260 FROGS, TOADS, AND NEWTS [CH. VIII 



dorsal aorta. Close to their junction is given off a large 

 vessel which conveys blood to the digestive viscera. The 

 dorsal aorta passes backwards, giving off arteries to the 

 kidneys and back, and eventually bifurcates into large 

 arteries, one for each leg. The blood which passes through 

 the capillaries of the intestines, stomach and spleen is 

 gathered up into the hepatic portal vein which passes to 

 the liver, and there breaks into capillaries which penetrate 

 between the liver cells. It is by this arrangement that 

 the food absorbed from the digestive organs is temporarily 

 deposited as glycogen and fat within the liver by the 

 activity of the liver cells. There is also brought to and 

 distributed in the liver by the anterior abdominal vein 

 blood from the hind limbs, bladder, and ventral body wall. 

 The remainder of the blood from the hind legs is taken by 

 the sciatic and iliac veins into the renal portal veins, which, 

 running up the outer border of the kidneys right and left, 

 break into spacious capillaries within the substance of the 

 kidneys themselves. Here nitrogenous waste matter is 

 eliminated from the blood, which then issues into the 

 posterior vena cava, and is thus returned to the heart. 

 The lymphatic portion of the circulatory system is very 

 extensively developed. In addition to the lymphatic 

 vessels and capillaries that permeate all the organs of the 

 body there are between the skin and the underlying 

 muscles numerous large lymph sacs separated from one 

 another by thin connective tissue partitions which pass 

 from the skin to the muscles, and which are constant in 

 their positions. It is the presence of these sacs which 

 makes the frog's skin appear to fit so loosely. The lymph 



