222 THE LOWER PRIMATES 



LEVEL OF THE EMERGENCE OF THE SIXTH NERVE (FIG. 1 23) 



A remarkable feature at this level of the brain stem in mycetes is the 

 appearance in its entire course of the emergent root of the abducens nerve. 



FIG. 123. MYCETES SENICULUS. LEVEL OF EMERGENCE OF SIXTH NERVE. 



CEN, Central Gray Matter; cow, Ventral Spinocerebellar Tract; mf, Mesial Fillet; nab, Abducens Nucleus; 

 NBE, Nucleus of Bechterew; nr. Nucleus of Rolando; n6, Abducens Nerve; N7, Facial Nerve; n8, Auditory 

 Nerve; pd, Predorsal Bundle; pl. Posterior Longitudinal Fasciculus; pv, Pyramid; ref, Reticular Formation; 

 scp, Superior Cerebellar Peduncle; so, Superior Olive; trd, Descending Trigeminal Tract; trp, Trapezoid 

 Body; TUR, Tractus Uncinatus of Russel (Hook Bundle). [Accession No. 148. Section 230. Actual Size 

 18X7 mm.) 



The origin of this nerve is seen in its nucleus (Nab), and its course directly 

 ventrad through the trapezoid body (Trp ), the lateral portion of the mesial 

 fillet (Mf), and its emergence lateral to the pyramid (Py), are exceptional 

 in cross sections of the primate stem. No fibers of the pons are as yet appar- 

 ent at this stage. The central gray matter (Ccn ) is a narrow zone, which 

 in its mesial angle contains the second portion of the facial nerve (N7). 

 Its lateral angle is continuous with the nucleus of Bechterew (NBe). 



