THE EVOLUTION OF THE HUMAN FOOT. 



531 



In man, on the contrarv, the foot is arched and rests flat on the 

 ground in standino- and walking. 



It is this arch which, acting as a sort of spring, enables the foot, as 

 may easil}" 1)6 understood, to support a considerable weight;^' it is, 

 then, an improvement made with a view to walking, therefore it is not 

 peculiar to man alone, and exists well developed in plantigrade animals 

 who have considerable weight of body in comparison with the surface 

 of the astragalus. The armadillo has a well-marked arch. M. Casse, 

 in a very good paper on the ontogenetic development of the foot, 

 compares the human foot to a tripod whose points of support would 

 be the calcaneum and 

 the heads of the first 

 and fifth metatarsal 

 bones, and whose ^.. 

 summit, a broad cur- 

 V i 1 i n e a 1" surface 

 arched in t\vo direc- 

 tions, would be occu- 

 pied by the astrag- 

 alus. 



It is the astragalus, 

 indeed, that transmits 

 the weight of the 

 body to the tripod. 

 In order that the sys 

 tem mux be in equi- 

 librium it is evidently 

 necessary that this 

 astragalus should l)e 

 situated in the l)isec- 

 tor of the angle whose 

 apex is foi-med ])y 

 the posterioi' point of 

 support C. This is 

 precisely what occui's 

 in man, whose foot is 

 perfectly adapted to biped, j^lantigrade walking. M. Volkov noted 

 that, among the primates, the development of this arch is in direct pro- 

 portion to the more or less perfect adaptation to plantigrade walking. 



He studied separately the transverse arch and the longitudinal one. 

 First he calculated the value of the transverse arch l)y measuring and 

 comparing the actual lu-eadth of the tarsus following its curvature 

 from without inward, with the same breadth taken l)v projection; he 



«In fact the dimensions of tlie human foot are augmented in every direction when 

 it HU])ports the weight of the bod}-. 



/// ; 



Fig. 10.— Transverse arch (the foot is disarticulated in front of the 

 scaplioid and the calcaneum, and the anterior portion is here 

 shown). I, Gorilla. II, Negro. Ill, European. 1, lirst digital ray; 

 2, first cuneiform; 3, second cuneiform; 4, third cuneiform; 5, 

 cul)oid. (The center.s of figure of these bones are marked with 

 dots, and a line drawn through these dot.s forms a curve which 

 indicates the transverse arcli.) 



