The Frog. 79 



diagram. The names of the several vessels and the points at 

 which they vmite are there indicated, and an inspection will 

 serve instead of a description. In the same simple fashion the 

 blood is returned to the left auricle from the lungs. It should 

 be noted, however, that while generally the veins correspond to 

 the arteries, this is not the case with the cutaneous vein. This 

 vein joins the jugular system, while the cutaneous artery is 

 derived from the pulmonary artery. 



The blood from the renal organs and from the liver is also 

 returned directly to the heart by way of the posterior vena cava. 



From the rest of the body the blood is not returned 

 directly to the heart. "Vor femoral vein bifurcates in the pelvic 

 region into two vessels, of which one runs to the kidney, and 

 there breaks up into a series of capillaries ; the other branch 

 joins its fellow of the opposite side to form the anterior ab- 

 dominal vein, a vein running just below the muscles of the 

 abdomen, which can be seen through those muscles before 

 they are cut. This anterior abdominal vein divides anteriorly 

 into two branches, one for each of the two lobes of the liver, in 

 the interior of which it breaks up into a capillary network. A 

 minute twig, however, has been described as going directly to 

 the heart. The renal portal vein, as that branch of the femoral 

 which goes to the kidney has been termed, is reinforced by 

 the sciatic vein. Besides this renal poi'tal system, as the vessels 

 which pour their blood into the kidneys are collectively termed, 

 there is an hepatic portal system. The veins from the alimentary 

 canal unite to form a largish trunk, the portal vein ; this enters 

 the liver, and there breaks up into a capillary network. Thus 

 all the blood from the hind limbs passes on its way to the 

 heart either through the kidneys or through the liver, with the 

 exception of a small quantity which reaches the heart directly 

 by way of the small branch of the anterior abdominal already 

 referred to. 



The respiratory organs of the frog consist of a pair of 

 lungs ; these open by a short tube, which is strengthened by 

 certain cartilages, into the pharynx. Each lung is a sac 

 with thin walls, which are abundantly supplied with blood 

 capillaries, the branches of the pulmonary arteries. When the 



