**Core Concept**
The question requires knowledge of the anatomy of the hand, specifically the muscles that contain sesamoid bones. Sesamoid bones are small, embedded bones within tendons that provide additional leverage and protection to the surrounding muscles.

**Why the Correct Answer is Right**
The adductor pollicis muscle in the hand contains two sesamoid bones, known as the pisiform bone and the trapezium bone. These sesamoid bones are embedded within the tendons of the adductor pollicis muscle, which helps to increase the mechanical advantage of the muscle and protect the tendon from excessive stress and wear. The presence of sesamoid bones in the adductor pollicis muscle is a unique anatomical feature that distinguishes it from other muscles in the hand.

**Why Each Wrong Option is Incorrect**
**Option A:** Flexor pollicis brevis does not contain a sesamoid bone, and is primarily responsible for flexion of the proximal phalanx of the thumb.
**Option B:** Flexor pollicis longus does not contain a sesamoid bone, and is primarily responsible for flexion of the distal phalanx of the thumb at the interphalangeal joint.
**Option C:** Opponens pollicis does not contain a sesamoid bone, and is primarily responsible for opposition of the thumb.

**Clinical Pearl / High-Yield Fact**
The presence of sesamoid bones in the adductor pollicis muscle is an important anatomical feature that should be remembered by students of hand anatomy. This knowledge can be useful in understanding the mechanics of thumb movement and the potential consequences of injury to this muscle.

**✓ Correct Answer: D. Adductor pollicis**