‘THE PORTAL SYSTEM OF VEINS. 857 
with the superior mesenteric vein to form the portal vein, which passes to the liver. 
These veins, together with their tributaries, constitute the portal system. All 
the vessels of this system are devoid of valves. 
The portal vein (vena porte) is a wide venous channel, about three inches 
long, which conveys blood from the stomach, from the whole of the intestine, 
except the terminal portion of the rectum, and from the spleen and pancreas to 
the liver. Unlike other veins, it ends like an artery by breaking up into branches, 
which ultimately terminate in capillaries in the substance of the liver; from these 
portal capillaries the hepatic veins (p. 848), which also receive the blood conveyed 
Pylorie vein 
Cystic vein 
Coronary vein 
Stomach 
Portal vein 
Splenic vein 
Superior _— 
mesenteric vein eee 
Right gastro- ———W 
epiploic vein 
Pancreatico- _— 
duodenal vein 
Middle colic _—— 
vein 
Inferior mesenteric 
vein 
Superior mesenteric 
artery 
Right colic 
. eee 
veln 
Tributaries 
corresponding 
— with vasa 
intestina 
arteries 
Tleo-colie vein - 
Fic. 591.—THE PortTAL VEIN AND Its TRIBUTARIES. 
to the liver by the hepatic artery, arise; and as these open into the inferior vena 
cava, the portal blood ultimately reaches the general systemic circulation. 
The portal vein commences by the union of the superior mesenteric and the 
splenic veins behind and to the left of the neck of the pancreas, and either in 
front of the left border of the inferior vena cava, at the level of the body of the 
first lumbar vertebra, or in front of the upturned extremity of the lower portion 
of the head of the pancreas. It ascends in front of the inferior vena cava, and 
behind the neck of the pancreas and the first part of the duodenum, to the lower 
border of the foramen of Winslow, where it passes forwards, in the right pancreatico- 
gastric fold of peritoneum, and enters the lower border of the gastro-hepatic 
