86 K. S. L ASHLEY AND S. I. FRANZ 



of trials. Number 11 was slower and required an average of 

 9.0 seconds per trial but did not make a single error or react in 

 any way to the entrance to the cul de sac in twenty-five trials. 



After the first operation all these animals had shown a per- 

 fect retention of the habit, in spite of a practically complete 

 destruction of the frontal poles of both hemispheres. The sec- 

 ond operation probably did little additional harm to number 10 

 beyond cutting the fimbria on both sides. In number 12, how- 

 ever, large areas on the dorsal and orbital surfaces of both hemi- 

 spheres were destroyed. In number 11 practically all the dorsal 

 and lateral surfaces of the cortex overlying the gyri hippocampi 

 and between them and the frontal poles was destroyed. 



The effects of the first operation, taken in conjunction with 

 the other experiments of the same series, indicate rather clearly 

 that the persistence of the habit was not conditioned by the 

 functional integrity of the frontal pole. The second operation 

 resulted in the elimination of not less than half of the cortex of 

 the dorsal convexity and the combined destruction resulting 

 from all the operations performed on these animals, certainly 

 includes not less than two thirds of the cortex, leaving only the 

 occipital regions, the ventral surface, and the gyri hippocampi 

 intact. We are justified in concluding therefore that no part 

 of the cortex in front of the caudal end of the corpus callosum 

 and above the level of the floor of the lateral ventricles is con- 

 cerned with the retention of simple kinesthetic-motor habits. 



Experiments with the inclined-plane box 



The simple maze offered some disadvantages for a study of 

 retention owing to the fact that it did not require a reaction that 

 was sufficiently well defined to be certainly recognizable in the 

 retention tests. It seemed best therefore to use some more com- 

 plex habit in the later experiments for the sake of getting a more 

 clearly defined series of activities and also with the possibility 

 that the more complex habit, involving different types of reac- 

 tion, might reveal a selective effect of the cerebral lesion upon 

 certain types of activity. The inclined-plane box (2) was 



