In humans, a typical rib consists of a wedge-shaped head at the posterior end that articulates with the vertebral body, a tubercle that articulates with the same  numbered thoracic vertebra,  a central shaft (body) and an anterior (sternal) end.  Located on the inferior portion of the inner surface of the body is a costal groove that contains blood vessels and nerves.  Of the 12 pairs of ribs, all but the last two pairs are attached to the sternum either directly or indirectly at their anterior ends by costal cartilages.  For this reason,  the last two pairs of ribs (which have their costal cartilages embedded in the muscles of the body wall) are  often called the "floating ribs".