244 



THE ORGANS 



special dental germ forms a sort of cap, the latter being known from its sub- 

 sequent function as the enamel organ, the papilla itself giving rise to the pulp 

 and dentine. The dental germs are at this stage connected with each other by 

 remaining portions of the dental shelf, and with the surface epithelium by 

 remains of the original invagination. The next step is the almost complete 

 separation of the special dental germs and ridge from the surface epithelium 

 (Fig. 146), and the formation around each special dental germ of a vascular 

 membrane, the denial sac. The attenuated strand of epithelial cells, which 



Epithelium of mouth 



} Enamel cells 



Uental sac 



Bone of jaw- 



Blood-vessel 



Remnant of 

 enamel pulp 



Papilla 



Fig. 148. — Longitudinal Section of a Developing Tooth of a New-born Puppy. 



(Bonnett.) Late Stage- 



still maintains a connection between the dental germs and the epithelium of 

 the gums, is known as the neck of the emanel organ and it is from this that an 

 extension soon occurs to the inner side of the dental gerrris of the milk teeth, to 

 form the dental germs of the permanent teeth (Fig. 147, c). Into the latter, 

 connective-tissue papillae extend as in the case of the milk teeth. There are 

 thus present as early as the fifth month of fa?tal existence the germs of allmilk 

 and of some permanent teeth. 



The ENAMEL is formed by the enamel organ. At the stage represented in 

 Fig. 149, it consists of three layers: (i) The outer enamel cells, somewhat flat- 



