rib [AS, roof] , one of the 12 pairs of arches of bone forming a large part of the thoracic skeleton. The first seven ribs on each side are called true ribs because they articulate directly with the sternum and vertebrae. The remaining five ribs are called false ribs. The first three attach ventrally to ribs above; the last two are free at their ventral extremities and are called floating ribs. True ribs are also known as vertebrosternal ribs; false ribs as vertebrocostal ribs; and floating ribs as vertebral ribs. See also thorax.
