adult chordotonal organ of prothoracic segment anterior prothoracic chordotonal organ anterior chordotonal organ aCO Chordotonal organ attached at one end to the anterior wall of the thorax immediately below the prosternal sense organ at the articulation of the head, and to the hypotremal apodeme at the other end (Power, 1948). The two (bilateral) organs extend posterolaterally, forming a V shape in the horizontal plane (Power, 1948). The joint between the arms of the V is directed posteromedially and pressed against the anterolateral corner of the prothoracic neuromere (Power, 1948). A thick, short group of fibers, the prothoracic chordotonal nerve, connects this organ to the ventral nerve cord (Power et al., 1948). neck chordotonal organ VFB:FBbt_00007656 PCO FBbt:00007656 prosternal chordotonal organ fly_anatomy.ontology prothoracic chordotonal organ