4 o2 SCIENCE PROGRESS 



so uniform a character that observations made on one jaw 

 will apply to all chimpanzee jaws. As a matter of fact, variety 

 in the details of the contour of the crowns, and in the size 

 of the cusps, as well as in the actual size of the teeth, show as 

 great a range as in human jaws. Commonly the long axis 

 of the lower molars of the chimpanzee exceeds that of the 

 transverse axis, as is also the case in some modern human 

 jaws, but it is by no means unusual to find teeth wherein these 

 axes are equal, as is the rule in modern human teeth. 



Even where the teeth of the chimpanzee are as large as 

 those of the Piltdown jaw, and such cases are rare, there is 

 no difficulty in distinguishing between the molars of the ape 

 and those of the man. In the Piltdown jaw the protoconid, 

 metaconid, and hypoconulid are conspicuously larger than 

 in those of the largest chimpanzee tooth, and these differences 

 are still more marked in the case of the normally smaller teeth 

 characteristic of the chimpanzee. Furthermore, the sulci 

 dividing the cusps one from another are longer, and far more 

 conspicuously marked, than in any human teeth, including the 

 teeth of the Piltdown jaw (fig. 3, B). The widest part of the 

 crown, in the chimpanzee tooth, is immediately above the 

 roots, the grinding surface being conspicuously less in diameter. 

 In human teeth, including the teeth of the Piltdown jaw, the 

 crown passes almost insensibly into the root, and is not 

 perceptibly wider or longer at its base than at its grinding sur- 

 face ; the reverse is the case with the molars of the chimpanzee. 

 It is idle indeed to pretend that the molars of the chimpanzee 

 are indistinguishable from those of the Piltdown jaw. As 

 Prof. Keith has already remarked, radiographs of the Piltdown 

 jaw show that they are of the typical " taurodont " type, 

 therein differing conspicuously from the molars not only of 

 the chimpanzee but of all the great apes. 



A careful study of the unworn chimpanzee molars carried 

 on side by side with human molars, also unworn, will speedily 

 show yet other important differences between them. Those 

 of the chimpanzee differ, for example, emphatically from all 

 human teeth in having the external cusps — protoconid, hypo- 

 conid, and hypoconulid — sharply denned by deep sulci (fig. 3, B), 

 and this is true even where the hypoconulid is degenerate. The 

 contours of the grinding surface at their circumference vary 

 so widely that no importance can be placed thereon in this 



