CETACEA. 427 



§ 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 P or pus, and 

 exhibits the most elementary forms of the type of 

 the mammalia, of which they represent the earl}^, 

 or rudimental stage of developement. Here, as 

 before, we have to seek these first elements 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 develope- 

 ment proceeding with more rapidity, and raising 

 structures of greater dimensions in aquatic than in 



also from their having small bony appendices, articulated with them 

 by a regular joint at their extremities, and corresponding exactly, 

 both in shape and situation, to the ribs, of which they may, in fact, 

 be considered as 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 rudimental ribs 

 are attached also to the eighth vertebra. Trans. Zool. Soc. i. 113. 

 The Bradypus torqxiatus, which has been said to possess eight cer- 

 vical 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.) De Blainville, however, maintains that these animals 

 present real exceptions to the rule. See Comptes Rendus, ix. 762. 



