Functions of the Cerebellum. 621 



the left optic thalamus crossing over to the right superior peduncle of 

 the cerebellum, and vice versa, from the right thalamus to the left pedun- 

 cle. On account of the decussation of the optic nerves, this second de- 

 cussation puts each eye into relationship chiefly with the part of the 

 cerebellum on its own side. This accounts for the fact that electrical 

 irritation of the cerebellum contracts the pupil of the eye on the same 

 side. Lesions of any part of the tract connecting the ej^es with the 

 cerebellum, as the corpora quadrigemina, optic thalamus, superior pe- 

 duncles, and their intermediate nervous connections, have the effect to 

 disturb the functions of equilibrium. 



It has been found that ' ' section of the horizontal semicircular canal 

 in the ear of pigeons, on both sides, induces a rapid, jerking, horizontal 

 movement of the head from side to side, and a tendency to turn to one 

 side, which manifests itself whenever the animal attempts to walk for- 

 wards. " If a vertical canal on each side be cut, the movement is ver- 

 tical and violent. These movements continue for months. Similar re- 

 sults occur from like operations upon the ears of rabbits. These phe- 

 nomena indicate that the sense of hearing enters into the combination 

 of stimuli concerned in certain muscular co-ordinations, and the elim- 

 ination of a subdivision of this stimulus deranges the habitual normal 

 balance, and renders the animal dizzy, with an effect similar to that in- 

 duced by partial blindfolding. 



The anterior division of the auditory nerve, which is connected with 

 the ampullae and the semicircular canals, sends some of its fibres di- 

 rectly to the cerebrum, while others appear to ascend to the cerebellum 

 through the restiform tract. Lesions, or diseases of the cerebellum, do 

 not, however, cause deafness either in man or the other mammals. But 

 the anatomical connection between the semicircular canals and the cere- 

 bellum, is no doubt the reason why injury to the canals has the same ef- 

 fect as injury to the lobes of the cerebellum. Section of the superior 

 vertical canals causes loss of balance forwards, and so does lesion of 

 the anterior part of the middle lobe of the cerebellum. Section of the 

 posterior vertical canals causes a tendency to fall backwards, and so 

 does injury to the posterior part of the median lobe. Section of the 

 horizontal canals causes a lateral rotary motion, and so does injury to 

 the lateral lobes of the cerebellum. 



It is clear from these facts that a part of the afferent stimuli, upon 

 which the functions of the cerebellum are founded, come from the ears, 

 and are auditory stimulations. Whether it be found that the functions 

 of the cerebellum include general muscular co-ordinations, or only such 

 as relate to the preservation of a normal equilibrium, we should con- 

 sider it antecedently probable that there must be some connection be- 

 tween it and the eyes. The dizziness caused by whirling around, or by 



