38 TOOTH-QERMS. 



germ and the deiitine-germ. The existence of a spe- 

 cial cement-germ is very doubtful, some writers assert- 

 ing, others denying its existence. * * * 



'' Tooth-germs are never formed upon the surface, 

 but are situated a httle distance beneath it, lying in 

 some animals at a considerable depth. Every known 

 tooth-germ consists in the tirst instance of two por- 

 tions, and two only, the enamel and dentine germs. 

 These are derived from distinct sources, the former 

 being a special development from the epithelium of 

 the mouth, the latter from the more deeply lying parts 

 of the mucous membrane. Other things, such as a 

 tooth-capsule, may be subsequently and secondarily 

 formed. The existence of an enamel-organ in an early 

 stage is independent of any subsequent formation of 

 enamel by its own conversion into a calcified tissue, for 

 I have shown it to be found in the germs of teeth 

 whicli have no enamel; in fact, in all tooth-germs 

 whatever. 



"That part of the tooth-germ destined to become 

 dentine is often called the dentine papilla, having 

 acquired this name from its papilliform shape; and in 

 a certain sense it is true that the enamel-organ is the 

 epithelium of the dentine papilla. Yet, although not 

 absolutely untrue, such an expression might mislead 

 by implying that the enamel organ is a secondary de- 

 velopment, whereas its appearance is contemporaneous 

 "with, if not antecedent to, that of the dentine-germ. 

 The most general account that I am able to give of the 

 process is, that the deeper layer of the oral epithelium 

 sends dow^i into the subjacent tissue a process, the 

 shape and structure of whicli is, in most animals, dis- 

 tinguishable and characteristic before the dentine- 

 germ has taken any definite form. This process en- 



