STKUCTUBE OF MUSCLE. 



81 



also towards the centre ; but the middle of the 

 nuclei are at first confined, remains for some 

 time unaltered (fig. 93). Eventually the change 

 in structure extends to this also, and the nuclei 

 pass gradually to occupy their ordinary position 

 under the sarcolemma, which by this time has 

 become formed. 



The muscular substance of the heart (cardiac 

 muscle) is composed of transversely striated 

 muscular fibres, which differ from those of 

 voluntary muscle in the following particulars : 

 their striations are less distinct ; they have no 

 sarcolemma ; they branch and unite with neigh- 

 bouring fibres, and their nuclei lie in the centre 

 of the fibres. Moreover, the fibres are com- 

 posed of a series of short cylindrical cells (figs. 

 94, 95) joined together end to end, each cor- 

 responding to one of the nuclei. The lines of 

 junction of these cells may sometimes be seen 

 in longitudinal sections stained with haema- 

 toxylin or carmine ; but they come much more 

 distinctly into view in sections of the fresh tissue 

 of silver. 



K 



fibre, to which the 



FIG. 93. DEVELOPING 



MUSCULAR FIBRE PROM 

 FCETUS OF 2 MONTHS. 



(Ranvier.) 



p, central protoplasm with 

 several! nuclei, n, scat- 

 tered in it ; , commenc- 

 ing sarcolemma, with 

 striated muscular sub- 

 stance developing imme- 

 diately beneath it. 



stained with nitrate 



FIG. 94. MUSCULAR FIBRES FROM THE 

 HEART, MAGNIFIED, SHOWING THEIR 

 CROSS-STRLE, DIVISIONS, AND JUNC- 

 TIONS. (Schweigger-Seidel.) 



The nuclei and cell -junctions are only repre- 

 sented on the right-hand side of the figure. 



FlG. 95. SIX MUSCULAR FIBRE-CELLS 



FROM THE HEART. (Magnified 425 

 diameters.) 



a, line of junction between two cells ; 6, c, 

 branching of cells. (From a drawing by 

 J. E. Neale.) 



