A large number of the non-deciduate Mammalia are oonveniently
comprehended under the title of the Ungulata
it may be open to question whether the group thus named
represents a single order, or more than one.
In all the Ungulata
the placenta is either diffuse, that is to
say, the villi are scattered evenly over the surface of the
chorion; or it is cotyledonary, in which latter case, the villi
are accumulated in distinct patches on the chorion. These
patches are called cotyledons.
have milk-teeth, succeeded vertically by
teeth of the permanent set. The teeth consist of enamel,
dentine, and cement, and the grinders have broad crowns,
with tuberculated, ridged, or folded enamel.
Clavicles are never present. The limbs have not more
than four complete digits. The ungual phalanges are clothed
in obtuse horny sheaths, which are commonly very thick and
go by the name of hoofs.
Upon these the weight of these
quadrupeds is usually supported, whence they have been
Some few, however, rest the weight of
the body upon the under surfaces of the phalanges, or are digitigrade.
The metacarpal and metatarsal bones are elongated,
and take a vertical, or much inclined position.
In the female, the mammae are either few in number, when
they are inguinal in position; or numerous, when they are disposed
in two rows along the abdomen.
The intestiie is very generally provided with a caecum of
The cerebral hemispheres always exhibit convolutions,
which are usually very numerous; and, when the brain is
viewed from above, the surface of the cerebellum is largely
are divisible into the Perissodactyla
, though it is probable that the attempt to
define these groups will break down with the increase of our
knowledge of fossil forms.
|Fig. 93. - A, Front aspect of the left tarsus of a Horse.-1. Calcaneum. 2. Astragalus. 3.
Naviculare. 4. Ectocuneiform. 5. Caboides.
B, Posterior aspect of the left metatarsus of a Horse.-1. The metatarsal of the third digit
2, 3. The metatarsals of the rudimentary digits.
1. In the Perissodactyla
, the number of the dorso-lumbar
vertebrae is not fewer than twenty-two. The third digit of
each foot is symmetrical (Or at least very nearly so.) in itself, and the toes of the hindfoot
are odd in number (Fig. 93, B). The femur has a third
trochanter (Fig. 100-3
). The two facets upon the front face
of the astragalus are very unequal; the less articulating with
the cuboid bone.
In the skull, the tympanic bone is small; and, as in sundry
other Mammals, the root of the pterygoid process of the
sphenoid is perforated by an aperture or canal.
The posterior premolar teeth are, generally, very like the
molars. The stomach is simple, and the caecum exceedingly
The teats are inguinal, or situated in the groin. When
the head is provided with horny appendages, they are entirely epidermal
and devoid of a bony core; and they are placed in the middle line of the skull.
consist of the existing families Equidae,
, and Tapiridae
, and of the extinct Palaeotheridae
. The Equidae
, or Horses and Asses, have one toe on
each foot-the third-much longer and larger than the rest.
The latter are represented only by their metacarpal or metatarsal
bones, the inner and outer toes being absent, or represented
by mere ossicles (as rudiments of their metacarpals or
metatarsals) in all existing Equidae
. But, in the extinct Hipparion
the second and fourth digits were complete, though
small and like dew-claws; while the miocene Anchitherium
which most nearly approaches the Palaeotheridae
, has the lateral
toes much larger, and taking their share in supporting
the weight of the body.
|Fig. 94. - A, right fore-foot of a Horse.-1. Radius. 2. Groove In the front face of the radius us. 3. Scaphoides. 4. Lunare. 5. Cuneiforme. 6. Pisiforme. 7. Magnum. 8. Unciforme. 9. Meticarpale, iii. 10. Metacarpale, iv. 11. Sesamoid bones in the ligaments
at the back of the motacarpo-phalangeal articulation. 12. Proximal phalanx (fetter-bone). 13. Widdle phalanx (coronary). 15. Distal phalanx (coffin-bone). 14. Sesamoid
bono in the tendon of the flexor perforans (called "navicular" by Veterinarians).
The dental formula is i
. 3.3/3.3 c.
3.3/3.3 The tooth here counted as the first premolar may be a milk-tooth,
as it appears to have neither predecessor nor successor, and
The molar teeth present an outer wall, which is bicrescentic
in transverse section; and two inner ridges, which are
curved more or less inward and backward, and correspond respectively
with the anterior and the posterior crescents of the
outer wall. The valleys may be more or less completely filled
up with cement, which also coats the tooth. The incisors are
similar in form in each jaw, and in Equus
crowns present a wide and deep median cavity, formed by a
fold of the enamel.
