74 



THE ESSENTIALS OF HISTOLOGY. 



FIG. 82. PORTION OF A MEDIUM - 



SIZED HUMAN MUSCULAR FIBRE, 

 SHOWING THE INTERMEDIATE 

 LINE MENTIONED IN THE TEXT. 



(Sharpey.) 



If instead of focussing the surface of 

 the fibre it be observed in its depth, 

 an appearance different from that 

 shown in fig. 81 is frequently visible, 

 namely, a fine dotted line bisecting 

 each clear stripe (fig. 82) ; this ap- 

 pearance is often considered to re- 

 present a membrane (Krausds mem- 

 brane), which subdivides the sarco- 

 styles at regular intervals (see p. 77). 

 But Krause's membrane is rarely, if 

 ever, visible in fresh muscle, and it is 

 much more probable that the line in 

 question is an interference line, caused 

 by the light being transmitted between 

 disks of different refrangibility. Hay- 

 craft believes that the cross-striation 

 of voluntary muscle is entirely due to 

 refractive effects produced by a vari- 

 cosity of the component sarcostyles, 

 but in view of the entirely different 

 manner in which the substance of the 

 dark and clear stripes behave to many 

 staining reagents, and especially to 

 chloride of gold when applied as 

 directed in Lesson XVL, sec. 3, this 

 position must be regarded as unten- 

 able. 



Besides the sarcolemma and striated substance, a muscular fibre also 

 exhibits a number of oval nuclei which have the usual structure 

 of cell-nuclei : the chromoplasm often has a spiral arrangement. 

 Sometimes there is a little granular substance (protoplasm) at each 

 pole of the nucleus, and the nuclei with the adjacent protoplasm 

 are then spoken of as muscle-corpuscles. In mammalian muscle the 

 nuclei usually lie immediately under the sarcolemma (figs. 80, 81, 83), 

 except in certain fibres, which entirely compose 

 the red muscles of some animals, such as the 

 rabbit, and which occur scattered amongst the 

 ordinary fibres in mammalia generally. In these 

 the nuclei are distributed through the thickness 

 of the fibre, and this is also the case in all the 

 muscular fibres of the frog. In some muscle- 

 fibres, such as those of the diaphragm, which 

 FIG. 83. SECTION OF A MUS- 

 CULAR FIBRE, SHOWING are in constant activity, the protoplasm of the 

 AREAS OF COHNHEIM. musc i e _ c0 r p uscles is often greatly developed. 

 The transverse section of a muscle shows the fibres to be nearly 

 cylindrical in figure. Between the fibres there is a certain amount of 

 areolar tissue, which serves to support the blood-vessels and also unites 

 them into fasciculi : the fasciculi are again united together by a larger 

 amount of this intramuscular connective tissue (endomysiuin). 



