## **Core Concept**
The flexor retinaculum, also known as the transverse carpal ligament, is a fibrous band that forms the roof of the carpal tunnel. It plays a crucial role in maintaining the position of the tendons and the median nerve within the carpal tunnel. Several structures pass deep to this retinaculum.

## **Why the Correct Answer is Right**
The structures that pass deep to the flexor retinaculum include the tendons of the flexor digitorum profundus, flexor digitorum superficialis, and flexor pollicis longus, along with the median nerve. The **palmaris longus tendon** does not pass deep to the flexor retinaculum; instead, it inserts into the palmar aponeurosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The median nerve does pass deep to the flexor retinaculum, providing sensation to the palmar surface of the thumb, index, middle finger, and the lateral half of the ring finger.
- **Option B:** The tendons of the flexor digitorum profundus do pass deep to the flexor retinaculum, contributing to the flexion of the fingers.
- **Option C:** The tendons of the flexor digitorum superficialis also pass deep to the flexor retinaculum, aiding in finger flexion.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is **carpal tunnel syndrome**, which occurs due to compression of the median nerve as it passes under the flexor retinaculum. Symptoms include numbness, tingling, and weakness in the hand, particularly affecting the thumb, index, and middle fingers.

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