16 



THE FROG 



be seen on the left side, passing from the muscles of the back to the 

 dorsal surface of the kidney. On the ventral surface of each kidney 

 you will see the conspicuous renal veins which pass toward the 

 mid-line to unite and form a single median vessel, the postcaval vein. 

 This vein passes through the liver and part has been removed with 

 the liver; find the cut end anterior to the kidneys. Understand by 

 what vessels blood enters and leaves the kidneys and what the blood 

 loses and gains in these organs. 



(d) Lift the tip of the ventricle of the heart and observe the thin- 

 walled sinus venosus on the dorsal surface of the heart. A circular 



/nterce/Ju/or space 

 /c/mphat/c s^ /^"^ 



^esse/ 



ve/n 



ce//3 



cap/7/or/€5 



Fig. 17. — The capillaries and lymphatics in relation to cells throughout the 



body; diagrammatic. 



opening in the sinus venosus will be seen; this is the place where the 

 postcaval vein enters the heart. If your specimen has been dissected 

 carefully, you will be able to find the two precaval veins which enter 

 the sinus venosus anteriorly on each side. From what regions of the 

 body do these veins return blood to the heart? 



(e) Supplement what you have been able to see in your own 

 specimen by observations on demonstration specimens. Study the dia- 

 grams of the circulatory system so that you become thoroughly ac- 

 quainted with the names and distribution of the principal blood ves- 



