The coelom of birds (pigeon) is well developed and divided into two cavities, anterior thoracic and posterior abdominal cavities, by a membranous oblique septum or diaphragm. The thoracic cavity has two dorso-lateral pleural cavities, each enclosing a lung. The two pleural cavities are separated from each other by the antero-ventral pericardial cavity enclosing the heart lying in the middle between the ventral portions of the pleural cavities.
The abdominal cavity lies posterior to the diaphragm and is called a peritoneal or abdominal cavity which contains the rest of the visceral organs such as digestive, excretory, reproductive organs suspended by mesenteries. Coelom is filled with a watery coelomic fluid and is bounded by peritoneum.