712 THE HIGHER ANTHROPOIDS 



capacity as directors of locomotion, to the niorc mobile explorative organ 

 dctei iniiK'cl by the higher stages ol mamial dillerentiatioii. 



i\ . The Vestibi lai^ Nuclei in Their Relation to the 

 Balancing Mechanism 



The problem of maintaining the balance of thi- bod\' appears to be sub- 

 ject far less to variations according to mode of life than most of the tunction.s 

 in the i)rain stem which have an exohitional signihcanee. In spite of well- 

 defined differences in adaptation either to arboreal living or something 

 approaching terrestrial life, there are many Ihictuating gradients between 

 these two extremes of specialization. All primates alike develop requirements 

 w hieh impose upon the balancing mechanism nearly the same burden. \\ hat 

 one species may lack in one particular, it compensates for by o^•eI■-dc•\ elop- 

 ment in another direction. This reciprocal rise and fall in equilibratory needs 

 is fairly elleeti\'e in striking a balance for this function throughout the order. 

 Among the great anthro[)oids, the chimpanzee presents in its Deitcrsal 

 nucleus a higher coeflicient than either the gorilla or orang-outang. In this 

 developmi'iit the gorilla is not far behind its a|)|)arentl\ better balanced 

 confrere; while the orang shows what a]>]ieais to be a real interiority in the 

 central control of its balancing mechanism. It seems probable that because ol 

 its great length of arm, this latter form has de\ t'lii|)rd less of the tendencies 

 essential to terrestrial locomotion, while both of the uxhcv anthroijoids have 

 partially adapted themselxes to locomotion upon the ground and in some 

 degree to the upright posture. The orang's eapabilit\ as a tree-dwi'ller has 

 none of the remarkable specialization si'eii in the gil)bon, and although it 

 manages to make t lu' best of its aiboit'al en\ ironmt'iit, its locomotion through 

 the trees is relatiwiy deliberati' and slow, it has none ol the showy agility 

 which characterizes many of the lighter apes and e\ en the chimpanzee. 



