COMMON ILIAC ARTERIES. 341 



and to the muscles of the back, whilst the other takes its course be- 

 hind the quadratus lumborum muscle and supplies the abdominal 

 muscles. The first lumbar artery runs along the lower border of the 

 last rib, and the last along the crest of the ilium. In passing between 

 the psoas muscles and the vertebrae, they are protected by a series of 

 tendinous arches, which defend them and the communicating branches 

 of the sympathetic nerve from pressure during the action of the muscle. 



The SACRA MEDIA arises from the posterior part of the aorta at its 

 bifurcation, and descends along the middle of the anterior surface of 

 the sacrum to the first piece of the coccyx where it terminates by in- 

 osculating with the lateral sacral arteries. It distributes branches to 

 the rectum and anterior sacral nerves, and inosculates on either side 

 with the lateral sacral arteries. 



Varieties in the Branches of the abdominal Aorta. The phrenic 

 arteries are very rarely both derived from the aorta. One or both 

 may be branches of the coeliac axis ; one may proceed from the gastric 

 artery, from the renal, or from the upper lumbar artery. There are 

 occasionally three or more phrenic arteries. The coeliac axis is very 

 variable in length, and gives off its branches irregularly. There are 

 sometimes two or even three hepatic arteries, one of which may be 

 derived from the gastric or even from the superior mesenteric. The 

 colica media is sometimes derived from the hepatic artery. The 

 spermatic arteries are very variable both in origin and number. The 

 right spermatic may be a branch of the renal artery, and the left 

 a branch of the inferior mesenteric. The supra-renal arteries may be 

 derived from the phrenic or renal arteries. The renal arteries present 

 several varieties in number ; there may be three or even four arteries 

 on one side, and one only on the other. When there are several 

 renal arteries on one side, one may arise from the common iliac 

 artery, from the front of the aorta near its lower part, or from the in- 

 ternal iliac. 



COMMON ILIAC ARTERIES. 



The abdominal aorta divides opposite the fourth lumbar vertebra 

 into the two common iliac arteries. Sometimes the bifurcation takes 

 place as high as the third, and occasionally as low as the fifth lumbar 

 vertebra. The common iliac arteries are about two inches and a half 

 in length ; they diverge from the termination of the aorta, and pass 

 downwards and outwards on each side to the margin of the pelvis 

 opposite the sacro-iliac symphysis, where they divide into the internal 

 and external iliac arteries. In old persons the common iliac arteries 

 are more or less dilated and curved in their course. 



The Right common iliac is somewhat longer than the left, and forms 

 a more obtuse angle with the termination of the aorta ; the angle of 

 bifurcation is greater in the female than in the male. 



Relations. The relations of the two arteries are different on the 



