CEREBELLUM 177 



cortex which sends fibres to the basal ganglia, which in turn 

 send out the outgoing fibres. 



Functions 



Removal of the cerebellum deprives the animal, for a time 

 at least, of the power of balancing itself. This may be easily 

 demonstrated in the pigeon (fig. 96, p. 185). But in some 

 cases, when slowly progressing disease has destroyed the organ, 

 no loss of equilibration has appeared, and in other cases the 

 cerebellum has been congenitally almost absent, and yet the 

 individual has not shown any sign of want of power of main- 

 taining his balance. Evidently, therefore, some other part of 

 the brain can compensate for its absence. 



The manner in which the cerebellum acts has been chiefly 

 elucidated by removing parts of the organ and keeping the 

 animals under observation for prolonged periods. If one side 

 of the cerebellum be removed the first symptoms are (1) a tonic 

 contraction of the muscles of the limbs of the same side by 

 which the fore limbs may be powerfully extended, and an 

 arching of the body with the convexity towards the side of the 

 lesion, while the animal may be driven round its long axis to the 

 opposite side. (2) These irritative symptoms soon pass off, and 

 the animal then manifests inadequacy or weakness in the limbs 

 of the affected side, so that it droops to that side, and, if a 

 quadruped, may circle to that side. (3) After some weeks these 

 symptoms disappear, and the loss of one side of the cerebellum is 

 apparently completely compensated for. 



When in the dog compensation has been established, 

 destruction of the cerebral cortex of the opposite side leads 

 to a reappearance of the muscular inadequacy. 



Electrical stimulation of the cerebellum has yielded results 

 somewhat difficult of interpretation, but the most recent investi- 

 gations seem to show that stimulation of the cortex with 

 currents strong enough to produce movements when applied to 

 the discharging part of the cerebral cortex (see p. 209) do not 

 produce manifest effects, but that comparatively weak currents 

 applied to the basal ganglia do produce movements, the most 

 manifest of which are the conjugate movements of the eyes, 

 and the eyes and head to the side stimulated. 



It has been further found that powerful stimulation may 



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