CH. LI.] FUNCTIONS OF THE CEREBELLUM 751 



disturbed condition of the animal contrasts very forcibly with the 

 sleepy state produced by removal of the cerebrum (see fig. 446, p. 723). 



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. 

 Impulses also pass out to the cord (see p. 685), but the exact course of 

 some of the descending tracts 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 



Vi Arm QrVi pr A fopft firr A^Q^ Fm. 459. This is a reproduction of a 



nemiSpner 3 (8Q( ng. 40y;. photograph of a lunatic's brain lent 



In Order that the Cerebellum may me by Dr Fricke. One cerebral and 



,-, . ., the opposite cerebellar hemisphere 



Send OUt impulses in thlS Way, it IS are atrophied. 



necessary that it receive impulses which 



guide it by keeping it informed of the position of the body in space. 

 These impulses, we have already insisted, though afferent are non- 

 sensory; they travel by paths which at the start, however, are 

 offshoots from those which carry the real sensory impulses to the 

 cerebrum. These afferent impulses originate from or are associated 

 with the impulses which in the cerebrum produce sensations of the 

 four following kinds : 



1. Tactile. 3. Visual. 



2. Motorial. 4. Labyrinthine. 



1. Tactile impressions. The importance of the tactile sense is 

 obvious ; and in diseases of the afferent tracts, loss of that sense in 

 the lower limbs leads to disturbances of equilibrium ; in such cases 

 a man has difficulty in balancing himself while standing with his 

 eyes shut. Sherrington, however, has shown how comparatively 

 unimportant is the loss of tactile sensibility from the feet. A cat, 

 in which the feet have been completely desensitised by division of 

 all their nerves, can stand and walk without obvious inconvenience. 

 It is not until the sensitiveness of the joints, especially in the upper 

 segments of the limb, is interfered with that marked disturbances 

 of balance are noticeable. 



2. Material* impressions. Another important sense is that which 



