THE FUNCTIONS OF THE CEKEBELLUM 403 



posture of the body as a whole in relation to its environment, which is at 

 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. That the compensation, which is slowly acquired after extirpa- 

 tion of the cerebellum, is of cerebral origin is shown by the fact that subse- 

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

 the hemispheres, 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. w 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, especially of those 

 concerned in the maintenance of posture, an effect which is especially 

 marked -in the absence of the cerebral hemispheres and is responsible for 

 the condition known as decerebrate rigidity. As a centre of conjunction 

 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 regards the 

 cerebellum as the central organ of the muscular senses. Hughlings Jackson expressed 

 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. 



DESTRUCTIVE LESIONS OF THE CEREBELLUM IN MAN 



The general results of the lesions of the cerebellum in man are broadly similar to 

 those described for animals. As in these, the effects of unilateral lesions are always 

 limited to the same side of the body. 



One invariable result is diminished tone of the muscles on the same side of the body. 

 This does not necessarily involve diminution or absence of the tendon reflexes ; in fact, 



