 The pharyngeal jaws of teleosts , a second set of jaws contained within the throat , are composed of five branchial arches , loops of bone which support the gills . The first three arches include a single basibranchial surrounded by two <unk> , ceratobranchials , <unk> and pharyngobranchials . The median basibranchial is covered by a <unk> . The fourth arch is composed of pairs of ceratobranchials and <unk> , and sometimes additionally , some pharyngobranchials and a basibranchial . The base of the lower pharyngeal jaws is formed by the fifth ceratobranchials while the second , third and fourth pharyngobranchials create the base of the upper . In the more basal teleosts the pharyngeal jaws consist of well @-@ separated thin parts that attach to the neurocranium , pectoral girdle , and hyoid bar . Their function is limited to merely transporting food and they rely mostly on lower pharyngeal jaw activity . In more derived teleosts , the jaws are more powerful with left and right ceratobranchials fusing to become one lower jaw ; the pharyngobranchials fuse to create a large upper jaw that articulates with the neurocranium . They have also developed a muscle that allows the pharyngeal jaws to have a role in grinding food in addition to transporting it . 
