rib rib 12 In humans: The twelfth rib has a single articular facet on the head, which is of rather large size. It has no necks or tubercles, and is pointed at its anterior ends. The twelfth has angle nor costal groove; it is much shorter than the eleventh rib, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first rib. [WP,unvetted]. MA:0001412 costa XII NCIT:C52767 EMAPA:19540 UBERON:0004611 Wikipedia:Twelfth_rib SCTID:244667008 twelfth rib FMA:8515