[Fig. 88].—Arrangement of the Tendons of M. palmaris longus, M. flexor sublimis digitorum, and M. flexor profundus digitorum, with Mm. lumbricales.

The integument, fibrous pads, and the palmaris longus (except the ends of its tendons) have been removed; the flexor sublimis has been cut. a, cut ends of tendons of M. palmaris longus; b, tendons of M. flexor sublimis digitorum, ulnar division; b′, radial part of M. flexor sublimis digitorum; c, tendons of M. flexor profundus digitorum (c′, the common tendon); d, M. abductor digiti quinti; e, M. flexor brevis digiti quinti; f, Mm. lumbricales (f′, their tendons). 1, transverse ligament of wrist; 2, annular ligaments.

M. pronator quadratus ([Fig. 87], a).—A thick quadrangular muscle whose fibres run obliquely between the distal ends of the ulna and radius.

Origin by fleshy fibres from about the distal half of the ventral (flexor) surface or border of the ulna and from the interosseous membrane adjacent to the area. The fibres pass obliquely distad toward the radial side to their

Insertion by fleshy fibres into the ventral (flexor) surface of the radius distad of the area of origin of the fifth head of the profundus.

Relations.—Outer surface with the flexor profundus. Inner surface with the radius, ulna, and interosseous membrane.

Action as indicated by the name.

4. Muscles of the Hand.

A. Between the Tendons.

—Mm. lumbricales ([Fig. 88], f, f′).—Four small muscles in the palm of the hand.