POISON APPARATUS OF VENOMOUS SNAKES 59 



In the opisthoglyphous snakes the fangs are short and have usually much 

 shallower furrows than the proteroglypha. The fangs differ greatly in their 

 magnitude according to the snakes. The viperine and crotaUne snakes pos- 

 sess the best-developed and longest fangs, while the elapine and hydrophine 

 families have much shorter ones. A fang an inch long is not uncommon in 

 Crotalus and Lachesis. It is hardly necessary to mention that the poison 

 fangs are provided with a regular pulp-cavity which occupies a space just 

 behind the groove or canal separated with a thin septum of dentine and 

 enamel. 



The relation of the poison duct to the fang has often been misinterpreted. 

 Niemann* even reproduced a picture in which the poison duct was shown to 

 enter directly into the base-opening of the canal of the fang. But Mitchell 

 as early as i860 described the real method by which the poison duct communi- 

 cates with the groove of the poison fang. It is by means of the cavity sur- 

 rounding the base of the tooth and inclosed by the mucous membrane folds 

 which constitute the proximal portion of the vagina dentis. In Crotalus 

 Mitchell discovered the presence of certain muscular fibrillae in the mucous- 

 membrane sheath, which apparently serves as a sphincter. This arrangement 

 has the advantage that in the replacement of the fang the connection will 

 not in any way be affected, in spite of the change of the position of a new 

 fang. The sphincter which has been found by Mitchell near the termination 

 of the duct in the Crotalinae appears to be absent from the proteroglyphous 

 ColubrincT, while in Hydrophiinae a non-striated muscle is present near the 

 base of the fang. 



POISON GLANDS. 



(Plate 20, A, B, c, D.) 



Glandula venenata were not definitely discovered until a correct account 

 was given by Fontana. Schlegel (1828) found in many snakes with furrowed 

 posterior teeth a large gland which opens its duct only at the base of this tooth. 

 Duvernoy (1832) then found that a similar gland exists also in numerous sus- 

 pected snakes. The poison gland of fangless snakes is not exactly equal to 

 the fully developed venom gland of fang-possessing reptiles, but is a mixed 

 gland, consisting of anterior grayish-red portion and posterior grayish-white 

 portion. The latter is provided with only one duct. After the careful studies 

 of Rudolphi, Meckel, and Leydig (1873) it became clear that the posterior 

 portion is of the nature of a serous gland, while the anterior portion is that 

 of a mucous gland. It is noteworthy that a serous gland comes for the first 

 time into existence in these snakes, but not in any class in the inferior evolu- 

 tional order, which, as in Amphibia, is provided with a mucous gland. In 

 the Mammalia the existence of the serous gland becomes universal. 



In the majority of venomous snakes the poison gland occupies a space 

 behind the eve and stretches backwards in length according to the size of the 



• Niemann, Arch. f. Naturgeschichte, 1892, I. 



