THE CAT 217 



veins: (a) the pulmonary veins, which bring arterial blood from 

 the lungs to the left auricle, and (b) the systemic veins, which 

 bring venous blood from the tissues and organs of the body to 

 the right auricle. 



The systemic veins may be further subdivided into two systems : 

 (a) the caval system, by which the blood is brought directly to 

 the heart, and (b) the portal system, by which the blood is taken 

 from the digestive tract and spleen directly to the liver, and thence 

 to the heart through the hepatic veins. 



The Portal System. This system consists of the portal vein and 

 several smaller veins which meet to form it. The portal vein and 

 the superior, or anterior, mesenteric, the largest of its tributaries, 

 have just been observed. The latter joins the portal near the 

 pyloric end of the stomach, bringing blood from the intestine. 

 Observe, without cutting the mesentery, the mesenteric veins, 

 which radiate to the superior mesenteric from every part of the 

 small intestine, accompanied everywhere by branches of the su- 

 perior mesenteric artery. A single large branch of the superior 

 mesenteric called the inferior or posterior mesenteric brings blood 

 from the large intestine. The gastrosplenic vein joins the portal 

 near the base of the superior mesenteric ; it is formed by the union 

 of branches from the spleen, stomach, pancreas, and great omen- 

 tum. Besides these veins the portal receives also a number of 

 smaller veins from the duodenum, pancreas, and stomach. 



Study all these veins, but without cutting the mesentery in 

 which they lie. Note also that alongside the mesenteric veins lie 

 the mesenteric arteries. These arteries are somewhat smaller than 

 the veins which accompany them and are a light pink in color, 

 whereas the veins are dark-colored. 



Exercise 9. Draw a diagram showing the portal system so far as 

 observed. 



The Digestive System (Continued). Lift up the intestine and 

 cut the mesentery where this joins it ; cut also the bile and the 

 pancreatic ducts. Straighten out the intestine from the stomach 

 to the anus. Be careful, however, not to injure the bladder, which 

 lies ventral to the rectum. The two ureters, also, which join the 



