Educational resource developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute (ICAR-IVRI), Bareilly.
📝 STANDARD DESCRIPTION:
Back of leg — extensors of hock + flexors of digits:
1. Gastrocnemius (2 heads — medial & lateral) — biggest; tendon = 'Achilles tendon' → tuber calcanei.
2. Superficial Digital Flexor (SDF) — wraps around the tuber calcanei (forms 'cap'); flexes digits.
3. Deep Digital Flexor (DDF) — has 3 heads; tendon goes around the medial side of hock; flexes digits.
4. Popliteus — small triangular muscle behind stifle.
Function: EXTEND the hock + FLEX the digits → 'push-off' in walking.
Nerve: TIBIAL nerve — branch of sciatic.
📚 DETAILED DESCRIPTION:
CALF MUSCLES — BACK OF THE LEG
These muscles form the calf of the leg. They EXTEND the hock and FLEX the digits — together they create the 'push-off' phase of locomotion.
1. GASTROCNEMIUS: Largest calf muscle; has medial and lateral heads from the supracondylar tuberosities of femur. Joins with the superficial digital flexor to form the common calcaneal tendon ('Achilles tendon'), which inserts on the tuber calcanei (point of hock).
2. SUPERFICIAL DIGITAL FLEXOR (SDF): Origin from supracondylar fossa of femur. Its tendon wraps around the top of the calcaneus, forming a 'cap' over the tuber calcanei, and continues distally to insert on P2 of each digit. Flexes the digits and extends the hock.
3. DEEP DIGITAL FLEXOR (DDF): Three heads (Lateral & Medial digital flexors + Tibialis caudalis). Their tendons join into one main tendon that passes around the MEDIAL side of the hock (through the tarsal canal) and inserts on P3 (flexor tubercle). Strongest digital flexor.
4. POPLITEUS: Small triangular muscle on the caudal aspect of stifle; flexes & medially rotates the leg at stifle.
NERVE SUPPLY: All these muscles are supplied by the TIBIAL NERVE (the bigger branch of the sciatic).
STAY APPARATUS LINK: Gastrocnemius + SDF together form a passive support that holds the hock extended without muscular effort — animal can stand or sleep without tiring.
// COMPARATIVE ANALYSIS
| HORSE |
Calcaneal tendon and SDF cap on tuber calcanei extremely strong; part of stay apparatus. |
| DOG |
Same plan; common rupture of Achilles tendon in working dogs. |
CLINICAL RELEVANCE
Tibial Nerve Paralysis: Animal cannot extend the hock → 'dropped hock' posture; fetlock knuckles forward.
Rupture of the Achilles tendon (Gastrocnemius rupture): Common in dairy cattle around calving; the hock drops to the ground (plantigrade stance).
