LYMPHATIC SYSTEM. 575 



II. The inferior vena cava begins between the kidneys, and 

 ends in the sinus venosus. Its components are as follows :- 



r c . f Efferent renal veins from the kidneys. 



I nff- i T"lOT" 



Genital veins from the reproductive organs. 

 ( Efferent hepatic veins from the liver. 

 The renal portal system, by which venous blood from the 

 posterior region niters through the kidneys on its way back 

 to the heart, is as follows on each side :- 



A posterior branch of the femoral vein from 

 the hind-limb forms the renal portal vein, 

 Renal portal ) which receives the sciatic from the back 

 system. ^ of the leg, and the dorso-lumbar veins 

 from the dorsal wall of the body, and 

 oviducal veins in the female. 

 The anterior branch of the femoral vein is called the 

 pelvic, and unites with its fellow of the opposite side, and 

 gives origin to a median vein which runs to the liver the 

 anterior abdominal. By means of an anastomosing branch, 

 the anterior branch of the femoral is also connected to the 

 sciatic. 



The hepatic portal system, by which venous blood from 

 the posterior region and from the gut passes through the 

 liver on its way back to the heart, is as follows : 



[Anterior abdominal vein, from the union of 

 the two pel vies, receiving tributaries from 

 Hepatic portal ) the bladder, ventral body-wall, and trun- 

 system. \ cus arteriosus. 



I Hepatic portal vein, from the union of veins 

 \ from the stomach, intestine, and spleen. 



III. The pulmonary veins which bring back purified blood 

 from the lungs, unite just before they enter the left auricle. 



Lymphatic system. The lymph is a colourless fluid, like blood 

 without red corpuscles. It is found in the spaces between the loose 

 skin and the subjacent muscles, in the pleuro-peritoneal cavity in which 

 heart, lungs, and other organs lie, in a sub-vertebral sinus extending 

 along the backbone, and in special lymphatic vessels which pass fatty 

 materials absorbed from the intestine into the venous system. There 

 are two pairs of contractile "lymph hearts'' at two regions where the 

 lymphatic system communicates with the veins. A pair lie near the 

 posterior end of the urostyle ; the other two lie between the transverse 

 processes of the third and fourth vertebra-. Their pulsations can be 

 seen on the back of the living frog. 



