Page 13

This page contains studies in red chalk, a medium also known as sanguine, primarily focusing on mechanical designs. No legible mirror-writing in Leonardo's hand is present on this side of the folio.

The main drawing in the upper and central portion of the page is a study of a mechanical joint or wing mechanism. It shows a central axis with various connecting rods and a curved, ribbed structure. This work is characteristic of Leonardo's investigations into human flight and his efforts to mimic the mechanics of nature through engineering.

A mechanical study in red chalk depicts a complex hinge or joint mechanism. Leonardo explores the structural arrangement of struts and curved members. These forms were likely inspired by the anatomy of bird or bat wings to achieve flexible movement and structural support in a flying machine.

In the lower-left corner, there is a secondary sketch of a triangular frame or support structure with internal bracing, drawn in perspective.

This perspective sketch shows a triangular wooden frame with cross-bracing. It likely represents a study for a stable base or a component of a larger hoisting device or war machine.