Overview
It arises deep, between the two heads of the gastrocnemius. Its tendon winds around the gastrocnemius tendon, becomes superficial, forms a cap over the calcaneal tuber held by retinacula, and continues along the plantar surface of the metatarsus.
Origin
Lateral supracondylar tuberosity of the femur.
Insertion
Middle phalanges of digits II to V.
Action
Flexes the digits and extends the tarsus.
Innervation
Tibial nerve (n. tibialis).
Clinical relevance
If the retinaculum holding it on the calcaneus tears, the tendon luxates, usually laterally. It is described most often in Shetland Sheepdogs and Collies.