Abdomen:Muscles:Anterolateral abdominal muscles and aponeuroses

The **external oblique muscle** is the the largest and the most superficial (outermost) of the three flat muscles of the lateral anterior abdomen.

* It is thin and irregularly quadrilateral
* Function: pull the chest downwards and compress the abdominal cavity, which increases the intra-abdominal pressure as in a valsalva maneuver. Also limited actions in both flexion and rotation of the vertebral column.

**Origin:** eight digitations from the external surfaces and inferior borders of the fifth to twelfth ribs. The lower four interdigitate with the costal fibres of latissimus dorsi and the upper four with the serratus anterior.

**Insertion:** the lowest ribs fibres pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest (creating a free posterior border); the middle and upper fibers, directed downward and forward, become aponeurotic at approximately the midclavicular line and below the umbilicus.

This aponeurosis formed from fibres from either side of the external oblique decussates at the linea alba in front of the rectus muscle. inferiorly it extends down from the ASIS to the pubic tubercle which forms the **inguinal ligament.**

Innervation

The external oblique muscle is innervated by ventral branches of the lower 6 thoracoabdominal nerves and the subcostal nerve on each side (T7-T12).

Blood supply

* cranial portion by the lower 6 intercostal arteries
* caudal portion by a branches of either the deep circumflex iliac artery or lumbar arteries or the iliolumbar artery.

Lymph drainage

* region above umbilicus drain to pectoral group
* region below umbilcius drain to superficial inguinal nodes

The **internal oblique muscle** is the intermediate muscle of the abdomen, lying between the external oblique and transverse abdominal muscle. Its fibers run perpendicular to the external oblique muscle, superomedially to the costal margins and along it. Fibres become aponeurotic at the tip of the 9th costal cartilage. below the costal margin, the aponeurosis split around the rectus muscles and two layers rejoin in the linea alba.

**Origin:** thoracolumbar fascia of the lower back, the anterior 2/3 of the iliac crest (upper part of hip bone) and the lateral half of the inguinal ligament.

**Insertion:** inferior borders of the 10th through 12th ribs and the linea alba

Halfway between the umbilicus and the pubic symphysis, the posterior layer of the internal oblique aponeurosis end in a curved free margin forming the arcuate line.

Innervation

The internal oblique is innervated by the lower intercostal nerves (T7-T12), as well as the iliohypogastric nerve and the ilioinguinal nerve (L1).

Blood supply

* cranial portion by the lower 6 intercostal arteries
* caudal portion by a branches of either the deep circumflex iliac artery or lumbar arteries or the iliolumbar artery.

Lymph drainage

* region above umbilicus drain to pectoral group
* region below umbillicus drain to superficial inguinal nodes

The **transverse abdominal muscle** is the innermost muscle layer of the anterior and lateral abdominal wall deep to the internal oblique muscle. It helps to compress the ribs and viscera, providing thoracic and pelvic stability.

**Origin:** lateral 1/3 of the inguinal ligament, from the anterior 3/4th of the inner lip of the iliac crest, up to the inner surfaces of the cartilages of the lower six ribs, interdigitating with the diaphragm, and from the lumbodorsal fascia.

**Insertion:** the lower fibers curve inferomedially and insert the internal oblique muscle, into the crest of the pubis and pectineal line, forming the inguinal conjoint tendon. The upper fibers pass horizontally to the midline and insert into the linea alba (aponeurosis of the internal oblique) behind the rectus muscle. Below the arcuate line, the aponeurosis pass entirely in front for the rectus muscle.

Innervation

The transverse abdominal is innervated by the lower intercostal nerves (thoracoabdominal, nerve roots T7-T12), as well as the iliohypogastric nerve and the ilioinguinal nerve (L1).

Blood supply

* cranial portion by the lower 6 intercostal arteries
* caudal portion by a branches of either the deep circumflex iliac artery or lumbar arteries or the iliolumbar artery.

Lymph drainage

* region above umbilicus drain to pectoral group
* region below umbilcius drain to superficial inguinal nodes