DEVELOrMEXT OF THE TEETH. 315 



the future tooth-crown. It is received, into a coiTesponding dimple of 

 the enamel-germ, which now comes to resemble in form an inverted 

 cup, and fits upon the papilla (fig. 214, B,/'). 



Goodsir described the process somewhat differently. According to 

 his account the papilla3 first appear in the bottom of the undivided 

 groovo, and separate loculi are then formed for them by partitions 

 which grow across its deeper part. They thus become lodged in pits 

 which are partitioned off" at the bottom of the original groove, and this 

 .condition was termed by him the follicuJar stage. It is represented in 

 fig. 21G, and in diagrammatic section in fig. 215, Nos. 3 and 4. 



According to the same observer, the order in which the papillre appear 

 is very regular. That of the anterior milk molar is the first (7th 

 week) ; that of the canine next (8th week) ; the incisor papillae next 

 (9th week), the central before the lateral ; and that of the posterior 

 milk molar last (lOth week). The several papillse of the upper jaw- 

 appear a little earlier than the correspomling ones of the lower. The 

 groove is said to become separated by partitions in corresponding order, 

 and the follicular stage to be completed by the 14th week. The open 

 pits are next closed, and the included enamel-germ cut oflP from connec- 

 tion with the superjacent epithelium, and finally the sides of the groove 



Fis. 215. 







6 



Fig. 215. DTAGKA'M^r.'VTIO OuTLTXr,:? OF SeCTIOKS THEOUGir THE DeXTAL GeRMS AND 



Sacs, at Diffekent Stages of Development (from Goodsir). 

 1, the primitive dental groove of the lower jaw cut across in a fa>tus of about six- 

 weeks ; 2, a papiHa rising within the dental groove ; 3, 4, and 5, represent the folli- 

 cular stage in which the papilla is seen sunk within the follicle, and the lips of the 

 follicle (opercnla) advancing towards each other, gradually meet and close in the 

 follicle ; 5, may be looked upon as representing the section indicated by the line a h, 

 in fig. 216, through the sac of an incisor tooth, in which a lunated depression (o 

 is left behind ; in G,°th2 sides of the groove are seen to close ; in 7, the union of the 

 lips being complete, the follicle becomes a closed sac s, containing the dental pulp p, and 

 having behind it the lunated depression c, now also enclosed, and forming the cavity of 

 reserve for the germ of the corresponding permanent tooth ; in the remaining outlines, 

 S to 12, are shown the commencement of the cap of dentine on the pulp, the subsequent 

 steps in the formation of the milk tooth, and its eruption through the gum (11) ; also the 

 gradual changes in the cavity of reserve, the appearance of its papilla, its closure to form 

 the sac of the permanent tooth, its descent into the jaw, behind and below the milk 

 tooth, and the long pedicle (12) formed by its upper obliterated portion. The epithelium 

 which covers the gum, and also that which occupies the dental follicles and sacs, is not 

 represented in these diagi'ams. 



above the separate germs coalesce in its whole length— the process 



