There are twelve pairs of ribs surrounding the thoracic cavity. The ribs connect to the sternum through a bridge of cartilage. This creates a cage that supports and protects the heart, lungs, trachea, aorta and pulmonary artery.

The lower five ribs connect to the sternum through a long cartilage bridge called the costal arch. Between the ribs are the intercostal muscles. They work in conjunction with the diaphragm to produce breathing.