THE COMMOX ILIAC ARTERIES. 



559 



other. These vessels are enclosed in one or more layers of polyhedral granular cells, 

 and the whole structure is invested in a capsule of connective tissue which sends 

 in trabeculge, dividing the interior into a number of spaces in which the vessels 

 and cells are contained. Nerves pass into this little body from the sympathetic, 

 but their mode of termination is unknown. Macalister believes the glomerulus of 

 vessels " consists of the condensed and convoluted metameric dorsal arteries of the 

 caudal segments imbedded in tissue which is possibly a small persisting fragment 

 of the neurenteric canal." 



THE COMMON ILIAC ARTERIES. 



The abdominal aorta divides into the two common iliac arteries. The bifurca- 

 tion usually takes place on the left side of the body of the fourth lumbar vertebra. 

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

 termination of the aorta, they pass downward and outward 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 longer than the left, and passes more 

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

 peritoneum, the small intestines, branches of the sympathetic nerve, and, at its 

 point of division, the ureter. Behind, it is separated from the fourth arid fifth 

 lumbar vertebrae, with the intervening intervertebral disc, by the two common 

 iliac veins. On its outer side, it is in relation with the inferior vena cava and 

 the 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, and the superior hsemorrhoidal artery ; and is crossed 

 at its point of bifurcation by the ureter. It rests on the bodies of the fourth and 

 fifth lumbar vertebrae, with the intervening intervertebral disc. The left common 

 iliac vein lies partly on the inner side, and partly beneath the artery ; on its 

 outer side, the artery is in relation with the Psoas magnus muscle. 



PLAN OF THE RELATIONS OF THE COMMON ILIAC ARTERIES. 



In front. 

 Peritoneum. 

 Small intestines. 

 Sympathetic nerves. 

 Ureter. 



Outer side. 



Vena cava. 

 ! Right common 



iliac vein. 

 Psoas muscle. 



Behind. 



Fourth and fifth lumbar vertebrae. 

 Right and left common iliac veins. 



Inner side. 



Left common 

 iliac vein. 



In front. 

 Peritoneum. 

 Sympathetic nerves. 

 Superior haemorrhoidal artery. 

 Ureter. 



Outer side. 



Psoas magnus 

 muscle. 



Behind. 



Fourth and fifth lumbar vertebrae. 

 Left common iliac vein. 



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

 Psoas magnus, ureters, and the surrounding cellular tissue, and occasionally give 

 origin to the ilio-lumbar or renal arteries. 



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. 



The point of division is subject to great variety. In two-thirds of a large number of cases 

 it was between the last lumbar vertebra and the upper border of the sacrum being above that 



