RODENTIA. 
83 
Order VI. RODENTIA. 
The Rodentia, or Gnawing Animals (Case 8, Divs. B-F), are 
characterized by their want of canine teeth and by the peculiar 
structure and great development of their incisors. The majority 
of Rodents have only a single pair of incisors above and below : 
these teeth are large, curved, and adapted to gnawing purposes by 
possessing sharp, chisel-like edges, formed by the hard outer coat of 
Fig. 42, 
Skeleton of a Squirrel. 
c, carpus ; cd, caudal vertehrse ; cl, clavicle ; cv, cervical vertebrae ; d, dorsal 
vertebrae ; fh, fibula ; fm, femur ; h, humerus ; I, lumbar vertebrae ; 
me, metacarpus ; mt, metatarsus ; ph, phalanges ; pelvis ; r, radius ; 
s, sacral vertebrae ; sc, scapula 5 sk, skull ; tb, tibia ; ts, tarsus 5 u, ulna. 
enamel, which is restricted to their front surfaces, and wears away 
more slowly than the softer dentine or tooth-core. These teeth, 
besides, continue during the whole life of the animal to grow 
from their roots as fast as they wear down at their tips. Should, 
however, one of them get destroyed or diseased, the corresponding 
tooth in the opposite jaw, wRich ought to have been worn down by 
it, continues to grow until it may even bring about the death of 
the animal by preventing the mouth from closing, and thus causing 
G 2 
