POISONOUS SERPENTS. 229 



adder (Vipera) , the asps or hooded-snakes (Naja), the rattle-snakes 

 (Crotalus), the cophias and fer-de-lance {Trigonocephalus) , the poison 

 fangs acquire their largest size, and are associated only with their 

 successors : these are clustered in greater or less number behind them, 

 presenting the same structure, but of a size proportionate to their degree 

 of development, and further differing in being loosely imbedded in the 

 thick and wide mucous gum, which likewise conceals the fixed and 

 functional fang in its ordinary position of retraction and repose. This 

 fang is more strongly curved backwards than the ordinary teeth, 

 but its acute and slender apex is frequently bent slightly in the con- 

 trary direction, as in the rattle-snake, (PI. 65, fig. 8, b). 



The mechanism by which the short maxillary bone and the 

 poison-fang are rotated backwards and forwards upon the ginglymoid 

 joint that connects the maxillary with the pr3efrontal and palatine 

 bones has already been noticed, and, as some description of the 

 secreting apparatus to which the peculiar modification of the venoms- 

 fang is subservient might here be expected, I have selected for its 

 illustration the accurate figure which Prof. Muller has given of the 

 salivary and poison-glands in the Trigonocephalus lanceolatus in his 

 great work on the Glandular System. (1) 



The poison-glands (PI. 65, fig. 12, «) occupy the sides of the posterior 

 half of the head ; each consists of a number of elongated narrow lobes, 

 extending from the main duct which runs along the lower border of the 

 gland, a, upwards and slightly backwards : each lobe gives off" lobules 

 throughout its extent, thus presenting a pinnatified structure ; and each 

 lobule is subdivided into smaller secerning caeca, which constitute 

 the ultimate structure of the gland. The whole gland is surrounded 

 by a double aponeurotic capsule, &, b, of which the outermost and 

 strongest layer is in connection with the muscles by whose contraction 

 the several cseca and lobes of the gland are compressed and emptied of 

 their secretion. This is then conveyed by the duct, c, in the course 

 of the dotted line, e, to the basal aperture of the poison-canal of the 

 fang. We may suppose, that as the analogous lachrymal and salivary 

 glands in other animals are most active during particular emotions, so 

 the rage which stimulates the venom-snake to use its deadly weapon 



(1) De Glandularum Secernentium Structura Penitiori, fol. tab. vi, fig. 1, p. 55. 



