JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATE XVII, 



Illustrating Mr. Tomes's paper on the Cuticula Dentis. 



Fig. 



1. — Section of a portion of the crown of a human bicuspid in which the 

 cement is contiiiued over the outside of the enamel. At the point 

 c the enamel was altogether absent, its place being taken by cement 

 which was continued over the enamel both above and below this 

 part; at e a layer of cement sufficiently thick to contain lacunae 

 is seen oveilying the enamel a. At the point d the dentinal tubes 

 are seen to be rather irregularly waved and to branch out beneath 

 the cement, thus conclusively proving that the abnomality existed 

 from the time of the first formation of iLe dentine. X 45 diameters^ 

 a. Enamel. 6. Dentine, d. Dentine, c, e. Cement. 



2. — Portion of enamel from the crown of a human molar tooth, on the 

 outer surface of which there is a depression occupied by a single 

 large lacunal cell, x 125 diameters. 



3. — Fragment of enamel from the side of a deep fissure in the masticating 

 surface of a human molar tooth, to which is attached a cluster of 

 lacunal cells. X CO di&melers. To the right is a single lacunal cell 

 more highly magnified. 



4. — Transverse section through the enamel of the grinding surface of a 

 human molar tooth. The section passed through three deep fissures 

 with similar contents to the one here figured, which is seen to be 

 filled up by a cluster of lacunal cells, x 60 diameters. 



5 . — From the thickened cemeutum of an exostosed human tooth-fang. The 

 lacunas have the appearfince of being enclosed in a capsule of 

 appreciable thickness, but in other places a single line only can be 

 distinguished as surrounding them. X 250 diameters. 

 6. — Half of the crown and a portion of the root of a bicuspid tooth. The 

 grinding surface was deeply fissured, and previously to treatment 

 with acid the contents of the fissure were too opaque for examina- 

 tion. The section has been treated with dilute acid until a portion 

 of the enamel has been dissolved away, setting free Nasmyth's 

 membrane a', o, d, which has been but little disturbed from its 

 original position. The mass which occupied the fissure d is seen to 

 be a part of Nat myth's membrane a, a', which, having been set free 

 from the surface of the enamel e, has been torn in one place. Below 

 the termination / of the enamel the lower fragment of the mem- 

 brane is seen to be continuous with the outermost layer of the 

 cement c. The membrane in this section is seen as a riband-like 

 structure, which is folded on itself in one or two places where it is 

 detached from the remnant of the enamel. The width of the 

 riband, as here seen, corresponds to the original thickness of the 

 tooth section, the real thickness of Nasmyth's membrane, when 

 seen edgewise, being very small, except where it fills up a fissure 

 as at d. 



rt, a'. Nasmyth's membrane, d. Nasmyth's membrane in 

 fissure of enamel, h. Dentine, e. Enamel. /. Point of 

 termination of enamel, c. Cement. 



