274 



STRUCTURE AND DEVELOPMENT OF THE TEETH. 



lial layer a furrow, also filled with epithelium, forms in the jaw, the dental groove, 

 which thus runs beneath the base of the dental ridge. The dental groove grows 

 deeper throughout its entire length, acquiring a form resembling the transverse sec- 

 tion of elongated formative epithelial cells; this is the enamel organ. From the 

 depth of the jaw there grows toward the enamel organ a conical papilla, formed of 

 mucous tissue, the dentinal papilla (Fig. 104, c), in such a way that its apex sup- 



FIG. 102. ,4, Section of a Tooth at the Junction (6) between Dentine and Enamel: a, enamel; c, dentinal 

 tubules; B, enamel prisms greatly magnified ; C, the same prisms in transverse section. 



ports the enamel organ like a double cap. The connecting parts of the enamel 

 organ, lying between the dentinal papillae of the separate teeth, now disappear, 

 through hyperplasia of the connective tissue, which next gradually surrounds the 

 dentinal papilla and its enamel organ as the dental sac (Fig. 104, d, Fig. 105). 

 Of the epithelial cells of the enamel-organ those (Fig. 105, 3) that cover the 

 head of the papilla as a continuous layer form cylindrical epithelium, which later, 



FlG. 103. Transverse Section of the Root: a, 

 cement, with bone-corpuscles; &, dentine with 

 dentinal tubules; c, junction between the two. 



a 



FIG. 104. a, Dental ridge; b, 

 enamel orga.n; c, site of the 

 beginning dentinal papilla; 

 d, first trace of the dental sac. 



bv calcification, hardens into the enamel prisms. The layer of cells of the double 

 cap however, which is turned upward toward the dental sac (Fig. 105, i), flatten! 

 out softens down and through a process of horny metamorphosis becomes the 

 cuticula while the epithelial cells lying between the two layers gradually under- 

 go complete atrophy through a peculiar intermediary metamorphosis in which 

 they resemble the star-shaped cells of mucous tissue (Fig. 105, 2). Accordi 



