14 THE FROG 



Recall the action of the heart if observed in Exercise 4. What is its 

 function? 



(b) Blood leaves the heart through the truncus arteriosus which 

 arises from the right side of the ventricle, runs obliquely forward over 

 the ventral surface of the auricles, and then divides into right and left 

 branches, each of which subdivides in the same manner. Using your 

 forceps and a dissecting needle, follow the right branch as it divides 

 into three arteries. The most anterior branch is the carotid artery 

 which goes to the head. The most posterior branch of the truncus 

 arteriosus is the pulmo-cutaneous artery which runs to the lungs, after 

 sending a branch to the skin. The middle branch is the systemic 

 artery which runs first in a dorsal and then in a posterior direction. A 

 subclavian artery arises from the systemic artery and passes to the 

 fore leg by the side of a conspicuous white nerve. Follow the right 

 systemic artery posteriorly and find its place of union with the left 

 systemic artery to form the dorsal aorta. At the place of union a large 

 branch, the coeliaco-mesenteric artery, is given off and runs through 

 the mesentery to the digestive tract; this artery will have been partly 

 removed. The dorsal aorta runs posteriorly in the mid-dorsal line. 

 Carefully free the right margin of the right kidney and lift it enough 

 to see the delicate renal arteries that pass from the dorsal aorta to the 

 kidneys. Determine how the renal arteries arise and trace their distri- 

 bution on the ventral surface of each kidney; use your handlens. Pos- 

 terior to the kidneys the dorsal aorta divides to form the two iliac 

 arteries which carry blood to the hind legs. Make a drawing (X 5) 

 of the heart and principal arteries as thus dissected, from the ventral 

 view; the kidneys are not to be shown. Use arrows to indicate the 

 direction of blood flow. Be sure you know to what organs these vessels 

 are carrying blood; the general relationships are shown in Fig. 16 A. 

 Larger frogs in which a colored mass has been injected into the 

 arteries should be examined if available. 



Exercise 14. — The Veins. 



(c) Some of the principal veins, especially those making up the 

 hepatic portal system, were removed from your specimen with the 

 digestive and reproductive organs. In the region of the kidneys the 

 veins should be in i)lace. Find the renal portal veins that extend from 

 the hind legs to the lateral margins of the kidneys, just anterior to 

 where the ureters emerge. Lift the outer edge of the right kidney 

 and trace the right renal portal vein as it branches on the dorsal 

 surface of the kidney. What is a portal vein? The dorso-lumbar 

 vein, which has been cut on the right side in freeing the kidney, can 



