From Bulfinch's Mythology: The Unicorn - anthology.

From Bulfinch's Mythology: The Unicorn - anthology. Representing holiness and chastity, the legendary unicorn was a frequent symbol in the art and literature of the Middle Ages. Although the 19th century American mythologist and writer Thomas Bulfinch noted some similarities between the fabled beast and certain animals, his own beliefs concurred with those who concluded that the unicorn was merely the product of imaginative invention. From Bulfinch's Mythology: The Unicorn By Thomas Bulfinch Pliny [Pliny the Elder], the Roman naturalist, out of whose account of the unicorn most of the modern unicorns have been described and figured, records it as 'a very ferocious beast, similar in the rest of its body to a horse, with the head of a deer, the feet of an elephant, the tail of a boar, a deep, bellowing voice, and a single black horn, two cubits in length, standing out in the middle of its forehead.' He adds that 'it cannot be taken alive'; and some such excuse may have been necessary in those days for not producing the living animal upon the arena of the amphitheatre. The unicorn seems to have been a sad puzzle to the hunters, who hardly knew how to come at so valuable a piece of game. Some described the horn as movable at the will of the animal, a kind of small sword, in short, with which no hunter who was not exceedingly cunning in fence could have a chance. Others maintained that all the animal's strength lay in its horn, and that when hard pressed in pursuit, it would throw itself from the pinnacle of the highest rocks horn foremost, so as to pitch upon it, and then quietly march off not a whit the worse for its fall. But it seems they found out how to circumvent the poor unicorn at last. They discovered that it was a great lover of purity and innocence, so they took the field with a young virgin, who was placed in the unsuspecting admirer's way. When the unicorn spied her, he approached with all reverence, crouched beside her, and laying his head in her lap, fell asleep. The treacherous virgin then gave a signal, and the hunters made in and captured the simple beast. Modern zoologists, disgusted as they well may be with such fables as these, disbelieved generally the existence of the unicorn. Yet there are animals bearing on their heads a bony protuberance more or less like a horn, which may have given rise to the story. The rhinoceros horn, as it is called, is such a protuberance, though it does not exceed a few inches in height, and is far from agreeing with the descriptions of the horn of the unicorn. The nearest approach to a horn in the middle of the forehead is exhibited in the bony protuberance on the forehead of the giraffe; but this also is short and blunt, and is not the only horn of the animal, but a third horn, standing in front of the two others. In fine, though it would be presumptuous to deny the existence of a one-horned quadruped other than the rhinoceros, it may be safely stated that the insertion of a long and solid horn in the living forehead of a horse-like or deer-like animal is as near an impossibility as anything can be. Source: Bulfinch, Thomas. Bulfinch's Mythology: The Age of Fable, The Age of Chivalry, Legends of Charlemagne. New York: Random House, 1934.