Labyrinth and Semicircular Canals in the Human Ear. 255 



function, of the horizontal canals in the perfect organ when the 

 head is moved to the left. 



The application of the same principle of explanation to the 

 same canals when the head moves to the right, and to the ver- 

 tical canals when the head moves backwards or forwards, is so 

 obvious that it need not now be dwelt upon. 



When the head is held erect, or probably when recumbent in 

 a horizontal position, I apprehend that each membranous am- 

 pulla will occupy the centre of its osseous envelope, so that at 

 neither extremity of the former will pressure be exerted upon it 

 by the latter. 



If under these circumstances the horizontal membranous 

 canal of the left ear were cut, I apprehend that the severed por- 

 tions would overlap each other ; so that the extremity of the 

 membranous ampulla of the same canal which is furthest from 

 the vestibule would be forcibly driven into the corresponding 

 portion of the osseous ampulla. If this view be correct, it will 

 be seen, by reference to the foregoing argument, that the same 

 signal will have been conveyed to the brain as if the head had 

 moved to the right ; that is, warning will have been given to the 

 muscles whose function it is to counteract a motion of the head 

 to the right, to bring themselves into action ; whence we might 

 expect that a motion of the head to the left would ensue. As 

 soon as this motion has been completed, however, it is to be an- 

 ticipated that the sudden and perhaps violent motion of the 

 poor animal under the pain of the operation would make this 

 part of the membranous labyrinth oscillate in the contrary direc- 

 tion, so as to drive the membranous ampulla of the same canal 

 into the opposite extremity of its osseous sac, and thus the signal 

 to move the head to the right would be given. 



In this way, I think, may be accounted-for the alternate mo- 

 tion of the head from right to left and from left to right which 

 is stated to have resulted from cutting the left horizontal canal 

 of the pigeon. We may see also how that further result of the 

 experiment might be anticipated which is related to have oc- 

 curred — that is, that the pigeon would by degrees learn to dis- 

 regard the anomalous indications of its left ear, and rely wholly 

 on those of the right ear alone, which preserved their normal 

 character. 



On the other hand, the cutting of both the horizontal canals 

 would destroy all the means with which nature has provided 

 the animal for ascertaining and measuring the direction and ex- 

 tent of the motions to right and left of its head, and would thus 

 leave it in that state of incapacity to control those motions which 

 is described by M. Flourens. 



The effect of cutting the several vertical canals was, for the 



