102 K. S. LASHLEY AND S. I. FRANZ 



seconds. The average time for the last five trials was: to plane, 

 15.4 seconds; to door, 2.4 seconds. Retention was tested on 

 the second day after the operation. She reacted promptly to 

 the problem-box situation, never pausing except at the door 

 and at the plane. She tripped the plane by one of two methods; 

 either she jumped up from in front of the door so that her hind 

 feet struck the free end of the plane, or, this method failing, she 

 turned and pushed the plane down with her fore feet. These 

 were the methods used before the operation. The average 

 time required for the first five trials of the retention tests was: 

 to plane, 37.6 seconds; to door, 9.6 seconds. 



Lesion (plate III, fig. 24). Right hemisphere. There is a 

 small lesion on the antero-dorsal convexity corresponding to 

 the extent of the opening of the skull. From this a transverse 

 cut extends ventrad through the union of the forceps of the 

 corpiis callosum with the external capsule to the base of the 

 olfactory bulb. Its effects are limited to the lateral face of the 

 cortex where there is a narrow degenerated area along the edges 

 of the cut, widening on the orbital surface. 



Left hemisphere. The lesion is almost identical with that 

 on the right but less extensive on the orbital surface. 



Destruction of the antero-lateral faces of the cortex in this animal 

 resulted in practically no loss of the habit. 



Frontal region destroyed: animals showing questionable retention 



after operation 



Experiment 25. The frontal poles of the cerebrum of a small 

 male rat, 143 days old, were destroyed by incisions through two 

 large openings in the parietal bones, 5 mm. back of the fronto- 

 parietal suture. The animal had previously been given 45 

 trials in the inclined-plane box. The average time required for 

 the first five trials was: to plane, 575 seconds; to door, 40 sec- 

 onds. The average time for the last five trials of training was: 

 to plane, 9.6 seconds; to door, 2.8 seconds. 



Retention was first tested on the fourth day after the opera- 

 tion as the animal was quite stuporous up to this time and had 

 to be fed by hand. On this and the following day he moved 



