start stage end stage hyoid muscle levator operculi levator operculae Hyoid muscle that originates at the ventrolateral margin of the pterotic and inserts in the dorsomesial edge of the opercle. The levator operculi is responsible for jaw depression, its force of contraction is transmitted through the opercular series and the interoperculo-mandibular ligament to the lower jaw. ZFA:0000537 zebrafish_anatomy TAO:0000537 larval:protruding-mouth adult