128 TOPOGRAPHICAL ANATOMY OF THE 



three main branches for the central and right and left lateral lobes. 

 (d) The g astro- duodenal artery (a. gastroduodenalis) runs to the 

 beginning of the duodenum, where it divides into the right gastro- 

 epiploic and pancreatico-duodenal arteries. The first named (a. 

 gastroepiploica dextra) gains the greater curvature of the stomach by 

 passing between the pancreas and the stomach, and ends by anastomos- 

 ing with the left gastro-epiploic artery derived from the splenic. The 

 pancreatico-duodenal artery (a. pancreaticoduodenalis) soon divides into 

 pancreatic and duodenal branches. The former (ramus pancreaticus) 

 supplies the adjacent part of the pancreas. The duodenal branch 

 (ramus duodenalis) follows the border of the mesoduodenum and ends by 

 anastomosing with the first intestinal artery. 



V. PORTiE. — It is by way of the short but wide portal vein that the 

 blood is removed from the intestines (except the rectum), the stomach, 

 the pancreas and the spleen. Or, in other words, the drainage area of 

 the portal vein is the same as the distribution area of the coeliac, cranial 

 mesenteric and caudal mesenteric arteries, except that, instead of 

 draining the liver, the portal vein carries blood to this gland. 



The portal vein is formed close to the stem of the cranial mesenteric 

 artery by the union of the cranial mesenteric, caudal mesenteric and 

 splenic veins. The two last named vessels frequently unite into a short 

 trunk before the cranial mesenteric joins them. Thus constituted, the 

 portal vein pursues a short course immediately ventral to the caudal vena 

 cava before it penetrates the portal ring of the pancreas. Once clear of 

 the pancreas, the vein passes to the porta of the liver between the two 

 layers of the gastro-hepatic ligament, and so, dividing into three main 

 branches, enters the liver in company with the hepatic artery and the 

 bile duct. 



(1) V. mesenterica cranialis. — The cranial mesenteric vein is a 

 fairly close companion of the artery of the same name. Its tributaries 

 are : — Eighteen to twenty intestinal veins ; the ileo-ccecal vein, 

 corresponding to the ileo-cjfico-colic artery, except that there is no 

 tributary equivalent to the ventral colic artery ; the right colic vein, 

 beginning in branches in the wall of the left ventral and left dorsal 

 colon and draining also the right ventral and right dorsal parts of this 

 tube. The right colic vein is, therefore, mainly at any rate, equivalent 

 to the dorsal and ventral colic arteries. 



A small vessel assists in the drainage of the right dorsal colon, and 

 is connected with the right colic vein on the one hand, and with either 

 the caudal mesenteric or the middle colic vein on the other. 



(2) V. viesenterica caudalis. — The caudal mesenteric vein is formed 



