Joel Elkins, age 10, of Gadsden, Ala., for his question:

HOW MANY RIBS DOES A PERSON HAVE?

Twenty four rib bones enclose the chest in the human body. There are 12 ribs on each side of the body, each connected to the vertebral column or backbone by small joints called costovertebral joints.

In the front of the body, the uppermost seven ribs on each side connect to the sternum or breastbone, and they are called "true ribs." The five lower ribs, called "false ribs," do not connect directly to the sternum.

Each of the upper three false ribs is attached to the rib above with cartilage or gristle. The lower two: ribs are attached only to the backbone. They are known as floatin ribs.

The spaces between the ribs, called intercostal spaces, contain arteries, veins, muscles and nerves.

The ribs perform two functions: they protect the heart and lungs and they also move up and down and, together with the diaphragm, control the movement of air in and out of the lungs.