240 MICROSCOPIC ANATOMY OF THE TEETH 



seen more or less parallel with the dentine surface 

 (fig. 144), and in young, growing teeth treated with silver 

 nitrate by the Cajal process these parallel lines are seen to 

 be concentrically arranged. This part of the subject, 

 however, will be further considered under the development 

 of the dentine. 



The Granular Layer of Tomes. Within the marginal portion 

 of the dentine and in contact with the cement, although 

 sometimes separated from it by a clear layer, is seen a line 



FIG. 144. Adult human molar affected by caries. Action of acids of caries, 

 showing striation and contours as in figs. 178 and 179. ( x600.) 



of dark contours, angular or crescentic in form, which has 

 a granular appearance under the microscope, and owing 

 to this appearance was named ' the granular layer of 

 Tomes ', Sir John Tomes having been the first to describe it. 

 These small spaces are usually confined to the dentine 

 beneath the cement, but are occasionally, although rarely in 

 man, found under the enamel. They appear to be a normal 

 portion of the structure of the dentine and are found in 

 all teeth ; the tubes of the dentine communicate with them 

 by their fine terminal branches. The rounded contours of 

 the calcifying substance are seen to surround them, and 



