52 VERTEBRATA. REPTILIA. 



immediately after taking food. And on another 

 occasion, I heard a frog distinctly utter its peculiar 

 cry several minutes after it had been swallowed by 

 the Snake."* 



The venomous Serpents resemble the others in 

 most of their external characters, but the structure 

 of the mouth is very different. The upper jaw is 

 destitute of the small ordinary teeth found in the 

 former, but is furnished in their stead with a single 

 long, curved, and tubular tooth, which usually lies 

 down upon the jaw, and is hidden in a fold of the 

 skin, but, when the Serpent wishes to bite, is erected. 

 The tube of the tooth passes into a little bag in the 

 gum, filled with a liquid poison secreted by glands 

 for the purpose ; and the act of biting, by the pres- 

 sure of the fang upon the poison-bag, causes the 

 fluid to be .forced through the tube into the wound. 

 The result of the admixture of this substance with 

 the blood is well known, but the effects vary in 

 violence according to climate, season, health, both 

 of the reptile and the victim, and other causes. 

 The two rows of teeth are present in the palate, 

 as in other Serpents. 



Crotalus^ the Rattlesnake. 



The very singular appendage to the tail of these 

 reptiles has given them their name : it consists of 



* Brit. Rept. p. 51 t K^araAv, krotalon, a rattle. 



