40 C. WINKLER. THE CENTRAL COU1ISE 



tig. X). EWALD himself, thinks that the farther turning of the head is a 

 voluntarily accomplished movement. It is easier for the pigeon, to 

 have its head turned for 360 than for 180, and the length of 

 its movable neck permits it to do so. 



That what the rabbit corrects by rolling round its longitudinal 

 axis, the pigeon does in bending round its neck till 360. 



Besides , the peculiar anatomical relations of the octavus-system 

 in the pigeon offer a clue to the behaviour of this animal shortly 

 after one-sided removal of the labyrinth. 



When observing attentively the newly-operated pigeon after one- 

 sided removal of the labyrinth, we find that it presents a 

 slight ressemblance with the pigeon, in which the labyrinth has 

 been removed on both sides. At least the ressemblance is far greater 

 than with itself after three weeks. 



As a fact the one-sided extirpation of the labyrinth in a pigeon 

 does signify for the central nerve-system a very grave lesion in the 

 primary octavus-nuclei of the operated side and a less grave but impor- 

 tant lesion in the primary octavus-nuclei opposite to the side of the ope- 

 ration. The pigeon, whose labyrinth has been removed on one side, is 

 in the first days equivalent to an animal on which the removal of the 

 labyrinth on both sides has been incompletely performed. It is 

 only afterwards that gradually the preponderance of the one-sided 

 disturbances appear in such an animal. Especially under the influence 

 of emotions or other stimuli , the turning of head and neck occurs 

 suddenly. If the characteristic turning of head and neck are seen 

 they ressemble in all points that of the rabbit. But, and there 

 lies the difference , it only appears by intervals. However the pre- 

 vailing at the slightest occasion of the preponderance of the one-sided 

 head-and neck-inner vation is permanent in pigeons, as is likewise the 

 atony of the extremities at the operated side. 



In the rabbit, where the N. octavus does not end into the 

 octavus-nuclei on both sides, as it does in the pigeon, the 

 post-operative results are different. Here the operation produces 

 a maximum of one-sided disturbance of innervation, not a double- 

 sided disturbance. Therefore this disturbance attains its maximum 

 directly after the operation, but gradually it diminishes. To a 

 certain degree only it is compensated. The characteristic turning of 

 head, neck and eyes remains for ever, though it also increases by 

 intervals. 



The pigeon has another anatomy of the VIII th nerve as the rab- 

 bit. The one-sided removal of the labyrinth repercutes on both 

 sides of the central system. Therefore in the first days there is a 



