PAPIO CVNOCEPHALUS 323 



to the emerging fibers forming the fourth portion of the seventh nerve is the 

 substantia gelatinosa (NR), lateral to which is the now dense and compact 

 mass of the descending trigeminal tract. 



LEVEL AT THE MIDDLE OF THE PONS VAROLU SHOWING THE ENTERING FIBERS 

 OF THE FIFTH OR TRIGENHNAL NERVE (FIG. I51) 



At this level several noteworthy features make their appearance. The 

 most important of these is the broad band of entering fibers of the fifth nerve 

 which make their way through the middle peduncle (Mcp ), passing backward 

 as a dense mass of myelinated fibers (N5), of which the more lateral por- 

 tion constitutes the sensory root of the trigeminal nerve, and the more 

 mesial, the motor root. Sensory fibers are seen terminating in the cephalic 

 portion of the substantia gelatinosa which here is somewhat convoluted 

 m Its appearance and is for this reason spoken of as the convolutiones 

 quinti (NR). Mesial to this, and somewhat ventrally placed, are the more 

 densely myelinized bundles of fibers taking origin in a nuclear mass, the 

 nucleus masticatorius of the fifth nerve (NM). Two of the chief con- 

 necting links of the cerebellum appear at this level. The first is the middle 

 cerebellar peduncle (Mcp) situated in the most ventral position of the 

 section and sweeping outward and backward to enter the cerebellum and dis- 

 tribute Its fibers to the lateral lobes of that organ. It represents the connection 

 of the cerebral ct)rtex with the hemispheres of the cerebellum. The second 

 great connecting link in the cerebellar system shown in this section is the 

 superior cerebellar peduncle (Sep) situated in the lateral extremity of 

 the fourth ventricle and representing fibers arising in the dentate nucleus, 

 which form the great efferent pathway for impulses out of the cerel)ellum, 

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

 of the muscles. 



