170 HANNOVER, ON DKNTAL TISSUES. 



the stellate tissue, we venture to speak positively on this 

 question. 



If the cement then is really developed within the actinen- 

 chyma, as Dr. Hannover describes it to be, the establishment 

 of the fact will simply prove that his " cement-germ" {i. €., 

 stellate tissue of enamel-organ) has as little to do with the 

 cement, as the membrana intermedia has with the stratum 

 intermedium or Nasmyth's membrane. 



It may be worth while, before concluding this notice, to 

 consider in a few words the present state of our knowledge 

 of the development of the teeth. 



In an essay published in this Journal some years ago (vol. i, 

 p. 149), Prof. Huxley endeavoured to prove that all the dental 

 tissues, whether cement, enamel, or dentine, are developed 

 beneath the basement membrane of tlie dental sac, Avliich, 

 on the dental papilla itself, has received the name of membrana 

 preformativa; and that the so-called enamel-organ — consisting 

 from within outwards of the membrana adamantince, the 

 membrana intermedia of Hannover, the stellate tissue, and 

 the deep layer resembling the membrana intermedia, next the 

 basement membrane of the sac — was to be regarded as a 

 transitory epithelial structure, which has as little connection 

 with the development of the tooth as the various modifications 

 of the epithelium of the root-sheath of a hair have with that 

 of the shaft of the hair. 



Evidence was oiFered, 1st, that the enamel-fibres, from 

 their first appearance, lie beneath Nasmyth's membrane. 

 2dly. That Nasmyth's membrane is continuous with the 

 membrana preformativa. 3dly. That no traces of cells or 

 endoplasts can be discovered within the enamel-fibres nor in 

 the dentine, and that these tissues are not produced by the 

 direct calcific conversion of pre-existing elements. 4thly. 

 That the cement is morphologically the continuation of the 

 enamel, but whether it is or is not developed by conversion 

 from the pulp was left an open question. 



The first of these statements has received fiill confirmation 

 from subsequent observers, including M. Ley dig, in his 

 recently published, valuable ' Lehrbuch d. Histologic,' p. 291. 



The second assertion has been confirmed by M. Lent, and is 

 not directly controverted in Mr. Tomes's paper on the De- 

 velopment of the Enamel, published in the IStli number of 

 this Journal. 



The third statement appears to be justified whenever 

 writers on this question state what they have observed, and 

 not their conclusions from their observations. We are not 



