fossa is contracted ; the olfactory fossa is of moderate size,
and situated directly in front of the cerebral.
The nasal cavities are very large, and both sets of
tnrbinals well developed, including an upper or nasoturbinal
lamella. The olfactory chambers attain their maximum of
156 THE SKULL. [chap.
development in some of the Porcupines (Hystrix), where
nearly all the bones of the upper part of the cranium are
expanded by great air sinuses formed within their walls. In
the Hare, and some others, the two optic foramina in the
orbitosphenoids are confluent ; and in consequence, in the
(dried skull, there is a direct aperture of communication
/between the orbits above the craniofacial axis.
The supraoccipital is more or less vertical, and does
not extend far on to the upper surface of the cranium.
There is often a distinct interparietal. There are generally
moderately developed paroccipital processes, which in the
Capybara (Hydrochcerus) are of great length, curving for-
wards and compressed laterally. They are. also very large
in the Coypu [Myopotamus).
The parietals are moderate or small. The frontals, except
in the Squirrels, Marmots, and Hares, have little more than
a rudiment of a postorbital process, and there is never any
marked corresponding process arising from the zygoma, so
that the orbit is perfectly continuous with the temporal fossa.
The latter is always very small.
In a very remarkable East African genus, Lop/iiomys, a
/broad bony lamella extends from the upper part of the
) parietal outwards and downwards to join a similar ascending
( plate from the malar, and so forming an arched covering
to the temporal fossa, an arrangement unknown in any
other mammal, but recalling that met with in the tortoises.
The whole of the superior surface of the cranial bones of
' this animal are covered with miliary granulations, disposed
with perfect regularity and symmetry.1
The nasals are both long and wide, and generally extend
so far forwards as to make the anterior nares quite terminal
and vertical, or even with a downward inclination. In
1 See A. Milne-Edwards, Nouv. Archiv. du Museum, iii. 1867.
x] R0DENT1A. 157
Hystrix their development is enormous, but this is chiefly
owing to their breadth and backward extension over the
great nasal chambers and air sinuses. They are narrowest
in Bathyergus and its allies.
The premaxillae are large, and lodge the great curved
incisor teeth,1 and always send a narrow prolongation back-
wards by the side of the nasals to join the frontals.
In the larger number of Rodents there is a great vacuity,
in the anterior or maxillary root of the zygoma of varying
size and form, apparently an enormous dilatation of the
infraorbital foramen, and through which a portion of the
masseter muscle passes (see Fig. 55). It is sometimes as |
large as the orbit itself, with which it communicates freely S
posteriorly, underneath a vertical bar, formed by the
maxilla in front, and by the lachrymal and malar behind.
Its inferior boundary is a slender zygoma-like horizontal
bar, formed by the maxilla alone. In the Rats it is a
vertical fissure dilated superiorly. In the Viscacha (Lagos-
tomus), the true infraorbital foramen is separated from the
large antorbital vacuity by a thin ascending bony lamella.
In Castor, Lepus, Bathyergus, Sciurus, Arctomys, and some
others, the infraorbital foramen is of the usual size. ^/
In the Hares, the facial surface of the maxilla is curiously
reticulated.
The zygoma is present in all, of various degrees of thick-
ness, but always either straight or more or less curved
downwards, and usually not much arched outwards. Its
anterior and posterior roots are formed by the maxilla
and squamosal respectively, the malar intervening. In
many cases the last-named bone extends backwards, applied
1 These teeth, though first developed in the gum covering the pre-
maxilla, have their roots, when fully developed, in the maxilla. This
does not invalidate their determination as incisors.
158 THE SKULL. [chap.
to the under surface of the zygomatic process of the
squamosal to form the outer side of the glenoid articular
surface. In the spotted Cavy (Cculogenys), the zygoma has
an enormous vertical expansion, with a rugose or pitted outer
surface, and a large fossa in the inner side of the maxillary
portion, with which the cavity of the mouth communicates
in the recent state.
The lachrymal bone usually presents both orbital and
facial surfaces, but the orifice of the canal (lachrymal
foramen) is always well within the margin of the orbit. In
the Beaver, and many others, the facial portion is reduced
to a mere tubercle, and in the Hare the lachrymal is entirely
within the orbit.
The palate of the Rodents is usually narrow. In the long
space intervening between the incisor and molar teeth, it
has no definite lateral margins, but rounds off insensibly
on to the sides of the face. In this region the anterior
palatine foramina form very conspicuous longitudinal slits, of
specially large size in the Hares. The portion of the palate
situated between the molar teeth is often very narrow
anteriorly, and ends posteriorly in a thickened excavated
border. In the Hare it is reduced to a short transverse
bridge, extending across the middle line between the pre-
molar teeth. In the Capybara and Guinea Pig the alveolar
border of the maxilla is very long, and presents the remark-
able peculiarity of extending backwards beneath the orbit
to unite with the squamosal at a level with the anterior
border of the glenoid fossa. It thus forms the outer border
of a large conical cavity, opening posteriorly, bounded on
the inner side by the pterygoids, above by the alisphenoids,
and below by the palatines.
The pterygoids are always simple subquadrate lamellae,
early ankylosed with the basisphenoids, often sending a
x.] RODENTIA. 159
well-marked hamular process backwards, which unites with
the auditory bulla in Hystrix, Lagostonms, Bathyergus, &c.
There are usually well-marked pterygoid fossae, and the sides
of the alisphenoids are often perforated by an alisphenoid
canal. In Hystrix the hamular process is slightly bullate.
The squamosal forms a considerable part of the outside
wall of the cranium, but in consequence of the large size of
the united tympano-periotic, the root of the zygomatic
process is thrown very forward on the side of the skull,
and the posterior part of the body of the squamosal which
unites with the occipital is reduced to a long, rather narrow
strip, interposed between the parietal and periotic. When
the mastoid bullae are greatly developed, as in Pedetes
Per
Fig. 55. — Side view of skull of Cape Jumping Hare {Pedetes caffer), \. Sq squamosal ;
Pa parietal ; AS alisphenoid ; Fr frontal ; OS orbitosphenoid ; L lachrymal ;
Na nasal ; PMx premaxilla ; Mx maxilla ; Ma malar ; Ty tympanic; ExO ex-
occipital ; Per points to the large supratympanic or mastoid bulla.
(see Fig. 55), this does not reach as far backwards as the
occipital, and is a slender curved process, which clasps the
outside of the bulla, and appears to hold it in its place.
The glenoid fossa is situated on the under side of the
posterior root of the zygoma. In its most typical form (as
160 THE SKULL. [chap.
in the Capybara, Viscacha, Aguti, Paca, &c.) it is narrow
and concave transversely, with prominent inner and outer
edges, the latter being often formed, as before mentioned,
partly by the hinder end of the malar. In the Beaver the
glenoid fossa has considerable breadth. In the Porcupines,
Marmots, Squirrels, Rats, &c, no raised inner margin is
developed, and the fossa passes insensibly into the side of
the skull wall. In the Hare it is a transversely oval hollow,
with a prominent rounded anterior margin.
The tympanic is ankylosed to the periotic, but not to the
squamosal ; it generally develops a tubular meatus, which in
the Hare is directed upwards and backwards, in the Beaver
outwards and forwards. In the Porcupines, as well as in
most of the smaller Rodents, the meatus is short. In the
Capybara it is fissured below.
There is always a considerable tympanic bulla, which is!
often supplemented by a bulla developed above the tym-
panic cavity, apparently in the periotic. In some genera
(Pedetes, Dipus, Chinchilla) this attains an enormous size
(see Fig. 55, Per), and forms a rounded prominence on the
posterior external angle of the skull, interposed between
the squamosal, parietal, and occipital. Usually, the mastoid
portion of the periotic only appears on the surface for a
small space in front of the exoccipital. In the Beaver, it
forms a conspicuous angular process.
The periotic is never ankylosed with any of the bones
of the cranium, other than the tympanic. On its inner
surface the floccular fossa is nearly always wide and deep,
but it is absent, or nearly so, in the Capybara, Paca, and
Porcupine. The place of attachment of the hyoid arch is
an inconspicuous depression in the usual situation, and the
tympanohyal is never distinct. This is in relation with the
rudimentary condition of the anterior cornu of the hyoid.
x.] RODENTIA. 161
In the mandible, the symphysial portion is narrow, curving
upwards, and rounded laterally, with a single large alveolus
on each side. The coronoid process is never large, and is
often rudimentary or absent, in relation to the small develop-
ment of the temporal fossa and muscle ; while the portion
adjacent to the angle is greatly developed, showing marked
masseteric and pterygoid fossae, and often with its lower
edge expanded laterally, or slightly incurved. The angle is
rounded in the Hares, but it is more often produced into a
long backward process, more or less pointed and upturned.
The condyle is considerably elevated, with a rounded
articular surface, usually longer from before backwards than
from side to side.
The hyoid has a transversely extended basihyal and a
straight compressed rod-like thyrohyal, often ankylosed with
the basihyal. The anterior arch is long, but mostly liga-
mentous, the ossification being usually confined to the lower
part (cerato- and epi-hyals). In the Hares, the basihyal is
deep from above downwards, and compressed, keeled, or
pointed in front.
CHAPTER XL
THE SKULL IN THE UNGULATA, HYRACOIDEA AND
PROBOSCIDEA.
Order Ungulata. Sub-order Perissodactyla. — In the
Horse the whole skull is greatly elongated, chiefly in con-
sequence of the immense size of the face as compared with
the hinder or true cranial portion. The basal line of the
skull from the lower border of the foramen magnum to the
incisor border of the palate is very nearly straight. The
occipital and ethmoid planes are nearly perpendicular to
this line, the latter inclining slightly forwards. The ten-
torial plane, strongly marked by inward projecting ridges of
bone, slopes obliquely backwards at an angle of 45 °. The
cerebral fossa is a smooth and regular oval, broad and
rounded in front, and with no distinct division into
anterior and posterior portions. The olfactory fossa is
short, but deep from above downwards. The pituitary fossa
is very shallow, and there are no distinct clinoid processes.
The alisphenoid is very obliquely perforated by the foramen
rotundum, but the foramen ovale is confluent with the large
foramen lacerum medium behind. There are considerable
frontal and sphenoidal air sinuses, but the former do not
extend any great distance over the brain-cavity.
In front of the cerebral cavity, the great tubular nasal
cavities are provided with well-developed turbinal bones,
chap, xi.] UNGULATA. 163
and are roofed over by very large nasals, broad behind, and
ending in front in a narrow decurved point. The opening
of the anterior nares is prolonged backwards on each side
of the face between the nasals and the elongated slender
premaxillae. The latter expand in front, and are curved
downwards to form the semicircular alveolar border which
supports the large incisor teeth.
The orbit is rather small in proportion to the size of the
whole skull, but very distinctly marked, being completely
surrrounded by a strong ring of bone with prominent
edges. The lachrymal occupies a considerable space on
the flat surface of the cheek in front of the orbit, and
below it the malar does the same. The latter sends a
horizontal or slightly ascending process backwards below
the orbit, to join the under surface of the zygomatic
process of the squamosal, which is remarkably large,
and instead of ending, as usual, behind the orbit, runs
forwards to join the greatly developed postorbital pro-
cess of the frontal, and even forms part of the posterior
iand inferior boundary of the orbit — a very exceptional
arrangement (see Fig. 56).
The palate is very narrow in the interval between the
incisor and molar teeth, in which are situated the large
anterior palatine foramina. Between the molar teeth it
is broader, but it does not extend further back than the
penultimate molar and ends in a rounded excavated border.
It is mainly formed by the maxillae, as the palatines are
very narrow. The pterygoids are delicate slender slips of
bone attached to the hinder border of the palatines, and sup-
ported externally by, and generally ankylosed to, the rough
pterygoid plates of the alisphenoid, with no pterygoid fossa
between. . They slope very obliquely forwards, and end in
curved, compressed, hamular processes. There is a distinct
m 2
164
THE SKULL.
[CHAP.
alisphenoid canal for the passage of the internal maxillary
artery.
The base of the cranium is long and narrow. The
glenoid surface for the articulation of the mandible is
greatly extended transversely, concave from side to side,
convex from before backwards in front, and hollow behind,
and is bounded posteriorly, at its inner part, by a prominent
postglenoid process (Fig. 56,/^).
Fig. 5b. — Side view of the posterior part of the skull of a Horse, \. Fr frontal (the
line points to the postorbital process) ; Sq squamosal ; Pa parietal ; SO supra-
occipital ; ExO exoccipital : or occipital condyle ; pp paroccipital process ; Per
mastoid portion of periotic ; pt post-tympanic process of squamosal ; th tympano-
hyal ; Ty tympanic; pg postglenoid process of squamosal ; As alisphenoid (che
line points to the plate of the bone which bridges over the alisphenoid canal) ; Ma
malar.
The squamosal (Sq) enters considerably into the forma-
tion of the temporal fossa, and besides sending the zygo-
matic process forwards, it sends down behind the meatus
auditorius a post-tympanic process (pt), which aids to
hold in place the otherwise loose tympano-periotic bone.
Behind this the exoccipital gives off a very long paroccipital
process (//).
UNGULATA.
16:
The periotic and tympanic are ankylosed together, but not
with the squamosal. The former has a wide but shallow
floccular fossa on its inner side, and sends backwards a
considerable " pars mastoidea " which appears on the outer
surface of the skull {Per) between the post-tympanic process
of the squamosal and the exoccipital. The tympanic (Ty)
forms a tubular meatus, directed outwards and slightly
backwards. It is not dilated into a distinct bulla, but ends
in front in a pointed styliform process. It completely
embraces the truncated cylindrical tympanohyal (///), which
is of great size, corresponding to the large development of
the whole anterior arch of the hyoid.
The stylohyal (Fig. 57, sh) is of great
size, compressed, and expanded at the
upper end, where it sends off a triangular
posterior process. Below the stylohyal,
and usually becoming ankylosed with it,
is a small nodular bone (epihyal), and
then the arch is completed by a short
cylindriform ceratohyal {ch). The basi-
hyal (bh) is rather flattened from above
downwards, arched with the concavity be-
hind, and sends forwards a long, median,
pointed, compressed " glossohyal " pro-
cess. The thyrohyals (th) are compressed
bars projecting backwards from, and in
adult animals completely ankylosed to,
the lateral extremities of the basihyal.
Each ramus of the mandible has a
long, straight, compressed, horizontal
portion, graduallv narrowing towards Fig. 57.— Superior surface
. . of hvoid bones of horse,
the symphysis, where it expands laterally J. sk stylohyal ; ch cera-
/ r J. ' , , , • tohyal; bh basihyal; th
to form with the ankylosed opposite thyrohyai.
1 66 THE SKULL. [chap.
ramus the wide semicircular, shallow alveolar border for
the incisor teeth. The region of the angle is expanded
and compressed, with a thickened rounded border without
any process. The condyle is greatly elevated above the
alveolar border; its articular surface is very wide trans-
versely, and narrow and convex from before backwards.
The coronoid process is slender, straight, and inclined
backwards.
The skull of the Rhinoceros resembles that of the Horse
in many essential features, but the occipital region is of
much greater extent vertically, the form of the cranial cavity
being concealed externally by large occipito-paiietal air-
cells. There is no postorbital process to the frontal, so
that the orbit is not divided from the temporal fossa.
There is a conspicuous rough antorbital projection on the
lachrymal bone just in front of the lachrymal foramen.
The nasals are very large and strong, early ankylosed to-
gether, arched from before backwards, and pointed ante-
riorly. The most elevated part of their upper surface is
roughened, and supports the great median horn which
characterizes the genus. In some species a posterior rough,
but less elevated, surface indicates the attachment of a
second horn. In some of the extinct species the meseth-
moid cartilage was ossified nearly as far forwards as the ex-
tremity of the nasals, which is not the case with any existing
species. The premaxillae are very small, and do not extend
anteriorly beyond the level of the front end of the nasals.
The hinder border of the palate is deeply excavated, the
horizontal plates of the palatines being very narrow. The
pterygoids are very slender, as in the Horse, but placed more
vertically. There is a distinct alisphenoid canal. The
squamosal sends down a very long conical, postglenoid pro-
xi.] UNGULATA. 167
cess parallel with, and equalling, or sometimes exceeding,
in length, the paroccipital process. The meatus auditorius
lies in a deep groove between the postglenoid and the post-
tympanic processes of the squamosal ; the latter articulates
with the exoccipital, completely excluding the mastoid from
the external surface of the skull.
The tympanic and periotic are ankylosed together, but
not with the squamosal. They are both very small. The
under surface of the tympanic is rough, forms no distinct
bulla, and is much encroached upon posteriorly by the very
large tympanohyal, which presents a circular, flat, rough,
inferior surface, half an inch in diameter (in an adult
Sumatran Rhinoceros). Externally, the tympanic is pro-
duced into a rough, irregular, inferior wall to the auditory
meatus. The periotic internally shows the internal auditory
meatus near its lower part, but no distinct depression for
the flocculus ; it is prolonged upwards and outwards into
a small mastoid portion, which, as before said, does not
appear on the outer surface of the skull.
The mandible has a very wide condylar articular surface,
and slender recurved coronoid process, a rounded, somewhat
incurved angle, a compressed, rather narrow, horizontal por-
tion, and a shallow depressed symphysis.
The hyoid is much like that of the Horse, and has a
glossohyal process from the middle of the basihyal.
The Tapirs present some singular modifications of the
same type of skull.
As in the Rhinoceros, there is no separation between the
orbit and temporal fossa, but the anterior nares are of
immense size, and extend backward above the orbits, being
separated from them only by a thin plate of bone, instead
of a broad, flat surface, as in the Horse and Rhinoceros.
i68 THE SKULL. [chap.
The nasal bones are short, broad behind, pointed in front,
much elevated, and supported by a tolerably well ossified
mesethmoid, which spreads out laterally at its upper end.1
The inferior and lateral margins of the great narial apertures
are entirely formed by the maxillae, which extend up to meet
the nasals, neither frontals nor premaxillae taking any share
in them. The ethmoturbinals are small, while the maxillo-
turbinals, on the other hand, are very extensive, though
their plications are comparatively simple. A conspicuous
feature in the upper part of the face is a groove, which
extends backwards on the side of the dilated hinder end
of the nasal bone, and curves inwards to form a rounded
depression over the naso-frontal suture. The form and size
of this depression vary in different species. It lodges an air
sinus, with cartilaginous walls extending upwards from the
nasal chamber. In front of the nares, the rostrum formed
by the maxillae with the premaxillae in front, is produced,
compressed anteriorly, and curved downwards.
The base of the cranium resembles generally that of the
other Perissodadyla. There is an alisphenoid canal, and
large postglenoid and post-tympanic processes; the latter
joins the paroccipital process of the exoccipital, but above
their point of union a narrow slip of the mastoid appears
on the surface of the skull. The periotic is not ankylosed
to the squamosal or to the tympanic, which is exceedingly
rudimentary, forming a small irregular floor to the tympanic
cavity, with an oval lip for the attachment of the membrana
tympani, and always becomes detached in macerated skulls.
The mandible is chiefly noticeable for the great rounded
incurved posterior projection of the angle.
1 In one species ( T. Bairdii) the ossification of the mesethmoid extends
far in advance of the nasal bones, and is clasped and supported below
by ascending plates from the maxillae.
I.]
UNGULA TA.
169
The hyoid has a simple, elongated stylohyal without pos-
terior process at the upper end, but .one other ossification in
the anterior cornu, and no glossal process to the basihyal.
Fig. 58. — Longitudinal and vertical section of skull of a Sheeo [Ovis aries), £.
PMx premaxilla; MT maxilloiurbinal ; Na nasal ; ET ethmoturbinal ; ME
niesethmoid ; Fr frontal ; OS orbitosphenoid ; AS alisphenoid ; Pa parietal;
SO supraoccipital ; Per periotic ; ExO exoccipital ; BO basioocipital ; pp par-
occipital process ; Ty styliform process of tympanic ; BS basisphenoid ; PS pre-
sphenoid: Pt pterygoid: PI palatine; Vo vomer; Mx maxilla: cp coronoid
process ; cd condyle ; j symphysis of mandible ; sh stylohyal ; eh epihyal ; ch
sratohyal ; bh basihyal ; th thyrohyal.
:
uborder Artiodactyla. — The skull of the Sheep, as one
of the best known and easily procurable examples of this
group, may be first described, though in some respects it
is rather peculiarly modified.
170 THE SKULL. [chap.
On comparing the section of the cranium (Fig. 58) witr
that of the Dog, it will be seen that there is a great differenc
in the relation of the principal elements to each other, in*
much as the face is bent downwards on the basicranial axis
so that when the latter is horizontal, the upper surface
the face looks forwards and the palate backwards. The
occipital foramen is terminal posteriorly, the tentorial plane
nearly vertical, so that the cerebellar fossa is altogether
behind the cerebral, but the plane of the cribriform plate
is horizontal, and the olfactory fossa altogether beneath the
anterior portion of the cerebral fossa.
The occipital, region is small and sloping forwards..
There are long paroccipital processes (//). In very young
skulls a distinct interparietal bone is present, but in the
specimen figured this has coalesced with the parietals
(SO). The two parietals (Pa) unite very early at the
sagittal suture. The frontals (Fr) are large, and usually
(except in some domestic races) develop from their outer
surface conical, curved, bony processes, cancellous within,
which are called the " horn cores," as they form the internal
support of the true horns. The nasals (Na) are long and
pointed in front. The premaxillae (PMx) are slender, with
a shallow alveolar border, bearing no teeth, and forming the
anterior and lateral boundaries of large anterior palatine
foramina. The lachrymals are large, and form a con-
siderable portion of the side of the face in front of the
orbit, but the foramen is entirely, within the margin.
The olfactory chamber is large. The turbinals are greatly
developed ; the upper lamina of the ethmoturbinal or "naso-
turbinal" is distinct, and extends over the scroll-like maxillo-
turbinal (MT), but does not ankylose with the nasal.
The orbit is large, nearly circular, with a complete,
prominent margin, formed below by the large malar, which
UNGULATA.
7i
extends considerably on the side of the face, and posteriorly
sends a process upwards to meet the po'storbital process of
the frontal, and is continued backwards to join the zygomatic
process of the squamosal.
The palate bones (PI) are of moderate extent; their
horizontal plate is deeply notched posteriorly. The pterygoids
{Ft) are broad above, but end below in a narrow lamella,
with a hamular process projecting backwards. The basi-
occipital (BO), seen from below, is square, with eminences
for muscular attachments at each of its four angles. The
basisphenoid (BS) is much contracted laterally. The pos-
terior clinoid processes are large, and the pituitary fossa
deep.
The squamosal is small, and scarcely appears in the interior
of the skull. The glenoid facet is rather extensive, and
slightly convex, and there is a postglenoid process and
foramen. The tympanic is not ankylosed to the periotic ; it
forms a complete tubular external auditory meatus, and a
considerable, but simple, bulla, narrowing to a sharp-pointed
process anteriorly (Ty). The periotic (Per) is rather small,
without any fossa for the flocculus ; its mastoid portion
forms a distinct, narrow, rough surface on the outer side of
the skull, between the hinder border of the squamosal and
the exoccipital. The tympanohyal is very large, cylindrical,
curved, and almost completely embedded in the tympanic,
between the inferior wall of the meatus and the outer wall
of the bulla.
The extracranial portion of the hyoid consists of large
compressed stylohyals (sh), with a prominent posterior
process near the upper end, short but well-ossiried epi-
hyals (eh) and ceratohyals (eh), and a basihyal represented
by a small rounded nodule of bone, to which the straight
thyrohyals (///) are not ankylosed.
172 THE SKULL. [chap.
The mandible has a broad flat condyle (cd), a long
slender coronoid process (cf), a rounded angle, a rather
slender horizontal portion, contracted and with a sharp
upper edge in front of the molar teeth, and expanded
anteriorly for the lodgment of the incisors.
The Ox agrees generally with the Sheep in its cranial
characters. The face is bent down on the basicranial axis
almost in the same manner. The occipital surface is flat,
and terminates above in a broad transverse ridge, which
extends between the horn cores. The parietals are ex-
tremely narrow above, and placed almost entirely behind
this ridge. They unite very early with the interparietal and
supraoccipital. The intercornual ridge of the frontals is
excavated by large air-cells, communicating with those of
the horn cores, and is especially developed when the horns
are large. Unlike the parietals, the frontals are of very
great extent, and have a broad and flattened upper surface.
The tympanies are compressed and scarcely at all bullate.
They end anteriorly in long compressed styliform processes,
and become firmly ankylosed with the periotic and squa-
mosal. The under surface of the meatus auditorius has a
compressed ridge. The large tympanohyals are entirely em-
bedded in the tympanic, only the rough lower surface for
articulation with the stylohyal being exposed.
The mandible and hyoid are like those of the Sheep, but
the basihyal is rather more developed, and has a rounded,
anterior, median projection.
Many Ruminants (especially among the Cervida) have a
vacuity of varying extent on the side wall of the face,
between the frontal, lachrymal, maxillary and nasal bones, '
leading in the macerated skull into the nasal chamber, but
xi.] UNGUfrATA. 173
closed in the living animal by membrane. Most of the(
Deer and Antelopes have also a large depression on the
facial surface of the lachrymal bone, called the suborbital or
lachrymal fossa, though it has nothing to do with the tears,
but lodges a glandular fold of the integument, which secretes
a peculiar unctuous and odorous substance. In most Deer
the orifice of the lachrymal canal is double, and situated on
the margin of the orbit, whereas in most of the hollow-
horned ruminants it is single and placed well within the
margin. There are however exceptions in both cases.
In the Deer the axis of the face is nearly in the same
line with that of the cranium, so that when the basicranial
axis is horizontal the nose is directed forwards instead of
downwards, as in the Sheep and Ox. The animals of this
family have no permanent horn cores continuous with the
cranium and ensheathed by true horns, but have short pro-
cesses on the frontal bones (pedicles), from which branching
antlers of true osseous structure are annually developed
and shed. These, as a rule, are only present in the males,
while the horns of the Bovidce and Antilopidce are usually
common to both sexes.
Among the Antelopes, the Saiga (Saiga tartarica) is very
remarkable for the conformation of the upper part of the
face. The anterior nares extend backwards almost to a
level with the front edge of the orbits, and have an unusual
vertical expansion. The nasal bones are aborted or coa-
lesced with the frontals. The turbinals are very short.
The lachrymals enter largely into the side walls of the
anterior nares. The ascending processes of the premaxillae
are small, and very widely separated from the nasals. In
the living animal the edges of these greatly expanded narial
apertures are continued forwards into a truncated, almost
proboscidiform muzzle without any bony support, giving the
174 THE SKULL. [chap.
contour of the face a totally different appearance from that
presented by the skull.
In the Elk (Alces), and a small Abyssinian Antelope
(Neotragus saltiana), the nasal bones are very much shorter
than they are in ordinary ruminants.
The Tylopbdd (Camels and Llamas) and the Tragulina
differ from most of the Pecora, and resemble the non-
ruminating Artiodactyles in having the tympanic bulla
filled with cancellated bony tissue.
The skull of the Pig shows in section that the axis of the
face is bent down upon the basicranial axis almost as much
as in the Sheep, a disposition which increases with age.
Though the form of the cranial cavity is not very different
from that of the Sheep, the external appearance of the
hinder part of the skull is greatly changed by the elevated
and backward sloping occipital crest, formed by the union
of the supraoccipital (concave from side to side posteriorly)
and the parietals. The latter have their outer and inner
surfaces widely separated in the adult Pig by .large air-cells.
The frontal is broad and flat between the orbits, and
sends out a small postorbital process, which does not join the
zygoma. The face is greatly elongated, tapering forwards,
and compressed laterally. The nasals are long and narrow,
and the apertures of the nares small and nearly terminal.
The premaxillae send up long processes on each side of
the nasals, which, however, do not meet the frontals. The
lachrymal has a considerable facial portion ; and, as in
other Ungulata, the malar encroaches considerably on the
face, uniting with the lachrymal.
At the anterior extremity of the mesethmoid a peculiar
ossicle {prenasal) is developed, which strengthens the cartila-
ginous snout.
xt.| UNGULATA. 175
The palate is long and narrow, and extends posteriorly
beyond the last molar tooth. The pterygoid fossae are well
marked, being chiefly formed by the well-developed ptery-
goid plates of the alisphenoid; the true pterygoids are very
slender. There are very long, slender, compressed par-
occipital processes, curved forwards.
The squamosal and tympanic are ankylosed together; th
floor of the long, narrow, upward-directed auditory meatu:
is formed by the tympanic, wedged in a cleft of the squa
mosal, between the hinder edge of the glenoid fossa (ther
being no postglenoid process) and a long descending post
tympanic process which articulates with the exoccipital.
Inferiorly the tympanic is dilated into a very prominent-1
bulla, peculiarly elongated vertically, and rather compressed
from side to side. The interior of this bulla is filled with
cancellous bony tissue.
The periotic is small and not ankylosed to the tympanic or
squamosal. The mastoid portion is quite rudimentary, bein
merely a short scale-like prolongation upwards and back
wards, lying on the inner surface of the squamosal, and
making no appearance on the external surface of the skull
The tympanohyals are very inconspicuous, being small, and
situated at the bottom of a deep fossa on the outer and
posterior side of the tympanic bulla.
The mandible has a high ascending portion behind, a
transverse condyle, a very small coronoid process, and a flat
expanded angle, rounded posteriorly.
The hyoid of the Pig is very different from that of most
other Ungulata. The basihyal is very small. The thyrohyals
are large, broad and flat, and ankylosed to the basihyal, but
with their extremities cartilaginous even in old animals.
There is a well-ossified ceratohyal, not ankylosed with the
basihyal, but the greater part of the anterior arch is a long
1 76 THE SKULL. [chap.
cartilaginous band, with one, or sometimes two, slender
ossifications near the middle part, representing the stylohyal.
The skull of the Hippopotamus resembles that of the
Pig in many essential features, although its external form is
greatly modified. The brain cavity is very small, and the
face immensely developed. The orbits project outwards in
an almost tubular manner, and their margins are nearly, and
in some cases quite, complete posteriorly. The face is con-
tracted laterally in front of the orbits, and then expands
widely into a massive truncated muzzle, which supports the
great canine and upper incisor teeth.
The anterior narial orifice is nearly circular; it is bounded
by the extremities of the narrow, but greatly elongated
nasals above, and laterally by the prominent, rounded,
rugged and massive premaxillse. At the anterior and lower
part of the orbit, the lachrymal is dilated into a great thin-
walled bony capsule, of such delicacy that it is nearly always
destroyed in the skeletons preserved in museums. This
opens into the nasal air-passages and has no connection
with the lachrymal apparatus. A similar but smaller dilata-
tion exists in many of the Pecora,
The palate is long and narrow, and extends posteriorly a
short distance behind the last molar teeth. The internal
pterygoids end in well-marked stout hamular processes. The
glenoid surface of the squamosal is very much extended,
but not bounded externally by a projection from the malar,
as in the Pig, and the inner half of its posterior margin is
produced into a tolerably well-marked postglenoid process.
The paroccipital process is long and conical, but far less
conspicuous than in the Pig. The tympanic bulla is pro-
portionately smaller, and of a trihedral form, ending in an
antero -inferior pointed process. Its interior is filled with
xi.] UNGULATA. 177
cancelli, as in the Pig. As in that animal, there is a long
narrow meatus auditorius, directed upwards and backwards
in a fissure between the postglenoid and post-tympanic
processes of the squamosal, the floor being formed by a
compressed, ridged prolongation of the tympanic, which
is at a very early age completely fused with the squamosal.
The periotic is very small, remains longer distinct, though
ultimately ankylosing with the conjoined squamoso-tym-
panic, and has only a rudiment of a mastoid portion, which
is quite confined to the interior of the cranium.
The tympanohyal is slender, ankylosed to the back of the
tympanic, and in the adult skull sunk in a deep fossa,
between that bone and the exoccipital, which also gives exit
io the facial nerve.
The mandible is of immense size and weight. The
:ondyles rise very little above the level of the molar teeth.
The coronoid process is small and much recurved. The
angle is greatly expanded and everted, rounded behind, and
terminating below in a distinct process, projecting down-
wards and forwards. The horizontal rami are compressed
in their middle portion, but widen anteriorly into a very
broad and massive truncated symphysial portion, which
supports the huge incisor and canine teeth.
In the hyoid apparatus, the basi- and thyro-hyals ankylose,
and are something like those of the Pig. The anterior arch
consists of three well-ossified pieces of subequal length.
Order Hyracoidea. — The skull of the Hyrax presents
many affinities with that of the Perissodactyla, others with
the Rodentia, and some characters peculiar to itself.
The cranium is high and truncated behind, the occiput
nearly vertical, the tentorial and olfactory planes oblique,
the olfactory fossa rather small.
178 THE SKULL. [chap.
There is a small distinct interparietal. The frontal region
is broad and flat. The zygoma is tolerably strong, and
formed mainly of the malar, which extends backwards so as
to form the outer wall of the glenoid fossa, but it is supported
anteriorly by a strong process from the maxilla. The orbit
/ is bounded posteriorly by well-marked postorbital processes
J which sometimes meet, the lower one from the malar, and
j the upper one from the parietal (a very unusual condition).
The lachrymal is small, and scarcely extends at all on to
the face, but sends outwards a strong antorbital process (as
in the Rhinoceros and Elephant). The face is short, and
compressed laterally. The nasal bones are wide posteriorly,
and anteriorly are either truncated, or more produced at
their outer than their inner margins. The premaxillae do
not send up processes to meet the frontals, as in all
Rodents.
The palate is not produced posteriorly beyond the middle
of the last molar tooth. The palate bones are large. The
pterygoids very slender. There are well-marked pterygoid
fossae, and alisphenoid canals. The paroccipital processes
are long and slender. The glenoid fossa is wide transversely,
and with a considerable postglenoid process. The periotic
and tympanic are ankylosed together, but usually remain
distinct from the squamosal. The tympanic forms a
moderate-sized bulla, and a spout-like floor to the external
auditory meatus, between the glenoid and post-tympanic
processes of the squamosal. The periotic has a very slight
floccular depression, and sends backwards no distinct mas-
toid process. The pituitary fossa is very shallow, without
clinoid processes. The foramen rotundum and foramen
ovale are distinct perforations through the alisphenoid. The
optic foramen pierces the large orbitosphenoid near its
hinder margin.
xi.] I1YRAC0IDEA. 179
The mandible has a high and exceedingly broad ascending
portion, its hinder margin being produced far behind the
condyle, but the angle is rounded, and without any distinct
process. The condyle is much extended transversely, and
narrow from before backwards, especially in its inner half,
for externally it is somewhat rounded. The coronoid pro-
cess is small and recurved.
