694 



BLOOD-^'ASCULAR SYSTEil OF THE HORSE 



traverses the posterior part of the pancreas very obliquely, inclines ventrally and 

 a little to the right, and reaches the portal fissure of the liver. Here it divides into 

 three branches which enter the liver and ramify in the substance of the gland like 

 an artery, terminating in the lobular capillaries. From the lobules the blood passes 

 into the hepatic veins and through these to the posterior vena cava. Thus the 

 blood which is distributed to the stomach, nearly the entire intestinal tract, the 

 pancreas, and the spleen, passes through two sets of capillaries prior to its return 

 to the heart, viz., the capillaries of these viscera and of the liver. 



1. The anterior mesenteric vein (V. mesenterica cranialis) is the largest of 

 the portal radicles. It is situated to the right of the artery of like name, and its 

 tributaries correspond in general to the branches of the artery. The dorsal colic 

 vein usually unites with the ventral one at the pelvic flexure, thus forming a single 

 trunk (V. colica dextra) which runs between the right parts of the colon. There is, 



Fig. 591. — Portal Vein of Horse. 

 a, Intrahepatic part, &, extrahepatic part, of portal vein; c, anterior gastric vein; d, right gastro-epiploic vein; 

 e, pancreatico-duodenal vein: /, splenic vein; /', left gastro-epiploic vein; £?, posterior gastric vein; /j, posterior mesen- 

 teric vein; i, naiddle colic vein; k, left colic vein; k', anterior hsemorrhoidal vein; m, jejunal trunk; m', jejunal veins; 

 o, right colic vein; o', ventral colic vein; o", dorsal colic vein; o"\ small collateral vein connecting dorsal colic and 

 posterior mesenteric veins ; 2?, ileal vein; g, caecal veins; 7, liver; 77, spleen; 777, stomach; 7F, duodenum; T", jejunum; 

 VX, caecum; T'77, ventral parts of great colon; T777, pelvic flexure; IX, dorsal parts of great colon; -Y, small colon; 

 XI, rectum. (After Schmitz.) 



however, a small vein on the right dorsal colon which is connected bj' numerous 

 branches with the right colic vein; it joins the posterior mesenteric vein or its 

 middle colic radicle. The veins of the small intestine (Vv. intestinales) unite to 

 form a short trunk. 



2. The posterior mesenteric vein (V. mesenterica caudalis) is the smallest of 

 the radicles of the portal vein. It accompanies the artery in the colic mesentery, 

 and its rectal branches (Vv. hsemorrhoidales craniales) anastomose with those of 

 the internal pudic vein. It receives the middle colic vein from the initial part of 

 the small colon and also the small vein of the right dorsal colon, as mentioned above. 



3. ■ The splenic vein (V. lienalis) is the very large satellite of the splenic artery. 

 It is formed by the union of two radicles at the base of the spleen. On leaving the 

 hilus of the spleen it passes medially between the anterior pole of the left kidney and 

 the saccus csecus of the stomach and above the left end of the pancreas, receives 



