Along their course, nerves T7 to T12 and L1 supply branches to the anterolateral abdominal wall muscles and the underlying parietal peritoneum. All terminate by supplying skin:
Nerves T7 to T9 supply the skin from the xiphoid process to just above the umbilicus.
T10 supplies the skin around the umbilicus.
T11, T12, and L1 supply the skin from just below the umbilicus to, and including, the pubic region (Fig. 4.38).
Additionally, the ilio-inguinal nerve (a branch of
L1) supplies the anterior surface of the scrotum or labia majora, and sends a small cutaneous branch to the thigh.
Numerous blood vessels supply the anterolateral abdominal wall. Superficially: the superior part of the wall is supplied by branches from the musculophrenic artery, a terminal branch of the internal thoracic artery, and the inferior part of the wall is supplied by the medially placed superficial epigastric artery and the laterally placed superficial circumflex iliac artery, both branches of the femoral artery (Fig. 4.39).
At a deeper level: the superior part of the wall is supplied by the superior epigastric artery, a terminal branch of the internal thoracic artery; the lateral part of the wall is supplied by branches of the tenth and eleventh intercostal arteries and the subcostal artery; and the inferior part of the wall is supplied by the medially placed inferior epigastric artery and the laterally placed deep circumflex iliac artery, both branches of the external iliac artery.
The superior and inferior epigastric arteries both enter the rectus sheath. They are posterior to the rectus abdominis muscle throughout their course, and anastomose with each other (Fig. 4.40).
Veins of similar names follow the arteries and are responsible for venous drainage.
Lymphatic drainage of the anterolateral abdominal wall follows the basic principles of lymphatic drainage:
Superficial lymphatics above the umbilicus pass in a superior direction to the axillary nodes, while drainage below the umbilicus passes in an inferior direction to the superficial inguinal nodes.
Deep lymphatic drainage follows the deep arteries back to parasternal nodes along the internal thoracic artery, lumbar nodes along the abdominal aorta, and external iliac nodes along the external iliac artery.
The groin (inguinal region) is the area of junction between the anterior abdominal wall and the thigh. In this area, the abdominal wall is weakened from changes that occur during development and a peritoneal sac or diverticulum, with or without abdominal contents, can therefore protrude through it, creating an inguinal hernia. This type of hernia can occur in both sexes, but it is most common in males.
The inherent weakness in the anterior abdominal wall in the groin is caused by changes that occur during the development of the gonads. Before the descent of the testes and ovaries from their initial position high in the posterior abdominal wall, a peritoneal outpouching (the processus vaginalis) forms (Fig. 4.41), protruding through the various layers of the anterior abdominal wall and acquiring coverings from each:
The transversalis fascia forms its deepest covering.
The second covering is formed by the musculature of the internal oblique (a covering from the transversus abdominis muscle is not acquired because the processus vaginalis passes under the arching fibers of this abdominal wall muscle).
Its most superficial covering is the aponeurosis of the external oblique.
As a result the processus vaginalis is transformed into a tubular structure with multiple coverings from the layers of the anterior abdominal wall. This forms the basic structure of the inguinal canal.