HUMAN ANATOMY ATLAS - G. L. Bilich - 2014

Muscular System

MUSCLES OF THE SHOULDER GIRDLE

The Muscles of the shoulder girdle (Pectoral Girdle) surround the shoulder joint anteriorly, superiorly, and posteriorly. The superficial layer is formed by the deltoid Muscle, while the deep layer comprises the supraspinatus, infraspinatus, teres major, teres minor, and subscapularis muscles.

The deltoid muscle (m. deltoideus) is a thick, convex, triangular plate located directly beneath the Skin. This muscle covers the shoulder joint from the front, top, back, and lateral side, creating the rounded contour of the shoulder. The multipennate deltoid muscle originates by a short tendon from the anterior border of the lateral third of the clavicle, the lateral margin of the acromion, the spine of the scapula, and, partially, from the infraspinatous fascia. The fascicles of its three portions (corresponding to their origin), separated from one another by Connective Tissue septa, converge laterally toward the lateral aspect of the humerus and insert into its deltoid tuberosity (see Figs. 303, 304, 305, 306). The superficial fascicles of the deltoid muscle are fleshy, whereas the deep ones are tendinous. The anterior border of the deltoid muscle borders the superior margin of the pectoralis major muscle. Between these muscles lies a narrow, triangular deltopectoral groove (sulcus deltoideopectoralis), which widens near the clavicle. The subdeltoid bursa (bursa subdeltoidea) is situated beneath the deltoid muscle, between the deep lamina of the Fascia of the same name and the greater tubercle of the humerus; in approximately 10% of cases, it communicates with the cavity of the shoulder joint.

As an anatomical variant, the scapulocostodeltoid muscle—known as Calori's muscle—arises from the lateral border of the scapula and inserts into the deltoid muscle or its aponeurosis. This muscle is highly variable in shape and attachment (Luigi Calori, 1807–1896, an Italian anatomist).

Function: The deltoid muscle abducts the arm from the trunk up to the horizontal level; its anterior clavicular part flexes the shoulder, medially rotating it, and lowers the raised arm; its posterior part extends the shoulder, laterally rotating it simultaneously, and lowers the raised arm.

Innervation: Axillary nerve (C_V—C_VI).

Blood supply: Thoracoacromial artery, posterior circumflex humeral artery.

The supraspinatus muscle (m. supraspinatus) is a flat, triangular plate located in the supraspinous fossa and covered superiorly by the trapezius muscle. It originates from The surface of the supraspinous fossa of the scapula and the supraspinatous fascia. The muscle fascicles pass laterally and insert by a short tendon into the superior facet of the greater tubercle of the humerus (Figs. 307, 308, 309, 310). The tendon passes beneath the coracoid process and the coracohumeral ligament, where it blends with the capsule of the shoulder joint.

Function: The supraspinatus muscle abducts the shoulder when the scapula is fixed, acting as a synergist to the deltoid muscle; it pulls the capsule of the shoulder joint upward, protecting it from pinching.

Blood supply: Suprascapular artery, circumflex scapular artery.

Innervation: Suprascapular nerve (C_V—C_VI).

The infraspinatus muscle (m. infraspinatus) is a flat, triangular plate located in the infraspinous fossa, covered by the deltoid and trapezius muscles. It originates from the surface of the infraspinous fossa of the scapula and the infraspinatous fascia. The muscle fascicles converge laterally and superiorly, pass posterior to the shoulder joint, and insert into the middle posterior facet of the greater tubercle of the humerus via a short tendon (see Figs. 307, 309, 310). In the area of attachment to the bone, There is a subtendinous infraspinatus synovial bursa (bursa subtendinea musculi infraspinati).

Function: The infraspinatus muscle laterally rotates (supinates) the shoulder and adducts it toward the trunk, and pulls on the Joint Capsule, into which some of its fascicles blend.

