THE PINNIPEDIA. 423 



elastic ligaments are very strong, and tlie median phalanx 

 is excavated, in order to allow of the lodgment of the 

 retracted phalanx on one side of it. 



b. The Pmnipedia, or Seals and Walruses, are those Car- 

 nivora which come nearest the Cetacea. The tail is united, 

 by a fold of skin which extends beyond its middle, with the 

 integument covering the hind legs. These are, in most 

 species, permanently stretched out in a line with the axis of 

 the trunk. The pinna of the ear is small or absent. The toes 

 are completely united by strong webs, and the straight nails 

 are sometimes reduced in number, or even altogether abor- 

 tive. The inner and the outer digits of the pes are very 

 large. The incisors vary in number and lose their cutting 

 foi"m. The premolar and molar teeth are similar in cha- 

 racter, and never have more than two fangs. There is no 

 lachrymal bone or canal. 



The brain-case of the cranium is generally much more 

 rounded than that of other Carnivora; and, in some genera, 

 the supra-orbital processes of the frontals are very largely 

 developed. In both of these characters, and in the great 

 breadth and complication of the convolutions of their cere- 

 bral hemispheres, as well as in their relatively small olfactory 

 nerves and anterior commissure, the Pinnipedia approach 

 the Cetacea. 



Thei-e are three groups of Pinnipedia : the Otaridce, the 

 Trichechidce, and the Phocidce. 



1. The Otaridce, or Eared Seals, are so termed because 

 the ear possesses a distinct though almost rudimentary 

 pinna. These Seals have long necks, and can stand or 

 walk upon all fours, the hind limbs being capable of sup- 

 porting the body in the ordinary way. 



In many respects, these animals are closely allied with the 

 Bears ; and by no part of their organization is this more 

 clearly shown than by the skuU, which in its general 

 form, its large supra-orbital processes, the small and rugged 

 bulla tyvipani, the perforation of the alisphenoid by a 

 canal, and the presence of a crest on the inner sm-f ace of 

 the parietals, is extremely ursine. 



