DEVELOPMENT OF THE TEETH. 



the subjacent mucous structure is wedge-shaped, so that its 

 section has the form of a V. 



As soon as this primitive band is formed, which occurs at 

 the sixth or seventh week, a flat band projects from its inter- 

 nal surface, near the mucous structure, which Legros and 

 Magitot call the epithelial band. This also extends over the 

 entire length of the jaws. It is thin, flattened, with its free 

 edge curved inward and toward the jaw, and is composed, at 

 first, of a central layer of polygonal cells, covered by a layer 

 of columnar epithelium. 



At certain points, these points corresponding to the situa- 

 tions of the true dental bulbs, there appear rounde(J enlarge- 

 ments at the free margin of the epithelial band just de- 

 scribed. Each one of these is developed into one of the 

 structures of the perfect tooth. The mechanism of the for- 

 mation of this, which is called the enamel-organ, and of the 

 dental bulb is as follows : 



A rounded enlargement appears at the margin of the epi- 

 thelial band. This soon becomes directed downward (adapting 

 our description to the lower jaw) and dips into the mucous 

 structure, being at first connected with the epithelial band by 

 a narrow pedicle, which soon disappears, leaving the enlarge- 

 ment enclosed completely in a follicle. This is the dental 

 follicle, and has no connection with the wedge-shaped band 

 which we described first. While this process is going on, a 

 conical bulb appears at the bottom of the follicle. The enam- 

 el-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 the enamel ; the dental bulb, 

 which is provided with vessels and nerves, becomes the 

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

 dentine, or ivory, is developed in successive layers. The 

 cement is developed by successive layers upon that portion of 



