These joints (Articulationes sternocostales) are diarthroses formed by
the junction of the cartilages of the sternal ribs with the sternum. The
articular ends of the cartilages (except the first) are somewhat
enlarged, and present surfaces of cylindrical curvature. The articular
surfaces on the sternum for the first pair of cartilages are placed
close together on the dorsal border of the cariniform cartilage
(Manubrium sterni); the other seven are placed laterally at the junction
of the segments. The capsules are strong and tight; the first pair of
joints has a common capsule, and the cartilages articulate with each
other medially. The lower ends of the first pair of ribs are firmly
attached to each other by dense fibrous tissue, which is prolonged
forward along the upper margin of the cariniform cartilage and is
continuous behind with the sternal ligament. Each of the other capsules
is reinforced dorsally by the =superior costo-sternal ligament=
(Ligamentum sternocostale radiatum), composed of radiating fibers which
blend with the sternal ligament. The movement is rotation around a
nearly vertical axis, except in the case of the first pair of joints.