The lungs have a conical shape with a rounded apex and broad base. They have two surfaces - a costal surface in contact with the rib cage and a mediastinal surface against the mediastinum. The right lung is heavier with three lobes divided by fissures, while the left lung is lighter with two lobes and a cardiac notch. Both lungs receive arterial blood from the pulmonary arteries and drain venous blood through the pulmonary veins. They are surrounded and protected by the pleura, a smooth membrane covering the lungs and lining the thoracic wall.