HANNOVER ON DENTAL TISSUES 481 



Evidence was offered, 1st, that the enamel-fibres, from their first 

 appearance, lie beneath Nasmyth's membrane. 2dly. That Nasmyth's 

 membrane is continuous with the meinbrana preforinativa. 3dly. That 

 no traces of cells or endoplasts can be discovered within the enamel- 

 fibres nor in the dentine, and that these tissues are not produced 

 by the direct calcific conversion of pre-existing elements. 4thly. 

 That the cement is morphologically the continuation of the enamel, but 

 whether it is or is not developed by conversion from the pulp was 

 left an open question. 



The first of these statements has received full confirmation from 

 subsequent observers, including M. Leydig, in his recently published 

 valuable ' Lehrbuch d. Histologie,' p. 291. 



The second assertion has been confirmed by M. Lent, and is not 

 directly controverted in Mr. Tomes's paper on the Development of 

 the Enamel, published in the 15th number of this Journal. 



The third statement appears to be justified whenever writers on 

 this question state what they have observed, and not their conclusions 

 from their observations. We are not aware that any one has as yet 

 absolutely seen endoplasts or their remains in distinctly formed or 

 forming enamel or dentine. 



Mr. Tomes, in the excellent essay we have cited, endeavours to 

 prove that Nasmyth's membrane is formed by the union of the ends 

 of the cells of the meinbrana adamantincE, which coalesce into a mem- 

 brane ; and this view would undoubtedly relieve one of much difficulty 

 in understanding the formation of the enamel, and would bring it 

 nearly into the same category as that of molluscan shell ; but until 

 it can be shown that Nasmyth's membrane is not continuous with the 

 niembrana preformativa, and is not an alteration of it, we must adhere 

 to the view that the enamel is, like the dentine, formed under the 

 nienibj'ana preformativa. Hitherto no one has attacked this side of 

 the argument, nor has the evidence derived from the obvious con- 

 tinuity of the membrana preformativa over the whole surface of the 

 teeth in fishes and Amphibia been in any way shaken. 



I I 



