Now, in addition to these there are other respects in which the dwindling condition of wisdom-teeth is manifested--particularly with regard to the pattern of their crowns. Indeed, in this respect it would seem that even in the anthropoid apes there is the beginning of a tendency to degeneration of the molar teeth from behind forwards. For if we compare the three molars in the lower jaw of the gorilla, orang, and chimpanzee, we find that the gorilla has five well-marked cusps on all three of them; but that in the orang the cusps are not so pronounced, while in the chimpanzee there are only four of them on the third molar. Now in man it is only the first of these three teeth which normally presents five cusps, both the others presenting only four. So that, comparing all 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 regarded as reversionary. For these facts I am indebted to the kindness of Mr. C. S. Tomes. [Illustration: FIG. 24.--Molar teeth of lower jaw in Gorilla, Orang, and Man. Drawn from nature, nat. size (_R. Mus. Coll. Surg._).] (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 normal 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, however, 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 expression of impoverished nutrition during the growth of the bone. [Illustration: FIG. 25.--Perforation of the humerus (supra-condyloid foramen) in three species of Quadrumana where it normally occurs, and in Man, where it does not normally occur. Drawn from nature (_R. Coll. Surg. Mus._).]