First lines of physiology, being an introduction to the science of life; written in popular language . d oft some filaments to associate them-selves with other trunks whose functions are of a dif-ferent character from their own. From the combinationof these ditlerent sets of fibres new^ nervous cords areformed. Each fibre of these compound cords retainsthe same function that it exercised in the parent ororiginal trunk to which it previously belonged, but thewhole nerve, resulting from the assemblage of fibresfrom different sources, enjoys all the functions of thedifterent trunks that send bran
First lines of physiology, being an introduction to the science of life; written in popular language . d oft some filaments to associate them-selves with other trunks whose functions are of a dif-ferent character from their own. From the combinationof these ditlerent sets of fibres new^ nervous cords areformed. Each fibre of these compound cords retainsthe same function that it exercised in the parent ororiginal trunk to which it previously belonged, but thewhole nerve, resulting from the assemblage of fibresfrom different sources, enjoys all the functions of thedifterent trunks that send branches to assist in formingit. As one of these secondary nerves approaches theparts with w^hich it is designed to communicate, ittransmits to them branches or bundles of fibres, most of which contain fila-ments from all theparent trunks, but atlength these filamentsare separated fromeach other, and eachconveys to its finaldestination the samepowers that it pos-^ sessed when it firstleft its nervous cen-tre. Let me give youan example. In fig,37 you see a repre-sentation of the ori-gin of four of lliG. Origin of Bpiiial Nerves. PLEXUS OF NERVES. 145 nerves of feeling, and four of the nerves of motion inman: these all originate from the spinal marrow — anervous centre closely associated with the brain, andoccupying a canal formed by the bones of the back, aswill be explained in the after part of this volume: a isthe spinal marrow; J\ the membranes lining the canalin which it is placed; h is the original trunk of a nerveof feeling, commencing from the spinal marrow by manylittle bundles of filaments with similar functions, andunited into one cord at d. If you cut this cord, allfeeling will be instantly destroyed in those parts of thebody to which these filaments are distributed, but thepower of muscular motion will remain. At c, is seenthe original trunk of the nerve of motion, designed tosupply the same parts of the body. It originates fromthe spinal marrow in a similar manner, an
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