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Abdominal muscles cover the anterior and lateral abdominal region and meet at the anterior midline. These muscles of the anterolateral abdominal wall can be divided into four groups: the external obliques , the internal obliques , the transversus abdominis , and the rectus abdominis .
The muscle extends from the pubic symphysis, pubic crest and pubic tubercle inferiorly, to the xiphoid process and costal cartilages of the 5th–7th ribs superiorly. [1] [2] The rectus abdominis muscle is contained in the rectus sheath, which consists of the aponeuroses of the lateral abdominal muscles.
The rectus sheath (also called the rectus fascia [1]) is a tough fibrous compartment formed by the aponeuroses of the transverse abdominal muscle, and the internal and external oblique muscles. It contains the rectus abdominis and pyramidalis muscles, as well as vessels and nerves. [2]
The linea alba is formed by the union of aponeuroses (of the muscles of the anterior abdominal wall [2]) that collectively make up the rectus sheath. The linea alba attaches to the xiphoid process superiorly, and to the pubic symphysis inferiorly. It is narrow inferiorly where the two recti abdominis muscles are in contact with each other ...
The arcuate line of rectus sheath (the arcuate line or the semicircular line of Douglas) is a line of demarcation [1] corresponding to the free inferior margin of the posterior layer of the rectus sheath [2] inferior to which only the anterior layer of the rectus sheath is present [3] and the rectus abdominis muscle is therefore in direct contact with the transversalis fascia. [1]
The muscle fibers run from these points superomedially (up and towards midline) to the muscle's insertions on the inferior borders of the 10th through 12th ribs and the linea alba. In males, the cremaster muscle is also attached to the internal oblique.
The external oblique functions to pull the chest downwards and compress the abdominal cavity, which increases the intra-abdominal pressure as in a Valsalva maneuver.It also performs ipsilateral (same side) side-bending and contralateral (opposite side) rotation: the right external oblique would side-bend to the right and rotate to the left, and vice versa.
Abdominal muscles have many important functions, including breathing, coughing, and sneezing, and maintaining posture and speech in a number of species. [4] Other abdominal functions are that it helps "in the function of support, containment of viscera, and help in the process of expiration, defecation, urination, vomiting, and also at the time of childbirth."