APPENDIX. 433 



Now in the long hairs we have a relation of the outer 

 cuticle to the cortex very similar to that of Nasmyth's mem- 

 brane to the dentine before the development of the enamel, 

 and the conclusion is obvious, that as the development of the 

 inner layer of the cuticle takes place by the differentiation of 

 the intermediate substance between the cuticle and cortex, 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 determine definitely which should be accepted. 



Finally comes the question of interpretation of the phe- 

 nomena of development of the dental tissues, and the deter- 

 mination of the homologies of the latter with the pre-existing 

 elements of the mucous membrane. Professor Kolliker's views 

 are stated in the text. He considers 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. Taking for granted that the 

 membrana preformativa was a basement membrane, and further- 

 more, the received doctrine that a basement membrane 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 in- 

 tegumentary organs, however, has led us to reflect more closely 

 upon this matter, and to inquire what is a basement mem- 

 brane, and what is the real distinction 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 System/ 

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

 be content merely to state our conclusions that the existence of 

 a basement membrane, i. e., of a structureless membrane, inter- 

 nal 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. 



it. 28 



