dome-shaped
The Diaphragm The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the diaphragm Figure 11.17 . It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.