The hyoid apparatus of the Hyrax is unlike that of any
other known Mammal. The basihyal is oval, transversely
extended and flat, with a small median eminence on its
anterior border, and an emarginate posterior border, only
ossified in the centre, and prolonged laterally, without any
definite segmentation, into broad, flattened, slightly curved
cartilaginous thyrohyals. Articulated to the anterior and
external angles of the basihyal are two large, triangular,
flattened bones (ceratohyals), each with a long process
projecting forwards and meeting in the middle line, so
as to enclose (with the anterior margin of the basihyal) a
triangular space. There is no other cartilage or bone in the
anterior arch, unless a very minute pyramidal bone, described
by Brandt as articulating with the mastoid process of the
skull, represents the stylohyal.1
Order Proboscidea. — The skull of the only existing
animals of this order, the Elephants, presents many very
remarkable features. As the brain-case increases but little
in size during growth, and as the exterior wall of the skull
is required to be of great superficial extent to support the
trunk and the huge and ponderous incisor teeth or tusks, and
to afford space for the attachment of muscles of sufficient
size and strength to wield the skull thus heavily weighted,
OU1
1 Mem. de l'Acad. Imp. de St.-Petersbourg," VIIe Serie, tome xiv.
o. 2, p. 68. 1869.
N 2
180 THE SKULL. [chap.
an extraordinary development of air-cells takes place in the
cancellous tissue between the outer and inner surface walls or
" tables " of nearly all the bones of the cranium, separating
them in some cases as much as twelve inches apart (see Fig.
60). These cells are not only formed in the walls of the
cranium proper, but are also largely developed in the nasal
bone and upper part of the premaxilla and maxilla, the
bones forming the palate and the basicranial axis, and even
extend into the interior of the ossified mesethmoid and the
vomer. Where two originally distinct bones come in contact
the cells pass freely from one to the other, and almost all the
sutures become completely obliterated in old animals.
The intercellular lamellae in the great mass which sur-
rounds the brain-cavity superiorly and laterally mostly
radiate from the inner to the outer table, but in the other
bones their direction is more irregular. Like the similar
but less developed air-cells in the skulls of many other
Mammals, they are entirely secondary to the original growth
of the bones. In the young African Elephant's skull figured
(from an animal about six months old, see Fig. 59), their
formation has scarcely commenced, and as the sutures are
still quite distinct, and the bones not distorted by these
cellular dilatations, they are in a much better state for,
studying their connections and characteristics.
When the basicranial axis is placed in a horizontal
position, it will be seen that the foramen magnum is quite
posterior, and its plane nearly vertical. The cranial cavity
is elongated and depressed (more so in the African than the
Indian Elephant), the tentorial plane nearly vertical, so that
the cerebellar fossa is altogether behind the cerebral fossa.
The latter is broad behind and contracted laterally in front.
The olfactory fossa is large, and placed altogether below
the anterior part of the cerebral fossa, the cribriform plate
XL 1
PROBOSCIDEA.
Ih Sfjr Pen
181
JPS
7>Mj!
africanns), taken somewhat to the right of the middle line, so that the meseth-
an
ME^
^pn
Fig. 60. — A section of the cranium of a' full-grown African Elephant, taken to the left
of the middle line, and including the vomer (Vo), and the mesethmoid {ME),
an anterior, and pn posterior narial aperture, j1*.
1 82 THE SKULL. [chai\
being nearly horizontal. The ridge which separates the
anterior from the posterior division of the cerebral fossa is
very well marked. The pituitary fossa is very shallow, and
there are no distinct clinoid processes. The supraoccipital
(SO) is high, and inclines greatly forwards; so that the occi-
pital surface looks upwards as much as backwards. In the
adult skull (Fig. 60) the lateral parts of the occipital region
(rounded smoothly off in the young state) are vastly expanded
and leave between them a deep median depression, with a
rugged floor, and a partial bony septum at the bottom, into
which the ligamentum nuchae is inserted. The median por-
tion of the supraoccipital never becomes expanded by air-
cells. The parietals (Pa) are very large, and form the greater
part of the lateral walls of the cranium. The frontals (Fr)
are narrow from before backwards, and produced laterally
into elongate supraorbital processes, which send out small
postorbital processes, not, however, completely separating
the small orbit from the large and high temporal fossa.
The most remarkable feature in the face is the form and
position of the anterior narial orifice (an). It is wide trans-
versely, very short from above downwards, placed very high,
and is directed upwards and forwards, almost as much as in
the Whalebone Whales. The nasal bones (No) which bound
it above are very thick, short, broad behind, and conical
in front, and contain large air-cavities. The inferior and
lateral margins of the orifice are formed entirely by the pre-
maxillae (PMx), which send processes up to join the nasals
and frontals. In front of the nares the face is prolonged
into a somewhat quadrate, depressed, alveolar process, trun-
cated in front, concave above, rounded laterally, formed by
the premaxillae above and at the sides, and by the maxillae
below. This contains the roots of the great incisor teeth
or tusks.
xi.] PROBOSCIDEA. 183
The lachrymal is small, placed almost entirely within
the margin of the orbit, and ends anteriorly in a projecting
antorbital process. The zygomatic arch is slender and
straight, the malar being small, and forming only the middle
part of the arch, the anterior portion of which is (unlike
that of all Ungulates) formed by the maxilla.
The elongated, tubular nasal cavity forms a sigmoid
curve, being directed (from below) at first forwards, then
upwards, then forwards. The olfactory chamber is a
comparatively small fossa in the middle third of its posterior
wall, filled by the complex ethmoturbinals. The maxillo-
Iirbinals are but rudimentary, the narial passage being quite
ee.1 The floor of the palate is completed posteriorly by
ell-developed palatines (PI). The pterygoid (Pt) is slender
id very early ankylosed with the pterygoid process of the
isphenoid, which is greatly expanded, and hollowed in
ont, being spread round the dilated posterior margin of
the alveolar portion of the maxilla, and aiding to close the
great alveolar cavity of the hindermost molar tooth.
The squamosal (Sq) forms a considerable part of the cranial
wall, extending outside the small alisphenoid to meet the
frontal, and externally sends off a broad post-tympanic pro-
cess, which meeting (though not uniting with) the hinder bor-
der of the glenoid fossa in front, bounds the bony external
auditory meatus, to which the tympanic contributes very
little. The latter bone is, in the young specimen, completely
united with the periotic, but not with the squamosal. In-
feriorly it forms a large, rounded, but not very prominent
auditory bulla, deeply notched on its inner side by the
canal for the internal carotid artery (e c). The periotic
(Per) presents a large surface within the cranium without
I1 The elongated proboscis probably supplies their place functionally
184 THE SKULL. [chap. xi.
any floccular fossa. The mastoid portion is very small, and
does not appear on the surface of the cranium. There
are no paroccipital or postglenoid processes. At the bottom
of a deep fossa between the squamosal, exoccipital, and tym-
panic, the tympanohyal is distinctly seen, with the stylo-
mastoid foramen to its outer side. The exoccipitals are
not perforated by a condylar foramen, neither is the ali-
sphenoid perforated, but it is grooved in front for the
foramen rotundum, and behind for the foramen ovale.
The mandible is of a very peculiar shape. The ascending
portion of the ramus is high, and terminates in a rather small
rounded condyle, wider from side to side than from before
backwards. The posterior border is thick, but rounded off
gradually into the inferior edge, without any projection at
the angle. The coronoid process is compressed, and but
very little elevated. The horizontal portion is very massive
and rounded to support the great molar teeth ; it unites
with its fellow in front in a narrow, prolonged, spout-like
symphysis.
The stylohyals are forked at their upper extremity, the
posterior process being greatly developed. They taper
below to a point which is connected by a long ligament with
the basihyal. The thyrohyals are long, compressed, and
ankylosed to the basihyal.1
1 See A. H. Garrod. Proc. Zool Soc. 1875, p. 365.
CHAPTER XII.
THE SKULL IN THE CETACEA AND THE SIRENIA.
Order Cetacea. — The animals of this order exhibit some
remarkable modifications in the characters of the skull.
I will first select for description that of a young example
of one of the Odontoceti or Toothed Whales, the common
round-headed Dolphin or Globicephalus of our coasts. Fig.
6 1 represents a vertical median section of this skull. It will
be seen that the cerebral cavity is of a very unusual shape,
being short and broad, but extremely high and contracted
above — in fact, somewhat in the form of a truncated cone,
with rounded edges. The bones of the basicranial axis are
curved upwards at each extremity. They consist of the'
ankylosed basioccipital (BO) and basisphenoid (BS) sepa-
rated by a vertical fissure from the presphenoid (BS) and
mesethmoid (ME), which are also ankylosed, though their
original line of separation can still be traced. The pituitary
fossa scarcely forms a distinct concavity, and the clinoid^
processes are almost obsolete. The mesethmoid is very;
large, and consists of (i) a high and broad vertical plate,
which closes in the vacuity between the frontals in the
anterior part of the cerebral cavity, and corresponds to the
cribriform plate of the ordinary Mammal, though with but few
Id small perforations ; (2) an anterior rod-like, somewhat
1 86 THE SKULL. [chap.
compressed, pointed prolongation from the lower part of this
plate, which extends forwards in the groove of the vomer
( Vo) almost to the extremity of the rostrum, and which in
great part remains permanently cartilaginous. This corre-
sponds with the septal cartilage of the nose of other Mam-
mals, although owing to the altered position of the nares it
has here little relation with these passages.
The cranial cavity is formed chiefly of the cerebral fossa,
the cerebellar fossa being relatively small, and the olfactory
fossa entirely wanting.
The optic nerve passes out through a deep notch, some-
times a foramen, in the hinder border of the orbitosphenoid.
The alisphenoid is not perforated, the foramen rotundum
being confluent with the large sphenoidal fissure, and the
foramen ovale with a large infundibuliform opening between
the alisphenoid, parietal, exoccipital, basioccipital, and basi-
sphenoid, in the bottom of wThich is seen the inner surface
of the periotic (Per), which in the Cetacea makes no projec-
tion into the cerebral cavity. The anterior part of this
opening corresponds to the foramen lacerum medium with
the foramen ovale, the hinder part to the foramen lacerum
posterius.1 The squamosal (Sq) appears in the outer bound-
ary for a very small space, between the parietal and the
exoccipital. The condylar foramen pierces the exoccipital,
near its anterior edge. The large or nearly circular carotid
canal has a peculiar position, passing through the basisphe-
noid, near its middle, in a direction from below upwards,
forwards, and inwards.
The bones forming the walls of the cranial cavity are dis-
posed in a very remarkable manner. The occipital surface
1 In the adult of the same species, the fommen ovale is separated
from the large opening common to the seventh and eighth pair of nerves
by a strong bony partition formed by the ossified tentorium cerebelli.
CETACEA.
[87
is of great size, and slopes upwards and forwards. The
foramen magnum is large, and looks directly backwards ; its
lower lateral margins are bounded by large oval condyles?
which meet in the middle line below, and are formed by
Na IP
EjcO
Fig. 61. — A section of the skull of a young Dolphin {Globicephalus melas\ \. PAfx
prtmaxilla ; Mx max<lla ; MR ossified poitiun of tne mesethmoid; an anterior
nares ; Na nasal ; IP interparietal ; Fr frontal ; Pa parietal ; SO supraoccipital ;
ExO exoccipital ; BO basioccioital ; Sq squamosal ; Per periotic ; AS alisphenoid ;
PS presphenoid ; Pt pterygoid ; fin posterior nares ; PI pa^tine ; Vo vomer ;
* symphysis of mandible; id inferior dental canal ; cp coronoid piocess; erf con-
dyle ; a angle ; s/i stylohyal ; bh basihyal ; th thyrohyal.
the exoccipitals, with a small portion of the basioccipital.
Above the foramen, the immense supraoccipital (SO), with
which an interparietal (IP) is ankylosed, extends forwards
beyond the vertex, to be wedged in between the frontals,
completely excluding the parietals from the upper region of
1 88 THE SKULL. [chap.
the cranium. These latter (Pa) form the greater part of the
sides of the narrow high temporal fossae, and are ankylosed
with the supraoccipital above, although the different elements
of the occipital are still distinct. The frontals (Fr) are broad
from side to side, being prolonged outwards into the arched
supraorbital plates, but are almost entirely covered by lamel-
liform extensions of the maxillae, which leave but a thin
strip of the frontals visible on the external surface of the
cranium. The temporal fossa is bounded below and in
front by a stout postorbital process of the frontal, very nearly
meeting the broad zygomatic process of the squamosal. The
orbit is elongated from before backwards ; at its anterior
extremity is a rounded antorbital prominence, formed by
the junction of the maxillae, frontal and malar; below, it is
bounded by a long and very slender styliform zygomatic
process of the malar, which arises from near the anterior and
inner angle of the body of the bone, and passes backwards,
slightly curved downwards, to articulate with the extremity
of the zygomatic process of the squamosal. There is no
distinct lachrymal bone, or canal.
The special modification of the bones of the face has
relation chiefly to the peculiar position of the nasal passages,
which, instead of passing forwards above the roof of the
mouth to the anterior extremity of the face, are directed
upwards and somewhat backwards towards the vertex of the
cranium; the external narial orifices being situated quite on
the top of the head, the part which first appears above the
surface of the water when the animal rises for the purpose of
respiration. The whole nasal cavities are small, and they are
(as far as concerns their bony walls) simple canals, entirely
destitute of turbinals. Though their direction is in the main
vertical, they are not straight, but curve round the anterior
end of the brain cavity, both upper and lower orifices (an and
xii.] CETACEA. 189
pn) being directed somewhat backwards. They are com-
pressed before backwards above, but wider and more round
below. The nasal bones (No), instead of being lamelliform,
and roofing over the nasal passages, are reduced to nodular
masses, lying in depressions in the frontals, but forming as
usual the hinder boundary of the anterior narial openings.
In front of these openings, the face stretches out into
an elongated, depressed, pointed beak, or rostrum, formed
by the premaxillae and maxillae surrounding the vomer and
mesethmoid cartilage. The premaxillae send prolongations
upwards to form the lateral boundaries of the narial orifice,
and it is remarkable that these are not quite symmetrical,
that of the left side being the shortest. The orifice itself,
moreover, is rather inclined towards the left. Between the
antorbital process of the maxilla and its rostral prolongation
ta deep notch, the "antorbital notch." The upper surface
the face, near this notch, has several very large foramina
• the transmission of branches of the fifth nerve.
The elongated, pointed, and convex palate is formed
chiefly by the maxillae (Fig. 62, Mx), the premaxillae (PMx)
only appearing for a short space near the apex. Behind
the maxillae, the palatines (PI) are somewhat wide laterally,
but towards the middle line form an exceedingly narrow
strip, inserted between the maxillae and the pterygoids (Ft);
the latter are greatly developed; besides forming the outer
wall of the posterior nares, each sends a lamella inwards,
which nearly (in most Dolphins, completely) meets its fellow
in the middle line, and so prolongs the bony palate back-
wards. This process, moreover, is reflected outwards again
from its inner or lower edge, and, joining with a projecting
plate from the palatine, encloses a large cavity, open only
behind, which contains the post-palatine air sinus. The
mer ( Vo) is of great size, extends forwards nearly to the
190
THE SKULL.
[chap.
apex of the rostrum, embracing the mesethmoid cartilage,
and posteriorly reaches for a considerable distance beneath
FM£
Fig. 62. — Under surface of the cranium of a young Dolphin (Globicephalus melas), ),.
BO basioccipital ; ExO exoccipital ; Per posterior (mastoid) process of periotic ;
Ty tympanic; Sg squamosal; AS alisphenoid ; OS orbitosphenoid ; ZM zygo-
matic process of malar ; Fr supraorbital process of frontal ; Ma body 0/ malar ;
Ft pterygoid ; PI palatine ; Mx maxilla ; PMx premaxilla ; Vo vomer ; gf
glenoid fossa of squamosal ; tg deep groove on squamosal for meatus auditorius
externus, leading to tympanic cavity ; £/" condylar foramen.
the basisphenoid. It forms as usual the inner wall of the
posterior narial apertures. Behind these apertures the base
xii.] CETACEA. 191
of the skull is flat in the middle line, but with prominent
lateral elevations formed by the basioccipital, continuing
the pterygoid ridge backwards. The glenoid fossa (gf) is
a shallow, oval facet, on the inner and under surface of the
zygomatic process of the squamosal.
The periotic region of the skull differs much from that
of most Mammals. On the side of the base of the cranium
is a large recess, bounded below by the prominent edge of
the basioccipital on the inner side, by a projecting edge of
the exoccipital (paroccipital process) behind, by the base
of the zygomatic process of the squamosal externally, and
by a long curved process from the same bone in front, and
communicating with the cranial cavity above by an irregular
opening between the exoccipital and the alisphenoid. In
this recess lies a bone of singular shape which, having only
a ligamentous connection with the surrounding bones, is
easily separated from the rest of the cranium in maceration,
and is hence often wanting in specimens in museums. This
is the united tympanic and periotic, ankylosed in the adult,
but in young specimens still separable into its two com-
ponent parts.
The tympanic (Ty) is a hollow, bullate bone, broad,]
rounded and bilobate behind, and pointed in front. It/
is open above, the hinder part being however in relation
with the periotic. Through the anterior spout-like end the
Eustachian canal passes. At the upper border of the outer
side, rather behind the middle, is an irregular or somewhat
crescentic opening, bounded in front by a prominent lip;
this is the meatus auditorius externus, closed in the living
animal by the membrana tympani.
The periotic is a rounded, very dense bone, characterized
as usual by having on its inner or cerebral side the large
meatus auditorius internus, and on the surface turned
192 THE SKULL. [chap.
towards the tympanic cavity the fenestra ovalis and rotunda.
These two bones are separated along their inner margin by a
narrow fissure, the " tympano-periotic fissure;" but they are
united externally in front of the external meatus auditorius,
and more firmly posteriorly, where a tongue-shaped process
(Per) projects backwards and outwards, fitting into a groove
formed by the junction of the squamosal and exoccipital,
and which is the principal point of attachment of the
tympano-periotic to the rest of the skull. This process
resembles in its relations the mastoid of ordinary Mammals,
but in young Cetaceans it may be seen to be composed of
two nearly equal parts, in close apposition with each, the
inferior being derived from the tympanic, and the superior
from the periotic, so that the latter alone can represent the
"pars mastoidea" of other Mammals.
The mandible (Fig.6i) consists of a pair of nearly straight
compressed rami, wide behind and gradually narrowing to
the symphysis (s), where they usually become ankylosed in
adult animals. The condylar articular surface (cd) is small,
and looks almost directly backwards, being placed on the
hinder edge of the ramus. The coronoid process (cfi) is
quite rudimentary. The angle is square and flat. .The
entrance to the dental foramen on the inner side is ex-
tremely wide and infundibuliform.
The ossified portion of the hyoid in the true Dolphins
consists of a large subcylindrical, slightly curved stylohyal on
each side, and a flattened crescentic median bone, composed
of the ankylosed basihyal and thyrohyals. The stylohyal is
connected above by a slender cartilaginous rod to a small
ossified tympanohyal, which becomes ankylosed to the
periotic in the usual situation, close to the stylomastoid
foramen ; it has also a strong ligamentous attachment to
the prominent rough paroccipital process of the exoccipital.
xii.] CETACEA. 193
Between the stylohyal and the basihyal are one or two dis-
tinct short cartilages articulated together by synovial joints,
one of which occasionally becomes ossified.
In many of the Delphinidce the rostral portion of the skull
proportionally more elongated and compressed than in
le species just described ; notably so in Pontoporia, a South
.merican genus. In this animal the mandible has a very
>ng symphysial portion, the two rami being parallel and
mkylosed for more than half their length, and diverging
>nly in the posterior portion.
The Sousou, or Platafiista, a Dolphin inhabiting the
■ivers of South Asia, has also a remarkably elongated and
>mpressed rostrum and mandible, and the cranial portion
>f the skull presents several structural peculiarities. The
)rbit is extremely small, the temporal fossa large, and
le zygomatic processes of the squamosal are greatly
jveloped. From the outer edge of the ascending plates
>f the maxillae, which lie over the frontals, great crests of
>ne, smooth externally, but reticulated and laminated on
leir inner surface, rise upwards, and, curving inwards, nearly
leet in the middle line, above the upper part of the face.
The Physeteridce, including the genera Zifihius, Hy-
vodon, Physeter, and their allies, present several special
odifications of the skull. The bones of the face and
cranium, meeting at the vertex, are raised so as to form a
more or less elevated transverse prominence or crest behind
the anterior nares, generally curved forwards at its upper
edge. The bone which corresponds to the malar in other
iolphins is usually divided into two, one of which may
present the lachrymal. The pterygoid bones are thick,
oduced backwards, meeting in the middle line for a
►nsiderable space, concave on their outer side, but not
194 THE SKULL. [chap.
involuted to form an outer wall to the post-palatine air sinus.
In some of the Ziphiince, the rostrum is very dense, the
anterior prolongation of the mesethmoid being either
partially or completely ossified, and ankylosed with the
surrounding bones.
In Hyperoodon, the crest at the vertex is high and mas-
sive, being formed by the nasals, the ascending plates of the
premaxillae and maxillae, the frontals and supraoccipital.
Separated from this crest by a depression, there is on each
maxilla, at the commencement of the rostral portion of the
skull, a very thick and high longitudinal ridge.
An easy transition from this cranium leads to that of
the great Sperm Whale or Cachalot (Physeter macrocephalus),
which of all Mammals is perhaps the most modified from
the ordinary type. The transverse vertical crest and the
longitudinal maxillary crests are united, to form the walls
of a great semicircular basin, surmounting the whole of
the back part of the cranium, open only above and in
front. The bones composing this wall are the same as in
Hyperoodon, but excessively expanded and flattened. The
rostrum is broad at the base, gradually narrowing to the
front, and immensely elongated. The great supracranial
cavity lodges the oily substance which, when refined, is
known as spermaceti.
The skull of the Cachalot is remarkable for its want of
symmetry, especially in the region of the anterior narial
apertures, of which the left is very much larger than the
right. In consequence of the small increase in the size of
the brain cavity, compared with that of the external parts of
the head in these enormous animals, the foramina through
which the nerves pass out of the lateral parts of the base
of the skull, are long channels excavated through immense
bony masses. The petro-tympanic bone, which is scarcely
COd
xii.] CETACEA. 195
larger than that of some of the small Dolphins, is situated
at the bottom of such a channel, at the distance of fourteen
inches from the inner wall of the brain cavity. In the
general principle of their conformation, these bones do not
differ from those of the ordinary Dolphins, but the tongue-
shaped backward projection before described is greatly
elongated and laminated, being composed of a large num-
ber of distinct thin plates, only held together by their com-
mon attachment to the tympanic. These fit into grooves
between the squamosal and exoccipital, their extremities
appearing on the outer surface of the skull, and they serve
to attach the petro-tympanic more firmly to the cranium
than is the case in the other Toothed Whales.
The hyoid in Physeter and in the allied genus Kogia is
remarkable for the great breadth and flatness of the basi- and
the thyrohyals, which, moreover, do not usually become
ankylosed, as in most Dolphins.
The cranium of the Whalebone Whales (suborder Mysta-
•eti) never shows that deviation from bilateral symmetry
so frequent in the Toothed Whales. The cranial cavity
has much the same general form, and the bones around are
disposed in a somewhat similar manner, but the parietals
meet at the top of the skull, although completely overlaid
and concealed externally by the great supraoccipiral.
The anterior nares are not directed upwards and back-
wards as in the Dolphins, but approach more in position to
those of the ordinary mammalia, being arched over by the
frontals, which are of considerable antero-posterior thickness
at this part (see Fig. 63, J?r.), and also by moderately-deve-
loped nasals (Na), meeting by a flattened surface in the
middle line. The nares are still near the most elevated part
of the head, and the premaxillae and maxillae, with the
vomer and mesethmoid cartilage, are produced in front of
o 2
1 96 THE SKULL. [chap.
them into a long tapering rostrum, narrow, compressed, and
much arched in the Right Whales (Balcena) ; broader, de-
pressed, and nearly straight in the Rorquals (Balcenoptera).
An essential difference between the Whales and the
Dolphins is the presence in the former of an olfactory organ,
of the same type as in other mammals, though in a compara-
tively rudimentary condition. In the skull of an adult Green-
land Whale (Balcena mysticetus), the olfactory fossa of the
cerebral cavity is eight and a half inches in length, scarcely
more than half an inch high, and one and a half inches
wide. It runs forward from the anterior part of the floor of
the cerebral fossa, through the great mass of bone formed by
the unijari of the frontal, mesethmoid and presphenoid. In
front it divides into two compartments, each somewhat oval
and dilated, with a concave floor, about an inch in extent
in either direction, perforated with foramina. This floor is
the cribriform plate. In the hinder wall of the great narial
passage is a narrow vertical slit, twelve inches in length,
very near the middle line ; this is the opening of the
olfactory chamber of the nasal cavity, which is bounded
by the under surface of the cribriform plate above, by the
flat mesethmoid on the inner side, and has its outer wall
raised into several longitudinal elevations of very simple
character, representing the ethmoturbinal bones.
In the Rorquals {Balcenoplera) the olfactory fossa is less
elongated, the foramina of the cribriform plate larger and
more numerous, and the ethmoturbinals better developed.
The supraorbital processes of the frontals are very long
and narrow in the Right Whales, but broader in the Rorquals;
they are not covered by plates from the maxillae, as in the
Dolphins. The orbit is small and completed below by a
small curved malar, quite different from that of the
Dolphins. There is a small wedge-shaped lachrymal inter-
XII.]
CETACEA.
197
posed between the antorbital processes of the frontal and
maxilla and the malar.
The palate is long and narrow, with a strong keel or
ridge in the middle line. The surface on each side, sloping
upwards and outwards, is perforated by many large foramina
to permit the passage of blood-vessels and nerves to the
matrix of the baleen, or " whalebone," which covers it in
the living animal. It is chiefly formed by the maxilla,
behind which are large palatines and very small and widely
separated pterygoids.
Fr
riG. 63. — Section of the skull of a fcetal Southern Right Whale (Baltzna australis), ft .
PMx premaxilla ; Na nasal ; Fr frontal ; Pa parietal ; SO supraoccipital ; OS
orbitosphenoid ; AS alisphenoid ; EscO exoccipital ; Per periotic ; BO basi-
occipital ; Ty tympanic ; BS basisphenoid ; Sq glenoid articular surface of squa-
mosal ; Pt pterygoid ; PI palatine ; PS presphenoid ; Vo vomer ; M x maxilla ;
cp coronoid process of mandible ; cd condyle ; dg dental groove ; mg remains of
groove which lodged Meckel's cartilage. No part of the mesethmoid is ossified.
The zygomatic process of the squamosal is an immense
■ihedral pillar in Balcena, having the large shallow glenoid
fossa on its under surface removed considerably from the
niddle of the cranium, so as to give sufficient width to the
198 THE SKULL. [chap.
hinder part of the capacious mouth. The periotic and
tympanic are formed much on the same principle as in the
other suborder, and in adult animals are completely excluded
by a considerable distance from the cranial cavity, owing to
the thickness of its walls. Instead of the small flattened
tongue-shaped process projecting backwards from these bones,
there is a long pyramidal tenon-like process, which fits into
a groove in the squamosal and appears on the external sur-
face of the skull like, though more solid than, that of the
Cachalot. In addition to this another process projects out-
wards and backwards, and the two together hold the bones
much more firmly in their place than in the Toothed Whales.
The tympanohyal is a large conical bony mass, with a
truncated base, with which the stylohyal is connected, and
firmly ankylosed by its apex to the periotic.
The mandible differs much from that of the Toothed
Whales. The two rami of which it is composed are not com-
pressed and straight, but rounded and arched outwards, and
never have extensive, flat, opposed symphysial surfaces, but,
curving towards each other, meet at an angle in front, where
they are held together by strong bands of fibrous tissue.
The hyoid arch is formed essentially on the same plan as
in the other Cetacea. The basihyal has a pair of pro-
cesses placed side by side on its front edge, to which
the anterior cornua are attached ; the hinder edge is exca-
vated. In Balana the thyrohyals are cylindrical, and thicker
towards their free extremities. In Balcenoptera musculiis they
are cylindrical and tapering, in B. rostrata, flat and pointed
externally. They always ankylose with the basihyal.
Order Sirenia. — The animals belonging to this order,
restricted at the present time to only two genera, which were
ormerly, but quite erroneously, included among the Cetacea,
XII.]
SIRENIA.
199
have skulls constructed on a very peculiar type, though with
some affinities both to the Ungulata and the Proboscideia.
Many of the special modifications are adaptations to their
ExO
Fig. 64. — Section of the skull ot an African Manati (Manatus senegalensis), \
PMx premaxilla ; Vo vomer; Mx maxilla; Fr frontal ; ET ethmoturbinal ;
ME mesethmoid ; Fr frontal ; Pa parietal ; Sq squamosal ; SO supraoccipital ;
ExO exoccipital ; rer periotic ; BO basioccipital ; Ty tympanic ; AS alisphenoid ;
BS basisphenoid ; PS presphenoid ; Pt pterygoid ; PI palatine ; Mx maxilla ;
cp coronoid process of mandible; cd condyle; a angle; s symphysis; sk stylo-
hyal ; bh basihyal ; th thyrohyal.
aquatic mode of life, and it is in these alone that they
present any resemblances to the Cetacea.
—
200 THE SKULL. [chap.
which may be taken as a type of the order, is remarkable
for the massiveness and density of structure of the bones of
which it is formed. There are no air sinuses in any part,
and most of the bones when cut through appear as hard and
solid as ivory. This character is not peculiar to the skull,
but shared with it by the ribs, and other bones, and must
add much to the general specific gravity of this slow-moving
animal, and aid in keeping it to the bottom of the shallow
water in which it dwells, while feeding on fuci and other
aquatic vegetables.
The cerebral cavity is very different from that of the
Cetacea, being small as compared with the size of the
animal, rather elongated and laterally compressed, truncated
at each end, and with the upper surface flattened. The
cerebellar fossa is large, and altogether behind the cerebral ;
the olfactory fossa is distinct, but small and narrow, bounded
on the inner side by a strongly-developed " crista galli " from
the mesethmoid. The foramen magnum is of great size ; its
plane looks backwards and downwards. The supraoccipital
(SO) is inclined forwards, but does not extend beyond the
ridge bounding the occipital region ; the roof of the cere-
bral fossa of the cranial cavity being formed by the parietals
(Pa). The upper surface of the skull is very narrow, and
flat or slightly arched in the longitudinal direction j its
sides, which are parallel for a considerable distance, join
at a right angle the vertical inner wall of the great temporal
fossa. The squamosal has an extremely massive and
long zygomatic process, flattened on the outer surface, and
posteriorly it sends down a strong triangular post-tympanic
process, articulating with a rough projecting edge of the
exoccipital. Above this, between the squamosal, supra-
occipital, and exoccipital, is a considerable vacuity in the
cranial wall, partly filled by the periotic (Per). The lower
xii.] SIRENIA. 201
vacuity, between the exoccipital and alisphenoid, common
to all skulls, is of immense extent.
The frontals (Fr) are narrow, and run backwards between
the parietals to the upper part of the cerebral fossa of the
brain cavity, and forwards a short distance over the nasal
cavities ; each is produced anteriorly into a long narrow
process, inclining outwards and downwards, between the
temporal fossa behind, and the great anterior narial openings
in front, forming the roof of the orbit. This cavity has a
very prominent margin, especially below and in front, where
it is formed by the very largely developed malar. This bone
sends upwards a conspicuous postorbital process, which
nearly (in some cases completely) meets that of the frontal,
and then is continued below the zygomatic process of the
squamosal as far as the wide shallow glenoid fossa, and
sends down from its middle a broad flattened process with a
thickened and rough inferior border. There is a very small
scalelike and imperforate lachrymal in the usual situation at
the anterior and inner angle of the orbit. The antorbital
foramen of the maxilla is very large.
One of the most peculiar features cf the upper surface of
the face is derived from the position of the anterior nares,
which is a further modification of that met with in the Tapirs
among the Ungulata, and presents some approach to that
so characteristic of the Cetacea. Taken together they form
a large lozenge-shaped aperture, which extends backwards
considerably behind the orbits. Their sides are formed by
the ascending processes of the premaxillse below, and by
the supraorbital processes of the frontals above, no trace of
nasals being found in most skulls, though these bones are
occasionally present in a most rudimentary condition attached
to the edge of the frontals, far away from the middle line,
a condition quite unique among the Mammalia, or only
202 , THE SKULL. [chap.
approached in some of the Dolphins. In the floor of the
great narial opening is seen the vomer ( Vo), of very delicate
structure, and posteriorly the ossified portion of the mes-
ethmoid (ME) of considerable vertical extent. The olfac-
tory chamber of the nasal cavity is greatly compressed from
side to side, and contains a series of simple, longitudinally
placed ethmoturbinals, of which the upper one is very
much the largest. There are no maxilloturbinals in any
skulls which I have examined.
In front of the narial opening the face is prolonged into
a narrow rostrum, formed by the premaxillae, supported
below and at the sides by the maxillae. The under
surface of this is very rugose, and in life supports a horny
plate. There is a large, oval, single, median anterior palatine
foramen. The palate is long and narrow between the two
parallel rows of numerous molar teeth. It does not extend
beyond the last of these, and is formed almost entirely by
the maxillae, the horizontal plates of the palate bones
being very narrow. Behind each row of teeth is a massive
descending rough process, formed by the union of the
palatine, pterygoid plate of the alisphenoid, and true
pterygoid. Posteriorly this has a longitudinal groove
corresponding to the pterygoid fossa. Behind these the base
of the skull contracts in width, leaving a large opening on
each side of the basioccipital, between the alisphenoid in
front and the exoccipital behind, and only partially filled by
the tympanic and periotic.
The two last-named bones are ankylosed together, but not
to any of the other bones of the skull, and though freely
moveable in the dried skull, they are retained in their place
by the overhanging process of the squamosal.
The tympanic (Ty) consists of a large and very solid half-
ring, with its lower margin considerably thickened and
xn.j SIRENIA. 203
produced downwards ; but not forming any bulla, or any
tubular meatus. It is only attached to the periotic by its
extremities, and close to the inner side of its posterior
attachment is a well-marked tympanohyal ankylosed to the
periotic.
