. A treatise on nervous and mental diseases, for students and practitioners of medicine. h the paracentral lobule, will contain the centre for theleg of the opposite side of the body, the middle third will containthe centre for the arm upon the opposite side of the body, and thelower third will contain the centre for the muscles of the head and ANATOMY, 25 neck of the opposite side of the body. It must be remembered thatthis division into thirds is purely arbitrary, and that it is utterlyimpossible to say just where one centre commences and where an-other terminates ; indeed, as we shall have
. A treatise on nervous and mental diseases, for students and practitioners of medicine. h the paracentral lobule, will contain the centre for theleg of the opposite side of the body, the middle third will containthe centre for the arm upon the opposite side of the body, and thelower third will contain the centre for the muscles of the head and ANATOMY, 25 neck of the opposite side of the body. It must be remembered thatthis division into thirds is purely arbitrary, and that it is utterlyimpossible to say just where one centre commences and where an-other terminates ; indeed, as we shall have occasion to see, the centresof the cortex shade into one another to a certain extent. There hasbeen considerable discussion and consequent variance of opinionamong physiologists and pathologists as to the subdivision in thesethirds of the motor area. Thus Ferrier minutely subdivides thismotor region, as is indicated in Fig. 6, basing his localizationslargely upon his experiments upon the brain of the monkey, althoughhe is particular to state that the centres of the human brain, as he. CLOSURE OF EYELIDSTHE OPPOSITE MOST EV/ERSIOtJOF OPPOSITE LIP RETRACTION OFOPP ANGLE OF MOUTH. I I ROLLING LIPSI I OPENING RAISING BOTH LIPS. ELEVATION OFOPP. UPPER LIP. CONTRACTION OFOPR& UPPERHALF OF ORBICULARIS ORIS. PhotograjDh (enlarged twice) of the outer surface of the left half of the brain of anorang-outang, showing centres—R. Fissure of Rolando IP. Interparietal Occipito-parietal fissure. S. Fissure of Sylvius. PC. Praecentral fissure. (Hoesley.) has indicated them by this method of analogy, are only approxi-mately correct, inasmuch as the movements of the hand and arm, forinstance, are more complex and diiferentiated in man than in themonkey, whilst in the human being there is nothing to correspondMath the prehensile movements of the lower limbs and tail of themonkey. Horsley and Beevor have outlined this region in a some-what similar manner to Ferrier
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