* DEVELOPMENT OF THE TEETH. 115 



Fig. 26. twelve montlis, it has progressed to a 



considerable extent upon these as well as 

 upon the incisors and the lower cuspi- 

 dala. At the sixth or seventh year of 

 age the whole of the permanent teeth are 

 more or less ossified, and the incisors are 

 so far completed as to be nearly ready to 

 make their appearance through the gum. 

 At this period there are no less than 

 forty-eight teeth in the two jaws, the twenty deciduous and 

 the twenty-eight permanent, which are in different degrees of 

 development. The last molars do not begin to ossify till the 

 ninth year, and are the last of all to make their appearance 

 through the gum, whence they have received the name of denies 

 sapientice or wisdom teeth. 



— The permanent teeth, which are more in number and 

 individually of larger size and form a larger arch than the 

 temporary, are developed at successive intervals, so as to 

 correspond exactly, with the increasing size of the jaws from 

 the infantile to the adult state. Hence they cannot correspond 

 in position with the deciduous teeth ; the outer permanent 

 incisor will rise up near the cuspidatus, and the permanent 

 cuspidatus near the first molar of the deciduous set. 

 — Exactly in proportion as the bodies of the permanent teeth 

 are completed and approach the gum, the roots of the decidu- 

 ous are removed by absorption, till finally the bodies of the 

 latter only are left fixed mechanically in the gum, and are 

 tumbled off" at the slightest effort. The process of the removal 

 of the fangs is not perfectly understood ; it is not as was once 

 supposed produced by the pressure of the subjacent tooth, for 

 very frequently the commencement of absorption is at the 

 neck, and not at the root of the tooth, where no pressure can 

 come, and occasionally takes place even where the germ of the 

 permanent tooth has been destroyed. It is more probably 

 owing to the enlarged vessels of the growing permanent teeth, 

 which come from the same branch with those of the deciduous, 

 carrying off" all its blood by derivation, which leads to the 



