RODENTS OR GNAWING ANIMALS 
(Glires ) 
ANIMALS of this group may be recognized at once by the 
peculiar arrangement of their teeth. In the front of the mouth 
are two large conspicuous teeth (incisors) in each jaw, which 
meet vertically like two pairs of chisels, and form a very power- 
ful apparatus for gnawing or cutting. The remaining teeth are 
broad flat-topped grinders (molars) placed in the back of the 
mouth while between the two, where the tearing teeth (canines) 
of the carnivorous animals are situated, the jaws are quite bare. 
The large gnawing teeth are further peculiar in being curved and 

Longitudinal section through Beaver skull. 
I Incisor tooth showing long curved base. M The four molars. (After Lydekker.) 
deeply rooted in the jaws, while they also grow continuously 
from the base as they wear away at the tip, so that they never 
become ‘‘ worn out.” 
Rodents range in size from the beaver to the mouse and in 
habits they exhibit the greatest diversity; some are burrowers, as 
the gophers and marmots, others are terrestrial as the rabbits, 
still others like the muskrat are aquatic, while the flying squirrel 
is even able to launch himself through the air. 
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