These are the distinctive characters of the Equidae
may be useful to add some special details respecting the anatomy
of the Horse as a familiar example of the perissodactyle
The Horse has seven cervical vertebrae, twenty-four dorsolumbar
(eighteen or nineteen of which are dorsal), five sacral,
and about seventeen caudal vertebrae. The atlas has very
wide lateral processes, the faces of which look obliquely downward
and forward, and upward and backward. The centra
of the other cervical vertebrae are much elongated, strongly
convex in front, and correspondingly concave behind. The
neural spines are obsolete in all but the seventh. The liga-mentum nuchae
is a great sheet of elastic tissue, which extends
from the spines of the anterior dorsal vertebrae to the occiput,
and is fixed, below, into the neural arches of the cervical vertebrae.
In the dorsal region, the opisthocoelous character of the
centra of the vertebrae gradually diminishes, though the anterior face of
the centrum of the last lumbar is still distinctly convex.
The spines of these vertebrae increase in length to
the fourth or fifth. The spine of the sixteenth is vertical,
those in front inclining backward, and those behind a little
In none of these vertebrae do the prezygapophyses bend
round the postzygapophyses of the vertebra in front, as is
often the case in the Artiodactyla
. The transverse processes
of the penultimate, and of the last, lumbar vertebras present
concave facets upon their posterior margins, which articulate
with convex facets developed upon the anterior margins of
the last lumbar and first sacral vertebrae respectively.
|Fig. 95. - A cervical vertebra of a Horse.-1. The rudimentary spine. 2, 3. Tie pre- and
post-zygapophyses. 5. The convex anterior face of the centrum. 9. Its concave posterior
face. 6. 7. The transverse processes and rudimentary ribs.
In the skull, the plane of the supra-occipital is inclined
upward and forward, and gives rise to the middle part of a
transverse ridge which is continued at the sides into the squamosal.
The ridges which limit the origins of the temporal
muscles above, unite in the middle line posteriorly, and thus
produce a low sagittal crest. The orbit is bounded behind by
the united post-orbital processes of the frontal and the jugal.
The lachrymal aperture lies in the orbit. The nasal bones
unite, for a short distance only, with the premaxilla. There
is no prsenasal bone. The posterior margin of the palate is
opposite the penultimate molar tooth. TTie glenoidal surface
is transversely elongated and convex from before backward.
The tympanic bulla is not very large, and is rugose inferiorly.
It is not anchylosed with the surrounding bones. The
post-tympanic process of the squamosal does not approach
the post-glenoidal process of the same bone, below the meatus
The proper mastoid process is distinct, but short. There
is a long and strong paramastoid developed from the ex-occipital.
|Fig. 96. The Skeleton of the Horse.
The rami of the mandible are anchylosed at the symphysis.
The perpendicular part of each ramus is long, the condyle
transverse and convex from before backward, and the narrow
coronoid process rises far above the level of the condyle. In
a longitudinal section of the skull the cerebral chamber lies
almost altogether in front of that for the cerebellum.
The structure of the limbs of the Horse is such
as might be expected from its preeminent cursorial powers.
That excessive development of the epidermis which gives
rise to a nail
takes place, in the Horse, not only upon the
dorsal surface of the terminal joint of the digit, but upon its
ventral surface and sides, and thus produces a hoof.
|Fig. 97. - Longitudinal median section of the foot of a IIerse.-13, 14, 18. The three phaslanges. 16. The navicular sesamoid. 5. The flexor perforatus. G. Tho flexor perforans
19. The hoof.
The animal is supported by these greatly-developecl nails,
and hence is said to be unguligrade.
The long axis of its
phalanges are greatly inclined to the surface upon which it
stands, while those of the metacarpals and metatarsals are perpendicular
and greatly elongated. The wrist of the Horse
thus comes to occupy the middle of the length of its fore-leg,
and constitutes what is improperly called the "knee." The
heel is similarly raised to the middle of the hind-leg, and is
termed the "hoek." The forearm and the leg are free, but
their motions are almost restricted to an antero-posterior
plane. The forearm is fixed in the prone position. The arm
and thigh are closely applied to the sides of the body and enclosed
in the common integument, so as to be capable of very
little proper motion. At the same time, the axis of the humerus
is inclined obliquely backward and downward, at right
angles with the long axis of the scapula; and that of the
femur obliquely forward and downward at right angles with
that of the os innominatum
; and the long axes of both these
bones make a great angle with those of the forearm and leg
respectively. Each limb thus forms a sort of double C spring,
upon the top of which the weight of the body is supported-
in the hind-limbs by means of the solid connection of the ilia
with the sacrum; in the fore-limbs, by the great muscular
slings formed by the serratus magnus
and the levator anguli
The scapula is long and narrow;
the low spine has no acromion; the
coracoid process is small, and there is
|Fig. 98. - Front view of the red carpas of a Horse.-1. Cunelforme 2. Lunare. 3. Scaphoides. 4. Pisiforme. 5. Unciforme. 6. Magnum. 7. Trapezoides.
