This is the first accurate depiction of the spine in history, with its distinct sections and curvatures all correctly shown. Leonardo had to capture the three-dimensional forms of the body in two-dimensional images. In the upper part of the sheet he depicts the spine in profile and from the front – two views at 90 degrees to one another, like the elevations of an architectural drawing. And at lower left he demonstrates how the first and second vertebrae of the neck fit onto the third, using the convention of the ‘exploded view’.