192 Anatomy of the Rabbit. 



(taeniae coli) . Two of these bands are free, while the third 

 is enclosed by the supporting peritoneum, the mesocolon. 

 The two free bands run together toward the anterior end 

 of the first limb. 



(b) The transverse colon (colon transversum) is a short seg- 

 ment, beginning forwards on the right and crossing the 

 middle line transversely to the left, where it bends sharply 

 backward, and is replaced by the descending colon. 



(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 por- 

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

 of its relation to the inferior mesenteric artery and sympathe- 

 tic 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 side of the 

 animal. Lay out the mesenterial small intestine, so that the mesen- 

 tery and its bloodvessels are exposed. Remove the lymph glands 

 from about the base of the superior mesenteric artery, first noting 

 their position at the root of the mesentery. They receive afferent 

 lymphatic vessels from the wall of the intestine, and send off efferent 

 vessels to one another and to the lymphatic trunks. 



Trace the branches of the superior mesenteric artery as follows : 



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

 (frequently two) arising from the left wall and passing to the 

 transverse colon. 



(b) The inferior pancreaticoduodenal artery (p. 189) 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 caecuin 

 (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. 



