424 THE ABDOMINAL AORTA. 



below by dividing into two trunks, named the common iliac arteries. 

 The bifurcation usually takes jilace about half way down the body of 

 the fourth lumbar vertebra, a little to the left of the middle line ; a 

 point which is nearly on a level with a line drawn from the one crista 

 ilii to the other, and opposite the left side of the umbilicus. 



The anterior surface of the abdominal aorta is successively in apposi- 

 tion with the pancreas and the splenic vein, the left renal vein, the 

 third portion of the duodenum, and the peritoneum. The vena cava 

 lies along its right side, the right cms of the diaphragm being inter- 

 posed at the upper part of the a!)domen ; close to the same side are the 

 thoracic duct and the azygos vein, which are placed between the aorta 

 and the right crus of the diaphragm. The aorta is also covered in 

 front by meshes of nerves derived from the sympathetic, and numerous 

 lymphatic vessels and glands. 



BiiAXCiiES. — The abdominal aorta gives numerous l)ranches, which 

 mav be divided into two sets, viz., those which supply the viscera, and 

 those which are distributed to the walls of the abdomen. The former 

 consists of the coeliac artery, the superior mesenteric, the inferior me- 

 senteric, the capsular, the renal, and the spermatic arteries ; whilst in 

 the latter are included the phrenic, the lumbar, and the middle 

 sacral arteries. The first three of the visceral branches arc single 

 arteries. 



Varieties. —P/n'rv of Bh-'ision. — In more than three-fourths of a considerable 

 number of cases, the aorta divided either upon the fourth himbar vertebra, or 

 upon the intervertebral disc below it ; in one case out of nine it was below, and in 

 about one out of eleven al)ove the spot thus indicated. In ten bodies out of eveiy 

 thirteen, tlie division of the great artery took place within half an inch above or 

 below tlae level of the iliac crest ; and it occurred more frequently below than 

 above the fourth intervertebral space. (R. Quain. op. cit. p. 41.j.) An instance 

 of bifurcation immediately below the origin of the right renal artery is recorded 

 by Haller (Disputat. Anatom. t. vi. p. 781.) 



UniiHunl Branch. — A very remarkable case is recorded of the existence of a 

 large i^ulmonary branch which arose from the abdominal aorta, close to the creliac 

 artery, and after passing ujiwards through the oesophageal opening in the dia- 

 phragm, divided into two branches, ■\\'hich were distributed to tlie lungs near their 

 l)ases. (Referred to by R. Quain in his work " On the Arteries," p. 41G.) 



A.— VISCERAL EnANCIiES OF THE ABDOMIITAL AORTA. 



The CCELIAC ARTERY or AXIS, a short and wide vessel, arises from the 

 aorta close to the margin of the diaphragm. It is directed forwards 

 nearly horizontally, and is not more than half an inch long. It is 

 behind the small omentum, and lies close to the left side of the lobulns 

 Spigelii of the liver, and above the pancreas, the two semilunar ganglia 

 being contiguous to it, one on each side. This artery divides into three 

 brauchcG, viz., the coronary artery of the stomach, the hepatic and the 

 splenic, which separate simultaneously from the end of the artery like 

 radii from an axis. 



Varieties. — The ccrllnc a.v\.^ is occasionally partly covered at its origin by the 

 diaphragm. It may lie longer than usual, in which case its branches are not given 

 off together; or it maybe entirely wanting, the coronary, hepatic, and splenic 

 arteries arising separately from the aorta. In some cases the co'liac artery gives 

 off only two branches at its division (the coronary and the splenic), the hepatic 

 being supplied from another source. Rarely, it gives more than three branches 



