SIMIA SAT^■RUS, THE ORANG-OUTANG 499 



prcscMits the lower aimlc ol' the fourth Ncntriclc whose lloor is IjouikIccI l)y the 

 ik'xations loniud l)\ the eiiiieus aiul the cla\a. The lloor contains the usual 

 inarkin<i;s inclieating the trifi;onuni hypogiossi and the fovea vagi. As the 

 lateral recesses are apj)roachecl tlie two elevations formed by the clava and 

 euneus decrease in height and linall\- attain the level of the lloor itself. 

 At this point the enti'ring libi'rs constitutnig the striae acusticac cross the 

 lloor toward tlu' niidhne, most of tluin with an oblicjuity downward and 

 inward. .As the\ i-ntir the \entiieular ca\it\' these libers either cross or 

 become submerged w ithm an t'lexation situated near the lateral recess. This 

 elevation is the \estibular iinmenee. In the orang its prominence in the lloor 

 ol the xcntricU' rs relati\ely less pronounced than in the lower and intc'r- 

 inediate ])runates, but somew hat more conspicuous than in the chnnpan/.i'c, 

 gorilla and man. A median sulcus s\ inmctricallx di\ides the lloor of the 

 ventricle into two longitudinal haKis. 1 lu' iijjjx'r angle of the \entricular 

 chamber is contained m tlu' metcncephalic portion of the stem. Above the 

 striae acusticac a slight eie\ation marks the position of the nucleus abdu- 

 centis. In other particulars the markings u[)on the \entricular lloor are rather 

 indelinite. The lateral walls ot this portion ol the \entricle arc lormed b\ the 

 converging superior tx'rt'bellar pcdunck's. Ihe \'entricular ea\it\ itself 

 becomes more attenuated as the caudal orilice oi' the Sylvian aqueduct is 

 approached. 



The Pons \ ahomi. L pon the \entral surface at the cephalic extremity 

 of the oblongata a marked bulbo|)ontile sulcus draws tln' liiu- ol demarcation 

 btlwecn the bulb and the pons \ arolii. Ihe latter struct lux- is lairix large 

 and jjromment. Standing out conspicuously m the base ol the brain, it is 

 indicative of an animal possessed of a considerable connection between the 

 cerebral hemispheres and the lateral lobes of the cerebellum. The inference 

 ])erinissible Irom such an ainj:)le i)allio-cerebellar communication is that the 

 motor organization ol orang represents a relatively wide range of skilled 



