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Muscles of the Pectoral Girdle

Q: Where does the teres minor muscle originate and insert?

The teres minor muscle (m. teres minor) originates from the upper part of the lateral border of the scapula. The muscle lies in the infraspinous bed, covered by the infraspinous fascia, and its upper margin borders the lower edge of the infraspinatus muscle. It inserts into the greater tubercle of the humerus, specifically blending into its lower facet, lying inferior to the tendon of the infraspinatus muscle.

Q: What functions does the subscapularis muscle perform?

The subscapularis muscle (m. subscapularis) performs medial rotation of the arm, depression of the raised arm, adduction of the arm, and anterior-to-posterior arm movement. Additionally, as part of the rotator cuff, it provides dynamic stabilization of the shoulder joint and rotation of the humeral head. The deep tendinous bundle of the muscle forms the floor of the biceps tendon sheath, contributing to its stability, while the superficial fibers form the roof of the intertubercular sulcus.

Q: What is the blood supply and innervation of the teres major muscle?

The teres major muscle (m. teres major) is innervated by the thoracodorsal nerve (segments C5–C8), which arises from the posterior cord of the brachial plexus. Specific information regarding the blood vessels supplying this muscle is not detailed in standard sources. Together with the latissimus dorsi and subscapularis muscles, it participates in medial rotation, adduction, and depression of the raised arm.

Musculi cinguli membri superioris

For medical students3 min readUpdated 2026-10-10

The muscles of the pectoral girdle (shoulder girdle) are a specialized group of muscles that provide a wide range of movements at the glenohumeral joint. According to classification, they are distinct from the muscles of the free upper limb and topographically connect the pectoral girdle structures to the trunk and free limb.

CompositionThe group includes precisely 6 muscle bellies

Primary RoleProviding mobility and stabilization of the shoulder joint

Shoulder CuffThe supraspinatus muscle is a critical element of the rotator cuff

General Classification of Upper Limb Muscles

The entire muscular system of the human upper limb is conventionally divided into two major topographical groups:

Muscles of the pectoral girdle — their primary task is connecting the bones of the girdle, such as the clavicle and scapula, to the trunk, as well as controlling the shoulder joint.
Muscles of the free upper limb — this group is responsible for the direct movements of the arm, forearm, and hand in space.

Directly belonging to the pectoral girdle (mm. cinguli membri superioris) are 6 muscles, whose coordinated action enables the shoulder joint to perform complex biomechanical tasks. These include:

Deltoid muscle (m. deltoideus)
Supraspinatus muscle (m. supraspinatus)
Infraspinatus muscle (m. infraspinatus)
Teres minor muscle (m. teres minor)
Teres major muscle (m. teres major)
Subscapularis muscle (m. subscapularis)

Deltoid Muscle (m. deltoideus)

A large, superficially positioned muscle that forms the rounded contour of the shoulder.

Anatomical Landmarks:

Origins (O): muscle fibers arise from the lateral third of the clavicle, the acromion, and the spine of the scapula.
Insertion (I): fibers converge and firmly attach to the deltoid tuberosity of the humerus (tuberositas deltoidea humeri).
Functional Features (A): The muscle has a complex structure, and its fibers can work either independently or synergistically. Upon general contraction, it abducts the arm (up to 60°). The anterior fibers are responsible for flexion and medial rotation (pronation) of the arm, while the posterior fibers perform the opposite task—extending the arm and lateral rotation (supination).

Blood Supply and Innervation: Tissue perfusion is supplied by the posterior circumflex humeral artery (a. circumflexa humeri posterior) and the thoracoacromial artery (a. thoracoacromialis). Innervation is provided by the axillary nerve — n. axillaris (segments C₅–C₆).

Clinical Feature: To reduce friction between the deep surface of the muscle and the greater tubercle of the humerus, the synovial subdeltoid bursa (bursa subdeltoidea) is located here.

Supraspinatus Muscle (m. supraspinatus)

An essential element of the scapular muscular apparatus, concealed beneath the trapezius muscle.

