The foot plays a fundamental role in maintaining upright walking posture and balance, so it must provide a strong base while allowing for small, accurate movements.  The foot can be split into dorsal and plantar compartments, the latter of which contains significantly more muscles.

Dorsal Compartment

Although many extrinsic muscles attach within the dorsal compartment, there are only three intrinsic muscles which act on the foot and two extrinsic muscles which act on the foot rather than the ankle. 

Extensor Digitorum Longus - The extensor digitorum longus is a deep-lying extrinsic muscle that lies runs down the length of the tibia.

• Attachments - Originates from the tibia and transitions into a tendon, passes into the foot, splits into four, and attaches to the toes.
• Actions - Extension of the toes.

Extensor Digitorum Brevis - The extensor digitorum brevis muscle is a deep-lying intrinsic muscle lying beneath the tendon of the extensor digitorum longus.

• Attachments - Originates from the heel and attaches to the toes.
• Actions - Extension of the toes.

Extensor Hallucis Longus - The extensor hallucis longus is a deep-lying extrinsic muscle lying beneath the extensor digitorum longus.

• Attachments - Originates from the fibula and attaches to the big toe.
• Actions - Extension of the big toe.

Extensor Hallucis Brevis - The extensor hallucis brevis muscle is an intrinsic muscle of the foot lying between the extensor digitorum longus and lateral to extensor hallucis longus.

• Attachments - Originates from the heel and attaches to the big toe.
• Actions – Extension of the big toe.

Dorsal Interossei - There are four dorsal interossei located between the metatarsals. Each arises from two metatarsals.

• Attachments - Originates from the sides of metatarsals one to five (big toe to little toe). The first muscle attaches to the medial side of the phalanx of the second toe. The second to fourth interossei attach to the lateral sides of the phalanxes of toes two to four.
• Actions - Abduct and flexes digits two to four.

Plantar View of Foot

The muscles, tendons, and ligaments of the sole of the foot with flexor digitorum brevis shown in red.

This diagram shows the flexor digitorum brevis in relation to the abductor quinti diciti, abductor hallucis, and central plantar aponeurosis.

Plantar Compartment

The muscles of the plantar compartment play a key role in stabilizing the arch of the foot and controlling the digits, providing the necessary strength and fine movements to maintain balance and posture and promote walking.

Abductor Hallucis - The abductor hallucis muscle is located on the medial side of the sole.

• Attachments - Originates from the heel and attaches to the base of the big toe.
• Actions - Abducts and flexes the big toe.

Flexor Digitorum Brevis - The flexor digitorum brevis muscle is located laterally to the abductor hallucis and lies in the middle of the sole of the foot.

• Attachments - Originates from the heel and attaches to all the toes excluding the little toe.
• Actions - Flexes the toes at the proximal interphalangeal (between the phalanges preoxmales and phalanges mediae) joints.

Abductor Digiti Minimi - The abductor digiti minimi muscle is located on the lateral side of the foot.

• Attachments - Originates from the heel and attaches to the little toe.
• Actions - Abducts and flexes the little toe.

Quadratus Plantae - The quadratus plantae muscle is located superior to the flexor digitorum longus tendons.

• Attachments - Originates from the heel and attaches to the tendons of flexor digitorum longus.
• Actions - Assists flexor digitorum longus in flexing the lateral four toes.

Lumbricals - The lumbricals are four small skeletal muscles, accessory to the tendons of the flexor digitorum longus and numbered from the medial side of the foot.

• Attachments - Originates from the tendons of flexor digitorum longus. Attaches to the toes.
• Actions - Flexes at the metatarsophalangeal (between the metatarsals and phalanges proximale) joints, while extending the interphalangeal joints (between the phalanges proximale and phalanges mediae).

Flexor Hallucis Brevis - The flexor hallucis brevis muscle is located on the medial side of the foot.

• Attachments - Originates from the plantar surfaces of the cuboid and lateral cuneiform bones in the sole of the foot and attaches to the big toe.
• Actions - Flexes the big toe.

Adductor Hallucis - The adductor hallucis muscle is located laterally to the flexor hallucis brevis.

• Attachments:  The adductor hallucis originates from the bases of the first four metatarsals, and also from the plantar ligaments before attaching to the big toe.
• Actions: Adduct the big toe and maintains the arch of the foot.

Plantar Interossei - The three plantar interossei lie beneath rather than between the metatarsal bones. Each is connected with one metatarsal bone.

• Attachments - Originates from the medial side of metatarsals three to five. Attaches to the medial sides of the phalanges of digits three to five.
• Actions - Adducts and flexes digits three to five.

Flexor Digiti Minimi Brevis – Similar to the interossei in structure, the flexor digiti minimi brevis muscle is located on the lateral side of the foot underneath the metatarsal of the little toe.

• Attachments - Originates from the base of the fifth metatarsal and attaches to the base of phalanx of the little toe
• Actions - Flexes the little toe.