ENAMEL 



113 



as in the squirrel, and extend across the inner two-fifths 

 of the enamel. In transverse section they form a diamond 

 pattern and become parallel and waved in the outer portion, 

 but in the outer layer there is also some intercrossing 

 faintly to be seen and an appearance of diamond-shaped 

 spaces. 



In the Rats and Mice (Muridaa) there is also a decussation 

 of the laminae on the inner half of the enamel. The prisms 

 are, as seen in longitudinal section, at an angle of 55 to 



a 



d 



FIG. 63. Enamel of Rat. s. Papillae and vessels in the enamel organ ; 

 a. ameloblasts ; e. enamel ; d. dentine, (x 250.) 



the dentine surface and form a diamond-shaped pattern 

 in this area. They are slightly curved (fig. 63), the curvature 

 being most evident near the dentine, and in the outer part 

 of the enamel they proceed in a single layer in straight lines 

 at an angle of 25 with the surface of the dentine. Sir John 

 Tomes speaks of the lamellae as being serrated, andC. S. Tomes 

 says, ' The borders of the individual prisms are slightly 

 serrated, the serrations of contiguous rods interlocking ' (fig. 

 64). An examination of thin sections of rat enamel cut by 

 the Weil process suggests, however, that these projections are 

 not a portion of the prisms but of an interprismatic calcified 

 material which separates the prisms from one another, as the 



MUMMERY j 



