Whether the human ought to lack a tail naturally.
Next one asks whether a human ought to lack a tail naturally.
1. It seems not. Tails are conferred upon animals for covering the anus, which is a nerve-filled and delicate member, in order to cover and safeguard it from injuries, like cold and other such things. Since the human, however, needs to safeguard the anus no less than other animals, therefore he will no less lack a tail. Avicenna reveals the fact that there is a need to safeguard the anus when he discusses the things it undergoes, etc.
2. Moreover, animals' tails contribute to motion. For if the tail is removed from a bird, a fish, or a dog, its motion will be retarded. This is why wise hunters never shorten the tails or the ears on their dogs, because this would clearly harm their hunting, because they are directed through the powerful movement of these members to go after prey, just as is a ship by oars. Otherwise, their movement would be hesitant. And a little below the Philosopher will say that a dog that loses its tail will not dare to cross a bridge because it may fall, just as a ship sinks without an oar. Since a human needs to be made fit for motion no less than other animals, so he ought no less to be deprived of a tail.
The Philosopher says the opposite, and it is clear to the sens-es.
One must respond that tails are given to animals for two reasons: as a covering for the anus, and as an aid to motion, just as the two arguments above conclude. But the human does not need a tail as a covering. For he has reason and the intellect, through whose intervention he can prepare for himself a covering and other things that are given naturally to others. Nor does he need a tail for the sake of motion, because ease of locomotion in the human depends on the arrangement of the hip, the leg, and the foot, to which a tail adds nothing.
And, moreover, the human sits and rests on the posterior part and the anus, and a tail would prove an impediment to this rest and sitting.
Furthermore, many nerves extend through the vertebrae of the back in the posterior part toward the anus, and in the human these nerves are bent back toward the penis. So the nerves, which in other animals extend toward the tail, proceed in the human to the penis, and for that reason the human has, among all the animals, the greatest and strongest penis for its size, erect as a spear. Thus it penetrates a virginal vulva, which is harder and stronger and more difficult to penetrate and open up with the penis than is the same one in other animals, owing to the excessive narrowness of the womb. It is clear on account of this.
On to the arguments. One should say that although in other animals the tail contributes to covering and motion, this is not the case in the human. And the reasons have been discussed.
Why birds imitate the human in speech more than the other animals.
Further one asks why birds imitate the human in speech more than the other animals.
1. And the contrary seems the case. For those parts of birds that conform more closely to the parts of the human ought to imitate him more in their operations. But the parts of walkers are of this type, because at least their tongues conform more to the human tongue than does the bird's; therefore, etc.
2. Furthermore, the animals that have greater discretion ought to participate more in the principle of discretion. But walkers, like the dog and the ape, participate more in discretion or in a likeness of discretion than does the bird. This is evident, because the ape learns to stitch cloth together and the dog learns to serve, which is a sign of great discretion. Therefore, such animals as these should imitate the human more, so it seems, in speaking than does the bird.
The opposite is evident to the senses, because the parrot, the magpie [pica], and the jackdaw [monedula] imitate the human in speaking, and one never sees a walker speak.
To this, one should respond that birds, especially, imitate the human in speaking, and birds having a broad tongue do this, because two things are required for speaking: apprehension of something heard and the suitability of the instrument. But now it is the case that some birds apprehend quite easily and their tongues have quite suitable nerves and can move flexibly toward their palate and they have a broad, wide windpipe [canna pulmonis], well disposed in the throat. This is why such birds especially can imitate the human in giving voice. And this happens especially among birds that make a sound [vox] in the throat, for those forming a sound at the tip of the beak, like the sparrow, nightingale, and similar ones, cannot perform this operation. Walking animals have more earthy vocal instruments, and the nerves of their tongues are not as well suited as are those of the aforementioned birds, and that is why they cannot adapt their instruments to form a voice.
1. To the first argument one should reply that although parts of other walking animals may conform better to human parts in terms of shape and motion, they conform less well in the formative principles of voice.
2. To the second argument one must reply that although the dog and the ape and such animals are more teachable in certain areas, nevertheless their organs of voice are not so well formed as those of birds, as has been said, and for that reason, etc.
-  The term is synonymous with trachea, but, as this is also a term A. employs, "windpipe" is used to keep the two distinct.
-  Note that A. carefully uses vox throughout this passage both to mean human articulate sound, "voice," and formed sound such as that of a bird's chirp.
-  It is interesting that before scientists hit on using sign language in apes, many an experiment had failed trying to teach a chimpanzee to form simple words since an ape's vocal equipment is simply not up to the task.