54 MICROSCOPIC ANATOMY OF THE TEETH 



spaces between the branches are filled with supplementary 

 prisms (fig. 17). We thus see that, at all events in one order 

 of the Mammalia, the branching and interposition of prisms 

 is at least one of the methods adopted by nature to over- 

 come this difficulty. 



Variation Pickerill (14) has given another explanation of the mode 



meter of ^J which he considers this difficulty of the widening 



enamel of the enamel at the periphery is overcome. He denies 



the existence of supplemental prisms, but says that the 



FIG. 17. Enamel of Phacochcerus (Wart-hog) showing 

 branching of enamel columns. 



enamel prisms taper somewhat from the surface to the den- 

 tine margin. He has measured a large number of prisms 

 across their diameter, both at the dentine margin and at the 

 enamel surface, and describes a marked increase in their 

 diameter both in native and in European races. 



According to this view each enamel prism would be 

 a cone with its base at the surface of the enamel, and he 

 compares the arrangement with that of the prisms in the 

 outer layer of the Pinna shell. From a series of measure- 

 ments he gives the following average diameter of the prisms : 

 On the buccal curve of the teeth, at the amelo-dentinal 



