The<unk>  is a non-delineated group of structures in the thorax (chest), surrounded by loose connective tissue.  It is the central compartment of the thoracic cavity. It contains the heart, the great vessels of the heart, esophagus, trachea, thymus, and lymph nodes of the central chest.
Mediastinum
Thoracic cavity
Chest
Hilum of lung
Bronchus
Tracheal bronchus
Neck
Mediastinal pleura