Part 38

a, M. supraspinatus; b, part of insertion of M. rhomboideus; c, M. infraspinatus; d, M. teres major; e, M. spinodeltoideus; f, M. acromiodeltoideus; g, caput longum of M. triceps brachii; h, caput laterale of M. triceps brachii; i, M. brachialis; j, M. biceps; k, M. brachioradialis; l, M. extensor carpi radialis longus; m, M. extensor communis digitorum (m′, tendon of same); n, M. extensor lateralis digitorum; (n′, tendon of same); o, M. extensor carpi ulnaris (o′, tendon of same); p, M. extensor indicis proprius; q, fifth head of M. flexor profundus digitorum; r, M. flexor carpi ulnaris. 1, vertebral border of the scapula; 2, spine of the scapula; 3, greater tuberosity of the humerus; 4, olecranon; 5, transverse ligament of the wrist.]

Origin.--Its superficial fibres are continuations of the clavotrapezius (Fig. 68, d); other fibres have origin from the clavicle and from a raphe laterad of the clavicle which is common to this muscle and the clavotrapezius. It passes distad along the cranial surface of the arm, growing narrower as it approaches the convexity of the elbow.

Insertion.--Eight to ten millimeters from the ulna it joins the brachialis muscle (Fig. 79, i) to be inserted with it by a flat tendon (Fig. 79, i; Fig. 87, c) upon a rough area on the medial surface of the ulna just distad of the semilunar notch, and about midway between the dorsal and ventral borders.

Relations.--Outer surface with the integument. Inner surface with the pectoralis major (Fig. 65, l), biceps (Fig. 77, g), lateral head of the triceps (Fig. 75, h), acromiodeltoid (Fig. 75, f), and brachialis (Fig. 80, h). Medial border with the pectoantibrachialis (Fig. 65, m). Lateral border free except near the insertion, where it is in relation with the brachialis.

Action.--Flexor of the antibrachium.

=M. supraspinatus= (Fig. 75, a) occupies the whole of the supraspinatus fossa of the scapula. It is covered by strong fascia which stretches from the free edge of the spine to the coracoid border of the scapula and to the coracoid half of its vertebral border.

Origin (Fig. 76, b) by fleshy fibres from the whole surface of the supraspinatus fossa, from the above-mentioned fascia, and from the subscapularis (Fig. 77, a) craniad of the coracoid border of the scapula.

Insertion (Fig. 83, a).--It passes over the capsule of the shoulder-joint, to which it is closely attached, and is inserted into the free border of the great tuberosity ventrad (or proximad) of the fossa for the infraspinatus (Fig. 83, c).

Relations.--Outer surface with the spinotrapezius (Fig. 68, j), acromiotrapezius (Fig. 68, h), levator scapulæ ventralis (Fig. 68, f), clavotrapezius (Fig. 68, d), and cleidomastoid (Fig. 65, h). Inner surface with the scapula. The distal end of the coracoid border is closely related to the pectoralis minor (Fig. 79, f). The glenoid border is related to the origin of the deltoidei.

Action.--Extends the humerus after it has been flexed on the scapula.

=M. infraspinatus= (Fig. 75, c).--This fills the infraspinatus fossa, its fibres converging to the insertion on the great tuberosity of the humerus.

a, M. infraspinatus; b, M. supraspinatus; c, origin of M. biceps; d, M. acromiodeltoideus; e, M. teres minor; f, M. levator scapulæ ventralis; g, M. spinodeltoideus; h, M. acromiotrapezius; i, M. rhomboideus; j, M. teres major; k-l, line of insertion of M. spinotrapezius.]

Origin (Fig. 76, a).--By fleshy fibres from the whole infraspinatus fossa, and by a raphe between it and the teres major (Fig. 75, d), and sometimes by fibres from the teres minor (Fig. 80, c), triceps, spinodeltoideus (Fig. 75, e), spinotrapezius (Fig. 68, j), and subscapularis (Fig. 77, a).

Insertion (Fig. 83, c).--By a flat tendon which passes over the capsule of the joint, into the ventral half of the infraspinatus fossa on the great tuberosity of the humerus. (The dorsal half of the fossa is covered by a synovial bursa.)

