THE PORTAL SYSTEM OF VEINS 681 



conveyed to the inferior vena cava by the hepatic veins. From this it will be seen 

 that the blood of the portal system passes through two sets of minute vessels, 

 viz., (a) the capillaries of the digestive tube, spleen, pancreas, and gall-bladder; 

 and (b) the sinusoids of the liver. In the adult the portal vein and its tributaries 

 are destitute of valves; in the fetus and for a short time after birth valves can be 

 demonstrated in the tributaries of the portal vein; as a rule they soon atrophy 

 and disappear, but in some subjects they persist in a degenerate form. 



The portal vein (vena portce) is about 8 cm. in length, and is formed at the level 

 of the second lumbar vertebra by the junction of the superior mesenteric and lienal 

 veins, the union of these veins taking place in front of the inferior vena cava and 

 behind the neck of the pancreas. It passes upward behind the superior part of 

 the duodenum and then ascends in the right border of the lesser omentum to the 

 right extremity of the porta hepatis, where it divides into a right and a left branch, 

 which accompany the corresponding branches of the hepatic artery into the sub- 

 stance of the liver. In the lesser omentum it is placed behind and between the 

 common bile duct and the hepatic artery, the former lying to the right of the latter. 

 It is surrounded by the hepatic plexus of nerves, and is accompanied by numerous 

 lymphatic vessels and some lymph glands. The right branch of the portal vein 

 enters the right lobe of the liver, but before doing so generally receives the cystic 

 vein. The left branch, longer but of smaller caliber than the right, crosses the left 

 sagittal fossa, gives branches to the caudate lobe, and then enters the left lobe of 

 the liver. As it crosses the left sagittal fossa it is joined in front by a fibrous cord, 

 the ligamentum teres (obliterated umbilical vein) , and is united to the inferior vena 

 cava by a second fibrous cord, the ligamentum venosum (obliterated ductus venosus). 



Tributaries. The tributaries of the portal vein are: 





Lienal. Pyloric. 



Superior Mesenteric. Cystic. 



Coronary. Parumbilical. 



The Lienal Vein (v. lienalis; splenic vein) commences by five or six large branches 

 which return the blood from the spleen. These unite to form a single vessel, which 

 passes from left to right, grooving the upper and back part of the pancreas, below 

 the lineal artery, and ends behind the neck of the pancreas by uniting at a right 

 angle with the superior mesenteric to form the portal vein. The lienal vein is 

 of large size, but is not tortuous like the artery. 



Tributaries. The lineal vein receives the short gastric veins, the left gastro- 

 epiploic vein, the pancreatic veins, and the inferior mesenteric veins. 



The short gastric veins (vv. gastricce breves), fouror five in number, drain the fundus 

 and left part of the greater curvature of the stomach, and pass between the two 

 layers of the gastrolienal ligament to end in the lienal vein or in one of its large 

 tributaries. 



The left gastroepiploic vein (v. gastroepiploica sinistra) receives branches from 

 the antero-superior and postero-inferior surfaces of the stomach and from the greater 

 omentum; it runs from right to left along the greater curvature of the stomach 

 and ends in the commencement of the lienal vein. 



The pancreatic veins (vv. pancreaticce) consist of several small vessels which drain 

 the body and tail of the pancreas, and open into the trunk of the lienal vein. 



The inferior mesenteric vein (v. mesenterica inferior) returns blood from the rectum 

 and the sigmoid, and descending parts of the colon. It begins in the rectum as 

 the superior hemorrhoidal vein, which has its origin in the hemorrhoidal plexus, 

 and through this plexus communicates with the middle and inferior hemor- 

 rhoidal veins. The superior hemorrhoidal vein leaves the lesser pelvis and crosses 

 the left common iliac vessels with the superior hemorrhoidal artery, and is con- 

 tinued upward as the inferior mesenteric vein. This vein lies to the left of its 

 artery, and ascends behind the peritoneum and in front of the left Psoas major; 



