DEVELOPMENT OF THE ENAMEL 157 



calcification of the interprismatic substance takes place, at 

 all events to a very great degree, independently from the 

 calcification of the prisms. 



It can be seen in figs. 86 arid 87 that at the honeycomb 

 region the fibres of the Tomes' processes spread out in a fan 

 shape, the fibres from neighbouring processes crossing one 

 another and intermingling, to be again drawn together to 

 form the columns of the prismatic substance of the enamel. 

 We thus see that the ultimate bundles of fibres which form 

 the basis of the enamel prisms do not appear to be the 

 direct prolongations of one particular ameloblast, but are 

 contributed to by those in contact with it on either side. 



As was first pointed out by Dr. Andrews of Boston, there Fibrillar 

 is a delicate organic fibrillar foundation to enamel as there 

 is in dentine, an organic network or scaffolding in which 

 calcification takes place. The fibres described by Andrews 

 were the prolongations of the Tomes' processes so clearly 

 seen in marsupial enamel, and which, as' previously described, 

 are seen to extend all across the area of forming enamel to 

 the dentine, when the process of calcification is but very 

 little advanced. 



There are also other delicate fibres passing in a transverse 

 direction, which are very evident in marsupial forming enamel 

 and which are also derived from the ameloblast cells (fig. 89). 

 This fibrillar foundation is also very evident in the enamel 

 of the rat, as shown in Leon Williams's illustration on p. 22 

 of his paper taken from a preparation by the author, and 

 the fibres, as he says, ' bear a striking resemblance to the 

 effect produced by tearing a woven fabric of any sort'. 

 Further evidence of the existence of this substructure in 

 enamel is afforded by the experiment described on p. 104, 

 where a delicate membrane-like foundation was left on the 

 slide after the decalcification by strong acids, and the tubes 

 of the enamel remained undisturbed within its substance. 



Also in ground sections of marsupial enamel which had 

 been treated with alcoholic fuchsin there is in many places 

 an appearance of transverse stained lines which are evidently 

 portions of the transverse fibres which have escaped calcifica- 

 tion (fig. 53 B). 



The existence of a fibrillar condition in forming enamel is 



