RODENTIA. 83 



Order VI. RODENTIA. 



The Rodentia, or Gnawing Animals (Case 8, Divs. B-F), are [Case 8.] 

 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 vertebrae ; c/, clavicle ; CD, cervical vertebrae ; d, dorsal 

 vertebrae ; fb, fibula ; fm, femur ; h, humerus ; I, lumbar vertebrae ; 

 me, metacarpus ; mi, metatarsus ; ph, phalanges ; pv, pelvis ; r, radius ; 

 s, sacral vertebrae ; $c, scapula ; sk, skull ; tb, tibia ; ts } tarsus ; w, 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, which 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 



G2 



