Why bulging eyes indicate a disturbed power of discretion and why sunken eyes indicate acute vision.
Why an overlarge aperture and immobility in the eye indicate immodesty, and mobility indicates inconstancy.
Second, one asks about the physiognomy of the eye. And first, why bulging eyes indicate a disturbed power of discretion and why sunken eyes indicate acute vision. Second, one asks why an overlarge aperture and immobility in the eye indicate immodesty, and mobility indicates inconstancy.
To the first, one must reply that the eyes originate in the brain, which is moist. Thus bulging eyes are a sign of a lot of moisture coming from the brain, and this is an indication of a disturbance in the brain's powers. In addition, the further a power is stretched out from its source, the weaker it is, and this is why bulging eyes are an indication of a weak power. But sunken eyes are nearer to the brain and to the first principle of sight, and the [visual] rays are better unified in these. Thus they attest to an acute visual power.
To the second question one must reply that the eye's immobility indicates that nature does not control the eye very well. But if a person should freely keep his eyes always unmoving, then he himself acts badly, and he does this freely, and this is an indication that he is not ashamed of acting badly. And this is why an overlarge aperture and immobility in the eye (as when one perceives that a person is not moving his eyes and keeps them fixed for a long time) is a sign of shamelessness. Movement of the eyes arises from excess heat, because heat is easily movable. According to Avicenna, this is a sign of inconstancy and of a deceiver [insidiator] passing from image to image, and these people are deceivers and robbers, etc.
Why ears may be located on various parts of the head although the eyes, nevertheless, are located close together.
Why ears are twisted on the inside.
Why all animals have movable ears, but the human alone has immovable ears.
Why melancholy animals have long ears.
Now one asks about the ear.
First, why ears may be located on various parts of the head although the eyes, nevertheless, will be located close together.
Second, one asks why ears are twisted on the inside.
Third, one asks why all animals have movable ears, but the human alone has immovable ears.
And fourth, why melancholy animals, like the ass, the hare, the mule, the stag, and the cow, have long ears.
To the first, one must reply that sound, which is the proper sensible for the ears, multiplies in air moved in a circular fashion in the manner of wave-like water, as can be seen when circles emanate out from the place where a rock is thrown into the water. And this is why the ears are located on opposite sides of each other, so that sound may be heard from everywhere, because if they were on one side they would not hear from all sides, nor would the sound, should it travel a long distance, be heard everywhere, etc. This is why it diffuses itself spherically. But "anything that is seen is seen at an angle" whose base is in the thing seen and whose apex [ conus] is at the eye, and a visual discrimination does not occur before it approaches the optic nerve. And this is why the eyes are situated together, so that what is seen by one eye and by the other at straight lines can establish an angle at the optic nerve, because the more acute the angle of the apex [ acutior conus] the better is the object seen. And this is why a small eye is much better, because the visual rays are better united in it and the angle [angulus] is more acute, etc.
To the second question one must reply that sound is amplified with a tremor of the air. And this is why the interior of the ear is twisted and winding, so that a sort of bending back of the air may occur and so that the sound will redound better in the ear.
Another reason is that the air is warmed by the bending and is altered and purified in this twisting so that no cold approaches the temporal bone [ospetrosum] of the brain and injures it, which is sensible, because cold from outside is the cause of rheum and especially damages the brain itself, which has a weak heat.
To the third question one must reply that the ears descend from the brain along intermediary nerves. But now it is the case that too much moisture in the nerves is a cause of immobility, just as occurs in paralytics, whose members are not born for motion owing to too much moisture of the nerves, which relaxes them. But among all the animals the nerves descending to the ears of a human are the moistest, and this is why they are more immovable. This is demonstrated by the fact that the human brain is colder and moister, and this is to temper the heat of the heart; therefore, etc.
In addition, there are no muscles in the ears of a human, which mediate voluntary motion in an animal. But there are muscles in the ears of other animals, and this is why they are movable at will.
To the fourth question one must reply that melancholy animals are naturally timid owing to their weak heat and shortage of spirits. Indeed, a small amount of heat is unable to warm a large heart, just as a small fire cannot warm a large furnace. This is why it suits them to hear from a greater distance, so that, like the roebuck [capreolus], they may more quickly take flight, and this is why wise nature made their ears double and gave them long earsfor the sake of flight, which is their protection, so that they will perceive hunters at a distance.
Another reason is that cartilage exists and is made from melancholy matter, and the ear is composed of cartilage. Then argue: The more the melancholy matter abounds, the more reasonable it is that the melancholy members will be stretched out. And this is why melancholy animals have long ears.