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Nerve-Supply.-The nerve to the coracobrachialis comes from the 7th or 6th and 7th cervical nerves. Incorporated with the musculo-cutaneous, the nerve separates to supply the muscle before the latter nerve pierces it.
Action.-The muscle assists the biceps to raise the arm and draw it medially.
M. Biceps Brachii.-The biceps brachii arises by two tendinous heads. (1) The short head (caput breve) is attached in common with the coracobrachialis to
the tip of the coracoid process of the scapula (Fig. 333, p. 372). Concealed by the deltoid and tendinous at first, this head forms a separate fleshy belly, which is united to the long Triceps: lateral head head by an invest
ment of the deep fascia. (2) The long head (caput longum) arises by a round tendon from the supraglenoidal tuberosity at the root of the coracoid process and from the labrum glenoidale on each side. Its tendon passes through the cavity of the shoulderjoint, and, emerging from the capsule beneath the transverse humeral ligament (invested by a prolongation of the synovial membrane), it occupies the intertubercular groove of the humerus extensor muscles where it is covered
by a fascial prolongation of the tendon of the pec
FIG. 340.-MUSCLE ATTACHMENTS TO
FIG. 341.-MUSCLE - ATTACHMENTS TO toralis major. In
fleshy belly united
to that derived from the short head by an envelope of deep fascia.
The insertion of the muscle is likewise twofold. (1) The two bellies become connected to a strong tendon, attached deeply in the hollow of the elbow to the rough dorsal portion of the tubercle of the radius (Figs. 335, p. 375, and 348, p. 389). A bursa separates the tendon from the volar portion of the tuberosity. (2) From the medial and anterior part of the tendon, and partly in continuity with the fleshy fibres of the muscle, a strong membranous band (the lacertus fibrosus) extends, distally and medially, over the hollow of the elbow to join the deep fascia covering the origins of the flexor and pronator muscles
of the forearm. Its proximal part is thickened and can be felt subcutaneously as a crescentic border.
In the arm the biceps conceals the brachialis muscle and the musculo-cutaneous nerve. Its medial border is the guide to the position of the brachial artery and median nerve.
The biceps is an extremely variable muscle. Its chief anomalies are due to an increase or diminution in the number of origins. A third head of origin is common (10 per cent), and usually arises from the humerus, between the insertions of the deltoid and coracobrachialis. Two or even three additional heads may be present at the same time. The long head of the muscle may be absent, or may take origin from the intertubercular groove. The muscle may have an additional insertion into the medial epicondyle of the humerus, or into the fascia of
Nerve-Supply. The biceps is supplied by the musculo-cutaneous nerve (C. 5. 6.).
Actions. The actions of the biceps are complex, in that they affect three articulationsthe shoulder, humero-radial, and radio-ulnar joint. The muscle raises and draws forward the humerus at the shoulder-joint, it flexes the elbow-joint, and it supinates the forearm. The combination of these actions results in a simple movement like that of raising the hand to
M. Brachialis.-The brachialis (O.T. brachialis anticus) is a large muscle arising from the distal two-thirds of the anterior aspect of the body of the humerus and from the intermuscular septum on each side (Figs. 340 and 341, p. 380).
Clasping the insertion of the deltoid proximally, it ends distally in a strong tendon, which is inserted, deep in the hollow of the elbow, into the anterior ligament of the elbow-joint, the distal surface of the coronoid process, and slightly into the immediately adjacent part of the volar surface of the body of the ulna (Fig. 348, p. 389). The lateral part of the muscle arising from the lateral epicondylic ridge and lateral intermuscular septum forms a slip more or less separate, which may be partially fused with the brachioradialis muscle.
It is concealed for the most part by the biceps muscle in the arm. It forms the floor of the cubital fossa, and covers the anterior aspect of the elbow-joint.
Nerve-Supply. It is supplied by the musculo-cutaneous nerve (C. 5. 6.); and also (in most instances) at its lateral border by a fine branch of the radial nerve (C. (5.) 6.).
Action. This muscle is a flexor of the elbow-joint.
