VIII 



THE HIND-BKAIN 



427 



The middle peduncles (crura ad pontem) are largely composed 

 of afferent fibres to the cerebellum, which arise in the cells of the 

 pontine nuclei. They cross in the median line of the pons and 

 terminate in the cerebellar cortex of the opposite side. Since the 

 cells of these crossed ponto-cerebellar fibres are in relation with 

 the final ramifications of the fibres which have their origin in the 

 cortex of the frontal and temporal lobes of the brain, it follows 

 that each cerebral hemisphere is indirectly connected with the 

 opposite half of the cerebellum on the opposite side by these fronto- 

 temporo-pontine paths (Fig. 227, a, &). 



According to Kamon y Cajal, efferent fibres from Purkinje's cells 



FIG. 226. Sections of dog's mesencephalon, showing degenerations following extirpation of right 

 half of cerebellum. (Marchi's method.) A, section at level of nucleus of origin of 3rd nerves ; 

 a, a, red nuclei of Stilling, that to the left much degenerated, that to the right less so ; 6, 

 fibres of 3rd nerves degenerated on the side of the extirpation ; d, posterior longitudinal 

 bundle terminating in the nucleus of the 3rd nerves ; e, pes pedunculi ; /, inferior bundle of fillet 

 of Reil coursing to corpora quadrigemina. B, corresponding section at superior corpora quadri- 

 gemina ; a, a, red nuclei, as above ; b, posterior longitudinal bundle ; c, optic tract partially 

 degenerated on the side of the extirpation ; d, inferior bundle of fillet of Reil running near the 

 corpora geniculata to the corpora quadrigemina ; e, pes of cerebral peduncle. 



also run through the middle peduncles, cross in the pons, and then 

 descend in the lateral column of the cord to terminate round the 

 motor cells of the ventral horn. According to Marchi and Mingazzini, 

 some of these efferent fibres run to the pontine nuclei, thence 

 fibres arise which ascend vertically through the cerebral peduncle 

 on the opposite side. By these indirect cerebello-cerebral paths 

 the cerebellum can influence the cerebrum on the opposite side 

 (Fig. 227, c, d). Finally, according to Bechterew and Mingazzini, 

 fibres of the middle peduncle, which arise in the cerebellar cortex, 

 cross the raphe of the pons, run up its sides, and end in the 

 formatio reticularis (Fig. 227, ,/) 



The inferior peduncles (crura ad medullam) contain both 

 afferent and efferent fibres, the former predominating. The fibres 



