The EXTENSOR OSSIS METACARPI POLLICIS (abductor pollicis longus) is placed immediately below the supinator brevis. It arises from the ulna, interosseous membrane, and radius, and is inserted into the base of the metacarpal bone of the thumb. Its tendon passes through the groove immediately in front of the styloid process of the radius.

Relations. By its superficial surface with the extensor carpi ulnaris, extensor minimi digiti, extensor communis digitorum, fascia of the forearm and annular ligament. By its deep surface with the ulna, interosseous membrane, radius, tendons of the extensor carpi radialis longior and brevior, and supinator longus, and at the wrist with the radial artery. By its upper border with the edge of the supinator brevis; by its lower border with the extensor secundi and primi internodii. It is crossed by branches of the posterior interosseous artery and and nerve.

The EXTENSOR PRIMI INTERNODII POLLICIS (extensor pollicis brevis vel minor) the smallest of the muscles in this layer, arises from the interosseous membrane and radius, and passes through the groove with the extensor ossis metacarpi, to be inserted into the base of the first phalanx of the thumb.

Relations. The same as the preceding muscle, with the exception of the extensor carpi ulnaris. The muscle accompanies the extensor ossis metacarpi.

The EXTENSOR SECUNDI INTERNODII POLLICIS (extensor pollicis longus vel major) arises from the ulna, and interosseous membrane. Its tendon passes through a separate groove in the radius, and is inserted into the base of the last phalanx of the thumb.

Relations. By its external surface, the same as the extensor ossis metacarpi. By its deep surface with the ulna, interosseous membrane, radias, wrist joint, radial artery, and metacarpal bone of the thumb. The muscle is placed between the extensor primi internodii and extensor iudicis.

The EXTENSOR INDICIS (indicator) arises from the ulna, as high up as the extensor ossis metacarpi pollicis, and inferiorly from the interosseous membrane. Its tendon passes beneath the posterior annular ligament to be inserted into the aponeurosis of the common extensor tendon of the index finger.

Relations. The same as the preceding muscle, with the exception of the hand, where the tendon rests on the metacarpal bone of the fore finger and second interosseous muscle, and has no relation with the radial artery.

FIG. 182.

DEEP LAYER OF MUSCLES OF THE POSTERIOR ASPECT OF THE FOREARM. 1. Humerus. 2. Olecranon. 3. Ulna. 4. Anconeus. 5. Supinator brevis. 6. Extensor ossis metacarpi pollicis. 7. Extensor primi internodii pollicis. 8. Extensor secundi internodii pollicis. 9. Extensor indicis. 10. First dorsal interosseous muscle. The other three dorsal interossei are seen between the metacarpal bones of their respective fingers.

The tendons of the extensors, as of the flexor muscles of the forearm, are provided with synovial bursæ as they pass beneath the annular ligament: those of the back of the wrist have separate sheaths, formed by the posterior annular ligament.

Actions. The anconeus is associated in its action with the triceps extensor

cubiti: it assists in extending the forearm on the arm. The supinator longus and brevis effect the supination of the forearm, and antagonize the two pronators. The extensor carpi radialis longior and brevior and extensor carpi ulnaris, extend the wrist in opposition to the two flexors of the carpus. The extensor communis digitorum restores the fingers to the straight position after they have been flexed by the two flexors, sublimis and profundus. The extensor ossis metacarpi, primi internodii, and secundi internodii pollicis, are the special extensors of the thumb, and serve to balance the actions of the flexor ossis metacarpi, flexor brevis, and flexor longus pollicis. The extensor indicis produces extension of the index finger, and is therefore named "indicator," and the extensor minimi digiti supplies that finger with the power of exerting a distinct extension.

MUSCLES OF THE HAND.

Radial or Thenar Region.

Abductor pollicis,

Flexor ossis metacarpi (opponens),

Flexor brevis pollicis,
Adductor pollicis.

Dissection. The hand is best dissected by making an incision along the middle of the palm, from the wrist to the base of the middle finger, and crossing it at

96

FIG. 183.

