The bones of the chest and upper back combine to form the strong, protective rib cage around the vital thoracic organs such as the heart and lungs. The rib cage also anchors the bones of the head, neck, shoulders, and arms to the trunk of the body. Powerful muscles that move the head and arms attach to these bones as well. The bones of the chest and their joints also support the upper body’s weight.
Twelve pairs of ribs extend laterally and anteriorly from the thoracic vertebrae to meet at or near the sternum. The sternum is a thin, flat, blade-shaped bone that is commonly known as the breastbone. Ribs are long, flat, curved bones no more than a centimeter or two in width and a few millimeters in depth. The seven superior pairs of ribs connect directly to the sternum via the costal cartilage and are collectively known as the true ribs. The five pairs of ribs inferior to the true ribs are considered to be false ribs because they do not connect directly to the sternum. Within the false ribs are a subgroup known as the floating ribs (pairs 11 and 12) that do not connect to the sternum at all and only form joints with the thoracic vertebrae. The ribs curl around the thorax to provide protection to the heart and lungs on all sides from external forces. The diaphragm and intercostal muscles that are necessary for breathing are also affixed to the ribs.
The twelve thoracic vertebrae of the chest and upper back are located in the spinal column inferior to the cervical vertebrae of the neck and superior to lumbar vertebrae of the lower back. Thoracic vertebrae interlock tightly by overlapping their spinous processes, giving stability to the spine in this region. Thoracic vertebrae are the only vertebrae that form joints with ribs; each pair of ribs is connected to one thoracic vertebra on its posterior end.
The clavicle and scapula, known collectively as the pectoral girdle, attach to the axial skeleton at the sternum. The pectoral girdle bones move the shoulder joint in many different directions to improve the flexibility of the upper limbs. These bones and the muscles that move them allow you to elevate, depress, abduct, adduct, and rotate the shoulder joint to give the arms an extremely free range of motion.
