70 MICROSCOPIC ANATOMY OF THE TEETH 



form and direction, as are the connecting or wing processes 

 of the prisms. That the membranous expansions and wing 

 processes are calcified, is shown both in man and the elephant 

 by examination with polarized light, and the very irregular 

 zigzag splitting of the wing processes, sometimes seen, may 

 be due to their fracture in teased preparations. 



While the needle -like splitting of the enamel in the 

 teased preparations may be due to the longitudinal fibrilla- 

 tion, as before suggested, the membrane -like fibrillar expan- 



FIG. 28. Enamel of Elephant photographed at a crack, showing prisms 

 in both longitudinal and transverse section. ( x 400. ) 



sions, the wing processes, and the bridges one would be 

 inclined to consider as due to the transverse fibrillation of 

 the matrix so apparent in the forming enamel of marsupials 

 where the teased preparations break up into laminae 

 (Plate III, figs. 12 and 13). 



These transverse fibrillar layers must also be incorporated 

 in the substance of the calcified prism. These grooved 

 prisms are not in direct contact with one another, being 

 separated by the interprismatic substance which is, as it 

 were, flowed around them, cementing together and com- 

 pacting the whole tissue. As Leon Williams pointed out, the 

 prisms being in many places round rather than hexagonal 



