THE CEREBELLUM 



617 



with those coming from the opposite side, while others pursue a straight 

 direction, terminating on the same side. Through the intervention of fibers 

 which arise in the red nucleus and ascend to the cerebral cortex, the hemi- 

 sphere is thus connected with both sides of the cerebellum, though chiefly 

 with the opposite side. 



Efferent fibers also leave the cerebellum by the middle peduncle and pass 

 directly to the nucleus pontis, around the cells of which their terminals 

 arborize. Efferent fibers also descend the inferior peduncles and constitute 

 the tract known as the Lowenthal and Marchi tract, situated in the antero- 

 lateral region of the spinal cord in its upper part. 



The afferent fibers come from a variety of sources. Those found in the 



FIG. 253. SECTION or CEREBELLAR 

 CORTEX. A. Outer or molecular 

 layer. B. Inner or granular layer. 

 C. White matter, a. Cell of Purk- 

 inje. b. Small cells of inner layer. 

 c. Dendrites of these cells, d. A 

 similar cell lying in the white matter. 

 (Stirling.} 



FIG. 252. VIEW OF CEREBELLUM IN SECTION, AND 

 OF FOURTH VENTRICLE, WITH THE NEIGHBORING PARTS. 

 (From Sappey.) i. Median groove fourth ventricle, 

 ending below in the calamus scriptorius, with the longi- 

 tudinal eminences formed by the fasciculi teretes, 

 one on each side. 2. The same groove, at the place 

 where the white streaks of the auditory nerve emerge 

 from it to cross the floor of the ventricle. 3. Inferior 

 peduncle of the cerebellum, formed by the restiform 

 body. 4. Posterior pyramid; above this is the calamus 

 scriptorius. 5, 5. Superior peduncle of cerebellum, or 

 processus e cerebello ad testes. 6, 6. Fillet to the side 

 of the crura cerebri. 7, 7. Lateral grooves of the crura 

 cerebri. 8. Corpora quadrigemina. (After Hirschfeld 

 and Leveille.) 



superior peduncles come from the red nucleus; those in the middle peduncles 

 from the nucleus pontis of the opposite side, having crossed or decussated at 

 the raphe* near the anterior surface of the pons; those contained in the in- 

 ferior peduncles are the most abundant and important, and are represented 

 by (i) the direct cerebellar tract, which terminates in the superior vermis 

 after decussation; (2) the anterior and posterior arcuate fibers, the former 

 coming from the gracile and cuneate nuclei of the opposite side, the latter 

 from the same side, which also pass to the superior vermis; (3) the acoustico- 

 cerebellar tract, composed of fibers which are the axons of the sensory 

 end-nuclei (Deiters) of the vestibular portion of the auditory nerve. It is 

 probable that all these fibers decussate prior to their final termination. 



