HANNOVER ON DENTAL TISSUES 479 



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. Hannover 

 justly states, figured by Professor Kolliker ; and we have repeatedly 

 seen it ourselves without feeling inclined to lay any very particular 

 stressupon its existence. If there is any advantage in calling {tmein- 

 ■brana intermedia, we shall be happy to adopt this term. But we must 

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

 Ihe following passage (p. no) of his memoir. 



" 4. Stratum intermedium. — The nucleated membrane, which dur- 

 ing the development of the tooth is closely united with the cement- 

 germ, and serves for the attachment of the nucleated end of the 

 enamel-cells, and to which we have given the name of membrana 

 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 

 ■cement-germ can only take place after the completion of the develop- 

 ment of the membrana intermedia. Hence in the crown it always 

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

 however, the cement-germ as a rule does not ossify, but becomes 

 .abortive on the crowns of teeth with conical dentine-germs, the fiiem- 

 .brana intermedia in such crown lies free, and in teeth which have not 

 been worn forms what Kolliker terms the cuticle of the enamel." 



Dr. Hannover then goes on to speak of the identity of his stratum 

 intermedium with the " persistent capsule " of Nasmyth ; and he de- 

 scribes the mode of raising up the membranous stratum, intermedium 

 in young teeth, by the action of dilute acids, which he states to have 

 been discovered by Erdl in 1843. 



Dr. Hannover appears to be unaware that this persistent capsule 

 ■or " Nasmyth's membrane," has of late been the subject of special in- 

 vestigation on the part of Professor Huxley, M. Lent, and Mr. Tomes, 

 and therefore he does not attempt to meet the obvious objections 

 which an acquaintance with the known relations of Nasmyth's mem- 

 brane in the young dental sac would have suggested. Inasmuch, in 

 fact, as Professor Huxley's statement, that Nasmyth's membrane lies 

 on the inner side of the cells of the membrana adamantince, between 

 these and the fibres of the enamel, has been confirmed both by M. 

 Lent and by Mr. Tomes, it will probably be admitted to be correct ; 

 and consequently the membrana intermedia of Dr. Hannover, which 

 lies outside the cells of the membrana adamantince, and is separated by 



