RENAL ARTERIES LUMBAR ARTERIES. 305 



The SigmoidecB are several large branches which are distributed 

 to the sigmoid flexure of the descending colon. They form arches, 

 and inosculate above with the colica sinistra, and below with the 

 superior ha3morrhoidal artery. 



The Superior hcemarrhoidal artery is the continuation of the 

 inferior mesenteric. It crosses the ureter and common iliac artery 

 of the left side, and descends between the two layers of the meso- 

 rectum as far as the middle of the rectum to w r hich it is distributed, 

 anastomosing with the middle and external heemorrhoidal arteries. 



The SUPRA-RENAL are two small vessels which arise from the 

 aorta immediately above the renal arteries, and are distributed to 

 the supra-renal capsules. They are sometimes branches of the 

 phrenic or of the renal arteries. 



The RENAL ARTERIES (emulgent) are two large trunks given off 

 from the sides of the aorta immediately below the superior mesen- 

 teric artery ; the right is longer than the left on account of the posi- 

 tion of the aorta, and passes behind the vena cava to the kidney of 

 that side. The left is somewhat higher than the right. They divide 

 into several large branches previously to entering the kidney, and 

 ramify very minutely in its vascular portion. The renal arteries 

 supply several small branches to the supra-renal capsules. 



The LUMBAR ARTERIES correspond with the intercostals in the 

 chest ; they are four or five in number on each side, and curve 

 around the bodies of the lumbar vertebrae beneath the psoas muscles, 

 and divide into two branches; one of which passes backwards 

 between the transverse processes and is distributed to the vertebra 

 and spinal cord and to the muscles of the back, whilst the other 

 takes its course behind 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 inosculating 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 cceliac 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 creliac 

 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 



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