634 



PHYSIOLOGY OF THE CEREBRUM 



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But there is one result which stands 

 out very prominently: the higher the 

 rank of the animal in the scale, the 

 greater is the variety of isolated move- 

 ments which can be obtained by 

 sharply localized stimulation i. e., 

 the greater is the number of excitable 

 points and hence the higher is the de- 

 gree of localization. This fact to- 

 gether with the close similarity of 

 structure between the simian brain 

 and the human brain makes the results 

 on monkeys of the utmost importance 

 from the standpoint of human physi- 

 ology; consequently we shall describe 

 the experiments on these animals, 

 which we owe to Beevor, Horsley, 

 Schafer and Sherrington, somewhat 

 fully. 



The arrangement of the fissures 

 and convolutions in the monkey's 

 brain corresponds exactly to that of 

 the human brain, or, more correctly 

 speaking, it can be regarded as a sim- 

 plified schema of the human brain. 

 Reference to Figs. 285 and 286 will 

 make this fact apparent without fur- 

 ther description. 



The motor cortical zone of the 

 monkey's brain extends over parts of 

 both the median and convex surfaces 

 of the hemisphere. On the convex 

 surface it consists of the two central 

 convolutions and of the immediately 

 adjacent parts of the frontal convolu- 

 tions. On the medial side the greater 

 part of the gyrus marginalis belongs 

 to this zone. 



Within this great motor zone can 

 be distinguished areas for the larger 

 divisions of the body musculature: 



FIG. 284. Structure of the cortex of the con- 

 volutions bordering on the fissure of Rolando, 

 after Cajal. The figure to the right represents 

 the structure of the anterior central con- 

 volution, that to the left the structure of the 

 posterior central. 1, Plexiform layer; 2, small pyramidal cells; 3, medium-sized pyramidal 

 cells; 4, large superficial pyramidal cells; 5, small star-shaped cells; 6, large, deep pyramidal 

 cells; 7, layer of spindle-shaped and triangular cells. 



