1 68 VERTEBRATES. 



This is the portal vein. Trace the veins back into the mes- 

 enteries and make out their connection with the intestines. 

 This is the portal circulation which carries most of the 

 digested food, as new blood, into the regular channels of 

 the circulation. Follow this large blood vessel into the 

 dorsal vein, now the postcaval, and into the right auricle 

 of the heart. Lift the apex of the heart and see the large 

 veins, the prccaval, entering the same auricle from the an- 

 terior part of the body. 



v,4) Find if you can a blood vessel to the left side. 

 Trace it back to the lung. Is it divided ? You have already 

 found the method of supplying the lungs with blood, now 

 find the passage back to the heart. Compare this method 

 of oxygenating the blood with that of the fish. Make a 

 diagrammatic drawing of the entire circulation. 



(5) Remove the heart and study it. The membraneous 

 covering is called the pericardium. Remove it and study 

 the form, shape, and general structure of the heart. Note 

 the number and location of the openings into the heart 

 and the aortic arch going from the heart. 



Draw the heart (X2). 



Cut the heart from right to left exposing the inner cham- 

 bers. How many? The upper ones are the right and 

 left auricles, the lower one the ventricle. Note the struc- 

 ture of each and explain how the work of the heart is ex- 

 pedited by the structure. Study the valves at the base of the 

 auricles and explain their use. Compare the heart with 

 that of the fish. Make an enlarged drawing of the inner 

 view of the heart. 



(6) What is the condition of tho blood when it flows 

 into the right auricle? What is its condition when it emp- 



