Write a short note on rib cage.

The rib cage is a bony structure in the chest that protects vital organs like the heart and lungs.

It is made of 12 pairs of ribs, the sternum (breastbone), and the thoracic vertebrae of the spine. The ribs form a semi-flexible cage that expands and contracts during breathing. 

The upper seven pairs are true ribs attached directly to the sternum, the next three pairs are false ribs, and the last two are floating ribs attached only to the spine. Muscles between the ribs, called intercostal muscles, help in inhalation and exhalation. 

The rib cage also supports the shoulder girdle and maintains the shape of the chest cavity.