This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Injuries of the large nerves of the forearm are followed by much disability. When these nerves are divided in wounds it is desirable to unite the ends immediately. The reunion of nerve-trunks which have been divided some time previously is also occasionally necessary.
These operations demand on the part of the surgeon an accurate knowledge of the topography of the part. For our purpose we may consider the nerves of the forearm as being of two kinds - trunks and branches. There are two main trunks - the median and the ulnar; the superficial (radial), and deep (interosseous) branches of the radial (musculospiral), and forearm branches of the median and ulnar form the second class. The main trunks simply traverse the forearm to be distributed in the hand, therefore injury to them shows itself by disabilities of the hand. The branches supplying the forearm, if of sensation, rarely give rise to any serious effects requiring surgical interference. The motor branches enter the muscles of the forearm so high up that paralysis usually is seen only when the nerves are injured in the region of the elbow or above. The high entrance is caused by the bellies of the muscles being above and the part below being tendinous (Fig. 331).
Fig. 331. - The nerves of the forearm.
The median nerve at the elbow-joint lies internal to the brachial artery, which lies next and internal to the biceps tendon. It lies on the brachialis anticus muscle and under the bicipital fascia. It crosses the ulnar artery obliquely a short distance below its origin. The artery curves toward the ulnar side while the nerve has a slight curve toward the radial side; between the two passes the ulnar head of the pronator radii teres muscle. The nerve then proceeds downward between the superficial and deep layers of muscles. It lies on the flexor profundus digitorum and is covered by the flexor sublimis; about 5 cm. above the annular ligament it becomes more superficial and lies in the interval between the palmaris longus and flexor carpi radialis tendons and touching them. It then passes under the annular ligament to enter the palm of the hand. A branch of the anterior interosseous artery called the comes nervi mediant accompanies the nerve in the forearm.
The median nerve gives off muscular, volar (anterior) interosseous, and palmar cutaneous branches, besides those in the hand.
The superficial flexor muscles, with the exception of the flexor carpi ulnaris, are supplied by branches directly from the main trunk near the elbow; the one to the pronator radii teres usually comes off above the elbow. The deep flexor muscles, with the exception of the inner half of the flexor profundus digitorum, are supplied by the volar ( anterior) interosseous branch.
The volar (anterior) interosseous nerve leaves the main trunk of the median just below the elbow and accompanies the volar (anterior) interosseous artery, lying on the interosseous membrane between the flexor longus pollicis and the flexor profundus digitorum. It supplies the flexor longus pollicis and radial half of the flexor profundus muscles as well as the pronator quadratus.
The palmar cutaneous branch is given off just above the annular ligament and comes to the surface between the palmaris longus and flexor carpi radialis tendons. It passes over the annular ligament to be distributed to the thenar eminence and palm of the hand.