Origin by fleshy fibres from the outer (palmar) surface of the tendon common to the ulnar four parts of the profundus (c′).
Insertion (f′).—The four slips are flat at their origin. Each becomes cylindrical and curves about the base of one of the four ulnar digits and is inserted into the radial side of the base of the first phalanx close to its ventral border.
[Fig. 89].—Deep Muscles of the Palm of the Hand.
![[Fig. 89]](#3418956513767812439_illo184lg.jpg.id-3486675223777435876.wrap-0.html.html){kind=link}
a, M. flexor brevis pollicis; b, M. adductor pollicis; c, M. interosseus of second digit (M. flexor brevis digiti secundi); d, M. adductor digiti secundi; e, M. interosseus of third digit; f, M. interosseus of fourth digit; g, M. opponens digiti quinti; h, M. interosseus of fifth digit (M. flexor brevis digiti quinti); i, M. abductor digiti quinti. 1-5, the digits in order.
Action.—Bend the digits toward the radial side.
B. Muscles of the Thumb.
—M. abductor brevis pollicis ([Fig. 77], w) (includes also the opponens pollicis of man).—A very minute, probably rudimentary muscle.
Origin from the transverse ligament (1) which connects the prominent fibrous, hairless projection that lies over the pisiform bone with the radial border of the head of the radius. The muscle passes radiodistad and ends in a very slender tendon, the insertion of which is into the base of the first phalanx of the thumb.
M. flexor brevis pollicis ([Fig. 89], a).