572 



THE HIGHER ANTHROPOIDS 



ventral surface presents two well-defined ])yramids separated by a ventro- 

 median sulcus. At the caudal extremity ol the pyramid mterlaeing libers ot 

 the decussation may be discerned upon the surface. Lateral to the pyramid. 



FIG. 254. VENTRAL SURFACE OF THE BRAIN STEM, CHIMPANZEE. 



lActual Lint;tli 48 mm.] 



Ki;v TO Dia(;kam. cercbr. I'edlncle, Cerebellar Peduncle; op- (.miasm, Optic Chiasm; op. ped. space, 

 0[>tic<)pcdunciiIar Space; vent. med. si i.c:is, Ventrcimedian Sulcus. 



and separated from it by the |)reoli\ary sulcus, is a well-defined olixary 

 eminence, which in turn is separated from the tuberculum tiigcmini b\ the 

 postolivary sulcus. The dorsal surface ol the ()blon<j;ata presents tlu' two 

 characteristic divisions, the inlraNcntricular and the \entricular ])ortion. 

 The inf ravt'iitricular portion is characterized b\ tlu' ap[:)earance of a well- 

 defined clorsomedian septum, on t-itlu'r side of which may be setn the ele\a- 

 tions produced l)\' the libers and nucleus const it ut mti; the cla\a. The usual 

 dorsal paramedian sulcus separates the cla\a from ihe cuiu'us, which latter 

 appears to be the lari^er ol these two surlace elexalions. i-iom this fact it 

 may be inferred that the sensory importance of this area has increased, due 



