688 THE HIGHER ANTHROPOIDS 



olivary nucleus ( nco-olivi'). The next portion to appear is tlie mesial acces- 

 sory nucleus which is situated veiitromesial to the mam olivary nucleus. The 

 chief nucleus shows a considerable advance in the complexity of the convo- 

 lutions and reduplications which characterized it in the chimpanzee. The 

 fundus is broad and presents a number of plications. The dorsal and mesial 

 plates of this nucleus are thrown into extensive folds, while their dorsal 

 extremities turn somewhat inward to run parallel with the median line. 



The mesial accessory nucleus of the olive (mesial paleo-olive) a])pears 

 as a flat band in apposition to the mesial plate of the chiet olive with which it 

 is parallel. It becomes continuous with the upper extremit\ ot the mesial 

 plate near the cephalic extremity of the latter. The dorsal accessory nucleus 

 (dorsal paleo-olive) extends along the dorsal surface of the main nucleus 

 embedded in the reticular formation. It forms a narrow band of gray matter 

 with its mesial extremity turned somewhat in the ventrodorsal plane. As the 

 chief nucleus extends upward, the dorsal accessory nucleus becomes contin- 

 uous with its dorsal plate. The cei^halic limit of the oli\ary nucleus is in the 

 lower pontile region where the nuclear substance gradually disappears by 

 merging with the reticular matrix. 



The Reticllar Fokmahon 



71u' reticular formation appears in the upper cer\ical levels situated 

 between the substantia gelatinosa Rolancli and the \fntral gray column. It 

 increases in size as it is followed upward, replacing the xfiitral gray column 

 which merges with it and then extt'iuls to the midline to become contiguous 

 at various points with its tellow ol the opposite side. 



In the lower ventricular le\els it sup|)orts the inlerior olivarx complex 

 which is embedded in its \t'ntral surface. The leticular lormation is more or 

 less ciuadrilateral in shape with a veiitromesial, a \ enlrolateral, a dorsal and a 



