APPENDIX. 429 



by Professor Kb'lliker, and which amounts to this, that all the 

 tunics of the teeth are the result of calcareous deposition from 

 the pulp, the so-called " enamel organ" taking no direct share 

 whatever in the process. This view was based upon ob- 

 servations made upon the teeth of all the principal orders of the 

 Vertebrata, i. e. } the Mackerel, the Skate, the Frog, the Calf, 

 and Man; and subsequent observations on these and on other 

 animals, have only confirmed our belief in the substantial 

 truth of the matters of fact there stated. 



The keystone of the theory of dental development there 

 enunciated is the fact, that, in all the orders of the Yertebrata, 

 a membrane homologous with the so-called " persistent cap- 

 sule," discovered, in 1839, by Mr. Nasmyth, and which we have 

 therefore denominated " Nasmyth' s membrane" can be demon- 

 strated covering the enamel of the teeth and extending over 

 the dentine, to be continuous with the membrana preformativa 

 and basement membrane of the sac, in an incompletely formed 

 tooth ; or with the surface of the cement, in a fully developed 

 one. Nasmyth's membrane, in fact, is at first the membrana 

 preformativa more or less altered. 



We hold this statement to be incontrovertible, nor less so 

 the correlated doctrine, that the enamel and cement, as well 

 as the dentine, are developed beneath Nasmyth's membrane, 

 between it and the pulp; that the enamel is, consequently, 

 during the whole course of its formation, separated from the 

 enamel-organ by Nasmyth's membrane; and that, therefore, 

 the direct conversion of the long cylinders of the epithelium into 

 the fibres of the enamel, strongly as their mutual resemblance 

 may suggest the notion, is, to say the least, highly improbable. 



Thirdly, we have met with no facts in opposition to what we 

 have stated with regard to the mode of development of dentine 

 and the relation of the latter to the pre-existing elements of 

 the pulp, and we believe that there is every reason to regard 

 what we have there called the * Deposition theory," as an 

 established position. According to this theory, the dentine is 

 not the result of the conversion of the elements of the pulp ; 

 the endoplasts of the latter never becoming engaged in the 

 calcareous deposit, as they are in bone ; but the young dentine 

 is formed by a deposit of transparent calcareous granules in a 

 thin layer between the pulp and the membrana preformativa. 



