Final answer:
The triceps brachii and anconeus muscles function to extend the forearm at the elbow joint, with the triceps providing the primary force for extension and the anconeus assisting in this movement.
Step-by-step explanation:
The function performed by the triceps brachii and anconeus muscles is to extend the forearm at the elbow joint. The triceps brachii is a three-headed muscle that actively contributes to this extension, while the anconeus assists in this action. In contrast to the biceps brachii, which acts as a flexor of the elbow joint, the triceps brachii serves as an extensor and opposes the flexion motion created by the biceps.
During daily routines, these muscles are not used equally; for example, we tend to use our biceps more due to lifting against gravity. However, when you need to straighten your arm, the triceps brachii contracts and this contraction is aided by the small anconeus muscle, providing a coordinated extension of the forearm.