Abductor hallucis
The first layer of the plantar region of the foot contains three muscles, namely, abductor hallucis, flexor digitorum brevis and abductor digiti minimi. The abductor hallucis muscle is among the largest and most superficial muscles of the plantar foot. At its origin, it has attachments to the flexor retinaculum, medial process of the calcaneal tuberosity and the plantar fascia. Abductor hallucis inserts into the medial plantar tubercle of the base of the proximal phalanx of the hallux. It also has some distal attachments to the medial sesamoid bone of the first metatarsophalangeal joint.
Abductor hallucis has two primary functions - these are flexion and abduction of the great toe. By placing two fingers over the medial aspect of the muscle belly of abductor hallucis and asking your subject to repeatedly abduct their hallux against slight resistance, you will be able to perceive the action of abductor hallucis. If your subject has difficulty abducting their hallux, asking them to perform repeated flexions of the hallux will achieve a similar effect.