False Fetal Facts
This is one of the very rare instances that Leonardo was erroneous about something. A fetus's heart does beat and it's lungs do take in the liquid in the womb without drowning. It is also possible that a child could stay alive within the womb for a very brief time even if the mother were to die although depending on its gestation it would require life support. The idea that a "single soul" encompasses both is probably only true for a short time - up until the fetus has matured enough to live outside of the womb. The earliest surviving preemie is 22 weeks in the womb. There is some evidence that certain things that the mother/ child experiences while in the womb does affect the infant but it's unclear if this is because of what the child senses through the stomach or if the mother's senses are connected directly to fetus in such a way that they could share sensations. It would be interesting if there were really some type of "shared consciousness" between an infant and mother as Leonardo suggests.
"Nature puts the soul into the body which forms the child; that is the soul of the mother, which first constructs in the womb the form of the man and in due time awakens the soul that is to inhabit it. And this at first lies dormant and under the tutelage of the soul of the mother, who nourishes and vivifies it by the umbilical vein, with all its spiritual parts, and this happens because this umbilicus is joined to the placenta and the cotyledons, by which the child is attached to the mother. And these are the reason why a wish, a strong craving or a fright or any other mental suffering in the mother has more influence on the child than on the mother."
"In the case of this child the heart does not beat it does not breathe and because it lies continually in water, And if it were to breathe it would be drowned, and breathing is not necessary to it because it receives life and is nourished from the life and food of the mother And this food nourishes such a creature in just the same way as it does the other parts of the mother, namely the hands, feet and other members And a single soul governs these two bodies, and the desires and fears and pains are common to this creature as to all the other animated members.
And from this it proceeds that a thing desired by the mother is often found engraved upon those parts of the child which the mother keeps in the time of such desire and sudden fear kills both mother and child. We conclude therefore that single soul governs the bodies and nourishes the two bodies.