OPHIDIA. 191 



pedicle, analogous to the external pterygoid apophysis of the sphenoid 

 bone, and are very movable; in them is fixed a sharp pointed per- 

 vious tooth, through which flows a Hquor secreted by a large gland, 

 situated under the eye. It is this liquor which, poured into the 

 wound made by the tooth, produces effects, more or-less violent, 

 according to the species of the reptile in which it is secreted. This 

 tooth, when the animal does not wish to use it, is concealed in a 

 fold of the gum, and behind it are several germs destined to replace 

 it, in the event of its being broken in a wound. These venomous 

 teeth have been termed by naturalists movable fangs, but in fact it is 

 the maxillary bone which moves; there are no other teeth in it, so 

 that in this kind of dangerous serpents only the two rows of palatine 

 teeth are to be seen in the upper part of the mouth. 



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 derived their com- 

 mon name of Vipers, a contraction of viviparous. 



Venomous serpents with isolated fangs have external characters 

 very similar to those of the preceding ones, but in the greater num- 

 ber 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 partial indication of their disposition. 

 They form two great genera, Crotalus and Vipeka, the second of 

 which has been variously subdivided, and some smaller ones which 

 group around them. 



Crotalus, Lin. 



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 distingxiishing character is the rattle which terminates the tail. It 

 is formed by several scaly cornets loosely fitted into each other, which move 

 and produce the peculiar noise from which they receive their name when- 

 ever they crawl or shake that part of the body. The number of these cor- 

 nets increases with age, an additional one being always found after each 

 moult. There is a little round indentation or pit behind each nostril. All 

 the species whose habitat is v/ell asceilained are from America. The dan- 

 ger resulting from the bite of these noxious reptiles is in proportion to the 

 warmth of the climate or of the season; their natural disposition, however, 

 is tranquil, and they are rather slow and heavy in their motions, never bi- 

 ting unless provoked, or to kill the prey on which they feed. 



Their principal food consists of Birds, Squirrels, &c. It has long been 

 supposed that it possesses the faculty of rendering them powerless by its 



