ABDOMINAL AORTA AND BRANCHES. 489 



artery. In the hollow of the hip-bone is the iliacus muscle which unites 

 below with the large psoas. 



The ABDOMINAL AORTA (fig. 171, b] extends from the last dorsal ver- 

 tebra to the left side of the body of the fourth lumbar vertebra, where it 

 divides into the common iliac arteries. Its commencement is between 

 the pillars of the diaphragm, and its termination is placed on the left side 

 of the umbilicus, and nearly on a level with the highest part of the crest 

 of the hip-bone. 



The chief connections of the vessels with surrounding parts have been 

 before referred to (p. 444), but some deep vessels in relation with it come 

 now into view. As the aorta lies on the spine it rests on the left lumbar 

 veins, which end in the inferior cava. And between it and the right crus 

 of the diaphragm lie the vena azygos major, and the thoracic duct. Along 

 the sides of the vessel are the lumbar lymphatic glands, from which large 

 vessels run beneath it to end in the beginning of the thoracic duct. 



The branches of the aorta are numerous, and arise in the following 

 order : First, are the diaphragmatic arteries, two in number, which leave 

 the sides of the vesselimmediately it appears in the abdomen. Close to 

 the tendinous ring of the diaphragm, the single trunk of the cooliac axis 

 arises from the front : and about a quarter of an inch lower down, also on 

 the front, the trunk of the superior mesenteric artery begins. Half an 

 inch lower the renal arteries, right and left, take origin from the sides of 

 the aorta. On the lateral part of the vessel, close above each renal, is 

 the small capsular branch ; and below the renal is the spermatic artery. 

 From the front of the arterial trunk, one to two inches above the bifurca- 

 tion, springs the inferior mesenteric artery ; and from the angle of division 

 the small middle sacral artery runs downwards. Four small lumbar 

 branches on each side come from the posterior part of the vessel, opposite 

 the bodies of the lumbar vertebrae. 



The branches may be classified into two sets one to the viscera of the 

 abdomen (visceral), and another to the abdominal wall (parietal). 



The visceral branches are crcliac axis, superior and inferior mesenteric, 

 renal, capsular, and spermatic. This set has been examined, except the 

 renal, capsular, and spermatic. 



The renal arteries (fig. 171, c) leave the aorta nearly at a right angle, 

 and are directed outwards, one on each side. Near the kidney each di- 

 vides into four or five branches, which enter the renal substance between 

 the vein and the ureter. Each artery lies beneath its companion vein, 

 being surrounded by a plexus of nerves, and supplies small twigs to the 

 suprarenal body (inferior capsular), to the ureter, and to the fatty layer 

 about the kidney. 



The arteries of opposite sides have some differences. The left is the 

 shortest, owing to the position of the aorta : the right crosses the spine, 

 and passes beneath the vena cava. 



The middle capsular artery is a small branch which runs almost trans- 

 versely outwards to the suprarenal body : this offset anastomoses with the 

 other branches of the suprarenal body from the renal and diaphragmatic 

 arteries. It is of large size in the foetus. 



The spermatic artery of the testicle (fig. 171, d) is remarkable for its 

 small size in proportion to its length ; for leaving the cavity of the abdo- 

 men ; and for having the part in the abdomen straight, but that in the 

 cord tortuous. 



From its origin below the renal, the vessel passes downwards along 