The periotic (Per) is large, and rounded externally. It
forms a very considerable part of the inner wall of the
cranium. Besides the portion containing the organ of hear-
ing, it has a large solid upper part, of somewhat kidney
shape, lying in a groove in the squamosal (Sq). This has
a large anterior prominence, to which the anterior limb
of the tympanic ring is ankylosed, and a smaller rounded
posterior projection, corresponding with the mastoid of other
Mammals, and mentioned before as appearing on the ex-
ternal surface of the skull, in the vacuity between the supra-
iccipital, exoccipital, and squamosal.
The foramina at the base of the skull are very few and
simple, as nearly all the nerves appear to pass out either by
the rather small sphenoidal fissure, or by the great confluent
median and posterior foramina lacera. There is a small
optic foramen passing through the middle of the orbito-
sphenoid, but the alisphenoid is imperforate, and even the
condylar foramen in the exoccipital for the hypoglossal
nerve, so constant in all Mammals (except the Elephant), is
represented by a groove (in some instances with a narrow
bridge across it) on the anterior edge of the bone. There
is no distinct carotid canal.
The mandible is exceedingly different from that of the
Cetacea, and is formed of the same dense heavy bone as the
rest of the skull. The rami are firmly united by a symphysis
(s) of moderate extent in front, and diverge widely behind.
The posterior border is of considerable vertical depth, the
condyle (cd), with its obliquely placed, oval, convex arti-
204 THE SKULL. [chap. xii.
cular surface, being raised high above the horizontal alveolar
border. The coronoid process icp) is large and directed for-
wards. The angle (a)is well marked, thickened, and somewhat
inflexed, but does not form a distinct process. The lower
border of the ramus is very thick, rounded from side to side,
and concave from before backwards. The symphysial portion
is compressed laterally, but its upper surface forms a some-]
what expanded, rugose surface, concave in the middle line,
to which a horny plate is attached in the living animal.
In a perfectly adult West Indian Manati (Af. australis),
in the Leyden Museum, the anterior arch of the hyoid has
a single, slender, slightly curved bone (stylohyal), three
inches long, cylindrical at its upper end, and laterally com-
pressed below, attached above by a broad, short ligament,
chiefly to the exoccipital, but also to the squamosal and
tympanic. The basihyal is a broad, flat, reniform plate, and
the thyrohyals are not ossified.
In the other existing Sirenian, the Dugong (Halicore), from
the Indian Seas, the skull resembles that of the Manati in
its essential characters, especially the form of the brain case,
the condition of the tympano-periotic bones, and the form
and situation of the anterior nares ; but it differs mainly in
the great development of the premaxillary bones, which curve
downwards in front, and lodge large descending tusks. The
deep, compressed symphysial portion of the mandible is
bent down in a corresponding manner. The zygoma is less
massive, the orbit is not closed behind, and the lachrymal
bone is more developed. The nasals are absent or quite
rudimentary.
CHAPTER XIII.
THE SKULL IN THE EDENTATA, MARSUPIALIA, AND
MONOTREMATA.
Order Edentata. — The different families of this hetero-
geneous group present some remarkable variations in their
cranial characters.
One of the most extremely modified forms is the Great
Anteater {Myrmecophaga jubata. Fig. 65). The whole skull
is very greatly elongated and narrow, and its upper surface
smooth and cylindriform. The occipital plane slopes upwards
and forwards. The parietals are narrow, but the frontals much
elongated. The olfactory fossa of the cerebral cavity is very
large ; the cribriform plate greatly expanded, and the ethmo-
turbinals much developed, and consisting of very numerous,
delicate lamellae. Anteriorly, the face is produced into a
very long, tubular rostrum, rounded above and* flattened
below, and with terminal nares. This rostrum is composed
of the mesethmoid, ossified for more than half its length,
the vomer, the maxillae, and the long and narrow nasal
bones ; the prem axillae (PMx) being extremely short and
confined to the margin of the anterior nares. There are no
teeth in either jaw. The zygomatic arch is incomplete, the
styliform malar {Ma) only articulating with the maxilla in
front, and not reaching the very short zygomatic process of
the squamosal (Sq). The lachrymals (Z) are distinct, and
206
THE SKULL.
[chap.
have a large perforation in front of the margin of the orbit.
There are no postorbital pro-
cesses to the frontals, or any
other demarcation between the
orbits and the temporal fossa.
The palate is extremely
elongated, and produced back-
wards as far as the level of
the external auditory meatus
by the meeting in the middle
line of the largely-developed
pterygoids (Ft). The glenoid
fossa is a shallow oval facet,
with its long diameter from
before backwards.
The periotic, tympanic, and
squamosal are ankylosed toge-
ther. A small mastoid portion
appears on the outer side of
the skull, forming a roughened
surface between the squamosal
and the exoccipital. The tym-
panic (Ty) is somewhat trian-
gular in form, slightly bullate,
and not prolonged into an au-
ditory meatus. In front of the
tympanic cavity, and freely
communicating with it, is a
FMx?$$jf considerable air sinus, formed
Fig 65.— Under-surface of the cranium between the pterygoid (Pt) and
of the Great Anteatei {Myrmeco/>haga
jubaia), \. so supraoccipnai ; bo basi- the ahsphenoid (^4.5j,and caus-
occipital ; ExO exoccipital ; Ty tym- . . . . ,
panic ; Pt pterygoid ; Sq. squamosal ; ing an OVal prominence 111 the
A S ahsphenoid ; OS orbitosphenoid ; ., c , ,
At malar ; L lachrymal ; PI palatine; Side 01 the palate.
Atx maxilla ; PMx premaxilla.
xin.] EDENTATA. 207
In another species of the same genus, M. Tamandua,
there is a second similar but smaller sinus, anterior to this,
in the side of the palatine bone.
The mandible is very long and slender, with an exceed-
ingly short symphysis, no distinct coronoid process, and
a slightly elevated, elongated, flattened, condylar articular
surface.
The anterior cornu of the hyoid is very long and slender.
Its proximal end is ligamentous, and its distal portion con-
tains two distinct ossifications. The thyrohyals become
united by bone to the very narrow basihyal.
The skull of the little Tree Anteater (Cydothurus didac-
tylus) besides being shorter, and much arched in the longi-
tudinal direction, differs mainly from that of Myrmecofihaga
in not having the long canal of the posterior nares closed
by bone below, as neither the pterygoids nor the greater
part of the palatines meet in the middle line. The tym-
panic is more bullate. The mandible has a prominent,
narrow, recurved coronoid, and a well-developed angular
process ; it is strongly curved downwards in front.
In the Armadillos of the restricted genus Dasypus, in-
cluding D. sexcinctus, villosus, and minutus, the cranial
portion of the skull is broad and depressed ; the facial
portion triangular, pointed in front, and much depressed.
The anterior narial orifice is small, terminal, and directed
forwards and downwards. There is a completely ossified
tympanic bulla, ankylosed with the rest of the skull, per-
forated on the inner side by the carotid canal, and con-
tinued externally into an elongated bony meatus auditorius,
with its aperture directed upwards and backwards. The
zygoma is complete. The pterygoids are small, and send
no horizontal plates inwards to complete the bony palate, as
i in the Anteater. The mandible has a well-marked ascending
208 THE SKULL. [chap.
posterior portion, supporting a transversely extended con-
dyle, and a high, slender coronoid process.
In all the other genera of Armadillos the tympanic is al
mere half-ring, loosely connected with the surrounding bones.
The hyoid arch is strongly ossified. The anterior cornu
consists of three bones. The thyrohyals ankylose with the
basihyal.
In the Scaly Anteaters or Pangolins (genus Manis), the
skull is somewhat in the form of an elongated cone, with
the small end turned forwards, and very smooth and free from
crests and ridges. The occipital plane slopes upwards and
forwards. There is no distinction between the orbit and
the temporal fossa, which together form a small oval depres-
sion near the middle of the side of the skull. There are
short zygomatic processes on the maxilla and the squa-
mosal, but the arch is incomplete in most species, owing to
the absence of the malar. There is likewise no distinct
lachrymal bone. The plane of the anterior narial aperture
looks forwards and upwards. The premaxilla is produced
along the side of the nasals towards, but not reaching, the
frontals. The palate is long and narrow. The Pterygoids
extend backwards as far as the tympanies, but do not meet
in the middle line below. The tympanic is ankylosed to
the surrounding bones, and more or less bullate, but not
produced into a tubular auditory meatus. The hinder part
of the squamosal is often dilated with air-cells, forming a
rounded prominence at the outer posterior angle of the skull.
The rami of the mandible are edentulous, very slender
and straight, without any angle or coronoid process. From
near the anterior extremity of the upper edge a sharp conical
tooth-like process projects upwards and outwards. The
condyle is a slightly expanded flattened surface, not raised
above the level of the rest of the ramus.
xiii.] EDENTATA. 209
In the Cape Anteater {Orycteropus) the skull is moderately-
elongated and dilated in front of the orbits. The facial por-
tion is subcylindrical and slightly tapering. The lachrymal
forms a considerable part of the side of the face. The
zygoma is complete and slender. There is a small post-
orbital process. The premaxillae are short and widely
separated from the frontals. The palate ends posteriorly in
the thickened transverse border of the palatines, and is not
continued back by the pterygoids. The tympanic is annular,
and not ankylosed to the surrounding bones.
The mandible is slender anteriorly, but rises high pos-
teriorly, with a slender recurved coronoid, and an ascending
pointed process on the hinder edge below the condyle;
which is small, oval, and looks forwards as much as up-
wards.
The hyoid arch is completely ossified. The basihyal
is a thin bar, narrow in the middle. The thyrohyals are
not ankylosed to it. The ceratohyals are thick. There is
a small (apparently epiphysial) ossification between the epi-
hyal and the stylohyal.
The Three-toed Sloths (genus Bradypus) have a high
compressed skull, and an extremely short face. The cranial
cavity is oblong, and rather high and compressed. There is no
fossa on the periotic for the flocculus. The olfactory fossae
are large. The plane of the occiput is vertical, or sloping
slightly forwards and upwards. The frontal region is dilated
with air sinuses. There is a small postorbital process.
The lachrymal is very small, and the canal is external to
the margin of the orbit. The malar is attached to the
frontal, lachrymal, 'and maxilla in front, curves downwards
and outwards, and then divides into a descending and a high
ascending branch; but neither of them join the straight
210 THE SKULL. [chap.
zygomatic process of the squamosal. The nasals are short
and wide. The anterior nares are nearly vertical, or rather
inclining downwards. The premaxillae are exceedingly
rudimentary, only the palatal portion being present, without
any ascending process j they unite with each other across
the middle line, but not with the maxillae, hence they are
generally lost in macerated skulls. The palate is narrow,
especially posteriorly, and not produced behind the molar
teeth. The pterygoids form large plates with prominent
rounded borders, compressed in some, and inflated in
other species. The glenoid fossa is narrow from side to
side. The tympanic, squamosal, and periotic are ankylosed
together. The former forms a considerable bulla, but no
tubular meatus. There are large supratympanic air sinuses
and a well-marked ossified tympanohyal.
The mandible has a comparatively high horizontal por-
tion, rounded in front with a very small median triangular
process at the upper border. The coronoid process is high
and slender. The condyle is small ; its articular surface is
convex from side to side, short and nearly straight from before
backwards. The angle forms a broad compressed posterior
projection, with a slightly incurved lower border.
The stylohyals are large, compressed, and curved, with a
prominent posterior process near their upper end. The
basihyal is small, and ankylosed with the thyrohyals, so that
they form together a V-shaped bone.
The skull of the Two-toed Sloth (Cholcepus didactylus),
though generally similar to the last, presents in some points
marked deviations from it. Even in aged specimens, in
which almost all the sutures are obliterated, the tympanic
is a mere ring, incomplete at the upper margin, and but
slightly connected with the other bones around. The
premaxillae are more developed, and become ultimately
xiii.] EDENTATA. 211
ankylosed with the maxillae. The pterygoids are much
smaller, but sometimes are bullate.
The upper margin of the mandible is produced anteriorly
into a spout-like process. The condyle is scarcely above
the level of the molar teeth, and is wide from side to side.
The angular projection is smaller and thicker.
The hyoid (in an old specimen) has a strongly ossified
anterior arch, consisting of two bones of nearly equal length,
the proximal one with a stout rounded process projecting
backwards and outwards from near its upper end.- The
second is bent at a right angle near its lower end, and may
result from the ossification of two elements. The basi- and
thyro-hyals are ankylosed to form a wide U-shaped bone.
. Order Marsupialia. — The skull of the large carnivorous
Marsupial, the Thylacine {Thylacinns cynocephalus), resembles
so closely that of a Dog in its general aspect, that it will be
well to commence an account of the peculiarities of the
crania of Marsupials generally by comparing these two
skulls.
It will be seen by the section (Fig. 66) that the brain cavity
of the Thylacine is very much smaller than that of the Dog
(Fig. 45) in relation to the size of the rest of the cranium,
or to that of the whole animal, a sign of great inferiority
of organization. This diminution affects chiefly the cere-
bral fossa ; the cerebellar fossa is nearly equal in size,
but it is placed more directly behind the cerebral, and is
not in the least overlapped by it, as in the Dog. The
occipital plane is vertical, or even inclining forwards above.
The tentorial plane is nearly horizontal. The olfactory
fossa, though smaller in vertical extent than that of the Dog,
is more produced anteriorly. Thus in form, as well as in
relative size, the cerebral cavity is far more reptilian than
that of the Dog. The basicranial axis is very straight, and
p 2
THE SKULL.
[CHAP.
is continued forwards in the same line by the basifacial
axis. The pituitary fossa forms no distinct depression, and
there are no posterior clinoid processes. The ossified
portion of the mesethmoid {ME) is extensive, and termi-
nates anteriorly in a nearly vertical line. The vomer ( Vo)
is very shallow from above downwards. The turbinal
Fig. 66 — Section of the skull of the Thylacine (Thylacinns cynocepkalus), \.
MT maxilloturbinal ; E T ethmoturbinal ; ME ossified portion of mesethmoiu ;
Fr frontal; Pa parietal; SO supraoccipital ; ExO exoccipital ; Per periotic ;
BO basioccipital ; Sq squamosal ; AS alisphenoid ; BS basisphenoid ; OS orbito-
snhenoid; PS prespheiioid ; /"/pterygoid; PI palatine; Vo vomer; Mx maxilla ;
PMx premaxilla ; cd condyle of mandible ; a angular process.
bones resemble generally in their extent and disdosition
those of the Dog.
Externally the conformation of the zygomata, temporal
fossae, orbits, maxillae, premaxillae, and nasals are strikingly
similar to those of the Dog; but the lachrymal bone of the
Thylacine is larger both within and without the orbit, and
it has one perforation within, and either one or two just
xin.] MAKSUPIALIA. 2 1 3
external to the margin of the orbit. The palate has a pair
of large oval vacuities between the molar teeth. The ptery-
goid plates are very thin. The glenoid fossa is rather more
expanded from before backwards than in the Dog, and the
malar extends so far back beneath the zygomatic process of
the squamosal as to form the outer edge of the glenoid cavity.
The postglenoid and paroccipital processes are developed
much as in the Dog ; the former has rather greater lateral
extent. A great difference is seen in the condition of the
tympanic, which in the Thylacine is quite rudimentary, forms
no bulla, and is not ankylosed to the other cranial bones,
so that in the dried skull it is nearly always detached. On
the other hand, the hinder part of the alisphenoid is dilated
into an oval thin-walled capsule, which is connected with
the front of the tympanic cavity. The periotic is not
ankylosed to the squamosal, has a very large floccular fossa
within, and a mastoid portion forming a long, narrow strip
visible in the outer side of the occipital surface of the skull,
between the squamosal and the exoccipital, almost exactly
as in the Dog. The exoccipital is perforated by the con-
dylar foramen ; but the carotid foramen, instead of passing
through the inner edge of the tympanic bulla, perforates
the basisphenoid, passing very obliquely forwards and in-
wards. The large alisphenoid is pierced by the fora-
men ovale near its posterior margin, and by the foramen
rotundum near the front. The orbitosphenoid is very small,
and not perforated, the optic nerve passing out through the
sphenoidal fissure.
The ascending ramus of the mandible is less elevated
than that of the Dog, the condyle being almost on the same
level as the- molar teeth. The coronoid process has a more
backward inclination. The masseteric fossa has a powerful,
ternally projecting lower border, and the angular process
.
2i4 THE SKULL. [chap.
is flattened from above downwards, and inclined consider-
ably inwards.
The hyoid (Fig. 67) is constructed on a totally different
type from that of the Dog. It consists of a small flat
lozenge-shaped basihyal (bh), surmounted by flattened,
triangular, imperfectly ossified ceratohyals (c/i), partially
ankylosed to the basihyal, and without any other ossifica-
tions in the anterior cornua. The thyrohyals (th) are tole-
rably long, flattened bars, meeting in the middle line at their
Fig. 67. — Upper surface of hyoid of Thylacine (nat. size), bh basihyal ; ch ceratohyal
(anterior cornu) ; th thyrohyal (posterior cornu).
attachment to the basihyal, and with their free, or laryngeal,
extremities expanded, but still cartilaginous in the perfectly
adult animal from which the above figure was taken.
All the other animals of the sub-class which contains
the single order Marsupialia, however their skulls may
differ in general appearance from that of the Thylacine,
agree with it in the following important particulars : —
1. The brain cavity is small, with the cerebellar fossa
entirely behind, and the olfactory fossa entirely in front
of the cerebral fossa. There are, however, degrees in
this respect, the Kangaroos representing one extreme, with
xiir.] MARSUPIALIA. 215
large, more vaulted cerebral fossa, and the Opossums and
Dasyures the other.
2. There is no distinct pituitary fossa, orclinoid processes.
3. The ossification of the mesethmoid is extensive, and
has an abrupt, nearly vertical, anterior termination.
4. The nasal bones are large, and the anterior nares more
or less terminal.
5. The zygoma is complete, but the orbit has not a
perfect posterior boundary.
6. The malar is large, reaches the lachrymal anteriorly,
and extends posteriorly beneath the zygomatic process of
the squamosal, to form part of the outer wall of the glenoid
fossa.
7. The perforation in the lachrymal is usually upon, and
frequently external to, the anterior boundary of the orbit.
8. The ascending processes of the premaxillse never
quite reach the frontals.
Pq. The palate has often, but not always, large vacuities
ar its posterior margin.
10. The pterygoids are always small and lamelliform.
11. The alisphenoids are more or less dilated, and form
the anterior wall of the tympanic cavity, which is often quite
open below in the dried skull. It may be noted as a special
peculiarity in the Kangaroos, that the alisphenoid extends
backwards beneath the tympanic cavity to join the long
paroccipital process of the exoccipital. In the larger mem-
bers of the group it can scarcely be said to form a distinct
bulla, but in some of the Hypsiprynmi (Rat Kangaroos) it is
immensely , expanded. In the Koala (Phascolarctos), the
alisphenoid bulla is very large, elongated vertically and
compressed, having a very similar appearance in fact to the
tympanic bulla of the Pig.
12. The tympanic is small, simple, and annular in
s
2l6
THE SKULL.
[chap.
some ; in others it forms a short external auditory meatus,
but it is never ankylosed to any of the other bones of
the cranium,
13. The periotic sends backwards a distinct mastoid,
which appears as a narrow strip of bone of considerable
vertical extent, between the squamosal and exoccipital, on
the side of the occipital region of the skull.
14. There are almost always conspicuous paroccipital
processes.
15. The internal carotid artery perforates the basi-
sphenoid.
16. The optic foramen is confluent with the sphenoidal
fissure.
17. The mandible has {Tarsipes excepted) an inverted
border to the angle.
X
Fig. 68. — Upper surface of hyoid of
Wombat {Phascolomys latifrons). bh
bashyal ; ch ceratohyal ; s/i stylohyal;
th thyrohyal.
Fig. 69. — Hyoid of Kangaroo {Macro-
pus), eh epihyal ; bh basihyal ; th
thyrohyal.
18. The hyoid has a small, more or less lozenge-shaped
basihyal, broad ceratohyals, the remainder of the anterior
cornu usually unossified, and stout, somewhat compressed
thyrohyals.
Order Monotremata. — Both the animals of this group
present very singular modifications of the cranium.
The cerebral cavity, unlike that of the lower Mar-
supialia or the Reptiles, with which they have so many
II.]
MONOTREMATA.
217
structural affinities, is large and hemispherical, flattened
below and arched above, and about as broad as long. The
broad cribriform plate of the ethmoid is nearly horizontal.
The walls are very thin, and smoothly rounded externally,
and the sutures become completely obliterated in adult
skulls, so that it is very difficult to trace out the boundaries
of the component bones. In both species, the broad occi-
pital region slopes upwards and forwards, and the face is long
and much depressed, though of very different shape in each.
In the Echidna (Fig. 70) the squamosal is large and very
compressed, the zygomatic process arising very far forward ;
the slender horizontal zygoma being completed by a styliform
malar, confluent with the maxilla.
The face is produced into a long
tapering rostrum, rounded above
from side to side, and concave
below in the same direction.
The anterior nares form an oval
opening on the upper surface near
the apex, bounded entirely by the
premaxillae, for the nasals do not
appear to reach so far forwards.
The alveolar borders are narrow
and rounded, without trace of
teeth. The palate is produced
backwards, by very large palatine
bones (PI), considerably beyond
the glenoid fossa. The narial
canals have very little extent ver-
tically, but the true Olfactory Fig. 70.— Under surface of cranium
, ... of Echidna {Echidna hystrix), f .
chambers are large, and provided bo basioccipitai ; Exo exocci-
• , , 1 • 1 , • , pital; Per perintic ; m malleus;
With Complex tUrbinals, Which, in sq squamosal ; Ty tympanic ; Pt
•1 . , - , . pterygoid ; PI palatine ; Mx max-
accordance with the horizontal ilia ; pmx premaxiiia.
2i 8 THE SKULL. [chap.
position of the cribriform plate, are mostly placed verti-
cally.
The pterygoids (Pt) are flattened, horizontal, oval plates, '
attached to the obliquely truncated postero-external extremi-
ties of the palatines, and form part of the floor and the inner
wall of the tympanic cavity, an arrangement not met with in
any other Mammal. The tympanic (Ty) is a very slender
ring, incomplete for a small space at the upper and outer
end, and does not become ankylosed to the periotic. The
latter [Per) is large, has no fossa for the flocculus, sends out
a large expansion (pterotic), forming a portion of the cranial
wall between the squamosal, parietal, and occipital, the
lower and hinder part at least of which corresponds with
the mastoid portion.
Each ramus of the mandible is a mere slender style, with-
out any ascending portion, and with but rudiments of
coronoid process and angle. The condyle is very small,
elongated from before backwards, and very narrow.
Fig. 71. — Lower surface of hyoid of Echidna {Echidna hystrix). eh epihyal
ch ceratohyal ; bh basihyal ; th thyrohyal.
The hyoid (Fig. 71) has a well-ossified, transversely
extended, flattened and arched (with the concavity for-
wards), basihyal (bh). The anterior cornu has only two
ossifications {ch and eh), apparently the epi- and cerato-hyal,
as the upper one has a long ligamentous connection with
xiii.] " MONOTREMATA. 219
the cranium in the situation of the stylohyal. There are
broad, flattened, curved thyrohyals {th), expanded at their
laryngeal extremities.
n the Ornithorhynchus the brain case is smaller than in
the Echidna, and rather more depressed ; very broad behind,
and narrowing anteriorly. The olfactory fossa is compara-
tively small. There are well-marked posterior clinoid pro-
cesses. The falx cerebri is largely ossified, forming a strong
median partition to the upper part of the cerebral cavity.
The zygoma is compressed, and of considerable vertical
depth, and sends up a well-marked postorbital process ; its
hinder root arises very far back on the cranium.
The glenoid fossa is wide and concave transversely. The
zygomatic process of the maxilla is widened inferiorly into
an oblong, concave, roughened surface for the attachment of
the horny plate, which takes the place of the molar teeth.
The face is broad and much flattened. It runs out
anteriorly into two diverging processes, each formed by* the
premaxilla, supported by a pointed process of the nasal on
the inner, and the maxilla on the outer, side. These bend
towards each other at their extremities, but do not meet in
the middle line. They support the partly horny, partly
membranous beak, which fills up the space between them,
and extends considerably on each side and in front. There
is a distinct median ossification in the triangular interval
between the diverging premaxillary bars, placed in, or in
front of, the anterior extremity of the mesethmoid cartilage,
and apparently corresponding to the so-called " prenasal J'
of the Pig. The infraorbital foramen is very large, cor-
responding to the large size of the nerves distributed to the
sensitive sides of the beak. The periotic has a wide and
floccular fossa.
deep
220 THE SKULL. [chap. xiii.
The mandible has, rather behind the middle of each
ramus, an oblong expansion for a horny tooth, corre-
sponding to that on the maxilla. Behind this it curves
gradually upwards to the expanded and transversely ex-
tended articular surface. There is no distinct angle, the
coronoid process is small and directed much inwards, and
on the external surface there is a very deep masseteric
fossa. Anteriorly the rami of the mandible have a very,
slight symphysial connection, in front of which their ex-
panded, flattened terminations again diverge from each
other. The apertures for the entrance and for the exit of
the branches of the inferior dental nerve are remarkably
large.
CHAPTER XIV.
THE SHOULDER GIRDLE.
Having finished the consideration of the axial portions of
the skeleton, we now turn to the appendicular parts, which
consist of two pairs of limbs, anterior and posterior.
The anterior limb is present, and fully developed, in all
Mammals, being composed of a shoulder girdle and three
segments belonging to the limb proper, viz. the upper arm
or brachium, the fore-arm or antibrachium, and the hand or
menus.
The Shoulder Girdle in the large majority of Mammals
is in a comparatively rudimentary, or rather modified, con-
dition. Its true structure and its relations to the pelvic
girdle can only be understood by a reference to its condition
in the lower vertebrates.1
Each side of the girdle consists primitively of a curved
rod of cartilage, placed vertically (in the horizontal position
of the body), the upper or dorsal end being free, vthe inner
side lying upon, though not united with, some of the anterior
thoracic vertebrae or ribs, and the inferior or ventral end
being attached to the side of the presternum.
1 On this subject see W. K. Parker's valuable work before cited, and
also Gegenbaur's " Untersuchungen zur Vergleichenden Anatomie," 2tes
Heft, 1865.
222 THE SHOULDER GIRDLE. [chap.
Near, or rather below, the middle of the outer surface of
this rod is a more or less cup-shaped depression, the glenoid
cavity, to which the head of the humerus, or bone of the
upper arm, is articulated. The whole rod is separated at
this spot into two divisions, which ossify from separate
nuclei. The upper or dorsal division is the scapula, the
lower or ventral division is the coracoid.
In all Mammals above the Ornithodelphia the greater part
of the coracoid is aborted, but a portion of its upper ex-
tremity always remains attached to the scapula as a process,
or sometimes as a most inconspicuous nodule, and occa-
sionally rudiments of the lower end are found attached to
the sternum. The scapula, on the other hand, is always
greatly developed.
A supplementary bone, developed in a different manner,
being, at least in the greater part of its extent, ossified from
membrane,1 frequently forms an anterior bar, in front of the
coracoid, passing between the scapula and the anterior end
of the presternum ; this constitutes the clavicle. It is often
rudimentary, and very frequently entirely absent, in Mammals.
Though the scapula may be considered as essentially
an elongated rod or bar of bone (a condition most nearly
retained in the Mole), it usually has three projecting plates
or ridges arranged around the longitudinal axis, and three
surfaces or fossae bounded by these, the variations in the
extent and form of which give rise to the principal diversities
in the form of this bone in different Mammals.
In the most usual position of the scapula (see Fig. 72), one
of these plates (a/) projects forwards, this is the pnesca*?/ la of
Parker, and its edge constitutes the anterior border (cb) of the
scapula ; another (pf) projects backwards, constituting the
1 When it has a cartilaginous basis (as has been described by Gegen-
baur in Man) this is not a portion of the true primitive shoulder girdle.
XIV.]
GENERAL CHARACTERS.
223
postscapula, and its edge is the posterior border (gb) ; a third
projects outwards, constituting the mesoscapula of Parker,
called more commonly the spine (s). The first-named border
(cb) terminates below by joining the coracoid, and hence, to
avoid the inconvenience of a term which is only expressive
when the bone is in a particular position, it may be called
coracoid border; the second (gb) joins the prominent margin
of the glenoid fossa, and may, for the same reason, be called
FlG 72.— Right scapula of Dog {Cam's famzliaris), J. pf po«tscapular fossa ; af
prescapular fossa ; gb glenoid or posterior border; cb coracoid or anterior border ;
s spine ; a acromion ; gc glenoid cavity ; c coracoid ; ess indicates the position of
the coraco-scapular suture, obliterated in adult animals by the complete ankylosis
of the two bones ; ss suprascapular border.
glenoid border ; the third (s) has a free end, usually more or
less prolonged into a curved, flattened process, called the
acromion (a).
The flat or concave surfaces or fossae between these pro-
jecting lamellae are — (1) the prescapular or anterior fossa
(af), between the coracoid border and the spine, called, in
works on human anatomy, "supraspinous fossa;" (2) the
nP>
224 THE SHOULDER GIRDLE. [chap.
postscapular fossa (pf), between the glenoid border and the
spine, also called " infraspinous fossa ; " and (3) the sub-
scapular fossa, between the coracoid and glenoid borders,
on the side of the scapula opposite to the spine.
The greater part of the scapula is ossified by edostosis (as
the shaft of a long bone), from a single centre, which is
placed not far from the middle of the bone ; but this ossifi-
cation does not extend into a certain portion of the superior
extremity. This part {suprascapula) either remains cartila-
ginous or "is feebly ossified by one or more endosteal
patches, or by the creeping upwards of such deposit from
within the main bone " (Parker). When the spine runs
out into a projecting acromial process, more or less of its
terminal portion is ossified separately as an epiphysis.
The coracoid always ossifies from one or more separate
centres, and remains for some time suturally connected
with the scapula, though firmly ankylosing with it by the
time the animal has attained maturity. Sometimes (as in
the Sloths) it forms a considerable part of the glenoid fossa ;
sometimes (as in most Carnivora and Ungulata) it is a mere
nodule, which becomes blended with the anterior margin of
the fossa.
In the Ornithodelphia (see Fig. 80), as in Birds and Rep-
tiles, the coracoid is largely developed, and articulates with
the presternum, and there is in addition a plate of bone in
relation with its anterior edge called epico)'acoid. A small
-iplate of cartilage or bone, often found attached to the side
j of the presternum in certain Rodents and Insectivores, is
Hconsidered by Parker as representing the epicoracoid of
the Ornithodelphia, and by Gegenbaur as the sternal ex-
tremity of the true coracoid; the middle part of which is |
undeveloped.
The clavicular arch, when completely developed, extends
xiv] GENERAL CHARACTERS. 225
from the free acromial extremity of the spine of the scapula
to the anterior extremity of the presternum.
It consists mainly of an elongated rod of bone, ossified
usually in fibrous tissue, but at either extremity are certain
patches of true cartilage, which may become converted into
bone, or may sometimes degenerate into fibro-cartilage.
These are thus described and named by Mr. Parker. At
the scapular extremity of the clavicle, there is often a piece
of cartilage, considered to be segmented off from the end
of the mesoscapula, and hence called mesoscapular segment
(Fig. 73, mss). At the sternal extremity there may be two
distinct pieces, the one (pe) nearest the clavicle being the
supposed homologue of a displaced fragment of the pre-
coracoid of the lower vertebrates. The one (pst) nearest the
sternum is called omostemum by Parker, and episternum by
Gegenbaur, who considers it homologous with the so-called
episternum (interdavide, Parker) of the Ornithodelphia and
Lizards. *'
Spedal CJiaraders of the Shoulder Girdle in the Different
Groups of the Mammalia.
Order Primates. Man. — In the ordinary erect position of
the human body, the suprascapular border is directed back-
wards and inwards, and is commonly called the " base " or
" vertebral border ,; of the scapula ; the glenoid cavity looks
forwards and outwards; the glenoid border, called "ex-
ternal " or " axillary," looks downwards and rather forwards ;
and the coracoid border is " superior." The postscapular
fossa is much developed, and the suprascapular border is
long, straight, and forms an acute angle with the glenoid
border. At the junction of the coracoid border of the
£ula with the coracoid bone, there is a more or less well-
ted notch (coraco-scapular notch). The spine is well
•
226
THE SHOULDER GIRDLE.
[chap
developed, and the acromion large and curved forwards near
its extremity.
The coracoid forms a well-marked hook-like process ; it
contributes a very small part to the glenoid fossa, and unites
with the scapula about the time of puberty.
The clavicle (Fig. 73, d) is a strongly-developed sigmoid
bone, remarkable for the very early age at which it com-
mences to ossify, in fact before any other bone of the body.
Fig. 73. — The human sternum and right shoulder girdle at a very early period of
development (from an embryo 5J inches long) after Parker, \\. The dotted parts
are still cartilaginous ; the inner surface of the sternum and clavicle, and outer
surface of the scapula are represented, ost omosternum, afterwards developed
into the interarticular fibro-cartilaginous disk. ; pc precoracoid of Parker ; cl shaft
of the clavicle; ntss mesoscapular segment of Parker; a acromion; c coracoid;
gc glenoid cavity of scapula ; gb glenoid border ; cb coracoid border ; af anterior,
or "supraspinous," fossa; ^posterior, or " infraspinous, " fossa; ss suprascapular
border.
The outer extremity is, in the young state, tipped with
cartilage (the mesoscapular segment, Parker, mss), which
ossifies by extension of bone from the rest of the clavicle.
It is connected with the acromion by a small oval, flat,
synovial articulation. The inner end (pc) is also cartilagi-
nous for some time, but ossifies separately by endostosis,
xiv.] PRIMATES. 227
forming an epiphysis. This extremity is attached to the
presternum by synovial articulation, but with a disk-like
fibro-cartilage (ost) interposed, which, according to Parker,
is a degeneration of the " omostemal " element.
In the Gorilla the scapula is very like that of Man. In
the Chimpanzee it is peculiarly elongated, the suprascapular
margin being extremely oblique and long, at the expense
of the greatly reduced coracoid border. The acromion and
coracoid are largely developed. In the lower Monkeys the
form of the scapula is quite different, the coracoid and
glenoid borders being nearly equal, and the suprascapular
border comparatively short and straight.
