Interchondral Articulations (articulations of the cartilages of the ribs with each other). The contiguous borders of the sixth, seventh, and eighth, and sometimes those of the ninth and tenth, costal cartilages articulate with each other by small, smooth, oblong facets. Each articulation is enclosed in a thin articular capsule, lined by synovial membrane and strengthened laterally and medially by ligamentous fibers which pass from one cartilage to the other. Sometimes the fifth costal cartilages, more rarely the ninth and tenth, articulate by their lower borders with the adjoining cartilages by small oval facets; more frequently the connection is by a few ligamentous fibers. [ http://en.wikipedia.org/wiki/Interchondral_articulations ]