CH. XLVII.] CONNECTIONS OF THE CEREBELLUM 683 



The superior peduncle : the axons of the cells of Purkinje mainly 

 terminate in the nucleus dentatus, and the other subsidiary masses 

 of grey matter situated in the interior of the cerebellum ; from the 

 cells of these nuclei a fresh relay of fibres issues, conveying impulses 

 from the cerebellum to other parts, but mainly to the opposite 

 cerebral hemisphere ; these fibres constitute the superior cerebellar 

 peduncle. They cross the middle line, give off numerous collaterals 

 to the red nucleus of the opposite side, and also to the nucleus of the 

 opposite third nerve. The majority terminate in the optic thalamus, 

 whence a fresh relay continues the impulse to the cerebral cortex. 

 This therefore is the cerebello -cerebral path. 



After the fibres of the superior peduncle have crossed the middle 

 line, they give off descending branches which run towards the bulb 

 and cord, though whether they reach as far down as the spinal cord 

 is doubtful. There is, however, a cerebello-spinal path ma the red 

 nucleus with which the fibres that issue from the cerebellum com- 

 municate after crossing, for it is from the red nucleus that the 

 bundle of Monakow arises which crosses the middle line and is seen 

 in the cord as the rubro-spinal or prepyramidal tract ; it terminates 

 in the anterior horn of the spinal grey matter. The cerebello-spinal 

 path therefore exhibits a double crossing; the first is that of the 

 superior peduncle to reach the opposite red nucleus, and the second 

 is that of the bundle of Monakow; in this way the cerebellar hemi- 

 sphere is linked to the same side of the spinal cord. 



In addition to all these fibres, the superior peduncle also 

 contains some fibres of the spino - cerebellar tracts, which 

 after ascending the spinal cord, bulb and pons turns round and 

 course back along the superior peduncle into the cerebellum; 

 these fibres are distributed mainly to the lower part of the 

 vermis. 



The next figure (fig. 422) shows the principal connections of the 

 cerebellum in a diagrammatic way. 



Beginning at the bottom, we see one of the cells of a spinal 

 ganglion (s.G.) sending its peripheral axon to the skin (s.) ; its central 

 axon enters the spinal cord and ascends its posterior column, to 

 terminate in the posterior column nuclei of the bulb. This is marked 

 "to Bulb." This is the first segment of the sensory path to the 

 cerebrum, but its further course is not shown. 



The entering fibre of the posterior root gives off collaterals to the 

 spinal grey matter ; some of these pass to cells in the posterior horn 

 (P.H.C.), from which a fresh relay carries on the impulse to anterior 

 horn cells, one of which (A.H.C.) is seen sending its axon ma the 

 anterior root, to end in the muscular fibre M. 



Other collaterals terminate by synapses around the cells of 

 Clarke's column (c.c.). Two of these cells are shown; this is the 



