236 ANATOMY OF THE RABBIT 



(d) The pancreas (Fig. 5, p. 17). Its principal portion is 

 here seen as a diffuse brownish mass lying in the mesoduo- 

 denum (cf. pp. 94 and 131) sometimes associated with a 

 considerable amount of fat. Its duct (d. pancreatis) opens 

 into the posterior portion of the ascending limb. 



The extraordinarily diffuse form of the pancreas and, more 

 particularly, the wide separation of the opening of its duct from 

 that of the bile duct (these two having a common termination in 

 many mammals, including man) are associated with the lengthening 

 of the duodenum as of other parts of the intestine in the herbivore. 



(e) The superior pancreaticoduodenal artery, a branch of the 

 gastroduodenal (see p. 230), passes backward on the first 

 portion of the descending limb. 



(/) The inferior pancreaticoduodenal artery (a. pancreatico- 

 duodenalis inferior), a branch of the superior mesenteric 

 (p. 240), enters the mesoduodenum from the left side and 

 supplies the major portion of the loop. An anterior branch 

 anastomoses with (e). 



3. In the mesenterial small intestine, the following features may 

 be identified: 



(a) The lighter coloration, due to the thicker wall and greater 

 vascularity, of the first or duodenal portion, thus distin- 

 guished as the jejunum (intestinum jejunum). 



(b) The darker coloration, due to the thinner wall, which allows 

 the contents to show through, and diminished vascularity 

 of the terminal or caecal portion, thus distinguished as the 

 ileum (intestinum ileum). The two portions are not dis- 

 tinctly separable. The circular folds (plicae circulares), 

 or valvulae conniventes, of the mucous tunic, which in 

 many mammals contribute to the thickness of the wall in 

 the duodenum and jejunum, are, in the rabbit, not definitely 

 expressed. 



The colour difTerences are not usually well indicated in 

 embalmed animals. 



(c) The mesentery, the peritoneal support of the mesenterial 

 small intestine, is distinguished in its major portion by its 

 broad frill-like character, which allows great freedom of 



