The contents of the thorax include the heart and lungs (and the thymus gland); the (major and minor pectoral muscles, trapezius muscles, and neck muscle); and internal structures such as the diaphragm, the esophagus, the trachea, and a part of the sternum known as the xiphoid process). Arteries and veins are also contained – (aorta, superior vena cava, inferior vena cava and the pulmonary artery); bones (the shoulder socket containing the upper part of the humerus, the scapula, sternum, thoracic portion of the spine, collarbone, and the rib cage and floating ribs).