Although we have no evidence to show that the Egyptians understood the use of clay models, we have some idea of the process by which they were enabled to do without them, and of the nature of their professional education. The chief Egyptian museums possess works which have been recognized as graduated exercises in the technique of sculpture. They are of limestone, and of no great size--from four to ten inches high. The use of these little models is shown to have been almost universal by the fact that Mariette found them on nearly every ancient site that he excavated. Their true character is beyond doubt.[321] At Boulak there are twenty-seven sculptured slabs which were found at Tanis. One is no more than a rough sketch, just begun. By its side is a completed study of the same subjects. Some of these slabs are carved on both sides; on others we find one motive treated twice, side by side, once in the state of first sketch, and again as a finished study. The plaques which bear the heads of cynocephali, of lions and lionesses, are remarkable for the freedom of their execution (Figs. 260, 261, and 262).[322] The same may be said of fifteen royal heads found at Sakkarah. They should be examined together. They range[323] in order from No. 623, which is a roughly-blocked-out sketch, to 637, a finished head. One of these models is divided down the middle, so as to give accent to the profile. A few of them are squared in order to test the proportions. But even here no canon of proportion is to be found. "If the squares were based upon some unchanging unit, they would be identical in every model in which they occur. But in one of these heads we find three horizontal divisions between the uræus and the chin; in another four. In most cases the number of the squares seems to have been entirely due to the individual caprice or convenience of the artist. There are but two examples in which another rule seems to have been followed; in them the proportions of the squares are identical, and their intersections fall upon the same points. All that may be fairly deduced from this, however, is that they are the work of the same hands."[324] A second series of royal heads was found at Tanis; others have been discovered in the Fayoum. Boulak also possesses models of the ram, the jackal, and the uræus, of arms, legs, hands, &c. Upon a plaque from Tanis the figure of Isis appears twice, once as a sketch and once as a finished study. [321] MARIETTE, _Notice du Musée_, Nos. 623-688. [322] Nos. 652-654 of the _Notice du Musée_. [323] In the Boulak catalogue. [324] MARIETTE, _La Galerie de l'Égypte Ancienne à l'Éxposition du Trocadéro_, pp. 69, 70. [Illustration: FIG. 260.--Head of a Cynocephalus.] [Illustration: FIG. 261.--Head of a Lion.] [Illustration: FIG. 262.--Head of a Lioness.]