CEREBRAL FUNCTION IN THE RAT 93 



trained on the inclined-plane box for 75 trials. The average 

 time per trial for the first five trials of learning was: to plane, 

 916 seconds; to door, 85 seconds. The average for the last five 

 trials was: to plane, 2.8 seconds, to door, 2.2 seconds. 



Retention was tested on the second day after the operation. 

 At this time the animal was active and showed no abnormal 

 symptoms. She was given ten trials on this day with the fol- 

 lowing average time per trial: to plane, 51 seconds; to door, 

 14 seconds. 



The animal's behavior toward the problem box was in all 

 respects normal. Her exploratory movements were restricted 

 to the plane and in seven of the trials she tripped the catch by 

 pushing the plane down with her fore feet, a stereotyped method 

 which she used before the operation. 



FIG. 7. TOTAL EXTENT OF LESIONS IN THE CONTROL ANIMALS (EXPERIMENTS 



17, 18 and 19) 



Lesion (plate III, fig. 19).' Right hemisphere. There is an 

 extensive lesion of the cortex extending from the anterior border 

 of the hippocampus to the knee of the corpus callosum and 

 narrowing rapidly as it extends laterad on the orbital surface. 

 It is continued over the orbital surface as a lesion of the external 

 capsule around the upper half of the corpus striatum with degen- 

 eration of the overlying cortex. 



Left hemisphere. There is a lesion similar to that on the 

 right over the dorsal convexity but it is broader over the tem- 

 poral region and extends downward only to the upper level of 

 the lateral ventricle. 



This animal, after the destruction of the cortex over the temporal 

 and a portion of the orbital surface of both hemispheres, showed 

 no deterioration of the habit previously formed. 



The perfect retention of the habit by these three animals 



