THE TEETH OF REPTILES. 251 



and meeting over it, we shall have a fair conception of the 

 nature of the tube in a poison fang, which is thus really 

 outside the tooth ; which might thus, as least in its canali- 

 culated part, be regarded as a thin flattened tooth bent round 

 so as to form a tube. Just as there are gradations in the 

 armature of the maxillary bone, which link together the 

 extreme form of the harmless Python, and the venomous 

 Rattlesnake, so there are gradations in the form of the 

 poison tooth, in the degree in which the groove is converted 

 into a canal. 



In colubrine poisonous snakes the canal is visible on the 



exterior of the tooth, where an apparent fissure marks the 

 point where the two lips of the groove have met. Thus the 

 poison fang of Hydrophis, although in a part of its length 



(') Transverse section of tooth-sac of poison fang of Viper, prior to the 

 complete closure of the poison tube by the meeting together of the two 

 cornua of the dentine. 



