660 THE VASCULAR SYSTEMS 



is generally half an inch below and to the left of the umbilicus, but as the position of this struc- 

 ture varies with the obesity of the individual, it is not a reliable landmark as to the situation of 

 the bifurcation of the aorta. 



Applied Anatomy. Aneurisms of the abdominal aorta near the coeliac axis communicate in 

 nearly equal proportion with the anterior and posterior parts of the artery. 



When an aneurismal sac is connected with the back part of the abdominal aorta, it usuallv 

 produces absorption of the bodies of the vertebra^, and forms a pulsating tumor that presents 

 itself in the left hypochondriac or epigastric regions, and is accompanied by symptoms of dis- 

 turbance in the alimentary canal. Pain is invariably present, and is usually of two kinds a 

 fixed and constant pain in the back, caused by the tumor pressing on or displacing the branches 

 of the solar plexus and splanchnic nerves; and a sharp lancinating pain, radiating along those 

 branches of the lumbar nerves which are pressed on by the tumor; hence the pain in the loins, 

 the testes, the hypogastrium, and in the lower limb (usually of the left side). This form of 

 aneurism usually bursts into the peritoneal cavity or behind the peritoneum in the left hypo- 

 chondriac region; or it may form a large aneurismal sac, extending down as low as Poupart's 

 ligament; hemorrhage in these cases being generally very extensive, but slowly produced, and 

 not rapidly fatal. 



\Vhen an aneurismal sac is connected with the front of the aorta near the coeliac axis it forms 

 a pulsating tumor in the left hypochondriac or epigastric region, usually attended with symptoms 

 of disturbance of the alimentary canal, as nausea, dyspepsia, or constipation, and is accom- 

 panied by pain, which is constant, but nearly always fixed in the loins, epigastrium, or some 

 part of the abdomen ; the radiating pain being rare, as the lumbar nerves are seldom implicated. 

 This form of aneurism may burst into the peritoneal cavity or behind the peritoneum, between 

 the layers of the mesentery, or, more rarely, into the duodenum; it seldom extends backward 

 so as to affect the vertebral column. 



The abdominal aorta has been tied several times, and although none of the patients perma- 

 nently recovered, still, as Prof. Keen's lived forty-eight days, the possibility of the reestablish- 

 ment of the circulation is proved. In the lower animals this artery has been often successfully 

 tied. The chief difficulty in the dead subject consists in isolating the artery in consequence of its 

 great depth; but in the living the embarrassment resulting from the proximity of the aneurismal 

 tumor, and the great probability of disease in the vessel itself, add to the dangers and diffi- 

 culties of this formidable operation. 



The collateral circulation would be carried on by the anastomosis between the internal mam- 

 mary and the deep epigastric; by the free communication between the superior and inferior 

 mesenteries if the ligature were placed above the latter vessel; or by the anastomosis between 

 the inferior mesenteric and the internal pudic when (as is more common) the point of ligation 

 is below the origin of the inferior mesenteric; and possibly by the anastomoses of the lumbar 

 arteries with the branches of the internal iliac. 



Branches. The branches of the abdominal aorta may be divided into three 

 sets visceral, parietal, and terminal. 



Visceral Branches. Parietal Branches. 



( Gastric. Inferior phrenic. 



Coeliac Axis < Hepatic. . Lumbar. 



( Splenic. Middle sacral. 



Superior mesenteric. 

 Inferior mesenteric. 



Suprarenal. Terminal Branches. 



Renal. Common iliac. 



Spermatic or ovarian. 



The coeliac axis, or artery (a. coeliaca) (Figs. 468 and 469), is a short, thick 

 trunk, about half an inch in length, which arises from the aorta, close to the 

 margin of the opening in the Diaphragm, behind the posterior parietal perito- 

 neum, above the pancreas, and below the twelfth thoracic vertebra, and, passing 

 nearly horizontally forward (in the erect posture), divides into three large 

 branches, the gastric, hepatic, and splenic, occasionally giving off one of the 

 phrenic arteries. 



