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thumb which produce the thenar eminence, the three muscles of the little finger, which form the hypothenar eminence, and the interossei muscles, which are deeply placed between the metacarpal bones.
Muscles of the Thumb.
The short muscles of the thumb are the abductor, opponens, and flexor brevis (with its deep portion, interosseus primus volaris), and the adductor muscle, subdivided into two heads-oblique and transverse.
M. Abductor Pollicis Brevis.-The abductor pollicis brevis (O.T. abductor pollicis) arises by fleshy fibres from the tubercle of the navicular, the ridge of the greater multangular, the volar surface of the transverse carpal ligament, and from
Lesser multangular bone-
Flexor carpi radialis
First dorsal interosseous muscle
First volar interosseous muscle
Abductor digiti quinti (origin)
Flexor carpi ulnaris (insertion)
Flexor carpi ulnaris (insertion)
Second dorsal interosseous
Adductor pollicis (origin
Third dorsal interosseous
FIG. 351.-MUSCLE-ATTACHMENTS TO THE VOLAR ASPECT OF THE CARPUS AND METACARPUS.
tendinous slips derived from the insertions of the palmaris longus and abductor pollicis longus muscles (Fig. 350, p. 391). Strap-like in form, and superficial in position, it is inserted by a short tendon into the radial side of the first phalanx of the thumb at its proximal end, and into the capsule of the metacarpo-phalangeal joint.
Nerve-Supply.-Median nerve (C. 6. 7.).
Actions. The muscle acts on the thumb at both the carpo-metacarpal and metacarpophalangeal joints. It abducts and draws forward the thumb.
M. Opponens Pollicis.-The opponens pollicis arises by fleshy and tendinous fibres from the volar surface of the transverse carpal ligament and from the ridge on the greater multangular bone. It is partially concealed by the preceding muscle.
Extending distally and laterally it is inserted into the whole length of the lateral border and the radial half of the volar surface of the first metacarpal bone (Fig. 351, p. 392).
Nerve-Supply.—Median nerve (C. 6. 7.).
Action. It acts solely on the first metacarpal bone, in the movement of opposition of the thumb.
M. Flexor Pollicis Brevis.-The flexor pollicis brevis consists of two parts. a. The superficial part of the muscle, partly concealed by the abductor pollicis brevis, arises, by fleshy and tendinous fibres, from the distal border of the transverse carpal ligament, and sometimes from the ridge of the greater multangular.
It is inserted into the radial side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon of insertion.
b. The deep part of the muscle (interosseus primus volaris) arises from the medial side of the base of the first metacarpal bone.
It is inserted into the medial side of the base of the first phalanx of the thumb along with the adductor pollicis.
This little muscle is deeply situated in the first interosseous space, in the interval between the adductor pollicis obliquus and the first dorsal interosseous It may be regarded as homologous with the volar interossei muscles, with which it is in series.
Nerve-Supply. Median nerve (C. 6. 7.).
Actions. It is a flexor of the thumb and assists also in the movement of opposition of the thumb to the fingers.
M. Adductor Pollicis. The adductor pollicis is separated into two parts by the radial artery.
(1) The oblique head lies deeply in the palm, covered by the tendons of the long flexors of the thumb and fingers. It arises by fleshy fibres from the volar surfaces. of the greater and lesser multangular and capitate bones, from the sheath of the tendon of the flexor carpi radialis, from the volar surfaces of the bases of the second, third, and fourth metacarpal bones, and from the volar ligaments connecting these bones together (Fig. 351, p. 392).
It is inserted by a tendon, in which a sesamoid bone is developed, into the medial side of the base of the first phalanx of the thumb. At its lateral border a slender slip separates from the rest of the muscle, and passing obliquely, deep to the tendon of the flexor pollicis longus, is inserted into the lateral side of the base of the first phalanx along with the superficial part of the flexor pollicis brevis.
(2) The transverse head, lying deeply in the palm beneath the flexor tendons, arises by fleshy fibres from the medial ridge on the volar aspect of the body of the third metacarpal bone, in its distal two-thirds (Fig. 351, p. 392), and from the fascia covering the interosseous muscles in the second and third spaces.
Triangular in form, it is directed laterally, over the interossei muscles of the first two spaces, to be inserted by tendon into the medial side of the base of the first phalanx of the thumb along with the oblique head.
