588 



OPHIDIA 



CHAP. 



wall of the poison-gland ; the anterior and posterior ends of the 

 gland are held hj another strong band, which stretches from 

 the maxilla to the mandibular joint. The whole is so arranged 

 that the acts of opening the jaws (by the digastric muscles) and 

 the erection of the fang -bearing maxillaries are enough to 

 mechanically squeeze the contents out of the poison-gland. A 



Fig. 154. — Explanation of tlie biting mechanism of a rattlesnake. la and 2b, 

 position of the apparatus when the mouth is shut. Ila and lib, position of the 

 apparatus when the mouth is opened widely ; the spheno-pterygoid muscle (P.e) is 

 contracted, the pterygoid {Pt) is pulled forwards, the transverse bone or ectopterygoid 

 (Tr) ])uslies the maxillary (J/), rotates it and thereby causes the poison-fang (./) to 

 assume an erect position. Bi, Digastric muscle, contraction of which lowers, or 

 opens, the lower jaw ; O, the groove or pit characteristic of the Crotaliue snakes ; 

 J, poison-fang ; M, maxillary ; J', i)alatine ; P.e, spheno-pterygoid muscle ; Pm, 

 premaxillary ; Pt, jjterygoid ; Q, quadrate ; Sq, squamosal ; T.a, insertion of the 

 anterior temporal muscle, by contraction of which the mouth is shut ; cf. Fig. 179 

 (p. 647) ; Tr. transvt-rsum or ectopterygoid ; X, origin and insertion of a muscle 

 and a strong ligament, contraction of which draws the maxillary and its tooth back 

 into the position of rest and assists in shutting the mouth. 



portion of the anterior temporal muscle is attached to the 

 capsule of the poison-gland. 



An excellent account of the nature and of the effect of the 

 venom of Snakes has been written by Charles J. Martin.^ The 

 following condensed account has been abstracted from it : — 



" The poison is a clear, pale yellow, or straw-coloured fluid, 



' Clifford Allbutt's System of Medicine, vol. ii. London, 1896, p. 809. 



