Final answer:
The bone on the thumb side of the forearm is known as the radius, and it is critical for movement at the wrist joint.
Step-by-step explanation:
The bone on the thumb side of the forearm is called the radius. The ulna is located on the medial side (the side closer to the body), while the radius is on the lateral side (the thumb side). They are both part of the skeletal structure of the forearm and play a crucial role in forearm and hand movements such as flexion, extension, pronation, and supination. The radius is also essential for the wrist joint's range of motion.