538 THE HIGHER ANTHROPOIDS 



The mesial surface of the retieuhir lormatioii throughmit its entire 

 extent is more or less smooth and separated from its U-llow nl thi' opposite 

 side h\ the loniritudinal liber traets near the raphe. Abo\e tlie le\el of the 

 substantia gelatinosa trigemini, and the vestibular and cochlear complexes, 

 the reticular formation expands and forms almost the entire' mass of the teji- 

 mcntum ot the upper pons and mesencephalon, it reaches the surlacc and 

 sends a mim[)er ol prolongations backward, one ol which lorms an iiuest- 

 ment o\er the suj)erior cerebellar peduncle as this liber tract approaches the 

 mesencephalic tegmentum. \ entrallx the reticular lormation comes into close 

 contact with the dorsal portion ol the lateral buttress oi the pontile nucleus. 

 Latcrall\' and mesiall\- it is in contact w ith the mesial buttress, while between 

 teshe two points ol a])])osition the \entral surface ol the reticular lormation 

 and the dorsal suriace ol the jjontile nucleus are separated by the trapezoid 

 body. In tlu' mesencephalon the reticular lormation is irregular in outline. 

 It is penetrated from behind forward by the superior cerebellar peduncle 

 which gradually sinks deeper into the tegmentum, thus allowing more of 

 the reticular formation to form on its lateral aspect. The diAclopment in the 

 mesencephalon ol the nucleus ruber presents a massi\e condensation in the 

 reticular formation. The reticular lormation of the mesencephalon, followed 

 upward toward the [)oint ot transition into the dienci'phalon, demonstrates 

 the continuity ol these two structures, the reticular formation of the mesen- 

 cephalon merging with the indiflercnt zona incerta of tin- intcrbrain. The 

 lateral surface ol the reticular lormation in the lower mesencephalic area is 

 crossed from belore backward b\ a di'pression produced by the passage of 

 the lateral lillet. In the mtercollicular region a continuation of the formatio 

 reticularis passes dorsalls and mesially to separate the two colliculi. In 

 the most cephalic j^ortion of the midbrain the retuiilai formation gives 

 origin to a similar dorsal prolongation which separates the superior colliculus 

 from contact w ith the nuclear masses of the epithalamus and metathalanuis. 



