A singular modification of the type, and one which forms a necessary link in our present inquiry, is seen in monkeys, in which, owing to their arboreal life and the consequent substitution of climbing for walking, the pads have become low, flattened mounds, and the usual hard covering has softened to a soft epidermis marked with curiously disposed ridges, the seat of a highly developed tactile sense. The volar surface of the paws thus forms a delicate organ of touch, specially adapted to perceive the varying conditions of the tree-boughs, a power
often of vital importance to the animal (Fig. 3). The epidermic or papillary ridges cover the entire volar surfaces and designate the position of the typical pads by elaborate patterns in the forms of scrolls, loops and whorls as may be seen by a comparison of the figures with the typical diagram. It will be noticed, however, that aside from the usual ten pads, there is seen a small accessory hypothenar, situated between the hypothenar and the third palmar, and that upon the fingers, aside from the apical patterns, there are suggestions of loops and other figures placed upon the first and second joints. The morphological significance of these extra parts is not known at present, and it is probable that they have not other meaning than an attempt to increase still farther the sensitiveness of the surface in places not covered by the original pads.
To supply the next and final link in our chain of reasoning the reader may be asked to consult his own hand and compare it with Fig. 3. Upon this the apical pads, or patterns, as they may now be called, will be easily seen, much as in the Micmac drawings, and it is probable that one at least of the palmar patterns, and perhaps also the hypothenar, will be in evidence. Individual human hands differ greatly, however, in the patterns represented, the limits in the authors collection of one hundred palm-prints being shown in Fig. 4, both taken from whites of American parentage, yet differing from each other in the matter of patterns more than the first and more atavistic one differs from that of the monkey. In the same way Fig. 5 represents the extremes of a collection of about sixty sole-prints where the differences are as great as in the palms.