Drawing of the Uterus of a Pregnant Cow - by Leonardo da Vinci

A page from a notebook showing the dissection of a pregnant cow. The drawings show the two-chambered bovine uterus, with a calf in the upper chamber. In the lower study Leonardo removes the uterine wall to show the calf; the placenta is represented as a pattern of small ovals.

Around the lower drawing Leonardo da Vinci wrote:

This drawing below contains the third and fourth sloughed membranes [chorion and amnion] of the animal enclosed in the uterus. These membranes are united, that is, they are in contact with each other, and that which is more superficial is united with this [the uterus] through the fleshy rosettes [cotyledons] which interlock and stick together as burrs do with each other. And at birth the infant carries with it these two coats with half the thickness of these rosettes, and the other half remains within the uterus of the mother, which then in contracting joins them together ... in such a way that they would never appear to have been separated. And the sloughed membrane in contact with the animal which is born has none of these fleshy rosettes."