THE PHYSIOLOGY OF THE SENSE OF TOUCH U5 



the raising of the mouths of the ducts of the sudoriparous glands 

 being subservient to this by affording a necessary amount of 

 moisture to make the hand or foot more adhesive, either to a 

 cyhndrical or spherical object. Dr. Hepburn draws attention 

 to the fact that the ridges, though comparatively low, must 

 cause a certain amount of friction and thereby prevent shpping, 

 and refers also to the moist clammy state of the palm and sole of 

 monkeys as of material value to their firmness of grasp. In view 

 of the fact that prehension among these creatures is of two 

 kinds, for cyhndrical and spherical objects, it is clear that there 

 is a reason for the opposite arrangements of transverse and 

 longitudinal ridges which accommodate themselves to the two 

 classes of objects. 



The second use of the papillary ridges, given by Dr. Galton in 

 a dubious manner, is the one to which attention is chiefly drawn 

 in this work. He refers almost entirely to the patterns on the 

 human finger-tips without reference to the more rudimentary 

 plans and patterns exhibited in the lovv'er Primates and certain 

 still lower mammals. An endeavour will be made to show that 

 in man as well as in most lower forms, the fimction of subserving 

 the sense of touch is a much more important and certain use of 

 the ridges than the above opinion would suggest. 



It is necessary to refer again to the general and particular 

 arrangements of the papillary ridges, and a sufficient number of 

 species are shown in the present series to illustrate the chief 

 features of these arrangements. The oblique, lotigitudinal, and 

 transverse are the earhest and simplest types of arrangement, 

 excepting the radiating pattern of squirrels, hedgehogs, and others 

 which are probably accidental in the sense that they are deter- 

 mined by the shape of the eminences on which they He. De- 

 partures from these three simple types begin to appear low down 

 in the series, and may be classified as arches, loops, and ivJiorls. 

 This classification has been employed by Dr. Galton very exten- 

 sively in his statistical studies, and is, for this purpose, of great 

 value as an aid to biometrical investigation. He takes these 

 phenomena as he finds them, but there is a further interest in 

 them, if they are considered in the making, as the accompanying 



K 



