456 MYOLOGY 



tendons of the Abductor pollicis longus and of the Extensores pollicis long 

 brevis. 



The Extensor indicis proprius (Extensor indicis) is a narrow, elongated muscle, 

 placed medial to, and parallel with, the preceding. It arises, from the dorsal sur- 

 face of the body of the ulna below the origin "of the Extensor pollicis longus, and 

 from the interosseous membrane. Its tendon passes under the dorsal carpal 

 ligament in the same compartment as that which transmits the tendons of the 

 Extensor digitorum communis, and opposite the head of the second metacarpal 

 bone, joins the ulnar side of the tendon of the Extensor digitorum communis 

 which belongs to the index finger. 



Variations. Doubling; the ulnar part may pass beneath the dorsal carpal ligament with the 

 Extensor digitorum communis; a slip from the tendon may pass to the index finger. 



Nerves. The Brachioradialis is supplied by the fifth and sixth, the Extensores carpi radialis 

 longus and brevis by the sixth and seventh, and the Anconseus by the seventh and eighth cervical 

 nerves, through the radial nerve; 'the remaining muscles are innervated through the deep radial 

 nerve, the Supinator being supplied by the sixth, and all the other muscles by the seventh cervical. 



Actions. The muscles of the lateral and dorsal aspects of the forearm, which comprise all 

 the Extensor muscles and the Supinator, act upon the forearm, wrist, and hand; they are the 

 direct antagonists of the Pronator and Flexor muscles. The Anconams assists the Triceps in 

 extending the forearm. The Brachioradialis is a flexor of the elbow-joint, but only acts as such 

 when the movement of flexion has been initiated by the Biceps brachii and Brachialis. The 

 action of the Supinator is 'suggested by its name; it assists the Biceps in bringing the hand into 

 the supine position. The Extensor carpi' radialis longus extends the wrist and abducts the hand. 

 It may also assist in bending the elbow-joint; at all events it serves to fix or steady this' articula- 

 tion. The Extensor carpi'radialis brevis extends the wrist, and may also act slightly as an abductor 

 of the hand. The Extensor carpi ulnaris extends the wrist, but when acting alone inclines the 

 hand toward the ulnar side; by its continued action it extends the elbow-joint. The Extensor 

 digitorum communis extends the phalanges, then the wrist, and finally the elbow. It acts prin- 

 cipally on the proximal phalanges, the middle and terminal phalanges being extended mainly 

 by the Interossei and Lumbricales. It tends to separate the fingers as it extends them. The 

 Extensor digiti quinti proprius extends the little finger, and by its continued action assists in 

 extending the wrist. It is owing to this muscle that the little finger can be extended or pointed 

 while the others are flexed. The chief action of the Abductor pollicis longus is to carry the thumb 

 laterally from the palm of the hand. By its continued action it helps to extend and abduct the 

 wrist. The Extensor pollicis brevis extends the proximal phalanx, and the Extensor pollicis 

 longus the terminal phalanx of the thumb; by their continued action they help to extend and 

 abduct the wrist. The Extensor indicis proprius extends the index finger, and by its continued 

 action assists in extending the wrist. 



VI. THE MUSCLES AND FASCIA OF THE HAND. 



The muscles of the hand are subdivided into three groups: (1) those of the 

 thumb, which occupy the radial side and produce the thenar eminence ; (2) those 

 of the little finger, which occupy the ulnar side and give rise to the hypothenar 

 eminence ; (3) those in the middle of the palm and between the metacarpal bones. 



Volar Carpal Ligament (ligamentum carpi wlare). The volar carpal ligament 

 is the thickened band of antibrachial fascia which extends from the radius to the 

 ulna over the Flexor tendons as they enter the wrist. 



Transverse Carpal Ligament (ligamentum carpi transversum; anterior annular 

 ligament) (Figs. 421, 422). The transverse carpal ligament is a strong, fibrous 

 band, which arches over the carpus, converting the deep groove on the front of 

 the carpal bones into a tunnel, through which the Flexor tendons of the digits 

 and the median nerve pass. It is attached, medially, to the pisiform and the 

 hamulus of the hamate bone; laterally, to the tuberosity of the navicular, and to 

 the medial part of the volar surface and the ridge of the greater multangular. It 

 is continuous, above, with the volar carpal ligament; and below, with the palmar 

 aponeurosis. It is crossed by the ulnar vessels and nerve, and the cutaneous 

 branches of the median and ulnar nerves. At its lateral end is the tendon of the 





