noun, plural: mediastina
(anatomy) The region between two parts of an organ
(anatomy) The partition between the thoracic cavities
The mediastinum in general pertains to the region between two parts of an organ. It may specifically refer to as well to the partition between the right and the left thoracic cavities. In humans, the mediastinum is the central partition that lies within the thorax. It is enclosed by two inner pleural walls. In front of it is the chest wall. On its sides are the lungs and at the back is the spine. The mediastinum includes the thoracic viscera except for the lungs. The mediastinum, therefore, contains: heart (and its vessels), esophagus, trachea, thoracic duct, thymus, phrenic nerves, cardiac nerves, and lymph nodes that lie on the center of the chest.
The mediastinum is comprised of two divisions: upper (also called superior) mediastinum and lower (also called inferior) mediastinum. In between the upper and the lower mediastina is a plane called a thoracic plane. The lower mediastinum can be further divided into three regions based on the position relative to the pericardium: (1) anterior mediastinum, which is in front of the pericardium, (2) middle mediastinum, which contains the pericardium, and (3) posterior mediastinum, which is at the back of the pericardium.
Word origin: Latin mediastinus( “midway”)