LOWER MESENTERIC VESSELS. 441 



and the distribution, but at each branching the size of the vessels dimin- 

 ishes. From the last set of arches twigs are sent to the intestine on both 

 aspects of the tube, and anastomose round it. 



The branches of the large intestine are three in number, ileo-colic, right 

 colic, and middle colic arteries. 



c. The ileo-colic artery (o) arises from the right side of the trunk, and 

 divides at the ca3cum into branches which encircle the head of the colon. 

 A descending offset is distributed to the lower part of the ileum, and to 

 the caecum and the vermiform appendix ; whilst an ascending offset sup- 

 plies the beginning of the ascending colon, and anastomoses with the right 

 colic artery. 



d. The right colic artery (c?) is commonly an offset of the preceding, 

 instead of a separate branch from the trunk. Near the ascending colon it 

 divides into ascending and descending pieces, which anastomose with the 

 ileo-colic artery on one side, and with the middle colic on the other. 



e. The middle colic branch (c) springs from the upper part of the artery, 

 and entering between the layers of the transverse meso-colon divides into 

 two diverging branches : the right one anastomoses with the artery to the 

 ascending colon, and the left inosculates on the descending colon with a 

 left colic branch (fig. 144, c) of the inferior mesenteric artery. The 

 intestinal twigs are united in arches before entering the gut, like those to 

 the small intestine. 



The superior mesenteric vein (fig. 146, b) commences in that part of the 

 intestinal tube to which the artery is distributed. Its radicles unite into 

 one trunk, w r hich accompanies the artery beneath the pancreas, and there 

 joins the splenic vein to form the vena portae. 



At the lower border of the pancreas it receives the right gastro-epiploic 

 "branch of the stomach, and the pancreatico-duodenal veins (fig. 146, c). 



The mesenteric lymphatic gands are numerous between the layers of the 

 mesentery. An upper group lies by the side of the artery, and contains 

 the largest glands ; and a lower group, near the intestine, is lodged in the 

 intervascular spaces. The chylilerous vessels of the small intestine, and 

 the absorbents of the part of the large intestine supplied by the superior 

 mesenteric artery, pass through the mesenteric glands in their course to 

 the thoracic duct. 



Along the side of the ascending and the transverse colon are a few 

 other small lymphatic glands meso-colic, which receive some absorbents of 

 the large intestine. 



Dissection (fig. 144). By drawing the small intestine over to the right 

 side, the dissector will observe the inferior mesenteric artery on the front 

 of the aorta a little above the bifurcation. The peritoneum should be re- 

 moved from it, and the branches should be traced outwards to the remain- 

 ing half of the large intestine : a part of the artery enters the pelvis, but 

 this will be dissected afterwards. On the artery and its branches the in- 

 ferior mesenteric plexus of nerves ramifies. 



The mesenteric vein is to be followed upwards, away from the trunk of 

 the artery, to its junction with the splenic, or with the superior mesenteric 

 vein. 



On the aorta the dissector will meet with a plexus of nerves, which is 

 to be left uninjured. 



The inferior mesenteric artery (fig. 144, b) supplies branches to the 

 part of the large intestine beyond the transverse colon ; and communi- 



