Frogs

Frog?? heart is a 3-chambered structure, made of two anterior dark coloured artria or auricles (right and left), and a single posterior conical and pink coloured ventricle. The heart of frog has two additional chambers: sinus venosus and truncus arteriosus. Sinus venosus is a dark coloured, thin walled and triangular chamber attached dorsally to heart. It is formed by the union of three large caval veins, two anterior precavals and one posterior postcaval. Deoxygenated blood from the body travels towards heart in three large vessels, two anterior venae cavae and single posterior vena cava, all the three opening into sinus venosus. When sinus venosus contracts, its deoxygenated venous blood is forced into the right auricle through sinuauricular aperture.