v///: ///: /rx. 9-21 



J. VV,7/i. These organs are developed in the interior of a cavity, 

 tin ! iiltil follicle or oc, by means of the elements of three germs: 

 !: belonging tu the ivory, another to the enamel, and a third to the 

 eenentam. 



/'///</>. The dental follicle is an oval cavity with walls composed of 



two layers: the external is fibrous and complete; the internal, soft or 



nous, is allied at the bottom to the ivory germ. The latter is a 



prominence which is detached from the bottom of the follicle, and has the 



shape of the tooth. Its structure comprises, in the centre, delicate 



connective tissue provided with vessels and nerves, and on the surface a 



layi r of elongated cells. At the summit of the follicle, facing the ivory 



germ, is the enamel germ ; it is exactly applied to the dental pulp which it 



invests like a cap, and is composed of a small mass of mucous connective 



red by a layer of cylindrical cells, joined to the buccal epithelium 



by thv <i"l>' rini'-nliun ilt-iiti*. The cementum organ manifestly exists in the 



Foal, according to M. Magitot. The base of the ivory germ has been found, 



hut it disappears rapidly after having performed its function. 



How are the different parts of the dental follicle developed ? On the 



Borders of the maxillae the epithelium of the buccal mucous membrane 

 forms aii elongated eminence the dental ridge. Below this ridge, the 

 epithelium constitutes a bud which develops in size, and is sunk iu the 

 mucous membrane : this is the enamel germ ; it has a layer of cylindrical 

 e< 11> i-n its deep surface, and in its centre are round cells. After a certain 

 time, it is only joined to the epithelium by a very thin line of cells the 

 inti-nlnui '/- ttli#. "NVhile this enamel germ grows downwards, it covers, 

 by its base, a connective bud which rises from the mucous derma. The 

 i'Uil.s are reciprocally adapted to each other, and around them the 

 connective tissue condenses, and gives rise to the walk of the follicle. It 

 will therefore be seen, that the enamel organ is a dependency of the 

 epithelium, and the ivory organ a production of the mucous derma. 



Fonmitinn of the icury, enamel, and cementum. The ivory and enamel 

 are developed by the modification of the elements situated at the surface of 

 their !_'eim. 



It has been shown that the germ of the ivory, or dental pulp, had 

 exactly the form of the future tooth ; consequently the ivory which arises 

 from its periphery offers the shape of this tooth. The irory (dentine) is 

 constituted by the cells of the germ, which elongate, send out prolongations 

 the dental fibres that ramify and anastomose, and by an intercellular 

 substance which is impregnated with calcareous matter, is moulded around 

 tin s ti!>rcs. ami firms tin- dental canalieuli. 



The enamel is derived from the deep cells of its germ, which are 

 eln'_';ite.l and prism-shaped, and are calcified in becoming applied to the 

 surface "f the ivory. 



The cementum is develop- <1 at the expense of the walls of the follicle, 

 according to the mode of ossification of tin connective tissue. 



Eruption. As the ivory is formed, the tooth increases in length and 



presses the enamel germ upwards; the latter, constantly mmpiessi .1. 



uies atrophied, and finally d \\lcn the t ",th has reucln 1 the 



summit of the follicle. In th-- same way tin- youn^ organ pierces tho 



dental follicle and gum, and makes itrf eruption externally. 



Such is the mode of development of tin cailnc.ms teeth, and the per- 

 manent ones are formed in the same manner. There is seen, during the 

 development of the enamel germ of tho temporary tooth, u bnd detaching 