The head of the humerus looks
backward, and the distal articular surface
of the bone is completely ginglymoid.
The two bones of the antibrachium
are anchylosed; the shaft of the
ulna becomes exceedingly slender, and
its small distal end is distinguishable
only with difficulty. The articular surface
for the carpal bones is, therefore,
almost wholly furnished by the radius.
There are seven carpal bones, the trapezium
being obsolete. A line prolonging
the axis of the third metacarpal
and that of the os magnum
not pass through that of the lunare,
but corresponds more nearly with the
junction between scaphoides
The pollax and the fifth digit
are supressed, or represented only by minute nodules
of bone, and the only complete digit is the third; the
second and the forth being represented only by the splint-like
metacarpal bones. The third metacarpal,
which is somewhat flattened from before backward, is
nearly symmetrical in itself. Careful observation, however,
shows the inner moiety to be rather the broader.
There are two large sesamoid bones (the greater sesamoids)
developed in the ligaments which connect the metacarpal with
the basal phalanx; and one transversely-elongated sesamoid
gives attachment to the tendon of the perforating flexor, and
lies upon the ventral aspect of the joint between the middle
and the distal phalanx.
The ossa innominata
are elongated, and their long axes,
on the length of which depends the proportional size of the
"quarter" of a Horse, form an acute angle with the spine.
The crests of the ilia are wide and directed transversely, and
the symphysis pubis is very long.
|Fig. 99. - The ossa innominata of a Horse viewed from the left side and behind.-1. The
crest of the ilium. 2. The surface by which it articulates with the sacrum. 4. The
acetabulum. 6. The ischium.
The femur has a large third trochanter (9
, Fig. 100), into
which the glutaeus maximus
is inserted. Its head presents a
deep pit for the round ligament, and there is a peculiar and
very characteristic fossa (10
) on the inner and posterior face of
the distal moiety of the bone.
The proximal end of the fibula is reduced to a mere rudiment;
its shaft is not represented by bone; and its distal end
is anchylosed with the tibia, and has the appearance of being
an external malleolar process of that bone. The distal end
of the tibia presents two deep, obliquely-directed concavities,
which correspond with the convexities of the astragalus.
There are six or seven tarsal bones, according as the entoand
meso-cuneiform bones remain distinct or become anchylosed.
The astragalus (Fig. 93 A, 94 B) is extremely characteristic.
It presents two convex ridges separated by a deep
fossa, and directed obliquely from behind and within, forward
and outward, to the tibia; and it has a nearly flat distal face,
not borne upon any distinct neck, which articulates almost
wholly with the naviculare, presenting only a very small facet
to the cuboid.
The naviculare and the ecto-cuneiform
are peculiarly broad and flattened
in form (Fig. 93 A, 94 B).
The metatarsus and digits repeat the
arrangements of the fore-limb; but the
principal metatarsal is more slender in
its proportions, and is flattened from
side to side rather than from before backward
(Fig. 93 B, 94 B).
As might be expected, the principal
peculiarities of the muscular system of
the Horse are to be observed in the
The serratus magnus
and the levator
(which really form one
muscle), together with a sterno-scapurlaris
form the great sling already mentioned,
by which the weight of the forepart
of the body is transmitted to the
anterior extremities. The power of
abduction is hardly needed by a purely
cursorial animal; hence the deltoid is
reduced to its scapular portion, which is
very small. On the other hand, the
pro-and re-tractors, the flexors and extensors,
are well developed. The supra
are large. There is a great cephalo-humeralis
, answering to
the clavicular portions of the human
sternomastoid and of the deltoid, which
run into one another, in consequence of
the total absence of the clavicle. The
anterior portion of the sternomastoid is
fixed to the mandible, and thus becomes
The latissimus dorsi
are very large, as are the flexors and extensors of the antibrachium.
The supinators and pronators are wanting; but there is
a distict extensor minimi digiti
, the tendon of which unites
with that of the extensor communis.
