1414 



VENOUS SYSTEM. 



from the diaphragm, and correspond accu- 

 rately to the phrenic arteries from the aorta. 



The hepatic v?im may be considered as 

 forming an adjunct to the portal venous 

 system, in connection with which they will be 

 briefly noticed. 



PORTAL VENOUS SYSTEM. One remarkable 

 class of the veins of the abdomen, those of 

 the chylopoietic viscera, do not terminate 

 directly in the vena cava, but unite to form a 

 large trunk vena portcs, which enters the 

 liver, and, branching out like an artery (hence 

 the name vena arteriosd), forms a capillary 

 system in the substance ot that organ. 



The trunk of the vena portts is formed by 

 the coalescence of several large veins, which 

 return the blood from the stomach, spleen, 

 pancreas, and from the entire of the intes- 

 tinal tract, with the exception of the lower 

 part of the rectum, many of the veins of which 

 ojjen into the internal iliac vein, as has been 

 already mentioned. 



The veins which form the porta are the 

 following: the superior and inferior mesen- 

 teric, the splenic, gastric, duodenal, and pan- 

 creatic, veins. All these are destitute of valves. 



1. Inferior mesenteric vein. The veins of 

 the upper portion of the rectum (superior 

 h(smorrhoidal veins), sigmoid flexure of the 

 colon, and descending colon, unite to form 

 this vein, which ascends behind the inferior 

 transverse portion of the duodenum and the 

 pancreas, and opens into the splenic vein. 

 3iv means of the free communications which 

 exist between the inferior haemorrhoidal veins 

 and the haemorrhoidal and vesical plexuses, 

 the system of the vena portse is connected 

 with that of the general systemic circulation. 



2. The splenic vein arises in the spleen, and, 

 accompanying the splenic artery (which lies 

 superior to the vein), follows a transverse 

 direction from left to right, and passes behind 

 the pancreas to unite with the superior me- 

 senteric vein. 



Besides its proper splenic roots the splenic 

 vein receives the veins which correspond to 

 the " vasa brevia/' as also the epiphic, pancre- 

 atic, and inferior mesenteric veins. 



The gastric veins, of which the coronary 

 (coronaria ventriculi] is the most considerable, 

 likewise terminate in the splenic vein. 



3. The superior mesenteric vein (grande 

 mesara'ique, Cloquet) receives the venous ca- 

 pillaries from the duodenum and all the small 

 intestines, also from the ascending and trans- 

 verse portions of the colon, and passes behind 

 the pancreas, where it unites with the splenic 

 vein. The superior mesenteric vein corre- 

 sponds to the artery of the same name, and is 

 placed anterior and to the right of it. 



The trunk of the vena portce, formed by 

 the union of these two great veins (splenic 

 and superior mesenteric), is placed at first 

 behind the head of the pancreas, to the right 

 of the spinal column, and a little to the left 

 of the inferior vena cava : it next ascends, 

 with an obliquity backwards and to the right 

 side, between the layers of the gastro hepatic 

 omentum to the transverse fissure of the 

 liver ; after becoming slightly enlarged (sinus 



of the vena portce), it there divides into two 

 branches, which pass horizontally into the 

 right and left hepatic lobes respectively. Its 

 principal anterior relations are the follow- 

 ing : the head of the pancreas and the duode- 

 num, the hepatic artery, and the ductus cho- 

 ledochus ; to the two latter vessels it is 

 related, whilst traversing the gastro-hepatic 

 omentum ; it is surrounded by branches of 

 lymphatic vessels and of the hepatic plexus of 

 nerves. 



The portal veins, and their subdivisions in 

 the liver, surrounded by a prolongation from 

 the capsule of Glisson, arc contained within 

 the " portal canals," and are each accompanied 

 by a branch of the hepatic artery, and by a 

 branch of the hepatic duct. From these arise 

 the vaginal and interlobular branches, which, by 

 their inosculations, form plexuses which are 

 similarly named. The interlobular veins sur- 

 round the lobules on their capsular surfaces, 

 and ultimately, having been joined by the 

 terminal branches of the hepatic artery, enter 

 the lobules (forming the interlobular veins}, and 

 terminate by inosculating with the intra/obn- 

 lar (hepatic) veins: "this plexus interposed 

 between the interlobular portal veins and the 

 intralohular hepatic vein constitutes the venous 

 part of the lobule, and may be called the 

 lo'jtifar venous plexus.'* (Kiernan.) 



" The portal vein collects the venous blood 

 from the chylopoietic viscera, and then circu- 

 lates it through the lobules : it likewise re- 

 ceives the venous blood, which results from the 

 distribution of the hepatic artery to the struc- 

 tures of the liver: these two sources of supply 

 constitute the two origins of the portal vein, 

 the abdominal origin and the hepatic origin."* 



The blood conveyed to the liver by the 

 branches of the vena portae is conveyed back 

 again into the general circulation by the he- 

 patic veins. 



Hepatic veins. These veins arise in each 

 lobule, from the lobular venous plexus, by a 

 vein termed, from its position, intralobulnr. 

 The intralobular veins unite with others termed 

 sublobular, which, by their coalescence from 

 the venae cavae hepaticae, these latter, usually 

 four in number, leave the liver at its thick 

 margin, and open into the vena cava inferior, 

 where that vein passes between the Spigelian 

 and right lobes of the liver. 



C. CARDIAC VEINS. 



The proper veins of the heart form a sepa- 

 rate system of small extent, which commit ni* 

 cates 'with the right auricle of the heart by 

 the great cardiac vein. Their principal trunks 

 are thus distinguished : 



1 . Great cardiac vein (anterior or great co- 

 ronary vein}. This vein commences on the 

 anterior surface of the heart, near its apex, 

 and ascends in the anterior interventricular 

 groove, as far as the base of the ventricles, 

 where, bending abruptly to the left, it gains 

 the back of the heart by passing round the 

 left margin of the organ in the deep horizontal 

 groove between the left auricle and the left 



* Vide Vol. HI. p. 168., Art. LIVER. 



