A HUMAN FINGER-TIP 
The palms of the hands and soles of the feet are covered with little ridges or corrugations, which 
are supposed to be useful in preventing the grasp from slipping; whence the name of friction- 
skin has been given to these surfaces. 
the one above is a loop on the left forefinger. 
The ridges are developed into various patterns; 
The ridges are studded with the openings of 
the sweat glands, the elevated position of which is supposed to prevent them from being 
clogged up; further, the moisture which they secrete perhaps adds to the friction of the skin. 
Photograph by John Howard Payne. 
the ridges themselves, it is suggested 
that they serve at least two purposes: 
to give increased delicacy to the sense 
of touch, and to furnish a surface which 
will prevent slipping. 
Walter Kidd,* the chief defender of 
the tactile theory, points out that if 
friction were the only use of this 
corrugated skin, it would hardly be 
necessary on the sole of man’s foot; 
since prior to the time when he wore 
shoes his feet were planted on grass and 
’The Sense of Touch in Mammals and Birds. 
It is true that the finger tips are especially sensitive, but the nature of 
theory, to some extent. 
relation between this sensitiveness and the ridges is not proved. 
(Fig. 12.) 
rocks where the slight friction offered 
would be of little value. He thinks 
that the pattern on the sole rather 
increases the tactile sensibility of that 
region, and aids a man in keeping his 
balance when he walks. But such 
theories are not very convincing, par- 
ticularly as man may be supposed to 
have inherited his sole-pattern from ape- 
like ancestors whose feet were adapted 
to clinging to the boughs of trees. 
The idea that this skin is, as Wilder 
London, 1907. Galton also accepted this 
The skin is a mosaic of tiny 
sensorial areas, touch spots, cold spots, warm spots and pain spots being widely and irregularly 
distributed. 
On the finger tips the touch corpuscles are frequent—about twenty-one per square 
centimeter on the index finger, while there are only two to eight per square centimeter on other 
parts of palm and on the sole. 
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