4&^ THE MECHANICAL FUNCTIONS. 



<§ 2. Cetacea. 



Remarkable exemplifications of the law of uni- 

 formity of organic structure are furnished by the 

 family of the Cetacea, which includes the whale, 

 the cachalot, the dolphin, and the porpus, and 

 exhibits the most elementary forms of the type 

 of the mammalia, of which they represent the 

 early, or rudimental stage of developement. 

 Here, as before, we have to seek these first ele- 

 ments among the inhabitants of the water : for 

 whenever, in our progress through the animal 

 kingdom, we enter upon a new division, aquatic 

 tribes are always found to compose the lowest 

 links of the ascending chain. Here, also, we 

 observe organic developement proceeding with 

 more rapidity, and raising structures of greater 

 dimensions in aquatic than in terrestrial animals. 

 The order Cetacea comprises by far the largest 



rudiments. These small bones have been observed, both by 

 Meckel and by Cuvier, attached to the ninth vertebra: and 

 Mr. T. Bell has recently not only confirmed the observations of 

 these anatomists, but has farther discovered, that similar rudi- 

 mental ribs are attached also to the eighth vertebra. (See Phi- 

 losophical Magazine, third series, iii. 376). The Bradypus 

 torquatus, which has been said to possess eight cervical vertebrae, 

 will, perhaps, on closer examination, be hereafter found not to 

 deviate, any more than the three-toed sloth, from the normal 

 type, as regards the number of these vertebrae. Instances have 

 occurred of supernumerary cervical processes, or ribs in the human 

 skeleton. (See Edinburgh Medical and Surgical Journal, xl. 304.) 



