Answer
In some evaluations ribs 3-9 are considered the typical ribs. The features in these ribs proximally are a head, a neck, and a tubercle. The smooth wedge-shaped head inserts between two vertebrae and articulates with the vertebral facets. Each margin of the head has a smooth articular (costal) facet-- a superior articular facet and an inferior articular facet. The superior articular facet articulates with the facet of the vertebra above the rib; the inferior articular facet articulates with the superior vertebral costal facet of the vertebra below. The tubercle of the rib articulates with transverse costal facets on each side of the same numbered vertebra. Beyond the tubercle each rib curves around the side of the chest, and progresses towards the sternum. The curved portion is called the angle of the rib; the shaft is the rest of the bony part of the rib distal to the angle and towards the sternum. This shaft ends distally as a squarish rough area.
Beyond the angle the shaft is wide and flat. In a living human, the the costal cartilage begins at the end of the shaft and covers the rest of the distance to the sternum in ribs 2-7. Each of the ribs 2-7 has its own costal cartilage and so are called true ribs.
Work Step by Step
The inferior margin of the shaft of a rib typically has a groove-- the costal groove --which is a pathway for intercostal blood vessels and intercostal nerves.
Note. Ribs 1,2,10,11 and 12 are special in different in various ways.
