268 MANUAL OF HISTOLOGY. 



name of " enamel germ" has been given (1 d). Its walls are formed of 

 narrow cells arranged perpendicularly, and its interior is taken up by 

 small round cells. 



Later on may be seen how various parts of this enamel germ (3) increase 

 in breadth at their deepest half, at those spots where the development of 

 the several dental papillae is to take place, thus preparing the way for the 

 formation of the individual enamel organs (2 d). It is the small round 

 cells of the interior just mentioned which principally occasion this enlarge- 

 ment, in that they gradually become transformed into the already well- 

 known non- vascular gelatinous tissue (fig. 181) with stellate elements (2 e). 



After this the formation of the dental germ or tooth papilla (2 / ) takes 

 place. This grows, upwards against the under surface of the enamel organ 

 belonging to it, and soon transforms the shape of the latter into that of a 

 thick cap covering it over. 



The parietes of the follicle are now laid down from the adjacent tissue 

 of the mucous membrane, but gradually and but ill-defined, and soon we 

 may recognise an external and more closely interwoven stratum (2 A), and 

 a thick internal layer of softer and looser texture (2 g), 



In fig. 257 (3) we have represented the stage of development in 

 question. At / is seen the dental germ projecting upwards, beneath 

 which the lumen of a considerable vessel appears which has been cut 

 across (i), and the commencing bony portion of the upper jaw-bone (&). 

 This germ passes continuously into the substance of the still unfinished 

 walls of the tooth follicle, whose external layer is to be seen at h, and 

 internal at g. 



But we recognise also, at the same time, that the style (d) of the 

 enamel organ (e) has become strongly narrowed, owing to the growth 

 upwards of the walls of the sac, a process which is destined to effect a 

 separation of the enamel organ from the mouth. 



But before this the formation of an organ of the future takes place from 

 the style, namely, of the secondary enamel germ. This plays the same 

 part in the rudiments of the permanent teeth as its predecessor did in the 

 formation of the milk-teeth (Koelliker). 



A leaf of epithelium is seen to spring from this style, and to sink down 

 into the tissue of the mucous membrane in a manner similar to that 

 described as occurring in the formation of the first enamel organ. This 

 leaf lies beside the latter in a central position. From this it would 

 appear that the permanent teeth have for their formation 'a new dental 

 germ, but the old enamel organ (4). 



When the further progress of this striking and interesting series of 

 changes leads to the obliteration of the stalk-like connecting bands of 

 epithelium between the summit of the enamel organ and the epithelium 

 of the jaw, we arrive at the phase of development presented to us in 

 fig. 256 : the parietal portions of the tooth sac have closed over the 

 enamel organ, covering it in. 



REMARKS. 1. Literature is very rich in essays on the development of the teeth. 

 Compare (beside the older and more recent German writings) Goodsir, in the Edin- 

 burgh Med. and Surg. Journ., 1838, No. xxxi. 1 ; Huxley, in the Quart. Journ. of 

 Microsc. Science, vol. iii. p. 149, vol. x. p. 127, and vol. xix. p. 166; Magtiot, 

 Atudes sur le dfveloppement et la structure des dents humains, Paris, 1856 ; and also 

 Comptesrendus, I860, p. 424 ; Guillot in the Annal. des scienc. nat.., 2 Sgrie, Tame 

 ix. p. 22 1 ; Jolly in the same, 3 Serie, Tome ii. p. 151 ; Robin et Magitot in the 

 Journ. de la physiologic, Tome iii. p. 1, 300, 663, and Tome iv. p. 60 ; as also in 

 the Gaz. mfd. de Paris, 1860-61, in many places. 2. For a long time Goodsir* 



