HYLOBATES HOOLOCK, THE GIBBON 



419 



In the ventricular portion of the dorsal surface appears the caudal angle 

 of the fourth ventricle bounded laterally by the elevations of the clava and 

 cuneus. At the angle of this ventricle is the trigonum hypoglossi which 



FIG. 198. DORSAL SURFACE OF BRAIN STEM, HYLOBATES HOOLOCK. 



[Actual Length 45 mm.] 

 Key to Diagram, d. m. septum, Dorsomedian Septum; dorso. med. fissure, Dorsomedian Fissure; inf. 

 COLL., Inferior Colliculus; sup. cerebr. ped., Superior Cerebellar Peduncle; sup. coll., Superior Colliculus; 

 TUB. tricem. ,TubercuIum Trigeniini; 4TH ven.. Fourth Ventricle. 



marks the position of the nucleus of the twelfth nerve; lateral to it, and 

 separated from it by the sulcus limitans, is situated the fovea vagi above 

 the dorsal nucleus of the pneumogastric nerve. The lateral walls constituted 

 by the cuneus and clava become progressively reduced in altitude as they 

 proceed cephalad, and finally at the level of the lateral recess have reached 

 the plane of the ventricular floor. At this level, fibers of the eighth nerve make 

 their entrance, as the striae acusticae; most of these fibers pass directly 

 transversely inward to the dorsomedian sulcus. Below the level of the striae 



