628 Hepburn — The Papillary Ridges on the Hands and Feet of Monkeijs and Men. 



Apart from any question of the functions of papillary ridges, Kollmann* 

 conceives them to be formed through lateral pressure between nascent structures. 

 Still such a mode of growth will not explain the formation of the patterns. 



Attention has also been drawn to finger-prints of monkeys by Allix,t who 

 gives an elaborate series of illustrations along with his Memoir. I have examined 

 these figures under a large magnifying-glass, and they convey the impression that 

 they are interpretations rather than drawings, and consequently their value as 

 absolute reproductions of monkey finger-prints is diminished. 



Sweat- Glands — A consideration of papillary ridges would be incomplete, if 

 no notice were taken of the associated sweat-glands : and that for two reasons — 

 first, because of the great number of sweat-glands in those regions where 

 papillary ridges are found ; and second, because of the association of the mouths 

 of the sweat- ducts with the summits of the papillary ridges. Sweat-glands attain 

 their numerical maximum in the palm of the hand, and they are not materially 

 reduced in numbers in the sole of the foot. Making due allowance for the fact 

 that sweat-glands are always most numerous in regions devoid of hairs, and 

 for the further fact that a moist surface increases the acuteness of the sense of 

 touch, I am of opinion that these reasons do not fully account for their great 

 numbers in the sole of the foot, where the acuteness of the sense of touch is 

 considerably less pronounced than in the hand. Again, there must be some 

 definite reason for the constant opening of the sweat-ducts on the summit of the 

 ridges, instead of in the intervening furrows. It seems a fair assumption that 

 their point of opening is that which is best suited for the expression of the secre- 

 tion during such an act as that of grasping; whereas, if the orifices had been 

 situated in the furrows between the ridges, the same act would have led to the 

 compression and closure of the orifices of the sweat-ducts. 



As the result of careful scrutiny of the monkey impressions in my possession, 

 I may state that the papillary ridges are remarkably distinct, and the intervening 

 furrows very pronounced, notwithstanding the small size of the hands and feet of 

 the animals in question. Now, while prominent papillary ridges are no doubt of 

 much value in connection with the sense of touch, whether as providing for 

 increased sensibility for surfaces thickly covered by epidermis, or as endowing 

 the palm and sole with a frictional sensibility of a discriminating kind, I am of 

 opinion that these explanations do not exhaust the possible functions performed by 

 papillary ridges, any more than they account for the direction of the ridges or 

 their arrangement in the form of patterns. 



Certain monkeys and opposums possess prehensile tails, the ventral surfaces of 



* Kollmann. Der Testapparat der Hand der menscliliclien Kassen und der Afifen. Quoted by 

 Galton, 9. v. 



t Allix. Ann. Sc. Nat., 5th series, vol. ix., 1868. 



