POISON APPARATUS 



63 



which is ensheathed in a thick fold of mucous 

 membrane, the vagina dentis. By means of the 

 movable maxillary bone (supra, p. 49) hinged to the 

 prefrontal, and connected with the tranverse bone 

 which is pushed forward by muscles set in action by 

 the opening of the mouth, the tubular fang is erected 



d g e 6 c a' 



Fig. 13 — Poison Apparatus of Rattlesnake: Venom Gland 

 and Muscles (Lateral View). (After Duvernoy) 



a, Venom gland ; a\ venom duct ; b, anterior temporal muscle ; 

 b', mandibular portion of same ; c, posterior temporal muscle ; 

 d, digastricus muscle ; e, posterior ligament of gland ; /, sheath 

 of fang ; g, middle temporal muscle ; h, external pterygoid 

 muscle ; i, maxillary salivary gland ; /, mandibulary salivary 

 gland. 



and the poison discharged through the distal orifice 

 in which it terminates. 



In some of the Proteroglyphous Colubrids, as we 

 have seen, the poison fangs are not tubular, but only 

 channelled and open along the anterior surface ; and 

 as the maxillary bone in these snakes is more or less 

 elongate, and not or but slightly movable vertically, 



