part_of part of part of located_in (type level) located in located in located_in trunk coelemic cavity lumen mesenchyme septum transversum transverse septum A thick plate of mesodermal tissue that occupies the space between the thoracic cavity and yolk stalk in the early embryo, forming a transverse partition partially separating the coelomic cavity into thoracic and abdominal portions. It gives rise to the central tendon of the diaphragm[VHOG].