Clinical Anatomy: The Muscles of the Foot
You can divide the foot muscles into groups based on their locations — either in the sole of the foot (the bottom or plantar area) or the dorsum on the top of the foot. Most of the muscles are in the sole. The muscles in the sole of the foot are located in four layers. They don’t work as intricately as the small muscles in the hands; they mostly work together to support the arches of the foot. They’re innervated by the medial and lateral plantar nerves.
The muscles in the first layer originate on the calcaneus and insert on the toes:
Abductor hallucis: Inserts on the proximal phalanx of the big toe; abducts and flexes the big toe
Flexor digitorum brevis: Inserts on the middle phalanges of the lateral four toes; flexes the toes
Abductor digiti minimi: Inserts on the lateral side of the proximal phalanx of the little toe; abducts and flexes the little toe
The second layer has the following two muscles:
Quadratus plantae: Originates on the calcaneus and inserts on the tendon of the flexor digitorum longus muscle; helps the flexor digitorum longus flex the second through fifth toes
Lumbricals (numbered first through fourth): Originate on the flexor digitorum longus tendons and insert on the proximal phalanges of the lateral four toes; flex the proximal phalanges and extend the middle and distal phalanges of toes two through five
The third layer has the following three muscles:
Flexor hallucis brevis: Originates on the cuboid and lateral cuneiform and inserts on the proximal phalanx of the big toe; flexes the proximal phalanx of the big toe
Adductor hallucis: Originates on the bases of the second, third, and fourth metatarsals and inserts on the proximal phalanx of the big toe; adducts the big toe (in other words, moves the big toe toward the midline of the foot)
Flexor digiti minimi brevis: Originates on the base of the fifth metatarsal and inserts on the base of the proximal phalanx of the little toe; flexes the little toe
The fourth layer contains plantar and dorsal interossei that originate on the metatarsals and insert on the proximal phalanges. The plantar interossei adduct the toes, and the dorsal interossei abduct the toes (in other words, they move the toes away from the midline of the foot).
The muscles on the dorsum of the foot are the extensor digitorum brevis and extensor hallucis brevis (which actually form one muscle). They originate on the superolateral surface of the calcaneus and insert into the proximal phalanges of the toes (the hallucis brevis goes to the big toe). They extend the toes.