Ribcage. Computer artwork of the pectoral girdle and ribcage as seen from the front. The spine, which consists of blocks of bone (vertebrae) separated by spongy intervertebral discs, runs down the center. The ribcage is made up of twelve pairs of curved bones that attach to the spine at the back and the sternum (not clearly seen) at the front. In front of the ribcage at top are the collar bones (clavicles) and behind the ribcage at top are the shoulder blades (scapulas). These make up the pectoral girdle. The clavicles and scapulas articulate with the upper arm bones (humerus) to form the shoulders.