Radial and ulnar extensors
of the carpus are also present. The, flexor perforatus
has only a single tendon, which splits, and is attached, as
usual, to the sides of the middle phalanx. The flexor perforans
also has only a single tendon, which pierces the
former, and is inserted into the lesser sesamoid and the distal
of the third digit are represented only by
the ligaments which connect the greater sesamoid bones with
the metacarpal, and in which a few muscular fibres are sometimes
found. There are said to be two others, one for each
lateral metacarpal, and a lumbricalis.
In the hind-limb, the femoral muscles are in the Horse
the same as in Man, but enormously developed. There is
no tibialis anticus, peronaeus longus,
, nor any tibialis
The extensor longus digitorum
has a head which arises
from the external condyle of the femur; there is a simple extensor
The flexor hallucis
and flexor digitorum perforans
into the single perforating flexor tendon for the distal phalanx;
while the perforated tendon is the termination of that of the plantaris
, which passes over a pulley furnished by the calcaneum.
|Fig. 100. - The left femur of a Horse, posterior view - 1. Head 2. Great grand trochanter 3. Third trochanter 4. Lesser trochanter 5. Pit for round ligament. 10. Fossa. 11. Condyles.
The deciduous or milk dentition of the Horse has the following
4.4/4.4 It is complete at birth,
with the exception of the outer incisors, which appear before
the foal is nine months old. The incisors have the same structure
as in the adult. The canines and first deciduous molars
are simple and very small, the canines being smaller than the
molars. In the upper jaw, the other deciduous molars all have
the same structure. The outer wall of the tooth is bent in
such a manner as to present, from before backward, two concave
surfaces separated by a vertical ridge. From the anterior
end, and from the middle, of this outer wall, two laminae of
the crown pass inward and backward, so as to be convex inward
and concave outward, and thus to include two spaces
between themselves and the outer wall. From the inner surface
of the hinder part of each of these crescentic laminae a
vertical pillar is developed, and the inner surface of the pillar
is grooved vertically. The outer wall, the laminae, and the
pillars, are all formed of dentine and enamel, thickly coated
with cement. The attrition which takes place during mastication
wears down the free surfaces of all these parts, so as, in
the long-run, to lay bare a surface of dentine in the middle of
each, surrounded by a band of enamel, and, outside this, by
the cement with which the interspaces are filled. The band
of enamel is simple and unplaited. The general pattern of
the worn surface may be described as consisting, externally,
of two longitudinal crescents, one behind the other, and with
their concavities turned outward which arise from the wear
of the wall; internal to these, of two other crescents, partly
transverse in direction, and connected by their anterior ends
with the wall, which arise from the wear of the laminae; and
attached to the inner surface of these, two hour-glass-shaped
surfaces, produced by the wear of the grooved pillars.
In the mandible, the structure of the molars and the resulting
pattern are quite different. The outer wall presents
two convex surfaces separated by a longitudinal depression,
and thus reverses the conditions observable in the upper
molars. The result of the wear of this is, necessarily, two
crescents, the concavities of which are turned inward. A
vertical pillar, longitudinally grooved on its inner face, is developed
on the inner face of the tooth at the junction of the
anterior and posterior crescents, and gives rise to a deeply
bifurcated surface when worn. A second smaller pillar appears
in connection with the inner face of the posterior end
of the outer wall.
Thus the grinding surface of the upper molars may
be represented by four crescents with two inner pillars; and that
of the lower molars by two crescents with two inner pillars.
The upper crescents are concave outward; the lower concave
inward; and by this arrangement, together with the unequal
wear of the dentine, enamel, and cement, a permanently uneven
triturating surface is secured.
As is the general rule among Mammals, the first permanent
molar is the first permanent tooth which appears (unless the
eruption of the inner incisor be contemporary with it), and it
comes into place and use long before the deciduous molars are
shed and replaced by the premolars. Hence, when the last
premolar comes into place as a fresh and unworn tooth, the
first molar, which lies next to it, is already considerably worn.
This disparity of wear is maintained for a long time, and
furnishes a very useful means of distinguishing the last premolar
from the first molar in the adult, when, as in the Horse,
the premolars and molars are very similar.
The first deciduous molar usually falls out when the first
premolar appears, and is not replaced; but it is occasionally
retained. AH the other milk-teeth have successors, and there
are three permanent molars. Consequently the dental formula
of the adult Horse is i.
The permanent canines are the last teeth to be fully developed,
and, in the mare, they do not often make their appearance.
