Leonardo returned to the study of the brain after a gap of almost twenty years, but now he could work with human material.

His earlier drawings, displayed in the previous gallery, embodied the traditional belief that the brain contains three bulbous ventricles arranged in a straight line. A rudimentary dissection would have shown him that the brain does indeed contain cavities, but not of this form.

In a brilliant experiment, Leonardo injected molten wax into the ventricles to determine their true shape. Further dissections of the brain demonstrated that the nerves had no direct connection to the ventricles. He thus abandoned the ancient belief that the ventricles housed the mental faculties.