The three families of the Pinnipedia are denominated in technical language the Trichechidæ,[205] the Otariidæ,[206] and the Phocidæ.[207] The first has but one living representative, the Walrus, or Morse; the second contains the so-called Sea Lions and Sea Bears, more distinctively known as Eared Seals; in the third family are ranged the ordinary Seals, contra-distinguished as Earless Seals. Sufficiently different among themselves in general aspects and habits, as to be recognised at a glance, the three families, nevertheless, have characteristic features common to all, wherefrom the sub-order has received its name. Their toes are united nearly throughout by a web of membrane, as in a duck’s foot, which converts the paws into broad, fin-like organs (the flippers), well adapted for swimming purposes. This feather-footed, pinnipedal condition is associated with a shortening of the upper segments of the limbs, and such peculiar attachment especially of the hind-legs as to leave little more than the feet free. The body is long, usually ample and fleshy at the neck and shoulders, but narrows taperingly behind towards the rump. The head is either flattish and elongated or more or less rounded, but in all cases relatively small to the bulk of the animal. External ears are absent save in the Otary family, which possess a diminutive, conical, or pear-shaped ear-conch. The eyes are full, and often expressive, though usually on land bearing a drowsy look, from their vision being adapted for a watery medium. Unless as the merest rudiment, there are no eyelashes or eyebrows. The muzzle is dog-like, but with long, stiff, though exceedingly mobile moustaches. In the Walrus, however, chiefly on account of its huge tusks, this part of the face is immensely dilated, fleshy, and covered with great pliable bristles, like knitting-needles in calibre; these latter and tusks being adaptations suited to the animal’s mode of feeding. The skin of the body fits loosely, and there is a thick layer of oily fat beneath, its amount depending on general condition, season, and sex. The hairy covering is of two sorts, a stouter, coarser, and at the roots a much shorter, softer kind. As it appears ordinarily, the hair seems uniform and short, and when wetted it clings close to the skin, so that the surface then is smooth and polished, becoming rougher as it dries. Now, it is the soft under-wool, which is in great abundance in some of the Sea Lions only, that constitutes the fur of commerce. [Illustration: SKELETON OF OTARIA IN THE ATTITUDE OF WALKING. (_Reduced after Murie._)]