STRIATED MUSCLE 



81 



sar. 



Muscle of Adult Sucker. A superficial examination shows that the 

 entire muscular body-mass of this fish is composed, on each side of the 

 spine, of a series of regularly bent plates or myotomes, fitting closely to 

 one another and joined sur- 

 face to surface by layers of 

 connective tissue, or septa. 

 The myotomes lie, as far as 

 their shape allows, at right 

 angles to the body axis. 



Under the low power it 

 will be seen that each plate 

 or myotome is a mass of 

 fibers which stretch from 

 surface to surface, and 

 which lie exactly parallel 

 with the body axis and 

 consequently with each 

 other. They thus are fre- 

 quently attached to the sep- 

 tum at a small angle. 



Under the high power 

 (Fig. 81) each fiber appears 

 at first sight to be composed 

 of a series of thread-like 

 and regularly marked struc- 

 tures, the fibrillae, which 

 run parallel to each other 

 the entire length of the 

 fiber. Still closer attention 

 will show that this mass of 

 fibrillae does not alone con- 

 stitute the fiber, but that it 

 occupies the larger part of 

 the real fiber, which is a 

 mass of sarcoplasm con- 

 taining nuclei and bounded 

 on its surface by a thin, 

 tough membrane, the sarcolemma. 

 the entire surface of the fiber. 



FIG. 6 1. -Longitudinal section of a bit of muscle from 

 the sucker, Catostomus. As the scale will not permit 

 of fine detail, a semidiagrammatic sketch in the lower 

 corner serves to show the relations of dark and light 

 elements in the three contraction stages of the fibril. 

 The chief figure shows the Q-stripe separated as in B. 

 cap., capillaries containing blood cells and blood plate- 

 lets; sar., sarcoplasm; mus.n., muscle nuclei; ., con- 

 nective-tissue nuclei. X 1000. 



The sarcolemma adheres closely to 



The sarcoplasm fills the entire long cylindrical muscle cell and, be- 

 sides the prominent bundles of fibrillae which lie in it, there are also many 

 nuclei of a specific character which distinguish them as muscle nuclei 

 when compared with any other nucleus in their locality. They are 