M. Triceps Brachii.-The triceps brachii is the only muscle on the posterior aspect of the arm. It arises by three heads: a lateral and a medial head, from the humerus, and a long or middle head, from the scapula. (1) The long head (caput longum) begins as a strong tendon attached to a rough triangular surface on the axillary border of the scapula just below the glenoid cavity (infra-glenoidal tuberosity) (Figs. 333, p. 372, and 337, p. 376). This gives rise to a fleshy belly which, after passing between the teres major and teres minor muscles, occupies the middle of the back of the arm. (2) The lateral head is attached by fibres, partly tendinous and partly fleshy, to the curved lateral border of the humerus from the insertion of the teres minor proximally to the radial groove distally, and receives additional fibres from the posterior surface of the lateral intermuscular septum (Fig. 341, p. 380). Its fibres are directed distally and medially over the radial groove, concealing the radial (musculo-spiral) nerve, the profunda brachii artery, and the medial head of the muscle, to the tendon of insertion. (3) The medial head arises by fleshy fibres from an elongated triangular area on the posterior surface of the humerus, extending proximally to the level of the insertion of the teres major, and distally nearly to the margin of the olecranon fossa (Fig. 341, p. 380). It also arises, on each side, from the intermuscular septum,-from the whole length of the medial septum, and from the part of the lateral septum which is below the passage of the radial nerve.
The three heads of origin are inserted, by a broad and membranous common tendon, into an impression occupying the posterior part of the proximal end of the olecranon of the ulna (Fig. 355, p. 397), and into the deep fascia of the forearm on each side of it. The long and lateral heads join the borders of the tendon of insertion, and the medial head is attached to its deep surface. A small
thick-walled bursa separates the tendon of the triceps from the posterior ligament of the elbow-joint and the proximal end of the olecranon.
The muscle is superficial in almost its whole extent. The long (scapular) head is concealed at its origin by its relation to the teres muscles, between which it passes.
The subanconæus is a small muscle occasionally present. It consists of scattered fibres arising from the distal end of the posterior surface of the humerus, deep to the triceps, and it is inserted into the posterior ligament of the elbow-joint.
Nerve-Supply. -The several heads of the muscle are supplied separately by branches of the radial nerve. The lateral head receives fibres from C. (6.) 7. 8.; the long and medial head from C. 7. 8. The medial head has a double supply. One nerve enters its proximal part, another (ulnar collateral nerve of Krause) enters the distal part of the muscle.
Actions. The triceps is the extensor muscle of the elbow-joint. The long head also acts as an adductor of the humerus at the shoulder-joint.
The chief action of these muscles (excepting the coracobrachialis) is on the elbow-joint, producing along with other muscles flexion and extension. The flexor muscles are much more powerful than the extensors.
The superficial fascia in the forearm presents no exceptional features. On the dorsum of the hand it is loose and thin; in the palm it is generally well furnished with fat, forming pads for the protection of the vessels and nerves. It is closely adherent to the palmar aponeurosis and to the skin, especially along the lines of flexure.
M. Palmaris Brevis.-The palmaris brevis is a quadrilateral subcutaneous muscle which lies in the medial side of the hand, under the superficial fascia. It arises from the medial border of the thick central portion of the palmar aponeurosis and from the volar surface of the transverse carpal ligament of the wrist, and is inserted into the skin of the medial border of the hand for a variable distance. It covers the ulnar artery and nerve, branches of which supply it. Its action is to wrinkle the skin of the medial border of the hand, and by raising up the skin and superficial fascia, to deepen the hollow of the hand.
The deep fascia of the forearm and hand is continuous above with the deep fascia of the arm. In the proximal part of the forearm it is strengthened by additional fibres around the elbow; in front, by fibres from the lacertus fibrosus (semilunar fascia) of the biceps; behind, by the fascial insertions of the triceps; and laterally, by fibres derived from the humeral epicondyles in relation to the common tendons of origin of the flexor and extensor muscles of the forearm which in part take their origin from them. It is attached to the dorsal margin of the ulna, and affords increased attachment to the flexor and extensor carpi ulnaris and the flexor digitorum profundus muscles. Above the wrist the volar part of the fascia is pierced by the tendon of the palmaris longus, and by the ulnar artery and nerve. At the wrist it gains attachment to the bones of the forearm and carpus, is greatly strengthened by addition of transverse fibres, and constitutes the transverse carpal and dorsal carpal ligaments.
