622 



THE TEETH. 



threads. Extremely fine thorns traverse in a vertical direction the light 

 space between two neighboring enamel-rods, even where a fiber is not visible. 

 (See Fig. 268.) 



The rods of the enamel, on an average, are half the diameter of the col- 

 umns of the basis-substance in dentine ; therefore four columns of the former 

 will correspond to two of the latter. Sometimes in the cross-section of an 

 enamel-rod I met with roundish formations occupying the center of the rod, 

 one or two in number, which, owing to a denser granulation and a surround- 

 ing shell, have the appearance of nuclei. The enamel-fibers run a very 

 straight course toward the surface, and are here usually a trifle thicker than 

 near the boundary of the dentine. 



The outermost surface of the enamel is covered by flat epithelia (Nas- 

 myth's membrane), which, in the transverse section, have the appearance of 



flat spindles ; not infrequently there also 

 p 7-, occurs a stratified epithelium on the surface 

 of the tooth. The enamel-fibers are in con- 

 nection with these epithelial bodies, which, 

 if detached, show delicate offshoots adhering 

 at regular intervals the broken enamel- 

 fibers. Sometimes the surface of the enamel 

 is coated by a thin, uniform layer, with regu- 

 larly scattered nuclei. 



At the place of junction of the enamel 

 with the dentine a direct connection is often 

 seen between the enamel and dentine fibers. 

 The latter, through repeated bifurcations, 



ing formations like nuclei; the light being closely brought together, continue 

 interstices between the rods traversed their course into the enamel-fibers without 



any interruption. The direction of the fibers 

 of the two tissues, however, is almost never 

 identical, inasmuch as the enamel-rods, and 



consequently the enamel-fibers, as a rule, owing to their wavy course in this 

 situation, are obliquely intercepted upon the dentine. 



We can very often trace dentinal fibers up into the enamel in a varying 

 distance, without a distinct union between the enamel and dentine-fibers, as 

 the former do not reach the surface of the dentine, but terminate above its 

 level at different heights, while the zone close above this is occupied by a 

 delicate, irregular net-work analogous to that of the dentine. (See Fig 269.) 

 In many places the dentinal canaliculi upon entering the enamel suddenly 

 become enlarged, and form more or less distinctly spindle-shaped cavities of 

 greatly varying diameters, analogous to the spindle-shaped enlargements at 

 the boundary of the cementum. These enlargements run either in the main 

 direction of the dentinal canaliculi or deviate obliquely. They invariably con- 

 tain bioplasson bodies, which plainly show the reticular structure, and some- 

 times contain one or more compact clusters to be considered as nuclei. The 

 spindle-shaped bodies, on their proximate ends, are in direct connection with 

 the terminations of the dentinal fibers which have arisen from their repeated 

 bifurcations, while on the distal end they may show delicate fibers viz. : 

 enamel-fibers or delicate conical thorns traversing the light space between 

 the surface of the bioplasson body and the wall of the cavity. These thorns 

 are lost to sight on passing into the net- work at the bottom of the enamel. 



FIG. 268. CROSS-SECTION OF 

 ENAMEL. 



EH, rods of enamel, partly exhibit- 



by delicate beaded fibers, EF, or by 

 vertical thorns. Magnified 2000 di- 

 ameters. 



