Realdo Colombo

Realdo Colombo, Columbus (c. 1516-1559) was a professor of anatomy and a surgeon at University of Padua (1544-1559). He was a pupil of Vesalius and his successor. He published a book of anatomy - De re anatomica in which he corrected some of ommissions and errors of his master. His contribution to anatomy and medicine in general:

showed that lens lies to the front of the eyeball not in the centre
showed that arteries expand with each heartstroke
showed that the pulmonary valve closes during diastole preventing reflux
demonstrated that blood flows from the right side of the heart through lungs

His discoveries paved path for William Harvey discoveries of circulation of blood. Harvey studied in Padua some 50 years later.