Which muscle passively extends the hock when the stifle is extended?

Which muscle passively extends the hock when the stifle is extended?

• A. Gastrocnemius
• B. Tibialis Anterior
• C. Peronius Tertius
• D. Superficial Digital Flexor

Answer: (C)

The key idea is the reciprocal mechanism that links the stifle and the hock, controlled by the peronius tertius. This tendon forms part of a system that keeps the knee and ankle moving together. When the stifle extends, tension in the peronius tertius pulls the hock into extension, so the hock extends passively without a separate muscle contraction. This coordinated action helps maintain a straight limb during weight-bearing and propulsion. The other muscles either act to actively move the joints (for example, there are muscles that extend or flex the hock when they contract) or influence other parts of the limb, but they don’t produce the passive stifle-to-hock extension that the peronius tertius does.

The key idea is the reciprocal mechanism that links the stifle and the hock, controlled by the peronius tertius. This tendon forms part of a system that keeps the knee and ankle moving together. When the stifle extends, tension in the peronius tertius pulls the hock into extension, so the hock extends passively without a separate muscle contraction. This coordinated action helps maintain a straight limb during weight-bearing and propulsion. The other muscles either act to actively move the joints (for example, there are muscles that extend or flex the hock when they contract) or influence other parts of the limb, but they don’t produce the passive stifle-to-hock extension that the peronius tertius does.