DEVELOPMENT OF THE TEETH 



261 



The Enamel Germ. The enamel germ or enamel organ soon 

 differentiates into three layers : 1, an inner enamel epithelium 

 which forms the enamel prisms ; 2, an outer enamel epithelium 

 which lines the dental sac ; and 3, an intervening enamel pulp. 



The Inner Enamel Epithelium. The innermost cells of the 

 enamel organ, viz., those which rest directly upon the dental pa- 

 pilla, soon become elongated and attain a cylindrical form. A 

 cuticular border appears upon the inner extremities, and as the 



ZL Pn 



LFL- -' 



LF- 



LFL : 



Pf, 



FIG. 219. DENTAL ANLAGES FROM A HUMAN FETUS 40 MM. LONG. 

 Letters as in the preceding figure. ZFZ, anlage of the groove between the lip and 

 the mandibular process ; Pp, dental papilla ; Z, outline of the margin of the tongue. 

 x 60. (After C. Rose.) 



calcareous substance of the enamel begins to be deposited fine 

 processes are seen extending inward from the extremities of the 

 enamel cells, Thomes* processes. It is around these processes that 

 the permanent enamel is deposited to form the enamel prisms. 



