THE SALIVARY AKD OTHEK GLANDS OP THE COLIIBEID^. 525 



functional poison-tooth. The maxilla in the Viperidaa is 

 certainly more specialized than that in any other group of the 

 Ophidia, both with regard to its extreme shortness and the 

 nature of the poison-teeth, intermediate conditions being ex- 

 hibited by the marine snakes Enhydris and PJaturus *. In the 

 latter genera there are two adult functional poison-fangs 

 present side by side at the anterior extremity of the maxilla, 

 developed more or less simultaneously t, and it would appear 

 that in the evolution of the Viperine forms these teeth, special- 

 ized as iu the above-mentioned marine snakes, were originally 

 present, but that after they had become placed side by side and 

 the maxilla shortened to the utmost, their development became 

 no longer simultaneous, but strictly alternate J. 



The Eelation of the Poison-duct to the Teeth. 



The method by which the poison-duct communicates with the 

 groove of the poison-fang is well known, viz., by means of the 

 cavity surrounding the base of the tooth and enclosed by the 

 muscular folds which constitute the proximal portion of the 

 vagina dentis ; but even so recently as 1892, the communication 

 has been described and figured as effected by a fine hair-like duct 

 supposed to enter the basal opening of the groove itself §. For 

 many reasons this would obviously be an inconvenient arrange- 

 ment, since the duct would require a new terminal portion for 

 each new tooth, whereas with the existing arrangement of folds 

 round the base of the tooth, injury or loss of the latter does not 

 in any way affect the apparatus for the transmission of the 

 secretion to the tooth. Another advantage in there being no 

 direct communication between the duct and the basal opening of 

 the groove, lies in the fact that the new tooth does not occupy 

 exactly the same position as the old one by reason of the 

 development taking place alternately from two parallel series. 



The sphincter which occurs near the termination of the duct 



* Cf. Boulenger, ' Fauna of British India : Eept. k Batrachia,' p. 394. 



t Each is developed from a single series of successional teeth, and as two adult 

 fixed teeth are not always present at the same time the development is not 

 exactly simultaneous, but very slightly alternate. 



\ This development has been wholly misunderstood by S. Weir Mitchell, 

 " Researches upon the Venom of the Rattlesnake," Smithson. Contrib. Knowl. 

 vol. xii. (1860), pp. 18, 19. 



§ F. Niemann, I. c. 



