THE PHYSIOLOGY OF THE SENSE OF TOUCH 151 



{d) On the heel of adult man ridges are found suirounding 

 it, of the average depth of one inch from the plantar surface, 

 and in one particular case of a woman aged forty-nine, the 

 depth of this area on each foot measured was one and a half 

 inches from the plantar surface. 



Ckim'panzee. — An instance of papillary ridges on the extensor 

 surfaces of the digits of the hand, on the terminal phalanges, 

 was brought forward at the Zoological Society* attributable 

 to the habit of this Ape in walking, by which it supports its 

 weight on the extensor surfaces of the digits ; these were absent 

 from the corresponding surfaces on the foot. A similar condi- 

 tion, with aberrant papillary ridges, has been foimd on the 

 digits of the hand of the Orang. 



Lemur brunneus. — Shows well-marked ridges on the extensor 

 surfaces of the terminal phalanges extending to the lateral 

 borders of the nail, and nearly to the middle hne of the digit, 

 where the ridges from the two sides are only separated by a 

 narrow triangular space. 



Hedgehog, Figs. 12, 13, and Kinkajou, Figs. 9, 10, show rudi- 

 mentary ridges on their digits and palm and sole, these parts 

 not being capable of use in prehension. 



(5) The pulps of man's fingers have highly developed patterns, 

 and these are more variable and complex than those of any 

 other part of any of the Primates, and these are the most 

 sensitive areas in any hand or foot. In this instance the con- 

 nection between sensibiUty and complexity of pattern of ridges 

 is intimate. 



The pulps of the toes in man are less sensitive than those 

 of the lingers, and the patterns of the second, third, fourth, 

 and fifth digits simple, and these digits are relatively weak in 

 fmiction compared with the hallux. 



In nearly all Monkeys and Anthropoid Apes simple ellipses 

 are found on the pulps of the hand and foot, which accords with 

 the lower function of these parts in the Primates below Man. 



(6) The imbrication of the papillary ridges on the digits of 

 man, and on the hallux and ball of the hallux, the former be-ng 



* "Proc. Zool. Soc." 1904, p. 263, 



