The varied blood supply of the colon and rectum has been described. It may be stated that the efficiency of any surgeon's hand is primarily dependent on the knowledge that guides it. Significant anatomic facts are described herein. An important blood supply to the terminal ileum comes from the generally unknown ileal artery, which, when absent, creates a critical, poorly vascularized area and thus an inappropriate area for an anastomosis. This right colic artery may be absent in 2 per cent. It may arise in common with the middle colic trunk (52 per cent). The middle colic artery is absent in 3 per cent. It occurs as a separate branch in 44 per cent and may be derived from celiac artery rarely. The inferior mesenteric artery divides into the left colic, which ascends to the splenic flexure, and a descending branch that continues downward as the superior rectal artery. The left colic artery may not reach the splenic flexure. The marginal artery may be interrupted or weakly represented at the splenic flexure. Therefore, one should perform a ligation of the left colic vessel before its bifurcation if the splenic flexure is to be preserved. The superior rectal artery is the main blood supply of the rectum. Its branching on the rectum is varied, but it has a rich anastomosis with the other rectal arteries, namely, the middle rectal and inferior rectal arteries. Sudeck's point is not critical. The middle rectal artery varies in number and origin and is not essential provided the inferior rectal artery is intact. The anatomy of the anal canal is described. The rectum is for a short distance surrounded by the anal canal with the external sphincter. The internal sphincter is the end of circular muscle of the rectum. The external sphincter can be thought of as one continuous muscle divided by longitudinal bands into three main parts: subcutaneous, superficial, and deep. Below the pectinate line in the anal canal, the nerve supply, lymphatic drainage, blood supply, and epithelium are different from that in the rectum.