540 THE HIGHER ANTHROPOIDS 



complete sheath is formed around the ])\raiiiid. The pontile nuelei luse at 

 the midhne. Passin<i; throu^^h the eavity of the nuelear sheath are strands 

 whieh produce the numerous bridges of gray matter separating the palho- 

 spinal and palHo-pontile hhers into smaUer groups. Tlie dorsal jjortion of the 

 hileral buttress is in contact with tlie \entroIateraI angle ol the reticular 

 formation and a similar arrangement |jresents itsell m regard to the dorsal 

 part of the mesial buttress. The dorsal surface of the deep la\ er of the |)ontile 

 nuclei and the ^'entral surfact' of the reticular formation art' not m actual 

 contact on account of the dcxt'lopment at this point of the \arious longitu- 

 dinal fibers. The pontik' nuclei begin to diminish as the isthmus is apj)roaclied 

 and rather rapidly come to a termination. The superhcial layer, together 

 with tlu' lateral and mesial buttresses, first begin to dmiimsh and then 

 disajjptar, lca\ing the deep nuclear layer to continue upward and become 

 conllueiit with the substantia nigra. The latter seems, therefore, to be sup- 

 ported by the upper extension of the two buttresses and throughout its 

 extent by tlie deep layer of tiie pontile nuclei. 



The Vestibular Complex 



The vestibular complex hrst ap|3ears as a small triangular collection of 

 nuelear material located between the lateral aspect ol the lloor ol the lourtii 

 ventricle and the upper dorsal j)orti()n of the nucleus of Burdach. It rajjidly 

 expands in size, acting as a wedge w Inch ser\es to separate the \entricular 

 floor from the latter nucleus. A prolongation is carried forward vcntrally, 

 which separates the mlcrior cerebellar peduncle Irom the ]:)()ntik' tegmentum. 



At the mid-\'ent iieular lc\'el and dorsal to the nucleus ol Deiters, the 

 nucleus triangularis of Sehwalbe ap])ears. It lies beneath the lloor of 

 the ventricle. This nuclear mass continues upward to a j)oint at which the 

 ventricle begins to close, wlure it rai)idl\ terminates. The triangular nucleus 

 in the mid-ventricular Icxel is separated Irom the Ncntricular gray matter 



