84 K. S. LASHLEY 



Lesion: Plate II, figure 11. The brain could not be sectioned owing 

 to the presence of a large piece of bone which had become imbedded in 

 the right hemisphere, extending into the lateral ventricle. The black 

 area in the diagram indicates the extent of the large cyst occupying the 

 parietal lobes of both hemispheres, as determined by gross dissection. 

 The cortex in this area was completely absorbed, so that the thalamus 

 and lateral ventricles were exposed. All of the cortex and that part 

 of the corpus callosum overlying the lateral ventricals was destroyed. 



Number 12. Small female, about 150 days old. Both parietal lobes 

 were injured by an operation similar to that performed on number 11. 

 Recovery was normal without sensory or motor disturbance. Train- 

 ing was begun 27 days after operation and progressed normally. 



Number of trials required for learning 81 



Per cent of total cortex destroyed 15.2 



Lesion: Plate II, figure 12. The lesion extends caudad from the 

 region of the f ronto-parietal suture to the anterior border of the hippo- 

 campus and laterad to the level of the floor of the lateral ventricles, 

 involving the middle portion of the corpus callosum. 



Number 18. Small male, about 100 days old. The parietal lobes 

 were injured as in the case of number 11. Recovery was rapid and 

 training was begun 18 days after operation. The animal's reactions 

 were prompt from the first and selective reactions to the platforms 

 appeared on the fourth trial. 



Number of trials required for learning 41 



Per cent of total cortex destroyed 31.5 



Lesion: Plate II, figure 13. On the right hemisphere the lesion ex- 

 tends from the knee of the corpus callosum caudad to the middle of the 

 hippocampal lobe. Laterad it extends to the orbital surface and is 

 continued as two narrow cuts which extend almost to the olfactory 

 tracts and are united internally by a section through the external cap- 

 sule which is outlined by small cysts. The lesion of the left hemisphere 

 is similar in position but extends caudad only to the anterior margin 

 of the hippocampus and laterad only to the plane of the upper limit of 

 the lateral ventricle. 



Number 14- Small male, about 100 days old. The parietal lobes 

 were injured with a thermo-cautery. Recovery was rapid, but a slight 

 right paresis persisted. Training was begun 25 days after operation. 

 He reacted promptly to the problem-box situation but soon developed 



