126 CHARLES MIDLO AND HAROLD CUMMINS 



It seems hardly likely that the parallelism between the 

 intermembral indices of pattern intensity and extremity 

 lengths in higher primates is merely coincidental. The factor 

 responsible for this association cannot be identified. It is 

 possible, of course, that the growth rates which make for 

 greater extremity lengths are in some way linked with those 

 growth forces which condition pattern expression. This does 

 not seem very plausible, on account of the discrepant placings 

 of genera of monkeys in the seriation just presented. We have 

 been considering the relative lengths of upper and lower 

 extremities and the relative intensities of palm and sole with- 

 out regard to the absolute values. Hylobates, for example, 

 has a pattern intensity (combining palm and sole) which is 

 just half that of Pongo, though the extremities in Hylobates 

 are relatively much longer. Search for the explanation must 

 be made elsewhere than in mere size, relative or absolute. 

 It is not impossible that the correlation between differences 

 in lengths of upper and lower extremities and in their pattern 

 intensities are linked because of common locomotor habits. 

 When the higher primates are listed in the order of decreasing 

 arborealness (Hylobates, Pongo, Pan, Gorilla, Homo) the 

 seriation does not correspond exactly to that based on the 

 intermembral indices. At the same time, a precise conformity 

 might not be manifested among features of the kinds here 

 compared, especially when it is impossible to draw nice dis- 

 tinctions in functional use of the members. Making such 

 allowances, there may be significance in the standing of Pongo 

 and Hylobates at the top of all three lists; Hylobates is the 

 more aboreal and the more active brachiator, but we cannot 

 draw such fine distinctions in habit as in structural features 

 which can be compared quantitatively. Man stands at the 

 bottom of all three lists, and while the places of Gorilla and 

 Pan are reversed in the order of decreasing arborealness as 

 compared with their position based on the intermembral in- 

 dices, the two genera at least lie in an intermediate position, 

 and the remarks just made in reference to Pongo and 

 Hylobates apply equally to them. 



