Thoracic cavity

The thoracic cavity is the major internal space of the trunk, defined by the musculoskeletal wall of the thorax (thoracic vertebrae, ribs, sternum, and diaphragm).

It houses and protects the vital organs of the respiratory and cardiovascular systems. This space is subdivided by serous membranes, the pleurae, into two pleural cavities (right and left), each containing a lung, and a central compartment called the mediastinum. The mediastinum contains the heart, major vessels, trachea, esophagus, thymus, and lymph nodes.

In dogs and cats, the right and left pleural cavities communicate through a fenestrated mediastinum. Ruminants and horses possess a more continuous mediastinum, which reduces or prevents direct communication between the pleural cavities. Humans have a fully closed mediastinum, completely isolating the two pleural cavities.