THE PORTAL VEIN 675 



(4) The lumbar veins [vv. lumbales], four to five on either side accompany the lumbar 

 arteries and collect venous blood from the muscles of the back and abdomen. They terminate 

 bj^ passing beneath the tendinous arches of the psoas major, along the sides of the lumbar 

 vertebra?, and opening into the vena cava inferior. The veins of the left side are longer than 

 those of the right and pass behind the aorta. Each vein receives a dorsal tributary corre- 

 sponding in distribution to the dorsal branch of the lumbar artery. Between the dorsal tribu- 

 taries and the posterior vertebral venous plexus there occurs a free communication. There 

 is also an anastomosis between the main lumbar veins and the anterior vertebral venous plexus 

 around the bodies and transverse processes of the lumbar vertebrae. By means of these 

 communications the intervertebral veins, the internal and external vertebral and spinal plexuses 

 are partly drained. In addition to these anastomoses the lumbar veins are connected with one 

 another and with common iliac, hypogastric, ilio-lumbar, renal, azygos and hemiazygos veins 

 by means of the ascending lumbar vein (p. 663). 



(5) The inferior phrenic veins [v. phrenica inferior] follow the course of the inferior phrenic 

 arteries; the right opens into the vena cava direct; the left into the suprarenal, the left renal, or 

 the vena cava. 



(6) The hepatic veins [vv. hepaticae], the largest tributaries of the vena cava, return the 

 blood from the liver. Commencing in the substance of the liver (see Liver), they converge as 

 they approach its posterior surface, and unite to form two or there large trunks, which open 

 into the vena cava as it lies in the fossa venae cavae. Some smaller vessels from the caudate 

 lobe, and other parts of the liver in the nighbourhood of the caval fossa, open directly into the 

 vena cava. The hepatic veins contain no valves, but, in consequence of opening obliquely 

 into the vena cava, a semilunar fold occurs at the lower magin of each orifice. 



THE PORTAL VEIN 



The veins corresponding to the inferior mesenteric, the superior mesenteric, 

 and to some of the branches of the coeUac artery, do not join the vena cava in- 

 ferior direct, but unite to form a common trunk — the portal vein. 



This vein enters the liver, and breaks up in its substance into sinusoids 

 from which the blood is again ultimately collected by the hepatic veins, and carried 

 by them into the vena cava inferior. The terminal branches of the hepatic artery 

 also empty into the hepatic sinusoids, and their blood likewise finds its way 

 finally into the hepatic veins, and thence into the vena cava inferior. The portal 

 vein and its tributaries have no valves. 



The portal vein [v. portae] (fig. 531), is a thick trunk 7 or 8 cm. (3 in.) in length. 

 It is formed behind the head of the pancreas, opposite the right side of the body 

 of the second lumbar vertebra, by the union of the superior mesenteric with the 

 splenic veins. It passes upward and to the right behind the superior part of the 

 duodenum, and then between the layers of the lesser omentum. In the latter 

 situation it passes in front of the foramen epiploicum and is accompanied by 

 the hepatic artery and the hepatic duct. Finally it enters the porta of the liver, 

 and there divides into a right and a left branch. In this course the hepatic artery 

 and the common bile duct are in front, the former to the left, the latter to the 

 right. It is surrounded by branches of the hepatic plexus of the sympathetic 

 nerve, and by numerous lymphatic vessels and some glands. The connective 

 tissue sheath enclosing these structures is called the fibrous capsule of GlissoD 

 [capsula fibrosa, Glissoni]. Just before it divides it is somewhat dilated, the 

 dilated portion being called the sinus of the portal vein. The division into right 

 and left branches takes place toward the right end of the porta of the liver. 

 The right branch is shorter and thicker than the left, and supplies the right 

 lobe of the liver and a branch to the quadrate lobe. The left branch is longer and 

 smaller than the right, and supplies the left lobe, and gives a branch to the caudate 

 (Spigelian) and quadrate lobes. It is joined, as it crosses the left sagittal fossa, 

 by a fibrous cord, known as the ligamentum teres hepatis (obliterated vena 

 umbilicalis), and posteriorly by a second fibrous cord, the ligamentum venosum (ob- 

 lietrated ductus venosus). The position of the original course of the umbilical 

 vein across the left portal is marked, In. adult fife, by a dilation of the latter 

 vein, called the umbilical recess. 



Tributaries. — The pyloric, the coronary (gastric), the cystic, the superior 

 mesenteric, and the splenic. 



The pyloric vein begins near the pylorus in the lesser curve of the stomach, and, running 

 from left to right with the right gastric artery, opens directly into the lower part of the portal 

 vein. It receives branches from the pancreas and duodenum. 



The coronary vein [v. coronaria ventriculi] (fig. 533) runs with the left gastric artery at 

 first from right to left, among the lesser curvature of the stomach, toward the cardiac end, and 

 then, turning to the right, passes across the spine from left to right to end in the portal trunk a 



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