Structure of the rib cage

The rib cage provides a protective enclosure for the heart and lungs. It is made up of bones and cartilages.

The thoracic spine behind, the breastbone (sternum) in front and the ribs on either side complete the rib cage.

It is somewhat conical in shape being narrow above and broad below.

The sternum is a flat bone situated in the midline in front. It consists of three parts. The upper end is called manubrium, the middle portion body and the lower xiphoid process. The xiphoid process looks prominent in a newborn baby.

The upper border of manubrium articulates with the clavicles (collar bones) on either side. On the sides it articulates with the cartilage which joins it with the first rib. The cartilage of the second rib joins the sternum at the junction of manubrium and the body.

The borders of the body articulate with the cartilages of third, fourth, fifth and the sixth ribs. The cartilage of the seventh rib joins the sternum at the junction of the body and the xiphoid process.

Ribs: There are twelve ribs on either side making up a total of 24 ribs. They form arches on the sides of the bony cage. The ribs are slightly elastic in nature. The first seven ribs are directly attached to the sternum in front through cartilages and are called true ribs.

The remaining five are called false ribs. Out of these the first three are attached to the cartilages of true ribs above. The last two are free at their anterior ends and are not attached to any structure. They are called floating ribs.

The ribs are attached in such a way that there are spaces in between them. These spaces are called inter-costal spaces. Each rib has an anterior end, posterior end and a body. The anterior end is attached to the sternum through a cartilage.

The posterior end has a head at the tip followed by a narrow portion called the neck and a bony prominence called the tubercle. The head has two articular surfaces separated by a ridge of bone. These articular surfaces articulate with the bodies of two adjacent vertebrae.

The tubercle has a smooth area which articulates with the end of the transverse process of the lower of the two vertebrae with which the head articulates. The inner side of the body has a groove for the blood vessels and nerve.

The first rib has certain unique features. It is flat and broad. It is the shortest of all the ribs. Its surfaces look upward and downward while those of other ribs face inward and outward. Hence the borders face inward and outward. Its head has only one articular facet for articulation with the body of the first thoracic vertebra.

The eleventh and twelfth ribs have only a single articular area on the head. They have no necks or tubercles.

There are muscles in between the ribs. They are called inter-costal muscles. They are arranged in two layers-external (outer) inter-costal muscles and internal (inner) inter-costal muscles. There are eleven external and eleven internal inter-costal muscles on each side. These muscles play an important role in the mechanics of breathing.

Return from rib cage to human body