The rib cage is a bony and cartilaginous structure that surrounds the thoracic cavity and protects the lungs and heart. It is composed of 24 ribs in humans, 12 on each side, and is made up of the ribs and their corresponding attachments to the sternum (breastbone) and the vertebral column. The ribs are divided into true and false ribs. The true ribs are the first seven, and the false ribs are the last six. The false ribs are attached to the sternum by cartilage only. The rib cage is semi-rigid but can be expanded to have the ability to increase in size. The small joints that are present between the ribs and the vertebrae can permit a gliding motion of the ribs on the vertebrae while breathing and during other activities. The rib cage helps to protect the lungs and the heart, and it also helps to move the thoracic cavity.

In summary, the rib cage is a structure that protects the lungs and heart and is composed of 24 ribs in humans, 12 on each side, and their corresponding attachments to the sternum and the vertebral column. The ribs are divided into true and false ribs, and the rib cage is semi-rigid but can be expanded to increase in size.