APPENDIX. 793 



so that of the enamel may take place in the same way in relation to 

 Nasmyth's membrane and the dentine. 



These would appear to be the alternatives concerning the development 

 of the enamel. At present facts would seem to be wanting to deter- 

 mine definitely which should be accepted. 



Finally comes the question of interpretation of the phenomena of de- 

 velopment of the dental tissues, and the determination of the homolo- 

 gies of the latter with the pre-existing elements of the mucous mem- 

 brane. Professor Kolliker's views are stated in the text. He consi- 

 ders the dentine and the cement to be the calcified corium of the mucous 

 membrane, while the enamel is the calcified epithelium. 



The view we have ourselves taken is that cement, dentine, and enamel, 

 are calcifications in the same constituent of the mucous membrane, and, 

 in fact, that they entirely belong to its corium or dermal element. Tak- 

 ing for granted that the membrana preformativa was a basement mem- 

 brane, and furthermore, the received doctrine that a basement mem- 

 brane marks the boundary between the dermal and epidermal elements 

 of integument or mucous membrane, it was, in fact, impossible to come 

 to any other conclusion. An extensive study of the integumentary 

 organs, however, has ]ed us to reflect more closely upon this matter, and 

 to inquire what is a basement membrane, and what is the real distinc- 

 tion between the epidermic and the dermic elements of a membrane ? 

 We cannot here enter into the grounds for our conclusions (which will 

 be stated in full in a forthcoming article on the " Tegumentary Sys- 

 tem," in Todd's "Cyclopaedia of Anatomy and Physiology"), but must 

 be content merely to state our conclusions that the existence of a base- 

 ment membrane, i. e., of a structureless membrane, internal or external 

 to it, proves nothing with regard to the dermic or epidermic nature of 

 an organ, but that we must be guided entirely by the direction of its 

 growth and metamorphosis. Every integument and every mucous 

 membrane may, in fact, be distinguished into three portions ; a central 

 plane of indiiferent tissue, from which growth and metamorphosis take 

 place externally, to constitute the representative of epidermis or epithe- 

 lium, to which we propose to give the name of ecderon ; while internally, 

 growth and metamorphosis take place from the central plane, so as to 

 constitute the representative of the derm or u mucosa,". which we have 

 termed the enderon. 



Now the dental pulp is a process of the whole integument, and its 

 outer surface, although bounded by a " basement membrane," truly 

 represents the deepest layer of the ecderon of ordinary integument, 

 while its inner substance belongs to the enderon. Although, therefore, 

 the dentine is not a calcified cellular epidermis, it is a calcified ecderon, 

 and grows in the same manner as an ecderon would do. The cement 



