132 A MANUAL OF DENTAL ANATOMY. 



" enamel cells," (enamel epithelium, internal epithelium of 

 the enamel organ). 



The enamel organ, then, consists (proceeding from with- 

 out inwards) of an " external epithelium," a " stellate reti- 

 culum," a " stratum intermedium," and an " internal epithe- 

 lium," the external and internal epithelia being continuous 

 at the edges or base of the enamel organ, while at its summit 

 the external epithelium remains still, through the medium 

 of the " neck of the enamel organ," in continuity with the 

 cells of the " stratum Malpighi." 



Thus the enamel organ is entirely derived from the oral 

 epithelium, with which, by means of its "neck," it long 

 retains a connection, so that it, and whatever products it 

 may afterwards give rise to, are obviously to be regarded as 

 " epithelial structures." But it is the enamel organ alone 

 which is directly derived from the epithelium ; the origin of 

 the dentine germ is quite distinct. 



In the embryonic tissue of the jaws, some little distance 

 beneath the surface, and at a point corresponding to that 

 ingrowth of cells and subsequent enlargement of the same 

 which goes to form the enamel organ, appears the first trace 

 of a dentine germ.Q This appears as a mere increase in 

 the opacity of the part, without at first any visible structural 

 change, and it occupies the concavity of the enamel organ. 

 Thus the dentine germ appears early, indeed almost simul- 

 taneously with the formation of a definite enamel organ, but 

 the enamel organ is far in advance of it in point of structural 

 differentiation, and the earliest changes which result in the 

 formation of the enamel organ are strikingly visible before a 

 dentine germ can be discovered. According to Dursy the 



( T ) The term "dental papilla," although eminently convenient, is asso- 

 ciated with an erroneous feature of the older views upon tooth develop- 

 ment ; where it is employed in the following pages, the student must 

 guard against the misconception that free papillae at any time exist in any 

 animal. 



