2QO 



REPTILES. 



thrive. They swarm in Surinam, in French Guiana, in Peru, in 

 Brazil ; and in the neighbourhood of the Lower Orinoco they are 

 so abundant that when the natives set fire to the brushwood and 

 grass with which the country is covered, whole armies of formid- 

 able species sally forth in crowded ranks to the number of thou- 

 sands at a time, putting all to flight before them. In cold coun- 

 tries only a few are to be found in a large extent of territory : they 

 grow scarce as we go north, and totally disappear in the polar 

 regions. 



In the Venomous Serpents the teeth of the upper jaw are generally 

 deficient or very small, with the exception of two of large size, which consti- 

 tute, perhaps, the most terrible weapons met with in the animal creation. 

 These poison-teeth, placed one on each side, are attached to moveable bones 



FIG. 312. POISON-FANGS. 



FIG. 313. POISON-GLAND. 



(Fig. 312). When not in use they are laid flat upon the roof of the mouth, 

 where they are covered by a fold of the gums ; but when the animal is irritated 

 or about to strike its prey, they are plucked up 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 sub- 

 stance of these organs 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 Rattlesnakes (Crotalus)* owe their name to a singular apparatus 

 which terminates the tail, and which distinguishes them from all other serpent.s. 

 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 instrument is shaken with extreme rapidity, and thus produces 

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



Rattlesnakes attain a length of five or six feet, and even more. They in- 



* KporaXov, crotalon, a rattle or castaiict. 