Ligamentum Carpi Transversum.-The transverse carpal ligament (O.T. anterior annular ligament) is a band about an inch and a half in depth, continuous, proximally and distally, with the deep fascia of the forearm and the palm of the
hand. It is attached laterally to the navicular and large multangular; medially to the pisiform and os hamatum; and it forms a membranous arch binding down, in the hollow of the carpus, the flexor tendons of the fingers, and the median nerve. It is divided into two compartments, the larger accommodating the tendons of the flexors of the digits and the median nerve, the smaller (placed laterally) containing the tendon of the flexor carpi radialis. There are three synovial membranes in these compartments: one for the flexor carpi radialis tendon, and two others, which often communicate together, enveloping the tendon of the flexor pollicis longus and the flexor tendons of the fingers respectively. The surface of the ligament is crossed by the palmar branches of the median and ulnar nerves; by the tendon of the palmaris longus muscle, which is attached to its surface; and by the ulnar artery and nerve, which are again bridged over and protected by a band of fibrous tissue, called the volar carpal ligament, which passes from the pisiform bone and the superficial fascia to the surface of the transverse carpal ligament. To the distal border of the ligament are attached the palmar aponeurosis in the centre, and the superficial muscles of the thumb and the muscles of the little finger on each side.
Ligamentum Carpi Dorsale.-The dorsal carpal ligament (O.T. posterior annular ligament) is placed at a more proximal level than the transverse carpal ligament. It consists of an oblique band of fibres about an inch broad, continuous proximally and distally with the deep fascia of the forearm and hand. It is attached laterally to the lateral side of the distal end of the radius, and medially to the distal end of the ulna (styloid process), the carpus, and the ulnar collateral ligament of the wrist. It is crossed by veins, by the superficial ramus of the radial nerve, and by the dorsal branch of the ulnar nerve. Six compartments are formed deep to it by the attachment of septal bands to the distal ends of the radius and ulna. Each compartment is provided with a mucous sheath, and they serve to transmit the extensor tendons of the wrist and fingers in the following order from lateral to medial side:
(1) Abductor pollicis longus and extensor pollicis brevis, (2) Extensores carpi
FIG. 342.-THE PALMAR, APONEUROSIS.
radiales, longus and brevis, (3) Extensor pollicis longus, (4) Extensor digitorum communis and extensor indicis proprius, (5) Extensor digiti quinti proprius, (6) Extensor carpi ulnaris.
The thin deep fascia of the dorsum of the hand is lost over the expansions of the extensor tendons on the fingers. Between the metacarpal bones a strong layer of fascia covers and gives attachment to the interossei muscles.
Aponeurosis Palmaris.-The palmar aponeurosis is of considerable importance. In the centre of the palm it forms a thick triangular membrane, the apex of which joins the distal edge of the transverse carpal ligament, and, more superficially, receives the insertion of the tendon of the palmaris longus muscle. The fascia separates below into four slips, one for each finger. The slips are nected together by transverse fibres, which form, beneath the webs of the fingers, the superficial transverse metacarpal ligament (fasciculi transversi). More distally
FLEXOR DIGITORUM SUBLIMIS
-ABDUCTOR POLLICIS LONGUS
ABDUCTOR DIGITI QUINTI
TENDONS OF FLEXOR DIGITORUM each slip separ
FLEXOR DIGITORUM SUBLIMIS
ates into two parts, to be connected to the sides of the metacarp 0phalangeal joints and the first phalanx of the medial four digits. In the cleft between the two halves of each slip the digital sheath is attached and extends distally on to the finger. The lateral borders of this triangular central portion of the palmar aponeurosis are continuous with thin layers of deep fascia, which cover and envelop the muscles of the thenar and hypothenar eminences. The medial border gives origin to the palmaris brevis muscle (p. 382).
FIG. 343.-SUPERFICIAL MUSCLES AND TENDONS IN THE PALM OF THE LEFT HAND.
The digital sheaths (vagina mucosa) are tubular envelopes extending along the palmar aspect of the digits and enclosing the flexor tendons. Each consists of a fibrous sheath attached to the lateral borders of the phalanges and inter-phalangeal joints, and continuous proximally with the palmar aponeurosis. Opposite each inter-phalangeal articulation the digital sheath is loose and thin; opposite the first two phalanges (the first only in the case of the thumb) it becomes extremely thick, and gives rise to the ligamenta vaginalia, which serve to keep the tendons closely