104 A MANUAL OF DENTAL ANATOMY. 



Professor Huxley described it as being identical with the mem- 

 brana performativa ; that is to say, with a membrane which covered 

 the dentine papilla prior to the occurrence of calcification, and 

 which afterwards came to intervene between the formed enamel 

 and the enamel organ. The objections to the acceptance of this, 

 view of its nature are so inextricably wrapped up with other ob- 

 jections to Professor Huxley's theory of the development of the 

 teeth, that they cannot profitably be detailed in this place ; it will 

 suffice to say, that evidence and the weight of authority alike point 

 to there being no such true membrane as this membrana performa- 

 tiva in the place in question. 



Waldeyer holds that it (i.e., Nasmyth's membrane) is a product of 

 a part of the enamel organ. After the completion of the formation 

 of the enamel he believes that the cells of the external epithelium 

 of the enamel organ become applied to the surface of the enamel 

 and there cornified ; in this way he accounts for its resistance to 

 reagents, and for its peculiar smell when it is burnt. 



Its extreme thinness, so far as it goes, is an objection to this 

 supposition : a more weighty argument against it is the absence of 

 analogy for such a peculiar change, by which one portion of the 

 same organ is calcified, and the rest cornified ; and again, what be- 

 comes of these cells in those teeth in which cementum is deposited 

 in bulk over the surface of the enamel ? According to the statement 

 of Dr. Magitot, the layer of cells in question (external epithelium 

 of the enamel organ) is atrophied before the time of the completion 

 of the enamel ; a fact which, if confirmed, is fatal to Waldeyer' a 

 explanation. And Dr. Magitot, in his most recent paper on the 

 subject (Journal de 1'anatomie, &c., 1881), gives his adherence to 

 the view that it is cementum. 



Kolliker, who dissents strongly from the views of Waldeyer, and 

 admits some uncertainty as to its nature, provisionally regards it aa 

 a continuous and structureless layer furnished by the enamel cells 

 after their work of forming the fibrous enamel was complete ; a 

 sort of varnish over the surface, as it were. 



This would not account for the occurrence of lacunae in it. 



THE TOOTH PULP. 



The Tooth Pulp, occupying the central chamber, or pulp 

 cavity, is the formative organ of the tooth, and consequently 

 varies to some extent in its anatomical character according 

 to its age. As well as being what remains of a formative 

 organ, it is the vascular and nervous source of supply 

 whence the dentine mainly derives its vitality. 



