Which of the following muscles turns the hand inward?

The correct choice is the pronator muscle, which is responsible for turning the hand inward, a movement known as pronation. This action involves the rotation of the forearm that allows the palm of the hand to face down or inward toward the body. The pronator teres and pronator quadratus are the primary muscles involved in this movement.

In contrast, flexor muscles primarily serve to bend the wrist and fingers, while extensor muscles are responsible for straightening these parts. The supinator muscle performs the opposite function; it turns the hand outward, allowing the palm to face up or outward. Understanding the specific roles of these muscles is essential for proper technique and movements within nail technology and other related fields.