DEVELOPMENT OF THE TEETH. 



829 



this process is going on, a conical bulb appears at the bottom of the follicle. 

 The enamel-organ, formed from the epithelial band, becomes excavated, or 

 cup-shaped, at its under surface, and fits over the dental bulb, becoming 

 united to it. 



The tooth at this time consists of the dental bulb, with the enamel-organ 

 closely fitted to its projecting surface. The enamel-organ is developed into 



10. 



FIG. 310. Temporary and permanent teeth (Sappey). 



1, 1, temporary central incisors; 2, 2, temporary lateral incisors ; 3, 3, temporary canines ; 4, 4, tempo- 

 rary anterior molars ; 5. 5, temporary posterior molars ; 6, 6, permanent central incisors ; 7, 7, per- 

 manent lateral incisors; 8, 8, permanent canines; 9, 9, permanent first bicuspids ; 10, 10, permanent 

 second bicuspids ; 11, 11, first molars. 



the enamel ; the dental bulb, which is provided with vessels and nerves, be- 

 comes the tooth-pulp ; and upon the surface of the dental bulb, the dentine 

 is developed in successive layers. The cement is developed by successive 

 layers, upon that portion of the dentine which forms the root of the tooth. 

 As these processes go on, the tooth projects more and more, the upper part 

 of the wall of the follicle gives way and the tooth finally appears at the sur- 

 face. 



The permanent teeth are developed beneath the follicles of the tempo- 

 rary, or milk-teeth. The first appearance is a prolongation or diverticulum 

 from the enamel-organ of the temporary tooth, which dips more deeply into 

 the mucous structure. This becomes the enamel-organ of the permanent 

 tooth ; and the successive stages of development of the dental follicles and 

 the dental pulp progress in the same way as in the temporary teeth. As 

 the permanent teeth increase in size, they gradually encroach upon the roots 

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