1546 



HUMAN ANATOMY. 



The Molars. — These teeth — three on each side — are distinguished by the large 

 crown, into which the neck expands, the number of cusps on the surface, and the 

 greater subdivision of the root. Those of the lower jaw are the larger ; and in both 

 jaws the first is the largest and the last (called from its late appearance the wisdom- 

 tooth) the smallest. The crow?is are convex on both the buccal and lingual sides, 

 but nearly plane on the others. The enamel ends in a nearly straight line all the way 

 round. The grinding surfaces are four-sided ; those of the upper are somewhat dia- 

 mond-shaped, the buccal anterior angle being rather in front ; those of the lower are 

 nearly parallelograms, the long diameter being antero-posterior. Typical upper 

 molars have four cusps at the angles ; typical lower ones have an additional cusp at 

 the posterior border ; but in the upper jaw the first is the only one that can be called 

 typical. 



In the upper molars the largest cusp is the anterior lingual, which is connected 

 by a ridge (the cingulum) to the posterior buccal. The posterior lingual cusp is the 

 smallest. A minute rudimentary cusp is found on the lingual surface of the anterior 

 lingual cusp, usually too small to reach the grinding surface, and often hard to recog- 

 nize. Not counting this, the first upper molar has four cusps in more than 90 

 per cent. Owing to the cingulum, the grooves on the grinding surface are best 

 described as two oblique ones, the first from the anterior border to the middle of the 



Fig. 1303. 



A B 



First 



First 



Fig. 1304. 

 Upper molars 



Another first 

 Lower molars 



Another first 



Second 



'Ui^ 



Second 



Second molar teeth of left 

 side, labial {A) and lateral 

 {B) aspects. (Leidy.) 



Triturating surfaces of molar teeth of right 

 side. The upper margin of the figures corresponds 

 to the labial surface. ( Leidy. ) 



buccal, the second from the lingual border to the middle of the buccal. They are 

 deepest at the middle. They appear on the buccal and lingual sides, deeper on the 

 former, but rarely reach the gum. They may end in a pit, a favorite seat of caries 

 (Tomes). The crown of the second upper molar presents three chief forms (Miihl- 

 reiter). It may have four cusps and differ but slightly from the first molar. The 

 lingual surface is relatively narrower and the posterior lingual cusp smaller. In the 

 second form the last-mentioned cusp is wanting. The cingulum persists and the 

 grinding surface is approximately triangular. The third form is compressed from 

 side to side into a very narrow diamond, with the anterior buccal cusp in front and 

 the posterior lingual behind. Three and four cusps are about equally common in this 

 tooth in Caucasians, but the lower races have more often four. The crown of the 

 upper wisdom-tooth presents many remarkable variations. The posterior lingual 

 cusp is wanting in about two-thirds of the cases. The crown may be strongly com- 

 pressed, as has been described for the second molar, but with greater variation. In 

 size the wisdom-tooth may be very large or very small. 



The crowns of the lower molars are divided by a crucial fissure, the main line 

 running antero-posteriorly. The hind part of this splits so as to enclose the fifth 

 cusp, which is near or actually at the buccal side. The effect of this is to form a 

 cavity at the crossing of the lines in the middle of the crown. The lines on the sides 



