94 Darwin, and after Darwin. 



these genera together, it appears that the numbei 

 of cusps is being reduced from behind forwards ; 

 the chimpanzee having lost one of them from the 

 third molar, while man has not only lost this, but 

 also one from the second molar, and, it may be added, 

 likewise partially (or even totally) from the first molar, 

 as a frequent variation among civilized races. But, on 

 the other hand, variations are often met with in the 

 opposite direction, where the second or the third 

 molar of man presents five cusps in the one case 

 following the chimpanzee, in the other the gorilla. 

 These latter variations, therefore, may fairly be re- 

 garded as reversionary. For these facts I am indebted 

 to the kindness of Mr. C. S. Tomes. 



(10) Perforations of the humerus. The peculiarities 

 which we have to notice under this heading are two in 

 number. First, the supra- condyloid foramen is a nor- 

 mal feature in some of the lower Quadrumana (Fig. 25), 

 where it gives passage to the great nerve of the fore- 

 arm, and often also to the great artery. In man, how- 

 ever, it is not a normal feature. Yet it occurs in a 

 small percentage of cases viz., according to Sir W. 

 Turner, in about one per cent., and therefore is regarded 

 by Darwin as a vestigial character. Secondly, there is 

 inter-condyloid foramen, which is also situated near 

 the lower end of the humerus, but more in the middle 

 of the bone. This occurs, but not constantly, in apes, 

 and also in the human species. From the fact that it 

 does so much more frequently in the bones of ancient 

 and also of some savage races of mankind (viz. in 20 

 to 30 per cent, of cases), Darwin is disposed to regard 

 it also as a vestigial feature. On the other hand, Prof. 

 Flower tells me that in his opinion it is but an ex- 



