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Obliquus internus abdominis
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The Obliquus Internus abdominis
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Femoral sheath laid open to show its three compartments
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The (or "Obliquus internus abdominis") is the intermediate muscle of the abdomen, lying just underneath the
External Oblique and just above (superficial to) the
Transverse Abdominal Muscle . Its fibers run perpendicular to the
External Oblique , beginning in the
Thoracolumbar Fascia of the lower back, the anterior 2/3 of the
Iliac Crest (upper part of hip bone) and the lateral half of the
Inguinal Ligament . The muscle fibers run from these points superiomedially (up and towards midline) to the muscle's insertions on the inferior borders of the 10th thru 12th ribs and the
Linea Alba (abdominal midline seam.)
It performs two major functions. First, it acts as an antagonist (opponent) to the diaphragm, helping to reduce the volume of the thoracic (chest) cavity during exhalation. When the
Diaphragm contracts, it pulls the lower wall of the chest cavity down, increasing the volume of the lungs which then fill with air. Conversely, when the
Internal Oblique s contract they compress the organs of the abdomen, pushing them up into the
Diaphragm which intrudes back into the chest cavity reducing the volume of the air filled lungs, producing an exhalation.
Secondly, its contraction rotates and side-bends the trunk by pulling the rib cage and midline towards the hip and lower back, of the same side. It acts with the
External Oblique of the opposite side to achieve this torsional movement of the trunk. For example, the right
Internal Oblique and the left
External Oblique contract as the torso flexes and rotates to bring the left shoulder towards the right hip. For this reason, the internal obliques are referred to as "same side rotators."
- Moore, Keith L; & Dalley Arthur R (2006). ''Clinically Oriented Anatomy'' (5th ed.). Lippincott Williams and Wilkins. ISBN 0781736390.
- {Link without Title}
