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Any of the muscles of the front and side walls of the abdominal cavity. Three flat layersthe external oblique, internal oblique, and transverse abdominis musclesextend from each side of the spine between the lower ribs and the hipbone. The abdominal muscles attach to aponeuroses, connective tissue sheaths that merge toward the midline, sheathing the rectus abdominis muscle on each side of the midline. The abdominal muscles support and protect the internal organs and take part in exhaling, coughing, urinating, defecating, childbirth, and motion of the trunk, groin, and lower limbs.
This entry comes from Encyclopædia Britannica Concise. For the full entry on abdominal muscle, visit Britannica.com.
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