532 MANUAL OF ZOOLOGY. 



these forms is elongated and somewhat fish-like in shape, 

 covered with a short dense fur or harsh hairs, and terminated 

 behind by a short conical tail. All the four limbs are present, 

 but are very short, and the five toes of each foot are united 

 together by a membrane, so that the feet form powerful 

 swimming-paddles. The hind-feet are of large size, and are 

 placed far back, their axis nearly coinciding with that of the 

 body (figs. 203, 204). From this circumstance, and from the 

 fact that the integument often extends between the hind-legs 

 and the sides of the short tail, the hinder end of the body 

 forms an admirable swimming-apparatus, similar in its action 

 to the horizontal tail-fin of the Cetacea and Sirenia. The tips 

 of the toes are furnished with strong claws, but their powers of 

 terrestrial locomotion are very limited. The ears are of small 

 size, and are mostly only indicated by small apertures, which 

 the animal has the power of closing when under water. The 

 bones are light and spongy, and beneath the skin is a layer of 

 fat or blubber. The dentition varies, but teeth of three kinds 

 are always present, in the young animal at any rate. The 

 canines are always long and pointed, and the molars are 

 generally furnished with sharp cutting edges. 



Fig. 204. The Greenland Seal (Pkoca Grcenlandica.) 



The section Pinnigrada includes the two families of the 

 Seals (PhoddcK) and Walruses (Trichetida). The Seals are 

 distinguished by having incisor teeth in both jaws, and by the 

 fact that the canine teeth are not disproportionately developed. 

 They form a very numerous family, of which species are found 

 in almost every sea out of the limits of the tropics. They 

 abound, however, especially in the seas of the Arctic and 

 Antarctic regions. They live for the most part upon fish, and 



