📝 STANDARD DESCRIPTION:
Front of leg — extensors of hock + flexors of digits' extensors:
1. Tibialis Cranialis (Anterior) — main FLEXOR of the HOCK.
2. Long Digital Extensor — extends digits + flexes hock.
3. Lateral Digital Extensor — extends 4th digit (ox).
4. Peroneus Tertius (Fibularis tertius) — STRONG TENDINOUS BAND in horse/ox; passive component of the RECIPROCAL APPARATUS.
5. Extensor Digitorum Brevis — small.
Nerve: PERONEAL (FIBULAR) nerve — branch of sciatic.
📚 DETAILED DESCRIPTION:
FRONT-OF-LEG MUSCLES
These muscles lie on the cranial (front) aspect of the leg between stifle and hock. They are mainly: hock flexors and digital extensors.
1. TIBIALIS CRANIALIS: Largest cranial muscle. Origin from tibial tuberosity; inserts on metatarsus. Main flexor of the hock (lifts the foot off the ground in the swing phase).
2. LONG DIGITAL EXTENSOR: Origin from extensor fossa of femur (above the lateral condyle); the long tendon runs down the front of the leg and over the hock to the digits, inserting on the extensor processes of the phalanges. Extends the digits and flexes the hock.
3. LATERAL DIGITAL EXTENSOR: Smaller; supplies the lateral (4th) digit in ox.
4. PERONEUS TERTIUS (Fibularis tertius): An entirely TENDINOUS cord (no muscle fibres) in horse and ox. It runs from the extensor fossa of femur to the tarsus.
This is a key part of the RECIPROCAL APPARATUS — it links the stifle and hock together so that when the stifle flexes the hock automatically flexes too. (You can demonstrate this on a slaughtered horse leg: pull on the peroneus tertius and the hock bends.)
5. EXTENSOR DIGITORUM BREVIS: Small muscle on dorsum of tarsus.
NERVE SUPPLY: All these muscles are innervated by the PERONEAL (FIBULAR) NERVE, which runs over the lateral side of the stifle (around the head of fibula) — making it vulnerable to injury here.
// COMPARATIVE ANALYSIS
| HORSE |
Peroneus tertius is fully tendinous → reciprocal apparatus. Rupture causes 'dropped hock'. |
| DOG |
Peroneus tertius is muscular (not tendinous); no reciprocal apparatus. |
CLINICAL RELEVANCE
Peroneal Nerve Paralysis: Animal cannot lift the foot → toe drags on the ground (knuckling at the fetlock). Common after recumbency on hard ground (cattle, horses).
Rupture of Peroneus Tertius (Horse): Hock can be extended while stifle is flexed — abnormal independent movement.
