472 THE INTERMEDIATE PRIMATES 



essential to adapt the ocular muscles to the needs of binocular vision. Among 

 the intermediate primates, the interocular connection is considerably more 

 extensive m baboon than in macacus or gibl^on. The explanation of this 

 preeminence in the baboon may be sought in the nature of its habitat and 

 mode of Hfe. Living as it does in open places, its range of vision is conse- 

 quently much wider and it requires adjustment to varying distances much 

 more than is the case of the tree-chvcinng animals whose visual fields are 

 naturally circumscribed by the foliage among which they pass their lives. 

 Thus in all probability, responding to the need for rapid adjustment of far 

 and near vision, the baboon has developed a quality of visual perception which 

 in certain respects surpasses that of the other intermediate primates. The 

 longitudinal coefficients of the oculomotor decussation in baboon, macacus 

 and gibbon are given in the appended tabulation: 

 Longitudinal Coefficients of Oculomotor Decussation in Intermediate Primates 



From these figures it is apparent that, when contrasted with the lower 

 primates, the degree of internuclear connection in the nuclei conti^olling 

 the eye muscles of the intermediate group is much greater. This denotes a 

 specialization in visual function in passing upward from the lower extremity 

 of this order, in the interest of a higher type of ocular control. It especially 

 introduces those elements of vision which give more exact perception con- 

 cerning distance, perspective and contour. 



Were it possible to summarize all of the progressive specializations 

 which have been noted, it might be said that whatever the variations and dif- 

 ferences among the intermediate primates, these species as a group show 

 definite, even decisive advances in all of the structural details regulating the 



