MARSUPIALIA. 
99 
The family of Orycteropodidce contains one genus only, the 
Aard-varks, which have teeth, of a highly peculiar and com- 
plex structure, each tooth consisting of a very large number of 
separate parallel dental systems, all closely packed together. In a 
transverse section they present an appearance not unlike that of a 
piece of cane. These teeth are preceded by a set of minute milk- 
teeth, mere remnants of a former functional set, which show indi- 
cations of a division into diflferent groups, such as premolars 
and molars. The zygoma is complete, and there are well-deve- 
loped clavicles. 
The Common Aard-vark [Orycteropus afer), an animal of about 
the size of a pig, is represented by a skeleton in Case 23, Div. E. 
Order XL MARSUPLiLIA, or Pouched Animals. 
The principal characteristic by which the skeletons of Marsu- 
pials differ from those of all the previous Orders is the presence of 
a pair of long slender bones, attached to the anterior edge of the 
pelvis. These are known as the marsupial bones,’^ owing to their 
close neighbourhood to the external marsupial pouch *. In their 
skulls the Marsupials differ from other Mammals by having the 
angle of the lower jaw much bent inwards, and forming a well- 
marked internal process. Teeth are always present, and separable 
into different classes, but, with the exception of the last premolar, 
not preceded by milk-teeth. The incisors are generally unequal 
in number in the two jaws, and range from | to Dorso-lumbar 
vertebrae invariably 19. 
The Marsupials are divided primarily into two great groups : 
in the first, as in the Rodents and Ungulates, the incisors are few 
in number, but large and powerful, and the canines, at least in 
the lower jaw, are either entirely absent or small and rudimentary ; 
while the second possess, like the placental Carnivora, small and 
numerous incisors and large and sharp canines. The former are 
called Diprotodont and the latter Polyprotodont 
To the former group belong the Kangaroos, Phalangers, and 
* They are absent in one genus only, Thylacinm. 
t “With two front teeth.” 1 “With many front teeth. ^ 
H 2 
