180 DIGESTION. [CHAP. xxm. 



prematurely resorted to, when there is no evidence, from its tense 

 or inflamed state, that it is offering any undue obstacle to the pro- 

 gress of the organ beneath. 



The ossification of the permanent teeth commences a little before 

 birth with that of the anterior molars, and in the course of the first, 

 second, and third years, it proceeds gradually in the incisors, the 

 canines, and bicuspids. Their position in the jaw, meanwhile, has 

 been undergoing change. The cavities of reserve, from which the 

 development of the ten anterior permanent molars proceeds, are at 

 first placed between the milk sacs and the gum ; but as the papilla 

 are formed, as already explained, they recede behind, or to the 

 inner side, and also pass deeper in the jaw, and ultimately get be- 

 neath them, acquiring by degrees their alveolar cavities, and being 

 closely and somewhat irregularly packed. As the anterior molar is 

 developed, it soon comes to occupy the tuberosity of the maxilla and 

 the base of the coronoid process in the respective jawS, and, after- 

 wards, by the lengthening of the alveolar arch, descends into place 

 on a level with those before it. As this occurs, the cavity of re- 

 serve, situated over it, furnishes the papilla and sac for the second 

 molar, which soon occupies the tuberosity or coronoid process, and 

 then descends to behind the anterior one, a portion of the cavity of 

 reserve being still left to furnish the hindmost molar or wisdom 

 tooth in the same manner. As these several teeth descend to the 

 alveolar arch, the jaw is proportionally lengthened by a suitable ad- 

 dition from behind ; so that the circular arch, of which the alveoli 

 at first consisted, is altered into an elliptical one. 



As the permanent teeth are being prepared to penetrate the gum, 

 the bony partitions which separate their sacs from those of the tem- 

 porary teeth are absorbed; the fangs of the temporary teeth are 

 removed by a very singular natural process ; and the permanent 

 teeth come to be placed directly under the now loose crowns of the 

 temporary ones, which finally detach themselves and allow the per- 

 manent teeth to take their places in the mouth. While it is impos- 

 sible not to admire the evidence of design furnished by this exqui- 

 site process, it seems sufficient to assign it physiologically to that 

 general law which determines the form and size of the several parts 

 of organized beings. It has been supposed that elongated produc- 

 tions of the cavities of reserve, which have been carried down from 

 the surface with the permanent tooth sacs, serve to re-direct them to 

 their proper places as they rise through the gum. But it may be 

 asked, what served previously to carry down the pulps aright, and 

 to form these gubernacula ? It is manifest that we must ascend to 



