DETERMiyA I l(t.\ (>1-A(,1:L\ HATls. •_'-;.-> 



of the individual almost as clearly as m'. The third (last) molar 

 is somewhat deaeneratt'd, and both lor this reason and owing to its 

 position farthest batk in the row the five stages of wear described 

 above are not nearly so sharply separated from each other as in the 

 case of m' and m". The posterior premolar behaves somewhat 

 ditierently from the molars ; its sharply pointed cusp is the highest 

 in the postcauine row, and its function is no doubt (so long as it 

 retains this shape) chiefly to keep the food in position while it is 

 acted upon by the molars ; being not a " crusher"' like the molar, 

 but rather (together with the canine) a "fork," it is differently 

 afiected by the wear ; in the earlier years of the individual it is 

 more slowly worn than the molars, but a time comes (usually some- 

 where about the fourth stage) when the originallj- high cusp is 

 worn low and at the same time all molars much flattened down, and 

 it would seem that now the animal finds it advantageous to use it 

 more as an additional crusher ; from this period onwards it wears 

 down much more quickly ; as an indicator of age it is on the whole 

 too capricious, too irregular in wear. The anterior premolar is a 

 small rudiment ; and the only remark it calls for in this connection 

 is that, in spite of its minute size, it cannot be functionless ; it is 

 eas}'^ to see that it is acted upon by the high cusp of the posterior 

 lower premolar, and it shows progressive stages of wear like all 

 other teeth (with one exception pointed out below) ; even in extreme 

 old age it is never absent. The upper canines are so simple, hook- 

 like in shape, as to be of little value for our present investigation ; the 

 sharply pointed tip is, of course, worn blunt and the tooth graduallj' 

 shortened, but it follows rather the rule of the posterior upper pre- 

 molar, i.e., the effect of the wear is slower in the earlier than in the 

 later years, and the progress of the w^ear is somewhat irregular ; in 

 the majority of sktills in the second stage the tip of the canine is 

 clearl}^ slightly blunt, but there are other skulls in the same stage 

 in which the canines would be hard to distinguish from those in the 

 first stage. The minute upper incisors show very distinct signs of 

 wear ; they bite, not against the lower incisors (which close in far 

 in front of the upper ones), biit against the inner cingulum of the 

 lower canines. The lower molars have a simple W-shape, i.e., three 

 cusps (1, 2, and 3) on the inner, two (4 and 5) on the outer side, 

 cusp 6 and the heel (7) are absent ; but in spite of the fact that 

 they are considerably less complicated than the upper molars, I find 

 that any of them might be used to measure the wear and age of the 

 individual, though they are much more difficult guides than the 

 first and second upper molars. The rudimentary middle lower pre- 

 molar is usually squeezed out to the external side of the tooth row, 

 though occasionally (in about 15 per cent, of the individuals) it is 

 halfway or completely in row ; it is sometimes external on one 

 side of the jaw. more or less in row on the other ; though even 



