188 CHARLES MIDLO AND HAROLD CUMMINS 



SUMMAKY 



1. This study was designed as a search for evidences bear- 

 ing on morphological principles of dermatoglyphics and to 

 test the value of dermatoglyphics as indicators of affinities 

 among the primates. The material comprises, in addition 

 to extensive records of human dermatoglyphics, the palms 

 and soles of thirty-five genera adequately representative of 

 both prosimians and simians. 



2. Ridge-bearing skin is essentially continuous over the 

 whole palm and sole in Old World monkeys, gibbon, great 

 apes and man. In New World monkeys and in prosimians 

 there exists wide diversity in the extent of definitely formed 

 ridges. Ridge-formation, an advance in epidermal specializa- 

 tion, is confined primitively to the summits of volar pads. The 

 ventral surface of the terminal portion of the tail in three 

 New World monkeys (howler, spider monkey, woolly monkey) 

 is similarly specialized. Ridging of volar and caudal skin 

 enhances friction in contact and gives increased acuity of the 

 tactile sense ; there is question as to which of these functions, 

 if either, may have been concerned primarily in the evolution 

 of epidermal structure. 



3. The breadths of epidermal ridges (in the palmar hypo- 

 thenar region of thirteen genera) tend to vary inversely with 

 hand length, but the association between ridge breadth and 

 hand size is loosed by the existence of factors which control 

 ridge breadth independently. The unlikenesses of ridge 

 breadth in relation to hand length among different genera 

 exceed the unlikenesses existing in a single genus represented 

 by hand lengths varying according to age. 



4. A basic plan of volar pads and of dermatoglyphic fields 

 is presented, supplementing previous schemes by the addition 

 of elements which had been either unrecognized or not system- 

 atized heretofore. The plan is an idealized composite, based 

 in part on the dermatoglyphics and the pads as observed post- 

 natally and in part on the pads in fetal stages. The topography 

 of pads and other irregularities of the volar relief coincides 



