468 



THE INTERMEDIATE PRIMATES 



reason of the structural differentiation in its hand, its mode of life in the 

 trees, its general reaction within its habitat seems to possess a wider range 

 of motor differentiation. It may be that the gibbon is equally cndo^^•ed in 

 these respects. Being a more or less reclusive animal concerning whose behav- 

 ior in the free state less is known than of the macacus, it is impossible to say 

 at present that its manual performances are actually inferior to those of 

 the macaque. The figures do not indicate such a condition. Yet it is 

 possible that because of the rather low degree of differentiation in the lower 

 limbs and feet, much more responsibility is imposed upon the forelimbs and 

 hand. This, at least, would explain why the pontile nuclei are large in the 

 gibbon. The division of labor between the hands and the feet in macacus 

 and baboon is nearly equal; in the gibbon there is a marked inequality which 

 gives the forelimb and the hand over-emphasis in their motor responsibility. 

 The coefficients of the pontile nuclei of the baboon, macaque and gibbon are 

 given in the appended tabulation. While the planimeteric dimensions in 

 gibbon are somewhat larger than in the other species, the estimated mass of 

 the nuclei is nearly ccjual in them all. 



More significant, however, than the comparison between the several 

 members of the intermediate primate group, is the fact that all of these three 

 species show a definite superiority in their pontile nuclei over the lower 

 primates. This superiority is striking and decisive, leaving no doubt that in 



