. The brain as an organ of mind. f the groups of motor cells, at different levels of thecord are also connected with one another into single or multiple com-binations, by longritudinal commissural fibres whose length variesaccording to the distance apart of the cell groups thus united forconjoint activity. These longitudinal connecting fibres of differentlengths, as they pass from cell-group to cell-group, have beenascertained (on the basis of clinico-pathological evidence suppliedby persons suffering from spinal disease) to traverse, in part atleast, the posterior columns of the Cord. Bilater
. The brain as an organ of mind. f the groups of motor cells, at different levels of thecord are also connected with one another into single or multiple com-binations, by longritudinal commissural fibres whose length variesaccording to the distance apart of the cell groups thus united forconjoint activity. These longitudinal connecting fibres of differentlengths, as they pass from cell-group to cell-group, have beenascertained (on the basis of clinico-pathological evidence suppliedby persons suffering from spinal disease) to traverse, in part atleast, the posterior columns of the Cord. Bilateral groups of these cells, existing at various levels in thetwo anterior cornua, though differing much from one another inthe number of the units involved and in the width of the area overwhich they are distributed, are conceived to be the Spinal andMedullary Nervous Mechanisms needful for the execution of avastmultitude of Reflex, or Primary Automatic Movements, also of all * See pp. 26, 52. Chap. XXVI.] VOLUNTARY MOVEMENTS. 559. —— ~:«^ Fig. 178.—Groups of Cells in connection with the Anterior Roots of the SpinalNerves, a§ seen in a transverse section through one of the Anterior Cornua in theSpinal Cord of a Sheep. (Flint after Dean.) A. Emergence of the anterior rootsfrom the Cornua of Orey Matter; b, b, b Cells connected with one another by long,slender, intercellular processes, and also with the fibres of the Anterior of fibres are seen crossing one another in almost every directioa. 660 WILL AND degrees of complexity. It is probably because these several cell-and-fibre mechanisms are so perfect in their arrangement, thateach one of the Movements in question is capable of being evoked?with machine-like regularity in response to appropriate stimuliim-pinging upon and passing through them.* The mechanisms for the production of many of such Movementsmay have been originally developed far back in the history of ourrace or of antecedent races. But others of
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