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. 
