PORCUPINES. 
85 
almost invariably one premolar above and below^ a peculiarly twisted 
lower jaw, variable palatine foramina, generally no postorbital pro- 
Fig. 43. 
/. fibula ; t, tibia. 
cesses, and separate shin-bones. The animals forming this section 
are very variable both in size and osteological characters. The 
most noteworthy are the true Porcupines [Hystrix), which have 
Fig. 44. 
Skull of Common Porcupine {Hystrix cristata). The outer part of the 
bone of the lower jaw has been removed, to show the whole length of 
the lower incisor tooth. 
i, incisor teeth ; m, molars ; pm, premolars. 
the facial part of the skull curiously dilated (see fig. 44) ; the 
Capybara [Hydrochoerus capyhara)^ the largest of the Rodents; 
