ABDOMINAL CAVITY 317 



nerves, lymph vessels and lymph glands will be exposed, and the 

 anastomoses of the branches of the middle colic artery with 

 branches of the right colic artery will be displayed. 



After the structures in the right part of the transverse meso- 

 colon have been secured and cleaned throw the small intestine 

 over to the right side and make two incisions through the peri- 

 toneum on the left part of the posterior wall of the abdomen ; 

 one, a transverse incision, from the upper end of the root of the 

 mesentery to the upper end of the descending colon, and the 

 other along the left side of the root of the mesentery from its 

 upper to its lower end. After the incisions have been made 

 reflect the left half of the lower layer of the transverse meso- 

 colon towards the transverse colon and display the anastomoses 

 of the left branches of the middle colic artery with the upper 

 branches of the left colic artery, and the associated veins, lymph 

 vessels, lymph glands and nerves. When those structures have 

 been cleaned reflect the peritoneum on the left part of the pos- 

 terior wall of the abdomen downwards and to the left. When the 

 reflection is completed and the extra-peritoneal fat has been re- 

 moved the dissector will find that he has exposed a greater number 

 of structures than he did when he removed the peritoneum 

 covering the posterior wall of the abdomen to the right of the 

 root of the mesentery. In the median plane, below the root 

 of the mesentery, lies the lower part of the abdominal portion 

 of the aorta, dividing, opposite the fourth lumbar vertebra, into 

 the two common iliac arteries, each of which is continued down- 

 wards into the corresponding external iliac artery. On the 

 surface of the aorta is the aortic plexus of nerves, which must 

 be carefully preserved. To the right of the aorta is the lower 

 part of the inferior vena cava, and to the right of and below the 

 left common iliac artery is the left common iliac vein. Spring- 

 ing from the front of the aorta, about one and a half inches 

 above its bifurcation and to the left of the median plane, is the 

 inferior mesenteric artery. The inferior mesenteric artery runs 

 downwards on the left of the aorta to the left common iliac 

 artery, where it becomes the superior hsemorrhoidal artery. 

 Before it becomes the superior haemorrhoidal it gives off the left 

 colic branch, and two or more sigmoid branches. The left colic 

 branch passes to the left, towards the descending colon, and 

 divides into an ascending and a descending branch, which run 

 towards the upper and the lower parts of the descending colon 

 respectively. The sigmoid branches run downwards and later- 

 ally towards the lower part of the iliac colon. To the left of the 

 inferior mesenteric artery is the inferior mesenteric vein, which 

 ascends to the root of the transverse meso-colon. As it ascends 

 it crosses behind the left colic artery and in front of the internal 

 spermatic vessels ; when it reaches the root of the transverse 

 meso-colon it disappears behind the lower border of the pan- 

 creas, which is exposed in the upper part of the area under 

 consideration. To the left of the lower part of the inferior 

 mesenteric vein are the internal spermatic vessels, which pass 

 behind the sigmoid and left colic arteries, or their branches, and 

 then behind the inferior mesenteric vein ; they also disappear above 

 behind the pancreas. In the upper and left angle of the area, in 

 the concavity of the left flexure of the colon, is the lower part of 

 the left kidney, and, descending along its medial border, the 



