It would be reasonable for you to imagine that a complete obstruction of the lower end of the aorta would be lethal. After all, its terminal branches, the iliac arteries, not only supply the whole of both the lower limbs, but also the buttocks, the perineum and the pelvic organs. However, such a lesion, especially if it develops gradually to allow collateral channels to dilate, is compatible with survival. This is because there are a number of collateral channels which anastomose between the aorta above the obstruction and the arteries below. The most important of these communicating channels links the superior and inferior epigastric arteries in the deep layer of the anterior abdominal wall. The superior epigastric artery arises from the internal thoracic artery, which itself is a branch of the subclavian artery in the neck. The inferior epigastric artery arises from the external iliac artery immediately before it enters the upper thigh to become the common femoral artery. Hence this link-up between the subclavian artery at the root of the neck and the femoral artery in the groin!