518 



Vertehrata. 



forwards, tliat the animal can walk upon them. Each foot has five 

 digits provided with straight claws ; all are webbed, and the membrane 

 is prolonged beyond the tips of the toes as a more or less well- 

 developed ridge of skin. The digits of the fore limb decrease in 

 length and strength from the first to the fifth (the first and second, 

 however, are about equally strong) • on the hind limb the first and 

 fifth are stronger and usually also longer than the other three ; the 

 tail is short; the pinnse small or absent; the eyes large; the nares 

 mere slits, which close spontaneously by the elasticity of their walls, 

 but are opened by a muscular apparatus; the hair is usually close- 

 set, smooth, and sleek ; with, sometimes, a thick covering of wool 

 below ; the new-born animal is generally covered with a woolly fur 

 which is sometimes shed before birth: the vibrissa are very strong. 

 Below the skin there is a thick layer of adipose tissue (blubber). 



Fig. 414. 



Fig. 415. 



Fig. 414. Pes of a young Sea Elephant, a astra- 

 galus, c oaloaneum, n oentrale, c' — c^ cuneiforms, ch cuboid ; 

 I—V first-fifth toes.— After Flower. 



Fig. 415. Upper teeth of the Sea Elephant; the 

 milk teeth are drawn below the teeth of the permanent set. 

 — After Flower. 



There are usually f incisors (or a smaller number, rarely f ) ; they 

 are more conical than those of the Carnivora, and do not form a 

 continuous cutting edge in closing : the canines are usually feebler 

 than in Carnivora, but otherwise similar. Of the molars, p | and 

 m ^, are usually present; they are practically all alike, usually 

 similar to the interdigitating teeth of the Carnivores or simple and 

 conical ; they are relatively feeble. The milk teeth are rudimentary, 

 they are either absorbed before, or shed quite soon after, birth. 



It may also be mentioned that the hiadermost portion of the skull is very 

 broad, whilst the interorbital region is usually much compressed. The lower jaw 

 is generally feeble ; lachrymal bone and duct are absent ; the lachrymal gland 

 is smaU, the Harderian gland well developed : the placenta, as in the Carnivores, 

 is zonaiy. 



