

THE ABDOMINAL AORTA 607 



vessel which supplies the whole length of the small intestine, except the superior 

 part of the duodenum; it also supplies the cecum and the ascending part of the colon 

 and about one-half of the transverse part of the colon. It arises from the front 

 of the aorta, about 1.25 cm. below the celiac artery, and is crossed at its origin by 

 the lienal vein and the neck of the pancreas. It passes downward and forward, 

 anterior to the processus uncinatus of the head of the pancreas and inferior part 

 of the duodenum, and descends between the layers of the mesentery to the right 

 iliac fossa, where, considerably diminished in size, it anastomoses with one of 

 its own branches, viz., the ileocolic. In its course it crosses in front of the inferior 

 vena cava, the right ureter and Psoas major, and forms an arch, the convexity of 

 which is directed forward and downward to the left side, the concavity backward 

 and upward to the right. It is accompanied by the superior mesenteric vein, 

 which lies to its right side, and it is surrounded by the superior mesenteric plexus 

 of nerves. 



I Branches. Its branches are: 

 Inferior Pancreaticoduodenal. Ileocolic. 



Intestinal. Right Colic. 



Middle Colic. 

 The Inferior Pancreaticoduodenal Artery (a. pancreaticoduodenalis inferior) is given 

 off from the superior mesenteric or from its first intestinal branch, opposite the 

 upper border of the inferior part of the duodenum. It courses to the right 

 between the head of the pancreas and duodenum, and then ascends to anastomose 

 with the superior pancreaticoduodenal artery. It distributes branches to the head 

 of the pancreas and to the descending and inferior parts of the duodenum. 



The Intestinal Arteries (aa. intestinales; vasa intestini tenuis) arise from the convex 

 side of the superior mesenteric artery. They are usually from twelve to fifteen 

 in number, and are distributed to the jejunum and ileum. They run nearly parallel 

 with one another between the layers of the mesentery, each vessel dividing into 

 two branches, which unite with adjacent branches, forming a series of arches, the 

 convexities of which are directed toward the intestine (Fig. 535) . From this first 

 set of arches branches arise, which unite with similar branches from above and below 

 and thus a second series of arches is formed ; from the lower branches of the artery, 

 a third, a fourth, or even a fifth series of arches may be formed, diminishing in 

 size the nearer they approach the intestine. In the short, upper part of the mesen- 

 tery only one set of arches exists, but as the depth of the mesentery increases, 

 second, third, fourth, or even fifth groups are developed. From the terminal 

 arches numerous small straight vessels arise which encircle the intestine, upon 

 which they are distributed, ramifying between its coats.. From the intestinal 

 arteries small branches are given off to the lymph glands and other structures 

 between the layers of the mesentery. 



The Heocolic Artery (a. ileocolica) is the lowest branch arising from the concavity 

 of the superior mesenteric artery. It passes downward and to the right behind the 

 peritoneum toward the right iliac fossa, where it divides into a superior and an 

 inferior branch; the inferior anastomoses with the end of the superior mesenteric 

 artery, the superior with the right colic artery. 



The inferior branch of the ileocolic runs toward the upper border of the ileo- 

 colic junction and supplies the following branches (Fig. 536) : 



(a) colic, which pass upward on the ascending colon; (6) anterior and posterior 

 ecal, which are distributed to the front and back of the cecum ; (c) an appendicular 

 artery, which descends behind the termination of the ileum and enters the mesen- 

 teriole of the vermiform process; it runs near the free margin of this mesenteriole 

 and ends in branches which supply the vermiform process; and (d) ileal, which run 

 upward and to the left on the lower part of the ileum, and anastomose with the 

 termination of the superior mesenteric. 



