574 THE HIGHER ANTHROPOIDS 



decrease in elevation as the lateral reeess is approached and at this point ha\e 

 reached the jjhiiie ot the \entrieular lloor. It is m this region that the incom- 

 ing libers of the acoustic ch\ ision ol the eighth ner\e enter the \entricle 

 whose lloor thcv cross as the striae acusticae. The floor ot the \entricle con- 

 tains the trigoinini h\poglossi beneath which is located the nucleus ol the 

 twelfth cranial nerve and latiral to which is the fovea vagi marking the 

 position ol the dorsal vagal nucleus. Other markings in this region are 

 e\tremcl\ dillicult to discern. Two hunt elexations appear in the \ (.'ntricular 

 lloor 111 the region of the lateral recess indicating the position ol the \'estil)ular 

 nuclei. As compared w ith some of the more delinitely arboreal lorms ol pri- 

 mates, these elevations are not so [jronounci'd, but still show a degree ol 

 prominence which indicates a balancing mechanism m chimpanzee charged 

 with large resjjonsibilities m the general organization ol the animal's motor 

 activity. The cephalic angle of the fourth \entriclc, aside from the ele\ation 

 marking the presence of the nucleus abducentis, and the gradual decrease in 

 its diameters as the ventricle approaches the caudal oriiice of the Sylvian 

 aqueduct, shows no particularly outstanding feature. The lateral walls are 

 formed b\ the middle and superior cerebellar [jeduncles. in general, the mark- 

 ings of the oblongata, lioth u])on its \cntral and dorsal surfaces and m the 

 region of the xcntricic, are much less striking than is the case m man or even 

 in the gorilla. The markings are somewhat more clearl\ dclined than m the 

 intermediate primates. 



Tui£ Pons Varolii. At the cephalic limit of the oblongata upon its 

 N'entral surface appears the bulbopoiitik' sulcus which sej^arates the bulb 

 from the pons Varolii. This structure is a fairl\ pronounced leaturc ol the 

 brain stem in chimpanzee. It does not, how c'\-er, attain the proportions which 

 are characteristic of it in man or in gnrilla. Its latt'ral extremities arc con- 

 tinued to form the middle cert'bellar pt'tlunclc which approaches and enters 

 the cerebelluiii to form ultimate connections with tlu- lateral lobes ol this 



