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the forearm between the two heads of origin of the muscle), and the ulnar artery. The tendon serves as a guide to the artery in the distal half of the forearm.
Nerve-Supply.--Ulnar nerve (C. 8. T. 1.).
Actions. The flexor carpi ulnaris is a flexor and adductor of the wrist, and an accessory flexor of the elbow-joint.
2. Intermediate Layer.
M. Flexor Digitorum Sublimis.-The flexor digitorum sublimis occupies a deeper plane than the four previous muscles. It has a threefold origin, from the humerus, radius, and ulna. (1) The chief or humeral head of origin is from the medial epicondyle of the humerus by the common tendon, from the ulnar collateral ligament of the elbow, and from adjacent intermuscular septa. (2) The ulnar head of origin is by a slender fasciculus from the medial border of the coronoid process of the ulna, proximal and medial to the origin of the pronator teres (Fig. 348, p. 389). (3) The radial head of origin is from the proximal two-thirds of the volar margin of the radius by a thin fibromuscular attachment (Fig. 348, p. 389).
The muscle divides in the distal third of the forearm into four parts, each provided with a separate tendon which goes beneath the transverse carExpansion of extensor tendon pal ligament, passes through the palm
-FLEXOR DIGITORUM SUBLIMIS
of the hand, and enters the correspond-
Within the digital sheath each tendon is split into two parts by the tendon of the flexor digitorum profundus; after surrounding that tendon
FIRST LUMBRICAL MUSCLE
FIRST DORSAL INTER-
FIG. 347. THE TENDONS ATTACHED TO THE
the two parts are partially re-united on its deep surface, and are inserted, after partial decussation, in two portions into the sides of the second phalanx.
The vincula tendinum form additional insertions of the muscle. They consist of delicate bands of connective tissue enveloped in folds of the mucous sheath, and are known as the vincula longa and brevia. The vinculum breve is a triangular band of fibres containing yellow elastic tissue (ligamentum subflavum), occupying the interval between the tendon and the digit for a short distance close to the insertion. It is attached to the front of the inter-phalangeal articulation and the head of the first phalanx. The ligamentum longum is a long narrow band extending from the back of the tendon to the proximal part of the palmar surface of the first phalanx.
Nerve-Supply.--Median nerve (C. 6.).
Actions. The muscle is a flexor of the elbow, wrist, metacarpo-phalangeal and first (proximal) interphalangeal joints.
3. Deep Layer.
M. Flexor Digitorum Profundus.-The flexor digitorum profundus is a large muscle arising from the ulna, the interosseous membrane, and the deep fascia of the forearm, under cover of the flexor digitorum sublimis and the flexor carpi ulnaris. Its ulnar origin is from the volar and medial surfaces of the bone in its proximal two-thirds, extending proximally so as to include the medial side of the olecranon, and to embrace the insertion of the brachialis muscle into the coronoid
process. It arises laterally from the medial half of the interosseous membrane in its middle third (Figs. 348, p. 389, and 349, p. 390), and medially from the deep fascia of the forearm dorsal to the origin of the flexor carpi ulnaris.
The muscle forms a broad thick tendon which passes beneath the transverse carpal ligament, covered by the tendons of the flexor digitorum sublimis, and enveloped in the same mucous sheath, and divides, in the palm, into four tendons for insertion into the terminal phalanges of the fingers. The tendon associated with the forefinger is usually separate from the rest of the tendons in its whole length.
Biceps brachii (insertion)
Flexor digitorum profundus (origin)
Pronator quadratus (origin)
From their origins the muscles cles are directed distally to the lateral side of each of the metacarpo-phalangeal joints, to be inserted into the capsules of these articulations, the lateral border of the first phalanx, andchiefly into the lateral side of the extensor tendon on the dorsum of the phalanx. The lumbricales vary considerably in number, and may be increased to six or diminished to two.
FIG. 348.-MUSCLE-ATTACHMENTS TO THE RIGHT RADIUS
Nerve-Supply. The flexor digitorum profundus is supplied in its lateral part by the volar interosseous branch of the median nerve (C. 7. 8. T. 1.); and in its medial part by the ulnar nerve (C. 8. T. 1.). The lateral two lumbricales are supplied by the median nerve (C. 6. 7.), and the medial two muscles by the ulnar nerve (C. 8. (T. 1.)).
Actions. The flexor digitorum profundus is a powerful flexor of the wrist. It also flexes the fingers at the metacarpo-phalangeal joint, and acts in a similar way at both the interphalangeal joints.
The lumbrical muscles act as flexors of the fingers at the metacarpo-phalangeal joints, and
(by their attachment to the extensor tendons) as extensors of the fingers, acting on both interphalangeal joints.
M. Flexor Pollicis Longus.-The flexor pollicis longus arises, beneath the flexor digitorum sublimis, by fleshy fibres, from the volar surface of the body of the radius in its middle twofourths, and from a corresponding portion of the interosseous membrane. It has an additional origin, occasionally, from the medial border of the coronoid process of the ulna (Fig. 348, p. 389). Its radial origin is limited proximally by the oblique proximal part of the volar margin of the radius and the origin of the flexor digitorum sublimis, and distally by the insertion of the pronator quadratus muscle.
The muscle ends, proximal to the wrist, in a tendon, which passes over the pronator quadratus into the hand beneath the transverse carpal ligament, and is enveloped in a special mucous sheath.
In the palm the tendon is directed distally along the medial side of the thenar eminence, between the flexor brevis and adductor muscles of the thumb, to be inserted into the base of the terminal phalanx of the thumb on its volar surface.
FIG. 349. THE DEEPEST MUSCLES ON THE VOLAR ASPECT
The muscle is placed deeply in the forearm, being concealed by the superficial layer of muscles and by the flexor digitorum sublimis.
Nerve-Supply.-Volar interosseous branch of the median (C. 7. 8. T. 1.).
Actions. The muscle is a flexor of the wrist and thumb, acting in the latter movement on the metacarpal bone and both phalanges.
M. Pronator Quadratus.-The pronator quadratus is a quadrilateral fleshy muscle, occupying the distal fourth of the forearm. It is placed beneath the deep flexor tendons, and arises from the distal fourth of the volar margin and surface of the ulna (Fig. 348, p. 389).
It is directed transversely laterally to be inserted into the distal fourth of the volar surface of the radius, and into the narrow triangular area on its medial side, in
front of the attachment of the interosseous membrane (Fig. 348, p. 389).
The pronator quadratus is subject to considerable variations. It may even be absent; or it may have an origin from radius or ulna, or from both bones, and an insertion into the carpus.
The muscle is placed deeply in the distal part of the forearm, and is wholly concealed by the tendons of the muscles which descend, under cover of the transverse carpal ligament, to the wrist and fingers. The radial artery and its accompanying veins pass over it at its insertion into the radius.
FIG. 350.-THE PALMAR MUSCLES (Right Side).
Nerve-Supply.-Volar interosseous branch of the median nerve (C. 7. 8. T. 1.).
Action. The muscle acts along with the pronator teres in producing pronation of the forearm.
SHORT MUSCLES OF THE HAND.
The short muscles belonging to the hand, in addition to the palmaris brevis and the lumbrical muscles, already described, include the six muscles of the