3i8 THE INTERMEDIATE PRIMATES 



convey to the cerebellum atlereiit impulses necessary for the proper mani- 

 tenance of cerebellar function. In this sense, the size of the restiform body 

 (ICP) becomes significant as an index to the degree of afferent influx 

 received by the cerebeHum. The size of this structure in the baboon indicates 

 an animal fairly well equipped in coordinative control, although by no 

 means as abundantly supphed in this respect as many of the higher apes. 



Ventral to Deiters' nucleus is a dense mass of descending fibers, the 

 descending trigeminal tract (Trd) and mesial to it, the substantia gelati- 

 nosa (NR). Ventral to the latter structure is a large diffuse mass of gray 

 matter constituting the nucleus faciahs for the innervation of the facial 

 muscuhiture. From this nucleus are seen streaming inward and backward a 

 number ot myelinated fibers m spray-hke fashion toward the floor of the 

 fourth ventricle. This is the first portion of the facial nerve. 



The most ventral portion of the section is occupied by the compact 

 bundles of the pyramidal tract (Py) immediately dorsal to which is a 

 collection of crossing fibers constituting the secondary axons of the auditory 

 pathway. 



I 



LEVEL OF THE CEREBELLAR NUCLEI (pIG. 1 49) 



At the level of the cerebellar nuclei several structures which afford a 

 basis for estimating the functional capacity of the cerebellum make their 

 appearance. These are the cerebellar nuclei. A portion only of the cere- 

 bellum is shown in this section. The organ itself consists of a central 

 division, the vermis (Ver), and two lateral lobes or hemispheres (Cbl). 

 The mesial portion of the lateral lobes, the medullary vestibule, is shown. 

 Situated in this vestibule is an irregular, diffuse collection of gray matter, 

 the nucleus dentatus (Ndt). In this nucleus arise most of the fibers leaving 

 the cerebellum, thus providing the major efferent path for cerebellar 

 impulses concerned in coordinative control of the muscles. The size and 



