Fig. 11- 2. Horizontal sections through the hand. A is through the metacarpals and shows the palmar aponeurosis and the "mid palmar" and "thenar" spaces separated from each other by an oblique septum attached to M.C.3. Actually there are many such septa tending to subdivide the central compartment. The superficial palmar arch and the digital branches of the median nerve (not shown) lie between the palmar aponeurosis and the flexor tendons. Ab.P.B., abductor pollicis brevis; F.D.P., flexor digitorum profundus; F.D.5., flexor digitorum superficialis; F.P.B., flexor pollicis brevis; F.P.L., flexor pollicis longus; Op.P., opponens pollicis. B is through the distal row of carpal bones and shows the flexor retinaculum and the carpal tunnel (or canal), which contains the median nerve and the flexor tendons. The ulnar nerve and artery pass anterior to the flexor retinaculum, although they are covered by a fascial layer and the palmaris brevis. The extensor tendons have been omitted from both drawings. The inset shows the palmar aponeurosis, palmaris longus, and flexor retinaculum, as well as the levels of the sections. (Modified from Castaing and Soutoul.) For a section at C, see fig. 10-5. Click for high resolution image.