Beneath the ribcage are the two cone-shaped lungs. The broad, concave base of each lung rests on the dome-shaped diaphragm muscle. Superiorly, each lung converges into a narrow apex, which projects into the thoracic space under the clavicle.
Most of the outer lung surface lies adjacent to the ribs and is thus called the costal surface. The space between the lungs containing the heart, esophagus, nerves, lower trachea, and primary bronchi is called the mediastinum. Lining this region is the mediastinal surface of the lungs. A cardiac notch (or impression) is present along the mediastinal surface of the left lung. A portion of the heart extends obliquely into this depression. Midway along the mediastinal surface, is a depression called the hilum or hilus. The major blood vessels, bronchi, and nerves enter and leave the lungs at this area. Together, these structures make up the root of the lung.
