12 K. S. LASHLEY 



determined by reference to internal structures. When any 

 marked departure from average proportions appeared, the 

 three sections corresponding most closely to levels 18, 23, 

 and 29 were selected and the position of the others determined 

 by interpolation. 



The extent of the lesion on each section was next deter- 

 mined under higher magnification and marked on the camera 

 sketch. Measurements were made on the sketch and trans- 

 ferred to the corresponding level on the diagram with pro- 

 portional dividers. The points so determined were checked 

 with the original sketch of the lesion made at necropsy, the 

 points connected by the best fitting line, and the enclosed 

 areas inked in. 



To estimate the extent of the lesion the following method 

 was used. The areas included between the parallel lines on 

 the diagrams were treated as rectangles. The total length 

 of these included within the diagram of the lesion gave the 

 area of the lesion in arbitrary units, and this divided by the 

 total length of the rectangles included in the entire diagram 

 of the cortex gave the percentage of the cortex destroyed. 

 In the measurements the entire diagram of the dorsal aspect 

 was included, but only those portions of the lateral aspects 

 lying below the level of the corpus callosum. This allows 

 roughly for the overlapping of the dorsal and lateral aspects. 



This method gives a crude measure of the percentage of 

 the neopallium destroyed by the operation. The absolute 

 percentage is not accurate, since the effects of perspective in 

 the diagram and the exact limits of the neopallium are dis- 

 regarded, but the use of the same method for all brains makes 

 the percentages comparable. Repeated measurements of the 

 same brain indicate an accuracy of d= 5 per cent for individual 

 determinations. 



With the completion of the diagrams, the sections were 

 reexamined for lesions to subcortical structures, especially 

 the fornix, hippocampus, thalamus, and colliculi. Lesions to 

 these structures were rated in four grades: 0, no injury; 

 1, slight injury (estimated 10 per cent or less); 2, medium 



