472 ZOOLOGY SECT, 



represented only by a few bristles about the mouth. In the 

 Whale-bone Whales the nostrils have two external slit-like 

 apertures; in the Toothed Whales, Porpoises, and Dolphins, on 



FIG. 1052. Killer (Orca gladiator). (After True.) 



the other hand, the two nostrils unite to open by a single' 

 crescentic valvular aperture. 



In the Sirenia also the body is fish-like, with a horizontal caudal 

 fin, the fore-limbs flipper-like, the hind-limbs absent, and the 

 integument almost hairless. But the body is distinctly depressed, 

 and the head is by no means so large in proportion as in the 

 Cetacea, and has a tumid truncated muzzle, not far back from 

 the extremity of which the nostrils are situated. There is no 

 dorsal fin. The eyes are small, the pinn-ie of the ears absent. 

 The digits are in some cases provided with claws. 



In the Ungulata vera the claws or nails of other Mammals are 

 replaced by thick solid masses, the hoofs, investing the ungual 

 phalanges and bearing the weight of the body. The number of 

 digits is more or less reduced, and the limbs as a whole are usually 

 specially modified to act as organs of swift locomotion over the 

 surface of the ground, their movements being restricted, by the 

 nature of the articulations, to antero-posterior movements of 

 flexion and extension. The metacarpal and metatarsal regions 

 are relatively very long. In the Artiodactyla the third and 

 fourth digits of each foot form a symmetrical pair. In the 

 Ruminants vestiges of the second and fifth digits are also commonly 

 present ; but these are usually not functional, never reaching the- 

 ground, though in the Reindeer they are better developed than in 

 the others, and have the effect of preventing the foot from so- 

 readily sinking in the snow. In the Camels the third and fourth digits- 



