DEVELOPMENT OF THE ENAMEL 173 



within a substance also dialysed through the inner amelo- 

 blastic membrane. 



Large irregular-sized bodies are formed in this substance 

 and by their fusion form the iriterprismatic material. As 

 shown by the present author, these bodies take the form of 

 large radial calcospherites such as are formed by carbonate 

 of lime in the artificial experiments, and they are seen to 

 be revealed in certain cases of caries and erosion. In fully 

 formed perfect mammalian enamel these elements become 

 so fused together and veiled by the dense deposit of the lime 

 salts that it is difficult or almost impossible to detect them 

 in many situations. 



With regard to the origin of tubular enamel two funda- 

 mentally different opinions have been held. C. S. Tomes 

 considers that the tubes are entirely an enamel formation, 

 and are due to the calcification commencing at the septa 

 of the honeycomb and gradually closing up towards the 

 centre of what may be described as the cell of the honey- 

 comb ; in non-tubular enamels this closure is complete and 

 a solid enamel prism results ; in tubular enamels the calcifica- 

 tion does not reach the centre but remains open and uncalci- 

 fied as the tube. 



The calcification of all mammalian enamel he would look 

 upon as a centripetal process, and he would deny the exis- 

 tence of a true interprismatic substance in finished enamel. 



The other view is that held by Professor von Ebner and 

 the author, that the tubes of the enamel are not an enamel 

 organ product but are true dentinal tubes included in the 

 enamel. The arguments in favour of this view are given in 

 the chapter on tubular enamel so far as the finished tissue 

 is concerned. In developing enamel it is not considered 

 that there is any evidence of an open space in the honey- 

 comb, but the fibres of the Tomes' process enter, interlace, 

 and are rearranged in the honeycomb region, and the 

 deposit of the lime salts, as described by Leon Williams, 

 takes place within them as a regular deposit of calcified 

 granules arranged longitudinally, the interprismatic sub- 

 stance being separately formed and in marsupials remaining 

 in great part uncalcified for a considerable time. The spaces 

 described above between the forming enamel prisms at the 



