58 



THE MUSCULAR TISSUES 



are prone to arrange themselves in rows, which, as seen in transec- 

 tion, appear to radiate more or less distinctly, from the central axis 



in which the nucleus lies, 

 and toward the periphery 

 of the cell. 



Heart muscle fibres 

 occur in groups or bun- 

 dles which are united by 

 delicate membranes of 

 connective tissue, 

 Nuc the endomysium, 

 whose finer fibres 

 penetrate between the 

 individual muscle cells. 

 The normal amount of 

 connective tissue occur- 

 ring among the heart 

 muscle fibres is, however, 

 never very large. The 

 bundles of muscle fibres, 

 from the peculiar figure- 

 of-eight arrangement of the fibrous bands, characteristically inter- 

 lace with one another, so that in sections from small pieces of the 

 cardiac wall individual muscle fibres will be cut in all conceivable 

 directions. 



\ 



a en 



FIG. 60. THE CENTRAL PORTION OF THE PRECEDING 



FIGURE, MORE HIGHLY MAGNIFIED. 

 a, cement substance uniting the ends of the mus- 

 cle cells ; this can also be seen at several other points 

 and even in the preceding section if carefully studied ; 

 en, endothelium of the blood vessels ; Nuc, nucleus 

 of the cardiac muscle cell. Hematein and eosin. 

 x 500. 



t 



FIG. 61. TRANSECTION OF A GROUP OF CARDIAC 

 MUSCLE FIBRES FROM A PAPILLARY MUSCLE 

 OF THE HUMAN HEART. 



Hematein and eosiu. x 550. 







^ 



FIG. 62. DEVELOPING MUSCLE FIBRES 



FROM THE HEART OF A HUMAN 

 EMBRYO AT SEVEN MONTHS. 



Fibrillae are well developed at the 

 periphery ; the undifferentiated cyto- 

 plasm in the center presents a clear 

 appearance and in some cases is 

 partially occupied by the nucleus. 

 Hematein and eosin. x 750. 



