IV. Muscles of the Forearm
The forearm, or antebrachium, contains many more muscles than the arm. There are at least twenty that you need to be aware of. These muscles are responsible for movement of the forearm, wrist, and digits. You need to know both the general location and function of these muscles. As in the arm, the muscles of the forearm fall into two groups- a flexor/pronator group and an extensor/supinator group. The flexor/pronator group occupies the anterior compartment of the forearm. This group of muscles arises from or in line with the medial epicondyle of the humerus, which is known as the common flexor attachment. The extensor/supinator group occupies the posterior compartment of the forearm. This group of muscles arises from or in line with the lateral epicondyle of the humerus, which is known as the common extensor attachment. Use the information on the following pages to become familiar with the important terms below.
Anterior Muscles of the Forearm
The anterior muscles of the forearm fall into the flexor/pronator group. The superficial flexor muscles all arise from a common tendon attached to the medial epicondyle of the humerus, known as the common flexor attachment. You can verify this for yourself by palpating the medial epicondyle as you flex your wrist and fingers. The deeper flexor muscles do not actually arise from the medial epicondyle, but their origins are in line with it (as you will see in the diagrams on the following pagers). All of the flexor muscle, except for the brachioradialis (which is supplied by the radial nerve), are supplied by the median and ulnar nerve. The distal tendons of these muscles cross the anterior surface of the wrist. Most of these tendons are held in place by the flexor retinaculum, a thickening of the deep fascia of the forearm. The anterior muscles of the forearm can be divided into three functional groups based on whether they pronate the forearm, flex the hand, or flex the digits.
Functional groups
These muscles can also be divided into three groups based on location. There are four superficial muscles (which all arise from a common tendon), one intermediate muscle, and three deep muscles.
Anatomical Groups
Superficial and Intermediate Muscles of the Anterior Forearm
The following diagrams and chart provide information about the intermediate and superficial flexor muscles. Try to visualize how the attachments demonstrated in the diagrams account for the functions described in the chart.
Surface Anatomy of the Anterior Forearm
The following two pictures should help you relate what you know about the superficial flexor muscles to what you can observe on your own forearm. The top picture demonstrates how to locate the position of the four superficial flexor muscles. The thumb of the person's left hand is placed posterior to the elbow, around the medial epicondyle of the humerus, to which the common flexor tendon of these muscles is attached. The fingers represent the positions of the muscles. The bottom picture demonstrates important surface landmarks at the wrist.
The following diagrams and chart provide information about the deep flexor muscles of the forearm. Note that none of them arise from the common flexor attachment. Again, try to visualize how the attachments demonstrated in the diagrams account for the functions described in the chart.
Anterior Muscles of the Forearm
Posterior Muscles of the Forearm
There are twelve muscles in the posterior forearm. Nine of these are extensors of the forearm and hand. The three exceptions are the brachioradialis, anconeus, and supinator. The brachioradialis is actually a flexor of the forearm, but is included here because it is innervated by the radial nerve. We already encountered the anconeus muscle when we discussed extensors of the arm. The supinator muscle supinates the forearm, but is also innervated by the radial nerve. The remaining nine muscles are all extensors and are all innervated by the radial nerve. The superficial extensors originate at or near the lateral epicondyle, known as the common extensor attachment. The distal tendons of these muscles cross the posterior wrist where they are held in place by the extensor retinaculum. These nine muscles can be divided into three functional groups based on whether they extend the hand, fingers, or thumb.
Functional goups:
Use the diagrams and charts on the following pages to correlate the attachments of the above muscles with their functions. It's not necessary to memorize the attachments but try to understand how shortening of each muscle causes extension of the hand, fingers, or thumb.
Superficial Muscles of the Posterior Forearm
Deep Muscles of the Posterior Forearm
Muscles of the Posterior Forearm
