120 



THE ESSENTIALS OF HISTOLOGY 



The dentine is composed of a bard dense substance like bone, but 

 containing no Haversiaii canals or lacuna?. It is pierced every wbere, 

 bowever, by fine canaliculi (dentinal tubules, figs. 152, 153), which 

 radiate outwards from a central cavity which, during life, contains the 

 pulp. The tubules branch at acute angles as they pass outwards ; 

 their branches become gradually finer towards the periphery of the 



FIG. 150. VERTICAL 

 SECTION OK A TOOTH 

 I'M situ. (15 diame- 

 ters.) 



c, is placed in the pulp- 

 cavity, opposite the 

 cervix or neck of the 

 tooth ; the part nbove 

 is the crown, that below 

 is the root (fang). 1, 

 enamel with radial and 

 concentric markings ; 



2, dentine with tubules 

 and incremental lines ; 



3, cement or crnsta pe- 

 trosa,with bone corpus- 

 cles ; 4, dental perios- 

 teum ; 5, bone of lower 

 jaw. 



dentine. The tubules have a proper wall of their own, which can be 

 isolated by steeping a section of tooth in strong hydrochloric acid. In 

 the living tooth they are occupied by protoplasmic fibres, which are pro- 

 longed from the superficial cells of the pulp. 



The intertubular substance rs for the most part homogeneous, but 

 here and there indications can be seen of its deposition in the form of 

 globules. This is especially the case near the surface of the dentine, 



