TOMES, ON THE DEVELOPMENT OF THE ENAMEL. 219 



which the nuclei, or bodies very like them, fill up the whole 

 of the sheath, and become calcified : fig. 6 illustrates this 

 condition. It may generally be found in the opaque white or 

 brown teeth frequently seen in strumous subjects. A little 

 practice will enable the histologist to recognize teeth which 

 will yield specimens like the one figured. 



Many authors have noticed the transverse striation of the 

 enamel fibres. The structural condition I have described is 

 but a more-perfect development of that which is but faintly 

 marked in the striation, and a less-perfect development of the 

 enamel itself. 



In looking over a series of sections of teeth, we shall not 

 fail to find other exceptional conditions than that I have 

 described, and these must be also regarded as the results of 

 imperfect development. I allude to the irregularly-granular 

 state of the enamel fibres found in patches scattered here and 

 there amongst highly-developed tissue. At such points the 

 granularity is in many specimens confined to the interior of 

 the fibre, the sheath appearing clear and structureless. In- 

 deed, this deviation from the normal state appears due to the 

 calcification of the columns of the enamel organ, prior to that 

 change by which the granularity disappears, and the fibre 

 becomes transparent. 



Mr. Huxley has referred to the " persistent capsule " de- 

 scribed by Mr. Nasmyth, and considers it to be identical with 

 the memhrana preformativa. In several specimens Avhich have 

 been decalcified, after being reduced sufficiently thin for 

 microscopic examination, this membrane is obviously con- 

 tinuous with the cementum of the fang, and in other specimens, 

 which have not been treated with acid, I find the membrane 

 thickened in the deep depression of the crown of molar teeth, 

 and there tenanted by a distinct lacuna. The occurrence of 

 these two circumstances would indicate that Nasmyth's mem- 

 brane is cementum, rather than membrana preformativa. The 

 general absence of lacuna in this membrane is due to its want 

 of sufficient thickness to contain them, just as we find these 

 bodies wanting in the cementum of the fang when the layer 

 of that tissue is very thin. 



Apart, however, from this apparently-structureless layer 

 described by Mr. Nasmyth, we may sometimes observe a 

 diminution in the fibrous character of the enamel at the termi- 

 nations of the fibres on the surface of the tooth, and also at the 

 terminal edge of the enamel on the neck of the tooth. In 

 each of these situations appearances may be found which 

 suggest the idea that a fluid blastema became calcified, and 

 that the fibres had in the process become fused, and more or 



