Chap. XXI.] 



TEETH. 



substances of the tooth. It forms a complete invest- 

 ment of the pulp cavity of the crown and fang, being 

 slightly thicker in the 



former than in the latter U=^^^=^ 



region. The dentine is El^^SS^ 



composed of (Fig. 104) : 



(1) a homogeneous ma- 

 trix; this is a reticular 

 tissue of fine fibrils im- 

 pregnated with lime- 

 salts, and thus resem- 

 bles the matrix of bone ; 



(2) long fine canals, the 

 dentinal canals or tubes 

 passing in a more or less 

 spiral manner, and ver- 

 tically from the inner 

 to the outer surface of 

 the dentine. These tubes 

 are branched; they open 

 in the pulp cavity with 

 their broadest part, and 

 become finer as they 

 approach the outer sur- 

 face of the dentine. 

 Each canal is lined with 

 a delicate sheath the 

 dentinal sheath. Inside 

 the tube is a fibre, the 

 dentinal fibre, a solid 

 elastic fibre originating 

 with its thickest part 

 at the pulp side of the 

 dentine from cells lining 



the outer surface of the pulp, and called odontoblasts. 



On the outer surface of the dentine, both in the 



region of the enamel and crusta petrosa, the dentinal 



Fig. 104. From a Section through 

 a Canine Tooth of Man. 



a, Crusta petrosa, with large bone cor- 

 puscles ; b, interglobular substance; 

 c, dentinal tubules. (Waldeyer, in 

 Strieker's Manual.) 



