Origin by fleshy fibres from the adjacent borders of the os magnum and scapholunar bones and from the fascia which bridges the intervening groove for the flexor carpi radialis.
Insertion by a short tendon into the base of the first phalanx of the pollex.
Action.—Flexor of the thumb.
M. adductor pollicis ([Fig. 89], b).
Origin by fleshy fibres from the ventral border of the os magnum. It curves about the base of the first metacarpal on its ulnar side to its insertion.
Insertion by fleshy fibres into the base of the first phalanx of the pollex on its ulnar side.
C. Muscles Lying between the Metacarpals.
—Mm. interossei ([Fig. 89]).—Small stout muscles lying on the palmar surfaces of the metacarpals of the second, third, fourth, and fifth digits.
Origin by fleshy fibres from the ventral or lateral surfaces of the bases of the metacarpals. Near the distal end of the metacarpal each divides into two masses which pass onto the lateral surfaces of the metacarpal, so as to leave the ventral surface of the distal end exposed.
Insertion partly onto the lateral surfaces of the base of the first phalanx and its sesamoids, and partly by a slender tendon ([Fig. 84], h) which is continued dorsad to join the extensor tendon of the digit.