4^6 



II IE HIGHER ANTFIROPOIDS 



The Basal Surface of the Bkai\ 



Upon tlu' basal surlacc ol tlu' hrain, the luiiiisplKTc iii the trontal region 

 shows the two eharaeteristic orbital concavities which are lairlv well marked 



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FIG. 226a. KK;ni LATERAL SL RFACE OF BRAIN, ORANG-OL TANG. 



■|Actii;il length q6 mm.] 



altliough gradiiallv losing their lateral boundaries. Mcsially these concavities 

 are bounded by two marked projections, lorming the inti'rorl)ital keels 

 N\ hieli ari' more prominent than m the higher anthropoids and less pronounced 

 than in the lower and intermediate forms. The olfactory bulb and tract are 

 detachable Ironi the orbital surlace as far back as thi' trigonum ollactorium. 

 A small ()llact()r\- lissure separates a rudinuntar\ g\ rus rectus from the 

 ma|or orbital eon\-olutions. The tip of the temporal lobe is sharply separated 

 from the orbital surfact' 1)\ the horizontal limb of the S\l\ian fissure, and 

 presents a lairl\- well-dehned uncus on its nu'sial surlace. In the occipital 

 region the cerebellar conca\it\' is well marked. It is t'speciall\ pronounced in 

 its median portion where it forms a w ell-de'fiiu-d postspk'iiial fossa. 



