THE FUNCTIONS OF THE CEREBELLUM 



fault. The animal, in the case of the dog, therefore attempts to correct the 

 tendency to fall to one side or other at each step by making its basis of 

 support as wide as possible, and gradually acquires a peculiar gait, consisting 

 of a series of springs, in which the two fore limbs and two hind limbs act 

 together, the diagonal movements of the fore limbs being practically 

 abandoned. 



In lesions of the cerebellum in man the most marked symptoms are 

 the cerebellar ataxy and the occurrence of tremors, ' astasia,' on the perform- 

 ance of willed movements. The ataxy has the same origin as that in the dog ; 

 each spinal act of locomotion tends to throw the centre of gravity outside 

 the line of support, and the tendency to fall thus brought about is voluntarily 

 compensated by abduction of the corresponding limb. A staggering gait is 

 thus produced, which is practically identical with that of a drunken man, and 

 presents no trace of the over-action of muscles so characteristic of spinal 

 ataxy. That the compensation, which is slowly acquired after extirpation of 

 the cerebellum, is of cerebral origin is shown by the fact that extirpation of 

 the cerebral hemispheres, or even of the motor areas of the hemispheres, 

 after extirpation of the cerebellum, at once abolishes the power of movement 

 which has been reacquired, and after the motor areas are destroyed on both 

 sides the loss of power of progression is permanent. 



These experiments show that the cerebellum, in Sherrington's words, 

 must be regarded as the head ganglion of the proprioceptive system, acting 

 as a centre where arrive the afferent impulses from the cord, the fifth nerve 

 and especially from the labyrinth. It influences, through the superior 

 peduncle, the cerebral cortex and furnishes the subconscious basis for the 

 guidance of the motor functions of the latter organ. Through its connections 

 with the nuclei of the bulb and the efferent tracts arising therefrom, it aug- 

 ments the tonic activity of all the muscles of the body, an effect which is 

 especially marked in the absence of the cerebral hemispheres and is respon- 

 sible for the condition known as decerebrate rigidity. As a centre of conjunc- 

 tion for the afferent impressions from the muscles and those from the laby- 

 rinth it co-ordinates the segmental reflexes, which determine the relative 

 posture of each limb, with those originating in the labyrinth and determining 

 the position of the head. Thus the whole mechanism provides for a mainten- 

 ance of equilibrium of the body as a whole, and for the proper balancing 

 of the reflex movements of the different limbs with those of the trunk 

 during all the changes in the position of the centre of gravity attending 

 locomotion. 



The view here put forward really includes the various descriptions of the functions 

 of the cerebellum which have been given by different authorities. Thus Luciani 

 describes the cerebellum as an organ which by unconscious processes exerts a continual 

 reinforcing action on the activity of all the spinal centres. Munk ascribes to the 

 cerebellum the function of maintaining bodily equilibrium. Lewandowsky regaids 

 the cerebellum as the central organ of the muscular senses. Hughlings Jackson ex- 

 pressed many years ago an important characteristic of the cerebellum when he wrote 

 that the cerebellum is the centre for continuous movements, and the cerebrum for 

 changing movements. All these descriptions come under Sherrington's conception 

 of the cerebellum as head ganglion of the proprioceptive system. 



