26 MICROSCOPIC ANATOMY OF THE TEETH 



the vertically directed labio-dental lamina and the hori- 

 zontally placed dental lamina or tooth-band. 



Prominences arise on the tooth-band, near to, but not 

 at the margin of the lamina, on its labial aspect. These 

 prominences become the enamel organs of the milk teeth. 

 The free margin of the lamina behind these germs gives rise 

 to the sticcessional permanent teeth, the permanent molars 

 being formed from that portion of the lamina which grows 

 backwards beyond the limits of the milk dentition. 



The germs of the teeth become separated and detached 

 from the lamina by the absorption of the connecting bridges. 



Each dentine germ or papilla is formed beneath the cap of 

 the enamel organ, and is produced in the mesodermic tissue, 

 which, according to Dursy, is differentiated as a continuous 

 opaque band round the jaws, corresponding to the epithelial 

 dental lamina from which the enamel is formed. 



These papillae appear in the band in the positions corre- 

 sponding to those of the future teeth, while the intermediate 

 portions become atrophied and disappear like the bridges 

 of the epithelial lamina. 



The margins of the dentine germ are described as grow- 

 ing up and around the epithelial enamel organ, forming 

 the tooth-sac from which the cement and periodontal 

 membrane are produced. It is doubtful if this is a correct 

 description, and this enclosure of the enamel germ may 

 with more probability be considered to be due to the con- 

 densation and proliferation of the surrounding connective 

 tissue. 



The histology of the enamel and dentine organs and the 

 tooth follicle will be described in another chapter. 



The accompanying table carries the development of the 

 teeth up to the time of birth. The eruption of the permanent 

 teeth will be better considered in works on dental anatomy ; 

 no work on the histology of the teeth would, however, be 

 complete without some account of the development of these 

 organs. 



In fig. 9 is shown the tooth germs in their crypts in the 

 upper jaw of a foetal pig, and in fig. 10 a more advanced 

 germ from the pig in which the calcification of the dentine 

 and enamel is further advanced. 



