The first through seventh ribs have a direct anterior atachment to the sternum
(by cartilage) and these ribs are called true ribs (vertebrosternal ribs)
- articulations of the cartilages of the true ribs with the sternum are arthrodial
joints, with the exception of the first, in which the cartilage is directly
united with the sternum, and which is, therefore, a synarthrodial articulation
The remaining five pairs of ribs are called false ribs because their
costal cartilages do not attach directly to the sternum. The cartilages of the
eighth, ninth and tenth ribs attach to each other and then to the cartilage
of the seventh rib. These false ribs are also known as vertebrochondral ribs.
The eleventh and twelfth false ribs are designated as floating (vertebral
ribs) - this is because their anterior ends do not attach even indirectly
to the sternum. They attach only posteriorly to the thoracic vertebrae.