WINGS OF BIRDS. 
19 
the length of the radius. Its action is to bend the fore-arm obliquely dowm- 
wards and inwards. 
The small muscles on the hand may be described afterwards. Let us now 
turn to the upper surface of the cubitus, seen in Fig. 1. 
The most external muscle of which a portion is seen along and behind the 
ulna, is the flexor carpi ulnar 16 , already described. 
22. The next muscle is the extensor carpi ulnaris^ which arises from the lower 
extremity of the outer condyle of the humerus, runs along the middle of the 
fore-arm, with the ulna immediately behind, and terminates in a long slender 
tendon, which passes over a pulley at the extremity of the ulna, and is inserted 
into the posterior edge of the radial metacarpal bone. Its action is to extend the 
hand, and, when extended, to bring it upwards. It is not by any means an 
adductor of the hand, as stated in various books. 
' 23. Extensor primi digiti^ arises from the outer condyle of the humerus, runs 
along the fore-arm, parallel and anterior to the last, and forms a very slender 
tendon, which, passing over that of the next muscle, goes to be inserted into the 
base of the bone of the first finger, which it draws upwards and backwards. 
24. Extensor digitorum arises from the outer condyle of the humerus, and from 
the anterior edge of the ulna, and the posterior edge of the radius; its tendon 
passes over the wrist joint, and runs along the radial metacarpal bone, to be in¬ 
serted into the last phalanx. Sometimes several slips are given off by this ten¬ 
don. It pulls the hand or pinion upwards and outwards. 
25. Extensor carpi radialis brevis arises also from the inner condyle, and from 
nearly the whole length of the inner edge of the radius, and is inserted by a 
slender tendon into the prominence at the base of the metacarpal bone, near that 
of the extensor carpi radialis longior, 15, already described, which is the muscle on 
the anterior edge of the fore-arm. 
There now remain the small muscles on the hand. 
The first finger, g^ has three muscles. 
26*— Flexor primi digiti arises from the base of the radial metacarpal bone, 
and is inserted into that of the first finger, which it draws downwards. 
27— Adductor primi digiti arises from the metacarpal bone, and is inserted 
along the inner or posterior edge of that of the first finger, which it draws towards 
the next. 
28. — Abductor primi digiti arises from the insertion of the tendon of the 
supinator radii longus, 15, and draws the first finger outwards from the second. 
29. — Abductor digiti majoris arises from the whole length of the outer edge of the 
radial metacarpal bone, and is inserted into the base of the first phalanx, which 
it draws forward. 
ZO*’—Adductor digiti arises from the ulnar carpal bone, and the whole length of 
