ribs

Ribs are curved bones that form the rib cage, a protective framework for the thoracic organs and a key component of human respiration. In adults, there are 24 ribs arranged in 12 pairs on the left and right sides.

Each rib has a head, neck, tubercle, and a long shaft. The head articulates with the bodies of two adjacent thoracic vertebrae, and the tubercle articulates with the transverse process of the corresponding vertebra. Along the bottom edge of each rib runs the costal groove, through which intercostal nerves and vessels pass. Most ribs are connected anteriorly to the sternum via costal cartilage.

Ribs are classified by their connection to the sternum: true ribs (ribs 1–7) attach directly to the sternum through their own costal cartilage; false ribs (ribs 8–10) connect indirectly via cartilage connecting to the rib above; and floating ribs (ribs 11–12) do not reach the sternum at all.

The rib cage works with the sternum and thoracic muscles to protect the heart, lungs, and major vessels, while also enabling breathing. During inhalation, intercostal muscles and the diaphragm expand the chest cavity, allowing air to fill the lungs; exhalation involves the relaxation of these muscles.

Anatomical variation is common, including supernumerary ribs or differences in rib length. Clinically, ribs are a common site of fractures after trauma and are routinely evaluated in thoracic imaging. Ribs also occur in other vertebrates with species-specific counts and shapes adapted to their biology.