The rib bones (os costale)

The human has 12 pairs of ribs, which, together with the thoracic vertebrae (vertebrae thoracicae) and the breastbone (sternum), make up the chest (thorax).

There are seven real pairs of ribs (costae verae) and five false pairs of ribs (costae spuriae). Each individual rib consists of the rib bone (os costale) and the rib cartilage (cartilago costalis).

Rib bones have a complicated curvature. At the spinal column (columna vertebralis) the rib starts with the rib head (caput costae). The rib bone progresses backwards via the rib neck (collum costae) to the rib tubercle (tuberculum costae). This is where the rib body (corpus costae), begins, which curves round to the front with the rib angle (angulus costae).

The rib body shows a threefold curvature: it bends from the back (dorsal) towards the abdomen (ventral), and at the same time from the top at the back to the bottom at the front, so that the ends of the ribs are lower at the front. In addition, the rib body turns along its length, so that the outer edges of the rib are turned slightly outwards. This curvature is not present in the first rib, which runs practically horizontally.

The real ribs (costae verae)

In contrast to the false ribs (costae spuriae), the real ribs are not only connected to the spinal column (columna vertebralis) via the costovertebral joint, they are also connected to the breastbone (sternum) by the sternocostal joints (articulationes sternocostales).

This latter connection consists partly of synchondroses, i.e. solid connections generated from cartilage tissue, and partly of synovial joints.

At the 1st, 6th and 7th rib there are mostly synchondrotic connections, at the 2nd to 5th rib usually sterncostal joints (articulationes sternocostales). In both cases the rib cartilage (cartilago costalis) lies on the incisures of the side edges of the breastbone (incisurae costales), with the first-mentioned ribs forming a direct cartilage connection, whereas the 2nd to 5th rib have a pronounced joint cavity.

Here the articular capsule is a direct continuation of the periosteum of the ribs. From the perichondreum of the rib cartilage, ray-shaped ligaments (ligamenta sternocostalia radiata) fan out to the front of the breastbone to connect the periosteum to form a solid connective tissue plate.
 

The false ribs (costae spuriae)

In contrast to the real ribs (costae verae), the "false" ribs have no direct connection to the breastbone (sternum).

The 8th to 10th pair of ribs form part of the structure of the costal arch (arcus costalis). The 11th and 12th rib end freely suspended between the muscles of the lateral abdomen wall.

False ribs are only joined to the chest by the costovertebral joints. Apart from the 11th and 12th rib, all ribs have two articular surfaces. These consist of a rib transverse process joint (articulatio costatransversaria) and a rib head joint (articulatio capitis costae).

Each rib transverse process is located between a rib tubercle (tuberculum costae) and the transverse process of the corresponding vertebra (i.e. 5th rib with transverse process of the 5th vertebra). The rib neck is also connected to the vertebral transverse process via the corresponding reinforcing ligament, the rib transverse process ligament (ligg. costotransversarium) with the vertebra transverse process. The rib head joint is located between the rib head (caput costae) and the vertebra.

Apart from the 1st, 11th and 12 rib, these connections consist of bilocular joints, because each rib forms an articular connection with the upper or lower edge of two superimposed vertebrae.