260 



THE DIGESTIVE SYSTEM 



porary teeth, which are produced by a growth and thickening of 

 the mesenchymal connective tissue cells at the site of each tooth 

 germ. This thickening of the connective tissue forms the anlage 

 . f s 9 . of the dental papilla. 



->' v-v"/\ : :y.*-X':""- "'/:-. ; : "/ ... That portion of the 



dental ridge which 

 spreads out laterally to 

 cover the dental papilla 

 of each tooth forms 

 its enamel germ, from 

 which the dental en- 

 amel is eventually pro- 

 duced. Further devel- 

 opment of the enamel 

 germ and dental papil- 

 la causes the former to 

 surround the papilla 

 like a cap. 



During the third 

 month of fetal life the 

 anlages of all the prim- 

 itive teeth are formed 

 in the above manner. 

 At about the same time, 

 also, a lateral growth 

 from the lingual side of 

 the thin portion of the 

 dental ridge which still 

 connects the enamel 

 germs with the oral 

 epithelium, forms the 

 anlages of the permanent teeth. The molars arise at a later 

 period and in a similar manner by a dorsal extension of the dental 

 ridge which grows backward through the connective tissue of the 

 alveolar process as a solid cell column from which the enamel 

 germs are formed and into which the dental papillae grow. 



Further development of the dental anlage includes the differ- 

 entiation of the enamel germ on the one hand and of the dental 

 papilla on the other. From the former the enamel and the cuticu- 

 lar membrane arise ; the latter produces the dental pulp and the 

 dentine. 



FIG. 218. DEVELOPING TOOTH FROM A HUMAN EMBRYO 



17 MM. LONG. 



LF, dental groove ; M, oral cavity ; OK, m.esoblast 

 of upper jaw; 6>Z, epithelium of the primitive upper 

 lip, and UL, of the lower lip; ZL, dental ridge. 

 x 120. (After C. Eose.) 



