320 THE SOLIDS. 



second the special development of their several constituents 

 will be treated of. 



Into the various particulars in reference to the general 

 development of the teeth as organs, it would be inconsistent 

 with the design of this work t^ enter at any length. It will 

 be sufficient to observe that preparations are made for the 

 formation of the milk teeth at a very early period of intra- 

 uterine life ; that the first trace of the future tooth is mani- 

 fest in the form of a papilla placed in the primary dental 

 groove, and consisting of granular and nucleated cells ; that 

 around this papilla a membrane is developed, with an open 

 mouth, thus forming a follicle ; from the margins of this aper- 

 ture processes of the mucous membrane, of which the follicle 

 is constituted, are developed, and these uniting with each 

 other close the opening, and convert the follicle into a 

 sac. With the closure of the mouth of the follicle, the first 

 or follicular stage of the development of the teeth is ter- 

 minated, and the second or saccular stage commences. The 

 number of opercula developed from the margins of the follicles 

 is determinate, being two for the incisives, three for the 

 canines, and four or five for the molars. In the second or 

 saccular stage, the papilla takes the form of the tooth, of 

 which it is the representative, the base dividing in the case 

 of the molars into fangs, and its apex assuming the shape of 

 the crown of the tooth, in the place of which it stands : in 

 this stage also a blastemic matter, consisting of plasma and 

 nucleated cells is developed in the space intervening between 

 the papilla and the sac, and adherent to the inner surface of 

 the membrane of the latter, by which indeed it is generated ; 

 lastly, the papillae become capped with tooth substance or 

 dentine. 



With the passage of the teeth through the gums the 

 saccular stage terminates, and the third or eruptive stage is 

 entered upon. 



The second or permanent teeth pass through stages pre- 

 cisely similar to those of the first or milk teeth, the papilla? 

 and follicles being developed in crescent-shaped depressions 

 placed in the posterior walls of the follicles of the milk 



