170 QN LATERAL PEESSURE. 



coated with enamel, and bold in outline, but 

 almost invariably more or less irregular in posi- 

 tion. Under these conditions, in the act of 

 sucking (which becomes extremely difficult, and 

 sometimes almost impossible in the case of a very 

 deep and pointed arch), there will be 7io lateral 

 expansion of the tongue. All the effort will be 

 required to reach the apex of the vault, and the 

 tongue will be drawn up and thickened vertically. 

 Hence the action of the muscles external to the 

 arch will be to press the teeth inwards, and to 

 cause them to assume an irregular line and to 

 overlap one another; the two upper maxillae in 

 extreme cases having the appearance of being 

 compressed together inwards. 



It is under these circumstances that the con- 

 traction of the jaws will be found to follow the 

 extraction of a tooth; and it is more especially 

 desirable in this form of mouth to retain the 

 crowns of the temporary teeth in the mouth as 

 long as possible, — as close up to the period of 

 their successors coming up to replace them as 

 possible, and not to remove them unless under 

 the most urgent necessity. In all cases of re- 

 moving one tooth to make room for another, it 

 is most essential to notice the stage of the latter, 

 and not to attempt the operation until after the 

 period of its maturity, or the space may be filled 

 up in a way not intended. In the shallow palate 

 there is no fear of the arch contracting through 



