lung
One of a pair of organs of respiration in the chest in which aeration of the blood takes place. As a rule, the right lung is slightly larger than the left and is divided into three lobes (an upper, a middle, and a lower), while the left has but two lobes (an upper and a lower). Each lung is irregularly conical in shape, presenting a blunt upper extremity (the apex), a concave base following the curve of the diaphragm, an outer convex surface following the inner curve of the ribs, an inner or mediastinal surface, a thin and sharp anterior border, and a thick and rounded posterior border.