THE CEREBRAL HEMISPHERES 



159 



searches into the minute structure of the brain were 

 made upon the mouse. Brodmann has pubHshed an 

 extensive series of anatomical studies (summarized in 

 his book published in 1909) on the regional differences 

 between various parts of the cortex in many animals, 

 including the rabbit and several other small mam- 

 mals. The cortical areas of the mouse have been simi- 

 larly mapped by Isenschmid (1911), De Vries (191 1), 

 and others. The most ambitious and valuable re- 

 search in this field is that of Fortuyn (1914), who de- 

 scribes in detail the cortical patterns of nine species 

 of rodents, including the rabbit, mouse, and rat. A 

 good summary of his conclusions is given by Sugita 

 (1917-1918). 



Figure 38 presents copies of Fortuyn's diagrams of 

 the lateral and dorsal aspects of the rat's cerebrum, 

 illustrating the arrangement of the structurally dif- 

 ferent cortical areas. The electrically stimulable cor- 

 tical fields of the rat as charted by Lashley (1921) 

 are shown in Figure 40. 



Comparing the anatomical and physiological 

 charts, the excitable cortex seems to be represented 

 chiefly in Fortuyn's areas/,/', n, and m'. The de- 

 scription of these areas tells us that they are all char- 

 acterized by thin granular (IV) layers and unusually 

 large pyramidal cells in layer V, these features being 

 especially characteristic of the much more sharply de- 

 fined excitable cortex of higher animals. But it should 

 be emphasized that these features are only very 



