

OTOLITH SACS OF THE INNER EAR 477 



the perception of the position of the head and thus indirectly in perceiving the 

 position of the whole body. 



After removal of the entire membranous labyrinth from both sides the 

 pigeon on casual examination exhibits no particularly prominent symptoms 

 for some months after the operation. But on closer investigation one finds 

 that all the muscles are abnor- 

 mally atonic, that the animals 

 have a certain disinclination to 

 move, that they cannot fly, and 

 finally that their ability to recog- 

 nize the position of their bodies 

 is diminished. 



The muscular weakness occa- 

 sioned by the operation is demon- 

 strated by the following experi- 

 ment. A small lead ball weighing ^ 189 _ pigeon twenty davs after removal of the 



20 g. IS suspended Oil a thread and right mem branous labyrinth, after J. R. Ewald. 



the thread is fastened by means of The head has been turned once around to the 



modeler's wax to the beak of a right, 



pigeon whose labyrinths have been 



removed. If the ball hangs in front, it draws the head far downward, but the 

 relatively strong muscles of the back of the neck are able to lift it and to dangle 

 it about. The head follows the pendulumlike movements of the ball apparently 

 without concern but in reality quite powerlessly until at last in the course of 

 its swinging the weight is thrown around over the back. Immediately this 

 happens the head is held by the ball in the position shown in Fig. 187. The 

 muscles which otherwise would lift the head from this position are too weak to 

 do so now that the labyrinths are wanting. 



The following experiment shows how the sensations of position are affected. 

 A pigeon deprived of its labyrinth is blindfolded by drawing a leather cap over 

 its head. Because of the muscular weakness the head falls down over the back 

 and the muscular sensation fails to apprise the nerve centers of the fact. Since 

 the visual impulses do not now compensate for this deficiency, the animal no 

 longer has any correct notion of the attitude of its head, and will allow it to 

 remain in this unnatural position. 



After removal of the labyrinth on one side only the disturbances are less 

 severe, so that the animals can still fly and can take food without difficulty. 

 But they are not by any means normal, for the peculiar rotations of the head 

 first described by Flourens, and which cease after bilateral extirpation, at 

 times make their appearance. 



During the first days following the operation the pigeon begins to incline its 

 head toward the operated side. The turning increases more and more as time 

 goes on, and finally may amount to complete rotation (Figs. 188 and 189). The 

 explanation is, that by removing one labyrinth, say the right, the muscles which 

 normally prevent the head from falling to the right are greatly weakened. 



There is a decline in the functional power of other muscles after extirpa- 

 tion of one labyrinth. According to Ewald each labyrinth is connected by way 

 of the central nervous system with all the voluntary muscles of the body, 



