part of part of Homo sapiens rib 1 zone of bone organ facet of first rib 2026-03-19T00:00:00Z A zone of bone organ on the head of the first rib forming a single, oval articular surface that articulates exclusively with the body of the first thoracic vertebra. Unlike typical ribs, the head of the first rib is not divided into two demifacets because it does not articulate with the vertebra above. David Osumi-Sutherland