The triceps brachii is a muscle located along the back of the humerus (upper arm bone) that is responsible for extension of the forearm. It is divided into three sections, the medial, lateral, & long head.
The biceps brachii is divided into two sections, the short & long head. It crosses the shoulder joint & assists in medial rotation, abduction, adduction, & flexion. In the elbow joint, it can also flex & supinate (rotate) the forearm.