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Latissimus Dorsi Muscle

Q: Which wall of the axillary fossa is formed by the latissimus dorsi?

The latissimus dorsi (m. latissimus dorsi) contributes to the formation of the posterior wall of the axillary fossa. Along with it, the posterior wall is formed by the teres major (m. teres major), subscapularis (m. subscapularis), and the long head of the triceps brachii (caput longum m. tricipitis brachii).

Q: To which layer of superficial back muscles does the latissimus dorsi belong?

The latissimus dorsi (m. latissimus dorsi) belongs to the first muscular layer. It is part of the superficial back muscle group located superficial to the fascia, responsible for moving the upper limb. In this layer, its fibers run inferolaterally from superomedial. The divergence of the borders of the latissimus dorsi and the external oblique abdominis forms a weak point in this first layer—the lumbar triangle (Petit's triangle).

*musculus latissimus dorsi*

For medical students2 min readUpdated 2026-10-10

The latissimus dorsi is a large, triangular flat muscle that covers the lumbar region and lower half of the thoracic region. It is responsible for adduction, extension, and medial rotation of the arm, and plays a key role in pulling the torso upward when the upper limbs are fixed.

InsertionCrest of the lesser tubercle of the humerus

InnervationThoracodorsal nerve (C6–C8)

Blood SupplyThoracodorsal artery and posterior intercostal arteries

AntagonistsPartially — superficial chest muscles

Origin and Insertion

The latissimus dorsi has an extensive origin spanning a significant portion of the trunk's skeletal framework. Its fibers originate from the following anatomical structures:

Spinous processes of the lower thoracic and all lumbar vertebrae (Th7 to L5).
Dorsal surface of the sacrum, forming a strong aponeurosis in the lower back.
External lip of the iliac crest of the hip bone.
Lower 3–4 ribs, where muscular slips frequently interdigitate with other muscle groups.

From this broad origin line, the muscle fascicles converge upward and laterally, gradually narrowing into a thick tendon that inserts onto the crest of the lesser tubercle of the humerus. Consequently, the muscle connects the spine and pelvis to the upper limb, dictating its biomechanical properties.

Biomechanics and Functions

Due to its anatomical layout, the musculus latissimus dorsi exerts a powerful action on the shoulder joint. Several main actions are recognized:

Adduction of the arm — pulls the abducted arm back toward the trunk.
Extension of the arm — moves the upper limb posteriorly.
Medial rotation (pronating) of the arm — rotates the humerus inward around its longitudinal axis.

The muscle's action with fixed upper limbs (e.g., during pull-ups) is particularly significant. In this scenario, the origin and insertion points swap roles: upon contraction, the latissimus dorsi pulls the torso up toward the upper limbs.

Blood Supply and Innervation

Functioning as such a massive muscle requires adequate blood supply and robust neural control.

Innervation is supplied by the thoracodorsal nerve (nervus thoracodorsalis), which arises from spinal nerve roots C6–C8.
Blood supply is provided by the thoracodorsal artery (arteria thoracodorsalis), along with branches of the posterior intercostal arteries (arteriae intercostales posteriores), which nourish the muscle slips originating from the ribs and spine.

Topographic Comparison: Deep Muscles of the Back

Unlike the superficial latissimus dorsi, deep back layers consist of entirely different structures. The deepest back muscles are the rotator muscles (musculi rotatores).

Their anatomical features:

Divided into long rotators and short rotators (rotatores longi and breves).
Innervated by spinal nerves throughout the entire length from C1 to L1.
Function: rotate vertebrae around the longitudinal axis and play a critical role in proprioception, providing the brain with feedback on spinal column position.

Superficial Chest Muscles as Functional Partners

To fully understand shoulder girdle biomechanics, it is essential to know the anterior trunk muscles that act synergistically or antagonistically with back muscles.

Muscle	Origin and Insertion	Innervation	Functions
Pectoralis major (m. pectoralis major)	Clavicle, sternum, cartilages of ribs II–VII, rectus sheath → crest of the greater tubercle of the humerus	Medial and lateral pectoral nn. (C5–Th1)	Adduction, medial rotation, flexion of the arm. Assists with inspiration when fixed
Pectoralis minor (m. pectoralis minor)	Ribs II–V → coracoid process of the scapula	Medial pectoral n.	Pulls scapula anteriorly and inferiorly, assists with inspiration
Subclavius (m. subclavius)	Rib I → groove on the inferior surface of the clavicle	Subclavius n. (C5–C6)	Stabilizes the clavicle, depresses it
Serratus anterior (m. serratus anterior)	Ribs I–IX → medial border and inferior angle of the scapula	Long thoracic n. (C5–C7)	Protracts and rotates the scapula upward, fixes it against the thoracic wall

Mnemonic

To easily remember the primary action of the latissimus dorsi with free arms, picture a freestyle swimmer's stroke: the arm is forcefully adducted to the body, extended backward, and medially rotated (turned inward).

Frequently asked questions

Which wall of the axillary fossa is formed by the latissimus dorsi?

The latissimus dorsi (m. latissimus dorsi) contributes to the formation of the posterior wall of the axillary fossa. Along with it, the posterior wall is formed by the teres major (m. teres major), subscapularis (m. subscapularis), and the long head of the triceps brachii (caput longum m. tricipitis brachii).

What fascia covers the latissimus dorsi and forms a sheath for it?

The latissimus dorsi is covered by the thoracolumbar fascia (fascia thoracolumbalis). In the lumbar region, it forms sheaths for several muscles, including the latissimus dorsi (m. latissimus dorsi).

Additionally, like other superficial back muscles, it is covered by the superficial back fascia—a thin subcutaneous layer containing adipose tissue, vessels, and nerves. The thoracolumbar fascia itself blends with the fascia of the latissimus dorsi and the aponeurosis of the abdominal muscles.

Which muscles act as synergists to the latissimus dorsi during arm adduction?

Synergists of the latissimus dorsi in arm adduction include the pectoralis major (m. pectoralis major), teres major (m. teres major), and subscapularis (m. subscapularis), as established anatomical sources note their involvement in shoulder adduction. The pectoralis minor is not listed among adductors in standard references.

To which layer of superficial back muscles does the latissimus dorsi belong?

The latissimus dorsi (m. latissimus dorsi) belongs to the first muscular layer. It is part of the superficial back muscle group located superficial to the fascia, responsible for moving the upper limb.

In this layer, its fibers run inferolaterally from superomedial. The divergence of the borders of the latissimus dorsi and the external oblique abdominis forms a weak point in this first layer—the lumbar triangle (Petit's triangle).

What structure serves as the insertion point for this muscle?

The latissimus dorsi inserts onto the crest of the lesser tubercle of the humerus.

What happens to the trunk if the upper limbs are rigidly fixed (e.g., on a pull-up bar)?

When the upper limbs are fixed, the latissimus dorsi acts as the primary prime mover to pull the torso upward.

Which spinal cord segments give rise to the nerve supplying the latissimus dorsi?

The muscle is innervated by the thoracodorsal nerve, whose fibers originate from cervical segments C6, C7, and C8.

Go deeper

Anatomy of the deep back muscles: short and long rotators
Biomechanics of the shoulder joint and the role of chest muscles in arm adduction
Innervation of superficial chest muscles: medial and lateral pectoral nerves
Topography of the serratus anterior and its role in scapular stabilization
Blood supply to the back muscles: posterior intercostal artery system