13

MUSCLES OF THE HAND. 1. Annular ligament. 2, 2. Origin and insertion of the abductor pollicis muscle; its middle portion has been removed. 3. Flexor ossis metacarpi, or opponens pollicis. 4. Superficial portion of the flexor brevis pollicis. 5. Deep portion of the flexor brevis pollicis. 6. Adductor pollicis. 7, 7. The lumbricales muscles, arising from the deep flexor tendons, upon which the figures are placed. The tendons of the flexor sublimis have been removed. 8. One of the tendons of the deep flexor, passing between the two terminal slips of the tendon of the flexor sublimis to reach the last phalanx. 9. The tendon of the flexor longus pollicis, passing between the two portions of the flexor brevis to the last phalanx. 10. Abductor minimi digiti. 11. Flexor brevis minimi digiti. The edge of the adductor ossis metacarpi is seen projecting beyond the inner border of the flexor brevis. 12. Pisiform bone. 13. First dorsal interosseous muscle, the abductor indicis.

each extremity by a transverse incision, then turning aside the flaps of integuFor exposing the muscles of the radial region, the removal of the integument and fascia on the radial side will be sufficient.

ment.

The ABDUCTOR POLLICIS (brevis) is a small thin muscle, which arises from the trapezium bone and annular ligament. It is inserted into the base of the first phalanx of the thumb.

Relations. By its superficial surface with the external portion of the palmar fascia; by its deep surface with the flexor ossis metacarpi. At its inner side it is separated by a narrow cellular interspace from the flexor brevis pollicis. This muscle must be divided from its origin, and turned aside, in order to see the next. The FLEXOR OSSIS METACARPI (opponens pollicis) arises from the trapezium and annular ligament, and is inserted into the whole length of the metacarpal bone. Relations. By its superficial surface with the abductor pollicis. By its deep

Inter

surface with the trapezo-metacarpal articulation and metacarpal bone. nally with the flexor brevis pollicis. The flexor ossis metacarpi may now be divided from its origin and turned aside, in order to show the next muscle.

The FLEXOR BREVIS POLLICIS consists of two portions, between which lies the tendon of the flexor longus pollicis. The external portion arises from the trapezium and annular ligament; the internal portion from the trapezoides and os magnum. They are both inserted into the base of the first phalanx of the thumb, having a sesamoid bone in each of their tendons to protect the joint.

Relations. By its superficial surface with the external portion of the palmar fascia. By its deep surface with the adductor pollicis, tendon of the flexor carpi radialis, and trapezo-metacarpal articulation. By its external surface with the flexor ossis metacarpi and metacarpal bone. By its inner surface with the tendons of the long flexor muscles and first lumbricalis.

The ADDUCTOR POLLICIS is a triangular muscle; it arises by a broad origin from the metacarpal bone of the middle finger; the fibres converge to its insertion into the base of the first phalanx of the thumb, where it is united with the inner head of the flexor brevis.

Relations. By its anterior surface with the flexor brevis pollicis, tendons of the deep flexor of the fingers, lumbricales, and deep palmar arch. By its posterior surface with the metacarpal bones of the index and middle finger, the interossei of the second interosseous space, and the abductor indicis. Its inferior border is subcutaneous.

Ulnar or Hypothenar Region.

Palmaris brevis,

Abductor minimi digiti,

Flexor brevis minimi digiti,
Adductor ossis metacarpi.

Dissection. Turn aside the ulnar flap of integument from the palm of the hand; in doing this, a small subcutaneous muscle, the palmaris brevis, will be exposed. After examining this muscle, remove it with the deep fascia, in order to bring into view the muscles of the little finger.

The PALMARIS BREVIS is a thin plane of muscular fibres about an inch in width, which arises from the annular ligament and palmar fascia, and passes transversely inwards to be inserted into the integument of the inner border of the hand. Relations. By its superficial surface with the fat and integument of the ball of the little finger. By its deep surface with the ulnar portion of the palmar fascia, which separates it from the ulnar artery, veins, and nerve, and from the muscles of the inner border of the hand.

The ABDUCTOR MINIMI DIGITI is a small tapering muscle which arises from the pisiform bone, where it is continuous with the tendon of the flexor carpi ulnaris, and is inserted into the base of the first phalanx of the little finger, and into the expansion of the extensor tendon.

Relations. By its superficial surface with the internal portion of the deep fascia and palmaris brevis; by its deep surface with the adductor ossis metacarpi and metacarpal bone. By its inner border with the flexor brevis minimi digiti.

The FLEXOR BREVIS MINIMI DIGITI is a small muscle arising from the unciform bone and annular ligament, and inserted into the base of the first phalanx. It is sometimes wanting.

