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CHAPTER VIII. 



REPTILIA. 



§ 1. Terrestrial Vertehrata in general. 



The numerous tribes of vertebrated animals wbich are 

 Strictly terrestrial, or destined to move on land, differ widely 

 in their modes of progression, and in the mechanical advan- 

 tages of their formation. The greater number are quadru- 

 peds; some formed for climbing trees, others, for burrowing 

 in the earth; some for treading on sandy plains, some for 

 scaling precipices. A. few seem scarcely capable of ad- 

 vancing; others outstrip the winds in fleetness. Some fami- 

 lies of reptiles are entirely destitute of any external organs 

 of motion, the whole trunk of the body resting on the ground : 

 while man occupies a place where he stands, alone, being 

 distinguished by the exclusive faculty of permanently sus- 

 taining himself on the lower extremities. 



In reviewing the developments and the mechanical func- 

 tions exhibited by so great a diversity of structures, I shall 

 commence with an examination of those amphibious reptiles 

 which appear to form an intermediate link in the chain con- 

 necting the strictly aquatic, with the terrestrial vertebrated 

 animals: then, taking up this latter series, I shall consider 

 the more sim.ple conformation, and less perfect motions of 

 terrestrial animals destitute of limbs; and gradually ascend 

 to those in which the support and progression of the body is 

 effected by extremities, more and more artificially formed: 

 concluding w^ith the human structure, which terminates this 

 extensive series. 



