AND TEETH OF THE OPISTHOGLYPHA. 



317 



PSAMMMOPHIS SIBILANS. 



This is one of the most highly-developed of the opisthoglyphous 

 snakes. The very appearance of text-fig. 21 will reveal the 

 fact that it is more ferocious and is capable of doing more harm 

 than Dryophis. The structure of the teeth and gland positively 

 prove that it is so, and this is emphasized in the description in 

 the first part of this paper. 



Looking at the poison gland, one finds that it has assumed a 

 distinct and definite shape, quite separate from the superior labial 

 gland. The poison fang has moved still further forward in the 

 buccal cavity than in Dryophis. It is straighter, and it lies 

 directly below the eye. The shape of the poison fang is of 

 importance, i. e. being straight and not bent backward. The 

 fang that is bent backward at an angle is of more use in inflicting 



Text-figure 21. 



rt f 



Fsammopliis sibilans. Dissection of head from the right side. /. fang; H.ff. 

 Harderian gland ; i.l.ff. inferior labial gland ; p.<j. parotid gland ; r.t. reserve 

 tooth. X 3. 



a wound on prey that is already in the mouth, while a straight 

 tooth is of greater use as a weapon of oflence and defence, as it 

 can inflict a wound on prey that is outside the mouth. Another 

 improvement has taken place ; the groove has become deeper, 

 and extends through the whole length of the tooth, ending at 

 the very tip. It has also shifted from the side of the tooth 

 to the front, in order to be still nearer the opening of the duct, 

 which opens in front of the tooth sac as in the highly-developed 

 poisonous snakes. 



It is unfortunate that I have not been able to examine sections 

 of this genus to see the connection of duct with the teeth ; but I 

 have seen only one specimen, and it was kindly lent to me by 

 Miss Procter, of the British Museum, for purposes of observation 

 but not for sectioning. 



