Rodents or Gnawing Animals 



Such diversity of habits naturally produces great differences 

 in structure, but no matter what individual peculiarities a rodent 

 may possess, the characteristic "gnawing teeth" remain the same 

 in all, and serve at once as the "ear-mark" of the group. 



Our rodents are grouped in the following families. 



I. Rabbits and hares (Tamily Leporidce). Hind legs very much 

 longer than the front pair, so that the animals progress by 

 leaps. Ears long, tail very short and up-turned, usually 

 white on the under or exposed side. Peculiar in having 

 a small pair of rudimentary front teeth at the base of 

 the upper pair of large ones. 



Leg of Beaver. Leg of Rat. 



Showing the Tibia (T) and Fibula (F) Showing Tibia and Fibula united, 

 separate for their entire length. (After Lydekker.) 



(After Lydekker.) 



II. Pikas (Tamily Ochotonidce). Legs nearly equal, no tail, 

 otherwise like the rabbits although the general form is 

 more like a large rat. (Exclusively Western.) 



III. Porcupines (Family Erethi^ontidce). Skin with numerous 



sharp spines interspersed among the hairs. 



IV. Gophers ^Family Geomyidce). Rat-like animals, living in 



subterranean burrows, eyes very small, fore legs modified 

 for digging like those of a mole. No projecting ear, 

 curious pouches on each side of the face, opening out- 

 side near the mouth. 



72 



