MOTOR AREAS OF THE HUMAN BRAIN 



This is the reason that movements are produced on stimulation of the 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 limb, figure 414. 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. 414. Diagram to Show the Relative Positions of the Several Motor Tracts in Their 

 Course from the Cortex to the Crus. The section through the convolution is vertical; that through 

 the internal capsule, 1C, horizontal; that through the crus again vertical. CN, caudate nucleus; 

 O TH, optic thalamus; La and L$, middle and outer part of lenticular nucleus; f, a, I, face, arm, 

 and leg fibers. The words in italics indicate corresponding cortical centers. (Gowers.) 



mouth, shoulder, elbow, digits, abdomen, lip, knee, digits. These fibers come 

 for the most part from the portion of the cortex on either side of the fissure of 

 Rolando, but chiefly from the anterior central gyrus, hence called the Rolan- 

 dic area. But the areas for the head and eyes lie more anteriorly in the 

 frontal lobe, to the front of the precentral sulcus that for the head above 

 that for the eyes, and an area for the trunk (not indicated in the figure 414) 

 is situated more toward the middle line of the hemisphere, internal to that for 

 the leg. Those fibers, passing between the occipital lobe and the optic thal- 

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

 called fibers of the optic radiation. In like manner, from the inferior cor- 

 pora quadrigemina and the internal geniculate bodies, fibers which make 

 up the auditory radiation pass to the auditory center. 



