Labyrinth and Semicircular Canals in the Human Ear. 253 



rabbits of two months old were selected. In the case of the 

 anterior vertical canal, which presented greater difficulty, the age 

 had to be reduced to fifteen days. 



In the first two cases the results of the experiments, with 

 some unimportant variations, were the same in character as those 

 of the corresponding experiments upon birds. 



When one horizontal canal only was cut, the: head of the animal 

 in repose was always to the side of the section; but when both 

 horizontal canals were cut, the head resumed its natural position. 

 In the latter case, not merely the head, but the fore legs, and, 

 indeed, the entire fore part of the animal, partook of the oscilla- 

 tory movement from right to left and vice versa. 



It was found difficult to operate on the anterior vertical canal 

 without injuring the brain, by which the results of the experi- 

 ments were complicated with those flowing from the lesion of 

 the latter. In the few cases in which this cause of error was 

 avoided, the results of the experiments were precisely similar to 

 those of the corresponding experiments on birds. 



It is consolatory to think that the rabbits experimented upon 

 did not seem to suffer the pain which was experienced by the 

 pigeons ; nevertheless M. Elourens does not appear to have 

 succeeded in keeping alive the former beyond a month in one case, 

 and a week in another. 



II. Assuming that experiments operated on the semicircular 

 canals of the human ear resembling in character those performed 

 by M. Flourens upon pigeons and upon rabbits would be at- 

 tended by like results, I now proceed to explain how the occur- 

 rence of such results may be accounted for. 



The membranous labyrinth, I conceive, must be regarded in 

 the light of a delicate balance, which, being suspended in the 

 perilymph contained in the vestibule and semicircular canals, 

 upon each movement of the head changes its position in the 

 irregularly shaped bony cavity within which it is confined, and 

 is thus enabled, in a manner presently to be described, to trans- 

 mit to the mind or subordinate directing principle such intelli- 

 gence respecting the motions of the head as may be necessary 

 with a view to their regulation, variation, and maintenance. 



The membranous labyrinth is supported by nervous filaments, 

 which, leaving the inner wall of the osseous labyrinth, after tra- 

 versing the perilymph, penetrate within as well the membra- 

 nous vestibule (sinus communis) as the ampullae, with one of 

 which each canal is provided, and diffuse themselves over these 

 parts of the membranous labyrinth to the exclusion of every 

 other. 



The experiments of M. Flourens show that motion of the 

 head forwards is governed by the anterior vertical canals, mo- 



