What forms the lower boundary of the thoracic cavity?

What forms the lower boundary of the thoracic cavity?

• A. Clavicle
• B. Ribs
• C. Intercostal muscles
• D. Diaphragm

Answer: (D)

The key idea is understanding what forms the bottom edge of the chest cavity. The diaphragm is the muscular partition that separates the thoracic cavity from the abdominal cavity and acts as its floor. At rest it forms a dome that intrudes into the thorax, and with breathing it contracts and moves downward, increasing the space for the lungs to expand. This muscular boundary truly marks the lower limit of the thoracic cavity. The clavicle sits at the top of the chest and helps form the upper border. The ribs and the intercostal muscles contribute to the walls of the thoracic cavity but do not define its lower boundary.

The key idea is understanding what forms the bottom edge of the chest cavity. The diaphragm is the muscular partition that separates the thoracic cavity from the abdominal cavity and acts as its floor. At rest it forms a dome that intrudes into the thorax, and with breathing it contracts and moves downward, increasing the space for the lungs to expand. This muscular boundary truly marks the lower limit of the thoracic cavity.

The clavicle sits at the top of the chest and helps form the upper border. The ribs and the intercostal muscles contribute to the walls of the thoracic cavity but do not define its lower boundary.