382 



SERPENTS. 



are attached to moveable 



bones (Fig. 312). When 

 not in use, they are laid 

 flat upon the roof of the 

 month, where they are co- 

 vered by a fold of the gums ; 

 but when the animal is irri- 

 tated or about to strike its 

 prey, they are plucked up 

 Fig 312.— poisox-faxgs. from their concealment and 



stand out like two lancets. Each fang is traversed by 

 a canal, not, as it is generally described, excavated in the 

 substance of the tooth, but formed by bending, as it were, 

 the tooth upon itself, so as to enclose a narrow channel 

 through which the poison flows. The glands in which the 

 poison is elaborated (Fig. 313) occupy a considerable space 

 on each side of the head. The substance of these organs 



Fig. 313.— poison gland. 



is spongy, and composed of cells that communicate with 

 the poison-duct, whereby the venom is conveyed to the 

 base of the fang, and instilled into the wound inflicted by 

 these fatal instruments. 



The Rattle-snakes {Crotalus)* owe their name to a singular appa- 

 ratus wbieli terminates the tail, and which distinguishes them from 

 all other Serpents, It consists of a series of horny scales, loosely 

 fitting into each other like a nest of boxes, which vibrate and sound 

 when the animal moves. Even while they are at rest this instru- 

 ment is shaken with extreme rapidity, and thus produces a noise 

 sufficiently loud to be heard at a distance of many yards. 



Eattle-snakes attain a length of five or six feet, and even more. 

 They inhabit America, and are dreaded on account of the virulence 

 of their poison. In general, they do not bite except when provoked, 



* KporaKoi/, crotalon, a rattle or Castanet. 



