184 REPTILIA. 



naturalists moveable 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 serpent 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 common 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 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 partial indi- 

 cation of their disposition. They form two great genera, CROTALUS and 

 VIPEUA, the second of which has been variously subdivided, and some smaller 

 ones which group around them. 



CROTALUS, Linnaeus. 



Rattlesnakes are pre-eminently conspicuous for the intensity of their venom. 

 As in the 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 bv 

 several scaly cornets loosely fitted into each other, which 

 move and produce the peculiar noise from which they receive their name 

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

 cornets 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 well ascertained are from America. The danger result- 

 ing 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 biting unless 

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



Their principal food consists of birds, squirrels, &c. It has long been sup- 

 posed 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 his mouth ; this, however, is not so, and the reptile in question seizes its 

 prey while under the agitation and terror produced by its appearance. 



In most of the species there are scales on the head similar to those on the 

 back. 



The C. horridut or the Diamond Rattlesnake, the C. durissus or the Banded 

 Rattlesnake, and the C. miliaris or the Ground Rattlesnake, a smaller species, 

 but the most dangerous of the three, all inhabit the United States. The most 

 common is the durissus ; the miliaris, although furnished like the others with 

 an apparatus of three or four cornets at the end of the tail, can make no noise 

 with them. The plates on the head are arranged as in the genus Coluber. 



