614 
Fig. 4. 
Fig. 3. Longitudinal section of adult human heart muscle. S small sarcoplasmic 
dises; F fibril bundle; X KrAUsE’s membrane. 
Fig. 4. Cross-section of adult human heart muscle. The section is through a part 
of the cell either above or below the nucleus. C central sarcoplasm mass; S small 
sarcoplasmic disc; /' fibril bundle. 
situated the nucleus, surrounded by sarcoplasm free from fibril bundles. 
This projects outward to surround the fibril bundles, which are most 
irregular in outline, as represented in Fig. 4. Usually at the peri- 
phery, the fibril bundles consist of flat leaf-like masses, which radiate 
towards the centre, and in most cases present clear spaces and more 
lightly staining parts within them, indicating that they are composed 
of smaller elements, or fibrils. 
The fibril bundles are entirely surrounded in every case by sarco- 
plasm, which is seen in cross section to be broken up into definite 
circles or discs, much smaller than the discs described in longitudinal 
section. They will be spoken of as “the small sarcoplasmic discs”. 
Around each bundle there are four or five of these small sarcoplasmic 
discs, which form a sort of rosette, the centre of which is the fibril 
bundle. Such a rosette, made up of several small sarcoplasmic discs, 
corresponds to a cross section of one of the large sarcoplasmic discs 
described in longitudinal sections. When two complete structures like 
this occur together, i. e., when two large discs exist side by side, the 
fibril bundles are separated from one another by two small sarcoplas- 
mic discs, as in Fig 4.4; while in some cases two bundles have small 
discs in common, as in Fig. 46. The first instance would correspond 
with the part of the fibre seen in Fig. 3A, where one large disc 
contains a single fibril bundle; while the second would be represented 
in longitudinal section by Fig. 3.6, where one large disc has at least 
two fibril bundles. 
