482 STRUCTURE AND DEVELOPMENT OF TEETH. W. WALDETER. 



into the margin of the jaw, but is rendered deeper by the increased 

 elevation of the margins. I believe, however, that we must draw a 

 distinction between the small primary dental groove with its epithe- 

 lium and the true enamel germ. The latter is a secondary formation 

 which, although proceeding from the epithelium of the primary dental 

 groove, is yet distinguished from this, both by its sudden attenuation, 

 by the difference in its direction, especially in the case of the incisor 

 teeth, and by its microscopic characters. The epithelium of the den- 

 tal groove, with the exception of the deepest layer, consists of large 

 spherical or flattened transparent cells. The cells of the deepest 

 layer are columnar, and are immediately continuous with the similarly 

 formed cells situated at the periphery of the enamel germ, whilst the 

 cells at the centre of the enamel germ are dark, granular, and round. 

 Even at a later period we must still distinguish between the con 

 tinuously enlarging dental groove and the enamel germ (see fig. 

 101.) Whether the enamel germ penetrates by its <Jwn growth into 

 the blastema of the jaw, as I have described (49), or becomes more 

 deeply imbedded in consequence of an increase in height of the 

 dental walls, it will perhaps be difficult to decide. The small primary 

 dental groove superjacent to this, which is not always present, may 

 however be identified with the dental groove of Arnold (12) and the 

 primitive dental groove of Goodsir. Both overlooked the enamel 

 germ, and imagined the teeth to be developed from isolated papillse in 

 their dental groove. 



A series of remarkable changes soon take place in the more 

 deeply seated portions of the enamel germ, especially at the 

 several circumscribed spots corresponding to the later developed 

 milk teeth. The spheroidal cells forming the central part of 

 the enamel germ begin to increase with rapidity, so that the 

 germ becomes conically elongated, assuming the form of a club, 

 which is continuous by means of a relatively narrow neck 

 with the epithelial cone of the dental groove. Coincidently 

 the dentine germ increases in a contrary direction, forming 

 a club-shaped mass, and projects upwards into its base, so 

 that the enamel germ comes to invest the dental papilla like 

 a cap. The connection between the several portions of the 

 enamel germ then become dissolved, probably in consequence of 

 an increase of the connective tissue of the dental ridges, so that 

 now a special division of the enamel germ, which since the 

 time of Purkyne (14) has been called the enamel organ, cor- 



