CLASS REPTILIA. 89 



tMs form applying with equal truth to the common Viper 

 of Britain. 



The Rattlesnake (Crotalus horridus) has entirely the 

 form which we generally understand by the term " snake- 

 like," having a long, cylindrical body, tapering towards 

 the tail (fig. 40). The body is completely destitute of 

 limbs, and is covered with an armour formed of small 

 overlapping horny scales. Some of the scales which 

 cover tlae head are of larger size than the others, and 

 there is also a row of oblong shields which are continued 

 along the whole lower surface of the animal from the head 

 to the end of the tail. The tail terminates in a singular 

 organ knoAvn as the " rattle," which the animal shakes 

 when alarmed or intending to bite. The rattle is really 

 a mere appendage of the skin, and is composed of a num- 

 ber of horny pyramidal joints, loosely united together. 

 The animal, lastly, sheds its skin periodically. 



The head is somewhat triangular, broadest behind (fig. 

 40), and supported upon a comparatively slender neck. 

 The eyes have the peculiarity that they are not furnished 

 with movable eyelids, but are covered by a transparent 

 continuation of the skin. This gives the animal a pecu- 

 liar fixed and stony stare. Between the eye and the 

 nostril on each side is also to be noticed a deep depression 

 or pit. 



At the front of the head is placed the mouth, within 

 which we shall find some of the most characteristic struc- 

 tures in the anatomy of the Rattlesnake. The tongue is 

 forked, capable of being protruded from the mouth at 

 mil, and, when protruded, maintained in rapid vibration. 

 The tongue, however, in spite of appearances, is a per- 

 fectly harmless organ, and the offensive weapons of the snake 

 are to be found in the teeth (fig. 41). The two halves 

 of the lower jaw are very loosely united together in front, 

 so as to allow of their free separation, and they carry 

 each a series of pointed conical teeth, directed backwards, 

 and amalgamated with the substance of the jaw itself (Z). 

 Behind, each half of the lower jaw is united with the skull 

 by a peculiar movable bone {q), which is known as the 



