Muscles of the foot: 3rd and 4th layers of sole

3rd layer (3), 4th layer (2)

Muscles of the 3rd layer of the sole

Flexor hallucis brevis, ADductor hallucis, flexor digit minimi brevis

Flexor hallucis brevis

P.A.: Plantar surfaces of cuboid and lateral cuneiforms

D.A.: Both sides of base of proximal phalanx of 1st digit

Innervation: Medial plantar nerve (L5,S1)

Main Action: Flexes proximal IP joint of 1st digit

Adductor hallucis

P.A.:

• Oblique head: bases of metatarsals 2-4

• Transverse head: plantar ligaments of MTP joints

D.A.: Tendons of both heads attach to lateral side of base of proximal phalanx of 1st digit

Innervation: Deep branch of lateral plantar nerve (S1-S3)

Main Action: Traditionally said to adduct 1st digit; assists in maintaining transverse arch of foot by pulling metatarsals medially

Flexor digit minimi brevis

P.A.: Base of 5th metatarsal

D.A.: Base of proximal phalanx of 5th digit

Innervation: Superficial branch of lateral plantar nerve (S1-S3)

Main Action: Flexes proximal IP joint of 5th digit, thus assisting with flexion of digit

Muscles of the 4th layer

Plantar interossei (3 muscles), Dorsal interossei (four muscles)

Plantar interossei (3 muscles)

P.A.: Plantar aspect of medial sides of shafts of metatarsals 3-5

D.A.: Medial sides of bases of phalanges of 3rd-5th digits

Innervation: Lateral plantar nerve (S1-S3)

Main Action: Adduct and flex digits 3-5 at MTP joints

Dorsal interossei (4 muscles)

P.A.: Adjacent sides of shafts of metatarsals 1-5

D.A.:

• 1st: medial side of proximal phalanx of 2nd digit

• 2nd-4th: lateral sides of 2nd-4th digits

Innervation: Lateral plantar nerve (S1-S3)

Main Action: ABduct and flex digits 2-4 at MTP joints