THF, TEETH 



331 



During the third month of fetal life the anlages of all primitive 

 (deciduous, mill-, or temporary} teeth are formed in the above manner. 

 At about the same time, also, a posterior growth upon the lingual side 

 of the thin portion of the dental shelf which still connects the enamel 

 germs with the oral epi- f . f f ._. . . 



thelium, forms the anlages .:';,'; v /'/.: V-.'"! : ^'-'"-X ' \: X : . . 



of twenty of the permanent 

 teeth. The twelve addi- 

 tional permanent molars 

 arise at a later period and 

 in a similar manner by a 

 dorsal extension of the 

 dental lamina which grows 

 backward through the con- 

 nective tissue of the alveo- 

 lar process as a solid cell 

 column from which the en- 

 amel germs are formed 

 and into which the dental 

 papilla grow. 



Further development 

 of the dental anlage in- 

 cludes the differentiation 

 of the enamel germ 011 the 

 one hand and of the dental 

 papilla on the other. From 

 the former the enamel and 

 the cuticular epitli dial 

 membrane arise ; the latter 

 produces the dental pulp 

 and the dcntin. 



THE ENAMEL GERM. 

 The enamel germ or 



enamel organ soon differentiates into three layers: (1) an inner enamel 

 ej/i/lieUum which forms the enamel prisms; (2) an outer enamel e/nlln'- 

 I In in which lines the dental sac; and (3) an intervening enamel pulp. 



Tin; IN x KII ENAMEL EPITHELIUM. The innermost cells of the 

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

 soon become elongated and attain a cylindrical form. The nucleus 

 moves toward the distal pole, and the original basal end becomes modi- 



FIG. 311. DEVELOPING TOOTH FROM A HUMAN 

 EMBRYO 17 MM. LONG. 



LF, dental groove; M, oral cavity; OK, meso- 

 blast of upper jaw; UK, anlage of lower jaw; OL, 

 epithelium of the primitive upper lip, and UL, 

 of the lower lip; ZL, dental lamina (labiodental 

 strand). X 120. (After C. Hose.) 



