The superior mesenteric artery starts from the anterior wall of the abdominal aorta at about the height of the first lumbar vertebra, descends behind the splenic vein and the head of the pancreas, crosses the anterior aspect of the pancreatic hook, enters the mesenteric root of the small intestine between the inferior margin of the pancreas and the horizontal part of the 12 fingers, and proceeds obliquely down to the right to the right iliac fossa where its end anastomoses with the ileocecal branch of the ileocolic artery. The main trunk of the superior mesenteric artery is in the shape of an arch that is slightly convex to the left, and from the convex side of the arch, the pancreaticoduodenal artery and more than ten jejunal and ileal arteries are issued in turn, and from the concave side of the arch, the mesocolic artery, right colic artery and ileocolic artery are issued in turn. The inferior pancreaticoduodenal artery is a small artery that travels posteriorly to the right via the superior mesenteric vein and is divided into two branches, anterior and posterior, which anastomose with the superior anterior and posterior pancreaticoduodenal arteries, respectively. This artery sometimes originates from the first jejunal artery. 2. The jejuno-ileal artery originates from the convex side of the superior mesenteric artery, about 12-16 branches, and travels in the mesentery. The superior ones are distributed in the jejunum and the inferior ones in the ileum are called ilealarteries. Each artery is divided into ascending and descending branches and anastomoses with the ascending and descending branches of the adjacent mesenteric artery to form the first level of the arterial arch. The branches of the arterial arch then anastomose to form the second level arch, which can form the third, fourth and fifth level arches in turn. Many small rectal (canal) arteries emanate from the last level of the arterial arch and enter the wall of the small intestine from the mesenteric margin of the small intestine, but there are few anastomoses between these arteries, especially the mesenteric margin of the small intestine has poor blood flow. Generally, there is only one level of arterial arch in the proximal segment of jejunum, and the number of arterial arch levels increases gradually to 4-5 levels in the end of jejunum and proximal segment of ileum, but then decreases to 1-2 levels in the end of ileum. The rectal artery is long and thick in the jejunum and short and small in the ileum. The middlecolic artery starts from the concave side of the superior mesenteric artery at the lower edge of the head of the pancreas, then enters the transverse colonic mesentery and travels to the right front; it is divided into two branches, the left and the right. The right branch travels up to the right and anastomoses with the ascending branch of the right colonic artery at the right curvature of the colon; the left branch travels to the left and anastomoses with the ascending branch of the left colonic artery, which is called the Riolan arterial arch. The left and right branches send small branches to distribute in the transverse colon during the journey. The right colonic artery starts from the superior mesenteric vein below the beginning of the middle colonic artery, or starts from the common stem with the middle colonic artery, and travels right through the deep peritoneal surface of the posterior abdominal wall, and divides into ascending and descending branches near the left margin of the ascending colon. The ascending branch anastomoses with the right branch of the mesocolic vein; the descending branch anastomoses with the superior trunk of the ileocolic artery. This artery gives off small branches distributed in the upper 2/3 of the ascending colon and the right curvature of the colon. 5.Ileocolic artery ileocolicartery is the most inferior branch of superior mesenteric artery on the concave side, which runs obliquely downward to the right in the deep peritoneal surface of the posterior abdominal wall, and is generally divided into two trunks: upper and lower. The upper trunk anastomoses with the descending branch of the right colic artery; the lower trunk descends and anastomoses with the end of the superior mesenteric artery to form an arch. The branches along the way are as follows: (a) colicbranch, also called ascending branch, runs obliquely upward to the right and is distributed in the lower 1/3 of the ascending colon. (b) The anterior and posterior cecal arteries emanate from the anterior and posterior cecal arteries and travel downward to the right, respectively, through the anterior and posterior cecum, and are distributed in the intestinal wall.