Renal portal system brings blood from internal organs to their kidneys. It is not present in the mammals.

Arteries have no internal valve whereas veins have internal semilunar valves to prevent backflow of blood.

Three large veins; the right and left anterior venecavae or precavals and a single posterior venecavae or postcaval open by separate pores into the right atium.

The right upper chamber of the heart (right atrium) receives deoxygenated blood from the body through the vena cava and pumps it into the right ventricle, which then sends it to the lungs to be oxygenated. Eustachian valve lies at the junction of the inferior vena cava and right atrium.

Phrenic artery supplies blood to the diaphragm.

It supplies oxygenated blood from the lungs to the left atrium of the heart.

It carries blood from some of the posterior parts of the body to the kidneys in most lower vertebrates and including typically two trunks. Here only sciatic vein of the frog pours its blood.

Tricuspid valve is present between the right atrium and left ventricle.

The endothelium is the thin layer of cells that lines the interior surface of blood vessels and lymphatic vessels.

The conus arteriosus is a conical pouch formed from the upper and left angle of the right ventricle in the chordate heart from which the pulmonary trunk arises. Pylangium (the first and undivided part of the aortic trunk in the amphibian heart) is present here.

Earthworm has closed type of circulatory system. Here blood is pumped through a closed system of arteries, veins, and capillaries. Capillaries surround the organs, making sure that all cells have an equal opportunity for nourishment and removal of their waste products.

A single posterior mesenteric artery arises from the dorsal aorta.

The pressure difference between systolic and diastolic pressures is the pressure change to create the pulse, which is the pulse pressure.

The occipital artery supplies blood to the posterior region of the skull and the upper jaw.

This carries deoxygenated blood from various parts of alimentary canal.

These are the mixed nerves innervating the muscles of larynx, pharynx, oesophagus, gullet, stomach, heart, etc.

Spiral valve is found in the pylangium.

It is a small, flattened and ellipsoidal mass of self excitatory nodal fibres embedded in the wall of right atrium near the opening of right anterior vena cava.