THE MARINE CARNIVORA 191 



etc.); (2) the *Trichechid*,X Walruses; and (3) the Thocid<e, or 

 True Seals. The first-named family (which is not represented by 

 any British species) still possesses small ear conches or outer ears. 

 It has an alisphenoid canal for the passage of the carotid artery 

 at the base of the skull. Its members are able to use their hind 

 limbs in a normal mammalian fashion, and, in fact, to walk with 

 them. The muzzle is rather bear-like, and the nostrils are 

 situated in the normal position at the end of the muzzle. The 

 testes, instead of being entirely retained within the body, as in 

 the Walruses and True Seals, descend into a scrotum. The Otariids 

 also have a postorbital process rising out of the zygomatic arch, or 

 cheek bone, and assisting to define the orbit of the eye. This is 

 less observable in the True Seals, but is present in the Walrus. 



On the other hand, the molar teeth of the Otariids are even 

 more degenerate and simplified than in the True Seals, and 

 although they are able to turn their hind limbs forward for 

 walking, the structure and appearance of the feet are more 

 specialised than in the True Seals, because beyond the bony ends 

 of the toes and their nails the webbed skin is prolonged consider- 

 ably into a deeply lobed margin. The fore paw, or flipper, is also 

 highly modified, having no outwardly separable fingers, while the 

 terminal phalanges are only armed with small, useless nails. 1 In 

 the conformation of the fore limb the Otariids are much more 

 specialised than the True Seals. 



FAMILY: TRICHECHID^E. THE WALRUSES 



Odobanus rosmarus. THE WALRUS 



It is doubtful whether there are two species of Walrus, or 

 whether the differences between North Pacific, Arctic, and Atlantic 

 forms are any more than a marked variation of sub-specific 

 character. The characteristics of the Walrus family can be best 

 illustrated in describing the only known genus and species of this 

 remarkable Pinnipede. 



The walruses anatomically are more nearly related to the eared 



1 In the hind feet the three middle toes of the Otariids retain longer and 

 stronger claws. 



