556 YEINS. 



from the left lobe, open obliquely into the vena cava; that from the middle 

 of the organ and lobulus Spigelii having a straight course. The hepatic veins 

 run singly, and are in direct contact with the hepatic tissue. They are destitute 

 of valves. 



PORTAL SYSTEM OF VEINS. 



The Portal Venous System is composed of four large veins, which collect the 

 venous blood from the viscera of digestion. The trunk formed by their union 

 (vena portae) enters the liver and ramifies throughout its substance; and its 

 branches again emerging from that organ as the hepatic veins, terminate in the 

 inferior vena cava. The branches of this vein are in all cases single, and 

 destitute of valves. 



The veins forming the portal system are, the 



Inferior mesenteric. Splenic. 



Superior mesenteric. Gastric. 



The inferior mesenteric vein returns the blood from the rectum, sigmoid 

 flexure, and descending colon, corresponding with the ramifications of the 

 branches of the inferior mesenteric artery. Ascending beneath the peritoneum 

 in the lumbar region, it passes behind the transverse portion of the duodenum 

 and pancreas, and terminates in the splenic vein. Its haemorrhoidal branches 

 inosculate with those of the internal iliac, and thus establish a communication 

 between the portal and the general venous system. 1 



The superior mesenteric vein returns the blood from the small intestines, and 

 from the caecum and ascending and transverse portions of the colon, correspond- 

 ing with the distribution of the branches of the superior mesenteric artery. 

 The large trunk formed by the union of these branches ascends along the right 

 side and in front of the corresponding artery, passes in front of the transverse 

 portion of the duodenum, and unites behind the upper border of the pancreas 

 with the splenic vein, to form the vena portae. 



The splenic vein commences by five or six large branches, which return the 

 blood from the substance of the spleen. These uniting form a single vessel, 

 which passes from left to right behind the upper border of the pancreas, and 

 terminates at its greater end by uniting at a right angle with the superior 

 mesenteric to form the vena portae. The splenic vein is of large size, and not 

 tortuous like the artery. It receives the vasa brevia from the left extremity 

 of the stomach, the left gastro-epiploic vein, pancreatic branches from the pan- 

 creas, the pancreatico-duodenal vein, and the inferior mesenteric vein. 



The gastric is a vein of small size, which accompanies the gastric artery from 

 left to right along the lesser curvature of the stomach, and terminates in the 

 vena portae. 



The Portal Vein is formed by the junction of the superior mesenteric and 

 splenic veins, their union taking place in front of the vena cava, and behind 

 the upper border of the great end of the pancreas. Passing upwards through 

 the right border of the lesser omentum to the under surface of the liver, it 

 enters the transverse fissure, where it is somewhat enlarged, forming the sinus 

 of the portal vein, and divides into two branches, which accompany the rami- 

 fications of the hepatic artery and hepatic duct throughout the substance of the 

 liver. Of these two branches the right is the larger but the shorter of the two. 

 The portal vein is about four inches in length, and, whilst contained in the 

 lesser omentum, lies behind and between the hepatic duct and artery, the former 

 being to the right, the latter to the left. These structures are accompanied by 



1 Besides this anastomosis between the portal vein and the branches of the vena cava, other 

 anastomoses between the portal and systemic veins are formed by the communication between 

 the left renal vein and the veins of the intestines, especially of the colon and duodenum, and 

 between superficial branches of the portal veins of the liver and the phrenic veins, as pointed 

 out by Mr. Kiernan (Todd and Bowman). 



