The origin of the muscle is the lower borders of the transverse processes of lumbar vertebrae (L1-L5), inner surface of the ilium, sides of the bodies of the last thoracic vertebra (T12), all the lumbar vertebrae (L1-L5), intervertebral fibrocartilages, and base of sacrum.

The origin of the quadratus lumbar muscle is the lower edges of the transverse processes of the lumbar vertebrae (L1-L5), internal surface of the ilium, sides of the bodies of the last thoracic vertebra (T12), all lumbar vertebrae (L1- L5 ), intervertebral fibrocartilages and base of the sacrum.

Explanation:

We are referring to the quadratus lumbar muscle, therefore to the iliotransverse muscle fibers.

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