168 HUMAN TOOTH 



lustre. It forms the entire boundary of the 

 pulp cavity, with the exception of a small 

 portion at the base of the fangs. 



The dentine, or ivory, consists of a vast num- 

 ber of tubes or canaliculae called the ' ivory 

 tubes.' They are shown in the illustration as 

 extremely fine tubes, pursuing an undulatory 

 course, at first curving, then bifurcating, and 

 continually giving out numerous fine lateral 

 communicating branches. 



The enamel covers the body of the crown. 

 It is thickest at the opposing surface, decreas- 

 ing towards the neck, where it terminates. 

 The enamel is covered by a very thin mem- 

 brane, which contains calcareous matter. This 

 can be dissolved by the action of muriatic 

 acid. 



The enamel has a fibrous aspect, and ap- 

 pears of a bluish-white colour by reflected 

 light, and of a greyish-brown by transmitted 

 light. It is very brittle, and so hard as to 

 strike fire with steel. It consists of numerous 

 solid fibres, or prisms, mostly six-sided, wavy, 

 and transversely striped. These usually ex- 



