4 oo SCIENCE PROGRESS 



of (the) posterior of m2, with the middle of (the) interior 

 border of mi , will if continued forward in front of (the) incisors, 

 converge rapidly with the sagittal line similarly extended . In 

 the great apes ... a line passing through the middle of (the) 

 posterior border of M2 and the middle of (the) anterior 

 of mi is essentially parallel to the sagittal line. In the 

 Hominidae the inward curve of the toothrow normally begins 

 with the first lower molar. The axis of this tooth prolonged 

 backwards diverges rapidly from a line parallel to the sagittal 

 plane and crosses the posterior of m2 on (the) outer side of 

 (the) middle : continued still further it passes through the 

 condyle. That of the second tooth similarly prolonged, while 

 diverging slightly from a line parallel to the sagittal plane, 

 passes considerably to (the) -inner side of (the) condyle. In 

 all living genera of great apes, and in the fossil Propliothecus, 

 Dryopithecus, and Sivapithecus, the axes of the two teeth lie 

 in one line essentially parallel to the sagittal line, and passing 

 further to (the) inner side of (the) condyle than is the case 

 with the axis of m2 in the Hominidae." The reference to 

 the sagittal plane must be ignored since, according to Mr. 

 Miller, the Piltdown jaw is that of an ape ; regarded as a 

 human jaw the greater intercondylar width of necessity causes 

 a wide divergence from the median plane of the condyles. 



The foundations of this argument are very insecurely laid. 

 To begin with, there is no justification for the assumption 

 which Mr. Miller makes, that the toothrow in chimpanzees is 

 invariably straight. It is indeed commonly so, but an examina- 

 tion of a sufficiently large series of jaws will show that in some 

 the molars are ranged along a backward and inward curve, 

 and such instances I have reason to suspect are indicative of 

 racial differences. But accepting Mr. Miller's interpretation, 

 the application thereof fails, if only because the toothrow in 

 human megadont jaws is also, commonly, as straight as in 

 chimpanzees. Nor is there any justification for the statement 

 that in the chimpanzee jaw the " robust character of the 

 toothrow is carried forward through the large double-rooted 

 premolar to the strongly functional canine," while in " all 

 known Hominidae" the toothrow becomes " abruptly weakened " 

 by the conspicuously inferior size of the premolars ; for in 

 some chimpanzee jaws the premolars are emphatically small, 

 while in megadont human jaws they may be of large size. 



