17 



centre of a great part of the tooth, is really on the outside 

 of the tooth, the canal in which it is lodged and protected 

 being formed by a longitudinal inflection of the dentinal 

 parietes of the pulp-cavity. This inflection commences a 

 little bevond the base of the tooth, where its nature is 

 readily appreciated, as the poison duct there rests in a slight 

 groove or longitudinal indentation on the convex side of 

 the fang ; as it proceeds it sinks deeper into the substance 

 of the tooth, and the sides of the groove meet and seem to 

 coalesce so that the trace of the inflected fold ceases, in 

 some species, to be perceptible to the naked eye ; and the 

 fang appears, as it is commonly described, to be perforated by 

 the duct of the poison-gland. In the ffydrophis the groove 

 remains permanently open. From the position of the 

 poison-canal it follows that the transverse section of the 

 tooth varies in form at difierent parts of the tooth : at the 

 base it is oblong, with a large pulp-cavity of a correspond- 

 ing form, with an entering notch at the anterior surface ; 

 further on, the transverse section presents the form of a 

 horse-shoe, and the pulp-cavity that of a crescent, the horns 

 of which extend into the sides of the deep cavity of the 

 poison-fang : a little beyond this part the section of the 

 tooth itself is crescentic, with the horns obtuse and in con- 

 tact, so as to circumscribe the poison -canal ; and along the 

 whole of the middle four-sixths of the tooth the sec- 

 tion * * * shows the dentine of the fanor inclosinof the 

 poison-canal, and having its own centre or pulp-canal in 

 the form of a crescentic fissure situated close to the concave 

 border of the inflected surface of the tooth. The pulp- 

 cavity disappears, and the poison-canal again resumes the 

 form of a groove near the apex of the fang and terminates 

 on the anterior surface in an elons^ated fissure." 



On one point this description is somewhat imperfect and, 

 I may venture to say, unsatisfactory ; it speaks of '' a canal 

 in which it [the poison duct] is lodged and protected" and 



3 



