**Question:** Arm muscle not supplied by musculocutaneous nerve

**Core Concept:** The musculocutaneous nerve is a branch of the brachial plexus, which provides motor innervation to the lateral cutaneous nerve of the arm and the flexor muscles of the forearm.

**Why the Correct Answer is Right:** The arm muscle not supplied by the musculocutaneous nerve is the brachialis muscle. The brachialis muscle is part of the flexor group of forearm muscles, and it contributes to elbow flexion. It receives its motor innervation from the ulnar nerve, not the musculocutaneous nerve.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Correct Answer):** The brachialis muscle is not supplied by the musculocutaneous nerve.
B. **Option B:** The radialis muscle is supplied by the radial nerve, not the musculocutaneous nerve.
C. **Option C (Incorrect):** The coracobrachialis muscle receives motor innervation from the musculocutaneous nerve.
D. **Option D (Incorrect):** The biceps brachii muscle is supplied by the brachialis and radial nerves, not the musculocutaneous nerve.

**Clinical Pearl / High-Yield Fact:** The brachialis muscle's innervation is crucial to understand for clinical scenarios involving elbow injuries or surgical procedures, as misidentification of the nerve supply can lead to significant functional deficits.

**Correct Answer:** C.