THE CEREBELLAR PEDUNCLES. 



85 



divided in the middle line and turned aside. When this is done the superior crura, 

 with the superior medullary velum stretched out between them, are brought into 

 view. Their further course in the mid-brain will be subsequently traced. 



The fibres of the superior peduncle pass almost entirely out of the interior of the 

 dentate nucleus (intraciliar fibres), but some fibres curve round the outer side of this 

 without passing into it (extraciliar), and some of the mesial fibres are traceable 

 directly into the white substance of the worm. Probably many of the fibres of 

 these peduncles which emerge from the dentate nucleus are connected with its cells, 

 but others pass in bundles through the grey lamina which composes it, without 



Fig. 62. FIGURE SHOWING THE THREE PAIRS 



OP CEREBEIiLAR PEDUNCLES. ( From 



Sappey after Hirschfeld and Leveille. ) 



On the left side the three cerebellar pe- 

 duncles have been cut short ; on the right 

 side the hemisphere has been cut obliquely 

 to show its connection with the superior and 

 inferior peduncles. 



1, median groove of the fourth ventricle ; 

 2, the same groove at the place where the 

 auditory striae emerge from it to cross the 

 floor of the ventricle ; 3, inferior peduncle 

 or restiform body ; 4, funiculus gracilis ; 



5, superior peduncle ; on the right side the 

 dissection shows the superior and inferior 

 peduncles crossing each other as they pass 

 into the white centre of the cerebellum ; 



6, fillet at the side of the crura cerebri ; 



7, lateral grooves of the crura cerebri ; 8, 

 corpora quadrigemina. 



being thus connected. They appear to go eventually to the superficial grey matter 

 of the laminas. 



From the superior medullary velum longitudinal fibres can be traced passing into 

 the white centre of the worm. These are chiefly fibres belonging to the antero- 

 lateral ascending cerebellar tract (see pp. 25 and 65). 



Many, if not most, of the fibres of the superior peduncle originate in cells within the 

 cerebellum, and undergo degeneration as the result of lesions of that organ (see p. 93). But 

 in a case, reported by Mendel, of lesion of the left thalamus opticus, a well-marked bundle of 

 degenerated fibres was traceable through the tegmentum of the left side mesial to the nucleus 

 tegmenti, across to the right side at the deoussation of the superior peduncles, and along the 

 outer side of the right superior peduncle to the right hemisphere. 



The middle peduncles (crura ad pontem), distinguished by the small size of their 

 fibres, coming from the pons Varolii, enter the lateral part of the white matter in two 

 main bundles. One of these, composed of the superior transverse fibres of the 

 pons which pass obliquely downwards over the others (fig. 30, ), radiates into 

 the lateral and lower parts of the medullary centre of the hemispheres. The 

 other bundle, which is formed of the lower transverse fibres of the pons, is joined 

 at its passage into the white centre by the restiform body or inferior peduncle 

 (fig. 30, &), and the fibres of both turn upwards and radiate into the upper parts 

 of the medullary centre of the hemisphere, and partly into the upper part of the 

 worm (but most of the pons fibres enter the hemisphere). Those peduncular 

 fibres which pass into the worm are derived chiefly from the restiform body, and 

 include the large fibres of the dorso-lateral cerebellar tract, most of which go to the 

 same side but some pass across to the opposite side. Those which enter the hemi- 

 sphere curve over the corpus dentatum, and are termed by Stilling the semicircular 

 fibres (fig. 60, s). They come mainly from the opposite olivary through the resti- 

 form body. A small part of the fibres of the restiform body is said by Stilling to 

 end in the corpus dentatum. 



