ENAMEL 83 



a stain which shall be capable of penetrating as perfectly 

 as possible. 



In accordance with the author's views on the nature of 

 tubular enamel, the fact that the tubes of the dentine 

 occasionally penetrate the enamel in human teeth can be 

 well understood. 



We find penetration of the enamel by dentinal tubes the 

 main characteristic of the tissue in the marsupials, and 

 we also see a similar penetration in other orders of the 

 higher Mammalia, as Hyracoidea, Rodentia, and Insectivora, 



FIG. 39. Fibrous bundles at amelo-dentinal junction. 

 Hypoplastic enamel. ( x 50.) 



which show a reversion to the condition in the marsupials, 

 and in human teeth we have an indication of survival of, 

 or reversion to, the tubular enamel of these other orders 

 of the Mammalia. 



Imperfections of structure at the dentine margin are 

 frequently met with in human enamel, areas in which both 

 prisms and interprismatic substance have a coarsely granular 

 appearance. 



Radiating bundles of fine fibres are also very frequently 

 seen which appear to be connected with dentinal tubes 

 entering the enamel (fig. 39). These defects of structure 

 are much more apparent at the amelo-dentinal junction 



G2 