The upper canines are distant from the outer incisors,
while the lower canines are quite close to them. In both jaws
there is a wide interval, or diastema
, between the canines and
The deep valley of the incisor teeth becomes filled up with
masticated matter, and thus the dark "mark" is produced.
As the incisors wear down, the mark changes its form in consequence
of the differences in the transverse section of the
valley at different points; and eventually, when the wear has
extended beyond the bottom of the valley, it disappears. The
presence or absence of the "mark" thus serves as an indication
of age. The structure and patterns of the grinding surfaces
of the permanent molars are essentially the same as those
of the milk-molars; but the enamel becomes more or less
plaited; and, at an advanced period of life, the development
of the long teeth is completed by the formation of roots. It
is important to notice that the last molar of the Horse is not
more complex in its structure than the other molars, and that
the last milk-molar is not more complex than the premolar
which succeeds it.
The alimentary canal of the Horse is about eight times as
long as the body. The stomach, simple in its form, presents
a cardiac and a pyloric division, which are sharply distinguished
by the dense epithelium which lines the inner surface
of the former.
The caecum is enormous, having fully twice the volume of
the stomach. There is no gall-bladder. A cartilage is developed
in the septum of the heart. There is no Eustachian
valve, and only one anterior cava remains. The aorta divides
immediately after its origin into an anterior and a posterior
trunk; the latter becomes the thoracic aorta; the former is
the source of the arteries for the head and the anterior ex
tremities, giving off first the left subclavian, and then as
an "innominata" supplying the right subclavian and the
The trachea divides into only two bronchi, no accessory
bronchus being given off to the right lung. In the brain the
following points are worthy of notice: The medulla oblongata
presents corpora trapezoidea.
The flocculi do not project at
the sides of the cerebellum, and the vermis and lobes of the
cerebellum are unsymmetrically convoluted. The cerebral
hemispheres are elongated and subcylindrical, and do not
overlap the cerebellum when the brain is viewed from above,
The sulci are very deep, and separate numerous gyri, upon the
upper and outer surfaces of the hemispheres. The uncinate
gyrus (or natiform protuberance) and the region which answers
to the insula are not hidden by the overlapping of the convolutions
in the lateral aspect of the brain. The Sylvian fissure
is indicated. The corpus callosum is large, and the anterior
commissure is of moderate size. The posterior cornu
of the lateral ventricle is wanting.
Large air-sacs are connected with the Eustachian tubes.
The testes pass into a scrotum, but the unguinal canal remains
The prostate is single. Cowper's glands are present, and
there is a large uterus masculinus
. The large penis is sheltered
within a prepuce and is retracted by a special muscle,
which arises from the sacrum.
The uterus is divided into two cornua, and the vagina of
the virgin mare is provided with a hymen. The period of
gestation is eleven months. The yelk-sac of the foetus is
small and oval. The allantois spreads over the whole interior
of the chorion and covers the amnion, which is vascular. The
minute villi which it supplies with vessels are evenly scattered
over the whole surface of the chorion.
The existing Equidae
, are naturally restricted to Europe,
Asia, and Africa; and are distinguished into the Horses,
which have homy patches on the inner sides of both pairs of
limbs-above the wrist in the fore-limb and on the inner side
of the metatarsus in the hind-limb; and the Asses, which
possess such callosities only on the fore-limbs.
Fossil remains of Equidae and abundant in the later tertiary
deposits of Europe, Asia, and the Americas; but the
group is not known to be represented earlier than the miocene,
or later eocene, epoch.
The Equidae are among the very few groups of Mammalia
the geological history of which is sufficiently well known, to
prove that the existing forms have resulted from the gradual
modification of very different ancestral types. The skeleton
of the older pliocene and newer miocene Hipparion
closely resembles that of an Ass, or a moderate-sized Horse.
There is a curious depression on the face in front of the orbit,
somewhat like that which lodges the "larmier" of a stag
(traces of which are observable in some of the older species
); otherwise the cranium is altogether like that of
a Horse. Again, the shaft of the ulna is very slender, but it
is larger than in the Horse, and is distinctly traceable throughout
its whole length although firmly anchylosed with the
radius. The distal end of the fibula is so completely anchylosed
with the tibia, that, as in the Horse, it is difficult to
discern any trace of the primitive separation of the bones.
But, as has been already mentioned, each limb possesses three
complete toes-one strong, median, and provided with a large
hoof, while the two lateral toes are so small that they do not
extend beyond the fetlock-joint. In the fore-limb, rudiments
of the first and fifth toes have been found.
