MAMMALS. 



389 



have descended from some wolf stock; but others think 

 that dogs and wolves are distinct, and even that our com- 

 mon dogs represent several originally distinct kinds or 

 species. 



The hysenas are intermediate between the cats and dogs 

 in many respects. They have the back teeth fitted for 



. : 



FIG. 173. The harbor seal (Phoca vitulina). After Elliott. 



% 



crushing. In the cats, of which there are more than fifty 

 species, the teeth are usually if, c^, pm%, m\, while the 

 claws are retractile into sheaths. Our domestic cat appar- 

 ently had its origin in Egypt, while ancient Greece and 

 Rome lacked our familiar puss, its place being taken by 

 domesticated martens. Among the cats the tiger, lion, 

 panther, leopard, and puma rank first, and with them are 

 associated the wildcats and lynxes. 



In external form the Pinnipedia (seals and walruses) have 

 little resemblance to the other carnivores, but in structure, 



