Latissimus dorsi

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ΕΤΥΜΟΛΟΓΙΑ

Latin. Literally 'very wide of the back'

Latissimus dorsi is a large muscle of the lower back, axilla and shoulder.

Contents

Surface Anatomy

Latissimus dorsi
Latissimus dorsi.GIF
System: Muscle
Function: Extends, adducts and medially rotates the humerus; also helps in respiration
Origin: Spine of T7, all spinous processes and supraspinous ligaments from T8 to the end of the sacrum, the lumbar fascia, posterior third of the iliac crest, lower four ribs and inferior angle of the scapula
Branches:
Insertion: Floor of the spiral groove of the humerus
Arterial supply:
Venous drainage:
Lymphatic drainage:
Innervation: Thoracodorsal nerve (C6 - C8)
Vertebral levels:
Search for Latissimus dorsi in Gray's.

The wide origin of latissimus dorsi is palpable where it is not covered by trapezius. It forms the posterior wall of the axilla and is easily palpable there.

Shape

Latissimus dorsi is a triangular flat muscle, covering the lumbar and lower thoracic areas. It contracts as it moves laterally into a relatively small fascicle which attaches to the humerus. It arises by tendinous fibres from the spinous processes of the lower thoracic vertebrae, and indirectly from the lumbar and sacral vertebrae, the crest of the ilium and supraspinal ligament via the lumbodorsal fascia. It arises from the lateral part of the ilium through a muscular connection, and from the lower four ribs via muscular digitations which interdigitate with external oblique. Its upper fibres pass transversely, its middle fibres obliquely superolaterally and its lower fibres almost vertically upwards, to converge as a thick fascicle. This crosses the inferior angle of the scapula and receives a few fibres from it. It then curves around the inferior border of teres major, and twists at this point so that its inferior fibres become superior and vice versa. It ends as a quadrilateral tendon which inserts into the intertubercular groove of the humerus. Its lower end unites with the tendon of teres major, and the deep fascia of the upper arm.

The muscle forms the border of a number of different areas:

Actions

Joints Affected

Origin

Insertion

  • Intertubercular groove of the humerus

Nerve Supply

Relations

Clinical Relevance

Variations

  • Attaches to a variable number of thoracic vertebrae
  • The number of costal attachments varies
  • Fibres may not attach to the iliac crest
  • A muscular branch, the axillary arch, may arise from the upper edge of the muscle in the middle of the posterior fold of the axilla, to cross the axilla in front of its neurovascular structures, in about 7% of people
  • A fibrous or muscular slip passes from the lower border of the tendon near its insertion to the long head of triceps
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