Part 36

Action.—Assists in flexing the forearm upon the arm. Protects the structures in the anterior part of the elbow-joint.

THE MUSCLES OF THE FOREARM AND THE HAND

Extensor metacarpi radialis longior Supinator brevis Extensor digitorum communis Pronator brevis Flexor metacarpi radialis Extensor ossis metacarpi pollicis Pronator longus Extensor indicis longus Flexor digitorum sublimis Flexor digitorum profundus Flexor carpi ulnaris Flexor carpi ulnaris brevior

=Extensor Metacarpi Radialis Longior= (Fig. 13, No. 17). Location.—Superior to the radius.

Origin.—By two strong tendinous heads; the outer from the tubercle of the external condyle of the humerus, just above the origin of the tendon of the tensor patagii brevis; the inner and stronger portion from the tubercle found above the oblique trochlear facet of the distal end of the radius.

Insertion.—Becoming a flat, broad, and strong tendon at about the middle of the forearm, finally becomes inserted to the apex of the anchylosed first metacarpal of the carpo-metacarpus.

Shape.—A thick, fusiform belly, tendinous at both extremities.

Relations.—By the side of the pronator brevis.

Action.—Raises the hand, and draws it forward toward the radial margin of the forearm and retains it on the same side.

=Extensor Digitorum Communis= (Fig. 15, No. 2). Location.—The upper metacarpal region.

Origin.—Immediately below the tubercle of the external condyle of the humerus.

Insertion.—By a small tendon to the outer side of the base of the pollex, and at a mid-point upon the anterior rim of the proximal phalanx of the middle finger.

Shape.—Small spindle-shaped, becoming tendinous at about the middle of the forearm.

Relations.—Occupies the middle of the group of muscles on the outer side of the forearm.

Action.—An extensor of the digit.

=Supinator Brevis= (Fig. 14, No. 7). Location.—The superior part of the radius.

Origin.—From the external condyle of the humerus below the origin of the tendon of the extensor digitorum communis.

Insertion.—To the outer side of the shaft of the radius, for nearly one-third of its length.

Shape.—Thin, slender.

Relations.—Inferiorly, with the bone.

Action.—A supinator of the radial region, and antagonistic to the pronators.

=Flexor Metacarpi Radialis= (Fig. 15, No. 10). Location.—The lowest of the group of three muscles on the outer part of the forearm.

Origin.—By two tendinous heads, the longer from the external condyle of the humerus, and the other just beyond the base of the olecranon.

Insertion.—Becomes tendinous at about the middle of the shaft of the ulna and inserts to a prominent process on the proximal third of the posterior part of the shaft of the mid-metacarpal.

Shape.—Fusiform.

Relations.—Inferiorly, the anconeus and superiorly, the extensor digitorum communis.

Action.—A powerful flexor of the hand.

=Pronator Brevis= (Fig. 13, No. 18). Location.—Supero-lateral side of the forearm.