Relations.--Outer surface with the spinotrapezius (Fig. 68, j), spinodeltoid (Fig. 68, i), acromiodeltoid (Fig. 68, g), teres major (Fig. 75, d), and levator scapulæ ventralis (Fig. 68, f). Inner surface with the scapula. Glenoid border with the teres minor (Fig. 80, c), the teres major (Fig. 75, d), and the long head of the triceps (Fig. 75, g).

Action.--Rotates the humerus outward.

=M. teres minor= (Fig. 80, c).--A small muscle from the glenoid border of the scapula to the proximal end of the humerus.

Origin (Fig. 76, e) by a sheet of tendinous fibres from the glenoid border of the scapula beginning about one-fifth the length of the border from the glenoid fossa and extending to its middle. It is often attached to the infraspinatus (Fig. 80, b) and the caput longum of the triceps (Fig. 75, g).

Insertion (Fig. 83, d) by a short tendon into the tubercle just distad of the infraspinatus fossa on the great tuberosity of the humerus.

Relations.--Outer surface with the spinodeltoideus (Fig. 75, e), acromiodeltoideus (Fig. 75, f), and the infraspinatus (Fig. 80, b). Inner surface with the lateral (Fig. 75, h) and long (Fig. 75, g) heads of the triceps and the capsule of the joint.

Action.--Assists the infraspinatus to rotate the humerus outward.

B. MUSCLES ON THE MEDIAL SURFACE OF THE SHOULDER.

(Fig. 77.)

=M. subscapularis= (Fig. 77, a).--A triangular mass from the subscapular fossa to the lesser tuberosity of the humerus.

Origin (Fig. 78, a).--From the whole subscapular fossa except along the fusiform area for the attachment of the levator scapulæ and the serratus anterior near the vertebral border, and except over a quadrangular area about one centimeter long near the glenoid angle. The origin is by fleshy fibres directly from the periosteum except along two or three lines marked by oblique ridges. To these lines are attached tendinous fibres. At the glenoid border the area of origin sometimes occupies part or the whole of the surface of the fossa for the origin of the teres major, so that the teres arises from the fascia on the surface of the subscapularis. At the coracoid border some of the fibres may take origin from the adjacent fascia of the supraspinatus (Fig. 77, d).

Insertion (Fig. 82, b).--The fibres converge to the glenoid border, and the insertion is by a strong, flat tendon into the dorsal border of the lesser tuberosity of the humerus.

M. epitrochlearis, M. clavobrachialis, and the breast-muscles have been removed. a, M. subscapularis; b, insertion of M. levator scapulæ and of M. serratus anterior; c, M. teres major; d, M. supraspinatus; e, M. latissimus dorsi (e′, cut edge of that part which becomes united with the bicipital arch); f, M. coracobrachialis; g, M. biceps brachii (the capsule of the joint has been laid open to show its tendon); h, cut insertions of pectoralis muscles; i, caput longum of M. triceps brachii; j, long portion of caput mediale of M. triceps brachii; k, intermediate portion of caput mediale of M. triceps brachii; l, short portion of caput mediale of M. triceps brachii; m, cut end of M. clavobrachialis; n, M. brachioradialis; o, M. extensor carpi radialis longus; p, M. extensor carpi radialis brevis; q, M. pronator teres; r, M. flexor carpi radialis; s, M. palmaris longus (s′, its tendons); t, M. flexor carpi ulnaris (t, ulnar head; t′, humeral head); u, third head of M. flexor profundus digitorum; u′, fifth head of M. flexor profundus digitorum; u″, one of the tendons of M. flexor profundus digitorum; v, M. pronator quadratus; w, M. abductor brevis pollicis; x, ulnar part of M. flexor sublimis digitorum. 1, transverse ligament of the wrist.]

Relations.--Lateral surface with the scapula and the capsule of the shoulder-joint. Medial surface with the levator scapulæ (Fig. 73, h), serratus anterior (Fig. 73, i), part of the scalenus (Fig. 73, f), the transversus costarum (Fig. 73, j), and the coracobrachialis (Fig. 77, f). Cranial border with the supraspinatus (Fig. 77, d). Caudal border with the teres major (Fig. 77, c) and infraspinatus (Fig. 75, c).