154 A MANUAL OF DENTAL ANATOMY. 



sequence of calcification having extended less far at this 

 central portion of the cell. 



In other words, if the forming enamel were freed from 

 the adherent enamel cells, its surface would be pitted, 

 each little pit marking the centre of an enamel prism \ and 

 if a thin section of this immediate surface could be taken 

 off, it would be pierced with holes at regular intervals. 



The enamel cell with its process is like an odontoblast with 

 a very short dentinal fibril, which has been pulled out of the 

 formed dentine, and the nature of the " Tomes' processes " is 

 well illustrated in the enamel organs of marsupials. It 

 will be remembered that their enamel is permeated by a 

 large number of canals, which become continuous at the 

 junction of the dentine and enamel, with the dentinal tubes. 

 Accordingly the enamel cell of a marsupial, engaged in the 

 formation of a permanently tubular enamel, is just like an 

 odontoblast in that it has a long, fine process, pulled out of 

 the already formed enamel. 



As the youngest part of the enamel has by no means 

 attained to its full hardness, it is quite possible to obtain, in 

 small pieces, sections parallel to its surface ; the nearer they 

 are to the surface, the larger will be the perforations, show- 

 ing what has already been stated respecting calcification 

 commencing at the periphery of each cell to be true. And 

 it is possible, by the use of an acid, to obtain such sections 

 upon a larger scale, for under the influence of such a reagent, 

 this youngest layer of the enamel peels off in a sheet, 

 bringing with it in places enamel cells, in places enamel 

 prisms, adhering to its opposite sides. When destitute of 

 adherent enamel cells or prisms, this so-called membrane is 

 foraminated ; and the processes of the ends of the enamel 

 cells are fitted into and passed through these perforations. 



The real nature of the membrane which could be raised 

 from the surface of growing enamel was first demonstrated 

 by my father, and his explanation has been accepted by 



