16 CHARLES MIDLO AND HAROLD CUMMINS 



ridges, whatever may be the hand length and size of the 

 animal, might suggest that the proper performance of their 

 functions depends perhaps as much upon absolute size of the 

 ridge structure as upon proportionate development of the 

 ridges and bodily dimensions. A small animal may or may 

 not have finer ridges than a larger one, but in any case its 

 ridges are proportionately coarser, as if limits of ridge breadth 

 were imposed by factors which are more or less independent 

 of the regulation of body size. There must exist, in addition to 

 this regulation of ridge breadth, some genetic mechanism 

 which is concerned with the more specific determination of 

 limits within a single genus. Chimpanzee, as before noted, 

 possesses narrower ridges than man, and though our present 

 observations are confined to one or at most two individuals 

 of each genus, it is clear that still finer ridges occur in some 

 other forms (table 2). 



THE BASIC PLAN OF VOLAR PADS AND OF 

 DERMATOGLYPHIC CONFIGURATIONS 



The volar pads of primates have been studied by several 

 workers, notably Kollman (1883-1885), Klaatsch, Hepburn, 

 Whipple, Schlaginhaufen and Kidd ('07). These authors 

 agree in a common plan of the typical mammalian pads, com- 

 prising three series of pad elevations : on the terminal seg- 

 ments of digits; a series of three or four interdigital pads 

 lying in the distal region of the palm or sole ; two more 

 proximally situated pads, the thenar and hypothenar. In ad- 

 dition to this complement of typical pads, termed by Whipple 

 primary, there occur in ' ' some of the highly specialized forms 

 such as Galago .... extra pads, which, as they show no 

 evidence of a general homology with pads of other orders of 

 mammals, may be regarded as secondary developments arising 

 from the peculiar needs of adaptation and will be referred to 

 as secondary pads" (Whipple). As pointed out especially by 

 Whipple and by Wilder (1897), alteration of the typical mam- 

 malian plan may occur through suppression of individual 

 pads and expansion and fusion of neighboring pads. A fair 



