part of develops from postgenal trichoid sensillum VFB:FBbt_00004170 fly_anatomy.ontology FBbt:00004170 Trichoid sensillum of the postgena of the adult head, located in the medial region, ventral to the premandibular bristles (Haynie and Bryant, 1986). There are approximately six of these on each side (Haynie and Bryant, 1986). postgena trichoid sensillum ventral occipital bristle presumptive postgenal sensillum