386 PULMONARY VEINS. 



that organ by several large veins ; it is larger than the splenic artery, 

 and perfectly straight in its course. It passes horizontally inwards 

 behind the pancreas, and terminates near its greater end by uniting 

 with the superior mesenteric and forming the portal vein. It receives 

 in its course the gastric and pancreatic veins, and near its termination 

 the inferior mesenteric vein. 



The Gastric veins correspond with the gastric, gastro-epiploic, and 

 vasa brevia arteries, and terminate in the splenic vein. 



The VENA PORT.E, formed by the union of the splenic and superior 

 mesenteric vein behind the pancreas, ascends through the right border 

 of the lesser omentum to the transverse fissure of the liver, where it 

 divides into two branches, one for each lateral lobe. In the right 

 border of the lesser omentum it is situated behind and between the 

 hepatic artery and ductus communis choledochus, and is surrounded 

 by the hepatic plexus of nerves and lymphatics. At the transverse 

 fissure each primary branch divides into numerous secondary branches 

 which ramify through the portal canals, and give off vaginal and inter- 

 lobular veins, and the latter terminate in the lobular venous plexus of 

 the lobules of the liver. The portal vein within the liver receives the 

 venous blood from the capillaries of the hepatic artery. 



PULMONARY VEINS. 



The pulmonary veins, four in number, return the arterial blood from 

 the lungs to the left auricle of the heart ; they differ from the veins in 

 general, in the area of their cylinders being very little larger than the 

 corresponding arteries, and in accompanying singly each branch of the 

 pulmonary artery. They commence in the capillaries upon the 

 parietes of the bronchial cells, and unite to form a single trunk for 

 each lobe. The vein of the middle lobe of the right lung unites with 

 the superior vein so as to form the two trunks which open into the left 

 auricle. Sometimes they remain separate, and then there are three 

 pulmonary veins on the right side. The right pulmonary veins pass 

 behind the superior vena cava to the left auricle, and the left behind 

 the pulmonary artery ; they both pierce the pericardium. Within the 

 lung the branches of the pulmonary veins are behind the bronchial 

 tubes, and those of the pulmonary artery in front ; but at the root of 

 the lungs the veins are in front, next the arteries, and then the bronchi. 

 There are no valves in the pulmonary veins. 



