THE SPECIAL ANATOMY OF THE FROG 43 



2. The hepatic portal system (Holmes, p. 277). A portal system is one in 

 which the venous blood does not return directly to the heart but enters a system 

 of capillaries in some organ from which the venous blood is then collected by a 

 systemic vein. There are two portal systems in the frog, the hepatic portal sys- 

 tem in which the interposed capillaries are in the liver, and the renal portal system 

 where they are in the kidney. Spread out the liver with its lobes turned 

 forward so that the pancreas is visible. Find a large vein ascending through 

 the substance of the pancreas and forking on the dorsal surface of the liver. 

 This is the hepatic portal vein which breaks up into a system of capillaries 

 in the liver. The left fork of the hepatic portal vein sinks into the substance 

 of the posterior part of the left lobe of the liver. The right fork connects 

 with the anterior abdominal vein which also forks and then penetrates the 

 liver. Trace the hepatic portal vein posteriorly and note that it is formed 

 by the union of veins from the stomach, pancreas, spleen, and small and 

 large intestines. All of the blood from the digestive tract therefore enters a 

 capillary system in the liver, from which it flows into the postcaval vein by 

 way of the hepatic veins. What is the purpose of this arrangement? Consult 

 Holmes, p. 153. 



3. The renal portal system. Expose the kidneys and find along the outer 

 lateral edge of each a conspicuous vein, the renal portal vein, which enters the 

 substance of the kidney. Trace the renal portal vein posteriorly. At about the 

 middle of the kidney it receives a vein, the dorso-lumbar vein, from the muscles 

 of the back. Posterior to the kidney it is seen to be formed from two veins 

 which come from the leg. The outer of the two veins is the femoral, the inner, 

 the sciatic. At the point where each femoral vein enters the coelome, it gives 

 off a branch, the pelvic vein, which runs along the posterior wall of the coelome 

 to the median line where it joins the other pelvic. This union of the two pelvic 

 veins produces the abdominal vein, which joins the hepatic portal vein as 

 described above. The abdominal vein is thus a connection between the renal 

 and hepatic portal systems, and blood from the hind legs may return to the 

 heart either by way of the kidneys or by way of the liver. In the kidneys the 

 renal portal vein breaks up into capillaries, from which the blood is collected by 

 the postcaval vein. 



4. The pulmonary veins. From each lung a pulmonary vein passes dorsal 

 to the sinus venosus and enters the left auricle. These veins are sometimes 

 difficult to locate. Turn the heart forward holding it down with the finger so 

 that it will be stretched. Pull away with a forceps the coronary ligament of 

 the liver so as to expose the lungs. A short straight vessel will be found running 

 from the inner border of the base of each lung obliquely toward the sinus venosus. 

 These two pulmonary veins join just under the beginning of the left precaval vein 

 and penetrate the left auricle at that point. 



