990 THE VASCULAE SYSTEM. 



of the little toe. At first it passes posteriorly, along the lateral side of the foot 

 and distal to the lateral malleolus, lying on the peronseal retinacula (O.T. ext. ann. 

 lig.), in company with the nervus suralis ; then it passes posterior to the lateral 

 malleolus, and along the lateral border of the tendo calcaneus, still in company 

 with the nervus suralis, to the middle of the calf, proximal to which it is continued 

 in the superficial fascia, accompanied by the superficial sural artery, to the distal 

 part of the popliteal fossa, where it pierces the deep fascia, and terminates in the 

 popliteal vein. It communicates, round the medial side of the leg, with the great 

 saphenous vein, and through the deep fascia with the deep veins, and it contains 

 from six to twelve bicuspid valves. 



Tributaries. It receives tributaries from the lateral side of the foot, the lateral 

 side and back of the heel, the back of the leg, and, occasionally, a descending tributary 

 from the back of the thigh. Just before it pierces the popliteal fascia it frequently gives 

 off a small branch which ascends round the medial side of the thigh and unites with the 

 medial superficial femoral vein to form the accessory saphenous vein. In that way a 

 communication is established between the great and small saphenous veins, which may 

 become enlarged, and constitute the main continuation of the small saphenous vein. 



THE POKTAL SYSTEM. 



The veins which form the portal system are the portal, the superior and 

 inferior mesenteric and the splenic veins and their tributaries. They convey blood 

 to the liver (1) from almost the whole of the abdominal and pelvic parts of the 

 alimentary canal, (2) from the pancreas, and (3) from the spleen. The tributaries 

 of origin correspond closely with the terminal branches of the splenic, and the 

 superior and inferior mesenteric arteries, after which they are named and which 

 they accompany for a considerable distance. The larger or terminal vein.s, how- 

 ever, leave their associated arteries ; the inferior mesenteric vein joins the splenic 

 vein, and the latter unites with the superior mesenteric vein to form the portal vein, 

 which passes to the liver. AD the larger vessels of this system are devoid of 

 valves, but valves are present in the tributaries. 



Vena Portse. The portal vein is a wide venous channel, about 75 mm. (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 the 

 capillaries, which also receive the blood conveyed to the liver by the hepatic artery, 

 the hepatic veins arise ; and, as the hepatic veins 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, posterior and to the left of the neck of the pancreas, and either 

 anterior to the left border of the inferior vena cava, at the level of the body of the 

 second lumbar vertebra, or in front of the upturned extremity of the processus 

 uncinatus of the head of the pancreas. It ascends, anterior to the inferior vena 

 cava and posterior to the neck of the pancreas and the first part of the duodenum, 

 to the lower border of the epiploic foramen (Winslow), where it passes forwards, in 

 the right gastro-pancreatic fold of peritoneum, and enters the lower border of 

 the gastro-hepatic ligament. Continuing its upward course, it lies posterior to 

 the bile-duct and hepatic artery, and anterior to the epiploic foramen (Winslow) ; 

 it ultimately reaches the right end of the porta hepatis, where it ends by dividing 

 into a short and wide right and a longer and narrower left branch. Just before 

 its termination it enlarges, forming the sinus of the portal vein. 



The right branch generally receives the cystic vein and then enters the right lobe 

 of the liver, in which it breaks up into numerous branches which terminate in the 

 portal capillaries around the periphery and in the substance of the liver lobules. 



The left branch runs from right to left, along the porta hepatis, giving off 

 branches to the caudate and quadrate lobes ; it crosses the umbilical fossa, and 

 ends in the same manner as the right branch, but in the substance of the left 

 lobe of the liver. 



