150 THE SENSE OF TOUCH IN ANIMALS 



done so in a manner similar to that of the Anthropoid Apes, 

 involving considerable lateral folding, and that these animals 

 show a prevailing longitudinal direction of the ridges, instead 

 of the prevaihng transverse direction shown on the sole of 

 man's foot, it becomes perfectly clear that prehension has 

 nothing whatever to do with the present arrangement of the 

 ridges on the greater part of the foot of Man. 



Summary of argument. — The arguments in favour of the view 

 that one of the primary uses of the papillary ridges in the 

 Primates is that they subserve sensation, may be summed up 

 as follows : 



(1) The ridges are always associated with abundant papillae, 

 many of which contain touch-corpuscles, and the papillae mostly 

 project into or toAvards the ridges rather than the furrows. 



(2\ Arches, loops, and whorls represent degrees of departure 

 from a primitive arrangement, and enable a larger area of ridge- 

 covered surface to be exposed to contact, relatively to the size 

 of the part. 



(3) The sole of Man's foot, which is employed only in support 

 and locomotion with sensation, and which has not been employed 

 in prehension for a very long period of time, is highly endowed 

 with ridges, and these are, in the main, placed transversely, 

 thus differing from those of Monkeys and Anthropoid Apes. 



(4) Papillary ridges develop in parts where they are not 

 normally present on the hand and foot, when they have no 

 relation to prehension. The following instances of these aberrant 

 ridges may be mentioned, 



Man. — (a) Ridges frequently appear on the radial side of 

 the extensor surface of the index-finger to nearly the middle 

 line of the finger, and more on the right than the left hand. 



(6) The extensor surface of the fifth digit of the foot shows 

 ridges when it is distorted by boots, 



(c) In children who bite their nails badly, ridges develop on 

 the extensor surfaces of the pulps down to the free edge of the 

 nail, and in the case of a man whose nails were kept particularly 

 short, because of rough mechanical work done by him, ridges 

 were found well developed down to the free edges of the nails. 



