The abdominal external oblique muscle (also external oblique muscle, or exterior oblique) is the largest and outermost of the three flat

abdominal muscles The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso ...

of the lateral anterior abdomen.

Structure

The external oblique is situated on the lateral and anterior parts of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the tors ...

. It is broad, thin, and irregularly quadrilateral, its muscular portion occupying the side, its

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...

the anterior wall of the abdomen. In most humans (especially females), the oblique is not visible, due to subcutaneous fat deposits and the small size of the muscle. It arises from eight fleshy digitations, each from the external surfaces and inferior borders of the fifth to twelfth ribs (lower eight ribs). These digitations are arranged in an oblique line which runs inferiorly and anteriorly, with the upper digitations being attached close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages. The five superior serrations increase in size from above downward, and are received between corresponding processes of the serratus anterior muscle; the three lower ones diminish in size from above downward and receive between them corresponding processes from the

latissimus dorsi The latissimus dorsi () is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word latissimus dorsi (plural: ''latissimi dorsorum'') comes from L ...

. From these attachments the fleshy fibers proceed in various directions. Its posterior fibers from the ribs to the iliac crest form a free posterior border. Those from the lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poste ...

; the middle and upper fibers, directed downward (inferiorly) and forward (anteriorly), become aponeurotic at approximately the midclavicular line and form the anterior layer of the rectus sheath. This aponeurosis formed from fibres from either side of the external oblique decussates at the linea alba. The aponeurosis of the external oblique muscle forms the inguinal ligament. The muscle also contributes to the

inguinal canal The inguinal canals are the two passages in the anterior abdominal wall of humans and animals which in males convey the spermatic cords and in females the round ligament of the uterus. The inguinal canals are larger and more prominent in males. ...

. The internal oblique muscle is just deep to the external oblique muscle.

Nerve supply

The external oblique muscle is supplied by ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side.

Blood supply

The cranial portion of the muscle is supplied by the lower intercostal arteries, whereas the caudal portion is supplied by a branches of either the deep circumflex iliac artery or the iliolumbar artery.

Function

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 The Valsalva maneuver is performed by a forceful attempt of exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut while expelling air out as if blowing up a balloon. Variations of the maneuver can ...

. 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. The internal oblique muscle functions similarly except it rotates ipsilaterally.

Society and culture

Oblique strain

The ''oblique strain'' is a common baseball injury, particularly in pitchers. In both batters and pitchers it can affect the contralateral (leading) side external oblique, or the trailing internal oblique.

Training

* Crunches *Side plank * Sit-ups

Additional images

File:External_oblique_posterior.PNG, Posterior view of muscles connecting the upper extremity to the vertebral column. Posterior part of abdominal external oblique muscle labeled. File:Gray393.png, The subcutaneous inguinal ring. File:Gray1097.png, Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas. File:Gray1215.png, The left side of the thorax. File:Gray_abdomen_front_surface_en.png, Surface anatomy of the front of the thorax and abdomen. File:LumbarTriangle.jpg, Lumbar triangle File:Slide8hel.JPG, External abdominal oblique muscle. Anterior abdominal wall. Deep dissection. Anterior view.

References

External links

* * {{Authority control Abdomen Muscles of the torso Spine flexors Spine lateral flexors Spine rotators