THE MUSCULAR SYSTEM. 



IVIYOLOGY. 



By A. M. PATERSON. 



THE movements of the various parts and organs of the body are brought about by 

 the agency of muscle-cells, which are characterised by a special histological structure 

 and by the special function of contracting in length under the influence of a proper 

 stimulus. 



There are three classes of muscle-cells : (1) the striated, and usually voluntary 

 muscle-cells, out of which the skeletal muscular system is constructed ; (2) the non- 

 striated, involuntary muscle-cells, occurring in the walls of vessels and hollow 

 viscera, etc. ; and (3) the cardiac muscle-cells, striated but involuntary, of which the 

 substance of the heart is composed. 



The following section deals solely with the skeletal muscles, the structure, 

 arrangement, and mechanical action of which are based, upon a common plan. 



The cells of which the skeletal muscles are composed are long, narrow, and 

 characterised by a peculiar striation, which is different from the striation of 

 the muscle-cells of the heart ; they also differ both in structure and function 

 from the non-striated muscle-cells which occur in viscera and vessels. 



A typical skeletal muscle consists of a fleshy mass enveloped in a membranous 

 aponeurosis or fascia, and provided at its extremities or borders with membranous 

 or tendinous attachments to bone, cartilage, or fascia. 



Each muscle is made up of a number of fasciculi or bundles, arranged together 

 in different muscles in different ways, so as to give rise to the particular form of 

 the muscle in question. The fasciculi are clothed and connected together by a 

 delicate connective tissue, the perimysium externum, continuous externally with the 

 fascia enclosing the muscle. 



Each muscular bundle or fasciculus is composed of a number of narrow, elon- 

 gated muscle-cells or fibres, held together by a still more delicate connective tissue, 

 the perimysium internum. This tissue is connected on the one hand with the sarco- 

 lemma or cell- wall of the muscle-cell, and on the other hand with the coarser 

 tissue of the perimysium externum enclosing the muscular bundles. 



By -means of these connective tissue envelopes the muscle-cells, the essential 

 agents of motor activity, are brought into firm and intimate relation with the 

 osseous or other attachments of the muscle. Through the agency of sarcolemma, 

 perimysium internum, perimysium externum, fascia, and tendon, the muscle- 

 cell when it contracts can produce a precise and definite effect upon the structure 

 to be moved. 



Each muscle is supplied by one or more nerves, which, in their course 

 through the muscle, separate into smaller and smaller branches, ultimately, by 

 their terminal filaments (axons), forming special end-organs in relation to each 

 muscle-cell. 



While a muscle may thus be looked upon as an organ endowed with particular 

 properties, and executing a definite movement in response to a stimulus by the 

 simultaneous contraction of its constituent cells, the various muscles may further 

 be considered in groups, associated together by mode of development, nerve-supply, 

 and co-ordination of action. For example, we speak of the hamstring muscles of 



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