Structure of the thoracic duct wall in human

In the human thoracic duct wall the direction and the ascending angle of the smooth muscle cells are not necessarily fixed according to the site, but as a rule the smooth muscle cells of the interior layer of the tunica media ascend longitudinally at about 80° with their origin at the internal elastic membrane and connect to the circular muscle of tunica media that ascends at angle of about 10° and terminates at the external elastic membrane. At the exterior side of tunica media it becomes often longitudinal and sometimes it forms the exterior layer. The smooth muscle cells which connect the middle layer and exterior layer from the interior layer run in a specific arc line. In the case where a pair of valves cover the thoracic wall, at the site between the two valves there can be observed no longitudinal muscle of the interior layer. Generally the internal elastic membrane is incomplete, and often it forms longitudinal networks, but there is sometimes the case where morphologically it forms a well arranged internal elastic membrane.