528 THE HIGHER ANTHROPOIDS 



TIk' iiitcnuic'lt'cU" c'omnuinication [x'lwccii the two s\ ninictiical cli\isioiis 

 of tin- nuclei supplying impulses to the eye muscles depends ujjon the extent 

 to which the commissural and deeussatmg hhers are de^•eloped. Then- exten- 

 sive development in the orang denotes a unification ot the \ isual jjroccss 

 calculated to produce a high degree ol hmocular \ ision. The libers of the 

 oculomotor nerve ( N 3 ) pass forward to the oculomotor sulcus, whence they 

 emerge at the base ol the brain in the optico-peduncular space. In their course 

 they pass, some through and some around, a large nuclear structure which 

 has diflerentiated in the \cntromesial portion ol the reticular lormation 

 and constitutes the red nucleus (NRu). Not only the size biit the clear 

 delmition of this nucleus in the midbrain shows a distinct ad\ance m its 

 organization as compared with the lower and intermediate primates. It 

 supplies collateral exidence which, m coniunction with the increased size 

 of the lateral lobes of the cerebellum, with the increased com[)lexit\ of the 

 dentatt' nucleus and with the increased size of the superior cerebellar pedun- 

 cle, indicates that coordination has undergone considerable expansion in 

 passing upward to this higher lorm of anthropoid. Such must necessarily be 

 the case m \iew ol the animal's high dillerentiation ol upper extremity and 

 hand. Com])ared with tlie gibbon, for example, the orang-outang employs 

 the hand lor man\ pur|)oses much more humanoid in character and rctjuirmg 

 the organization ol a wider range ol mo\-cmcnt. The greater (k'hnition and 

 larger size ol the red nucleus in this form signillesan extension ol coordmatixc 

 control. The reticular lormation is less extensix'c than in the lowt'r lorms and 

 in its \-entral portion contains the libers of the nu'sial liilct iMf). The 

 latter separates the rt'ticular lormation 1 Ret I Irom a laigt' nuclear mass 

 extending oblitjuely across the dorsal aspect of tlu' peduncle, the substantia 

 nigra fSbn). What the exact physiological signilicanci' ol this structinx- 

 may be is still 111 doui)t, although the control of certain automatic associated 

 movements has been attributed to it. 



