The chest cavity is bounded by the chest wall and below by the diaphragm. It extends upward into the root of the neck about one fingerbreadth above the clavicle on each side. The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The chest cavity can be divided into a median partition, called the mediastinum, and the laterally placed pleurae and lung