CEREBRAL FUNCTION IN THE RAT 



121 



for food and again learned in fifty trials. The average time re- 

 quired and the total number of errors made in successive groups 

 of five trials are given in table 3. 



Microscopical examination of the brain showed (plate II, fig. 



37): 



TABLE 3 



Rate of learning for the rat described in experiment 37 



Right hemisphere. Destruction of the greater part of the 

 convexity of the cortex from the occipital portion of the corpus 

 callosum to the knee, involving the greater part of the corpus cal- 

 losum and exposing the lateral ventricle and extending around the 

 anterior face of the caudate nucleus to the cortex, separating 

 the anterior pole to the level of the olfactory fibers. The fibers 

 of the anterior pole have been absorbed, leaving a large cyst. 

 The longitudinal incision extends backward from the transverse 

 lesion to the middle of the caudate nucleus, then along the 

 course of its fibers, through the external capsule to the cortex, 

 producing, apparently, very little destruction. 



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

 lar to that on the right. The transverse lesion passes just in 

 front of the knee of the corpus callosum and diagonally forward 

 to the base of the olfactory lobe, severing the entire anterior 

 pole to the level of the olfactory tracts. There is invasion of 

 the anterior end of the caudate nucleus by hemorrhage. The 

 longitudinal incision seems to have passed along in the lateral 

 ventricle and to have done little damage. There is an extensive 

 superficial lesion extending over the occipital lobe. 



