Hepburn — The Papillary Ridges on the Hands and Feet of Monkeys and Men. 531 



doubt that their palms are capable of considerable lateral folding, as is clearly- 

 indicated by the pronounced longitudinal skin creases -which their palms sbo-w, 

 and I believe that it is in this latter class of movements that the palmar papillary 

 ridges provide increased security for the grasp. The hands bring j)rimarily grasping 

 organs -which perform their functions in virtue of different degrees of the po-sver 

 of bringing the opposing muscles into play, purely transverse papillary ridges are 

 scarcely to be found except on the palmar surfaces of the second phalanges. In 

 the palm itself, transverse ridges are scarcely to be seen, although a small number 

 of ridges less oblique than elsewhere, are to be found in some cases immediately 

 on the proximal side of the eminences opposite the inter-phalangeal clefts. Again, 

 -where the grasping po-wer of the pollex is feeble, and the movements of the palm 

 supply the deficiencies of this digit, ridges may be seen occupying the centre 

 of the palm, and running in its long axis from the interval bet-ween the thenar 

 and hypothenar eminences to-wards the roots of the fingers, as in the hand of the 

 sooty mangabey. 



In considering the arrangement of the papillary ridges in the sole of the foot, 

 it is necessary to bear in mind that in primates this organ plays an important part 

 in prehension, as -well as in supporting the -weight of the animal. The hallux is 

 situated on the inner border of the foot at a varying distance from the heel, 

 and its position influences the disposition of the papillary ridges. In this -way 

 -we may recognise t-wo areas in the sole of the foot, one situated bet-ween the 

 hallux and the heel, and the other bet-ween the hallux and the roots of the toes. 

 In the hinder area, -which -we may regard as principally associated with support, 

 the papillary ridges practically run transversely, as may be seen by reference to 

 feet of the spider-monkey, the dog-faced baboon (PI. xlv.), and the orang. If 

 either of these creatures were standing upon a cylindrical object, like the branch 

 of a tree, with the feet transverse to its long axis, and -without bringing the 

 grasping power of the hallux into operation, these transverse ridges would be 

 parallel to the long axis of the branch, i. e. in the most favourable position for 

 assisting in maintaining the hold. 



In the feet of the mandrill (PI. xlvi.) — or of the black ape (PI. xlvii.) — the same 

 condition may be noted, but in them the hallux is situated further back, and the 

 heel is thereby somewhat cleft or double, hence the prehensile power of the sole is 

 brought nearer to the heel, and, consequently, there is an obliquity introduced 

 into the direction of the papillary ridges, which at once shows that the position 

 they would assume in the act of grasping a cylindrical object would be one more or 

 less parallel to the long axis of the object grasped. The same fact is emj^hasized 

 in the foot of the orang-utan, viz. the distinct obliquity of the papillary ridges in 

 the grasping area, in addition to their general transverse direction in the more 

 especially supporting area. 



