What is the main anatomical structure that divides the thoracic cavity from the abdominal cavity?

The diaphragm serves as the primary anatomical structure that separates the thoracic cavity from the abdominal cavity. This dome-shaped muscle plays a crucial role in respiration, contracting and relaxing to facilitate breathing. The diaphragm defines the boundary between these two cavities, with the thoracic cavity above it housing the lungs and heart, while the abdominal cavity below it contains organs such as the stomach, intestines, and liver.

Additionally, the ribs, thoracic wall, and pleura, while important structures associated with the thoracic cavity, do not function as the dividing barrier between the thoracic and abdominal cavities. The ribs form the protective cage around the thorax, the thoracic wall provides structural support, and the pleura are membranes that line the lungs and thoracic cavity, but none of these structures fulfill the role of division that the diaphragm does.