Part 41

FIG. 82.--MEDIAL SIDE OF HUMERUS, WITH THE AREAS OF ATTACHMENT OF MUSCLES.

FIG. 83.--DORSAL SURFACE OF THE LEFT HUMERUS, WITH THE AREAS OF ATTACHMENT OF MUSCLES.

Fig. 81.--a, M. subscapularis; b, M. supraspinatus; c, Mm. teres major and latissimus dorsi; d, M. pectoralis minor; e, deep layer of M. pectoralis major; f, superficial layer of M. pectoralis major; g, M. acromiodeltoideus; h, M. spinodeltoideus; h′, caput laterale of M. triceps; i, M. brachialis; j, second portion of M. brachialis; k, M. extensor carpi radialis longus; l, M. extensor carpi radialis brevis; m. M. extensor communis digitorum; n, M. extensor lateralis digitorum; o, M. extensor carpi ulnaris; p, short portion of caput mediale of M. triceps; q, M. pronator teres; r, M. palmaris longus; s, third and fourth parts of M. flexor profundus digitorum; t, M. flexor carpi radialis; u, second head of M. flexor profundus digitorum.

Fig. 82.--a, M. supraspinatus; b, M. subscapularis; c, M. pectoralis minor; d, long portion of caput mediale of M. triceps; e, M. coracobrachialis; f, Mm. teres major and latissimus dorsi; g, intermediate portion of caput mediale of M. triceps; h, deep layer of M. pectoralis major; i, superficial layer of M. pectoralis major; j, M. anconeus; k, short portion of caput mediale of M. triceps; l, M. pronator teres; m, M. flexor carpi radialis; n, second head of M. flexor profundus digitorum; o, third and fourth heads of M. flexor profundus digitorum; p, M. palmaris longus; q, M. flexor carpi ulnaris.

Fig. 83.--a, M. supraspinatus; b, M. subscapularis; c, M. infraspinatus; d, M. teres minor; e, long portion of caput mediale of M. triceps; f, M. coracobrachialis; g, g′, M. brachialis; h, intermediate portion of caput mediale of M. triceps; i, M. anconeus; j, short portion of medial head of M. triceps; k, M. pronator teres; l, second and third heads of M. flexor profundus digitorum; m, M. palmaris longus; n, M. extensor carpi ulnaris.]

Insertion (Fig. 86, d).--The lateral surface of the ulna from the distal margin of the semilunar notch to the proximal end of the olecranon. The muscle covers the capsule of the joint and is closely adherent to it.

Relations.--Outer (dorsal) surface with the caput laterale (Fig. 75, h) and the intermediate portion (Fig. 80, j) of the caput mediale. Inner surface with the bones and the capsule of the joint.

Action.--Keeps the capsule tense and probably rotates the ulna slightly so as to pronate the hand.

3. =Muscles of the Antibrachium or Forearm.=

Fascia of the Forearm.--The muscles of the forearm are not in contact with the skin, but are covered by the strong =antibrachial fascia=. This consists of two layers. The =superficial= one is a continuation of the general subcutaneous fascia of the arm; it covers the forearm as a continuous sheet which becomes thinner distad, and is finally lost near the wrist. The =deep= layer forms a dense, tendinous sheet which is closely applied to the muscles. It begins partly as a continuation of the general fascia of the arm, partly from the tendons of the triceps and epitrochlearis muscles. The sheet is attached to the dorsal surface of the ulna, between the extensor carpi ulnaris and the first head of the flexor profundus digitorum. It surrounds the forearm as a continuous sheath. On the lateral surface it dips between the extensor muscles, becoming closely attached to them and forming a partial sheath for each; it is attached with special firmness to their tendons. On the medial side of the arm the fascia passes smoothly over the flexors without dipping between them; it is continuous, however, with the border of the pronator teres, and distad of this muscle it is firmly attached to the radius.

