132 MICROSCOPIC ANATOMY OF THE TEETH 



continuation of the same material seen in the ameloblast cell 

 itself. The existence of these processes has been doubted 

 by some authorities, who look upon it as an artificial product 

 caused by the dragging or pulling away of the forming 

 enamel from the ameloblast cell ; but a study of marsupial 

 enamel organs where they are continued into fibres which 

 pass across the whole area of the forming enamel, renders 

 it impossible to doubt their existence as a definite and 

 important part of the cell, as will be better understood 

 after the development of the enamel in marsupials has been 

 considered (see p. 153). 



inner and In developing enamel, membranes have been described 

 amelo between the ameloblast cells and the forming enamel, and 

 blastic also between these cells and those of the stratum inter- 

 medium. 



The question of the existence of membranes in these 

 situations has been the subject of much controversy. Pro- 

 fessor Huxley held the view that there was a ' membrana 

 preformativa ' between the ameloblasts and the forming 

 enamel, arid that the calcification of enamel took place 

 by the transference of crystallizable products through a 

 membrane. 



This theory has been revived by Leon Williams and others. 

 Williams (30), in his study of enamel, is convinced of the 

 existence of these membranes, and has called them the outer 

 and inner ameloblastie membranes. The outer membrane 

 intervenes between the stratum intermedium and the 

 ameloblasts, and the inner ameloblastie membrane separates 

 the ameloblasts from the forming enamel, but is pierced by 

 the Tomes' processes. An examination of many sections 

 of developing teeth prepared in different ways will, we think, 

 clearly show that such membranes really exist, or certainly 

 a substance which retains its continuity when the cells have 

 fallen away from it, perhaps the thickened cell walls united 

 at their margins., Fig. 78 shows the outer ameloblastie 

 membrane in the enamel organ of Macropus, where the 

 ameloblasts have become detached from its under side and 

 it still persists as a distinct membrane, and Leon Williams 

 has published a photograph in the illustrations to his 

 paper which shows the inner ameloblastie membrane 



