Rib cage
The structure formed by the thoracic vertebrae and ribs, the sternum (breastbone), and the costal cartilages (that attach the ribs to the sternum).
A cage is an enclosure made of 'open work' that usually houses animals.
The rib cage was thought to resemble an animal cage (although the largest 'animals' it holds are the heart and lungs).
The rib cage is also called the thoracic cage.