Abstract
In this study, I examined bilateral asymmetries of maximum length, articular breadth, and the geometric properties of the first metacarpal bone of 37 recent Japanese and 24 Jomon shellmound males. There were statistically significant differences between right and left sides in all variables except for maximum length of the recent Japanese. Correlations among bilateral asymmetries in articular breadth and geometrical moments of inertia IY and J were statistically significant. This was interpreted to indicate that the side with a wider range of articular mobility has a stronger action of the opponeus pollicis muscle. Significant correlations between the bilateral asymmetries of the first metacarpal bone and the humerus were found for the investigated geometric properties except in IX of the first metacarpal bone. In the Jomon shellmound males, there were statistically significant side differences in maximum length and in articular breadth, but not in the geometric properties. These results were interpreted as follows; 1) There were qualitative differences in the function of the upper limb of the Jomon shellmound males in age groups before and after approximately 20 years. 2) Over the age of 20, they engaged in activities with opposition of the thumb and mechanical load on the humerus that produced equivalent overall loads on both sides. 3) The bilateral differences in articular breadth indicate differential use of the right and left hands.