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Fig. 303. Muscles of the right upper limb (fasciae removed), anterior view:

1 — Flexor digitorum profundus; Tendons; 2 — - Tendon sheath; 3 — Thenar eminence; 4 — Extensor carpi radialis longus; 5 — Brachioradialis; 6 — Deltoid; 7 — Clavicle; 8 — Pectoralis major; 9 — Biceps brachii; 10 — Braehialis; 11 — Pronator teres; 12— Flexor carpi radialis; 13 — Palmaris longus; Tendon; 14 — Flexor digitorum superficial is; Tendon; 15 — Flexor carpi ulnaris; Tendon; 16 — Flexor retinaculum; 17— Hypothenar eminence; 18 — Flexor digitorum superficialis; Tendons

Fig. 304. Muscles of the right upper limb and chest, lateral view:

1— Dorsal interossei; 2 — Extensor pollicis longus: Tendon; 3 — Extensor retinaculum; 4 — Extensor pollicis brevis; 5 — Extensor digitorum; Tendon; 6 — Radius; 7— Extensor carpi radialis brevis; 8— Extensor digitorum; 9 — Anconeus; 10 — Olecranon; 11 — Lateral intermuscular septum of arm; 12 — Triceps brachii; Tendon; 13 — Latissinius dorsi; 14 — Triceps brachii, lateral HEAD; 15 — Triceps brachii, long head; 16 — Teres major; 17— Teres minor; 18— Infraspinous fascia; 19 — Trapezius; 20— Spine of scapula; 21 — Acromion; 22— Sternocleidomastoid; 23 — Clavicle; 24 — Pectoralis major; 25 — Deltoid; 26 — Pectoralis major, abdominal part; 27 — Serratus anterior; 28 — Rectus sheath, anterior layer; 29 —External oblique; 30 — Biceps brachii; 31 — Brachialis; 32— Lateral epicondyle; 33— Brachioradiaiis; 34 — Extensor carpi radialis longus; 35 — Flexor carpi radialis; 36 — Flexor pollicis longus; 37 — Abductor pollicis longus; 38— Abductor pollicis longus; Tendon; 39— Extensor pollicis brevis; Tendon; 40 — Adductor pollicis

Fig. 305. Muscles of the right upper limb (fasciae and extensor retinaculum removed), posterior view:

1— Extensor carpi ulnaris; 2 — Anconeus; 3 — Teres major; 4 — Teres minor; 5 — Infraspinatus; 6 — Trapezius; 7— Acromion; 8 — Deltoid; 9 — Triceps brachii; 10 — Brachioradialis; 11— Extensor carpi radialis longus; 12— Extensor carpi radialisbrevis; 13— Extensor digitorum; 14 — Dorsal interossei

Blood supply: Circumflex scapular artery, suprascapular artery.

Innervation: suprascapular nerve (C_V—C_VI).

The teres minor muscle is an elongated, cylindrical muscle positioned inferior to the infraspinatus and partially covered by the scapular part of the deltoid muscle (Fig. 310, see Fig. 307). It originates from the lateral border of the scapula and the infraspinous fascia, courses superiorly and laterally, and inserts into the lower posterior facet of the greater tubercle of the humerus (see Fig. 309). Some of its muscle bundles blend into the capsule of the shoulder joint.

Action: The teres minor laterally rotates (supinates) the arm, acting as a synergist to the subscapularis and the scapular part of the deltoid; it also pulls on the capsule of the shoulder joint, preventing its impingement.

Blood supply: circumflex scapular artery and suprascapular artery.

Innervation: suprascapular nerve (C_V).

Table 46. Muscles of the Upper Limb

Fig. 306. Deltoid muscle, right, all other muscles removed (A — lateral view, B — posterior view, C — origin and insertion sites of the deltoid muscle (diagram)):

1 — Shaft of humerus; Body of humerus; 2 — Scapula; 3 — Deltoid, spinal part; 4 — Deltoid, acromial part; 5 — Spine of scapula; 6 — Acromion; 7 — Clavicle; 8 — Deltoid, clavicular part; 9— Deltoid tuberosity; 10— Scapula, costal surface; 11 — Coracoid process

Fig. 307. Muscles of the right shoulder girdle: supraspinatus, infraspinatus, teres minor, subscapularis, posterior view:

1 — Scapula, inferior angle; 2 — Scapula, medial border; Crest of lesser tubercle; Medial lip; 3 — Spine of scapula; 4 — Supraspinatus; 5 - Scapula, superior angle; 6 — Acromion; 7 - Coracoid process; 8 - Greater tubercle; 9 — Teres minor; 10 — Shaft of humerus; Body of humerus; 11 — Infraspinatus; 12— Scapula, lateral border

Fig. 308. Muscles of the right shoulder girdle: supraspinatus, infraspinatus, teres minor, subscapularis, anterior view:

