What is the difference between venous and arterial leg ulcers; and how do they look?

Clearly different : Arterial ulcerations appear necrotic. No evidence of pink healing tissue at the base and the wound edges are grey or black. Venous ulcers usually have clean pink bases with pearly borders.

Ulcer artery vs vein: Venous ulcers are due to high blood pressure of the veins resulting in the leakage of fluid into the tissues of the legs. Compression of the lower extremities and surgery on the veins can correct this. Ischemic ulcers are due to problems with arteries. There are larger arteries and small microscopic ones and either or both can have blockages. They usually can be discerned from each other.

Up or down part 1: Leg veins return blood against gravity to the heart. It is propelled up by leg muscle contraction and prevented from falling back down by a series of 'check' valves. If valves fail blood pools both preventing new blood from bringing oxygen and causing fluid to get out & swelling. Arterial ulcers are caused by blocked arterial circulation carrying oxygen down away from the heart. Continued?