The structure indicated is the internal iliac artery.

The abdominal aorta bifurcates into the left and right common iliac arteries at approximately the level of the fourth lumbar vertebra. The common iliac arteries then divide into the external and internal iliac arteries.

The internal iliac artery has an anterior trunk and posterior trunk. The branches of these trunks are anatomically variable and have several different configurations from person to person. The posterior trunk gives rise to three branches:

1. Iliolumbar artery
2. Lateral sacral arteries
3. Superior gluteal artery

The branches of the anterior trunk are much more variable, but tend to give rise to the following arteries:

1. Umbilical artery – gives rise to superior vesical artery
2. Obturator artery
3. Inferior vesical artery (vaginal artery in women)
4. Middle rectal artery
5. Internal pudendal artery
6. Inferior gluteal artery
7. Uterine artery (in women)

The internal iliac artery is the main artery of the pelvis and supplies the pelvic walls and the viscera that are contained within the pelvis, as well as the musculature of the gluteal region and muscles located medially in the thigh.

Learn all about the anatomy of the internal iliac artery in this anatomy tutorial.