1 - Shaft of humerus; Body of humerus; 2 — Crest of lesser tubercle; Medial lip; 3 — Crest of greater tubercle; Lateral lip; 4 — Coracoid process; 5 —- Intertubercular sulcus; Bicipital groove; 6— Lesser tubercle; 7 — Greater tubercle; 8 — Acromion; 9 — Scapula, superior angle; 10- Supraspinatus; 11 — Scapula, superior border; 12— Suprascapular notch; 13 — Scapula, medial border; 14 — Subscapularis; 15 — Scapula, inferior angle

Fig. 309. Origin and insertion of muscles: supraspinatus, infraspinatus, and teres minor (diagram):

1 — Teres minor; 2 — Infraspinatus; 3 — Supraspinatus

The teres major muscle is cylindrical and somewhat flattened, situated near the lateral border of the scapula and covered by the distal tendon of the latissimus dorsi. It originates from the lower part of the lateral border and the inferior angle of the scapula, as well as from the infraspinous fascia. The muscle inserts via a broad, flat tendon into the crest of the lesser tubercle of the humerus, inferior and slightly posterior to the insertion of the latissimus dorsi tendon (see Fig. 310). The muscle bundles of the teres major course along the lateral border of the scapula, crossing the humerus from the medial side inferior to the level of the surgical neck. A subtendinous bursa of the teres major muscle (bursa subtendinea musculi teretis majoris) is located near the insertion site.

Action: With a fixed scapula, the teres major extends the arm at the shoulder joint, pronates it, and adducts the elevated arm to the trunk. With a fixed upper limb, it pulls the inferior angle of the scapula laterally and displaces it anteriorly.

Fig. 310. Muscles of the right upper limb, posterior view:

1 — Triceps brachii, long head; 2 — Teres major; 3 — Infraspinatus; 4 — Inferior angle; 5 — Teres minor; 6 — Supraspinatus; 7— Spine of scapula; 8 — Deltoid; 9 — Triceps brachii, lateral head

Fig. 311. Origin and insertion of the subscapularis muscle (diagram):

1 — Supraspinatus

Fig. 312. Muscles of the left pectoral girdle, posterior view:

1 — Spatium axilare mediale; Triangular space; 2 — Spatium axilare laterale; Quadrangular space; 3 — Triceps brachii, long head; 4 — Triceps brachii, lateral head; 5 — Glenohumeral joint; Shoulder joint; Joint capsule; Articular capsule; 6 — Humerus, surgical neck; 7 — Deltoid; 8 — Subdeltoid bursa; 9 — Acromion; 10 — Omohyoid, inferior belly; 11 — Levator scapulae; 12 — Superior angle; 13 — Rhomboid minor; 14 — Supraspinatus; 15 — Trapezius; 16 — Rhomboid major; 17 — Spine of scapula; 18 — Infraspinatus; 19 — Teres minor; 20 — Teres major; 21 — Inferior angle; 22 — Serratus anterior; 23 — Latissimus dorsi

Innervation: subscapular nerve (C_V–C_VII).

Blood supply: subscapular artery.

The subscapularis muscle (m. subscapularis) is a thick, triangular muscle located in the subscapular fossa. It arises from the costal surface of the scapula, its lateral margin, and partially from the subscapular fascia via muscular bundles. Passing laterally, the muscle inserts via a flat tendon into the lesser tubercle and the crest of the lesser tubercle of the humerus (Fig. 311, see Fig. 308). The tendon of the subscapularis lies adjacent to the anteroinferior surface of the shoulder joint capsule, and the inferior margin of the muscle contacts the teres major. Between the subscapular tendon and the shoulder joint capsule lies the subtendinous bursa of the subscapularis muscle (bursa subtendinea musculi subscapularis), which typically communicates with the cavity of the shoulder joint.

Function: The subscapularis muscle pronates the arm, medially rotates it, and adducts it toward the trunk.

Blood supply: subscapular artery.

Innervation: subscapular nerve (C_V–C_VII).

Between the clavicle and the scapula, a small and rare anatomical variant may occasionally be found: Rousseau's muscle (syn.: deep acromioclavicular muscle, m. acromioclavicularis profundus) (named after Louis François Emmanuel Rousseau, 1788–1868, a French anatomist and histologist). Covered by the deltoid muscle, it originates from the clavicle at the junction of its middle and lateral thirds and inserts into the apex of the acromion of the scapula.