At the wrist the fascia becomes attached to the longitudinal ridges on the dorsal surface of the head of the radius, bridging thus the intervening grooves and holding the tendons in place between the ridges. The fascia then continues to form the dorsal fascia of the hand. On the ventral side of the wrist the fascia becomes thickened to form a strong =transverse ligament= (Fig. 77, 1), which is attached at its radial and ulnar ends to the carpus, and which holds in place the tendons of the flexor muscles. Distad of the transverse ligament the fascia spreads out in the palm of the hand, and becomes united with the fibrous pad which is situated here. On the fingers the fascia becomes attached to the phalanges, forming tendinous sheaths, the so-called =vaginal ligaments=, for the flexor muscles. Near the base and the head of the first phalanx strong, narrow, ring-like bands, the =annular ligaments= (Fig. 88, 2), are formed in these sheaths; these surround and bind down the tendons of the flexor muscles.

A. MUSCLES ON THE ULNAR AND DORSAL SIDE OF THE FOREARM (extensors and supinators) (Fig. 75, p. 158).

=M. brachioradialis= or supinator longus (Fig. 75, k; Fig. 77, n).--This is a ribbon-like muscle lying on the lateral side of the brachium and the ventrolateral border of the antibrachium just beneath the superficial fascia. It connects the humerus and the radius.

Origin.--By a thin tendon from about the middle fifth of the dorsal border of the humerus, or sometimes proximad of the middle. The muscle curves over the outer surface of the brachialis (Fig. 75, i), to which it is closely applied, and runs along the lateral border of the antibrachium to its insertion.

Insertion by a short tendon into the ridge which forms the ventral limit of the groove on the outer surface of the styloid process of the radius and upon the adjacent ligaments.

Relations.--Outer surface with the integument, and at the proximal end with the caput laterale of the triceps (Fig. 75, h). Inner surface with the brachialis (i), the extensor carpi radialis longus (l) and brevis, and the extensor communis digitorum (m).

Action.--Supinator of the hand.

=M. extensor carpi radialis longus= (Fig. 75, l; Fig. 77, o).--This lies along the radial side of the forearm, and connects the humerus and the second metacarpal.

Origin (Fig. 81, k) from the middle portion of the lateral supracondyloid ridge between the origin of the brachialis (j) and the anconeus. About the middle of the forearm the muscle ends in a slender tendon (Fig. 84, e) which passes through the groove on the radial side of the dorsal surface of the distal end of the radius.

Insertion (Fig. 84, c).--The tendon passes across the carpus and is inserted onto the dorsal surface of the base of the second metacarpal on the radial side just distad of the groove for the radial artery.

Relations.--Outer surface at the proximal end with the caput laterale of the triceps (Fig. 75, h), farther distad with the integument and the brachioradialis (k); the distal tendon with the extensor pollicis brevis (Fig. 84, d). Radial surface with the brachialis (Fig. 75, i) and the integument. Ulnar surface with the extensor carpi radialis brevis (Fig. 77, p), and near the proximal end with the extensor communis digitorum (Fig. 75, m).

Action.--Extensor of the hand.

=M. extensor carpi radialis brevis= (Fig. 77, p).--A slender muscle from the humerus to the third metacarpal.

Origin (Fig. 81, l) from the distal part of the lateral supracondyloid ridge distad of the extensor longus. Near the carpus the muscle ends in a slender tendon which passes through the groove with the extensor longus tendon. The tendon then diverges from the extensor longus and has its

Insertion (Fig. 84, f) into the radial side of the dorsal surface of the base of the third metacarpal.

Relations.--Outer surface with the extensor longus (Fig. 77, o), the integument, and distad with the extensor pollicis brevis (Fig. 84, d). Radial surface with the extensor longus. Ulnar surface with the extensor communis digitorum (Fig. 75, m) and the extensor brevis pollicis. Inner surface with the pronator teres (Fig. 77, q), supinator (Fig. 85, b), and extensor brevis pollicis (Fig. 85, a).

Action.--Extensor of the hand.

a, M. extensor communis digitorum; b, M. extensor lateralis digitorum; c, M. extensor indicis; d, M. extensor brevis pollicis; e, M. extensor carpi radialis longus; f, M. extensor carpi radialis brevis; g, M. extensor carpi ulnaris; h, tendons of the interossei. 1, transverse ligament of the wrist.]