316 MUSCLES AND FASCIA. 



4. To the inner side of the latter, for the tendons of the Extensor communis 

 digitorum, and Extensor indicis. 5. For the Extensor minimi digiti, opposite the 

 interval between the radius and ulna. 6. For the tendon of the Extensor carpi 

 ulnaris, grooving the back of the ulna. The synovial membranes lining these 

 sheaths are usually very extensive, reaching from above the annular ligament 

 down upon the tendons, almost to their insertion. 



The palmar fascia forms a common sheath which invests the muscles of the 

 hand. It consists of a central and two lateral portions. 



The central portion occupies the middle of the palm, is triangular in shape, of 

 great strength and thickness, and binds down the tendons in this situation. It is 

 narrow above, being attached to the lower, margin of the annular ligament, and 

 receives the expanded tendon of the Palmaris longus muscle. Below, it is broad 

 and expanded, and opposite the heads of the metacarpal bones divides into four 

 slips, for the four fingers. Each slip subdivides into two processes, which inclose 

 the tendons of the Flexor muscles, and are attached to the sides of the first pha- 

 lanx, and to the glenoid ligament ; by this arrangement, four arches are formed, 

 under which the Flexor tendons pass. The intervals left in the fascia between 

 the four fibrous slips transmit the digital vessels and nerves, and the tendons of 

 the Lumbricales. At the point of division of the palmar fascia into the slips above 

 mentioned, numerous strong transverse fibres bind the separate processes together. 

 The palmar fascia is intimately adherent to the integument by numerous fibrous 

 bands, and gives origin by its inner margin to the Palmaris brevis ; it covers the 

 superficial palmar arch, the tendons of the 'Flexor muscles, and the branches of the 

 median and ulnar nerves; and on each side it gives off a vertical septum, which 

 is continuous with the interosseous aponeurosis, and separates the lateral from the 

 middle palmar group of muscles. 



The lateral portions of the palmar fascia are thin fibrous layers, which cover, 

 on the radial side, the muscles of the ball of the thumb ; and, on the ulnar side, 

 the muscles of the little finger ; they are continuous with the dorsal fascia, and in 

 the palm, with the middle portion of the palmar fascia. 



MUSCLES OF THE HAND. 



The muscles of the hand are subdivided into three groups. 1. Those of the 

 thumb, which occupy the radial side. 2. Those of the little finger, which occupy 

 the ulnar side. 3. Those in the middle of the palm and between the interosseous 

 spaces. 



EADIAL EEGIOIST. 



Muscles of the Thumb. 



Abductor Pollicis. 



Opponens Pollicis or Flexor Ossis Metacarpi. 



Flexor Brevis Pollicis. 



Adductor Pollicis. 



The Abductor Pollicis is a thin, flat muscle, placed immediately beneath the 

 integument. It arises from the ridge of the os trapezium and annular ligament ; 

 and, passing outwards and downwards, is inserted by a thin, flat tendon into the 

 radial side of the base of the first phalanx of the thumb. 



Relations. By its superficial surface, with the palmar fascia. By its deep sur- 

 face, with the Opponens pollicis, from which it is separated by a thin aponeurosis. 

 Its inner border is separated from the Flexor brevis pollicis by a narrow cellular 

 interval. 



The Opponens Pollicis is a small triangular muscle, placed beneath the pre- 

 ceding. It arises from the palmar surface of the trapezium and annular ligament : 

 passing downwards and outwards, it is inserted into the whole length of the meta- 

 carpal bone of the thumb on its radial side. 



Relations. By its superficial surface, with the Abductor pollicis. By its deep 



