12 Struciufe and Economy 



Linneus, however, afterwards followed Aristotle, in justly 

 considering them as a tribe of creatures which resembled 

 quadrupeds in disguise ; since, unlike fishes, they not only, as 

 we have seen, breathe the air by means of true lungs, but 

 they closely resemble quadrupeds in much of their general 

 construction, in their manners, in their intelligence, and in the 

 energy of their senses. Their hearts, also, which propel warm, 

 red blood, present no material modification in their structure 

 from those of quadrupeds. Their other viscera somewhat 

 resemble those of the ruminantia, and the size of their brain 

 often even exceeds that of the generality of the mammalia. 



Being, therefore, mammalia in their economy and their struc- 

 ture, they, in fact, only resemble fishes in inhabiting the same 

 element, and in possessing that external fish-like form, which, 

 being the best adapted for aquatic avocations, necessarily oc- 

 casions differences in the details of their internal structure. 

 The most obvious and striking peculiarities, which first attract 

 our notice in the skeleton of the cetacea, are the enormous 

 size of the head, in the whales ; the almost entire absence of 

 neck ; the length and similarity of the bones of the spine ; 

 their ribs being comparatively few in number ; the shortness 

 of their arms ; and the absence of hinder extremities, an os 

 sacrum, and a true pelvis. Whales have, nevertheless, the ru- 

 diments of the latter, although the two bones which represent 

 it, neither unite before, nor are they attached to the vertebrae. 



The excessive shortness of their necks, although composed, 

 generally, of only one bone less than the longest neck of a 

 quadruped — as that of the giraffe, for example — renders any 

 separate motion of their heads almost impossible, since the 

 bones of the neck of the whale kind are excessively thin, and 

 immoveably joined together. This, I am disposed to consider 

 as a condition favourable to rapid progression, as that of birds 

 is assisted by the immoveable state of the spine of the back, 

 by which their centre of gravity is rendered less liable to be 

 varied, and their bodies to be thrown out of equilibrium 

 during their rapid flight ; for, did the spine of the back of a 

 bird possess great flexibility, its centre of gravity would be 

 probably changed by every extra effort of either wing ; and to 

 counteract the same tendency, therefore, the necks of whales 



