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applied to the bones during flexion of the fingers. Within each digital sheath are the flexor tendons, enveloped in a mucous sheath which envelops the tendon and lines the interior of the sheath. The mucous linings of the digital sheaths extend a short distance proximally in the palm, and in some cases communicate with the large mucous sheaths enclosing the flexor tendons beneath the transverse carpal ligament. There may be a separate distinct mucous sheath for each digit; but most commonly only the sheaths for the three middle digits are separate; those of the flexor pollicis longus and the flexor tendons of the little finger usually communicate with the mucous sheaths placed beneath the transverse carpal ligament.
THE MUSCLES ON THE ANTERIOR AND MEDIAL ASPECTS
The muscles on the anterior and medial aspects of the forearm comprise the pronators and the flexors of the wrist and fingers. In the forearm they are arranged in three strata: (1) a superficial layer consisting of four muscles which radiate from the medial epicondyle of the humerus, from which they take origin by a common tendon. They are named, from radial to ulnar side, pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. These muscles conceal the muscle which by itself constitutes (2) the intermediate stratum-the flexor digitorum sublimis, and this again conceals, for the most part, (3) the deep layer of muscles, including the flexor digitorum profundus covering the ulna, the flexor pollicis longus on the radius, and the pronator quadratus, which is more deeply placed than the previous muscles, and stretches across the forearm between the distal portions of the radius and ulna.
I. Superficial Muscles.
M. Pronator Teres. The pronator teres is the shortest muscle of this group. It has a double origin: (1) a superficial head (caput humerale), the main origin, partly fleshy, partly tendinous, from the most distal part of the medial epicondylic ridge of the humerus and from the medial intermuscular septum, from the medial epicondyle of the humerus, from the fascia over it, and from an intermuscular septum between it and the flexor carpi radialis (Fig. 346, p. 387); (2) a deep head (caput ulnare), a slender tendinous slip from the medial side of the coronoid process of the. ulna, which joins the superficial origin of the muscle on its deep surface (Fig. 348, p. 389). The median nerve separates the two heads from one another.
The muscle passes distally and laterally to be inserted by tendon into an oval impression on the middle of the lateral surface of the body of the radius (Figs. 346, p. 387, and 348, p. 389). The fibres of the muscle are twisted on themselves, so that the most proximal humeral fibres form the most distal fibres of the tendon of insertion, and the most distal humeral fibres and those arising from the coronoid process are most proximal at the insertion.
The pronator teres forms the medial boundary of the hollow of the elbow. It is superficially placed, except near its insertion, where it is covered by the brachioradialis muscle and by the radial vessels and superficial branch of the radial
Nerve-Supply.-Median nerve (C. 6.).
Action.-The muscle is a flexor of the elbow-joint and a pronator of the forearm.
M. Flexor Carpi Radialis.-The flexor carpi radialis muscle takes its origin from the common tendon from the medial epicondyle of the humerus, from the fascia over it, and from the intermuscular septa on either side.
Its fleshy belly gives place, in the distal half of the forearm, to a strong round tendon which, at the wrist, enters the hand in a special compartment under cover of the transverse carpal ligament, and after occupying the groove on the large multangular bone, is inserted into the proximal ends of the second and third metacarpal
bones on their volar surfaces (Fig. 351, p. 392). The chief tendon is that to the second metacarpal bone.
The muscle is superficial except near its insertion. Its tendon, in the distal half of the forearm, is an important guide to the radial vessels, which are placed to its radial side. After passing beneath the transverse carpal ligament the tendon is concealed by the origins of the short muscles of the thumb, and is crossed, from medial to lateral side, by the tendon of the flexor pollicis longus. Besides the mucous sheath enveloping the tendon beneath the ligament, a mucous bursa is placed beneath the insertion of the tendon.
Nerve-Supply.-Median nerve (C. 6.).
Actions. This muscle has a threefold action. It is mainly a flexor of the elbow and wrist, but it also acts as an accessory pronator of the forearm.
M. Palmaris Longus.-The palmaris longus arises also from the common flexor tendon from the medial epicondyle of the humerus, from the fascia over it,
M A1 2 3 B 4 5 CD 6
and from intermuscular septa on each side.
It forms a short fusiform muscle, which ends, in the middle of the forearm, in a long flat tendon. This pierces the deep fascia, near the wrist, E and passing over the transF verse carpal ligament, is inserted (1) into the surface of the transverse carpal ligament, and (2) into the apex of the thick central portion of the palmar aponeurosis. A tendinous slip is frequently sent to the short muscles of the thumb and the fascia covering
FIG. 344.-DISTAL SURFACE OF A SECTION ACROSS THE RIGHT them.
