^BLeg^b ^Bulcers. ^bIllustration showing different types of ulcer (open sore which fails to heal) on human legs. There are multiple small ulcers on the left knee called ^Igummas, ^i which are characteristic of the late stages of untreated syphilis. The left leg shows swollen varicose veins where valves inside the veins fail to work, preventing blood from draining properly from the lower leg. The tissues may become starved of oxygen and nourishment which can lead to varicose ulcers such as that on the left ankle. An ischaemic ulcer, caused by insufficient blood supply (possibly as a result of diabetes), has developed on the foot, and trauma has caused an ulcer on the right shin.