156 MICROSCOPIC ANATOMY OF THE TEETH 



appears to be present in all mammalian tooth-germs the 

 so-called ' honeycomb '. 



At the point where the Tomes' processes enter the enamel, 

 a structure is seen resembling a section of the cells of a honey- 

 comb. This appears to consist of a substance on the border- 

 land of calcification. It is resistant to acids, and exists only 

 during the early stages of enamel formation. C. S. Tomes 

 describes this structure as identical with the fenestrated 

 membrane above described, which is raised from the surface 

 of forming enamel by the action of acids ; but, as already 

 shown, this fenestrated membrane also becomes detached 

 without the action of an acid, and would thus not appear to 

 have a very intimate connexion with the forming enamel. 

 Tomes considers that, although probably present in all 

 mammalian enamels, the honeycomb is much more con- 

 spicuous and of greater depth in marsupials (26). It is 

 much more evident in oblique sections than in those that 

 are directly transverse, and he describes the Tomes' pro- 

 cesses as entering this structure and filling up the orifices 

 between the septa, the fibres adhering to the septa when 

 the enamel is pulled away from the ameloblasts. 



He consequently concludes that the process of calcifica- 

 tion is a centripetal one, commencing at the septa of the 

 honeycomb and gradually filling up the spaces between 

 them. In marsupials, the centre remaining open owing to 

 this process of gradual closing in of the space being incom- 

 plete, a tube remains in the central axis of the prism. In 

 non-tubular enamel calcification advances to the complete 

 closing and obliteration of this central tube. C. S. Tomes 

 would thus look upon the tubes in marsupial enamel as 

 entirely a product of the enamel organ, and their connexion 

 with the tubes of the dentine with which they become con- 

 tinuous as a secondary matter. 



According to this view of enamel calcification, there 

 would be no true interprismatic substance. 



It would appear as if the honeycomb was a structure of 

 a transitory nature, and according to the present author's 

 view it acts more as a directing structure to the fibres of 

 the Tomes' processes than as a permanent constituent of 

 the enamel prisms, for the evidence is very strong that the 



