382 THE INTERMEDIATE PRIMATES 



forms the superior medullary velum above the beghmino; of the Sylvian 

 aqueduct (IT), are the decussathig fibers of the fourth or trochlear 

 nerve (N4) as they emerge from the brain stem. This ner\e supphes the 



FIG. 179. MACACUS. LE\EL OF THE EMERGENCE OF THE TROCHLEAR NERVE. 

 CEN, Central Gray Matter; ctt, Central Tegmental Tract; it. Iter; lf. Lateral Fillet; mcp, Middle Cerebellar 

 Peduncle; mf, Mesial Fillet; N4, Trochlear Nerve; pd, Predorsal Bundle; pl, Posterior Longitudinal Fascicu- 

 lus; PN, Pontile Nuclei; pns. Pons; py. Pyramid; ref. Reticular Formation; rst, Rubrospinal Tract; scp, 

 Superior Cerebellar Peduncle; spt, Spinothalamic Tract. [Accession No. 149. Section 305. Actual Size 

 18 X 12 mm.] 



superior obhque muscle of the eyeball and is the only one of the cranial nerve 

 series which undergoes complete decussation before its emergence. 



The three layers of the pons Varolii arc still clearly defined and further 

 opportunity is afforded to estimate the extensiveness of the pontile nuclei 

 (PN) whose bearing upcMi the de\elopment of skilled mo\'ements has 