The clavicle is well developed in all, and all its correlates
are present; the omosternum being generally converted
during growth into a fibro-cartilaginous intra-articular disk.
In the various members of the Order Insectivora there is
a great difference in the construction of the shoulder girdle.
In the Mole {Talpa) and its immediate allies Scalops and
Condyiura, the scapula is extremely high and narrow, and
appears to be ossified entirely from one centre. The spine
and acromion are very little developed. The bone commonly
called clavicle, but which may be a combination of coracoid
and clavicle, is of remarkable form, being nearly cuboid. It
is formed primitively of a mass of cartilage, on the anterior
aspect of which the true (membrane-developed) clavicle is
engrafted. It articulates inferiorly with the presternum, and
superiorly with the humerus, and is connected with the
scapula only by a fibrous band. The two articulations of
the upper end of the humerus, the one with the scapula, and
the other with the coraco-clavicle, are separated by a strong
ligamentous partition.
In the Cape Golden Mole (Chrysochloris) the condition of
these parts is quite different. The scapula is long and
Q 2
228
THE SHOULDER GIRDLE.
[CHAP.
narrow, but flattened. The spine sends a flat process back-
wards near its middle, and a long slender " metacromial"
process from its extremity. The clavicle is very long, slender,
and curved. The " mesoscapular segment " forms a distinct,
though minute, bone between the clavicle and scapula.
In the Shrews (Soricidce) the scapula (see Fig. 74) is
also long and narrow, and the slender acromion ends in
two long diverging processes, of which the anterior (a)
supports the clavicle and the posterior (ma) is called
" metacromion." The mesoscapular segment (mss) is a
Fig. 74. — Shoulder girdle with upper end of sternum (inner surface) of Shrew (Sorex),
after Parker, x 7. ps presternum ; srl first sternal rib ; sr2 second sternal rib ;
ec partially ossified " epicoracoid" of Parker, or rudiment of the sternal extremity
of the coracoid ; ost omosternuro ; pc rudiment of precoracoid (Parker) ; cl cla-
vicle ; itiss ossified "mesoscapular segment;" a acromion; ma metacromial
process ; c coracoid.
/distinct bone. The clavicle (cl) is long and slender. It has
/a small piece of cartilage (pc) attached to its inner end.
'The omosternum (ost) is cartilaginous or partially ossified,
and there is a considerable triangular flattened rudiment
of the inner end of the coracoid (ec) attached to the pre-
sternum.
In the other Insectivora the general form of the scapula
xiv] CH1R0PTERA. 229
is more normal. In Galeopithecus the coracoid is greatly
developed and bifurcated.
All known members of the order have large clavicles, with
the exception of Potamogale, a rare aquatic form from
West Africa.
In the Chiroptera the scapula is large, of an oval form,
and chiefly formed by the postscapular fossa, the anterior
fossa being extremely small. The former is divided into
two or three subfossse by ridges. The spine is short and
moderately high, with a large and simple acromion. The
coracoid is long and curved, often simple (as in Pteropus)
sometimes forked (as in Pipistrellus).
The clavicle is very long and curved. The " mesoscapular
segment " on the outer end is soon lost, but the precoracoid
ossifies separately. The omosternum is reduced to a
cuneiform fibro-cartilage. A rudiment of the sternal end of
the coracoid is often present as " a flat, reniform flap of
cartilage, feebly ossified by endostosis, wedged in between
the clavicle and the first rib " (Parker).
The Rodentia offer great diversities in the condition of
the shoulder girdle. The scapula is generally high and
narrow, and the acromion long. Sometimes the acromio-
scapular notch is so deep, that the actual spine only occupies
a short space near the supra-scapular border, and it is com-
pleted by a very long and slender acromion (as in the Coypu,
Myopotamus). There is often a long metacromion, as in the \
Hare ; but in others, as the Beaver, there is no such process.
The coracoid is always a small blunt hook.
In a few forms the clavicle is altogether absent, in some it
is well developed, and various intermediate stages between
these two extremes are met with. In some species, as the
Guinea Pig and Rabbit, although no trace of this bone is
found at birth, it becomes developed at a later period. In
230
THE SHOULDER GIRDLE.
[CHAP.
both of these it is very short, and is suspended by long
ligaments between the scapula and the sternum. (See Fig.
75.) In many species, as in the Porcupines, in which the
clavicular arch is more complete, the true clavicle is con-
nected with the presternum by a long cartilaginous omo-
sternum. In others, as the Beaver, this is replaced by a"
ligamentous band. Rudiments of the sternal end of the
coracoid are often present, sometimes cartilaginous, some-
times ossified.
Fig. 75.— Shoulder girdl**, with uppei end of sternum (inner surface), of a young
Rabbit {Lcpus cuniculus), after Parker, §. fis presternum ; sr first sternal rib
ost omosternal cartilage ; pc precoracoid cartilage ; cl ossified clavicle ; mss carti-
laginous mesoscapular segment ; c coracoid ; a acromion ; ma metacromion ; aj
anterior fossa ; /£/* posterior fossa.
In the Carnivora the anterior and posterior fossae of
the scapula are nearly equal in area. (See Fig. 72, p. 223.)
The spine and acromion are fairly developed, the latter
often with a broad metacromial process. The coracoid is
much reduced. According to Parker a portion of the
scapula, near the coracoid border, ossifies from an indepen-
dent centre. The clavicle is sometimes absent, and when
present varies much in its development, but is always
rudimentary and suspended in the muscles, never reaching
XIV.]
CARNIVORA.
2\\
either the acromion or sternum. In the Felidce it is slender
and curved, being longer than in any other members of the
order. In the Canidce it is very short, and rather broad and
flat. In most of the Ursidce it is absent.
In the Seals both acromion and coracoid are much re-
duced, but the latter is a distinct bone in young animals,
and forms a considerable part of the glenoid cavity. The
whole scapula is much curved backwards, being almost
sickle-shaped, and the suprascapular epiphysis is very large
id slowly ossified.
In the Eared Seals (Otaria) the scapula has a different
form, the prescapular fossa being very much larger than the
posterior, and with a strong vertical ridge, parallel to the spine.
None of the Pinnipedia have clavicles.
Fig. 76.— Right scapula of Dolphin {Delphinus tiirsio), \. gc glenoid cavity
acromion ; c coracoid ; ^/"postscapular fossa ; rt/prescapular iossa.
Order Cetacea. — In the true Dolphins and nearly all the
Odontoceti the scapula is usually very broad and flat, or fan-
shaped. (See Fig. 76.) The prescapular fossa (a/) is ex-
emely reduced ; the acromion (a) is a long flat process,
tre,
232 THE SHOULDER GIRDLE. [chap.
with a very narrow base of attachment, projecting for-
wards ; the coracoid (c) is rather long, flattened, and parallel
with the acromion.
In the Cachalots (Physeter) the scapula is formed on the
same general plan, but is comparatively high and narrow.
The postscapular fossa is very concave, and the sub-
scapular fossa convex. The Gangetic Fresh-water Dolphin
(P/atanista) has a flat flabelliform scapula, with the pre-
scapular fossa entirely absent, and the acromion placed on
the anterior edge, the spine and the coracoid border having
coalesced.
Among the Whalebone Whales, Balcenopiera has a broad
fan-shaped scapula, like that of the true Dolphins, with
long parallel acromion and coracoid processes, and a supra-
scapular border which remains permanently in a cartilaginous
condition. In the Right Whales (Balcena) the scapula is
more massive and not so broad, and the coracoid is much
reduced. In Megaptera the scapula is triangular, and neither
the coracoid nor the acromion forms a distinct process.
None of the Cetacea possess clavicles.
The scapula of the Sirenia is formed on quite a different
plan, being rather like that of the Seals in shape, narrow,
and curved backwards. The anterior fossa is nearly as
large as the posterior. The spine is moderately developed,
and the slender acromion points downwards. The coracoid
forms a moderate-sized conical process. There are no
clavicles.
In the Ungulata the scapula is always high and rather
narrow. The prescapular and postscapular fossae are often
subequal. The acromion and coracoid are never much
developed. The clavicle is always absent.
The Pecora (see Fig. 77) have all a very large and very
slowly and imperfectly ossified suprascapular region (ss) ;
XIV.]
UNGULA TA.
233
when this is removed, as is almost always the case with
macerated bones, the upper border of the scapula is very
straight. The acromion usually forms a distinct process,
but is quite absent in the Giraffe, which has the longest and
narrowest scapula of the group.
Fig. 77. — Right scapula of Red Deer {Cervus elaphus), \. ss partially ossified
suprascapular border ; pf postscapular fossa ; af anterior or prescapular fossa ;
a acromion ; c coracoid ; gc glenoid cavity.
In the Horse the scapula is long and slender, the supra-
scapular border is rounded, and slowly and imperfectly
ossified. The spine is very slightly developed ; rather above
the middle its edge is thickened and somewhat turned back-
wards ; it gradually subsides at the lower extremity without
forming any acromial process. The coracoid is a prominent
rounded nodule.
In the other Perissodactyles, and in the Pigs and Peccaris,
2J4 THE SHOULDER GIRDLE. [chap.
there is a strongly-marked retroverted triangular process
on the middle of the edge of the spine, and no true
acromion ; but in the Hippopotamus there is a small
acromion and no distinct mid-spinous process. In this
animal the coracoid is rather long and upturned.
In the Tapir the coraco-scapular notch is remarkably
deep.
The Hyrax manifests its affinity with the Ungulata in the
form of the scapula, which is generally triangular, with a
small spine, most prominent and with a retroverted edge
near the middle, and gradually subsiding at each extremity,
so that there is no trace of an acromial process.
The Elephant has a largely developed postscapular fossa
and a narrow anterior fossa. The glenoid border is short,
arrd forms a very prominent angle posteriorly with the
unusually long suprascapular border. The spine is promi-
nent, and has a very strongly marked process projecting
backwards from near the middle and a moderate-sized
acromion. The coracoid is small and rounded.
The Edentata present some very interesting conditions
of the shoulder girdle.
In the Cape Anteater (Orycteropus) the scapula is of
the most normal form, with well-developed acromion and
coracoid. The middle of the border of the spine is thick-
ened and retroverted, and there is a well-marked meta-
cromion. The clavicle is strong, curved, and dilated at its
sternal end.
In the Pangolins (Mam's) the scapula is broad, and rounded
above, the anterior margin gently passing into the superior.
The prescapular fossa is broader than the postscapular. The
suprascapular region remains cartilaginous. The acromion
is very small. The coracoid is extremely rudimentary, but
with a separate ossific nucleus. There are no clavicles.
XIV.]
EDENTA TA.
235
In the Anteaters (Myrmecophagd) the scapula is also broad
and rounded, so that there is no distinct angle between the
anterior and superior margin. The anterior margin is pro
duced, to meet the large adze-shaped coracoid, over the
coraco-scapular notch, converting it into a foramen. The
spine has a triangular process in the middle, and a long
slender acromion, without distinct metacromion. The post-
scapular fossa is nearly equally divided by a second spine.
It is generally stated that there are no clavicles in this
genus, but inaTamandual found rudimentary, flat clavicles,
~q inch in greatest extent, embedded in muscles.
Fig. 78.— Right scapula of Great Armadillo (Priodontes gigas), \. pf postscapula
fossa ; «/prescapular fossa ; gc glenoid cavity ; csn coraco-scapular notch c cora-
coid ; a acromion ; h articular surface for humerus.
The small climbing Cyclothurus didactylus has moderate,
gently curved clavicles.
I In the Armadillos {Dasypodidce) the scapula is rather
236 THE SHOULDER GIRDLE. [chap.
curved ; in many cases it has a distinct articular facet on
its inner surface for the upper end of the humerus. (See
Fig. 78, h.) There is a second spine on the postscapular
fossa, and always a well-developed clavicle.
In the Sloths (Bradypodidce, Fig. 79) the prescapular
region (qf) is larger than the postscapular (/>/). The spine
arises from little more than the middle third of the bone,
vertically. In the' young of both genera of this family the
acromion is a long strip of cartilage connecting the spine
with the end of the coracoid, while the coracoid border of
the scapula and the coracoid bone join each other in front,
Fig. 79 — Right scapula and clavicle of Two-toed Sloth (Choloepiis hoffmanni), §.
qf prescapular fossa ; pf postscapular fossa ; gc glenoid cavity ; a acromion ;
c coracoid ; cs/"coraco-scapular foramen; cl clavicle.
converting the coraco-scapular notch into a small oval fora-
men (csf). This condition remains in the Two-toed Sloth
( Cholccpus) and the extinct Megatherium ; but in Bradypus
the acromion gradually becomes reduced in size, losing its
xiv.] MARSUPIALIA. 237
connection with the coracoid, and finally remains a mere
styliform, or slightly flattened process.
The coracoid in both forms is unusually large, ossifies
ectosteally according to Parker, and has an epiphysis on its
free hook-like extremity.
The clavicle (cl) of Choloepus is well developed, attached
externally to the loop of bone on the scapula, formed by the
united extremities of the acromion {a) and coracoid (<:),
and internally by the intervention of a long fibro-carti-
laginous " omosternum " (degenerating into a mere ligament
in the adult) to the presternum. In Bradypus the clavicle
is very small, and separated by a long interval from the
sternum. It originally articulates at its scapular end, as in
Cholcepus; but in consequence of the atrophy of the acro-
mion, it is left attached to the end of the coracoid, in which
nusual situation it remains through adult life.
In the Marsupialia the scapula is tolerably uniform in
shape. The acromion is long, and the coracoid small, of a
somewhat hooked form, and thick at the base. It ossifies
Ir a separate endosteal nucleus.
The clavicle is present in all known Marsupials except
e Bandicoots (Peramelzdce). It has always a " mesosca-
pular segment " at its outer end, and a " precoracoid seg-
ment " at its sternal end ; these are, however, not ossified.
Most generally it is attached to the acromion by a rather
strong ligament, but in the Wombat by a synovial articu-
lation. It is usually connected to the presternum by omo-
sternal cartilages of varying length, best developed in the
Didelphidm.
The shoulder girdle of the MoNOTREMATA-(see Fig. 80)
differs widely, in many points, from that of any other
Mammal, and far more resembles that of the Lizards.
The scapula is rather long and narrow, and (especially in
un
■
she
2^8
THE SHOULDER GIRDLE.
[CHAP
the Ornithorhynchus) curved backward and pointed, sickle-
like, at its upper end. Instead of three it presents but two
distinct borders and two surfaces ; but the more convex
border (s), which is turned forwards and outwards in its
natural position, has a small projection (a) near its lower
end, which affords attachment to the clavicle, and is evidently
the acromion ; and the whole border may be considered to
represent the spine. Following the indications afforded by
the attachment of the muscles, it appears probable that the
whole inner surface represents the prescapular fossa of the
Fig. 80.— Side view of right shoulder girdle of a young Echidna {Echidna kystrix), §.
ss suprascapular epiphysis; ssf subscapular fos^a; pf postscapular fossa; cb
coracoid border; gb glenoid border; s spine; a acromion; ess coraco -scapular
suture; gc glenoid cavity; c coracoid; ec epicoracoid ; cl clavicle; ic interclav.cle;
ps presternum.
ordinary Mammalian scapula, and that the anterior portion
of the outer surface (pf) is the postscapular fossa, and the
posterior portion of the same surface (ssf) the subscapular
fossa, these two being divided below by a slight ridge (gb),
which runs to the edge of the glenoid cavity, and from which
x i v ,] MONO TREM4 TA. 239
the long head of the triceps muscle takes origin. This
ridge then answers to the posterior or glenoid border of the
ordinary Mammal, and the hinder border of the Monotreme's
scapula (cb) would correspond to the anterior or coracoid
border. If this is really the case, the scapula of the Mono-
treme and that of the Cetacean offer the widest contrast,
the supposed primitive trihedral rod being flattened in
opposite directions. In the Cetacean scapula there are two
nearly parallel surfaces, the postscapular and the subsca-
pular fossae ; while the third, the prescapular fossa, is reduced
to the smallest possible width — quite obsolete, in fact — in
Platanista. In the Monotreme the last-named fossa is so
expanded that the other two, instead of being parallel to
each other on opposite sides of the bone, are brought almost
into one plane, which is parallel and opposite to the sub-
scapular fossa.
*The coracoid [c] is a stout subcylindrical bone, expanded
its extremities, taking at its upper end a considerable
share in the formation of the glenoid cavity, and becoming
firmly ankylosed with the scapula. At its lower end it
articulates to the side of the presternum, just in front of the
first rib.
Placed in front of the inner end of the coracoid is a
broad, flat, shield-like plate of bone (epicoracoid, ec), the
rounded inner border of which passes beyond the median
line, overlapping the corresponding bone of the opposite
side. In the Echidna the left lies superficially to the
right, while in the Ornithorhynchus this disposition is
reversed.
Upon the front end of the presternum, lying below its
anterior continuation (proosteon, see p. 84) and also below
the epicoracoids, is a large azygous T-shaped bone (ic, see
also Fig. 43, p. 85), which has no homologue in any other
24o THE SHOULDER GIRDLE. [chap. xiv.
Mammal, called interclavicle. Its lower end is broad, and
rests on the expanded straight upper margin of the pre-
sternum ; it contracts somewhat above, before dividing into a
pair of nearly horizontal-, slightly curved arms, which extend
outwards towards, though not quite reaching, the acromion.
This bone differs from the presternum, and the small proosteal
plate behind its lower extremity, as well as the coracoids
and epicoracoids, in being developed in membrane.
The clavicles (d) are simple, elongated, slightly curved,
thin, splint-like bones, resting upon the anterior surface of
the arms of the interclavicle, pointed and not quite meeting
internally, and dilated and articulating directly with the
acromion at their outer end.
CHAPTER XV.
THE ARM AND FORE-ARM.
the upper segment of the limb proper there is always
one bone, the Humerus ; in the second segment, two bones
placed side by side, the Radius and the Ulna.
The Humerus (except in some of its extreme modifica-
tions) is more or less elongated and cylindrical. It is
described as having a shaft, and two extremities. The upper
or proximal extremity has a smooth, convex, generally more
or less rounded head (Fig. 81, h), the axis of which is
directed upwards and backwards.1 This, in the living
animal, is covered with , sl thin layer of cartilage, and
articulates by a synovial joint with the glenoid cavity of the
shoulder girdle. The head is marked off from the shaft
very indistinctly by a constriction called the neck, imme-
diately below which, upon the anterior surface of the bone,
are two rough prominences (t and /') for the attachment of
muscles, called tuberosities, separated from each other by a
groove (bg) called the bicipital groove, as the tendon of the
biceps muscle runs in it after arising from the margin of the
glenoid fossa. The tuberosities are generally distinguished
The terms of relative position here used are those which the bone
assumes in the ordinary attitude of a quadruped while standing or
walking.
242 THE ARM AND FORE-ARM. [chap.
as great (t) and s?nall (tf) from their relative size in Man and
most Mammals ; the former is also called external, and the
latter internal, from their relative situation in the most usual
position of the bone ; radial and nbiar are also terms
applied to them in relation to their situation, one on the
side of the humerus with which the radius, and the other on
the side with which the ulna, is connected below.
Fig. 8i- — Anterior surface of right humerus of Wombat Fhascolomys vombatus), \.
h head: bg bicipital groove; t great or radial tuberosity; t' small or ulnar
tuberosity; dr deltoid ridge; sr supinator ridge; cf supra-condylar foramen;
ec external condyle ; ic internal condyle; ar articular surface for radius ; au arti
cular surface for ulna.
The lower or distal extremity of the humerus is some-
what flattened, and usually has a broad, semi-cylindrical
articular surface, which is received into a corresponding
concavity on the upper end of the bones of the fore- arm.
This is called the trochlea (ar and au). On each side, and
rather above this surface, is a prominence called the condyle^
one of which is external, or radial (ec), the other internal, or
ulnar (ic). The latter is usually the most prominent. In
xv.] GENERAL CHARACTERS. 243
the middle of the lower end, between the condyles, and
above the thickened articular border, the bone is very thin,
having a hollow both in front and behind. The latter,
which is the deepest, is called the anconeal fossa, as it
receives a projecting part of the anconeal process, or ole-
cranon, of the ulna, when the fore-arm is fully extended.
It often happens that these two fossae are so deep that they
meet, and there is in consequence a vacuity in the bone
called the supratrochlear or intercondylar foramen. There is
usually a prominent ridge running upwards for some distance
on the shaft from the external condyle, called the ectocondylar
or supinator ridge {sr), which affords a wide surface of origin
for the supinator muscles of the fore-arm. When much
developed this ridge terminates above at the groove for the
passage of the musculo-sphlral nerve. When the edge of the
bone above the inner condyle is much developed, it is some-
times grooved, but more often obliquely perforated from
above, downwards and forwards, by a supracondylar foramen
(cf), through which the median nerve and brachial artery
may pass. Lastly, somewhere towards the anterior sur-
face of the middle of the shaft, on the outer side, there is
usually a roughened, elevated, longitudinal ridge (dr), some-
times developed into a tuberosity, for the insertion of the
deltoid muscle, and hence called the deltoid ridge. The
lower end of this ridge is separated from the upper end of
the supinator ridge by a wide and shallow groove, wind-
ing in a spiral manner downwards and forwards round the
outer side of the shaft of the bone, and indicating the
course of the musculo-spiral nerve.
The whole of the shaft of the humerus is developed
ectosteally from a single centre of ossification, but at each
extremity there is a large epiphysis : the upper one in-
cludes the head and both tuberosities, and is usually formed
r 2
244 THE ARM AND FORE-ARM. [chap.
by the coalescence of two distinct endosteal nuclei ; the
lower one includes the whole inferior articular surface with
the condyles, and is formed of three or four originally dis-
tinct centres of ossification. The lower epiphysis unites to
the shaft before the upper one.
The skeleton of the second segment of the upper limb, the
fore-arm or antibrachium, consists of two bones called radius
and ulna, placed side by side, articulating with the humerus at
their proximal, and with the carpus at their distal, extremity.
In their primitive or unmodified condition, these bones
may be considered as placed one on each border of the
limb, the radius being preaxial, and the ulna postaxial.1
The radius articulates above with the preaxial (external)
side of the humerus, the ulna with the postaxial (internal)
side of the humerus.
This position is best illustrated in the fore-limb of the
Cetacea (see Fig. 99), where the two bones are fixed side by
side and parallel to each other, the preaxial border being
external, and the postaxial border internal, in their whole
extent.
In the greater number of Mammals, the bones assume a
very modified and adaptive position (as will be explained
more fully in the chapter on the comparison of the fore and
hind limbs), usually crossing each other in the fore-arm, the
radius in front of the ulna, so that the preaxial bone
(radius), though external (in the ordinary position of the
limb) at the upper end, is internal at the lower end : and
the hand being mainly fixed to the radius, also has its pre-
1 So termed (by Prof. Huxley) in relation to the central axis of the
limb, when it is extended out from the body in its primitive embryonic
position, the extensor surface of the arm and back of the hand being
upwards or dorsal, and the flexor surface of the arm and palm of the
hand being downwards or ventral.
xv.] GENERAL CHARACTERS. 245
axial border internal. In the large majority of Mammals,
the bones are fixed in this position ; but in some few, as
in Man, a free movement of crossing and uncrossing, or
pronation and supination, as it is termed, is allowed between
them, so that they can be placed in their primitive parallel
condition, when the hand (which moves with the radius) is
said to be supine, or they may be crossed, when the hand is
said to be prone.
■ In most Mammals which walk on four limbs, and in which
e hand is permanently prone, the ulna is much reduced in
size, and the radius increased, especially at the upper end ;
and the articular surface of the latter, instead of being con-
fined to the external side of the trochlea of the humerus,
extends all across its anterior surface, and the two bones,
instead of being external and internal, are anterior and
posterior (see Figs. 82, 83, and 84, p. 248.)
The ulna is always characterised by a conspicuous, more
or less compressed prolongation, extending upwards beyond
the excavated humeral articular surface (sigmoid notch), and
serving as the point of attachment to the extensor muscles
of the fore-arm, called the olecranon or anconeal process.
Each of the bones of the fore-arm has commonly a
principal centre of ossification for the shaft, and an
epiphysis at either end.
Special Characters of the Bones of the Arm and Fore-
arm in the different Groups.
Order Primates. — In Man the humerus is long, slender,
and straight, with a large globular head. Neither the tube-
rosities, nor the deltoid and supinator ridges, are much
developed. The internal condyle is prominent, but there
is no supracondylar foramen as a normal condition.
246 THE ARM AND FORE- ARM. [chap.
though not usually, perforated. The lower articular surface
is divided by a groove into a pulley-like internal portion
{trochlea) for the ulna, and a smaller rounded portion {capi-
tellum), confined to the front side of the bone, for the radius.
The whole bone is somewhat twisted on its longitudinal
axis. Supposing it is so placed that a line drawn hori-
zontally through the axis of the head passes directly back-
wards, another line drawn through the condyles would
not cross this at a right angle, as in most of the inferior
Mammals, bflt its outer end would be directed forwards.
The radius has the head or proximal end expanded, disk-
shaped, and cupped at its extremity, which is applied to
the capitellum of the humerus (see Fig. 82). Below this
expanded head the bone is comparatively slender, but
increases in size as it approaches the lower end, which is
wide from side to side ; the surface next the ulna being
hollowed to receive the lower end of that bone, while the
opposite side is produced into the radial styloid process.
The inferior surface is hollowed for articulation with the
carpus. The whole bone is slightly curved. Not far below
the head is a rough prominence, into which the tendon of
the biceps flexor muscle is inserted.
The ulna has a large sigmoid excavation above for
articulation with the trochlea of the humerus ; the pointed
elevated anterior edge of this is called the coronoid process.
The olecranon is scarcely produced upwards beyond the
hinder edge of the articular surface. Below this, on the radial
side, is a smaller excavation, in which the edge of the disk-
like head of the radius plays, being held in its place in the
living state by a strong annular ligament, which encircles
it. The ulna is straighter than the radius, and gradually
diminishes in size to the lower end, where it terminates in a
rounded surface, which articulates with the hollow in the
xv.] PRIMATES. 247
lower end of the radius ; and also, though not very directly,
with the upper surface of the carpus. By the side of this is
a small conical process, the ulnar styloid process.
The movement of these bones upon the humerus at the
elbow-joint is simply that of a hinge, formed mainly by the
articular surface of the ulna. In pronation and supination,
which is more free and complete than in any other Mammal,
the ulna is stationary, and the radius moves ; the upper end
only on its own axis, being fixed to the side of the ulna by
the annular ligament, but the lower end rotates round the
lower end of the ulna, carrying the hand with it.
I The higher Apes have the axis of the humerus almost as
uch twisted on itself as in Man ; and they also, almost^
one among Mammals, resemble Man in not having the?)
ecranon process of the ulna prolonged upwards beyond1/
e sigmoid notch. Even in the Baboons these specialty
ithropoid characters are lost. The humerus has no supra-
>ndylar perforation in any of the Old World Simiina, nor in
teles, Mycetes or Hapale among the American Monkeys ;
but in the remaining genera of Cebidce, and in most of the
Lemurs, such a perforation is found. In the Aye-Aye
(Chiromys) the supinator ridge is remarkably developed.
The radius and ulna are distinct in all ; in the higher forms
(especially the Gorilla) greatly curved, leaving a large space
between them in the middle of the fore-arm. The power
of supination and pronation, which in the hi?her forms
almost equals that enjoyed by Man, is much reduced in
the inferior types of the order, although never entirely lost.
In the Carnivora the head of the humerus has no
longer that hemispherical form, so well marked in the higher
Primates. The tuberosities are strong and rough, and
project upwards beyond the level of the head. The shaft
much curved forwards. The deltoid ridge is strong, and
isr
248
THE ARM AND FORE- ARM.
[chap.
extends far down on the bone, especially in the Bears.
The inner condyle is prominent. The anconeal fossa is
deep. A supracondylar foramen exists in the Felidce, and in
most of the Viverridce, Mustelidcz, and Procyonidce, but not
in the Canidce, Hycenidce, or Ursidce.
Fig. 82.
Fig. 83.
Fig.
Anterior aspect of the bones forming the right elbow-joint of Man (Fig. 82) ; of tli
Dog (Fig. 83); of the Red Deer (Fig. 84) ; all ^. k humerus; r radius; n ulna.
The radius differs from that of Man, inasmuch as its
upper end is broad, flattened, and extends further across the
front of the humeral articular surface, forming part of the
hinge (see Fig. 83) ; and, although it is never ankylosed with
the ulna, scarcely any appreciable amount of movement is
allowed between them. The ulna has a large compressed
olecranon, and a shaft gradually tapering to the lower
extremity.
In the Pinnipedia the bones of the anterior limb are very
short and stout. The humerus has a remarkably prominent
deltoid ridge, and usually no supracondylar foramen, though
XV. ] INS EC Tl VOU A. 249
this is present in the Common Seal (Phoca vitulind). The
upper end of the ulna, and conversely the lower end of the
radius, are much expanded.
In most of the Insectivora the bones of the arm gene-
rally resemble those of the Carnivora. In the Hedgehog
(Ertnaceus) there is no supracondylar foramen in the
humerus, but a large supratrochlear perforation. In Cen-
tetes, Rhynchocyon, and nearly all the other genera, there
»a supracondylar foramen.
The radius and ulna are generally completely developed
and distinct ; but in Galeopithecus, Macroscelides and Petro-
droj/ius, they are fused together inferiorly.
The Mole ( Talpa) and its allies have a humerus of ex-
traordinary form, being very short, and extremely broad
and flattened at both extremities, though contracted in the
middle. In addition to the narrow oval head for articulation
with the glenoid cavity of the scapula, there is a larger
saddle-shaped surface, which articulates by a separate syn-
ovial joint with the outer end of the coraco-clavicle. The
deltoid ridge is very prominent, joining the inner tuberosity
above. From each condyle a slender bony process extends
upwards. There is a supracondylar foramen. The ulna has
a greatly developed olecranon, with a narrow keel behind,
and expanded laterally at the extremity.
In the Cape Golden Mole. (Chrysochloris) the humerus
is much more slender generally than in the true Moles, but
the inner condyle is extremely elongated. The olecranon
is long, narrow, and incurved. The fore-arm has a third
bone, extending from the palmar surface of the carpus
almost to the elbow, where it has a free termination. This
appears to be an ossification in one of the flexor tendons.
I The Chiroptera have a long slender humerus, having a
250 THE ARM AND FORE-ARM. [chap.
is no supracondylar perforation. The ulna is extremeb
reduced, only the upper third being present, and that anb
losed with the radius, which forms almost the whole of th<
lower articular surface of the elbow-joint. There i
detached sesamoid ossicle on the olecranon.
In the Rodentia the humerus varies much in its charac-
ters. It is long, slender, and straight, with a very slight
deltoid ridge, a narrow and laterally compressed inferior
end, and without prominent condyles in the Hares and
Agutis. But in the Beaver the deltoid and supinator ridges,
and the inner condyle, are strongly developed. All inter-
mediate conditions occur in different genera. As a general
rule there is a large supratrochlear perforation, but no
supracondylar foramen. In the Coypu (Myopotamus) the
deltoid ridge is an extremely salient, compressed, and
everted tuberosity.
In the fore-arm the two bones are nearly always dis-
tinct, though closely applied to each other. The breadth
of the upper end of the radius, and the amount of rota-
tion permitted upon the ulna, vary much in different
genera.
In the great order Ungtjlata the humerus is stout and
rather short. The outer tuberosity is very large, and gene-
rally sends a strong curved process inwards, overhanging the
bicipital groove (not, however, in the Horse and Camel).
The deltoid ridge is usually not strongly marked, and placed
rather high on the bone.; but in the Rhinoceros it is a very
salient ridge. The lower end is always particularly straight
and flat on the inner side (see Fig. 84, p. 248), the condyle
forming no prominence, and there is never a supracondylar
foramen. The outer condyle and the ridge above it are
rather more developed.
The radius is large at both ends, and superiorly extends
xv. I CETACEA. 251
across the whole of the humeral trochlear surface (see Fig.
84). The ulna is a complete and distinct bone in the Pi
Hippopotamus, Tapir, and Rhinoceros. In the Ruminants
it is more or less rudimentary and fixed behind the radius.
In the Camel the two bones become completely coalesced.
In the Horse the olecranon and upper part of the shaft
alone remain, firmly ankylosed to the radius.
In the Proboscidea the humerus is remarkable for the
great development of the supinator ridge. The ulna and1
radius are quite distinct, and permanently crossed. The*
upper end of the latter is small, while the ulna not only
contributes the principal part of the articular surface for the /
humerus, but has its lower end actually larger than that of;
the radius, a condition almost unique among Mammals.
In Hyrax the humerus is straight/ with, a very prominent
outer tuberosity, moderate deltoid ridge, rather compressed
inferior extremity, large supratrochlear, but no supracon-
dylar, perforation. The ulna and radius are complete and
subequal, often ankylosing together in old animals.
In the Cetacea, the bones of the arm and fore-arm are
usually very short, broad, and simple in their characters
(sec Fig 99). The humerus has a large globular head, which
moves freely in the glenoid cavity of the scapula, the tubero-
sities are fused into one, the bicipital groove being absent ;
the lower end is broad and flattened, and its inferior surface
is divided into two nearly equal flat surfaces placed side by
side (one external, the other internal), and meeting at a very
obtuse angle. The equally flat upper surfaces of the radius
and ulna are applied to these and so united that scarcely
any motion is permitted between them, and often in old
animals ankylosis takes place at the joint.
I he ulna and radius are parallel to each other without
252 THE ARM AND FORE-ARM. [chap.
developed olecranon process projecting directly outwards
from the shaft of the bone ; the radius is extremely simple
in form, wider below than above.
In the Rorquals (Balmnoptera and Megapterd) these
bones are considerably elongated.
In the Sirenia the bones of the fore-limb are formed on
a different type, as there is a distinct, though small and
simple, trochlear articulation at the elbow-joint. In the
Dugong, the humerus is small in the middle of the shaft,
and expanded at each end. The tuberosities are very pro-
minent, especially the outer one, and the bicipital groove is
distinct. The internal condyle is prominent, the anconeal
fossa small, and there is no supracondylar perforation. In
the humerus of the Manati the bicipital groove is obsolete,
the two tuberosities coalescing, as in the Cetacea. In other
respects it resembles that of the Dugong.
