**Core Concept**
The median nerve is a vital nerve in the upper limb, responsible for innervating muscles involved in thumb opposition, flexion, and abduction. The median nerve arises from the brachial plexus and traverses the arm, forearm, and hand to supply muscles and provide sensory innervation.

**Why the Correct Answer is Right**
The median nerve supplies all intrinsic muscles of the hand except the thenar muscles' abductor pollicis brevis, which is actually innervated by the _frontal nerve, a branch of the accessory nerve_. However, the correct answer is another muscle, the **abductor pollicis longus**, which is innervated by the posterior interosseous nerve, a branch of the radial nerve. The median nerve does supply the flexor pollicis longus and the thenar muscles' flexor pollicis brevis and opponens pollicis. The nerve also supplies the lumbricals to the index and middle fingers and the first dorsal interosseous muscle.

**Why Each Wrong Option is Incorrect**
**Option A:** Not relevant to the question, but the median nerve does supply the flexor pollicis longus and the thenar muscles' flexor pollicis brevis and opponens pollicis.
**Option B:** Not relevant to the question, but the median nerve does supply the lumbricals to the index and middle fingers and the first dorsal interosseous muscle.
**Option C:** Not relevant to the question, and this is not a muscle of the thumb.
**Option D:** Not relevant to the question, and this is not a muscle of the thumb.

**Clinical Pearl / High-Yield Fact**
Remember that the median nerve supplies all intrinsic muscles of the hand except the abductor pollicis longus, which is innervated by the posterior interosseous nerve, a branch of the radial nerve.

**Correct Answer:** D.