36 K. S. LASHLEY AND L. E. WILEY 



is a good bit of individual variation in the positions of the 

 boundaries of the fields and probably even more distortion 

 resultant from our methods of plotting the lesions and, finally, 

 a good bit of uncertainty in determining the exact boundaries 

 of the fields by direct histological methods, 7 there is no ac- 

 curate means available for determining the amount of destruc- 

 tion in the different functional areas. As an approximate 

 measure, a transparent diagram of Lashley's modification of 

 Fortuyn's diagram of cytoarchitectural fields was superim- 

 posed upon the diagram of the lesions for each case, and the 

 percentage of the total cortex destroyed within each field 

 was measured with a planimeter. 



On the basis of these percentage measurements, we selected 

 cases in which the extent of lesion in one field was three or 

 more times as great as in any other field and in which the total 

 extent of lesion in any except the primary field did not exceed 

 5 per cent of the total cortex. The cases assigned to the four 

 principal areas were the following: 



ff'n (motor) : 17, 18, 32, 41, 64, 65, 70, 75, 76, 80, 111. 



j (somesthetic) : 2, 4, 7, 9, 20, 34, 47, 73, 74, 78, 85, 94, 102, 106. 



p (auditory) : 1, 3, 6, 11, 19, 39, 40, 52, 79, 98, 100, 103, 105. 



w (visual) : 10, 14, 35, 36, 44, 66, 69, 71, 72, 97, 99, 104, 113. 



For each of these groups the average extent of lesion and the 

 average of errors (less first trial) in learning maze V were 

 computed. These constants are given in table 18 and graphic- 

 ally in figure 3. The average destruction for the four groups 

 is so nearly the same that the differences may be disregarded. 

 In comparison with the average for normal animals in maze V 

 (33.1 ± 4.2 errors) all of the groups were markedly retarded. 

 For the motor, visual, and somesthetic fields the training 

 records are essentially equal, the differences between the 



7 A survey of the literature on the cytoarchiteeture of the brains of rodents 

 by the senior author reveals that the disagreements among investigators in this 

 field are so great as to cast doubt upon the significance of most of the areas 

 differentiated. No two investigators have used the same criteria for distinguish- 

 ing the areas and such criteria as have been defined are purely relative. The 

 confusion is particularly striking within the areas called auditory and somesthetic. 



