TEETH OF KEPTILES. 



397 



Poison-fangs of A, Viper ; B, Cobra (in section) ; 

 c, Hydrophis. v. 



the 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 deiitinal parietes of the 

 pulp-cavity, fig. 270, c. This 269 



inflection commences a little A 



beyond the base of the tooth, 

 where its nature is readily 

 appreciated, as the poison- 

 duct there rests in a slight 

 groove or longitudinal inden- 

 tation on the convex side of 

 the fang, fig. 269, A, B, v ; 

 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 percepti- 

 ble 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 Hydrophis the groove remains permanently open, as in fig. 

 269, c. 



From the position of the poison-canal it follows that the 

 transverse section of the 

 tooth varies in form in dif- 

 ferent parts of the tooth : at 

 the base it is oblong, with a 

 large pulp-cavity of a cor- 

 responding form, with an 

 entering notch at the ante- 

 rior surface, fig. 268, c; 

 farther on, the transverse 

 section presents the form of 

 a horseshoe, 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 sec- 

 tion of the tooth itself is 

 crescentic, with the horns obtuse and in contact, so as to circum- 

 scribe the poison-canal ; and along the whole of the middle four 



270 



Section of poison-fang of Cobra, rnagn. v. 



