ON LATERAL PEESSUBE. 167 



the jaws to exjpand^^^ and the consequent separation 

 of the temporary teeth which they contain. But 

 if we take a similar section of a case of irregu- 

 larity, we shall find a very different state of 

 things. 



Fig. 18. 



The form of the palate in Fig. 18 will at once 

 indicate the absence of any support on the teeth, 

 being derived from the pressure of the sides of 

 the tongue ; and wanting this, it leaves them, as 

 regards the position they assume, at the mercy of 

 some other force which then regulates the forma- 

 tion of the dental arch. 



If a lower incisor be removed on account of 

 irregularity, or if a bicuspid be extracted from the 

 upper jaw to make room for the cuspid, what is 

 the power which causes the teeth to fill up the 

 space in the one case, and brings the cuspid into 

 the vacancy in the other ? It will not be the force 

 of growth in the case of the lower incisors, because 

 these teeth will be fully grown before such a pro- 

 ceeding would be Seemed necessary. In the case 

 of the cuspid, it might be supposed, on a super- 

 ficial view of the matter, to be capable of effecting 

 it. But were the upper lip to be held up and 

 prevented from touching the cuspid, I have no 