The teeth are exceedingly like those of the Horse, but the
crowns of the molars are shorter; and, in the upper jaw, that
which, in the true Horses, is a large fold of the inner face of
tho tooth becomes a detached pillar. The smaller plications
of the enamel are also more numerous, close-set, and complicated.
On the outer face of the lower milk-molars there is a
column such as exists in the Stags. Of this a rudiment exists,
as a fold, in the corresponding teeth of the existing Horse.
In the genus Anchitherium
, all the known remains of
which are of older miocene (and, perhaps, newer eocene) age,
the skeleton in general is still extraordinarily like that of a
Horse. The skull, however, is smaller in proportion than in
the Horse, and the jaws are more slender. The hindermost
molar tooth is situated farther back under the orbit, and the
orbit itself is not completely encircled by bone, as it is in the
Horses and Hipparions.
The shaft of the ulna is stouter than in Hipparion
, and is
less closely united with the radius. The fibula appears, at any
rate in some cases, to have been a complete though slender
bone, the distal end of which is still closely united with the
tibia, though much more distinct than in the Hipparions and
the Horses. In some specimens, however, the middle of the
shaft seems to have been incompletely ossified. Not only are
there three toes in each foot, as in Hipparion
, but the inner
and the outer toes are so large that they must have rested
upon the ground. Thus, so far as the limbs are concerned, the Archithericum
is just such a step beyond the Hipparion
is beyond the Horse, in the direction of a less
specialized quadruped. The teeth are still more divergent
from the Equine type. The incisors are smaller in proportion,
and their crowns lack tbe peculiar pit which characterizes
those of Equus
The first grinder is proportionately
much larger, especially in the upper jaw, and like
the other six has a short crown and no thick coat of cement.
The pattern of their crowns is wonderfully simplified. The
fore and hind ridges run with but a slight obliquity across the
crown, and the pillars are little more than enlargements of the
ridges, while in the lower jaw these pillars have almost disappeared.
But the foremost of the six principal grinders is still
somewhat larger than the rest, and the posterior lobe of the
last lower molar is small, as in the other Equidae
In all those respects in which Anchitherium
the modern Equine type, it approaches that of the extinct Palaetheria
; and this is so much the case that Cuvier considered
the remains of the Anchitherium
with which he was
acquainted to be those of a species of Palaeotherium.
In the Rhinocerotidae
the second, third, and fourth toes
are nearly equally developed in both the fore-and the hind feet.
The dental formula is i.
1.1/1.1 or i.
But the teeth differ from those of the Horse in many other
respects besides the number of the incisors and the absence of
canines. Thus, the upper incisors differ greatly in form from
those which are situated in the lower jaw; and, in some species,
incisors are absent. Their crowns are not folded as in
the Horse. The peculiarities of the grinding teeth will be
The skin is very thick and may be converted into a jointed
armor; the hair is scanty. The upper lip is much produced
and is very flexible. In some species one, or sometimes two,
horns are attached in the middle line to the nasal or frontal
bones. But these horns are formed, as it were, by agglomeration
of a great number of hair-like shafts.
The distal phalanges of the tridactyle feet of the Rhinoceros
are invested by small hoofs; but these do not entirely
support the weight of the body, which rests, in great measure,
upon a large callous pad developed from the under face of the
metacarpal and metatarsal regions; these are much shorter
than in the Horse.
The dorso-lumbar vertebrae are twenty-two or twenty-three,
of which twenty are dorsal. There are four sacral and twenty-two caudal.
The cervical vertebrae, as in the Horse, are
strongly opisthocoelous, and the transverse processes of the
last lumbar articulate with those of the penultimate lumbar
and with the sacrum.
The skull differs from that of the Horse in the absence of
any frontal or zygomatic processes in consequence of which
the orbit and temporal fossa form one cavity. The nasals are
immense, and are separated from the premaxillae by a wide
extent of the maxilla on each side. The premaxillae are relatively
small and reduced to little more than their palatine portions.
The glenoidal surface of the mandible is transverse
and convex. The squamosal sends down an immense postglenoidal
process, which is longer than either the post-tympanic
or the paramastoid. It unites with the post-tympanic
to form a kind of false auditory meatus, in the absence of any
proper ossified canal of that kind. The periotic and the tympanic
bones are anchylosed, the tympanic being a mere irregular
hoop of bone. The pars mastoidea
is completely hidden
by the junction of the short post-tympanic with the long par
amastoid. The hinder margin of the bony palate is opposite
the middle of the antepenultimate molar.
