In Ars Poetica Horace writes:
quid dignum tanto feret hic promissor hiatu?
parturient montes, nascetur ridiculus mus.
I get the meaning of the Latin, though admittedly by looking at a translation but I want to understand the actual Greek proverb that it comes from. C.O. Brink has a lengthy commentary on this passage. One annoying thing about Latin commentaries is that they are often written for super-experts in Latin, not for the student and even worse, they assume you already know Ancient Greek. Here is Brink's commentary:
answers the preceding question (quid dignum. . . feret?) with a Greek proverb, transposed to the fut. tense to suit the tense of the question. For the proverb see CPG, 1. 378, 4, II. 733. 4 ὤδινεν ὄρος, εἶτα μυν ἀπέτεκεν alluded to by the first two words in Lucian, Conscr. Hist. 23, in a similar though not identical setting. Immisch, p. 112 n., has drawn attention to the parallel, but his conclusions are implausible. Lucian objects to προοίμια λαμπρὰ καὶ τραγικὰ και εισ ὑπερβολὴν μακρά where the body of the narrative is puny, H. objects to a proem (however short) announcing a large subject when its execution must fall short of the expectation raised , cf 136-9 n., 197 n., and below 143 non fumum ex fulgore. Phaedrus, Iv. 23 (24) has made a short fable out of the proverb, the moral being qui, magna cum minaris, extricas nihil. The proverb made into a skit, in Sotadean metre, on the minute body of Agesilaus and ascribed to the Egyptian King Tachos, is cited by Athen. xrv. 616 d ὤδινεν οροσ Ζεῦς δ' ἐφοβεῖτο, το δ' ἔτεκεν μυν. This, if historical, dates the proverb back to the fourth century B.C., but I should be loath to spin Hellen- istic literary affiliations out of its metrical form, as Immisch, p. 25, is inclined to do. One might note however that the proverb makes better sense in Lucian's context than in H's and Lucian may therefore preserve its original application. The age of the proverb, its greek provenance and the literary contexts in Lucian and the Ars might possibly point to a common Hellenistic source.
I want to know how the Greek proverb that Brink quotes is to be translated. I get what point Horace is trying to make as Brink points out "H. objects to a proem (however short) announcing a large subject when its execution must fall short of the expectation raised," so mountain would be a symbol for an ambitious artistics goal and mouse would be the result which would be a symbol for pathetic.