Such beautiful works of art as these last show the influence which the great athletic festivals, and especially the Olympian, exerted on the development of Greek sculpture. In the gymnastic training carried on in the gymnasium and palæstra, which culminated in these festivals, the Greek sculptor found an unrivaled opportunity to study the naked human figure in its best muscular development and in every pose. In fact, we may say with Furtwaengler that without athletics Greek art would be inconceivable.[573] To quote from another work of the same scholar: “The gymnastically trained bodies of these slim boys and youths and vigorous men are evidence of the ennobling effect of athletics. Presented in complete nudity they are not faithful portraits from life, but motives or models from the palæstra transformed and exalted to the highest ideal of physical beauty and strength. They are the most splendid human beings that the art of any period has created.”[574] CANONS OF PROPORTION. In attempting to identify a given statue as the copy of a work by this or that master, certain well-known canons of proportion, which were taught and practiced by various Greek sculptors and schools, must be taken into consideration. [Illustration: FIG. 4.—Bronze Head of an Olympic Victor, from Herculaneum. Museum of Naples.] Greek art may, like Greek philosophy and poetry, be summarized under the names of three qualities which constantly occur in classical literature—συμμετρία, εὐρυθμία or ῥυθμός, and ἀναλογία.[575] Symmetry may be defined as “that technical regard for the placing of the parts to the best advantage,” the symmetrical arrangement of the parts of a statue or group of figures.[576] Rhythm, following Vitruvius,[577] is that _tertium quid_ which is indispensable to true art. Analogy (Latin _proportio_)[578] refers to the measured ratio of part to part in any given work of art, whether in architecture, painting, or sculpture. Most scholars nowadays interpret symmetry and analogy as the same thing. Pliny[579] says that _symmetria_ has no Latin equivalent, and in several passages[580] keeps the Greek word, as does Vitruvius. Here Otto Jahn rightly says _proportio_ or _commensus_ would have adequately translated it.[581] P. Gardner explains the word properly as “the proportion of one part of the body as measured against another.”[582] Brunn held that, as symmetry was the relation of part to part in a statue at rest, rhythm expressed this relationship in one represented in motion.[583] The simplest illustration of rhythm is seen in walking: when the right foot is advanced the left arm swings out in rhythm, and so the balance of the body is kept. Rhythm, therefore, has to do with balance in motion, and may refer equally to cadence in poetry and music and to movement in sculpture. An excellent example in sculpture is afforded by Myron’s _Diskobolos_ (Pls. 21, 22, and Figs. 34, 35),