Ans. The posterior compartment is another compartment located in the upper I'm along with the anterior compartment. This compartment has a single muscle. Triceps Brachii is the name of the muscle. This muscle has three heads. That's the reason it is known as triceps. Long headMedial headLateral headThe major function of the Triceps Brachii is to extend the arm from the elbow. All three heads of triceps brachii originated and are linked to the internal parts of the shoulder and elbow.