Tendon. Light micrograph of a longitudinal section through normal human sinew (tendon). Fibre bundles are seen running horizontally in shades of red. The dark spots are cell nuclei; white spaces represent areolar tissue between the bundles. Tendon is an example of regular connective tissue. It is inelastic and serves to attach muscle to bone. It consists of parallel arrays of collagenous fibres produced by cells known as fibroblasts. The fibres are arranged in bundles; the primary bundles are surrounded by fibroblasts, while groups of primary bundles are separated by areolar tissue. Magnification: x50 at 35mm size.