(1) medial and lateral recesses at either side of the urogenital mesentery of the embryo; (2) superior recess of the vestibule of the lesser peritoneal space; with the formation of the diaphragm, a portion of the right recess is cut off and becomes the infracardiac bursa; the portion below the diaphragm becomes the superior recess of the lesser peritoneal sac; the left recess is lost. SYN: pneumatoenteric.