The thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the descending aorta and contained in the posterior mediastinal cavity. The thoracic aorta begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth thoracic vertebra, at the aortic hiatus in the diaphragm where it becomes the abdominal aorta.