PLATI<: 2 



EXPLANATION OF P'IGURES 



22 A group of atrial discs, comprising modified portion of myofibrils of the 

 extent of one and two sarcomeres. 



23 Atrial disc of fundamental straight-band form, associated with which 

 are other complete and partial sarcomeric modifications of myofil)rils. The 

 disc-area here stains more deeply. 



24 Very complicated atrial disc of the distorted serrated type, certain 

 portions of which are interconnected by light-staining membranes, perhaps 

 telophragmata. 



25 Transverse section of an atrial trabecula with larger peripheral disc 

 (above) and scattered sub-central smaller disc elements. 



26 Portion of a longitudinal section of a secondarily dividing fiber from left 

 ventricle. The telophragmata in the several branches are at different levels. 



27 Irregular type of disc from left ventricle apparently produced by a 

 splitting of an originally coarse trabecula into subdivisions, with dislocation of 

 the discs due to imequal tensions during contraction in the resulting smaller 

 fibers. The lightly-staining connecting membranes are perhaps remnants of 

 distorted telophragmata. 



28 Semidiagrammatic drawing of a transverse section of a slender moderator 

 band, showing peripherally on opposite surfaces two branches of the right limb 

 of the atrioventricular bundle (A.V.B.). The muscular tissue is grouped into 

 two large bundles (M), the larger bundle containing a large central arteriole 

 (A), and a small peripheral venule (F). X 13 diameters. 



29 Portion of moderator-band musculature in longitudinal section, showing 

 the simpler branched condition, and the abundant band-type of discs. X 535. 



30 Portion of a longitudinal section of a trabecula from the moderator band 

 showing a central relaxed area, and terminal contracted areas. The contracted 

 areas stain more deeply and show only the contraction bands and alternating 

 lighter-staining discs. The contracted areas have a considerably greater diame- 

 ter than the relaxed portion. Iron-hematoxylin and van Gieson's stains. 



31 Group of simple discs of fiber from moderator band, overlying a nucleus- — 

 where neither tendons not intercellular cement could be expected to occur. 



32 Portion of a longitudinal section of a fiber from the moderator band, 

 stained in iron-hematoxylin, showing the festooned sarcolemma, an intercalated 

 disc at the level of a displaced telophragma, the Q-, J- and //-discs. 



33 A band-form of disc from the moderator l)an(l extending completely 

 around the periphery of the fiber, but passing in opposite directions on the 

 opposite surface, thus assuming a short spiral form. Prolxxbly similar to disc, 

 figure 3, a and h. 



334 



