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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