Which tendons form the reciprocal apparatus in the hind limb stay mechanism?

Which tendons form the reciprocal apparatus in the hind limb stay mechanism?

• A. Peroneus tertius and superficial digital flexor tendon.
• B. Flexor carpi ulnaris and common digital extensor
• C. Deep digital flexor tendon and gastrocnemius
• D. Biceps femoris and semimembranosus

Answer: (A)

The hind limb stay mechanism relies on a reciprocal linkage that ties the stifle and hock together so they move in unison during weight-bearing. This linkage is formed by the peroneus tertius tendon crossing between the stifle and hock and the superficial digital flexor tendon running down the back of the limb to the distal phalanx. Together, these two tendons coordinate the motion of the two joints: when the stifle extends, the hock is compelled to extend as well, and when the stifle flexes, the hock flexes accordingly. This makes standing energy-efficient and stabilizes the limb in a fixed position.

The other options involve structures that don’t create this hind-limb reciprocal link (they’re either forelimb structures or other tendons not forming the stay apparatus connection between the stifle and hock).