Light micrograph of a longitudinal section through a large vein showing, from the top, the tunica intima with the endothelium and a thin subendothelial connective tissue. Then a middle layer formed by a few bundles of circular cross-sectioned myocytes. The majority of the wall is occupied by intermingled bundles of collagen fibres belonging to the tunica adventitia. Two small nerve fibre bundles can be seen in the adventitia.