14 CHARLES MIDLO AND HAROLD CUMMINS 



has an equivalent ridge count, 30. Again, in two specimens 

 with hand lengths nearly four times as great (Alouatta and 

 Pan) the counts are but little smaller (27.0 and 23.3 respec- 

 tively). Forms having practically equal hand lengths may 

 exhibit quite different ridge counts, as in Saimiri and Aotus, 

 Erythrocebus and Lemur, Lagothrix and Magus, Alouatta 

 and man. 



The range of ridge counts in the thirteen genera (table 2) 

 approaches that of the Cummins and Spragg series of twenty 

 chimpanzees (18.2 to 33.9), composed of animals of different 

 ages in which the hand lengths range from 11.7 cm. to 22.0 cm. 

 In a series of human hands with the same lengths, the ridge 

 counts range from 15.9 to 26.5. The greater coarseness of 

 ridges in the human hand as compared with chimpanzee thus 

 indicates a generic difference in the breadth of ridges, occur- 

 ring independently of hand length. The observations here 

 reported on a series of genera, with disproportions of hand 

 lengths and ridge counts, further indicate the existence of 

 generically unlike tendencies in ridge breadth. The upper 

 and lower limits of the observed ridge counts per centimeter, 

 36 and 16, probably at least closely approach the actual ex- 

 tremes of variation in ridge breadth. The breadths of epi- 

 dermal ridges, like other dimensional characteristics, seem- 

 ingly are fixed or limited by some fundamental genetic mecha- 

 nism, and this mechanism is in part independent of hand size. 



The hand length/ridge-count index was not used in the cited 

 studies of human and chimpanzee palms. Because of this 

 omission the index is now applied to the hypothenar area of 

 these series, and the results are presented for comparison 

 with the general primate material. From the latter material, 

 table 2, two specimens are excluded (Cebus capucinus and the 

 specimen of Pithecus first in the list) in order to confine this 

 analysis to one representative of each genus. The 200 human 

 subjects have indices ranging from class centers (5-unit 

 classes) 72 to 152. The mean is 104.7 and the standard devia- 

 tion 12.5; the coefficient of variation is 11.9. In chimpanzee 

 the index ranges from 40 to 121. The mean is 55.9, the standard 



