RAT, 55 



Spread out a portion of the mesentery supporting the 

 intestine and notice in it small vessels. Some of these 

 will be found to be single, others, two close together. The 

 double vessels are arteries and veins. They can be dis- 

 tinguished by tracing them towards the middle line of 

 the body. The veins unite in a large vein (mesenterial 

 vein) which follows along the colon, thence into an anterior 

 fold, where it is joined by other veins (gastric) from the 

 stomach and (splenic) from the spleen. From the union 

 of these is formed the portal vein, which enters the liver 

 from behind. The small arterial branches arise from a 

 mesenterial artery which accompanies the mesenterial vein 

 for some distance and then can be traced back to the 

 median line of the dorsal surface of the body-cavity, 

 where it joins the great arterial trunk, the aorta. From 

 the aorta, just in front of the origin of the mesenterial 

 artery, arises the cceliac axis or artery, which gives off a 

 branch to the liver (hepatic artery), and then divides into 

 splenic and gastric arteries, going to the spleen and stom- 

 ach respectively. Trace these arteries. Where does the 

 hepatic enter the liver? 



The single vessels in the mesenteries are the lymphatics. 

 Their purpose is to carry the products of digestion for- 

 ward and eventually empty them into the blood-vessels. 

 These lymphatics unite in a lymphatic duct, which runs 

 closely parallel to the mesenterial artery and empties into 

 a thoracic duct running parallel with the aorta. 



Sketch the blood-vessels (X2) so far made out on a 

 sheet large enough to accommodate the whole circulatory 

 apparatus of the rat. 



In the mesentery supporting the duodenum find the 

 fatty-looking, irregular pancreas. Where does its duct 

 enter the intestine? 



