8o4 HUMAN ANATOMY. 



Variations. — The inferior mesenteric artery may be wanting, its place being supplied by 

 branches from the superior mesenteric. It occasionally gives rise to the middle colic artery or 

 to an accessory renal vessel. 



4. The Inferior Phrenic Arteries. — The inferior phrenic arteries (aa. 

 phrenicae inferioresj (Fig. 718) most frequently arise from the abdominal aorta, either 

 singly or by a common trunk, immediately beneath the aortic opening of the dia- 

 phragm and above the cceliac a.\is. They are directed upward and laterally over 

 the crura of the diaphragm, to which they supply branches, and in this portion of 

 their course they also give off superior suprarenal branches (rami suprarenales 

 superiores} to the suprarenal bodies. Over the region where the crura pass into the 

 diaphragm proper, each inferior phrenic divides into an internal and an external 

 branch. The former is the smaller of the two, and passes inward towards the oeso- 

 phageal opening of the diaphragm, where it anastomoses with its fellow of the oppo- 

 site side to form an arterial ring from which branches descend upon the oesophagus, 

 supplying the lower portion of that structure and anastomosing with the oesophageal 

 branches of the gastric artery. 



The external branches are directed laterally upon the under surface of the dia- 

 phragm, supplying it. They pass as far forward as the costal and sternal origins of 

 the diaphragm, anastomosing with the musculo-phrenic, superior epigastric, and 

 superior phrenic branches of the internal mammary arteries, while other branches 

 ramify over the lateral portions of the diaphragm, anastomosing with the lower inter- 

 costals and perforating the central tendon to anastomose with the pericardial arteries 

 and with the diaphragmatic branches of the thoracic aorta. 



Variations.— The inferior phrenic arteries are very variable in their origin. One fre- 

 quently takes its origin from the coeliac axis or from one of its branches, or both may arise from 

 the a.xis. They have also been observed to arise from the superior mesenteric or the renal, or 

 from the abdominal aorta below the superior mesenteric. They also vary considerably in volume. 



5. The Suprarenal Arteries. — The suprarenal arteries, sometimes termed the 

 middle siiprarenals (aa suprarenales mediae) (Fig. 718) to distinguish them from the 

 suprarenal branches of the inferior phrenic and renal arteries, are a pair of small 

 but constant branches which arise from the sides of the abdominal aorta, almost oppo- 

 site the origin of the superior mesenteric artery. They pass outward and slightly 

 upward over the crura of the diaphragm to the suprarenal bodies, where they anasto- 

 mose with the other suprarenal branches. 



6. The Renal Arteries.— The renal arteries (aa. renales) (Figs. 718, 1591) 

 are two large stems which arise from the sides of the abdominal aorta a little below 

 the origin of the superior mesenteric. Usually the two arteries are opposite each 

 other, but frequently that of the right side arises a little lower down than that of 

 the left side. They are directed outward and slightly downward towards the kidneys, 

 each artery, before reaching the hilum, dividing into from three to five branches, 

 which enter the substance of the kidney independently at the hilum. 



Relations. — In their course towards the kidneys the renal arteries rest upon the 

 lower portions of the crura of the diaphragm and more laterally upon the upper part of 

 the psoas muscles. The right artery is somewhat longer than the left, owing to the 

 position of the abdominal aorta a little to the left of the median line, and it passes behind 

 the inferior vena cava. Both vessels are almost concealed beneath the corresponding 

 renal veins, and at the hilum of the kidney the majority of the terminal branches pass 

 in front of the upper portion of the ureter, only one or two passing behind it. 



Branches.- -Near its termination each artery gives off branches which pass to the adipose 

 tissue surrounding the kidney, and a ureteral branch which supplies the upper part of the ureter, 

 anastomosing with the ureteral branch of the spermatic (or ovarian) artery. More proximally 

 it gives origin to an inferior suprarenal branch (a suprarenalis inferior) which passes upward to 

 the lower part of the suprarenal body and anastomoses with the other branches which go to 

 that structure. 



Variations. — Not infrequenth' the division of the renal arteries into their terminal branches 

 takes place early, sometimes immediately at their origin, several stems arising directly from the 

 aorta and passing outward to the kidney. Accessory renal branches may arise from the abdomi- 



