AND TKETH OF THE OPISTHOGLYPHA. 



315 



Regarding the duct, it no longer opens into the vestibule, but 

 directly into the tooth sac. The opening of the vestibule into the 

 mouth cavity is closed, and the Cooth sac becomes comparatively 

 bigger. If in text-fig. 16 the opening of the vestibule into the 

 mouth is closed, and at the same time the thin membrane, to 

 which West refers and which is also shown in text-fig. 15, 

 atrophies so that the cavities of the vestibule and tooth sac are 

 confluent with one another, the condition, as shown in text- 

 fig. 18 of Ghrysopelea, is arrived at. I have shown that the two 



Text-figure 18. 



Glirysojpelea ornata. Transverse section of the head in the region of the poison 

 gland, its ducts, the tooth sac, and the fang. h.v. blood-vessel ; duct.'p.g. 

 duet of the poison gland ; f. fang ; 'p.g. poison or parotid gland ; r.t. reserve 

 tooth; t.s. tooth sac. X 63. 



cavities really become confluent in Tropidonotus and Lycodon 

 near to the opening into the mouth. The evidence in favour of 

 the theory that such changes have been brought about is shown 

 by the fact that the duct in Chrysopelea opens, not into the 

 mouth, but into the middle of the tooth sac. 



In conclusion, then, we see that Chrysopelea is higher in grade 

 than Oxyhelis, for the reason that the duct of the poison gland 

 opens directly into the tooth sac and that there is a deeper groove 

 in the fang. 



Dryophis mycterizans. 



This snake is in many respects much more advanced than 

 Chrysopelea. The parotid gland is more highly developed, and 

 has become a distinct organ, though it still remains embedded in 

 the superior labial gland. At the same time, the secretion of the 

 gland becomes more poisonous ; it has been proved that the bite 

 of this snake is fatal to small animals (West). The fangs (text- 

 fig. 19) have shifted a little forward in the jaw, and are therefore 



