A typical adult rib cage has 24 ribs, twelve on each side. They arc from the spine toward the chest and form a movable basket around the heart and lungs.
The upper seven pairs reach the breastbone on their own cartilage. The next three share a cartilage path, and the last two float, ending in the muscle of the back. That mix lets the cage expand when you breathe.
A few people are born with an extra rib. The everyday plan is still twelve pairs — armor that has to move.
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