## **Core Concept**
The flexor retinaculum is a fibrous band in the wrist that forms the roof of the carpal tunnel. It is crucial for understanding which structures pass through or under this retinaculum. The carpal tunnel contains several key structures.

## **Why the Correct Answer is Right**
The **median nerve** and tendons of the **flexor digitorum profundus**, **flexor digitorum superficialis**, and **flexor pollicis longus** pass under the flexor retinaculum. The **palmaris longus** tendon, however, does not pass under the flexor retinaculum; instead, it inserts into the palmar aponeurosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Typically, structures like the median nerve and flexor tendons pass under the flexor retinaculum.
- **Option B:** Also passes under the flexor retinaculum as part of the carpal tunnel contents.
- **Option C:** Similarly, another structure that passes under the flexor retinaculum.
- **Option D:** This option correctly identifies a structure that does not pass under the flexor retinaculum.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is **carpal tunnel syndrome**, which involves compression of the median nerve under the flexor retinaculum. Symptoms include numbness and tingling in the median nerve distribution.

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