Willis, Thomas, 1621–75, English physician and anatomist. He became professor at Oxford in 1660 and in 1666 established a practice in London. An authority on the brain and the nervous system, he discovered the 11th cranial nerve and a circle of arteries at the base of the brain (the circle of Willis). He was the first to note the presence of sugar in the urine of diabetics. His works, written in Latin, include Of the Anatomy of the Brain, illustrated by Sir Christopher Wren, published in 1664, and translated in The Remaining Medical Works … of Doctor Thomas Willis (1681).