THE PORTAL SYSTEM. 923 



(c) The left colic vein (v. colica sinistra) has its origin in the walls of the descending colon, 

 anastomosing above with the middle colic and below with the sigmoid veins. It passes medially 

 to open into the upper part of the inferior mesenteric. 



4. The Gastric Vein. — The gastric vein (v. coronaria ventriculi) (Fig. 772) 

 accompanies the gastric artery along the lesser curvature of the stomach. It has its 

 origin at the pyloric end of the stomach, where it anastomoses with the pyloric vein, 

 and passes at first from right to left along the lesser curvature, receiving tributaries 

 from the upper part of both surfaces of the stomach. At the opening of the 

 oesophagus into the stomach it makes connections with the oesophageal veins, and 

 then bends upon itself and passes from left to right behind the posterior wall of the 

 lesser sac of the peritoneum, and terminates either in the portal vein or in the splenic 

 shortly before its union with the superior mesenteric. 



The peculiar reflected course of the gastric vein is readily understood if it be remembered 

 that the adult position of the stomach is a secondary one. When first formed the long axis of 

 the stomach is practically vertical, the pyloric end being directed downward, and a vein starting 

 at the pylorus will have a direct ascending course to the portal vein. When the stomach as- 

 sumes its adult position the course of the vein with reference to the viscus does not alter, and 

 consequently it passes from pylorus to cardia, and must then bend back upon itself to reach the 

 portal vein. 



5. The Pyloric Vein. — The pyloric vein (v. pylorica) (Fig. 772) accompanies 

 the pyloric branch of the hepatic artery. It takes its origin at the pyloric end of the 

 stomach, where it anastomoses with the gastric vein, and passes downward to open 

 into the portal. 



6. The Cystic Vein. — The cystic vein (v. cystica) (Fig. 772) returns the 

 blood from the walls of the gall-bladder and opens usually into the right trunk of the 

 portal vein. It is frequently represented by two separate stems. 



7. The Parumbilical Veins. — The parumbilical veins (vv. parumbilicales) are 

 a number of small veins which have their origin in the anterior abdominal wall in the 

 neighborhood of the umbilicus and pass upward in the fold of peritoneum which 

 contains the round ligament of the liver. They anastomose below with both the 

 superficial and deep epigastric veins and also with small vessels which pass down- 

 ward alongside of the urachus to empty into the vesical plexus. Above, the majority 

 of them enter the quadrate and left lobes of the liver, but one of them, the vena 

 supraumbilicalis, enters the substance of the round ligament at a varying level and 

 opens into the more or less extensive lumen of that structure, which represents the 

 umbilical vein of foetal life. This lumen appears to persist in the majority of cases, 

 although greatly reduced in size from that of the umbilical vein, and may extend 

 throughout almost the entire length of the round ligament, although perhaps, more 

 usually, it is limited to its upper part, and opens into the right trunk of the portal 

 vein. When the lumen is entirely obliterated it is possible that the supraumbilical 

 vein, which has also been termed the accessory portal vein, may open directly into 

 the portal vein. 



Collateral Circulation of the Portal Vein. — Considering the fact that the portal vein 

 terminates in capillaries in the substance of the liver, it is evident that certain pathological 

 conditions, such as cirrhotic changes, which may occur in that organ, will more or less completely 

 interfere with the return of the blood to the heart from the intestine, spleen, and pancreas, by 

 producing an obliteration of the capillaries. The possibilities of a collateral circulation are 

 therefore important, and a number of routes occur by which, under stress, the blood of the 

 portal venous system may pass around the liver and reach the heart through one of the other 

 systems. The functional capabilities of these various routes are furthered by the fact that none 

 of the tributaries of the portal vein possess valves except in their finer branches, and the blood 

 can therefore flow in them in a reverse direction if necessary. The principal collateral routes 

 are as follows : 



1. Through the gastric vein the blood may pass to the oesophageal veins and thence to the 

 azygos and hemiazygos veins. When this route is functional the oesophageal veins become 

 enlarged and frequently varicose, forming contorted elevations upon the surface of the oesophagus. 



2. Through the superior hemorrhoidal veins connections are made by way of the hemor- 

 rhoidal plexus with the hemorrhoidal branches of the internal iliac. These connections seem, 

 however, to be less frequently functional than either the cardiac or parumbilical routes. 



