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K. S. LASHLEY AND S. I. FRANZ 



the operation. He required only thirty trials to learn to go to 

 the right. He was then required to go to the left and the earlier 

 habit was completely overcome in twenty trials. The records 

 of time and errors are given in table 1. 



TABLE 



Rate of learning for rat described in experiment 85. In this and the following 



tables the average time per trial and the total number of errors 



are given for successive groups of five trials 



He was killed 30 days after the operation. Microscopic 

 examination of the brain showed (plate II, fig. 35) : 



Right hemisphere. A transverse lesion beginning above the 

 posterior end of the corpus callosum and extending forward 

 almost horizontally to the anterior pole, above the level of the 

 corpus callosum. There is a superficial lesion of the lateral 

 surface of the occipital lobe resulting from a knife cut which 

 separated the cortex from the underlying fibers. A similar lesion 

 extends over the orbital surface, separating nearly half of the 

 lateral surface of the cortex from the underlying fibers and de- 

 stroying the fibers of the external capsule back to the level of 

 the hippocampus. The lateral ventricle was not reached by the 

 injuries and the subcortical ganglia are intact. 



Left hemisphere. The lesion on the dorsal convexity is simi- 

 lar to that on the right. There is a transverse lesion completely 

 severing the frontal pole just in front of the caudate nucleus. 

 A lesion on the orbital surface following the course of the ex- 

 ternal capsule to the anterior end of the hippocampus has com- 

 pletely destroyed a lens-shaped area on the orbital surface. 

 The cerebral nuclei are intact. 



