THE DEVELOPMENT OF THE TEETH. 



117 



other, with that clothing the convexity of the jaw and giving 

 attachment to the teeth. 



No sharp line of demarcation at any time marks off the 

 base of the dentine papilla from the tissue which surrounds 

 it, and from which it springs up, as would be the case in 

 mammalian or reptilian tooth germs ; all that can be said 

 is, that the dentine germs are cellular, the cells being large 



FIG. 57 ( ! ). 



and rounded, while in the rest of the mucous membrane 

 the fibrillar elements preponderate, so that it passes by 

 imperceptible gradations into the densely fibrous gum, found 

 on the exposed border of the jaw. 



(!) Transverse section of lower jaw of a Dog-fish, a. Oral epithelium. 

 6. Oral epithelium passing on to flap. c. Protecting flap of mucous mem- 

 brane (thecal fold), d. Youngest dentine pulp. e. Youngest enamel 

 organ. /. Tooth about to be shed. y. Calcified crust of jaw. 



