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Whether parts in an animal have a location like the parts of the universe.
Next one asks whether parts in an animal have a location like the parts of the universe.
1. It seems not. For it happens that the front of a man is oriented toward the right side of heaven and the right is toward the left. Therefore, the location of parts in the animal does not correspond to their location in the universe.
2. Again, that seems to be the root from which other things arise. Now, however, the sensitive and motive powers flow from the head. Therefore, the head is the root of a human. But the root of a living thing is below, as is clear in plants. Therefore, below in an animal is not below for the universe, etc.
The Philosopher says the opposite.
One must reply that because local motion is properly directed toward somewhere, differences of position are perceived in the universe according to diverse principles of local motion. So, that by which heavy things begin to be moved is said to be above in the universe and that by which light things begin to be moved is said to be below. But the right [side] in the universe is the one from which the movement of the heavens begins and this is from the east. But the "front" in the universe is that toward which the stars are moved after they rise, and this is our hemisphere. In an animal, "above" and "below" are understood with respect to the movement of food, and because an animal receives its food through the mouth, but plants through the root, this is why the head is "above" in the animal and the root is "above" in the plant. But right and left are understood with respect to local motion, since that part is to the right side in an animal by which the animal begins locomotion. But front and back are understood with respect to sensitive motion. The front part is the one in which the senses are located, because the animal moves toward that part. "Above" in a human, then, is directed toward the "above" of heaven, and the right side in a human is understood with respect to the principle of local motion, just as is the right side of heaven. And the front of the human is that part to which motion proceeds, just as it does in heaven. And this is why the Philosopher says that the parts of the human are situated according to the location of the parts in the universe. But this is not the case in other animals; in them "above" is not in the direction of the "above" of heaven, nor is "below" toward "below," but rather in between these.
1. To the first argument one must reply that this occurs even though the front of the human is toward the "above" of heaven; nevertheless, "above" is understood in the same sense in both human and in the universe.
2. To the second, one must reply that the root of an animated thing is properly said to be its "above" and not its "below," as the argument accepts. This is why, etc. For although the plant's root is "below," with respect to the universe, it is nevertheless "above" with respect to the plant, etc.
Whether the brain is naturally cold and moist.
Why the brain is divided into front and rear and not right and left.
Why a human has such a large brain in proportion to his body size.
Next one asks whether the brain is naturally cold and moist.
1. It seems not. Because, according to the Philosopher in the second book of On the Soul, sense and movement do not occur without heat. But sense and motion proceed from the brain. Therefore, it is reasonable that the brain should be warm.
2. Again, when the nerves are very moist, the members are paralyzed. In order that motion arise from the brain and without paralysis, it is necessary, it seems, that the brain be dry because, as Galen says in his On Illness and Accident, the nerves' dryness assists motion, as is apparent in madmen. Therefore, the brain is warm and dry.
Second, one asks why the brain is divided into front and rear [and not right and left], since other members are divided into right and left, like the eye and ear, the hand, foot, etc. Therefore, the same scheme should apply to the brain.
Third, one asks why a human has such a large brain in proportion to his body size, while others have a smaller one, like the horse and others. Now, the human is "the most noble animal," as it says in the text. Therefore, he ought naturally to have larger formal parts and smaller material ones. But the material parts are cold and moist in relation to the warm and dry. Therefore, as is apparent, he ought to have a smaller brain than the others, since it is cold and moist and these are the material ones, etc.
To the first argument one must reply that the vapors and fumes ascending from the nutritive parts ascend to the brain. If, then, the brain were warm in its own right [ de se], it would be immediately inflamed owing to the large quantity of vapors ascending the furnace of the entire body, as is the case in a furnace, and if it were woody and dry, it would immediately burst into flame from the smoke.
And this is the reason why nature bestows on it a cold and moist complexion, so that the warm organs, and especially the heart, may be tempered by its coldness, and so that its coldness might be tempered by the heat of the others.
Again, two pathways come from the heart to the brain. If the brain were hot, its heat would be turned back upon the heart, and it would kindle the heart's heat, and, as a result, in a very short time the animal would be suffocated. And this is why it is necessary for the brain to be naturally cold.
Further, the brain is the receptor for all the sensible species, and that which is moist receives them best, and this is why it is necessary for the brain to be moist. And because the spirits cross through the brain, it is necessary for it to be fatty, in order to strengthen the spirits by means of its oiliness and fat. And because fat is viscous, the brain is viscous, in order to retain well the species it received, just as bird lime [viscus] holds a bird.
To the first argument one must reply that, although the brain is neither warm nor dry in itself, nevertheless it receives warmth and dryness from the heart (to which, in location, it is opposed) and from the fumes and spirits coming to the brain, and therefore it has heat sufficient for the sensitive powers and dryness sufficient for the motive powers.
To the second argument one must reply that sense and motion arise in the brain. But sensation is an affect [ passio] and motion is an action, since to sense is to undergo and to move is to act. This is why it is necessary that these powers flow out from different parts. But the senses, like sight, smell, and taste, flow from the anterior part, and this is why the posterior part of the brain is necessarily left for the motive powers. And this is the reason why the brain is divided into two parts, of which the first is moister owing to the influence of the sensitive powers [vires sensitivae] while the posterior part is dryer owing to the motive powers [virtutes motivae].
With this, a response to the argument is clear.
To the third question one must say that a human is especially temperate. This is the reason why nature saw to it that the human brain was in proportion to the heart, so that each may be returned to a balanced temperament by the other, and this is why they are located opposite one another. But other animals are not so temperate, and this is why in other animals the brain is not proportioned to the heart, and this is the reason why the human brain is larger than is the brain in other animals. Another reason is that there are more internal senses, like reason, etc., in the human than in others, and because internally they have organs, or chambers, through which they act; for this reason it is necessary that the brain be larger than in other animals.
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