H^'LOBATES HOOLOCK, THE GIBBON 443 



(Cen), is the reticular formation ( Ref), in this species somewhat reduced 

 in size and prominence as compared with the lower forms. This reduction 

 is due largely to the emergence from it of the large red nuclear mass. In the 



FIG. 210. GIBBON. LE\EL OF THE SUPERIOR COLLICULUS. 

 CEN', Central Gray Matter; cp, Cerebral Peduncle; ctt, Central Tegmental Tract; mf. Mesial Fillet; mgb. 

 Mesial Geniculate Body; noc. Nucleus Oculomotorius; nru, Nucleus Ruber; N3, Oculomotor Nerve; pd, 

 Predorsal Bundle; pl, Posterior Longitudinal Fasciculus; ref. Reticular Formation; sbn. Substantia Nigra; 

 sc, Superior Colliculus. [Accession No. 141. Section 350. Actual Size 30 X 16 mm.] 



lateral extremity of the section is seen a small protul^erance, the mesial 

 geniculate body (Mgb). The gray matter of this nucleus seems to be 

 confluent with another large nuclear aggregation situated ventromesial to 

 it, the substantia nigra (Sbn). This mass of gray matter extends obliquely 

 inward and forward from the region of the mesial geniculate body toward 

 the optico-peduneular space and separates the basal portion of the mesen- 



