THE CENTRAL NERVOUS SYSTEM 689 



the internal capsule behind the motor fibres), the cerebral 

 cortex itself. 



The efferent pyramidal path from the cortex is broken 

 by but one relay of nerve-cells, the motor cells of the anterior 

 horn and the cranial nuclei ; or at any rate if another inter- 

 venes (p. 687) its axon is of insignificant length, and it con- 

 stitutes rather a joint between two segments of the nervous 

 path than an independent segment. The afferent path is 

 interrupted by at least two relays with axons of considerable 

 length. One of the cells is situated in the ganglion on the 

 posterior root, another in the medulla ; and on some of the 

 routes another, or even more than one, is intercalated 

 between the medulla and the cortex. 



Connections of the Grey Matter of the Cerebellum with the 

 Periphery and other Parts of the Central Nervous System. 

 Numerous as are the nervous ties of the cerebral cortex, those of the 

 grey matter of the cerebellum are, in proportion to its mass, still 

 more extensive, and perhaps not less important. Speaking broadly, 

 we may say that the restiform body connects chiefly the dentate 

 nucleus and the grey matter of the worm with both sides of the 

 spinal cord and medulla oblongata, and through them with the peri- 

 phery. The fibres which it receives from the direct cerebellar tract 

 of its own side, and the gracile and cuneate nuclei of its own and 

 of the opposite side, it carries to the worm ; the fibres which reach 

 it from the olivary nucleus of the opposite, and also in smaller 

 numbers from that of the same side, run mainly to the dentate 

 nucleus. The middle peduncle is in the main a link between the cere- 

 bellar cortex and the cerebral cortex of the opposite side, through the 

 relay of the pontine grey matter. The superior peduncle connects 

 chiefly the dentate nucleus of one side with the cortex of the opposite 

 cerebral hemisphere through the red nucleus of the tegmentum of 

 the crus cerebri on the opposite side. Since the cortex of the 

 cerebellum is linked to the dentate nucleus the superior peduncle 

 affords an indirect connection between it and the cerebral cortex. 

 Through the restiform body afferent impulses pass up to the cerebel- 

 lum. From the cerebellum they may proceed to the cerebrum. So 

 that the path by the restiform body, dentate nucleus, and superior 

 peduncle may form an alternative route for afferent impressions pass- 

 ing from the periphery to the great brain a path broken by at least 

 four relays of nerve-cells. The cerebellar hemisphere may be con- 

 nected by an efferent path through the nucleus of Deiters and the 

 descending anterc-lateral tract with the motor roots of the same side. 

 An uncrossed connection also exists between the cerebellum and the 

 vestibular branch of the auditory nerve, through one of its nuclei 

 of origin, and possibly between it and other cranial nerves, such as 

 the optic and trigeminal. 



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