The fine structure of snake myocardium

Snake myocardium has been studied using standard methods and tannic acid mordanting. In both atria and ventricle, cells were arranged in fascicles with little connective tissue, up to 20 cells per fascicle, and few differences between cells of atria and ventricle. Cell (fiber) size varied from 8 to 12 micrometers in the nuclear area with a few cells up to 14 micrometers in ventricle, and cells generally were spindle-shaped, tapering toward the extremities where relatively simple intercalated discs were seen. Few myofibrils per cell were present and poorly delineated. Transverse tubules were absent and sarcoplasmic reticulum was poorly developed and, apparently, even absent from some cells. All cells contained micropinocytotic vesicles associated with the surface plasmalemma and subsarcolemmal caveolae. In addition to intercalated discs, intercellular junctions showed spot desmosomes, small and sparse gap junctions and fasciae adherentes of two types, one associated with Z-bands, one independent of Z-bands. Nerve fibers and nerve endings were numerous, particularly in atrium. These findings are discussed in relation to the structure of mammalian myocardium.