No. 3] A. STUDY IN FOOT STRUCTURE. 311 



tion can be seen in the figures, but it has been subjected to 

 geometrical demonstration. The method of inquiry has been 

 previously explained. By it I find that the trapezoid has from 

 a third to a half the volume it should have. The reason for its 

 thinness is plain; it allows metacarpal II to complete the system 

 of interlocking by a bearing on the magnum ; but with the 

 Lamarckian principle the facts are incompatible. The same 

 disproportion continues in Menodus, and it can be seen, in 

 perhaps a less degree in the recent tapir, hippopotamus, and 

 rhinoceros. 



But the principle of use stimulating growth and the opposite 

 has been applied far more minutely. To elucidate, I find Pro- 

 fessor Osborn's summaries^ most available, stating that in the 

 evolution of teeth, new cusps have arisen where, in earlier forms, 

 were shown the effects of wear. Here on a single centre dif- 

 ferential use has resulted in differential growth. The place and 

 the direction of growth have been determined by impact. 



Now if this principle is true in the teeth, it must be of gen- 

 eral application. The carpus is a better field for its operation, 

 since the bones in weight-bearing are held rigidly together. 

 Indeed, displacement in the carpals has been thus explained,^ 

 while the terms impact and strain have been freely connected 

 with all foot structures. Inclination and complication of sur- 

 faces and correlation must be accounted for. Is it in accordance 

 with the law that regions of special pressure are regions of 

 growth, compensating for that pressure, and producing structure 

 adapted to meet it } I propose here to apply the principle to 

 one test case, discussing it more generally later on. 



There is and always has been a region of special impact and 

 strain in the anterior face of the foot as compared with the 

 posterior face, and especially in its outer border, which is in 

 action under severe leverage when the limb first strikes the 

 ground. Applying here the physiological principle derived from 

 the teeth, it is found that while in that case it produced a struc- 

 ture presumably adapted to the circumstances, here it would 

 spoil the joint. Wherever applied in the carpus, its tendency 

 is to lift the bones apart on points and ridges. I have pointed 

 out structures in this foot which I think meet and distribute 



1 Am. Nat., 1888, pp. 1074; July, 1889; February, 1891. 



2 OsBORN, " Evolution of the Ungulate Foot," Trans. Am. Phil. Soc, Vol. XVI. 



