TEETH. 



711 



which commence at the pulp cavity, and pass up to the 

 enamel. 



Czermak discovered that the curious appearances of 

 globular conglomerate formations in the substance of 

 dentine depend on its mode of calcification and the 

 presence of earthy material ; and he attributes the contour 

 lines to the same cause. Contour markings vary in in- 

 tensity and number ; they are most abundant in the root, 

 and most marked in the crown. Vertical sections exhibit 

 them the best; as fig. 342, No,. 1. In preparing a specimen, 

 first make the section accurately, 

 then decalcify it by submersion in 

 dilute muriatic acid ; then dry it 

 and mount in Canada balsam with 

 continued heat, so as to allow the 

 specimen to soak in the fluid resin 

 for some time before it cools. It is 

 the white opacity at the extremity 



of the Contour markings which Fi?. 843.— Trtmsverst section &j 



. r t? • Tooth of Pristis, showing ori- 



gives the appearance of rings on fie es of medullary canals, with 



the tOOth-fang. systems of radiating fibres 



//mi ,i -i h (tubuli) analogous to the 



" I he tOOth-SUDStance appears, Haversian canals in true 



savs Czermark, " on its inner sur- boDe - 

 face, not as a symmetrical whole, but consisting of balls 

 of various diameter, which are fused together into a 

 mass with one another in different degrees, and on which 

 the dentinal tubes in contact with the germ cavity are 

 terminated. By reflected light, back-ground illumination, 

 one perceives this stalactite-like condition of the inner 

 surface of the tooth-substance very distinctly, by means of 

 the varied illumination of the globular elevations, and by 

 the shadows which they cast. Here one has evidently to 

 do with a stage of development of the tooth-substance ; 

 for the older the tooth is, the less striking in general are 

 these conditions, and the more even is the surface of the 

 wall of the germ-cavity. In very old teeth considerable 

 unevenness again makes its appearance ; these, however, 

 are not globular, but have a cicatrised, distorted appear- 

 ance. It is best to make the preparation from a tooth of 

 w T hich the root is not perfectly completed. With such 

 preparations, one is readily convinced that the ground- 



