Exstrophy-epispadias complex (EEC) refers to a spectrum of birth defects that includes epispadias, classical bladder exstrophy, and exstrophy of the cloaca and several variants. EEC is characterized by a visible defect of the lower abdominal wall and other problems. In normal development, the cloacal membrane temporarily separates the cloaca (final part of the intestine) into urogenital and anal regions, and it ruptures after fusing with a structure known as the urogenital septum, which is made up of the tissue that will form the abdominal muscles (mesoderm). If the cloacal membrane does not fuse correctly with the urogenital septum, it does not form the mesoderm and, as a result, the abdominal muscles do not form. The exact timing of the rupture determines whether the child is born with isolated epispadias, classic bladder exstrophy, or cloacal exstrophy. Depending on severity, EEC may involve the urinary system, musculoskeletal system, pelvis, pelvic floor, abdominal wall, genitalia, and sometimes the spine and anus. There is no known cause for EEC. The University of Michigan has a webpage about the development of the embryo and its parts, including the formation of the cloaca.