History of All Cloven-Hoofed Quadrupeds

Although all horns are solid, we shall say that those which are full are more solid than those which are empty and hollow; for a full reed is more solid and robust than a hollow one. Likewise in number, although for most there are two, namely one from each side of the head,
Why the unicorn is in the middle of the forehead.

there are nevertheless some which have only one and a singular horn, some which have three, and likewise some which have four. Those to which it is singular have obtained it on the forehead, the reason for which is assigned in the same place by the Philosopher. There are also those armed with a single horn, such as the Oryx, and that which we have said is called the Indian ass; the Oryx is cloven-hoofed, while that ass is whole-hoofed. Truly, those which have one bear the horn fixed in the middle of their head. For in this way, each part will especially possess the horn, since the middle is equally common to both extremes. It may rightly seem that a unicorn is whole-hoofed rather than cloven-hoofed. For a hoof, whether solid or cloven, has the same nature as a horn. Therefore, it is consistent for the same animals to have both a split hoof and a [split] horn simultaneously. The splitting of the hoof and horn also occurs from a defect of nature. Therefore, when nature had given an abundance of material to the hoof of whole-hoofed animals, it rightly took it away from above, and made the animal a unicorn.

Whether unicorns move their horns to either side.

But it should now be asked whether unicorns of this sort move their horns to the left and right; for if they do so, as it is most likely they do, nature itself would still have to be blamed for not making them cloven-hoofed. For the Philosopher said in that place that the greatest part of animals, just as the body is distinguished by the right and left sides by which they move themselves, so also they bear two horns for that same reason, by the character of their own nature. And the argument which the Philosopher brings forward concerning the whole hoofs of unicorn animals seems to be of little weight, for the oryx is cloven-hoofed, yet a unicorn; the rhinoceros is cloven-hoofed, and it too is a unicorn.

Lib. 8. c. 21. Placement.

We also read in Pliny that there are Indian oxen with one horn and three horns. There are also rams endowed with four horns, there are some that have received five, and likewise some with six. Thus horns also vary in placement: for in some they are in the center of the forehead, as in the oryx; in others, on the nose, as in the rhinoceros; in most, on the crown of the head. Furthermore, other differences of horns can be established, since some are immobile, as in most,
In which animals horns are mobile.

others are mobile in the manner of ears, as in Phrygian oxen, as Aristotle testifies in these words:
Lib. 8. c. 21.

The horns adhere to the skin rather than to the bone, whence it happens that in Phrygia and elsewhere there are oxen that move their horns just like little ears. And besides oxen of this sort, the Yale also moves its horns. Pliny is the witness: The Yale (he says) is the size of a hippopotamus, with the tail of an elephant, of a black or tawny color, with the jaw of a wild boar, having mobile horns longer than a cubit, which it sets up alternately in a fight, and varies them, pointing them forward or obliquely, however reason may have shown.

2. Hist. 1. In which animals horns fall off. Lib. 11. c. 37. 3. de animal. tra. 2. c. 1. 3. de par. 2.

Again, in some animals the horns fall off, in others they remain. For although Aristotle says that only the stag’s horns fall off every year, beginning from two years of age, while for the others they are permanent unless lost through some force—and Pliny agrees with him—we nevertheless see that roe deer, elk, and several others have deciduous horns, a fact which Albert was not ignorant of. Aristotle says that horns fall off for stags both for the sake of utility, so that they may be relieved of the burden, and out of necessity, because of their weight. Moreover, horns are more robust in some than in others, and more suitable for some to repel an injury, and for others to inflict one.
Sex.

Finally, there is also a difference in sex, for the females either lack horns, or have smaller ones than the males, just as their other weapons are also weaker. For the males are both more robust and bolder, as the same Philosopher judged when he says:
3. de par. 1.

The parts that pertain to attacking or defending, and which are granted by nature to those which either alone or before others can use them, and in whom the power of using them is chief, such as a tooth or if there be any other such thing; and since males are more robust and more spirited, for that reason such parts are given either to them alone or to them better. For those which are necessary to be had in females also, such as those adapted for food, the females indeed have, but less so than the males; however, those which pertain to no necessary matter, they lack.

Why horns are smaller in females.

Wherefore in the genus of stags, while the males have horns, the females lack them. Also the horns of cows and bulls differ between themselves. We see the same thing also in sheep. Thus he says. One reason is given by some, another by others. There are those who refer it to the coldness of the body, and those who refer it to a defect of matter. For they say that nature also attempted in females what was characteristic of the species, but lacked the matter, since in every genus of living things the female truly possesses less earthy residue; and therefore the more noble individuals in the species of sheep are held to be horned, because they obviously approach more closely to the nature of males in the habit of their body; hence they also better bear the injuries of their surroundings.
The horns of a hind.

Thus the hind has, as it were, certain rudiments of horns, yet nature, for the reason provided, was unable to complete them.
Where there are oxen without horns. 8. Hist. 28. Lib. 11. 37.

Those, however, who attribute it to the coldness of the body, with which the female sex is endowed, rely chiefly on the authority of Hippocrates, who left it attested in his work On Airs, Waters, and Places that in Europe, around the Maeotian marsh among the Scythians called Nomads, there are oxen without horns; for in rendering the reason for this matter, he says that the severity of the cold in that region is immense. This same point, they say, can also be established by the testimony of Aristotle, who records that in Africa rams are born already horned—and not only the males, as Homer writes, but also the females—while, on the contrary, in Pontus throughout the province of the Scythians, none have horns. It seems, therefore, that this occurs because Africa is hot, while Scythia is cold; since excessive cold weakens the native heat; and therefore, when we see certain sheep that are horned, they exist as warmer than the rest.
Difference of horns according to Pliny.

Pliny also touched upon the principal differences of horns: Horns (he says) indeed belong to many, both of aquatic and marine creatures and of serpents