CEREBRAL FUNCTION IN THE RAT . 79 



tion of the habit, evidenced either by relatively few errors in 

 the first trials of the retention tests or by survival of individual 

 peculiarities of reaction to the maze. Details of these experi- 

 ments have been given in the earlier paper. The extent of the 

 cerebral lesion has now been determined for each animal and a 

 report of the findings will be given in the first section of this 

 paper. 



The experiments are here given the same numbers as in the 

 first article and page references for each experiment are given to 

 facilitate reference to the original description. A brief estimate 

 of the degree of retention is included for each animal with the 

 record of the total number of errors made during the first fifteen 

 trials of training and the first fifteen of the retention tests. This 

 is followed by the description of the lesions. 



In the diagrams prepared for this section of the paper we have 

 figured only so much of the lesion as is obvious, either from the 

 total separation of the injured parts from the remainder of the 

 brain, the complete degeneration of the cortex, or the unmistak- 

 able section of the descending tracts. In every case it is prob- 

 able that the lesion affected a much more extensive area than 

 that indicated but it has seemed best to restrict the description 

 to the obvious destructions. 



After certain of the animals (experiments 8, 9, 10, 11, 12 and 

 13) had recovered from the effects of the operation and had 

 given evidence of the retention of the habit a second operation, 

 designed to destroy the temporal or occipital regions, was per- 

 formed. The description of the second lesion is included with 

 that of the first, in the animals which survived; the effects of 

 the operation will be described in experiment 15. 



Experiment 1 (page 8). Almost perfect retention. Errors: 

 learning 5, retention 1. 



Lesion (plate II, fig. 1). There is a transverse cut extending 

 diagonally across both cerebral lobes. From above the knee of 

 the corpus callosum on each side it passes out along the forceps 

 of the callosum to the external capsule and thence to the cortex, 

 1.5 mm. behind the base of the olfactory bulb. Below, on the 

 left, the lesion extends to the floor of the lateral ventricle, on 



