The thoracic cage protects the heart and lungs and gives the breathing muscles a frame to work on. It is made of 12 pairs of ribs, the sternum and the thoracic vertebrae.
The ribs
Ribs 1 to 7 are true ribs that join the sternum directly through their own cartilage. Ribs 8 to 10 join through the cartilage above, and ribs 11 and 12 float free at the front.
The sternum
The sternum has three parts: the manubrium, the body and the xiphoid process. The sternal angle, where the manubrium meets the body, marks the level of the second rib.
Breathing movements
When the diaphragm and intercostal muscles contract, the ribs lift up and out like a bucket handle and the chest gets bigger, drawing air in.
Under each rib
The intercostal vein, artery and nerve run along the lower edge of each rib. That is why needles enter the chest just above a rib.
At the bedside
For CPR, compress the lower half of the sternum and avoid the xiphoid. Count rib spaces down from the sternal angle to find landmarks such as the second intercostal space for needle decompression and the fifth for ECG leads.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).