Ml \SCLK 



85 



centre of the cell the perinuclear earcoplasm is made up entirely 

 of these disks. 



Seen in transverse section (Figs. 51 and 53), the cell consists 

 of darkly staining masses which are cross-sections of the fibril 

 bundles. These are band-shaped and radially arranged at the 

 periphery of the cell, and are smaller and columnar nearer the 

 centre. Between these there are definite disks of unstained 

 substance. From this it will be seen that the cell protoplasm 

 contains a network which consists of the fibril bundles and the 

 membranes surrounding the disks of sarcoplasm. The rnem- 



FIG. 52. 



FIG. 53. 



Longitudinal section of adult hu- 

 man heart muscle. S, sarcoplasmic 

 disks; F, fibril bundle; A", Krause's 

 membrane. (MacCallum.) 



Cross-section of adult human heart mus- 

 cle. The section is through a part of the cell 

 either above or below the nucleus. (7, central 

 sarcoplasm mass , S, sarcoplasmic disk ; F, 

 fibril bundle. (MacCallum.) 



branes join with the fibril bundles at the lines known as Krause's 

 membranes, and the whole forms a continuous network. 



With regard to the manner in which heart muscle cells in 

 the higher mammals are joined together, two appearances com- 

 monly met with must be mentioned. In some cases, especially 

 where there is a certain degree of oedema in the muscle, the 

 fibril bundles present a row of thickenings on each side of the 

 cement line. These form what Przewoski termed the stratum 

 granulosum terminate (Fig. 54). From each of these thicken- 

 ings one or more fine filaments pass across the cement line to 

 meet those from the opposite cell. The two series of filaments 

 meet at a delicate line in the centre of the cement line. The 



