Final answer:
The supinator muscle is a spiral muscle that curls around the proximal portion of the radius and performs supination of the forearm by rotating the radius laterally.
Step-by-step explanation:
The spiral muscle that curls around the proximal portion of the radius and performs supination of the forearm by rotating the radius laterally is the supinator muscle. This muscle is located on the posterior portion of the forearm, along with the brachioradialis and the superficial and deep forearm extensors. When the supinator muscle contracts, it moves the palm and forearm anteriorly, resulting in supination of the forearm.