PORTAL VEIN. 437 



viscera form the portal vein, Avhose blood is conveyed by the 

 medium of the hepatic veins. 



The Phrenic or Diaphragmatic veins commence in the fleshy 

 portion of the diaphragm, forming two or three large branches, 

 which enter the cava as it passes through the foramen dextrum. 



The Hepatic veins are numerous, and commence by intra- 

 lobular branchlets in the capillary terminations of the hepatic 

 artery and vena porta. These discharge into sublobular veins, 

 which unite, j)assing upwards and forwards, unaccompanied by 

 arteries. Leaving the gland in the anterior fissure, they enter 

 the cava by a number of minute oblique openings, and usually 

 one or two larger ones. 



PORTAL VEIN. 



(Fig. 166.) 



The portal vein commences in the sublumbar region, near the 

 anterior mesenteric artery, concealed by the pancreas, and is 

 formed by the union of three large branches, which return the 

 blood from the visceral organs of digestion. It is directed for- 

 wards with an inclination to the right, passes through the pan- 

 creatic ring below the vena cava, reaches the j)Osterior fissure of 

 the liver, and, entering the gland, it is distributed like an artery, 

 finally terminating in the hepatic veins. The branches which 

 form the portal vein are the anterior and "posterior mesenteric, 

 and gastro-splenic veins. 



The anterior mesenteric vein is large ; its divisions exactly corre- 

 spond to the branches of the anterior mesenteric artery, wdiile the 

 posterior mesenteric vein is made up of branches corresponding to 

 those of the posterior mesenteric artery. The gastro-splenic vein 

 is large, formed by the union of the left g astro -epiploic, sp)lenic, 

 and gastric satellites of the splenic artery, and the posterior 

 gastric vein. The portal thus formed receives the right gastro- 

 ep)iploic vein, the latter receiving ih-d pyloric, duodenal, and pan- 

 creatic veins, all satellites of the corresponding arteries. The 

 anterior gastric vein enters separately. 



The Renal veins have very thin walls, and are formed by the 

 union of the veinlets which leave the hilus of the kidney, and a 

 branch from the suprarenal capsule. The left renal having to 

 cross the posterior aorta, is the longer. 



The Spermatic veins leave the testicles and enter the sper- 