Relations. By its superficial surface with the internal portion of the palmar fascia, and palmaris brevis. By its deep surface with the adductor ossis metacarpi and metacarpal bone. Externally with the abductor minimi digiti, from which it is separated near its origin by the deep palmar branch of the ulnar nerve and communicating artery. Internally with the tendons of the flexor sublimis and profundus. The ADDUCTOR OSSIS METACARPI (opponens), or adductor minimi digiti, arises from the unciform bone and annular ligament; and is inserted into the whole length of the metacarpal bone of the little finger.

Relations.

- By its superficial surface with the flexor brevis and abductor minimi digiti. By its deep surface with the interossei muscles of the last metacarpal space, metacarpal bone, and flexor tendons of the little finger.

Palmar Region.
Lumbricales,

Interossei palmares,

Interossei dorsales.

The LUMBRICALES, four in number, are accessories to the deep flexor muscle. They arise from the tendons of the deep flexor; the first and second from the palmar side, the third from the ulnar, the fourth from the radial side; and are inserted into the aponeurotic expansion of the extensor tendons on the radial side of the fingers. The third, or that of the tendon of the ring finger, sometimes bifurcates, at other times it is inserted wholly into the extensor tendon of the middle finger.

Relations. - In the palm of the hand with the flexor tendons; at their insertion, with the tendons of the interossei and the metacarpo-phalangeal articulations.

The PALMAR INTEROSSEI, three in number, are placed upon the metacarpal bones, rather than between them. They arise from the base of the metacarpal bone of one finger, and are inserted into the base of the first phalanx and aponeurotic expansion of the extensor tendon of the same finger. The first belongs to the index finger; the second, to the ring finger; the third to the little finger; the middle finger being omitted.

Relations.

By their palmar surface with the flexor tendons and deep muscles in the palm of the hand. By their dorsal surface with the dorsal interossei. On one side with the metacarpal bone, on the other with the corresponding dorsal interosseous muscle.

[FIG. 184.

[FIG. 185.

PALMAR INTEROSSEOUS MUSCLES. 1. First palmar interosseous; adductor indicis. 2. Second palmar interosseous; adductor of the ring finger. 3. Third palmar interosseous; adductor of the little finger.]

DORSAL INTEROSSEI.

DORSAL INTEROSSEOUS MUSCLES. 1. First dorsal interosseous muscle; abductor indicis. 2, 3. Second and third dorsal interossei; both abductors of the mid-finger. 4. Fourth dorsal interosseous; abductor of the ring finger.]

Turning to the dorsum of the hand, the four dorsal interossei (bicipites) are seen in the four spaces between the metacarpal bones.

They are bipenniform muscles, and arise by two heads, from adjoining sides of the bases of the metacarpal bones. They are inserted into the base of the first phalanges, and into the aponeurosis of the extensor tendons.

The first is inserted into the index finger, and from its use is called abductor indicis; the second and third are inserted into the middle finger, compensating its exclusion from the palmar group; the fourth is attached to the ring finger; so that each finger is provided with two interossei, with the exception of the little finger, as may be shown by means of a table, thus:

Little finger, remaining palmar.

Relations. By their dorsal surface with a thin aponeurosis, the fascia dorsalis profunda, which separates them from the tendons on the dorsum of the hand. By their palmar surface with the muscles and tendons in the palm of the hand. By one side with the metacarpal bone; by the other with the corresponding palmar interosseous. The abductor indicis is in relation by its palmar surface, with the adductor pollicis and flexor brevis pollicis. The radial artery passes into the palm of the hand between the two heads of the first dorsal interosseous muscle (abductor indicis); and the perforating branches of the deep palmar arch, between the heads of the other dorsal interossei.

names.

Actions. The actions of the muscles of the hand are expressed in their Those of the radial region belong to the thumb, and provide for three of its movements, abduction, adduction, and flexion. The ulnar group, in like manner, are subservient to the same motions of the little finger, and the interossei are abductors and adductors of the several fingers. The lumbricales are accessory in their actions to the deep flexors; they were called by the earlier anatomists fidicinii, i. e., fiddlers' muscles, from an idea that they might effect the rapid movements by which the performer is enabled to produce the various notes on that instrument.

In relation to the axis of the hand, the four dorsal interossei are abductors, the three palmar adductors. It will therefore be seen that each finger is provided with its proper adductor and abductor, two flexors, and (with the exception of the middle and ring finger) two extensors. The thumb has moreover a flexor and extensor of the metacarpal bone; and the little finger a flexor of the metacarpal bone (opponens) without an extensor.

The actions of the muscles of the upper extremity, arranged after the plan of Dr. Barclay, are as follows: :