MONKEY HAND-PRINTS 149 



covered with papillary ridges and grooves precisely similar 

 to those on the hands and feet of monkeys, but invariably 

 arranged; in simple transverse lines across the tail, so that 

 in the act of grasping they would be parallel to the long 

 axis of the branch around which the tail was coiled. 

 Clearly, then, papillary ridges are primarily connected 

 with the grasping power, and when they are intended 

 solely for that function, they are so arranged as to be 

 parallel to the axis of the object grasped. As regards 

 this function of the papillary ridges. Dr. Hepburn observes 

 that although they are comparatively low, "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 the 

 numerous papillary ridges which are capable of intimate 

 adaptation to the surface of the object grasped." 



In a later passage the same observer adds that, apart 

 from the hook-like manner in which the orang-utan and 

 the American spider-monkeys employ their hands in trapeze- 

 like movements, there can be no doubt that the palms are 

 capable of a considerable amount of lateral folding, as is 

 proved by the creases to which allusion has been already 

 made. And it appears probable that the papillary ridges 

 are designed to afford increased firmness of grasp when 

 the palms are thus folded. Consequently, simple transverse 

 ridges on the palms, except in the second joints of the 

 fingers, are conspicuous by their absence ; and we find 

 instead the complicated patterns on the eminences already 

 described. 



