Rib (costa) is the anatomical name for a curved, flattened bone forming part of the chest wall. Ribs lie on either side of the chest, extending from the spine towards the front or side of the trunk. Together with cartilage and neighbouring bones, they support and protect the chest contents.
Where are the ribs located?
There are normally 12 pairs of ribs, numbered from above downwards. They form the lateral walls of the thorax, the region of the trunk between the neck and abdomen. Posteriorly, meaning towards the back, they join the thoracic vertebrae, the bones of the spine within this region.
Most ribs curve forwards and downwards. Their anterior ends, towards the front, continue into costal cartilages: flexible supporting tissue that connects most ribs directly or indirectly to the sternum, the breastbone. The lowest ribs end in the abdominal wall rather than reaching the sternum.
Intercostal spaces are the gaps between adjacent ribs. These contain muscles, nerves and blood vessels. Deep to the ribs lies the pleura, the thin membrane associated with the lungs and the inner chest wall; the lower ribs also overlie upper abdominal organs, including the liver and spleen.
What are true, false and floating ribs?
A true rib attaches to the sternum through its own costal cartilage. A false rib does not have this direct connection. Floating ribs are a subgroup of false ribs whose anterior ends have no connection to the sternum or to the cartilage of the rib above.
| Rib group | Rib numbers | Anterior attachment |
|---|---|---|
| True ribs | 1–7 | Each reaches the sternum through its own costal cartilage |
| False ribs with an indirect attachment | 8–10 | Cartilage joins the costal cartilage above |
| Floating ribs | 11–12 | No attachment to the sternum or cartilage above |
The tenth rib's anterior attachment varies: its cartilage may join the cartilage above, or its anterior end may be free. The joined cartilages of the lower, non-floating ribs contribute to the costal margin, the curved lower border of the front of the rib cage.
What are the parts of a typical rib?
Typical ribs have a common arrangement of landmarks, usually described using ribs 3–9. A typical rib's posterior end carries the joint surfaces, including two facets on the head separated by a crest, while its long, curved shaft forms much of the chest wall.
The main landmarks are:
- Head: the posterior end, bearing articular facets, or smooth surfaces that meet neighbouring bones at joints.
- Neck: the short region between the head and the tubercle.
- Tubercle: a projection at the junction of the neck and shaft, with a facet for a vertebra and a rough area for ligament attachment.
- Angle: the region where the shaft bends most sharply, just beyond the tubercle.
- Shaft: the curved main portion, with outer and inner surfaces and upper and lower borders.
- Costal groove: a channel along the lower part of the inner surface of the shaft.
The costal groove shelters the main intercostal vein, artery and nerve. These run between layers of the intercostal muscles, which occupy the spaces between ribs. The shaft ends anteriorly where the bone meets its costal cartilage.
Which joints connect a rib to neighbouring structures?
The head of a typical rib joins the body of its corresponding thoracic vertebra and the body of the vertebra above. It also meets the intervening intervertebral disc, the pad of supporting tissue between vertebral bodies. This connection is called the joint of the head of the rib.
The tubercle joins the transverse process of the corresponding vertebra, a bony projection extending sideways from the vertebral arch. This forms the costotransverse joint. Ligaments, strong bands of connective tissue, reinforce these posterior joints while allowing movement.
At the front, the costochondral joint connects rib bone to costal cartilage. It is a primary cartilaginous joint that permits essentially no movement at the connection itself. The sternocostal joints connect the cartilages of true ribs to the sternum, while interchondral joints connect neighbouring costal cartilages in the lower chest.
How do atypical ribs differ?
Atypical ribs depart from the usual arrangement of the head, shaft or joint surfaces. The left first rib is short, broad and flattened from above downwards. Its upper surface has grooves for the subclavian vein and artery, major vessels passing between the chest and upper limb, separated by a projection for the anterior scalene muscle of the neck.
The left second rib is longer than the first and has a rough area for attachment of serratus anterior, a muscle that connects the ribs to the shoulder blade. Its shape is intermediate between the first rib and the more typical ribs below.
The left eleventh rib and left twelfth rib each have a single facet on the head and lack a tubercle. They therefore have no costotransverse joint. The twelfth rib also lacks a distinct angle and costal groove.
What do ribs do during breathing?
Ribs help protect the lungs, heart and major vessels while providing attachment sites for muscles of the chest, back and abdominal wall. Their curved arrangement combines a protective framework with the ability to move.
During inspiration, the phase of breathing in, rib elevation increases the dimensions of the chest. Upper rib movement mainly increases the front-to-back dimension, while movement of lower ribs mainly increases its side-to-side dimension. These patterns are commonly called pump-handle and bucket-handle movements.
How can you identify a rib in the 3D model?
In the 3D model next to this article, rotate and zoom the chest, then select and isolate a rib to examine its shape. Hide or fade other selected structures, or switch layers to change the view. You can also cut a section along the sagittal, coronal or transverse plane, or pull parts apart, then rotate and zoom again.