SEC. 2. THE MECHANISMS OF COORDINATED 

 MOVEMENTS. 



When in a pigeon the horizontal membranous circular canal 

 of the internal ear is . cut through, the bird is observed to be 

 continually moving its head from side to side. If one of the 

 vertical canals be cut through, the movements are up and down. 

 The peculiar movements may not be witnessed when the bird is 

 perfectly quiet, but they make their appearance whenever it is 

 disturbed, or attempts in any way to stir. When one side only 

 of the head is operated on, the condition after a while passes away. 

 When the canals of both sides have been divided, it becomes much 

 exaggerated, lasts longer, and sometimes remains permanently. 

 And it is then found that these peculiar movements of the head 

 are associated with what appears to be a complete want of co- 

 ordination of all bodily movements. If the bird be thrown into 

 the air, it nutters and falls down in a helpless and confused 

 manner; it appears to have totally lost the power of orderly 

 flight. If placed in a balanced position, it may remain for some 

 time quiet, generally with its head in a peculiar posture; but 

 directly it is disturbed, the movements which it attempts to 

 execute are irregular and fall short of their purpose. It has great 

 difficulty in picking up food and in drinking; and in general 

 its behaviour very much resembles that of a person who is exceed- 

 ingly dizzy. 



It can hear perfectly well, and therefore the symptoms cannot 

 be regarded as the result of any abnormal auditory sensations, such 

 as ' a roaring ' in the ears. Besides, any such stimulation of the 

 auditory nerve as the result of the section, would speedily die away, 

 whereas these phenomena may be permanent. 



