mesothoracic cleft pleural cleft FBbt:00004607 https://www.ento.csiro.au/biology/drosophila/melanogaster.html?pleural%20suture fly_anatomy.ontology Fold of the adult lateral mesothorax that extends dorsoventrally from the leg articulation to the base of the wing by a sinuous course. Internally, it forms an infolding or phragma that acts as a support for the wing and the leg articulation.