THE JAW OF THE PILTDOWN MAN 403 



connection. But all chimpanzee teeth agree in that the 

 protoconid and metaconid are united by a broad ridge showing 

 a steep face posteriorly, and a deeply grooved upper surface 

 (fig. 3, B). This is a feature which never occurs in human 

 teeth where the ridge slopes gradually to the bottom of a 

 cruciform valley, while in chimpanzee teeth the centre of the 

 crown is occupied by a cup-shaped depression. Traces of this 

 depression are to be found in some megadont human jaws, 

 apparently also in the Piltdown jaw. Traces of the groove 

 at the top of the ridge connecting the protocone with the 

 metacone occur commonly in human molars. The cruciform 

 valley, characteristic of the human molar, cuts the crown 

 into four subequal moieties : this is never the case with the 

 chimpanzee molar ; since when lines answering to these valleys 

 are drawn across the tooth, the transverse crosses the longi- 

 tudinal axis obliquely. 



Not the least characteristic feature of the worn surface 

 of the teeth is the extreme thinness of the enamel, wherein 

 thej'' differ most emphatically from the teeth of the Piltdown 

 jaw and from modern human teeth. Yet, curiously enough, 

 Mr. Miller brushes this point aside as of no importance. And 

 no less characteristic is the condition of the grinding surface 

 of the crowns of worn molars of the chimpanzee. Contrary 

 to Mr. Miller, I have in no single instance yet found these 

 teeth with the surface worn to a perfectly level table at right 

 angles to the vertical axis of the tooth. This is a common 

 feature of human teeth, and is most conspicuous in those of 

 the molars of the Piltdown man. In those of the chimpanzee, 

 on the contrary, the outer sides may be worn down to the 

 very base of the enamel while the cusps of the inner side are 

 reduced to no more than half their original height. That the 

 molars of the chimpanzee should occasionally present a per- 

 fectly flat surface need occasion no surprise, since, on the 

 other hand, human teeth occasionally present the obliquely 

 worn surface characteristic of the Chimpanzee, as for example 

 in the case of the Moriori and some ancient Egyptians. This 

 being so, the extremely flat surfaces of the crowns of the 

 Piltdown molars should have given Mr. Miller occasion for 

 reflection, having regard to the rule which undoubtedly 

 obtains among the chimpanzees in this particular. At least 

 it should have occurred to him that the wear of the teeth 



