322 THE INTERMEDIATE PRIMATES 



This section is notable also as showing the beginning of the middle cere- 

 bellar peduncle (Mcp) which consists of the collected axons arising from the 

 pontile nuclei to complete the connection between the hemispheres of the 

 cerebrum and the cerebellum. 



Two of the cranial nerves also appear in the section. One is the sixth 

 cranial nerve (N6), whose nucleus abducens (Nab) lies immediately beneath 

 the floor of the ventricle in the central gray matter. A large number of myeli- 

 nated fibers pass forward from the nucleus to emerge at the bulbopontile 

 sulcus. The nervus facialis (seventh cranial nerve) ( Ny ), in its second portion, 

 appears as a circular bundle of fil)ers immediately beneath the iloor of the 

 fourth ventricle and mesial to the nucleus abducentis. The fourth portion of 

 this nerve is seen extending obliquely forward and outward from the nucleus 

 abducentis, and running a course divergent with the emergent libers of the 

 abducens nerve. The seventh nerve supplies the muscles of facial expression, 

 while the sixth nerve innervates the external rectus muscle of the eyeball. 



In the lateral angle of the ventricular space, and occupying a position 

 immediately lateral to the subependymal gray matter, is a collection of cells 

 constituting one of the vestibular nuclei, the nucleus of Bechterew (^NBe). 

 Dorsal to the nucleus of Bechterew, and forming the lateral boundary of the 

 ventricular space, is a large oval mass of myelinated fibers, the superior 

 cerebellar peduncle (Sep). This bundle represents the aggregation of nerve 

 fibers for impulses arising in the cerebellum and destined for the several 

 lower levels of the neuraxis in the interest of coordinative control of the 

 muscles. Along its dorsal aspect is a narrow bundle of deeply myelinized 

 libers, the ventral spinocerebellar tract (Gow), which follows this circuitous 

 course to enter the cerebellum. 



In the central portion of the section are the crossing libers constituting 

 the upper portion of the trapezoid body (Trp) at whose lateral extremity 

 is a nuclear collection, the superior olivary body (SO). In a position lateral 



