Intrinsic foot musculature and extrinsic tendon insertion variations are common. Muscular variations are potentially symptomatic and may complicate imaging interpretation. The medial plantar nerve supplies the AbH and FHB, while the deep branch of the lateral plantar nerve supplies the AdH. In the fourth layer, the tibialis posterior tendon inserts to the navicular and medial cuneiform, and the tibialis anterior tendon inserts to the medial cuneiform and first metatarsal. The medial and lateral heads of the FHB originate from the cuneiforms and plantar calcaneonavicular (spring) and long plantar ligaments and insert, via the medial and lateral sesamoids of the first metatarsophalangeal joint, to the proximal hallucial phalanx. The oblique head of the AdH originates laterally from the cuboid, lateral cuneiform and from the bases of the second and third metatarsals and inserts on the lateral base of the proximal hallucial phalanx, while the transverse head arises from metatarsophalangeal joints of the third–fifth digits. The third layer contains the two heads of both the adductor hallucis (AdH) and flexor hallucis brevis (FHB). In the second layer, the flexor hallucis longus tendon passes deep to the flexor digitorum longus tendon to insert on the base of the distal hallucial phalanx.
Several muscles move the hallux, or great toe: in the first layer, the abductor hallucis (AbH) arises from the medial calcaneus, plantar aponeurosis, and flexor retinaculum to insert distally on the medial proximal hallucial phalanx base. The first, most superficial layer contains the flexor digitorum brevis, abductor hallucis, and abductor digiti minimi the second layer contains the quadratus plantae and four lumbricals the third contains the adductor hallucis, flexor hallucis brevis, and flexor digiti minimi the fourth and deepest layer contains the dorsal and plantar interossei. The plantar foot contains four layers of intrinsic muscles, interspersed with tendons of extrinsic leg muscles that insert into the foot.