A, PRONATOR TERES (insertion); B, FLEXOR CARPI RADIALIS; C, FLEXOR
DIGITORUM SUBLIMIS; D, PALMARIS LONGUS; E, FLEXOR CARPI ULNARIS;
The palmaris longus is the Smallest muscle of the forearm. In the distal third of the
H, EXTENSOR POLLICIS LONGUS; I, EXTENSOR DIGITORUM COMMUNIS AND forearm its tendon is placed EXTENSOR DIGITI QUINTI PROPRIUS; J, ABDUCTOR POLLICIS LONGUS; K, directly over the median nerve, along the radial border
EXTENSOR CARPI RADIALIS BREVIS; L., EXTENSOR CARPI RADIALIS LONGUS;
M, BRACHIORADIALIS. a, Radius; b, Interosseous membrane; c, Ulna.
1, Superficial ramus of radial nerve; 2, Radial artery; 3, Volar inter- of the tendons of the flexor osseous artery; 4, Volar interosseous nerve (underneath flexor pollicis
longus); 5, Median nerve; 6, Ulnar artery; 7, Ulnar nerve; 8, Dorsal digitorum sublimis.
interosseous artery; 9, Dorsal interosseous nerve.
The palmaris longus is the
most variable muscle in the body, and is often absent (10 per cent). Nerve-Supply.-Median nerve (C. 6.). Actions. The muscle assists in flexion of the elbow and wrist. It also by tightening the palmar aponeurosis deepens the hollow of the hand and helps to flex the fingers.
M. Flexor Carpi Ulnaris.-The flexor carpi ulnaris muscle has a double origin, from the humerus and from the ulna. (1) It arises from the common tendon attached to the medial epicondyle of the humerus, from the fascia over it, and from a lateral intermuscular septum. (2) By means of the deep fascia of the forearm it obtains an attachment to the medial border of the olecranon and the dorsal margin of the ulna in its proximal three-fifths.
The fleshy fibres join a tendon which lies on the anterior border of the muscle and is inserted into the pisiform bone, and in the form of two ligamentous bands (piso-hamate and piso-metacarpal) into the hamulus of the os hamatum, and the proximal end of the fifth metacarpal bone (Fig. 351, p. 392).
The muscle is superficially placed along the medial border of the forearm. It conceals the flexor digitorum profundus muscle, the ulnar nerve (which enters
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
FLEXOR CARPI ULNARIS EXTENSOR
FLEXOR CARPI RADIALIS. (tendon)
PALMARIS LONGUS (tendon)
FLEXOR CARPI ULNARIS (tendon)
ABDUCTOR POLLICIS LONGUS
FIG. 345. THE SUPERFICIAL MUSCLES OF
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).
-FLEXOR DIGITORUM SUBLIMIS
FIRST LUMBRICAL MUSCLE
(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 car-Expansion of extensor tendon pal ligament, passes through the palm of the hand, and enters the corresponding digital sheath of a finger. At the wrist the four tendons are arranged in pairs, those for the middle and ring fingers in front, and those for the fore and little fingers behind, and are surrounded by a mucous sheath, along with the tendons of the flexor digitorum profundus, beneath the transverse carpal ligament. In the palm of the hand the tendons separate, and conceal the deep flexor tendons and lumbrical muscles.
FIRST DORSAL INTER-
FIG. 347. THE TENDONS ATTACHED TO THE
Within the digital sheath each tendon is split into two parts by the tendon of the flexor digitorum profundus; after surrounding that tendon 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 lecranon, 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.
Each tendon enters the digital sheath of the finger deep to the tendon of the flexor digitorum sublimis, which it pierces opposite the first phalanx, and is finally inserted into the base of the terminal phalanx. Like the tendons of the flexor sublimis, those of the deep flexor are provided with vincula, viz., vincula brevia attached to the capsule of the second interphalangeal articulation, and vincula longa, which are in this case connected to the tendons of the subjacent flexor digitorum sublimis.
Mm. Lumbricales. The lumbricales are four small cylindrical muscles associated with the tendons of the flexor digitorum profundus in the palm of the hand. The two lateral muscles arise, each by a single head, from the radial sides of the tendons of the flexor digitorum profundus destined respectively for the fore and middle fingers. The two medial muscles arise, each by two heads, from the adjacent sides of the second and third, and third and fourth tendons.
From their origins the muscles 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, and chiefly into the lateral side of the
Brachialis muscle (insertion)
Flexor digitorum sublimis (radial origin)
Pronator quadratus (insertion)
Flexor digitorum sub-
Flexor digitorum profundus (origin)
Pronator quadratus (origin)
FIG. 348.-MUSCLE-ATTACHMENTS TO THE RIGHT RADIUS
extensor tendon on the dorsum of the phalanx. The lumbricales vary considerably in number, and may be increased to six or diminished to two.
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