156 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



In the root the tubules radiate directly to the ce- 

 mentum, showing only the primary curves. Many 

 fine branches pass in all directions from tubule to 

 tubule. The dent in next to the cementum contains 

 many small irregular spaces that connect with the 

 dentinal tubules. They present a granular ap- 

 pearance in ground sections, and are therefore 

 called the granular layer of Tomes. These spaces are 

 filled by the enlarged ends of the dentinal fibrils, 

 which are cell processes of the 

 odontoblasts , while the fibrils 

 also fill the dentinal tubules. 

 The layer of Tomes may some- 

 times be found beneath the 

 enamel, but is never well 

 marked. 



The dento-enamel junction 

 presents rounded projections. 

 This scalloped appearance has 

 given rise to the view that 

 certain dentinal tubules pass 

 for a short distance into the 

 enamel. In ground sections, 

 irregularly branched dentinal 

 spaces are often found at a uniform depth from the 

 surface. These are the inter globular spaces of Czer- 

 mak and represent areas of imperfectly developed 

 dentin. Lastly, the sheaths of Neumann represent 

 the inner wall of the dentinal tubules, and may be 

 regarded as differentiated and more resistant ground 

 substance. 



The formation of dentin continues for an indef- 



Fig. 114. Section of den- 

 tin at right angles to the 

 tubules (Noyes). 



