Which structures form the hind limb reciprocal apparatus and coordinate stay mechanism?

Which structures form the hind limb reciprocal apparatus and coordinate stay mechanism?

• A. Lacertus fibrosus and extensor carpi radialis
• B. Suspensory ligament and distal sesamoidean ligaments
• C. Patellar locking mechanism
• D. Peroneus tertius and the superficial digital flexor tendon

Answer: (D)

The hind limb reciprocal apparatus is a mechanical link between the stifle and the hock that ensures they move in concert. The tendon of the peroneus tertius runs from the distal femur across both joints, so when the stifle flexes or extends, the hock follows in the same motion. The superficial digital flexor tendon runs along the caudal aspect of the limb and participates in this linkage, helping transmit movement and force across the joints. Because these two tendons cross both the stifle and hock, they synchronize joint action, producing coordinated movement during the gait and contributing to the stay mechanism by keeping joints aligned under load. Other options involve different structures (forelimb components, other ligaments, or separate stay mechanisms) that do not form this hind limb reciprocal linkage.