218 MOSTLY MAMMALS 
to the martens and weasels, but specially modified for the 
needs of an aquatic life, and furnished with teeth adapted 
to seize and hold the slippery prey on which they subsist. 
Since, however, they are much less exclusively aquatic 
than seals, spending much of their time on shore, their 
structural variations from the ordinary mammalian type 
are far less marked than is the case in the members of 
the latter group. The toes, for instance, are not webbed, 
and neither pair of limbs shows a tendency towards a 
paddle-like form, although both are relatively short. In 
addition to this shortening of the limbs, the points chiefly 
noticeable as adaptations for swimming are the great breadth 
and flatness of the head, the small size of the ears, the 
absence of a distinctly defined neck, the elongated and 
flattened body, moderately long and powerful tail, and the 
denseness and softness of the fur. As regards the teeth, 
it will suffice to mention that while these conform to the 
general marten type, the hinder ones are remarkable for 
the greater extent of grinding surface, the last upper molar 
especially being distinguished by the peculiarly squared 
form of its crown. In all these teeth the cusps are re- 
markably strong and sharp, and thus suited for piercing 
the scales of fish. 
Contrast these features with those distinctive of the sea- 
otter—which, by the way, is the only representative of 
its kind. In addition to its being a shorter- and thicker- 
bodied creature, with a still broader muzzle and no 
definable neck at all, the sea-otter is at once distinguished 
by the structure of its hind-feet, which are fully webbed, 
and so lengthened and expanded as almost to simulate 
paddles ; the extremities of the toes being, it is said, 
turned down beneath the sole when on land. The tail, 
too, is thicker, less tapering, and more flattened than that 
