Question

the ventricles have thick muscular walls whereas the auricles have thin walls. why do you think muscular walls are necessary in the ventricles and not in the auricles

Answer 1

auricles just have to push blood from auricles to ventricles which is a SHORT distance thus their walls are not muscular enough
but ventricles, on the other hand, have to push blood away from the heart to long distances (right ventricle sends blood to lungs and left ventricle sends blood to the entire body) thus, they are more muscular to facilitate this flow of blood

Answer 2

VENTRICLES -- because they have to carry blood in high pressure

AURICLES -- because they have to carry blood in low pressure