560 THE ARTERIES 



From the anastomotic loops formed between the termination of the superior 

 mesenteric, the ileo-coHc, the right colic, and the middle cohc arteries, secondary 

 loops are derived whence branches pass to the termination of the ileum, theca'cum, 

 the vermiform appendix, the ascending colon, and half the transverse colon. These 

 branches on reaching the intestine divide into two, one of which i)asses in front, 

 and the other behind the intestine, and, after encircling it, anastomose with each 

 other and with the neighl)ouring circlets above and below. 



(5) The intestinal branches, or vasa intestini tenuis, arise from the convex 

 side of the superior mesenteric, and, varying from twelve to sixteen in numl)er, 

 radiate in the mesentery, where each divides into two branches, which inosculate 

 with similar branches given off from the branch above and below. From the 

 primar}^ loops thus formed, secondary loops are derived in like manner, and from 

 these tertiary, and at times quaternary, or even quinary loops. From the ultimate 

 loops terminal Ijranches pass on to the intestine through the triangular interval left 

 at the spot where the mesentery is reflected on to tlie nuiscular coat of the gut. On 

 reaching the Avail 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. These 

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

 mesentery and the mesenteric glands. 



The variations in the superior mesenteric artery are numerous. (A) It may be double. (B) 

 It may give oif accessory brunches to the liver, stomach, pancreas, spleen, and gall-bladder. (C) 

 It may give oif branches normally derived fiom other sources, namely, the hepatic or its right or 

 left branch, the cystic, the gastro-duodenal or its right gastro-epiploic branch, the gastric or the 

 pancreatica magna. (D) It may give off the left colic and su])erior liEemorrhoidal, thus taking 

 the place in whole or in ])art of the inferior mesenteric. (E) Its colic and intestinal branches 

 may vary considerably in their origin and course, and in the number of primary and secondary 

 loops that they form. (F) A rare abnormality described by Hyrtl is the persistence of an 

 omphalo-mesenteric artery running to the neighbourhood of the umbilicus and giving off a branch 

 to the urachus, or a branch to the liver through the falciform ligament, or a branch to the rectus 

 anastomosing with the epigastrtc. 



THE RENAL ARTERIES 



The renal arteries come off one on each side of the abdominal aorta, a little 

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

 lumbar vertebra. They pass transversely outwards across the crura of the dia- 

 phragm to the kidneys, the riglit being on a slightly lower plane and somewhat longer 

 than the left, and passing bebind the inferior vena cava. In front of each is the 

 corresponding renal vein. Behind each at the hilum of the kidney is the com- 

 mencement of the ureter. Before entering the kidney the}- lireak up into three or 

 four terminal branches. The distribution of the arteries in the kidney is descrilied 

 under the anatomy of that organ. 



Each renal artery gives off the following branches: — 



(a) The inferior suprarenal, Avhich ascends to the suprarenal body. 



(/>) The capsular or peri-renal branches to the capsule of the kidney and 

 peri- renal fat. 



(c) The ureteral branch to the U})per end of tlie ureter. 



Variations in the renal arteries are common. (A) The right and left renal may arise from 

 the aorta by a common stem. (B) They may arise from the aorta lower than usual ; the kidneys 

 then being also below their usual situation. (C) There may be several renal arteries on each side, 

 or the renal artery may divide close to its origin into several branches. (I)) The renal artery on 

 one or both sides may arise from the bifurcation of the aorta, from the ctmimon iliac, the internal 

 iliac, the inferior mesenteric, or the middle sacral artery. (K) The right artery may cross in front 

 of, instead of l)eliin(], the vena cava. (F) The branches of the renal artery may perforate the 

 substance of the kidney instead of entering at the hilum. ((li ) The renal artery may give origin 

 to branches normally derived from other vessels, as tlie phrenic, the hepatic or its right branch 

 from the right renal, the middle sui)rarenal, some of the colic arteries, the s])erniatic, one or more 

 of the lumbar arteries, or the greater pancreatic artery. (H) Accessory renal arteries, varying in 

 size and generally derived from the aorta, are common. Tliey may enter the kidney at almost 

 any ])art of the organ. 



