The Thoracic Cage: Ribs

A typical rib has three main parts: the head, neck, and body. The head articulates with costal facets of thoracic vertebrae, while a small bump called the tubercle on the neck joins the transverse process of the same-numbered vertebra. The body, or shaft, contains a costal groove along its inferior margin for blood vessels and nerves to pass through.

True ribs, ribs 1-7, attach directly to the sternum through their costal cartilages. False ribs, ribs 8-12, attach indirectly to the sternum. Ribs 8-10 connect to the cartilage of the 7th rib, while ribs 11-12, called floating ribs, do not attach to the sternum at all and terminate within the abdominal wall musculature.

All 12 pairs of ribs articulate posteriorly with thoracic vertebrae T1-T12. The articular facet in each rib's head joins the costal facets of two vertebrae: the same-numbered vertebra and the one above it. The tubercle on the rib's neck articulates with the transverse process of the same-numbered vertebra.

The costal groove is a shallow groove located along the inferior margin of each rib. Blood vessels and nerves pass through this groove, allowing them to travel safely along the rib without obstruction. This anatomical feature protects vital neurovascular structures during respiration and movement.

Intercostal muscles between the ribs contract and relax during respiration, changing the width and depth of the thoracic cage. When these muscles contract during inhalation, they increase the volume of the thoracic cavity. During exhalation, they relax, decreasing the cavity's volume and facilitating air expulsion.

The angle of the rib is the point on the rib where it has its highest degree of curvature, located just posterior to the tubercle. The angles of all ribs form the posterior extent of the thoracic cage, providing structural support and defining the cage's posterior boundary.

The thoracic cage comprises 12 pairs of ribs along with the sternum and costal cartilages. These ribs are classified as true ribs (1-7), false ribs (8-10), and floating ribs (11-12). Together with thoracic muscles, they form the thoracic cavity wall and are part of the overview of the axial skeleton.