H^'LOBATES HOOLOCK, THE GIBBON 437 



substantia gclatinosa. From this nucleus many fibers pass dorsally and mesi- 

 ally toward the angle of the fourth ventricle to form the tractus mesence- 

 phalicus trigemini. 



FIG. 206. GIBBON. LEVEL THROUGH THE MIDDLE OF THE PONS. 

 Mcp, Middle Cerebellar Peduncle; mf. Mesial Fillet; N5, Trigeminal Nerve; pn, Pontile Nuclei; pns. Pons; 

 FY, Pyramid; ref, Reticular Formation; scp, Superior Cerebellar Peduncle; tur, Tractus Uncinatus of 

 Russel (Hook Bundle). [Accession No. 141. Section 186. Actual Size 21 X 16 mm.] 



The central gray matter occupies a position mimediately beneath the 

 floor of the fourth ventricle and serves to form the lateral ventricular bound- 

 ary. At the lateral extremity of the section is a dense mass of fibers, the 

 superior cerebellar peduncle (Scp), an index concerning the degree of 

 coordinative control which the animal possesses. Compared with the other 

 intermediate primates, the gibbon shows no marked increase in this par- 



