COMMON ILIAC. 507 



that he has found in several birds the middle sacral arteries terminating in a 

 bunch of interlacing and anastomosing capillaries, but without any capsule, and 

 it is rendered in the highest degree probable, if Arnold's observation be correct, 

 that several small saccular bodies, of a somewhat similar kind, may be found 

 connected with the middle sacral artery. 



For a more detailed description of this body, we would refer to the elaborate 

 account in " Luschka's Anatornie," and to the authorities quoted in Dr. Macal- 

 ister's paper, as well as to a monograph by Dr. "W". Mitchell Banks, reprinted 

 in 1867 from the " Glasgow Medical Journal." 



COMMON ILIAC ARTERIES. 



The abdominal aorta divides into the two Common Iliac Arteries. The bifur- 

 cation usually takes place on the left side of the body of the fourth lumbar 

 vertebra. This point corresponds to the left side of the umbilicus, and is on a 

 level with a line drawn from the highest point of one iliac crest to the other. 

 The common iliac arteries are about two inches in length ; diverging from the 

 termination of the aorta, they pass downwards and outwards to the margin of 

 the pelvis, and divide opposite the intervertebral substance, between the last 

 lumbar vertebra and the sacrum, into two branches, the external and internal 

 iliac arteries ; the former supplying the lower extremity ; the latter, the viscera, 

 and parietes of the pelvis. 



The right common iliac is somewhat larger than the left, and passes more 

 obliquely across the body of the last lumbar vertebra. In front of it are the 

 peritoneum, the ileum, branches of the sympathetic nerve, and, at its point 

 of division, the ureter. Behind, it is separated from the last lumbar vertebra 

 by the two common iliac veins. On its outer side, it is in relation with the in- 

 ferior vena cava, and right common iliac vein, above; and the Psoas Magnus 

 muscle below. 



The left common iliac is in relation, in front, with the peritoneum, branches 

 of the sympathetic nerve, the rectum and superior haemorrhoidal artery; and is 

 crossed, at its point of bifurcation, by the ureter. The left common iliac vein 

 lies partly on the inner side, and part beneath the artery ; on its outer side, the 

 artery is in relation with the Psoas Magnus. 



Branches. The common iliac arteries give off small branches to the perito- 

 neum, Psoas muscles, ureters, and the surrounding cellular membrane, and 

 occasionally give origin to the ilio-lumbar, or renal arteries. 



PLAN OF THE EELATIONS OF - THE COMMON ILIAC ARTERIES. 



In front. In front. 



Peritoneum. Peritoneum. 



Small intestines. Sympathetic nerves. 



Sympathetic nerves. Eectum. 



Ureter. Superior haemorrhoidal artery. 



Ureter. 



Outer side. Inner side. / \ Older side. 



Vena eava. Left common / _Left \ Psoas muscle. 



Eight common iliac vein. 



iliac vein. 

 Psoas muscle. 



Bclu'rxL Behind. 



Right and Left common Left common 



iliac veins. iliac vein. 



Peculiarities. The point of origin varies according to the bifurcation of the aorta. In three- 

 fourths of a large number of cases, the aorta bifurcated either upon the fourth lumbar vertebra, 

 or upon the intervertebral disk between it and the fifth ; the bifurcation being, in one case out 

 of nine below, and in one out of eleven above this point. In ten out of every thirteen cases, 

 the vessel bifurcated within half an inch above or below the level of the crest of the ilium ; 

 more frequently below than above. 



