RECONSTRUCTION Ol TROGLODYTES GORILLA 695 



liculus. 1 he latter rests niesiall\ upon xUc incliilereiit dorsal !j;ra\ matter w hllc 

 laterally it Is partially supported by the meseiieepiialie retieular formation. 

 The Iat(,'ral lillet, as it emerges from the trapezoid body, courses oblic|uel\ 

 backward and u])\\ ard o\ er the surlace oi the meteneephalic and mesenceph- 

 alic tegmentum. It produces a deep groove m the tegmentum of the mesen- 

 cephalon as it a])pr()aches its destination in the mferior eolliculus. 



Cephalicall\- the inlerior eolliculus is separated from the su[)erior eol- 

 liculus b>' the dorsal prolongation of the mesencephalic reticular formation 

 lying in tlie intereollicular furrow. Passing from the lateral surface of the 

 inferior eolliculus cephahcall\ and ventrally is a groo\-e produced bv the 

 inferior brachium which connects the inferior eolliculus with the mesial 

 geniculate body. 



The superior eolliculus is supported mesially b\ the indilierent dorsal 

 gray matter and laterally by the lateral prolongation of the reticular forma- 

 tion. Mesially the two colliculi arc connected across the midline by the supe- 

 rior and inicrior collicular commissures. Cephalically the superior eolliculus 

 is continuous with a thin strip of gray matter, a dorsal reticular prolongation, 

 which passes forward to merge with the epithalamic gray matter. 



The Substantia Nigr.\ 



The substantia nigra apjjears as a contiiniation of the dorsal laver of the 

 pontile nuek'us. The supjiort derived from the lateral and mesial buttresses, 

 which was so conspicuous in the lower primate species, continues in these 

 higher forms. The substantia nigra presents a ventral surface in contact with 

 the desctnding pallio-spinal and pallio-pontile libers. .MesialU it is in con- 

 tinuity w ith the indilierent interpeduncular gray matter. Laterallv it is con- 

 tinued oLitward into rather close contact with the mesial geniculate body, 

 |)resenting a Miitral, hook-shaped prolongation. In this lateral portion is 

 lound the specialization in the substantia nigra from which nerve fibers seem 



