536 THE HIGHER ANTHROPOIDS 



the wntrolatcral angle of the ncuraxis. It begins just below the le\el ol the 

 fourth ventricle, extending its two branehes mesiallx' and somewhat ciorsally 

 toward the median raphe. Both the dorsal and the ventral branehes show 

 marked reduplieation. The ventral accessory oli\ary nucleus begins at the 

 level in which the main nucleus arises. It extends upward as a Hat band 

 applied to the ventral asjX'Ct of the main nuclear mass. It approaches 

 the cephalic limit of the main nucleus, becoming continuous with 

 the dorsal extremity of the ventral branch near its summit. The dorsal acces- 

 sorv olivary nucleus begins below as an mconspicuous mass at about the 

 same level as the main olivary nucleus. It ra|)idly extends in a ventrodorsal 

 direction, lying as a Hat band dorsal to the mesial half ol the dorsal branch 

 of the main nucleus. At the cephalic extremity of the principal nucleus it 

 becomes conlluent with the dorsal extremity of the dorsal branch. The entire 

 C()mj)lex extends as far upward as the midventricular level oi the brain 

 stem, where it disappears by merging with the reticular matrix. Its ventral 

 surface is in contact with the pyramidal tract and the ventral portion of the 

 mesial iillet. Its iLindus is covered onlv b\ the external arcuate libers, while 

 its dorsal surface is in contact with the \entral suriace of the reticular 

 lormation. 



The Reticular FoRMAriox 



At a point slightl\ above the lowest sections of the reconstruction, the 

 ventral gra> column becomes detached from the central gray by the decussat- 

 ing pyramidal libirs. This gray column is soon replaced by the reticular 

 formation with which it merges and e\entually disappears. The reticular 

 formation itself is seen in the lowest lexels of the reconstruction as a small 

 collection of mixed gray and whitt' matti'i' on the outer suriace ol the \-entral 

 gray column. This rapidl\ incrt'ases m size as it is lollowed upward. It 

 extends dorsad to come into contact with the substantia gelatinosa Rolaiidi. 



