318 DISSECTION OF THE BABBIT 



which lies close alongside the posterior vena cava 

 and, entering the liver, divides into branches supply 

 ing its several lobes. 



The portal system can readily be seen in a freshly killed 

 animal on opening the abdomen and turning the viscera aside. 

 The veins are of large size and usually gorged with blood, 

 and care must be taken not to injure them, as they bleed very 

 freely. 



The following are the main trunks which unite to 

 form the portal vein, 

 i. The Heno-gastric vein returns blood from the 



walls of the stomach and from the spleen. 

 ii. The duodenal vein returns blood from the 



duodenum and pancreas. 



iii. The anterior mesenteric vein is formed by the 

 union of veins from the whole length of 

 the small intestine, and from the caecum, the 

 colon, and the greater part of the length of 

 the rectum. 



iv. The posterior mesenteric vein lies in the meso- 

 rectum or hindmost part of the mesentery, and 

 returns blood from the terminal portion of the 

 rectum. 



3. The pulmonary system consists of the pulmonary veins, 

 which have already been described (p. 313). 



C. The Arteries. 



The arteries form two distinct systems, of which one, the 

 aortic system, conveys arterial blood from the left ventricle to 

 all parts of the body ; while the other, or pulmonary system, 

 carries venous blood from the right ventricle to the lungs. 

 The arteries are thicker- walled, and hence paler in colour than 

 the veins. 



The aortic system should be dissected first. Clean the 

 aorta along its whole length, and follow the arteries arising 

 from it to their distribution. 



1. The aorta arises from the base of the left ventricle, 

 and, turning towards the left side to form the arch of 



