288 



COMPARATIVE PHYSIOLOGY. 



Enamel is made up of elongated hexagonal prisms set almost 

 vertically in the dentine (Fig. 236). 



It is the hardest suhstance known in the animal body, con- 

 sisting almost entirely of inorganic material ; and when lost is 

 but indifferently if at all replaced. 



6-1 





Fig. 240.— Tooth of cat in situ (Waldeyer). 1, enamel; 3, dentine; 3, cement; 4, peri- 

 osteum of alveolar cavity; 5, tone of jaw; 6, pulp cavity. 



Dentine is traversed by the dentine tubules (Fig. 337), 

 which radiate outward from the pulp cavity. 



