ENAMEL 



109 



enamel prisms are for the most part viewed longitudinally 

 from dentine to surface. Examining, in the first place, 

 a transverse section of Beaver's enamel, the separation into 

 two layers is very distinctly seen (fig. 59). The inner portion, 

 which extends not quite half-way across the width of the 

 enamel, is traversed by lines arranged at right angles to one 

 another and making an angle of 45 with the dentine surface. 

 The crossing prisms lie in different laminae, all those of one 

 lamina passing in the same direction and being crossed by 



FIG. 59. Enamel of Beaver, d. Dentine ; a. inner layer of enamel 

 decussating layers ; 6. outer layers of enamel. ( X 225. ) 



those of the superimposed lamina which lie at right angles 

 to them. If it were possible to obtain a sufficiently thin 

 -section exactly parallel to the layers, the prisms would be 

 seen in the single layer to be all passing in the same direction ; 

 but it is not possible to make such a section, as the layers are 

 not in the same longitudinal plane as the dentine but are 

 inclined from the perpendicular. 



A little less than half-way across the enamel each indivi- 

 dual prism, whether passing from right or left, is bent 

 upwards, and they all lie parallel to one another to the 

 surface, their direction being at an angle of about 70 to 

 the dentine surface. At the point where they alter their 

 direction they show a slight sigmoid curve. 



