THE FROG 15 



Tip the intestine to the right and note, in the mesentery 

 just in front of spleen, the common intestinal artery coming from 

 the mid-dorsal line. It soon divides into anterior and posterior 

 branches. The anterior is the cceliac axis, the other the anterior 

 mesenteric artery. Follow the coeliac axis to its division into a 

 ventral gastric artery going to the stomach and a gastro-hepatic 

 trunk which soon divides into an hepatic artery going to the liver 

 and a dorsal gastric artery going to the stomach. What regions 

 of the stomach do the two gastric arteries supply? Does the 

 hepatic artery enter the liver near the bile-duct? Where does 

 the pancreatic artery connect with the other vessels? 



In the same way follow the branches of the anterior mesen- 

 teric: first a short splenic artery to the spleen, next branches to 

 the intestine and a haemorrhoid artery to the anterior part of the 

 rectum. 



Sketch these arteries in red on a sheet which shall later con- 

 tain the whole arterial system. 



Note also small veins in the mesentery paralleling the arterial 

 twigs. These unite to form the intestinal vein. Trace this forward, 

 finding the entrance of splenic and gastric veins. How many 

 trunks of the latter come from the stomach? All these veins 

 unite to form the hepatic-portal vein which enters the liver. 

 Does the abdominal vein connect with this? Does the portal 

 enter the liver by a single trunk? 



Sketch this portal system in the drawing of the veins. 



At either side of the liver, projecting into the body cavity 

 from in front, is a lung. Inflate with blowpipe from the glottis. 

 Sketch the blood-vessels (pulmonary arteries and veins) in the 

 walls. How many branches to each? Cut across a lung. Are 

 there small air-sacs throughout or are they confined to the walls? 

 Which are more internal, arteries or veins? Sketch a bit of the 

 lung showing these points. 



Cut across the stomach at the cardiac end and across the 

 intestine just in front of the rectum. Trim the mesenteries close 

 to the alimentary tract and remove the latter from the body. 

 Split it lengthwise with the scissors and examine the internal 

 surface with the hand-lens, noting the differences in the character 

 of the lining in the different parts. 



The urogenital organs are now exposed. In the posterior part 

 of the body cavity will be found a pair of mesonephroi (' kidneys ')i 