The two bones of the fore-arm are, in both genera, about
equally developed, and generally ankylose together at both
extremities.
Order Edentata. — In the Sloths the humerus is long
and straight, slender and cylindrical in the greater part, but
flattened and laterally expanded at the lower end. The
head is hemispherical, the tuberosities moderately developed,
and subequal in size, the deltoid ridge very indistinct. In
the Two-toed Sloths (Cholcepus) the humerus is shorter and
broader than in JBradypus, and has a large supracondylar
perforation, which is wanting in the latter genus.
The radius and ulna somewhat recall those of the
Primates in their form, and they are capable of a con-
siderable amount of pronation and supination. The
olecranon process scarcely projects beyond the sigmoid
articular surface.
The humerus in all the remaining Edentates is stout and
yv. 1 MARSUPIALIA. 253
broad, and remarkable for the great development of the
points of muscular attachment, as the tuberosities, deltoid
and supinator ridges, and internal condyle. These all reach
their maximum of development in the Armadillos, animals
which make great use of their fore-limbs in scratching and
burrowing. The supracondylar foramen is present in all.
The radius and ulna are also well developed and distinct
in all, but with no great amount of motion permitted
Ietween them. The olecranon is always long and strong.
Order Marsupialta. — In the burrowing Wombat (Phasco-
miys) the humerus is stout, very broad at the lower end,
nd with strongly developed deltoid and supinator ridges
(See Fig. 81, p. 242.) These characters prevail generally
throughout the order, though in a less maiked degree. The
supracondylar foramen is almost always present, some of
the Dasyures being exceptions.
The radius and ulna are always distinct and well-developed
bones. The upper end of the radius is small and rounded,
and more or less rotation is permitted between the bones,
n in the carnivorous forms.
In both the genera of animals constituting the order
Monotremata, the humerus is something like that of the
Mole, short and extremely broad at both extremities, with
greatly produced inner and outer condyles, though con-
tracted at the middle of the shaft.
The radius and ulna are stout, and rather flattened at the
lower end, where they are of about equal size, and closely
applied together. The upper end of the olecranon is
widely expanded laterally.
CHAPTER XVI.
THE MANUS.
The terminal segment of the anterior limb is the hand or
mantis.1 Its skeleton consists of three divisions : (i) The
carpus, a group of small, more or less rounded or angular
bones, with flattened surfaces applied to one another, and,
though articulating by synovial joints, having scarcely any
motion between them ; (2) the metacarpus, a series of
elongated bones placed side by side, with their proximal
ends articulating by almost immoveable joints with the
carpus ; (3) the phalanges, or bones of the digits, usually
three in number to each, articulating with one another by
freely moveable hinge-joints, the rirst being connected in
like manner to the distal end of the corresponding meta-
carpal bone.
To understand thoroughly the arrangement of the bones
of the carpus in Mammals, it is necessary to study their
1 " On account of the ambiguity arising from the as yet unsettled con-
notation of the terms ' hand' and 'foot,' I think it better, in a scientific
treatise, to disuse them altogether, and ... to adopt for the anterior
extremity (the carpus and all beyond it) the term manus, and for the
homotypal posterior segment the term pes. The all but necessity for
distinct hovwlogical terms for such parts is obvious." — MlVART, On the
Appendicular Skeleton of the Primates, Phil. Trans. 1867.
, hap. xvi. 1 GENERAL CHARACTERS. 255
condition in some of the lower vertebrates.1 Fig. 85
represents the manus in one of its most complete, and at
the same time most generalized, forms, as seen in one of
the Water Tortoises (Chelydra serpentina).
The carpus consists of two principal rows of bones, an
upper or proximal row, containing three bones, to which
( le^enbaur has applied the terms radiate (r), intermedium (1),
and ulna re (u), the first being on the radial or preaxial side
plG. 85.— Dorsal surface of the right manus of a Water Tortoise {Chelydra ser-
pentina , after Gesjenbaur. u ulna; R radius; u ulnare; /intermedium; r radia'e ;
ccentrale; i — 5 the five bones of the distal row of the carpus; mx — »?5 the five
metacarpals.
of the limb. The lower, or distal, row contains five bones,
called carpale i, 2, 3, 4, and 5 respectively, commencing on
the radial side. Between these two rows, in the middle of
• carpus, is a single bone, the centrale (e).
n this very symmetrical carpus, it will be observed that
the radia/e supports on its distal side two bones, carpale 1
See Gegenbaur, " UntersuchuKgen zur Vergleichenden Anatomie,''
Heft, Carpus und Tarsus. 1864.
256 THE MANUS. [chap.
and 2 ; the intermedium is in a line with the centrale and
carpale 3, which together form a median axis of the hand,
while the itlnare has also two bones articulated with il
distal end, viz. carpale 4 and 5. Each of the carpals of th<
distal row supports a metacarpal.
In the carpus of the Mammalia, there are usually twc
additional bones developed in the tendons of the flexor
muscles, one on each side of the carpus, which may be
called the radial and ulnar sesamoid bones ; the latter is
most constant and generally largest, and is commonly known
as the pis/form bone. The fourth and fifth carpals of the
distal rows are always united into a single bone, and the
centrale is often absent. As a general rule all the other
bones are present and distinct, though it not unfrequently
happens that one or more may have coalesced to form
a single bone, or may be altogether suppressed.
The table below shows the principal names in use for the
various carpal bones. Those in the second column, being
most generally employed by English anatomists, will be
adopted in the following pages : —
Radialc
— Scaphoid
= Naviculare.
Intermedin in
= Lunar
- Semilunare, Lunalum.
Ulnare
= Cuneiform
= Triqntfmm, Pyramidale.
Centrale
= Central
= Intermedium (Cuvier).
Carpale 1
= Trapezium
= Multangulum ma/us.
Carpale 2
= Trapezoid
= Multangulum minus.
Carpale 3
= Magnum
— Capita turn.
Carpale 4 )
Carpale 5 \
= Unciform .
= Ilamatum, Uncinaium.
The metacarpal bones, with the digits which they sup-
port, never exceed five in number, and are distinguished by
numerals, counted from the radial towards the ulnar side.
The digits are also sometimes named (I) pollex, (II) index,
(III) meditts, (IV) annularis, and (V) minimus. One or more
xvi.] GENERAL CHARACTERS. 257
may be in a very rudimentary condition, or altogether
suppressed. If one is absent, it is most commonly the
first.
Excepting the Cetacea, no Mammals have more than three
halanges to each digit, but they may occasionally have
wer by suppression or ankylosis.
The first or radial digit (also called pollex) is an exception
the usual rule, one of its parts being constantly absent, for
hile each of the other digits has commonly a metacarpal
d three phalanges, it has only three bones altogether.
hether the missing one is the metacarpal or one of the
halanges, is a subject which has occasioned much dis-
ssion, but has not yet been satisfactorily decided. In
cordance with the most usual custom, the proximal bone
this digit will here be treated of as a metacarpal.1
The terminal phalanges of the digits are often specially
odified to support the nail, claw or hoof, and are called
ungual phalanges."
Very frequently a pair of small sesamoid bones are
veloped in connection with the tendons passing over the
lmar surface of the articular heads of the metacarpals and
phalanges, and occasionally (as in the Armadillos) a larger
bone of similar nature is met with in the middle of the same
surface of the carpus and metacarpus. More rarely similar
bones occur on the dorsal surface of the phalangeal articu-
lations.2
Each of the carpal bones ossifies from a single nucleus.
The metacarpals and phalanges have each a main nucleus
Ir the greater part of the bone, and usually an epiphysis at
ra
1 See Allen Thomson " On the Ossification of the First Metacarpal
>ne." (J own. Anat. and Physiology, Vol. III. p. 131.)
2 These are almost always lost in prepared skeletons, but they occur
istantly in the common dog.
258 THE MANUS. [chap.
one end only, this being the distal end of the metacarpals
(except the first), and the proximal end of the first metacarpal
and of all the phalanges. In many of the Cetacea epiphyses
are found at both ends of the bones, and the same takes
place regularly in the Elephant Seal (Macrorhinus pro-
boscided), and occasionally in some other Mammals.
In Man the carpus (see Fig 86) is short and broad. Its
upper border, by which it articulates with the radius, forms a
regular curve, with the convexity upwards. It has the three
bones of the proximal row — the scaphoid (s), lunar (/), and
cuneiform (c) — distinct ; also the usual four bones of the
FlG. 86. — Bones of the right human carpus, £. .s scaphoid ; / lunar ; c cuneiform ;
tin trapezium; td trapezoid; /// magnum; u unciform; p pisiform; I— v the
metacarpals.
distal row, but no central. There is a well-developed rounded
ulnar sesamoid (the pisiform bone,/) which articulates by a
smooth facet with the cuneiform, but no radial sesamoid.
The trapezium (////) has a saddle-like articular surface for the
moveable first metacarpal. The magnum (;;/), as its name
implies, is the largest bone — rather an exceptional condition
among Mammals ; it has a large rounded part or head
projecting upwards and fitting into a concavity in the distal
surface of the bones of the proximal row. The unciform
(//) has a strong hook-like process from its palmar surface
curved towards the radial side.
xvi. j GENERAL CHARACTERS. 259
The first metacarpal is shorter, though somewhat broader
than any of the others. It is articulated in a different plane
from them, its palmar surface facing towards the ulnar side
of the hand, and it is capable of a considerable range of
movement. The other four metacarpals are nearly equally
developed, diminishing slightly from the radial to the ulnar
side ; their shafts are slender and rather compressed,
especially towards the palmar aspect; but they enlarge at
each extremity, particularly at the rounded distal end or
head. They are so articulated with the carpus as to allow
of very little motion. The phalanges are of the normal
number to each digit, all broad, convex on their dorsal, and
flattened or slightly hollowed on their palmar, side. The
proximal is the largest, and the ungual the smallest. The
latter is flattened and slightly expanded or spatulate at its
terminal portion. Those of the first digit or thumb are
I:outer than any of the others, those of the fifth digit (little
nger) are the most slender. The third digit is the longest,
le second and fourth somewhat shorter and nearly equal,
le fifth considerably shorter, and the first still more so.
esamoid bones are only developed behind the metacarpo-
halangeal joint of the pollex.
In the other Primates, the manus is generally longer and
arrower than in Man, and as a general rule the first digit or
iiumb is less developed and less freely moveable. In the
genera Troglodytes and Simla, as in Man, the proximal
surface of the carpus articulates with the radius alone, in all
others it articulates also with the ulna. The scaphoid and
lunar bones are always distinct. An additional bone (os ce?i-
trale, Gegenbaur,- Fig. 87, ce) is present in all, except in the
Gorilla and Chimpanzee, and some of the Lemurs. This
is considered by some anatomists to be a dismemberment
of the scaphoid. The pisiform is present in all, and gene-
s 2
260 THE MANUS. [CHAP.
rally of a more elongated form, and more salient than in
Man ; and there is usually a small rounded radial sesamoid
(rs) articulating moveably to the border of the scaphoid
and trapezium, and connected with the tendon of the flexor
carpi radialis.
In the Potto (Perodicticus) there is an additional bone in
the palmar side of the carpus, an ossification in the ligament
connecting the palmar processes of the trapezium and
unciform bones, and forming with these processes a com-
plete bony ring, through which the flexor tendons pass.1
FlG. 87. — Bones of the carpus of a Baboon (Cynocephalus anttlvs). \. s scaphoid ;
I lunar ; c cuneiform ; / pisiform ; ce central ; rs radial sesamoid ; tin trapezium ;
td trapezoid; m magnum ; u unciform; 1 — v the metacarpals.
The metacarpals and phalanges are of the complete and
normal number in all, with the following exceptions. In the
African genus of Long-tailed Monkeys (Colobus), and also in
the American Spider Monkeys (A teles), the thumb is rudi-
mentary, having usually but one very minute phalanx, in
addition to the metacarpal. In the Potto {Perodicticus) and
some allied Lemurince, the second (or index) digit is very
much shorter than the others, and has but two rudimentary
phalanges.
The phalanges are generally more curved than in Man,
1 Mivart, "On the Appendicular Skeleton of the Primates;" Phil.
Trans. 1867.
CARNIVORA.
261
lost notably so in the Orang. The hand of the Mada-
iscar Aye- Aye (Chiromys) is remarkable for the extreme
ttenuation of the bones of the third digit.
In the Carnivoma, the scaphoid and lunar bones always
:oalesce into a single scapho-lnnar bone (Fig. 88, si), with
hich it is probable the centrale is united, as it never appears1 ,
a distinct bone, except sometimes in very young animals.
'ig. 88. — Bones of the carpus of a Bear (Ursus americanus), %. si scapho-lunar
bone ; c cuneiform ; p pisiform ; u unciform ; m magnum ; td trapezoid ; tm tra-
pezium ; rs radial sesamoid ; i — v the metacarpals.
'he radial accessory ossicle or sesamoid (rs) is generally
>resent. All have five digits, with the complete complement of
>halanges, except the Hyaena, in which genus the pollex is
'presented only by a rudimentary metacarpal. This digit is
isually much reduced in size, and often, as in the Dog, docs
lot reach the ground in walking. It is best developed in
le bears and allied forms. The first metacarpal is never
lore freely moveable than any of the others. As a general
ile the middle digit is somewhat the longest, the second and
>urth nearly equal to it, the fifth shorter, and the first the
jhortest.2
1 See B. G. Wilder, "On the Composition of the Carpus in Dogs."
hill. Cornell University, Vol. I. p. 301, 1874.
"2 The fissiped Carnivora have been divided into two groups, accord-
to the position of the feet in walking — the Plantigrade, or those
lat place the whole of the palmar and plantar surface to the ground ;
262 THE MANUS. [chap.
As the toes are nearly always armed with large, strong,
/ curved, and sharp claws (see Fig. 89), the ungual phalanges
(p/13) are large, strongly compressed, and pointed, and they
develop from their base a broad thin lamina of bone (b),
which is reflected over the root (a) of the horny claw, and
holds it more firmly in its place. In those genera, as Felist
Fig. 89. — The phalanges of the middle digit of the manus of the Lion {Felis leo), £.
p/il proximal phalanx: p/i2 middle phnlanx ; phi ungual phalanx ; a the central
portion forming the internal support to the horny claw ; b the bony lamina reflected
around the base of the claw.
in which the claws are retractile, the middle phalanx (p/i 2)
is deeply hollowed on its ulnar side to receive the ungual
phalanx when folded back upon it, in the quiescent state of
the foot.
In the Pinnipedia, the manus is broader and flatter
than in the terrestrial Carnivora. The scaphoid and lunar
coalesce. The ulnar side of the carpus is much reduced,
the unciform being especially small, and consequently the
fifth metacarpal articulates partly with the cuneiform of the
and the Digitigrade, or those that walk only upon the phalanges, the
metacarpals and. metatarsals being vertical and in a line with the fore-
arm or leg. This distinction, however, is quite an artificial one, and
every intermediate condition exists between the extreme typical planti-
grade gait of the bears and the true digitigrade action of the cats and
dogs. In fact, the greater number of the Carnivora belong to neither
of these groups, but may be called "subplantigrade," often, when at
rest, applying the whole of the sole to the ground, but keeping the heel
raised to a greater or less extent when walking.
•I.I
INSECTIVORA.
2(>.
proximal row of the carpus. The pisiform is small. The
first digit is nearly as long as the second ; the remainder
gradually diminish in length to the fifth. The ungual pha-
langes in the ordinary Seals are slender, pointed, slightly
curved, and not much compressed. In the Otariidce they are
(longed beyond the part which bears the very small claw,
id flattened and truncated at the ends, being continued
iwards in the living animal as cartilaginous rays, which
ipport lobed expansions of the skin.
WG 90.— Bones of fore-arm and manus of Mole {Talpa europcra), X 2. R radius;
U ulna ; j scaphoid ; I lunar; c cuneiform ; / pisiform ; u unciform ; m magnum ;
td trapezoid ; tin trapezium ; ce central ; rs radial sesamoid (falciform) ; 1— v the
digits.
Among the Insectivora, the scaphoid and lunar coalesce
Galeopithecusj Tupaia, Cen fetes, Solenodon, Erinaceus, and
mnnura. but in most of the other forms these bones are
264 THE MAN US. [chap.
distinct. A distinct os centrale is found in all except in
Galeopithecus, Potamogale, Chrysochloris, and Sorex.
There are nearly always five digits, but Rhynchocyon and
Chrysochloris have but four. The whole hand is generally of
moderate size, with pointed, conical, slightly curved, ungual
phalanges.
In common with every segment of the anterior extremity*
the manus of the Mole (Ta/pa) and its immediate allies is
extremely modified to suit its fossorial habits (see Fig 90).
It is extremely broad and strong, its breadth being increased
by the great development of the radial sesamoid (rs), which,
being sickle-shaped, has received the special name of os
falciforme. The ungual phalanges are very large, and cleft
at their extremities.
In the Chiroptera, the hand is especially modified in a
totally different manner, constituting the organ of flight.
!In the carpus the scaphoid and lunar are united, and in
some genera (as Pteropus) the cuneiform is joined with them,
so that the proximal row contains but a single bone. There
(is no centrale. The pisiform is very small.
The pollex is short, divaricated from the other digits, not
enveloped as they are, in a cutaneous expansion, and armed
with a curved claw. The other digits are extremely long and
slender.
In the Frugivorous Bats {Pteropus) the second digit has a
short ungual phalanx and claw, but in each of the other
digits the middle phalanx is elongated, and gradually tapers
to the termination, the ungual phalanx being absent.
In the Insectivorous Bats, the pollex alone has a claw.
and the elongation of the other digits is chiefly due to the
metacarpals, the phalanges being small and very slender,
and usually only two in number, except in the third digit,
which generally has three.
RODENTIA.
265
. In the Rodentia, the scaphoid and lunar are very
generally united (as in Castor, Dasyprocta, Hydrocha'nts,
Capromys, Schirus, Arciomys, Mus, &c), but riot in all. An
os centrale is present in many, as Lepus, Dasyprocta, Hydro-
chcerus, Capromys, and Castor, while in other genera it is
absent. There is very frequently an accessory ossicle on the
radial side of the carpus, which is particularly large in the
Heaver (Fig. 91). There are nearly always five digits, with
Fig. 91. — Bones of the manus of the Baaver {Castor canadensis), f.
the normal number of phalanges, though sometimes (as in
Hydrochcerus) the pollex is rudimentary or suppressed.
In the Cape Hyrax (Fig. 92, p. 266) there is an additional
carpal bone (ce), which is probably the os centrale, though
in form and situation it looks as if it. were a dismemberment
of the proximal part of the trapezoid (td). The scaphoid
266
THE MAN US.
[chap
and lunar are not united, and there are five digits, of which
the first is extremely small, and has only one minute
nodular phalanx. In another species, If. dorsalis, the pollex
Fig. 92. — Bones of the manus of Cape Hyrax {Hyrax capensis), nat. size.
it reduced to a short metacarpal ; the fifth digit has but
two phalanges, and the centrale is united with the trapezoid.
The ungual phalanges of the three middle digits are small,
and somewhat conical in form.
In the Elephant the manus is short and broad, the carpal
bones are massive and square, and articulate by very flat
surfaces ; they consist of scaphoid, lunar and cuneiform, a
pisiform and the usual four bones of the distal row, all
distinct, without the centrale. There are five digits, with
short stout phalanges, the terminal ones being very small
and of irregular form.
UNGULA TA.
267
Order Ungulata. — All the known animals of this order
agree in the complete suppression of the pollex, in the
absence of an os centrale, and in the complete separation of
the scaphoid and lunar. The carpus is very compact, the
bones being generally more or less square, and articulating
Fig. 93.
Fig. 93 Fig 94.
-Bones of the manus of Tapir ( Tapirus iiidicus), I.
Fig. 95.
Fig. 94. — Bones of the manus of Rhinoceros {Rhinoceros sumatrensis\
Fig. 95. — Bones of the manus of a Horse (Eqmis caballus), ^. 11 and iv rudimentary
metacarpals.
by flat surfaces with each other, and with the radius and
ulnar above. They are eminently digitigrade, the limb
being entirely supported on the ungual phalanges, which are
large, and encased in a hoof.
Khe digits are arranged according to one or the other of
268 THE MANUS. [chap.
two distinct types, each characteristic of, and giving name
to, one of the sub-orders.
1. The Perissodactyla, or " odd-toed " Ungulates, have the
middle or third digit the longest, and symmetrical in itself,
the free border of the ungual phalanx being evenly rounded.
The second and fourth toes may be subequally developed, as
in the Rhinoceros (Fig. 94), or they may be represented
only by mere splint-like rudiments of their metacarpals, as in
the Horse (Fig. 95). All intermediate conditions are met
with in various extinct forms, as Palceotherium, Anchitheriu?n\
and Hipparion. In the Tapir (Fig. 93) there are four
complete toes, in consequence of the fifth being developed,
though it scarcely reaches the ground in walking. In other
respects the foot resembles that of the Rhinoceros, the third
toe being longest, and symmetrical in itself, and having on
each side of it the nearly equal second and fourth. In the
Rhinoceros there is a rudiment only of the fifth metacarpal.
In the Horse (Fig. 95), the three bones of the first row of
the carpus are subequal. The second row consists of a
very broad and flat magnum (m), supporting the great third
metacarpal, having to its radial side the trapezoid (id), and
to its ulnar side the unciform (//) which are both small, and
articulate distally with the rudimentary second and fourth
metacarpals. The pisiform is large and prominent, flattened
and curved; it articulates partly to the cuneiform, and
partly to the lower end of the radius. The single digit
consists of a moderate-sized proximal, a very short middle,
and a wide, semilunar, ungual phalanx. There is a pair of
large nodular sesamoids behind the metacarpophalangeal
articulation, and a single, transversely extended, " navicular"
sesamoid behind the joint between the second and third
phalanx.
2. The Artiodactyla have the third and fourth digits almost
X VI.]
UNGULA TA.
269
equally developed, and their ungual phalanges flattened on
their inner or contiguous surfaces, so that each is symmetri-
cal in itself, but when the two are placed together they form a
figure symmetrically disposed to a line drawn between them.
Or, in other words, the axis or median line of the whole
Fig. 98.
Fig. 96. — Bones of the manus of Pig {Sus scrofa), \.
Fig. 97. — Bones of the manus of Red Deer [Cervus elaphus), \.
Fig. 98. — Bones of the manus of Camel (Came/us bactrianus), \.
manus is a line drawn between the third and fourth digits,
while in the Perissodactyles it is a line drawn down the
centre of the third digit.
In the Suma, Pigs (Fig. 96), Peccaries, and Hippopotamus,
the second and fifth toes are well developed, though always
270 THE MANUS. [chap.
considerably smaller than the third and fourth, all four
metacarpal bones are distinct, and the manus is compa-
ratively broad. The second row of carpal bones in the
Pig consists of a small trapezoid, a moderate-sized magnum,
and a large unciform. In the Hippopotamus there is also a
trapezium.
In the ruminating sections of the sub-order (Figs. 97 and
98), the third and fourth metacarpals, though originally
distinct, become more or less conjoined, generally so as to
form what appears externally to be a single bone, though
traces of their separate origin always remain ; the two distal
articular surfaces are quite distinct, each supporting a digit.
The lateral (second and fifth) metacarpals and digits are
generally rudimentary, sometimes completely absent. Some-
times not even the hoofs remain, as in the Giraffe, Prongbuck
(Antilocaprd), and some other Antelopes; sometimes the
hoofs alone, as in the Sheep and Ox, supported, it may be,
by irregular nodules of bone, rudiments of the ungual
phalanges. In the Deer (Fig. 97), the three phalanges are
complete, sometimes with the lower end of the metacarpal,
tapering above, and not directly attached to other parts of I
the skeleton of the foot. In other species rudiments of the jj
proximal ends only of the metacarpals are present.
In the Tragulina these metacarpals are completely deve- I
loped, and articulate with the carpus. In Hyomoschus, \
belonging to this section, the third and fourth metacarpals
commonly remain distinct through life, so that the manus of
this animal scarcely differs from that of one of the Sitina. -
The Tylopoda or Camels, differ considerably from the
1 The last-named condition occurs in most of the deer of the Old
World, the former in all the American deer, with Alces, Rangifer,
Hydropotes, and Capreolus. See Sir Victor Brooke, Proc. Zoological
Society, 1874, P- 36-
XVI.] CETACEA. 271
true Ruminants in the structure of the fore-foot (see Fig.
98). In the carpus the trapezoid and magnum are distinct,
as in the Suina and Pcrissodactyla, whereas these bones are
confluent in the Pecora and Tragulma. There are no traces
of any metacarpals or digits, except the third and fourth.
The metacarpals of these are very long and, as in the Pecora,
confluent throughout the greater part of their length, though
separated for a considerable distance at the lower end. The
distal articular surfaces, instead of being pulley-like, with
deep ridges and grooves, are simple, rounded, and smooth.
The proximal phalanges are expanded at their distal ends,
and the wide and depressed middle phalanges are imbedded
in a broad cutaneous pad, forming the sole of the foot, on
which the animal rests in walking, instead of on the hoofs,
as in other Ruminants. The ungual phalanges are very
small and nodular, not flattened on their inner or opposed
surfaces, and not completely encased in hoofs. These
characters are better marked in the true Camels than in the
Llamas.
In the animals constituting the order Cetacea, the manus
has undergone a special modification, being converted into
a simple, flattened, oval or falciform, usually pointed flipper
or paddle, showing externally no signs of division into sepa-
rate digits, nor any traces of nails or claws. The skeleton,
however, consists, as in other Mammals, of a carpus,
metacarpus, and either four, or more commonly five, digits,
the great peculiarity of which is, that the number of pha-
langes is not limited to three, as in all other animals of
class, but may extend even to twelve or thirteen,
n the Whalebone Whales, a large portion of the
skeleton of the hand remains permanently cartilaginous, and
the cartilages composing the various carpal bones and pha-
langes are confluent or slightly separated from each other
272 THE MAN US. [chap.
by interposed tracts of fibrous tissue, without any synovial
\ joints. Nodules of bone are deposited in the centre of
some of these cartilaginous masses, and slowly reach the
surface as the animal attains maturity : there are commonly
not more than five such ossifications. The phalanges
\ appear like cylindrical or slightly flattened bony masses,
; with roughly truncated ends, set in a continuous rod of
J cartilage. In this way a certain amount of flexibility and
elasticity is secured in the flipper, but beyond this there
is no actual motion between the various bones of which
' it is composed.
The manus of the Right Whale (Balcena mysticetus) is
comparatively short and very broad, having all five digits
present, and being also extended on the ulnar side by a
flattened cartilage projecting from the edge of the carpus,
probably representing the pisiform bone. In an adult speci-
men there are only three distinct ossifications in the carpus.
The numbers in the digits are respectively I. I, II. 4, III. 5,
IV. 4, and V. 3. In the Rorquals (Balanoptera) the first digit
is absent, and the manus is of an extremely elongated and
narrow form. The carpus has five ossifications, and the
number of phalanges varies somewhat in different species.
In the Odontocetes, the ossification of the skeleton of
the manus is usually more complete than in the Whalebone
Whales, the carpal bones generally coming in close contact
at their edges, and assuming a somewhat polygonal form.
The phalanges are also better ossified, often having epi-
physes at each extremity, and they are connected together
by imperfect synovial joints. They are always very much
flattened, and their extremities being truncated and their
sides nearly parallel, they are either square or oblong
in form. In size they gradually decrease to the end of
the digit, the last often consisting of minute nodules or
XVI. j
CETACEA.
273
granules, so irregularly or im-
perfectly ossified, and so easily
lost in cleaning, that it is in
many cases impossible, when
describing the skeleton of one
of these animals, to give the
exact number of phalanges to
h digit.
The determination of the
homologies of the carpal bones
of the Cetacea with those of
other Mammalia is beset with
difficulties, and has conse-
quently led to some differences
of opinion among those anato-
mists who have attempted it.
Moreover every species ap-
Iears liable to certain indivi-
ual variations, and sometimes
le different sides of the same
nimal are not precisely alike,
either in the arrangement, or
even the number of the carpal
ossifications.
The pisiform is occasionally
represented by a small ossifi-
cation on the ulnar border of
the carpus. Excluding the
above, the carpus of the Odon-
tocetes appears never to con-
sist of more than six bones,
Iree belonging to the proximal, and three to the distal
Fig
99. — Dorsal surface of bones of
right anterior limb of Round-headed
Dolphin {Globiocephalus melas), ^n.
The shaded portions of the digits are
cartilaginous.
274 THE MANUS. [chap.
The three bones of the proximal row are constant,
and may easily be identified as corresponding to the scap-
hoid, lunar and cuneiform of human anatomy, or the
radiale, intermedium, and ulnare of Gegenbaur. The middle
one is usually the largest and most thoroughly ossified. v
The three bones of the distal row are generally represented
by distinct ossifications (corresponding apparently with the
trapezoid, magnum, and unciform) in the genera Hyperoodon,
Beluga, and Monodon.
In most cases (see Fig. 99) the bones of the distal row of
the carpus are reduced to two, which appear to correspond
best with the trapezoid and unciform, the magnum being
either absent or amalgamated with the trapezoid.1
The trapezium appears never to be present as a distinct
bone, although the first metacarpal so often assumes the
characters and position of a carpal bone, that it may easily be
taken for it.
The cuneiform always directly supports the fifth meta-
carpal, and frequently some part of the fourth. Moreover,
in those species in which the ulnar side of the carpus is
greatly reduced, as Globiocephalus, the fifth metacarpal is
even connected with the ulna.
In the Cachalot {Physeter) many of the carpal bones, in
addition to the usual central nucleus, have epiphysial ossifi-
cations developed in the periphery of the cartilage, which
ultimately unite with the central piece of bone.
All the Cetacea with teeth have five digits, though the
first is usually rudimentary, and in close contact with the
metacarpal of the second. In some forms, as Physeter,
Byperoodon, Monodon, Beluga, Inia, Platan is fa, and Or en,
the manus is short, broad, and rounded at its distal
1 For the reasons for these determinations, see " On the Osteology of
the Sperm Whale ; " Trans. Zoological Society, vol. vi. p. 360.
SIRENIA.
275
extremity ; the digits being nearly equally developed, spread-
ing from each other, and without any excessive number of
phalanges. In the Grampus (Oral) all the phalanges are
broader than they are long.1 In the Round-headed Dol-
phins (Globiocephalus, Fig. 99), on the other hand, the manus
is extremely elongated, narrow, and pointed. This elongation
mainly due to the great development of the second, and,
lough to a less extent, of the third digit ; the fourth and
fth being quite short, and having but few phalanges. The
lumber of phalanges (including the metacarpals) in the
iifferent digits are respectively I. 4, II. 14, III. 9, IV. 3,
id V. 1.
In the common Dolphin (Delphinus) the manus has the
ime essential form, though in a less exaggerated degree,
le numbers of the phalanges being I. 2, II. 10, III. 7, IV. 3,
ind V. i. The digits are all in close contact.
Order Sirenia. — Though in external form, and in being
enclosed in an undivided integument, the terminal segment
>f the fore limb of the animals constituting this order
mch resembles that of the Cetacea, its skeleton is totally
Iifferent.
The carpus is short and broad. In the genus Manatus
the seven most usual bones of this region are all distinct,
though there is no pisiform. The trapezoid is very small,
md placed almost on the dorsal surface of the trapezium.
?he cuneiform is large, and supports the greater part of the
fth metacarpal. In Halicore many of the bones of the
trpus usually coalesce ; thus the first row may consist of
'o bones, a scapho-lunar and a cuneiform, and all the
mes of the second row may unite together.
In both genera the digits are five in number, with
This genus is remarkable for the imperfect ossification of the carpal
mes.
T 2
276
THE MANUS.
[CHAP.
moderately elongated and flattened phalanges, which are
never increased in number beyond the limit usual in the
Mammalia.
Among the animals constituting the
Order Edentata there is great diversity
in the structure of the fore-foot. They
agree, however, in wanting an os centrale,
and (with the exception of Mam's) in the
presence of distinct scaphoid and lunar
bones.
In the existing Sloths the whole manus
is long, very narrow, habitually curved, and
terminating in two or three pointed, curved
claws, in close apposition with each other,
incapable, in fact, of being divaricated, so
that it is reduced to the condition of a
hook, by which the animal suspends itself
to the boughs of the trees among which
it lives.
The carpus is small, and articulates by
ioo.— Bones of the a smooth rounded surface with the lower
right manus of the
Two-toed sioth (c/10- encj 0f the radius. In the Three- toed
hrpus didactyuts). ^.
Sloths (genus Bradypus) it consists of
distinct scaphoid, lunar, and cuneiform bones in the first
row, but usually of only two bones in the second row, the
unciform, and a connate magnum and trapezoid, the trape-
zium being generally ankylosed to the rudimentary first
metacarpal.1 There is a small rounded pisiform, but no
radial sesamoid. The first and fifth metacarpals are present
in a rudimentary condition, but bear no phalanges. The
three middle digits are nearly equally developed. The
proximal phalanges are extremely short, and become soon
1 See Journal of Anatomy and Physiology, vol. vii. p. 255.
art
di<
xvi.] EDENTATA. 277
ankylosed to the ends of the metacarpals, so that in adult
animals one of the usual bones of the digit appears to be
entirely wanting. The middle phalanges are long and com-
pressed. The ungual phalanges are also long, much com-
pressed, gently curved, and pointed. Bony laminae reflected
from their bases encase and support the roots of the claws.
In the Two-toed species (genus Cholcepus, Fig. 100), the
magnum and trapezoid are distinct. The functional digits
are the second and third, and there are rudiments of the first
and fourth metacarpals, though not of the fifth. The proximal
phalanges (pl) are extremely short, as in Bradypus, but do
not ankylose with the metacarpals. The ungual phalanges
e not so long as in Bradypus.
In the Pangolins (Mam's) the scaphoid and lunar are united,
ut all the other carpal bones are distinct. There are five
igits with the complete number of phalanges, which, except
the pollex, are short and broad. The distal ends of the
gual phalanges have deep median clefts. This phalanx in
e third digit is immensely developed, and considerably so
the fourth. The first, second, and fifth digits are com-
ratively small.
In the Cape Anteater (Orycteropus) the pollex is entirely
pressed, but all the other digits are well developed, and
erminate in subequal, compressed, ungual phalanges of
moderate size. The second and third digits are nearly
equal, the fourth and fifth shorter. A sesamoid bone is
developed on the dorsal side of the metacarpo-phalangeal
articulations.
