Which of the following best describes the action of the semimembranosus muscle?

• A. Adduct limb, flex stifle
• B. Extend hip, flex stifle
• C. Draw limb caudally, extend hip
• D. Flex tarsus, extend stifle

Answer: (B)

The semimembranosus muscle is primarily responsible for two key actions: extending the hip joint and flexing the stifle joint. It is one of the hamstring muscles located in the posterior compartment of the thigh, and it plays a significant role in the movement of the hind limb.

When the semimembranosus muscle contracts, it extends the hip, aiding in actions such as propulsion during locomotion. In addition, it flexes the stifle, which is necessary for activities such as crouching or changing direction while running. This dual functionality makes it an essential muscle for the overall mobility of the hind limb.

In contrast, the other options describe actions that do not accurately reflect the function of the semimembranosus muscle. For example, adducting the limb or extending the stifle are actions associated with different muscles. Therefore, describing the semimembranosus as both extending the hip and flexing the stifle aptly captures its primary roles in locomotion and movement efficiency.