A bdominal A orta 351 



of the umbilicus. Above the umbilicus the aorta may be felt pulsating, 

 and may there be readily compressed in a thin subject 



Sometimes the bifurcation is a little above, sometimes a little 

 below, the fourth lumbar vertebra. 



Relations. It rests upon the four upper lumbar vertebrae, the left 

 lumbar veins, and the beginning of the thoracic duct. 



Anterior to it are the lesser omentum and stomach, pancreas and 

 splenic vein, left renal vein, the third part of the duodenum, and the 

 mesentery, and along its whole course is a dense interlacement of 

 sympathetic nerves. (The left renal vein, crossing to the vena cava 

 in front of the aorta, is the exception to the rule that above the dia- 

 phragm the large veins are in front of the large arteries, whilst below 

 it they pass behind.) 



To the right side is the vena cava; this is separated from the 

 aorta above by the right crus, the beginning of the thoracic duct, and 

 the large azygos vein. To the left are the left crus and the psoas, the 

 tail of the pancreas, and the kidney. 



Aortic aneurysm. When injecting a subject for dissection through 

 the aortic arch, the abdominal aorta often gives way just where the 

 cceliac arises ; there, also, aneurysm is apt to form during life. It is 

 evidently a weak spot. When an aneurysm comes from the front of 

 the aorta a pulsating tumour is noticed in the epigastric or in the 

 upper part of the umbilical region ; but a tumour of the pyloric end of 

 the stomach, pancreas, or transverse colon may also give rise to this 

 symptom, for the abdominal aorta advances far towards the anterior 

 abdominal wall. 



The aneurysm is best examined on flexing the trunk, so as to 

 slacken the abdominal wall, and by getting the patient to expire fully 

 so that the lower costal cartilages may sink. The bowels should 

 previously be well opened. 



Pain in the back is a sign of the aneurysm ; for the sympathetic 

 filaments along the aorta are associated with the lumbar nerves 

 through the ganglia, and pain is reflected from these filaments to the 

 spinal trunks, and along the posterior divisions of those nerves to the 

 skin of the dorsi-lumbar region. A careless practitioner might satisfy 

 himself with calling such pains * lumbago.' 



The aneurysm may, by disturbing the sympathetic plexus, pro- 

 duce indigestion and sickness ; or, by constant pressure, may cause 

 absorption of the bodies of the lumbar vertebrae, and may even bear 

 upon the roots of the lumbar nerves. Pressure may also cause per- 

 sistent neuralgia in the abdominal wall, testicle, groin, and thigh. The 

 tumour may bulge against the diaphragm, oesophagus, and stomach, 

 causing dyspnoea, dysphagia, and vomiting, and possibly a constant 

 pain in the epigastrium. In some cases the pains are less when the 

 patient lies upon his face, for then the tumour falls away from the 

 nerves. The tumour may compress the transverse colon ; it may thrust 



