Posterior Compartment, Upper Arm
In the upper arm’s posterior compartment, there are two muscles located behind the humerus. One of these muscles is called the triceps brachii or triceps, which plays a crucial role in stabilizing the shoulder joint and aiding in forearm extension and flexion. Unlike any other muscle in the back of the upper arm, the triceps brachii is composed of three heads. Another muscle in this compartment is the anconeus muscle, which is an extension of the triceps. The anconeus muscle is positioned across the elbow and assists in the extension of both the elbow and forearm rotation.
Superficial Layer Muscles of the Anterior Compartment in the Forearm
The muscles in the anterior compartment of the forearm are located on the inner side and have important roles in rotating the forearm, as well as flexing the wrist and fingers. This layer consists of four muscles.
Beginning with the ulnar side of the forearm, we have the flexor carpi ulnaris muscle. Its main function is to flex and adduct the wrist, bringing it closer to the body. Moving towards the center, we find the palmaris longus muscle, which is absent in approximately 10% of the population. This muscle plays a role in flexing the hand at the wrist.
Continuing further, we come across the flexor carpi radialis muscle. This muscle not only adducts the hand, but also flexes and adducts the wrist. Finally, we have the pronator teres muscle, which assists in forearm rotation by aiding pronation (turning the palm downward) and supination (turning the palm upward).