Anatomy of the arm

Anatomically speaking, the arm is the part of the upper limb that is between the shoulder and the elbow joint.

It has only one bone called the humerus, and an intricate network of muscles, vessels and nerves distributed around it.

The arm muscles are divided into two compartments separated by the humerus and the medial and lateral intermuscular septae.

The first one is the anterior compartment, and this one houses muscles responsible for elbow flexion. So it’s not a surprise that the anterior compartment is also called the flexor compartment.

Then there’s the posterior compartment. This one houses muscles responsible for elbow extension. So it’s also called the extensor compartment.

These two compartments mainly act on the elbow joint, but some muscles can also act on the glenohumeral joint.

Now, the anterior compartment contains three muscles: the biceps brachii or simply the biceps; the brachialis; and the coracobrachialis muscles. The biceps muscle usually has two heads, a short head and a long head.

The short head attaches to the coracoid process of the scapula and descends anteromedially to the head of the humerus, while the long head attaches to the supraglenoid process of the scapula and descends in the intertubercular or bicipital groove.

It is held in the bicipital groove by the transverse humeral ligament, which extends from the lesser to the greater tubercle of the humerus to turn the groove into a canal for the tendon of the long head.