part of part of chest costal arch http://upload.wikimedia.org/wikipedia/commons/3/3d/Gray115.png costal margin arcus costalis UBERON:0002225 The costal margin, sometimes referred to as the costal arch, is the medial margin formed by the false ribs, which in humans is from the eighth rib to the tenth rib. SCTID:367767002 MA:0001396 FMA:7569 subcostal arch Wikipedia:Costal_margin FMA:7570 we treat margin and arch in FMA as equivalent here, as a temporary measure. This may be split in future. We follow MA in making this a part of the rib. UMLS:C0230143 NCIT:C52715 arcus costae EMAPA:37491 rib anatomical line