These come according to no particular chronology, or any assumed order of importance. If you want to read a good history of the grotesque, I recommend Frances Barasch's The Grotesque: A Study in Meanings. Part one of Peter Ward-Jackson's Some Main Streams and Tributaries in European Ornament from 1500 to 1750 is also a great survey from the art perspective.
[Ulisse Aldrovandi (1642) Monstrorum Historia]
I'm going to start with Horace, because he is an interesting example of grotesque theory's tendency to adopt those who wrote about what is now termed 'grotesque' long before the word itself was actually conceived.
Horace begins his Ars Poetica or "The Art of Poetry" (18BC) with these lines (I'm not sure this is the best translation, but there you go):
"If a painter were willing to join a horse's neck to a human head and spread on multicolored feathers, with different parts of the body brought in from anywhere and everywhere, so that what starts out above as a beautiful woman ends up horribly as a black fish, could you my friends, if you had been admitted to the spectacle, hold back your laughter? Believe me, dear Pisos, that very similar to such a painting would be a literary work in which meaningless images are fashioned, like the dreams of someone who is mentally ill, so that neither the foot nor the head can be attributed to a single form. "Painters and poets," someone objects, "have always had an equal right to dare to do whatever they wanted." We know it and we both seek this indulgence and grant it in turn. But not to the degree that the savage mate with the gentle, nor that snakes be paired with birds, nor lambs with tigers" (1-33).
[Ambroise Pare (1582) Des Monstres et Prodiges]
Mismatched, imaginary bodies are here equated with inconsistency in poetic vision. To write well one must hold to a single premise, not place ideas together in a confusing manner. As he comments a few lines down: "let the work be anything you like, but let it at least be one, single thing."
He also includes this rather amusing snark:
"Near the gladiatorial school of Aemilius, a most incompetent craftsman will mold toenails and imitate soft hair in bronze but he is unsuccessful with his complete work because he does not know how to represent a whole figure. If I wished to compose something, I would no more wish to be him than to live with a crooked nose although highly regarded for my black eyes and black hair" (32-37).Oh snap.
So there is no point perfecting the ingredients if you are unable to bring them together to form a convincing whole. It is interesting to note the value judgment at play here, for it is one that many others have shared. Grotesque bodies were often seen to transgress the laws of nature and God's divine plan - depicting things that could never, and should never, exist. Weirdness is to be avoided, stick with the familiar and your work will be approved of.
In Horace we also see how easily the line dividing art and literature is blurred. The hybrid bodies sketched and painted by artists are so suggestive he cannot help but observe their analogous counterpart in patchy writing.
[Fortunio Liceti (1665) De Monstris]
Montaigne later quotes Horace when offering his own, albeit brief, commentary on the grotesque. Significantly, he does so while likewise crossing the border between art and literature.
He begins his essay "On Friendship" (sometimes translated as "Of Friendship") like this:
"Considering the proceeding of a Painters worke I have, a desire hath possessed mee to imitate him: He maketh choice of the most convenient place and middle of everie wall, there to place a picture, laboured with all his skill and sufficiencie; and all void places about it he filleth up with antike Boscage or Crotesko [grotesque] works; which are fantasticall pictures, having no grace, but in the variety and strangenesse of them."
After duly admiring the grotesques, he compares them to his own writings:
"And what are these my compositions in truth, other than antike workes, and monstrous bodies, patched and hudled up together of divers members, without any certaine or well ordered figure, having neither order, dependencie, or proportion, but casuall and framed by chance?"
Montaigne then quotes Horace's line about the woman with a fish tail "Definit is piscem mulier formosa supernè."
A woman faire for parts superior,
Ends in a fish for parts inferior.
Once again the grotesque is evoked to describe a writer's attempts at creation. The assemblage of body parts is analogous to the assemblage of words and ideas. The final text is thus imagined as a form of grotesque body.
Gregor Reisch (1517) Margarita Philosophia]
This all reminds me of Mary Shelley's comment in the introduction to Frankenstein: "I bid my hideous progeny go forth and prosper."
Speaking of which, doesn't this sound familiar?
Woah. I only just noticed that.