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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
  The Flexor digiti quinti brevis (Flexor brevis minimi digiti) lies on the same plane as the preceding muscle, on its radial side. It arises from the convex surface of the hamulus of the hamate bone, and the volar surface of the transverse carpal ligament, and is inserted into the ulnar side of the base of the first phalanx of the little finger. It is separated from the Abductor, at its origin, by the deep branches of the ulnar artery and nerve. This muscle is sometimes wanting; the Abductor is then, usually, of large size.
  The Opponens digiti quinti (Opponens minimi digiti) (Fig. 426) is of a triangular form, and placed immediately beneath the preceding muscles. It arises from the convexity of the hamulus of the hamate bone, and contiguous portion of the transverse carpal ligament; it is inserted into the whole length of the metacarpal bone of the little finger, along its ulnar margin.

Variations.—The Palmaris brevis varies greatly in size. The Abductor digiti quinti may be divided into two or three slips or united with the Flexor digiti quinti brevis. Accessory head from the tendon of the Flexor carpi ulnaris, the transverse carpal ligament, the fascia of the forearm or the tendon of the Palmaris longus. A portion of the muscle may insert into the metacarpal, or separate slips the Pisimetacarpus, Pisiuncinatus or the Pisiannularis muscle may exist.

Nerves.—All the muscles of this group are supplied by the eighth cervical nerve through the ulnar nerve.

Actions.—The Abductor and Flexor digiti quinti brevis abduct the little finger from the ring finger and assist in flexing the proximal phalanx. The Opponens digiti quinti draws forward the fifth metacarpal bone, so as to deepen the hollow of the palm. The Palmaris brevis corrugates the skin on the ulnar side of the palm.

3. The Intermediate Muscles
Lumbricales.Interossei.
  The Lumbricales (Fig. 427) are four small fleshy fasciculi, associated with the tendons of the Flexor digitorum profundus. The first and second arise from the radial sides and volar surfaces of the tendons of the index and middle fingers respectively; the third, from the contiguous sides of the tendons of the middle and ring fingers; and the fourth, from the contiguous sides of the tendons of the ring and little fingers. Each passes to the radial side of the corresponding finger, and opposite the metacarpophalangeal articulation is inserted into the tendinous expansion of the Extensor digitorum communis covering the dorsal aspect of the finger.

Variations.—The Lumbricales vary in number from two to five or six and there is considerable variation in insertions.
  The Interossei (Figs. 428, 429) are so named from occupying the intervals between the metacarpal bones, and are divided into two sets, a dorsal and a volar.
  The Interossei dorsales (Dorsal interossei) are four in number, and occupy the intervals between the metacarpal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metacarpal bones, but more extensively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the first phalanges and into the aponeuroses of the tendons of the Extensor digitorum communis. Between the double origin of each of these muscles is a narrow triangular interval; through the first of these the radial artery passes; through each of the other three a perforating branch from the deep volar arch is transmitted.
  The first or Abductor indicis is larger than the others. It is flat, triangular in form, and arises by two heads, separated by a fibrous arch for the passage of the radial artery from the dorsum to the palm of the hand. The lateral head arises from the proximal half of the ulnar border of the first metacarpal bone; the medial head, from almost the entire length of the radial border of the second metacarpal bone; the tendon is inserted into the radial side of the index finger. The second

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