右横書き (hiragana みぎよこがき, romaji migi yokogaki)
Compound of 右 (migi, “right”) + 横書き (yokogaki, “horizontal writing”), itself from 横 (yoko, “horizontal, side, sideways”) + 書き (kaki), the stem noun form of verb 書く (kaku, “to write”). The kaki changes to gaki due to rendaku (連濁).