Part 37

Origin.—From just above the internal condyle of the humerus.

Insertion.—The tendon passing obliquely across the interosseous space and is inserted to the ulnar side of the shaft of the radius, just beyond the juncture of the proximal and the middle thirds.

Shape.—Fusiform.

Relations.—Superior to the pronator longus.

Action.—Pronates the forearm, and flexes the forearm upon the arm.

=Pronator Longus= (Fig. 14, No. 6). Location.—Lateral side of the radio-ulnar region.

Origin.—From the middle of the internal condyle of the humerus.

Insertion.—To the shaft of the radius just beneath the pronator brevis.

Shape.—Massive, ellipsoidal.

Relations.—Between the pronator brevis and flexor digitorum profundus.

Action.—A pronator.

=Extensor Ossis Metacarpi Pollicis= (Fig. 13, No. 23). Location.—Slightly interposed between the ulna and radius.

Origin.—Immediately in front of the greater sigmoid cavity of the ulna.

Insertion.—To the palmar side of the base of the first metacarpal, in common with the extensor metacarpi radialis longior.

Shape.—Delicate, straight.

Relations.—Superiorly, the extensor indicis longus, and inferiorly, the anconeus and the flexor digitorum profundus.

Action.—Extends the hand upon the forearm.

=Anconeus= (Fig. 15, No. 4). Location.—Between the ulna and the radius.

Origin.—By a short, strong, subcylindrical tendon from the lower posterior of the external condyle of the humerus.

Insertion.—To the latero-radial side of the ulna somewhat beyond its middle.

Shape.—Fusiform.

Relations.—Superiorly, the extensor indicis longus, and inferiorly, the ulna.

Action.—A flexor of the forearm.

=Extensor Indicis Longus= (Fig. 13, No. 22; Fig. 15, No. 13). Location.—Infero-lateral to the radius.

Origin.—From about one-half the surface of the proximal portion of the radius.

Insertion.—Possesses a long tendon which passing over a groove at the distal end of the ulna and receiving muscular fibers at the base of the metacarpus, extends down the anterior part of the hand and is inclosed in a sheath in front of the superior part of the first phalanx of the index-finger. This tendon is inserted into the anterior upper rim of the distal phalanx.

Shape.—Small, thin.

Relations.—Supero-laterally with the radius.