FORCED MOVEMENTS 153 



It is thus the muscles directly or indirectly connected 

 with the left side of the medulla oblongata (in the 

 acoustic segment) which show a decrease in tension 

 after the destruction of the left ear. Accordingly, the 

 left side of the medulla is connected with the raising 

 muscles of the left eye and the lowering muscles of 

 the right, eye, as well as with the lowering muscles of 

 the left pectoral fin and the raising muscles of the 

 right pectoral fin. If we start with the idea that all 

 the muscles of an eye or a fin form a common whole, 

 a kind of semidecussation is present. It is, however, 

 not only the muscles of the fins that undergo such 

 changes of tension, but probably also the muscles of 

 the spinal column. 



If the symmetrical muscles of the organs of loco- 

 motion possess different tension, the usual stimuli for 

 locomotion must naturally lead to unsymmetrical in- 

 stead of symmetrical movements. When the lower- 

 ing muscles predominate in the right pectoral fin and 

 the raising muscles in the left, the animal, when these 

 fins are used, will come under the influence of a couple 

 of forces which must produce a rolling movement 

 around the longitudinal axis of its body toward the 

 left. As long as the animal swims slowly, rolling mo- 

 tions do not occur, for they are compensated for. 

 The friction of the fish in the water will suffice to 

 destroy a slight rolling motion. But if the animal 

 attempts to swim rapidly, e. g., if it be excited, it be- 

 gins to roll. These rolling motions are called forced 

 movements, a poorly selected term. The same move- 



