280 MICROSCOPIC ANATOMY OF THE TEETH 



rings are drawn out into laminae which pass more or less 

 parallel to the surface of the dentine. Fig. 179 shows the 

 drawing out of the marginal striae, which remain equidistant 

 from one another. It is seen in this figure that the dentine, 

 in a thin section, splits along these lines of lamination, the 

 splitting not only following the extended laminae but also 

 the contours of the round bodies themselves, where they have 

 not been drawn out in this manner. It will be noticed that 

 the lines remain absolutely parallel and never join with 



FIG. 179. Calcoglobulin contours in forming dentine. 

 Unerupted premolar. ( x 600.) 



one another in the same layer. This form of lamination 

 of the dentine would thus appear to have nothing to do 

 with physiological lines of growth, but to be due to a purely 

 physical cause, the extension of the elements of the globular 

 bodies in parallel lines. In teeth in a further stage of develop- 

 ment the rounded contours are to a very great extent lost, 

 and only the parallel striae remain as evidence of the original 

 structure. 



In the completed dentine the striae are hidden by the 

 dense calcification, but as shown above, occasionally 

 revealed in caries by the action of the bacterial acid products 



