THE TEETH OF REPTILES 109 



the tube being like the outside of the tooth, al- 

 though the interior is not lined with enamel in all 

 species. The tube opens a short distance from 

 the point like a hypodermic needle, so that the 

 point must be well implanted before injection can 

 take place. These teeth are much recurved when 

 erectile, and lie flat against the roof of the mouth 

 in a fold of mucous tissue when not in use; they 

 are raised by the moving backward of the lower 



Fig. 35. — Teeth of Rattlesnake (Crotalus adamanteus) . 



jaw and quadrate bone, which pushes the upper 

 maxillary forward and erects the fang when the 

 strike is made. They are reproduced when lost 

 by a vascular pulp situated posteriorly. In the 

 Eattlesnake, ten reserve teeth have been found. 

 All the viperine poisonous snakes — the Rattle- 

 snakes, Puff-Adders, Vipers, etc. — have the poi- 

 son apparatus highly specialized. The maxillary 

 bone carries no teeth back of the poison fang. In 

 the species having these teeth permanently erect, 



