What were the changes in the structure of chairs during the Song Dynasty?

Song dynasty chairs gradually progress, the use of increasingly common. Hebei Julu site unearthed wooden chair, 1.13 meters high, chair width of 0.59 meters, the chair has ink inscription, indicating the Northern Song Dynasty Chongming three years. Wooden chair with four feet are round wood, and to the outside slightly side, feet and feet with similar appendages between the support wood connected. There is inward slightly curved high back, no armrests. Sichuan Luzhou Song tomb excavated chair, backrest is round, and has appeared armrests. Zunyi, Guizhou unearthed Song dynasty chair, back on the horizontal wood at both ends carved into the shape of a bird's head.