The genus Hyrax
, which is the
sole member of this group, was referred by Pallas to the Rodents; and by Cuvier,
who demonstrated that it could not be a Rodent, it was placed among the Ungulata,
in the immediate neighborhood of Rhinoceros
, without any better evidence than
that afforded by the characters of the molar teeth. Prof.
Brandt, of St. Petersburg, in an elaborate memoir just published,
arrives at the conclusion that it is a "gliriform Ungulate,"
intermediate, in a certain sense, between the Rodents
and the Ungulata;
but, still, more Ungulate than Rodent. It
appears to me to be neither Ungulate nor Rodent, but the
type of a distinct order, in many respects intermediate between
, on the one hand, and Rodentia
on the other.
The small, Rabbit-like, animals comprised in the genus Hyrax
are plantigrade, and provided with four visible toes in
front and three behind. The nails are not hoof-like, but
nearly flat, except the innermost of the biud-foot, which is
peculiarly curved. The body is covered with fur, and the muffle
, or snout, is split, as in the Rodents. There is a pendulous
penis, but no scrotum; and there are four inguinal and
two axillary teats.
There are from twenty-nine to thirty-one dorso-lumbar
vertebrae, which is the greatest number known in any terrestrial
mammal. Twenty-one or twenty-two of these are dorsal.
No mammal, except Choloepus
, the two-toed Sloth, possesses
so large a number of dorsal vertebrae as this. The transverse
processes of the last lumbar vertebra articulate with the
sacrum, as is the case in many Ungulate Mammals. In the
skull, the post-orbital processes, which are chiefly furnished by
the parietal and the jugal, nearly meet. Part of the articular
facet for the mandible is formed by the jugal, which extends
forward until it comes into contact with the lachrymal bone.
The base of the external pterygoid process is perforated by a
canal, as in Perissodactyla
. There are large
pre-and post-tympanic processes, and the post-tympanic is
much shorter than the par-occipital process. The premaxillae
are large, and unite extensively with the nasal bones; the
perpendicular ramus of the mandible is very wide, and somewhat
like that of the Tapir in shape. The posterior margin
of the bony palate is opposite the anterior edge of the last
The scapula is devoid of an acromion process, as in the Perissodactyla.
There are no clavicles, but the coracoid process
is well developed. The ulna is complete, and a rudiment
of the pollex is present. In the carpus, a line prolonging the
axis of the third metacarpal bisects the os magnum
and the lunare
, which is not the case in any Ungulate Mammal.
In the hind-limb, the femur possesses a small third trochanter,
which is not nearly so conspicuous as in some Rodents.
The tibia and fibula are complete. The extremity of
the inner malleolus articulates with a shelf-like process of the
astragalus, the distal face of which bone has no facet for the
cuboid. The digits i.
are not represented even by rudiments.
The terminal phalanx of ii.
is longitudinally cleft.
The dentition of the adult is i.
4.4/4.4, and m.
3.3/3.3. The outer upper incisors are very small, and soon
fall out; the inner, which are very large, curved, and have a
thick coat of enamel on their anterior faces, continue to grow
throughout life, as in Rodents. The lower incisors have
crowns denticulated at the edges, like those of Galeopithecus
and some Bats. They bite upon a callous pad which lies behind
the upper incisors. The patterns of the upper and lower
molar teeth are very similar to those of the corresponding
teeth in Rhinoceros
. As in the Horse, part of the Eustachian
tube is dilated into a thin-walled sac extending on the inner
side of the bulla tympani
from the pterygoid processes to the
exit of the ninth nerve.
A slight constriction marks oiF the cardiac from the pyloric
division of the stomach. The cardiac portion is lined by a
dense epithelium. The intestine is provided with three caeca-one in the ordinary
position, and two placed much lower
down on the colon, opposite one another, and terminating by
pointed ends. There is no gall-bladder. The ureters open,
not near the neck of the bladder as in Mammals generally, but
near the fundus, as in some few Rodents.
The male has vesiculae seminales,
prostatic and Cowperian
glands. The uterus is two horned, and the vulva and anus are
surrounded by a common fold of integument.
In the foetus the yelk-sac and the vitello-intestinal duct
early disappear. The amnion is not vascular. The allantois
spreads over the interior of the chorion, and gives rise to the
broad zone-like placenta, which is composed of both maternal
and foetal parts. The maternal vessels pass straight through
the thickness of the placenta toward its foetal surface, on
which they anastomose, forming meshes, through which the
vessels of the foetus pass toward the uterine surface of the
The species of the genus Hyrax
are found only in Syria
and Africa. No fossil Hyraecoidea
The Discoidea. - The Mammalia with discoidal placentae
are the Rodentia
, the Cheiroptera
, the Insectivora
, and the Primates.