1. (c) The venous system
The venous system includes veins which bring the blood to the heart from various parts of the body.
There are two pre caval veins and a post caval vein. These three veins unite and open into the sinus
venosus. Each pre caval vein is formed of three branches namely external jugular vein, innominate vein
and sub-clavian vein. The external jugular collects the blood from the tongue and floor of the buccal
cavity. The innominate vein collects from the brain and other regions of the head and shoulder. The
sub clavian collects the blood from the fore limb and skin. From each lung, the blood is collected by a
pulmonary vein. These two pulmonary veins open into the left auricle.
The post caval vein collects the blood from the hind limbs, kidneys, gonads and the alimentary canal
and empties the blood into the sinus venosus. From the hind limbs, the blood is collected by a femoral
vein and sciatic vein on each side. The femoral vein divides into femoro-renal vein and a pelvic vein on
each side. The femoro-renal vein combines with sciatic on each side and forms the renal portal vein,
giving many branches to the kidney. From each kidney, four renal veins collect the blood and these
four pairs of renal veins unite to form the post caval vein which opens into the sinus venosus. Gonadial
vein from the gonad on each side opens into the first renal vein.
The two pelvic veins arising from the femoral veins unite to form the anterior abdominal vein. This runs
forwards, divides and breaks up into capillaries in the liver. A vein from the heart, the cardiac vein
joins the anterior abdominal vein. The veins from the stomach, intestine, pancreas, spleen and other
parts of the alimentary canal unite into a large hepatic portal vein which enters the liver and breaks up
into capillaries.
By wasim sir
The venous system includes two portal systems in frog. The femoral, sciatic and renal portal veins start
in capillaries in the hind limbs and end in capillaries in the kidneys. This is known as the renal portal
system. Similarly, the hepatic portal vein starts in capillaries in the alimentary canal and ends in
capillaries in the liver, forming the hepatic portal system. The heart muscles are supplied with a
branch of the carotid trunk and the blood from the heart muscles are collected by a pair of veins. The
blood of frog is similar to that of other vertebrates. It contains plasma in which are suspended RBC’s,
WBC’s and platelets or thrombocytes, RBC’s are oval, biconvex and nucleated, containing haemoglobin.
