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Tendon fibres, coloured transmission electron micrograph (TEM). A tendon is made up of parallel bundles of collagen fibres. Part of a fibroblast cell (purple) is seen across lower centre, with its nucleus (red/white) at lower left. Fibroblasts secrete collagen fibres, the main component of tendons. Tendons are inelastic, though with a degree of flexibility, and attach a muscle to a bone. Magnification: x15,000 at 6x7cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER)