**Core Concept**
The musculocutaneous nerve is a branch of the brachial plexus that primarily supplies the muscles of the anterior compartment of the arm, including the biceps brachii, brachialis, and coracobrachialis.

**Why the Correct Answer is Right**
The musculocutaneous nerve arises from the lateral cord of the brachial plexus and innervates the muscles mentioned above, playing a crucial role in elbow flexion and forearm supination. It also provides sensory innervation to the skin of the lateral forearm through its terminal branch, the lateral cutaneous nerve of the forearm.

**Why Each Wrong Option is Incorrect**
**Option A:** This option should list the muscles supplied by the musculocutaneous nerve, such as biceps brachii, brachialis, and coracobrachialis. If incorrect, it would be a distractor listing muscles supplied by other nerves, like the radial nerve (e.g., triceps brachii) or the median nerve (e.g., flexor carpi radialis).
**Option B:** This option should be the correct answer, listing a muscle not supplied by the musculocutaneous nerve. A common example is the triceps brachii, which is supplied by the radial nerve.
**Option C:** This option should be a distractor listing a muscle supplied by the musculocutaneous nerve, like the biceps brachii.
**Option D:** This option should be a distractor listing a muscle supplied by another nerve, like the median nerve (e.g., pronator teres).

**Clinical Pearl / High-Yield Fact**
The musculocutaneous nerve is also known as the "nerve to the biceps" due to its primary innervation of the biceps brachii muscle. This fact can help distinguish it from other nerves in the upper limb.

**Correct Answer: B. Triceps brachii**