The Hand of Man.

Fig. 59.—W. K. Right hand draw­ing of pap­il­lary ridges, made from im­pres­sions.

Beginning with the tips of man’s fingers and excluding the wonderful patterns which Galton did so much to elucidate and bring into order, we find the ridges are placed, to a remarkable extent, parallel with the skin-flexures which will be treated in the next chapter. I term the thumb and fingers D 1, 2, 3, 4, 5 for the sake of accuracy (Fig. 59). Over the last joints (distal) of all the digits the ridges suddenly diverge from their directions in the patterns of the pulps, and become arranged transversely to the axis of the digits. This arrangement is observed on the remaining segments of the digits except, very significantly, on the outer or radial side of D 2 and the inner or ulnar side of D 5 where they slope more or less towards the palm. Their lines thus cross slightly those of the skin-flexures in these small areas. On the radial side of D 1 this slope appears in a minor degree, but here it coincides with those of the flexures. On the palm are similar arrangements of the ridges near the radial and ulnar borders, and especially on the two great eminences, thenar and hypothenar, also at the bases of digits 2, 3, 4 and 5. Over the rest of the palm they are arranged in a longitudinal or oblique direction. These brief descriptions are enough to show the close correspondence of the arrangement of the ridges with the flexion of the numerous joints of the hand. An observer can demonstrate this by holding up the open hand in a good light and flexing the fingers slightly, which brings nearly all the ridges adjacent to the joints into directions parallel with one another, the greater lengths of D 3 and 4, and their closer functional connec­tion with one another, producing thus a transverse arrangement, and in D 1, 2 and 5 a more oblique one. In the palm this correspondence of ridges with flexion lines of joints is not found so much except in the central part of this surface. But the oblique and longitudinal ridges of the palm where it becomes concave in the action of folding the hand over a globular object are well shown there also to correspond with such action.

This general grouping of ridges is seen, mutatis mutandis, to belong to all the palms and soles of lower Primates, and the illustrations given will speak for themselves, so that little need be said on each.