The document discusses the anatomy of the mediastinum and thoracic cavity. It describes the divisions of the mediastinum into superior, inferior, anterior, middle and posterior portions. It identifies the structures located in the superior mediastinum, including the thymus gland, brachiocephalic veins, and sternum muscles. It also describes the azygos and hemiazygos veins, trachea, arch of the aorta, and major veins that drain into the superior and inferior vena cava.