This medieval bestiary feel very much like the etymologies in Sanskrit works like Yaska’s _Nirukta_. Both of them shift between what we’d now think of as etymology (i.e. finding plausible historical roots for words), and a more alien sense that the word, through etymology, somehow captures the entire nature of the thing described. I suppose in the West this goes back to the “Platonism without Plato” that drives medieval scholasticism, and there is something pretty similar in India.
The he-goat is a wanton and frisky animal, always longing for sex; as a result of its lustfulness its eyes look sideways – from which it has has derived its name. For, according to Suetonius, hirci are the corners of the eyes. Its nature is so very heated that its blood alone will dissolve a diamond, against which the properties of neither fire nor iron can prevail.
Also, like all these books, it is a very pretty thing.