SI. MIA SAT\"RUS, THE ORANG-OUTANG 527 



pifsidt'S is c'xtcnsnc, hut hccaust' thr imisclc-s tluiustU rs, howt'Ncr delicate 

 and small, arc capal^lc ot produtin^ the most exactly ad|iistcd ol all move- 

 ments 111 the body. Ocular moxements are so minutel\- ada|ited to the func- 

 tion ot \ision, that the slightest de\iation ot the I'xi'ball olOne or both sides 

 will disturb the process ol \isual lusion, or produce other defects in visual 

 perce])tion sullicient to disorganize the special sense ol sight. The object of 

 conjugating the exelxdls so that their \ isual axes shall remain in parallel, or 

 be convergent to that degree necessary lor the prompt binocular lusion in near 

 vision, requires the most delicate of muscular mechanisms for its achieve- 

 ment. This acti\it\, in addition to the immediate read|ustments necessary 

 to distant vision, exerts a lar-r(,'aching mlluence upon all neokmetic organi- 

 zation. There can Ix' no question that \ision operates as an essential, sup- 

 plementary aid both m the acc]uisition and m the control ol a vast number ol 

 highly skilled motor acti\ities. 



So important a musculaturt' as that of the eyeballs requires a compli- 

 cated nuclear structure for the linal distribution of its innervating impulses. 

 The visual distance recei)tors of the two eyes are in reality one organ in the 

 primates; at least, they are dual onl\ in the sense of their morphological 

 organization. l-*hysiologically their object is to give their possessor a unilied 

 impression of the world u])on which he gazes, without reduplication, without 

 distortion, without acUentitious mobilitx. Since the two eyes, serving this 

 purpose, act as a single organ, the two nuclei b\ which the eye muscles are 

 moti\ated so operate in unison that they ma\ be rightlx considered a single 

 nucleus. This unity in structural design of the oculomotor nucleus is deter- 

 mined b\ a close internuclear communication across the midline pro\ ided by 

 a great number of crossing libers w Inch |xiss from one side to the other, the 

 oculomotor, commissural and decus.satmg axons. These libers conjugate 

 the oculomotor, nuclear groups on the right and left side and so produce 

 the desired unity. 



