n :  any of three arteries supplying esp. the rectum:  a  :  one arising from the internal pudendal artery and supplying the lower part of the rectum and the perineal region - called also inferior hemorrhoidal artery , inferior rectal artery   b  :  one arising from the internal iliac artery and supplying the middle part of the rectum - called also middle hemorrhoidal artery , middle rectal artery   c  :  one that is a continuation of the inferior mesenteric artery and that supplies the upper part of the rectum - called also superior hemorrhoidal artery , superior rectal artery  .
 
 
 
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