Which of the following structures does the flexor hallucis longus not pass under?

The flexor hallucis longus is a muscle located in the posterior compartment of the leg that is primarily responsible for the flexion of the big toe. It runs along the posterior aspect of the ankle and passes through various bony structures as it courses toward its insertion at the base of the distal phalanx of the great toe.

One significant structure that the flexor hallucis longus passes under is the sustentaculum tali, which is a projection on the calcaneus that supports the talus and serves as a pulley for the muscle, aiding in its function. Similarly, it passes under the navicular bone, which helps in the mechanics of foot movement, and it passes near the talus as it moves toward the toes.

In contrast, the cuboid bone is situated more laterally in the foot and does not directly interact with the path of the flexor hallucis longus. This muscle does not pass beneath or directly under the cuboid, making it the correct answer. Understanding the anatomy and trajectory of the flexor hallucis longus is crucial in pedorthics, as it helps in evaluating foot mechanics and designing appropriate footwear or orthotic devices.