Abdominal internal oblique muscle
|Abdominal internal oblique muscle|
|Muscles of the trunk.|
|The Obliquus internus abdominis.|
|Latin||Musculus obliquus internus abdominis|
|Gray's||subject #118 412|
|Origin||Inguinal ligament, Iliac crest and the Lumbodorsal fascia.|
|Insertion||Linea alba, Pecten Pubis (via Conjoint tendon) and ribs 10-12.|
|Nerve||Thoracoabdominal nn. (T6-T11), Subcostal n. (T12), Iliohypogastric n. (L1) and Ilioinguinal n. (L1)|
|Actions||Compresses abdomen; unilateral contraction rotates vertebral column to same side.|
Its fibers run perpendicular to the external oblique muscle, 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 point superiomedially (up and towards midline) to the muscle's insertions on the inferior borders of the 10th through 12th ribs and the linea alba (abdominal midline seam).
In males, the cremaster muscle is also attached to the internal oblique.
The internal oblique 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 obliques 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 muscle 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."
See also 
- Moore, Keith L; & Dalley Arthur R (2006). Clinically Oriented Anatomy (5th ed.). Lippincott Williams and Wilkins. ISBN 0-7817-3639-0.
Additional images 
- -120586161 at GPnotebook
- LUC inab
- SUNY Figs 35:07-05 - "Incision and reflection of the internal abdominal oblique muscle."
- SUNY Anatomy Image 7526
- internal+oblique+muscle at eMedicine Dictionary