The four lumbricals muscles of the foot are small and present in the intermediate layer on the plantar surface. They are accessory to the tendons of flexor digitorum longus. They are numbered from medial to lateral.
Their origins vary:
- the lateral three lumbricals arise from both sides of the cleft where each flexor digitorum longus tendon diverges to the digits
- the medial lumbrical arises from the medial border of the first tendon of flexor digitorum longus
Passing distally, each muscles runs along the medial side of its respective nearest toe of the lateral four toes. It inserts into the dorsal extensor expansion on the proximal phalanges.
The lumbricals have differing innervations:
- first lumbrical is from the medial plantar nerve (L4,L5)
- second to fourth lumbrical is from the lateral plantar nerve (S2, S3)
The lumbricals of the foot act on the lateral four toes to:
- extend them at the interphalangeal joints
- flex them at the metatarsophalangeal joints