SIMIA SAIMUS, THE ORANG-OUTANG 523 



clue to tlu' tact that llxv \ mtrifular chatnhcr is approaching the caudal 

 orifice ol the SvKian aqut'chict. I hi' lloor ol the' \entiich' shows no particular 

 luich'ai" s|)eciahzation. In It are the transxerse hhers constituting^ the third 

 portion of the lacial ncr\c m its eiiier<ient course from the l)rain, know n as 

 the genu facialis (N"). Entering: m rehition to the be<iinnin^ ol the inicldle 

 cerebellar peduncle are the lihers ol the dorsal root ol tlu' trigeminal ner\'c 

 (N5). These libers pass inward to come into relation with a somewhat con- 

 \'oluted mass of gray matter, the ce|jhalic extremity ol the substantia 

 gclatinosa trigcmini, here torming the com olutiones ciuinti (NR), and 

 ventral to it a large homogeneous nucleus from w hich arise the fibers forming 

 the motor root of the trigeminal ner\e, the nucleus masticatorius. The lateral 

 walls of the fourth \entricle at this le\el arc prockiced b\ tln' massive col- 

 lection of libers constituting the superior cerebellar peduncle (Sep). 



LE\EL OF THE INFERIOR COLLICULLS (FIG. 238) 



At this le\el the contour of the section is considerably moditied by the 

 appearance of two elevations m the roolplate of the midbrain. These are the 

 inferior colliculi ( ICt directly connected with the auditor\- system, since they 

 serve as relay stations in that pathway. They were formerly of greater func- 

 tional importance than in this or other jjrimates. The ventral aspect ot the 

 section still retaining some of the |)ontile constituents is ol [)articular interest 

 as it indicatt'S the transition from the pontile level of the stem to the di\erg- 

 ing cerebral |)cduncles. A dee[) \entral sulcus in the pons indicates the posi- 

 tion at which the dixarication will occur, while at the junction between the 

 basis and tegmentum in tlu' midline, a small space marks the position of the 

 foramen caecum anticum. The central gray matter (Cen) entirely sur- 

 rounds the Sylvian aqueduct and in its vcntromesial portion is specialized 

 to form the trochlear nucleus, or nucleus of the fourth cranial ner\e ( N4), 

 whose emergent fibers are seen collected in a dense bundle occupying a posi- 



