On the fetus before and after birth.
Further one inquires whether a woman, once she has been impregnated, can be impregnated again before the birth.
And it seems not. Because after impregnation the opening of the womb closes, and therefore, etc.
The Philosopher says the opposite occurs in many cases.
Second, one inquires why it is that twins often survive when both are male or both are female, but if they are of different sexes, often either one or the other dies.
Third, one inquires whether the fetus's head ought to exit first.
And it seems not. Because a lower part ought naturally to seek out the area below. But feet are lower parts. Therefore, etc. The Philosopher <says> the opposite.
Fourth, one inquires why, when the fetus is born, it immediately cries and places its hand to its mouth.
Fifth, one inquires why in the first age infants sleep a lot, almost all day and all night, and why they are particularly moved to sleep by lullabies and the use of a cradle.
Last, why convulsions are particularly generated in infants.
To the first question one must reply that both a woman and a mare abound in semen, because they use a more noble nutriment, and this is why they can be impregnated twice. This is why the Philosopher says that in many places it happens that a woman gives birth to one child and then three months later gives birth to twins. This would not occur unless after the first impregnation there is a second.
To the argument one must reply that although the opening of the womb closes naturally after the first impregnation, owing to the very great pleasure that she has during intercourse it often happens that she opens it, and also it happens on account of the penis [veretrum] opening its gate, etc.
To the second, one must reply that a male is produced from a stronger heat than a female is, and this is why it is formed and fashioned more quickly in the uterus than a female, and because of its quicker formation its exit also follows more quickly. And this is why, when it happens that in the uterus there are both male and female at the same time, either the female blocks the male's exit or the male accelerates the female's exit, and this is why often it happens that one or the other dies. When, however, both are male, then they agree in their matter and in their active cause, and in such a case they are formed at the same time and consequently have an almost simultaneous exit, and for this reason they live longer, healthier, and better than do other twins. And because the matter is the same and resembles the agent [cause], this is why so often twins like this are alike in their bodily appearance and in many of their dispositions.
To the third, one must reply that the upper parts like the head are more quickly formed in the uterus than are the lower parts, and they are larger in the uterus relative to the lower parts, and as a result they are heavier, and every heavy object inclines downward. This is why when childbirth approaches, the fetus turns its head downward. And in addition to this is the cause noted by Avicenna, that the fetus struggles to exit on account of the number of its needs. For it desires food, which it does not have in great quantity, and it desires to draw in air, which it does not have, and in the same way it wants more space, which it does not have. But the pathway for food and air is in the head, and the head is larger than the other members, and this is why the head naturally turns to the opening of the vulva.
To the fourth, one must reply that everything that is unaccustomed is a source of pain and is as if contrary to nature. But the child [ partus] or fetus in the uterus exists as if in a warm bath, and when it is born it is exposed to the cold air, which is just like something contrary to it, and this exposure is the cause of its cry. In like manner, it naturally desires food and desires to draw in air, and nature incites and almost persuades the fetus that its mouth is the pathway for food and respiration, and this is why it naturally places its hand to its mouth when it emerges.
To the fifth, one must reply that the cause of sleep is the elevation of vapors to the brain and their coagulation on account of the brain's coldness, because "sleep is the binding up of the senses" that are external, according to Aristotle in On Sleep and Waking. And the vapors that are condensed in the head because of the brain's coldness block the pathways for the spirits, which administer the senses, and this is why the external senses immediately cease from their operations and sleep is induced, and vapors like this abound in infants. Nevertheless, not every vapor like this is a cause for a long sleep but only a particularly sweet and soothing vapor, and not a pungent one. For in the senses there are many vapors and fumes that are choleric and melancholic and very capable of penetrating the membranes [ miringae] of the brain.
To the sixth, one must reply that things to which we are accustomed are pleasing, and the fetus in the uterus is constantly in motion because it is moved and carried along by the womb's movement. This is why movement pleases it when it is outside the uterus. But another reason is that one intense operation withdraws from before another. In this sense, the infant's movement causes an arousal of the heat, an elevation of vapor, and a weakening of the brain, and this movement is therefore a cause of sleep because it makes the external senses cease from their operations.
And in addition an internal pleasure deflects the external powers from their operations, and a gentle motion and lullabies cause pleasure inside the infant. Therefore, the powers withdraw with heat and spirit to the interior and, as a result, the exterior parts are abandoned and are almost deprived of their influence [a suoregimine]. Therefore, they sleep, etc.
To the seventh, one must reply that a spasm is caused by a weakness in the nerves. And this can occur from too much dryness, just as it is evident that a piece of parchment placed close to the fire is quickly curled up and becomes wrinkled owing to the moisture's consumption. Or it can occur owing to an excessive moisture and softness in the nerves, and this is the cause in infants because they live on a moist nutriment and use it almost continuously, like brute beasts. This is why spasms occur in them quite often, owing to the weakness and softness of their nerves. If this were universal throughout all their parts, "they would die within seven days," as is said in the text. If, however, "they escape the seventh day," they are frequently cured, but they suffer more on the fourteenth day because the moon, which has dominion over all that is moist, has a greater effect on the fourteenth day.