The _________ divides the thorax and the abdomen.DiaphragmPleuraPericardiumSeptum

The correct answer is Diaphragm.

Explanation:

The diaphragm is a dome-shaped muscle that separates the thoracic cavity, which contains the lungs and heart, from the abdominal cavity. It plays a crucial role in respiration, as its contraction increases the volume of the thorax and pulls air into the lungs. The other options, such as pleura, pericardium, and septum, are structures associated with the thorax but do not serve to divide the thorax from the abdomen.

• Pleura: Membranes surrounding the lungs.
• Pericardium: Membrane enclosing the heart.
• Septum: A wall dividing two cavities, for example, the septum in the heart, but not separating the thorax from the abdomen.

Thus, the diaphragm is the key anatomical structure that divides these two regions.