CH AGP 2 ERs Xa 
RopENTS,—continued. 
THE PorcUPINE-LIKE RODENTS. 
Families OCTODONTID#, HYSTRICIDZ, ete. 
The Rodents described in the present chapter, which include the whole of the 
remaining members of the order, with the exception of the hares, rabbits, and 
picas, are distinguished from all those described above by the conformation of the 
lower jaw. In both the squirrel-like and mouse-like groups, the angular, or lower 
posterior process of the lower jaw, it will be remembered, takes its origin from the 
inferior edge of the socket of the lower incisor teeth. In the present group, on 

SKELETON OF THE CANE-RAT. 
the other hand, this process originates from a prominent ridge on the outer side 
of the jaw; the position of this ridge being shown in the figure of the skeleton of 
the cane-rat. All the members of the group are further characterised by the 
stoutness of the zygomatic or cheek-arch of the skull; and also by the bones of 
the lower leg (tibia and fibula) being perfectly distinct from one another. 
The porcupine-like Rodents are very characteristic of America, and more 
especially of the southern half of that continent. Thus the whole six families 
into which the group is divided occur in America, while only two of them have 
any Old World representatives. Of the latter, the porcupine family is almost 
cosmopolitan; while the Octodontide are represented in the Old World only in 
Africa, south of the Sahara. With the exception of one species, these Rodents 
have one pair of premolar teeth in each jaw. 
