730 A MANUAL OP ANATOMV 



left kidney, and it divides into two branches, ascending and 

 descending. The ascending branch anastomoses with the left branch 

 of the middle colic, and the descending branch with the ascending 

 branch of the superior sigmoid artery. The arches thus formed 

 supply branches to the left extremity of the transverse colon and 

 the descending colon, which in their course form secondary and 

 tertiary arches. 



Sigmoid Arteries. — ^These are usually three in number, superior, 

 middle, and inferior, but they frequently arise as a single trunk. 

 They pass downwards and to the left over the psoas magnus, and 

 supply the lower part of the descending colon, the iliac colon, and 

 the pelvic colon. The superior sigmoid artery, which lies, as a 

 rule, behind the peritoneum, divides into two branches, ascending 

 and descending. The ascending branch forms an arch with the 

 descending branch of the left colic, and the descending branch 

 passes between the two layers of the pelvic meso-colon, where 

 it anastomoses with the middle sigmoid artery. The middle and 

 inferior sigmoid arteries pass between the two layers of the pelvic 

 meso-colon, where they form arches with the descending branch 

 of the superior sigmoid, with one another, and with the superior 

 hemorrhoidal artery. The branches of these arches form secondary, 

 or even tertiary, arches before the terminal branches are given off. 



The superior hemorrhoidal artery is the continuation of the 

 inferior mesenteric, and will be found described on p. 875, 



inferior Mesenteric Vein. — ^This vein is formed by tributaries 

 which return the blood from the parts of the large intestine supplied 

 by the inferior mesenteric artery. It lies at first near the left side 

 of its artery, but soon leaves it and ascends on the left psoas 

 magnus, where it lies on the left side of the aorta behind the peri- 

 toneum. In this course it crosses the left spermatic artery and 

 left renal vein. It finally passes behind the pancreas with an 

 inclination to the right, and usually terminates in the splenic 

 vein. It may, however, open into the angle of junction of the 

 splenic and superior mesenteric veins, or into the superior mesenteric 

 vein, near its termination. The inferior meseftteric vein and its 

 tributaries are destitute of valves, so that the blood can regurgitate 

 in cases of portal obstruction. 



Inferior Mesenteric Sympathetic Plexus. — This plexus is derived 

 from the left half of the aortic plexus. It forms a tough sheath 

 round the artery, and furnishes offshoots with its branches. 



Inferior Mesenteric Glands. — These glands are situated around the 

 root, and along the trunk and branches, of the inferior mesenteric 

 artery. Those around the root of the vessel constitute the inferior 

 mesenteric group of the pre-aortic glands. 



Their afferent vessels are derived from (i) the lower part of the 

 descending colon, (2) the iliac colon, (3) the pelvic colon, and (4) some 

 of the lymphatics of the rectum. 



Their efferent vessels pass to the inferior mesenteric group of pre- 

 aortic glands. 



