The next family is that of the walruses, or _Odobaenidae_, the single
generic representative of which is in some respects intermediate
between the _Phocidae_ and _Otariidae_, but has a completely aberrant
dentition. Walruses have no external ears, as in the _Phocidae_; but
when on land the hind-feet are turned forwards and used in
progression, though less completely than in the _Otariidae_. The upper
canines are developed into immense tusks, which descend a long
distance below the lower jaw. All the other teeth, including the lower
canines, are much alike, small, simple and one-rooted, the molars with
flat crowns. The skull is without post-orbital process, but has an
alisphenoid canal. In the young the dentition is i. 3/3, c. 1/1, p.
and m. 5/4, but many of these teeth are, however, lost early or remain
through life in a rudimentary state, concealed by the gums. The teeth
which are usually developed functionally are i. 1/0, c. 1/1, p. 3/3,
m. 0/0; total 18. Vertebrae: C. 7, D. 14, L. 6, S. 4, Ca. 9. Head
round. Eyes rather small. Muzzle short and broad, with a group of
long, very stiff, bristly whiskers on each side. The remainder of the
hair-covering very short and closely pressed. Tail rudimentary.
Fore-feet with subequal toes, carrying five minute flattened nails.
Hind-feet with subequal toes, the fifth slightly the largest, with
cutaneous lobes projecting beyond the ends as in _Otaria_; first and
fifth with minute flattened nails; second, third and fourth with
large, elongated, subcompressed pointed nails. The two species are
_Odobaenus rosmarus_, of the Atlantic, and the closely allied _O.
obesus_, of the Pacific. (See WALRUS.)
[Illustration: FIG. 7.--Skull and dentition of Australian Sea-Bear
(_Otaria forsteri_).]