Chapter 47
2. The Dorsal Antibracial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The superficial group.
Brachioradialis Extensor Carpi Radialis Longus Extensor Carpi Radialis Brevis Extensor Digitorum Communus Extensor Digitai Quinti Proprius Extensor Carpi Ulnaris Anconius The brachioradialis supinator longus is the most superficial muscle on the radial side of the forearm.
It arises from the upper two thirds of the lateral supracondylar ridge of the humerus and from the lateral intramuscular septum, being limited above by the groove for the radial nerve. Interposed between it and the brachialis are the radial nerve and the anastomosis between the anterior branch of the profunda artery and the radial recurrent.
The fibers end above the middle of the forearm in a flat tendon, which is inserted into the lateral side of the base of the styloid process of the radius. The tendon is crossed near its insertion by the tendons of the abductor pollicis longus and extensor pollicis brevis. On its honor side is the radial artery.
Variations In fusion with the brachialis, tendon of insertion may be divided into two or three slips, insertion partial or complete into the middle of the radius. Physiculi to the tendon of the biceps, the tuberosity or oblique line of the radius, slips to the extensor carpi radialis longus or abductor pollicis longus, absence rarely
doubled. The extensor carpi radialis longus, extensor carpi radialis longiore, is placed partly beneath the brachioradialis. It arises from the lower third of the lateral supracondylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the common tendon of origin of
the extensor muscles of the forearm. The fibers end at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius beneath the abductor pollicis longus and extensor pollicis brevis. It then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the extensor carpi radialis brevis, immediately behind the styloid
process. It is inserted into the dorsal surface of the base of the second metacarpal bone, on its radial side. The extensor carpi radialis brevis, extensor carpi radialis brevior, is shorter and thicker than the preceding muscle beneath which it is placed.
It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles, from the radial collateral ligament of the elbow joint, from a strong aponeurosis which covers its surface, and from the intermuscular septa between it and the adjacent muscles. The fibers end about the middle of the forearm in a flat tendon, which is closely connected
with that of the preceding muscle, and accompanies it to the wrist. It passes beneath the abductor pollicis longus and extensor pollicis brevis, then beneath the dorsal carpal ligament, and is inserted into the dorsal surface of the base of the third metacarpal bone on its radial side. Under the dorsal carpal ligament, the tendon lies on the back of the radius in a shallow
groove, to the oner side of that which lodges the tendon of the extensor carpi radialis longus, and separated from it by a faint ridge. The tendons of the two preceding muscles pass through the same compartment of the dorsal carpal ligament in a single mucous sheath. Variations.
Either muscle may split into two or three tendons of insertion to the second and third, or even the fourth metacarpal. The two muscles may unite into a single belly with two tendons. Cross slips between the two muscles may occur. The extensor carpi radialis intermedius rarely arises as a distinct muscle from the humerus,
but is not uncommon as an accessory slip from one or both muscles to the second or third or both metacarpals. The extensor carpi radialis accessorius is occasionally found arising from the humerus with or below the extensor carpi radialis longus and inserted into the first metacarpal, the abductor pollicis brevis, the first dorsal interosseus, or elsewhere.
The extensor digitorum communus arises from the lateral epicondyle of the humerus by the common tendon, from the intermuscular septa between it and the adjacent muscles, and from the antibracial fascia. It divides below into four tendons, which pass, together with that of the extensor indusus proprius, through a separate compartment of the dorsal carpal ligament, with enimucous
sheath. The tendons then diverge on the back of the hand and are inserted into the second and third phalanges of the fingers in the following manner. Opposite the metacarpophelangial articulation, each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint.
After having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx and is reinforced in this situation by the tendons of the interossei and lumbar callus. Opposite the first interphalangel joint, this aponeurosis divides into three slips, an intermediate and two collateral.
The former is inserted into the base of the second phalanx, and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangel joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the extensor indusus propreus, which lies
on its honor side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateral word to the second tendon, and the other passing from the same tendon downward and medial word to the fourth.
Occasionally, the first tendon is connected to the second by a thin transverse band. Variations. An increase or decrease in the number of tendons is common. An additional slip to the thumb is sometimes present. The extensor digiti quinti propreus, extensor minimi digiti, is a slender muscle placed
on the medial side of the extensor digitorum communis, with which it is generally connected. It arises from the common extensor tendon by a thin tendinous slip from the intermuscular septa between it and the adjacent muscles. Its tendon runs through a compartment of the dorsal carpal ligament behind the distal radioulnar joint, then divides into two as it crosses the hand, and finally joins the expansion
of the extensor digitorum communis tendon on the dorsum of the first phalanx of the little finger. Variations. An additional fibrous slip from the lateral epicondyle, the tendon of insertion may not divide or may send a slip to the ring finger.
Absence of muscle rare, fusion of the belly with the extensor digitorum communis not uncommon. The extensor carpial narrus lies on the ulnar side of the forearm. It arises from the lateral epicondyle of the humerus by the common tendon, by an aponeurosis from the dorsal border of the ulna in common with the flexor carpial narrus and the flexor digitorum profundus, and from the deep fascia of the forearm.
It ends in a tendon, which runs in a groove between the head and the styloid process of the ulna, passing through a separate compartment of the dorsal carpal ligament and is inserted into the prominent tubercle on the ulnar side of the base of the fifth metacarpal bone. Variations. Doubling.
Reduction to tendinous band. Insertion partially into fourth metacarpal. In many cases, 52%, a slip is continued from the insertion of the tendon anteriorly over the aponeurosis digitorum communis to the fascia covering that muscle, the metacarpal bone, the capsule of the metacarpophylandia articulation, or the first failings of the
little finger. This slip may be replaced by a muscular fasciculus arising from or near the pisiform. The anconius is a small triangular muscle which is placed on the back of the elbow joint and appears to be a continuation of the triceps brachii. It arises by a separate tendon from the back part of the lateral epicondyle of the humerus.