Nerve-Supply. Deep branch of the ulnar nerve (C. 8. (T. 1.)).
Muscles of the Little Finger.
The short muscles of the little finger are the adductor, opponens, and flexor brevis digiti quinti.
M. Abductor Digiti Quinti.—The abductor digiti quinti is most superficial. It arises from the pisiform bone and from the tendon of the flexor carpi ulnaris and its ligamentous continuations (Fig. 351, p. 392).
It is inserted by tendon into the medial side of the base of the first phalanx of the little finger.
Nerve-Supply. Deep branch of the ulnar nerve (C. 8. (T. 1.)).
Actions. The muscle separates the little finger from the ring finger, and assists in flexion of the finger at the metacarpo-phalangeal joint.
M. Opponens Digiti Quinti.-The opponens digiti quinti arises under cover
of the preceding muscle, by tendinous fibres, from the transverse carpal ligament and from the hamulus of the os hamatum.
It is inserted into the medial margin and medial half of the volar surface of the fifth metacarpal bone in its distal three-fourths (Fig. 351, p. 392).
V1, first; V2, second; and V3, third volar interosseous muscles.
Nerve-Supply.-Deep branch of the ulnar nerve (C. 8. (T. 1.)).
Action. The muscle acts only on the metacarpal bone, drawing it forward, so as to deepen the hollow of the hand.
The Interosseous Muscles.
The interosseous muscles of the hand occupy the spaces between the metacarpal bones. They are arranged in two sets, volar and dorsal.
Mm. Interossei Volares.-The volar (O.T. palmar) interossei are three in
M. Flexor Digiti Quinti Brevis. -The flexor digiti quinti brevis may be absent or incorporated with either the opponens or abductor digiti quinti. It arises, by tendinous fibres, from the transverse carpal ligament and from the hamulus of the os hamatum (Fig. 351, p. 392).
It is inserted along with the abductor into the medial side of the first phalanx of the little finger.
Nerve-Supply.-The deep branch of the ulnar nerve (C. 8. (T. 1.)).
Actions.-Flexion of the little finger at the carpo-metacarpal and metacarpophalangeal joints.
FIG. 353.-MUSCLE-ATTACHMENTS TO THE DORSAL ASPECT OF THE RIGHT METACARPUS.
number, occupying the medial three interosseous spaces. Each arises by a single head; the first from the medial side of the body of the second metacarpal bone; the second and third from the lateral sides of the bodies of the fourth and fifth metacarpal
bones respectively (Fig. 352, p. 394). Each ends in a tendon which is directed. distally behind the deep transverse metacarpal ligament, to be inserted into the dorsal expansion of the extensor tendon, the capsule of the metacarpo-phalangeal articulation, and the side of the first phalanx of the finger; the first is inserted into the medial side of the second finger; the second and third into the lateral sides of the fourth and fifth fingers. The deep part of the flexor pollicis brevis (interosseus primus volaris) is to be regarded as the homologous muscle of the first interosseous space.
Mm. Interossei Dorsales.-The dorsal interossei are four in number. Each arises by two heads from the sides of the metacarpal bones bounding each interosseous space (Figs. 353, p. 394, and 354, p. 395).
Each forms a fleshy mass, ending in a membranous tendon which, passing distally, behind the deep transverse metacarpal ligament, is inserted exactly like the volar muscles into the dorsal aspect of each of the four fingers. The insertion of the first dorsal interosseous muscle is into the lateral side of the index finger; the second muscle is attached to the lateral side of the middle finger; the third
FIG. 354.-DORSAL INTEROSSEOUS MUSCLES OF THE HAND (seen from the Volar Aspect).
muscle to the medial side of the same finger; and the fourth muscle to the medial side of the ring finger.
The interosseous muscles of the hand in some cases have a disposition similar to that of the corresponding muscles of the foot (p. 435).
Nerve-Supply. The deep branch of the ulnar nerve (C. 8. (T. 1.)).
Actions. The interossei muscles act in a similar way to, and along with, the lumbricales, flexing the fingers at the metacarpo-phalangeal joints, and extending them at the interphalangeal joints. In addition, the dorsal interossei serve to abduct the fingers into which they are inserted (fore, middle, and ring fingers) from the middle line of the middle finger; the volar muscles on the other hand are adductors of the fingers into which they are inserted (fore, ring, and little finger) towards the middle line of the middle finger.
