Questions: Into which vessel does the thoracic duct drain? Right subclavian vein Left jugular vein Right jugular vein Left subclavian vein

The answer is the fourth one: Left subclavian vein.

Explanation for each option:

1. Right subclavian vein: Incorrect. The thoracic duct does not drain into the right subclavian vein. The right lymphatic duct drains into the right subclavian vein.

2. Left jugular vein: Incorrect. While the thoracic duct is located near the left jugular vein, it does not directly drain into it.

3. Right jugular vein: Incorrect. The thoracic duct does not drain into the right jugular vein.

4. Left subclavian vein: Correct. The thoracic duct drains into the junction of the left subclavian vein and the left internal jugular vein. This is the correct vessel where the thoracic duct empties lymph into the bloodstream.

In summary, the thoracic duct drains into the left subclavian vein.