XIII 



PHYLUM CHORDATA 



475 



the upper jaw. The eyes are small, the pinnae of the ears enormous. 

 The tail is small. The skin is very thick, and provided with only 

 a, scanty hairy covering. 



In the Carnivora the typical number of digits is sometimes 

 present, or, more usually, there are five in the fore- and four in the 

 hind-foot, or four in each. The extremities of the digits are pro- 

 vided with compressed curved claws, which may be very long and 

 sharp, when they are capable, when not in use, of being retracted 

 into a sheath of skin situated at their bases ; or relatively short 

 3,nd blunt, when they are incompletely, or not at all, retractile. The 

 Dogs (Can idee} and Cats (Felidce) are digitigrade, the Bears 

 { Ursidce) and allied groups plantigrade. The Otters (Lutra) differ 

 from the rest in having short limbs with the toes connected by 

 webs of skin. 



The Pinnipedia (Fig. 1053) have the proximal segments of the 

 limbs short, so that the arm and thigh, and nearly all the fore-arm 





FIG. 1053. Seal (Phoca >vituli,ia). 



and leg, are enclosed in the common integument of the trunk, and 

 the manus and pes elongated. The Earless Seals (Phocidce) are 

 much more completely adapted to an aquatic life than the Eared 

 Seals (Ota ri idee) and Walruses (Trichechidce), being unable to flex the 

 thigh forwards under the body, so that the hind-limbs may aid in 

 supporting the weight, and thus being only able to drag themselves 

 along very awkwardly when on dry land. The pinna of the ear is 

 absent in the Earless Seals and Walruses, well developed in the 

 Eared Seals. The surface in all is covered with a thick soft fur. 

 In the Fur Seals there are two kinds of hairs those of the one 

 kind being longer and coarser, and scattered through the more 

 numerous shorter and finer hairs composing the fur proper. A 

 remarkable feature of the Walruses is the presence of a pair of 

 large tusks the enlarged canine teeth projecting downwards 

 from the upper jaw. 



Though some of the Rodents (Beavers, W T ater Yoles) are aquatic, 

 some (Squirrels and Tree-Porcupines) are arboreal, while others 



