The posterior intercostal arteries from the thoracic aorta are distributed to the lower nine intercostal spaces, and these anastomose in front with the anterior branch of the internal thoracic (internal mammary artery) or musculophrenic artery [1]. The lower two posterior intercostal arteries continue anteriorly from the intercostal spaces into the abdominal wall and anastomose with the subcostal, superior epigastric, and lumbar arteries. They provide blood flow to the lateral part of the abdominal wall. The subcostal arteries are the last pair of branches from the thoracic artery and are situated below the 12th rib. Each artery pierces the aponeurosis of the origin of the transversus abdominus and passes forward between this muscle and the obliquus internus finally anastomosing with the superior epigastric, lower posterior intercostal, and lumbar arteries.

The internal mammary artery (internal thoracic artery) arises from the subclavian artery and descends to the level of the sixth intercostal space and divides into the musculophrenic artery and superior epigastric artery. For each of the upper six intercostal spaces, it gives two branches known as the anterior intercostal arteries. The musculophrenic artery descends and gives off branches to the seventh, eighth, and ninth intercostal spaces that are distributed in a manner similar to the intercostals from the internal mammary artery (internal thoracic artery). The musculophrenic artery supplies the hypochondriac region of the abdominal wall and the anterolateral muscles.

The superior epigastric artery descends and enters the sheath of the rectus abdominus and finally anastomoses with the inferior epigastric artery. The superior epigastric artery supplies blood to the rectus abdominis and the superior portion of the anterolateral abdominal wall.