534 MANUAL OF ZOOLOGY SECT. 



not in use, of being retracted into a sheath of skin situated 

 at their bases ; or relatively short and blunt, when they are 

 incompletely or not at all retractile. The Otters (Lutrci) 

 differ from the rest in having short limbs with the toes 

 connected by webs of skin. 



The Pinnipedia, or Seals and Walruses, have the 

 proximal segments of the limbs short, the arm and 

 thigh and nearly all the fore-arm and leg being enclosed in 

 the common integument of the trunk, and the manus and 

 pes elongated. The Earless Seals (PhoddcR) are much more 

 completely adapted to an aquatic life than the Eared Seals 

 (Otariidce] and Walruses (Trichechida\ 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 Stals 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 Rodent la (Beavers, Water- Voles) are 

 aquatic, some (Squirrels and Tree-Porcupines) are arboreal, 

 while others (the majority of the order) lead a terrestrial life, 

 and are active burrowers ; they are on the whole a very uni- 

 form group, and exhibit few such remarkable modifications 

 as are to be observed in some of the other orders of Ma'mmals. 

 They are nearly all furry animals with five-toed limbs and 

 with a dentition similar in its leading features to that 

 of the Rabbit (p. 500). The tail is usually elongated, 



