530 



MANUAL OF ZOOLOGY 



SECT. 



Toothed Whales, Porpoises, and Dolphins, on the other 

 hand, the two nostrils unite to open by a single crescentic 

 valvular aperture. The Whale-bone Whales are toothless 

 and are characterised by the presence of " baleen " or 



whale-bone, in the form of 

 numerous triangular horny 

 plates (Fig. 299) hanging 

 vertically downwards from 

 the roof of the mouth. In 

 the Toothed Whales, on the 

 other hand, more or fewer 

 teeth are developed in the 

 jaws. 



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 de- 

 pressed, and the head, which 

 is by no means so large in 

 proportion as in the Ceta- 

 cea, has a tumid trun- 

 cated muzzle, not far back 

 from the extremity of which 

 the nostrils are situated. 

 There is no dorsal fin. 



In the section Ungulata 



vera, comprising all the more typical members of the 

 order Ungulata, the claws or nails of other Mammals are re- 

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

 phalanges and bearing the weight of the body. The 



FIG. 299. Section of upper jaw, (a), 

 with baleen-plates, of Balaenoptera. 

 (After Owen.) 



