If a painter should wish to unite a horse 's neck to a human head, and spread a variety of plumage over limbs[ of different animals] taken from every part[ of nature], so that what is a beautiful woman in the upper part terminates unsightly in an ugly fish below; could you, my friends, refrain from laughter, were you admitted to such a sight? Believe, ye Pisos, the book will be perfectly like such a picture, the ideas of which, like a sick man 's dreams, are all vain and fictitious: so that neither head nor foot can correspond to any one form. "Poets and painters[ you will say] have ever had equal authority for attempting any thing. "We are conscious of this, and this privilege we demand and allow in turn: but not to such a degree, that the tame should associate with the savage; nor that serpents should be coupled with birds, lambs with tigers. 