NORMAL HISTOLOGY. 



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FIG. 72. Diagrams illustrating struct- 

 ure of striated muscle-fibre. A, usual 

 view; B, correct view, showing sustentac- 

 ular septa continued across fibre from 

 sarcolemma. Z, intermediate disk (Zwi- 

 schenscheibe'); J, light band; Q, trans- 

 verse disk (Querschfibe) \ M, median disk 

 (Mittelscheibe); S, sarcolemma. (After 

 M. fleidenhain.) 



segments of the fibrillae, lying side by side within the sarcolemma, produces 

 the impression of the dark band; the similar relation of the less dense and 



slightly staining segments produces the light 

 band. If it were possible to isolate the 

 mm mi mm individual contractile fibrillae, each would 



exhibit the details shown in the accompany- 



*, ing diagram (Fig. 72). The dark broad 



M transverse disk ( Q) of anisotropic substance 



is succeeded at each end by the light band 

 (J J) of isotropic substance. The light 

 band is subdivided by a delicate line, the 

 intermediate disk (Z), also known as 

 Krause*s membrane. The sequence which 

 by repetition makes up the contractile fibrilla 

 is, therefore, Z-\-J-\-Q-\-J-\-Z. In 

 favorable preparations, the transverse disk 

 appears less dense and lighter midway be- 

 tween its ends where it is traversed by a 

 delicate line (M), t\\e median disk (Hensen) 

 or middle membrane (Heidenhain). The 

 striped muscle of certain insects exhibits an 

 additional band, the accessory disk, subdivid- 

 ing the light zone, J. The interpretation 

 of these details, shown as ordinarily seen 

 under moderately high magnification in 

 Fig. 73, has been the subject of vexed discussion. This has been particularly 

 true of the significance of the intermediate disk or membrane of Krause, 

 which is attached to the 

 inner surface of the sarco- 

 lemma and extends com- 

 pletely across the muscle- 

 fibre. This arrangement,, 

 however, does not imply 

 that the fibre is composed 

 of a series of separate dis- 

 coidal segments, but rather 

 that the membrane serves 

 to maintain in definite 

 order the contractile fibril- 

 lae, which, while perhaps 

 attached to the mem- 

 brane, pass uninterrupted- 

 ly through it. 



The distribution of the 

 contractile fibrillae with- 

 in the fibre is not uni- 

 form, since the fibrillae are 

 grouped into minute bun- 

 dles, the muscle-columns or 

 sarcostyles. This arrange- 

 ment is shown in transverse 

 sections of muscular tissue (Fig. 74), in which the individual fibres are 

 seen to be made up of stippled areas separated by clear lines. These areas, 



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FIG. 73. Photograph of striated mammalian muscle, showing 

 the usual appearance under moderately high magnification. 

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