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.
The flexor tendons cover the wrist anteriorly and the extensors posteriorly. With the flexor group we may consider the pronator quadratus. A third or radial group comprises the extensor carpi radialis longior and brevior and the brachioradialis.
The tendons on the front of the wrist occupy four different planes or levels. The most superficial layer embraces the flexor carpi radialis, the palmaris longus, and the flexor carpi ulnaris. Of these three the palmaris longus is the nearest to the skin as it inserts in the palmar fascia in front of the annular ligament. The flexor carpi radialis slips under the upper portion of the annular ligament to insert into the base of the second metacarpal bone. The flexor carpi ulnaris inserts into the pisiform bone and continues onward to the base of the fifth metacarpal bone and the unciform process of the unciform bone.
Fig. 345. - Dissection showing the fascias of the anterior portion of the wrist. The superficial layer is continuous with the palmaris longus muscle and palmar fascia; the deep layer is continuous with the anterior annular ligament.
The second layer of tendons is composed of the four tendons of the flexor sub-limis digitorum. They fill the space between the palmaris longus and the flexor carpi ulnaris.
The third layer is composed of the four tendons of the flexor profundus digitorum toward the ulnar side and the flexor longus pollicis toward the radial side.
The fourth and last layer is formed by the pronator quadratus. This lies directly on the bones and covers their lower fourth.
It is sometimes necessary to divide these tendons in cases of contraction of the wrist, hence the desirability of being able to recognize and locate them.
The deep fascia covering the anterior muscles of the forearm is comparatively thin. As it approaches the wrist it divides into two layers. The superficial layer is thin and runs over the tendons of the palmaris longus and flexor carpi radialis muscles and the ulnar artery and nerve. It is continuous below with the palmar fascia. To the ulnar side it passes over the flexor carpi ulnaris muscle to be continuous with the posterior annular ligament. It is not attached to the ulna, but slides over it as it follows the movements of the hand in pronation and supination (Fig. 345).
The deep layer of the deep fascia covers the flexor sublimis digitorum and passes downward beneath the flexor carpi radialis and brachioradialis muscles. It is continuous below with the anterior annular ligament.
The deep layer blends with the superficial layer to the radial side of the flexor carpi radialis, and then merges with the posterior annular ligament to form the sheath of two of the extensor muscles of the thumb.
On the ulnar side the deep layer passes over the ulnar artery and vein and under the flexor and extensor carpi ulnaris muscles, forming the posterior portion of their sheaths, and then merges with the posterior annular ligament.
The anterior annular ligament is attached on the ulnar side to the pisiform bone and unciform process of the unciform bone and on the radial side to the trapezium and tuberosity of the navicular (scaphoid).
Beneath the annular ligament pass the median nerve, the flexor sublimis, flexor profundus, and flexor longus pol-licis tendons. These tendons are embraced in two sheaths, one for the flexor longus pollicis and the other for the flexors of the other four fingers, the sheath for the little finger extending to the insertion of the profundus tendon into the distal phalanx. The tendinous sheaths accompany the tendons for a distance of 2.5 to 5 cm. (1 to 2 in.) above the annular ligament. Posteriorly. - On the posterior surface of the wrist the tendons may be divided into two groups, an extensor group and a radial group. The extensor group is divided into a superficial and deep set. The superficial set is composed of the extensor communis digitorum, the extensor minimi digiti and the extensor carpi ulnaris. The deep set is composed of the extensor ossis metacarpi pollicis, extensor brevis pollicis, extensor longus pollicis, and extensor indicis. The radial group, on the posterior and outer surface of the radius, is composed of the extensor carpi radialis longior, the extensor carpi radialis brevior, and the brachioradialis (Fig. 346). The first two lie beneath the deep extensor muscles, thus practically forming a third layer. All the tendons of the posterior and radial group of muscles, with the exception of the brachioradialis, pass beneath the posterior annular ligament into the hand. The brachioradialis inserts into the base of the styloid process of the radius.