1558 



HUMAN ANATOMY. 



dental ledge becomes more and more attenuated until finally it is broken ; its remains 

 appear for some time as nests or islands of epithelial cells embedded within the young 

 connective tissue of the alveolar border. 



The Dental Papilla. — This structure first appears shortly after the beginning 

 expansion of the club-shaped developing enamel-organ as a condensation of the meso- 



FiG. 1317. 



B 



Detital ledge 



Thickened 

 oral epithelium 



Labio-dental 

 strand 



Dental ledge! 



Enamel- 

 organ 



Inner layer 

 of enamel- 

 organ 



Dental 

 papilla 



Epithelial 

 sheath 



Frontal sections, showing four early stages 



tooth-developmenl. 



A, j5, X too; C, D, X 60. 



blast beneath the epithelial ingrowth. The papilla consists for a time of a close 

 aggregation of small, round, proliferating cells ; with the differentiation of the layers 

 of the enamel-organ, the elements occupying the periphery of the dental papilla 

 become elongated and arranged as a continuous row of cylindrical cells over the api- 

 cal portion of the papilla beneath the capping enamel-organ. These cylindrical meso- 

 blastic cells are the odontoblasts, the active agents in the formation of the dentine. 



