part of continuous with mesothoracic segment propleural air sac adult spiracle adult ventral external mesothorax adult anterior thoracic spiracle Manning and Krasnow (1993) assign this spiracle to the mesothoracic segment, as we have done here, despite recording its origin as being from tracheoblasts associated with the humeral (dorsal prothoracic) disc. adult prothoracic spiracle adult spiracle 1 FBbt:00004609 fly_anatomy.ontology https://www.ento.csiro.au/biology/drosophila/melanogaster.html?anterior%20spiracle The anterior-most spiracle of the adult thorax. It is located in the ventral mesothorax and opens out into the propleural air sac. adult thoracic spiracle