INTEGRATION OF MOVEMENTS IN LEARNING IN THE RAT 483 



but is diverted as is shown in diagram C. Progression may be 

 then a short distance to the right or even to the plane, reversed 

 and continued to the left of the problem. In one or two cases 

 in rats in which progression was to the right of the problem and 

 in which the left ipsilateral fore thrust had a stronger extensor 

 tone than the right ipsilateral fore thrust in the beginning of 

 learning, the extensor tone of the left ipsilateral thrust decreased 

 and progression continued to the left of the problem to the plane. 

 Very seldom is it the case that progression continues to the right 

 of the problem when a left ispilateral fore thrust has a stronger 



---n 





..-Q 



V 



f 



ABC 



FIG. 5. DIRECTIONS TO THE PLANE 



extensor tone than the right ipsilateral fore thrust. In some 

 instances when no fore ipsilateral reflex thrust could be evoked, 

 progression was then to the right or to the left of the problem. 

 The left or right center of the cord then may predominate, for, 

 if progression is to the left, the appearance of a weak left ipsi- 

 lateral fore thrust will condition diverting of the direction of 

 progression to the right; and if a right ipsilateral fore thrust 

 appears, progression is usually diverted from the right of the 

 problem to the left and continues thereafter to the left. From 

 the results obtained from these observations, there always 



