DENTINE 



247 



more or less spiral course of the tubes, but the degree of 

 curvature varies very greatly in different teeth and in 

 different parts of the same tooth. This arrangement of 

 the tubes gives rise to an appearance in the dentine described 

 as Schreger's lines. These lines are parallel with the surface Schreger 

 contour of the dentine, and are due to the primary curva- 

 tures of the tubes coinciding with one another in the 

 thickness of the dentine. 



The contour lines of Owen also describe markings due Contour 



lines of 

 Owen. 



'( R 





FIG. 151. Branching of dentinal tubes just beneath the enamel (silver 

 pyridin). Ground section. </. Interglobular space. (x250.) 



to the same cause, and others due to the presence of rows of 

 interglobular spaces which occur in great abundance in the 

 teeth of Cetacea and in the ivory of the Elephant's tusk. 



In some places tubes are seen to terminate in branches 

 within the substance of the dentine (figs. 124 and 147). 



In transverse sections of dry dentine the tubes appear 

 as round holes within the matrix with a strongly-marked 

 surrounding border giving them the appearance of rings 

 (fig. 152). This appearance, however, is somewhat deceptive, 

 even very thin sections having an appreciable thickness. 

 The appearance may be due to this fact, and the double 



