66 REPTILIA. 



All these venomous species^ whose mode of production is 

 well known, bring forth living young ones, as their eggs are 

 hatched without being laid, from which circumstance is de- 

 rived their common name of Vipers, a contraction of vivipa- 

 rous. 



Venomous serpents with insulated fangs have external cha- 

 racters very similar to those of the preceding ones, but in the 

 greater number the jaws are very dilatable, and the tongue 

 very extensible. The posterior portion of their head being 

 broad, generally gives them a ferocious aspect, which is a par- 

 tial indication of their disposition. They form two great ge- 

 nera, Crotalus and Vipera, the second of which has been 

 variously subdivided, and some smaller ones which group 

 around them. 



Crotalus, Lin.(l) 



Rattlesnakes are pre-eminently conspicuous for the intensity of 

 their venom. As in Boa, there are transverse simple plates under 

 the body and tail; but their most distinguishing character is the 

 rattle which terminates the tail. It is formed by several scaly cor- 

 nets loosely fitted into each other, wkich move and produce the pe- 

 culiar noise from w^hich they receive their name whenever they 

 crawl or shake that part of the body. The number of these cornets 

 increase with age, an additional one being always found after each 

 moult. There is a little round indentation or pit behind each nos- 

 tril. (2) All the species whose habitat is well ascertained are from 

 America. The danger resulting from the bite of these noxious 

 reptiles is in proportion to the warmth of the climate or of the sea- 

 son; their natural disposition, however, is tranquil, and they are ra- 

 ther slow and heavy in their motions, never biting unless provoked, 

 or to kill the prey on which they feed. 



Although the Rattlesnake never ascends trees, its principal food 

 consists of birds, squirrels, &c. It has long been supposed that it 

 possesses the faculty of rendering them powerless by its breath, or 

 even of charming them, as it is called, by which they are compelled 

 to leap into its mouthy this, however, is not so, and the reptile in 



(1) Crotalus, from nfOT a.\ov . 



(2) See Russel and Home, Phil. Trans. 1804, pi. iii, p. 76. 



