THE FROG 167 



dividing. Can you tell which division of the heart this 

 comes from? This arterial trunk is called the aorta. Find 

 its point of division, from which two branches {right and 

 left carotid) go to each side. Dissect away carefully the 

 surrounding tissues and disclose the divisions of each branch. 

 Where does the first branch leave the main artery? Where 

 does it seem to go? It is called the anterior carotid and 

 supplies the head. Follow the artery along to the next 

 branch, where it divides going to the lungs and the skin. 

 What is the office of this blood vessel? Is there a reason 

 for its going to the skin? Does this help to explain why 

 the frog can stay so long under water? Trace the third 

 artery, noting its anterior and posterior divisions. Where 

 does the anterior division go? Trace the posterior division 

 back to the formation of the large dorsal artery by uniting 

 with the corresponding branch of the other side. 



(2) Follow the dorsal aorta back. Does it give off 

 branches? Where? What is the object of each? Follow 

 it down to the posterior end, and note its separation into 

 two divisions, the iliac arteries, which go to the legs. 



(3) Trace the veins back toward the heart. Do you 

 find a corresponding vein for each artery? Do you find a 

 dorsal vein in close proximity to the dorsal aorta? Can 

 you trace the ventral blood vessel that was seen before the 

 opening of the body wall, back to the dorsal vein? Study 

 closely the circulation of the kidneys. From what vessel 

 does the blood which enters the kidney come ? To which one 

 does it go after circulating through the kidneys ? The cir- 

 culation through the kidneys is called the renal circulation. 

 Trace the vein formed from both kidneys forward to the 

 liver and notice the additions made to it from the mesenteries, 



