Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: pairs of muscles, the simultaneous action of several nerve centres becomes necessary. How can the simultaneous discharge of several centres be effected ? One obvious method suggests itself at once. If the centres, whose simultaneous discharge is needed, were all connected with another centre, then the discharge of this other common centre would set all the rest discharging simultaneously. Suppose A, B, and C to be three nerve centres actuating the muscles of the chest, abdomen, and throat respectively, by means of the nerves a a, b b, and c c, and suppose that from each of these centres there goes a cord or channel of communication to a common centre at D. Then the discharge of D will set going simultaneously the discharges of A, B, and C, and will produce simultaneous action of the three sets of antagonistic groups of muscles which these three centres represent. Again, the muscles of nose, neck, and mouth might be represented in three other centres, E, F, and G, and these be grouped together by a central station at H, and then H and D connected with a still more comprehensive station at I; and then the discharge of I would bring about simultaneous action of the whole of the muscular apparatus employed in forced respiration It is obvious that any number of muscles can be brought into simultaneous and duly proportioned action by a similar arrangement of duly proportioned channels proceeding from a single centre ; and by such an apparatus even the movements of equilibration, which demand simultaneous and duly proportioned action of almost all the muscles of the body, can be actuated. The majority of our acts do not, however, depend solely on the simultaneous action of muscles. In walking, for instance, while a number of muscles must act simultaneously to produce each movement ...