168 HANNOVER, ON DENTAL TISSUES. 



cells, and which lies within the cement-germ, between it and the enamel- 

 cells. It appears in transverse sections of the germ as a fine white line ; is 

 a tolerably firm and opaque membiaue, and consists of a structureless mass, 

 in which very numerous small, round or oval, angular or pointed nuclei, 

 without distinct nucleoli, are imbedded. The boundary towards the cement- 

 germ is sharp and linear, and the cells of the cement-germ are pressed 

 against it (fig. 11 a). The boundary towards the enamel-cells, which lie 

 upon the opposite surface, is also well defined (fig. 19 a). The enamel-cells 

 may be detached with tolerable ease, whilst it is only with difficulty that 

 the memhranci intermedia can be separated from the cement-germ. It is, 

 therefore, best examined in connection with the cement-germ, and, indeed, 

 in the teeth of the new-born infant. In order to observe the attached 

 enamel-cells, the membrane may be folded, because in thin sections the 

 enamel-cells easily fall off. 



"The thickness of the memhrana intermedia differs considerably in dental 

 sacs of different ages. In the persistent teeth of tlie new-born infant it is 

 hardly visible to the naked eye ; in their milk-teeth it is very easily recog- 

 nisable, in consequence of its white colour, and lias considerably increased 

 in thickness ; it is thickest, perhaps, about the constricted part or neck of 

 the dentinal germ, with v/hich it is also more intimately connected. Tig. 19 a 

 shows its thickness in the deciduous molar of a new-born infant. 



" The membrcma ifdermedia does not belong to the crown or the enamel 

 alone, for it is continued uninterruptedly upon the fang, here separating the 

 dentine from the cement, and, as in the crown, lying upon the inner surface 

 of the cement-germ. However, I have not been able to demonstrate it here 

 in an isolated form, because, immediately on the formation of the outermost 

 layer of dentine, it coalesces with it, and cau be recognised only from its 

 appearance in the complete tooth, where we shall find it as the stratum 

 intermedium. If we consider the memhrana intermedia as a whole, it may be 

 regarded as a sac-like structure which is inclosed within the dental sac, so 

 that the cement-germ is situated between the memhrana intermedia and the 

 dental sac ; perhaps the membrane becomes reflected over the inner surface 

 of the dental sac." 



Now there can be no doubt as to the existence of this 

 layer. It was^ as we have seen^ described by Nasmyth ; it is, 

 as Dr. HannoA^er justly states^ figured by Professor KoUiker j 

 and we have repeatedly seen it ourselves without feeling 

 inclined to lay any very particular stress upon its existence. 

 If there is any advantage in calling it memhrana intermedia, 

 we shall be happy to adopt this term. But we must demur 

 to Dr. Hannover's view of its tdtimate fate, as contained in 

 the following passage (p. 110) of his memoir. 



"4. Stratum intermedium. — The nucleated membrane, which during the 

 development of the tooth is closely united with the cement-germ, and serves 

 for the attaciunent of the nucleated end of the enamel-cells, and to which 

 we have given the name of memhrana intermedia, is always sufficiently 

 obvious in the perfect tooth, though much changed. It receives its persistent 

 form only after the enamel-cells are calcified throughout their whole length ; 

 since it lies between the enamel-cells and the cement, the ossification of the 

 cartilaginous cemeut-germ can only take place after the completion of the 

 development of the memhrana intermedia. Hence in the crown it always 

 separates the enamel, in the root, the dentine, from the cement. Since, 



