126 K. S. LASHLEY AND S. I. FRANZ 



pus striatum is cut through in sagittal section for its full length 

 and the lesion filled by a large clot which extends down into 

 the cerebral peduncle, cutting through its fibers obliquely. The 

 anterior portion of the caudate nucleus is replaced by a clot, 

 the remainder is much shrunken. The antero-lateral surface 

 of the thalamus shows indications of degeneration. 



Left hemisphere. There is destruction of all tissues above 

 and including the corpus callosum. A transverse lesion extends 

 diagonally from behind the knee of the corpus callosum to the 

 base of the olfactory bulb, severing the anterior pole. The 

 lateral ventricle is collapsed and all the cortex laterad to it is 

 replaced by scar tissue. The external capsule lies free in a cyst 

 laterad to the corpus striatum and, in the occipital lobe, is re- 

 placed by a large cyst. The corpus striatum is degenerated. 

 The fornix is largely destroyed. The thalamus is intact. 



In this animal the destruction of all the cortex above and in front 

 of the corpus callosum and laterad to the left lateral ventricle with 

 partial degeneration of the right and complete degeneration of the 

 left caudate nuclei, destruction of the fornix and injury to the thala- 

 mus on the right was followed by inability to solve the simple maze 

 but did not preclude the formation of simple habits as evidenced 

 by the gradual appearance of stereotyped modes of response to the 

 maze. 



The -course of learning in these different animals is compared 

 with the average of normal individuals trained under the same 

 conditions in figure 13. The animals described in experiments 

 35 and 37 were apparently normal in behavior and learned in 

 about the same amount of practice as is required by normal rats. 

 The animals in experiments 36 and 38 learned to go to the right 

 quite readily but had a great deal of difficulty in readjusting to 

 the problem when they were required to overcome the first habit 

 and learn to turn to the left. The rat in experiment 39 was un- 

 able to learn the problem in more than three hundred trials. 

 However, even this animal showed marked improvement in the 

 time required for running the maze during the early part of 

 practice. In experiments 38 and 39 a part of the difficulty 

 experienced by the animals was clearly due to a persistent hemi- 



