continuous with adult cervical trachea adult cibarial muscle tracheal branch frontal head air sac FBbt:00003102 fly_anatomy.ontology Largest tracheal air sac of the adult head, extending ventrally and anteriorly to the brain. It corresponds to the expansion of a ventral branch of the cervical trachea. It flanks the cibarium and extends forward and upward around the gnathal ganglion and brain to the level of the antennae and the ptilinal suture. A small dorsal branch extends into the antenna and forms the antennal air sac. head air sac