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HANDBOOK OF PHYSIOLOGY. 



includes within a membrane a fine network anastomosing at the poles of 

 the nucleus with the contractile fibrils. The ends of fibres are usually 

 single, sometimes divided. Between the fibres is an albuminous cementing 

 material or endomysium in which are found connective-tissue corpuscles, 

 and a few fibres. The perimysium is continuous with the endomysium 

 in the fibrous connective tissue surrounding and separating the bundles 

 of muscle cells. 



(2.) Striated or Striped Muscles, 



Distribution. The striated muscles include the whole of the volun- 

 tary muscles of the body, the heart, and those muscles neither completely 

 Toluntary nor involuntary, which form part of the walls of the pharynx, 

 and exist in certain other parts of the body, as the internal ear, urethra, 

 etc. 



Structure. All these muscles are composed of fleshy bundles called 

 fasciculi, inclosed in coverings of fibro-cellular tissue or perimysium, by 



FIG. 274. 



FIG. 275. 



FIG. 274. A small portion of muscle natural size, consisting of larger and smaller fasciculi, seen 

 in a transverse section, and a. the same magnified 5 diameters. (Sharpey.) 



FIG. 275. Muscular fibre torn across; the sarcolemma s;ill connecting the two parts of the 

 fibre. (Todd and Bowman.) 



which each is at once connected with and isolated from those adjacent to 

 it (Fig. 274). Each fasciculus is made up of several smaller bundles, 

 similarly ensheathed. A bundle is made up of muscle fibres with small 

 processes and connective-tissue cells between them or endomysium. 



Each muscular fibre is thus constructed: Externally is a fine, trans- 

 parent, structureless membrane, called the sarcolemma, which in the 

 form of a tubular investing sheath forms the outer wall of the fibre, and 

 is filled up by the contractile material of which the fibre is chiefly made 

 up. Sometimes, from its comparative toughness, the sarcolemma will 

 remain untorn, when by extension the contained part can be broken 

 (Fig. 275), and its presence is in this way best demonstrated. The 

 "fibres, which are cylindriform or prismatic, with an average diameter of 

 about ^1-0 of an inch, are of a pale yellow color, and apparently marked 

 by fine stride, which pass transversely round them, in slightly curved or 



