THE TEETH 



335 



^ 



. ^' ': ii '"-"'" 



If 



of which retain a characteristic epithelial appearance. The thin layer 

 formed by the uncalcified bases of the adamantoblasts, which stilL-cover 

 the free surface of the enamel at the eruption of the tooth, remains as 

 the highly cornified dental cuticular membrane (of Nasmyth). This is 

 soon lost over the crown by 

 reason of mechanical wear. l 



THE OUTER ENAMEL EPI- 

 THELIUM. T h e outermost 

 cells of the enamel germ are 

 immediately in contact with 

 the mesenchyma of the prim- 

 itive jaw. This connective tis- 

 sue forms, toward the end of 

 the third month, a vascular in- 

 vesting sheath or dental sac, 

 which incloses the entire den- 

 tal germ and finally, by grad- 

 ually encroaching upon the 

 narrow neck which still con- 

 nects the enamel germ with the 

 dental lamina, severs the con- 

 nection of these organs so that 

 the primitive tooth lies free 

 within the dental sac. The 

 outer enamel epithelium, which 

 lines all portions of the dental 

 sac except at the base of the 

 dental papilla, forms several 



FIG. 316. A PORTION OF FIG. 315, NEAR THE 

 APEX OF THE DEVELOPING TOOTH. 



a, enamel epithelium; 6, ameloblasts; c, 

 enamel; d, dentin; e, odontoblasts; /, border 

 of the dental pulp. Between the formed 

 enamel and the ameloblasts Tomes' processes 

 can be seen. Hematein and eosin. X 550. 



layers of flattened epithelial 



cells. Remnants of this cell 



layer frequently persist, in re- 



lation to the inner margin of the bony alveolus whose wall is produced 



by intramembranous ossification in the connective tissue surrounding the 



embryonic dental sac. 



THE ENAMEL PULP. This structure is produced by a remarkable 

 differentiation which occurs within the mid-portion of the enamel organ. 

 The epithelial cells of this region, which at first appear to form a 

 delicate syncytium, become separated by wider and wider intercellular 

 spaces, and are thus drawn out into stellate forms with long anastomosing 

 processes. The resulting cells closely resemble in form the connective 



