DEVELOPMENT OF THE TEETH. 



155 



the enamel-germ of each of the milk-teeth (fig. 178, D,/, and this 

 eventually becomes the germ of the corresponding permanent tooth. 

 It gradually enlarges, acquires a papilla, forms an enamel-organ, in 



FIG. 179. A SECTION THROUGH THE 



ENAMEL-ORGAN AND DENTAL SAC FROM 

 THE TOOTH OF A CHILD AT BIRTH. (250 



diameters.) (Kolliker.) 



a, outer dense layer of the dental sac ; b, inner 

 looser texture of the same with capillary blood- 

 vessels and a somewhat denser layer towards 

 the enamel-organ ; c, spongy substance ; d, 

 inner cells ; and e, outer cellular layer of the 

 enamel-organ. 



FIG. 180. PART OF SECTION OF DEVELOP- 

 ING TOOTH OF YOUNG RAT, SHOWING 

 THE MODE OF DEPOSITION OF THE DEN- 

 TINE. (Highly magnified.) 



, outer layer of fully calcified dentine ; I, un- 

 calcified matrix, with a few nodules of calca- 

 reous matter ; c, odontoblasts with processes 

 extending into the dentine ; d, pulp. The 

 section is stained with carmine, which colours 

 the uncalcified matrix, but not the calcined 

 part. 



iort, passes through the same phases of development as its parent 

 germ, and when the milk-tooth drops out of the jaw in consequence of 

 the absorption of its roots (by osteoclasts) the permanent tooth grows 

 up into its place. 



But there are six permanent teeth in each jaw which do not succeed 



