SIMIA SAT^RUS, THE ORANG-OUTANG s^5 



tion ill the margin of tlu' tt'iitial pray matter. Latcrallv, the central gray 

 matter contains tlie mcsenceplialic root of the fifth nerve and in a more 

 \x'ntral ])osition are the- dense l)iiiidles constituting the j^osterior longitudinal 

 lasciculus ( PL I. The boundary line hetweeii the basis and tegmentum at 

 this k'\-el is indicated b\ trans\-ersel\ disposed bundles forming the mesial 

 lillel (iMlj, lateral to which arc' the hbers constituting the large fasciculus 

 of the lateral lillet (Li ), an important intermediar\ s\sttin of fibers in the 

 auditory ]xith\\a\-. The most important structure at this le\-el is, however, 

 represented by the colliculus, as its s|)c'cialization forms a relay station for 

 the auditory sense. The colliculus is less prominent than in the lower \ crte- 

 brates and considerably less so than in the lower and intermediate' primates. 

 It still retains many vestiges of its former histological s]:)ecialization. A 

 number of strata may still be discerned m it, reminiscent of its stratification 

 111 the miramammalian \ crti-brate. 



LE\EL OF THE SUPERIOR COLLICULUS (FIG. 239) 



At this level the section shows those changes peculiar to the appearance 

 of the cerebral pechmcles m the basal region and the t'lexation caused b\ the 

 more cephalic i^rommenccs in the C[uadrigeminal plate. The superior colliculi 

 (SC) a])pear as delimti-lx' specialized structures which inicidsco])i(.ally show 

 a faint degree ot stratilication. Their cle\ation is less pronounced than is 

 the case in certain others ot the primate series, irom their general character 

 the inference seems iustified that the lunction w hich the\ represent, namely, 

 vision, could at best be but iiu'lli'ctuallx carried on bv them. I heir \fstigial 

 condition as comparid with the lower vtMtebrates is so jjronounced, both 

 as to size and histological detail, as to suggest a decrease in tunctional 

 acti\it\ . The process of \isiial delegation to the occipital lobe of the cerebral 

 hc-misphere, which in these studies has become so familiar a subject of discus- 

 sion, is exident in tlu' orang. The continuation ol this telencephahzation is 



