Thorax

The thorax, or chest, is the central body region between the neck and the abdomen. It contains the thoracic cage and the main thoracic organs, including the lungs, heart, great vessels, esophagus, trachea, and thymus. It is bounded superiorly by the thoracic inlet and inferiorly by the diaphragm, with its sides formed by the rib cage and intercostal muscles.

The thoracic skeleton consists of the sternum anteriorly, 12 pairs of ribs with costal cartilages, and the thoracic portion of the vertebral column. The ribs form intercostal spaces that contain intercostal muscles, vessels, and nerves running in the costal grooves.

The thoracic cavity is divided into two pleural cavities, each surrounding a lung, and the central mediastinum. The mediastinum houses the heart and pericardium, the great vessels, the trachea, esophagus, and the thymus (more prominent in children). The lungs are enclosed by visceral and parietal pleura, with the pleural cavity providing a potential space for fluid or air.

The lungs: the right lung has three lobes and the left lung has two, separated by fissures. The diaphragm is the primary muscle of respiration, aided by intercostal and accessory muscles. Nerves and vessels run in the intercostal spaces, with the intercostal nerves and vessels along the bottom of each rib, and the phrenic nerves supplying the diaphragm. The thorax serves protective, respiratory, and conduit roles, linking the neck and abdomen through its openings and vasculature.