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

abdominal muscles 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 abd ...

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 gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

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

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

the anterior wall of the abdomen. In most humans, the oblique is not visible, due to subcutaneous

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

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 The serratus anterior is a muscle of the chest. It originates at the side of the chest from the upper 8 or 9 ribs; it inserts along the entire length of the anterior aspect of the medial border of the scapula. It is innervated by the long thor ...

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 dorsi'') 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 superolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posterio ...

; the middle and upper fibers, directed downward (inferiorly) and forward (anteriorly), become aponeurotic at approximately the

midclavicular line {{short description, None Anatomical lines, or "reference lines," are theoretical lines drawn through anatomical structures and are used to describe anatomical location. The following reference lines are identified in '' Terminologia Anatomica'' ...

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 The aponeurosis of the abdominal external oblique muscle is a thin but strong membranous structure, the fibers of which are directed downward and medially. It is joined with that of the opposite muscle along the middle line, and covers the whole ...

forms the

inguinal ligament The inguinal ligament (), also known as Poupart's ligament or groin ligament, is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which an indirect inguinal hernia may ...

. The muscle also contributes to the

inguinal canal The inguinal canal is a passage in the anterior abdominal wall on each side of the body (one on each side of the midline), which in males, convey the spermatic cords and in females, the round ligament of the uterus. The inguinal canals are lar ...

. 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, as if blowing up a balloon. Variations of the maneuver can be ...

. 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

*Side plank

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 external oblique muscle Muscles of the torso Spine flexors Spine lateral flexors Spine rotators