FORCED MOVEMENTS 155 



ing and circus-motions may occur after injury to the 

 brain in front of this segment, wherever places are 

 met with which are directly or indirectly connected 

 with the acoustic segment. This is the case, for in- 

 stance, after a one-sided lesion of the pons or the 

 cerebral hemispheres in rabbits and dogs. In both 

 animals circus-motions occur after destruction of the 

 cerebral hemispheres, in rabbits toward the intact side, 

 in dogs toward the injured side. All the facts prove 

 that the semidecussations take place in the vicinity of 

 the acoustic segment and not farther down. In man, 

 so far as I know, circus-motions have never been ob- 

 served ; this is probably due to his upright walk. It 

 would be interesting to make the experiment of having 

 patients afflicted with certain diseases (for instance, 

 diseases of the inner ear) walk on all fours (with 

 closed eyes) and to observe whether circus-motions 

 occur. 



As we have already mentioned, it is a well-known 

 fact that in Arthropods after destruction of one half 

 of the supraoesophageal ganglion circus-motions can 

 occur. That they need not occur has been shown by 

 Miss Hyde and also by Bethe (4 and 5). According 

 to the investigations of the latter author these circus- 

 motions in Invertebrates are called forth by very dif- 

 ferent disturbances in the muscle-tension. It is often 

 due simply to a disturbance in the muscle-tension of 

 the extremities of one side, the other side being ap- 

 parently normal. In Crustaceans, associated changes 

 of position of the extremities can also occasionally 



