IMPLANTATION AND RELATIONS OF THE TEETH. 



1555 



teeth are all in contact with their neighbors, there being no break or diastema in the 

 upper jaw between the incisors and canines for the points of the canines of the lower 

 jaw. The canines project very little beyond the line of the free edges. The crowns 

 increase in size from the incisors to the first molars and then decrease. The ver- 

 tical distance from the gum to the free edge regularly diminishes from the median 

 incisors backward, with the exception of the canines. The lines of the teeth above 

 and below are practically of the same length. When the mouth is closed the superior 



canines lie to the outer side of the 



FIG. 1313. inferior ones, opposite the ends of 



m b c the lips ; thus the median upper 



incisors impinge on both the lower 

 ones of the same side, and the 

 upper lateral incisors strike both 

 the lower lateral and the canine. 

 In the same way the point of the 

 cusp of the upper first bicuspid 

 rests between the points of both 

 the inferior ones, and that of the 

 second on both the second lower 

 and the first molar. The first 

 upper molar has, perhaps, a quar- 

 ter of its grinding surface on that 

 of the inferior second molar, but a 

 smaller part of the second upper 

 molar rests on the lower wisdom- 

 tooth. The smaller size of the 

 upper wisdom-tooth brings its posterior border into line with that of the lower. This 

 arrangement causes the opposed crowns to interlock to a certain extent, but not so 

 closely that grinding movements cannot occur between them. The advantage of each 

 tooth coming in contact with two is evident after the loss of a tooth, as the one cor- 

 responding to it is not rendered useless. In the upper jaw the incisors have a marked 



FIG. 1314. 



Dental arches seen from before. Letters in this and subsequent 

 cuts indicate the groups of teeth : i, incisors ; c, canines ; b, bicus- 

 pids ; m, molars. 



Dental arches seen from behind. 



forward inclination, and overlap the lower, concealing nearly a third of their crowns, the 

 mouth being closed. The crowns of the upper bicuspids look pretty nearly downward 

 and those of the molars slant outward. This is very marked in the wisdom-tooth and 

 may be very slight in the first molars. The lower incisors have the front surfaces nearly 

 vertical ; the molars have an inward slant, so as to bring their axes into the same line 



