152 THE SENSE OF TOUCH IN ANIMALS 



in a distal, and the latter in a proximal direction, is apparently 

 an adaptation for the purpose of increasing the sensibility of 

 the skin in these regions. 



It is true that some of the instances here noted of the formation 

 of aberrant papillary ridges on certain unusual areas of the hand 

 and foot, are not incompatible with the broader view of Miss 

 Whipple as to " friction-skin," but they are conclusive against 

 the prehension-theory of Dr. Hepburn. 



(7) The function or functions of the ridges themselves are 

 intimately associated with the various directions or patterns 

 which they assume, whether in the simple transverse, oblique, 

 or longitudinal directions, or in the more complex directions 

 which are called " patterns." The structure of a papillary 

 ridge is altogether too highly developed and pecuHar to the 

 ventral surfaces of the hand and foot, to be separated from some 

 elements of the acts of walldng and prehension, and when it 

 is seen on reviewing a large series of mammaHan forms, that 

 there is a growing complexity of the grouping of these ridges 

 up to those of man, the conclusion is forced upon one that there 

 is an important meaning in the variations of pattern. 



Dr. Hepburn dismisses the patterns of the human and Simian 

 hand and foot as secondary results of the shape of the eminences 

 on which they are found, whereas Miss Whipple attaches to 

 them a great importance as being arrangements by which the 

 ridges are so placed as to be at right angles to the force which 

 tends to cause shpping in walking or prehension, or to the 

 resultant of several forces therein concerned. This theory of 

 Miss Whipple's is exceedingly difficult to work out in a review 

 of a large series of hands and feet. This is seen in the case 

 of the elHpses of papillary ridges which are so common on the 

 terminal phalanges of the digits, both of hand and foot, of many 

 Primates, or even lower mammals, such as Didelphys azarce. 

 Figs. 3, 4 ; Petaurus sciurea, Figs. 5, 6 ; Lemur hrunneus. 

 Figs. 13, 14 ; or Lemur catta, Figs. 15, 16 ; Nycticebus 

 tardigradus, Figs. 17, 18. It is not necessary to mention more 

 than these few cases, but similar elhpses are seen in nearly all 

 Monkeys. Such elHptically arranged ridges could not, by any 



