16 niYSIOLOGY AND TOXICOLOGY 



although it runs through the centre of the tooth, is really on the outside of the 

 tooth. The bending of the dentine beyond it, begins a little beyond the base of 

 the tooth, where the poison duct rests in a slight groove, or longitudinal indenta- 

 tion, on the convex side of the fang ; as it proceeds, it sinks deeper into the sub- 

 stance of the tooth, and the sides of the groove meet and 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." 



The tooth fang, in the Eattlesnake, has a peculiar double curve. The lower 

 curve is large, and has an anterior convexity ; the upper involves only two or three 

 lines of the length of the tooth from the point down, and is nearly straight, or 

 presents a slight concavity anteriorly. The whole length of the fang, from point 

 to base, was ^^ of an inch in a snake, four feet two inches long. One-tenth of an 

 inch below the point in this tooth, the poison canal opened on the anterior, or con- 

 vex surface of the fang. Above this, the fang was solid ; as the true pulp cavity 

 terminated some distance lower down. The point of this singular weapon is brittle, 

 but of an exquisite fineness. The tooth thus described, is firmly anchylosed to the 

 submaxillary bone, its base being luted to the portion of bone around its side and 

 anterior aspect. Posteriorly, the bone possesses a hollow, in which is lodged the 

 tooth sac. In the open mouth of this alveolar process, within the mucous mem- 

 brane, and upon the pterygoid bone, lie one behind and below another, the reserve 

 fangs, each smaller than the one in front, and less and less developed, until the 

 situation of the last which is visible, is marked by a minute papilla alone. I have 

 counted from eight to ten of these on each side. A very good account of their 

 gradual development has been given by W. J. Burnett.^ The details do not 

 directly concern us here. 



When the fang is lost by a natural process, it is replaced within a few days. 

 When violently displaced, several weeks sometimes elapse before the next fang is 

 fixed firmly enough to be useful to the snake. 



If the functional fang be lost or shed, the next tooth gradually assumes its 

 position, but of the mode in which the communication is re-established between 

 the poison duct and the fissure of the lower part and front of the new tooth, we 

 have had no correct knowledge until a recent period. 



Burnett states, that " the original tooth follicle appears to him to become the 

 poison gland or sac." He then goes on to support this view briefly, still speaking 

 of the poison gland as possibly accompanying the tooth in its forward movement. 

 Dr. Burnett must have made this statement under a misconception, as it is well 

 known there is no poison sac or gland at the base of the fang, or in immediate 

 connection with it. 



More recently, the subject of the development of the fangs and the mode in 

 which the fixed fang is replaced, when shed or broken, have been carefully studied 

 by my friend, Dr. Christopher Johnston, of Baltimore, whose skill as an observer. 



• W. J. Burnett, M. D., Boston Nat. Hist. Soc, vol. iv. p. 311-323. 



