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. _Origin_ by fleshy fibres from the outer (palmar) surface of the tendon common to the ulnar four parts of the profundus (_c′_). _Insertion_ (_f′_).--The four slips are flat at their origin. Each becomes cylindrical and curves about the base of one of the four ulnar digits and is inserted into the radial side of the base of the first phalanx close to its ventral border. [Illustration: FIG. 89.--DEEP MUSCLES OF THE PALM OF THE HAND. _a_, M. flexor brevis pollicis; _b_, M. adductor pollicis; _c_, M. interosseus of second digit (M. flexor brevis digiti secundi); _d_, M. adductor digiti secundi; _e_, M. interosseus of third digit; _f_, M. interosseus of fourth digit; _g_, M. opponens digiti quinti; _h_, M. interosseus of fifth digit (M. flexor brevis digiti quinti); _i_, M. abductor digiti quinti. 1-5, the digits in order.] _Action._--Bend the digits toward the radial side. B. MUSCLES OF THE THUMB.--=M. abductor brevis pollicis= (Fig. 77, _w_) (includes also the opponens pollicis of man).--A very minute, probably rudimentary muscle. _Origin_ from the transverse ligament (1) which connects the prominent fibrous, hairless projection that lies over the pisiform bone with the radial border of the head of the radius. The muscle passes radiodistad and ends in a very slender tendon, the insertion of which is into the base of the first phalanx of the thumb. =M. flexor brevis pollicis= (Fig. 89, _a_). _Origin_ by fleshy fibres from the adjacent borders of the os magnum and scapholunar bones and from the fascia which bridges the intervening groove for the flexor carpi radialis.