The helicine branches of uterine artery (or helicine arterioles, or spiral arteries) are small arteries which temporarily supply the endometrium of the uterus during the luteal phase of the menstrual cycle. In histology, identifying the presence of these arteries is one of the most useful techniques in identifying the phase of the cycle. [ http://en.wikipedia.org/wiki/Helicine_branches_of_uterine_artery ]