THE MUSCLES ON THE DORSAL SURFACE OF THE FOREARM.
The group of muscles occupying the lateral side of the elbow and the dorsal surface of the forearm and hand include the supinator muscles of the forearm and the extensors of the wrist and digits. They are divisible into a superficial and a deep layer.
The superficial layer comprises seven muscles, which are in order, from the radial to the ulnar side of the forearm, the brachioradialis, the two radial extensors of the carpus, the extensor digitorum communis and extensor digiti quinti proprius, the extensor carpi ulnaris, and the anconæus.
The deep muscles are five in number: one, the supinator, extends between the proximal parts of the ulna and radius; the others are the special extensors of the thumb and forefinger, viz., the abductor pollicis longus, extensor pollicis longus and extensor pollicis brevis, and extensor indicis proprius. They cover the dorsal surface of the bones of the forearm and the interosseous membrane, and are almost wholly concealed by the superficial muscles. Only the abductor pollicis longus and the extensor pollicis brevis become superficial in the distal part of the forearm, where they emerge between the radial extensors of the carpus and the extensor digitorum communis.
M. Brachioradialis. The brachioradialis arises, by fleshy fibres, from the anterior aspect of the proximal two-thirds of the lateral epicondylic ridge of the humerus, and from the anterior surface of the lateral intermuscular septum (Fig. 340, p. 380).
The muscle lies in the lateral side of the hollow of the elbow, passes distally along the lateral border of the forearm, and ends about the middle of the forearm in a narrow, flat tendon which is inserted, under cover of the tendons of the abductor pollicis longus and extensor pollicis brevis, by a transverse linear attachment, into the proximal limit of the groove for the above-named muscles on the lateral side of the distal extremity of the radius. Some of its fibres gain an attachment to the ridge on the volar margin of the groove, and others spread over the surface of the groove for a variable distance (Figs. 355, p. 397, and 348, p. 389).
Nerve-Supply. -The muscle is supplied by a branch of the radial nerve (C. 5. 6.) in the hollow of the elbow.
Actions. The muscle is primarily a flexor of the elbow-joint. It is also a semi-pronator and semi-supinator of the forearm, bringing the limb from the supine or prone position, into a position in which the radius is uppermost. It thus assists both the pronator and supinator muscles.
M. Extensor Carpi Radialis Longus.-The extensor carpi radialis longus arises, by fleshy fibres, from the anterior aspect of the distal third of the lateral epicondylic ridge of the humerus, from the anterior surface of the lateral intermuscular septum, and from the common tendon of origin of succeeding muscles, attached to the lateral epicondyle (Figs. 356 and 357, p. 399).
In the distal half of the forearm, it ends in a tendon which passes beneath the dorsal carpal ligament, to be inserted into the dorsal surface of the base of the second metacarpal bone on its radial side (Fig. 353, p. 394).
The muscle is concealed in its proximal part by the brachioradialis, and its tendon, in the distal half of the forearm, is crossed, obliquely, by the abductor pollicis and by the extensor pollicis brevis.
Nerve-Supply. The muscle is supplied by a branch of the radial nerve in the hollow of the elbow (C. (5.) 6. 7. 8.).
Actions. The muscle is an extensor of the wrist, and also an accessory flexor of the elbow
M. Extensor Carpi Radialis Brevis.-The extensor carpi radialis brevis arises from the common tendon, from the radial collateral ligament of the elbow, from the fascia over it, and from intermuscular septa on either side.
It passes distally, in the dorsal surface of the forearm and under the dorsal carpal ligament, in close relation to the previous muscle, to be inserted, by a tendon, into the bases of the second and third metacarpal bones (Fig. 353, p. 394). bursa is placed beneath the two radial extensor tendons close to their insertion.
It is practically concealed, in the forearm, by the extensor carpi radialis longus, and in the distal half is crossed obliquely by the abductor pollicis longus and the extensor pollicis brevis. The tendons of the two muscles are crossed, on the dorsum of the wrist, by the tendon of the extensor pollicis longus.
Nerve-Supply.--The deep branch of the radial nerve (C. (5.) 6. 7. (8.)).
Actions. Like the long extensor, this muscle extends the hand at the wrist; and is a subsidiary flexor of the elbow-joint.