360 THE AXATOilY OF VERTEBRATED ANIMALS. 



molar and molar teeth are similar in character, and never 

 have more than two fangs. There is no lachrymal bone or 

 canal. 



The brain-case of the cranimn is generally much more 

 rounded than that of other (Jarnivora y 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 cerebral 

 hemispheres, as well as in their relatively small olfactory 

 nerves and anterior commissure, the Plnnipedia approach the 

 Cetacea. 



There are three groups of Plnnipedia : tlie Otarldce, the 

 Trichechidce, and the Phocidm. 



1. The OtaHdm^ 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 supporting 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 skull, which in its general form, its large 

 supra-orbital processes, the small and rugged hidla tympmii^ 

 the perforation of the alisphenoid by a cana], and the presence 

 of a crest on the inner surface of the parietals, is extremely 

 ursine. 



2. The TrichecTiidm^ or Walruses, are devoid of external 

 ears, but resemble the Otaridcie in their mode of standing and 

 walking. The skull resembles that of the Bear in the same 

 respects, but the muzzle is distorted by the enormous develop- 

 ment of the superior canines. The Walruses resemble the 

 Bears in another point, namely, in the presence of a supple- 

 mentary bronchus ; the right bronchus, before it reaches the 

 lung, dividing into two trunks, a large and a small. The thy- 

 roid cartilage is deeply excavated, in front, by a triangular 

 fissure ; and the epiglottis is extremely small. 



In the brain, the remarkably large and richly convoluted 

 hemispheres cover the cerebellum, and present a rudimentary 

 posterior cornu. The anterior commissure is very small, as 

 are the olfactory nerves. 



The dentition of the Walrus is extremely peculiar. In the 

 adult, there is one simple conical tooth in the outer part of the 

 premaxilla, followed by a huge tusk-like canine, and three, 

 short, simple-fanged teeth. Sometimes, two other teeth, 

 which soon fall out, lie behind these, on each side of the upper 



