The Abdominal Walls

Blood vessels and nerves of the lung | Main Anatomy Index | Inguinal region

Last updated 30 March 2006

The Abdomen

• The abdomen is the part of the trunk that lies between the thorax and the pelvis. It lies between the thoracic diaphragm and the pelvic brim.
• The abdominal cavity extends superiorly into the osteocartilaginous thoracic cage to about the 5^th anterior intercostal space.

• The abdomen contains:

1. the peritoneal cavity;
2. the GI organs comprising the inferior part of the oesophagus, the stomach, the intestine;
3. the liver and biliary system;
4. the pancreas;
5. the suprarenal (adrenal) glands;
6. the kidneys and the superior parts of the ureters;
7. nerves, lymphatics, and blood vessels.

Back to top

The Abdominal Walls

• Although the abdominal wall is continuous, it is helpful for descriptive purposes to subdivide it into: (1) the anterolateral abdominal wall; and (2) the posterior abdominal wall.

The Anterolateral Abdominal Wall

• Most of this wall consists of 3 muscular layers, each of which have its fibres running in different directions.

Surface Anatomy of the Anterolateral Abdominal Wall

• The umbilicus is the obvious feature.
• This puckered scar represents the former site of attachment of the umbilical cord.
• In physically fit people, the umbilicus lies at the level of the intervertebral disc between L3 and L4 vertebrae.
• This is midway between the xiphoid process and the pubic symphysis.

• The linea alba (L. alba, white), is a median fibrous white line or band.
• This line divides the anterior abdominal wall into right and left halves.
• It lies in the anterior median line and is clearly visible in thin muscular persons.

• The linea semilunaris is a curved line or groove (convex laterally) that extends from the 9^th costal cartilage to the pubic tubercle.
• This indicates the lateral border of the rectus abdominis muscle.

Fascia of the Anterior Abdominal Wall

Superficial Fascia

• This superficial fascia consists of one layer that contains a variable amount of fat.
• The superficial fascia just above the inguinal ligament can be divided into two layers:

• There is a fatty superficial layer (Camper's fascia) containing a variable amount of fat.
• There is also a membranous deep layer (Scarpa's fascia) containing fibrous tissue and very little fat.
• The superficial vessels and nerves run between these two layers.

• The membranous deep layer is continuous with the superficial fascia of the thigh, the fascia lata.
• This layer is also continuous with the superficial fascia of the perineum (Colles' fascia) and with that investing the scrotum and penis and the labia majora.

The Deep Fascia

• This is a very thin strong layer over the superficial muscles and cannot be easily separated from them.

Back to top

Muscles of the Anterolateral Wall

Click here to go to the muscles of the anterolateral abdominal wall (external oblique, internal oblique, transverse abdominis and rectus abdominis muscles).

The Rectus Sheath

• The rectus sheath is the strong, incomplete fibrous compartment for the rectus abdominis muscle.
• It forms by the fusion and separation of the aponeurosis of the flat abdominal muscles.

• At its lateral margin, the internal oblique aponeurosis splits into two layers, one passing anterior to the rectus muscle and the other passing posterior to it.
• The anterior layer joints with the aponeurosis of the external oblique to form the anterior wall of the rectus sheath.
• The posterior layer joins with the aponeurosis of the transversus abdominis muscle to form the posterior wall of the rectus sheath.

• The fibres of the anterior and posterior wall of the rectus sheath interlace in the medial line to form a complex tendinous raphe, called the linea alba, which is an intermixture of the aponeurotic fibres of the oblique and transverse abdominal muscles.
• It is narrow inferior to the umbilicus, but is wide superior to it. The groove is visible in the skin superficial to it in thin muscular persons.
• The linea alba lies between the two parts of the rectus abdominis muscle; the umbilicus is located just inferior to its midpoint.

• Superior to the costal margin, the posterior wall of the rectus sheath is deficient because the transversus abdominis muscle passes internal to the costal cartilages and the internal oblique muscle is attached to the costal margin. Hence, superior to the costal margin, the rectus muscle lies directly on the thoracic wall.

• The inferior 1/4 of the rectus sheath is also deficient because the internal oblique aponeurosis does not split to enclose the rectus muscle.
• A crescentic border called the arcuate line marks the inferior limit of the posterior wall of the rectus sheath.
• The position of this line is usually midway between the umbilicus and the pubic crest.
• Inferior to the arcuate line, the aponeuroses of the three flat muscles pass anterior to the rectus muscle to form the anterior layer of the rectus sheath.

"Actually, all the lateral abdominal muscles have bilaminar aponeuroses which blend and cross each other in a complex fashion." (Ashwell, ANAT2007 Visceral Anatomy for Medical Students, Lecture Notes, 1998)

Back to top

Blood Supply of the Anterolateral Abdominal Wall

1. Branches of the internal thoracic artery: the superior epigastric and musculophrenic arteries.
2. Branches of the external iliac artery: the inferior epigastric and deep circumflex arteries.
3. Inferior phrenic artery, branch of the abdominal aorta.
4. Lower posterior intercostal and subcostal arteries, branches of thoracic aorta.
5. Lumbar arteries, from abdominal aorta.

Nerve Supply of the Anterolateral Abdominal Wall

• The skin and muscles of the anterior abdominal wall are supplied mainly by the ventral rami of the inferior six thoracic nerves (i.e., the continuation of the inferior intercostal nerves, T7 to T11) and the subcostal nerve (T12).
• The inferior part of the abdominal wall is supplied by two branches of the ventral ramus of the first lumbar nerve via the iliohypogastric and ilioinguinal nerves.

• The main trunks of the intercostal nerves pass anteriorly from the intercostal spaces and run between the internal oblique and transversus abdominis muscles.
• The plane between these muscles, known as the neurovascular plane, corresponds with a similar plane in the intercostal spaces.

• The inferior intercostal, subcostal and lumbar arteries accompany the nerves of this plane. The common nerve supply of the skin and the muscles of the anterolateral wall explain why palpating the abdomen with cold hands causes the muscles of the abdominal wall to contract.

Back to top

The Posterior Abdominal Wall

Muscles of the Posterior Abdominal Wall

Click here to go to the muscles of the posterior abdominal wall (psoas major, iliacus and quadratus lumborum muscles).

Blood Supply of the Posterior Abdominal Wall

• The lumbar arteries from the aorta.

Nerve Supply of the Posterior Abdominal Wall

• Psoas major: ventral rami of L1-L3 spinal nerves.
• Iliacus: branch of femoral nerve (L2-L3).
• Quadratus lumborum: ventral rami of T12, L1-L4.

Back to top