208 DR DAVID HEPBURN ON 
with a frictional sensibility or power of discriminating the 
texture and quality of the surface over which they may be 
rubbed. Undoubtedly the palm and the sole possess this. 
discriminating faculty, but in this respect they are no better 
endowed than other parts of the skin which possess no 
papillary ridges ; and, besides, the presence of a discriminating 
quality will not account fora pattern in one position and 
its absence in another. 
Returning now to the question of the sweat glands, the 
mouths of whose ducts always open on the summits of 
papillary ridges when they are found together, I have to add 
that sweat glands are not only more numerous to the square 
inch in the palm and sole than in any other part, but that, as. 
between palm and sole, there is no very material difference 
in their numbers. Now, although sweat glands are always. 
more numerous in regions devoid of hair, and although 
moisture favours the sense of touch, yet neither of these 
reasons fully accounts for their great numbers, nor for the 
regularity. with which the mouths of the ducts open upon 
the summits of the ridges and not in the intervening 
furrows. So far, therefore, while a variety of functions may 
be credited to the papillary ridges and their associated 
sweat glands, yet neither singly nor in combination do these 
functions necessitate the arrangement of papille in ridges, 
nor the arrangement of ridges in patterns, together with the 
elevation of the mouths of sweat ducts to the summits of 
the ridges. 
Before entering upon the discussion of what I apprehend 
to be the real function of papillary ridges, I wish to recall 
attention to the series of pronounced integumentary grooves. 
which channel the skin of the palm and sole, distinct from 
those almost invisible furrows which intervene between 
papillary ridges. These grooves are foldings of the skin 
which result from the action of definite groups of muscles, 
so that they merely indicate the nature of the closing 
movement of the hand and foot when these members grasp: 
or close upon an object. 
In the apes the main direction of these grooves is trans- 
verse to the long axis of the hand and foot, and they express 
a closing movement which utilises the hand as a hook in 
