MOTOR AREAS OF THE HUMAN BRAIN 



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white matter after the superficial gray matter of the animal's brain has been 

 sliced off. 



These motor fibers are those which arise from the pyramidal cells of the 

 cortex. From the motor area of the cortex they converge to the internal cap- 

 sules, and pass down to the crus. In the internal capsule the fibers which 

 pass to the pyramidal tracts of the spinal cord occupy that part known as 

 the knee (genu) and the anterior two-thirds of the posterior limbs of the cap- 

 sule, figure 404. In this district the fibers for the face, arm, and leg are in 

 this relation: those for the face and tongue are just at the knee, and below or 

 behind them come first the fibers for the arm and then those for the leg. 



The more accurately known arrangements of these fibers in the monkey's 

 brain, named in order, from above down, are those for the eye, head, tongue, 



FIG. 404. Showing the geniculo-calcarine optic pathway. (Meyer, copied from 



Gushing.) 



mouth, shoulder, elbow, digits, abdomen, hip, knee, digits. These fibers 

 come for the most part from the portion of the cortex in front of the fissure of 

 Rolando, chiefly from the precentral gyrus, hence called the Rolandic area. 

 Those fibers, passing between the occipital lobe and the thalamus and 

 superior corpora quadrigemina, are concerned with vision, and are called 

 fibers of the optic radiation. In like manner, from the inferior corpora 

 quadrigemina and the internal geniculate bodies, fibers which make up the 

 auditory radiation pass to the auditory center in the superior temporal gyrus. 

 The term motor centers is applied to cortical areas which are concerned 

 with the development of voluntary motor impulses. It must not be assumed 

 that the motor cells of the area initiate such impulses. These centers react 

 only in response to afferent nerve impulses which flow in upon them. This 



