I094 HUMAN ANATOMY. 



3. The olivo-cerebellar fibres, chiefly from the opposite inferior oHvary nucleus but to a 

 limited extent also from the nucleus of the same side. They contribute in large measure to the 

 formation of the lateral part of the restiform body and, on reaching the cerebellum, end within 

 the cortex of the hemisphere and worm, as well as within the hbre-complex enveloping the 

 nucleus dentatus. Whilst for the most part afferent, it is probable that some of the fibres within 

 the tract are efferent and hence conduct impulses in the contrary direction. 



4. Fibres from the nucleus lateralis of the medulla, which pass to the cortex of the cere- 

 bellar hemisphere. 



5. Fibres from the arcuate nucleus, which pass to the cerebellar cortex. 



6. The nucleo-cerebellar tract, comprising fibres from the cells within the reception-nuclei 

 of the trigeminal, facial, vestibular, glosso-pharyngeal and vagus nerves. The tract occupies 

 the median part of the peduncle and ends chiefly in the roof-nucleus of the same and of the 

 opposite side. 



7. Other fibres pass in reversed direction from the roof-nucleus to the dorso-lateral 

 (Deiters') vestibular nucleus of the auditory nerve and thence, as the vestibulo-spinal tract, 

 descend through the medulla into the antero-lateral column of the cord. 



8. Additional vestibular (and, possibly, other sensory) fibres pass without interruption by 

 way of the restiform body to the roof-nuclei and constitute the direct sensory cerebellar tract 

 of Edinger. 



The Middle Cerebellar Peduncle. — The middle peduncle (brachium pontis), 

 which continues the pons laterally into the medulla of the cerebellum, transmits the 

 fibres whereby the impulses arising within the cerebral cortex are conveyed to the 

 cerebellum. It does not establish diredt connections between the cerebellar hemi- 

 spheres, as it might be supposed to do from its transverse position and intimate 

 relation with the cerebellar hemisphere, such bonds from side to side passing 

 exclusively by way of the commissures within the worm. 



The chief constituents of the middle peduncle are : 



1. The continuations of the fronto-cerebellar and temporo-occipito-cerebellar tracts, the 

 fibres of which arise from the cortical cells within the frontal, temporal and occipital lobes 

 respectively, descend through the internal capsule and the cerebral crus, and end around the 

 cells of the pontile nucleus. From the latter cells arise the ponto-cerebellar fibres, the imme- 

 diate constituents of the middle peduncle, that for the most part cross the mid-line and traverse 

 the peduncle to be distributed to all parts of the cortex of the hemispheres and of the worm and, 

 possibly, also to the nucleus dentatus. A small number of these fibres do not decussate, but 

 pass from the pontile cells to the cerebellar cortex of the same side. It should be remembered 

 that the pontile nuclei are also influenced by cortical impulses that descend by way of the pyram- 

 idal tracts, since numerous collaterals from the component fibres of these motor paths end 

 around the pontile cells. 



2. Efferent cerebello-pontile fibres, distinguished from the afferent fibres by their larger 

 diameter, originate as axones of the Purkinje cells and pass from the cerebellar cortex through 

 the middle peduncle into the dorsal part of the pons, where, alter crossing the mid-line, they 

 are believed (Bechterew) to end within the tegmentum in relation with the cells of the nucleus 

 reticularis tegmenti close to the raphe. The assumption, often made, that many of the efferent 

 cerebello-pontile fibres end around the cells of the nucleus pontis, lacks the support of the more 

 recent observations. 



The Superior Cerebellar Peduncle. — The superior peduncle (brachium con- 

 junctivum) forms, with its fellow of the opposite side, the important pathway by which 

 the cerebellar impulses are transmitted to. the higher centres and, eventually, to 

 the cerebral cortex, as well as indirectly to the spinal cord. 



Its chief constituents are fi) the cerebello-rubral and (2) the cerebello-thalamic fibres 

 collectively knoivn as the cerebello-tegmental tract. The principal components of tlie latter are 

 the fibres arising from the cells of the dentate nucleus, which, emerging from the hilum of the 

 coq^us dentatum and receiving augmentations from the roof-nucleus and, probably, to a limited 

 extent from the cortex of the worm, become consolidated into the rounded arm that skirts the 

 supero-lateral boundary of the fourth ventricle. Converging with the tract of the opposite side 

 towards the mid-line, the peduncle sinks ventrally and disappears beneath the corpora quadri- 

 gemina, many of its fibres continuing their course throui^h the tegmentum of the cerebral peduncle 

 in'cO the subthalamic region and the thalamus. On reaching a level corresponding to that of 

 the upper third of the inferior colliculi of the quadrigeminal bodies, the tracts of the two sides 

 meet and begin to intermingle, the decussation of the superior peduncle (Fig, 960) thus estab- 



