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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
  The Adductor pollicis (obliquus) (Adductor obliquus pollicis) arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the Flexor carpi radialis. From this origin the greater number of fibers pass obliquely downward and converge to a tendon, which, uniting with the tendons of the medial portion of the Flexor pollicis brevis and the transverse part of the Adductor, is inserted into the ulnar side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon. A considerable fasciculus, however, passes more obliquely beneath the tendon of the Flexor pollicis longus to join the lateral portion of the Flexor brevis and the Abductor pollicis brevis.


FIG. 426– The muscles of the thumb. (See enlarged image)

  The Adductor pollicis (transversus) (Adductor transversus pollicis) (Fig. 426) is the most deeply seated of this group of muscles. It is of a triangular form arising by a broad base from the lower two-thirds of the volar surface of the third metacarpal bone; the fibers converge, to be inserted with the medial part of the Flexor pollicis brevis and the Adductor pollicis (obliquus) into the ulnar side of the base of the first phalanx of the thumb.

Variations.—The Abductor pollicis brevis is often divided into an outer and an inner part; accessory slips from the tendon of the Abductor pollicis longus or Palmaris longus, more rarely from the Extensor carpi radialis longus, from the styloid process or Opponens pollicis or from the skin over the thenar eminence. The deep head of the Flexor pollicis brevis may be absent or enlarged. The two adductors vary in their relative extent and in the closeness of their connection. The Adductor obliquus may receive a slip from the transverse metacarpal ligament.

Nerves.—The Abductor brevis, Opponens, and lateral head of the Flexor pollicis brevis are supplied by the sixth and seventh cervical nerves through the median nerve; the medial head of the Flexor brevis, and the Adductor, by the eighth cervical through the ulnar nerve.

Actions.—The Abductor pollicis brevis draws the thumb forward in a plane at right angles to that of the palm of the hand. The Adductor pollicis is the opponent of this muscle, and approximates the thumb to the palm. The Opponens pollicis flexes the metacarpal bone, i. e., draws it medialward over the palm; the Flexor pollicis brevis flexes and adducts the proximal phalanx.

2. The Medial Volar Muscles (Figs. 426, 427)
Palmaris brevis.
Flexor digiti quinti brevis.
Abductor digiti quinti.
Opponens digiti quinti.

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