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: Kabbits and hares (ramily Leporida). 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 th: 
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) 
MM: Pikas (Family Ochotonid@). Legs nearly equal, no tail, 
otherwise like the rabbits although the general form is more 
like a large rat. (Exclusively Western.) 
III. Porcupines (Family Erethizontide). Skin with numerous 
sharp spines interspersed among the hairs. 
IV. Gophers (Family Geomyid@). 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 outside near the 
mouth. 
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