The _____ pairs of ribs are subdivided into two main groups: _____ or _____ ribs (pairs ___ through ___) and ______ ribs (pairs ___ through___). The first group attaches directly to the ______ by individual ______. The second group is subdivided into ______ ribs (pairs ___ through____), which attach ______ by joining costal cartilage of the rib above, and _______ or ________ ribs, which do not attach to the sternum at all.