Is the thoracic cavity dorsal to the abdomniopelvic cavity?
The thoracic cavity is superior to the abdominopelvic cavity.
Neither. The main cavity is called the abdominopelvic cavity. A sub-cavity inside that is the pelvic cavity. That is where you will find the organs of reproduction. The dorsal cavity is along your back and skull. The thoracic is where your heart and lungs are. The abdominal cavity is a sub-cavity of the abdominopelvic cavity, its where your stomach and other related organs are.
Diaphragm is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity (heart, lungs & ribs) from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.
Cranial cavity - serous membranes dorsal cavity = the back ventral cavity - has the thoracic cavity which contains the lungs(parietal pleura and visceral pleura membranes) and the heart (parietal pericardium and visceral pericardium membranes), the abdominal cavity (parietal peritoneum and visceral peritoneum membranes) and the pelvic cavity which is also peritoneum membranes)