Final answer:
The movement that allows the turning of palms forward and backward is due to pronation and supination, which involve the rotation of the radius around the ulna.
Step-by-step explanation:
The ability to turn your palms forward and backward is thanks to pronation and supination. These are distinct movements of the forearm. In the anatomical position, when the palm of the hand faces forward, this is known as the supinated position. During supination, the radius and ulna are parallel. In contrast, pronation involves the motion that moves the forearm from the supinated position to the pronated (palm backward) position, with the radius crossing over the ulna at the distal radioulnar joint, forming an "X" shape. The muscles involved include the pronator teres and the pronator quadratus for pronation, and the supinator muscle for supination.