Rib

A rib is a long, curved bone that forms part of the chest skeleton. The ribs, connected to the spine at the back and the sternum at the front, form a cage-like structure known as the rib cage or thoracic cage. This cage protects the internal organs of the chest, particularly the lungs and heart, and also supports the mechanics of breathing.

Ribs are not rigid, immobile bones. When a person breathes, the intercostal muscles between the ribs and the diaphragm (the muscle separating the chest from the abdomen) raise and lower the ribs, which changes the volume of the chest cavity. This change allows air to enter the lungs and is expelled when breathing out.

Anatomy

A typical adult human has twelve pairs of ribs, twelve on each side. Each rib is connected at the back to one of the thoracic vertebrae of the spine. At the front, some ribs are connected to the sternum by cartilage, while others are attached directly. The bottom two pairs are usually not attached at the front and are called floating ribs.

Function

The primary function of the rib cage is protection. It shields the heart, lungs, major blood vessels, and parts of the liver and kidneys from external injury. It also serves as an attachment point for numerous muscles involved in breathing, arm movement, and support of the upper body.

Health and injury

Rib fractures are common injuries from falls or blunt force trauma to the chest. The most frequent symptom is pain that worsens with breathing or coughing. Severe rib injuries can result in punctured lungs or air and blood accumulating in the chest cavity. Rib bone marrow can also be sampled for medical testing.

Variation across species

Ribs are found in many species of vertebrate animals, but their number and structure vary. Some mammals and reptiles have many ribs distributed along the length of the body, while many birds have a limited number confined to the chest.