The thoracic vertebrae, ribs, costal cartilages, and sternum form the thoracic cage. It provides protection for the internal organs of the thoracic cavity and supports the superior trunk, pectoral girdle, and upper limbs.
Twelve pairs of ribs are attached to the thoracic vertebrae. The head of each rib articulates with the costal facet on the body of its own vertebra, and a tubercle near the head articulates with the costal facet on the transverse process. The head also articulates with the costal facet on the body of the vertebra superior to it. The shaft of each rib curves around the thoracic cage and slopes slightly inferiorly.
The superior seven pairs of ribs are attached directly to the sternum by the costal (kos ‘-tal) cartilages, which extend medially from the ends of the ribs. These ribs are the true ribs. The remaining five pairs are the false ribs. The first three pairs of false ribs are attached by cartilages to the costal cartilages of the ribs just superior to them. The last two pairs of false ribs are called floating ribs because they lack cartilages and are not attached anteriorly. The costal cartilages give some flexibility to the thoracic cage.
The sternum, or breastbone, is a flat, elongated bone located at the midline in the anterior portion of the thoracic cage. It consists of three bones that are fused together. The manubrium (mah-nu’-bre-um) is the superior portion that articulates with the first two pairs of ribs; the body is the larger middle segment, and the xiphoid
process is the small inferior portion.
A biopsy of red bone marrow may be made by a sternal puncture because the sternum is covered only by skin and connective tissue. Under local anaesthetic, a large-bore hypodermic needle is inserted into the sternum, and red bone marrow is drawn into a syringe.