326 



BRANCH CHORDATA 



Order V. Ceta'cea. — The whales must be regarded as true 

 mammals, since they nourish their young with milk. They are, 

 however, hairless, with the exception of a small number of hairs 

 about the muzzle in some species. They are perfectly aquatic, 

 never leaving the water. Their form is fish-like, with a large 

 and powerful tail horizontally flattened, with a fluke on each 

 side. The tail is the chief organ of locomotion, moving up and 

 down in a sort of rotary motion, and thus propelling the animal 

 from place to place.' 



:^ ) 



,ul^' 



:(m;^f\S^ 



The dugong. (From Brehm.) 



The fore limbs are fin-like paddles or flippers and are used as 

 balancers. Whales have lost all external trace of hind limbs, 

 but a pair of small vestigial bones is found embedded in the 

 body. A fleshy dorsal fin is generally present. 



Whales (Fig. 267) are distinguished by a great rounded cra- 

 nium, the elongation of jaws and face, and by a prow-like snout 

 of fat for the defense of the skull. The mouth is very large and 

 the throat extremely small. The nostrils are represented by a 

 single or double blow-hole far back on the snout, nearly on top 

 of the head. " When the whale breathes the expired air rushes 

 out through the nostrils. The vapor in this expired breath, 

 1 Bcddard, p. 173. 



