The First Rib is the broadest, shortest, and most sharply curved of the series. Scalenus anterior and scalenus medius attach to the first rib. The upper surface of the first rib presents a groove for the subclavian artery and a groove for the subclavian vein. These grooves are separated by the scalene tubercle (the insertion of the scalenus anterior muscle). The union of the first rib with the sternum is a synchondrosis (firmly joined by cartilage). Synovial joints exist between cartilages two to seven and the facets on the side of the sternum.