136 COMPAIUSONS OF STRUCTUr.E IN ANIMALS. 



of the to-\vering giraffe, or the flexible neck of 

 the sloth, with that of the whale or porpoise. 

 The contrast is in the extreme. 



Let us consider the habits and general form 

 of these aquatic mammalia. Their body 

 elongated, conical, and somewhat fish-like, is 

 covered with a naked oily skin ; their fore- 

 limbs are converted into paddles; hind-limbs 

 are wanting, but the elongated posterior part of 

 the body terminating in a broad horizontal 

 flipper is endowed with enormous power, 

 enabling them to lash the sea into foam. The 

 head appears to be a mere anterior portion of 

 tlie body, continued in the same Une and un- 

 separated by a neck — nor is it movable 

 independent of the body. These are animals 

 that plough the waves, that urge their course 

 through the trackless waters, head foremost, 

 with tremendous velocity. Their head, like 

 the prow of a vessel, has to meet "and overcome 

 the resistance of the fluid medium — hence the 

 fish-like immobility of the head, and absence of 

 apparent neck. In these marine creatures, the 

 cervical vertebrae are wedged together within 

 the smallest possible compass ; and not only so, 

 many of them are consolidated into one piece. 

 In some species,j only six qervical vertebra? 



