LYMPHATIC SYSTEM. 54$ 



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 : — 



I 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 of 



system. \ the leg, and the dorso-lumbar veins from 



I 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 pelvics, receiving tributaries from 

 the bladder, ventral body-wall, and trun- 

 cus arteriosus. 

 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. 



Mechanism of the heart. — We must now return to the 



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