THE TEETH. 



1547 



of the crowns are less deep than in the upper jaw. Sometimes the fifth cusp is wanting, 

 in which case the posterior part of the furrow does not divide and the arrangement is 

 remarkably symmetrical. Very rarely the first molar has a sixth cusp on the lingual 

 side. The first molar has five cusps in more than 90 per cent. ; the second four only 

 in more than 80 per cent. ; the third four rather more often than five. The buccal 

 cusps of the lower molars are worn down earlier than the lingual ones. 



The following tables from the independent researches of Rose ^ and of Zuckerkandl show 

 the percentage of frequency of different groupings of cusps. Although there is some discrepancy 

 in the percentages, both agree as to the most and least common arrangement in both jaws. 

 These statistics, like those of the separate teeth, apply to Europeans. (It is to be remembered 

 that a certain percentage of teeth cannot be included.) 



Cusps 

 Cusps 

 Cusps 



Upphr Jaw. 

 Molars. 



I 2 3 



 444 

 • 443 

 •433 



Per Cent. 

 Rose. Zuck. 



19.9 9.6 



28.9 28.7 



37.9 60.1 



Cusps 

 Cusps 

 Cusps 



Lower Jaw. 

 Molars. 

 I 2 3 



5 5 5 

 5 4 5 

 5 4 4 



Per Cent. 

 Rose. Zuck. 



^•5 

 305 

 50.0 



19.8 



3o^4 

 40.4 



The/angs of the first and second upper molars are two buccal and one lingual, 

 which latter is much the largest. It is often, especially in the first molar, grooved 

 on the lingual side. It is conical and strongly divergent. It often shows a tendency 

 to subdivision, which may actually occur, although rarely. The two buccal ones are 

 compressed antero-posteriorly and nearly vertical. The front one is the broader, and is 

 grooved before and behind. This is often the case with the other. The roots of the 

 upper wisdom-tooth are smaller ; the lingual is less divergent, and may be connected 

 by a plate with one of the buccal ones. AH may be fused more or less completely into 

 The roots of the inferior molars are two : an anterior and a posterior, of which 



one. 



Fig. 



i3o5^ 



B 



the former is rather the larger, both compressed from before 

 backward and, especially the first, deeply grooved, suggesting 

 the fusion of two. Sometimes, again especially in the first, 

 each root is bifid. Those of the wisdom-tooth are usually 

 nearer together, and are frequently fused into a common coni- 

 cal root. Apart from their position in the jaws, the roots of 

 the molars, excepting the upper wisdom-tooth, have a back- 

 ward slant of varying degree. Their twists and curves are 

 remarkably uncertain. Sometimes they converge and some- 

 times diverge unduly, hooking in either case under bone, so 

 as to make extraction difficult or impossible. The p?///)- 

 cavity of the molars is large, especially at the level of the 

 neck. In the upper teeth it is distinctly wider transversely 

 than from before backward. It has as many prolongations 

 towards the surface as there are cusps. There is a canal in 

 each root of the upper teeth. Those in the buccal fangs are 

 compressed, that in the lingual cylindrical. The anterior 

 fang of the lower molars has two canals which develop from 

 a single one. The posterior fang has but one. 



The milk molars are two in number. Like the perma- 

 nent ones, the lower are the larger ; but, unhke them, the 

 second tooth is larger than the first in both jaws. The crown 

 of both first molars presents a prominence on the buccal sur- 

 face near the root. The crown of the first upper molar is 



rather suggestive of a bicuspid, although there are two buccal cusps and one lingual. 

 The first inferior molar is relatively narrow and long from before backward. The 

 length of the buccal side is greater than that of the second permanent one. The 

 second molars resemble very closly the first permanent ones. The upper has four 

 cusps and a cingulum, the lower five cusps. The hollow in the crown of the tem- 

 porary molars is relatively deeper than that of the permanent ones, but smaller and 

 more divergent. They straddle the crowns of the developing bicuspids. 



^ Anatom. Anzeiger, Bd. vii., 1892. 



Temporary molar teeth 

 (.4, first; B, second) of left 

 side. Triturating surfaces of 

 crowns also shown. {Leidy.) 