In the true Anteaters (Myrmecophaga) all the usual carpal
nes are distinct. The unciform supports the fifth, fourth,
d a considerable part of the third, metacarpals. The first
digit is very slender, the second also slender, with com-
ressed phalanges of nearly equal length. The third digit
278 THE MANUS. [chap.
is immensely developed ; though its proximal phalanx is
extremely short, its ungual phalanx is so long that the
entire length of the digit exceeds that of the second. The
fourth has a long and rather slender metacarpal, and three
phalanges gradually diminishing in size, the ungual phalanx
being very small. The fifth has the metacarpal nearly as
long, but not so stout as the fourth, and followed by two
small phalanges, the last rudimentary and conical, and bear-
ing no nail.
The little Tree Anteater (Cyclothurus didactylus) has a
remarkably modified manus. The third digit is greatly
developed at the expense of all the others ; it has a stout,
short metacarpal, and but two phalanges, of which the most
distal is large, compressed, pointed, and much curved,
bearing a very strong hook-like claw. The second digit
has the same number of phalanges and bears a claw, but
is very much more slender than the third. The fourth is
represented only by a styliform metacarpal, and there are no
traces of either the first or fifth digits of the typical manus.
The pisiform is very large.
In the Armadillos (Dasypodida), the manus is stout and
broad, with strongly developed ungual phalanges, adapted
for digging and scratching. The fifth metacarpal articulates
with the cuneiform as well as the unciform. There is always
a very large palmar sesamoid. The digits are almost always
five in number, but vary much in relative size and structure.
In the six-banded Armadillos (genus Dasypus), all the
digits have the normal number of phalanges (see Fig. 101).
The first digit is rather short and especially slender; the
second is the longest, and has all the phalanges, as well as
the metacarpal, of nearly equal length ; the third has a long
metacarpal, then two short broad phalanges, the first being
especially short, and a long, curved, compressed, ungual
ED E NT A TA.
279
phalanx. The fourth and fifth are shorter, but present
the same general characters, and their metacarpals are also
reduced in length.
All the deviations from the normal type of manus ob-
served in the common Armadillos, when greatly exaggerated
produce the curiously modified condition seen in the Cabas-
sou (Xenurus unicinctus). The first and second digits are
Fig. 101. — Bones of the right manus of
the Hairy Armadillo (Dasypus viilo-
S7ts), §.
Fig. 102. — Bones of the manus of the
Great Armadillo {Friodontes gigas),i.
a an accessory carpal ossicle in front
of the pisiform, which is not seen in
the figure.
itill more slender and elongated, and retain the normal
number of phalanges ; but in the other three the metacarpal
is short and broad, the proximal phalanx is either sup-
pressed or incorporated with the metacarpal, as in some of
the Sloths, the middle phalanx is very short, but the ungual
28o THE MANUS. [chap.
phalanx is enormously developed, larger in the third than
in the fourth and fifth digits.
A still further modification of the same type is seen in
the extraordinary manus of the great Armadillo (Priodon-
tes gigas), the largest existing member of the group (Fig.
102). The metacarpals of the three outer toes are still
further reduced in length, the ungual phalanx of the third
is increased in size, while that of the fourth, and especially
the fifth, are greatly diminished.
In the genus Tolypeutes, the manus is formed on a some-
what similar type ; but in the Nine-banded Armadillos
(genus Tatusia) it is altogether different, the second and
third toes being subequal (the third the longest), with mode-
rate, conical, and slightly compressed ungual phalanges : and
the first and fourth also nearly equal and smaller, all with
the normal number of phalanges. The fifth is absent, or
(as in T. hybrida) represented by three very rudimentary
nodular bones.
Order Marsupialia. — The carpus never has a distinct
os centrale. It is commonly stated that there is a scapho-
lunar bone ; but the lunar, though always small, is distinct
in Didelphys, Perame/es, JDasyurus, Thylacinus, Phalajigista,
and Hypsiprymiius (where it is very minute) ; and its ab-
sence in Macropus appears to be due rather to suppression
than to coalescence with the scaphoid. In Phascolomys a
small lunar is present in some individuals, and not in
others.
With the exception of the genus Chaii'opus, all known
Marsupials possess the normal number of digits and pha-
langes, and the manus is short and rather broad, with
moderately developed, compressed, curved, ungual pha-
langes.
The little " pig- footed " insectivorous Marsupial Chceropus
MARSUPIALIA.
28]
casta not is, belonging to the family Perametidce, has a remark-
ably modified manus (see Fig. 104) in which only two
digits are functionally developed ; and as the metacarpals
are very long, and closely pressed together (though not
ankylosed), and the phalanges are short, and the nails rather
hoof-like, the whole manus has much general resemblance
FlG. 103 —Bones of manus of Bandicoot
[Perameles), X ij.
Fig. 104. — Bones of manus of Chorropns
castanotis, X 2.
to that of the Artiodactyle Ungulates. It presents, how-
ever, the essential difference that the functional digits are
the second and third of the normal series, instead of the
third and fourth. This is proved by comparing it with
the less modified manus of a true Perameles (Fig. 103).
The principal changes from the typical mammalian manus
—
282 THE MAHUS. [chap. xvi.
first and fifth digits ; while the second, third, and fourth
remain functional, with long ungual phalanges cleft me-
sially at their extremities. The third is longer than the
second, and this longer than the fourth. In Chceropus the
second and third remain, and retain their relative size,
though comparatively longer, more slender, and with smaller
ungual phalanges. The fourth digit is rudimentary, but
with the normal number of phalanges ; the first and fifth
are entirely suppressed. The carpal bones have their
normal relations, but the trapezium is exceedingly reduced,
Order Monotremata. — In the Echidna the carpus is
short and broad, and has a very complex articulation
with the distal ends of the radius and ulna. The first row
consists of a scapho-lunar and a cuneiform. There is no
central. The distal row has the usual four bones. The
pisiform is large, and articulates with the ulna as well as the
cuneiform, and there is a small radial sesamoid, articulating
with the scapho-lunar. There are also two large sesamoids,
sometimes united, in the palmar tendons. The digits are
five in number, all with the normal number of phalanges,
which are short and broad, except those that bear the
long, slightly curved, broad nails, with which the animal
scratches and burrows in the ground. The pollex is more
slender than the other digits ; it is of about the same length
as the fifth, the second and fourth are nearly equal and
longer, and the third slightly the longest.
In the Ornithorhynchus the manus is comparatively more
slender and elongated ; but the number and arrangement
of the bones are the same as in the Echidna.
CHAPTER XVII.
THE PELVIC GIRDLE.
posterior limb consists of a pelvic girdle and three
ments belonging to the limb proper, viz. the thigh, the
leg and the foot, or pes.
•The Pelvic Girdle is present in some form in all Mam-
Is, though in the Cetacea and the Sirenia it is in an
exceedingly rudimentary condition.
In all Mammals, except those belonging to the two
orders just named, each lateral half of the pelvic girdle
consists primitively, like the corresponding part of the an-
terior limb, of a rod of cartilage crossing the long axis of
the trunk, having an upper or dorsal, and a lower or ventral,
end. The upper end diverges from that of the opposite
side, but the lower end approaches, and, in most cases,
meets it, forming a symphysis, without the intervention of
any bone corresponding to the sternum.
The pelvic girdle differs from the shoulder girdle in being
articulated to the vertebral column, at a point near to, but
not at, the upper end of the rod.
Like the shoulder girdle, it bears on its outer side, near
the middle, a cup-shaped articular cavity {acetabulum or
cotyloid cavity, Fig. 105, .a, p. 284), into which the proximal
emity of the first bone of the limb proper is received.
extrc
284
THE PELVIC GIRDLE.
[chap.
Like the shoulder girdle it is divided, by its mode of
ossification, into an upper {dorsal) and a lower {ventral)
segment, and the point of union between these is near the
middle of the articular cavity.
Unlike the shoulder girdle of most Mammals, the lower
segment is always largely developed, and ossifies from two
Fig. 105.— Externa) surface of right innominate bone of a young Lamb {Ovis aries),
\. II ilium (gluteal surface) ; si supra-iliac border ; ab acetabular border; id i>chiai
border; Is ischium ; sp spine ; // tuberosity of ischium; P pubis; s symphysis;
thf thyroid or obturator foramen ; a acetabulum.
separate centres, which form an anterior and a posterior
bar, in contact above and below, but leaving a space
between them in the middle, filled only by membrane, and
called the thyroid or obturator foramen {thf).
The upper segment is named the ilium {II), the anterior
bar of the lower segment the pubis (P), and the posterior
bar the ischium {Is). In the process of growth these three
xvil] GENERAL CHARACTERS. 2§5
osseous pieces always coalesce into a single bone, called the
os innominatum.
This is further completed by the addition of epiphyses ;
one for the upper extremity of the ilium (corresponding to
the supra-scapular epiphysis of the shoulder), others for the
most prominent parts of the lower or free borders of the
pubis and ischium (symphysis pubis and tuber ischii), and
also certain epiphysial ossifications developed in the car-
tilage, at the place of junction of the three main elements.
There is never any secondary osseous bar in the pelvic
girdle corresponding to the clavicle of the upper extremity.
The ilium of Mammals is essentially an elongated, three-
sided, or prismatic bone, though the relative size and posi-
tion of the various surfaces and angles may differ greatly
in different species. In the most characteristic form, one
of the surfaces is internal, or directed towards the ver-
tebral column, articulating by a flat irregular surface with the
lateral " pleuropophysial " ossifications of the sacral verte-
bras. This may be called the sacral sicrj ace (see Figs. 106 and
107, p. 287, and Fig. 108, ss, p. 295.) Another is directed
mainly forwards, and may be called anterior or iliac (is), as
it gives origin to the iliacus muscle. The third is posterior
or gluteal (gs), as it gives origin to the gluteal muscles.
Of the borders one is external or acetabular (ab), as it
ends below at the margin of the acetabulum ; another is
antero-internal or pubic (pb), and the third is postero-internal
or ischial (ib), so called because they end below by joining
the pubis and the- ischium respectively.
The innominate bone is always placed more or less
obliquely to the vertebral column, the upper or iliac end
inclining forwards, and the lower or ischio-pubic end turning
backwards, contrary to the usual direction of the scapular arch.
In order to give still greater stability and fixity to the pelvic
in o]
286 THE PELVIC GIRDLE. [chap.
girdle, and to incorporate it more completely for mechanical
purposes with the vertebral column, there is, in addition to
the articulation between the ilium and true sacral vertebrae,
a very strong double ligamentous union between the ischium
and the side of the anterior caudal or pseudo-sacral vertebrae,
constituting the greater and lesser sacro-sciatic ligaments,
which are replaced in some Mammals (as most of the Eden-
tata) by a complete bony union.1
The two innominate bones, together with the sacrum,
constitute the pelvis, a complete circle of bone, or rather a
short tube. This has two outlets : an anterior (sometimes
called inlet or brim) bounded by the inferior surface of the
first sacral vertebra above, by the pubic borders of the
ilia laterally, and by the anterior borders of the converging
pubic bones, meeting at the symphysis below ; and a
posterior outlet, bounded by the posterior part of the
sacrum above, by the great sacro-sciatic ligaments laterally,
and by the converging posterior borders of the ischia below.
In consequence of the oblique position of the innominate
bones, the plane of the anterior outlet (in the horizontal
position of the body) looks downwards and forwards ;
that of the posterior outlet upwards and backwards ; but
these two planes are not exactly parallel, the long axis of
the cavity being usually more or less curved.
Modifications of the Pelvic Girdle in the different Groups
of Mammalia.
Order Primates. — The pelvis of Man is very consider-
ably modified from the usual form met with in Mammals.
1 Practically, though not morphologically, the pelvis is a part of the
trunk or axial skeleton. The functions of the hind limb in propelling
and raising the body necessitate that it should be so.
I]
MAN
2S7
The innominate bone (Fig 106) is remarkably broad in
proportion to its length. The ilium is flattened and ex-
panded, and has a greatly extended, almost semicircular,
supra-iliac border (si). The sacral surface (ss) is small, and
scarcely rises above the vertebral attachment. The iliac
106. — Ventral surface of right inno-
minate bone of Man, lf.
Fig. 107. — Ventral surface of right inno-
minate bone of Dog, 5.
ipra-mac border or crest of the ilium; ,s\y sacral surface; is iliac sunace ; ab
;etabular border: pb pubic border; ib ischial border of ilium ; a acetabulum;
,'roid foramen ; ti tuberosity of ischium ; s symphysis of pubis.
irface (is) is very broad and hollowed. The gluteal surface
is likewise much expanded, and, though presenting several
curves, is, in the main, convex. The acetabular border (ab)
is very short, and has a strong, rounded, rough prominence
for the attachment of the tendon of the rectus (extensor)
288 THE PELVIC GIRDLE. [chap.
muscle of the leg. The pubic border (pb) is slightly
marked, constituting the tinea arcuata interna, or tinea ilio-
pectinea of human anatomy. The ischial border (ib) is
short and deeply hollowed. The acetabulum (a) is large,
circular, with very prominent borders, incomplete only for a
small space on the infero-internal aspect.
The pubis and ischium are short, and widely divergent
from each other, so that the thyroid foramen (t/if) is elon-
gated in the direction across the main axis of the bones.
The symphysis (s) is rather short, and formed by the
pubis alone. Each of the apposed surfaces of bone is
capped by a plate of nbro-cartilage ; these are held to-
gether by strong ligamentous fibres, while between them
there is usually a more or less perfect synovial cavity.
Ankylosis at this spot, so common in the lower Mammalia,
very rarely takes place in Man.
The posterior and inferior border of the ischium is thick-
ened and rounded, and distinguished as the tuber ischii (ti).
Above this, on the hinder border of the same bone, is a
smooth, hollowed surface, called the lesser sciatic notch,
surmounted by an angular prominence called the spine;
above the spine the edge of the ischium passes into the
great concavity of the posterior or ischial border of the
ilium, and which is called the great sciatic, or, more pro-
perly, ilio-ischiatic notch. The strong ligaments (sacro-
sciatic) which pass from the side of the pseudo-sacral and
caudal vertebrae, the one to the tuber and the other to the
spine of the ischium, convert these notches in the living
body into foramina.
The anterior or superior (in the vertical position) outlet of
the pelvis is subcircular, usually rather broader from side to
side than from the vertebral to the pubic border. Its plane
is not far from a right angle with the axis of the vertebral
xvii. ] PRIMATES. 289
column. The posterior outlet is also very wide. In con-
sequence of the great curve of the sacrum, and the short-
ness of the symphysis, the axis of the whole pelvis is
strongly curved.
In all the Simiina the innominate bone, especially the
iliac portion, is more elongated than in Man ; the anterior
outlet of the pelvis is longer from above downwards, nar-
rower, and more oblique ; the tuberosities of the ischia are
re everted, and the spine and sciatic notches less marked.
In the highest forms, such as the Gorilla and Chimpanzee,
the upper part of the ilium is expanded, flattened, and everted,
the iliac surface being even wider than in Man, though much
flatter ; but in the Baboons and Monkeys, the whole ilium is
long and narrow, the sacral surface rises considerably above
the sacral articulation, the iliac surface is narrow, the gluteal
surface is very hollow, and the borders all approximate to
straight and parallel lines. In the Old World monkeys
the tuberosities of the ischia are greatly everted, and ter-
minate in broad, triangular, flattened, rough surfaces, to
which the ischial cutaneous callosities are attached.
In the true Lemurs the pelvis is very wide ; the ilia are
long, narrow, and have a sigmoid curve, while the pubes
approach each other at the symphysis at a very open angle,
giving an elegant lyre shape to the anterior outline of the
pelvis. On the other hand, in the genus Loris of the same
group (and to a less extent in Tarsius, Perodicticus, and
others) the cavity of the pelvis is remarkably narrow from
side to side ; the ilia are straight slender rods, from the
lower end of which the large, flattened, and compressed
Iubes project forward at a right angle, forming a prominent
eel at the symphysis.
In the Carnivora the pelvis is generally elongated and
arrow, the ilium and ischium being in a straight line, and
290 THE PELVIC GIRDLE. [chap.
of nearly equal length. In most species the ilia are straight,
flattened, and not everted above (see Fig. 107, p. 287) the iiiac
surface (is) is very narrow, and confined to the lower part of
the bone, as the acetabular and pubic borders meet in front
above ; the gluteal surface looks directly outwards and is
concave ; the sacral surface (ss) forms a broad flat plane
above the attachment to the sacrum, the crest being formed
by the united edges of the sacral and gluteal surfaces,
instead of the iliac and gluteal surfaces, as in Man. The
symphysis is long ; it includes part of both pubis and is-
chium, and commonly becomes completely osseous in
adult animals. The thyroid foramen (thf) is oval, with its
long axis parallel to that of the whole bone. The ischia
are wide and divergent posteriorly.
In the Hyaena the pelvis is shorter and wider than in most
other Carnivora, both the upper ends of the ilia and lower
ends of the ischia being considerably everted.
In the Bears the ilia are short and everted above.
In the Seals the pelvis is small, and of a different form
from that of the terrestrial Carnivora. The ilia are exceed-
ingly short, and with much everted upper borders ; the
pubes and ischia are very long and slender, enclosing a long
and narrow obturator foramen, and meeting at a symphysis
of very small extent, in which the bones of the two sides
are very slightly connected, and capable of being widely
separated during parturition.
The pelvis of the Insectivora varies considerably in
form. In Rhynchocyon, Macros celides, and Tupaia, the
symphysis is long, as in the Carnivora, and becomes
ankylosed ; in Erinaceus it is short, though the bones of
the two sides are in contact ; but in many other genera
the pubic bones are widely separated in the middle line
below.
xvii.] INSECTIVORA. 291
The Mole has an exceedingly long, narrow, and straight
pelvis, the innominate bones lying almost parallel with the
vertebral column. Both ilium and upper end of the
ischium are firmly ankylosed with the sacrum, leaving a
small sacro-sciatic foramen between them. Though the
pubic bones do not quite meet in the middle line below,
the brim of the pelvis is extremely contracted, and the
pelvic viscera pass below and external to the cavity instead
of through it. The pubes and ischia are very long and
straight, and inclose a large, but narrow, oval thyroid
foramen.
In the Chiroptera, the pelvis is small and narrow; the
ilia are rod-like, the pubes and ischia are not in a line with
them, but project forwards. The symphysis is often not
closed. There is usually a strongly developed "pectineal "
process, near the acetabular end of the anterior border of
the pubis, and which in some genera (e. g. Phyllorhina,
Tricenops, Asellia), is prolonged so far as to unite with a pro-
cess from the superior extremity of the ilium, inclosing an
oval foramen {preacetabular), as large as, or larger than, the
thyroid foramen.
In many of the Rodentia, as the Beaver, the ilia are
markedly trihedral, with sides of nearly equal extent ; but
in the Hares, the outer (acetabular) border is almost obso-
lete, the gluteal and iliac surfaces are confluent, and both
face outwards, and the internal surface is largely deve-
loped above the sacral attachment.
The pubes and ischia are always largely developed, flat,
and diverging posteriorly, the obturator foramen is of con-
siderable size, and the symphysis is long, and usually
becomes osseous; in the Guinea Pig (Cavia), however, it
remains ligamentous, and the bones are widely separated
Eng parturition,
u 2
292 THE PELVIC GIRDLE. [chap.
Order Ungulata. — In the Pecora the pelvis generally is
elongated. The ilium is expanded and everted at the
upper extremity ; but between the sacral attachment and the
acetabulum it is much contracted, and its borders rounded,
so that the divisions of its surfaces are no longer distinct.
There is usually a deep oval depression above the ace-
tabulum, just within the attachment of the rectus muscle.
The anterior outlet forms a regular oval with the long
diameter between the sacrum and symphysis. The latter
is very long, including a considerable portion of the ischia.
The margins of the bones are completed by large epiphyses
in this region, but ultimately coalesce across the middle line.
The ischia are much developed ; the tuberosities are large,
and have on the middle of their outer side a well-marked
conical process, directed outwards, and very characteristic
of this group of animals.
In the Giraffe the pelvis is shorter than in most of the
other Pecora ; the upper ends of the ilia are more expanded,
the thyroid foramen is nearly circular, and the supra-ace-
tabular fossa is almost obsolete.
These characters are still more strongly marked in the
Camels ; while, on the other hand, in the Pigs the pelvis is
elongated, and much resembles that of the Pecora, but the
supra-acetabular fossa is wanting.
In the Perissodactyla, the ilia are widely expanded above,
but much contracted on approaching the acetabulum. The
ischia are less elongated than in the Pecora, and the thy-
roid foramen is more circular.
The Elephant has a very peculiar pelvis, the form of the
ilium, and the arrangement of its surfaces, somewhat recalling
those of the human pelvis. The supra-iliac border or crest
is greatly extended and curves outwards and downwards.
The sacral surface of the ilium is narrow, and scarcely rises
i.] SIRENIA. 293
above the attachment to the sacrum. The iliac and gluteal
surfaces are widely expanded, especially at the upper part,
and, the pelvis being set nearly vertically to the vertebral
column, they face almost directly forwards and backwards.
The outer or acetabular border is short and deeply hollowed.
The pubic and ischial portions are comparatively small, the
atter being very little produced backwards beyond the
symphysis.
In the Sirenia, the pelvis is extremely rudimentary, being
mposed, in the Dugong, of two slender, elongated bones
on each side, placed end to end, and commonly ankylosing
together. The upper one, which represents the ilium, is
connected by a ligament with the end of the transverse pro-
cess of the sacral vertebra ; the lower one is the ischium,
or ischium and pubis combined, and approaches, though it
does not meet, its fellow of the opposite side.
In the adult Manati, the innominate bone is represented
by a single irregular triangular bone, connected by rather
long ligaments with the vertebral column above, and with
Be opposite bone across the middle line.
There is no trace of an acetabulum, or of any portion of
e limb proper in any of the existing Sirenia ; but in the
extinct Halitherium an acetabular depression and rudi-
mentary femur have been discovered.
In the Cetacea the pelvis is reduced to a pair of elon-
gated, slender bones (each of which ossifies from a single
centre), placed on each side of, and rather below, the ver-
tebral column, lying nearly parallel to its long axis (though
they converge somewhat anteriorly), and opposite the spot
where the chevron bones commence to be developed
neath the bodies of the vertebrae. These bones probably
represent the ischia, and their principal function is to
ive attachment to the crura of the penis or clitoris, as
g.v
294 THE PELVIC GIRDLE. [chap.
the case may be. Hence they are usually more largely
developed in the male than in the female.
In the Whalebone Whales they usually have a projecting
angle placed about the middle, near which, in some species,
a second small bone, which probably represents the femur,
is attached by ligament (see Fig. 112, p. 305). In a full-
grown male Rorqual {Balcenoptera musculus), sixty- seven feet
in length, each pelvic bone was sixteen inches long. In the
Greenland Whale (Balczna mysticetus,) they are rather shorter
and stouter. As might be expected, from the rudimentary
character of these bones, they vary considerably in size and
form in different individuals of the same species, and often
on the two sides of the same animal.
In the Dolphins, they are generally smaller, and more
simple than in the Whalebone Whales, and usually quite
straight, though sometimes arched, or presenting a sigmoid
curve.
Order Edentata. — In the Sloths, the pelvis is very short
and wide, with tolerably broad flattened ilia, and slender
pubes and ischia, inclosing a large oval thyroid foramen,
the inferior boundary of which, and the extremely narrow
ossified symphysis, are formed by the pubis alone. The
spine of the ischium is produced backwards to unite with
the transverse processes of some of the pseudosacral ver-
tebras, inclosing a . sacro-sciatic foramen. The sacro-iliac
articulation is commonly ankylosed.
In all the other Edentates the pelvis is more or less elon-
gated, the ilia trihedral, the ischia largely developed, the
pubes slender, the symphysis exceedingly short, but usually
ossified, and the thyroid foramen large. In all, except Oryc-
teropus, the ischia unite with the vertebral column. This
union is carried to its greatest extent in the Armadillos, in
which animals the broad transverse processes of as many as
MAN SUPI ALIA.
295
five pseudosacral vertebrae may coalesce with each other and
with the side of the ischium, converting the pelvis into a long
bony tube, the more so as the ilia are also firmly and exten-
sively united with the true sacrum. There is usually, especially
in Orycteropus, a strongly developed
ectineal " tubercle.
Order MARSUPrAUA. — In the Ame-
rican Opossums (Didelphys), the ilium
is a very simple, straight, three-sided
rod, thicker at its upper than at its
acetabular end, each side being nearly
equal in extent, hollowed, and sharply
defined by prominent straight borders.
In the Kangaroo (Macropiis, Fig.
108), the three surfaces of the ilium
are also well marked and nearly equal ;
but the whole bone is curved outwards
the upper end.
In the Thylacine and Dasyures the
ilia are compressed laterally, the ace-
tabular and pubic borders meeting
above in front, so that the iliac surface
is (as in the Carnivora) very narrow,
and disappears in the upper half of the
bone, the "crest" being formed by the
united edges of the sacral and gluteal
surfaces ; whereas in the wide, depressed
pelvis of the Wombat (Pkascolomys), the
flattening has taken place in the con-
trary direction, and the iliac surface
spreads out to form with the gluteal surface behind, a wide,
arching, supra-iliac border and crest.
The ischia and pubes are always largely developed, and the
Fig. 108.— Ventral surface
of innominate bone ot
Kangaroo {Macmpns
major), \. si supra-
iliac border ; s.y sacral
surface, is iliac sur-
face ; ab acetabular bor-
der ; pb pubic border of
ilium ; pt pectineal tu-
bercle ; a acetabulum ;
M/thyroid foramen ; ti
tuberosity of ischium ;
j symphysis ; m "mar-
supial" bone.
296 • THE PELVIC GIRDLE. [chap. xvn.
symphysis is long and generally ossified. In the Kangaroos
the pectineal tubercle (//) of the pubis is strongly developed. /
Nearly all Marsupials have a pair of elongated, flattened,
slightly curved bones (Fig. 108, m), moveably articulated
by one extremity to the anterior edge of the pubis, near the
symphysis, and, passing forwards, diverging from each other,
within the layers of the abdominal parietes. They are, in
fact, ossifications in, or intimately connected with, the inner
tendon or " pillar " of the external oblique muscle, and there-
fore come under the category of sesamoid bones. They
vary in size and shape in different species. In Didelphys
they are nearly as long as the ilia, while in the Kangaroo
they are scarcely half the length of that bone. Though
largely developed in the Dasyures, in the allied genus Thy-
larinus, they are represented only by small, unossified fibro-
cartilages.
These bones are commonly called " marsupial bones,"
though they have no special function relating to the ventral
pouch of the female, being nearly equally developed in both
sexes, and also in those species in which the marsupium is
not present.
In ' the Monotremata the pelvis is short and broad
The ilia are short, distinctly trihedral and everted above.
The ischia are large, and prolonged into a considerable
backward-directed tuberosity. The symphysis is long, and
formed about equally by pubes and ischium. The thyroid
foramen is round. The acetabulum is perforated as in Birds.
The pectineal tubercle is greatly developed. There are large
" marsupial " bones in both genera.
CHAPTER XVIII.
THE THIGH AND LEG.
The skeleton of the first segment of the limb proper
consists of an elongated, more or less cylindrical bone,
the femur, which is described as having a shaft and two
extremities.
The dorsal, or (in the ordinary position of the limb)
anterior surface of the shaft is smooth and rounded
from side to side, and generally arched somewhat for-
wards from above downwards ; the ventral or posterior
surface is more or less compressed, and has a rough longi-
tudinal ridge, the linea aspera.
At the proximal extremity is a hemispherical, smooth,
articular "head" (Fig. 109, h, p. 298) which fits into the
acetabulum of the innominate bone, and is generally more
round and more distinctly separated from the rest of the
bone by a constriction or " neck " (;/) than is the corre-
sponding part of the humerus. The axis of the head does
not coincide with that of the shaft of the bone, but crosses
it at an angle varying in different animals, being directed
towards the preaxial 1 or (in the ordinary position of the
limb) internal side, and slightly also towards the anterior
aspect. In nearly all Mammals there is a rounded depres-
1 See note to p. 244.
298
THE THIGH AND LEG.
[('HAP.
ft.
sion near the middle of the surface of the head into which
the ligamcntum tei'cs of the hip joint is inserted. Both
ligament and depression are, however,
wanting in the Orang Utan, Seals, Sea-
Otter, Elephant, Sloths, and the Mono-
tremata.
Immediately below the neck of the
femur are two tuberosities, called tro-
chanters. One (It) is a comparatively
small, conical eminence, situated rather
to the preaxial side, and called the
lesser trochanter. The other ( gt ) is
generally very prominent, projecting
upwards, as high or higher than the top
of the head, situated mainly on the
postaxial border of the bone, but curv-
ing inwards and backwards at its ex-
tremity j this is called the great tro-
chanter. To the posterior side of its
base there is usually a deep depres-
sion, the digital fossa.
In some Mammals, as the Perisso-
dactyle Ungulates, some Rodents and
Edentates, there is a compressed ridge
for muscular attachments, on the post-
axial side of the shaft, a short distance below the great
trochanter, distinguished as the third trochanter. (See Fig.
no, /', p. 303.)
The distal extremity of the femur is thickened, and has a
large trochlear articular surface for the bones of the leg.
This surface is narrow in front, and bounded by more or less
prominent ridges ; posteriorly it is divided by a deep median
notch (intercondylar) into two prominent rounded eminences,
FlG. 109. — Right human
femur, dorsal or ante-
rior aspect, 7. Ihe
boundary lines of the
various epiphyses are
shown, h head ; n neck ;
gt greater trochanter ;
it lesser trochanter; ec
external condyle ; ic in-
ternal condyle.
xvm.] GENERAL CHARACTERS. 299
called condyles (Fig. 109, ec and ic). The slightly elevated
roughed portions of bone above the articular condyles are
termed the tuberosities.
The femur has a main centre of ossification for the shaft,
and epiphysial centres for the head, for each trochanter, and
for the lower extremity. (See Fig. 109.) In most Mammals
the great trochanter and head coalesce together before they
join the shaft. The lower epiphysis is the last to become
united.
The skeleton of the second segment of the limb consists
of two bones, the tibia and fibula,1 of which the former
is the larger in all Mammals. These bones always lie in
their primitive, unmodified position, parallel to each other,
the tibia on the preaxial, and the fibula on the postaxial
side, and are never either permanently crossed or capable
of any considerable amount of rotation, as in the corre-
sponding bones of the fore limb. In the ordinary walking
>sition the tibia is internal, and the fibula external.
The tibia has an expanded proximal end, with a flat-
tened articular surface, divided into two slightly concave
facets, by a rough median eminence, to which the intra-
articular or crucial ligaments of the knee-joint are attached.
The shaft is usually more or less trihedral, with one flat
surface directed backwards, and one border forwards. The
upper end of this border is thickened into a rough tuberosity,
into which the tendon of the great extensor muscles of the
leg are inserted. The lower end is slightly expanded, and
has a somewhat square articular surface to receive the proxi-
mal bone of the tarsus, or astragalus. The inner (or pre-
axial) side of the bone is prolonged beyond this surface,
forming a process called internal malleolus, which is applied
Also occasionally called perone, whence "peroneal," applied to
tures in relation with it.
300 THE THIGH AND LEG. [chap.
to the side of the astragalus, giving additional strength to
the articulation, called "ankle-joint."
The fibula has a slender and generally compressed shaft,
and is somewhat expanded at each extremity. Its upper
end usually takes no part in the knee-joint, being con-
nected, by a separate synovial joint, with the tibia just
below that articulation. The lower end, however, forms
the outer side of the ankle-joint, under the name of
external malleolus.
In many Mammals the fibula is in a more or less rudi-
mentary condition, and it often ankyloses with the tibia at
one or both extremities.
As a general rule each of these bones has a principal
centre of ossification for the shaft, and an epiphysis at either
extremity.
In the neighbourhood of the knee-joint, certain sesamoid
bones are often found in connection with the tendons which
pass over the various bony prominences.
The largest and most constant is the patella, placed on
the anterior surface of the joint, in the conjoined tendon
of the four great extensor muscles of the leg, and having
a smooth articular facet, which plays upon the narrow
anterior part of the inferior articular surface of the femur,
and forms part of the wall of the cavity of the knee-joint.
This bone varies considerably in form, being in some cases
broad, flattened, or lozenge-shaped, and in others, laterally
compressed or oval. It is found in an ossified condition
in all Mammals, with the exception of a few of the Mar-
supialia.
There are also very frequently smaller ossicles, one
or two in number, situated behind the femoral condyles,
called fabellce; and occasionally there is a wedge-shaped
bone within the joint, lying on the articular surface of the
xvi ii.] PRIMATES. 301
tibia, an ossification of the internal interarticular semilunar
cartilage.
Special Characters of the Bones of the Thigh and Leg in the
various Groups.
In Man, the femur (see Fig. 109, p. 298) is long and
rather slender, the shaft is curved forwards, the head is
large and globular, the neck elongated and narrow.
In the Gorilla, the femur is much shorter and broader ;
the head is smaller and less globular, the neck is shorter
and set on the shaft more at a right angle. In the Chim-
panzee the femur more resembles that of Man. In the
Lemurs it is very slender and straight, the head is globular,
md the neck very short.
The tibia and fibula are distinct, and well developed in
ill the Primates, and are united with each other only at
their extremities. Fabellae are wanting in the highest forms,
>ut generally present in the others. The patella is usually
)road and flat, and more or less lozenge-shaped.
In the terrestrial Carnivora, the femur is straight, mode-
itely slender, and with rather a small head. The fibula is
slender, and in the Dogs curved towards the tibia, the lower
ilf being closely applied to that bone ; but in the Bears,
id many others, there is a considerable interval between
the bones throughout, except at their articular extremities.
rabellae are generally present.
In the Seals, the femur is exceedingly short, broad, and
Lttened, with a globular head and an extremely short neck.
'he fibula is almost as large as the tibia, especially at the
listal end. These bones are commonly ankylosed together
it their proximal extremities. '
Among the Insectivora, the Hedgehog has a strong
ridge below the great trochanter of the femur, and several
302 THE THIGH AND LEG. [chap.
other forms have a similar rudiment of a third trochanter.
As a general rule the fibula is slender, and in its lower half
ankylosed with the tibia, but it is complete and distinct in
the genera Galeopithecus, Tupaia, Centetes, Ericulus, and
Solenodon.
