Hepburn — The Papillary Ridges on the Hands and Feet of Monkeys and Men. 529 



which are provided with papillary ridges ; and while admitting that an increased 

 degree of sensibility is of much importance in connection with a prehensile organ, 

 I do not see that we thereby accomit for the fact that such prehensile tails have 

 the papillary ridges arranged transversely. A smooth moist surface would 

 undoubtedly be much better adapted for grasping ; but it would be extremely 

 difiScult for such a surface to suddenly release its hold ; and, moreover, it would 

 lose the discriminating sensibility of the papillary surface. 



It seems to me that the direction and the arrangement of the papillary ridges are 

 intimately associated with the act of grasping. Although they are comparatively 

 very low ridges, yet they must cause a certain amount of friction, and thereby 

 prevent slipping, while the naturally moist and clammy condition of the palm and 

 sole of monkeys must be of material assistance to the firmness of the grasp. A 

 man instinctively moistens the palms of his hands when he wishes to make his 

 grasp more secure ; and the grasping power of monkeys must be considerably 

 increased by the application of numerous moist papillary ridges which are capable 

 of intimate adaptation to the surface of the object grasped. 



Attention may now be more closely directed to certain distinct and practically 

 constant eminences on the flexor aspects both of the hand and foot of monkeys 

 and men. In the hand these eminences are situated as follows : — 



1st. Opposite each phalanx, but especially the terminal phalanx, where each 

 eminence develops in the form of a rounded pad. 



2nd. Three eminences situated in the palm above the clefts between the 

 digits. 



3rd. The thenar and hypothenar eminences. 



Similarly, in a monkey's foot corresponding eminences are found, the thenar 

 eminence being situated on the inner border of the foot, while the hypothenar 

 eminence has its place taken by the heel. Before discussing the significance of 

 these eminences, I would direct special attention to drawings of the hands and 

 feet of such animals as the Phalanger and Didelpliys vii-giniana, by Allix,* who 

 figures eminences covered by papillary ridges in a series of areas exactly similar 

 to those mentioned above, while the remainder of the hand or foot is represented 

 as quite scaly. 



In seeking an explanation of this series of eminences, we might claim that, in 

 the case of the hand, the muscles of the thumb and little finger, and in the case of 

 the foot, the muscles of the great and little toes, are respectively responsible for 

 the upheaval of corresponding elevations. No doubt they do act in this way to a 



* Loc. cit. 



