CHAPTER XXXIII. 



RODENTS, continued. 

 THE PORCUPINE-LIKE RODENTS. 



Families OCTODONTID^, HYSTEICIDJS, etc. 



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 Octodontidce 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. 