In the Chiroptera, the femur is slender and straight,
with trochanters of nearly equal size, and with a small
globular head, set on a very short neck, with its axis
pointing almost directly to the anterior or dorsal surfaces of
the bone. The fibula varies in condition. In Pteropus it is
extremely slender, and the upper end is atrophied, but in
many of the insectivorous Bats it is well developed.
In the Rodentia the femur varies much. In the Hares
and Squirrels it is long and slender, with a third trochanter
immediately below the great trochanter. In the Beaver it is
broad and flat, and has a strong ridge about the middle of
the outer side of the shaft. In many other forms neither of
these accessory prominences exist, but the great trochanter
is usually much developed.
In some forms, as the Beaver, the fibula is distinct,
strongly developed, and separated from the tibia, except at
the extremities, by a wide interosseous space. In others, as
the Hares, it is slender, and in its distal half united with the
tibia. The patella is generally elongated, fabellas are usually
developed, and there are often wedge-shaped ossifications in
the semilunar cartilages of the knee-joint.
In the Ungulata, the femur is rather compressed, espe-
cially at the lower end. There is no distinct constriction
of the neck, separating the head from the rest of the bone.
The great trochanter is very large, and usually rises above
the level of the head. The small trochanter is not very
salient, and sometimes, as in the Rhinoceros (Fig. no), is a
mere rough ridge. The inner edge of the anterior part of the
UiVGULA TA.
303
inferior articular surface is very prominent. In all the
Perissodactyles there is a strongly marked third trochanter
(/'), in the form of a compressed ridge curving forwards.
This is entirely absent in all the known Artiodactyles.
riG. no. — Anterior aspect of right femur ot Rhinoceros {Rhinoceros indicus), \.
k head ; t great trochanter ; t third trochanter.
The fibula is subject to great variations among the
lifferent members of the order. In the Rhinoceros, Tapir,
*ig, and Hippopotamus it is complete and distinct, though
slender in proportion to the tibia. In the Horse a mere
tyliform rudiment of the upper end is present.
In all Pecora and Tylopoda, a small distinct bone, having
very definite form, articulating with the lower end of the
tibia, and forming the external malleolus, appears to
represent the distal extremity of the fibula (see Fig. in).
'here is occasionally in addition a slender styliform rudi-
304 THE THIGH AND LEG [chap.
ment of the proximal extremity, but the two are never united
together by bone.
Fig.
-Anterior aspect of lower end of the right tibia and fibula of Red Deer
(Cervus elaph?{s), %. t tibia ; f fibula.
In the Tragulina, the fibula is long and slender, and com-
plete, but its lower end is indistinguishably blended with
the tibia.
The patella is well ossified, and usually somewhat trian-
gular, with the broad end upwards ; but fabellae are not
commonly developed in the Ungulata.
In the Hyrax there is a slight ridge on the femur in the
place of a third trochanter. The fibula is complete, thickest
at its upper end, where it generally ankyloses with the tibia.
The femur of the Elephant is long and very straight ; the
axis of the head is more in a line with that of the shaft than
usual. The great trochanter is not much developed, and
the small trochanter is nearly obsolete. The fibula is com-
plete, distinct, and slender, though considerably enlarged at
the lower end.
In the Cetacea, certain small nodular bones or cartilages
attached by fibrous tissue to the outer side of the pelvic
bone in some of the Whalebone Whales, are commonly
regarded as rudimentary and functionless representatives
XVI 1 1. J
CETACEA.
of the skeleton of the hind limb. In the Greenland Whale
(Fig. 112), there is a proximal, somewhat pear-shaped bone
(/), about eight inches in length, and a smaller conical distal
bone (/), which may represent the femur and tibia respec-
tively, as suggested by their discoverer, Professor Reinhardt.1
c; 112. — Side view ol bones of posterior extremity of Greenland Right Whale
(Baieena mysticetus), |. from Eschricht and Reinhardt. i ischium ; /femur;
/ accessory ossicle, probably representing the tibia.
[n Megaptera longimana there is but one such bone, and in
in adult Fin Whale {Balcenoptei-a muscidus\ sixty-seven feet
mg, this was found to be only represented by an oval
lodule of cartilage about the size of a walnut. Even this
wanting in some species of the group, as B. rostrata.
No trace of any structure representing the skeleton of
le hind limb, beyond the pelvis, has yet been detected in
my of the Odontocetes.
In none of the existing Sirenia are there any rudiments
)f the hind limb proper, but the extinct Halitherium had an
)ssified femur, articulated to a well-defined acetabulum in
le pelvis.
In the terrestrial and fossorial Edentata the femur is
generally short and broad. There is a third trochanter in
1 See " Recent Memoirs on the Cetacea ; " Ray Society, 1866, p. 134.
X
306 THE THIGH AND LEG. [chap.
the Armadillos and Orycta'ofius, and a sharp ridge along
the whole external border in Myrmecophaga. The fibula is
as long as the tibia. In the Armadillos these bones are
commonly ankylosed together at each extremity, but curve
away from each other at the middle, leaving a wide inter-
osseous space. In the Anteaters they are both nearly
straight and parallel.
In the Sloths the femur is long, slender, and flattened
from before backwards. There is no third trochanter ; the
head is large and globular, and placed near the middle of
the proximal end of the shaft, with the axis of which it
more nearly coincides than in most Mammals. The tibia
and fibula are complete, and more nearly equal in size than
in most Mammal?. They are both curved, so as to be
separated considerably in the middle part of the leg. The
lower end of the fibula has a conical prominence which
turns inwards, and fits into a depression on the outer side
of the articular surface of the astragalus, as a pivot into
a socket.
In none of the Marsupialia is a third trochanter pre-
sent on the femur. The fibula is always well developed,
and its upper extremity is often produced into a well-marked
process, to the top of which a sesamoid bone is not un-
frequently attached ; but, on the other hand, the patella,
except in the PeramelidcE, is unossified or quite rudimentary.
In the climbing Australian Phalangers and Koalas, which
have broad hind feet, with an opposable hallux, there is a
greater freedom of movement between the fibula and tibia
than in other Mammals, approaching in some degree to the
rotation often permitted between the radius and ulna.
In the Monotremata the femur (Fig. 113,/) is of very
remarkable form, being short, flattened from before back-
wards, narrow in the middle of the shaft, and very broad
XVIII.]
MONOTREMATA.
307
at each end ; the trochanters are both well developed, and
the head placed between them on a very short neck, and with
its axis directed quite towards the anterior or dorsal aspect
of the bone. The fibula (/') is large and straight j it has
a broad flattened process, completed, by an epiphysis, pro-
113. — Anterior aspect of bones ot right leg ot Ornilhorhynchus paradoxus,
/"femur ; t tibia; f fibula ; p patella.
jecting from the upper extremity above the point of articu-
lation with the tibia, much resembling the olecranon of the
fore limb. The tibia (/) is strongly curved in Ornilhorhynchus,
but straight in Echidna. In both genera the patella (/) is
fell developed.
x 2
CHAPTER XIX.
THE HIND FOOT OR PES.
The terminal segment of the hind limb is the foot or pes.
Its skeleton presents in many particulars a close resemblance
to that of the manus, being divisible into three parts : — (i) a
group of short, more or less rounded or square-shaped
bones, constituting the tarsus ; (2) a series of long bones
placed side by side, forming the metatarsus; and (3) the
phalanges of the digits or toes (see Fig. 114, p. 310).
The metatarsal bones never exceed five in number, and
the phalanges follow the same numerical rule as in the
manus, never exceeding three in each digit. Moreover, the
first digit (counting from the tibial side), or hallux, resem-
bles the pollex of the hand in always having one segment
less than the other digits.
The bones of the tarsus in many of the lower Vertebrata
closely resemble both in number and arrangement those of
the carpus, as shown in Fig. 85, p. 255. They have been
described in their most generalized condition by Gegenbaur
under the names expressed in the first column of the
following table.1 The names in the second column are
those by which they are most generally known in this
1 " Untersuchungen zur Vergleichenden Anatomic" Carpus und
Tarsus. 1864.
chap, xix.] GENERAL CHARACTERS. 309
country, and which will be used in the present work, while
in the third column some synonyms, occasionally employed,
are added.
Tibiale
Intermedium
1
=
Astragalus =
Talus.
Fibulare
=
Calcaneum —
Os calcis.
Centrale
=
Navicular =
Scaphoideum.
Tarsale I
=
Internal Cuneiform =
Entocuneiforme.
Tarsale 2
=
Middle Cuneiform =
Mesocu neiformc.
Tarsale 3
=
External Cuneiform =
Ectocuneiforme.
Tarsale 4
Tarsale 5
I
=
Cuboid.
The bones of the tarsus of Mammals present fewer diver-
sities of number and arrangement than those of the carpus.
The proximal row (see Fig. 1 14) always consists of two
bones, the astragalus (a, which according to Gegenbaur's
view represents the coalesced scaphoid and lunar of the
ind) and the calcaneum (c). The former is placed more
the dorsal side of the foot than the latter, and almost
clusively furnishes the tarsal part of the tibio-tarsal or
kle-joint. It has a rounded anterior or distal projection
lied the "head." The calcaneum, placed more to the
ntral or " plantar " side of the foot, is elongated back-
wards to form a more or less prominent tuberosity, the tuber
calcis, to which the tendon of the great extensor muscles of
the foot is attached. The navicular bone {n) is interposed
between the proximal and distal row on the inner, or tibial,
side of the foot, but on the outer side the bones of the two
rows come into contact. The distal row, when complete,
Ionsists of four bones, which, beginning on the inner, side,
re the three cuneiform bones, internal (^r1), middle (c2), and
xternal (c3), articulated to the distal surface of the navicular,
and the cuboid (cb) articulated with the calcaneum. Of these
the middle cuneiform is usually the smallest in animals in
3io
THE HIND FOOT OR PES.
[CHAP.
which all five digits are developed ; but when the hallux is
wanting, the internal cuneiform may be rudimentary or
altogether absent.
Fig. 114 —Bones of a right human foot, showing the epiphyses, 4. T tarsus; M
metatarsus; Ph phalanges; c calcaneum ; a astragalus ; cb cuboid ; n navicular;
c1 internal cuneiform ; c3 middle cuneiform ; <:3 external cuneiform ; the digits are
indicated by Roman numerals, counting from the tibial to the fibular side.
The three cuneiform bones support the first, second, and
third metatarsals respectively, the cuboid supports the fourth
and fifth ; they thus exactly correspond with the four bones
of the distal row of the carpus.
In addition to these constant tarsal bones, there may
be supplemental or sesamoid bones ; one situated near the
middle of the tibial side of the tarsus, largely developed in
many Carnivora and Rodents ; another, less frequent, on the
fibular side ; and a third often developed in the tendons
xix.] GENERAL CHARACTERS. 311
of the plantar surface of the tarsus. There is also usually
a pair of sesamoid bones opposite each metatarso-phalangeal
articulation, on its plantar aspect.
The development of the bones of the foot corresponds in
the main with that of the bones of the manus. Each tarsal
bone is ossified from a single centre, but the calcaneum has
in addition an epiphysis for the most projecting part or
tuberosity. The four outer metatarsals have each one
centre from which the shaft and proximal end is ossified,
and a large epiphysis at the distal end ; the first meta-
irsal (if it should be so called) and all the phalanges have
in epiphysis only at the proximal extremity. This rule is
ilmost universal, the most notable exception being found
in the Seals, in which animals (see Fig. 116, p. 315) each
>f the metatarsals and all the bones of the toes, except
the terminal phalanges, have epiphyses at both, ends of
the shaft.
Order Primates. — In Man (see Fig. 114) the foot is
>road, and in the ordinary standing position the whole
length of the plantar surface (at least its outer edge) rests
>n the ground, the main axis of the foot being at a right
ingle with that of the leg. The inner or tibial side of the
foot is arched before backwards, each extremity only rest-
)g on the ground.
The tarsus is longer than the metatarsus, and the latter is
longer than the digits, but the forms and relations of the tarsal
bones are quite characteristic of the general Mammalian
type, and the five digits are present with the complete
number of phalanges. The hallux is much stouter than anv
of the others, though usually not quite so long as the second
toe. Its metatarsal is articulated to a nearly flat surface on
the internal cuneiform, directed distally, so that it is placed
312 THE HIND FOOT OR PES. [chap.
in the same plane as the other toes, and cannot be freely
separated from, or opposed to, them. There are no supple-
mentary tarsal bones, and sesamoids are developed under
the metatarso-phalangeal joint of the hallux only. The
phalanges are much smaller, shorter, and more compressed
than are those of the manus. The ungual phalanges are
very small, depressed, and somewhat spatulate.
The principal distinction of the foot of the Simiina from
that of Man is that it is more or less modified into a grasping
organ. The tarsal and metatarsal bones and phalanges are
the same in number and relative position, but the articular
surface of the internal cuneiform for the hallux is saddle-
shaped, and is directed obliquely towards the inner or
tibial side of the foot. The consequence is that the hallux
is not only somewhat separated from the other digits, but
is also set in a different plane, so that when it is flexed it
turns towards the sole of the foot, and becomes opposed to
the others, much as the thumb does in the human hand.
It is this peculiarity of the pes which has given rise to the
term quadramanous, or " four-handed," often applied to this
group of animals.
The hallux is usually relatively shorter than it is in Man.
In the Orang (Simia satyrus) it is particularly short, and
often wants the terminal phalanx, while the metatarsals and
the phalanges of the other digits are long and curved, the
proportions of the three segments of the foot being exactly
the reverse of those of Man; as the tarsal segment is
shortest, and the phalangeal the longest.
The form of the articular surface of the astragalus, and
especially the free mobility of the navicular and cuboid
bones on the astragalus and calcaneum, cause the foot of
the Orang to be set very obliquely on the leg, so that when
placed on a level surface the fibular border only rests on the
XIX. j
PRIMA TES.
313
ground, and the sole is directed inwards. This position suits
well for grasping vertically-placed boughs of trees, but is ill
adapted for standing or walking on the ground. A similar
disposition is seen in a varying degree in most of the
Monkeys, but in none so markedly as the Orang, in which
animal all the peculiarities by which the simian is dis-
JV
[5— Right pes of Tars/us spectrum (nat. size), a astragalus ; c calcaneum
« navicular; c1 internal cuneiform; c2 middle cuneiform; c3 external cuneiform
cb cuboid ; 1 to v the digits. *
iguished from the human foot, are most strikingly
displayed.
There are usually two sesamoid bones behind each
metatarso-phalangeal joint, and a single one behind the
cuboid in the tendon of the peroneus longus muscle.
The structure of the foot of the Lemurina resembles
generally that of the Simiina, and is in fact one of the
3 H THE HIND FOOT OR PES. [chap.
principal bonds of union between these groups. The hallux
is large and opposable, with a flattened ungual phalanx.
The second digit in Lemur has a narrow, pointed, ungual
phalanx, while that of the other digits is flat and spatulate, as
in the Simiina. In Chiromys all the ungual phalanges, except
that of the hallux, are compressed, curved, and pointed.
In Perodicticus there is a supplemental ossicle in the
transverse ligament of the plantar surface of the tarsus,
corresponding to that met with in the carpus (see p. 260).
A remarkable elongation of the tarsal segment of the pes
occurs in the Galagos (Otolicnus), owing to the modification
of two bones, the calcaneum and the navicular ; the distal
portion of the former, and the whole of the latter, having the
form of nearly cylindrical rods placed side by side, while
the other bones retain nearly their normal form and propor-
tions. A precisely similar modification is carried to a still
greater extent in the genus Tarsius (see Fig. 115, p. 313).
All the terrestrial Carnivora have the normal number of
tarsal bones, with very little deviation from their normal
form and relations.
The hallux is present and well developed, though shorter
than the other toes in the Ursid<zy Procyonidce, Mustelidce,
and most of the Viverridce. In the Cam'dce, Hyce?iidce, and
Felidce, it is only represented by a rudimentary metatarsal.
The other four metatarsals and digits are always well de-
veloped and subequal. The ungual phalanges in the Felidce.
present the same characters as those of the fore limb (see
p. 262).
In the Bears, the foot is flat, broad, and plantigrade. In
the Dogs and Cats, it is longer and narrower, and the heel
is raised from the ground in walking.
In the Sea Otter (Enhydra), the hind foot approximates
to that of the Seals. It is very large and flattened, almost
XIX.]
CARNIVORA.
315
fin-like, and much everted ; but the hallux is still shorter
than any of the other digits, and the two outer toes are the
longest.
In the Seals the pes is completely modified for a special
purpose. It has no longer any function as an organ of
support or progression on land, and is habitually directed
backwards, with the dorsal surface outwards, and the
Fig. 116. — Dorsal surface of right pes of young Elephant Seal (Mac? orhinus pro-
boscidea), \, showing the epiphyses. The letters as before.
plantar surface in contact with the corresponding part of
the opposite limb. The calcaneum is very short, its tube-
rosity being almost obsolete. The two lateral digits (first
and fifth) are both longer and much stouter than the others ;
the middle digit is the shortest. In the Elephant Seal
(Macrorhmus proboscidea), all the phalanges (except the
316 THE HIND FOOT OR PES. [chap.
terminal ones) have epiphyses at both ends of the shaft
(see Fig. 116, p. 315).
In the Otariidcz, or Eared Seals, and the Walrus, which
use the hind feet in walking, these modifications from the
ordinary type are not so marked, the calcaneum having a
greater backward projection, and all the digits being of
nearly equal length. In both there is a large sesamoid on
the tibial side of the tarsus.
In the greater number of the animals of the order In-
sectivora the tarsus is quite normal, and there are five
digits, all with curved, pointed, moderately developed
ungual phalanges, the hallux being the shortest. In the
Mole, the pes is narrow, having none of the modifications
of structure observed in the manus, except that there is
an unusually large slender sesamoid on the tibial side of
the tarsus, corresponding to the falciform bone of the fore
limb. In the Water Moles (Myoga/e), the pes is remark-
ably large and almost fin-like.
In the African genera Petrodromus and Rhy?ichocyon, the
hallux is only represented . by a rudimentary metatarsal.
The last-named animal has a remarkably elongated pes,
produced partly by the length of the metatarsals, and partly
by a peculiar elongation of all the bones of the distal row
of the tarsus, the cuboid, and three cuneiform bones. Con-
trary to what occurs in the Galagos, the navicular and cal-
caneum are of normal proportions.
Order Chiroptera. — The tarsus is very short ; the tuber
calcanei a slender curved process ; the metatarsals are
equal and rather short ; the phalanges elongated and sub-
equal in length, the hallux being rather the shortest ; the un-
gual phalanges are long, curved, compressed, and pointed.
Order Rodentia. — The structure of the pes varies much in
different members of this order. In the Beaver, as in most
XIX.]
RODENTIA.
3*7
swimming quadrupeds, it is disproportionately large and
flat. The five digits are well developed, but the third and
fourth are considerably longer and stouter than the others.
The head of the fifth metatarsal is articulated to the outer
side of the fourth metatarsal, and not directly to the
cuboid. The middle cuneiform is very small. There is a
large sesamoid bone on the tibial side of the tarsus, articu-
lating with the astragalus, navicular, and
internal cuneiform. The tuberosity of
the calcaneum is long and obliquely
compressed.
The functional digits in other Ro-
dents may be five, as in the Rats, Por-
cupines, and Squirrels ; or the hallux
may be suppressed, as in the Hares ;
and occasionally the fifth digit is also
wanting, reducing the number to three,
as in the Capybara, Viscacha, and
Agouti. The last-named animal has the
three metatarsals elongated and closely
pressed together, and all the digits with
>hort subequal phalanges. A still further
modification of the same type leads to
the singular condition of pes met with in
the Jerboas (genus Dipus, see Fig. 117),
which at first sight much resembles that
of a bird. The three metatarsals are
ankylosed together to form a single bone, which supports
the three separate short digits, each with three phalanges,
"hese alone are applied to the ground, the tarsus and long
letatarsal segment being raised almost vertically. The
lallux is wanting or rudimentary, but in some species there
is a small fifth digit.
Fig. 117 - Bones of right
pes of Jerboa [Dipus
a-gyptius), f.
318 THE HIND FOOT OR PES. [chap.
All the animals of the order Ungulata are digitigrade,
the heel being raised from the ground, and the metatarsal
segment usually much elongated. There is never any trace
of a hallux. As in the corresponding segment of the fore
limb, the pes is formed upon one or other of two distinct
types, each characteristic of one of the sub-orders.
In the Perissodactyla, the third digit is the largest, in the
centre of the foot, and symmetrical in itself; the second
and fourth are smaller, and nearly equal in length, but some-
times quite rudimentary. A line drawn through the centre
of the foot passes through the axis of the third digit, and
the middle of the external cuneiform, navicular, and as-
tragalus. The distal surface of the astragalus has a large
articular surface for the navicular, and a very small one for
the cuboid; which bone is of comparatively less importance
than in the Artiodactyla, The calcaneum does not articu-
late with the lowrer end of the fibula.
The Rhinoceros (Fig. 118) and Tapir have all the usual
bones of the tarsus well developed. The internal cuneiform
has a curved process projecting backwards. The middle
cuneiform (c2) is very small. The whole foot is compara-
tively short and broad. The second and fourth toes are
well developed, being nearly as long as the middle toe. The
phalanges resemble those of the fore limb. In the Tapir
the pes differs from the manus in wanting the fifth digit.
In the Horse (Fig. 119), the middle toe is greatly
enlarged, and the second and fourth reduced to slender
styliform metatarsals, about three-fourths the length of the
second, but supporting no phalanges. The navicular (n)
and the external cuneiform (&) are very broad and flat.
The cuboid (cb) is small, and the internal and middle
cuneiform bones are small and united together.
Various gradational stages between the complete tridac-
XIX.]
UNGULA TA.
3'9
tyle foot of the Rhinoceros and the monodactyle foot of
the Horse are met with in extinct species of the Perisso-
dactyla.
Fig. 118. — Dorsal surface of right tarsus
of Rhinoceros (Rhinoceros sumatren-
sis, \.
Fig. 119— Dorsal surface of right tarsus
of Horse [Egnus caballus), \.
In the Artiodactyla the third and fourth digits are nearly
equally developed, and their ungual phalanges are flattened
>n their contiguous sides, so that together they constitute a
rmmetrical form. The second and fifth toes, when present,
re also equal, but smaller than the others. A line drawn
lough the centre of the foot has on its tibial side the
lird digit and metatarsal, the external cuneiform, the
ivicular, and half the astragalus ; and on its fibular side
le fourth digit and metatarsal, the cuboid and the other
ilf of the astragalus. The distal articular surface of the
320
THE HIND FOOT OR PES.
[chap.
astragalus is divided into two nearly equal facets, one for the
navicular and one for the cuboid. The calcaneum has an
articular facet for the lower end of the fibula.
In the Suina (Fig. 120) all the tarsal bones are distinct.
The four toes are well developed, and the metatarsals are
usually distinct. The foot is relatively shortest and broadest
in the Hippopotamus, the outer toes being nearly as long as
the others, and the ungual phalanges very short, broad,
and rounded in front. The Peccaries show a transition
cb „
Fig. 120. — Dorsal surface of right tarsus
. of Pig (Sus scrofa), £.
Fig. i2i. — Dorsal surface of right tarsal
of Red Deer [Cervus elap/ins), \.
towards the ruminating sections of the order in the reduc-
tion of the size of the outer toes and the confluence of the
third and fourth metatarsals. On the hind foot the fifth
digit is absent though the second is tolerably well developed.
xix.] UNGULATA. 321
In the Tylopoda the cuboid and navicular are distinct.
There is no internal cuneiform. The second and fifth digits
are entirely absent. The metatarsals of the third and
fourth are united except * at their lower extremity. The
phalanges resemble those of the fore-foot.
In the Tragidma the cuboid, navicular, and two outer
cuneiforms are united to form a single bone. The third and
fourth metatarsals are confluent. The second and fifth are
complete, extending from the small digits up to the tarsus,
but are very slender.
In all the Pecora (Fig. 121) the cuboid (cb) and navicular
(n) are united, as are the second and third cuneiform bones,
and in some T>ttr(Cervulus and Pudu) these latter are farther
united with the cubo-navicular ; the first cuneiform is always
distinct, though small.1 The third and fourth metatarsals
(m in. and m iv.) are united in the same manner as the
letacarpals, and the phalanges of the digits are very similar
to those of the manus. The second and fifth metatarsals are
ilways wanting ; the bones of the corresponding digits are
ibsent in the Giraffe and most of the Oxen, Sheep, and
Antelopes. In the Deer there are usually three small
phalanges to each of these digits, not directly articulated
with the rest of the skeleton. A large, oval sesamoid is
commonly present in the plantar surface of the tarsus.
The pes of the Hyrax closely resembles that of the
Rhinoceros, but the ungual phalanx of the second digit is
cleft almost to its base.
In the Proboscidea the pes is short and broad, but
smaller and more compressed than the manus, and in the
more rudimentary condition of the two lateral digits shows
a greater tendency to approach the Perissodactyle form.
1 See Sir Victor Brooke, Proceedings of the Zoological Society, 1874,
P- 34-
Y
322 THE HIND FOOT OR PES. [chap.
The three middle toes have the usual number of bones, but
the terminal phalanges are small and irregular in shape.
The first and fifth toes have each one phalanx beyond the
metatarsal. The astragalus is very flat, and has no articu-
lation with the cuboid. The internal cuneiform is produced
distally, as is the corresponding bone of the manus.
Order Edentata. — In the Sloths the pes much resembles
the manus in its general characters, being long, very narrow,
and curved, terminating in strong, compressed, pointed
ungual phalanges, supporting hook-like claws. The tarsus
is short ; the astragalus has a deep, cup-shaped cavity on its
outer side, into which a conical projection of the lower end
of the fibula is received.
The appellation " Two-toed " applied to the genus Cho-
Icepus refers only to the anterior limb, for in the pes the
three middle toes are functionally developed, and of nearly
equal size in both the genera of the family.
In Bradypus the tuber calcanei is long, compressed, and
widened at the extremity. The tarsal bones have a great
tendency to ankylosis. The first and fifth metatarsals are
very rudimentary, and support no phalanges. The proxi-
mal phalanges of the three middle digits are very short, and
coalesce very early with the metatarsals, as in the corre-
sponding part of the upper extremity.
In Cholo&pas, the tuberosity of the calcaneum is very
small. The tarsal bones remain distinct from one another.
The proximal phalanges of the three middle digits are
extremely short, but not ankylosed with the metatarsals.
The first and fifth metatarsals are about three-fourths of the
length of the others, flattened, and gradually diminishing in
size to their free ends.
In nearly all the members of the Entomophagous section
of the Edentata, the pes is much more normal in type, and
xix.] MARSUPIALIA. 323
adapted for plantigrade progression on the ground. It does
not even present any modifications corresponding to those
observed in the manus of the same animals. The normal
number of tarsal bones, and the complete number of pha-
langes, are always present in each digit. Of these the
second and third are usually the longest, the fourth next,
and the first and fifth shortest.
The little prehensile-tailed Tree Anteater (Cyclothurus
didactylus) has the pes modified into a climbing organ.
The hallux is rudimentary, consisting of a metatarsal and
one phalanx, concealed beneath the skin, but the four other
toes are subequal and much curved, with long, pointed,
compressed, ungual phalanges. The tuber calcanei is di-
rected towards the plantar surface, and parallel with it, and
extending to about double its length, is the greatly elongated
sesamoid ossicle of the tibial side of the foot. These
together support the prominent calcarine cushion to which
the nails are opposed in climbing.
In the Marsupialia, the hind foot is subject to great
modifications, some of the genera presenting very striking
deviations from the typical condition.
The seven bones usually found in the Mammalian tarsus
are always present and distinct from each other, but the
astragalus is relatively smaller and more flattened than in
Placental Mammals. In the climbing Marsupials espe-
cially, the articular surface for the fibula, instead of being
perpendicular to that for the lower end of the tibia, is
almost in the same plane with it ; and in all, the " head," or
portion of the bone which projects forwards to articulate
with the navicular, is very slightly developed.
In the American Opossums (JDidelphidce), the foot is
short and broad ; the -hallux is stout, placed at right angles
with, and opposable to, the other four digits ; it has a short,
y 2
324 THE HIND FOOT OR PES. [chap.
rounded terminal phalanx, which bears no nail. The other
digits are subequal, and have compressed, pointed, curved,
ungual phalanges.
In the Dasyuridce, the foot is comparatively narrow ; the
second, third, fourth, and fifth toes are subequal ; the hallux
is either very small, and placed close to the others, or com-
pletely suppressed, as in the Thylacine.
In the Wombats (Phascolomyid<z), the foot is short and
broad j the hallux is very short, with only one rounded
phalanx, and divaricated from the other toes. These are
nearly equal in length ; the fourth and fifth are stouter than
the second and third, thus showing a slight tendency towards
the condition met with in the next group.
In all the remaining Marsupials a peculiar condition of
the pes, called syndactylism, prevails. Whatever the con-
dition of the other toes, or whatever the general form or
function of the foot may be, the second and third meta-
tarsals and digits are very slender, and enclosed nearly to
their extremities in a common integument, so that they look
externally like one small toe with two claws.
In the Kangaroo (Macropus) the whole foot (Fig. 122) is
very long and narrow, and rests entirely on the ground in
the ordinary position of the animal. The tarsal segment is
short, the metatarsus very long. The cuboid is greatly
developed, the navicular and the three cuneiform bones
exceedingly small, in conformity with the condition of the
digits they respectively support. There is a sesamoid on
the plantar surface of the tarsus. The fourth metatarsal
and digit are enormously developed, the fifth moderately
so ; the second and third are nearly as long as the fifth, but
excessively attenuated. There is no rudiment of a hallux.
The ungual phalanges are conical, pointed, slightly curved
above, and flattened on the under surface. The whole foot
XIX.]
MARSUPIALIA.
325
is much compressed laterally, especially at its binder part,
so that the proximal ends of the second and third are
thrown behind that of the great fourth metatarsal, and en-
tirely concealed in a view of the dorsal surface of the foot.
The Tree-Kangaroos of New Guinea (Dendrolagus),
which habitually live among the boughs of large trees, have
el —
Fig. 122. -Rones of right pes of Kan-
garoo {M acropzis bennettii), \.
Fig. 123. — Rones of right foot of Pha-
langer {Phalangista vulpina), f .
the feet constructed on the same type, but shorter, and
more laterally extended.
In the leaf-eating, climbing Australian Opossums (Phalan-
gista,Y\g. 123) and Koalas (Phascolarctos) the second and
third toes are also very slender, but the fourth and fifth are
more equal, especially in length, the foot is broad, and
there is a strongly developed prehensile and opposable,
though nailless, hallux.
326
THE HIND FOOT OR PES.
The insect- and root-eating, ground-dwelling Bandicoots
(Peramelidcz) differing in many other respects from the
Kangaroos, have their hind-foot constructed on exactly
the'same type as in Macropus, even to the relative length
of the different digits, though there is often a. rudiment of
the metatarsal of the hallux. In one
remarkable genus (Choeropus), already
mentioned on account of the peculiar
structure of the manus (see Fig. 104,
p. 281), the same type is carried to a
great extreme, the fourth toe (see Fig.
124) remaining of a prodigious size
and the fifth being reduced to even
smaller dimensions than the second or
third.
Monotremata. — In both species
the seven usual bones of the tarsus are
complete and distinct,1 and the five
digits have the normal number of pha-
langes.
In the Ornithorhynchus the proximal
articular surface of the astragalus is
divided by a deep groove into two
distinct heads, one for the tibia, and
the other for the fibula, the latter
being the larger of the two ; the inner side has a cup-
shaped socket, into which fits an incurved conical process
from the lower end of the tibia. The tuberosity of the cal-
caneum is broad and bifid at the extremity, and directed
1 It has been stated that the cuboid in the Ornithorhynchus is divided
into two bones, as in some reptiles, one supporting the fourth and the
other the fifth metatarsal; but this is not the case in any specimen
which I have examined.
Km
.24.
Bones of right
foot of Choerofins casta-
notis (nat. size).
xix.] MONOTREMATA. 327
not backwards, but towards the tibial side of the foot. In
the male there is an additional, large, flat, curved ossicle,
on the hinder and tibial cside of the plantar aspect of the
tarsus, articulated chiefly to the tibia, which supports the
peculiar perforated horny spur characteristic of this sex, the
function of which has not been discovered. There is also a
small, rounded, supplementary ossicle, below the tibial edge
of the tarsus, near the articulation between the astragalus and
scaphoid. The metatarsals increase in length from the first
to the fifth. The phalanges are all rather long and slender.
The four outer toes are nearly equal \ the hallux is somewhat
shorter. The ungual phalanges are compressed, slightly
curved, and very sharp pointed.
In the Echidna the astragalus is large, with an irregular,
broad, rounded, proximal articular surface, not divided by
a groove, and with a much less distinct fossa, for the in-
ternal malleolus. The tuber calca?iei is directed forwards,
it is also bifid, and its external process is much longer than
the other and curved towards the plantar surface of the
foot. The spur of the male, and the ossicle which supports
it, are much smaller than in the Ornithorhynchus. The
metatarsals are shorter and broader ; they increase in length
from the first to the fifth. The hallux is very short, and has
a flattened, conical, ungual phalanx. The proximal and
middle phalanges are all very short and broad. The ungual
phalanx of the second digit is extremely long and falcate,
the others gradually diminish to the fifth. The ends of the
toes are turned outwards and backwards in the ordinary
position of the animal.
The ungual phalanges of both extremities in the Mono-
tremata have a deep median groove, near the base of the
under surface, leading at its distal extremity into a foramen.
CHAPTER XX.
THE CORRESPONDENCE BETWEEN THE BONES OF THE ANTE-
RIOR AND POSTERIOR EXTREMITY AND THE MODIFICA-
TIONS OF THE POSITIONS OF THE LIMBS.
That a general correspondence exists in the plan of con-
struction of the anterior and posterior extremity cannot fail
to strike the most superficial observer, though to follow out
this correspondence into all its details has severely exercised
the ingenuity of many an anatomist.
It would be quite beside the character of the present
work to give an historical account of the numerous and
very various views which have been held upon this sub-
ject,1 but I propose to lay before the student in a con-
densed form such portions of the general outcome of these
researches as appear to be most satisfactorily established,
premising, however, that all the statements hereinafter to
be made have not yet met with universal assent.2
1 For the bibliography of this question, see Mivart " On some Points
in the Anatomy of Echidna hystrix " (Linn. Soc. Trans, xxv. 1866) ;
and Rolleston " On the Homologies of certain Muscles connected with
the Shoulder Joint" {Ibid. xxvi. 1869). See also Humphry's "Ob-
servations in Myology," 1872.
