HANNOVER ON DENTAL TISSUES 477 



characterised by its osteal lacunae and medullary canals. The cement- 

 germ, however, lies in immediate contact neither with the enamel nor 

 with the dentine, but is separated from them by a peculiar membrane,, 

 not yet sufficiently distinguished ; this carries upon its inner surface 

 the enamel-cells, which are disposed perpendicularly upon the dentine, 

 and consequently it separates the cement-germ from the enamel-germ ; 

 but where the enamel-germ ceases it separates the cement-germ- 

 from the dentine-germ. We shall term this membrane the mevi- 

 bfana intermedia ^ in the complete tooth it appears as the strattcm 

 intermedium!' (p. 3.) 



The careful study and collation of different passages in Dr. 

 Hannover's work show that his dentine-germ is the dental papilla 

 of English writers ; that the enamel-germ is the membrana adamantince ; 

 that his membrana intermedia is the layer of what Nasmyth (' Re- 

 searches on the Development, &c., of the Teeth,' 1849, p. 107) 

 describes as " oval cells," seated on the deep surface of the stellate 

 tissue of the enamel-organ ; and that his cement-germ is nothing 

 more than the stellate tissue of the enamel-organ, which he confounds 

 with the vascular " actinenchyma " or peculiar connective tissue of the 

 proper wall of the dental sac. 



Under the head of the development of the enamel. Dr. Hannover 

 offers us nothing new ; but repeats, without bringing forward new 

 evidence, and as if it had never been disputed, the old view that the 

 enamel is produced by the direct calcification of the columnar cells of 

 the membrana adamantince. Nor can we find any essential difference 

 between Dr. Hannover's theory of the formation of the dentine and 

 that advocated by Professor Kolliker and others, except that he denies 

 the existence of a membrana preformativa, and affirms that — 



" This so-called membrane is, in my opinion, nothing but the 

 outermost layer of dentine-cells, in which dentification has just com- 

 menced." (p. 12.) 



How this can be reconciled with the unquestionable facts that the 

 membrana preformativa can be traced with great ease, uncalcified, on 

 to the primary cap of dentine, and that it is a structureless membrane 

 in which no trace of cells has ever yet been detected, we know not ; 

 but we are inclined to suspect that Dr. Hannover has never seen the 

 true membrana preformativa. 



As regards the membrana intermedia we are desirous to do Dr. 

 Hannover no injustice in endeavouring to explain, what seems to us 

 to be, his erroneous view of its functions and homologies in the adult 

 tooth, and we will therefore cite his account of it at length. 



