160 



MICROSCOPIC ANATOMY OF THE ORGANS. 



The enamel (substantia adamantina), which is the hardest of 

 all animal tissues, contains only 3-5 per cent, of organic sub- 

 stance. It is soluble in dilute acids without residue. It con- 

 sists of the so-called enamel fibres, which appear in the form of 

 hexagonal prisms, and are on this account known as enamel 

 prisms. These extend from the surface of the dentine to the 



FIG. 117. 





Longitudinal ground-section through the apex of a canine tooth from a three and a 

 half year old boy. The entrance of the dental caualiculi between the enamel prisms and 

 the course taken by the latter are shown. X 135. 



free surface of the enamel, and are thicker at the outer end 

 than near the dentine. They usually appear to be structure- 

 less, but under the influence of certain reagents they acquire a 

 striated appearance. They usually run radially and their 

 course is slightly wavy. They lie pressed together, and joined 

 with one another by a small amount of cement substance. The 



