An American text-book of physiology . ts and by many pathological observations some-thing is known of the motor centres in the human cerebral cortex. When CENTRAL NERVOUS SYSTEM, 693 the results are plotted they give a distribution such as is shown in Figure the same time all such figures are largely compiled from results obtainedou the monkey. It is here seen that the two central gyri are the principalseat of these areas, and that it is ouly along the great longitudinal fissure divid-ing the hemisjMiores that the motor areas extend beyond this limit in a cephalo-caudad tlirection. Perh
An American text-book of physiology . ts and by many pathological observations some-thing is known of the motor centres in the human cerebral cortex. When CENTRAL NERVOUS SYSTEM, 693 the results are plotted they give a distribution such as is shown in Figure the same time all such figures are largely compiled from results obtainedou the monkey. It is here seen that the two central gyri are the principalseat of these areas, and that it is ouly along the great longitudinal fissure divid-ing the hemisjMiores that the motor areas extend beyond this limit in a cephalo-caudad tlirection. Perhaps the relation most wortiiy of remark is the com-paratively small fraction of the cortex concerned with the direct control of thespinal cord cells. The motor areas in man are elaborated, not so much bythe increase in the number of the cells controlling the lower centres, as by anincrease in the number of those cells under the influence of which these areasreact. The relation of the areas in a frontal section is shown iu Figure Fig. 194.—Frontal section of the human cerebrum on the left side. The fibres forming the internal capsule ( ), the callosum ( ), and the anterior commissure (. — .— . — .—) have been indicated. T, cortical area for the trunk; L, cortical area for the leg; A, cortical area for the arm; F,cortical area for the face ; A, anterior commissure; C, callosum; CO, optic chiasma; NC, caudate nucleus;NL, lenticular nucleus; R, fornix; TO, thalamus; X, lateral ventricle. Sensory and Motor Regions.—If an attempt is made to unify the con-struction of the entire cortex by bringing the motor and sensory areas undera common law, it must be based on the fact that the system of neurons bring-ing impulses to the motor region forms part of the aiferent pathways from theskin and muscles. To Munk ^ is due the credit of having from the first lookedupon the responsive cortex as marked off into areas within which certain groupsof afferent fibres terminated, so
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