Latissimus Dorsi

Diagram of Posterior Muscles of the Human Body

Diagram of posterior muscles.

The latissimus dorsi muscles* are broad superficial muscles that extend across much of the back and around the sides of the upper-torso.


Origin, Insertion and Actions of the Latissimus dorsi muscles:

Points of Origin:
  • Spinous processes of vertebrae T7 to T12 (the lower 6 thoracic vertebrae) and L1-L5 (all the lumbar vertebrae) - in all cases via an extensive membrane called the thoracolumbar fascia or lumbodorsal fascia (alternative name for the same membrane)
  • Posterior part of the iliac crest (on the iliac bone)
  • Lowest 3 or 4 ribs
  • Inferior angle of the scapula bone
Point of Insertion:
  • Bicipital groove of humerus (bone).
Actions:
  • Adducts the arm at the shoulder joint
  • Extends the arm at the shoulder joint
  • Retracts (draws back) the arm.
  • Medially (inwardly) rotates the arm at the shoulder joint
  • Also facilitates limited movement at the lumbosacral joint (elevation of the pelvis) and at the scapulocostal joint (depression of the scapula and movements of the trunk/torso)

The latissimus dorsi muscle is labelled on the diagrams of the human anterior muscles and the human posterior muscles.

* Although the wide expanse of latissimus dorsi muscle is sometimes referred to in the singluar form (i.e. as one muscle) in general descriptions, it is actually two muscles - one on each side of the right- and left- sides of the body. That distinction is clear from the above information about the origin, insertion and actions of the latissimus dorsi muscles.
For example, the point of insertion of the latissimus dorsi muscle on the right-side of the body is on the right humerus bone and its actions include adducting the right arm. In the same way, the points of origin of the latissimus dorsi muscle on the left-side of the body include locations on the lowest 3 or 4 ribs on the left-side of the body and the actions of that (left) latissimus dorsi muscle include adducting the left arm.

More about Muscles:

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