The mandibular condyle is transverse and convex. The
perpendicular portion of the ramus is large, and the coronoid
process ascends slightly above the condyle. In a vertical and
longitudinal section of the skull, the form of the cerebral cavity
is seen to be similar to that of the Horse. The inner and
outer tables of the bony roof of the skull are separated by
The spine of the scapula has no acromion, but gives off a
strong recurved process from the middle of its length.
The radius and ulna are complete, but are anchylosed.
The carpus has the eight ordinary bones. In the manus
the digits ii., iii., iv., are complete, and a bony tubercle articulated
with the outer facet of the cuneiforme
v. The digit iii. is largest and longest, and its phalanges are
symmetrical in themselves; those of the digits ii. and iv. are
not symmetrical in themselves. The terminal phalanges have
somewhat the form of the coffin-bone of the Horse.
The ilia have wide, transversely-directed crests, as in the
Horse. The femur is provided with a very strong third trochanter.
The tibia and the fibula are complete, and the tarsus
has the ordinary seven bones. The pulley of the astragalus
is not very deeply grooved, and is hardly at all oblique. The
facet for the cuboid is very small. The metatarsals resemble
the metacarpals in their number and symmetry, but there is
no rudiment of the fifth.
In some species of Rhinoceros
there are 3.3/2.2 incisors in tlie
milk detention, and 1.1/2.2 or 1.1/1.1 incisors in the permanent dentition.
In the latter the upper incisors are large, long-crowned
teeth, very unlike the lower ones, of which it seems probable
that only one pair, in any case, are permanent teeth. In some
Rhinoceroses, as has been already stated, the adult is devoid
of incisor teeth.
There are no canines in either dentition. Of the four milkmolars,
the first, as in the Horse, is smaller than the others,
and is not replaced. The structure of both the upper and the
lower molars is substantially the same as in the Horse, but the
roots are developed much sooner; the laminae of the upper
molars take a much more transverse direction; the laminae of
the upper molars do not develop pillars, though accessory
crests may be developed from the two faces of the posterior
lamina; the lower molars have no pillars; and the cement
does not fill up the valleys between the wall and the laminae.
The cardiac division of the simple, though large stomach,
is lined by a white callous epithelium, as in the Horse. The
small intestine presents large processes or tags, half an inch
long or more, upon which the true villi are borne. The
caecum is very large, and the colon enormous. There is no
gall-bladder. The heart and brain are very similar to those
of the Horse.
The male can hardly be said to have a scrotum, as the
testes lie close to the abdominal ring. A prostate, vesiculae
seminales, and Cowper's glands, are present. The long penis
has a mushroom-shaped glans, and the animal is retromingent.
The cornua uteri are proportionately longer than in the mare.
The teats are two and inguinal in position. The characters
of the foetal membranes and the nature of the placentation are
At the present day the genus Rhinoceros
is confined to
Africa and Asia. The African species all have two horns,
a nearly smooth skin, and the adult has no incisors. The
Asiatic species have one horn only (except that of Sumatra,
which has two). The skin is marked out by deep folds into
shields, and the adults have well-developed incisors.
Rhinoceroses are known in the fossil state as far back as
the miocene epoch. R. tichorhinus
with the nasal septum
ossified, and a covering of long woolly hair, inhabited Europe
and Asia during the cold of the glacial epoch., R. incisivus
had four digits in the manus, and larger incisor teeth than any
existing species. R. hexaprotodon
had more numerous incisors
than any other species.
In the Tapiridae
there are four toes on the front-foot,
though the ulnar digit does not reach the ground. The hind foot
has three toes.
The dental formula is i.
The molar teeth each present two transverse, or slightly oblique
ridges, connected by a low wall externally.
The skin is soft and hairy, and the muzzle and snout are
prolonged into a short proboscis.
The Tapirs have twenty-three or twenty-four dorso-lumbar
vertebrae, of which nineteen or twenty are usually dorsal.
The centra of these vertebrae, and the transverse processes of
the last lumbars, have the same peculiarities as those of the
Horse and Rhinoceros. There are seven sacral and about
twelve caudal vertebra. The skull is partly Rhinocerotio,
partly Equine, in its characters. Thus there is a sagittal crest-
the post-tympanic processes are large, but they are not so
long as the paramastoids, and they do not unite with the postglenoidal
processes beneath the meatus. In these respects the Tapir is Horse-like,
but in the following it is more Rhinocerotio.
