6i2 THE HIGHER ANTHROPOIDS 



At a point soiiu'w hat below the niicl-vcntricular i^ortion of the sttin the 

 substantia gelatinosa shows the attenuation which is characteristic ol this 

 nucleus and which here had been termed the "waist" ot tlie nucleus. 

 Passing ccphalad, however, it rapidly- expands again and appears as a [prom- 

 inent feature.' in the cross section ol the pontile region. Its mesial surlace is in 

 close contact w ith the reticular lormation ol the m\ eleneephalon and meten- 

 ccphalon, which is hollowed out to receive this trigeminal nucleus. As the 

 point of transition between the metencephalon and the mesencephalon is 

 approached the nucleus gradually begins to disappear and it linallx merges 

 insensibly into the reticular formation of the Lipper metencephalon. 



The Inferior Olivary Nucleus 



This ULielear mass of gray matter has attained relatively large propor- 

 tions in the oblongatal sections. It is both extensive in size and complicated 

 in structure. Its fundus and the two branches which compose it are made up 

 of a complex series of plications and reduplications which thus greatly 

 increase the cell-bearing area ol the niuleus. The lundus is deep and directed 

 toward the ventrolateral angles of the oblongata. It reaches almost to the 

 periphery and produces a well-marked promiiunee on the surlace ol the 

 oblongata, the oli\ar\- eminence. It bi'gins below at a point corresponding to 

 the caudal end of the nucleus of Burdaeh and extends upward through the 

 metencephalon to a level corresponding with the maximum dexelopmcnt of 

 the vestibular com]jle\. 



Ihe ventral accessory olivary nucleus is ijresent as a well-developed 

 lamina of gra\' matter arising at almost the lowest \v\v\ ol tlu' duel nucleus 

 as a small collection of nueUar material in front ol the ventral branch of 

 the main nucleus. It continues upward closely applu'd to this \-ent ral branch, 

 to the cephalic extremity of thi' nucleus, where it graduall\ disapi)ears by 

 becoming conlUu'iit with the dorsal extension ol the \entral branch. 



