Which anatomical feature separates the thoracic and abdominal cavities?

The diaphragm is the anatomical feature that separates the thoracic and abdominal cavities. It is a dome-shaped muscle that plays a crucial role in respiration, contracting to allow air to enter the lungs and relaxing to expel air. The diaphragm also physically partitions the thoracic cavity, which contains the heart and lungs, from the abdominal cavity, which houses organs such as the stomach, intestines, and liver.

The rib cage, while providing structural support and protection for the thoracic cavity, does not serve to separate the thoracic and abdominal cavities. Similarly, the pleura are membranes surrounding the lungs and do not have a separating function between the two cavities. The pericardium is a protective sac surrounding the heart and is not involved in the division between the thoracic and abdominal spaces. Therefore, the diaphragm is the key structure that delineates these two important anatomical regions.