118 A MANUAL OF DENTAL ANATOMY. 



The dentine germs, and consequently the dentine, are 

 indisputably derived from the connective tissue of the 

 mucous membrane immediately subjacent to the epithe- 

 lium, nor can it be doubted that the enamel organs are 

 simply the modified epithelium of that same mucous 

 membrane. 



Of course there is nothing new in this conclusion, which 

 had been already arrived at by the study of other creatures, 

 but the sharks happen to demonstrate it with more clear- 

 ness than those other animals in whom the original nature 

 of the process is more or less masked by the introduction of 

 further complexities. 



Hence it is worth while to study carefully the relations 

 of the epithelium constituting the enamel organs with that 

 of the surface of the mouth. As has been already mentioned, 

 in the normal condition of the part there is no deep fissure 

 on the inner side of the jaw, but the epithelium passes 

 across (from the interspace between the third and fourth 

 teeth in the figure) on to the protecting fold of mucous 

 membrane (c in fig.) But although the epithelium is re- 

 flected across on to the thecal fold, it is also continued 

 downwards along the inner side of the developing teeth and 

 tooth germs, giving to each a complete investment, and 

 filling up the whole interval between the tooth germ and the 

 thecal fold. The epithelium in this situation does not, then, 

 consist simply of one layer going down on the one side and 

 covering the tooth germs, and then reflected up at the 

 bottom to coat the inner side of the thecal fold, but it is so 

 arranged as to have relation only to the tooth germs ; it is 

 termed " enamel organs " because over the tooth germs these 

 epithelial cells assume a marked columnar character, and 

 are very different in appearance from the epithelium else- 

 where. 



The terminal portion of this epithelium, or, in other 

 words, the youngest enamel germ, forms a bell-like cap over 



