ENAMEL 53 



trace, and although both C. S. Tomes (18 c) and Hope well 

 Smith (8) speak of them as being present in human enamel, 

 no record of their existence has been made by either photo- 

 graph or drawing so far as can be ascertained. 



It can, however, be shown that both branching and the 

 interposition of supplementary prisms are to be seen in 

 other mammalian enamels, and the probabilities are greatly 

 in favour of a similar condition being present in human 

 teeth. 



It would appear that if there is any evidence of branching 

 and the occurrence of supplemental prisms, we should be 

 most likely to see it in teeth in which the spreading out of 

 the enamel is greater than in human teeth. 



In the enamel of the Wart-hog (Phacochcerus) where these Supple- 

 conditions prevail it has been shown by the author in a recent ^ tary 

 communication (11 a) that the columns of prisms divide branching 

 dichotomously, and supplementary prisms are introduced p^,! m 

 between them. chcerus. 



The large third molar of Phacochcerus is a compound tooth 

 made up of from twenty-four to thirty denticles, arranged 

 in three rows, each denticle consisting of dentine surrounded 

 by an investing sheath of enamel and enclosed in cement. 

 The denticles, which form columns passing deeply into the 

 jaw, are united by the cement, and the whole forms a 

 compound tooth having many points of similarity with the 

 molar tooth of the Elephant. As the tooth becomes worn 

 down by mastication, the surface shows oval rings of dentine 

 surrounded by enamel, the intervals between the denticles 

 being filled up with cement. This disposition of the 

 enamel gives a much wider area at the circumference than 

 at the dentine junction, so that in the comparatively short 

 course of the enamel columns they would come to be very 

 wide apart at the surface if they maintained the same 

 diameter throughout. A thin section of one of these den- 

 ticles, where the enamel columns are seen radiating from 

 the dentine to the cement, shows that there is no apparent 

 increase in the diameter of the prisms or of the interprismatic 

 substance (which is very abundant in Phacochcerus) as they 

 approach the surface, but it also shows very distinctly that 

 the columns of prisms divide and branch and that the 



