MUSCLE. 



MUSCLE. 



trachea and bronchi, the dartos, the arteries, 

 veins, and lymphatics, the prostate gland, 

 fallopian tubes, urethra, villi of the small 

 intestines, the skin, iris, and beneath the 

 long-pleura, &c. 



Striated muscle. The structure of striated 

 is more complex than that of unstriated 

 muscular tissue. It consists of a number 

 of very slender fibres, called fibrillae, con- 

 nected into bundles, termed primitive bun- 

 dles or fasciculi, each of which is enclosed 

 in a sheath or sarcolernma. 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. 



Transverse section of a portion of the stern o-c)eido- 

 ma'toideus: a, outer perimysium; ft, inner perimy- 

 eium ; c, primitive and secondary muscular bundles. 



Magnified 50 diameters. 



Fig. 500. 



. Transverse section of the muscular fibres or primitive 

 bundles of the human gastrocnemius: a, sarcolemma 

 and interstitial connective tissue ; b, section of fibrillae 

 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 striae, which forms the most charac- 

 teristic appearance of the tissue. They also 

 exhibit irregular longitudinal striae, which 

 are the indications of the component fibrillae 

 (PI. 22. fig. 35). 



Fig, 501. 



1 j 



Portion of a primitive bundle treated with acetic 

 acid: a, sarcolemma ;6, single nucleus; c, twin nuclei 

 surrounded by granules of fat. 



Magnified 450 diameters. 



The sheath or sarcolemma, when separated 

 from the muscular substance by treatment 

 with water, acetic acid, and alkalies, in 

 which it is insoluble, forms a structureless, 

 transparent and smooth membrane. It is 

 perhaps most easily seen in the muscle of 

 fishes by simple dissection (PL 50. fig. 18). 

 On its inner side are numerous spindle- 

 shaped or lenticular nuclei (fig. 501). 



The ultimate or primitive fibrillae in man 

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

 exhibits numerous regularly alternating 

 light and dark portions (PL 22. fig. 36 b) ; 

 the relative positions 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 bundles; and their 

 lateral margins are perfectly straight. 



Different views have been taken of the 

 structure of the fibrillae, and, in fact, of the 

 general structure of muscle. Thus the ulti- 

 mate fibrillae have been described as monili- 

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

 pearance, however, arises from 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. 



