Which muscle moves the middle toes and aids in balance while walking?

The flexor digitorum brevis is the correct choice because it is specifically tasked with the flexion of the middle phalanges of the second, third, fourth, and fifth toes. This muscle plays a critical role in foot mechanics, particularly during walking, as it helps maintain balance by facilitating proper toe movement and providing support as the foot strikes the ground.

This muscle’s action enables the toes to grip the ground and helps distribute weight effectively, contributing to overall stability during movement. In this way, it is integral to walking and maintaining balance. The other muscles mentioned serve different functions, such as aiding in the movement of specific toes or ankles but do not primarily focus on flexing the middle toes in the manner that the flexor digitorum brevis does.