The Anterior Mediastinum exists only on the left side where the left pleura diverges from the mid-sternal line.
It is bounded in front by the sternum, laterally by the pleuræ, and behind by the pericardium. It is narrow, above, but widens out a little below. Its anterior wall is formed by the left Transversus thoracis and the fifth, sixth, and seventh left costal cartilages. It contains a quantity of loose areolar tissue, some lymphatic vessels which ascend from the convex surface of the liver, two or three anterior mediastinal lymph glands, and the small mediastinal branches of the internal mammary artery.