Human Anatomy - Kotsan I. Ya. 2009

Muscles and fascia of the upper limb
Muscles of the pectoral girdle

The Muscles of the Pectoral Girdle surround the shoulder joint on all sides. The superficial layer is formed by the deltoid Muscle, while the deep layer consists of the supraspinatus, infraspinatus, teres minor, teres major, and subscapularis muscles (Figs. 115, 116, 117).

The deltoid muscle (m. deltoideus) lies directly beneath the Skin and covers the shoulder joint anteriorly, posteriorly, superiorly, and laterally, giving the shoulder its characteristic rounded shape. The muscle is somewhat reminiscent of an inverted Greek letter "delta," from which it derives its name. The deltoid originates from the acromial end of the clavicle, the acromion, and the spine of the scapula, and inserts into the deltoid tuberosity of the humerus. Function: When all PARTS OF THE muscle contract, it abducts the arm to the horizontal plane (approximately 70°); the anterior fibers pull the arm forward (flexion) and medially rotate (pronate) it, while the posterior fibers pull the arm backward (extension) and laterally rotate (supinate) it. If the anterior part contracts simultaneously with the middle part, following the parallelogram of forces, the muscle flexes and slightly abducts the arm. If the middle part works together with the posterior part, extension and abduction of the arm occur simultaneously.

Innervation: axillary nerve (C_V–C_VI).

The supraspinatus muscle (m. supraspinatus) is triangular in shape and located beneath the trapezius muscle in the supraspinatous fossa of the scapula. It originates from this fossa and the overlying fascia, and inserts into the superior facet of the greater tubercle of the humerus and the capsule of the shoulder joint. Function: abducts the arm and pulls on the shoulder Joint Capsule, protecting it from impingement.

Innervation: suprascapular nerve (C_V–C_VI).

The infraspinatus muscle (m. infraspinatus) is partially covered by the deltoid and trapezius muscles. It is located in the infraspinatous fossa of the scapula.

It originates from the posterior surface of the scapula below its spine and from the infraspinatous fascia, and inserts into the middle facet of the greater tubercle of the humerus and the shoulder joint capsule. Function: adducts, supinates, and extends the arm at the shoulder joint. Additionally, during supination of the arm, it simultaneously pulls on the shoulder joint capsule, protecting it from impingement.

Innervation: suprascapular nerve (C_V–C_VI).

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Fig. 115. Muscles of the shoulder girdle and arm (lateral view, right arm)

1 — supraspinatus fascia, 2 — clavicle, 3 — acromion, 4 — deltoid muscle, 5 — biceps brachii, 6 — brachialis, 7 — brachioradialis, 8 — extensor carpi radialis longus, 9 — forearm fascia, 10 — anconeus, 11 — olecranon, 12 — medial HEAD of triceps brachii, 13 — tendon of triceps brachii, 14 — lateral head of triceps brachii, 15 — long head of triceps brachii, 16 — teres major, 17 — infraspinatous fascia, 18 — spine of scapula

The teres minor muscle (m. teres minor) lies inferior to the infraspinatus. It originates from the posterior surface of the scapula below the infraspinatus muscle and from the infraspinatous fascia. It inserts into the inferior facet of the greater tubercle of the humerus and the shoulder joint capsule. Function: assists in adduction, supination, and extension of the arm, and pulls on the shoulder joint capsule.

Innervation: axillary nerve (C_V).

The teres major muscle (m. teres major) lies closely against the latissimus dorsi. In shape, the muscle is quadrilateral rather than round, but in a living person during contraction, it truly forms a rounded elevation. In cross-section, this muscle also appears somewhat rounded. The teres major originates from the inferior angle and the lower part of the lateral border of the scapula, as well as from the infraspinatous fascia. It inserts via a broad, flat tendon into the crest of the lesser tubercle of the humerus. Function: adduction, pronation, and extension of the arm.

Innervation: subscapular nerve (C_V–C_VII).

The subscapularis muscle (m. subscapularis) is thick, broad, and triangular in shape, occupying nearly the entire costal surface of the scapula, from which it originates. The muscle inserts into the lesser tubercle of the humerus and the shoulder joint capsule. Function: pronates the arm and adducts it toward the trunk.

Innervation: subscapular nerve (C_V–C_VI).