Final answer:
The border of the popliteal fossa is formed by the tendons of the hamstring muscles including the biceps femoris, semimembranosus, and semitendinosus, as well as the gastrocnemius from the calf.
Step-by-step explanation:
The muscles that make up the border of the popliteal fossa are the tendons of the hamstring muscles from the posterior compartment of the thigh, which include the biceps femoris (laterally), semimembranosus, and semitendinosus (medially). Additionally, the calf muscles such as the gastrocnemius (superiorly) also contribute to the borders of the popliteal fossa. The popliteus muscle, found within the popliteal fossa, is responsible for flexing the leg at the knee and creates the floor of this space.