go6 THE CENTRAL NERVOUS SYSTEM 



parts of the body (labyrinth of ear, muscles, tendons, joints, viscera, 

 etc.) (p. 886). After removal of the whole cerebellum (in the dog 

 or monkey), there is at first rigidity and tonic spasm of certain 

 muscles, which contribute to the difficulty of co-ordinating their 

 movements. When this stage has passed, the muscles all over the 

 body, but especially those of the loins and hind-limbs, and those 

 which fix the head, are weaker than normal, are deficient in tone, 

 and contract with a peculiar want of steadiness (Luciani). When 

 one lateral half of the cerebellum is removed, the symptoms affect 

 especially the muscles on the same side. In extensive lesions of 

 the cerebellum in man what has been noticed is a marked inability 

 to maintain the upright posture, giddiness, a staggering gait, 

 twitching movements of the eyes (nystagmus), tremor accompany- 

 ing voluntary movements in a word, a general breakdown 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 cere- 

 bellum, 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 development have sometimes been recognised for the 

 first time at the necropsy. 



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. 857), 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 connection 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 cerebellum 

 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 communication of the grey matter of the cerebellum with every 

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



