4. The Thoracic Cavity

Posterior Mediastinum In Lesson 3, we discussed the subdivisions of the mediastinum as described by anatomists. As a summary, remember that the mediastinum is subdivided into superior and inferior parts. The inferior mediastinum is further subdivided into anterior, middle and posterior parts. The anterior boundary of the anterior part is the back of the sternum. Its posterior boundary is the pericardium of the heart.

The middle mediastinum is the pericardium and its cavity.

The anterior boundary of the posterior mediastinum is the posterior pericardial wall. The posterior boundary is the anterior surfaces of the bodies of thoracic vertebrae T5-T12.

In the dissection of cadavers, the posterior mediastinum is exposed by removing the pericardial sac and the heart. When this is done, we see the structures that lie immediately behind the pericardium. The relationships of the structures in the posterior mediastinum should also be studied on cross sections through the thorax and shown in the section on cross sections. In the following images, I have started out Level 1 with the pericardium.