326 ANATOMY OP THE CENTRAL NERVOUS SYSTEM. 



Comparative anatomy and experiments in degeneration uniformly show that 

 in the cerebellar connections one must sharply ditferentiate between the cortex of 

 the hemispheres and the cortex of the vermis; also between the cerebellar cortex 

 and the ganglia. On comparative anatomical grounds the author reckons the corpus 

 dentatum with the vermis. Not a small proportion of what is said in the literature 

 of degeneration on atrophy after injury of the hemispheres refers to injuries of the 

 lateral portion of the vermis. 



1. In the first place it may be determined that the cerebral connection — 

 first developed in mammals — is furnished by the irachia pontis and is ex- 

 clusively with the hemispheres of the cereiellum. Whence arises the ascending 

 fascicle which traverses the pons ending in the tegmentum? The arms of 

 the pons contain fibers from cells of the intrapontal ganglia: the same cells 

 with which the numerous collaterals of the cerebro-pontal tract connect. 

 S. E. y Cajal has demonstrated this. Even degenerations of long standing 

 involving the fibers of the pes do not cause complete degeneration of the 

 pons. The fact that after removal of a cerebellar hemisphere a large part of 

 the pons remains intact indicates that the fibers in question arise from the 

 pontal ganglia and not from the cerebellum. But, nevertheless, the dis- 

 appearance of a considerable number of fibers after the operation (Marchi, 

 Minghazzini, Ferrier, and Turner) makes it presumable that at least some of 

 the fibers of the pons arise from cells of the cortex of the cerebellum. 



2. It may be demonstrated by several methods that the anterior cere- 

 bellar peduncles arise from the nucleus dentatus; they may possibly also re- 

 ceive fibers from the neighboring cortex. Much the greater part of the fibers 

 end after decussation in the red niicleus of the tegmentum beneath the 

 anterior quadrigeminal bodies. A smaller part of the fibers end in the 

 nucleus ruber of the same side and send a few fibers farther forward to the 

 ventral region of the thalamus. (This last point is, however, not yet fully 

 established.) Since a tract from the caudal portion of the parietal lobe 

 ends at the nucleus ruber, it is evident that there exists here an indirect 

 cerebro-cerebellar connection. 



3. The posterior cerebellar peduncles are very much more complexly 

 constructed. In order to make their formation quite clear we mxist divide 

 them into (I) a median portion having connections with the sensory cranial 

 nerves, especially the acustieus, and into (II) the corpus restiforme proper, 

 conducting fibers from the opposite olivary body and from the spinal cord. 



The median portion and the tracts to the spinal cord are inherited from 

 remote antiquity; but only in the mammals do the bundles to the olivary 

 bodies become well marked. 



The corpus restiforme ends almost exclusively in the middle portion 

 (vermis) of the cerebellum, where its separate fascicles pass to different 

 regions. The region of the nucleus tegmenti, and this nucleus itself, is the 

 terminus of the nucleo-cerebellar apparatus. 



