<prompt> Posterior mdiastinum provides passage to all structures exceptOesophagusTracheaDescending thoracic aoaAzygous vein  <response>: Posterior MediastinumBoundariesAnteriorly: i Pericardium, ii bifurcation of trachea, iii pulmonary vessels, and iv posterior pa of the upper surface of the diaphragm.Posteriorly: Lower eight thoracic veebrae and intervening discs.On each side: Mediastinal pleura.Contents1. Oesophagus2. Aeries: Descending thoracic aoa and its branches.3. Veins: i Azygos vein, ii hemiazygos vein, and iii accessory hemiazygos vein.4. Nerves: i Vagi, and ii splanchnic nerves, greater, lesser and least, arising from the lower eight thoracic ganglia of the sympathetic chain.5. Lymph nodes and lymphatics: i Posterior mediastinal lymph nodes lying alongside the aoa, and ii the thoracic ductRef: BD Chaurasia; Volume 1; 6th edition 