Branchial arches, or
gill arches, are a series of bony "loops" present in fish, which support the
gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop
pharyngeal arches, though the eventual fate of these arches varies between
taxa. In
jawed fish, the first arch develops into the jaws, the second into the
hyomandibular complex, with the posterior arches supporting gills. In amphibians and reptiles, many elements are lost including the gill arches, resulting in only the oral jaws and a
hyoid apparatus remaining. In mammals and birds, the hyoid is still more simplified.