POISON-FANGS OF SERPENTS. 687 



the throat, efficiently prevent it from being pushed back again in the 

 opposite direction*. 



(1920.) In the venomous serpents, those teeth which are fixed to the 

 margin of the superior maxillary bone of the innoxious genera are gene- 

 rally deficient; and instead of them there is found an apparatus of 

 poison-fangs, constituting perhaps the most terrible weapons of attack 

 met with in the animal creation. The poison-teeth (fig. 337, a) are two 



Fig. 337. 



Structure of the poison-teeth of the Rattlesnake. 



in number, one fixed to each superior maxillary bone : when not in use, 

 they are laid flat upon the roof of the mouth, and covered by a kind of 

 sheath formed by the mucous membrane of the palate ; but when the 

 animal is irritated, or about to strike its prey, they are plucked up from 

 their concealment by muscles inserted into the upper maxillary bone, 

 and stand out like two long lancets attached to the upper jaw. Each 

 fang is traversed by a canal not, as it is generally described, excavated 

 in the substance of the tooth, but formed by bending, as it were, the 

 tooth upon itself, so as to enclose a narrow channel through which the 

 poison flows. The canal so formed opens towards the base of the tooth 

 by a large triangular orifice ; but at the opposite extremity it terminates 

 near the point of the fang by a narrow longitudinal fissure. The gland 

 wherein the poison is elaborated occupies the greater part of the temporal 

 fossa, and is enclosed in a white and tendinous capsule (fig. 337, b) ; the 

 substance of the organ is spongy, and composed of cells communicating 

 with its excretory duct (c), by which the venom is conveyed to the open- 

 ing at the base of the fang f. The poison- gland is covered by a strong 



* In the collection of Professor Bell there is a small snake which, having by mis- 

 hap attempted to swallow a mouse of too large size, and being quite unable, in conse- 

 quence of the mechanism referred to, to disgorge it, was found dead, and the skin and 

 muscles of its neck absolutely rent from excessive stretching. 



t Memoire sur les caracteres tires de 1'Anatomie pour distinguer les Serpens 

 venimeux des Serpens non-veninieux ; par M. Duvernoy (Ann. des Sc. Nat. xxvi.). 



