Overview
It arises between the two heads of the gastrocnemius. In the horse it is almost entirely tendinous: it keeps very few muscle fibres and works as a cable between the femur and the digit. Its tendon winds around the gastrocnemius tendon, becomes superficial and forms a cap over the calcaneal tuber, attached to it on both sides. It continues down the plantar surface of the metatarsus, forms a sleeve (manica flexoria) for the deep digital flexor tendon at the fetlock and ends on the first and second phalanges.
Unlike in the thoracic limb, the superficial digital flexor of the pelvic limb has no accessory ligament: its own attachment to the femur and calcaneus does that job.
Origin
Supracondylar fossa of the femur (fossa supracondylaris).
Insertion
Distal end of the first phalanx and proximal end of the second phalanx.
Action
Flexes the digit and extends the hock. Supports the fetlock when standing.
Innervation
Tibial nerve (n. tibialis).
Clinical relevance
- It is the caudal part of the reciprocal apparatus: with the peroneus tertius, which lies cranially, it couples stifle and hock so that one cannot flex without the other. Together with the patellar lock, it lets the horse sleep standing up.
- Luxation of the tendon off the calcaneal tuber, almost always laterally, causes swelling at the point of the hock and acute lameness.
- Subcutaneous calcaneal bursitis ("capped hock") results from knocks against stable or trailer walls.