552 



THE ARTERIES 



Variations in the Abdominal Aorta 



Variations in the abdominal aorta, except as regards its place of division and some irregu- 

 larity ill the origin and number of" its branches, are not common. According to Quain, in ten out 

 of every thirteen subjects examined, the bifurcation took place within half an inch above or below 

 the level of the highest part of the crest of the ilium. The commonest situation for its bifurca- 

 tion with reference to the vertebrse is perhaps opposite the lower border of the bodj'of the fourtli 

 lumbar, but it maj' divide oi)posite the disc between the fourth and fifth lumbar, or rarely oi)j»o- 

 site the fifth lumbar. A higher division than at the usual spot is less common. The arteiy, 

 however, has been found in exceptional instances dividing as high as the origin of the renal 

 arteries, or even as high as the second lumbar vertebra. 



The following rare variations have been met Avith : — (A) The aorta passing through tlie 

 oesophageal opening in the diaphragm. (B) The aorta lying on the right side of the vena cava; 

 the vein then passes over the upper part of the aorta to gain the caval opening. (C) The aorta 

 with a vena cava on each side, the left vein passing across the upper part of the artery to open 



Fig. 364. — Scheme of the Abdominal Aorta. ("NValsham.) 



LESSER OMENTUM 



Splenic vein 



PANCREAS 



Left renal vein 

 Superior mesenteric 

 artery 

 TRANSVERSE MESO-COLON 



THIRD PART OF DUODENUM 



TRANSVERSE COLON 

 MESENTERY 



SMALL INTESTINES 



GREAT OMENTUM 



Inferior mesenteric 

 artery 



THORACIC DUCT 

 Cceliac axis 



First lumbar vein 



RECEPTACULUM CHYLI 



Second lumbar vein 



PERITONEUM 



Third lumbar vin 



Fourth lumbar vein 



into the right vein just below the caval opening. (D) The aorta giving off a imbnonary branch 

 close to the origin of the cceliac axis, the abnormal vessel then passing through the oesophageal 

 opening, and supplying a branch to the lower lobe of each lung. 



The variations in the branches of the aorta are described under each branch. 



Branches of the Abdominal Aorta 



The branches of the abdominal aorta are given off in the following order 

 from ahove downwards (fig. 863): — 



(1) Right and left phrenic; (2) coeliac axis; (3) right and left suprarenal or 

 capsular; (4) right and left first lumbar; (5) su])erior mesenteric; (6) right and 

 left renal; (7) right and left si>ermatic; (8) right and left second lumbar; (9) 

 inferior mesenteric; (10) right and left third lumbar; (11) right and left fourth 

 lumbar; (12) right and left common iliac; (13) middle sacral. 



The above branches may be divided into the parietal, the visceral, and the 

 terminal. 



