Final answer:
The lungs are not contained within the mediastinum; they reside within the pleural cavities on either side of the mediastinum.
Step-by-step explanation:
The structure that is NOT contained within the mediastinum is d. lungs. The mediastinum is the central compartment of the thoracic cavity, surrounded by the pleural sacs of the lungs. It contains the heart within the pericardial cavity, the esophagus, trachea, and the main bronchi, but not the lungs themselves. The lungs are located in the pleural cavities, which are on either side of the mediastinum. The esophagus runs through the mediastinum and penetrates the diaphragm at the esophageal hiatus to enter the abdomen. The muscular diaphragm, located below the lungs, facilitates breathing and marks the end of the thoracic cavity.