How many ribs does a typical human have?

Twenty-four, in twelve pairs. Men and women have the same number, which is worth stating because the belief that men have one fewer - from the story of Adam and Eve - has been remarkably persistent. Vesalius said so in 1543 and it was controversial enough to be worth saying.

The top seven pairs attach to the breastbone directly, the next three via shared cartilage, and the last two attach to nothing at the front at all, which is why they are called floating ribs. About one person in two hundred has an extra pair at the neck, a cervical rib, which mostly causes no trouble and occasionally presses on the nerves to the arm.

The cage is not the rigid box it looks like. Ribs are hinged at the spine and swing up and out with every breath, increasing the volume of the chest so air is drawn in - you do not suck air in so much as make a bigger space and let the atmosphere fill it. That is why a serious rib injury is dangerous out of proportion to the break: it makes breathing painful, so people breathe shallowly, and shallow breathing invites pneumonia.