{Ribs+Sternum = Rib cage}. Rib cage has 12 pairs of ribs or 24 in number. Ribs are divided in three categories on the basis of their size and their connections with the front side of skeleton. True ribs - First 7 pairs {1–7} of rib bones are called true ribs. They connect strernum {breast bone} with coastal cartilage in the front and to the spine at the back by ligaments. [coastal cartilage is elastic in nature and helps the ribcage to expand during respiration].