## **Core Concept**
The flexor retinaculum is a fibrous band in the wrist that forms the roof of the carpal tunnel, allowing for the passage of the median nerve and flexor tendons. Structures superficial to it are located more towards the skin surface.

## **Why the Correct Answer is Right**
The palmaris longus tendon is indeed superficial to the flexor retinaculum. The flexor retinaculum is located deep to the palmaris longus tendon, which is one of the tendons that can be easily palpated on the wrist. This anatomical relationship is crucial for understanding wrist and hand anatomy.

## **Why Each Wrong Option is Incorrect**
* **Option A:** The **flexor carpi radialis** tendon, while in the wrist, is not specifically known for being superficial to the flexor retinaculum; it actually passes through a separate compartment.
* **Option B:** The **median nerve** passes deep to the flexor retinaculum, within the carpal tunnel, making it not superficial to it.
* **Option D:** The **ulnar nerve** and **ulnar artery** pass through Guyon's canal, which is superficial to the flexor retinaculum but more ulnar (on the little finger side), and not specifically described as being superficial in the context provided.

## **Clinical Pearl / High-Yield Fact**
A useful clinical correlation is that the palmaris longus tendon can be used as a landmark for identifying the location of the flexor retinaculum. The tendon of palmaris longus is often used in surgical procedures as a guide for the location of the flexor retinaculum.

## **Correct Answer:** C. Palmaris longus tendon.