PHYSIOLOGY OF MUSCLE TISSUE. 49 



A skeletal muscle is a complex organ consisting of muscular fibers, 

 connective tissue, blood-vessels, and lymphatics. The general body 

 of the muscle is surrounded by a dense layer of connective tissue, 

 the epimysium, which blends with and partly forms the tendon ; from 

 its inner surface septa of connective tissue pass inward and group 

 the muscle-fibers into larger and smaller bundles, termed fasciculi. 

 .The fasciculi, invested by this special sheath, the perimysium, are 

 irregular in shape, and vary considerably in size. The fibers of the 

 fasciculi are separated from one another and supported by a deli- 

 cate connective tissue, the endomysium. The connective tissue thus 

 surrounding and penetrating the muscle binds its fibers into a distinct 

 organ, and affords support to blood-vessels, nerves, and lymphatics. 

 The muscle fibers are arranged parallel to one another, and their 

 direction is that of the long axis of the muscle. In length they vary 

 from thirty to forty millimeters, and in diameter from twenty to 

 thirty micromillimeters. 



The vascular supply to the muscles is very great, and the disposi- 

 tion of the capillary vessels, with reference to muscle-fiber, is very 

 characteristic. The arterial vessels, after entering the muscle, are 

 supported by the perimysium ; in this situation they give off short, 

 transverse branches, which immediately break up into a capillary 

 network of rectangular shape, within which the muscle-fibers are 

 contained. The muscle-fiber in intimate relation with the capillary 

 is bathed with lymph derive^ from it. Its contractile substance, 

 however, is separated from the lymph by its own investing membrane, 

 through which all interchange of nutritive and waste materials must 

 take place. Lymphatics are present in muscle, but are confined to 

 the connective tissue, in the spaces of which they have their origin. 



The nerves which carry the stimuli to a muscle enter near its 

 geometric center. Many of the fibers pass directly to the muscle- 

 fibers with which they are connected ; others are distributed to blood- 

 vessels. Every muscle-fiber is supplied with a special nerve-fiber, 

 except in those instances where the nerve trunks entering a muscle 

 do not contain so many fibers as the muscle. In such cases the nerve- 

 fibers divide, until the number of branches equals the number of 

 muscle-fibers. The individual muscle-fiber is penetrated near its 

 center by the nerve, the ends being practically free from nerve 

 influence. The stimulus that comes to the muscle fiber acts primarily 

 upon its center, and then travels in both directions to the ends. 

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