Which artery runs posterior to the inguinal ligament?

The artery that runs posterior to the inguinal ligament is the femoral artery. Here are the steps to identify it:

1. Locate the inguinal ligament: This is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which structures pass from the abdomen to the lower limb.

2. Identify the femoral artery: This is the major artery supplying the lower limb. It is a continuation of the external iliac artery and becomes the femoral artery when it crosses under the inguinal ligament.

3. Trace the path of the femoral artery: After passing under the inguinal ligament, the femoral artery runs in the femoral triangle of the upper thigh, where it is easily palpable. It then continues down the back of the thigh (hence, posterior to the inguinal ligament).

So, the femoral artery is the artery that runs posterior to the inguinal ligament.