346 



VEKTEBllATE ANIMALS. 



The Seals and Walruses, forming the family Pinnigrada, are 

 distinguished from the other Carnivora by their adaptation 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 hav- 

 ing well-developed hind-limbs. The Seals (fig. 251) are character- 

 ised by having tricuspidate proemolar and molar teeth, the lower 

 incisors being- often reduced to four, and the canine teeth not being 

 of excessive size. They form a very numerous family, of which 

 species are found in most seas out of the limits of 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 {Trichecus) is distinguished 

 from the true Seals by the fact that in the adult only two of the 



Fig. 251. — Greenland Soal (Phoea Grosnlandlca), 



upper incisors are present ; whilst the upper canines are enor- 

 mously developed, and form two pointed tusks — fifteen inches or 

 more in length — which are directed downwards between the small 

 lower canines, and project considerably below the chin. The Wal- 

 rus 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 F/aittiijnule Carnivtira apply the whole or the greater part 

 of the sole of the foot to the ground in walking ; and this portion 

 of the foot is nearly or altogether destitiite of hairs, except in the 

 White Bear. The most typical members of the Plantigrada are 

 the Bears (Ursidw), of which the common Brown Bear and the 

 White or Polar Bear are familiar examples. The Bears are much 

 less purely carnivorous than the majority of the order, and, in 

 accordance with theii- omnivorous habits, the teeth do not exhibit 



