Ii7^ A MANUAL OF ANATOMY 



The muscle supports the abductor poUicis, and has the superficial 

 head of the flexor brevis pollicis along its inner border. 



3. Flexor Brevis Pollicis. — This muscle arises by two heads — a 

 large superficial or outer, and a small deep or inner. The super- 

 ficial head arises from the outer two-thirds of the lower border of 

 the anterior annular ligament, and the tuberosity of the trapezium. 

 The deep head (interosseus primus volaris) arises from the proximal 

 extremity of the first metacarpal bone on its inner aspect. 



Insertion. — The superficial head, along with the abductor pollicis, 

 is inserted into the outer side of the base of the first phalanx of 

 the thumb, a sesamoid bone being contained within it. The deep 

 head joins the adductor obliquus pollicis, and, along with it, is 

 inserted into the inner side of the base of the first phalanx of the 

 thumb. 



Nerve-supply. — The superficial head is supplied by the median 

 nerve, and the deep head by the deep division of the ulnar 

 nerve. 



Action. — To flex the metacarpo-phalangeal joint of the thumb, 

 and so to assist in opposition. 



4. Adductor Obliquus Pollicis — Origin. — By several bundles from 

 (i) the fronts of the bases of the second and third metacarpal bones ; 

 (2) the fronts of the trapezoid and os magnum ; and (3) the sheath 

 of the tendon of the flexor carpi radialis. 



Insertion. — ^The muscle, having received the small deep head of 

 the flexor brevis pollicis, is inserted, along with the adductor trans- 

 versus pollicis, into the inner side of the base of the first phalanx 

 of the thumb, a sesamoid bone being contained within it. 



In its course the muscle detaches, from its outer side, a large 

 fleshy bundle, which passes outwards behind the tendon of the 

 flexor longus pollicis and joins the superficial head of the flexor 

 brevis pollicis. 



Nerve-supply. — The deep division of the ulnar nerve. 



The muscle is directed downwards and outwards. 



Action. — To adduct the thumb and assist in opposition. 



The muscle has the superficial head of the flexor brevis pollicis on 

 its outer side, the tendon of the flexor longus pollicis lying between 

 the two, and the adductor transversus pollicis along its inner and 

 lower aspect, the radial artery passing between the two. 



5. Adductor Transversus PoUicis — Origin. — ^The distal two-thirds 

 of the anterior border of the shaft of the third metacarpal bone. 



Insertion. — (i) The inner side of the base of the first phalanx of the 

 thumb, along with the adductor obliquus pollicis and deep head of 

 the flexor brevis pollicis ; and (2) the inner margin of the tendon of 

 the extensor longus pollicis on the back of that phalanx. 



Nerve- supply. — The deep division of the ulnar nerve. 



The muscle, which is triangular, is directed outwards. 



Action. — ^To adduct the thumb and assist in opposition. It also 

 assists in extending the distal phalanx. 



The tendon of the flexor longus pollicis on its way to its insertion 



