MUSCLE. 



[ 524 ] 



MUSCLE. 



trachea and bronclii, tlie dartos, the arteries, 

 veins, and lymphatics, the prostate gland, 

 fallopian tubes, urethra, villi of the small 

 intestines, the skin, iris, and beneath the 

 lung-pleura. See. 



Striated muscle. — Tlie structure of striated 

 is more complex than that of unstriated 

 muscular tissue. It consists of a number 

 of very slender fibres, called fibrillfe, con- 

 nected into bundles, termed primitive bun- 

 dles or fasciculi, each of which is enclosed 

 in a sheath or sarcolemma. The primitive 

 bundles are again united into secondary and 

 tertiary bundles, the whole being bound 

 together by a mass of connective and elastic 

 tissue surrounding each of them, and form- 

 ing the perimysium. This arrangement is 

 best seen in a transverse section (fig. 499). 



Fig. 499. 



TranBTerse section of a portion of the sterno-cleido- 

 mastoideus: c, outer perimysium; b, inner perimy- 

 Bium ; c, primitive and secondary muscular bundles. 



Magnified 50 diameters. 



v 



i: 



Transverse section of the muscular fibres or primitive 

 bundles of the human gastrocnemius : a, sarcoh'mma 

 and interstitial connective tissue ; b, section of flbrillse 

 and intermediate substance. 



Magnified 350 diameters. 



The primitive bundles are from about 

 1-1000 te 1-200" in diameter, and of a 

 rounded or polygonal form (fig. .500). Their 

 surfaces are marked by a number of trans- 

 verse strife, which forms the most charac- 

 teristic appearance of the tissue. They also 

 exhibit irregular longitudinal stria?, which 

 are the indications of the component fibrillae 

 (PL 22. tig. 35). 



Fig. 501. 



Portion of a primitive bundle treated with acetic 

 acid: a, sarcolemma; b, single nucleus; c, twin nuclei 

 surrounded by granules of fat. 



Magnified 450 diameters. 



The sheath or sarcolemma, when separated 

 from the muscular substance b}' treatment 

 with water, acetic acid, and alkalies, in 

 which it is insoluble, forius a structureless, 

 transparent and smooth membrane. It is 

 perhaps most easily seen in the muscle of 

 tishes by simple dissection (PI. 50. fig. 18). 

 On its inner side are numerous spindle- 

 shaped or lenticular nuclei (fig. 501). 



The ultimate or primitive fibrillge in man 

 are about 1-20,000" in diameter, and each 

 exhibits numerous regidarly alternating 

 light and dark portions (PL '22. fig. 3G b); 

 the i-elative po.sitions of the two may, how- 

 ever, be made to change by altering the 

 focus ; but the dark bands are more highly 

 refractive than the white. The ends of the 

 fibrillae are distinguishable in transverse 

 sections of the primitive biuidles; and their 

 lateral margins are perfectly straight. 



Difierent views have been taken of the 

 structure of the fibrillar, and, in fact, of the 

 general structure of muscle. Thus the ulti- 

 mate fibrilloe have been described as monili- 

 form or beaded (PL 22. fig. 36 c) ; this ap- 

 pearance, however, arises fi-om an optical 

 illusion, connected either with imperfection 

 in the object-glasses used, viewing the 

 object in too much liquid, or the use of too 

 low an object-glass, and too high an eye- 

 piece. 



