Eustachian valve which is of no significance in the adult mammal, is a vestigial organ, a vestige of

Trilobed valve present between right atrium and ventricle in mammalian heart is

What is the function of nodal muscular tissue ?

Spiral valve is present in

Write the feature that distinguish between the two : Sino-atrial node and Atrio-ventricular node 

Draw a labelled diagram showing internal structure of heart.