488 ORGANS OF DIGESTION, 



mechanical pressure, but is a particular process in the animal 

 economy.* In farther proof, however, Mr. Hunter has seen two 

 or three jaws where the second deciduous grinders were shed- 

 ding by the decay of their roots, without there being under- 

 neath any tooth to press upon them ; and in another jaw he ob- 

 served the same circumstance in both grinders. In a female 

 patient, in whom the last temporary molar was loose, and was 

 pulled out in consequence, it was not succeeded by another 

 tooth. One of these patients at the time was aged twenty, and 

 the other thirty; from which it would appear, that though the 

 wasting of the fang of a deciduous tooth does not depend upon 

 the pressure of the permanent one, yet the latter determines, 

 in some measure, its expulsion, as, without some such influence, 

 the period of shedding would not have been so late. 



From these observations of Mr. Hunter, it would appear, 

 that the pressure of the permanent tooth is not indispensable to 

 the removal of the deciduous one in all cases ; yet I think it 

 will be most frequently found that much of the decay of the 

 root of the deciduous tooth is owing to its being absorbed by 

 the pressure of the body of the permanent one. The alveoli 

 of the latter, judging from my own observations, are seldom 

 so perfect towards the period of their protrusion as to form a 

 complete separation of the two orders of teeth, and even when 

 the alveoli are perfect, they are made to press upon the root of 

 the deciduous tooth by the evolution of the body of the perma^ 

 nent. 



Besides the deciduous teeth being loosened, as stated by Mr K 

 Hunter, by the absorption of their alveolar cavities while the 

 fangs are dissappearing, the following process occurs. The 

 permanent teeth protrude within the circle of the deciduous, 

 the arch of the latter is weakened, and its several pieces are in 

 that way detached by a force acting from within outwards; 

 this influence being much assisted by the obliteration of the al- 

 veolar cavities proceeding principally at their outer circumfe- 

 rence. The latter, however, is not so obviously the case with 

 the molar as with the incisive and canine teeth. 



The deciduous teeth, even before they are loosened by the 

 absorption of their fangs and of their alveolar processes, are 

 much more easily extracted in proportion than the adult teeth, 



Hunter, loc. 



