THE DEVELOPMENT OF THE TEETH. 173 



(i.) Between the dentine and the enamel (Henle). 

 (ii.) Between the enamel and the enamel organ, or out- 

 side the enamel (Huxley). 



(iii.) Between the dentine and the pulp (several writers of 

 less authority). 



We come next to those writers who deny its existence 

 altogether, explaining on other grounds the appearances 

 observed. 



Markusen believed that it was nothing more than the part 

 of the papilla first ossified ; and Dr. Lionel Beale definitely 

 denies the existence of a membrane in any one of the three 

 situations above detailed, as do also Hertz, Wenzel, and 

 Waldeyer. 



Messrs. Robin and Magitot have offered a plausible ex- 

 planation of the appearance of a limiting membrane over 

 the pulp, which is briefly this : the formative pulp is rich 

 in a clear substance of gelatinous consistency (which in 

 fact forms its chief bulk), and which reminds the observer 

 of the tissue contained in an umbilical cord. This is some- 

 what more dense towards the surface, where it forms a 

 matrix for the odontoblasts and projects beyond them, so 

 as to look, in section or at a thin edge, like a sort of 

 varnish to the papilla. From its greater density near the 

 surface, it may become corrugated, and so look like a 

 folded or torn membrane. I am quite inclined to agree 

 with the foregoing explanation. 



I am inclined to think, that but for the erroneous theories 

 that the dentine germ originated as a free papilla on the 

 surface, which would according to the prevalent view have 

 been necessarily invested by a basement membrane, we 

 should never have heard of a membrana preformativa. At 

 all events it is difficult to imagine that such a membrane 

 exists upon papilla formed at such a great distance from the 

 surface as those of the snake or the lizard (Figs. 61 and 62) ; 



