Sketches by Leonardo da Vinci on the anatomy of the brain. A. The layers of the scalp compared to an onion (1489). The earliest drawings by da Vinci on the ventricles of the brain show them to be connected to the eye and moving backwards, into the brain. In this drawing he also likens the meninges of the brain to the layers of an onion (left hand side of image). B. Studies of the eyes and brain (1508). Later studies by da Vinci on the neuroanatomy of man display a better understanding of the ventricles of the brain and of nerves permeating to peripheral areas. This increase in understanding is likely due to the use of wax casts made of the ventricular system of other 'lower' animals, such as the ox (see C). C. The cerebral ventricles of the brain of an ox (unknown date: 1508 - 1510). Here da Vinci describes the methodology of injecting warmed wax into the ventricular system of the ox, allowing it to cool, then visualising and sketching the mould that is made. Though not describing explicitly the use of bovine species, we can assume that da Vinci has by the presence of the bovine equivalent of the circle of Willis, the rete mirabilis, in the lower image. All images are reproduced by gracious permission of Her Majesty The Queen, from the Royal Collection © 2010, Her Majesty Queen Elizabeth II.