480 HANNOVER ON DENTAL TISSUES 



their entire length from Nasmyth's membrane, can have nothing to- 

 do with the latter. In fact, we believe that the " membrana intermedia '" 

 is an entirely transitory epithelial structure, and enters in no way inta 

 the composition of the tooth. 



We must express the same opinion with respect to the " stellate 

 tissue'' — Dr. Hannover's cement-germ. Dr. Hannover, after giving 

 an account of the early changes of the epithelial lining of the dental 

 sac, and the production of the stellate cells, in a manner not essentially 

 different from that contained in Mr. Nasmyth's last work, seems to us- 

 to make the mistake which has already been committed by more than 

 one writer on these subjects, of supposing the actinenchyma of the 

 thickened wall of the dental sac to be a later stage of the stellate 

 epithelial tissue — with which it has nothing to do, and from which it 

 is separated by the basement membrane of the dental sac. We have 

 in our possession figures, drawn long ago, of sections of the thickened 

 wall of the dental sac, in all essential respects corresponding with Dr. 

 Hannover's fig. 13 ; and having worked carefully over the relations of 

 the actinenchyma (which is nothing but such connective tissue as may 

 be met with in any soft young organ), with the stellate tissue, we 

 venture to speak positively on this question. 



If the cement then is really developed within the actinenchyma,, 

 as Dr. Hannover describes it to be, the establishment of the fact 

 will simply prove that his " cement-germ " {i.e., stellate tissue of 

 enamel-organ) has as little to do with the cement, as the mem- 

 brana 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), Professor Huxley endeavoured to prove that all the dental 

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

 the basement membrane of the dental sac, which, 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 adamantines the membrana intermedia of Hannover,, 

 the stellate tissue, and the deep layer resembling the membrana irUer- 

 media, 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. 