Its fibers diverge and are inserted into the side of the olecranon and upper fourth of the dorsal surface of the body of the ulna. The deep group. Supinator abductor pollicis longus extensor pollicis brevis extensor pollicis longus extensor indices propreus.
The supinator supinator brevis is a broad muscle curved around the upper third of the radius. It consists of two planes of fibers between which the deep branch of the radial nerve lies. The two planes arise in common, the superficial one by tendinous and the deeper by muscular
fibers, from the lateral epicondyle of the humerus, from the radial collateral ligament of the elbow joint and the annular ligament, from the ridge on the ulna which runs obliquely downward from the dorsal end of the radial notch, from the triangular depression below the notch, and from a tendinous expansion which covers the surface of the muscle. The superficial fibers surround the upper part of the radius and are inserted into the
lateral edge of the radial tuberosity and the oblique line of the radius, as low down as the insertion of the pronator teres. The upper fibers of the deeper plane form a sling-like fasciculus which encircles the radius above the tuberosity and is attached to the back part of its medial surface. The greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces
of the body of the radius, midway between the oblique line and the head of the bone. The abductor pollicis longus extensor os metacarpi pollicis lies immediately below the supinator and is sometimes united with it. It arises from the lateral part of the dorsal surface of the body of the ulna, below the insertion of the anconius, from the interosseous membrane, and from the middle third of the
dorsal surface of the body of the radius. Passing obliquely downward and lateralward, it ends in a tendon which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the extensor pollicis brevis, and is inserted into the radial side of the base of the first metacarpal bone.
It occasionally gives off two slips near its insertion, one to the greater multangular bone and the other to blend with the origin of the abductor pollicis brevis. Variations. More or less doubling of muscle and tendon with insertion of the extra tendon into the first metacarpal, the greater multangular, or into the abductor pollicis brevis or opponens
pollicis. The extensor pollicis brevis, extensor primi internadii pollicis, lies on the medial side of, and is closely connected with, the abductor pollicis longus. It arises from the dorsal surface of the body of the radius below that muscle, and from the interosseous membrane.
Its direction is similar to that of the abductor pollicis longus, its tendon passing the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb. Variations. Absence.
Fusion of tendon with that of the extensor pollicis longus. The extensor pollicis longus, extensor secondi internadii pollicis, is much larger than the preceding muscle, the origin of which it partly covers. It arises from the lateral part of the middle third of the dorsal surface of the body of the ulna below the origin of the abductor pollicis longus, and from the interosseous
membrane. It ends in a tendon, which passes through a separate compartment in the dorsal carpal ligament, lying in a narrow oblique groove on the back of the lower end of the radius. It then crosses obliquely the tendons of the extensories carpi radialis longus and brevis, and is separated from the extensor brevis pollicis by a triangular interval in which
the radial artery is found, and is finally inserted into the base of the last phalanx of the thumb. The radial artery is crossed by the tendons of the abductor pollicis longus and of the extensories pollicis longus and brevis. The extensor indusus perprius extensor indusus is a narrow elongated muscle placed medial
to and parallel with the preceding. It arises from the dorsal surface of the body of the ulna below the origin of the extensor pollicis longus, and from the entorosseous membrane. Its tendon passes under the dorsal carpal ligament in the same compartment as that which transmits the tendons of the extensor digitorum communus, and opposite the head of the second
metacarpal bone, joins the ulnar side of the tendon of the extensor digitorum communus, which belongs to the index finger. Variations Doubling The ulnar part may pass beneath the dorsal carpal ligament with the extensor digitorum
communus. A slip from the tendon may pass to the index finger. Nerves The brachioradialis is supplied by the fifth and sixth, the extensories carpi radialis longus and brevis by the sixth and seventh, and the anconias by the seventh and eighth
cervical nerves, through the radial nerve. The remaining muscles are innervated through the deep radial nerve, the supinator being supplied by the sixth, and all the other muscles by the seventh cervical. Actions The muscles of the lateral and dorsal aspects of the forearm, which comprise all the extensor
muscles and the supinator, act upon the forearm, wrist, and hand. They are the direct antagonists of the pronator and flexor muscles. The anconias assist the triceps in extending the forearm. The brachioradialis is a flexor of the elbow joint, but only acts as such when the movement of flexion has been initiated by the biceps brachii and brachialis.
The action of the supinator is suggested by its name. It assists the biceps in bringing the hand into the supine position. The extensor carpi radialis longus extends the wrist and abducts the hand. It may also assist in bending the elbow joint. At all events, it serves to fix or steady this articulation.
The extensor carpi radialis brevis extends the wrist and may also act slightly as an abductor of the hand. The extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side. By its continued action, it extends the elbow joint.
The extensor digitorum communis extends the phalanges, then the wrist, and finally the elbow. It acts principally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the interossei and lumbar calles. It tends to separate the fingers as it extends them.
The extensor digiti quinti perprius extends the little finger and by its continued action assists in extending the wrist. It is owing to this muscle that the little finger can be extended or pointed while the others are flexed. The chief action of the abductor pollicis longus is to carry the thumb laterally from
the palm of the hand. By its continued action it helps to extend and abduct the wrist. The extensor pollicis brevis extends the proximal phalanges, and the extensor pollicis longus the terminal phalanges of the thumb. By their continued action they help to extend and abduct the wrist.
The extensor indusus perprius extends the index finger, and by its continued action assists in extending the wrist. End of section 47. Recording by Salina Arter.