Origin (O): occupies the supraspinous fossa of the scapula (fossa supraspinata scapulae).
Insertion (I): the tendon attaches to the superior facet of the greater tubercle of the humerus (tuberculum majus humeri).
Biomechanics (A): acts as a synergist to the deltoid muscle, initiating arm abduction (responsible for the first 15–20° of movement). Additionally, it closely adheres to the joint, stabilizing it.
Innervation (N): suprascapular nerve, n. suprascapularis (C₅–C₆).
Blood Supply (V): suprascapular artery (a. suprascapularis) and circumflex scapular artery (a. circumflexa scapulae).

Clinically, this muscle is extremely important as it forms part of the rotator cuff—the structure most frequently prone to injuries and degenerative changes in sports medicine and traumatology.

Infraspinatus Muscle (m. infraspinatus)

A broad, flat muscle occupying most of the posterior surface of the scapula inferior to its spine.

Origin (O): arises from the walls of the infraspinous fossa of the scapula (fossa infraspinata scapulae).
Insertion (I): attaches to the middle facet of the greater tubercle of the humerus (tuberculum majus humeri).
Function (A): serves as a powerful lateral rotator (rotates the arm externally). A special role of this muscle is that upon contraction, it pulls the capsule of the shoulder joint away, effectively preventing its impingement between the articular surfaces during active movements.
Innervation (N): like the supraspinatus muscle, it is innervated by the suprascapular nerve — n. suprascapularis (C₅–C₆).
Blood Supply (V): receives arterial blood from the a. circumflexa scapulae and a. supraspinatus.

Mnemonic

Two "spinatus" muscles (supraspinatus and infraspinatus), two "teres" muscles (major and minor), the deltoid, and the subscapularis—an easy way to remember all 6 pectoral girdle muscles.

Frequently asked questions

Where does the teres minor muscle originate and insert?

The teres minor muscle (m. teres minor) originates from the upper part of the lateral border of the scapula. The muscle lies in the infraspinous bed, covered by the infraspinous fascia, and its upper margin borders the lower edge of the infraspinatus muscle. It inserts into the greater tubercle of the humerus, specifically blending into its lower facet, lying inferior to the tendon of the infraspinatus muscle.

What functions does the subscapularis muscle perform?

The subscapularis muscle (m. subscapularis) performs medial rotation of the arm, depression of the raised arm, adduction of the arm, and anterior-to-posterior arm movement. Additionally, as part of the rotator cuff, it provides dynamic stabilization of the shoulder joint and rotation of the humeral head. The deep tendinous bundle of the muscle forms the floor of the biceps tendon sheath, contributing to its stability, while the superficial fibers form the roof of the intertubercular sulcus.

Which muscles form the rotator cuff of the shoulder?

The rotator cuff of the shoulder is formed by a complex group of muscles whose tendons blend into the shoulder joint capsule and attach to the tubercles of the humerus. It includes:

Subscapularis muscle (m. subscapularis)
Supraspinatus muscle (m. supraspinatus)
Infraspinatus muscle (m. infraspinatus)
Teres minor muscle (m. teres minor)

These muscles provide dynamic joint stabilization and rotation of the humeral head.

What is the blood supply and innervation of the teres major muscle?

The teres major muscle (m. teres major) is innervated by the thoracodorsal nerve (segments C5–C8), which arises from the posterior cord of the brachial plexus. Specific information regarding the blood vessels supplying this muscle is not detailed in standard sources. Together with the latissimus dorsi and subscapularis muscles, it participates in medial rotation, adduction, and depression of the raised arm.

Which muscles initiate arm abduction?

Abduction is initiated by the supraspinatus muscle (providing the first 15–20 degrees), after which the deltoid muscle actively engages, carrying abduction further up to 60 degrees.

Which structure protects the joint capsule from impingement?

This function is performed by the infraspinatus muscle. During movements, it pulls back the capsule of the shoulder joint, preventing it from getting trapped between the bones.

From which spinal cord segments do these discussed muscles receive innervation?

The deltoid, supraspinatus, and infraspinatus muscles are innervated by branches of the brachial plexus, whose fibers originate from spinal segments C₅–C₆.

Go deeper

Anatomy of the teres minor muscle (m. teres minor)
Anatomy of the teres major muscle (m. teres major)
Topography and functions of the subscapularis muscle (m. subscapularis)
Structure and biomechanics of the rotator cuff
Blood supply of the shoulder joint and scapular anastomoses