1372 A MANUAL OF ANATOMY 



sulcus, within the lobulus gracihs; (5) the postgracile, or posterior 

 arcuate, sulcus, between the lobulus gracilis and the inferior semi- 

 lunar lobule ; and (6) the small horizontal sulcus within the inferior 

 semilunar lobule. 



Peduncles of the Cerebellum. — The peduncles are three in number 

 on either side, namely, superior, middle, and inferior, and they are 

 composed of fibres which enter, or emerge from, the central white 

 medullary substance. 



The superior peduncles are composed of efferent fibres, and are 

 at first concealed from view by the upper or anterior portions of 

 the hemispheres. After emerging from the hemispheres they pass 

 upwards on the lateral aspects of the dorsal surface of the pons 

 Varolii in a converging manner towards the quadrigeminal bodies. 

 They form the lateral boundaries of the upper part of the floor 

 of the fourth ventricle, and by their convergence they project 

 slightly over that part of the ventricle, so as to take part in its 

 roof. The superior medullary velum extends between the two 

 peduncles, and closes the interval between them. On reaching 

 the inferior pair of quadrigeminal bodies the two peduncles pass 

 beneath them and enter the mesencephalon, where their course 

 will be subsequently described (see Index). The most of the fibres 

 of each superior peduncle are derived from the corresponding 

 nucleus dentatus, but a few come from the grey matter of the 

 cerebellar cortex. 



The middle peduncles are of large size, and are formed by the 

 transverse fibres of the pons Varolii, these being gathered together 

 on either side into a large bundle, which passes backwards and 

 outwards into the white central medullary substance of the cor- 

 responding hemisphere. The fibres of each middle peduncle are 

 both afferent and efferent. The afferent fibres arise in the pons 

 from the cells of the nucleus pontis of the opposite side, and 

 terminate in arborizations around the cells of the cerebellar 

 cortex. The efferent fibres arise from the cells of the cerebellar 

 cortex of the same side, and terminate in arborizations around the 

 cells of the nucleus pontis, mostly on the opposite side. 



The inferior peduncles are principally composed of afferent fibres, 

 which are derived chiefly from the dorsal or direct cerebellar tract 

 and the olivo-cerebellar tract of either side. The fibres of the dorsal 

 cerebellar tract terminate in the cortex of the superior vermis on both 

 sides of the median line. The fibres of the olivo-cerebellar tract, which 

 are derived from the inferior olivary nucleus of the medulla oblongata 

 on the opposite side, terminate in the cortex of the vermis and 

 cerebellar hemisphere. The superficial arcuate fibres, which form 

 part of the inferior peduncle, are connected with the cortex of the 

 vermis and cerebellar hemisphere. 



White and Grey Matter of the Cerebellum. — In the hemispheres 

 and vermis the white matter is situated in the centre as the medulla, 

 and the grey matter is disposed superficially as the cortex. The 

 white matter in the interior of the vermis is known as the corpus 

 trapezoides. When sagittal sections of a hemisphere are made, the 



