Which nerve passes below the piriformis muscle?

The sciatic nerve is the largest nerve in the body and is formed from the lumbosacral plexus. It typically exits the pelvis through the greater sciatic foramen, and depending on anatomical variations, it often follows a path that lies beneath the piriformis muscle. The correct identification of the sciatic nerve's route is crucial in both surgical procedures and diagnosing conditions such as piriformis syndrome, where irritation of the nerve can lead to pain or dysfunction.

In contrast, the superior gluteal nerve passes above the piriformis muscle, innervating the gluteus medius and minimus muscles and thus does not fit the requirement of the question. Similarly, the femoral nerve and obturator nerve originate from more anterior branches of the lumbar plexus and primarily course through the pelvis without passing beneath the piriformis muscle. Their locations and functions are distinct and do not involve the route described in the question. Understanding the anatomy of the pelvis and the orientation of these nerves is essential for addressing surgical approaches and the management of nerve-related pathologies.