60 



THE MUSCULAE TISSUES 



teased preparations of fresh muscle fibres, in which the cell has 

 been ruptured by gentle but firm pressure. The cytoplasm is 

 frequently torn by this means, while the 

 cell membrane, being of a more resistent 

 nature, spans the interval between the rup- 

 tured ends of the cytoplasm. 



Within the cell membrane the cytoplasm 

 forms what may be termed a syncytium ; the 

 cell frequently attains an enormous size, 

 being, as a rule, several centimeters in length 

 but only 30 to 80 //, in breadth. Its shape is 

 that of a long cylinder with rounded or very 

 bluntly pointed ends. 



The many nuclei, sometimes numbering 

 hundreds for each muscle cell, are found at 

 the surface of the fibre, lying just beneath 

 the sarcolemma. The nuclei are ovoid in 

 shape and possess a distinct nuclear wall 

 and abundant chromatin. They are fre- 

 quently surrounded by a narrow rim of un- 

 differentiated cytoplasm, which is more 

 abundant about the poles of the nucleus. 

 The nuclei are also prone to accumulate at 

 the ends of the fibre, at its insertion into 

 the fibrous tissue of the tendon. 



The cytoplasm of the striated cells is 

 the most distinctly fibrillated of the several 

 types of muscle fibre. The ultimate fibritta 

 are arranged in small bundles, which are 

 separated by intervals of clear undiffer- 

 entiated sarcoplasm. As seen in cross sec- 

 tion this arrangement of the fibril bundles 

 gives rise to polygonal areas within the 

 muscle cell, the dark ends of the cut fibrils 

 being surrounded by lighter intervals of 

 sarcoplasm. These peculiar polygonal out- 

 lines are described as the areas or fields of 

 Cohnheim. 



The distribution of the fibrils in bundles 

 gives rise to distinct longitudinal striations, 

 which are visible even with the aid of very 



ij 



FIG. 64. STRIATED MUSCLE 

 FIBRES RUPTURED BY 

 TEASING, SHOWING THE 



SARCOLEMMA. 



a, ruptured end of the 

 muscle fibre ; jB, a bundle 

 of fibrils projecting from 

 the torn end ; m, a muscle 

 fibre ; w', a nucleus of the 

 muscle cell ; at p, the mus- 

 cle substance has shrunken 

 away from the sarcolem- 

 ma ; s, sarcolemma. Mod- 

 erately magnified. (After 

 Eanvier.) 



