1110 THE CEREBELLUM. [BOOK in. 



a matter of accident, that various structures, the seats of various 

 physiological processes, have, from morphological causes, been 

 gathered together into the body which anatomists call the cere- 

 bellum. The task of the physiologist is to unravel the ties 

 binding these various cerebellar structures with other parts of 

 the central nervous system, and so with various parts of the body 

 at large. 



We must content ourselves here with calling attention to two 

 or three broad and suggestive facts concerning its structure and 

 connections. 



In the first place, one striking fact about the cerebellum is the 

 very large development of commissural fibres connecting together 

 the superficial grey matter of the two hemispheres for the greater 

 part of their extent, and passing, not only through the pons ( 635) 

 as part of the middle peduncle, but also through the median 

 vermis. This great commissure is second only to the great 

 callosal commissure of the cerebrum ; and from the fact that 

 median lesions of the cerebellum, those which do most damage to 

 this commissure, are the most effective in causing incoordination 

 and forced movements, we may infer that it in some way plays 

 an important part in coordination. 



A second striking fact is one on which we have already just 

 dwelt, the connection, chiefly an uncrossed one, through the 

 inferior peduncle, with the afferent structures of the bulb and 

 spinal cord. We may now add, that the fibres of this peduncle 

 passing into the centre of the white matter of the cerebellar 

 hemisphere of the same side enclose the grey matter of the 

 nucleus dentatus and appear largely to end in that body, though 

 some pass on to the vermis. 



A third striking fact is the connection, this being, as far as we 

 know, wholly a crossed one, through the pons and pes, with the cere- 

 bral cortex, both of the extreme frontal region, and of the temporo- 

 occipital region, and possibly or even probably with more scattered 

 cortical elements of the parietal (motor) region. This connection 

 is one between cortex and cortex, or at least between cerebral 

 cortex and cerebellar superficial grey matter, for the fibres of the 

 middle peduncle passing from the grey matter of the pons which 

 serves as a relay end in the surface of the lateral hemisphere of 

 the cerebellum. The frontal cortical fibres passing to the pes 

 have a descending degeneration, that is from the cortex to the 

 pons, and we may probably assume that the similar temporo- 

 occipital fibres similarly degenerate downwards to the pons 

 ( 632). From this it has been inferred that this cerebro-cere- 

 bellar connection carries impulses from the cerebral cortex to the 

 cerebellum ; and it has been further inferred that these impulses 

 are of the nature of motor impulses. As we have more than once 

 urged, the character of degeneration, that is whether " ascending " 

 or " descending " is not a satisfactory proof of the direction taken 



