Already licensed as a Church of Scotland minister, John Barclay obtained a medical degree from the University of Edinburgh. He gave his own course of lectures in the city, specialising in comparative anatomy ? the study of similarities and differences in organisms. As a result of his research in this area, Barclay published a new system of anatomical names, which he proposed should be applied to the same organ in all positions of the body and in all animals.His pupils included Robert Knox and Robert Liston. He bequeathed his vast collection of specimens to the Royal College of Surgeons of Edinburgh.