PORTAL SYSTEM. 47T 



opposite the junction of the two venae innominate, the left in the left superior 

 intercostal or left internal mammary. The ttvo inferior phrenic veins follow the 

 course of the inferior phrenic arteries, and terminate, the right in the inferior vena 

 cava, the left in the left renal vein. 



The hepatic veins commence in the substance of the liver, in the capillary ter- 

 minations of the vena portce ; these branches, gradually uniting, form three large 

 veins, which converge towards the posterior border of the liver, and open into the 

 inferior vena cava, whilst that vessel is situated in the groove at the back part of 

 this organ. Of these three veins, one from the right and another from the left 

 lobes open obliquely into the vena cava; that from the middle of the organ and 

 lobus Spigelii having a straight course. The hepatic veins run singly, and are 

 in direct contact with the hepatic tissue. They are destitute of valves. 



POETAL 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, 

 the vena portas, enters the liver, 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 hemorrhoidal branches inosculate with those 

 of the internal iliac, and thus establish a communication between the portal and 

 the general venous system. 



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 portaj. 



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 pancreas, 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 

 portsB. 



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 ramifications of the 



