6i6 THE HIGHER ANTHROPOIDS 



passes deeper into the tegmentum. At the point w here the superior cerebellar 

 pedunele leaves the superior medullary vehim and approaches the tegmen- 

 tum a tliin extension of the reticular formation forms on its lateral aspect. 

 This thin la\er passes further dorsad until the superior cerebellar peduncle 

 is completely surrounded by mesencephalic reticular formation. From this 

 point the peduncle sinks deeply into the tegmentum of the pons, tunnelling 

 the reticular foiniation of the upper part of the metencephalon and the lower 

 levels of the mesencephalon until it reaches the midline where it decussates. 

 A termination lor most of its hbers is provided in the nucleus ridjcr. 



Just above the termination of the substantia gelatinosa tngemini 

 the lateral extension of the reticular formation is grooved by the passage of 

 the lateral lillet. This prolongation of the reticular formation gradually 

 envelops the lateral lillet as the latter sinks into the tegmentum to vnd in 

 connectioTi with the niienor colhculus. 



The format lo reticularis comes into such close contact with the surface 

 of the mesencejihalon that its lateral conformation is almost ich-ntical with 

 the surface of this segment of the neuraxis. It is separated from the lateral 

 angle of the inferior collicuUis b\ a space in which develops the group of 

 fibers lorming the inU'iior brachium. 



Abo\e this [ioint tlu' reticular formation si'cms to diminish in volume 

 and becomes conlluent with the indilferent gra\ matter ol the e|)ithalamic 

 and hypencephalie loiniations. I.aterall\ it merges with the reticular forma- 

 tion of tlu' dlencephalon. 



Between the superior and interior colliculi the reticular formation 

 gains the surlaci' of the mesencephalon m the mtercollieular furrow. Cephali- 

 callyit forms the latt-ral and \entral supj^orl tortlu' deep surface of the superior 

 colllculus. It does not tome into contact with the sujjerlieial layers ol the 

 colliculus due to the development of the superior brachium which passes 

 from the lateral aspect of the superior colliculus to the lateral geniculate body. 



