144 THE SENSE OF TOUCH IN ANIMALS 



arboreal carnivore, but one which does not use its hand and foot 

 for prehension. It is undoubtedly true that the skin which Miss 

 Whipple terms " friction-skin " does derive great value from 

 the roughened surface afforded by nodules, warts, rings, and 

 ridges, and so far, the mechanical view of the ridges is well 

 justified. But I cannot agree that it is possible or desirable 

 to put one function before another in a matter so complex as a 

 structure concerned in the evolution of the walking and pre- 

 hensile powers of a large ascending series of animal forms. How- 

 ever, the study of the sense of touch is independent of these 

 theoretical and controversial points, and may be followed on 

 its own merits without any need to estabhsh priority of origin 

 for one function or another. 



The chief points in connection with the anatomical facts 

 previously described which bear on the physiology of the sense 

 of touch are : 



(1) The functions of the papillary ridges. 



(2) The meaning of the patterns of the papillary ridges. 



(3) The functions of the papillse of the corium. 



(4) The relation of the papillary ridges to the papillje 



of the corium. 

 Functions of the 'papillary ridges. — (1) The interpretation of 

 the patterns assumed by the papillary ridges in different animal 

 forms is closely related to the question of the functions or uses of 

 these ridges. Dr. Galton has paid great attention to the classi- 

 fication of the patterns on the human fuiger-tips, but has not 

 gone further into the uses of the ridges, than to state that the 

 primary use of the ridges is to raise the mouths of the ducts of 

 the sudoriparous glands, so that the secretions may be more 

 easily got rid of, and that the secondary use is to assist in some 

 obscure way, the sense of touch. But Dr. Hepburn and Mr. 

 Lyddekker have clearly shown that in addition to these two 

 uses, the prehensile efficiency of the hand and foot of monkeys, 

 and even of the prehensile tails of American monkeys and 

 opossums, is increased by the ridges. The latter writer seems 

 to be more correct than Dr. Galton, in assigning as the primary 

 function of the ridges, the increased efficiency of prehension, 



