STRUCTURE OF MUSCLE 63 



can be seen that the stripes pass through the whole thickness of the 

 fibre ; they may therefore be looked upon as representing alternate 

 disks of dark and light substance. If the surface be very carefully 

 focussed, double rows of granules are seen lying in or at the bounda- 

 ries of the light streaks, and very fine longitudinal lines may, with a 

 good microscope, be detected running through the dark streak, and 

 uniting the minute granules (fig. 70). These fine lines, with their 

 enlarged extremities the granules, are known as muscle-rods ; they are 

 more conspicuous in the muscles of insects. 



FIG. 71. PORTION OF A MEDIUM- 

 SIZED HUMAN MUSCULAK FIBRE, 

 SHOWING THE INTERMEDIATE 

 LINE MENTIONED IN THri TEXT. 



FIG. 72. DIAGRAMMA- 

 TIC REPRESENTATION 

 OF A MUSCLE-CASE. 



an, muscle-prism, consist- 

 ing of a bundle of muscle- 

 rods ; is, fluid substance. 



If instead of focussing the surface of the fibre it be observed in its depth, 

 a different appearance is frequently visible, namely a fine dotted line bisecting 

 each clear stripe (fig. 71) ; but this appearance is probably due to an optical 

 effect caused by the light being transmitted between disks of different 

 refrangibility. 



The fine line bisecting the clear stripe is, however, taken by many histolo- 

 gists to represent a definite structure, and is often known as Krause's mem- 

 brane, having been described by Krause as connected with the sarcolemma and 

 dividing the muscle-fibre into so many flat compartments. Krause further de- 

 scribed these compartments as divided longitudinally by fine membranes, so 

 that the muscle-substance may, according to him, be regarded as composed of 

 little cylindrical ' cases ' (fig. 72) each containing in the centre a portion of the 

 dark disk, and, above and below this, portions of the light disks (which are 

 fluid according to this author). 1 



1 For other views regarding the structure of striated muscular fibre, the student 

 is referred to Quain's Anatomy, 9th edition, vol. ii. pp. 127 to 129. 



