908 THE CEREBELLUM. 



further forward, among others from the cerebral cortex. By functional 

 discharge of certain upper and cortical regions, the crossed cerebellar 

 hemisphere may, one can believe, be excited. The cerebellar excita- 

 tion so evoked can recoil by way of the anterior peduncle on the 

 cerebral hemisphere whence it started. After severing both the anterior 

 (superior) peduncles and the tracts from cerebrum to the pontine nuclei, I 

 found l " decerebrate rigidity " set in, a condition — opisthotonos, extensor 

 rigidity of limbs, retraction of neck, etc. — closely like that ensuing on 

 ablation of the cerebellum. It would seem that interruption of these 

 peduncles approaches in effect to removal of the cerebellum, a fact 

 which lays stress on the importance of the above cerebro-cerebellar 

 circuit as a factor in cerebellar action. On the other hand, the cerebellar 

 activity excited by action of the crossed cerebral hemisphere can, to judge 

 by the structural connections, react on the cranio-spinal motor root 

 nerve cells of its own side, i.e. of the side to which the pyramidal crossing 

 will mainly carry the impulses generated from the cortex cerebri. Thus, 

 one and the same cerebral discharge may perhaps pour upon the motor 

 root nerve cells a combination of cerebral and cerebellar impulses. 

 Destructive lesion of the cerebellum, by rendering the latter impulses 

 impossible, may upset the co-ordination of the movement to be 

 executed. 



No fact is clearer in the physiology of the central nervous system 

 than that many movements of great taxic complexity, e.g. of pro- 

 gression, etc., can be carried out in a co-ordinated manner in the 

 absence of the Eolandic cortex and of the cerebral cortex altogether. 

 It is also clear that lesions of the cerebellum greatly disturb these 

 movements ; the impression that they disturb them preponderantly 

 is perhaps illusory. There is some evidence that these movements 

 are related to the thalamencephalon, much in the same way as 

 higher movements, such as grasp of hand, are related to the cerebral 

 cortex. With the thalamencephalon the cerebellum has the same broad 

 structural linkage as with the cortex, only the linkage seems structurally 

 closer and more abundant. It is to these ties, rather than to those 

 connecting it with the cerebral cortex, that I would relate the disturb- 

 ance of attitude and locomotion so prominent among the results of 

 cerebellar ablation. 



The so to say highly technical movements ordered by the cerebral 

 cortex employ comparatively limited aggregates of musculature, e.g., speech 

 employing the muscles of the oral and laryngeal regions, grasp employing 

 the muscles of a single limb. The muscular mechanisms of progression 

 and pose, the innervation of which may, as above suggested, be centred 

 together, perhaps in the thalamencephalon, are of wider spatial distribu- 

 tion, and employ not one side of the trunk but both sides, not one limb 

 but all four. Often they probably involve the musculature of the entire 

 body. It is because of its intimacy of connection with such movements 

 as these that the cerebellum is an organ which justifies Hesiod's 6'<rw 

 'tt'a'sov ruuGv -n-avToc. The division into hemispheres and middle lobe is 

 founded merely upon gross anatomy. The organ commonly, probably 

 always, " functions " as a whole. Luciani is right to insist on this, and 

 the reason that it " functions " as a whole seems clearly because, it is 

 so largely a piece of mechanism that deals with the innervation, not 



1 Sherrington, Proc. Roy. Soc. London, 1S96, vol. lx. 



