^00 



IllL lllCliER ANlllROPOIDS 



pi-rformanccs, while the ncokinctic accjuisitions of the animal all\ it to that 

 grtjup ol the- pniiiatt's staiuliiig at or near the summit ol this oicKt. 



The eephalie l)oiinclai"\- of the jjoiis is inclieatecl by the pontopeduneular 



FIG. 227. \ENTRAL SURFACE OF BRAIN STEM OF ORANG-OL TANG. 



|Actu;il Length j-t iiiin.| 



Kev to Diagram. <:i;ki-.iii<. prdi nci e. Cerebral PidiincU--. I'v. Di ( ., P\ ramiclal Dttiissation; trap. BODy, 



Trapezoid Body; Till \KV, Sesentli Nerve. 



sulcus which marks the l)e<imninij; of the optico-peduncular space. The latter 

 is bounded caudall\- l)\ the di\ergeiit cerebral peduncles and cephalically 

 by till' optic chiasm and optic tracts. This space is proiniiU'iU in theorang's 

 bram, due to the conspicuous size ol the two cerebral peduncles. The dorsal 

 .surface ofthe midbrain contains the usual specialization ol the c|uadrigeminal 

 plates giving rise to the supt'rior and mlerior colliculi. Of tlu-si' the suptMior 

 colliculus IS somewhat more e\tensi\e, although ha\ing a less wt-ll-marked 

 surlace elevation. \\ hile tlu' diameters of the inlerior colliculus are less than 

 those of the superior colliculus, its cKa at ion is somew hat greater. The general 



