80 K. S. LASHLEY 



The brain was removed and fixed 78 days after the operation. 



Lesion: Plate I, figure 5. The lesion was practically identical in 

 form with that of number 4, but less extensive. The frontal pole was 

 largely destroyed by a section passing from the lateral ventricle out- 

 ward along the forceps of the callosum to the cortex. The cortex lat- 

 erad to the corpus striatum was not degenerated, but its connections 

 were almost certainly destroyed. This area is stippled in the diagram. 

 The cortex laterad to the hippocampus was completely degenerated. 

 The dorsal surface of the hemisphere was destroyed except for a narrow 

 band along the mesial and occipital borders. The corpus striatum was 

 intact but seemed to be separated from its posterior attachments. 



Number 6. Small female, 68 days old at the time of operation. 

 The left hemisphere was partly destroyed by a thermo-cautery. She 

 developed a slight paresis which persisted for only a few weeks. Train- 

 ing was begun 30 days after the operation. After 8 days the animal 

 became ill and training was suspended for 12 days. It was then re- 

 sumed and completed. 



Number of trials required for learning 49 



Per cent of total cortex destroyed 30.4 



The brain was removed and fixed 60 days after operation. 



Lesion: Plate I, figure 6. All the cortex on the dorsal surface from 

 the forceps of the corpus callosum to the posterior margin of the hip- 

 pocampus was destroyed. The lesion narrowed laterally to include only 

 the area overlying the corpus striatum and fornix. The latter bodies 

 were completely destroyed. 



The results of these tests are summarized in table 2. The 

 maximum number of trials required by any member of the group 

 was 141(1). The smallest number was 54 (3) . The average num- 

 ber of trials is 82.7. The average time required per trial on suc- 

 cessive day's training is shown in table 3. The total extent of 

 the lesions is shown in figure 3. Every portion of the left hem- 

 isphere and the greater part of the right was eliminated in one 

 or another test, without significantly increasing the amount of 

 practice required for learning. The maximum lesion appeared 

 in number 3 (plate I, figure 3), including practically the entire 

 left hemisphere. This animal learned more quickly than any 

 of the others. 



