86 THE CEKEBELLUM. 



The fibres of the middle peduncle, when traced ventralwards into the pons, 

 reach the middle line and there undergo decussation. After this intercrossing 

 many of their fibres appear to end in the grey matter which is so abundant in 

 the ventral part of the pons (nuclei pontis, fig. 49, n.p.). A certain number of fibres, 

 however, take a sagittal direction in the raphe and pass towards the reticular 

 formation, where they appear to give fibres to the posterior longitudinal bundle ; 

 by which means a direct connection seems to be established between the cerebellum 

 and the nuclei of the third, fourth, and sixth nerves (Mingazzini). 



The inferior peduncles (crura ad medullam) issue from the white matter of 

 the lateral hemispheres, between the other two, and pass forwards immediately 

 outside the superior peduncles to reach the lateral wall of the fourth ventricle. 

 Here they turn sharply downwards, at a right angle, and become the restiform 

 bodies of the medulla oblongata. 



The restiform body consists of several sets of fibres having a distinct 

 origin, and obtaining their medullary sheath at different periods of development. 

 These fibres are as follows : (1) Fibres of small size derived from the contra- 

 lateral lower olives. These, which are the last to become medullated, are seen 

 passing as arched fibres through the corresponding half of the medulla oblongata 

 and across the raphe to enter the hilum of the opposite olivary nucleus. After 

 passing through the band of grey matter, whether joining its cells or not is not 

 certainly known, these fibres appear to pass longitudinally upwards in the reticular 

 formation of the medulla oblongata and pons, and in the tegmentum of the cerebral 

 peduncle, and thus to reach the cerebral hemisphere without again crossing : 

 ultimately they are in' all probability connected with the cerebral cortex (? of the 

 psychomotor region only). The existence of this connection may probably explain 

 those cases in which atrophy of one of the cerebral hemispheres, especially of the 

 psychomotor region, has been found associated with atrophy of the inferior olive of 

 the same side and of the restiform body and cerebellar hemisphere of the opposite side. 



(2) Fibres which emerge from the adjacent cuneate nucleus (especially its outer 

 portion), and perhaps also from the gracile nucleus, and pass directly into the resti- 

 form body of the same side. These fibres may represent a bulbar ascending 

 cerebellar tract homologous with the dorso-lateral cerebellar tract of Flechsig which 

 is seen in the spinal cord, in which case the outer cuneate nucleus may very probably 

 represent Clarke's cell-column of the cord. 



According to some authorities, the restiform body also receives a contribution through 

 the arched fibres from the contra -lateral nucleus gracilis and nucleus cuneatus. 



(3) Fibres of the dorso-lateral ascending cerebellar tract of Flechsig, which are 

 traceable along the whole length of the cord from the lumbar region upwards, and 

 which pass into the restiform body, and through this mainly into the same side of 

 the worm. 



(4) Fibres of the descending cerebellar tract (see p. 25) which, after removal 

 of the cerebellar hemisphere, undergo degeneration down the whole length of the 

 antero-lateral column of the cord near its periphery (see p. 32, and fig. 71, A, B, C). 



(5) Fibres which are passing to or are derived from the root of the auditory nerve 

 and perhaps others to or from some of the other cranial nerves (see p. 93). 



MICROSCOPIC STRUCTURE OF THE LAMINA. 1 



Each lamina of the cerebellum has a central part or core of white substance 

 which is an offshoot (secondary or tertiary) from the white centre of the organ, 



1 Our knowledge of the actual relationship of cells and nerve-fibres in the cerebellar cortex has been 

 only quite recently entirely remodelled, owing to the introduction of the method invented by Golgi, and 

 its fruitful application firstly by Golgi himself and subsequently by Ramon y Cajal. 



