DERMATOGLYPHICS IN PRIMATES 11 



formed ridges are in general less extensive and less fre- 

 quently present than in the palm of the same genus. 



The common lack of complete ridge formation within 

 flexion furrows, noted especially in the palm, and in even the 

 higher primates including man, indicates the retention of 

 more primitive epidermal characteristics in these zones. It is 

 possible that incomplete ridge formation is associated with 

 nonparticipation of such zones in the functions served by the 

 more directly exposed contact surfaces, but it is possible also 

 that the furrows are distinguished by local peculiarities of 

 histogenesis with which function bears no relationship. The 

 construction of epidermal ridges has been shown by Abel 

 ( '35, '36) to be disturbed occasionally in the finger tips of 

 criminals, mental defectives and in some congenital defects 

 such as spina bifida, oxycephaly and malformations of the 

 hands. Irregularities of ridge formation exhibited in these 

 cases closely resemble the irregularities occurring in flexion 

 furrows. Abel's cases demonstrate arrests of epidermal-ridge 

 differentiation, and it is conceivable that the differentiation 

 of ridges in flexion furrows may be disfavored by influences 

 which are developmentally peculiar to these regions. 



Two chief functions have been ascribed to epidermal ridges. 

 One concerns the increase of frictional service in locomotion 

 and prehension, in recognition of which the areas so specialized 

 have been designated "friction-skin" by Whipple and by 

 Wilder. The other function is the heightening of tactile 

 sensibility indicated in the term ' l Tastlinien ' '. Though con- 

 siderable attention has been devoted to the question as to 

 which of these functions may be preeminent, the decisions 

 of those who have discussed the subject appear to have no 

 secure support. It must be conceded that both functions are 

 mediated by ridging of the skin, and for the lack of convincing- 

 evidences we are not inclined to subordinate one to the other. 

 No attempt can be made to evaluate their relative importance 

 without having a thorough knowledge of differential habits 

 among the genera and differences of use of hand and foot in 



