114 



K. S. LASHLEY 



The exact delimitation of the visual area has not been made 

 possible by these experiments, but the gross area determined 

 seems to correspond to the histological findings. The majority 

 of writers have localized the visual cortex of rodents on the pos- 

 teromedial aspect of the cortex, behind the caudal fibers of the 

 corpus callosum and in contact with the cerebellum (Isenschmid, 

 '11). This region remained uninjured in all but one of my cases. 

 It probably is not the part functional in the visual habit. Brod- 

 mann ('09), on the other hand, locates the area striata on the 

 dorsal convexity of the occipital pole in the rabbit and Isenschmid 



FIG. 12. THE TOTAL EXTENT OF THE LESIONS IN ANIMALS WHICH LOST THE HABIT 

 OF VISUAL DISCRIMINATION AFTER OPERATION 



The stippling shows the total area, the solid black the area common to all. 



('11) is inclined to favor this view in his studies on the cytoarchi- 

 tecture of the mouse's brain. Figure 12 shows the combined 

 extent of the lesions in the three occipital cases. Only a small 

 area on the dorsal convexity was destroyed in all three animals. 

 This covers approximately the region described by Brodmann 

 for rodents as the area striata. It is by no means certain, of 

 course, that the region destroyed was the region functional in 

 the habit, but the mass of evidence on cerebral function accumu- 

 lated from the rat gives little indication of shock effects and the 

 most probable interpretation of the data is that the loss of habit 

 resulted from the destruction of Brodmann's area striata. 



