ON LATERAL PRESSURE. 163 



the deris sapientice, and the latter coming up at a 

 considerable angle to the former, and having 

 caught the overhanging enamel, has literally 

 crushed its way into and embedded a portion of 

 its crown within it, the molar having been kept 

 down in its socket by the antagonism of the upper 

 teeth consequent upon the closure of the mouth. 

 The molars of the lower jaw are more especially 

 calculated to produce this injurious pressure 

 through their line of growth being forwards as 

 well as upwards, owing to the curvature of their 

 fangs. And wherever one tooth in its eruptive 

 stage has to come up between two others which 

 are too close together, and have not left room 

 between them for it, it will have to force its way 

 to its place, or else to the inside or outside of the 

 arch, according to circumstances ; and any pressure 

 upon the fang or fangs in the way, will only lead 

 to a portion of the latter being absorbed, while 

 any part of the crowns or the necks so circum- 

 stanced almost invariably ends in the decay of 

 of one or both. This effect of lateral pressure, 

 however, must be strictly confined to the period 

 prior to the teeth having attained their full eleva- 

 tion and become antagonized with their opponents. 

 Any pressure subsequent to this stage will belong 

 to one or other of the following sections. 



In the second division, lateral pressure is pro- 

 duced by the tension of the muscles of the lips 



M 2 



