678 



THE BLOOD-VASCULAR SYSTEM 



The inferior mesenteric vein [v. mesenterica inferior] (fig. 531) begins at the 

 rectum as the superior hsemorrhoidal vein. This emerges from the haemor- 

 rhoidal plexus in which it communicates freely with the middle and inferior 

 hsemorrhoidal veins. It passes out of the pelvis with the inferior mesenteric 

 artery; but, after receiving the sigmoid and left colic veins [vv. sigmoidese et 

 V, colica sinistra] which accompany the arteries of the same names, it leaves the 

 artery and runs upward on the psoas to the left of the aorta and behind the 

 peritoneum. On approaching the pancreas it turns medially, and passes obliquely 

 behind that gland to join the splenic vein just before the latter unites with the 

 superior mesenteric to form the vena portae. 



Fig. 533. — The Veins of the Stomach and the Portal Vein. 

 (From a dissection by W. J. Walsham.) 



Cystic vein 



Right branch of 

 portal vein 



Portal vein 

 Hepatic artery 



Hepatic artery 

 proper 

 Gastro-duodenal 

 branch of hepatic 

 artery 



Pyloric vein 



Right gastro- 

 epiploic vein 



Omental veins 



Left branch o( 

 portal vein 



Veins corres- 

 ponding to short 

 gastric arteries 



Left gastric artery 

 Hepatic artery 



Splenic artery 



Coronary vein 



Left gastro- 

 epiploic vein 



The adult portal vein and its tributaries contain no valves, a circumstance which adversely 

 affects the circulation of blood within this system. The liability to excessive pressure in the 

 most dependent part of the portal system is evidenced by the great frequency of the condition 

 known as piles, due to dilatation of the veins of the internal haunorrhoidal plexus. In early 

 life valves are present in the veins of the stomach and of the intestinal wall but these undergo 

 retrogression. 



The accessory portal veins. — Since the blood returning from the abdominal portion of the 

 dige.stive tract and spleen must pass through the hepatic capillaries before returning to the heart, 

 extensive ol)literation of these capillaries, such as occurs in certain diseases of the liver, would 

 prevent the return of the portal blood to the heart were it not for anastomoses between tribu- 

 taries of the portal vein and those of the caval systems, constituting what have been termed 

 accessory portal veins. Some of the more important of these are — (1) between the branches of 

 the coronary vein of the stomach and the a;soi)liageal veins which open into the vena azygos; 

 (2) between the parumbilical veins [vv. parumbilicalcs], which communicate with the portal 

 vein above and descend upon the ligamentum teres to the anterior abdominal wall to anastomose* 

 with the superior and inferior epigastric and superior vesical veins; (3) between the superior^ 

 and middle hiemorrhoidal veins, the latter opening into the hypogastric, and (4) between a 

 wide-meshed retro-peritoneal plexus of veins which communicates with the portal vessels 

 over the posterior surface of the liver and the veins of the pancreas, duodenum and ascending 

 and descending colon on the portal side, and with the plircnic and azygos veins on the systemic. 



