94 Darwin, and after Darwin. 
these genera together, it appears that the number 
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 humcrus.—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- 
