444 DISSECTION OF THE ABDOMEN. 



the intestine (sigmoid flexure) the branching of the nerves and the union 

 of contiguous twigs are well marked. Branches. Its secondary plexuses 

 are named from the arteries they accompany, viz., left colic, sigmoid, 

 and superior haemorrhoidal : they ramify on the vessels, and have a like 

 distribution. 



The hypogastric plexus, or the large prevertebral centre for the supply 

 of sympathetic nerves to the viscera of the pelvis, is situate in front of 

 the upper part of the sacrum. It is developed more on the sides than in 

 the centre ; and the nerves, which are large and flat, have a plexiform 

 arrangement, but without any intermixed ganglionic masses. 



By its upper part it receives the nerves on the aorta, and is joined by 

 some filaments from one or two of the upper sacral ganglia. Interiorly 

 the plexus ends in two parts, right and left, the last being the largest : 

 each is continued forwards by the side of the internal iliac artery to the 

 pelvic plexus of the same side, and to the viscera. 



CONNECTIONS OF AORTA AND VENA CAVA. 



Before the viscera are removed from the body, the connections of the 

 abdominal aorta and vena cava may be learnt. 



Dissection. To see the aorta above the origin of the superior mesen- 

 teric artery, it will be necessary to detach the great omentum from the 

 stomach, without injuring the gastro-epiploic artery along the great curve ; 

 and after raising the stomach and the spleen, to remove the peritoneum 

 from the surface of the pancreas. A short arterial trunk (coeliac axis) 

 above the pancreas is not to be cleaned now, otherwise the nerves about 

 it would be destroyed. 



The vena cava on the right side of the aorta may be followed as far as 

 the posterior border of the liver, where it disappears. The connections 

 of its upper part can be better observed after the dissection of the ves- 

 sels of the liver. 



The aorta enters the abdomen between the pillars of the diaphragm, 

 and divides into iliac arteries opposite the left side of the fourth lumbar 

 vertebra. At the beginning the vessel occupies the middle line of the 

 spine, but it gradually inclines to the left as it descends. 



In the abdomen the aorta lies behind all the viscera ; but it is crossed 

 more immediately by the pancreas and duodenum, which it touches with- 

 out the intervention of peritoneum. Its connections are the following : at 

 first it is covered by the solar plexus, and by the pancreas and the splenic 

 vein ; still lower (beyond the superior mesenteric artery) by the left renal 

 vein and the duodenum ; and thence to its termination by the peritoneum 

 and the aortic plexus. The vessel lies on the lumbar vertebrae, with the 

 pillars of the diaphragm embracing it at the beginning. To its right side 

 is the vena cava. Its relation to other deep parts is mentioned in p. 489. 



The vena cava inferior commences on the right side of the fifth lumbar 

 vertebra by the union of the common iliac veins, and reaches thence to 

 the heart. 



The venous trunk is placed on the right side of the vertebral column. 

 It lies close to the aorta, and is concealed by the same viscera as high as 

 the crus of the diaphragm ; but above that spot it is inclined away from 

 the artery, and ascending on the right of the crus of the diaphragm, is 

 imbedded in the posterior part of the liver for an inch or more. Lastly, 



