OKDEKS OF MAMMALIA. 



30? 



Tigers, Dogs, etc., in which the heel is raised from the ground, 

 and the animal walks upon tiptoe. 



The Seals and Walruses, forming the family Pinnigrada, 

 are distinguished from the other Carnivora by their adapta- 

 tion to an aquatic mode of life. In this respect they agree 

 with the thoroughly aquatic Whales and Dolphins, but they 

 differ from both the Cetacea and the Sirenia, not only in their 

 dentition, but also in always having well-developed hind-limbs. 

 The Seals (Fig. 154) are characterized by having incisor teeth 

 in both jaws, at the same time that the canine teeth are not 

 immoderately developed. They form a very numerous family, 

 of which species are found in most seas out of the limits of 



Fig. 154. — Greenland Seal (Phoca GfTomlcmtUca). 



the tropics. They abound, however, especially in the seas of 

 the Arctic and Antarctic regions. They are largely captured 

 both for their oil and for their fur. The Walrus or Morse 

 (Frichecies) is distinguished from the true Seajs by the fact 

 that in the adult only two of the upper incisors are present ; 

 while the upper canines are enormously developed, and form 

 two pointed tusks — ^fifteen inches or more in length — which are 

 directed downward between the small lower canines, and pro- 

 ject considerably below the chin. The Walrus is a large, 

 heavy animal, from ten to fifteen feet in length, which is found 

 in flocks in the Arctic seas, and is hunted both for its blubber 

 and for the ivory of the tusks. 



The Plantigrade Carnivora apply the whole or the great- 

 er part of the sole of the foot to the ground in walking ; and 



