30 THE SKATE 



and there giving off branches. These capillaries unite to 

 form veins which connect with the posterior cardinal vein. 



b. The Hepatic Portal System. In many of the speci- 

 mens the hepatic portal system shows up as dark-blue 

 tubes, the color being due to the presence of blood in the 

 veins. If your specimen does not show the veins clearly in 

 the region of the stomach and the intestine another speci- 

 men will be loaned to you from the general supply. The 

 veins are often near the yellow-colored arteries. 



The main hepatic vein is located in the hepatoduodenal 

 ligament near the bile duct. It receives branches from the 

 digestive tract and its derivatives. There are three main 

 tributaries. (1) The g^astric vein, which enters from the 

 left side, coming from the right margin of the stomach 

 and having a ventral and a dorsal vein from the spleen. 

 (2) The lienomesenteric vein enters the hepatic vein as the 

 middle vein. It has two main tributaries; a posterior 

 mesenteric from the left side of the intestine arising at 

 the end of the rectal gland and receiving branches from 

 the spiral valve attachments and the pancreas; and a 

 splenic from the right or medial end of the spleen. (3) 

 The pancreatico-mesenteric joins the hepatic vein from the 

 right side, coming mainly from the pancreas. Its main 

 tributaries are the anterior mesenteric from the region of 

 the duodenum, and a posterior gastric from between the 

 pylorus and the bend of the stomach. 



Drawing 15. Outline the hepatic portal system including the 

 digestive system with dotted lines. 



4. The Arterial System. 



A. The Ventral Aortcb and the Afferent Branchial 

 Vessels. 



These arteries are located in the tissue of the floor of 

 the mouth. They are filled with blood, which gives them a 



