THE COMMON ILIAC ARTERIES. 807 



These abdominal aneurisms are not uncommonly unsuspected until they have 

 reached a late stage, and may even rupture and cause death from hemorrhage with- 

 out having caused more than trifling inconvenience. In a number of cases the pain 

 — especially apt to be felt in the back — has been the only symptom complained of. 

 If a pulsating tumor, or one with a bruit, can be felt, it would be proper to approach 

 the region by an intraperitoneal or — in the case of the renals— possibly an extra- 

 peritoneal incision, and ligate the artery on the cardiac and distal sides of the sac. 



THE COMMON ILIAC ARTERIES. 



The common iliac arteries (aa. iliacae communes) (Figs. 724, 726) are usually 

 regarded as the terminal branches of the abdominal aorta, although in reality the 

 middle sacral artery forms the morphological continuation of that vessel, the common 

 iliacs being lateral segmental branches comparable to a pair of lumbar or intercostal 

 arteries. They arise opposite the body of the fourth lumbar vertebra and pass 

 obliquely outward, downward, and forward to about the level of the sacro-iliac articu- 

 lation, where they terminate by dividing into the internal and external iliac arteries. 



The two common iliacs diverge from each other at an angle of from 6o°-65° in 

 the male and somewhat more (68°-75°) in the female. On account of the position of 

 the abdominal aorta being slighdy to the left of the median line, the right artery is 

 slightly longer than the left, and is inclined to the median line at a slighdy greater angle. 



Relations. — The common iliac arteries are covered by peritoneum, which sepa- 

 rates them on the right from the terminal portion of the ileum and on the left from 

 the sigmoid colon. Anteriorly, each artery is crossed by the ureter, and in the female 

 by the ovarian artery and vein, and by the branches of the sympathetic cord which, 

 pass downward to the hypogastric plexus. The left common iliac is, in addition, 

 crossed by the superior hemorrhoidal branch of the inferior mesenteric artery. 

 Behind, the vessel of the left side rests upon the bodies of the fourth and fifth 

 lumbar vertebrae, that of the right side being separated from them by the right 

 common iliac vein and by the upper end of the corresponding vein of the left side. 

 Lower both vessels rest upon the psoas muscle. Laterally, they are also in relation 

 with the psoas and with the spermatic artery in the male and, in the case of the 

 vessel of the right side, with the upper part of the right common iliac vein. 

 Medially, are the common iliac veins and the hypogastric plexus. 



« Branches. — The common iliac arteries terminate by dividing into the external 

 and internal iliac arteries. In addition, they give rise only to small vessels which 

 pass to the subjacent psoas muscles and to the neighboring peritoneum and lymph- 

 nodes and the ureters. 



Variations. — A certain amount of variation occurs in the length of the common iliac arte- 

 ries, depending largely upon the level at which the bifurcation of the abdominal aorta occurs. 

 One or other vessel may give rise to the middle sacral artery or to an accessory renal artery. 



Practical Considerations. — The common iliac artery is very rarely the sub- 

 ject of aneurism. Direct cotnpressio?i of the artery may be made by either of the 

 plans described as applicable to the abdominal aorta, and should be applied about 

 one inch below and a half inch to the right or left of the umbilicus. While it is 

 easier to get rid of the intestines, as the vessel is placed more laterally, it is not 

 always easy to avoid compression of the aorta itself. 



Ligation of the common iliac may be required for aneurism lower down, espe- 

 cially of the upper part of the external iliac, or for wound, or as a preliminary to or 

 part of the procedure in the removal of pelvic growths. 



It may be effected by either : (i) The transperitoneal method, or (2) the extra- 

 peritoneal method, i. A median incision from umbilicus to symphysis, opening the 

 peritoneal cavity, the intestines being kept in the upper segment of the abdomen by 

 pads or by placing the patient in the Trendelenburg position, will give easy access 

 to the vessel. On each side it lies directly beneath the peritoneum, but there are 

 anatomical differences to which Makins has called attention. On the right side 

 the vessel is uncovered by any structure of importance, and may be reached by 

 dividing the peritoneum directly over it vertically. On this side the vena cava 



