Whether all animal members lead back to a single member.
Now one asks whether all animal members lead back to a single member.
1. It seems not. Because those things that have a different regimen do not lead back to some one member. But diverse members have a different regimen. Therefore, they do not lead back to some one member.
2. Again, those things which have a diverse end have no return to one member. But the members have diverse ends, for the end of the foot is to walk, and the end of the eye is to see; therefore, etc.
To the contrary. The lesser world imitates the greater world. But all the parts in the greater world lead back to a single thing. For individual things receive powers and influences from other things, and all receive these from a first, that is, from a first cause. Therefore, it will be the same in the lesser world, which is the human, and in every other animal that is a part of the world.
One must say that in every animal there is one first member, which is first by generation and by causality, and from which all others receive influence and power because in all things ordained to one end it belongs to the same agent to establish order among them. But all the members of an animal are ordered to one end to the preservation of the speciesand ordered by the same agent, which is the power in the seed. This is why it is necessarily required that the members be ordered among themselves. But it belongs to things that are ordered to reach a first principle, for otherwise the process would be infinite, a thing which neither nature nor art nor reason nor science endures; therefore, etc.
1. To the first argument one must reply that regimen is understood in two ways: as individual [speciale] or common. Different members have a different regimen in the individual, yet nevertheless they have one regimen in common. And this suffices for the basis of the principle, etc.
2. To the second, one must reply that an end is understood in two ways: proximate and mediated. Thus, although there may be one or another proximate end for any part whatsoever, nevertheless the mediated end is the same. So just as the eye exists immediately for the sake of sight, or the ear for the sake of hearing, and so too for the others, nevertheless each is further ordered to the conservation of the individual. And thus they all have one mediated and remote end, which is to conserve the animal in its existence, etc.
What is that first thing to which all the animal members lead back?
Further one asks what is that first thing to which all the animal members lead back.
It seems to be the brain. Because, although the senses are what make an animal an animal, the senses have their origin from the brain, and therefore, etc.
But it also seems to be the liver. Because that member seems to be the principal one through which all members are preserved and conserved and in which things that have been lost are restored. But this is accomplished by the liver, in which the nutritive power flourishes; therefore, etc.
But it also seems to be the testicles. Because that member appears to be the principal one through which a thing acquires being. But this happens through the generative members, as is clear. Therefore, etc.
To the contrary. Life is an animal's first act. Therefore, that in which life first exists is the first animal member. But according to the Philosopher life takes root in the heart, and he says that the heart is first to live and last to die, and Avicenna says that the heart is the first root of the powers. Therefore, the heart is the principal member.
One must reply that the animal body is divided into four regions. One is of the animal parts in which the sensitive and motive powers exist, and this is the head region. Another is of the natural parts in which the powers serving nutrition exist, like the power of the stomach, liver, veins, kidneys, and things of this sort. A third region is that of the spiritual parts, to which the heart and the lungs and the trachea [vocalis arteria] belong. And a fourth region is that of the members suitable for generation. Thus an animal is considered in four different ways, and in this sense there are various principal members positioned in the human. For some consider him from the standpoint of generation, and these have to posit that the members in which the semen exists, that is the testicles, are principal. Others consider him from the standpoint of nutrition, and these have to establish the liver as the principal member. Others consider him from the standpoint of sense and motion, and these posit that the brain is the principal member. And some consider him from the standpoint of the spiritual members, and these posit that the heart is the principal member. Therefore, there is a no small controversy between physicians and the Philosopher. For the physicians claim that the brain is the principal member because they pay attention to the senses and because they are
workers on things that are sensible. But the Philosopher posits the heart alone. And Avicenna says that the physicians must follow the Philosopher because he speaks more truthfully. For the heart is located in the middle of the animal just like a prince in his kingdom, and, just as the prince sends his commands and rules the individual parts of his kingdom through his ministers, so does the heart send life and power to the individual members by means of their organs. Now it sends sensation to the eyes and the ears through the brain as if through a minister, and it sends motion to the hands and feet similarly through the brain. But on each member it bestows the power of digesting, expelling, and attracting by using the liver just as if it were a bailiff. But it gives the power of reproduction to another external member by means of the seminal vessels. And therefore, according to the truth of the matter, the heart is the principal member. But the physicians consider the matter according to the senses, as it appears to them, and not according to the reality, and this is why, etc. Thus in the second book of On Heaven and Earth the Philosopher likens the superior bodies to the heart.
This reason also appears persuasive, because all the corporeal and material things in the universe lead back to spiritual ones, and therefore it seems similarly reasonable in animals that all members lead back to spiritual ones, among which the first one is the heart.
This is also clear to the senses because the dispositions and sufferings [ passiones] of individual members are borne back to the heart. For no injury occurs in any part of the body without that affect redounding to the heart. Thus the heart suffers with members in pain and shares the enjoyment of those experiencing pleasure.
To the argument one must reply that sense and motion, nutrition and generation can be related to some member in two ways, either with respect to its first root and true origin or with respect to its immediate principle of operation. If in the first way, then all these lead back to the heart, which is the first and
true principle of generation, and upon which the entire machinery of the body is constructed like a house on its foundation, and from which all the members first receive life. If in the second way, then sense and motion lead back to the brain because it is clear that senses, motions, and operations proceed from it. And thus nutrition leads back to the liver according to sense, and generation leads back to the seminal vessels, namely, the testicles.