Mediastinum

The mediastinum is an area of the body that lies within the thorax and is enclosed on the right and left by pleurae in the median sagittal plane of the thorax. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind. It is continuous with the loose connective tissue of the neck. 

The mediastinum contains the heart, the great vessels of the heart, the esophagus, the trachea, the phrenic nerves, the cardiac plexus, the thoracic duct, the thymus, and the lymph nodes of the central chest.

The mediastinum is divided into anterior, middle, and posterior regions.