Fabricius, Hieronymus (1537–1619)

Italian anatomist and embryologist. From 1574 he made detailed studies of the veins and blood flow and discovered the existence of one-way valves that direct the blood towards the heart. He also studied the development of chick embryos.

Fabricius also investigated the mechanics of respiration, the action of muscles, the anatomy of the larynx (about which he was the first to give a full description) and the eye (he was the first to correctly describe the location of the lens and the first to demonstrate that the pupil changes size).

Fabricius was born in Aquapendente, near Orvieto, and studied at Padua, where he was taught by anatomist Gabriel Fallopius. In 1565 he succeeded Fallopius as professor of anatomy, whose predecessors had been Andreas Vesalius and Matteo Colombo, and remained at Padua for the rest of his career. Fabricius built up an international reputation and attracted students from many countries, including William Harvey between 1600 and 1602.

Fabricius publicly demonstrated the valves in the veins of the limbs in 1579, and in 1603 published the first accurate description, with detailed illustrations, of these valves in De Venarum Ostiolis/On the Valves of the Veins. Although he mistakenly believed that the valves' function was to retard the flow of blood to enable the tissues to absorb nutriment, his work identified a key factor in the movement of blood around the body. Vesalius had shown that there were no holes in the septum (dividing wall) of the heart for the blood to pass between the chambers, as claimed by Galen; Colombo had shown the route that blood took between the heart and the lungs before flowing to the body; while the realization that once blood had flowed past Fabricius's one-way valves it would have to move on in the same direction greatly influenced Harvey, who eventually discovered the circulation of blood.

In his treatise De formato foetu/On the Formation of the Fetus (1600) – the first work of its kind – Fabricius compared the late fetal stages of different animals and gave the first detailed description of the placenta. In De formatione ovi et pulli/On the Development of the Egg and the Chick (1612) he made some erroneous assumptions; for example, that the sperm did not enter the ovum, but stimulated the generative process from a distance.