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CHAPTER VIII. 



REPTILIA. 



1 . Terrestrial Vertebrata in general. 



THE numerous tribes of vertebrated animals 

 which are strictly terrestrial, or destined to move 

 on land, differ widely in their modes of pro- 

 gression, and in the mechanical advantages of 

 their formation. The greater number are qua- 

 drupeds ; 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 advancing ; 

 others outstrip the winds in fleetness. Some 

 families of reptiles are entirely destitute of any 

 external organs of motion, the whole trunk of 

 the body resting on the ground : while man oc- 

 cupies a place where he stands alone, being 

 distinguished by the exclusive faculty of per- 

 manently sustaining himself on the lower extre- 

 mities. 



In reviewing the developements and the mecha- 

 nical functions exhibited by so great a diversity 

 of structures, I shall commence with an exami- 

 nation of those amphibious reptiles which appear 