Thus the tympanic is quite rudimentary; the post-glenoidal
process is larger than in the Horse; the orbit is not separated
from the temporal fossa; the nasals are widely separated
from the premaxillae; the premaxillae are very small, and
are early anchylosed.
The hinder margin of the osseous palate is opposite the
anterior edge of the penultimate molar. The mandibular rami
unite in a very long symphysis; the ascending portion of the
ramus is large, and projects-backward with a convex edge in
a remarkable manner. There is a high coronoid process.
In the fore-limb, the scapula has no acromion, and the
coracoid is a mere tubercle. The supraspinous fossa is very
much larger than in the Horse or Rhinoceros. The radius and
the ulna are complete, but not movable upon one another.
Although, by the completion of the fifth digit, in addition to
the second, third, and fourth, there are four digits in the
manus, the Perissodactyle character is manifested by the fact
that the third is longest, and symmetrical in itself, while the
others are asymmetrical. The femur has a strong third trochanter;
the fibula is complete; the astragalus more Rhinocerotio
than Equine. There is no trace of a hallux, but the
fifth digit of the pes appears to be represented by an osseous
In the presence of the full complement of incisors and
canines the Tapir is more Horse-like than Rhinocerotic, but is
still very peculiar; for the outer upper incisors are larger than
the canines, while the outer lower incisors are much smaller
than the canines, and are apt to fall out at a certain age. The
canines, are still more closely approximated to the incisors
than in the Horse, especially in the lower jaw, and, consequently,
the diastema is very large. The six posterior molars
in the upper jaw, and the five posterior molars in the lower,
present nearly the same structure. There is a low outer wall
with two slightly-marked concavities (in the maxillary teeth)
or convexities (in the mandibular teeth) on its outer face.
From this two ridge-like laminae run inward and a little backward
across the crown of the tooth. The valleys are broad
and shallow, and the coat of cement very thin. The molar
tooth of the Tapir thus represents the plan of structure common
to the Perissodactyle
in its simplest form. Deepen the
valleys, increase the curvature of the wall and lamina, give
the latter a more directly backward slope; cause them to develop
accessory ridges and pillars, and increase the quantity
of cement; and the upper molar of the Tapir will gradually
pass through the structure of that of the Rhinoceros to that
of the Horse.
In the anterior upper premolar (or milk-molar?) the anterior
moiety of the crown is incompletely developed. In the
anterior lower premolar the anterior basal process, which exists
in all the molars, is excessively developed, so that the
crown of the tooth assumes the bicrescentic pattern of the
Rhinoceros's lower grinder. This probably indicates the manner
in which the Tapiroid form of inferior molar is converted
into the Rhinocerotic, or Equine, form.
The stomach is simple and oval, the cardiac and pyloricorifices
being closely approximated. The caecum is proportionally
smaller than in the Horse or Rhinoceros. There is no
gall-bladder. The heart is devoid of a septal bone and of a
Eustachian valve. There is only a single vena cava anterior
and the aorta divides into an anterior and a posterior trunk.
There is no third bronchus. No distinct scrotum is present
There are vesiculae seminales and prostatic glands, but no
Cowper's glands. The placentation is diffuse. The teats are
two, and inguinal.
There are two or three species of Tapir at present
living in South America and one in Southwest China, Malacca, and
Sumatra. The genus Tapirus
has been found fossil in Europe
in rocks of miocene age. The closely-allied extinct genera Lophiodon
) carry the Tapiridae
back through the eocene epoch.
-These are all extinct animals, the
remains of which are found in the older tertiary rocks; and
which are closely allied, on the one hand, with the Horses and,
on the other, with the Tapirs.
The type of the family, Palaeotheridium,
Tapir in most respects, but has only three digits in the manus
as well as in the pes. The dental formula, however, is i.
3.3/3.3. The diastema is smaller than in the
Tapir, and the patterns of the grinding teeth of both jaws are more like those of the Rhinoceros.
e. The Macrauchenidae.
- The genus Macrauchenidae.
extinct form, which occurs in later tertiary or quaternary deposits in South America.
The feet are tridactyle, and the dental formula is i.
The teeth are disposed in a nearly
continuous series. The crowns of the incisors present a deep
fossa, as in the Equidae
. The molars are in part Equine, in
part Rhinocerotic in character. The skull is, on the whole.
Equine, but the nasal bones are very short and Tapiroid. The
vertebrae of the long nock are extraordinarily similar to those
of the Camelidae, and especially of the Llamas.