Whether a soul is one in number in some part that has been divided.
One asks further, whether a soul is one in number in some part that has been divided.
1. It seems that it is. For if a new soul were introduced into a part which was not there previously, either this would occur as an operation of nature or by means of an act of cutting-off alone. But it would not be as an operation of nature, because nature produces like from like, and in an act of cutting-off there is no soul acting on the whole to introduce form to the part. Nor would it be through the act of cutting-off alone, because generation is a boundary [terminus] for change and the act of cutting off is not a natural change but rather a violent one. Therefore, there can be no principle for introducing a new soul.
2. In addition, no change occurs from one soul into another soul unless there is [first] a resolution into prime matter, because when the soul withdraws then death occurs, and a living being does not arise from a dead one, just as wine does not come from vinegar, unless first it is reduced to prime matter. If then a new soul were introduced to the part that has been cut off, and which previously was under another soul, it would be necessary for it to be reduced to prime matter first. But this is not true, because there is nothing resolving it there.
On the contrary. It is impossible for something that is one and the same in number to perfect many materials at the same time. Therefore, the soul cannot be the same in number in diverse parts.
One must reply that the soul is not the same in number in those diverse parts that have been cut off, but it is the same in species. For just as the form of a continuous and undivided fire is single in act and yet there are many forms in its related potential [multae in potentia propinqua], in order to reduce that potency to act, all that is required is the dissolution of its continuity. So too the soul in these undivided animals is one in act and many in potency because the soul is extended as far as the extension of the matter, and division alone is required for the reduction of this potency to act. But the many are not one in number, since they are opposed. Since, then, many souls arise through division, just as many fires arise from the division of one fire, it follows that the soul will not be one in number in diverse parts.
1. To the first argument one must reply that a soul that is absolutely new is not introduced into a part that is cut off, but rather that the same soul which earlier was in potency is now in act. And it arises in act through division alone because it existed previously in a potency so closely related that nothing was lacking for it to exist in act, except removing an obstacle to it. But the obstacle was its continuity, and this is why dissolving that continuity causes this soul to exist in act. Nor, however, does it follow that it is one in number with a soul of another part, because those things differ in number whose material is different.
2. To the second argument one must respond that a thing having one soul in act and in perfection, cannot assume a new one, once that one has been cast aside, unless there should occur some reduction to prime matter. But this is not what was proposed, because the part did not have the soul previously in act, but only in potency, and therefore, etc.
Whether fleshiness on a person's head impairs the intellect.
One asks further whether fleshiness on a person's head impairs the intellect or whether a human head naturally ought not to be fleshy.
1. And it seems not. Because "sensation does not occur without heat," according to the second book of On the Soul. But the senses are located in the head, and the brain, which is a very cold member, is in the head. Therefore, it is fitting that there should be a hot part on the head which may temper that cold. But flesh is such a part, because it is especially hot and moist. Therefore, etc.
2. In addition, the head's fleshiness is repugnant, according to the Philosopher's explanation, only when there is impairment of the intellect. But the intellect, since it is not an organic power, cannot be impaired in its operation by a bodily part.
The Philosopher says the opposite.
One must reply that excessive fleshiness on the head does impair the intellect, and among animals only the human has a capacity for intellect, and this is why of all the animals the human head ought to be less fleshy in respect to its size. And the reason for this is that flesh, since it is moist and hot, contributes a great deal to digestion and, as a result, contributes to a natural power. But the natural and animal powers exist as contraries, as it were, and this is why that which contributes principally to one does not contribute to the other. Rather, just as flesh and bone have almost opposite complexions, and since flesh is hot, and is suited to the natural power, so too then bone is suited to the animal power. And this is why the natural memberslike the liver, spleen, and heartare fleshy and lack bones, whereas the head, in which the animal virtues are located, is on the contrary very bony and nerve-filled and less fleshy.
