150 



THE ESSENTIALS OF HISTOLOGY. 



The dentine is composed of a hard dense substance like bone, bnt 

 containing no Haversian canals or lacunae. It is pierced everywhere, 

 however, by fine canaliculi (dentinal tubules, figs. 175, 176), radiat- 

 ing 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. 172. VERTICAL 

 SECTION OF A TOOTH 

 in situ. (15 diame- 

 ters.) (Waldeyer.) 



c, is placed in the pulp- 

 cavity, opposite the 

 cervix or neck of the 

 tooth ; the part above 

 is the crown, that below 

 is the root (fang). l r 

 enamel with radial and 

 concentric markings ; 



2, dentine with tubules 

 and incremental lines ; 



3, cement or crusta pe- 

 trosa, with bone-corpus- 

 cles ; 4, dental perios- 

 teum ; 5, bone of lowei~ 

 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 appears for the most part homogeneous,, 

 but here and there indications can be seen in it of a globular forma- 



