708 



FUNCTIONS OF THE CEREBELLUM 



[C1I. XLIX. 



the occiput touching the breast, the vertex directed downwards, with 

 the right eye looking to the left and the left looking to the right, 

 the head being incessantly swung in a pendulum-like manner. 

 Cyon says it is almost impossible to give an idea of the perpetual 

 movements to which the animal is subject. It can neither stand, 

 nor lie still, nor fly, nor maintain any fixed attitude. It executes 

 violent somersaults, now forwards, now backwards, rolls round and 

 round, or springs in the air and falls back to recommence anew. It 

 is necessary to envelop the animals in some soft covering to prevent 

 them dashing themselves to pieces by the violence of their move- 

 ments, and even then not always with success. The extreme 

 agitation is manifest only during the first few days following the 

 operation, and the animal may then be set free without danger ; but 

 it is still unable to stand or walk, and tumultuous movements come 

 on from the slightest disturbance. But after the lapse of a fortnight 



Fio. 515. Diagram of semicircular canals, to show their positions in three planes at right angles to 

 each other. It will be seen that the two horizontal canals (H) lie in the same plane : and that the 

 superior vertical of one side (S) lies in a plane parallel to that of the posterior vertical (P) of the 

 other. (After Ewald.) 



it is able to maintain its upright position. At this stage it resembles 

 an animal painfully learning to stand and walk. In this it relies 

 mainly on its vision, and it is only necessary to cover the eyes with 

 a hood to dispel all the fruits of this new education, and cause the 

 reappearance of all the motor disorders." (Ferrier.) 



It is these canals which enable all of us to know in which direc- 

 tion we are being moved, even though our eyes are bandaged, and 

 the feet are not allowed to touch the ground. On being whirled 

 round, such a person knows in which direction he is being moved, 

 and feels that he is moving so long as the rate of rotation varies, 

 but when the whirling stops he seems, especially if he opens his 

 eyes, to be whirling in the opposite direction, owing to the rebound 

 of the fluid in the canals. The forced movements just described in 

 animals are due both to the absence of the normal sensations from 

 the canals and to delusive sensations arising from their irritation, and 

 the animal makes efforts to correct the movement which it imagines 

 it is being subjected to. 



