χορὸς ᾿εστὼς κυκλικῶς.—Tzetzes. Proleg. to Lycophron.
Hartung, on the Dithyramb.—Classical Museum, No. XVIII. p. 373. Mure’s literature of ancient Greece.—Vol. III., p. 85.
The number fifty is mentioned in the Epigram of Simonides, beginning ἠρχεν Αδείμαντος, in the above-mentioned prologue of Tzetzes, and in Pollux, Lib. iv., 15, who says that this number of the Chorus was used even by Æschylus up to the time when the Eumenides was represented. The number twelve is commonly mentioned by other authorities as having been used by Æschylus, while Sophocles is said to have increased it to fifteen, which afterwards became the standard number. Müller (Eumenides) ingeniously supposes that the tragic poets, so long as the exhibition by tetralogies lasted, got the original number of fifty from the public authorities, and divided it among the different pieces of the tetralogy. Blomfield’s notion (Preface to the Persae) that the Chorus to the Eumenides consisted of only three persons, though a kind word has been said in its favour lately (Mason in Smith’s Dict. of Antiq. voce Chorus), deserves, in my opinion, not a moment’s consideration, either on philological or æsthetical grounds. I may mention here further, for the sake of those to whom these matters are strange, that the Chorus holds communication with the other characters in a Greek play generally by means of its Coryphaeus or Leader, which is the reason why it is often addressed in the singular and not in the plural number.
Vit. Philos. III. 34. It will be observed that, if a third actor appears on the stage in some parts of the Orestean trilogy, this is to be accounted for by the supposition that, in his later plays, the poet adopted the improvements which his young rival had first introduced. The number of actors here spoken of does not, of course, take into account mutes or supernumeraries, such as we find in great numbers in the Eumenides, and more or less almost in every extant piece of Æschylus.
Poetics, c. xiii.