Anatomy · Muscles

Latissimus dorsi

The broadest muscle of the back

Back · superficial layer, moves the arm

A huge, flat, triangular sheet that covers the lower back and the lower half of the rib cage, then narrows to a twisted tendon in the armpit. It pulls the raised arm down and back, and is the main muscle of climbing, rowing and swimming pulls. Together with teres major it makes the fold of skin at the back of the armpit.

How to spot them

▸A broad triangle on the back, wide at the lower spine and hip crest, narrowing to a tendon at the armpit
▸Its lower fibres come from the spines of the lower six thoracic vertebrae, the iliac crest and the lowest ribs; all converge on the humerus
▸Forms the back wall of the armpit, together with teres major
▸Supplied by the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus

What to know

The broadest muscle of the back, a triangular sheet running from the lower spine to the upper arm bone

Latissimus dorsi — its name means broadest muscle of the back.

Its flat tendon twists through a half-turn before attaching to the floor of the groove between the tubercles of the humerus

Latissimus dorsi — it inserts into the intertubercular sulcus, just in front of teres major.

Pulls the raised arm forcefully down and back, as in climbing a rope or the pull phase of swimming

Latissimus dorsi — extension, adduction and medial rotation of the shoulder.

Its lower border helps to form the lumbar triangle, with the iliac crest and the external oblique, a weak spot where hernias can occur

Latissimus dorsi — the lumbar triangle of Petit.

Supplied by the thoracodorsal nerve, from the posterior cord of the brachial plexus, and by the artery of the same name

Latissimus dorsi — the nerve runs with the thoracodorsal artery on its deep surface.

A large flap of it, kept on its vessels, can be swung round to rebuild a breast or cover a defect on the chest wall

Latissimus dorsi flap — widely used in reconstructive surgery.

The muscle that gives a V-shaped taper to the upper body and is worked by pull-ups

Latissimus dorsi — the wide back of a swimmer or gymnast.

Key ideas

Because the tendon lies below and behind the armpit, the muscle works on the arm when the hand is fixed: it lifts the body up to the hand in a pull-up, as well as pulling the arm down to the body.
Its wide origin from the thoracolumbar fascia links the arm to the pelvis, so it also helps to transmit force across the back in walking and throwing.

Quick-fire facts

•The broadest muscle of the back, and among the largest in surface area in the body
•Origin: spinous processes of the lower six thoracic vertebrae (T7 to T12), the thoracolumbar fascia, the posterior iliac crest and the lower three or four ribs, plus a small slip from the tip of the scapula
•Insertion: floor of the intertubercular (bicipital) groove of the humerus
•Action: extends, adducts and medially rotates the arm at the shoulder joint
•Nerve supply: thoracodorsal nerve (roots C6 to C8), from the posterior cord of the brachial plexus
•Blood supply: thoracodorsal artery, from the subscapular artery
•The lumbar triangle (of Petit) lies between its lateral edge, the external oblique and the iliac crest; the triangle of auscultation is bordered by it, the trapezius and the scapula
•The tendon and teres major together form the posterior axillary fold
•It can be used as a muscle flap in breast reconstruction or to cover large defects because of its reliable blood supply

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Sources

TeachMeAnatomy — Latissimus dorsi
TeachMeAnatomy — Superficial back muscles