THE SUPINATOR BREVls. 89 



from the middle third or more of the ulna below the origin ; 

 anconeus, along the ulnar side of the extensor of the metacarpal 

 bone (fig. 36) ; and from the interosseous membrane below, for 

 about an inch. Its tendon, passing through a distinct sheath in the 

 annular ligament, deeply grooving the radius, is directed along 

 the dorsum of the thumb to be inserted into the base of the last insertion ; 

 phalanx. 



The belly of the muscle is covered by the extensor carpi ulnaris relations ; 

 and the extensors of the fingers, but the tendon becomes superficia. 

 close to the wrist. Below the annular ligament its tendon crosses 

 the extensors of the wrist and the radial artery. 



Action. It first extends both phalanges of the thumb, and and use. 

 then helps in moving backwards the metacarpal bone and the 

 hand. 



The EXTENSOR IXDICIS (indicator ; H) arises on the inner side of Indicator 

 the last muscle from the ulna for two or three inches (fig. 36), usually m 

 below the middle and from the lower part of the interosseous 

 membrane. Xear the wrist the tendon becomes free from muscular origin ; 

 fibres, and passing beneath the annular ligament with the common 

 extensor of the fingers, is applied to, and blends with the external insertion ; 

 tendon of that muscle in the expansion on the first phalanx of 

 the forefinger. 



Until this muscle has passed the ligament it is covered by the 

 superficial layer, but it is afterwards subaponeurotic. 



Action. The muscle can point the forefinger, even when the three and use. 

 inner fingers are bent ; and it will help the common extensor of the 

 digits in drawing back the hand. 



Dissection. To lay bare the supinator brevis, it will lie necessary Dissection 

 to detach the anconeus from the external condyle of the humerus, brevis!" 3 

 and to cut through the supinator longus and the radial extensors of 

 the wrist. After those muscles have been divided, the fleshy fibres 

 of the supinator are to be followed forwards to their insertion into 

 the radius ; and that part of the origin of the flexor profundus 

 digitorum which lies on the outer side of the insertion of the 

 brachialis anticus, is to be removed. 



The SUPIXATOR BREVIS (D) surrounds the upper part of the Origin of 

 radius, except at the tuberosity and the front of the bone below it. wtS-T^' 

 It arises from the external margin of the ulna for a distance of two 

 inches, as well as from a depression below the small sigmoid cavity ; 

 also from the orbicular ligament of the radius and the external 

 lateral ligament of the elbow-joint. The fibres pass outwards and 

 forwards, and are inserted into the upper third or more of the radius, and inser- 

 except at the fore and inner parts, reaching downwards to the tlon ' 

 insertion of the pronator teres, and forwards to the oblique line of 

 the bone (fig. 25, p. 61 ; and fig. 36). 



The supinator brevis is concealed altogether at the posterior and 

 external aspects of the limb by the muscles of the superficial layer ; 

 and anteriorly the radial vessels and nerve lie over it. The lower overlying 

 border is contiguous to the extensor ossis metacarpi pollicis, only and con- 

 the posterior interosseous vessels (a) intervening. Through the 



