VIII 



THE HIND-BKAIN 



425 



are ^**2 



The niedullated fibres of the white matter appear continuous 

 with the three peduncles which unite the cerebellum with the 

 brain -stem. 



Lying in the white matter, near the roof of the fourth 

 ventricle, are four masses or 

 nuclei of grey matter of 

 different sizes, which 

 symmetrically arranged on 

 either side of the organ. 

 The most medial is known 

 as the nucleus of the roof 

 (nucleus fastigii) ; the most 

 lateral is the nucleus den- 

 tatus, also known as the 

 corpus oh' vare cerebelli, from 

 its great resemblance to the 

 olive of the bulb. The two 

 small nuclei, respectively the 

 nucleus- globosus and emboli- 

 formis, are accessory nuclei 

 lying between the two pre- 

 ceding (Fig. 225). 



From the physiological 

 point of view it is important 

 to form a clear picture of the 

 relations of the cerebellum 

 to the rest of the nervous 

 system, by identifying the 

 afferent and efferent paths 

 that pass through the three 

 cerebellar peduncles. 



The fibres of the superior 

 peduncles (crura ad cere- 

 brum) arise for the most 

 part in the cells of the 

 dentate nuclei ; they run 

 forwards to the mesence- 

 phalon, decussate almost 

 completely beneath the cor- 

 pora quadrigemina, and ter- 

 minate in the nuclei rubri 

 of Stilling, which lie in the tegmentum of the mid-brain near 

 the regio subthalamica. From the cells of the red nuclei fibres 

 run out to the optic thalami. 



In addition to these efferent fibres the superior cerebellar 

 peduncles also contain a few afferent fibres (Mingazzini), which 

 probably arise in the thalami, pass through the red nuclei without 



Fio. 224. Section of cortex of cerebellum. (Sankey.) 

 a, pia mater ; 6, external layer ; c, layer of corpuscles 

 of Purkinje ; d, inner or granule layer ; e, white 

 matter. 



