THE GARDEN TOAD 23 



in the mesentery an irregular pinkish glandular structure 

 which leads by a small duct into the intestine. This gland 

 is the pancreas, and the duct is the pancreatic duct. ' From it 

 comes a secretion which aids in the digestion of food. Near 

 the upper end of the pancreas note a round nodular structure, 

 generally dark red. This is the spleen, a ductless gland, the 

 use of which is not altogether known. 



Make a drawing which will show as many of the organs 

 noted as possible. 



Technical Note. — Pass two pieces of thread under the rectum 

 near the pubic bone. Tie these threads tightly a short distance apart 

 and then cut the rectum in two between the threads. Now carefully 

 lift up the alimentary canal with attached organs (liver, etc.), and cut 

 it off near the region of the heart. 



How is the heart situated with regard to the lungs ? The 

 heart consists of a lower chamber with thick muscular walls, 

 the tip, called the ventricle, and two upper thin-walled 

 chambers, the right and left auricles. Can you make out • 

 these three chambers? The purified blood from the limgs 

 flows into the left auricle, while the venous blood from all 

 over the body laden with its carbon dioxid enters the right 

 auricle. From these two chambers the blood enters the 

 ventricle. Here the pure and impure blood are mixed. 

 From the ventricle the blood enters a large muscular tube 

 on the ventral side of the heart. This is the conus arteriosus, 

 which gives off three branches on each side; the anterior 

 ones, the carotid arteries, supply the head, the next ones, the 

 systemic arteries, or aortCB, carry blood to the rest of the body, 

 while the posterior vessels, the pulmonary arteries, go directly 

 to the lungs and there break up into fine vessels (capillaries) 

 where the carbon dioxid is given off and oxygen is taken 

 from the air. From the lungs the blood returns through the 

 pulmonary vein to the left auricle. Meanwhile the blood 

 which has passed through the systemic arteries and body 

 capillaries is collected again into other vessels going back 



