The mediastinum is the central compartment of the thoracic cavity, containing many vital organs and structures. Here's what doesn't reside within the mediastinum:

* Lungs: The lungs occupy the lateral spaces of the thoracic cavity, on either side of the mediastinum.

* Pleura: The pleura (visceral and parietal) are the membranes surrounding the lungs, also located outside the mediastinum.

Let me know if you'd like more details about the structures that *do* reside in the mediastinum!