The Intestines. 125 



(c) The descending colon (colon descendens) passes backward to 

 a point in front of the pelvis, where it is replaced by the 

 rectum. 



The descending mesocolon, which connects this portion 

 with the dorsal body-wall, should be noted on account of 

 its relation to the inferior mesenteric artery and sympathetic 

 plexuses. It is connected for a considerable distance with the 

 mesentery of the ascending limb of the duodenum. 



7. Displace the caecum, turning it over to the right. Lay out the 

 mesenterial small intestine, so that the mesentery and its bloodvessels 

 are exposed. Remove the lymph glands from about the base of the 

 mesenteric artery, and trace its branches as follows: 



(a) The middle colic artery (a. colica media), a small vessel arising 

 from the left wall and passing to the transverse colon. 



(b) The inferior pancreaticoduodenal artery (p. 122) arises at 

 the same level, but from the right wall. 



(c) The ileocaecocolic artery (a. ileocaecocolica), a large branch, 

 equalling in size the superior mesenteric trunk, is distributed 

 to the terminal portion of the ileum, the caecum (including 

 the vermiform process), and the ascending colon. Its branches 

 are arranged in two series, a proximal group being given off 

 near the point of origin of the main vessel, and a distal 

 group, including the terminal portion of the vessel, at about 

 two inches from the point of origin. 



The proximal branches include : 



(1) Small branches to the third, fourth, and fifth limbs 

 of the ascending colon. 



(2) The appendicular artery (a. appendicularis) to the 

 vermiform process. A branch of this vessel, given 

 off near the point of origin, passes to the ileum, 

 anastomosing with a branch of the superior mesen- 

 teric trunk. 



(3) An anterior ileocaecal artery to the terminal fourth 

 (third limb) of the caecum proper and related por- 

 tion of the ileum. 



(4) An anterior right colic artery to the flexure uniting 

 the first and second limbs of the ascending colon. 



(5) A posterior right colic artery to the second limb of the 

 ascending colon. This vessel anastomoses with (4) 

 and with the special branch to the third limb (1). 



The distal branches include : 



(6) A posterior ileocaecal artery to the middle portion 

 of the third limb of the caecum and the adjacent 

 portion of the ileum ; anastomosing with (3) . 



(7) A caecal artery to the posterior portion of the third 

 limb of the caecum. 



