4,-4 THE INTERMEDIATE PRIMATES 



.supports tin- cntiri' tianswrsi' (.■xtnit ol thr substantia nii^ra, tliickt'iiiufi; at 

 Ijoth the nu'sial and lateral (.■xtreniitics, w lure- thr deep ponlili' la\rr fuses 

 with the diirsal extremities of the mesial and lateral buttresses. It presents a 

 roui^hened xcntral surlaei.' in e()nlai.'t with the desc't'ndin;j; pallio-spmal and 

 palliii-pontile tracts. \U'siall\ it is eiuitinuous with the indillercait intca- 

 peduneular }.::ra\ matter, while laterall\ it presents a hooked extrcMiiitx whleh 

 conu's into elose relation w ith tlu' two <j;enKulatt' bodies. Cephalieally it lades 

 a\\a\ and set-nis to l)e eontinuous with tlu' subthalamie letieular lormatioii 

 and the zona ineerta. 1 lie s|)e(.Mali/at ion m its latcaal portion, Irom whieh 

 ncr\e libers pass mto the tegmentum, is well de\eloped. 



The C01.LICULI 



Tht'se strueturc's appear as speeiali/at ions in the dorsal extcaision ol 

 the ii'tieular lormation in {Uv niescaieephaloii. 1 lu' niKaior eollieulus, ot 

 moderate size, rests upon the latcaal extcaision ol the retuular lormation 

 and dorsoiiiesiallx upon the indiliereiit ij:ra\ matter wIiil'Ii lies in the median 

 line, it IS se|)arated Irom tin- superior eollieulus b\ the mtereollie-ular suleus 

 wliieli IS (n'eupie'd b\ a dorsal extension irom the meseiieephahe ix'lieular 

 formation. The superior eollieulus is niueh more I'Xteiisixe 111 size than the 

 inleiior t-ollieulus and is siinilarl\ situatt'd. its lateral extremit\ rests upon 

 tile lateral extension ol the iiU'siaKx-phahe reticular lormation, while itsdorsal 

 and mesial extreinitic's rest upon this same mdillereiit median ,!j;ra\ tissue. 



The xeiitral surlaees ol both eollieuli rest upon extensions ol the nieseii- 

 cephalie reticular formation wliieli prexeiits tlieiii Irom eoiiim.u into actual 

 contact with the central .u;ra\ matter. 



Tni£ Nlclels Rr bek 



The nucleus ruber is only inodcratel\ de\ eloped in gibbon, ap|)cariiiii; 

 in the' cephalic portion of the mesencephalon as a condensation m the mesial 



