478 THE MECHANICAL FUNCTIONS. 



the dolphin, the narwal, the cachalot, and the 

 whale ; animals which, however widely they 

 may differ in their habits and external con- 

 formation from terrestrial quadrupeds, possess, 

 in common with the latter, all the essential 

 characters of internal structure and of functions 

 above enumerated. These characters belong 

 also to the human species, which must conse- 

 quently, in its zoological relations, be ranked 

 as a genus of the class mammalia. So numerous, 

 indeed, are the analogies which connect the na- 

 tural families of this class with our own race, that 

 we must ever feel a deep interest in the accurate 

 investigation of their comparative anatomy and 

 physiology ; and it has been found, accordingly, 

 that the progress which has, of late years, been 

 made in this branch of science has materially 

 enlarged our knowledge of the structure, the 

 functions, and the physical history of man : 

 subjects with which our welfare has obviously 

 the closest and most intimate relation. 



The principle of analogy, which prevails so 

 generally in the inferior departments of the ani- 

 mal creation, may be also traced in the class 

 mammalia ; for we always find its influence 

 more conspicuous in proportion as the objects 

 comprehended in the natural series of beings are 

 more numerous and more diversified. Scarcely 

 any of the great natural assemblages of animals 



I 



