64 



MUSCULAR TISSUE 



[CH. VI. 



homogeneous, elastic in nature, and especially tough in fish and 

 amphibia. It may readily be demonstrated in a microscopic prepara- 

 tion of fresh muscular fibres by applying gentle pressure to the cover 

 slip; the contractile substance is thereby ruptured, leaving the 

 sarcolemma bridging the space (fig. 76). To the sarcolemma are 

 seen adhering some nuclei. 



FIG. 76. Muscular fibre torn across, the 

 sarcolemma still connecting the two 

 parts of the fibre. (Todd and Bow- 

 man.) 



FIG. 77. Muscular fibre of 

 a mammal highly mag- 

 nified. The surface of 

 the fibre is accurately 

 focussed. (Schafer.) 



The contractile substance within the sheath is made up of 



alternate discs of dark and light substance. 



Muscular fibres contain oval nuclei. In mammalian muscle these 



are situated just beneath the sarcolemma ; but in frog's muscle they 



occur also in the thickness of the mus- 

 cular fibre. The chromoplasm of the 

 nucleus has generally a spiral arrange- 

 ment, and often there is a little granular 

 protoplasm (well seen in the muscular 

 fibres of the diaphragm) around the poles 

 of each nucleus. 



If the surface of a fibre is carefully 

 focussed with a high power, rows of 

 apparent granules are seen lying at the 

 boundaries of the light streaks, and fine 

 longitudinal lines passing through the 

 dark streaks may be detected uniting the 

 apparent granules (fig. 77). 



In specimens treated with dilute acids 

 or gold chloride, the granules are seen to 

 be connected side by side, or transversely 

 also. This reticulum (fig. 78), with its 

 longitudinal and transverse meshes, is 



composed of an interstitial substance lying between the essentially 



contractile portions of the muscle. A muscular fibre is thus made 



FIG. 78. Portion of muscle-fibre of 

 water-beetle, showing network 

 very plainly. One of the trans- 

 verse networks is split off, and 

 some of the longitudinal bars are 

 shown broken oft: (After Mel- 

 land.) 



