278 DISSECTION OF THE HAND. 



The oprONENS POLLICIS, B, arises from the annular ligament beneath 

 the preceding, and from the os trapezium and its ridge ; it is inserted into 

 the front and outer border of the metacarpal bone for the whole length. 



This muscle is partly concealed by the preceding, though it projects on 

 the outer side. Along its inner border is the flexor brevis pollicis. An 

 insertion into the external sesamoid bone is described by Theile. 



Action. From its attachment to the metacarpal bone it is able to draw 

 that bone inwards over the palm of the hand, turning it at the same time, 

 so as to allow the ball of the thumb to be applied to the ball of each of the 

 fingers, as in picking up a pin. 



The FLEXOR BREVIS POLLICIS, c, is the largest of the short muscles of 

 the thumb : it consists of two pieces (inner and outer) at the insertion, but 

 these are united at the origin. Posteriorly it arises from the os trapezoides 

 and os magnum ; from the bases of the second and third metacarpal bones ; 

 and from the annular ligament, at the lower part. In front it is inserted 

 by two heads into the sides of the base of the first phalanx of the thumb, 

 the inner piece being united with the adductor, and the outer with the 

 abductor pollicis. A sesamoid bone is connected with each head at its 

 insertion. 



The tendon of the long flexor lies on this muscle, occupying the interval 

 between the processes of insertion ; and the deep palmar arch of the radial 

 artery issues from beneath the inner head. 



Action. The muscle bends the metacarpo-phalangeal joint, and assists 

 the ppponens in drawing the thumb forwards and inwards over the palm. 



The ADDUCTOR POLLICIS, D, is pointed at the thumb, and wide at the 

 opposite end. Its origin is fixed to the anterior or lower two-thirds of the 

 metacarpal bone of the middle digit, on the palmar aspect ; and its inser- 

 tion is attached, with that of the short flexor, to the inner side of the first 

 phalanx of the thumb. 



The cutaneous surface is in contact with the tendons of the flexor pro- 

 fundus and the lumbrical muscles ; and the deep surface lies over (in this 

 position) the first dorsal iriterosseous muscle, J, and the second and third 

 metacarpal bones with the intervening muscle. 



Actions. By its contraction the thumb is applied to the radial border of 

 the hand, and approximated to the fingers. 



SHORT MUSCLES OF THE LITTLE FINGER (fig. 84). There are com- 

 monly two muscles in the ball of the little finger, an abductor and an 

 adductor. Sometimes there is a short flexor between the other two. 



The ABDUCTOR MINIMI DIGIT!, E, is the most internal of the short 

 muscles. It arises from the pisiform bone and the tendon of the flexor 

 carpi ulnaris, and is inserted into the ulnar side of the base of the first 

 phalanx of the little finger; an offset from it reaches the extensor tendon 

 on the back of the phalanx. The palmaris brevis partly conceals the 

 muscle. 



Action. First it draws the little finger away from the others ; but con- 

 tinuing to act it bends the metacarpo-phalangeal joint. 



The FLEXOR BREVIS MINIMI DIGITI, F, appears often to be a part of 

 the abductor. Placed at the radial border of the preceding muscle, it 

 takes origin from the tip of the process of the unciform bone, and slightly 

 from the annular ligament ; it is inserted with the abductor into the first 

 phalanx. 



It lies on the adductor ; and near its origin it is separated from the 

 abductor muscle by the deep branches of the ulnar artery and nerve. 



