Prior to 1543, much of the understanding of the anatomy of the human body was based on work by the ancient Roman scientist and philosopher Galen of Pergamum. Galen's Institutiones Anatomicae, the first major treatise on anatomical form, was the gold standard for medical and anatomical education. However, Galen's work on human anatomy was primarily rooted in dissections of nonhuman primates—dissection of human remains was illegal—with human anatomy extrapolated from the anatomy of close relatives.
Organ JM. Andreas Vesalius: The Making, the Madman, and the Myth. JAMA. 2010;304(2):214-220. doi:10.1001/jama.2010.947