8 32 A MANUAL OF PHYSIOLOGY 



of the co-ordinating machinery, and especially of -the part of 

 it concerned in the movements necessary for locomotion, and 

 for the maintenance of the equilibrium of the body the so-called 

 cerebellar ataxia. There is no sensory paralysis and none of 

 voluntary movement, such as lesions of the cerebral cortex 

 produce, nor is there any psychical disturbance. In cases of 

 congenital defect of the cerebellum, the power of walking, and 

 even of standing, may be late in being acquired, and imperfect. 

 But it is remarkable what great deficiencies in the cerebellar 

 substance are often compensated for when established early in 

 life, so that even cases of marked atrophy or lack of develop- 

 ment have sometimes been recognised for the first time at the 

 autopsy. 



The connections of the cerebellum with other parts of the 

 central nervous system and with the periphery corroborate 

 the direct results of experiment. For, in addition to the visual 

 impressions, the most important afferent impulses concerned in 

 equilibration are those from the semicircular canals and vestibule 

 of the internal ear, the muscles, tendons, joints, etc., and certain 

 portions of the skin, such as that of the soles of the feet. And the 

 cerebellum, as we have seen (p. 779), is linked with all of these, 

 and has besides an extensive crossed connection through the 

 middle and superior peduncles with the opposite cerebral 

 hemisphere. The importance and extent of this crossed connec- 

 tion with the great brain is illustrated by the facts that in 

 disease atrophy or deficient development of one cerebellar 

 hemisphere is associated with a similar condition of the opposite 

 cerebral hemisphere, and that a lesion in one-half of the cere- 

 bellum affects chiefly the co-ordination of the movements of 

 the same side of the body that is to say, of the side connected 

 with the opposite cerebral hemisphere. 



We do not as yet know the full significance of this extraordinarily 

 free communicaticn of the grey matter of the cerebellum with every 

 part of the central nervous system. But it is evident that by the 

 broad highway of the restiform body, or the cross-country routes 

 from cerebral cortex to cerebellum, impulses may reach it from 

 every quarter ; while impulses passing out from it along its peduncles 

 may influence the motor discharge either indirectly through the 

 Rolandic cortex and the pyramidal tract, or more directly through 

 the antero-lateral descending spinal path that brings it into relation 

 with the nuclei of origin of the motor nerves. It is an organ so 

 connected that is suited to take cognizance of the multitudes of 

 afferent impressions concerned in the co-ordination of movements 

 and the maintenance of equilibrium, and to regulate the outflow 

 of efferent impulses in correspondence with the inflow of afferent. 



Sherrington points out that all the modern theories of cerebellar 

 function harmonize with his conception of the cerebellum as the head 

 ganglion of the proprio-ceptive system (p. 831) . The most influential 



