LYMPHATIC SYSTEM. 595 
The renal portal system, by which venous blood from 
the posterior region filters 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, which 
receives the sciatic from the back of the leg, and 
the dorso-lumbar veins from the dorsal wall of 
the body, and oviducal veins in the female. 
Renal portal 
system. 
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 
se two pelvics, receiving tributaries from the 
Hepatic portal bladder, ventral body wall, and _ truncus 
system. 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. There are numerous valves in the veins of the 
frog. 
Lymphatic system,.—The lymph is a colourless fluid, like blood 
without red corpuscles. It is found m 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 
afong 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 vertebrae, Their pulsations can be 
seen on the back of the living frog. 
Mechanism of the heart.—The right half of the ventricle, 
being nearer the right auricle, contains more impure blood, and it is 
from the right side of the ventricle that the truncus arteriosus arises, 
The middle of the ventricular cavity contains mixed blood. The 
left corner contains pure blood received from the pulmonary veins. 
