An American text-book of physiology . ass ofmuscles in the leg is five times greaterthan that in the arm, and this manytimes greater than that in the face andhead ; yet it is for the last area thatthe greatest cortical extension is of muscle and extent of corticalarea do not therefore go together. When the movements effected bythe muscles in these several areas areconsidered, we find that such move-ments become more complex and moreaccurate as we apj)roach the head, andit therefore accords with the facts toconsider the extension of the motorareas as correlated with the refinementof
An American text-book of physiology . ass ofmuscles in the leg is five times greaterthan that in the arm, and this manytimes greater than that in the face andhead ; yet it is for the last area thatthe greatest cortical extension is of muscle and extent of corticalarea do not therefore go together. When the movements effected bythe muscles in these several areas areconsidered, we find that such move-ments become more complex and moreaccurate as we apj)roach the head, andit therefore accords with the facts toconsider the extension of the motorareas as correlated with the refinementof the movements which they control—a relation which may be expressed ana-tomically as an increase in the numberof cortical cells controlling the relatedcel]-grou])s in the cord. Subdivision of Areas.—The areaswhich have been described are further subdivided, the subdivisions in the arm-area being the clearest. Here it is found that the stimulation of the upperpart of the arm-area gives rise to movements which start at the shoulder,. Fig. 188.—Horizontal section of the Iniinan cere-brum, showing the internal capsule on the leftside: F, frontal region; G, knee of the ;JVC, NC, caudate nucleus; NL, lenticular nucleus;O, occipital lobe: TO, thalamus; X, X, lateral ven-tricle. In the internal capsule the letters indicatethe probable position of tlie bundles of fibres whichupon stimulation give rise to movements of theparts named or which convey special sets of in-coming impulses; E, eyes; //, head; 7, tongue; M,mouth ; /-,shoulder; li. elbow ; D, digits ; A, abdo-men; P. hip; A, knee; f, toes; .S temporo-occip-ital tract; OC, fibres to the occipital lobe; OP, opticradiation (based on Horsley). CEXTI!. 1 /. NKR VO US SYSTEM. G91 while stimulation at the lower part of this area gives rise to movements firstinvolvino; the fingers, and especially the thumb. The centres from whichthese several reactions may he obtained occupy, as Fi<j;ure 184 shows, narrowfields across th
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