2 For an exposition of the very opposite hypothesis of "Antero-
posterior Symmetry,'" see Jeffries Wyman " On Symmetry and Homo-
logy in Limbs" {Proc. Boston Soc. Nat. Hist., June, 1867, p. 277) ; and
the elaborate series of papers by Dr. Elliott Cones, published in the
Medical Record (New York) for 1870.
chap, xx.] THE CORRESPONDENCE, &c. 329
In the first place, it is perfectly obvious that the fore and
hind limbs have each a similar division into four main seg-
ments ; the shoulder girdle, the arm, the fore-arm, and the
manus of the one representing respectively the pelvic girdle,
the thigh, the leg, and the pes of the other.
To proceed to further details, it is necessary to place the
limbs (at least in imagination) in an exactly corresponding
position — one, in fact, which is often impossible in the adult
animal on account of the modifications of the articular sur-
faces to suit the posture best adapted for the habits and
mode of life of the individual, but which is the position of
all limbs when they first appear as bud-like processes from
the side of the body of the embryo. In this position the
limbs are extended at right angles to the axis of the trunk
and parallel to each other, as in Fig. 125, a and b. There
is then to each limb a superior or dorsal surface (turned
towards the observer in the figure), an inferior or ventral
surface, and an anterior and a posterior edge. These last
are called by Professor Huxley preaxiai and postaxial (in
reference to the axis of the limb itself) to avoid the con-
fusion with anterior and posterior in the modified positions
they assume in Man and various animals. In the figures
the preaxial side is left light, and the postaxial side is
shaded.
The dorsal surface of the anterior extremity includes the
back of the hand and the extensor surface of the fore-arm
and arm. The dorsal surface of the posterior extremity
includes the dorsum of the foot, front of the leg, and the
extensor surface of the thigh. The preaxial border of the
anterior extremity has in it the pollex, the radius, the
condyle commonly called " external," and the greater tuber-
osity. The preaxial border of the posterior extremity in-
cludes the hallux, the tibia, the condyle commonly called
33o THE CORRESPONDENCE BETWEEN THE [chap,
A
Fig. T25. — Diagrammatic representation of the positions of the limbs of Mammalia.
The preaxial border is left light, the postaxial border shaded, in all the figures.
Limbs of the right side are represented in all cases. A dorsal aspect of the
anterior extremity in its primitive unmodified position; £-/> glenoid border of the
scapula ; s spine ; cb coracoid border ; ssf subscapular fossa ; pf postscapular (in-
fraspinal) fossa ; c coracoid : h humerus; gt greater, radial, or pteaxial tuberosity;
It lesser, ulnar, or postaxial tuberosity; ec external (in the modified position ,
radial, or preaxial condyle; ic internal, ulnar, or postaxial condyle ; r radius,
u ulna ; 1 pollex ; v fifth digit. B dorsal aspect of the posterior extremity in the
same position ; ab acetabular border of the ilium ; fb pubic border ; ib ischial
border ; gs gluteal surface : is iliac surface ; * ischium ; p pubis ; f femur ; It lesser,
tibial, or preaxial trochanter ; gt greater, fibular, or postaxial trochanter; ic in-
ternal (in the modified position), tibial, or preaxial condyle ; ec external, fibular,
or postaxial condyle ; t tibia ; f fibula ; 1 hallux; v fifth digit; c the anterior
extremity, wiih the humerus in the same position, but the eibow- and wrist -joints
bent ; d the posterior extremity in the same position.
" internal/'* and the lesser trochanter. All these parts, then,
should be regarded as serially homologous.
xx. I ANTERIOR AND POSTERIOR EXTREMITY. 331
Fig. 126. — Diagrammatic representation of the positions of the limbs of Mammalia
continued, e the anterior extremity with the same flexures as in c, but with the
whole limb rotated backwards. The preaxial side is external. The letters as
before, f the posterior extremity, with the joints bent, and the whole limb rotated
forwards, as in the. ordinary position of quadruped Mammals The postaxial side
is external, g the humerus in the same position as in e, but the fore-arm r. tated,
as in the ordinary position of quadruped Mammals. Whilst the preaxial side of
the humerus remains external, the postaxial side of the manus is now external.
h the anterior extremity of a Cetacean (Hyperoodou), dorsal surface, i the pos-
terior extremity of a Seal, dorsal surface.
Leaving for the present the shoulder and pelvic girdles
out of consideration, we will next consider the adaptive
changes which take place in the segments of the limb
proper in various animals. These will be best understood
by dividing them into stages (all of which are represented
in the diagram), though it is not meant to imply that the
332 THE CORRESPONDENCE BETWEEN THE [chap.
limbs actually go through so many distinct phases in the
course of development, as all the various modifications from
the primitive to the most adaptive positions may take place
gradually and even simultaneously.
In what may be considered the first stage of modification
(Figs, c and d), each segment of the limb is simply bent
upon the one above it. The proximal segments (humerus
and femur) remain unchanged in position, the dorsal surface
still looking upwards, and the ventral surface downwards ;
the middle segment is bent downwards, so that its ventral
surface faces inwards and its dorsal surface outwards ; and the
joints between these segments (elbow and knee) form pro-
minent angular projections. The third segment being bent
to a greater or less degree in the opposite direction to the
middle one, retains much of its primitive position, the dor-
sal surface being directed upwards and the ends of the digits
pointing outwards. The relations of the preaxial and postaxial
borders of the limb are unchanged. No Mammal habitually
carries its limbs in this position, although the climbing Galeo-
pithecus and the Sloths are not far from it. It is, however,
very nearly the normal position of some Reptiles, especially
the Tortoises, though it is ill adapted for anything but a
very slow and clumsy mode of progression.
The next change, and one which takes place at a very
early period in embryonic life, and which is one of the most
essential in giving the characteristic conformation of the
extremities of the higher Vertebrates, is a rotation of the
whole limb from the proximal end, though in opposite
directions in each case.
The anterior extremity (see Fig. e) is rotated from the
shoulder, through nearly a quarter of a circle, backwards, so
that the humerus, instead of being at a right angle to the axis
of the trunk, is nearly parallel with it, the elbow points back-
xx.] ANTERIOR AND POSTERIOR EXTREMITY. 333
wards, the preaxial side is outwards, and the postaxial side
towards the middle line of the body, and as long as the
radius and ulna retain their primitive parallel position, the
manus is placed with the ends of the digits directed back-
wards, the preaxial side being external.
The hind limb (see Fig. f) is, at the same time, rotated
from the hip to the same extent forwards, so that the femur
is also nearly parallel to the axis of the body, but with the
knee projecting forwards ; the preaxial side is inwards and
the postaxial side outwards ; the tibia and fibula are parallel,
the former internal and the latter external ; the foot has the
ends of the digits directed forwards, the hallux or preaxial
digit is on the inner, and the fifth or most postaxial digit
is on the outer, side.
In this position the hind limb remains, subject only to
minor modifications, in nearly all terrestrial Mammals ; but
the Walrus, and to a certain extent the Sea- Lions, alone
carry the fore limb as described above without further
modification.
The next stage, affecting the fore limb alone, consists in
the rotation of the lower end of the radius around the ulna,
which brings the distal extremity of the manus round from
the back to the front of the limb (see Fig. g). In most
Mammals the limb is permanently fixed in this position,
and the bones of the fore-arm become greatly modified in
consequence, as described in Chapter XV. It will now be
understood how, though the outer side of the humerus
corresponds with the inner side of the femur, in ordinary
quadruped progression, yet the outer side of the manus
corresponds with the outer and not the inner side of
the pes.
To these general conditions there are certain modifications
met with in some animals, and certain exceptions in others.
334 THE CORRESPONDENCE BETWEEN THE [chap.
The modifications with regard to the anterior extremity
are that the humerus may be quite horizontal, or its distal
end may incline upwards, or, as is much more frequently the
case, it may incline somewhat downwards, so that the dorsal
surface is posterior and the ventral surface anterior; the fore-
arm in the ordinary resting position may be quite vertical,
or inclined with its upper end backwards ; the whole of the
manus may rest entirely on the ground, as in the so-called
" plantigrade " or rather " palmigrade " animals, or the
proximal part, the tarsus and metatarsus, may be raised and
placed more or less vertically, the limb resting either on all
or only on the terminal phalanges, according to the com-
pleteness of the " digitigrade " mode of progression.
Similar modifications occur in the hind limb. The
femur is usually inclined with its distal end downwards, so
that the dorsal or "extensor" surface is anterior, and the
ventral or " flexor " surface posterior. In the Elephants it
is very nearly vertical. In most animals which occasionally
assume the upright position, as the Kangaroos and some
Rodents, the femur is ordinarily inclined upwards at its
distal extremity, so that the knee is above the acetabulum,
and the pelvis slung as it were between the two hind limbs.
In Man, on the other hand, in standing or walking the
femur is nearly vertical with the distal ends downwards, and
the pelvis is supported on the top of the limbs.
The positions of the limbs which are quite exceptional
are those of certain aquatic animals.
In the Cetacea (Fig. h) none of the segments of the
anterior limb undergo any deflection from the primitive
straight condition, nor is there any rotation of the bones of
the forearm. The only changes which take place are a partial
rotation backwards from the shoulder, and a slight turning
downwards of the preaxial border. In the Sirenia and the
xx. I ANTERIOR AND POSTERIOR EXTREMITY. 335
Seals, there is a slight bend at the elbow and the wrist,
but little or no rotation of the fore-arm.
In the hind limb of the Seal (Fig. 1) there is very little
flexure at the joints, and the whole limb is turned backwards
instead of forwards from the hip, and at the same time
rotated on its axis, so that the preaxial border becomes
turned downwards. The skeleton of this limb, therefore,
and that of the fore limb of the Cetacean, being retained
normally in almost exactly similar positions, are well adapted
for demonstrating the correspondence between the re-
spective bones of which they are composed (see Figs.
h and 1).
The necessity of the modifications in the direction of the
axes of the heads of the humerus and femur spoken of pre-
viously will easily be understood by a consideration of the
relative positions that these bones are adapted to assume.
Thus the axis of the head of the humerus in the majority of
Mammals is inclined towards the postaxial side of the shaft
of the bone, while that of the femur is inclined towards
its preaxial side.
Hitherto nothing has been said about the shoulder and
pelvic girdle, because the correspondence of their parts is
not so easily explained, nor so generally recognised, as that
of the segments of the limb proper. The following view
appears to be, of those yet suggested, the most probable.
It has been already shown (Chapters XIV. and XVII.)
that the lateral half of each girdle consists primarily of a
bar or rod placed vertically, and divided into an upper and
a lower segment, the point of attachment of the limb being
close to the junction of these two segments. The upper
segment in the fore limb is the scapula, in the hind limb the
ilium ; the lower segment in the fore limb is the coracoid,
in the hind limb the ischium and pubis.
336 THE CORRESPONDENCE BETWEEN THE [chap.
In every Mammal both scapula and ilium may be re-
solved into bars or rods of three-sided or prismatic form.
The two extremities of each bar are placed, as regards the
general position of the trunk, dorsally and ventrally. The
dorsal or upper extremity is capped by the suprascapular
epiphysis in the shoulder girdle, and by the corresponding
supra-iliac epiphysis in the pelvic girdle. The ventral
or inferior extremity enters into the formation of the
glenoid or the acetabular articular cavity, as the case
may be, and joins the coracoid or the ischial element of
the girdle.
The bar, supposed to be in a nearly vertical position, has
three surfaces and three borders. In what may be, at least
theoretically, considered their primary position, the surfaces
of each bar are — (i) Inner or vertebral, turned towards the
vertebral column; (2) Preaxial, corresponding to the preaxial
line of the limb (Fig. 125, a pf, b is); (3) Postaxial, cor-
responding to the postaxial line of the limb (a ssf, b gs). The
borders are — (1) External, in a line with the middle of the
dorsal surface of the limb, and terminating below at the
upper margin of the glenoid or acetabular cavity (a gb, b ah) ;
(2) antero-internal, terminating below in the acromion or
in the pubis (a s, b pb) ; (3) postero-internal, terminating
below in the coracoid, or the ischium, as the case may be
(a cb, b ib).
The correspondence between these parts of the scapula
and ilium will be better understood by placing them in
a tabular form, the middle column showing the names
expressed in the generalized or ideal condition applicable
to both in their primitive condition, and the column at each
side giving the special terms applied to each part in its
variously modified forms.
x J ANTERIOR AND POSTERIOR EXTREMITY. 337
SURFACES.
SCAPULA.
IDEAL.
PELVIS.
Prescapular fossa.
Supraspinous fossa.
Postscapular fossa.
Infraspinous fossa.
Subscapular fossa.
1. Vertebral.
2. Preaxial.
3. Postaxial.
Sacral surface.
Inner surface of ilium,
behind linea arcuata
interna, including the
articular surface for
the sacrum, and the
portion of the bone
above and below this.
Iliac surface.
Internal iliac fossa.
Gluteal surface.
BORDERS.
SCAPULA.
IDEAL.
PELVIS.
Glenoid border.
Posterior border in
most animals.
Axillary border in
Man.
Spine.
Coracoid border.
Anterior border in
most animals.
Superior border in
Man.
1. External.
2. Antero-internal.
3. Postero-internal.
Acetabular border.
Anterior border.
Pub:c border.
Linea arcuata interna.
Ischial border.
Posterior border.
As the humerus in ordinary quadruped Mammals is
rotated backwards from its primitive position, and the femur
z
338 THE CORRESPONDENCE BETWEEN THE [chap.
is rotated forwards, so that the preaxial side of the first
becomes external, and the really corresponding side of the
other becomes internal, so it is with the scapula and ilium.
Each has undergone a rotation on its own axis, through
nearly a quarter of a circle, and in the opposite direction
(see Fig. 126, e and f), so that the inner surface of the one
comes to correspond with the outer surface of the other,
the anterior border of the one with the posterior border of
the other. The long axis of each is also differently inclined,
the upper end of the scapula leaning backwards, while that
of the ilium is inclined forwards, which makes the resem-
blance between them seem still more obscure.
These views are considerably strengthened by a con-
sideration of the disposition of the muscles connected with
the various bones in question.1
The principal differences between the shoulder and pelvic
girdle of the Mammalia are two : — (1) The rudimentary con-
dition of the inferior or ventral section of the girdle (the
coracoid) in the former, as compared with the vast deve-
lopment of the corresponding part of the lower extremity;
(2) the free condition of the anterior as compared with the
posterior girdle. It is neither attached to the vertebral
column above, nor does it (except in the Monotremata) join-
trie opposite part in the middle line below. To compensate
for this, a clavicle is superadded to the anterior girdle in
many Mammals, for which there is no exact homologue in
the lower extremity.
It has been shown in Chapters XVI. and XIX. that
the terminal segments of each limb present a remarkable
general correspondence with certain constant differences.
1 See "On the CoiTespondence between the Parts composing the
Shoulder and the Pelvic Girdle of the Mammalia" {Journal of Anatomy
and Physiology, vol. iv. p. 239, 1870).
xx.] ANTERIOR AND POSTERIOR EXTREMITY. 339
There can be no question but that the carpus and tarsus,
the metacarpus and metatarsus, and the various digits
beginning at the pollex in the one, and the hallux in the
other, are really homologous ; the circumstance of the con-
stant absence of one of the bones of the preaxial digit in
both fore and hind limbs is most significant.
In the carpus and tarsus, the serial homology of the four
bones of the distal row in their respective order is generally
admitted, but with the other bones there is still some differ-
ence of opinion. Gegenbaur has, however, given good
reasons,1 derived chiefly from the results of tracing both
limbs back to their less modified condition in Reptiles and
Amphibia, for considering the astragalus as equivalent to
the scaphoid and lunar united, or the scapho-lunar bone of
the Carnivora &c. ; the calcaneum as representing the
cuneiform, and not, as often supposed, the cuneiform and
the pisiform (the latter being only a sesamoid); and the
navicular of the foot as representing the os centrale, found
only occasionally in the manus of Mammals.
1 " Untersuchungen zur Vergleichenden Anatomie," ites Heft, Carpus
und Tarsus, 1864.
INDEX
Aguti (Dasyprocta), 77, 160, 250, 265, 317.
A Ices (Elk), 174.
Anchitherium, 268.
Anoplotherinm , 67, n.
Anteater (Myrmccophagd), 41, 55, 56, 57,
62, 83, 84, 94, 205, 206, 234, 277, 306.
Antelope, 173. 321.
Antilocapra (Prongbuck), 270.
Ape, 18, 24, 25, 48, 66, 247 ; see also
Simiina.
A rctomys (Marmot), 157, 160, 265.
Armadillo (Dasypus), 7, 40, 56, 58, 62, 69,
84, 94, 207, 235, 253, 257, 278, 279, 294,
306.
Artiodactyla, 3, 24, 51, 92, 161, 169, 268,
303, 318, 319.
A teles (Spider Monkey), 47. 66, 247, 260.
Aye-Aye {Chiromys). 247, 261, 314.
B.
Baboon (Cynocephalus), 138, 139, 140, 260,
289.
Balcena (Whale), 37, 38, 80, 81, 92, 93, 196,
197, 198, 232, 272, 294, 305.
Balcenoptera (Fin Whale), 38, 39, 52, 81,
92, 93, 196, 198, 232, 252, 272, 294, 305.
Bandicoot (Perameles), 42, 43, 59, 237, 280,
281, 326.
Bat, see Chiroptera.
Bathyergus, 157.
Bear (Ursus), 49, 62, 66, 144, 146, 248, 261,
290, 301, 314.
Beaver (Castor), 21, 62, 67, 157, 158, 160,
229, 230, 250, 265, 291, 302, 317.
Beluga, 40, 274.
Brady pus, 41, 55, 85, 209, 236, 237, 252,
276, 277, 322 ; see also Sloth.
C.
Cachalot (Physeter), 40, 52, 53, 54, 79,
80, 93, 94. i93, i94» i95, 232, 274.
Camel, 35, 41, 91, 174, 250, 251, 269, 270,
292.
Capybara (Hydrochcerus), 33, 67 77, 156,
158, 160, 265, 317.
Carnivora, 3, 24, 31, 49, 62, 66, 75, 91,
230, 248, 261, 289, 301, 310, 314.
Castor (Beaver), 21, 62, 67, 144, 150, 157,
158, 229, 230, 265, 291, 302
Canidce, 91, 231, 248, 314, 317.
Cams (Dog), 15. 22, 31, 32, 49, 75, 9^-127,
144, 150, 223, 248, 261, 287, 301, 314.
Capromys, 50, 265.
Cat (Felts), 49, 63, 144, 147, 150, 262, 314.
Cavia (Guinea-Pig), 67, 229, 29c
Ccbidce, 138-141, 245.
Cebus, 139.
Centetes, 32, 50, 66, 152, 249, 263, 302.
Centetidce, 152.
Cercopithecus, 142.
Cervidce, 172.
Cervus (Deer), 34, 78, 173, 233, 248, 269,
270, 304, 320, 321.
Cetacea, 3. 25, 37, 52, 54, 62, 68, 79. 92,
181, 185, 231, C44, 251, 257, 271, 283, 293,
„ 304. 334. 335-
Cheetah, 150
Chelydra, 255.
Chinchilla, 160.
Chimpanzee ( Troglodytes), 31, 47, 48, 60,
75, 91, 138, 139, 227, 260, 289, 301.
Chiromys (Aye- Aye), 247, 261, 314.
Chiroptera, 3, 33, 50, 66, 77, 153, 229,
249. 264, 291, 302, 316.
Chlamydophorus, 69.
Chceropus, 280, 281, 282, 325, 326.
Cho'cepus, 10, 24, 41, 55, 85, 90, 210, 236,
252, 276, 322.
Chrysochloris, 50, 153, 227, 249, 264.
Ccelogenys (Pac=i), 158, 160.
Colobus, 260.
Condylura, 227
Coypu (Myopotamus), 156, 229, 250.
Crocodile, 60.
Cyclotliurus, 55, 56, 69, 84, 94, 207, 235,
322, 278.
Cynocephalus (Baboon), 138, 139, 140, 142,
260, 289
Cystophora, 49, 151.
Dasyprocta (Aguti), 77, 160, 265, 317.
Dasypus (Armadillo), 7, 41, 56, 58, 62, 69,
84', 94, 207, 235, 253, 257, 278, 279, 2Q4,
306.
342
INDEX.
Dasyure (Dasyurus), 215, 253, .280, 295,
296, 324.
Deer (Cervas), 34, 78, 172, 173, 233, 248,
269, 270, 304, 320, 321.
DelpJtinidcz, 40, 193.
Delphinus (Dolphin), 40, 52, 79, 91, 231,
275, 294.
Deiidrolagus, 323.
Desmodus, 66
Didelphia, 4.
Didelphys \ Opossum), 42, 43, 59, 70, 215,
237. 280, 295, 296, 323.
Dipus (Jerboa), 33, 160, 317.
Dog (Canis), 15, 22, 31, 32, 49, 62, 75, 96,
127, 144, 150, 223, 248, 261, 287, 301, 314-
Dolphin (De/phitius), 40, 52, 53, 79, 93,
231, 275, 294.
Dugong {Halicore), 36, 51, 82, 204, 252,
275. 293.
Echidna, 20, 43, 59, 62, 70, 86, 95, 217,
218, 238, 282, 307, 327.
E CENT ATA, 25, 33, 40, 55, 62, 69, 82, 94,
204, 234, 252, 276, 286, 294, 298, 305,
321.
Elephant {Elephas), 36, 51, 61, 67, 92, 127,
180, 181, 234, 266, 292, 298, 304, 321,
334-
Elephant Seal {Macrorhiuus), 258, 315,
3'6.
Elk {Alecs), 174.
Enhydris (Sea Otter), 298, 315.
Equns (Horse), 35.. 51, 77, 73, 92, 164, 233,
250, 251, 267, 26S, 303, 318, 319.
Ericuhts, 302.
Erinacens (Hedgehog), 50, 66, 76, 152,
249, 263, 290, 301.
Grampus (Orca), 40, 274 275.
Guinea Pig (Cavia), 67, 229, 291
Gymnura, 66, 152, 263.
H.
Halicore (Dugong), 36, 51, 82, 204, 252,
275, 293.
Iialitlierium, 293, 305.
Hapale, 247.
H apalidcr, 141.
Hare (Le/>us), 14, 33, 50, 67, 77, 157, 161,
229, 250, 265, 291, 302, 317.
Hedgehog {Erinacens), 50, 66, 76, 152,
249, 263, 290, 301.
Hipparion, 268.
Hippopotamus, 35, 79, 176, 234, 251, 269,
3^3> 320.
Horse {Eqiais), 35, 5-, 77, 79, 92, 164, 165,
?33, 250, 251, 267, 268, 303, 318, 319.
Hyaena, 49, 150, 261, 290.
Hycemdce, 91, 248, 314.
Hydrochoerus (Capyb^ra), 33, 67, 77, 156,
158, 160, 265.
Hylobates (Gibbon), 47, 75, 138.
Hyomoschus, 270.
Hyperoodon, 40, 52, 53, 90, 94, 193, 194.
274, 33i-
Ilypsiprymnus, 215, 280.
Hyracoidea 4, 177.
Hyrax, 4. 10, 24, 51, 67, 92, 177, 234, 251,
265, 266, 304, 321.
Hystrix (Porcupine), 67, 156, 157, 159,
230, 3*7-
I.
Into, 40, 52, 274.
Insectivoka, 3, 24, 32, 49, 66, 76, 150,
227, 249, 263, 290, 301, 316.
Felida, 32, 49, 91, 147. 149, 231, 248, 314.
Felis (Cat), 49, 63, 147, 149, 262, 314.
Fiber, 50.
Fin Whale {Balcenoptera), 38, 39, 52, 81,
92, 93, 196, 198, 232, 252, 272, 294, 305.
Fissipedia, 3.
G.
Galago, 48, 314.
Galeopithecus, 32, 50, 15 c, 229, 249, 563,
264, 302, 332.
Gibbon {Hylobates), 47, 48, 75, T38.
Giraffe, 35, 78, 233, 270, 292, 321.
Globicepkalus, 40, 53, 185, 187, 190, 273,
274.
Glyptodon, 58.
Gorilla {Troglodytes), \ 1, 47, 48, 61, 75, 91,
138, 139, 140, 227, 247, 260, 289, 301.
J.
Jerboa {Dipus\ 33, 160, 317.
K.
Kanoaroo [Macropus), 42, 59, 70, 215,
216, 280, 295, 296, 324, 325, 334.
Koala ( Phascolarctos), 42, 59, 70, 94, 215,
3°6. 325-
Kogia, 94, 195.
Lagostomus (Viscacha), 157, 159, 317.
Lagothrix, 30, 49, 142.
Lemur, 48, 143, 247, 260, 2S9, 301, 314.
Lemurina, 3, 31, 48, 62, 66, 91, 143, 144,
151, 260, 313.
INDEX.
343
Leopard, 63, 64, 150.
Lepus, 33, 265 ; see also Hare and Rabbit.
Lion, 150, 262.
Llama, 35, 174, 271.
Loncheres, 50.
' Lophiomys, 156.
Loris, 48, 289.
Lynx, 66, 150
Macrauchcnia, 35.
Macropus (Kangaroo), 42, 59, 68, 70, 215,
216, 280, 295, 296, 324, 325, 334.
Macrorhinus, 258, 315, 316.
Macroscehdes, 50, 151, 249, 290.
Man, 18, 20, 25, 26, 44, 61, 65, 73, 89, 90,
128-137, 226, 245, 248, 258, 286, 298, 301,
310, 3". 334-
Manati (Mauatus), 3, 21, 36, 51, 82, 92,
199,252,275,293.
iT/rtwz's (Pangolin, 25, 41, 55, 58, 60,69,
83, 208, 234, 276, 277.
Marmot (Arctomys), 156, 157, 160, 265-
Maksupialia, 4, 24, 25, 42, 59, 62, 70, 86,
94, 212, 237, 253, 280, 295, 306, 323.
Megaderma, 155.
Megaptera, 40, 93, 232, 252, 305.
Megatherium, 56, 236.
Metes, 49.
Mellivora, 49
Meuopoma, 60.
Mephitis, 49
Mole ( 7W/a), 32, 50, 69, 76, 77, 152, 222,
227, 249, 263, 264, 291, 316.
MONODELPHIA, 2
Monodon (Narwhal), 40, 274.
MONOTKEMATA, 5, 43, 59> 62, 7°, 85> 86,
88, 95, 216, 237, 253, 282, 296, 298, 306,
326.
Mormops, 155.
Moschus, 67.
Mus (Rat). 157, 158, 265, 317.
Mustela (Weasel), 49, 147. $
Musteiidce, 91, 146, 248, 314.
Mycetes, 30, 31, 49, 75, 138, i39> J42, M3-
247
Myogale, 32, 316.
Myopotamus (Coypu), 156, 229, 250.
Myrmccophaga (Anteaterj, 41, 55, 56, 57,
62, 83, 84, 94, 205, 206, 234, 277, 306.
Mystacoceti, 3, 37, 81, 195.
N.
Narwhal {Monodon), 40, 274.
Nasua, 49.
Nycticcbus, 48.
Odontoceti, 3, 40, 79- 93. 185, 231, 272,
294, 305.
Opossum (Didelphys), 43, 59- 7°, 215, 237.
280, 295, 296, 323.
Orang, (Simia), 31, 47, 48, 61, 75, 91,
138, 139, 140, 259, 261, 29S, 312.
Orca (Grampus), 40, 274, 275.
Ornithoueu'hia, 5, 43.
Ornithorhynchus, 14. 43, 44, 59, 62, 71,
85, 86, 95, 2119, 238, 239, 282, 307, 326.
Orycteropus, 41, 55, 58, 62, 69, .83, 94,
209, 234, 277, 294, 295, 306.
Otaria (Sea Lion), 49, 151, 231, 316, 333.
OtariidcF, 150, 262, 316.
Ox, 91, 172, 270, 321.
Paca (Coelogenys), 158, 160.
Palaotherivm, 268*.
Pangolin (Mam's), 25, 41, 55, 58, 69, 83,
208, 234, 276, 277.
Paradoxurus, 66.
Peccari, 232, 269, 320.
Pecora, 4, 33, 174, 232, 291, 303, 321.
Pedetes, 67. 159, 160.
Perameles (P.andicnot), 42, 43, 59, 237,
280, 281, 326.
Perissodactyla, 3, 24, 51, 92, 162, 168,
268, 292, 298, 303, 318.
Perodicticus (Potto), 49, 260, 289, ,314.
Petrodromus, 249, 316.
Phalangista, 42, 70, 280, 306, 325.
Phascolarctos (Koala), 42, 59, 70, 94, 215,
306, 325.
Phascolomys (Wombat), 42, 59, 62, 70, 95,
216, 237, 242, 253, 280, 295, 324.
Phoca (Seal), 49, 66, 150, 231, 249, 263,
290, 298, 301, 315, 331, 335-
Phoceena (Porpoise), 40, 65, 79, 93.
Physe.'er (Sperm Whale or Cachalot), 40,
52, 53, 54- 79, 93, 94, 193, 194, 232, 274.
Pig (S7ts), 21, 35, 78, 79, 80, 174, 233,
251, 269, 292, 303, 320
Finuipedia, 3, 76, 91, 231, 248, 262.
Pipistrellns, 229.
Platanista, 37, 40. 193, 232, 239, 274.
Pontoporia, 40, 193.
Porcupine (Hystrix), 67, 156, 157, 159,
160, 230, 317.
Porpoise (Phoc<pna^, 40, 65, 79, 93.
Potamogale, 32, 66, 229, 264-.
Potto (Perodicticus), 49, 260, 289, 314.
Primates, 3, 26, 46, 74, 90, 225, 245,
259, 284, 301, 310, 311.
Priodontes, 69, 84, 95, 235, 272, 280.
Prqboscioea, 4, 36, 79 251, 321.
Procyon, 49.
Procyonidte, 91, 146, 248, 314.
Prongbuck {Antiiocapra), 270.
Pse/tdorca, 40.
Pteropus, 77, ijS-^S- 229, 264, 302.
Puma, 150.
R.
Rabbit, 229. 230; see also Lepus.
Rat (Mui), 157, l6°- ^S, 3J7-
344
INDEX.
Rhinoceros, 35, 51, 79, 92, 166, 250, 251,
267, 268, 302, 303, 318, 319.
1\ hynchocyon, 50, 66, 76, 151, 249, 264,
290. 316.
Rkytina, 36.
Rodentia, 4, 24, 33, 50. 62, 67, 77, 155,
229, 250, 264, 291, 298, 302, 310, 317.
Rorqual (Balcrfioptera), 38, 39, 52, 81, 92,
93, 196, 198, 232, 252, 272, 294, 305.
Ru7>iitiantia, 4, 77.
Saiga, 173.
Sainiiris, 138.
Sauropsida, 44.
Seal ops, 227.
Sc iurus (squirrel), 157-161, 265, 317.
Seal (Phoca), 49, 66, 150, 231, 249, 263,
290, 298, 301, 315, 331, 335.
Sea-Lion (Utaria), 49, 151, 231, 316, 333.
Sea-Otter [Enhydris), 298, 315.
Sevinopithecus, 66.
Sheep, 61, 169. 270, 284, 321.
Shrew (Sorcx), 32, 50, 76, 153, 228, 264.
Sitttia (Orang), 31, 47, 48, 61, 74, 91, 138,
139, 140. 259, 261, 298, 312.
Simiijia, 66, 90, 137 et seq., 143, 144, 247,
289, 312.
Sikknia, 3, 18,36, 51, 62,68 82, 92, 198,
232, 252, 275, 283, 293, 305.
Sloth, 41, 55, 56. 61, 62, 69. 85, 90, 94.
209, 224, 236, 252, 276, 294, 298, 306,
322, 330. 332 ; see also Bradypus and
Ckoldpus.
Solenodon, 66, 262, 302.
Sorex (Shrew), 32, 50, 76, 153, 228, 264.
SoncidiP, 50, 22*.
Sperm-Whale (Pliyseter), 40, 52 53, 54,
80, 93, 94, 193, 1...4. 232, 274.
Spider Monkey (A teles), 47. 66, 247, 260.
Squirrel {Sciitrus), 156, 157, 160, 2O3. 317.
Suiua, 3, 35, 269, 320.
Sits (Pig), 21, 35, 78, 79, 174, 233, 251,
269, 292, 303, 320.
T.
Tapir (Tapirus), 35, 51, 77, 79, 92, 167,
234, 251, 267, 303, 318.
Tarsipes, 216.
Tarsius, 144, 289, 313, 314.
Tatusia, 280.
Thylacine {Thylacinus), 42, 70, 211, 212,'
214, 280, 295, 296.
Tiger, 147, 149, 150.
Tolypeutes, 280.
Tragulina, 4, 35, 174, 270, 304, 321.
Trichectcs (Walrus), 49, 316, 333.
Troglodytes, 260 ; see also Gorilla and
Chimpanzee.
Tupaia, 50, 66, 151, 263, 290, 230, 303. '
Tylvpoda, 4, 35, 174, 270, 321.
U.
Ungulata,'- 3, 14, 19, 33, 51, 62, 67, 77, .
91, 162, 232, 250, 266, 291, 298, 302, '
304. 317.
Ursidce, 91, 146, 231, 248, 314.
Ursus (Bear), 49, 66, 144, 145, 248, 261,
290, 301, 314.
Vesper ngo, 33.
Vise ac ha {Lagostomus), 157, 160,
Viverra, 49.
Viverruiw, 91, 149, 248, 314.
\V.
Walrus {Tricliecus), 49, 316, 333.
Weasel {Mustehi), 49, 147
Whale {Bahpjia), 37, 38 79-81, 90, 195,
196. 197, 198, 232, 271, 272, 294, 304,
305-
Wombat (P/iascolowy*), 42, 43, 59, 62,
70, 95, 246, 237, 242, 253, 280, 295, 324,
X.
Xenurus, 279.
Palpa (Mole), 32. 50, 76, 77, 152, 222,
227, 249, 264, 291, 316. Ziphius, 52, 94, 193.
W
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QL Flower, (Sir) William Henry,
821 An introduction to the
F6 osteology of the mammalia
1876
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