172 A MANUAL OF DENTAL ANATOMY. 



course that the " dentine papilla " was covered over by a 

 " basement membrane," or membrana preformativa. 



Thus this membrane necessarily intervened between the 

 enamel organ and the dentine papilla, and hence gave rise 

 to difficulties in the understanding of the calcifying process. 

 Henle considered that evidences of its presence speedily 

 became lost, but that ossification proceeded in opposite 

 directions upon the two sides of this membrane : from 

 within outwards in the case of the enamel, from without 

 inwards in the case of the dentine. 



Prof. Huxley, starting on the same hypothesis as to its 

 position, namely, that it was between the enamel organ and 

 the dentine papilla, came to a different conclusion as to its 

 after fate ; relying upon the fact that a continuous sheet of 

 tissue or membrane can be raised from the surface of the 

 developing enamel (see page 152), he concluded that this 

 was the original membrana preformativa, that it afterwards 

 became the Nasmyth's membrane, and that enamel was 

 developed without the direct participation of the enamel 

 organ, seeing that a membrane separated the two. My 

 reason for doubting the correctness of these conclusions has 

 been there given ; the membrane so demonstrable is, I 

 believe, artificial, and does not represent any naturally 

 existing structure. 



Kblliker strongly affirms the existence of the membrana 

 preformativa, and in the older edition of his Histology, held 

 that it became converted into Nasmyth's membrane ; al- 

 though he now gives a different explanation of the origin 

 of Nasmyth's membrane, I have not found a definite state- 

 ment as to his recent views of the ultimate fate of the 

 membrana preformativa. 



We have thus three destinations assigned to the mem- 

 brane^ covering the dentine papilla, or membrana prefor- 

 mativa. 



