A sheet of more than twenty drawings of cats and lions in a wide variety of positions; lying asleep, sitting, prowling, playing, fighting, and in one case frightened, standing with humped back and fur standing on end; in the lower half, drawn at an odd angle, is a study of a dragon, with its head bent back over his shoulder.

One of the most charming of all of Leonardo's drawings, it covers the full range of his modes from the most stylised and 'Leonardesque', in the coiling dragon, to the most acutely observed and unaffected, in the many studies of domestic cats. The most detailed studies, at centre right, show the cats sleeping, and seem to have been done directly from the life, with the subject motionless; by contrast the depictions of cats fighting had to be visualised on the basis of fleeting impressions. In most of the fights it is difficult to discern which limb belongs to which cat, and in the study at lower centre he has drawn the two cats locked together as a single unit, almost symmetrical, in the manner of a Romanesque carving. 

Surrounding the studies of domestic cats are seven drawings of a single lioness, mostly crouching or prowling. Lions were well enough known in Italy at the time – they were, for example, kept in a cage behind the Palazzo della Signoria in Florence, as one of the symbols of the city – and Leonardo shows in these drawings a clear understanding of their anatomy and proportions. But the unifying interest of the sheet is revealed by Leonardo's short and incomplete note at the bottom: 

Of flexion and extension 

This animal species, of which the lion is the prince because of its spinal column which is flexible… 

A closely related sheet of studies of horses (912331) carries a similar note, 'The serpent-like movement is the principal action in animals and it is double, the first occurring along its length and the second across its width.' The purpose of these studies is confirmed by a memorandum in his Manuscript E now in Paris, of c.1513-14: 'Write a separate treatise describing the movements of animals with four feet, among which is man, who likewise in his infancy crawls on all fours.' 

It is clear, therefore, that Leonardo's primary concern in these drawings was the variety of positions and movements attainable by members of the cat family, and that the dragon was added simply as a still more extreme case (as limited only the artist's imagination rather than by real anatomy). But while Leonardo expressed an interest in writing a treatise on animal movement – perhaps as displacement therapy for his treatise on human anatomy, work towards which had stalled at this time – there is no evidence that such a treatise was ever developed in any detail.