478 HANNOVER ON DENTAL TISSUES 



" 4. Meinbrana intermedia. 



" I have bestowed this name upon a membrane which has not as 

 yet received sufficient attention.^ It is a fine and dehcate membrane, 

 which must not be confounded with the membranous expansion of 

 the enamel-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 membrane, 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. 1 1 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 meinbrana 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 membrana intermedia differs considerably in 

 dental sacs of different ages. In the persistent teeth of the new-born 

 infant it is hardly visible to the naked eye ; in their milk-teeth it is 

 very easily recognisable, in consequence of its white colour, and has 

 considerably increased in thickness ; it is thickest, perhaps, about the 

 constricted part or neck of the dentinal germ, with which it is also 

 more intimately connected. Fig. 19 « shows its thickness in the 

 deciduous molar of a new-born infant. 



" The membrana intermedia 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 imme- 

 diately on the formation of the outermost layer of dentine, it coalesces 

 with it, and can be recognised only from its appearance in the com- 

 plete tooth, where we shall find it as the stratum intermedium. If we 

 consider the membrana 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 membrana intermedia and the 



1 KoUiker has, perhaps, figured it in his ' Mikroskopische Anatomie,' p. 99, fig. 211 1/, 

 without, however, recognising its true nature. What Tomes has termed " basement mem- 

 brane " appears to have been not exchisively the membrana intermedia. 



