756 



MAMMALIA. 



molluscs, and crustaceans. Absent from the tropics, they are repre- 

 sented on most of the coasts in temperate and Arctic zones. Many are 

 markedly gregarious. 



The upper parts of the limbs are included within the skin and general 

 contour of the body. There are five well-developed digits connected 

 by a web of skin. In the hind-foot the first and fifth toes are generally 

 stouter and longer than the rest. There are no clavicles. The tail is 

 very short. 



The small milk-teeth are absorbed before or immediately after 



birth. The incisors are always fewer than ; there are no carnassials ; 



the back teeth have pointed cusps, often sloping slightly backwards. 



The cranial cavity is rounded ; there is a characteristic interorbital 

 constriction. 



The brain is large and well convoluted. The eyes are large and 

 prominent, with a flat cornea. The external ear is small or absent. 



FIG. 373. The common seal. 



The caecum is very short. The kidneys are divided into lobules. 

 The mamma? are two or four in number, and lie on the abdomen. 

 The young are " precocious." 



Family Otariida 1 Eared or fur-seals, connecting the Pinnipeds with 

 the Fissipeds. The hind-feet can be turned forward and used on 

 land in the normal fashion. The palms and soles are naked. There 

 is a small external ear. The testes lie in an external scrotum. 



The sea-lion Otaria, -^'-i' - 2 Pacific and S. Temperate seas. 



2, I, 4, I 



Family Trichechidse Walruses, intermediate between the Otariida: 

 and the seals. The hind-feet can be turned forwards and used 

 on land. The upper canines form large tusks ; the other teeth 

 are small, single rooted, and apt to fall out ; those generally in 



use are * , but the dentition of the fcetus is 3I ^ 2 . 

 0130' 3131 