Moreover, fleshiness on the head makes the head heavy and weighed down. But the human naturally has an erect stature owing to the excellence of his heat. Therefore, fleshiness on the head causes a human to depart from his natural posture and impairs the direct flow that occurs from the heart to the superior parts. As a result, fleshiness on the head causes the impairment of the senses, and the operation of the intellect fails because of the weakness of the senses. Thus it is that children, when they have a head that is too fleshy, have poor discretion, and old people, likewise, since they have heads that are weighed down, do not have good powers of imagination or memory, because the spirits, which are the vehicles of the powers, cannot come there easily from the heart, and the animal spirits are not generated out of them. But digestion is poor, because the head's fleshiness draws the natural spirits from the liver to itself.
1. On to the arguments. To the first, one must reply that although the sensations do not arise without heat, nevertheless excessive heat impairs a sense, and this is clear by taking a look at places, seasons, and nutriment, for the intellect's operation cannot continue in places that are exceedingly hot nor does it occur as well in exceedingly hot seasons as it does in temperate places and seasons. Thus, if the head is too fleshy, the heat flowing up from the heart and likewise the heat conserved in the flesh displace the cold of the brain too much and hinder it from its proper operation.
2. To the second argument one must respond that although the intellect does not use an organ per se, nevertheless it does require other powers that do use organs, and these powers are hindered by too much fleshiness, and once they are hindered the intellect is hindered per accidens, because our intellect "is either a phantasm or does not exist without a phantasm," as is said in the third book of On the Soul, etc.
Question 10: Whether the upper part [of the body] in children is larger than the lower.
Next one inquires whether the upper part [of the body] in children is larger than the lower, and whether the contrary is true for youths and those more advanced in age, and whether the contrary condition occurs in beasts.
1. It seems not. The upper part is the one through which a living thing receives nutriment. Thus the root is high up on a plant. But the human being receives nutriment through the mouth, which is situated on the head, and the head is smaller in children than the rest of the body, and therefore, etc.
2. If one were to say that the upper part does not consist of only the head but of the head and the trunk together, then it seems that just as this part is larger in children than the lower part, the same will hold for a youth. Therefore, this cannot be understood this way.
The Philosopher says the opposite.
One must respond that among humans the upper part is larger than the lower during childhood, but during youth the opposite is the case, and the contrary to this occurs among brute animals. And the reason for this is that among all the animals the human has the largest brain in proportion to his body, and in childhood the brain is very cold and moist. And because nature produces the principal members first and sees especially to their nourishment, this is why in the beginning the upper part of the body is larger than the lower in the human. I understand the upper part to consist of everything from the top of the head to the lower part of the trunk. But over the course of time, heat flourishes in the human and begins to dissolve the superfluous moistures, which are in the upper part. Once these are dissolved, a freer pathway is open to the lower parts for nourishment, and this is why during youth the lower parts, like the tibias, the testicles, the penis, the anus, and the vulva, begin to grow larger. And an indication of this is that during childhood children do not walk erect, but they move and crawl like reptiles on their hands and feet, and this is owing to the weight of the upper part and the weakness of the lower part. Nevertheless, its larger size should not be understood simply in terms of quantity, but rather understood in terms of proportion, because the upper part is always larger quantitatively, but in the beginning it is disproportionately larger. But during youth the contrary is so for the lower part, because the head is not proportioned to the legs.
In other animals, however, the opposite is the case since the lower parts are larger at first. Thus the legs of a foal [pullus equinus] are not much shorter than the completed length they will have later, or have at the end. And the reason for this is that the body of animals such as these is supported by the lower parts, and this is why it is necessary that such parts be solid and very earthy. But there is earthiness in the semen of brute animals, and this is why a good bit of it is converted into the lower parts at the very beginning. But over the course of time the nutriment can be more easily converted into more rarefied parts (namely, those that are above) than into the dense parts, and this is why the upper part increases in size then, and the lower part is proportionally diminished.
1. On to the arguments. To the first, one must reply just as has already been said.
2. To the second, one must respond to the contrary, that the upper part is always quantitatively larger, but nevertheless it is not always larger in terms of proportion, and this is why, etc.
-  Unde radix sursum est in planta, which appears contrary to experience. Indeed the Aberdeen bestiary, ca. 1200, reminds us that a root, radix, is so called because it is fixed deep in the ground (Aberdeen University Library MS 24, fol. 78r).