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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 tors ...
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 to ...
. 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 In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (trip ...
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 that originates on the surface of the 1st to 8th ribs at the side of the chest and inserts along the entire anterior length of the medial border of the scapula. The serratus anterior acts to pull the scapula fo ...
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 ...
. 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 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 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 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. T ...
. The
internal oblique muscle The abdominal internal oblique muscle, also internal oblique muscle or interior oblique, is an abdominal muscle in the abdominal wall that lies below the external oblique muscle and just above the transverse abdominal muscle. Structure Its fib ...
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 The abdominal internal oblique muscle, also internal oblique muscle or interior oblique, is an abdominal muscle in the abdominal wall that lies below the external oblique muscle and just above the transverse abdominal muscle. Structure Its fib ...
.


Training

* Crunches *Side plank *
Sit-ups The sit-up (or curl-up) is an abdominal endurance training exercise to strengthen, tighten and tone the abdominal muscles. It is similar to a crunch (crunches target the rectus abdominis and also work the external and internal obliques), but s ...


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