Bone · Chest

First rib

The shortest, broadest and most sharply curved rib, lying almost entirely behind the collarbone. Unlike every rib below it, it is flattened top-to-bottom rather than side-to-side, and its upper surface carries two shallow grooves separated by a small scalene tubercle: the subclavian vein crosses in front of the tubercle and the subclavian artery behind it, with the lowest trunk of the brachial plexus lying against the artery. Its head bears a single facet, so it meets the first thoracic vertebra alone. It matters because everything travelling between the neck and the arm has to cross this one short, sharply curved bone.