MOUTH CAVITY. 



159 



the canals is harder and more resistant than the rest, and is 

 known as Neumann's dental sheath. 



The ground substance itself has a structure finely fibrous, 

 like that of ordinary bone. The fibrils are joined to form 

 bundles, which run mainly in the long axis of the tooth. 



In the dentine of the crown there is, near the outer enamel 

 surface, a layer of so-called inter globular spaces. These are 

 large or small spaces of irregular shape, situated in the calcified 



FIG. 116. 



Cement 



Tomes' 



granular 



sheath 



Dentine 



Part of a cross-section through a human incisor tooth in the region of the root. X 360. 



ground substance and filled with a soft substance which corre- 

 sponds with the uncalcified substance of the dentine (Plate 

 IX.). The dental canals pass through these spaces without inter- 

 ruption. These spaces are an indication of the unequal and 

 incomplete calcification of the dentine. 



In the lower parts of the tooth we find in the outer part of 

 the dentine the so-called Tomes' granular sheath, which is 

 nothing more than a layer of small interglobular spaces (Fig. 

 116). 



