1 68 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



touched motions of the eyes or head occur in the plane 

 of this canal. In this case we have to deal with a sim- 

 ple relation between the orientation of the canal and 

 the plane in which the organs or the whole body of 

 the animal move. This fact is just as mysterious 

 as the more general facts mentioned in this chapter. I 

 am inclined to assume that the peculiar relation be- 

 tween the semicircular horizontal canal and the motions 

 produced by the stimulation of this canal finds its 

 explanation through the facts mentioned in this chap- 

 ter. It is possible that the central endings of the 

 nerve of the horizontal canal are connected with the 

 motor elements in the medulla whose activity pro- 

 duces motions in the plane of the horizontal canal. 

 When Flourens made his experiments on the semi- 

 circular canals he found that there was a striking 

 resemblance between the effects of a destruction of 

 the canals and the sectioning of the crura cerebelli. 

 He came to the conclusion that there must be a sim- 

 ple relation between the direction of the fibres of the 

 crura cerebelli and the motion produced by them (3). 

 His observations are not in all points correct ; yet 

 with some modification his fundamental idea remains 

 true. The next chapter, on the cerebellum, will give 

 us some more data about his observations. 



It is possible for us to conceive from this how it 

 happens that the same optic stimulus or the same 

 space-perception is able to direct our eyes toward a 

 certain point, to turn our head in that direction, to 

 guide our finger thither, or to bring our legs into such 



