704 FUNCTIONS OF THE CEREBELLUM [CH. XLIX. 



If the cerebellum is removed in an animal, or if it is the seat of 

 disease in man, the result is a condition of slight muscular weak- 

 ness ; but the principal symptom observed is inco-ordination, chiefly 

 evidenced by a staggering gait similar to that seen in a drunken man. 

 It is called cerebellar ataxy. 



This condition is well illustrated in the figure on p. 703 (fig. 509) ; 

 the disturbed condition of the animal contrasts very forcibly with 

 the sleepy state produced by removal of the cerebrum (see fig. 492). 



In order that the cerebellum may duly execute its function of 

 equilibration, it is necessary that it should send out impulses ; this it 

 does by fibres that leave its cells and pass out through its peduncles ; 

 they pass out to the opposite cerebral hemisphere, and so influence 

 the discharge of the impulses from the cortex of the cerebrum. It 

 is also probable that impulses pass out to the cord (see dotted line 



in fig. 482), but the exact course of 

 these fibres, if they do exist, has still to 

 be worked out. 



The cerebellum thus acts upon the 

 muscles of the same side of the body 

 in conjunction with the cerebral hemi- 

 sphere 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 



me by Dr Fricke. One cerebral and hemisphere (S66 tig. 510). 



are e atr p o p p. cerebellar luaajs ^ m 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 im- 

 pulses 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 balance himself while 

 standing with his eyes shut. The same effect may be produced 

 experimentally by freezing the soles of the feet. 



Again, if the skin is stripped from the hind limbs of a brainless 

 frog, it is unable to execute such reflex actions as climbing an inclined 

 plane, which it can do quite well when the skin is uninjured. 



