598 THE BLOOD-VASCULAR SYSTEM 



each divides into two branches, which inosculate with similar branches given off from the 

 branch above and below. From the primary loops thus formed, secondary loops are derived 

 in Uke manner, and from these tertiarj^ and at times quaternary, or even quinary loops. From 

 the ultimate loops terminal jejunal and iliac branches [aa. jejunales et iliese] pass on to the muscu- 

 lar coat of the gut. These terminal vessels bifurcate, the two branches encircling the intestine, 

 and thus forming with those above and below a series of vascular rings surrounding the small 

 intestine throughout its whole length. The first intestial artery anastomoses with the pancre- 

 atico-duodenal arteries, and the last (the continuation of the main artery) with the ileo-colic. 

 These branches of the superior mesenteric in their course to the intestine also supply the 

 mesentery and the mesenteric glands. 



(3) The ileo-colic [a. ileocolica] descends behind the peritoneum toward the ceecum, where 

 it divides into a cohc branch which tracks upward beneath the peritoneum to anastomose with 

 the descending branch of the right cohc; and into an ihac branch which passes between the 

 layers of the mesentery and anastomoses with the termination of the superior mesenteric 

 artery. Near the site of division the ileo-cohc gives off anterior and posterior csecal branches. 

 From the latter of these arises a caeco-appendicular artery, to the cajcum and root of the vermi- 

 form process, and a main appendicular artery [a. appendicularis] (fig. 483). 



(4) The right colic [a. colica dextra] — sometimes given off as a common trunk either with 

 the middle colic or with the ileo-colic — passes to the right behind the peritoneum to the back 

 of the ascending colon, where it divides into an ascending branch, which anastomoses with the 

 descending branch of the middle colic, and a descending branch which anastomoses wuth the 

 ascending or colic branch of the ileo-colic. . 



(5) The middle colic [a. colica media], arising from the concavity of the superior mesenteric 

 a little below the pancreas, enters the transverse meso-colon, and divides into two branches — 

 one of which passes to the left and anastomoses with the ascending branch of the left colic; 

 the other, winding downward and to the right, anastomoses with the ascending branch of the 

 right colic. 



THE RENAL ARTERIES 



The renal arteries [aa. renales] come off one on each side of the abdominal 

 aorta, a Httle below the superior mesenteric and first lumbar arteries, on a level 

 with the first lumbar vertebra. They pass laterally across the crura of the 

 diaphragm to the kidneys, the right being on a slightly lower plane and somewhat 

 longer than the left, and passing behind the inferior vena cava. In front of each 

 is the corresponding renal vein, and behind, at the hilus of the kidney, is the com- 

 mencement of the ureter. Each artery as it enters the hilus usually divides into 

 three main stems, one of which passes toward the upper part of the pelvis, a second 

 to its middle portion, and a third to its lower. Each of these primary stems then 

 divides so that there result from seven to nine secondary branches, the majority 

 of which pass anterior to the pelvis, while the remainder are posterior to it (fig. 

 484). No anastomoses take place between the branches of the anterior and 

 posterior secondary stems and hence a longitudinal incision into the kidney along 

 its curved border, half way between the anterior and posterior calices, will cut 

 only terminal arteries. 



The branches of the renal arteries are : — 



(1) The inferior suprarenal [a. suprarenahs inferior] wliich ascends to the suprarenal body. 



(2) The capsular or peri-renal branches to the capsule of the kidney and peri-renal fat. 



(3) The ureteral l)ranch to the upper end of the ureter. 



THE MIDDLE SUPRARENAL ARTERIES 



The middle suprarenal artery [a. suprarcnalis media] comes off, one on each 

 side from the aorta, just above the first lumbar artery, and passes laterally to the 

 suprarenal l)ody, across the medial crura of the diaphragm a little above the renal 

 arteries. In the fcetus they equal the renals in size. In the adult they are much 

 smaller. 



They anastomose with the superior and inferior suprarenal arteries from the 

 inferior phrenic and renal arteries respectively. For the distribution of the 

 suprarenal vessels within the suprarenal bodies, see Section XII. 



THE INTERNAL SPERJVEATIC ARTERIES 



The internal spermatic arteries [a. spermatica interna], (fig. 479), right and 

 left, come oil' from Uiv. front of the abdominal aorta. They diverge from each 

 other as they descend over the aorta and psoas muscle to the abdominal inguinal 

 (internal abdominal) ring, where they are joined by the ductus deferens, and, pass- 



