he Lateral head is located on the outward facing side of the humerus. This head is most responsible for the horseshoe shape of the Triceps.
The Medial head is located towards the midline of the body.
The Long head along the bottom side of the humerus and is that largest of the three heads.
The primary function of the Tricep is to extend the elbow (straightening the arm).
The secondary function of the Tricep is fulfilled only by the Long head of the muscle, which is the bring the arm down towards the body (adduction). The Tricep shares this function with the Latissimus Dorsi.