**Question:** The supinator muscle is supplied by

A. Radial artery
B. Ulnar artery
C. Interosseous artery
D. Anterior interosseous artery

**Core Concept:**
The supinator muscle is a muscle of the forearm that plays a crucial role in supination (turning the palm downwards) of the forearm. It is composed of two heads: the long head, which originates from the lateral epicondyle of the humerus, and the short head, which arises from the radial styloid process. The supinator muscle is innervated by the radial nerve, which is a branch of the brachial plexus.

**Why the Correct Answer is Right:**
The radial artery is a major branch of the brachial artery, which lies deep to the biceps brachii muscle in the anterior compartment of the arm. After passing through the radial tunnel, the radial artery divides into two branches: the posterior interosseous artery and the anterior interosseous artery. The supinator muscle receives its blood supply from the posterior interosseous artery, which is a branch of the radial artery.

**Why Each Wrong Option is Incorrect:**
A. The ulnar artery supplies the muscles in the ulnar side of the forearm and does not contribute to the supinator muscle's blood supply.
B. The ulnar artery supplies the muscles on the ulnar side of the forearm and does not supply the supinator muscle.
C. The interosseous artery supplies the muscles in the interosseous space of the forearm and does not supply the supinator muscle.
D. The anterior interosseous artery supplies the muscles on the anterior side of the forearm and does not supply the supinator muscle.

**Clinical Pearl:**
The supination of the forearm is a crucial function for activities such as drinking from a cup or using a keyboard. Understanding the blood supply to the supinator muscle is essential for understanding the anatomy and clinical relevance of the radial tunnel syndrome, which can lead to symptoms like pain, paresthesia, and weakness in supination due to compression of the posterior interosseous nerve and artery.