There are 12 pairs of ribs which form the bony lateral walls of the thoracic cage.
(i) The first seven pairs are called true ribs because their anterior ends are attached directly to the sternum by means of small pieces of hyaline cartilage, the costal cartilages.
(ii) The eighth, ninth and tenth pairs of the ribs are called false ribs. They articulate by cartilage which are attached indirectly to the sternum. They are also called vertebrochondral ribs.
(iii) The last two pairs of ribs are called floating ribs because their anterior ends are not attached to either the sternum or the cartilage of another rib. The floating ribs protect the kidneys.
