**Core Concept**
The carpal tunnel is a narrow, fibrous passageway in the wrist that contains the median nerve and the tendons of the flexor muscles of the forearm. The median nerve and these tendons pass through the carpal tunnel, which is formed by the carpal bones and the transverse carpal ligament.

**Why the Correct Answer is Right**
The flexor carpi ulnaris tendon is not contained within the carpal tunnel. Instead, it is located on the ulnar side of the forearm and does not pass through the carpal tunnel. The carpal tunnel contains the tendons of the flexor digitorum profundus, flexor digitorum superficialis, and flexor pollicis longus muscles, which are responsible for wrist and finger flexion. The median nerve also passes through the carpal tunnel, providing sensation to the thumb, index, middle finger, and half of the ring finger.

**Why Each Wrong Option is Incorrect**
**Option A:** The median nerve is indeed contained within the carpal tunnel, and its compression can lead to carpal tunnel syndrome.
**Option B:** The flexor digitorum superficialis tendon is one of the tendons contained within the carpal tunnel.
**Option C:** The flexor pollicis longus tendon is also contained within the carpal tunnel.

**Clinical Pearl / High-Yield Fact**
The carpal tunnel is a common site for compression of the median nerve, leading to carpal tunnel syndrome, which can cause numbness, tingling, and weakness in the hand.

**✓ Correct Answer: D. Flexor carpi ulnaris tendon**