MONSIEUR CHAUVEAU'S THEORY. 41 



of the germs of the teeth which preceded them. In 

 mammals and reptiles, and in some of the batrachia, 

 new tooth-germs are developed from portions of tlieu* 

 predecessors. 



'' 7. In all animals examined the phenomena are yerj 

 uniform. A process dips in from the oral epithelium, 

 often to a great depth, its end becoming transformed 

 into an enamel-organ coineidentally with the formation 

 of a dentine-papilla beneath it. The differences lie 

 rather in snoh minor details as the extent to which a 

 eapsnle is developed, and therefore no such generali- 

 zation as that the teeth of fish in their development 

 represent only an earlier stage of the development of 

 the teeth of mammalia can be drawn.^' 



Monsieur A. Chanvean's theory of the development 

 of tooth-germs is as follows (" Comparative Anatomy 

 of the Domesticated Animals," p. 921) : 



*' The teeth are developed in the interior of a cavity, 

 named the dental folUcla or sac, by means of the ele- 

 ments of three germs, one belonging to the dentine, 

 another to the enamel, and a third to the cement. The 

 dental follicle is an oval cavity, with walls composed of 

 two layers. The external is fibrous and complete; the 

 internal, soft and gelatinons, is allied at the bottom to 

 the dentine-germ. The latter is a prominence, which 

 is detached from the bottom of the follicle, and has 

 the exact shape of the tooth. Its structure comprises, 

 in the center, delicate connective tissne, provided with 

 vessels and nerves, and on the surface a layer of elon- 

 gated cells. At the summit of the follicle, facing the 

 dentine-germ, is the enamel-germ. It is exactly ap- 

 plied to the dentinal-pulp, which it invests like a cap. 



