11.10: The Thoracic Cage: Ribs
Ribs are curved, flattened bones forming the thoracic cavity wall with the thoracic muscles. There are 12 pairs of thoracic ribs. The posterior ends of all the ribs articulate with the T1–T12 thoracic vertebrae. In contrast,the anterior ends of most ribs attach to the sternum via their costal cartilages.
Parts of a Typical Rib
A typical rib has a head, neck, and body. The posterior end of the rib is called the head, followed by a narrow neck. The head articulates primarily with the costal facet of the same numbered thoracic vertebra and, to a lesser degree, with the costal facet of the next higher vertebra. A small bump on the posterior surface of the neck is the tubercle, which articulates with the transverse process of the same numbered vertebra. The remainder of the rib is the body of the rib (shaft). Next to the tubercle is the angle of the rib, the point at which the rib has its highest degree of curvature. The angles of the ribs form the posterior extent of the thoracic cage. A shallow groove called the costal groove is found along the inferior margin of each rib for the passage of blood vessels and a nerve.
Rib Classifications
The ribs are classified into three groups based on their attachment to the sternum. Ribs 1–7 are true or vertebrosternal ribs, with their costal cartilage directly attached to the sternum. Ribs 8–12 are called false or vertebrochondral ribs, where the costal cartilage indirectly attaches to the sternum. In ribs 8–10, the costal cartilages are attached to each other and are together attached to the cartilage of the 7th rib. The last two false ribs, the 11th, and 12th, are also called floating or vertebral ribs. These are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 7.4 The Thoracic Cage (Ribs) - p 259-260
