Recto: The muscles of the upper spine. Verso: The muscles of the upper spine

Recto: five studies of the muscles of the back and shoulder labelled 1st to 5th, showing a sequence of dissection from superficial to deep. At lower right is one of Leonardo’s ‘thread diagrams’, combining the previous five drawings into a single schematic depiction, with each muscle represented by a cord along its line of action. Leonardo understood that for almost every muscle acting on a vertebra, another acts in the opposite direction, both effecting movement and stabilising the spinal column. Verso: notes on the muscles of the back, with two small drawings and a diagram demonstrating either the elevation of the ribs by the back muscles, or possibly the support of the neck by the muscles attached to the shoulder blades. Leonardo first studied anatomy around 1490, and he returned to the subject late in life. He intended to publish an illustrated treatise on the subject, but this was never completed, and the work of one of the great anatomists of the Renaissance thus had no discernible impact on the discipline. In the winter of 1510-11 Leonardo was apparently working in the medical school of the University of Pavia, alongside the professor of anatomy Marcantonio della Torre. He may have dissected up to 20 human bodies that winter. His investigations focussed on the mechanisms of the bones and muscles, and he developed novel illustrative techniques to convey the complexity of these mobile, layered, three-dimensional structures. Text adapted from Leonardo da Vinci: A life in drawing, London, 2018