MUSCLE. 

 Fig. 503. 



[ 445 



Transverse section of a portion of the sterno-cleido- 

 mastpideus. a, outer perimysium ; b, inner perimysium ; 

 c, primitive and secondary muscular bundles. 

 Magnified 50 diameters. 



Fig. 504. 



Transverse section of the muscular fibres or primitive 

 bundles of the human gastrocnemius : a, sarcolemma 

 and interstitial areolar tissue ; b, section of fibrillse and 

 intermediate substance. 



Magnified 350 diameters. 



cations of the component fibrillse (PI. 17. 

 fig. 35). 



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, trans- 

 parent and smooth membrane. It is perhaps 

 most easily seen in the muscle of fishes by 

 simple dissection (PI. 41. fig. 18). On its 

 inner side are numerous spindle-shaped or 

 lenticular nuclei (fig. 505). 



The ultimate or primitive fibrillse in man 

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

 exhibits numerous regularly alternating light 

 and dark portions (PI. 17. fig. 36/); the 

 relative positions of the two may, however, 

 be made to change by altering the focus. 

 The ends of the fibrillse are distinguishable 

 in transverse sections of the primitive bun- 



MTTSCLE. 

 Fig. 505. 



Portion of a primitive bundle treated with acetic acid. 

 a, sarcolemma ; b, single nucleus ; c, twin nuclei sur- 

 rounded by granules of fat. 



Magnified 450 diams, 



dies, 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 fibrillge have been described as monili- 

 form or beaded (PI. 17. 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. 



It often happens, especially when muscle 

 has been kept in spirit, that it separates 

 transversely into a number of flat disks (fig. 

 506) ; hence it has been viewed as consisting 



Fig. 506. 



A, a primitive bundle, magnified 350 diameters, partly 

 separated into disks, side view. B, the same, rather 

 more magnified, end view. 



