Intrinsic muscles of the foot by Daren Owen, Brisbane

The Intrinsic muscles of the foot are responsible for the flexion, extension, adduction, and abduction of the toes. In addition they help greatly in pronation and supination of the foot.

Layer 1

Intrinsic muscles of the foot
The first layer of intrinsic muscles of the foot
Flexor digitorum brevis

Origin: Medial process of the calcaneal tuberosity, plantar aponeurosis
Insertion: Middle phalanx of digits 2-5 vis slips of tendon
Function: Flexes digits 2-5
Abductor hallucis

Origin: Flexor retinaculum, medial process of the calcaneal tuberosity, and plantar aponeurosis
Insertion: Medial side of the base of he proximal phalanx of digit 1 (great toe, hallux)
Function: Abducts digit 1
Abductor digiti minimi

Origin: Primarily from the lateral process of the calcaneal tuberosity and the plantar aponeurosis
Insertion: Lateral side of the proximal phalanx of digit 5 (little toe)
Function: Abducts and flexes digit 5

Layer 2

Second intrinsic muscle layer
The second layer of intrinsic muscles of the foot
Quadratus plantae

Origin: Two slips via the medial and lateral sides of he calcaneus
Insertion: The two portions join and end in a flattened band at the tendon of the flexor digitorum longus
Function: Aids in flexing digits 2-5 by straightening he pull of the flexor digitorum longus.
Lumbricals

Origin: Tendons of the flexor digitorum longus
Insertion: Dorsal surface of the proximal phalanges 2-4 and the expansions of the tendons of the extensor digitorum longus
Function: Flexes digits 2-5
Intrinsic muscle layer 3
The third layer of intrinsic muscles of the foot

Flexor hallucis brevis

Origin: Plantar surface of the lateral cuneiform (3) and the cuboid bones.
Insertion: Two tendons into the proximal phalanx of great toe
Function: Flexes the great toe
Adductor hallucis (Oblique head)

Origin: Base of metatarsals 2-4
Insertion: Base of proximal phalanx of great toe
Function: Adducts great toe
Adductor hallucis (Transverse head)

Origin: Plantar metatarsopharangeal ligaments of the third, fourth, and fifth digit joints.
Insertion: Lateral side of the great toe
Function: Adducts the great toe
Flexor digiti minimi brevis

Origin: Fifth metatarsal
Insertion: Lateral side of the proximal phalanx of the small toe (digit 5)
Function: Flexes the small toe
Opponens digiti minimi

Note: This muscle is made up of the deep fibers of the flexor digit minimi brevis and is occasionally described as a distinct muscle and as such, will be described here.
Origin: Base of the fifth metatarsal bone
Insertion: Lateral part of the distal half of the fifth metatarsal bone
Function: Flexes the little toe and draws the fifth metatarsal medially and down.
Layer 4

Intrinsic muscle layer four
The fourth and final layer of intrinsic muscle of the foot are on the plantar and dorsal surfaces of the foot
Plantar interossei

Origin: Medial sides of the third, fourth, and fifth metatarsals
Insertion: Proximal Phalanx of the third, fourth, and fifth metatarsals
Function: Adducts the third, fourth, and fifth, digits
Dorsal interossei

Origin: Adjacent sides of the two metatarsal bones between which they are located
Insertion: Bases of the first phalanges of the second, third, and fourth toes, and into the aponeurosis of the tendons of the flexor digitorum longus
Function: The first muscle draws the the second digit medially towards the great toe, the second muscle draws the great toe laterally, the third and fourth muscle draws the third and fourth digits laterally as well.

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