534 



THE EVOLUTION OF THE HUMAN FOOT. 



cite first the alreacl}^ mentioned diminution, in the arboreal apes, of 

 the angle which the bod}^ of the bone makes with its head, and we will 

 also cite that peculiar torsion of the head of the astragalus, the major 

 axis of which is in man directed from above downward and from with- 

 out inward, while it tends to become horizontal in arboreals with feet 

 having- no arch, the apparent torsion in man being raanifestlA^ due to 

 the approximation of the great toe and the upward thrusting of the 

 lesser process of tlie calcaneum. 



Another very important modification is one to which M, Testut had 

 the merit of first calling attention; that is, the displacement of the 

 axis of the trochlear surface of the astragalus. Since the arboreal 

 apes have an inturned foot they have an astragalus whose trochlear 

 axis tends to occup}" a position farther and farther from the anatom- 

 ical axis. In man, because the foot has changed to a position at right 

 angles to the limit, the axis of the trochlear surface tends to approach 

 the anatomical axis nearer and nearer; that is to say, to coincide with 

 the ])isector of the angle C (fig. 11). By this character, too, the infe- 

 rior human races present, as 

 always, interesting features of 

 T-TTi /ni f^ r resemblance to the arboreal an- 



ili\ / ^ \ \ (^ ^ \ cestors. Since the trochlea of 



the astragalus fits, as is well 

 known, into the tibial mortise, 

 when its axis is displaced it must 

 iiecessarilv involve modifications 

 in the position and form of the 

 tibia which has for this reason 

 suffered a certain torsion from 

 without inward, whose efi^ects are shown even as far vip as the femur 

 (see fig. 1-i). 



To conclude, the position of the foot is modified by the develop- 

 ment of the arch — in climbers the sole is turned inward, in man it is 

 flat on the ground. It follows that the inferior tibial mortise must 

 look inward in the first, while in the two last it is horizontal, and here 

 again the negro stands between the European and the gorilla. 



1 do not wish to abuse 3"our patience longer, but, in terminating 

 this too long exposition, in which the great abundance of details, on 

 which 1 have been unable to expatiate, has, perhaps, been tiresome 

 and difficult to follow, I think it will be useful to recapitulate and to 

 sketch, in conclusion, what I understand to have been the course of 

 development of the human foot. 



The foot of nionkeys, as you have seen, shows a number of charac- 

 ters, which may be summarized as follows: 



It is turned inward, it is flat, its articulations are loose and mol)ile, 

 its first toe is mobile and separated. From these general characters 



Fig. 14. — Lower end of the tibia (a, rear view; B, view 

 from below). I, Gorilla. 11, Xegro. Ill, European. 



