Light micrograph showing bundles of muscle fibres of the heart in a longitudinal section. Cardiac muscle fibres exibit structural and functional characteristics intermediate between those of skeletal and visceral muscle fibres. The nuclei (violet) are elongated and, as best seen in transverse sections, centrally located in the cytoplasm. The intercellular spaces (white) are filled with delicate connective tissue and are extremely rich in blood capillaries. Many mitochondria (orange) are also seen: they are the sites of the cell's energy production. Magnification unknown.
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