Final answer:
The biceps brachii is a two-headed muscle that crosses the shoulder and elbow joints in a frog's arm. It flexes the forearm and assists in the supination of the forearm and flexion of the arm at the shoulder. The brachialis and brachioradialis muscles also play important roles in flexing the forearm.
Step-by-step explanation:
The biceps brachii is a two-headed muscle in the arm of a frog that crosses the shoulder and elbow joints. Its main functions are to flex the forearm and assist in supinating it, as well as flexing the arm at the shoulder. The deep muscle called brachialis provides additional power in flexing the forearm, while the brachioradialis muscle can flex the forearm quickly or help lift a load slowly.