684 FUNCTIONS OF THE CEREBELLUM. [OH. XLIX. 



which we have any certain knowledge by means of which the 

 cerebellum influences the motor discharge is as an elaborate cell 

 station on the course of sensory impulses to the cerebrum. 



The cerebellum thus acts upon the muscles of the same side 

 of the body in conjunction with the cerebral hemisphere of the 

 opposite side. The close inter-relation of one cerebral with the 

 opposite cerebellar hemisphere is shown in cases of brain disease, 

 in which atrophy of one cerebellar hemisphere follows that of the 

 opposite cerebral hemisphere (see fig. 507). 



In order that the cerebellum may send out impulses in this 

 way, it is necessary that it receive impulses which guide it by 

 keeping it informed of the position of the body in space. These 

 afferent impulses are of four kinds, namely : 



1. Tactile. 3. Visual. 



2. Muscular. 4. Labyrinthine. 



We will take these one by one : 



1. Tactile impressions. The importance of impulses from the 

 skin is shown in those diseases of the sensory tracts (especially 



locomotor ataxy) where there is 

 diminution in the tactile sense 

 in the soles of the feet. In such 

 cases the patient cannot stand 

 with his eyes shut. The same 

 effect may be produced experi- 

 mentally by freezing the soles of 

 the feet. 



Again, if the skin is stripped 

 from the hind limbs of a brain- 

 less frog, it is unable to execute 

 Fig. 507. This is a reproduction of a suc h reflex actions as climbing 



photograph of a lunatic s brain lent . 



me by Dr. Fricke. One cerebral and an inclined plane, which it Can 



the opposite cerebellar hemisphere j 11 u j.u i 



are atrophied. do quite well when the skin is 



uninjured. 



2. Muscular impressions. Quite as important as the tactile 

 sense from the skin is the muscular sense, the sense which 

 enables us to know what we are doing with our muscles. We 

 have hitherto chiefly spoken of the muscular nerves as being 

 motor ; they also contain sensory fibres ; these pass from the 

 muscles, and their tendons to the posterior roots of the spinal 

 nerves, and the impulses ascend the sensory tracts through cord 

 and brain to reach the cerebellum and the Rolandic area. In 

 some cases of locomotor ataxy there is but little loss of tactile 



