REPTILES 1383 



whose hindlegs are short and feeble, walks better, 

 but does not jump or swim so well as the frog.* The 

 Hyla, or tree-frog, has the extremities of each of its 

 toes expanded into a fleshy tubercle, approaching in 

 the form of its concave surface to that of a sucker, 

 and by the aid of which it fastens itself readily to the 

 branches of trees, which it chiefly inhabits, and along 

 which it runs with great agility. 



The salamander is an animal of the same class as 

 the frog, undergoing the same metamorphoses from 

 the tadpole state. It differs much, however, in re- 

 spect to the development of particular parts of the 

 skeleton. The anterior extremities of the salamander 

 make their appearance earlier than the hindlegs, 

 and the tail remains as a permanent part of the struc- 

 ture. The land salamanders have a rounded tail, but 

 the aquatic species, or Tritons, have it compressed 

 vertically; thus retaining the fish-like form of the 

 tadpole, and the same radiated disposition of the 

 muscles. 



In the class of serpents we see exemplified the 

 greatest possible state of simplicity to which a verte- 



* It is singular that the frog, though so low in the scale of 

 vertebrated animals, should bear a striking resemblance to the 

 human conformation in its organs of progressive motion. This 

 arises from the exertions which it makes in swimming being 

 similar to those of man in walking, in as far as they both result 

 from the strong action of the extensors of the feet. Hence, we 

 find a distinct calf in the legs of both, produced by the swell- 

 ing of similar muscles. The muscles of the thigh present, also, 

 many analogies with those of man ; particularly in the presence 

 of the long muscle called the sartorins, the use of which is to 

 turn the foot outward, both in stepping and in swimming. 



